Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In multi-hop routing, cluster heads near the base station act as relays for far cluster heads and thus will deplete their energy very quickly. Thus, hot spots in the sensor field result. This paper introduces a new clustering algorithm named an Unequal Multi-hop Balanced Immune Clustering protocol (UMBIC) to solve the hot spot problem and improve the lifetime of small and large scale/homogeneous and heterogeneous wireless sensor networks with different densities. UMBIC protocol utilizes the Unequal Clustering Mechanism (UCM) and the Multi-Objective Immune Algorithm (MOIA) to adjust the intra-cluster and inter-cluster energy consumption. The UCM is used to partition the network into clusters of unequal size based on distance with reference to base station and residual energy. While the MOIA constructs an optimum clusters and a routing tree among them based on covering the entire sensor field, ensuring the connectivity among nodes and minimizing the communication cost of all nodes. The UMBIC protocol rotates the role of cluster heads among the nodes only if the residual energy of one of the current cluster heads less than the energy threshold, as a result the time computational and overheads are saved. Simulation results show that, compared with other protocols, the UMBIC protocol can effectively improve the network lifetime, solve the hot spot problem and balance the energy consumption among all nodes in the network. Moreover, it has less overheads and computational complexity. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.asoc.2016.02.016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institution of Engineering and Technology  

Coverage is one of the most important performance metrics for wireless sensor network (WSN) since it reflects how well a sensor field is monitored. The coverage issue in WSNs depends on many factors, such as the network topology, sensor sensing model and the most important one is the deployment strategy. Random deployment of the sensor nodes can cause coverage holes formulation. This problem is non-deterministic polynomial-time hard problem. So in this study, a new centralised deployment algorithm based on the immune optimisation algorithm is proposed to relocate the mobile nodes after the initial configuration to maximise the coverage area. Moreover, the proposed algorithm limits the moving distance of the mobile nodes to reduce the dissipation energy in mobility and to ensure the connectivity among the sensor nodes. The performance of the proposed algorithm is compared with the previous algorithms using Matlab simulation. Simulation results clear that the proposed algorithm based on binary and probabilistic sensing models improves the network coverage and the redundant covered area with minimum moving consumption energy. Furthermore, the simulation results show that the proposed algorithm also works when obstacles appear in the sensing field.

DOI： 10.1049/iet-wss.2014.0085

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Energy hole problem is a critical issue for data gathering in wireless sensor networks. Sensors near the static sink act as relays for far sensors and thus will deplete their energy very quickly, resulting energy holes in the sensor field. Exploiting the mobility of a sink has been widely accepted as an efficient way to alleviate this problem. However, determining an optimal moving trajectory for a mobile sink is a non-deterministic polynomial-time hard problem. Thus, this paper proposed a mobile sink-based adaptive immune energy-efficient clustering protocol (MSIEEP) to alleviate the energy holes. A MSIEEP uses the adaptive immune algorithm (AIA) to guide the mobile sink-based on minimizing the total dissipated energy in communication and overhead control packets. Moreover, AIA is used to find the optimum number of cluster heads (CHs) to improve the lifetime and stability period of the network. The performance of MSIEEP is compared with the previously published protocols; namely, low-energy adaptive clustering hierarchy (LEACH), genetic algorithm-based LEACH, amend LEACH, rendezvous, and mobile sink improved energy-efficient PEGASIS-based routing protocol using MATLAB. Simulation results show that MSIEEP is more reliable and energy efficient as compared with other protocols. Furthermore, it improves the lifetime, the stability, and the instability periods over the previous protocols, because it always selects CHs from high-energy nodes. Moreover, the mobile sink increases the ability of the proposed protocol to deliver packets to the destination.

DOI： 10.1109/JSEN.2015.2424296

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

An energy detection-based active spectrum sensing scheme is proposed to carry out spectrum sensing and secondary transmissions simultaneously. It successfully avoids the widely used quiet periods, which have at least two shortcomings. First, periodical interruptions of secondary transmissions degrade the quality of service of secondary networks (e.g. decreasing the system capacity and increasing end-to-end packet delay). Second, frequent tight synchronisation is necessary but very difficult to implement in the distributed networks. With the assistance of the geolocations, the proposed sensing scheme is able to decompose the received power into the primary signal power, secondary signal power, and the device noise power. The power decomposition is formulated into a problem of solving a homogeneous linear equation set with a coefficient matrix involving only the distances among the primary users, secondary users, and the sensors. Through the decomposition, the primary signal power can be differentiated from the secondary signal power, which is generally treated as interference in spectrum sensing. When constructing the test statistic, such interference can be cancelled from the collected energy. As a result, the noise uncertainty problem, which significantly compromises the performance of the energy detection, can be greatly alleviated by noticing the fact that the interference dominates the noise uncertainty problem. Because the achieved signal-to-interference ratio can be improved by cancelling the interference, the detection errors in terms of the probability of false alarm and missed detection can be significantly reduced. Simulations verify the feasibility and efficiency of the proposed scheme. Copyright (c) 2013 John Wiley & Sons, Ltd.

DOI： 10.1002/ett.2731

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we investigate a low-complexity technique for simultaneous wireless information and energy transfer in multiple-input multiple-output relay channels. The proposed technique exploits the array configuration at the relay node and uses the antenna elements either for conventional decoding or for rectifying (rectennas). In order to keep the complexity low, a dynamic antenna switching between decoding/rectifying is proposed based on the principles of the generalized selection combiner (GSC); the L strongest paths are allocated for decoding while the remaining channel paths for rectifying (and vice versa). The optimal L as well as the allocation strategy that minimizes the outage probability are investigated via theoretical and numerical results. In addition, two performance bounds that provide the optimal performance without the limitation of GSC are proposed by solving a linear programming and a binary knapsack problem, respectively. The proposed technique is extended to scenarios with multi-user interference, where a zero-forcing receiver is used at the relay node; closed-forms expressions for the outage probability are also derived.

DOI： 10.1109/TCOMM.2014.032914.130722

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

We propose a novel adaptive filtering scheme named metric-combining normalized least mean square (MC-NLMS). The proposed scheme is based on iterative metric projections with a metric designed by combining multiple metric-matrices convexly in an adaptive manner, thereby taking advantages of the metrics which rely on multiple pieces of information. We compare the improved PNLMS (IPNLMS) algorithm with the natural proportionate NLMS (NPNLMS) algorithm, which is a special case of MC-NLMS, and it is shown that the performance of NPNLMS is controllable with the combination coefficient as opposed to IPNLMS. We also present an application to an acoustic echo cancellation problem and show the efficacy of the proposed scheme.

DOI： 10.1587/transfun.E97.A.800

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communication, Engineers, IEICE  

Geomagnetic information is informative because it has the ability to detect information about orientation by way of a ubiquitous device. However, a magnetic disturbance easily influences geomagnetic information. The magnetic disturbance detection method is needed in order to use geomagnetic information. Firstly, in this paper, the availability of geomagnetic information in Japan is investigated by field measurement work. Then, a new magnetic disturbance detection method which is better than the conventional method is proposed. The basic function of the proposed method is tested in actual condition.Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transfun.E96.A.2745

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This letter deals with a three-node cooperative network where the relay node harvests energy from radio frequency (RF) radiation. The source node is the only available RF generator and introduces a fundamental switching between energy harvesting and data relaying. A greedy switching (GS) policy where the relay node transmits when its residual energy ensures decoding at the destination is investigated. The GS policy is modeled as a Markov chain for a discretized battery; the stationary distribution and the outage probability of the system are derived in closed form expressions. In addition, an optimal switching policy that incorporates a-priori knowledge of the channel coefficients is proposed and solved by a mixed-integer linear programming formulation.

DOI： 10.1109/LCOMM.2012.091712.121395

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, the performance of a low duty factor (DF) hybrid direct sequence (DS) multiband (MB)-pulsed ultra wideband (UWB) system is evaluated over realistic propagation channels to highlight its capability of interference mitigation. The interference mitigation techniques incorporated in the DS-MB-UWB system is a novel design that includes the utilization of the frequency-agile multiple sub-band configuration and the coexistence-friendly low DF signaling. The system design consists of a Rake type receiver over multipath and multi-user channel in the presence of a coexisting narrowband interferer. The propagation channels are modeled based on actual measurement data. Firstly, by suppressing the power in the particular sub-band coexisting with the narrowband signal, performance degradation due to narrowband interference can be improved. It is observed that by fully suppressing the sub-band affected by the narrowband signal, a typical 1-digit performance improvement (e.g. BER improves from 10(-3) to 10(-4)) can be achieved. Secondly, by employing lower DF signaling, self interference (SI) and multi-user interference (MUI) can be mitigated. It is found that a typical 3 dB improvement is achieved by reducing the DF from 0.5 to 0.04. Together, the sub-band power suppression and low DF signaling are shown to be effective mitigation techniques against environment with the presence of SI, MUI and narrowband interference.

DOI： 10.1587/transfun.E94.A.2762

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, the impact of chip duty factor (DF) on direct sequence (DS), time hopping (TH) and hybrid DS-TH ultra wideband (UWB) systems is investigated in realistic environments. Rake receivers are designed to perform energy capture (EC) on received UWB signals over multipath and multi-user environment in the presence of narrowband interference. It is found that by applying lower DF in the signal design, multipath resolvability can be increased and system performance can be improved. However, in contrary to the common belief, lower DF does not always contribute to performance improvement. On the other hand, it is observed that at extremely low DF, EC capability may be compromised. causing performance degradation. The optimum DF values for respective systems are determined and discussed in this paper. Additionally, the strength and tradeoff for DS. TH and DS-TH UWB systems employing varying DF are investigated and compared over multipath and multi-user environment. In a multipath environment, a selective Rake receiver with less than 10 fingers is found to be sufficient for energy capture. In a single user environment, DS-UWB system has the most superior performance, followed by DS-TH-UWB and TH-UWB systems. And in a multi-user environment, DS-TH-UWB is found to outperform the rest, followed by DS-UWB and TH-UWB systems.

DOI： 10.1587/transfun.E93.A.1716

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

An exact expression of the average error rate is developed for a band-limited binary phase-shift keying (BPSK) system in the presence of adjacent channel interference (ACI) considering a Nakagami fading channel. The system employs a root-raised cosine (RRC) filter both in the transmitter and receiver sides and a transmitter power amplifier (PA) that may have nonlinear input/output characteristics. These practical considerations are accurately taken into account. By utilizing the characteristic function (CF) method of error-rate analysis, we interestingly blend the concepts of time and frequency domains and develop an error-rate expression that is simple and general for several system parameters, including adjacent channel separation, RRC filter roll-off factor, and PA output back-off (OBO). Hence, the error rate in the presence of cochannel interference (CCI) is obtained as a special case. The developed results for a single-branch receiver are then extended for diversity receivers, and several interesting observations are made.

DOI： 10.1109/TVT.2009.2037821

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

DOI： 10.1587/transfun.E92.A.2679

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper proposes a hybrid multiband (MB) ultra wide-band (UWB) system with direct sequence (DS) spreading. The theoretical error analysis for the DS-MB-UWB multiple access system with Rake receiver in the presence of multipath and narrowband interference is developed. The developed theoretical framework models the multiple access interference (MAI), multipath interference (MI) and narrowband interference for the designed UWB system. It is shown that the system error performance corresponding to the combining effects of these interference can be accurately modeled and calculated. Monte Carlo simulation results are provided to validate the accuracy of the model. Additionally, it is found that narrowband interference can be mitigated effectively in the multiband UWB system by suppressing the particular UWB sub-band co-existing with the interfering narrowband signal. A typical improvement of 5 dB can be achieved with 75% sub-band power suppression. On the other hand, suppression of UWB sub-band is also found to decrease frequency diversity, thus facilitating the increase of MAI. In this paper, the developed model is utilized to determine the parameters that optimize the UWB system performance by minimizing the effective interference.

DOI： 10.1587/transfun.E92.A.2167

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

A simple exact error rate analysis is presented for random binary direct sequence code division multiple access (DS-CDMA) considering a general pulse shape and flat Nakagami Fading channel. First of all, a simple model is developed for the multiple access interference (MAI). Based on this, a simple exact expression of the characteristic function (CF) of MAI is developed in a straight forward manner. Finally, an exact expression of error rate is obtained following, the CF method of error rate analysis. The exact error rate so obtained can be much easily evaluated as compared to the only reliable approximate error rate expression currently available, which is based on the Improved Gaussian Approximation (IGA).

DOI： 10.1587/transcom.E92.B.1808

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Exact bit error probabilities (BEP) are derived in closed-form for binary pulsed direct sequence (DS-) and hybrid direct sequence time hopping code division multiple access (DS/TH-CDMA) systems that have potential applications in ultra-wideband (UWB) communications. Flat Nakagami fading channel is considered and the characteristic function (CF) method is adopted. An exact expression of the CF is obtained through a straightforward method, which is simple and good for any arbitrary pulse shape. The CF is then used to obtain the exact BEP that requires less computational complexity than the method based on improved Gaussian approximation (IGA). It is shown under identical operating conditions that the shape of the CF, as well as, the BEP differs considerably for the two systems. While both the systems perform comparably in heavily faded channel, the hybrid system shows better BEP performance in lightly-faded channel. The CF and BEP also strongly depend on chip length and chip-duty that constitute the processing gain (PG). Different combinations of the parameters may result into the same PG and the BEP of a particular system for a constant PG, though remains nearly constant in a highly faded channel, may vary substantially in lightly-faded channel. A comparison of the results from the exact method with those from the standard Gaussian approximation (SGA) reveals that the SGA, though accurate for both the systems in highly-faded channel, becomes extremely optimistic for low-duty systems in lightly-faded channel. The SGA also fails to track several other system trade-offs.

DOI： 10.1093/ietfec/e91-a.11.3150

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Based on the characteristic function method, an exact error analysis is presented for low-duty pulsed direct sequence code division multiple access (DS-CDMA) systems in flat Nakagami fading channel. The presented method is simple and good for any arbitrary pulse shape. The computational involvement of the method is simpler than the method based on improved Gaussian approximation (IGA), which is the only reliable method currently available for calculating error probabilities of such systems.

DOI： 10.1109/LCOMM.2007.062020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper investigates the impact of chip duty factor (DF) in DS-UWB system with Rake receiver over AWGN and UWB indoor multipath environment corresponding to system parameters such as spreading bandwidth and chip length. Manipulating DF in DS-UWB system offers several advantages over multipath channel and thus, capable of improving system performance for better quality of communication. Although employing lower DF generally improves performance, in some exceptional cases on the other hand, degradation can be observed despite decreasing DF Therefore, the objective of this paper is to clarify the relationship between DF and DS-UWB system performance. We discovered that with constant processing gain and spreading bandwidth, performance improvement can be observed at DF lower than 0.17. Additionally, with spreading bandwidth as tradeoff parameter, significant performance improvement can only be observed below DF of 0.85.

DOI： 10.1093/ietfec/e89-a.11.3152

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, ultra-wideband (UWB) multiple access systems are introduced by using direct-sequence (DS) and hybrid direct-sequence time-hopping (DS/TH) code division multiple access (CDMA) that use arbitrary chip-duty of the spreading sequences. The bit error probabilities are presented. First of all, the variances of the multiple access interference are developed by investigating the collision properties of the signals. Afterward, various approximations are applied. The standard Gaussian approximation (SGA) for the DS system is shown to become extremely optimistic as the chip-duty becomes low. Though the hybrid system performs better, the SGA still remains optimistic. To obtain accurate results, Holtzman's simplified improved Gaussian approximation (SIGA) and Morrow and Lehnert's improved Gaussian approximation (IGA) are used. A shortcoming of the SIGA is rediscovered that renders it unusable for low-duty DS systems, especially, at high signal-to-noise ratio. However, for the hybrid system, the SIGA works as an excellent tool. The IGA is used to get accurate results for the low-duty DS systems. It is shown that lowering of chip-duty by keeping chip rate and chip length unchanged improves performance for asynchronous DS and both asynchronous and synchronous hybrid systems. However, under the same processing gain, a high-duty system performs better than a low-duty system. Performance of synchronous DS system remains independent of chip-duty.

DOI： 10.1093/ietfec/e89-a.6.1668

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, the impact of timing jitter in direct sequence ultra wideband (DS-UWB) system is investigated over multipath fading channel. Also, a novel hybrid direct sequence multiband UWB (DS-MB-UWB) system is proposed to mitigate the impact of timing jitter. We analyze and compare the system performance for conventional DS-UWB and hybrid DS-MB-UWB with Rake receiver in the presence of timing jitter over additive white Gaussian noise (AWGN) and multipath channel. Theoretical framework is developed to calculate the amount of average energy captured in the multipath profiles and symbol error rate (SER) considering the presence of timing jitter. It is found that DS-MB-UWB system, which employs multiple sub-bands is more jitter-robust than conventional DS-UWB systems. Besides, timing jitter is found to have different impacts on DS-UWB and DS-MB-UWB systems corresponding to different parameters such as number of sub-bands employed, pulse shape, center frequency, bandwidth, number of combined paths in Rake receiver and channel power delay profile (PDP). These different impacts are analyzed and discussed in the paper.

DOI： 10.1093/ietfec/e89-a.6.1657

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Error performance of DS-CDMA is discussed over independent Rayleigh faded multipath channel employing selective Rake (SRake) receiver. Simple-to-evaluate and accurate error probabilities are given following Holtzman's simplified improved Gaussian approximation (SIGA). Comparing with SIGA, the validity of standard Gaussian approximation (SGA) is then verified. It is shown that SGA is accurate for SRake until some number of combined paths beyond which it becomes optimistic. It is also shown that as compared to single user performance, the SRake performance is relatively less degraded by multiple access interference (MAI) while the number of combined paths is small.

DOI： 10.1093/ietfec/e88-a.11.3118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Performance of Rake reception of Ultra Wideband (UWB) signals is evaluated from energy capture perspective. In addition to ordinary all Rake (ARake) and selective Rake (SRake) receivers which are considered in conventional spread spectrum communications, we introduce optimum ARake and SRake receivers which include the estimation of delay of the combining multipaths. Impact of pulse-width is discussed on their performances considering the relationship between pulse-width and fading. Time hopping M-ary pulse position modulation (TH-MPPM) and binary phase shift keying (TH-BPSK) are considered as modulation schemes. Extensive simulation results are presented showing the performances of the Rakes introduced using IEEE 802.15.3a UWB channel models (CM1 to CM3). Performance of MPPM is shown for various values of M and modulation parameters. The impact of pulse-width is illustrated mainly using BPSK. It is shown that the total energy capture (i.e. by ARake) strongly depends on the pulse-width, and the shorter the pulse-width the more is the amount. The energy capture also varies a lot for employing either optimum or ordinary Raking method. Energy capture by SRake additionally strongly depends on the number of combined paths until the number is <= 20 for optimum SRake and <= 10 for ordinary SRake; however, afterwards saturating effects are seen. Several aspects regarding the performance versus complexity issue of Rake receivers are also discussed.

DOI： 10.1093/ietfec/e88-a.9.2339

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Simple-to-evaluate and accurate bit error probabilities are presented for impulse radio ultra-wideband multiple access systems that use time hopping sequences with pulse based polarity randomization and binary phase shift keying modulation. Simplified improved Gaussian approximation is used. It is shown that despite having the same processing gain, which is the multiplication of the number of frames per bit and chips per frame, different combinations of the parameters result in different performances. The theoretical results are validated by Monte Carlo simulations.

DOI： 10.1109/LCOMM.2005.09032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Performance of selective Rake (SRake) receiver is evaluated for direct sequence ultra wideband (DS-UWB) communications considering an independent Rayleigh channel having exponentially decaying power delay profile (PDP). BEP performances are shown. The results obtained are compared with similar results in a channel having flat PDP. Assumption of a flat PDP is found to predict the optimum spreading bandwidth to be lower and sub-optimum operating performance beyond optimum spreading bandwidth to be severely worse than that is achievable in a channel having exponentially decaying PDP by employing an SRake receiver having fixed number of combined paths. Optimum spreading bandwidth for SRake in a channel having exponentially decaying PDP is shown to be much larger than the one in a channel having flat PDP; that is specifically a good-news for UWB communications. Effects of partial band interference are also investigated. Interference is found to be less effective in exponentially decaying PDP.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This letter discusses the performance of online SNR estimation including fading parameter estimation for parallel combinatorial SS (PC/SS) systems. The PC/SS systems are partial-code-parallel multicode SS systems, which have high-rate data transmission capability. Nakagami-m distribution is assumed as fading channel model to cover a wide range of fading conditions. The SNR and fading parameter estimation considered in this letter is based on only a statistical ratio of correlator outputs at the receiver. Numerical results show that SNR estimation performance with fading parameter estimation is close to the one in the case of perfect fading parameter information, if the number of transmitting PN codes is less than a half of assigned PN codes.

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Language：English   Publishing type：Research paper (scientific journal)  

Peak and average power emissions of the newly emerging ultra wideband (UWB) radio are supposed to be limited by regulatory constraints. Impact of emission constraints on direct sequence (DS-) UWB communications that use arbitrary chip-duty is discussed in this letter. Depending on the communication pulse shape, a minimum chip-duty below which average emission cannot be increased with bandwidth, or in other words, permissible average emission limit cannot be reached due to the peak constraint is pointed. Effect of the emission constraints on the system capacity is also investigated and compared with the same with no constraint. It is shown that a peak constraint slows down the capacity increment with bandwidth. © 2004, The Institute of Electronics, Information and Communication Engineers. All rights reserved.

DOI： 10.1587/elex.1.483

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this paper, an online SNR estimator is proposed for parallel combinatorial SS (PC/SS) systems in Nakagami fading channels. The PC/SS systems are called as partial-code-parallel multicode DS/SS systems, which have the higher-speed data transmission capability comparing with conventional multicode DS/SS systems referred to as all-code-parallel systems. We propose an SNR estimator based on a statistical ratio of correlator outputs at the receiver. The SNR at the correlator output is estimated through a simple polynomial from the statistical ratio. We investigate the SNR estimation accuracy in Nakagami fading channels through computer simulations. In addition, we apply it to the convolutional coded PC/SS systems with iterative demodulation and decoding to evaluate the estimation performance from the viewpoint of error rate. Numerical results show that the PC/SS systems with the proposed SNR estimator have superior estimation performance to conventional DS/SS systems. It is also shown that the bit error rate performance using our SNR estimation method is close to the performance with perfect knowledge of channel state information in Nakagami fading channels and correlated Rayleigh fading channels.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Upper bounds on the bit error rate (BER) for maximum likelihood (ML) decoding are derived in convolutional coded parallel combinatorial spread spectrum (PC/SS) systems over additive white Gaussian noise (AWGN) channels. PC/SS systems can achieve higher data transmission than conventional multicode SS systems. To make the derivation tractable, we put a uniform interleaver between a convolutional encoder and a PC/SS transmitter. Since the PC/SS transmitter is employed as the "inner encoder," the bounds are obtained in a similar manner of the derivation in serially concatenated codes through a uniform interleaver. Two different error patterns in the PC/SS system are considered in the performance analysis. Numerical results show that the derived BER bounds are sufficiently accurate. It is found that the coded PC/SS systems outperform coded all-code-parallel DS/SS systems under the same data rate conditions if the number of pre-assigned PN codes increases.

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This paper proposes iterative demodulation/decoding for parallel combinatorial spread spectrum (PC/SS) systems. A PC/SS system conveys information data by a combination of pre-assigned orthogonal spreading sequences with polarity. In this paper, convolutional coding with a uniform random interleaver is implemented in channel coding, just like as a serial concatenated coding. A 'soft-in/soft-out' PC/SS demodulator based on a posteriori probability algorithm is proposed to perform the iterative demodulation and decoding. Simulation results demonstrate that the proposed iterative demodulation/decoding scheme bring significant improvement in bit error rate performance. This proposed decoding scheme achieves highspeed transmission by two approaches. One is a puncturing operation, and the other is to increase the number of transmitting sequences. In the latter approach, lower error rate performance is achieved comparing with that the punctured convolutional code is used to increase the information bit rate.

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This paper describes the multiple access performance of parallel combinatory spread spectrum (PC/SS) communication systems in nonfading and Rayleigh fading multipath channels. The PC/SS systems can provide the high-speed data transmission capability by transmitting multiple pseudo-noise sequences out of a pre-assigned sequence set. The performance is evaluated in terms of average bit error rate (BER) by numerical computation. In nonfading white gaussian channel, the PC/SS systems are superior to conventional direct sequence spread spectrum (DS/SS) systems under the identical spreading factor condition. In Rayleigh fading channel, the performance of the PC/SS system without diversity is poorer than that of the DS/SS system. By including the explicit and implicit diversity, the performance of the PC/SS system becomes better than that of conventional DS/SS systems. A longer spreading sequence is assignable to a PC/SS system having the spreading factor equal to that in the conventional DS/SS system. Hence, the error control coding is easily. It is found that the PC/SS systems including diversity and Reed-Solomon coding improves the multiple access performance.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Other Link： http://hdl.handle.net/10191/6196

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

The performance of parallel combinatory spread spectrum (PC/SS) communication systems in the frequency-nonselective, slowly Rayleigh fading channel is studied. Performance is evaluated by symbol error rate using numerical computation. To overcome the performance degradation caused by fading, we also studied the effects of selection diversity and Reed-Solomon coding applied to the PC/SS system. As a result, a remarkable improvement in error rate performance is achieved with Reed-Solomon coding and diversity technique. The coding rate for the maximum coding gain is almost a half of that in the additive white gaussian noise channel.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In order to utilize higher frequency bands above 6 GHz which is an important technical challenge in fifth generation mobile systems and ultra-high speed WLANs, radio propagation channel properties in large variety of deployment scenarios should be thoroughly investigated. This paper presented measurement results in an atrium entrance hall environment at an millimeter-wave band of 58.5 GHz assuming an indoor hotspot access scenario. In this measurement, the channel transfer functions of a wideband signal with 400 MHz bandwidth were measured by rotating high gain horn antennas with 12 and 30 degree half power beamwidth at 25 receiver positions. From the measured double-directional angular delay power spectrum, the multi-path clusters were roughly identified by local peak detection. This paper presented delay and angle domain intercluster characteristics and identified the propagation mechanism of each cluster comparing with ray tracing simulation. The measurement results revealed that the dominant mechanisms of the multi-path clusters are the first-order specular reflection from environment specific large walls and scattering by columns and square pillars.

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This paper presented an outdoor-to-indoor (O2I) channel measurement result at 58.5 GHz assuming an outdoor hotspot access scenario in 5G mobile systems and WLANs. Comparing the measurement results with ray-tracing (RT) simulation, dominant propagation mechanisms were identified. From the analysis, the propagation mechanism of eight multipath clusters were identified.

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This paper presented dominant propagation mechanisms in an outdoor open area environment through the channel measurement and ray-tracing (RT) simulation at an mm-wave band of 58.5 GHz assuming an outdoor hotspot access scenario in 5G mobile systems and WLANs. From the data analysis, multi-path clusters by first- and second-order reflection, first order diffraction and scattering mechanisms were identified. The measurement result revealed that the multi-path clusters have relatively small power less than approximately 20 dB to the direct path other than first-order reflection from nearby buildings that can be predicted in a deterministic manner, and the channel can he well expressed by the quasi-deterministic (Q-D) channel model which supports natural description of environment-specific deterministic components separately from the other random components. Based on Q-D model, this paper presented extracted statistical channel model parameters of the random components by using RT simulation.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electronics, Information and Communication Engineers  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

One of the primary objectives of Wireless Sensor Network (WSN) is to provide full coverage of a sensing field as long as possible. The deployment strategy of sensor nodes in the sensor field is the most critical factor related to the network coverage. However, the traditional deployment methods can cause coverage holes in the sensing field. Therefore, this paper proposes a new deployment method based on Multi-objective Immune Algorithm (MIA) and binary sensing model to alleviate these coverage holes. MIA is adopted here to maximize the coverage area of WSN by rearranging the mobile sensors based on limiting their mobility within their communication range to preserve the connectivity among them. The performance of the proposed algorithm is compared with the previous algorithms using Matlab simulation for different network environments with and without obstacles. Simulation results show that the proposed algorithm improves the coverage area and the mobility cost of WSN. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.compeleceng.2015.04.003

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Coverage has direct effect on the network performance, thus it considered as the measure of quality of service in WSNs. The deployment strategy of sensor nodes in the sensor field is the most critical factor related to the network coverage. So, in this paper a centralized deployment algorithm based on immune optimization algorithm is proposed to improve the coverage of mobile sensor networks. The proposed algorithm redeploys the random deployed sensor nodes to maximize the coverage area based on a probabilistic sensing model. Moreover, the proposed algorithm limits the moving distance of mobile sensor nodes to reduce the dissipated energy in mobility and to ensure the connectivity among the sensor nodes. The performance of the proposed algorithm is compared with the CSAPO algorithm using MATLAB simulation. Simulation results show that the proposed algorithm outperforms the CSAPO algorithm in terms of the network coverage, mobility cost and convergence speed.

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This paper presents a wideband full polarimetric directional channel measurement results at 58.5 GHz in a small office room environment assuming an indoor access-point (AP) scenario in the next generation mobile systems. The delay resolution was 2.5 ns from the signal bandwidth of 4100 MHz, and the double directional angular characteristics were achieved by rotating high gain horn antennas at both sides of transmitter and receiver. By identifying scattering objects from the measurement data analysis, some important observation about the channel properties were reported. The results reveal that there were a few number of dominant specular multipath components of which the relative power to that of the direct path ranged between -8 and -13 dB. It was also observed that the depolarization is not significant in most of the detected paths with cross-polarization ratio of larger than 14 dB.

DOI： 10.1109/PIMRC.2015.7343400

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

A Wireless Sensor Network (WSN) consists of spatially distributed autonomous sensors with sensing, computation and wireless communication capabilities. Each sensor generally has the task to monitor, measure ambient conditions, and disseminate the collected data towards a base station. One of the key points in the design stage of a WSN that is related to the sensing attribute is the coverage of the sensing field. The coverage issue in WSNs depends on many factors, such as the network topology, sensor sensing model, and the most important one is the deployment strategy. The sensor nodes can be deployed either deterministically or randomly. Random deployment of the sensor nodes can cause coverage holes formulation; therefore, in most cases, random deployment is not guaranteed to be efficient for achieving the required coverage. In this case, the mobility feature of the nodes can be utilized in order to maximize the coverage. This is Non-deterministic Polynomial-time hard (NP-hard) problem. So in this paper, the Immune Algorithm (IA) is used to relocate the mobile sensor nodes after the initial configuration to maximize the coverage area with the moving dissipated energy minimized. The performance of the proposed algorithm is compared with the previous algorithms using Matlab simulation. Simulation results show that the proposed algorithm improves the network coverage and the redundant covered area with minimum moving consumption energy.

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In this paper, we investigate a new technique for simultaneous wireless information and energy transfer in multiple-input multiple-output relay channels. The proposed technique exploits the array configuration at the relay node and uses the antenna elements either for conventional decoding or for rectifying (rectennas). In order to keep the complexity low, a dynamic antenna switching between decoding/rectifying is proposed based on the principles of the generalized selection combiner (GSC); the L strongest paths are allocated for decoding while the remaining channel paths for rectifying (and vice versa). The optimal L as well as the allocation strategy that minimizes the outage probability are investigated via theoretical and numerical results. In addition, two performance bounds that provide the optimal performance without the limitation of GSC are proposed by solving a linear programming and a binary knapsack problem, respectively.

DOI： 10.1109/ICC.2014.6883913

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This paper presents a cooperative spectrum sensing scheme for cognitive radio based on the FFT energy detection. The proposed cooperative sensing scheme utilizes the cross correlation between the output of the sensor of interest and composite output of other sensors. Simulation results show that the proposed cooperative sensing scheme is superior to conventional cooperative sensing using frequency domain correlation detection.

DOI： 10.1109/ISCE.2014.6884433

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Geomagnetic information is informative because it has the ability to detect information about orientation by way of a ubiquitous device. However, a magnetic disturbance easily influences geomagnetic information. The magnetic disturbance detection method is needed in order to use geomagnetic information. Firstly, in this paper, the availability of geomagnetic information in Japan is investigated by field measurement work. Then, a new magnetic disturbance detection method which is better than the conventional method is proposed. The basic function of the proposed method is tested in actual condition.

DOI： 10.1587/transfun.E96.A.2745

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：VDE  

In this paper, a novel regularization-parameter design for the adaptive proximal forward-backward splitting algorithm is proposed for sparse system identification. The regularization parameter is controlled adaptively based on sparsity of an estimated unknown system. The regularizer is designed by approximating an !p quasi-norm (0 < p < 1) linearly. Numerical examples show that the proposed algorithm is robust to the variation of the system sparsity.

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Different from the conventional networks with single secondary network, the spectrum sensing scheme for cognitive coexistent networks should not only detect the primary signal but also detect the secondary signals to avoid the interference with both the primary network and the operating coexistent secondary networks. Therefore, the sensing scheme in coexistent networks should be able to differentiate the primary signal from the secondary signals. Due to the heterogeneity of the secondary networks, the secondary signals may exploit different PHY modes (some of them may be the same as the primary PHY mode), which imposes difficulties in the coherent signal detection schemes. Aiming at overcoming such difficulties, this paper proposes a non-coherent spectrum sensing scheme with the assistance of the geo-locations of the primary and secondary nodes. In the proposed scheme, the differentiation between the primary and secondary signals is formulated into a problem of solving a non-homogeneous linear equation matrix. During the signal detection, the characteristics of both primary and secondary signals are not required. Both the analysis and the simulation results show the feasibility and efficiency of the proposed scheme.

DOI： 10.1109/ICCW.2013.6649257

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A geo-location assisted real-time in-band spectrum sensing scheme is proposed to carry out the spectrum sensing and secondary transmissions in parallel. It is able to avoid the widely used "quiet periods," which have at least the following two disadvantages. First, periodical interruption of the secondary transmissions will degrade the QoS of secondary networks (e.g., decreased system capacity, increased packet delay, etc.). Second, tight synchronization becomes necessary but very difficult to implement in the distributed networks. With the assistance of geo-locations of the primary transmitters and the secondary users, the proposed method is able to differentiate the target primary signal power from the co-channel and adjacent-channel interference produced by the simultaneous data transmissions in the secondary networks. Then, the interference can be cancelled when constructing the test statistic for the energy detectors. Both analyzing and simulation results show that the proposed method is able to successfully cancel the interference and can achieve a good performance.

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This paper provides an informative overview of the recently formed IEEE 802.24 Smart Grid Technical Advisory Group (TAG) and the role of IEEE 802 communications standards in Smart Grid. Communications are an integral part in the definition of the Smart Grid. Standards and recommendations developed by the IEEE 802 LAN/MAN Standards Committee (LMSC) and its Working Groups are a critical element in data communications for the smart grid.

DOI： 10.1109/OnlineGreenCom.2013.6731044

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SAGE PUBLICATIONS INC  

This paper proposes a noncoherent spectrum sensing scheme for the cognitive coexistent heterogeneous networks with the assistance of geolocation information of primary and secondary nodes. Different from the conventional networks with single secondary network, the spectrum sensing scheme in the coexistence scenario should not only detect the primary signal but also detect the secondary signals to avoid the interference with both the primary network and the operating coexistent secondary networks. Therefore, the sensing scheme in this case should be able to differentiate the primary signal from each kind of the secondary signals. However, in the coexistent heterogeneous scenarios, the secondary signals may exploit different PHY modes (some of them may be the same as the primary PHY mode), which imposes difficulties in the coherent signal detection schemes. Aiming to tackle this problem, the parallel detection of both primary signal and each kind of secondary signals is implemented through a proposed noncoherent power decomposition scheme. In this scheme, the power decomposition is formulated into a problem of solving a nonhomogeneous linear equation matrix. During the signal detection, the characteristics of both primary and secondary signals are not required. Both the analysis and the simulation results show the feasibility and efficiency of the proposed scheme.

DOI： 10.1155/2013/141480

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The performance of energy detection-based spectrum sensing is greatly compromised by the problem of noise uncertainty consisting of device noise uncertainty and environmental interference uncertainty. This paper first compares these two kinds of uncertainties and comes to the conclusion that the environmental interference dominates the noise uncertainty problem. Aiming at alleviating the environmental interference, this paper proposed a power differentiation scheme to differentiate the target primary signal from the environmental interference produced by the simultaneously transmitted secondary signals and the device noise. The differentiated target primary signal power, rather than the total received composited power used in most conventional schemes, is used to construct the test statics for the energy detection to improve the sensing performance. The proposed power differentiation scheme does not require any prior knowledge of the primary signal except the geolocations of the primary transmitters and secondary users, thus, is a non-coherent scheme. Simulation results show that the proposed scheme can effectively cope with the environmental interference and can greatly improve the performance of energy detection-based spectrum sensing.

DOI： 10.1109/ICON.2012.6506577

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Inter-symbol/frame interference analysis is presented for pulsed direct sequence (DS) and hybrid direct sequence time hopping (DS/TH) ultra-wideband (UWB) communications considering a frequency selective Nakagami fading channel. Following the analysis, error rate expressions are developed and performance comparison is presented for the systems. It is found that the performance of pulsed DS system may depend on pulse repetition rate (PRR), number of combined paths by Rake receiver and the channel profile in a kind of unpredictable manner. For low PRR, the DS system performs better than DS/TH irrespective of the channel profile. For medium to high PRR, DS and DS/TH systems may perform comparably in a channel with a single decaying profile. However, if the channel contains more than one decaying profiles like as in Saleh-Valenzuela model, the performance of DS may drastically degrade and perform worse than DS/TH at some values of PRRs. The performance of DS/TH is relatively less influenced by the shape of the channel profile. Theoretical results are verified by simulations.

DOI： 10.1109/VETECS.2009.5073389

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An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio.

DOI： 10.1109/WCNC.2009.4917717

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This paper proposes a noncoherent Rake receiver structure in M-ary code shift keying (CSK) direct sequence ultra-wideband (DS-UWB) communication systems. The proposed Rake receiver contains a selection combining of in-phase and quadrature components of each resolvable path at the matched filter output. Simulation results show that the proposed Rake receiver demonstrates superior error rate performance comparing with conventional noncoherent Rake receiver.

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An in-depth yet simple analysis is presented for binary direct sequence code division multiple access (DS-CDMA) systems considering a frequency selective Nakagami fading channel and maximal ratio combining (MRC) receiver. The inevitable inter-symbol interference as well as multiple access interference from simultaneous users are modeled elegantly and their characteristic functions (CF) are developed. Utilizing the CFs, the exact bit error probabilities are developed following the CF method of error rate analysis that claims the honor to be the first-to-publish reliable result for such channel and receiver. The CF based exact error rate is less computationally intensive than that can be obtained by traditional methods of approximation. The same method also lets us develop a new simpler approximate error rate. The exact method is utilized to investigate the range of parameters where approximations (existing and the new) would be accurate.

DOI： 10.1109/ICCW.2009.5208118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communication Engineers  

The interpolation of color pixel values prior to digital halftoning is discussed and a new color interpolation scheme is presented by a directional copy of color values in the gradient field of luma. Error diffusion quantization is combined with clustered-dot ordered dithering to prevent from contouring. Experimental results demonstrate that sharp and false color-free interpolation is obtained to produce color bilevel AM halftones with weak rosettes and no contouring artifacts.

DOI： 10.1587/elex.5.170

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An exact analysis is presented for equal gain combining of binary direct sequence code division multiple access (DS-CDMA) signals in frequency selective Nakagami fading channel. Following the analysis, expressions for exact characteristic function (CF) are developed for self-interference and multiple access interference. As a final outcome, exact bit error probabilities are presented for the system based on CF method. The presented method is simple and good for any arbitrary pulse shape, channel profile, total number of resolved paths and number of combined paths. Monte Carlo simulation confirms the analytical results. © 2008 IEEE.

DOI： 10.1109/VETECS.2008.424

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This paper proposes a cognitive interference-mitigation technique for a hybrid direct sequence (DS) multiband (MB) ultra wideband (UWB) system. Theoretical framework of the DS-MB-UWB multiple access system employing cognitive interference-detection and mitigation is constructed over multipath environment in the presence of a coexisting narrowband wireless system. Interference mitigation is achieved through partially suppressing the power of the particular sub-band coexisting with the narrowband signal. A typical error performance improvement of around 10 fold can be achieved by suppressing 75% power of the affected sub-band. Additionally, increasing the number of sub-bands is found to achieve more improvement than increasing the number of DS chips. This paper attempts to develop a cognitive mitigation technology able to obtain optimum performance improvement while maintaining the highest possible frequency diversity.

DOI： 10.1109/RWS.2008.4463439

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Multiple access analysis is presented for pulsed direct sequence (DS) and hybrid DS time hopping (DS/TH) ultra-wideband (UWB) communications considering a Saleh-Valenzuela type clustered frequency selective Nakagami fading channel. A general analytical framework is developed for modeling the multiple access interference (MAI) in low-duty systems that is substantially complicated than analysis of more commonly known DS-code division multiple access (CDMA). Using Rake receiver with maximal ratio combining (MRC), we are able to produce a simple error rate expression for general number of combined paths. The theoretical results are then used for performance evaluation and comparison of the two systems. Results show that in multiple access environment, a DS/TH system may gain many fold performance improvement as compared to a DS system.

DOI： 10.1109/PIMRC.2008.4699710

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Fractionally spaced Rake (FSRake) reception is proposed for non-coherent direct sequence ultra wideband (DS-UWB) wireless communication systems. In the FSRake reception, output signal of the pulse matched filter is sampled with a faster sampling rate than the chip rate of DS-UWB signal. Computer simulation is conducted to evaluate the performance of FSRake receiver in DS-UWB wireless system with M-ary code shift keying (MCSK-UWB) over IEEE802.15.3a multipath channel. Simulation results show that the non-coherent FSRake reception provides more than 4dB SNR gain at the 10(-5) bit error rate in comparison with the conventional non-coherent Rake reception, when the number of combining paths is six in 4-ary code shift keying UWB system over IEEE 802.15.3a CM 1.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An exact analysis is presented for equal gain combining of binary direct sequence code division multiple access (DS-CDMA) signals in frequency selective Nakagami fading channel. Following the analysis, expressions for exact characteristic function (CF) are developed for self-interference and multiple access interference. As a final outcome, exact bit error probabilities are presented for the system based on CIF method. The presented method is simple and good for any arbitrary pulse shape, channel profile, total number of resolved paths and number of combined paths. Monte Carlo simulation confirms the analytical results.

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Exact bit error probabilities (BEP) are derived in closed-form for an impulse radio (IR) multi-access system that employs a single transmit antenna and multiple receive antennas. The transmitted signal passes through a flat Nakagami fading channel and the signals received in multiple antennas are equal-gain combined (EGC) before detection. The characteristic function (CF) method is adopted to develop the BEP, where an exact expression of the CF of multi-access interference is obtained first through a straight forward method. The derived exact BEP expression is simple and good for any arbitrary number of receiving antennas and pulse shape. The theoretical BEP shows absolute match with the BEP obtained from simulations. © 2007 IEEE.

DOI： 10.1109/ICUWB.2007.4381004

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Based on the characteristic function method, new expressions of exact bit error probabilities are derived in closed-form for binary direct sequence code division multiple access (DS-CDMA) in flat Nakagami fading channel adopting a straight forward method. The method is simple and good for any arbitrary pulse shape. The results from exact analysis are then compared with those obtained through modeling the multiple access interference as Gaussian noise, for which also a new expression is given for error probability.

DOI： 10.1109/WCNC.2007.40

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Language：English   Publishing type：Research paper (international conference proceedings)  

Exact bit error probabilities (BEP) are derived in closed form for pulsed binary direct sequence ultra-wideband (DS-UWB) multiple access systems in flat Nakagami fading channel. The characteristic function (CF) method is adopted where an exact expression of the CF is obtained through a straight forward method. The method is simple and good for any arbitrary pulse shape. The results from exact analysis are then compared with those obtained from the standard Gaussian approximation (SGA), for which also a new expression is given for the error probability. It is shown that the shape of the CF depends considerably both on chip length and chip-duty and can be different even for the same processing gain (PG), since different combinations of the parameters may result into the same PG. In such a case, the BEP for a PG, however, though remains unchanged in a highly faded channel, may vary substantially in lightly faded channel. Irrespective of the chip length and chip-duty, the SGA is found quite accurate for highly faded channel, which, however, becomes extremely optimistic for low duty systems in lightly faded channels. © 2007 IEEE.

DOI： 10.1109/ICC.2007.677

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Exact bit error probabilities (BEP) are derived in closed form for pulsed binary direct sequence ultra-wideband (DS-UWB) multiple access systems in flat Nakagami fading channel. The characteristic function (CF) method is adopted where an exact expression of the CF is obtained through a straight forward method. The method is simple and good for any arbitrary pulse shape. The results from exact analysis are then compared with those obtained from the standard Gaussian approximation (SGA), for which also a new expression is given for the error probability. It is shown that the shape of the CF depends considerably both on chip length and chip-duty and can be different even for the same processing gain (PG), since different combinations of the parameters may result into the same PG. In such a case, the BEP for a PG, however, though remains unchanged in a highly faded channel, may vary substantially in lightly faded channel. Irrespective of the chip length and chip-duty, the SGA is found quite accurate for highly faded channel, which, however, becomes extremely optimistic for low duty systems in lightly faded channels.

DOI： 10.1109/ICC.2007.677

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Exact bit error probabilities (BEP) are derived in closed-form for hybrid direct sequence time hopping code division multiple access (DS/TH-CDMA) systems that have been recently widely used for ultra-wideband (UWB) communications. Flat Nakagami fading channel is considered. The characteristic function (CF) method is adopted where an exact expression of the CF is obtained through a straight forward method. The method is simple and good for any arbitrary pulse shape. The results from exact analysis are then compared with those obtained from the standard Gaussian approximation (SGA), for which also a new expression is given for the error probability. It is shown that the shape of the CF depends considerably both on frames per bit and chips per frame and can be different even for the same processing gain (PG), since different combinations of the parameters may result into the same PG. In such a case, the BEP for a PG, however, though remains unchanged in a highly faded channel, may vary substantially in lightly faded channel. Irrespective of several system parameters, the SGA is found quite accurate for highly faded channel, which, however, becomes quite optimistic for low duty systems in lightly faded channels.

DOI： 10.1109/VETECS.2007.623

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A hybrid direct-sequence (DS)-multiband ultrawideband (UWB) multiple access system is proposed and a simple error analysis is presented for the system considering a multipath channel. The error analysis facilitates to obtain simple-to-evaluate and accurate error probabilities based on Holtzman's simplified improved Gaussian approximation (SIGA), a method that has previously mainly been used in DS-CDMA. In this paper, we show that the method can also be used effectively for UWB multiple access systems. It is shown that despite having the same processing gain, which is some multiple of the multiplication of the number of frequency bands in use and pulses per bit, different combinations of the parameters result in different performances. Considering Rake type receiver, results are shown for both maximal ratio combining (MRC) and equal gain combining (EGC) and the validity of standard Gaussian approximation (SGA) is examined for various combined paths. The theoretical results are validated by Monte Carlo simulations.

DOI： 10.1109/ICU.2006.281626

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A simple multiple access analysis is presented for two types of multiband pulsed ultra-wideband (UWB) multiple access systems, both of which use modulated pulse train, one being uniform and the other being time hopping (TH). The analysis facilitates to obtain simple-to-evaluate and accurate error probabilities based on Holtzman's simplified improved Gaussian approximation. It is shown that despite having the same processing gain, which is some multiple of the multiplication of the number of frequency bands in use, frames per bit and chips per frame, different combinations of the parameters result in different performances. In addition, the UWB system using TH pulse train is shown to perform better than the one using uniform pulse train. System performances are presented for various system parameters- investigating tradeoffs among them and the validity of the standard Gaussian approximation is examined. The theoretical results are validated by Monte Carlo simulations.

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This paper proposes fractionally spaced selective Rake (FSRake) receiver for M-ary bi-orthogonal keying based direct sequence ultra wideband (MBOK DS-UWB) wireless systems. Conventional Rake receiver combines resolved matched filter outputs by sampling with pulse duration. In the proposed FSRake reception, matched filter output is sampled by the fractional duration of pulse. A certain number of strongest paths are combined among these sampled outputs. This proposed FSRakc receiver provides more energy capture than conventional Rake receiver. Simulation results show that the proposed FSRake reception provides more than 8dB SNR gain at the 10(-5) bit error rate in comparison with the conventional Rake reception in 2BOK.

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In this paper, we investigate the impact of chip duty factor (DF) on direct sequence (DS) ultra wideband (UWB) system with Rake receiver over multipath and multiuser environment in the presence of narrowband interference. By employing DS-UWB signals with varying DF, the system performance corresponding to different parameters such as data rate, signal to interference ratio (SIR), signal to noise ratio (SNR) and number of interfering users are investigated. We found that by using signals with lower DF, system performance can be improved without compromising processing gain and data rate. Additionally, interference mitigation of low DF signal is more effective in high SIR environment. We also discovered an optimum data rate where the relative best system performance can be obtained.

DOI： 10.1109/ICU.2006.281587

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE COMPUTER SOC  

In this paper, the impact of timing jitter an a carrier-based direct sequence ultra wideband (DS-UWB) systems over an additive white Gaussian noise (AWGN) and Rayleigh channel with exponentially decaying power delay profile (PDP) is investigated. A selective Rake (SRake) receiver is employed to capture the energy from the received signal. Gaussian distributed timing jitter is assumed to take place at the template generator of the SRake receiver. Theoretical framework to obtain the system bit error rate (BER) corresponding different system parameters such as signal to noise ratio (SNR), root-mean-square jitter (RMSJ), system bandwidth, center frequency and Rake fingers is presented. It is found that BER performance degrades significantly as RMSJ and center frequency increase, Employing wider system bandwidth also tends to degrade BER performance. Using higher SNR and number of Rake fingers is found to be able to improve the BER performance.

DOI： 10.1109/ICON.2005.1635668

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In this paper, ultra-wideband (UWB) multiple access systems are introduced by using direct-sequence (DS) and hybrid direct-sequence time-hopping, (DS/TH) code division multiple access (CDMA) that use arbitrary chip-duty of the spreading sequences. The bit error probabilities are presented. First of all, the variances of the multiple access interference are developed. Afterwards, various approximations are applied. The standard Gaussian approximation (SGA) for the DS system is shown to become extremely optimistic as the chip-duty becomes low. Though the hybrid system performs better. the SGA still remains optimistic. To obtain accurate results Holtzman's simplified improved Gaussian approximation (SIGA) and Morrow and Lehnert's improved Gaussian approximation (IGA) are used. A shortcoming of SIGA is rediscovered that renders it unusable for low-duty DS systems. However, for the hybrid system, the SIGA works as an excellent tool. The IGA is used to get accurate results for the low-duty DS systems. It is shown that lowering of chip-duty by keeping chip rate and chip length unchanged improves performance for asynchronous DS and both asynchronous and synchronous hybrid systems. However, under the same processing gain, a high-duty system performs better than a low-duty system. Performance of synchronous DS system remains independent of chip-duty.

DOI： 10.1109/WIRLES.2005.1549583

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In this paper, we present the impact of timing jitter on a Direct Sequence Ultra Wideband (DS-UWB) system in Additive White Gaussian Noise (AWGN) and multipath environment. Rake receiver is used to capture the multipath profile. Investigation is performed in ordinary and optimum Rake, each with all Rake (A Rake) and selective Rake (SRake). Additionally, the equal gain combining (EGC) maximal ratio combining (MRC) methods are also applied for each combination. We use two types of timing jitter, uniformly distributed and Gaussian distributed, with varying root mean square (RMS) to evaluate the different impacts on the communication system. The bit error rate (BER) of the system is presented corresponding to different parameters such as signal to noise ratio (SAW), RMS jitter and number of selected and combined paths. The simulation results show that optimum Rake is more severely affected by the presence of timing jitter. It is also observed that Gaussian distributed timing jitter has a greater impact to the system than that of the uniformly distributed at low RMS jitter. At higher timing jitter, the performance of ordinary Rake is similar to that Of optimum Rake, suggesting that the ordinary Rake is more practical than optimum Rake due to its lower system complexity.

DOI： 10.1109/WIRLES.2005.1549587

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A hybrid direct-sequence time-hopping (DS/TH) impulse radio (IR) ultra-wideband (UWB) multiple access system is proposed and a simple error analysis is presented for the system. The error analysis facilitates to obtain simple-to-evaluate and accurate error probabilities based on Holtzman's simplified improved Gaussian approximation (SIGA), a method that has previously mainly been used in DS-CDMA. In this paper, we show that the method can also be used effectively for IR UWB multiple access systems that use signals of low duty-cycle. It is shown that despite having the same processing gain, which is the multiplication of the number of frames per bit and chips per frame, different combinations of the parameters result in different performances. System performances are presented for various duty-cycles of the signals considering equal and unequal powers of the users and the validity of standard Gaussian approximation (SGA) is examined at those situations. The theoretical results are validated by Monte Carlo simulations.

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DOI： 10.1109/UWBST.2004.1320968

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Multiple antenna systems are promising architectures for overcoming the effects of multi-path interference an increasing the spectrum efficiency. In order to be able to investigate these systems, in this article, we derive generalized spatial correlation equations of a circular antenna array for two typical angular energy distributions: a Gaussian angle distribution and uniform angular distribution. The generalized spatial correlation equations are investigated carefully by exact and approximate analyses.

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Multiple antenna arrays are promising architectures for overcoming the efects of multipath interference and increasing the spectrum efficiency. In order to be able to investigate these systems, in this article, we derive generalized spatial correlation equations of a circular antenna array for two types of angular energy distributions: a Gaussian angle distribution, and uniform angular distribution. The ganaralized spatial correlation equations and BER (:Bit Error Rate) performance is investigated. It has been reported that spatial correlation and BER performance using linear array antenna, but very few attempts have been made at circular array antenna [5][7]. It was found from the result that BER of receiving arrival wave with uniform distribution is better than that with gaussian distribution.

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In this paper, we derive the SEP for time-hopping M-ary PPM (TH-MPPM) UWB communication systems as a function of captured SNR per symbol and simplify the results for TH-BPSK. For TH-MPPM system, we incorporate the effect of modulation index (b) on SEP. The results obtained give us way to evaluate the performance of Rake reception of UWB signals in dense multipath channels from energy capture perspective. We present more general type of results that can be applied for verities of Rake implementations. We present simulation results using IEEE 802.15.3a UWB channel models for various pulse-widths. We evaluate the performances of optimum and ordinary all Rake (ARake) and selective Rake (SRake) receivers in different channel models (CM1 to CM3). We compare relative costs of simplifying various Rake complexities. Conditioned on some parameters, we present an optimum pulse-width for UWB communications while SRake is employed.

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In this paper, we propose the soft boundary concept. achieved by dynamic tilted antenna to solve the issue of traffic congestion occurred in cellular wireless systems. The tilted antenna array can provide the merit of traffic balance and also achieve the optimization of the signal-to-interference ratio (SIR) at receivers by automatically tilting the antenna and implementing the soft boundary among cells, corresponding to the variation of traffic. According to our results, it is shown that power ratio control do not necessarily improved system performance when there is a large variation in traffic because it only control power levels. Also the properly chosen angle of tilt antenna can relieve the traffic congestion and perform the system performance optimization.

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DOI： 10.1109/ISPA.2003.1296902

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DOI： 10.1109/ICIP.2003.1246657

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In this paper, we derive spatial correlation functions of linear and circular antenna arrays for three types of angular energy distributions: a Gaussian angle distribution, the angular energy distribution arising from a Gaussian spatial distribution, and uniform angular distribution. The spatial correlation functions are investigated carefully. The spatial correlation is a function of antenna spacing, array geometry and the angular energy distribution. In order to emphasize the research and their applications in diversity reception, as an example, performance of the antenna arrays with MRC in correlated Nakagami fading channels is investigated, in which analytical formulas of average BER for the spatial correlation are obtained.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-INT SOCIETY OPTICAL ENGINEERING  

As an extra option, fine grayscale data that exceed eight bits per pixel are encoded into pseudogray colors in 8-bit sRGB color space to be displayed on an 8-bit sRGB CRT monitor. The characteristics of the pseudogray are investigated in terms of the CIELAB color difference and a*b* coordinates. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

DOI： 10.1117/1.1578492]

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The demand for wireless mobile communications has grown at a very high rate, recently. In order to solve the non-uniform traffic rates, the use of cell splits is unavoidable for balancing the traffic rate and maximizing total system capacity. For cell planning, a DS-CDMA cellular system can be comprise of different cell sizes because of different demands and population density of the service area. In this paper, we develop a general model to study the forward link capacity and outage probability of a DS-CDMA cellular system with mixed cell sizes. The analysis of outage probability is carried out using the log-normal approximation. When a macrocell is split into the three microcells, as an example, we calculate the multi-cross interferences between macrocells and microcells, and the forward link capacities for the microcells and the neighboring macrocells. The maximum allowable capacity plane for macrocell and microcell is also investigated. The numerical results and discussions with previous published results of reverse link are summarized.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this paper, we derive spatial correlation functions of linear and circular antenna arrays for three types of angular energy distributions: a Gaussian angle distribution, the angular energy distribution arising from a Gaussian spatial distribution, and uniform angular distribution. The spatial correlation functions are investigated carefully. The spatial correlation is a function of antenna spacing, array geometry and the angular energy distribution. In order to emphasize the research and their applications in diversity reception, as an example, performance of the antenna arrays with MRC in correlated Nakagami fading channels is investigated, in which analytical formulas of average BER for the spatial correlation are obtained.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：BEIJING UNIV POSTS TELECOMMUNICAT PRESS  

Diversity reception, a key technique derived against multi-path mitigation in wireless communication system, is examined and discussed. Especially, we present an approach to investigate perfect/imperfect channel detection when a simple transmit diversity scheme (STD)[9] are used in the wireless systems, which provide remarkable schemes for diversity transmission over Rayleigh-fading channels using multiple antennas. In order to effectively make use of the transmit diversity techniques, the same approach is extended to process the situation of two transmit antennas and N receive antennas in STD scheme (2 x N STD), in which the effects of perfect/imperfect channel detection and the diversity reception with independent and correlated Rayleigh-fading signals are evaluated and compared.

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Transmit diversity, a key technique derived against multi-path mitigation in wireless communication system, is examined and discussed. Especially, we present an approach to investigate perfect/imperfect channel detection when the maximal ratio receiver combined scheme (MRRC) and a simple transmit diversity scheme (STD) are used in the wireless systems, which provide remarkable schemes for diversity transmission over Rayleigh-fading channels using multiple antennas. In order to effectively make use of the transmit diversity techniques, the same approach is extended to process the situation of one transmit antennas and N receive antennas in MRRC scheme (1 x N MRRC) and two transmit antennas and N receive antennas in STD scheme (2 x N STD). The effects of perfect/imperfect channel detection and the diversity reception with independent and correlated Rayleigh-fading signals are evaluated and compared carefully.

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In this paper, the co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. Overall rate, bit error ratio (BER) and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss in this system with cellular architecture, W-CDMA applying interference cancellation (IC) shows a substantial difference in spectrum efficiency, the overlaid system can provide a greater overall rate arid higher spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system. The interference cancellation can significantly improve BER of the spectrum overlaid system.

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DOI： 10.1109/WCNC.2002.993486

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

in this article, the co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. Overall rate and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss in this system with cellular architecture, W-CDMA applying interference cancellation (IC) shows a substantial difference in. spectrum efficiency, the overlaid system can provide a greater overall rate and higher spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system.

DOI： 10.1109/ICCCAS.2002.1180601

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this paper, a simple and accurate on-line SNR estimator is proposed for parallel combinatorial SS (PC/SS) systems in Nakagami fading channels. The PC/SS systems are a kind of partial-code-parallel multicode DS/SS systems., Our proposed SNR estimator estimates the SNR at the correlator output by using a statistical ratio of the sum of correlator outputs for pre-assinged PN codes. We investigate the SNR estimation accuracy in Nakagami fading channels through computer simulations. Numerical results show that the the proposed SNR estimator brings superior estimation performance to that in conventional estimator that has proposed by Summers and Wilson [9]. In addition, we apply it to the convolutional coded PC/SS systems with iterative demodulation and decoding to evaluate the estimation performance from the viewpoint of error rate. By using our estimator, the bit error rate performance is close to the performance with perfect knowledge of the SNR information in Nakagami fading channels and correlated Rayleigh fading channels.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

next generation wireless communication is based on a global system of fixed and wireless mobile services that are transportable across different network backbones,network service providers and network geographical boundaries. Although the power control is essential for Direct Sequence Code Division Multiple Access (DS-CDMA) cellular systems to overcome the near-far problem, one of the most important problems for the system is handover management and its effects on the system. This paper presents an approach to investigate the effects of soft handover[1][2] and perfect power control[3][4] on the forward link in a DS-CDMA cellular system. Especially, the relationships between the size of handover zone and the capacity gain are evaluated under the log-normal shadow channel. Then the optimization of maximum forward capacity is very necessary to be done with the maximum size of soft handover zone to the various system characteristics.

DOI： 10.1109/ICCCAS.2002.1180632

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE COMPUTER SOC  

In this paper, we proposed a theoretical method in order to estimate the forward link outage probability and user capacity of a cellular system which are based on IS-95 CDMA standard, especially impact of power control strategy and voice activity monitoring on the system under long-term fading. According to the numerical results obtained in this paper, the power control strategy leads to approximately threefold the user capacity contrast to the situation without power control strategy. The power control strategy not only improves the desired signal to interference ratio in the reference user's receiver, but also offers uniform service to the user wherever it is located in the cell.

DOI： 10.1109/ICON.2001.962392

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper proposes iterative demodulation/decoding for parallel combinatorial spread spectrum (PC/SS) systems. The PC/SS systems convey the information data by a combination of pre-assigned spreading sequences with the polarity. In this paper, convolutional coding with random interleaver is implemented as channel coding, just like as a serial concatenated concatenated coding. A 'soft-in/soft-out' PC/SS demodulator based on a posteriori probability algorithm is proposed to perform the iterative demodulation and decoding. Simulation results demonstrate that the proposed iterative demodulation and decoding bring significant improvement in the bit error rate performance.

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This paper investigates the effects of using erasure information in Reed Solomon (RS) coded parallel combinatorial spread spectrum (PC/SS) communication systems over AWGN and Rayleigh fading channels. The PC/SS system is an advanced multicode direct sequence spread spectrum (DS/SS) system for high-speed data transmission. Our previous works have shown that the RS coded PC/SS systems provide significant improvement in error rate performance over conventional DS/SS systems. To achieve further performance improvement in the PC/SS systems, error-and-erasure decoding techniques are implemented in RS coded PC/SS receiver. To obtain the erasure location information, a threshold test for the squared ratio of the correlator outputs is applied. Simulation results show that the coded PC/SS system using the erasure information provides significant improvement in word error rate (WER) and bit error rate (BER). With errors-only decoding, the PC/SS systems cannot improve the error rate performance because of large SNR penalty introduced by coding. On the contrary, error-and-erasure decoding using erasure information still improves the performance of PC/SS systems.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

We introduce an extended EZW coder that uses flexible zerotree coding of wavelet coefficients. A flexible parent-child relationship is defined so as to exploit spatial dependencies within a subband as well as hierarchical dependencies among multi-scale subbands. The new relationship is based on a particular statistics that a large coefficient is more likely to have large coefficients in its neighborhood in terms of space and scale. In the flexible relationship, a parent coefficient in a subband relates to four child coefficients in the next finer subband in the same orientation. If each of the children is larger than a given threshold, the parent extends its parentship to the neighbors close to its conventional children. A probing bit is introduced to indicate whether a significant parent has significant children to be scanned. This enables us to avoid excessive scan of insignificant coefficients. Also, produced symbols are re-symbolized into simple variable-length binary codes to remove some redundancy according to a pre-defined rule. As a result, the wavelet coefficients can be described with a small number of binary symbols. This binary symbol stream gives a competitive performance without an additional entropy coding and thus a fast encoding/decoding is possible. Moreover, the binary symbols can be more compressed by an adaptive arithmetic coding. Our experimental results are given in both binary-coded mode and arithmetic-ceded mode. Also, these results are compared with those of the EZW coder.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley and Sons Inc.  

Edge enhancement is employed to improve visual perception of images that are unclear because of blur. In this paper, the point spread function is considered to be known, and a method of edge enhancement is proposed using wavelet expansion and vector quantization for multiresolution representation. With the proposed method, sharp images are prepared along with corresponding blurred images, and the local frequency characteristics are taught to a vector quantizer for subsequent edge enhancement. The local frequency characteristics are extracted from images by means of wavelet expansion and then classified and processed through the vector quantizer. Experiments with blurred images, including those with noise superposed, showed the proposed method to be efficient in edge enhancement and, at the same time, in noise suppression. © 1998 Scripta Technica.

DOI： 10.1002/(SICI)1520-6424(199901)82:1<87::AID-ECJA9>3.0.CO;2-I

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

A zerotree image-coding scheme is introduced that effectively exploits the inter-scale self-similarities found in the octave decomposition by a wavelet transform. A zerotree is useful for efficiently coding wavelet coefficients; its efficiency was proved by Shapiro's EZW. In the EZW coder, wavelet coefficients are symbolized, then entropy-coded far further compression. In this paper, we analyze the symbols produced by the EZW coder and discuss the entropy for a symbol. We modify the procedure used for symbol-stream generation to produce lower entropy. First, we modify the fixed relation between a parent and children used in the EZW coder to raise the probability that a significant parent has significant children. The modified relation is flexibly modified again based on the observation that a significant coefficient is more likely to have significant coefficients in its neighborhood. The three relations are compared in terms of the number of symbols they produce.

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Language：English   Publishing type：Research paper (other academic)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper investigates the effects of using side information in parallel combinatorial spread spectrum (PC/SS) systems over Rayleigh fading channels. The PC/SS system is an advanced multicode direct sequence spread spectrum system. Our previous works have shown that the Reed-Solomon (RS) coded PC/SS systems provide significant improvement in error rate performance over conventional DS/SS systems. To achieve further performance improvement in the PC/SS systems, error-and-erasure decoding techniques are implemented in the RS coded PC/SS receiver. Error rate performance of the proposed systyem is analyzed, and compared with that of the coded PC/SS system equipped with errors-only decoding.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We introduce a new zerotree scheme that effectively exploits the inter-scale self-similarities found in the octave decomposition by a wavelet transform A zerotree is useful to code wavelet coefficients and its effectiveness was proved by Shapiro's EZW. In the coding scheme, wavelet coefficients are symbolized and then entropy-coded. The entropy per symbol is determined from the produced symbols and the final coded size is calculated by multiplying the entropy and the total number of symbols.
In this paper, we analyze symbols produced from the EZW and discuss the entropy per symbol. Since the entropy depends on the produced symbols, we modify the procedure of symbol generation. First we extend the relation between a parent and children used in the EZW to raise the probability such that a significant parent has significant children. The proposed relation is flexibly extended according to the fact that a significant coefficient is likely to have significant coefficients in its neighborhood.
Our coding results are compared with the published results in paper [1] and improvements come from the use of lower entropy per symbol. We also give the comparison of the number of produced symbols.

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This paper investigates the effects of using error-and-erasure decoding in coded parallel combinatorial spread spectrum (PC/SS) systems over Rayleigh fading channels. The PC/SS system is an advanced multi-code direct sequence spread spectrum system for high-speed data transmission. Our previous works have shown that the Reed-Solomon (RS) coded PC/SS systems provide significant improvement in error rate performance over conventional DS/SS systems.
To achieve further performance improvement in the PC/SS systems, error-and-erasure decoding techniques are implemented in the RS coded PC/SS receiver. To obtain the erasure location information, a threshold for the signal-to-noise ratio is set at the correlator output.
Numerical results show that the coded PC/SS systems with error-and-erasure decoding provides significant improvement in the bit error rate (BER). With errors-only decoding, the PC/SS systems cannot improve the error rate performance because of large SNR penalty introduced by coding. On the contrary, error-and erasure decoding still improves the performance of PC/SS systems under multiple access environment.

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In image transmission, channel noise causes severe degradation in the quality of received images. Thus graceful degradation mechanism and error correction capability should be implemented in accordance with various image transmission scenarios. This paper presents a trial to address such a problem. In particular, the effect of error control coding (ECC) is investigated to protect the coded image quality against inevitable channel noise. Simulation results show that error control coding guarantees to receive images with the same PSNR as in the noiseless case when bit error rate (BER) is lower than 5 x 10(-3).

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This paper investigates the error rate performance of differential parallel combinatorial CDMA (DPC/CDMA) systems in frequency-nonselective and frequency-selective Rician fading channels. The DPC/CDMA system is one of the multi-code DS/CDMA techniques using orthogonal pseudo-noise (PN) sequences. The information data conveys by the combination of pre-assigned PN sequences and by the polarity the transmitting PN sequences. It conveys multiple information bits by the combination of pre-assigned PN sequences set, so that it is capable of making the data rate higher with longer PN sequences.
The bit error rate (BER) performance of uncoded and coded DPC/CDMA systems are analyzed by the standard Gaussian ay proximation for the cc-channel interference analysis. The effect of diversity and error control coding were considered throughout the analysis.
Numerical results show that the coded DPC/CDMA systems provide substantial BER improvement comparing with conventional DPSK-DS/CDMA systems. Using explicit diversity enhances the advantage of coded DPC/CDMA systems. If stronger line-of-sight signals are available in Rician fading channels, the coded DPC/CDMA systems are more advantageous even though the available spreading factor is small.

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This paper investigates the error rate performance of parallel combinatorial spread spectrum (PC:SS) communication systems that use coherent and differential multiphase modulation: multiphase parallel combinatorial spread spectrum (MPC/SS) communication systems. The PC/SS systems are multicode SS systems based on orthogonal pseudo-noise (PN) sequences. Data is transmitted by delivering a combination of multiple PN sequences among a set of pre-assigned PN sequences. In the MPC/SS systems, every PN sequence on transmission is modulated by q-ary coherent or differential phase shift keying (PSK). Symbol error rate (SER) and average bit error rate (BER) in coherent and differential MPC/SS systems are investigated. The BER comparison between the MPC/SS systems and simple multicode SS systems with q-ary coherent and differential PSF; is also presented. Numerical results show that the MPC/SS systems are superior to the conventional q-ary PSK systems, if they have equal spectral efficiency.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Inst. of Image Information and Television Engineers  

A scalable image coding method is presented. Spatial scalability is implemented by using a multiresolution representation produced by a wavelet expansion. Quality scalability is implemented by using a multiprecision representation produced by multistage zero run-length coding after nonlinear quantization. The data rate is controlled by threshold values and/or spatial resolution in the wavelet expansion. The coding method owes its fine scalability and higher compression to multiresolution decomposition, nonlinear quantization, multistage zero run-length coding and arithmetic coding. In addition to the simplicity in coding, edges and outlines are well preserved without blocking noise at low bit rates. A few examples are also given.

DOI： 10.3169/itej.51.1889

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Other Link： http://hdl.handle.net/10191/6195

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：I E E E  

This paper investigates the error rate performance of a multi-code DS/CDMA systems using the combination of PN codes and DPSK: differential parallel combinatorial code-division multiple access (DPC/CDMA) systems in Rayleigh fading channels. The bit error rate (BER) are calculated based on the average SNR with the standard gaussian approximation of the multiple access interferences. It is assumed that the explicit and implicit diversity are employed in the receiver. The EER performance of Uncoded and coded DPC/CDMA systems are presented, and are compared with that of conventional DPSK-DS/CDMA systems.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：PUBLISHING HOUSE ELECTRONICS INDUSTRY  

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This paper proposes differential parallel combinatory spread spectrum (DPC/SS) communication systems
one of the parallel combinatory spread spectrum (SS) communication systems the authors have been studying so far. the parallel combinatory SS system is a spectral efficient SS system in which the system transforms sever al bits of data into a combination of pseudonoise (PN) sequence with modulation of positive and negative signs and transmits them. The proposed DPC/SS system applies differential encoding to the positive or negative sign modulation of the PN sequences, and then they are transmitted. In the receiver, the combination of a transmitted sequence set is estimated by noncoherent detection and the coded sign is demodulated by differential detection. Thus, the receiver does not need to regenerate the phase of the carrier frequency. the proposed systems will be applicable to a mobile cellular system in which a large phase variation interferes with the communications. This paper evaluates the error performances. of the DPC/SS systems in additive white Gaussian noise (AWGN) channels and frequency‐nonselective, slowly Rayleigh fading channels. It also evaluates the effect of diversity in the Rayleigh fading channels. In the AWGN channel, the DPC/SS system is superior by I dB to the differential phase‐shift keying (DPSK) system and to the BPSK system in terms of required signal‐to‐noise ratio at 10‐8 bit error rate (BER) at the same spectral efficiency. In the Rayleigh fading channel, diversity reception in the DPC/SS system gains more improvement in the BER performance, as the number of branches increases, than that obtained in a direct‐sequence spread spectrum system with DPSK. Copyright © 1995 Wiley Periodicals, Inc., A Wiley Company

DOI： 10.1002/ecja.4410781007

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DOI： 10.1002/ecjc.4430760810

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In this paper, a spectrum management algorithm using weighted state transition is investigated for use of TV white space (TVWS) which is temporally and geographically vacant channels in TV broadcast band. Spectrum management is an important element of cognitive radio for operation over TVWS without interference to the incumbent TV broadcast and other licensed wireless communication systems. To decide the channel in operation based on the information of channel use from database and spectrum sensing results, a modified algorithm based on the spectrum management in the IEEE 802.22 and the IEEE 802.11af / 802.15.4m is proposed. Impact of miss detection probabilities to the performance is evaluated for avoiding harmful interference to licensed wireless systems by computer simulation. According to further investigations on harmful interference, some interference can decrease by using proposed spectrum management algorithm.

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This paper investigates the performance of low-complexity technique for simultaneous wireless information and power transfer (SWIPT) in multiple-input multiple-output (MIMO) relay channels. The relay transmission system has been composed by source node, relay node and destination node so far. In this study, MIMO antenna switching is introduced in SWIPT relay node to capture information and energy simultaneously. Furthermore, impact of introducing an interference node is also investigated. Simulation results show that the interference node contributes the performance of SWIPT MIMO relay system in the case of Rayleigh fading and low RF energy transfer efficiency.

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In this paper, a spectrum management algorithm using weighted state transition is proposed for use of TV white space (TVWS) which is temporally and geographically vacant channels in TV broadcast band. Spectrum management is an important element of cognitive radio for operation over TVWS without interference to the incumbent TV broadcast and other licensed wireless communication systems. To decide the channel in operation based on the information of channel use from database and spectrum sensing results, a modified algorithm based on the spectrum management in the IEEE 802.22 and the IEEE 802.11af/802.15.4m is proposed. Impact of miss detection and false alarm probabilities to the performance are evaluated for the secure reservation of operating channel and for avoiding harmful interference to licensed wireless systems by computer simulation.

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The widely used "quiet periods" have at least two shortcomings: periodical interrupting the secondary transmission will degrade the QoS of secondary networks, e.g., decreasing the system capacity, increasing end-to-end packet delay; tight synchronization, which is difficult to be implemented in the distributed networks, becomes necessary. Aiming to overcome such shortcomings, a geolocation based real time in-band spectrum sensing is proposed in this paper. By using the locations of the primary transmitters and the secondary users, the proposed method is able to differentiate the target primary signal power from the co-channel and adjacent-channel interference produced by the simultaneous data transmissions in the secondary networks. Consequently, the interference can be cancelled when constructing the test statistic for the energy detectors. No prior knowledge of the primary signal is required by the proposed method. Both analyzing and simulation results show that the proposed method is able to successfully cancel the interference and can achieve a good performance.

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In this paper, acquisition performance of direct sequence ultra wide band (DS/UWB)communication systems is analyzed. In UWB wireless packet transmission, it must complete the acquisition in the preamble that is placed at the top of the packet. Delay of the path under multipath fading environment influences the performance of a demodulation system depending on the timing captured by acquisition. In this paper, using peak detector and interval estimation is proposed to achieve faster and more accurate acquisition in multipath fading environment. Computer simulation is conducted to evaluate the acquisition performance of a DSμUWB system based on the IEEE802. 1 5.4a standard under multipath fading environment. Simulation results show that the peak detection and interval estimation is effective to capture the accurate peak of the matched filter output in the DS/UWB acquisition. In addition, the reduction of the acquisition time is achievable by optimal design of the capturing interval for the peak detection.

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This paper reviews the current trends and challenges regarding the use of “white space” in wireless communications, which is a freauency spectrum unused at a certain time and location. Regulatory issues related to the use of white space in the TV broadcast band (TV white space: TVWS) and standardization activities related to wireless communications in TVWS are described. the technical elements of cognitive radio incorporated in IEEE 802.22, which is the first IEEE standard for the use of TVWS, are reviewed. Finally, future problems to be solved to realize better use of the white space spectrum are also discussed.

DOI： 10.1587/essfr.6.250

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In this paper, acquisition performance of direct sequence ultra wide band (DS/UWB) communication systems is analyzed. In wireless packet transmissions, signal acquisition should be completed within duration of preamble that is placed at the top of the packet. In order to accomplish accurate and rapid acquisition of low-duty signal such as DS/UWB signal under multipath fading environment, the proposed acquisition system using the RAKE combining and the verification mode shows effect by computer simulation result. Also, we derived the average acquisition time theoretically considering the use of verification mode and multipath fading environment by using the Markov chain model. Numerical results shows some similarity comparing with the simulation results.

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This paper presents explores higher rate data transmission capability in IEEE802.22 wireless regional area network (WRAN). Since OFDM and multilevel modulation such as QAM are employed in the IEEE802.22, impact of nonlinearity is unavoidable to seek higher data rate by using higher-order modulation. In this paper, we have studied use of 4-dimensional (4-D) trellis coded modulation (TCM) in IEEE802.22 WRAN. Computer simulation has been conducted with consideration of multipath channel and nonlinearity of amplifier. Simulation results show that 4-D TCM-192QAM has better error rate performance than conventional coded 256QAM at similar data rate.

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In this paper, performance of wireless LAN is evaluated under operation over "white space" spectrum. Impact of transmission-error and presence of hidden-node are considered. For using the frequency band that is assigned to the specific wireless communication service, but not used temporally and geographically (called "white space"), availability of the operating band in wireless network should be monitored periodically. A promising approach for monitor the operating channel is placing "quiet period" in which all network nodes cease transmission. However, it seems difficult to place such quiet periods in wireless LAN that has a contention-based protocol. So far, we have proposed a method for introducing the quiet period in the IEEE802.11 wireless LAN. In this paper, throughput and response time performance considering hidden-node and transmission-error is evaluated through computer simulation. It is found that the degradation of throughput performance by the presence of hidden-node and transmission-error is diminished by using quiet period.

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In this paper, impact of adjacent channel interference is discussed in a low power wireless data transmission over "white space" spectrum. Use of low power wireless communication system over the adjacent frequency channel in which typically licensed wireless communication system is operating. OFDM modulation is considered in both licensed and low power wireless system for efficient use of radio frequency and minimizing the risk of mutual interference. Bit error rate performance of OFDM system is evaluated when the adjacent channel signal is added as an interference signal. Impact of the FFT size of OFDM, filter characteristics, and the signal structure of OFDM are also evaluated through computer simulation.

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This paper discusses a use of coded modulation in low power wireless broadband communication systems with wide area coverage. After the upcoming termination of terrestrial analog TV broadcasting service in July 2011, it is considered to use a part of newly vacant VHF band for "Customer Provided Mobile Communications." In this paper, trellis coded modulation (TCM) and multi-dimensional TCM has been applied to achieve higher data rate in limited bandwidth under a low power wireless data transmission scenario. Bit error rate performance has been evaluated under multipath fading channel. Simulation results show that significant performance improvement is achievable by using TCM and multi-dimensional TCM, especially in the case of high data rate.

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Acquisition performance in direct sequence ultra wide band (DS/UWB) packet radio transmission is evaluated over multipath fading channel. In packet transmission, a preamble sequence is placed at the top of the packet to perform initial acquisition of the packet of interest. If the acquisition is not completed within a certain time of the preamble, then the packet will be discarded. It may cause significant delay of packet transmission. In this paper, RAKE combining and verification mode is employed to combat multipath fading. Computer simulation is conducted to evaluate the acquisition performance of a DS/UWB system based on the IEEE802.15.4a standard under multipath fading environment. Simulation results show that, significant improvement of acquisition probability is achieved by using RAKE combining. Also, mean acquisition time becomes shorter when the verification mode is equipped with the DS/UWB acquisition system.

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This paper reviews standardization activities of cognitive wireless communication systems based on unlicensed use of vacant frequency spectrum assigned to terrestrial TV broadcast, so called "TV white space." First, overview of regulatory trends in US and Europe is described. Next, standard development activities of wireless network over TV white space are introduced in IEEE802 LAN/MAN Standards Committee (LMSC), especially in 802.22, 802.11, and 802.19. Standardization activities in other standard development organizations are briefly given in this paper.

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Low-rate, but highly reliable data transmission is an important feature in wireless communications for application of medical treatment, healthcare usage, and a control of industrial equipment etc. In this paper, we discuss the use of DS-UWB (direct sequence ultra wideband) technology toward highly reliable wireless communications. BPM-BPSK/DS-UWB standardized by IEEE802.15.4a is considered as an example of DS-UWB. The error rate performance of BPM-BPSK/DS-UWB system is evaluated in multipath fading channel when the effect of antenna-diversity and the forward error correction are considered.

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This paper discusses the possibilities of low power wireless broadband communication systems with wide area coverage. After the upcoming termination of terrestrial analog TV broadcasting service in July 2011, it is considered to use a part of newly vacant VHF band for "Customer Provided Mobile Communications". In this report, we propose a low power, wireless data transmission based on OFDM (orthogonal frequency division multiplexing) in this band. According to the link budget analysis based on the extended Hata model, it will be possible to accomplish a high-rate data transmission with more than 10Mbps and 10^<-5> bit error rate by 0.1W transmission power with 1.7km maximum coverage.

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This paper investigates an interference mitigation scheme for direct sequence ultra-wideband(DS-UWB)wireless communication systems based on wavelet packet-based waveform design. Since UWB signals use very wide frequency spectrum, it is necessary to equip with an appropriate interference mitigation scheme to coexist with conventional narrowband communication systems. In this paper, OFDM(orthogonal frequency-division multiplexing)signal is considered as a conventional narrowband signal. In the proposed scheme, the UWB terminal detects the OFDM signal by wavelet packet signal decomposition. The transmitting UWB waveform is generated by synthesizing the wavelet packet coefficients without that corresponds to the frequency band which may be occupied by the OFDM signal. Simulation results demonstrate that the proposed scheme effectively mitigate the interference from the UWB signal to the existing OFDM signal.

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This paper presents the performance of covariance-based spectrum sensing of ATSC digital TV (DTV) signal in IEEE802.22 wireless regional area network (WRAN). WRAN operates over a vacant frequency band that is originally assigned to the terrestrial TV broadcast by using cognitive radio technology. Spectrum sensing is a key function of cognitive radio to avoid harmful interference for incumbent devices. In this paper, detection performance of covariance-based spectrum sensing for ATSC signal is investigated. Impact of noise uncertainty and shadowing to the detection performance is also evaluated, and is compared with that of energy detection-based spectrum sensing.

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This paper presents the performance of spectrum sensing using frequency domain characteristic spectrum detection of ATSC digital TV (DTV) signal in IEEE802.22 wireless regional area network (WRAN). WRAN operates over a vacant frequency band that is originally assigned to the terrestrial TV broadcast by using cognitive radio technology. Spectrum sensing is a key function of cognitive radio to avoid harmful interference for incumbent devices. In this paper, detection performance of different decision statistics using frequency domain characteristics of ATSC signal is investigated by computer simulation. Impact of noise uncertainty to the detection performance is also evaluated.

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This paper presents the performance of trellis coded modulation (TCM) and multidimensional TCM in IEEE 802.22 wireless regional area network(WRAN). Higher coding rate and low error rate performance can be achieved at the same time by using TCM. In this paper, we have studied the BER performance of WRAN system with TCM and 4-dimensional (4-D) TCM in IEEE 802.22 WRAN channel. Simulation results show that 4-D TCM-192QAM has better error rate performance than conventional coded 256QAM and TCM-256QAM at the same data rate.

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This paper proposes a multilevel spectrum sensing scheme based on energy detector for ATSC digital TV (DTV) signal in IEEE802.22 wireless regional area network (WRAN). Considering spectrum management in IEEE 802.22 WRAN to decide the operating channel among the candidate frequency channel, a spectrum sensing algorithm using multilevel threshold and multiple decision statistics is proposed. The proposed scheme focuses quicker detection of incumbent (primary) signal and simpler structure than a signal specific spectrum sensing. Simulation results show that the proposed scheme has better detection performance with reasonable computational cost. It is also demonstrated that the proposed scheme can be effective to mitigate the impact of noise uncertainty comparing to conventional energy detection-based spectrum sensing scheme.

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This paper proposes an interference mitigation scheme for ultra-wideband(UWB) communication systems by using wavelet packets. Since the UWB systems occupy very wide frequency spectrum, it is necessary to equip with some appropriate interference mitigation scheme for existing narrowband wireless systems. In this paper, OFDM (orthogonal frequency-division multiplexing) signal is considered as a conventional narrowband signal. OFDM is adopted as an air interface of WiMax (world interoperability for microwave access), wireless LAN, etc. In the proposed scheme, the UWB terminal detects the existing OFDM signal, and deletes the wavelet packet coefficients which correspond to the frequency band occupied by the OFDM signal. Simulation results demonstrate that the proposed scheme effectively mitigate the interference from the UWB signal to the existing OFDM signal.

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In this paper, performance of non-coherent Rake reception is investigated in M-ary code shift keying (M-ary CSK) ultra-wideband (UWB) wireless system which is one of the impulse radio-based UWB. Non-coherent Rake reception does not require channel estimation and weighted combining which are necessary in coherent Rake reception. Although it is expected to simplify the receiver structure, performance degradation is unavoidable. In this paper, fractionally spaced Rak (FSRake) concept is applied to the non-coherent Rake reception, which aims at more energy capture and path diversity effect. FSRake reception resolves multipath by oversampling received signal at faster sampling rate than chip rate, and combine them. Error rate performance is evaluated by computer simulation in consideration of different receiver front-end before Rake combining. We also propose a new non-coherent Rake reception by using selection combining of in-phase and quadrature components of matched filter outputs, and demonstrate that it is effective to improve the error rate performance.

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Possibilities and challenges are discussed on future wireless communications with spectrum sharing approach. Demand of wide frequency spectrum has been increasing rapidly due to the recent development of various broadband radio interfaces. Also, emerging interest on ad-hoc network and sensor network will push such growing demand of frequency spectrum, because these networks will have a lot of wireless entities. However, radio frequency spectrum is scarce source; most of the frequency spectrum has been already allocated to various wireless services. Spectrum-sharing based wireless communications such as cognitive radio is a promising solution to use this limited spectrum resource more efficiently. However, many hurdles exist from the viewpoint of regulations and technology to put such spectrum-sharing based wireless technology to practical use. In this paper, ongoing technology development and problems under study are introduced in IEEE802.22 working group, which is working to standardize radio access technology including cognitive radio technology in wireless regional area network (WRAN). Through the introduction of IEEE802.22 standardization activities, we discuss technical barriers and potential technologies of cognitive radio technology for future spectrum-sharing based wireless communications.

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This paper presents the performance of spectrum sensing for ATSC digital TV (DTV) signal in IEEE802.22 wireless regional area network (WRAN). Spectrum sensing is a key function of cognitive radio, which uses a vacant frequency spectrum for communications by detecting signal from incumbent (primary) communication devices. In this paper, detection performance of energy detection-based spectrum sensing is investigated. Impact of noise uncertainty to the detection performance is examined, and effect of diversity detector is demonstrated to mitigate the impact of noise uncertainty.

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Digtal techniques are considered effective to implement compact recivers for DS-UWB wireless communications. This papers studies the use of Bandpass Sampling as a prospective technology for a digital Rake reciver in DS-UWB. Using computer simulation we estimated bit error probability, considering sampling jitter.

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IEEE 802.22, the Working Group on Wireless Regional Area Networks ("WRANs"), is a standardization body to develop a standard for a cognitive radio-based PHY/MAC/air-interface for use by license-exempt devices on a non-interfering basis in spectrum that is allocated to the TV Broadcast Service. In this paper, the aim and scope of IEEE 802.22 standard are described. Current status and future perspective on the 802.22 WRAN standardization are also introduced.

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Ultra-wideband (UWB) systems use pulses of extremely short duration. Hence, in communication over multipath channels, the performance can be improved by Rake type reception. In this study, the performance of fractionally spaced Rake (Fs_Rake) receiver is evaluated by considering a MBOK DS-UWB system. Fs_Rake combines paths which are resolved by oversampling the output of matched filter. Changing the number of samples per path, the performance of Fs_Rake is compared with ordinary Rake. In the simulation results, It is shown that the performance of Fs_Rake gets better than ordinary Rake reception. In addition, it is also shown that higher sampling rarte may even result in worse performance.

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This paper describes the interference mitigation capability of a direct sequence (DS) multiband (MB) ultra wideband (UWB) system over indoor multipath channel in the presence of narrowband interference. DS-MB-UWB system employs several sub-bands instead of a wide single band, thus capable of mitigating interference by only manipulating parameters of the particular affected sub-band. This paper investigates the advantages of suppressing the power of the affected sub-band for the purpose of narrowband interference mitigation. It is found that the more power of the affected sub-band is suppressed, the more the impact of interference can be reduced. Additionally, system performance in the presence of narrowband interference is also found to differ corresponding to parameters such as sub-band spreading bandwidth, signal to interference ratio (SIR), signal to noise ratio (SNR) and spectral location of the narrowband signal.

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A hybrid direct-sequence (DS)-multiband ultra-wideband (UWB) multiple access system is proposed and a simple error analysis is presented for the system considering a multipath channel. Holtzman's simplified improved Gaussian approximation (SIGA) method is used. It is shown that despite having the same processing gain, which is some multiple of the multiplication of the number of frequency bands in use and pulses per bit, different combinations of the parameters result in different performances. Considering Rake type receiver, results are shown for both maximal ratio combining (MRC) and equal gain combining (EGC) and the validity of standard Gaussian approximation (SGA) is examined for various combined paths (Lc). The theoretical results are validated by Monte Carlo simulations.

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In this paper, performance of hybrid direct sequence time hopping (DS/TH) ultra wideband (UWB) multiple access system is evaluated by computer simulation and compared with DS-UWB multiple access system. IEEE802.15.3a multipath channel is considered. For the Hybrid DS/TH-UWB, good performance is expected, because of using combination of spreading and time hopping sequence to detect the desired signals. For high duty, the two systems are shown to perform comparably. However, DS/TH-UWB is found to perform better than DS-UWB with duty lowering.

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Ultra-wideband (UWB) systems use pulses of extremely short duration. Hence, in communication over multipath channels, the performance can be improved by Rake type reception. In this study, the performance of fractionally spaced Rake (Fs_Rake) receiver is evaluated by considering a MBOK DS-UWB system. Fs_Rake combines paths which are resolved by oversampling the output of matched filter. Changing the number of samples per path, the performance of Fs_Rake is compared with ordinary Rake. In the simulation results, It is shown that the performance of Fs_Rake gets better than ordinary Rake reception. In addition, it is also shown that higher sampling rarte may even result in worse performance.

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This paper describes the interference mitigation capability of a direct sequence (DS) multiband (MB) ultra wideband (UWB) system over indoor multipath channel in the presence of narrowband interference. DS-MB-UWB system employs several sub-bands instead of a wide single band, thus capable of mitigating interference by only manipulating parameters of the particular affected sub-band. This paper investigates the advantages of suppressing the power of the affected sub-band for the purpose of narrowband interference mitigation. It is found that the more power of the affected sub-band is suppressed, the more the impact of interference can be reduced. Additionally, system performance in the presence of narrowband interference is also found to differ corresponding to parameters such as sub-band spreading bandwidth, signal to interference ratio (SIR), signal to noise ratio (SNR) and spectral location of the narrowband signal.

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In this paper, performance of hybrid direct sequence time hopping (DS/TH) ultra wideband (UWB) multiple access system is evaluated by computer simulation and compared with DS-UWB multiple access system. IEEE802.15.3a multipath channel is considered. For the Hybrid DS/TH-UWB, good performance is expected, because of using combination of spreading and time hopping sequence to detect the desired signals. For high duty, the two systems are shown to perform comparably. However, DS/TH-UWB is found to perform better than DS-UWB with duty lowering.

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This paper investing impact of quantization in Parallel Combinational (PC)-UWB that UWB applied parallel combination SS method. The PC/UWB communication is a method to aim at a high-speed data transmission by doing the state of data in the combination mapping of two or more diffusion signs. This paper wad assumed indoor use of UWB that investing impact of quantization in PC/UWB used the Rake reception in multipath fading cahannels. Especially, it examined concerning the weight coefficient used for the passing selection and the Rake synthesis in the Rake reception, and the reception performance that MRC (synthesis method compared with the maximum) that accurately presumed the weighting factor is better was shown. Moreover, the best reception performance was seen to exist depending on the passing synthesis number.

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This paper investigates the impact of chip duty factor (DF) on time hopping (TH) ultra wideband (UWB) and direct sequence (DS) TH-UWB communication systems over additive white Gaussian noise (AWGN) and UWB indoor multipath channel. We found that an optimum DF exists for both systems. Also, DS-TH-UWB is found to outperform TH-UWB systems in all DF.

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This document reports the international workshop on ultra wideband (UWB) technologies held in Yokosuka Research Park, December 2005.

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This paper investigates impact of quantization in Rake receiver for direct-sequence ultra-wideband(DS-UWB) system in multipath channel. In DS-UWB communication for high-rate data transmission, inter-pulse interference(IPI) is unavoidable because pulse repetition frequency generally becomes higher. Therefore, combining paths influenced by IPI degrades the performance of reception, and partial Rake (PRake) reception which combines less influenced paths shows better performance. In this paper, impact of quantization at the path selection and combining weight in the Rake reception is evaluated through computer simulation. Simulation results show that almost the same performance as in ideal Rake reception can be obtained by using when the quantization level is more than 32.

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Ultra Wideband(UWB) is a promising technology that enables high-rate short-range wireless communication with more than hundreds Mbps. It is necessary for UWB receiver to obtain high SNR because transmitted UWB signal must maintain very low level of power spectral density. Moreover, multipath fading is other element of performance degradation in indoor channel. In this paper, we proposed a selective Rake receiver that uses two or more template wave forms to reduce these problems. Performance of DS-UWB system with proposed selective Rake receiver is we investigated by computer simulation. Simulation results show that the proposed Rake receiver is effective to improve the error rate performance as the number of template waveform increases.

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Simple-to-evaluate and accurate bit error probabilities are given for binary DS-CDMA communications over independent Rayleigh faded multipath channels while Rake type of receivers are used. By extending the simplified improved Gaussian approximation (SIGA) of Holtzman for multipath channels, we show the accurate results based on SIGA and compare those with widely used standard Gaussian approximation (SGA). By considering flat and exponentially decaying power delay profiles (PDP) of the multipath channel, we investigate the effect of spreading bandwidth and the number of combined paths on the multiple access performance of the system. In other words, we investigate the validity of SGA of multiple access interference (MAI) as compared to the more accurate SIGA for multipath channel while all Rake (ARake) and selective Rake (SRake) receivers are employed. We show that the SGA is accurate 1) for ARake while the spreading is low and 2) for SRake until some number of combined paths, beyond which it becomes optimistic. Additionally, we show that the effect of MAI is much less pronounced in an SRake while the number of combined paths is small. The multiple access performance of the receivers and the validity of SGA also depend on the shape of the PDP.

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Effects of power control are investigated on the performances of asynchronous ultra wideband (UWB) direct sequence (DS) and hybrid direct sequence time hopping (DS/TH) code division multiple access (CDMA) that use low-duty signals. Sequences with random polarities are considered. For small to medium number of users, the hybrid DS/TH system is shown to perform much better than the DS system under perfect power control, provided that we compare the two systems under same processing gain, data rate, chip rate, chip-duty and chip length. However, in the absence of power control, performance of the hybrid system is found to degrade more. As a result, depending on the distribution of powers from all users and the number of users, the two systems may perform comparably or the hybrid system may even perform worse. Lowering of chip-duty with constant chip length is shown to bring more advantage for the hybrid system, which is later found to diminish under imperfect power control. Effects of variations in chip-duty and chip length under same processing gain are also investigated. Explanations to our findings are presented and comments on the choice of the signaling scheme are made.

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This paper presents the simulation of a Direct Sequence (DS) Multiband Ultra Wideband (UWB) communication system applying binary phase shift keying (BPSK) technique. The proposed system is a hybrid system of DS spreading and different center frequency in each chip waveform. Simulation results of system performance in multiple access (MA) channel are presented. In the MA channel simulation, corresponding bit error rate (BER) according to different number of simultaneous users is presented and analyzed. Both synchronous and asynchronous multiple access interference (MAI) are included in the simulation. Besides, system parameters such as chip duty factor, chip length and chip waveforms are also taken into consideration to see the effects on system performance.

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This document reports the international symposium on ultra wideband (UWB) held in Kyoto in May 2005.

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In this paper, we derive the bit error probabilities (BEP) for ultra wideband (UWB) direct sequence code division multiple access (DS-CDMA) communications using random sequences with arbitrary chip duty and pulse shape. In other words, we investigate the impact of chip duty and pulse shape on error probabilities for UWB DS-CDMA. Both synchronous and asynchronous users and carrier-less and carrier-based communications are considered. Additive white Gaussian noise (AWGN) is neglected. The decision statistics are developed. Then BEP equations are presented under Gaussian and simplified improved Gaussian approximations of the multiple access interference (MAI). Results obtained show that for certain chip length, pulse shape and BEP, the number of simultaneous users can be increased considerably in asynchronous system, if the chip duty is lowered. Again, the use of pulse shape having better autocorrelation property also helps to facilitate larger number of simultaneous users. A carrier-based system is found to perform better than a similar carrier-less system. Finally, simulation results are presented to validate theoretical derivations.

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In this paper we present extensive simulation results on various Rake reception of ultra wideband (UWB) signals over IEEE 802.15.3a realistic UWB channel models using BPSK modulation. Convolving the continuous time impulse response with the transmitted pulse and adding WON, we produce the multipath profile in front of the receiver. We show that the more the pulse-width gets shorter, the more fraction of the energy comes to the receiver through isolated paths. Oppositely, the wider is the pulse, the more fraction of the energy is in overlapped path and the more is the multipath fade. We show performance of all Rake (ARake) and selective Rake (SRake) receivers by optimal delay estimation and by ordinary method. We observe wide performance variations in the two methods. We also show an optimum pulse-width for an SRake receiver for each channel model (CM1〜CM3).

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Effects of partial band jamming on the performance of generalized selection combining (GSC) Rake receiver in direct sequence spread spectrum (DS-SS) communications have been investigated. Especially, we focus on effects of jamming on optimum spreading bandwidth for a fixed complexity GSC Rake receiver. The received signals are considered to undergo multipath fading over an independently and identically distributed (i.i.d.) Rayleigh channel, Expressions for performance measure at jamming environment have been derived as a function of system parameters and signal to jamming power ratio (P/J). A flat power delay profile (PDP) is considered for DS-SS. The idea is extended to direct sequence ultra wideband (DS-UWB) communications considering an exponentially decaying PDP. A fixed complexity GSC receiver designed to perform optimally for a given system bandwidth by outputting minimum achievable BEP, is found to perform sub-optimally in presence of jamming in both cases. However, effects of jamming are much less pronounced in case of a decaying PDP.

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This paper presents an overview and recent trends of ultra wide band (UWB) radio technology. UWB technology has been paid much attention as a promising candidate for very high-rate short-range wireless communication network. Since the Federal COmmunication COmmission (FCC) issued a First Report and Order that authorizes the commercial use of the UWB technology in February 2002, research and development (R&D) activities are under way in many wireless industries and research institutes. The UWB is an attractive radio technique for communications, radar and sensors, while it is a controversial technology because mutual interference to the existing wireless communication systems is unavoidable. This paper reviews some modulation technique for UWB communications. Regulation and R&D trends on UWB technology are also introduced.

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In this paper, we propose a M-ary time-hopping/code shift keying (M-ary Th/CSK) modulation for ultra-wideband (UWB) wireless communications. UWB transmission is a promising technology in the future high-rate wireless personal area network (WPAN). Since very short pulse is used in UWB system, transmitting signal occupies extremely wide bandwidth. In the proposed M-ary TH/CSK system, an element of time-hopped sequence is used for choosing a transmitting code sequence among pre-assigned codes. A set of optical orthogonal code and its cyclic shift is used as a set of pre-assigned codes. Transmitter and receiver configurations of M-ary TH/CSK system are described. Preliminary result of error rate performance is also displayed under AWGN environment.

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Fine grayscale data, which exceed eight bits per pixel, are mapped onto points around the achromatic axis in the 8-bit sRGB color space so as to be displayed on an 8-bit sRGB CRT monitor. The characteristics of the pseudo gray are investigated in terms of the CIELAB color difference and a^*b^* coordinates.

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In this work, we consider applying perfect reconstruction de-interlaing to intra-frame/field-based codec system so that the system structure can realize a rich scalability with one bit stream according to requirements for image quality. When the conventional field interleaving or separation is applied for an interlaced picture, the intra-frame/field-based codec system causes horizontal comb-shape artifacts at edges of motion part or aliasing. Due to these effects, the low-bitrate-decoded pictures are degraded around the edges. The proposed technique is shown that the pictures decoded on low bitrate causes less comb-shape artifacts except for extra-process and the one decoded on high bitrate are able to be kept the spacial-resolution. It is also shown that the efficient implementation and lossless implementation exist for a unique case.

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In order to solve the issue of non-uniform traffic occurred in cellular wireless systems, an approach of dynamic tilted antenna mechanism is proposed. Based on this, we discuss the available architecture of cellular systems and investigate the shift of the cell boundary (to be referred to as a soft boundary optimization).

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We derive the upper bound of the bit error rate for block coded parallel combinatorial spread spectrum(PC/SS) systems with an iterative demodulation/decoding. In this paper, the suitable selecting method for the constant weight code has been discussed by using the derived upper bound. The result is that constant weight codes made from a Hadamard matrix are superior to Shalwijk's constant weight codes on the block coded PC/SS systems with iterative demodulation/decoding from the viewpoint of the asymptotic error rate. We have also compared the bit error rate performances of Reed-Solomon coded systems with the performances of proposed demodulation/decoding systems. Bit error performance in the proposed systems are superior to that in Reed Solomon coded systems in the term of the required signal to noise ratio per bit for satisfying 10^<-6> BER.

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Parallel Combinatorial Spread Spectrum (PC/SS) Systems that is a partial-code-parallel multi-code direct sequence SS system has proposed for high-speed data transmission. In this paper, we propose a new channel decoding method for PC/SS systems based on iterative decoding and demodulation strategy by using soft-in soft-out PC/SS demodulator based on a posteriori probability (APP) algorithm, Bit error rate performance in AWGN channel is evaluated by computer simulation. Improvement derived from employing the decoding method is significant, about 4 dB gain has been observed compared to Reed Solomon coded systems in signal to noise ratio per bit at 10^<-5> bit error rate.

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In this paper, a hybrid method of wavelet zerotree image coding and forward error correction(FEC)by using product code is proposed for packet transmission.A modified packetization scheme for wavelet zerotree image coding is proposed to localize the impact of packet loss and bit errors.FEC coding by using Reed-Solomon product code is applied to protect image data from packet loss and bit errors.Computer simulation based on ATM(asynchronous transfer mode)network is performed.Results shows that the proposed method effectively works to protect compressed image data from packet loss and channel bit errors.

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This paper investigates a Reed Solomon(RS)coding scheme for multiphase parallel combinatorial spread spectrum(PC/SS)systems. In the PC/SS systems, multiple pseudo-noise(PN)sequences are simultaneously transmitted out of a pre-assigned spreading sequences set through mapping data onto a specific combination of PN sequences. Using M-ary PSK modulation enables increasing data rate in the PC/SS system. In this paper, the bit error performance is evaluated in RS coded multiphase PC/SS systems with errors-only decoding and error-and-erasure decoding. We also discussed the relations between the error rate performance and the total information bit rate. It is found that the PC/SS system with QPSK yields a superior performance both for error performance and data rate.

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In this paper, performance of Reed-Solomon (RS) coded parallel combinatorial spread spectrum (PC/SS) systems in fading channel is evaluated. The PC/SS system is one of multi-code direct-sequence SS systems. In the PC/SS systems, the data is converted into a combination of orthogonal PN sequences and polarities of transmitting PN sequences. Recently, coded PC/SS system by encoding only the data with respect to the combination have been proposed to achieve both high-speed data transmission and performance improvement. In this paper, the error rate performance of the proposed coded PC/SS system in Rayleigh fading channel is evaluated by computer simulation. Simulation results show that error rate in the data with respect to the polarity of orthogonal PN sequences dominates whole error rate in Raylengh fading channel. However, error rate in the data with respect to the combination is much better than that in conventional coded PC/SS system. Thus it is possible to achieve both high-speed data transmission and performance improvement in fading channel.

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In this paper, we propose a Reed Solomon (RS) coding scheme for parallel combinatorial spread spectrum (PC-SS) systems. The PC-SS system is one of multi-code dirct-sequence SS systems. In the PC-SS systems, the data is converted into two parts. One is combination of orthogonal PN sequences, and the other is polarity of transmitting PN sequences. In the previous study, it is found that error rate of the data with respect to the combination of orthogonal PN sequences dominates whole error rate in PC-SS systems. In this paper, only the data with respect to the combination is encoded by RS codes in the PC-SS systems. The error rate performance of the proposed system in AWGN channel is evaluated by computer simulation. Simulation results show that significant error rate improvement can be observed by the proposed scheme.

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In this paper, performance of wavelet-based SPIHT (set partitioning in hierarchical trees) image coding combined with channel coding is evaluated in burst error channels by computer simu1ation. (23,12) Golay code is applied as forward error correction (FEC) code. To disperse burst errors into each codewords, interleaving/deinterleaving is implemented in the transmitter and receiver. Simulation results show that SPIHT encoded image is severely damaged by burst errors, and received image quality cannot be recovered by using only FEC coding. Combined FEC coding and interleaving with sufficient depth yields significant improvement in received image quality. In burst error channel that average burst length is five, almost the same received image quality as in error-free channel can be maintained by applying Golay code and interleaving with depth 15, if average bit error rate is up to 2x1O^<-3>.

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In this paper, the decoding scheme of Reed-Solomon (RS) coded parallel combinatorial spread spectrum (PC-SS) communication systems is investigated in Rayleigh fading channel. Use of channel state information can provide error rate performance improvement in RS coded PC-SS systems by using error-and-erasure decoding. In the PC-SS systems, several sequences are selected and transmitted among preassigned PN sequences to convey data. Thus channel state information can be easily achieved in the PC-SS systems by using correlator outputs in the receiver. In this paper, we proposed two methods to achieve erasure location information. Simulation results show that the required E_b/N_O at 10<-3>BER with the proposed scheme is 2.5dB less than that with error-only decoding.

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