記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：電子情報通信学会  

本論文では,筆者らがこれまで検討してきた並列組合せSS通信方式の一方式として,差動並列組合せSS(DPC/SS)通信方式を提案する.並列組合せSS方式は,複数のデータビットを+,-の状態をもつ拡散系列の組合せに変換して送信することで周波数利用効率を高めたSS方式である.本論文で提案する方式は,送信する系列にかかる+,-の状態データに送信側で差動符号化を施し,受信側で<は拡散系列の組合せを包路線検波により復調し,また+,-の状態データを遅延検波を用いて復調する.このため,受信側で搬送波の位相を再生する必要がなく,伝送路における位相変動が激しい移動体通信に有効と考えられる.本論文では,DPC/SS通信方式の基本的な性能として,白色ガウス雑音のみの伝送路,レイリーフェージング伝送路における誤り率特性,またレイリーフェージング伝送路においてダイバーシチを適用した場合の効果を明らかにした.その結果,本方式を従来のDPSKやBPSK方式と同等のデータ伝送速度で加法性白色ガウス雑音伝送路に適用した場合,ビット誤り率10^<-8>における情報ビット当りの所要SN比を,DPSKやBPSK方式に比べて,1dB以上削減できることが明らかになった.またレイリーフェージング伝送路において受信側にダイバーシチを適用した場合,ブランチ数の増加に伴うビット誤り率の改善効果が従来のDPSKによる直接拡散SS方式に比べて大きいことが明らかになった.

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その他リンク： http://hdl.handle.net/10191/6196

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Institute of Electronics, Information and Communication Engineers  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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 &lt; p &lt; 1) linearly. Numerical examples show that the proposed algorithm is robust to the variation of the system sparsity.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Institute of Electronics, Information and Communication Engineers  

The interpolation of color pixel values prior to digital halftoning is discussed and a new color interpolation sheme 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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/UWBST.2004.1320968

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/ISPA.2003.1296902

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/ICIP.2003.1246657

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：〔信号処理学会〕  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/WCNC.2002.993486

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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 &apos;soft-in/soft-out&apos; 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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）   出版者・発行元：一般社団法人電子情報通信学会  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3169/itej.51.1889

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：電子情報通信学会  

ぼけによる劣化画像を視覚的に良好な状態にするために輪郭線の強調が行われる. 本論文では点広がり関数が既知の場合を対象として, 多重解像度表現の特徴をもつウェーブレット展開とベクトル量子化を用いた輪郭強調法を提案している. 本方法では, あらかじめ鮮鋭な画像とそれをぼかした画像を用意し, その局所的周波数特性をベクトル量子化器に学習させることにより輪郭強調に関する既知情報を得る. ウェーブレット展開により画像の局所的周波数特性を抽出し, それをベクトル量子化器によって分類・加工することによって輪郭強調を行う. 実際にぼけ画像および雑音の重畳したぼけ画像に対して提案方法を適用した結果, 輪郭強調と雑音抑圧とを同時に行えることがわかり, その有効性が検証された.

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その他リンク： http://hdl.handle.net/10191/6195

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：PUBLISHING HOUSE ELECTRONICS INDUSTRY  

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：日本語   掲載種別：学位論文（博士）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/ecjc.4430760810

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記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：I E E E  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：英語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

TVホワイトスペース(TV white space:TVWS)をコグニティブ無線技術により利用するためには,免許を受けている優先度の高いユーザ(既存局)への有害な干渉を回避し,かつ周波数帯域の有効利用を図る必要がある.コグニティブ無線技術の中で,どの周波数帯を使うかを選択するアルゴリズム(周波数マネジメント)は重要な要素ある.本稿では,IEEE 802.22及びIEEE 802.11af/802.15.4mにおける周波数マネジメントの性能評価を行い,さらにこれらの周波数マネジメントに対して重み付け状態遷移を用いた方法を検討した.また,既存局への有害な干渉について周波数マネジメントによって減らせる干渉量を分類し,周波数マネジメントの効果を検証する.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では,将来の無線センサネットワークへの応用を狙いとし,簡易な手法で実現される無線通信と無線エネルギーハーベスティングを組み合わせたMIMOリレー伝送システム(SWIPT MIMOリレー伝送システム)について検討を行った.従来,送信ノード・リレーノード・受信ノードで構成されていたリレー伝送システムに対して干渉ノードの導入が性能に与える影響を評価した.結果として,通信路において直接波が存在しない場合(フェージング環境がレイリーフェージング)やリレーノードにおける電力変換効率が低い場合において,干渉ノードの導入により,より良い特性が得られることがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

マルチパスフェージング環境下での超広帯域(Ultra Wide Band :UWB)無線パケット伝送において,最大値検出及び区間推定を用いる同期捕捉法を提案する.UWB無線パケット伝送では,パケットの先頭に付加されるプリアンブル期間内で同期捕捉を完了させなければならない.マルチパスフェージング環境下におけるパスの遅延は,同期捕捉によって取得されるタイミングに依存し,復調システムの性能に影響する.本稿では直接拡散型UWB(DS/UWB)を用いた無線伝送の標準の一つであるIEEE 802.15.4aにおけるDS/UWBプリアンブルを例に取り,計算機シミュレーションによる性能評価を行った.その結果,提案法が同期捕捉のためのピークのタイミングをマルチパス環境下でもより正確に捕捉できる効果を確認した.また,最大値検出における区間設計及び処理によって同期捕捉時間の短縮が可能である.

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記述言語：日本語   出版者・発行元：情報処理学会  

本論文では，GPSなどの衛星測位インフラを使用することが困難な屋内環境で，測位のためのインフラを必要とせず，かつ，メンテナンスが容易な歩行者の位置情報サービスを提供することを目的とした新しい歩行者位置推定法を提案し，その実現可能性について検討する．提案方式は，携帯電話に内蔵された歩数計とジャイロセンサを使用した慣性航法により推定した歩行者の歩行軌跡形状と相関が高い形状を持つ道路トポロジの組合せパターンを既存の歩行者用道路トポロジ情報の中から検索することで歩行者の位置を推定する．実際に携帯電話を使用して実施した評価実験により，提案方式が被験者の違いや歩行条件の違いから受ける影響量が提案方式を実現するうえで障害とならないことを確認した．さらに実際に携帯電話を使用した実験により川崎市の地下街で提案方式の実現可能性を調査し，提案方式が測位用のインフラを使用することなく歩行者の位置を推定できる可能性があることを示した．In this paper, a pedestrian positioning method based on a pattern matching technology is proposed for an environment without satellite positioning infrastructures such as GPS. The proposed method presumes a pedestrian's position by searching the trajectory shape estimated by the inertial navigation technology with pedometer and gyroscope built in the mobile phone, from the existing road topology data base for pedestrian. Experimental result shows that the proposed method has robustness about the influence of the difference in a pedestrian or the difference in walking behavior. In addition, the possibility of providing the present position information of the pedestrian in an actual under mall environment with no positioning infrastructure is shown.

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その他リンク： http://id.nii.ac.jp/1001/00088672/

記述言語：日本語   出版者・発行元：一般社団法人 電子情報通信学会  

本稿では，無線通信におけるホワイトスペースの活用に関して，その技術開発，標準化の現状と課題について述べる．まず「ホワイトスペース」の概念について述べ，それを利用するためのコグニティブ無線の概要を述べる．最近特に注目されているTVホワイトスペース（TVWS）に関する規制の検討状況と，それを利用してTVWS向け無線通信システムの標準化の動向を概説する．この中で特に標準化が完了したIEEE 802.22におけるTVWS利用のコンセプトと主なコグニティブ無線の技術要素について解説し，最後にホワイトスペースの利用に向けた今後の課題について論じる．

DOI： 10.1587/essfr.6.250

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記述言語：英語   出版者・発行元：[電子情報通信学会信号処理研究専門委員会]  

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記述言語：日本語   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では超広帯域(Ultra Wide Band:UWB)無線パケット伝送における同期捕捉特性の解析を行った.UWB無線パケット伝送では,パケットの先頭に付加されるプリアンブル期間内で同期捕捉を完了させなければならない.本稿では,これまで検討した低デューティ比な信号やマルチパスフェージング環境に対して有効なRAKE合成や確認モードを用いた同期捕捉システムについてシミュレーションによりその効果を確認した.さらにマルコフ連鎖モデルを用いた同期捕捉特性の理論解析を同期捕捉の確認モードの使用を考慮し,マルチパスフェージング環境への適用を考慮しつつ行い,平均同期捕捉時間の評価を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,IEEE802.22 WRAN(地域無線ネットワーク)における伝送速度の高速化に関する検討を行った.WRANでは一次変調にQAM,二次変調にOFDMを用いており,信号のピーク電力対平均電力比(PAPR)が大きくなる.このため増幅器などにおける非線形性の影響を強く受けてしまうことが懸念されている.本研究ではIEEE802.22通信システムにおいて一次変調に多次元符号化変調を適用し,伝送速度を高速化と非線形性の影響の軽減を狙いとした.計算機シミュレーションによる性能評価を行った結果,一次変調に符号化変調を用いることで通常の誤り訂正符号を使用した場合よりも伝送速度を高速化しても非線形性の影響が少ないことがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

利用可能な周波数帯域が逼迫している現在,時間的・空間的には利用されていない帯域であるホワイトスペース(WS)の利用が注目されている.本報告では,WSを利用する無線LANにおいて隠れ端末と伝送誤りが,全体の伝送特性に与える影響について検討した.WSを利用するには,既存の無線局への有害な干渉を避けるため運用中の周波数の状態を定期的にモニタする必要がある.その方法のひとつとして,セル内の全端末が送受信を停止するQuiet Periodを設ける方法が提案されている.無線LANの事実上の標準であるIEEE802.11では非同期分散制御を用いているため,全端末が同期してQuiet Periodを導入するのは容易でない.我々はこれまでにIEEE802.11のオプションであるPCF(集中制御)区間を利用し,この部分にquiet periodを導入する方法を提案した.本報告では,無線LANでは避けられない問題である隠れ端末の影響および伝送誤りを考慮し,提案したQuiet Periodの導入法がスループット・応答時間に与える影響についてシミュレーションを行い,性能を評価した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では,ホワイトスペースでの利用での利用を想定した小電力無線データ伝送における隣接チャネル干渉の影響について評価する.既存無線システムが利用している隣のチャネルを小電力無線データ伝送システムが利用するシナリオで,双方ともOFDMを用いた伝送を想定する.この際に小電力無線伝送システムが既存無線システムに与える干渉,および既存無線システムから受ける干渉について,計算機シミュレーションにより誤り率特性を求め,考察した.本稿では,OFDMパラメータとして,FFT点数,受信フィルタ,キャリア構造に変更を加え,誤り率特性の比較を行った.

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）   出版者・発行元：電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,VHF帯を利用した小電力無線データ伝送における変調方式について検討する.VHF帯は2011年7月のアナログTV放送停止に伴い再編が予定されており,一部を「自営通信」向けへ利用することが計画されている.本報告ではこの帯域での小電力データ伝送を想定し,限られた帯域の中で高い伝送速度を得るために符号化変調,およびWeiによる多次元符号化変調を一次変調として適用し,計算機シミュレーションによる性能評価を行った.その結果,特に伝送速度が高い場合において,通常の符号化と多値変調を用いた場合に比べて著しく性能が改善されることがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

マルチパスフェージング環境下での超広帯域(Ultra Wide Band : UWB)無線パケット伝送の同期捕捉について検討する.パケット伝送では同期捕捉などを行うためのプリアンブルがパケットの先頭に存在する.プリアンブル中の一定の時間中に同期捕捉が完了しない場合にはパケットが廃棄されるため,パケットの損失や再送による遅延などが生じる.本稿では直接拡散型UWB (DS/UWB)を用いた無線伝送の標準の一つであるIEEE802.15.4aにおけるDS/UWBプリアンブルを例に取りRAKE合成,同期確認モードの採用が同期捕捉特性に与える効果をシミュレーションにより評価する.RAKE合成により同期捕捉の正確性の向上,確認モードにより誤警報の低減による同期捕捉時間の高速化の効果を確認した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では,TVホワイトスペースを用いたコグニティブ無線システムの標準化動向について述べる.まずTVホワイトスペースに関する米国,欧州における法制化の動向を概観する.また米国で認められた地上波TV放送向けVHF/UHF帯における免許不要無線機器の利用に関する規制をもとにIEEE802委員会,特にIEEE802.22,IEEE802.11及びIEEE802.19で進められている標準化の動向について,その概要を解説する.またIEEE802以外の標準化の動向を一部紹介する.あわせてホワイトスペース型コグニティブ無線システムにおける課題を考察し,その将来展望について述べる.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

無線通信を医療・ヘルスケア用途や産業機器の制御などへ応用する際には,伝送データ速度は比較的低いものの極めて高い信頼性でリアルタイムに伝送できることが重視される場合がある.本研究では,このような高信頼無線通信へのDS-UWB(Direct Sequence Ultra Wideband)技術の適用の可能性について論じる.DS-UWBの一例として,IEEE802.15.4aで標準化されているBPM-BPSK/DS-UWBを用いる.マルチパスの影響を考慮し,アンテナダイバーシチや誤り訂正の効果についてシミュレーションによる性能評価を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

2011年7月に見込まれる地上アナログTV放送の終了に伴い,VHF帯のうち,170〜222MHzを「自営通信」向けに利用することが総務省で検討されている.本報告では,この自営通信帯域の利用を想定した小電力の広域ブロードバンド無線伝送の可能性について論じる,OFDMを用いた伝送を前提とし,一次変調やOFDMのパラメータに対する誤り率特性を計算機シミュレーションにより求めた,またそれを基に拡張Hataモデルを用いたリンクバジェット解析により,最大伝送距離の見積もりを試みた.その結果,屋外の見通し環境で,送信電力0.1Wのシステムで最大1.7kmの距離を10Mbps以上のデータ速度かつビット誤り率10^<-5>の信頼性で伝送できる可能性を見出した.また,伝送速度が高い場合,OFDMのガードインターバルとパイロットキャリア数による誤り率特性の比較を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,直接拡散型UWB(DS-UWB)におけるウェーブレットパケットを用いた干渉検出・回避技術の性能評価を行う.UWB(ultra-wideband)は,極めて広い周波数帯域を占有するため,既存の狭帯域無線システムと周波数を共用する必要があり,両システム間で相互干渉が生じるためUWB端末にDAA(detection and avoidance:干渉検出回避)機能を備えていることが求められている.本稿ではOFDM(orthogonal frequency-division multiplexing:直交周波数分割多重)信号を既存無線システムの信号として想定し,与干渉を低減する方法について,OFDM信号の検出見逃しを考慮した性能評価を行った.また検出結果に基づくUWB信号の生成法について検討した.シミュレーションにより,既存信号への与干渉を低減することができ,ある程度の効果が得られることを確認した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,IEEE802.22WRAN(地域無線ネットワーク)における共分散を用いたスペクトルセンシングについての検討を行う.IEEE802.22WRANは米国の地上波TV放送帯において,コグニティブ無線機能を用いた未利用周波数帯の検出・利用を行う半径数十kmのカバレッジを持つ固定無線ネットワークの規格である.スペクトルセンシングとはある周波数帯域においてTV放送などの既存無線システムの存在を検出するものである.本報告では受信信号でのサンプル値の共分散に基づく統計量を用いたスペクトルセンシングについて,雑音の不確定性やシャドウイング等の影響を考慮して性能評価を行い,エネルギー検出法に基づいたスペクトルセンシングとの比較検討を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では,IEEE802.22 WRAN(地域無線ネットワーク)におけるスペクトラムセンシングについて検討する.スペクトラムセンシングは周囲の電波環境を認識するコグニティ部無線技術の重要な要素技術である.本研究では,ATSC DTV信号の周波数スペクトル上の特徴を利用したスペクトラムセンシングについて,雑音の不確定性の影響などを考慮に入れてシミュレーションによる性能評価を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本稿では,IEEE 802.22 WRAN(地域無線ネットワーク)における符号化変調の適用について検討する.符号化変調は,通信路符号化と変調の組み合わせにより,高い符号化率と高い誤り訂正能力を実現する技術である.本稿ではIEEE 802.22通信システムにおいて,符号化変調,多次元符号化変調を一次変調として適用し,シミュレーションによる性能評価を行った.その結果,多次元符号化変調を用いることにより通常の誤り訂正符号を用いるよりも高い周波数利用効率を得つつ,より良好な誤り率特性を得られることがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では,IEEE802.22 WRANにおけるスペクトルマネジメントを考慮したスペクトルセンシングについて検討する.IEEE802.22は米国TV放送バンドにおいて,コグニティブ無線機能を用いて未利用周波数を検出・利用する地域無線ネットワークの規格である.本報告ではコグニティブ無線機能を実現するための主要な要素のひとつであるスペクトルセンシングについて,エネルギー検出器をもととして既存無線システムを検出する機能の拡張を試みる.ここではコグニティブ無線における周波数スペクトルマネジメントを考慮した多レベルスペクトルセンシングを提案する.提案法にについて,検出器出力における雑音電力の不確定性の影響を考慮に入れた計算機シミュレーションによる性能評価を行った.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

UWB(ultra-wideband)は,極めて広い周波数帯域を占有するため,既存の狭帯域無線システムと周波数を共用する必要があり,両システム間で相互午渉が生じる.いくつかめ国のUWBこ関する法律で,UWB端末にDAA(detection and avoidance:干渉検出回避)を備えていることが求められている.本検討では,既存の狭帯域システムとしてWiMax(world interoperability for microwave access)を例にとり,UWB信号による,WiMaxシステムのOFDM(orthogonal frequency-division multiplexing:直交周波数分割多重方式)信号への与干渉を低減する目的で,ウェーブレットパケットを用いた与干渉低減型UWBシステムを提案し,その性能評価を行った.

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記述言語：日本語  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では,パルス型UWB方式の一つであるM-ary符号変調UWB (M-ary CSK-UWB)システムにおけるノンコヒーレントRake受信について検討した.ノンコヒーレントRake受信は,コヒーレントRake受信に必要な通信路推定,重み付け合成が不要になり,受信機構成の簡略化が期待できるが,受信性能が劣化する恐れがある.本研究では,受信信号をチップレートより高いサンプリングレートでオーバーサンプリングし,利得の高いパスを合成する分数間隔Rake受信を適用し,マルチパス分解能とダイバーシチ効果の向上をねらいとした.Rake合成の前における受信信号の処理方法の違いが受信性能に与える影響を考慮し,計算機シミュレーションにより性能評価を行った.また,ノンコヒーレント受信の特徴を生かしたRake合成方式として受信信号の同相成分と直交成分を選択して合成するIQ選択Rake受信を提案し,受信性能の改善が可能なことを示した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では、コグニティブ無線などを用いた周波数共用型無線システムの可能性と課題について論じる。無線ブロードバンド伝送の発展に伴い、必要となる周波数帯域は増加の一途をたどっている。またアドホックネットワーク、センサネットワークなどの研究の進展により、家電機器などさまざまな機器に埋め込まれた無線デバイスは、将来飛躍的に増加するものと予想される。しかしすでに数多くの無線業務に様々な無線周波数が割り当てられており、前述の需要を満たす新たなまとまった周波数帯域の確保は困難になっている。この課題を解決するための手段として、コグニティブ無線技術を用いた周波数共用型無線システムが注目されている。しかしその実現には、法規制や技術面でさまざまなハードルがある。本報告では,特に周波数共用型無線システムの一つの典型的な例であるIEEE802.22地域無線ネットワークにおけるコグニティブ無線技術の標準化動向を紹介しつつ、その可能性と実現のための技術的課題について考察する。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では, IEEE802.22 WRANにおけるスペクトラムセンシングの性能評価を行う. IEEE802.22は米国TV放送バンドにおいてコグニティブ無線機能を用い,あいている周波数を検出・利用することで半径数十kmをカバーする無線ネットワークの規格である.本報告ではコグニティブ無線機能を実現するための主要な要素のひとつであるスペクトラムセンシングについて,エネルギー検出器を用いた方法の性能評価を行った.また検出器出力における雑音電力の不確定性の影響について考察し,その影響を緩和する方法について検討し,ある程度の効果が得られることがわかった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

DS-UWB無線伝送における受信機をコンパクトに実現するためにディジタル化は有力な手段である.本研究ではDS-UWBにおけるRake受信機のディジタル化の実現法の一つとしてアンダーサンプリングの導入について検討した.サンプリングの際のジッタなどを考慮し,誤り率特性をコンピュータシミュレーションにより評価した.

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記述言語：英語  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

IEEE802.22 Working Group(WG)は,米国において地上波TV放送向けに割り当てられている周波数帯(VHP, UHF帯)を用いて半径数十kmのカバレッジを持つ無線アクセスを実現する地域無線ネットワーク(wireless regional area network: WRAN)の標準化を行う作業グループである.既存のアナログTV放送,あるいは将来導入されるディジタルTV放送などの既存無線業務への干渉を避けつつ無線周波数の有効利用を図るため,コグニティブ無線技術の利用を前提としていることが特徴である.本稿では,IEEE802.22WGの概要と狙いについて述べ,標準化作業の経過とドラフト仕様の一部を紹介する.また現在検討されている課題と今後の標準化作業の見通しについても述べる.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

ウルトラワイドバンド(UWB)伝送では数百psec〜数nsecの極めて短時間のパルスを使用するため,マルチパス環境において,Rake受信を用いることで受信性能を改善することができる.本研究では,MBOK DS-UWB方式に分数間隔Rake (Fs_Rake)受信を適用したときの性能評価を行った.Fs_Rake受信は,整合フィルタ出力をオーバーサンプリングし,その出力をもとにRake合成をおこなう方式である.パルス幅あたりに分離するパスの分割数を変えて従来のRake受信と性能の比較をシミュレーションによりおこなった.その結果,Fs_Rake受信は,従来のRake受信と比較してよい性能が得られることを確認した.また,一部の分割数におけるFs_Rake受信は,他の分割数のときよりも性能が劣化した.

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

直接拡散(DS)マルチバンド(MB)ウルトラワイドバンド(UWB)通信システムについて、室内マルチパス通信路における狭帯域干渉の軽減に関する検討を行った。DS-MB-UWBシステムは複数のサブバンドを用いるため、既存の無線システムなどが存在するサブバンドのパラメタを調節し、既存システムへの与干渉を減らすことができる。しかしその場合、DS-MB-UWBが既存システムから受ける干渉の影響について評価する必要がある。本研究ではDS-MB-UWBにおいて既存システムからの狭帯域干渉があるサブバンドの電力を減らすことが性能に与える影響を調査した。狭帯域干渉が存在するサブバンドの電力を減らすことにより、DS-MB-UWBシステムにおける狭帯域干渉の影響を軽減出来ることがわかった。また、各サブバンドの拡散帯域、信号対干渉比(SIR)、信号対雑音比(SNR)や狭帯域干渉の周波数などのパラメタによって、システム性能が変わることが分かった。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

本論文では、直接拡散マルチバンド(DS-マルチバンド)UWB伝送のマルチパス通信路における多元接続性能を解析した。性能解析において必要となるマルチパスや他ユーザからの干渉を近似する手法として,Holtzmanが提案した簡易改良ガウス近似(SIGA)を用いた。Rake受信機を仮定し,Rake合成法としては最大非合成(MRC)及び等利得合成(EGC)を想定した。DS-マルチバンドUWBシステムにおいては,処理利得は1ビット当たりのパルス数と使用するバンド数の積となる。性能解析の結果,処理利得が等しくても、ビット当たりパルス数と利用版度数の組合せが異なれば,多元接続時に異なる誤り率特性が得られることがわかった。干渉の近似法としてこれまでに知られている通常のガウス近似(SGA)を用いた場合との性能比較を行い、SIGAの有効性を示した。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では,Ultra wideband (UWB)無線伝送において広く知られている直接拡散(DS)方式に時間ホッピング(TH)方式を組み合わせたハイブリッドDS/TH-UWB伝送における多元接続性能の評価を行った.ハイブリッドDS/TH-UWB伝送はDS用拡散系列とTH系列の組み合わせにより信号検出を行う事で良好な多元接続性能が期待される.通信路としてIEEE802.15.3aマルチパス通信路モデルを想定し,従来のDS-UWB伝送における多元接続性能との比較検討を行った.その結果,デューティ比が高い場合,DS/TH-UWBはDS-UWBとほぼ同程度の性能が得られた.一方,デューティ比が低くなるにつれてDS/TH-UWBの方がDS-UWBよりも性能が改善され非常に低いデューティ比の信号を用いた場合にはDS/TH-UWBはDS-UWBよりも良い性能を示す事が分かった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

ウルトラワイドバンド(UWB)伝送では数百psec〜数nsecの極めて短時間のパルスを使用するため,マルチパス環境において,Rake受信を用いることで受信性能を改善することができる.本研究では,MBOK DS-UWB方式に分数間隔Rake (Fs_Rake)受信を適用したときの性能評価を行った.Fs_Rake受信は,整合フィルタ出力をオーバーサンプリングし,その出力をもとにRake合成をおこなう方式である.パルス幅あたりに分離するパスの分割数を変えて従来のRake受信と性能の比較をシミュレーションによりおこなった.その結果,Fs_Rake受信は,従来のRake受信と比較してよい性能が得られることを確認した.また,一部の分割数におけるFs_Rake受信は,他の分割数のときよりも性能が劣化した.

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

直接拡散(DS)マルチバンド(MB)ウルトラワイドバンド(UWB)通信システムについて、室内マルチパス通信路における狭帯域干渉の軽減に関する検討を行った。DS-MB-UWBシステムは複数のサブバンドを用いるため、既存の無線システムなどが存在するサブバンドのパラメタを調節し、既存システムへの与干渉を減らすことができる。しかしその場合、DS-MB-UWBが既存システムから受ける干渉の影響について評価する必要がある。本研究ではDS-MB-UWBにおいて既存システムからの狭帯域干渉があるサブバンドの電力を減らすことが性能に与える影響を調査した。狭帯域干渉が存在するサブバンドの電力を減らすことにより、DS-MB-UWBシステムにおける狭帯域干渉の影響を軽減出来ることがわかった。また、各サブバンドの拡散帯域、信号対干渉比(SIR)、信号対雑音比(SNR)や狭帯域干渉の周波数などのパラメタによって、システム性能が変わることが分かった。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では,Ultra wideband (UWB)無線伝送において広く知られている直接拡散(DS)方式に時間ホッピング(TH)方式を組み合わせたハイブリッドDS/TH-UWB伝送における多元接続性能の評価を行った.ハイブリッドDS/TH-UWB伝送はDS用拡散系列とTH系列の組み合わせにより信号検出を行う事で良好な多元接続性能が期待される.通信路としてIEEE802.15.3aマルチパス通信路モデルを想定し,従来のDS-UWB伝送における多元接続性能との比較検討を行った.その結果,デューティ比が高い場合,DS/TH-UWBはDS-UWBとほぼ同程度の性能が得られた.一方,デューティ比が低くなるにつれてDS/TH-UWBの方がDS-UWBよりも性能が改善され非常に低いデューティ比の信号を用いた場合にはDS/TH-UWBはDS-UWBよりも良い性能を示す事が分かった.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では,並列組合せSS方式をUWBに適用した並列組合せUWB (PC/UWB)通信の性能評価を行った.PC/UWB通信はデータの状態を複数の拡散符号の組合せにマッピングすることで,高速データ伝送を狙った方式である.本研究では室内でのUWBの利用を想定し,マルチパスフェージング通信路でRake受信を用いたPC/UWB通信の性能評価をおこなった.特にRake受信におけるパス選択の方法とパス合成の方法の違いによる性能の比較評価を行い,選択Rake受信およびMRC(最大比合成法)がよりよい受信性能を示した.また等利得合成(EGC)においては最適な受信性能が得られるパス合成数が存在することがわかった.

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

2005年12月に横須賀リサーチパーク(YRP)にて開催されたウルトラワイドバンド(UWB)技術の国際ワークショップ(IWUWBT2005)に関して報告する.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本研究では, マルチパス通信路における直接拡散ウルトラワイドバンド(DS-UWB)システムで使用するRake受信機のディジタル化を想定した場合の性能評価を行った. 特に, Rake受信で行われるパス選択とRake合成に使用する重み係数を量子化した場合の影響について検討した. DS-UWBシステムでの高速データ伝送化は, 一般的にパルス繰り返し周波数が高くなるためパルス間干渉の影響を避けることができない. このため, 干渉の影響を受けたパスを合成することが受信性能の劣化につながることになり, 干渉の影響を受けたパスを合成する可能性が少ないpartial Rake(PRake)受信がよりよい受信性能を示した. パスを合成する際の重み係数はある程度の量子化が行われても受信性能の劣化が見られなかった.

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記述言語：日本語  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

Ultra Wideband(UWB)無線伝送方式は極めて短いパルスを連続して送信することで, 数百Mbpsといった超高速の無線伝送を可能にする技術である.UWB伝送では送信出力を雑音レベル以下にする必要があり, 受信側で高いSN比を得る方法が不可欠である.また, 主に屋内での利用を想定しているため, マルチパスフェージングの影響による受信特性の劣化が懸念される.本研究では, 受信側でより多くのエネルギーをかき集めるために複数のテンプレート波形を用いたSub-Optimum Rake合成法を提案し, 計算機シミュレーションにより性能評価を行った.その結果, テンプレート波形の数を増やすことで段階的に受信特性の改善を計れることがわかった.

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

Rake受信機が用いられた場合のマルチパスレイリーフェージング通信路におけるDS-CDMAのビット誤り率評価法を検討した。Holtzmanによる簡易型改良ガウス近似(SIGA)を用いた誤り率算出法をマルチパス通信路に拡張し, 広く用いられている通常のガウス近似(SGA)による方法と比較した。電力遅延プロファイル(PDP)としてフラットPDPおよび指数減衰PDPの2種類を考え, 拡散帯域幅と合成パス数が多元接続性能に与える影響について検討した。Rake受信としては, 受信したパスをすべて合成するall Rake (ARake)受信と利得の大きい数本のパスを合成する選択Rake (SRake)受信を想定し, マルチパス通信路におけるSGAおよびSIGAの有効性の比較を行った。その結果, SGAは1) 拡散率が低い環境におけるARake受信の場合2) 数本程度までのパスを合成するSRake受信については有効であるが, それ以外では誤り率を低く見積もることがわかった。また受信機における多元接続性能およびSGAの有効性はPDPの種類にも依存することがわかった。SIGAではPDPに関係なくシミュレーションにほぼ一致する誤り率特性が得られた。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

低デューティ比の信号を用いたウルトラワイドバンド(UWB)直接拡散CDMA(DS-CDMA)およびハイプリッドUWB直接拡散/時間ホッピングCDMA(DS/TH-CDMA)における電力制御の影響について検討した。ランダム系列を用いた非同期CDMAを仮定した。電力制御が完全な場合,同じデータ速度,処理利得,チップ速度,デューティ比,拡散符号長でユーザ数が比較的少ないときは,DS/TH-CDMAがDS-CDMAよりもよい性能を示す。しかし,電力制御がない場合,DS/TH-CDMAシステムは性能劣化が大きいことがわかった。また,ユーザ数や電力の分布によっては両システムはほぼ同等の性能を示すか,ハイブリッドDS/TH-CDMAのほうが性能が悪くなる可能性があることがわかった。一定のチップ長(パルス間隔)においてチップデューティ比を低くすることはハイブリッドシステムに有利となるが,電力制御が不完全な場合その効果は低くなる。同じ処理利得の条件で,チップデューティ比と拡散符号長を変化させた場合の性能についても合わせて検討した。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

直接拡散マルチバンドウルトラワイドバンド通信システムを提案し,性能評価を行った。提案システムは,直接拡散(DS)変調と,各チップに異なる中心周波数を持つパルス波形を用いたマルチバンド変調とのハイブリッドシステムである。計算機シミュレーションにより多元接続性能の評価を行い,同じ帯域幅を利用するシングルバンドDS-UWBシステムとの比較を行った。同期CDMAおよび非同期CDMAの場合について評価した。チップ速度,デューティ比,チップ波形が変わった場合の性能比較を行った。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

2004年5月に京都で開催されたウルトラワイドバンド(UWB)システムの国際合同シンポジウムに関して報告する.

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

ウルトラワイドバンド直接拡散CDMA(UWB DS-CDMA)におけるチップデューティ比とパルス波形の影響について検討した。UWB DS-CDMAにおけるビット誤り率特性について,デューディ比とパルス波形の影響を考慮し,他局間干渉をガウス近似及び簡易型改良ガウス近似を用いて解析した。同期CDMA及び非同期CDMAについて検討し,拡散系列はランダム系列を仮定した。AWGNの影響を無視し,理論解析とシミュレーションにより性能評価を行った。その結果,一定のチップ長(パルス間隔),パルス波形及びビット誤り率において,チップデューティ比が低くなった場合,非同期DS-UWB-CDMAの同時通信ユーザ数が大きく増加することがわかった。また,よりよい自己相関特性を持つパルス波形を利用することにより,同時通信ユーザ数の増加が図れること,キャリヤベースの波形を用いることで性能が改善されることを示した。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

マルチパス通信路におけるウルトラワイドバンド(UWB)信号のRake受信性能を評価した。マルチパス通信路におけるUWB伝送では,パルス幅が短くなるにつれ,より多くの割合の信号エネルギーが独立したパスとして受信される。これに対しパルス幅が長くなれば,遅れて受信したパルスのオーバーラップにより,散乱パスが多く受信されるようになる。この場合パスあたりの平均エネルギーは増加するが,よりシビアなマルチパスフェージングが生じる。本論文では,IEEE802.15.3a通信路モデルを用い,最適パス遅延推定を行う場合と,パルス幅あたりで区切った通常の場合におけるAll Rake受信と選択Rake(SRake)受信の性能評価と比較を行った。また,一定の複雑さを有するSRake受信における送信パルス幅の影響についても論じた。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

直接スペクトル拡散(DS-SS)伝送における一般化選択合成(GSC)Rake受信機について,狭帯域干渉が受信特性に与える影響について解析した。特に,一定の複雑さを持つRake受信機において,狭帯域干渉が最適拡散帯域幅に与える影響を評価した。また直接拡散型超広帯域(DS-UWB)伝送についても同様の検討を行った。通信路モデルは,独立なレイリー分布を有するマルチパスフェージング通信路とし,電力遅延プロファイル(PDP)としては,DS-SS伝送ではフラットPDF,DS-UWB伝送では指数減衰型PDPを仮定した。干渉のある環境におけるシステムパラメータと信号対干渉電力比(P/J)に対する誤り率特性の式を導出した。雑音のみの環境においてビット誤り率(BEP)を最小にするよう設計された最適GSC-Rake受信機は,干渉が入った場合準最適に動作することが,DS-SS,DS-UWB双方の場合について確認できた。特にDS-UWB伝送で,指数減衰型PDPを有する通信路の場合,狭帯域干渉の影響が大幅に少なくなることがわかった。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：映像情報メディア学会  

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記述言語：日本語   出版者・発行元：映像情報メディア学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

最近、Ultra Wide Band (UWB)技術い関する研究開発が各方面で活発になってきている。2002年2月に米連邦通信委員会(FCC)がUWB技術の商用利用に関する規制緩和を行なったが,その後欧州や日本などでもUWBの規制緩和に関する検討が進められている。また無線パーソナルエリアネットワーク(WPAN)の標準化を行なうIEEE802.15委員会のTG3aで検討中の無線規格では,UWB技術の採用が有力視されるなど,UWBの商用利用に向けた動きが加速している。一方でUWB信号が既存の通信システムやレーダなどに与える影響を懸念する声も依然根強い。本稿では,UWB技術の概要および特徴を延べ,現在検討されているUWB向け変調技術の例を紹介する。またUWBをめぐる規制緩和などの動き,UWBに関する最近の研究開発動向についてもあわせて紹介する。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

UWB-IR(Ultra Wide Bandwidth-Impulse Radio)伝送のためのM-ary時間ホッピング/符号シフトキーイング方式を提案する。UWB-IR方式は、時間幅がns単位の極めて短い時間のパルスを用い,極めて広い周波数帯域を利用してデータを伝送する方式である。提案方式は、Goodmanらによって提案されたMFSK-FH方式を時間ホッピングに適用し,その出力をあらかじめ用意した複数の符号系列の選択に利用する.用意する符号系列では1周期の中で複数のパルスを発生させることで、パルス当たりのピーク電力を抑えつつ、高速データ伝送が可能となる。本報告では提案システムの構成法に関する基礎検討と,誤り率特性の評価を行った。

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

1ピクセル8ビットを超える高階調モノクロームデータを擬似グレイデータにマッピングし、8ビットsRGBカラーCRTモニタに表示する方法を提案する。そして、擬似グレイの特性を色差と色度座標で評価する。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では, 完全再構成デ・インタレース化の動画像フレーム/フィールド内符号化への導入を検討する.そして, 各復号化の画像品質の要求に応じたスケーラビリティを一つのビットストリームで実現できるシステム構成を提案する.従来のフィールド合成をインタレース動画像に対して行なうと画像内の動いているオブジェクトのエッジ部に櫛状部分が発生する.また, フィールド分割を行なうとエイリアジングが発生する.この影響により, 直接フレーム/フィールド内符号化を行なうと, 低ビットレート復号の際, 目障りなちらつきが発生する.本提案法により, 低ビットレート復号において, 余計なフィルタ処理なくこのちらつきを抑え, 高ビットレート復号においては, 空間解像度を保持することが可能となることを示す.また, 特殊な場合について効果的実現法とロスレス実現法が存在することを示す.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

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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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

受信側で繰り返し復調/復号を行うブロック符合化並列組合せスペクトル拡散(PC/SS)システムについて、そのビット誤り率上界式を導出した。導出した上界式をもとに、PC/SS変調に用いる重み一定符号を選択する方法の検討およびリードソロモン符号化システムとの比較を行った。重み一定符号としてはSchalkwijkの重み一定符号とHadamard行列から構成した重み一定符号について検討を行った。その結果、繰り返し復調/復号を行うPC/SSシステムでは、漸近的な性能ではHadamard行列から構成した重み一定符号がよい性能を示し、またビット誤り率10^<-6>程度ではSchalkwijkの重み一定符号を用いたシステムがよい性能を示すことがわかった。リードソロモン符号化システムとの比較では、ビット誤り率10^<-6>を満たすために必要なビットあたりの信号対雑音電力比(E_b/N_0)で比較を行い、繰り返し復調/復号を行うブロック符号化システムが低いE_b/N_0で達成できることがわかった。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

高速データ伝送に対応したスペクトル通信方式である並列組合せSS(PC/SS)通信方式において、PC/SS復調器をAPPアルゴリズムによる軟入力軟出力PC/SS復調器として構成、通信路符号との繰り返し復号/復調からビット誤り率の改善を図った。計算機シミュレーションの結果、これまでPC/SS方式の誤り訂正符号として検討を行ってきた同符号化率リード・ソロモン符号を適用した場合と比較して、ビット誤り率 10^<-5> を満たすビットあたりの信号対雑音電力比において4dB程度のゲインが得られることがわかった。またパンクチャリングを行った場合におけるビット誤り率特性もまたシミュレーションから評価を行った。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では, 最近データ通信において主流になりつつあるパケット伝送における画像の効率的かつ信頼性の高い伝送法について検討した.画像符号化, 画像圧縮においては, 近年ウェーブレット変換係数のゼロツリー表現を用いた画像符号化法が高能率圧縮が可能な点から注目されている.本報告ではこれをパケット伝送向けに改良し, かつパケット伝送で生じうるパケット損失やパケット中の残留ビット誤りに対する耐性を高めるために, 積符号による誤り訂正を行うことにより, 高効率かつ高信頼な画像パケット伝送を実現したATMパケット伝送を前提とした計算機シミュレーションにより提案方式の有効性を確認した.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では、高速データ伝送を目的とした並列組合せSS(PC/SS)通信方式の符号化法について検討を行った。並列組合せSS方式では、データを複数の拡散系列の組合せに変換して伝送するが、送信する拡散系列に多相変調を用いることにより、伝送速度の高速化が可能である。本報告では、多相並列組合せSS方式に対し、リード・ソロモン符号による誤り訂正を適用し、レイリーフェージング通信路における誤り率特性の評価を行なった。復号法としては、通常の誤りのみの訂正と、SN比のしきい値による消失誤り訂正を仮定した。また、符号化による性能の向上と伝送速度の関係についても考察を行なった。その結果、QPSK変調を用いた場合に伝送速度および誤り率特性の両面で最も良好な性能が得られることがわかった。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では、リードソロモン(RS)符号化を組合せた並列組合せスペクトル拡散(PC/SS)通信方式のフェージング通信路における特性を検討した。PC/SS通信方式は、データを拡散系列の組合せとその状態に変換して伝送するマルチコードスペクトル拡散方式の一つである。先に我々は拡散系列の組合せに関するデータのみ誤り訂正を行ない、高速データ伝送と誤り率特性の改善の両立を図った符号化PC/SS方式を提案した。本報告ではこの符号化PC/SS方式のレイリーフェージング通信路における特性を計算機シミュレーションにより評価した。その結果レイリーフェージング通信路では送信する拡散系列の状態に関するデータの誤り率が全体の誤り率に強く影響することがわかった。しかしながら拡散系列の組合せに関するデータは消失誤り訂正により、単純に吠符号化とPC/SS方式を組合せるよりも良好な特性が得られることもわかった。

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

本報告では、マルチコードスペクトル拡散方式の1つである並列組合せスペクトル拡散(PC-SS)通信方式における符号化法について検討した。PC-SS方式では、データを拡散系列の組合せと送信する拡散系列の状態に変換することにより高速データ伝送を実現している。ここで、この拡散系列の組合せに関するデータの誤り率が全体の誤り率を支配することがこれまでの検討でわかっていた。本報告では、この組合せ部分にのみリードソロモン符号による誤り訂正を行なうことで、高速データ伝送と誤り率特性の改善の両立を図る方法を提案する。計算機シュミレーションにより性能評価を行った結果、全体の符号化率力が高くなったにもかかわらず、誤り率特性が改善されることがわかった。

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