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

DOI： 10.23919/eucap60739.2024.10501057

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

DOI： 10.23919/eucap60739.2024.10501117

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/lawp.2024.3363191

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

File： IEEE Access_Ikegami_Multipath-RTI_Millimeter-Wave_Radio_Based_Device-Free_Localization.pdf

DOI： 10.1109/access.2024.3379317

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

DOI： 10.1109/globecom54140.2023.10436897

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

In recent years, cluster-based channel models comprising clusters or groups of multipath components (MPCs) have found a lot of acceptance in the research community. However, such models are heavily clustering technique dependent where there is a primary lack of uniformity regarding distance measure or the number of initial parameters. In this work, four clustering techniques, using the same power-weighted MPC distance as the distance measure and having the same number of user-specified initial parameters are introduced. The newly evolved techniques with uniform assumptions are next compared in terms of the average Silhouette coefficient (ASC) to assess their clustering quality in terms of cluster compactness using data from an indoor measurement campaign. Since clustering techniques normally do not consider the propagation environment, the relevance of the clusters generated using the introduced techniques is also assessed with the measurement environment using ambiance-embedded spectra and ray tracing simulation. It is observed that the variation of KPowerMeans whose a priori parameters are environment and spectra-dependent performs better both numerically and qualitatively compared with the other techniques. Furthermore, it is observed that independent of the technique there are always clusters that cannot be verified from the environment irrespective of the ASC value. Thus, it is concluded that numerical measures are only indicative and should be used in conjunction with environment-based assessment for conclusive results.

DOI： 10.1109/TTHZ.2023.3313462

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

In this paper, a newly developed 300 GHz channel sounder is presented followed by a detailed description of test measurements and the subsequent results obtained to validate its working. An elucidation of the high-resolution double-directional channel measurement in a typical conference room scenario precedes the comparison of the results obtained for the current campaign to that obtained from an earlier campaign at 60 GHz for a similar setup. It is observed that a similar number of clusters for both the bands under investigation for all the transmitter (Tx) and receiver (Rx) positions are obtained from the generated power spectra. Any deviation is theorized to be caused either due to the usage of lower measurement bandwidth in the 60 GHz campaign or due to limited elevation expanse in the 300 GHz measurement. To identify the interacting objects (IOs) causing the clusters, environment-embedded angular power spectra (APS) and ray tracing simulations are used. The large-scale parameters (LSPs) are also evaluated for both campaigns. It is observed that signal propagation at 300 GHz is dominated more by the line-of-sight (LoS) path compared to 60 GHz. The results are also compared with other similar results from the literature.

File： IEEE Access_Indoor_Channel_Measurement_at_300_GHz_and_Comparison_of_Signal_Propagation_With_60_GHz.pdf

DOI： 10.1109/ACCESS.2023.3330653

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

DOI： 10.1109/isap57493.2023.10388587

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

DOI： 10.1109/isap57493.2023.10388731

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

DOI： 10.1109/isap57493.2023.10388574

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electronics, Information and Communications Engineers (IEICE)  

DOI： 10.1587/comex.2023spl0013

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

Owing to the unique attributes of the terahertz (THz) band (0.1-10 THz) adoption of millimeter and centimeter wave channel models to characterize THz communication seems unrealistic. In this context, a cluster-based channel model using multipath components extracted from measurement data can serve as a crucial step in understanding the propagation characteristics of THz signals. In cognizance of the prior fact, the current work uses the Subgrid CLEAN algorithm to extract the multipath components (MPCs) using the data from a measurement campaign conducted in a typical conference room at 300 GHz. The extracted MPCs were further clustered based on their temporal and spatial characteristics using the K-Power Means (KPM) technique. The effectiveness of the employed extraction technique is validated by comparing the extracted power spectrums (angle and delay) with the measured ones whereas the efficacy of the clustering algorithm is demonstrated by identifying the interacting objects (IOs) causing the same.

DOI： 10.23919/URSIGASS57860.2023.10265492

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Authorship：Corresponding author   Publishing type：Research paper (international conference proceedings)  

To realize the potential of the Terahertz band (0.1 - 10 THz) in providing high data rate, low latency, and improved reliability extensive measurement campaigns are the need of the hour. In this context, the current study presents the results from a first-of-its-kind measurement campaign conducted in a corridor and from corridor to room at 300 GHz. The investigated positions consist of both line-of-sight and non-line-of-sight cases. The measurement data is processed to generate the power delay profile and environment-embedded azimuth delay power spectra for the positions under study. A careful analysis of the generated results helps in identifying the dominant specular components for each position using ray tracing. We further confirm the poor penetration property of signals at 300 GHz through regular building materials like concrete and plasterboard. The current results lay the foundation for more extensive analysis to develop a channel model for one of the common yet unexplored indoor scenarios.

DOI： 10.23919/EuCAP57121.2023.10133137

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

Object detection is crucial in the field of wireless communication, as it helps in predicting the channel behavior and channel model parameters that are necessary for efficient communication. In recent years, various object detection techniques have been proposed for this purpose, ranging from traditional statistical methods to deep learning-based approaches. This paper provides a comprehensive review of object detection techniques for predicting wireless channel model parameters. Additionally, the paper discuss the advantages and limitations of different object detection frameworks such as YOLO, Faster R-CNN, and Mask R-CNN. Finally, the paper puts foward a conceptual introduction of a novel approach to utilize Faster R-CNN object detection technique andcomputer vision, to predict the scatterers and eventually estimate the channel characteristics of a wireless channel. The paper highlights the current challenges and future directions in object detection for wireless channel model parameters prediction. The dataset to train the deep learning model is generated from an example conference room environment panoramic images. The proposed approach can be applied in various wireless communication scenarios, such as 5G and beyond, to accurately predict the location of scatterers based on multipath clusters so as to optimize network design and improve the overall performance of the system.

DOI： 10.1109/ITC-CSCC58803.2023.10212703

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

To properly design multi-frequency millimeter-wave radio systems, it is essential to understand frequency-dependent site-specific propagation channel characteristics. This study conducted double-directional (D-D) channel measurements in a typical urban macrocell (UMa) environment using a 24/60-GHz dual-band channel sounder. Post-processing extracted multipath components (MPCs) from the measured data and then grouped them into several clusters. Here, the clustering was conducted with the composite datasets of 24 GHz and power-compensated 60 GHz MPCs to obtain common clusters at both frequencies. From the results, this study compared the scattering processes in the two frequency bands. The statistical characteristics obtained at two frequencies, such as the number, power differences distribution, and relative delay distribution, were compared and discussed.

DOI： 10.23919/EuCAP57121.2023.10133702

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

File： IEEE Access_Anirban_THz_Channel_Sounding_and_Modeling_Techniques_An_Overview.pdf

DOI： 10.1109/access.2023.3246161

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

This paper describes the 300 GHz channel sounder measurement system developed for Beyond 5G radio access systems. It also presents the results of double-directional channel measurements in a laboratory environment to validate the developed system. The measurement results show that several dominant multipath components were measured, and the angles of departure and arrival (AoD and AoA) were also in good agreement with those expected paths.

DOI： 10.1109/ISAP53582.2022.9998626

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

This paper reports the results of propagation channel measurements simultaneously performed at 24 and 60 GHz in an urban cellular access environment. A channel sounder with a phased-array antenna capable of high-speed beam steering was used to achieve double-directional full-azimuth scan measurements at the same position and at the same time at both frequencies. Statistical properties of the delay time of arrival, and the azimuth angles of departure and arrival, called large-scale parameters (LSPs), were obtained from the measured data. The results improve the accuracy of the currently widely used cluster-based millimeter-wave channel models for site-specific channel prediction.

DOI： 10.1109/ISAP53582.2022.9998592

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

This study aims at developing a cluster channel model validation method to evaluate the reproduction accuracy of small-scale fading. In this paper, the clustered multipath components (MPCs) obtained from the post-processing of the data measured in a specific scenario was evaluated as a first step. Here, the post-processing includes MPCs extraction and clustering. The small-scale fading generated by the cluster channel model was then statistically compared with the measured one in the same scenario. This procedure can give confidence that a set of channel measurement data is suitable for statistical modeling. This paper presented the developed configuration and a validation example.

DOI： 10.1109/PIMRC54779.2022.9977991

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

File： ACCESS3180780.pdf

DOI： 10.1109/ACCESS.2022.3180780

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

The use of millimeter-wave (mm-wave) bands has been expanding in new wireless communication systems such as fifth-generation (5G) mobile systems and WiGig WLANs. Since mm-waves have quasi-optical propagation characteristics, it is necessary to develop a channel model that can cover sitespecific characteristics of various environments. For this reason, a large amount of channel measurement data measured in a wide range of frequency bands covering mm-wave in various environments should still be required. In particular, it is necessary to obtain the angular channel characteristics on both sides of the transmitter and receiver, but this requires considerable time and cost. The authors' previous study developed a 60-GHz doubledirectional (D-D) channel sounder using commercial-off-the-shelf (COTS) phased-array beamforming RFs, and it has currently been extended to realize 24/60-GHz dual-band simultaneous measurement. In this paper, we detailed the design of the dualband D-D channel sounder. As a demonstration of the operation, some measurement results taken in typical urban macro-cell (UMa)/micro-cell (UMi) scenarios were quickly reported.

DOI： 10.1109/ICCWorkshops53468.2022.9814563

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

In recent years, the discovery and utilization of the millimeter-wave for the next generation of mobile communications have fuelled the demand to develop site specific and more accurate wireless channel models. Due to the dynamic and high interactive nature of the millimeter waves, accurate models which takes into consideration the effects of the interacting objects in the propagation environments are needed. This paper presents a development of a machine learning (ML) based prediction model for large scale channel parameter (LSCP) estimation by analyzing the interaction of the reflected multipath rays information with propagation environments. This is to capture the shape of the changing propagation environments more accurately. Utilizing the robustness of ML, a dynamic LSCP prediction model can be realized. The input parameters to the prediction model are transmitter (TX) and receiver (RX) positional coordinates, and the reflected rays' information such as the delay, angle of arrival, angle of departure, elevation angle of arrival, elevation angle of departure, and power gain. The proposed model was implemented using Random Forests. Ray tracing (RT) simulation was performed to calculate the input dataset of the LSCPs, and also the input datasets of the reflected rays. Cross validation was utilized to validate the model.

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

The authors have developed the Multipath-RTI (radio tomographic imaging) technique based on millimeter-wave (mm-wave) radios such as 5G mobile and WiGig LAN systems. Mm-wave radios can realize a highly accurate device-free localization (DFL) for smart home/smart building applications by utilizing the features that mm-wave radios usually have high delay and angle resolution, and thus is capable of separating the multi-path components (MPCs). The Multipath-RTI can drastically reduce the number of sensor nodes by using the virtual nodes created by multipaths. However, there are technical challenges to handle the multipaths and corresponding pathways. This paper proposed a practical data processing scheme for Multipath-RTI and presented some actual imaging results for DFL using double-directional channel sounding measurements.

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

DOI： 10.1587/comex.2021spl0026

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

This paper presented channel sounding measurement results obtained in outdoor open square environments at 60 GHz using a millimeter-wave (mm-wave) double-directional (DD) channel sounding system. Here, by using phased array beamforming transceivers a fast D-D channel acquisition in 180 degrees and 360 degrees azimuth range was achieved by configuring a 2 x 4 multipleinput-multiple-output (MIMO) time division-multiplexing (TDM) scheme that enables simultaneous use of two and four antenna arrays covering +/- 45 degrees at the transmitter and receiver, respectively. The half-power beam widths in the azimuth and elevation planes are 6 degrees and 45 degrees, respectively. Using the post-processing including multipath components (MPCs) extraction and clustering method, some observation on the multipath clusters obtained in these measurements was described and statistical characteristics of large- and small-scale parameters were presented.

DOI： 10.1109/VTC2021-FALL52928.2021.9625433

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

In recent years, propagation channel characteristics have been effectively used in several applications such as motion sensing and position detection. Considerable attention has been paid to channel-sounding methods that are easy to utilize using low-cost devices. This paper presents a device-free indoor location estimation method using the spatio-temporal features of radio propagation channels using a 2.4 GHz-band three-by-three multiple-input-multiple-output (MIMO) channel sounder developed using commodity wireless local area network (WLAN). The measurement results demonstrated a reasonable performance of the proposed method with a small number of antennas.

File： telecom-02-00012.pdf

DOI： 10.3390/telecom2020012

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Aiming at realizing sensing of the surrounding environment for smart homes/smart building applications, device-free localization techniques using radio propagation characteristics have gained interest. To realize such techniques it is often required that the accurate environmental information should be obtained in advance. In this study, the environment mapping method using millimeter-wave (mm-wave) ratio such as WiGig and 5G mobile communication systems was developed. Specifically, this study proposed a multi-dimensional Kirchoff Migration (KM) method using mm-wave systems which improves the performance by utilizing the high-resolution in delay time and angular channel responses.

DOI： 10.23919/ISAP47053.2021.9391142

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

To date various wireless systems using millimeter-wave bands have already been developed. However, the demand for more accurate channel models is still increasing. In this study, a millimeter-wave double-directional channel sounding system using commercial off-the-shelf RF transceivers is presented where an analog beamformer based electrical beam-steering offers a fast double-directional channel acquisition. In addition, this paper developed a high-resolution multi-path parameter estimation algorithm from the multi-dimensional power spectrum. Finally, as validation, the scattering processes were identified by comparing the path parameters extracted from the power spectrum obtained from measurements with the interacting objects in the real environment.

DOI： 10.23919/ISAP47053.2021.9391484

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In recent years, IoT and AI technologies have been developing rapidly. To utilize these technologies in home environment, it is important to capture and visualize environmental information in a house. This study developed an indoor positioning method using multi-path radio tomography imaging (RTI) based on millimeter-wave (mm-wave) radio systems such as 5G mobile and IEEE 802.11ad/ay WiGig which currently attract a great deal of attention. The extensive performance evaluation via computer simulation should be needed for the system design and optimal installation because the localization performance largely depends on various system conditions. This paper clarified the relationship between the performance and the setup conditions such as the size of the target environment and the placement of anchor nodes which are most important system parameters.

DOI： 10.23919/ISAP47053.2021.9391488

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

In recent years, since the propagation channel characteristics have been effectively used for applications such as motion sensing, position detection, etc. A great deal of attention is attracted to channel sounding methods easy to utilize using low-cost devices. This paper presents a device-free indoor location estimation method using spatio-temporal features of radio propagation channels using the 2.4-GHz band 3-by-3 MIMO channel sounder developed using commodity wireless LANs. The measurement results demonstrated a reasonable performance of the proposed method with small number of antennas.

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

This paper reports the measurement campaign and identification results of the millimeter-wave multi-path propagation characteristics at 61.5 GHz band in a passenger vehicle environment. Four measurement scenarios were assumed, and the propagation characteristics of the dominant paths in each were identified. From the results, it can be seen that the dominant paths are distributed along the line-of-sight (LoS) direction, but it could also be seen that some other communication links of which power are ranged from 10 to 15 dB smaller than that of the LoS component are available.

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

In the future, the importance of in-vehicle sensors will increase. The usage of wireless communications is considered to save the number of electric wires for connecting the sensors. In this paper, we show ray-tracing simulation and experimental measurement in passenger vehicle. From the comparison between simulation and measurement, it was seen that the angular path loss distributions were very similar even if the path loss of the reflected paths in measurement were about 20 dB or more larger than those of the corresponding paths in the simulation.

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

File： IEEE Access_Fast Double-Directional Full Azimuth Sweep Channel Sounder Using Low-Cost COTS Beamforming RF Transceivers.pdf

DOI： 10.1109/ACCESS.2021.3085325

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/TWC.2020.2992533

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

The IEEE 802.11ay channel models have been developed based on the quasi-deterministic (Q-D) channel modeling that considers environment specific property of millimeter-wave (mm-wave) propagation by representing multi-path channels as superposition of deterministic (called D-ray) and random clusters (called R-ray). Based on the Q-D model, this letter presented the inter-cluster parameters of the random clusters which were obtained from the double-directional channel measurement in an indoor entrance hall environment. Comparison between the parameters obtained in this study and those of the existing IEEE 802.11ay/MiWEBA model showed that both are reasonable values inferred from each corresponding environment.

DOI： 10.1587/comex.2020XBL0052

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

In radio channel measurements and modeling, directional scanning via highly directive antennas is the most popular method to obtain angular channel characteristics to develop and evaluate advanced wireless systems for high frequency band use. However, it is often insufficient for ray-/cluster-level characterizations because the angular resolution of the measured data is limited by the angular sampling interval over a given scanning angle range and antenna half power beamwidth. This study proposes the sub-grid CLEAN algorithm, a novel technique for high-resolution multipath component (MPC) extraction from the multi-dimensional power image, so called double-directional angular delay power spectrum. This technique can successfully extract the MPCs by using the multi-dimensional power image. Simulation and measurements showed that the proposed technique could extract MPCs for ray-/cluster-level characterizations and channel modeling. Further, applying the proposed method to the data captured at 58 :5 GHz in an atrium entrance hall environment which is an indoor hotspot access scenario in the fifth generation mobile system, the multipath clusters and corresponding scattering processes were identified.

DOI： 10.1587/transcom.2019ebp3055

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

DOI： 10.1587/transcom.2019hmp0005

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

DOI： 10.1109/ISMICT48699.2020.9152612

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Other Link： https://dblp.uni-trier.de/db/conf/ismict/ismict2020.html#Nagai020

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

This paper analyzes a scenario where single or multiple sensors placed on a parked car help the owner to find the car in a parking lot. It is assumed that the sensors communicate with the owner device over ultra-wide-band (UWB) and the owner device only records the received signal strength (RSS) values. Based on the RSS data, which are obtained from a field test, two algorithms are proposed, first, when there is only one UWB sensor transmitting from the car, and second, when there are three such transmitters available. For the single transmitter case, we used a multi-slope method for RSS-based ranging which yielded an average improvement of 2.5% in ranging accuracy over the basic linear regression model. For the three transmitter case, we are estimating distance of the receiver from the transmitters in an individual manner and then enhance the accuracy of the distance estimates with the knowledge of the other distances. The algorithm is simple, can act with heterogeneous sensor types and do not require time synchronization among transmitters, yet achieve an 8% improvement in ranging accuracy.

DOI： 10.1109/LATINCOM50620.2020.9282293

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Other Link： https://dblp.uni-trier.de/db/conf/latincom/latincom2020.html#SouryaDCPK20

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/ACCESS.2020.2991044

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Language：English   Publishing type：Part of collection (book)   Publisher：Institution of Engineering and Technology  

In this chapter, an intensive study of a novel human movement identification scheme using the radio signal strength in wireless body area network (WBAN) is presented. Since the WBAN channel characteristics are highly influenced by the human movement, the radio signal strength and its temporal variation can be used to determine the human movement without additional tools such as an accelerometer/gyroscope. This study included the process of developing the human movement identification system, performance assessment on different conditions including a vector size of the received signal levels, an antenna orientation, a classifier training algorithm, and a receiver location. It was found that the vector size of the received signal levels and the receiver location had strong impact on the identification accuracy. More than 80% of the identification accuracy can be achieved when using 30-40 received signal levels or the receiver location at thigh or upper arm. In addition, a feature selection method based on a correlation coefficient was used to remove redundant and less informative features. The classification results show that the comparable performance to the all feature vectors can be achieved by the subset feature vector with a lower computational cost.

DOI： 10.1049/PBHE011E_ch6

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

DOI： 10.1587/comex.2019xbl0093

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

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

In order to utilize higher frequency bands above 6 GHz, which is an important technical challenge in fifth generation mobile systems, radio propagation channel properties in a large variety of deployment scenarios should be thoroughly investigated. The authors' group has been involved in a fundamental research project aimed at investigating multipleinput- multiple-output (MIMO) transmission performance and propagation channel properties at microwave frequency above 10 GHz from 2009 to 2013, and since then they have been conducting measurement and modeling for high frequency bands. This paper aims at providing comprehensive tutorial of a whole procedure of channel modeling
multi-dimensional channel sounding, propagation channel measurement, analysis, and modeling, by introducing the developed MIMO channel sounders at high frequency bands of 11 and 60 GHz and presenting some measurement results in a microcell environment at 11 GHz. Furthermore, this paper identifies challenges in radio propagation measurements, and discusses current/future channel modeling issues as future works.

DOI： 10.1587/transcom.2017ISI0003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

To resolve the crowded radio spectrum problem observed in conventional microwave bands (below 6 GHz), new frequency bands higher than 6 GHz are being considered to facilitate the use of a much wider bandwidth for next-generation wireless systems. Various channel sounding measurements have been conducted to elucidate the radio propagation properties at such new frequency bands. For a high-frequency channel sounding measurement, directional scanning with high-gain antennas is a popular method adopted to save the development cost of a full antenna array. This letter presents the analysis of the maximum likelihood multipath component parameter estimation accuracy where a Gaussian beam antenna pattern obtained by the scaled von Mises distribution function is used for the ease of analysis. The numerical analysis shows that the angle estimation error is approximately proportional to the square of the antenna half-power beamwidth (HPBW) and the square root of the angular sampling interval (ASI), respectively, and the amplitude and phase estimation error is approximately proportional to the HPBW and the square root of the ASI, respectively. The intrinsic performance of the used antenna is also discussed.

DOI： 10.1109/LAWP.2017.2768434

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

This paper presents a clustering and tracking method that exploits the geometry of the scattering points (SPs) obtained from the measurement-based ray tracer. The multipath components (MPCs) were categorized into clusters by applying the KPowerMeans (KPM) framework to those SPs. The clusters were tracked by comparing the cluster-centroid SPs of the adjacent snapshots. The clusters were estimated based on the indoor environment geometry at 11 GHz, and their physical mechanisms were interpreted. The complexity and performance of this method was assessed and compared with that of conventional KPM by comparing the number of floating point operations (FLOPS) and the channel eigenvalues obtained from the reconstructed channel matrices, which were calculated by superposing the MPCs randomly generated from intracluster parameters. The verification of this method showed that most clusters were estimated and tracked according to the physical location of the scatterers in the environment with acceptable error. Moreover, the eigenvalues reconstructed from the proposed method were closer to the measured ones with less number of FLOPS, which indicates both accuracy and complexity improvement. The results also imply that multiple-input multiple-output performance is highly dependent on the radio propagation channel; therefore, it is imperative that clusters in the channel be determined accurately.

DOI： 10.1109/TAP.2017.2754417

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Language：English   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In the next-generation mobile communication system, the higher frequency bands from C-band to V-band are expected to be utilized because it has the potential to improve network capacity drastically by the available wideband spectrum. Since the characteristics of reflected and scattered radio waves from surrounding environments in those bands are thought to be quite different than at lower frequencies, the clarification of its influence on the multiple-input multiple-output (MIMO) transmission performance is a critical issue. In this paper, we focused on the characteristics of diffuse scattering in X-band, and conducted the MIMO channel measurements in indoor environments in the 11-GHz band. The frequency, angular, and polarization domain dense multipath component (DMC) propagation parameters were jointly estimated by using the RiMAX-based estimator. The measurement result showed the existence of significant DMC, which is thought to have originated from the floor, the ceiling as well as the walls. The angular spreads of the DMC tended to increase, and their decay factor tended to decrease as the room size decreased. It is also shown that the existence of DMC significantly affected the eigenvalue structure of the MIMO channel, which defines the MIMO transmission performance. The result is expected to be utilized for novel MIMO channel modeling in X-band that includes the DMC contribution.

DOI： 10.1109/TAP.2017.2728087

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

To use millimeter wave bands in future cellular and outdoor wireless networks, understanding the multipath cluster characteristics such as delay and angular spread for different polarization is very important besides knowing the path loss and other large scale propagation parameters. This paper presents result from analysis of wide-band full polarimetric double directional channel measurement at the millimeter wave band in a typical urban pico-cell environment. Only limited number of multipath clusters with gains ranging from -8 dB to -26.8 dB below the free space path loss and mainly due to single reflection, double reflection and diffraction, under both line of sight (LOS) and obstructed LOS conditions are seen. The cluster gain and scattering intensity showed strong dependence on polarization. The scattering intensities for v - v polarization were seen to be stronger compared to phi - phi polarization and on average 6.1 dB, 5.6 dB and 4.5 dB higher for clusters due to single reflection, double reflection and scattering respectively. In each cluster, the paths are highly concentrated in the delay domain with delay spread comparable to the delay resolution of 2.5 ns irrespective of polarization. Unlike the scattering intensity, the angular spread of paths in each cluster did not show dependence on polarization. On the base station side, average angular spread in azimuth and in elevation were almost similar with <= 3.3 degrees spread in azimuth and <= 3.2 degrees spread in elevation for v - v polarization. These spreads were slightly smaller than those observed for phi - phi polarization. On the mobile station side the angular spread in azimuth was much higher compared to the base station side. On average, azimuth angular spread of <= 11.4 degrees and elevation angular spread of <= 5 degrees are observed for v - v polarization. These spreads were slightly larger than in phi - phi polarization. Knowing these characteristics will be vital for more accurate modeling of the channel, and in system and antenna design.

DOI： 10.1587/transcom.2016EBP3303

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Body area network (BAN) is a fundamental technology to realize future ICT-based healthcare services and applications, where channel modeling plays an important role in designing more reliable BAN systems. The greatest challenge of the WBAN channel modeling is that the antennas operate in proximity to the human body. Near-field interactions between the antenna and the human body make it difficult to distinguish the contribution of the antennas within the channel response, i.e., the antennas are embedded in the channel. As a result, the characterized channels had to be always specific to the given antenna, and antenna optimization is difficult. Therefore, this paper proposed antenna deembedding by applying the spherical wave function channel modeling into the on-body channel. The finite-difference time-domain (FDTD) method was utilized to implement the concept. The proposed implementation was validated against the conventional antenna-embedded simulation. Furthermore, the antenna performance evaluation in terms of mean path gain during a specific body motion was demonstrated as an application. The simplified but practical version of the proposed approach, involving only the fundamental modes, was introduced. The obtained mean path gain was compared with the measurement.

DOI： 10.1109/TAP.2017.2655006

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In this paper, a novel approach of a human motion classification system in wireless body area network (WBAN) using received radio signal strength was developed. This method enables us to classify human motions in WBAN using only the radio signal strength during communication without additional tools such as an accelerometer. The proposed human motion classification system has a potential to be used for improving communication quality in WBAN as well as recording daily-life activities for self-awareness tool. To construct the classification system, a numerical simulation was used to generate WBAN propagation channel in various motions at frequency band of 403.5MHz and 2.45 GHz. In the classification system, a feature vector representing a characteristic of human motions was computed from time-series received signal levels. The proposed human motion classification using the radio signal strength based on WBAN simulation can classify 3-5 human motions with the accuracy rate of 63.8-95.7 percent, and it can classify the human motions regardless of frequency band. In order to confirm that the human motion classification using radio signal strength can be used in practice, the applicability of the classification system was evaluated by WBAN measurement data.

DOI： 10.1587/transcom.2015MIP0009

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For designing reliable wireless body area network (WBAN) systems, channel modeling plays an important role. Antenna de-embedding, in which the contribution of antennas is separately modeled from the channel, has been one of the biggest challenges in WBAN channel modeling. While the antenna de-embedding in mobile communication has been achieved by double-directional channel modeling, this approach can not be applied to the WBAN channel because the antennas are operating close to the human body. Instead, this paper evaluates an antenna de-embedding scheme using spherical-wave-functions (SWFs). The antennas are modeled by the spherical wave coefficients. The channel without the antennas is modeled by a mode-to-mode mapping matrix M which describes the relationship between the radiated and impinging spherical waves. This paper shows the numerical validation of the transmit antenna model. The E-field distribution throughout the region is successfully reproduced by the antenna model in the proposed approach.

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DOI： 10.1109/PIMRC.2016.7794754

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2016.html#WangchukUIKST16

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

DOI： 10.1109/PIMRC.2016.7794875

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2016.html#ArchasantisukAK16

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

DOI： 10.1109/PIMRC.2016.7794752

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2016.html#SaitoTK16

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

This paper proposes a novel approach to extracting the narrowband propagation channel from the communication link by de-embedding the impact of the antennas. In the proposed approach, the mode-to-mode mapping matrix M, which is the expression of the propagation channel in the spherical vector wave domain, is estimated by applying pseudo-inverse computation to the channel transfer functions with dedicated spherical arrays. The estimated M is truncated and only the dominant modes within the spatial bandwidth of the fields radiated from the finite volume of the spherical array are considered. Two types of spherical array are investigated: 1) an ideal array using tangential dipoles; and 2) a virtual array using dielectric resonator antenna (DRA). The ideal array is used for parameter investigation including the array radius and the spacing with regard to the size of M and the condition number of the excitation coefficient matrix, while the virtual DRA array is proposed as a practical implementation of the ideal array. The accuracy of the proposed approach has been validated numerically. The uncertainties of spherical array in practice, such as the influence of nonideally embedded array elements, cables, and fixtures, are considered in the validation. Moreover, the channel transfer functions reproduced by the de-embedded M are analyzed, given different target antennas at link ends. The gain and phase discrepancies as well as the antenna correlations of the reproduced channel transfer function are compared with the generated reference.

DOI： 10.1109/TAP.2015.2443854

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Finite-difference time-domain (FDTD) method is one of the promising approaches for the propagation prediction. However, since the computational domain includes both the antennas and the propagation environment, their coupling prevents evaluating individual contributions to the channel response. As a result, the simulation becomes always specific to the given antenna type or orientation and cannot be reused for other configurations. The simulation also requires the internal structure of the antenna which is often unavailable and/or difficult to be modeled. These problems can be addressed by antenna de-embeddeding which separatelymodels the antenna and the propagation environment, hence the purpose of this paper. In particular, this paper proposes the implementation of spherical-wave-function (SWF) channel modeling using the FDTD method. Instead of modeling the real antenna structures inside the computational domain, the single-mode spherical wave source and the observation points are utilized. The spherical wave source is achieved by a cubical dipole array. The spherical wave source is first validated, including the investigation of the effects of cell and array size. The narrow-band channel response synthesized by the proposed approach is then validated numerically through comparison with the transmission formula in free space and the conventional antenna-embedded simulation in the human shadowing environment as well.

DOI： 10.1109/TAP.2015.2414442

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To improve the outage performance of a wireless body area network (BAN), exploitation of the diversity in the channel obtained by letting different nodes cooperate and relay signals for each other is an attractive solution. We carry out multi-link channel measurements and modeling for all realistic locations of the on-body sensor nodes and for three different motion scenarios in a typical office environment to develop equivalent channel model for simple and practical cooperative transmission schemes. Using the developed model the performance of the transmission schemes are evaluated and compared. Incremental decode and forward relaying is found to be consistently better than the other schemes with gains of up to 16 dB at 10% outage probability, and an average gain of more than 5.9 dB for any location of the coordinator node. The best location of the coordinator node based on the performance is also determined. Such insights will be very useful in designing BANs.

DOI： 10.1587/transcom.E98.B.554

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Wireless body area networks (WBANs) are an emerging technology for realizing efficient healthcare and remote medicine for the aging society of the future. In order to improve the reliability of WBAN systems and support its various applications, channel modeling and performance evaluation are important. This paper proposes a simulation-based channel modeling for evaluating the performance of WBAN cooperative transmission schemes. The time series of path losses among seven on-body nodes are generated by the finite-difference time-domain method for seven body motions. The statistical parameters of the path loss for all the motions are also obtained. The generated path loss is then applied to the evaluation of the two-hop decode-and-forward relaying scheme, yielding an improvement in transmit power. From the evaluation of body motion, useful insights are obtained such as which relay links are more robust than others. Finally, the proposed approach is validated through comparison with a measurement-based approach.

DOI： 10.1109/JBHI.2014.2326424

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DOI： 10.1109/ISMICT.2015.7107490

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Other Link： https://dblp.uni-trier.de/db/conf/ismict/ismict2015.html#NaganawaTAK15

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

High frequency spectrum is expected to offer a wide bandwidth for future broadband cellular networks. This paper presents the measurement results of the outdoor urban cellular wideband channels at 11 GHz. The measurements at various urban cellular environments that are classified into macrocell, microcell and street-cell were conducted, where a wideband 24 x 24 MIMO channel sounder having 400 MHz signal bandwidth and dual-polarized 12-element uniform circular arrays were used. This paper presents large scale characteristics of 11 GHz wideband channels including path losses, shadowing, cell coverage, polarization properties and delay spread, which were calculated by the polarimetric beamforming both at transmitter and receiver. Large shadowing loss of approximately 20 dB was observed in NLoS condition, and from the outage calculation it was seen that the cell coverage with omni-directional antennas is limited to less than 100 m for 30 dB SNR. From the power delay profile (PDP), small RMS delay spreads with the mean value of less than 20 ns were observed.

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Wireless body area network (WBAN) is expected to be utilized in various fields such as health-care. One of its vital challenges is that dynamic channels suffer severely from fading. Therefore the characterization of WBAN channel is important and many researches have been done in this area. This paper presents a tri-polarized dynamic WBAN channel sounder to realize 3x3 dynamic channel measurement by applying time division multiplexing (TDM), and by using two tri-polarized dielectric resonator antennas (DRAs) and a multi-port oscilloscope. Due to the tri-polarized property of DRA, this present system can contribute to the antenna polarization dependency of WBAN channel as well as the measurement-based antenna de-embedding. In this paper, system configuration, parameter design, DRA antenna, calibration method, and measurement validation are presented.

DOI： 10.1109/ISMICT.2015.7107491

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Copyright © 2014 The Institute of Electronics, Information and Communication Engineers. This paper presents a 24 x 24 MIMO channel sounder that has been developed based on a scalable fully parallel MIMO architecture. It can be flexibly configured with 3 sub-transmitters and 3 sub-receivers, each of which consists of 8 RF ports. This flexibility allows the measurement for both purposes of double directional and multi-link MIMO channel measurements. Implementation issues related to the multi-link operation on the fully parallel architecture were successfully solved by appropriate system design and applying several calibration techniques. The performance of the developed system was validated by extensive test experiments. Finally, a multi-link channel measurement example in an indoor environment was presented demonstrating the capability of the proposed system.

DOI： 10.1587/transele.E97.C.994

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This paper presents a 24 x 24 MIMO channel sounder that has been developed based on a scalable fully parallel MINI architecture. It can be flexibly configured with 3 sub-transmitters and 3 sub-receivers, each of which consists of 8 RF ports. This flexibility allows the measurement for both purposes of double directional and multi-link MIMO channel measurements. Implementation issues related to the multi-link operation on the fully parallel architecture were successfully solved by appropriate system design and applying several calibration techniques. The performance of the developed system was validated by extensive test experiments. Finally, a multi-link channel measurement example in an indoor environment was presented demonstrating the capability of the proposed system.

DOI： 10.1587/transele.E97.C.994

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This paper presents the large scale parameters of wideband multipath channels based on extensive measurement campaigns in various indoor environments. The measurements were conducted with a wideband multiple-input multiple-output (MIMO) channel sounder having a bandwidth of 400 MHz at 11 GHz which is a challenging frequency for future mobile systems. In particular, polarization characteristics of path-loss, shadowing, cross-polarization power ratio (XPR), delay spread and coherence bandwidth are characterized. The measurement results show that the path-loss exponents range between 2.0 and 3.0 for none-line-of-sight (NLoS), 0.36 and 1.5 for LoS, respectively. Vertically and horizontally polarized transmissions have almost same path-gain, but in some corridor-room NLoS environments, the path-loss for HH is significantly large. In most cases, the RMS delay spreads are less than 20 and 50 ns for NLoS and LoS, respectively, and the average coherence bandwidth is less than 30 MHz. The Rician K-factors range between 2 and 3 dB for cross-polarization, and in large Hall environments, those for co-polarization are greater than 6.0 dB with 10% probability. Finally, some dominant propagation mechanism and site-specific behaviors are illustrated using the double-directional measurement results.

DOI： 10.1109/TAP.2013.2288633

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The event-driven network simulator NS-2 does not support frequency hopping (FH) and multi-channel operations, as well as the adjacent channel interference (ACI), in its current form. This paper introduces the key implementation methods to enable FH mobile ad hoc network (MANET) simulations in NS-2. The proposed simulator provides proper analysis in arbitrary topologies of FH-MANET.

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Automatic modulation classification (AMC) is an important function of radio surveillance systems in order to identify unknown signals. Many previous works on AMC have utilized signal cyclostationarity, particularly spectral correlation density (SCD), but many of them fail to address several implementation issues, such as the assumption of perfect knowledge of the symbol rate. In this paper, we discuss several practical issues, e.g. cyclic frequency mismatch, which may affect the SCD, and propose compensation techniques to overcome those issues. We also propose a novel feature extraction technique from the SCD, which utilizes the SCD of not only the original received signal, but also the squared received signal. A symbol rate estimation technique which complements the feature extraction is also proposed. Finally, the classification performance of the system is evaluated through Monte Carlo simulations using a wide variety of modulated signals, and simulation results show that the proposed technique can estimate the symbol rate and classify modulation with a probability of above 0.9 down to SNRs of 5 dB.

DOI： 10.1587/transcom.E96.B.1158

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Automatic modulation classification (AMC) involves extracting a set of unique features from the received signal.. Accuracy and uniqueness of the features along with the appropriate classification algorithm determine the overall performance of AMC systems. Accuracy of any modulation feature is usually limited by the blindness of the signal information such as carrier frequency, symbol rate etc. Most papers do not sufficiently consider these impairments and so do not directly target practical applications. The AMC system proposed herein is trained with probable input signals, and the appropriate decision tree should be chosen to achieve robust classification. Six unique features are used to classify eight analog and digital modulation schemes which are widely used by low frequency mobile emergency radios around the globe. The Proposed algorithm improves the classification performance of AMC especially for the low SNR regime.

DOI： 10.1587/transcom.E96.B.1030

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This paper proposes a parametric method of frequency-dependent I/Q imbalance compensation for wideband quadrature modulators using the spectrum measurement of a radio frequency (RF) signal that is easily performed by a general-purpose spectrum analyzer. The proposed method empirically estimates the frequency-dependent circuit parameters using only the magnitude of the frequency spectrum of the RF signal that is fed back from the spectrum analyzer. The frequency dependency of the I/Q imbalance effect generated by the difference between the overall frequency responses of the I and Q branches is modeled by frequency-dependent circuit parameters. By dividing the entire signal band into several sub-bands, the transmit signals are predistorted per sub-band in the frequency domain. To estimate the frequency-dependent circuit parameters, in this study, the modified method of steepest descent developed for single-band compensation is extended to the frequency-domain sub-band compensation scheme. We demonstrate the compensation effect by implementing an automatic sub-band circuit parameter estimation system. © 2012 IEEE.

DOI： 10.1109/TMTT.2012.2228215

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DOI： 10.1109/ISMICT.2013.6521696

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Other Link： https://dblp.uni-trier.de/db/conf/ismict/ismict2013.html#WangchukKT13

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DOI： 10.1109/ISMICT.2013.6521722

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Other Link： https://dblp.uni-trier.de/db/conf/ismict/ismict2013.html#FujieNKAT13

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

This paper presents a novel multiple-input-multiple-output (MIMO) channel sounding technique with a fully parallel transceiver architecture that employs a layered scheme of frequency and space-time division multiplexing. It offers inherent scalability of the number of antennas by a combination of multiple transceiver units and flexibility for both directional MIMO channel and multi-link MIMO channel measurements. This paper describes the principle of the channel sounding technique and formulates the signal processing that makes possible various scalable unit configurations. The influence of the transceiver imperfections such as I/Q imbalance (IQI) and phase noise (PN) on the measurement accuracy is discussed, and a multitone allocation scheme that is robust against IQI is also introduced. Using computer simulations, the measurement accuracy in the presence of IQI and PN is evaluated using the normalized mean square error, which provides a design guideline for the realization of hardware.

DOI： 10.1109/TIM.2012.2205510

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

Body area network is an emerging area of wireless communication for medical healthcare applications. This paper characterizes the narrowband wireless on-body channels under specific action scenarios by measurement at the three different sub-GHz frequencies of 444.5, 611, and 953 MHz, which are the candidate frequency bands of narrowband body area network systems with low data rates in IEEE 802.15.6 standard. The channel responses at ten different antenna positions were measured in an office room environment for the two dynamic action scenarios of "walking on the spot" (Action I) and "standing up/sitting down" (Action II). This paper provides generalized on-body channel models of Nakagami- and Weibull distributions for Actions I and II, respectively. Notably, this paper shows that the shadowing effect due to body movement is dominant over the multipath fading. The results were obtained by the statistical analyses of channel fading properties at three different frequencies including level crossing rate, average fade duration and channel dwelling time.

DOI： 10.1109/TAP.2012.2207937

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This letter proposes an automatic IQ imbalance compensation technique for quadrature modulators by means of spectrum measurement of RF signal using a spectrum analyzer. The analyzer feeds back only magnitude information of the frequency spectrum of the signal. To realize IQ imbalance compensation, the conventional method of steepest descent is modified; the descent direction is empirically determined and a variable step-size is introduced for accelerating convergence. The experimental results for a four-channel transmitter operating at 11 GHz are presented for verification.

DOI： 10.1587/transcom.E95.B.1864

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Spectrum sensing, a key technical challenge in cognitive radios (CR) technology, is a technique that enables the spectrum of licensed systems to be accessed without causing undue interference. It is well known that cyclostationarity detectors have great advantages over energy detectors in terms of the robustness to noise uncertainty that significantly degrades the performance as well as the capability to distinguish the signal of interest from the other interferences and noise. The generalized likelihood ratio test (GLRT) is a recognized sensing technique that utilizes the inherent cyclostationarity of the signal and has been intensively studied. However, no comprehensive evaluation on its performance enhancement has been published to date. Moreover high computational complexity is still a significant problem for its realization. This paper proposes a maximum ratio combining multi-cyclic detector which uses multiple cyclic frequencies for performance enhancement with reduced computational complexity. An orthogonal frequency-division multiplexing (OFDM) signal based on the ISDB-T (integrated services digital broadcasting terrestrial), a Japanese digital television broadcasting standard, was used in the evaluation assuming this as a primary system in WRAN (wireless regional area network) applications like IEEE 802.22.

DOI： 10.1587/transcom.E95.B.950

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Multiple-input multiple-output (MIMO) systems have attracted lots of attentions, for their potential for high gain in channel capacity. For evaluating the performance of MIMO systems in more practical situations, more accurate channel models are necessary; and channel measurement is necessary to estimate the parameters of the channel models [1] [2]. In [2], we developed a fully parallel wideband MIMO channel sounding system at 11GHz with 400MHz bandwidth, which utilized software defined radio (SDR) architecture and is considered more suitable for real-time evaluation of link-level performance and channel properties, comparing with switching-based time division multiplexing (TDM) sounder, that has been commonly used [3]. However, one of the drawbacks of the fully parallel MIMO channel sounder system is that it needs complex procedures of baseband circuit adjustment, radio frequency (RF) circuit compensation, and back-to-back (B2B) calibration measurement, comparing with switching-based system; and the complexity increases with the numbers of transmit (Tx) and receive (Rx) channels. Since currently, the sounder system developed in[2] has been extended into 24 × 24 MIMO sounder, it becomes a very serious problem that it will take very long time to carry out the B2B calibration measurement for all possible MIMO connections. In this paper, automatic system calibration schemes are introduced and a simplified B2B calibration method is also proposed to shorten the measurement time. © 2012 IEICE.

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The recent explosion of mobile Internet usage results in the need for higher data rate in future mobile communication systems. One of the key technologies to satisfy this requirement is the multilink transmission technique which utilizes the cooperative signal processing among spatially distributed multiple users and/or base stations, thus it is considered as more robust in ensuring the degree of freedom in spatial domain over the conventional single-link multiple-input-multiple-output (MIMO) systems [1]. However for the proper design and development of multi-link transmission systems, the level of inter-link channel correlation needs to be accurately modeled. Moreover since each user terminal and base station will also be equipped with multiple antennas, characterization of directional property at transmitter (Tx) and receiver (Rx) is also important for the design of array antennas. Previously, a lot of field measurement results reported focused on the characterization of multi-link propagation channel as summarized in [2]. However in the earlier works, channel stationarity is often assumed due to the limitations of channel sounder capabilities. Recently in [3], geometry-based multi-link channel modeling approach is proposed based on the measurement by dual-link MIMO channel sounder [4], and the propagation mechanisms which cause the correlation among two links are reported. Nevertheless, the existing results are still limited to specific frequency bands (below 2 GHz or 5 GHz) and environments, thus further evaluation based on the multi-link measurements is desired. © 2012 IEICE.

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In this paper, the shadowing correlations among the multiple links between a coordinate node and sensor nodes in wireless BAN systems were investigated by measurements under everyday-life scenarios. We have developed a body-worn RSSI (receive signal strength indicator) logging system with off-the-shelf ZigBee sensor devices at 2.4 GHz for long time continuous and synchronized measurement among sensor nodes. The cross correlation coefficients calculated within a short time window were statistically characterized. The shadowing correlation will become useful information to develop and evaluate a multi-hop relay and a cooperative transmission scheme for increasing the reliability and power efficiency. © 2012 IEEE.

DOI： 10.1109/EuCAP.2012.6206638

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

This paper proposed the skeleton model to generate human body models for predicting dynamic BAN channels by considering the simplified body geometry in analytical study. The numerical human body model was exported into skeleton in bvh (bio-vision hierarchy) file format. The cylinder body model is constructed by shaping the necessary bones of skeleton by cylinder. The feasibility of model is assessed by FDTD simulation. The results show reasonable agreement between channels calculated from the complex and simplified body models. By using skeleton, the motion data can be transferred into a small size file without losing necessary information for channel prediction. © 2012 IEEE.

DOI： 10.1109/EuCAP.2012.6206616

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In this paper, we performed six human movement simulation by a commercial software (Poser7). We performed FDTD simulations for body area network propagation with one transmitter and six receivers. Received amplitudes were calculated for every time frame of 1/30 s interval. We also demonstrated a polarization diversity effectiveness for dynamic wearable body area network propagation.

DOI： 10.1587/transcom.E94.B.2496

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In this report, we performed six human movement simulation by a commercial software (Poser7). We performed FDTD simulations for body area network propagation with one transmitter and six receivers. Received amplitudes were calculated for every time frame of 1/30 s interval. We also demonstrated a polarization diversity effectiveness for dynamic wearable body area network propagation. © 2011 IEEE.

DOI： 10.1109/ISMICT.2011.5759798

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DOI： 10.4108/icst.crowncom.2011.245915

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This paper presents research activity of the body area channel related studies by Tokyo Institute of Technology and National Information and Communications Technology, Japan. One of our goal is to make a practical wearable body area network propagation channel model during arbitrary body motions. First, we present the numerical simulated electromagnetic wave propagation wearable body area network channel during various human motions at 403.5 MHz. Second we present modeling dynamic on-body channel based on the three dimensional motion of on-body antennas. The simulation results were verified to the measured channel responses from the network analyzer operated simultaneously with motion capture. © 2011 EurAAP.

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Big natural or manmade disasters damage infrastructure and cause severe effect on civilizations. Existing telecommunication infrastructure goes down as well as power, water etc. Quick and effective rescue operation requires a collaborative communication infrastructure for the rescue teams. Emergency spectrum usage of the rescue teams is one of the major issues in such scenario. Different teams interfere with each other for lack of collaboration and infrastructure limitations. This study designed and developed a cognitive wireless sensor network that collects and forms a database of the active emitters on the disaster scene. This paper focuses especially on a distributed spectrum sensing scheme for the emergency radios. ©2010 IEEE.

DOI： 10.1109/ISCIT.2010.5665132

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In this paper, a centralized polling-based medium access (MAC) scheme, namely, the IEEE 802.11e hybrid coordinator function (HCF) controlled channel access (HCCA), is considered as an alternative to the current MAC protocol used in IEEE 802.11p for Wireless Access in Vehicular Environment (WAVE). At first, the limitations of the current enhanced distributed channel access (EDCA) are examined, and then a simple analytical performance evaluation of HCCA is provided. The results demonstrate that the HCCA scheme can be an alternative option to EDCA and could serve as an efficient channel access mechanism for vehicular communications.

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This paper presents a framework of multimode fully digital receiver implementation using direct RF-to-digital conversion. In this architecture the entire band including multiple RF systems is directly converted to digital by a wideband high speed ADC, and the RF systems can be easily switched by only digital signal processing with the minimum analog RF components. The digital RF front-end consists of parallel processing blocks for parallel data streams considering practical ADC's configuration. The RF signals are converted into baseband through digital IF stage and the data rates are made down by two steps of decimation. In this paper, a principle investigation into a dualmode system implementation is presented for simplicity. The circuit resource and the robustness to the spurs (spurious outputs) of an NCO (numerically controlled oscillator) in the proposed design will be presented. The proposed architecture was implemented with an FPGA on the developed prototype system and the operations were also verified.

DOI： 10.1587/transfun.E92.A.1056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER INTERNATIONAL PUBLISHING AG  

In the early deployment of electric toll collecting (ETC) system, multipath interference has caused the malfunction of the system. Therefore, radio absorbers are installed in the toll gate to suppress the scattering effects. This paper presents a novel radio propagation measurement system using the beamforming with 8-elmenet antenna array to examine the power intensity distribution of the ETC gate in real time without closing the toll gates that are already open for traffic. In addition, an identification method of the individual scattering objects with 3D visualization by using virtual reality modeling language will be proposed and the validity is also demonstrated by applying to the measurement data. Copyright (C) 2009 Minseok Kim et al.

DOI： 10.1155/2009/131576

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

This letter presents the characterization of an on-body propagation channel with a specific activity of a body on the basis of the measurement results of a male subject in a radio anechoic chamber. In order to capture the dynamic behavior of the channel, a commercial real-time channel sounding system for the 4.5-GHz narrowband was used. The measurement scenarios included two repetitive actions of walking on the spot and standing up and sitting down at 10 different receive antenna locations where the fading caused by the action was observed and statistically modeled.

DOI： 10.1109/LAWP.2009.2036570

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

On-body communication channels are of increasing interest as more and more wireless devices are wearable in medical, military, and personal communications. This letter presents an experimental investigation into the dynamic on-body channel with body movements. Based on statistical analyses of level crossing rate and fading duration, a three-state Fritchman model that considers both channel dwelling time and channel quality is proposed to describe the burst characteristics of on-body fading. The dynamic on-body channels are classified into unstable error-free state, constant error-free state, and error state. Parameters for the Fritchman model are estimated from the measured data.

DOI： 10.1109/LAWP.2009.2036749

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

DOI： 10.4108/ICST.PERVASIVEHEALTH2009.5945

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Other Link： https://dblp.uni-trier.de/rec/conf/ph/2009

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

DOI： 10.1109/PIMRC.2009.5450175

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2009.html#KimT09

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

The input impedance of an antenna fluctuates because of various usage conditions, which causes a mismatch between an internal circuit and an antenna. An automatic matching system solves this problem. then this paper presents a reconfigurable impedance tuner that has a set of fixed capacitors controlled by switching p-i-n diodes. A fast control algorithm for selecting the appropriate conditions of an impedance tuner is proposed and mounted on FPGA to demonstrate the performance.

DOI： 10.1093/ietele/e91-c.8.1348

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At present, when using space-time processing techniques with multiple antennas for mobile radio communication, real-time weight adaptation is necessary. Due to the progress of integrated circuit technology, dedicated processor implementation with ASIC or FPGA can be employed to implement various wireless applications. This paper presents a resource and performance evaluation of the QRD-RLS systolic array processor based on fixed-point CORDIC algorithm with FPGA. In this paper, to save hardware resources, we propose the shared architecture of a complex CORDIC processor. The required precision of internal calculation, the circuit area for the number of antenna elements and wordlength, and the processing speed will be evaluated. The resource estimation provides a possible processor configuration with a current FPGA on the market. Computer simulations assuming a fading channel will show a fast convergence property with a finite number of training symbols. The proposed architecture has also been implemented and its operation was verified by beam-forming evaluation through a radio propagation experiment.

DOI： 10.1093/ietcom/e91-b.4.1068

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

This letter evaluates a transmitter architecture using harmonic images in D/A conversion for generating RF signals. In generating harmonic images, the problems such as intermodulation distortion of DAC were investigated. We developed an evaluation system with two bandpass filter and a buffer amplifier. It was experimentally found that the RF signal up to around 400 MHz can be generated by a commonly used 14-bit DAC at the sampling rates of around 40 MHz with EVM less than 6.6%. This letter also presents a more feasible transmitter example having an IF stage with harmonic image extraction scheme and a typical RF upconversion stage.

DOI： 10.1093/ietcom/e91-b.4.1215

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Undersampling (or bandpass sampling) phase modulated signals directly at high frequency band, the harmful effects of the aperture jitter characteristics of ADCs (Analog-to-Digital converters) and sampling clock instability of the system can not be ignored. In communication systems the sampling jitter brings additional phase noise to the constellation pattern besides thermal noise, thus the BER (bit error rate) performance will be degraded. This paper examines the relationship between the input frequency to ADC and the sampling jitter in digital IF (Intermediate Frequency) downconversion receivers with undersampling scheme. This paper presents the measurement results with a real hardware prototype system as well as the computer simulation results with a theoretically modeled IF sampling receiver. We evaluated EVM (Error Vector Magnitude) in various clock jitter configurations with commonly used and reasonable cost ADCs of which sampling rates was 40 MHz. According to the results, the IF input frequencies of QPSK (16 QAM) signals were limited below around 290 (210) MHz for wireless LAN standard, and 730 (450) MHz for W-CDMA standard, respectively, in our best configuration.

DOI： 10.1093/ietisy/e88-d.7.1430

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

Undersampling (or bandpass sampling) phase modulated signals directly at high frequency band, the harmful effects of the aperture jitter characteristics of ADCs (Analog-to-Digital converters) and sampling clock instability of the system can not be ignored. In communication systems the sampling jitter brings additional phase noise to the constellation pattern besides thermal noise, thus the BER (bit error rate) performance will be degraded. This paper examines the relationship between the input frequency to ADC and the sampling jitter in digital IF (Intermediate Frequency) downconversion receivers with undersampling scheme. This paper presents the measurement results with a real hardware prototype system as well as the computer simulation results with a theoretically modeled IF sampling receiver. We evaluated EVM (Error Vector Magnitude) in various clock jitter configurations with commonly used and reasonable cost ADCs of which sampling rates was 40 MHz. According to the results, the IF input frequencies of QPSK (16 QAM) signals were limited below around 290 (210) MHz for wireless LAN standard, and 730 (450) MHz for W-CDMA standard, respectively, in our best configuration. Copyright © 2005 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1093/ietisy/e88-d.7.1430

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

DOA (Direction Of Arrival) estimation is a useful technique in various positioning applications including the DOA-based adaptive array antenna system. This paper presents a practical implementation of FPGA (Field Programmable Gate Array) based fast DOA estimator for wireless cellular basestation. This system incorporates spectral unitary MUSIC (MUltiple SIgnal Classification) algorithm, which is one of the representative super resolution DOA estimation techniques. This paper proposes a way of digital signal processor design suitable for FPGA and its real hardware implementation. In this system, all digital signal processing procedures are computed by the only fixed-point operation with finite word-length for fast processing and low power consumption. The performance will be assessed by hardware level simulations and experiments in a radio anechoic chamber.

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Computing the Eigen Value Decomposition (EVD) of a symmetric matrix is a frequently encountered problem in adaptive (or smart or software) antenna signal processing, for example, super resolution DOA (Direction Of Arrival) estimation algorithms such as MUSIC (MUltiple SIgnal Classification) and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Technique). In this paper the hardware architecture of the fast EVD processor of symmetric correlation matrices for the application of an adaptive antenna technology such as DOA estimation is proposed and the basic idea is also presented. Cyclic Jacobi method is well known for the simplest algorithm and easily implemented but its convergence time is slower than other factorization algorithm like QR-method. But if considering the fast parallel computation of the EVD with a hardware architecture like ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), the Jacobi method can be a appropriate solution, since it offers a quite higher degree of parallelism and easier implementation than other factorization algorithms. This paper computes the EVD using a Jacobi-type method, where the vector rotations and the angles of the rotations are obtained by CORDIC (COordinate Rotation DIgital Computer). The hardware architecture suitable for ASIC or FPGA with fixed-point arithmetic is presented. Because it consists of only shift and add operations, this hardware friendly feature provides easy and efficient implementation. In this paper, the computational load, the estimate of circuit scale and expected performance are discussed and the validation of fixed-point arithmetic for the practical application to MUSIC DOA estimation is examined.

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In the fifth-generation mobile communication system, the utilization of higher frequency band above 10 GHz has been widely investigated to improve the network capacity because the wide band spectrum is expected to be available. However in the higher frequency bands, in addition to the higher propagation loss, the diffuse scattering will affect the multipleinput multiple-output (MIMO) channel characteristic more significantly. In this paper, the 11 GHz band MIMO channel measurements were conducted in a LoS indoor environment to clarify the characteristics of diffuse scatters in the higher frequency band. Dense Multipath Component (DMC) parameters were estimated by using RiMAX algorithm. The measurement result shows that there was a strong DMC that was due to the diffuse scattering from the floor and the ceiling between the Tx and the Rx. The result also shows that the characteristics of the DMC had the directional and the polarization dependencies that were different from RiMAX DMC model.

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<p>Wireless body area network (WBAN) is a wireless sensor network inside, on or around the human body, and is expected to be utilized in medical and health-care applications. Dynamic behavior of radio propagation channel is important information for design and characterization of WBAN system. Various factors simultaneously influence the channel responses, such as position and orientation of antennas, electromagnetic interaction antenna and human body, and obstruction by human body itself. Therefore, it is rather difficult to analyze the propagation mechanism of dynamic WBAN channel. This paper reports the development of simultaneous measurement system of MIMO channel response and body posture of dynamic WBAN channel. Body posture information is utilized to synthesize numerical phantom for electromagnetic simulation via computer animation software. Comparison between measurement and predicted channel responses is possible by using the system, and some examples will be presented.</p>

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One of the ways to meet the growing demand for higher data rates is to exploit the large amount of spectral resources available in the mmWave frequency band. The unlicensed 60 GHz band with continuous bandwidths of more than 5 GHz is a very attractive candidate for use in small cells of the future heterogeneous cellular networks. High free space path loss and atmospheric attenuation in 60 GHz propagation channel necessitates the use of high gain directional antennas or antenna arrays. The channel characteristics including its directional properties in different environment is very important to be investigated for use of techniques like MIMO beamforming and array beamsteering. We develop a low cost 3-D mmWave channel sounding system with capability of measuring the power spectrum related to AoA and AoD of different paths. Measurement and directional analysis for a typical indoor laboratory environment is carried out.

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This paper presents a low-cost flexible channel sounder with the maximum bandwidth of 12.5MHz operating at various frequency bands within 400 - 4400 MHz developed by using GNU radio/USRP. This paper describes an improved work based on its previous channel sounding system and especially focuses on the techniques of timing synchronization and phase alignment which were hard to achieve in its previous work. Finally, The effect of improvement of previous work was demonstrated and validated by a DUT test.

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Elucidation of the space-time radio wave propagation characteristics is always an important fundamental task to develop new wireless transmission systems. For this purpose, we specifically developed a scalable full Multiple-Input Multiple-Output (MIMO) channel sounder to measure the radio channel at 11 GHz with bandwidth of 400 MHz which is a challenging frequency for future high bit-rate mobile communications. The measurement campaign in various indoor environment was conducted at Tokyo Institute of Technology. Individual paths are extracted from the measurement with the Space Alternating Generalized Expectation Maximization (SAGE) algorithm. For cluster based analysis, we used K-means algorithm for automatic clustering of the detected paths and the statistical characteristics of cross-, co-polarization ratio, delay spread and direction spread were investigated based on clustering result.

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High frequency spectrum is expected to offer a wider bandwidth for future broadband cellular networks. This paper presents the measurement results of the outdoor micro cellular wideband channels at 11 GHz. The heights of the BS antenna installed at the balcony of the apartment and MS antenna on the top of the measurement vehicle were 9 m and 3 m, respectively. The snapshots were taken at constant time interval while MS was moving around the area with radius of 200 m at the velocity slower than 10 km/h. A wideband 24 × 24 MIMO channel sounder having 400 MHz signal bandwidth and dual-polarized 12-element uniform circular antenna arrays were used. The polarimetric beamforming and SAGE algorithm were used for data analysis. This paper presents the path loss characteristics and the polarization properties for LoS and NLoS around corner areas, respectively, and RMS delay spread. Then, from the detail analysis for the specific area with radius of 60 m that was performed with the azimuth delay power spectrum and the estimated multipath parameters in terms of the MS position, a dominant propagation mechanism was discussed.

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High frequency spectrum is expected to offer a wider bandwidth for future broadband cellular networks. This paper presents the measurement results of the outdoor micro cellular wideband channels at 11 GHz. The heights of the BS antenna installed at the balcony of the apartment and MS antenna on the top of the measurement vehicle were 9 m and 3 m, respectively. The snapshots were taken at constant time interval while MS was moving around the area with radius of 200 m at the velocity slower than 10 km/h. A wideband 24 × 24 MIMO channel sounder having 400 MHz signal bandwidth and dual-polarized 12-element uniform circular antenna arrays were used. The polarimetric beamforming and SAGE algorithm were used for data analysis. This paper presents the path loss characteristics and the polarization properties for LoS and NLoS around corner areas, respectively, and RMS delay spread. Then, from the detail analysis for the specific area with radius of 60 m that was performed with the azimuth delay power spectrum and the estimated multipath parameters in terms of the MS position, a dominant propagation mechanism was discussed.

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