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

DOI： 10.1109/gcce59613.2023.10315678

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

DOI： 10.1109/GCCE59613.2023.10315597

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2023.html#YamadaDH23

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

DOI： 10.1109/GCCE59613.2023.10315294

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2023.html#MaesakiMHD23

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

DOI： 10.1587/transcom.2023ebp3009

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

DOI： 10.1109/GCCE59613.2023.10315591

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2023.html#OhbaDH23

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

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

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

DOI： 10.1109/ICCE-Taiwan58799.2023.10226659

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Other Link： https://dblp.uni-trier.de/db/conf/icce-tw/icce-tw2023.html#HouKKD23

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

DOI： 10.1109/WCNC55385.2023.10118703

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Other Link： https://dblp.uni-trier.de/db/conf/wcnc/wcnc2023.html#ZhuNKHD23

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

DOI： 10.1109/wcnc55385.2023.10118697

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

DOI： 10.23919/icact56868.2023.10079677

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

DOI： 10.1587/transcom.2022ebp3051

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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.2022ebp3062

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

DOI： 10.1109/WPMC55625.2022.10014789

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2022.html#DennoFH22

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

DOI： 10.1109/WPMC55625.2022.10014813

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2022.html#NagayamaKZHD22

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

DOI： 10.1587/transcom.2021ebp3213

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

DOI： 10.1109/APCC55198.2022.9943716

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Other Link： https://dblp.uni-trier.de/db/conf/apcc/apcc2022.html#MakabeDH22

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

DOI： 10.1109/GCCE56475.2022.10014227

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2022.html#TokuiTDU22

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

DOI： 10.1587/transcom.2021ebp3187

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

DOI： 10.1109/PIMRC54779.2022.9977753

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2022.html#ZhuNKHD22

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

DOI： 10.1109/PIMRC54779.2022.9977505

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Other Link： https://dblp.uni-trier.de/db/conf/pimrc/pimrc2022.html#DennoKH22

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

DOI： 10.1587/comex.2022xbl0028

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

DOI： 10.1587/comex.2022xbl0001

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

DOI： 10.1109/vtc2022-spring54318.2022.9860405

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

DOI： 10.1587/transcom.2021ebp3075

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

DOI： 10.1109/LifeTech53646.2022.9754939

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Other Link： https://dblp.uni-trier.de/db/conf/lifetech/lifetech2022.html#NagayamaZHHD22

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

DOI： 10.1109/access.2022.3153083

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

DOI： 10.1109/LifeTech53646.2022.9754835

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Other Link： https://dblp.uni-trier.de/db/conf/lifetech/lifetech2022.html#ZhuKHNHD22

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

DOI： 10.1109/ICCE53296.2022.9730575

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Other Link： https://dblp.uni-trier.de/db/conf/iccel/icce2022.html#HouZNHD22

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

In this paper, we propose a non-orthogonal multiple access with adaptive resource allocation based on factor graphs. The proposed non-orthogonal multiple access assigns multiple frequency resources for each device to send their packet. Even if the number of the devices is more than the frequency resources, the proposed non-orthogonal access allows all the devices to transmit their packets simultaneously for high capacity massive machine type communication (mMTC). Furthermore, this paper proposes adaptive resource allocation based on factor graphs that adaptively allocates the frequency resources to the devices for improvement of the transmission performances. This paper proposes two allocation criteria for the proposed adaptive allocation. This paper shows that the proposed non-orthogonal multiple access achieves superior transmission performance in 4-path Rayleigh fading channel with overloading ratio of 1.5, even without the adaptive resource allocation. The adaptive resource allocation enables the proposed non-orthogonal access to attain a gain of about 5 dB at the BER of 10(-4).

DOI： 10.1109/WPMC52694.2021.9700454

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

DOI： 10.1109/ICSPCS53099.2021.9660311

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Other Link： https://dblp.uni-trier.de/db/conf/icspcs/icspcs2021.html#DennoHH21

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

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

DOI： 10.1109/iscit52804.2021.9590603

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

DOI： 10.1587/comex.2021xbl0133

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

DOI： 10.1587/transcom.2020ebp3183

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

DOI： 10.1587/comex.2021etl0007

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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.2020ebp3180

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

DOI： 10.23919/icact51234.2021.9370597

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

DOI： 10.1109/LifeTech48969.2020.1570619143

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Other Link： https://dblp.uni-trier.de/db/conf/lifetech/lifetech2020.html#HouKD20

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

DOI： 10.23919/ICACT53585.2022.9728893

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Other Link： https://dblp.uni-trier.de/db/conf/icact/icact2022.html#HouYSWNHDS22

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

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

DOI： 10.1109/ACCESS.2021.3088123

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

DOI： 10.1109/ACCESS.2021.3053034

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

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Other Link： https://dblp.uni-trier.de/db/journals/ieicetb/ieicetb104.html#DennoSH21

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

DOI： 10.1587/transcom.2020EBP3045

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Other Link： https://dblp.uni-trier.de/db/journals/ieicetb/ieicetb104.html#DennoYH21

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

DOI： 10.1109/TBC.2020.3039679

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

DOI： 10.1109/APWCS50173.2021.9548758

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Other Link： https://dblp.uni-trier.de/db/conf/apwcs2/apwcs2021.html#TsugitaDH21

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

DOI： 10.1109/TBC.2020.2977514

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

DOI： 10.1109/LifeTech52111.2021.9391899

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Other Link： https://dblp.uni-trier.de/db/conf/lifetech/lifetech2021.html#ZhuNHD21

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

DOI： 10.1109/GCCE53005.2021.9622078

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2021.html#ZhuHNHD21

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

DOI： 10.23919/ICACT51234.2021.9370905

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Other Link： https://dblp.uni-trier.de/db/conf/icact/icact2021.html#HouYSWNHDS21

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

DOI： 10.23919/ICACT51234.2021.9370597

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Other Link： https://dblp.uni-trier.de/db/conf/icact/icact2021.html#HouKD21

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Graphyonline Publications PVT, Ltd.  

DOI： 10.15344/2456-4451/2020/159

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

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

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

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

DOI： 10.1587/transcom.2017ebp3203

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

DOI： 10.1109/ICSPCS50536.2020.9310008

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Other Link： https://dblp.uni-trier.de/db/conf/icspcs/icspcs2020.html#DennoTTH20

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

DOI： 10.1109/GCCE50665.2020.9291828

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2020.html#ZhuHHDO20

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

DOI： 10.1587/transcom.2019EBP3159

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Other Link： https://dblp.uni-trier.de/db/journals/ieicetb/ieicetb103.html#DennoIKFH20

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

DOI： 10.1109/WPMC50192.2020.9309510

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2020.html#FujiwaraDH20

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

Indoor localization technology, which can provide the location information of the target object or stochastic things, is becoming essential requirement for many applications and services such as Internet-of-Things (IoT), real-time control in the development of Fifth-generation (5G) technology. Leaky coaxial cable which can be used as antennas is able to detect the location of the user in a simple way due to its potential property. In this paper, we proposes a simple method to improve the localization accuracy of 2-D indoor localization using multiple LCX cables. In addition, we also evaluate the channel capacity loss due to the localization error of the LCX-MIMO using our proposed method.

DOI： 10.1017/ATSIP.2020.18

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

DOI： 10.1109/GCCE46687.2019.9015621

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2019.html#ZhuHDO19

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

DOI： 10.1109/GCCE46687.2019.9015428

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Other Link： https://dblp.uni-trier.de/db/conf/gcce/gcce2019.html#KameiTDU19

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

DOI： 10.1109/VTCFall.2019.8891589

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Other Link： https://dblp.uni-trier.de/db/conf/vtc/vtc2019f.html#DennoIFH19

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

This paper proposes adaptive sideband selection for periodic interference cancellation. The proposed selection improves SINR (Signal to Interference and Noise power Ratio) by providing selected sideband signals, even in environment some signals are received. An algorithm that selects such sideband signals is shown. The proposed selection are analyzed theoretically and evaluated by computer simulation. The proposed selection achieves 26dB better SINR performance than random selection in the channel with CIR (Carrier to Interference power Ratio) of 0dB and CNR (Carrier to Noise power Ratio) of 30dB, and achieves the same performance as the selection method that maximize SINR with computational amount of 1/100.

DOI： 10.14923/transcomj.2018wfp0011

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Authorship：Lead author,　Last author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Graphyonline Publications PVT, Ltd.  

DOI： 10.15344/2456-4451/2019/142

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

DOI： 10.1109/VTCSpring.2019.8746451

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Other Link： https://dblp.uni-trier.de/db/conf/vtc/vtc2019s.html#DennoSH19

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

DOI： 10.1109/WPMC48795.2019.9096064

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2019.html#DennoYH19

Authorship：Lead author,　Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1587/transcom.2018EBP3215

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet102b.html#DennoKIH19

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

DOI： 10.1587/transcom.2018EBP3346

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet102b.html#DennoNH19

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

DOI： 10.1109/TVT.2019.2942945

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

DOI： 10.1109/VTS-APWCS.2019.8851618

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Other Link： https://dblp.uni-trier.de/db/conf/apwcs2/apwcs2019.html#YamamotoDH19

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

This paper proposes an adaptive periodic interference cancellation for narrow-band wireless systems. The proposed cancellation mitigates performance degradation caused by undesired electromagnetic waves emitted from high voltage circuits such as inverters. The received signals are converted into frequency domain where the interference is cancelled with the replica of the interference. Because the phase noise of the undesired electromagnetic waves causes serious performance degradation in the proposed canceller, moreover, this paper proposes phase noise estimation which detects the phase noise of the periodic interference by using singular value decomposition. It is verified by computer simulation that the proposed canceller achieves a gain of 20dB in the environment with CNR of 20dB, INR (interference to noise power ratio) of 0dB.

DOI： 10.14923/transcomj.2018JBP3002

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

DOI： 10.1587/transcom.2017EBP3364

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet101b.html#DennoM18

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

DOI： 10.1109/ICSPCS.2018.8631747

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Other Link： https://dblp.uni-trier.de/db/conf/icspcs/icspcs2018.html#DennoKIH18

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

DOI： 10.1109/WPMC.2018.8712991

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2018.html#HashimotoDIOA18

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Image Information and Television Engineers  

DOI： 10.3169/mta.6.82

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

Leaky coaxial (LCX) cable can be used as antenna for wireless communication system and wireless power transfer which can be widely applied for many application scenarios including wireless service for IoT, automated factory using a large number of wireless devices. We have designed that one LCX cable can be used as two antennas which can releases the space requirement of MIMO deployment for wireless application. In this paper, we will further evaluate the 4-by-4 LCX-MIMO channel using one composite cable with two LCX cables. In addition, we also propose a low-complexity power allocation method for the LCX-MIMO system with the user's positional information (PI). The results show that the capacity is promising when the spacing between LCX cables is small as to 2cm. In addition, our proposed low-complexity power allocation has better capacity than that of using equal power allocation when SNR value is over the low range.

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

DOI： 10.1109/WPMC.2017.8301826

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2017.html#DennoMU17

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.14923/transcomj.2016JBP3048

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

DOI： 10.1109/ICSPCS.2017.8270450

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Other Link： https://dblp.uni-trier.de/db/conf/icspcs/icspcs2017.html#BabaD17

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

DOI： 10.1109/WPMC.2017.8301814

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Other Link： https://dblp.uni-trier.de/db/conf/wpmc/wpmc2017.html#ChikamoriTDU17

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

DOI： 10.1587/transcom.2016EBP3236

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet100b.html#CaoD17

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

DOI： 10.1587/transcom.2016EBP3064

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet100b.html#DennoU17

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

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Other Link： https://dblp.uni-trier.de/conf/wpmc/2016

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

In this letter, we present a random access protocol with success priority, success prioritized distributed coordination function (SP-DCF), based on IEEE 802.11 DCF. Success stations (STAs) are prioritized contentionlessly to transmit the next data frame in the transmit queue in a random manner. We develop a performance analysis model of SP- DCF which enables us to estimate a variety of performance indexes such as the throughput or the frame discard rate (FDR) in a high accuracy for saturated wireless networks. The numerical analysis and simulation results show that the proposed SP-DCF achieves higher throughput and lower FDR as compared with the conventional DCF especially for heavily-congested wireless networks.

DOI： 10.1587/comex.2016XBL0083

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Language：Japanese   Publisher：The Institute of Image Information and Television Engineers  

DOI： 10.3169/itej.70.23

CiNii Article

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

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

DOI： 10.1109/APSITT.2015.7217125

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Other Link： https://dblp.uni-trier.de/db/conf/apsitt/apsitt2015.html#MatsuoUMD15

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

DOI： 10.1109/APCC.2015.7412565

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Other Link： https://dblp.uni-trier.de/db/conf/apcc/apcc2015.html#DennoK15

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

DOI： 10.1587/transcom.E98.B.878

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Other Link： https://dblp.uni-trier.de/db/journals/ieicet/ieicet98b.html#TayaDYMUMY15

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

DOI： 10.1109/APSITT.2015.7217126

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Other Link： https://dblp.uni-trier.de/db/conf/apsitt/apsitt2015.html#NakaoUMD15

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

In this paper, a simple and accurate estimation on performance of the original IEEE 802.11 distributed coordination function (DCF) is presented. The performances obtained from the Bianchi's analytical model of the IEEE 802.11 DCF are compensated by means of (1) the number of consecutive successful transmissions and (2) the deferred slot time. The compensated performances including throughput, packet loss rate, and the average number of transmissions approximate to the simulation results with a high degree of accuracy under a number of conditions even when the minimum contention window is small. The analytical and simulation results show us the possibility of performance improvement by the sender priority.

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

In this paper, we propose a distributed coordination function with successful transmission priority (DCF-STP) based on IEEE 802.11 DCF. DCF-STP will enhance the throughput and reduce the frame discard rate (FDR) in wireless networks because the wireless station (WS) just after the successful transmission has an opportunity to transmit the next frame without contention. We also develop a performance analytical model which enables to estimate the throughput, FDR, and the average number of frame retransmissions with high accuracy for saturated wireless networks. The simulation results show the validity of the developed performance analytical model of DCF-STP and the characteristics in the coexistence of the conventional DCF and the proposed DCF-STP.

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

DOI： 10.1109/isanp.2014.7026492

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

DOI： 10.1109/wpmc.2014.7014807

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

This paper proposes a non-linear distortion noise power control method which uses clipping and in-band and out-of-band filtering methods for multi-band OFDM transmission. The proposed method selects appropriate clipping levels and filtering methods according to transmission power and required noise power conditions on own and the other system bands in a transmitter. The evaluation results show that the proposed method can control in-band and out-of-band distortion noise power so that required noise power conditions can be satisfied in multi-band transmission systems.

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

Iterative MIMO receivers with virtual channel are known to outperform linear detectors in overloaded multiple-input multiple-output systems with orthogonal-frequency division multiplex (MIMO-OFDM). This paper proposes a novel virtual channel detector that enables iterative MIMO receivers to achieve superior performance to the conventional receivers. Moreover, this paper proposes a novel signal estimation technique named as "extended maximum a posteriori probability (MAP) estimation" to select more reliable virtual channel. The proposed technique estimates the virtual channel with not only the a priori information on the virtual channels but also that on the real signals. The performance of the proposed detector with the extended MAP estimation is verified in a 6 x 2 MIMO OFDM system where the Turbo code is applied. The receiver with the proposed detector achieves much better performance than the conventional receivers. Actually, the proposed detector enables the MIMO receiver to achieve a gain of 3.0 dB at the BER of 10(-5), compared with conventional receivers with virtual channels, e.g., the soft input soft output (SISO) MAP detector with the same Turbo decoder. It is confirmed that the proposed receiver has by about one-fifth less complexity than the receiver with the SISO MAP MIMO detector.

DOI： 10.1109/ICSPCS.2014.7021069

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

This paper proposes a lattice-reduction-aided MIMO-OFDM receiver with virtual channels; the receiver enables an increase in the downlink transmission speed for a user where the number of transmit antennas is considerably higher than that of the receive antennas. However, the receiver has a higher computational complexity than conventional lattice-reduction-aided MIMO receivers. Accordingly, we also propose novel techniques to reduce the computational complexity for the lattice-reduction-aided MIMO receivers with virtual channels. The proposed MIMO receiver achieves superior performance in 10 x 2 MIMO-OFDM systems. Furthermore, the proposed techniques are shown to reduce the computational complexity to approximately 40% of the original configuration in the 10 x 2 MIMO-OFDM systems.

DOI： 10.1587/transcom.E96.B.263

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The present paper introduces a prototype design and experimental results for a multi-user MIMO linear precoding system. A base station and two mobile stations are implemented by taking full advantage of the software-defined radio. The base station consists of general purpose signal analyzers and signal generators controlled by a personal computer. Universal software radio peripherals are used as mobile stations. Linear spatial precoding and a simple two-way channel estimation technique are adopted in this experimental system. In-lab and field transmission experiments are carried out, and the bit error rate performance is evaluated. The impact of the channel estimation error under average channel gain discrepancy between two mobile stations is analyzed through computer simulations. Channel estimation error is shown to have a greater influence on the mobile station with the greater average channel gain.

DOI： 10.1587/transfun.E96.A.247

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This paper proposes a novel scheme called as "frequency domain imbalance estimation" that estimates the imbalance of the Hilbert transformer in heterodyne multimode/band receivers with baseband automatic gain control (AGC). The proposed scheme uses correlation matrices in the frequency domain. This enables the receivers to keep high transmission performance in spite of the imbalance of the analog Hilbert transformer, by offsetting the imbalance. Moreover, the baseband AGC relaxes the requirement of the baseband AID converter. The performance of imbalance estimation and imbalance cancellation is verified by computer simulation. As a result, it is shown that the proposed scheme not only estimates the imbalance of Hilbert transformer with extremely high precision, but also cancels the image-band interference such that it achieves the theoretical performance.

DOI： 10.1587/transcom.E96.B.271

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A transmission experiment of a multi-user MIMO system with user selection and linear spatial precoding is conducted and the results are reported. As a low-complexity user selection algorithm, the chordal distance-based user selection (CDUS) algorithm is employed. The testbed used in the experiment is implemented by taking full advantage of the software-defined radio. An amplify-and-forward-based simple channel estimation method is adopted. As a result of the experiment in a conference room, the CDUS algorithm improved both the power efficiency and the interference suppression accuracy compared to the round-robin user selection.

DOI： 10.1109/GLOCOM.2013.6831692

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This paper proposes an iterative frequency offset estimation based on singular value decomposition (SVD). The proposed technique achieves high resolution estimation of frequency offset even in the presence of strong co-channel and inter-symbol interference. Moreover, the proposed technique can estimate large frequency offset, e.g., ΔfT = 12.8 with high precision. The proposed technique comprises two new ideas. One is frequency offset estimation by using SVD and an adaptive filter. The other is iteration of the above frequency offset estimation followed by a frequency offset reduction. The iteration of the frequency offset estimation improves the estimation performance. In fact, it is evaluated by computer simulation that estimate the frequency offset normalized by a symbol duration, ΔfT = 12.8, in wireless sensor networks with direct sequence spread spectrum (DS-SS). © 2013 IEEE.

DOI： 10.1109/ISPACS.2013.6704533

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

This paper proposes a novel heterodyne multiband multiple-input multiple-output (MIMO) receiver with baseband automatic gain control (AGC) for cognitive radios. The proposed receiver uses heterodyne reception implemented with a wide-passband band-pass filter in the radio frequency (RF) stage to be able to receive signals in arbitrary frequency bands. Even when an RF Hilbert transformer is utilized in the receiver, image-band interference occurs due to the imperfection of the Hilbert transformer. In the receiver, analog baseband AGC is introduced to prevent the baseband signals exceeding the voltage reference of analogto- digital converters (ADCs). This paper proposes a novel technique to estimate the imperfection of the Hilbert transformer in the heterodyne multiband MIMO receiver with baseband AGC. The proposed technique estimates not only the imperfection of the Hilbert transformer but also the AGC gain ratio, and analog devices imperfection in the feedback loop, which enables to offset the imperfection of the Hilbert transformer. The performance of the proposed receiver is verified by using computer simulations. As a result, the required resolution of the ADC is 9 bits in the proposed receiver. Moreover, the proposed receiver has less computational complexity than that with the baseband interference cancellation unless a frequency band is changed every 9 packets or less. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.

DOI： 10.1587/transcom.E96.B.3124

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

This paper proposes a reduced-complexity multiband multiple-input multiple-output (MIMO) receiver that can be used in cognitive radios. The proposed receiver uses heterodyne reception implemented with a wide-passband band-pass filter in the radio frequency (RF) stage. When an RF Hilbert transformer is utilized in the receiver, image-band interference occurs because of the transformer's imperfections. Thus, the imperfection of the Hilbert transformer is corrected in the intermediate frequency (IF) stage to reduce the hardware complexity. First, the proposed receiver estimates the channel impulse response in the presence of the strong image-band interference signals. Next, the coefficients are calculated for the correction of the imperfection at the IF stage, and are fed back to the IF stage through a feedback loop. However, the imperfection caused by the digital-to-analog (D/A) converter and the baseband amplifier in the feedback loop corrupts the coefficients on the way back to the IF stage. Therefore, the proposed receiver corrects the imperfection of the analog devices in the feedback loop. The performance of the proposed receiver is verified by using computer simulations. The proposed receiver can maintain its performance even in the presence of strong image-band interference signals and imperfection of the analog devices in the feedback loop. In addition, this paper also reveals the condition for rapid convergence. Copyright © 2013 The Institute of Electronics.

DOI： 10.1587/transcom.E96.B.1540

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In a multi-user multiple-input multiple-output (MU-MIMO) system, zero-forcing precoding can completely eliminates inter-user interference when the perfect channel state information is available at the base station. However, in time-varying channels, the transmission performance of MU-MIMO systems is severely degraded due to inter-user interference. In this paper, channel prediction is employed for channel tracking, and in-lab experiments are carried out to confirm its performance. The bit error rate (BER) performance is measured and compared with the computer simulation results. Both in-lab experiments and the computer simulations show that channel prediction improves the BER performance.

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Physical layer network coding is able to improve frequency utilization efficiency in bi-directional wireless communications via a relay. This paper proposes a novel error correction scheme for physical layer XOR network coding. The proposed scheme not only improves transmission performance but also to reduce complexity at the relay. The proposed scheme applies a unitary precoding to offset phase rotation in the channel by exploiting the reciprocity between channels in the uplink and the downlink in systems with time division duplex (TDD). Moreover, a novel complexity reduced maximum likelihood detection technique is applied in the proposed scheme. It is evaluated by computer simulation that the proposed scheme attains a gain of 8dB at BER=10(-5) compared with AF network coding in a system with the use of OFDM.

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

The Lattice-reduction aided MIMO receiver with virtual channels has been proposed that can increase transmission speed for a user in downlinks. Although the proposed receiver achieves superior performance even when the number of receive antennas is much less than that of spatially multiplexed streams, however, the receiver has more computational complexity than conventional lattice reduction-aided MIMO receivers. Then, this paper proposes novel techniques to reduce computational complexity for lattice-reduction aided MIMO receivers with virtual channels. In fact, the proposed techniques are shown to reduce the computational complexity to about 40 % of the original configuration in 8 x 2 MIMO-OFDM systems. Even if the proposed techniques are applied, the MIMO receiver is also shown to achieve superior performance in 10x2 MIMO-OFDM systems.

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

This paper proposes a virtual layered successive detector with adaptive transmit signal phase rotation for quadrature amplitude modulation (QAM) that enables high speed communication even in downlinks of wireless communication systems. It is shown that the detection performance is degraded when the eigenvalue of a virtual channel becomes close to the power of the additive white Gaussian noise (AWGN). Therefore, adaptive transmit signal phase rotation is introduced for the detector to improve the transmission performance. For the transmit phase rotation, three techniques to search the rotation angles are proposed, which can reduce the feedback information from the receiver to the transmitter. Among the three proposed techniques, the technique called "iterative variable step step search" is shown to achieve the best performance. Actually, it is confirmed by computer simulation that the variable step search makes the detector attain about 17dB of a gain at the bit error rate (BER) of 10^-5 in 4×2 multiple-input-multiple-output (MIMO) systems.

DOI： 10.1587/transcom.E95.B.3232

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

This paper proposes an adaptive algorithm for adaptive arrays that minimizes the bit error rate (BER) of the array output signals in radio communication systems with the use of multilevel modulation signals. In particular, amplitude phase shift keying (APSK) is used as one type of multilevel modulations in this paper. Simultaneous non-linear equations that are satisfied by the optimum weight vector of the proposed algorithm are derived and used for theoretical analyze of the performance of the adaptive array based on the proposed algorithm. As a result of the theoretical analysis, it can be shown that the proposed adaptive array improves the carrier to interference ratio of the array output signal without taking advantage of the nulls. Furthermore, it is confirmed that the result of the theoretical analysis agrees with that of computer simulation. When the number of the received antenna is less than that of the received signals, the adaptive array based on the proposed algorithm is verified to achieve much better performance then that based on the least mean square (LMS) algorithm.

DOI： 10.1587/transcom.E95.B.69

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In this paper, implementation of a multi-user MIMO experimental system is presented. Linear spatial precoding and a simple two-way channel estimation technique are adopted in the experimental system. In-lab and field transmission experiments are carried out and the performance is evaluated. The impact of channel estimation error under average channel gain discrepancy between two mobile stations is analyzed by means of computer simulation. It is shown that channel estimation error has a greater influence on the mobile station with greater average channel gain.

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A practical and efficient vector quantization called partitioned vector quantization (P-VQ) based non-linear precoder for MIMO downlink broadcasting channels has been analyzed in this paper. P-VQ has been found to be an efficient way of reducing the memory requirements and search complexity in conventional VQ systems, especially for large MIMO. Simulation results reveal that P-VQ technique can enhance the overall quantization performance in terms of achieved capacity, bit error rate (BER) at a cost of reasonable additional complexity under certain feedback budgets. Tomlinson-Harashima precoding (THP), a power and complexity efficient precoding technique along with data dependent vector perturbation (VP) has been employed to meet the power constraint requirements of our system. Least-square (LS) channel estimation is performed at the user terminals to acquire their channel state information (CSI).

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In this paper, we propose a receiver using the concept of a "virtual channel" and Turbo codes for multiuser multiple-input multiple-output (MU-MIMO) systems with cooperating transmitters. In order to reduce feedback information from receivers, a precoding method with reduced channel state information (CSI) is needed. Although signals interfere with each other in such a system, the proposed receiver enables high-speed transmission by detecting signals iteratively. In the proposed iterative scheme, soft information is exchanged between virtual channel detectors and Turbo decoders to improve the bit error rate (BER) performance. We evaluate the performance of the proposed receiver in systems with two transmitters, each equipped with four antennas, and two receivers, each equipped with two antennas. The results show that the proposed receiver can improve the system performance owing to the iteration scheme.

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In this paper, the end-to-end packet error rate (PER) performance of a space-time block code (STBC) based multi-hop cooperative relaying system is discussed. This system consists of a source, a destination, and two STBC based cooperative relays in each hop. These relays decode their received packets and forward the packets only when no error is found. In this system, there are conditions where the end-to-end PER performance improves with the number of hops. The theoretical end-to-end PER performance of this system have been derived analytically. However, in real-world wireless systems, various practical issues, e. g., timing synchronization and imperfect channel estimation, have a large impact on the performance. To confirm the end-to-end PER performance of this system in actual setup, an in-lab experiment using a fading emulator and four transceivers is performed under Rayleigh fading environment. The experimental results clarify the PER performance of the STBC based multi-hop cooperative relaying system. In addition, the theoretical PER performance is also verified from the experimental results.

DOI： 10.1109/VTCFall.2012.6399343

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

Cognitive radios are of interest because they are capable of high frequency utilization efficiency. Multiband multiple-input multiple-output (MIMO) receivers based on heterodyne reception have been proposed for use in cognitive radios. This paper proposes a reduced-complexity multiband MIMO receiver that can achieve high performance by correcting the imperfection of the Hilbert transformer in the intermediate frequency (IF) band. However, the imperfection of the analog devices in the feedback loop causes poor performance. Therefore, a scheme for correcting the imperfection of the analog devices is proposed.

DOI： 10.1109/VETECS.2012.6239940

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

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

In this paper, a novel receiver architecture is proposed for multiple-input-multiple-output (MIMO) systems; the proposed architecture helps achieve superior performance in multipath fading channels when the number of layered streams exceeds the number of receiving antennas. In this architecture, the concept of "virtual channel" is adopted to attain diversity gain even when successive detection is applied for reducing computational complexity, while orthogonal frequency division multiplexing (OFDM) is employed to combat multipath fading. Actually, successive detection is carried out in all possible virtual channels, and the virtual channel with the minimum error probability is detected with the assistance of the maximum a-posteriori (MAP) decoder in the architecture. In addition, soft input and soft output (SISO) iterative detection is introduced in the virtual channel estimation scheme. The performance of the proposed architecture is verified by computer simulations. This architecture can be implemented with lesser complexity than that in maximum likelihood detection (MLD), but the gain in the former case exceeds that in the latter by 4.5 dB at the BER of 10(-3) for 4 x 2 MIMO-OFDM.

DOI： 10.1587/transcom.E94.B.1994

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

It is known that a heterodyne multimode receiver implemented with a single RF (Radio Frequency) receiver suffers from image-band interference due to imbalance, i.e. the phase error and the gain imbalance of the RF Hilbert transformer. The blind image band interference canceler with deterministic imbalance estimation that has been proposed mitigates the image-band interference. This performance of the image-band interference canceler is analyzed theoretically in this paper. As a result, it is revealed that estimation accuracy of the deterministic imbalance estimation is improved slightly as the imbalance becomes greater. In addition, it is also shown that the deterministic estimation achieves better performance as the power of image-band interference increases. The performance is confirmed by computer simulation.

DOI： 10.1587/transcom.E94.B.968

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

Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.adhoc.2010.07.005

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In this paper, we propose a virtual layered spacefrequency receiver with an ordered successive detector for multiuser multiple-input multiple-output (MU-MIMO) systems where multiple transmitters cooperate with one another. The proposed receiver enables high-speed transmission in the systems even if the transmitters know only partial channel state information (CSI). Actually, the receiver shows such superior performance when the concept of "virtual channel" is applied to cooperative MU-MIMO systems. Moreover, we propose an iterative detection scheme for the receiver
in this scheme, some signals from the Viterbi decoder are fed back to the ordered successive detector. The proposed iterative scheme helps improve the transmission speed when the number of cooperating transmitters is increased. We evaluate the performance of MIMO systems in which the transmitters have four antennas each and two users have two antennas. The receiver can double the transmission speed at the cost of 3 dB in E b/N 0 at a BER of 10 -4. Furthermore, the receiver can triple the transmission speed at the cost of 7 dB in E b/N 0 at a BER of 10 -4. When the system has three transmitters, we observe an error floor. However, the proposed iterative method can suppress the error to a value below BER = 10 -7. © 2011 IEEE.

DOI： 10.1109/VETECF.2011.6092886

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This paper presents an experimental setup of a multi-user MIMO linear precoding system. The experimental system consists of a base station with two antennas and two mobile stations. In this system, a two-way channel estimation technique is implemented in which mobile stations just send back the received signals along with their training sequences. In this technique, the base station can obtain the channel coefficients of both the uplink and the downlink. This two-way multiple-input multiple-output channel estimation technique has been proposed and mathematically analyzed in literature. Computer simulation results have been reported to identify the required hardware specifications for amplify and forward operation in mobile stations by examining the bit error rate performance. However, hardware implementation feasibility of this technique is not studied yet. In this paper, feasibility of a multi-user MIMO linear precoding system using two-way channel estimation technique is shown by in-lab experiments. © 2011 IEEE.

DOI： 10.1109/ICICS.2011.6173520

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

In this paper, we propose a virtual layered space-frequency receiver with an ordered successive detector for multiuser multiple-input multiple-output (MU-MIMO) systems where multiple transmitters cooperate with one another. The proposed receiver enables high-speed transmission in the systems even if the transmitters know only partial channel state information (CSI). Actually, the receiver shows such superior performance when the concept of "virtual channel" is applied to cooperative MU-MIMO systems. Moreover, we propose an iterative detection scheme for the receiver; in this scheme, some signals from the Viterbi decoder are fed back to the ordered successive detector. The proposed iterative scheme helps improve the transmission speed when the number of cooperating transmitters is increased. We evaluate the performance of MIMO systems in which the transmitters have four antennas each and two users have two antennas. The receiver can double the transmission speed at the cost of 3 dB in E-b/N-0 at a BER of 10(-4). Furthermore, the receiver can triple the transmission speed at the cost of 7 dB in E-b/N-0 at a BER of 10(-4). When the system has three transmitters, we observe an error floor. However, the proposed iterative method can suppress the error to a value below BER = 10(-7).

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Distributed antenna systems (DAS) are studied in order to improve the coverage area of wireless communication systems under transmit power constraint. In order to reduce the computational complexly among clusters, in DAS, it is imperative to control the inter-cluster interference in a decentralized way. In this paper, a distributed power control among clusters for single-user DAS based on Foschini-Miljanic's algorithm is proposed. The objective of the proposed algorithm is to mitigate the interference among clusters and satisfy the desired SINR at each mobile station (MS). In the algorithm, first signal power after MRC at MS in a cluster is calculated, then the transmit power of the BSAs in the corresponding cluster is updated according to the predefined transmit power ratio. In addition, the convergence condition is derived, and the performance of the proposed algorithm is evaluated through computer simulations. © 2011 IEEE.

DOI： 10.1109/ICICS.2011.6173525

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This paper proposes a novel receiver, named as "a virtual layered signal processing receiver for 16 QAM" for high speed signal transmission in wireless communication systems. In the proposed receiver, the ordered successive detection is applied with the concept of virtual channel, which enables to detect layered streams even when the number of the layered streams is more than that of the received antennas. Therefore, the proposed receiver can increase the transmission speed of the down link in which a receiver is implemented in small terminals with a small number of antennas. The proposed receiver unfortunately degrades compared with the maximum likelihood estimation (MLD), however, when the channel matrix of the virtual channel is not full rank. To avoid the performance degradation, this paper proposes a technique that transmit signal constellation is phase-rotated with information fed back from the receiver. Actually, it is confirmed by computer simulation that only 1-bit of feed back information is enough to achieve the upper bound in BER performance in a 2 x 1 MIMO system.

DOI： 10.1109/ICSPCS.2011.6140827

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Network coding is a promising technique for improving system performance in wireless multihop networks. In this paper, the throughput and fairness in single-relay multi-user wireless networks are evaluated. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding are used in the medium access control (MAC) sublayer in such networks. The fairness of wireless medium access among stations (STAs), the access point (AP), and the relay station (RS) results in asymmetric bidirectional flows via the RS; as a result the wireless throughput decreases substantially. To overcome this problem, an autonomous optimization of minimum contention window size is developed for CSMA/CA and network coding to assign appropriate transmission opportunities to both the AP and RS. By optimizing the minimum contention window size according to the number of STAs, the wireless throughput in single-relay multi-user networks can be improved and the fairness between bidirectional flows via the RS can be achieved. Numerical analysis and computer simulations enable us to evaluate the performances of CSMA/CA and network coding in single-relay multi-user wireless networks.

DOI： 10.1587/transcom.E93.B.3371

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

Network coding is a promising technique for improving system performance in wireless multihop networks. In this paper, the throughput and fairness in single-relay multiuser wireless networks are evaluated. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding are used in the medium access control (MAC) sublayer in such networks. The fairness of wireless medium access among stations (STAs), the access point (AP), and the relay station (RS) results in asymmetric bidirectional flows via the RS; as a result the wireless throughput decreases substantially. To overcome this problem, an autonomous optimization of minimum contention window size is developed for CSMA/CA and network coding to assign appropriate transmission opportunities to both the AP and RS. By optimizing the minimum contention window size according to the number of STAs, the wireless throughput in single-relay multi-user networks can be improved and the fairness between bidirectional flows via the RS can be achieved. Numerical analysis and computer simulations enable us to evaluate the performances of CSMA/CA and network coding in single-relay multi-user wireless networks.

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This paper considers two-hop wireless systems employing network coding and a carrier sense multiple access (CSMA) protocol. Network coding is a recent and highly regarded technology for the capacity enhancement of multiple unicast and multisource multicast networks. The two-hop wireless CSMA systems are often involved with the hidden node problem, but the impact of the hidden nodes on network coding has not been analyzed in theory. This paper provides explicit expressions of the throughput for single-relay two-hop wireless CSMA systems both without and with network coding. The throughput can be obtained from these expressions for given system parameters even when end nodes via the relay node are hidden each other. Furthermore it is shown that the transmit probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput for CSMA systems with network coding. It is clarified that the throughput for CSMA systems can be enhanced as compared with that for slotted ALOHA systems in case of non-hidden end nodes whereas it deteriorates considerably in case of hidden end nodes.

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This paper proposes a medium access control (MAC) protocol with network coding on relay nodes for contention-based multihop wireless relay networks. The proposed protocol is called coded packet priority access (CPPA) protocol in which coded packets have higher transmission opportunity than non-coded native packets at relay nodes. In this paper, the performance of coded packet immediate access (CPIA) protocols, which are a subclass of CPPA protocols, is evaluated for single-relay bidirectional symmetric traffic and upper and lower bounds of analytical throughput are derived for any given node traffic. It is shown that the lower bound approximates to the throughput obtained from computer simulations with high accuracy. The conventional slotted ALOHA protocol with network coding (SALOHA/NC) is required to adapt the transmission probability of relay node to a rational function of node traffic so as to maximize the throughput whereas the CPIA protocol achieves the maximal throughput only if the relay node transmits no native packets. Furthermore it is clarified that the CPIA protocol is superior to the S-ALOHA/NC protocol in delay for given retransmission probabilities of user nodes.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

This paper presents achievable regions in slotted ALOHA throughput both without and with network coding for one-relay two-hop wireless networks between two end node groups. In this paper, there are no restrictions on the total traffic and the number of end nodes per group. It follows that the relay node will be generally involved with asymmetric bidirectional traffic. This paper derives closed-form expressions of the throughput and packet delay per group both without and with network coding from a theoretical perspective regardless of whether the buffer on the relay node is saturated or not. Furthermore, we show that the maximum throughput per group with network coding can be achieved at the boundary of the relay buffer saturation and unsaturation which is expressed as the solution of a polynomial equation in two group node traffics. As a result, we clarify the enhancement of the achievable region in slotted ALOHA throughput by applying network coding.

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This paper proposes a novel OFDM demodulation scheme, which achieves superior performance even in fast time-varying multipath fading channels where the conventional OFDM demodulator degrades seriously because of time selectivity in the channel. The proposed scheme consists of several equalizers which equalize received signals with channel impulse responses at different time instants in parallel. A selector following these equalizers selects the most reliable signal from the outputs of these equalizers. Furthermore, the proposed demodulator employs an inter-carrier interference (ICI) canceler to mitigate degradation due to the time selectivity in the channels. In this paper, two novel ICI cancelers are proposed. Finally, the performance of the proposed OFDM demodulators are verified by means of computer simulation.

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This paper considers two-hop wireless systems employing network coding and a carrier sense multiple access (CSMA) protocol. Network coding is a recent and highly regarded technology for the capacity enhancement of multiple unicast and multisource multicast networks. The two-hop wireless CSMA systems are often involved with the hidden node problem, but the impact of the hidden nodes on network coding has not been analyzed in theory. This paper provides explicit expressions of the throughput for single-relay two-hop wireless CSMA systems both without and with network coding. The throughput can be obtained from these expressions for given system parameters even when end nodes via the relay node are hidden each other. Furthermore it is shown that the transmit probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput for CSMA systems with network coding. It is clarified that the throughput for CSMA systems can be enhanced as compared with that for slotted ALOHA systems in case of non-hidden end nodes whereas it deteriorates considerably in case of hidden end nodes. ©2010 IEEE.

DOI： 10.1109/ICC.2010.5502114

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In this paper, we propose an iteration scheme for the virtual layered space frequency communication architecture. The architecture enables the decoding of the transmitted orthogonal frequency division multiplexing (OFDM)-QPSK signals even if the number of spatial multiplexed layers is twice that of receiving antennas over multipath fading channels. In the proposed iteration scheme, the MAP decoder and detector exchange soft information on the virtual channel. Using the soft informations, the architecture achieves much higher performance with lower computational complexity compared to maximum likelihood detection (MLD) even when the punctured code is used. Consequently, a gain of 4.5 dB can be achieved at a BER of 10-3 compared to that achieved with the MLD in the 4 x 2 MIMO-OFDM system when the rate 3/4 punctured code is used. The performance of the proposed architecture is verified by carrying out computer simulations.

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This paper proposes a blind image-band interference canceller that enables heterodyne receivers with only a single receiver chain to demodulate signals in any frequency band. In this paper, such a receiver is called "multimode/multiband heterodyne receiver." If multimode/multiband receivers are desired to receive signals with carrier frequency ranging from several MHz to GHz, then, such receivers are not allowed to have a narrow band RF-BPF (Radio Frequency Band Pass Filter) at the RF front end. However, although heterodyne receivers have been applied to wireless systems due to their high performance, it is known that without an RF-BPF heterodyne receivers suffer from severe image-band interference. Therefore, a blind image-band interference canceller is proposed in this paper to mitigate the image-band interference. Moreover, a novel algorithm based on the CM (Constant Modulus) criterion is proposed to carry out the cancellation. Performance of the blind image-band interference canceller is theoretically analyzed and the performance of the proposed canceller is verified by computer simulation. As a result, it is shown that the blind image-band interference canceller achieves superior performance even in the presence of strong image-band interference, for example, CIR=-40dB. In summary, the proposed canceller makes it possible for the receiver with the single receiver chain to achieve multimode/multiband communications with high quality.

DOI： 10.1587/transcom.E92.B.2903

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

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.

DOI： 10.1109/JSAC.2009.090607

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In this study, we develop a virtual layered space-frequency communication architecture. This architecture enables the decoding of transmitted OFDM (Orthogonal Frequency Division Multiplexing)-QPSK signals even if the number of antennas at the transmitter is twice the number of antennas at the receiver over multipath fading channels. Furthermore, we propose two detection schemes called "hard replica" and "soft replica." In addition, in order to improve the performance of this architecture, we propose an iteration in which the receiver decodes the detected signals; through such iterations, this architecture can obtain path diversity and achieve high performance. When the transmitter has four antennas and receiver has two antennas, the proposed architecture achieves HER of 8 x 10(-4) using the soft replica at E-b/N-0 = 15 dB. Furthermore, by performing more iterations, it provides additional gains of 3 dB. The performance of the proposed architecture is verified using computer simulations.

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The regulation on power line communication (PLC) has been eased in Japan, and the frequency band between 2 and 30 MHz can be used for in-home PLC. Several different types of commercial PLC equipment are available in the market. Almost all of them include PLC adapters that interconvert Ethernet signals and power line signals. An in-home network can easily be constructed by using these PLC adapters because there are many power outlets in every room. However, there are various factors that tend to destabilize the communication among PLC adapters. These factors involve time-varying channel response and noise characteristics, which are both synchronized with the power frequency. In particular, it has been observed that the noise in a power line varies more significantly than the channel response. Therefore, many PLC adapters contain certain features to mitigate the time-varying noise in a power line. We show a number of examples of more significant variations in the channel response synchronized with the power frequency due to the switching regulators used. This paper deals with such a time-varying channel response synchronized with the power frequency. We show that the performance of the PLC adapters suffers due the time-varying channel response and analyze its influences on the PLC adapters. © 2009 Academy Publisher.

DOI： 10.4304/jcm.4.2.108-118

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

An indoor power line is one of the most attractive media for in-home networks. However, there are many technical problems for achieving in-home power line communication (PLC) with high rate and high reliability. One of such problem is the degradation in the performance of the in-home PLC caused by periodically time-varying channel responses, particularly when connecting the switching power supply equipment. We present a measurement method for power line channel responses and reveal the switching of the channel responses synchronized with power-frequency voltage when connecting switching power supply equipment in sending or receiving outlets. In this paper, we term them periodically switching channel responses. The performance of PLC adapters is seriously affected by the periodically switching channel responses. Therefore, we provide a modeling of the periodically switching channel responses by using finite impulse response (FIR) filters with a shared channel memory and construct a simulator for in-home power line channels including the periodically switching channel responses in order to evaluate the various communication systems through the power line. We present the validity of the proposed simulator through the performance evaluation of OFDM/64QAM over periodically switching channels with additive white Gaussian noise. Furthermore, we evaluate the influence of the periodically switching channel responses on the communication quality of a time-invariant modulation scheme by using the proposed simulator.

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This paper deals with a simple but essential two-hop wireless relay network employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement on multiple unicast and multisource multicast networks. However, the performance of network coding on wireless relay networks employing random access protocols has not been analyzed. This paper provides closed-form expressions for the throughput and delay on two-hop wireless relay networks both with and without network coding from a theoretical perspective of the slotted ALOHA protocol. The analytical results are derived by solving queueing systems for the buffer activity at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of slotted ALOHA with network coding on a twohop wireless relay network. Furthermore, this paper clarifies that the throughput is enhanced by controlling the transmission probability of the relay node such that it has considerable opportunity for network coding.

DOI： 10.1109/GLOCOM.2008.ECP.953

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The regulation on power line communication (PLC) has been eased in Japan and the frequency band between 2 and 30 MHz can be exploited for in-home PLC. Several commercial PLC equipments are available in the market. Almost all PLC equipments take on a form of PLC adapters interconverting Ethernet signals and power line signals. We can construct in-home network by these PLC adapters easily because there are many power outlets in every room. However there are various factors destabilizing the communication among PLC adapters. These factors involve time-varying channel response and noise characteristics which are synchronized with commercial power supply. In particular, it has been seen that the noise on power line has significant variations rather than the channel response. Therefore, many PLC adapters are taking some measures to mitigate the time-varying noise on power line. On the other hand, we show a number of examples of more significant variations of the channel response synchronized with power supply due to some kinds of switching regulators. In this paper, we deal with such the time-varying channel response synchronized with commercial power supply. We show that the PLC adapters suffer from the time-varying channel response and analyze its influence on the PLC adapters.

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In this paper, we propose an initial acuisition method for channel synchronization on in-home broadband power line communication (PLC). It has been considered that the time fluctuation in the transfer function has been smaller than that in the noise on the in-home broadband PLC. However, we have observed that the extensively and rapidly time fluctuation across the whole frequency band appears in the in-home PLC at the half of power cycle intervals while connecting some switching power supply devices. Such largely and quickly, time fluctuation makes the extensive degradation in performance of in-home PLC devices. Therefore, we should estimate the timing of time fluctuation and synchronize the in-home PLC systems with the estimated time fluctuation. We evaluate the performance of the proposed initial acquisition method under impulsive noise environments and investigate its feasibility for the real in-home PLC.

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This paper evaluates transmission performance and power-saving effect of the collaborative beamforming for wireless ubiquitous network systems. The evaluation of power-saving includes the power consumption for signal transmission to collaborative sensors in beamforming. The simulation result shows that the total power consumption of the beamforming with 3 collaborative sensors can be decreased to about 1/2 compared with that of a transmitting sensor without the beamforming in free-space propagation channels. In typical mobile propagation channels with shadowing, the total power consumption of the beamforming by using 3 collaborative sensors can be reduced to 1/7 of that without the beamforming. The above results confirm that the collaborative beamforming can be achieve lower power consumption, and greatly contributes to realize low-power transmission in wireless sensor network systems.

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The in-home broadband power line communication (PLC) is drawing attention to us lately. The broadband PLC has regulation issues for the coexistence with shortwave wireless systems. Therefore, orthogonal frequency division multiplexing (OFDM) is adopted for the broadband PLC. On the other hand the power line channels suffer from frequency selective fading. It is effective to load appropriate bits on each subcarrier in the OFDM for PLC. In this paper, we propose a bit loading algorithm that maximizes the bit rate by optimizing not only the bit quantity on each subcarrier but also the whole code rate of the forward error correction (FEC) code subject to constraints on the total bit error rate (BER) and power on each subcarrier. Furthermore, we investigate orthogonal frequency division multiple access (OFDMA) as a multiple access scheme on the in-home power line networks. We show that the proposed OFDMA scheme is superior to a time division multiple access (TDMA) scheme from the viewpoint of throughput by computer simulations.

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In-home PLC (Power Line Communication) is one of the most attractive in-home networkings. However, there are a lot of technical issues for the realization of PLC with high rate and high reliability. These issues include the influence of frequency selective and linear periodically time-variant (LPTV) channel synchronized with commercial power supply. In particular, we show that some kind of switching power devices impact deep and deterministic time selectivity for power line channels. The combination of OFDM (Orthogonal Frequency Division Multiplexing) and bit loading algorithm is a powerful tool to increase the bit rate or reliability for quasi-static frequency selective channels including power line channels. However, a quick response will be required for the execution of bit loading algorithm since power line channels are synchronized with commercial power supply. In this paper, we propose a fast bit loading algorithm based on the fractional knapsack algorithm to enhance the bit rate under the condition that the transmitted power is constant. Furthermore, we evaluate the achievable bit rate of the proposed algorithm for the SNR over a power line channel and compare it with the achievable bit rate based on water filling theory.

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We propose applying pulse amplitude modulated code shift keying (CSK/PAM) to indoor power line communication (PLC) for the high-speed data transmission at the low electromagnetic wave leakage. However, CSK/PAM system using conventional binary sequence, for example Gold sequence and M sequence, has error floor for real power line channels even with rake receiver because of the poor properties of odd auto and cross-correlation. Therefore, we propose extending binary sequence to real-valued sequence and we optimize performance in real-valued sequence by minimizing the even and odd, autoand cross-correlation values. We show that the CSK/PAM system using the optimized real-valued sequence can achieve better BER (Bit Error Rate) performance as compared with that using Gold sequence by computer simulation.

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Power line communication (PLC) is one of the most attractive communication methods for in-home networks. However, the emissions of unwanted electric waves from PLC system cause harmful interference to other radio communication systems with the same frequency band. Wavelet OFDM (Orthogonal Frequency Division Multiplexing) is expected to be an efficient modulation for PLC because it can make steep and deep notch for any frequency band in the transmit signal power spectrum. However, wavelet OFDM cannot implement the equalization by guard interval (GI) like OFDM and causes performance degradation in multipath channels including power line channels. In this paper, we apply ASCET (Adaptive Sine modulated / Cosine modulated filter bank Equalizer for Transmultiplexers) to wavelet OFDM and evaluate its performance over a multipath power line channel. In particular, we propose an estimation scheme of equalizer coefficients for ASCET that the required preamble becomes short. We compare the performance of OFDM with GI to that of wavelet OFDM with ASCET over the multipath power line channel by computer simulations. As a result, we show that the proposed scheme can achieve the approximately equivalent performance of OFDM with GI by using the shorter preamble as compared to the original scheme.

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Power line channel often suffers from impulsive interference generated by electrical appliances. Therefore, power line communication makes degradation due to such impulsive interference. We introduce Middleton's Class A noise model into a statistical model of impulsive noise environment.
In this paper, we apply LDPC (Low Density Parity Check) codes and sum-product decoding to additive white Class A noise (AWAN) channels. We propose a sum-product decoding which is suitable for AWAN channels. In addition, we show the BER (Bit Error Rate) performance of the proposed sum-product decoding in Class A noise environment by computer simulation.

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Language：Japanese   Publisher：京都大学電気関係教室・洛友会  

DOI： 10.14989/57883

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

Adaptive arrays for spatiotemporal signal processing are expected to be effective multipath measures in future high-speed mobile communications systems. However, a problem is the tremendous computational load in a hardware implementation because the number of weights that are adaptively controlled becomes extremely large. There fore, the key to its practical use is to reduce the computational load. In this paper, an adaptive array for processing subband signals that can substantially reduce the computational load was implemented in hardware by using a commercially available digital signal processor (DSP). First, we illustrated the scale of the hardware by the number of DSPs needed in each unit that performed the required signal processing. Next, we built a simple multipath environment of two waves in an anechoic chamber and performed experiments to demonstrate the basic performance and veri fled that performance nearly equal to the theoretical values was obtained. (C) 2002 Wiley Periodicals, Inc.

DOI： 10.1002/ecjc.1122

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As a way to realize an adaptive array of small size, low cost, and low power consumption, there exists a configuration method combining analog signal processing and digital signal processing. M-CMA has been proposed as a control algorithm for such an approach. However, when this approach is applied to an actual communication system, there arises the problem that the narrow-band filter in the receiver prevents M-CMA from converging to the desired solution. In this paper, in order to effectively operate an M-CMA adaptive array in the presence of a narrow-band filter, a configuration is proposed in which polyphase filters are used as narrow-band filters. Its superior interference suppression capability is confirmed by a theoretical analysis and computer simulation.

DOI： 10.1002/ecja.10021

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Asoftware antenna, which will be a key device realizing flexible and highly reliable wireless communications systems, is inherently matched with software defined radios(SDR).In this paper, first, key technologies on the software antenna are introduced. The technologies contain i)how to recognize the radio environment, ii)how to determine the optimum adaptive signal processing algorithm, and iii)how to reconfigure the digital beamforming circuit. Then, an image of a software antenna with reconfigurable eigenvector-beamspace configuration is presented. Finally, by assuming various propagation conditions, performance of the software antenna in terms of algorithm diversity is demonstrated.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Multimedia mobile communication systems are expected to be realized in the near future. In such systems, multipath fading can cause severe degradations of the quality of the communications due to its wide bandwidth, especially in urban areas. Adaptive array antennas can be attractive solution for overcoming the multipath fading. Suppression can be achieved with the adaptive array by cophasing and combining multipath signals in the space and time domain. On the other hand, the concept of software antenna has been proposed. The software antenna recognizes radiowave environments and appropriately reconfigures itself for the signal processing required by the recognized environment. Efficient implementations can be expected if these functions are realized by the software. In this paper, we propose two types of the adaptive array systems which is reconfigurable depending on the radiowave environment as a realization of the concept of the software antenna. They recognize the environment by using the eigenvalue decomposition of space domain correlation matrices and reconfigure their structures of the signal processing. The principle and performance are examined by theoretical means and through computer simulations.

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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)  

DOI： 10.1109/26.780451

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The authors have developed a single chip, 40 Mbit/s operation, 3-tap MLSE equalizer LSI. The LSI supports burst operation and is available for both QPSK and π/4-QPSK modulated signals. This paper shows the performance of a 5 GHz-Band 40 Mbit/s experimental system using this equalizer LSI. The main results are as follows; 1) The implicit diversity gain offered by the equalizer is 12 dB at the BER of 10-3. 2) The gain obtained in 2-branch diversity reception is 6 dB at the BER of 10-3. 3) In single branch operation, no error floor is observed when the BER is higher than 10-4. Furthermore, 2-branch diversity reception limits the irreducible bit errors to one tenth that of single branch reception. 4) The DC offset compensator effectively minimizes the degradation introduced by the DC offset caused by the imperfection of the demodulator. 5) The same performance is observed for both modulation schemes. The LSI can be used in wide band wireless applications like indoor wireless LAN systems and wide area wireless local loop systems.

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DOI： 10.1587/comex.2022COL0020

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DOI： 10.1109/LifeTech53646.2022.9754939

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Other Link： https://dblp.uni-trier.de/db/conf/lifetech/lifetech2022.html#NagayamaZHHD22

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DOI： 10.3169/itej.71.J80

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Language：Japanese   Publisher：電子情報通信学会  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this manuscript, an orthogonal frequency division multiplexing (OFDM) packet wireless communication system is implemented towards constructing a testbed for cooperative wireless communication systems. The system is composed of software defined radio (SDR) with universal software radio peripheral (USRP) and GNU Radio. OFDM modulation is constructed by the 1/4 scale model of IEEE802.11a standard. The observed OFDM frequency spectrum is compared with the spectrum mask of IEEE802.11a standard so that windowing is required to agree with it. Furthermore, the estimated channel state information (CSI) is shown in amplitude and phase spectrum to compensate the multipath fading. The experimental results show that the received sensitivity of -59 dBm attains at the packet error rate (PER) of 1% when subcarriers are modulated by quadrature phase shift keying (QPSK) and the received sensitivity of -61 dBm attains at 1% PER when subcarriers are modulated by binary PSK (BPSK).

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Bi-directional wireless relaying has been demonstrated to raise transmission throughput intensively as large as twice in throughput by applying physical layer network coding (PNC) when a pair of terminals exchange information via relay. With the aim to enhance the performance of relay system based on decode-and-amplify (DF) strategy, we propose a power control (PC) structure applied in Tomlinson-Harashima precoding (THP) used PNC scheme. The PC structure can be realized by adding a simple filter, aiming to control the transmission power without increasing bit error rate (BER). It is proved that the proposed PC structure can significantly reduce both transmission power and BER of bi-directional MIMO relay system, showing better performance than THP used PNC without PC structure.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The more signal streams than receive antennas are spatially multiplexed in overloaded multiple-input-multiple-output (MIMO) Spatial multiplexing which potentially enables wireless systems to achieve higher speed transmission. In overloaded MIMO systems, most conventional MIMO linear detectors have very poor transmission performance. In contrast with them, nonlinear detectors such as the maximum likelihood detector (MLD) achieve superior performance even in overloaded MIMO systems. On the other hand, MIMO receivers with virtual channels that achieve superior performance, even though the MIMO receiver can be implemented with much lower computational complexity than the MLD. Basically, the transmission signal vector is decomposed into a real signal vector and a rotation matrix in the receiver. The MIMO receiver with virtual channels comprises a linear detector to regenerate the real signal of the transmission signal and nonlinear detector to search the rotation matrix. The paper describes techniques to improve the real signal detection performance and the virtual channel detection performance. Performance of these techniques are evaluated by computer simulation.

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Language：English   Publisher：The Institute of Electronics, Information and Communication Engineers  

Bi-directional wireless relaying has been demonstrated to raise transmission throughput intensively as large as twice in throughput by applying physical layer network coding (PNC) when a pair of terminals exchange information via relay. With the aim to enhance the performance of relay system based on decode-and-amplify (DF) strategy, we propose a power control (PC) structure applied in Tomlinson-Harashima precoding (THP) used PNC scheme. The PC structure can be realized by adding a simple filter, aiming to control the transmission power without increasing bit error rate (BER). It is proved that the proposed PC structure can significantly reduce both transmission power and BER of bi-directional MIMO relay system, showing better performance than THP used PNC without PC structure.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we propose a MIMO receiver for the 16QAM modulation scheme by trellis coding. In the proposed system, it have take advantage of the trellis coded 16QAM that captures as an integral multi-level modulation 16QAM and coding. It is an effective method in that it allows high-speed communication while has a coding gain. To detect the stream When the number of receive antennas is less than that of transmit antennas, the virtual channels are introduced in the proposed receiver. Furthermore, this paper proposed to apply a gain-factor for the proposes receiver to employ the lattice-reduction for the virtual channels. While the use of virtual channels improves the transmission performance, the lattice-reduction makes it possible to detect more signal streams. In this paper, I was evaluated by computer simulation for BER characteristics and multiplication cost of the proposed MIMO receiver.

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Language：English  

DOI： 10.1109/ICWITS.2012.6417768

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Language：English  

DOI： 10.1109/ICCS.2012.6406202

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Language：Japanese  

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In a multi-user MIMO system which can increase the spectral efficiency in wireless communications, MIMO preceding can reduce signal processing complexity and power consumption of mobile stations. In this paper, experimental results of the universal software radio peripheral (USRP) are reported. Mobile stations for a multi-user MIMO preceding system are implemented by using USRP. The universal hardware driver (UHD) is used in this implementation. An advantage of using UHD is that it makes easier to manage timing of USRP. In addition, as laboratory experiments of USRP and UHD, it is shown that its frequency stability, time resolution and the error vector magnitude performance during amplify and forward operation.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

In wireless communications, a distributed antenna system (DAS) is a promising technique to increase the spectral efficiency. DAS consists of geographically distributed base station antennas, which enables to perform virtual MIMO transmission and achieve macro-diversity efficiency. DAS has many degrees of freedom such as antenna selection, clustering of antennas, and transmission schemes, and therefore it is complicated to analyze. In this paper, the cluster size in DAS is considered to be similar to the radius of cells in cellular systems. In clustering based on location, the coverage area of clusters and the area of base station antennas used for transmission can be set individually. The simulation results show that the optimal cluster size for base station antennas depends on the scheduling algorithm when analyzed in perspective of area spectral efficiency.

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This paper reports the performance of a multi-user MIMO linear precoding system using a two-way MIMO channel estimation technique. Hardware implementation feasibility of this technique is not studied yet. The experimental system consists of a base station with two antennas and two mobile stations. In this paper, feasibility of the multi-user MIMO precoding system using a two-way channel estimation technique is shown by in-lab experiments using a fading emulator.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper proposes a novel scheme to estimate the imbalance of the RF devices included in RF analog Hilbert transformer in heterodyne multimode receivers with baseband AGC, which enables the receiver to receive signals in arbitrary frequency band with realistic hardware complexity. The performance of the estimation scheme is verified by computer simulation in terms of the root mean square (RMS) of the estimation error, and the distribution of the error. Furthermore, it is also shown that the performance of the proposed scheme is enhanced by feeding the estimated value back to the RF analog devices. The performance is compared with that of conventional techniques.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Cognitive radios are of interest because they are capable of high frequency utilization efficiency. For the cognitive radios, a multimode MIMO receiver based on heterodyne reception has been proposed. This paper proposes the complexity reduced receiver to achieve high performance by correcting Hilbert transformer imperfection at the intermediate frequency (IF) band. However, imperfection of the analog circuit at the feedback loop causes poor performance. Therefore, the scheme for correcting the imperfection of the analog circuit is proposed.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper presents an experimental setup of a multi-user MIMO linear precoding system. The experimental system consists of a base station with two antennas and two mobile stations. In this system, a two-way channel estimation technique is implemented in which mobile stations just send back the received signals along with their training sequences. In this technique, the base station can obtain the channel coefficients of both the uplink and the downlink. This two-way multiple-input multiple-output channel estimation technique has been pro- posed and mathematically analyzed in literature. Computer simulation results have been reported to identify the required hardware specifications for amplify and forward operation in mobile stations by examining the bit error rate performance. However, hardware implementation feasibility of this technique is not studied yet. In this paper, feasibility of a multi-user MIMO linear precoding system using two-way channel estimation technique is shown by in-lab experiments.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper proposes a new control scheme between IEEE 802.11 (WLAN) devices and IEEE 802.15.4 (Wireless Sensor Network) devices, operating in the same radio frequency band. The new control scheme employs a hybird - station (H-STA) which has both network device functions to improve the transmission quality. The proposed control scheme enables to ensure data transmission quality of WSN with little performance degradation of WLAN throughput performances by using RTS (Request To Send), CTS (Clear To Send) and CTS-to-self packets. Results of computer simulations show that the beacon failure probability of WSN is the value less than 10 % when the WLAN system consists of 15 stations with saturated data traffic.

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This paper proposes new priority control schemes for a two-hop wireless relay system which employs the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol based on the IEEE 802.11e standard and a network coding method. The proposed priority control scheme which controls AIFSN or CW_<min> of wireless stations (STAs) improves the VoIP transmission quality and throughput performances of data transmission. Computer simulations show that the proposal schemes achieve the lower packet loss rate and delay for VoIP transmission and better uni-directional throughput performances of data transmission, compared with the conventional CW_<min> control scheme for an access point (AP) and a relay station (RS).

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Nowadays, cognitive radio draws attention because it can raise frequency utilization efficiency. For the cognitive radio, multimode receivers are required to make use of the empty frequency bands. On the other hand, MIMO spatial multiplexing is also focused on to increase transmission capacity. Moreover, the MIMO-MMSE receiver has been applied to the multimode reception. However, it is well known that performances of the MMSE filter is inferior to those of the other techniques. This paper proposes the structure of multimode MIMO-OSD receiver based on the heterodyne reception in order to improve BER performances. As a result of computer simulation, the proposed receiver can achieve superior BER performances even in the presence of strong imageband interference signals, and attain convergence within 200 symbols.

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