The Experts below are selected from a list of 20577 Experts worldwide ranked by ideXlab platform
M Sawahashi - One of the best experts on this subject based on the ideXlab platform.
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downlink transmission of broadband ofcdm systems part ii effect of doppler shift
IEEE Transactions on Communications, 2006Co-Authors: Yiqing Zhou, Jiangzhou Wang, M SawahashiAbstract:The orthogonal frequency and code division multiplexing (OFCDM) system with 2-D spreading (time- and frequency-domain spreading) is becoming a promising candidate for future broadband wireless communication systems. OFCDM is more attractive than orthogonal frequency-division multiplexing (OFDM) both by introducing frequency-domain spreading for frequency diversity provision and time-domain spreading for flexible data rate provision. To provide high-speed mobile services, multicode transmission is employed in conjunction with OFCDM. In a Gaussian or flat-fading Channel, multicode Channels are orthogonal. However, in a realistic wireless Channel, the orthogonality no longer maintains. Thus, multicode interference (MCI) is caused. This paper focuses on the investigation of the effect of Doppler shift on the downlink transmission of high-speed mobile OFCDM systems. A practical Channel estimation algorithm based on a code-multiplexed Pilot Channel is employed to track the variations of fading Channels. Hybrid MCI cancellation and minimum mean-square error (MMSE) detection proposed by the authors is employed as an efficient way to eliminate the MCI in the frequency domain. The system performance is analytically studied with imperfect Channel estimation to show how it is affected by parameters such as the window size in the Channel estimation, Doppler shift, the number of stages of the hybrid detection, the power ratio of Pilot to data Channels, spreading factor, and so on
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frequency domain Channel dependent scheduling employing an adaptive transmission bandwidth for Pilot Channel in uplink single carrier fdma radio access
Vehicular Technology Conference, 2006Co-Authors: Yoshiaki Ofuji, K Higuch, M SawahashiAbstract:This paper proposes frequency and time domain Channel-dependent scheduling employing an adaptive transmission bandwidth for the Pilot Channel for Channel quality indication (CQI) measurement in the uplink single-carrier (SC)-FDMA radio access. In the proposed scheme, a high multiuser diversity effect due to frequency domain Channel-dependent scheduling is gained by assigning a wide Pilot transmission bandwidth to user equipments (UEs) near a cell site, whereas the influence of the CQI measurement error is mitigated by assigning a narrow Pilot transmission bandwidth to UEs near the cell boundary at the cost of utilizing multiuser diversity in the frequency domain. System simulation results elucidate that the cell throughput using the adaptive Pilot transmission bandwidth with the predetermined threshold, TH SINR , of −6 dB is increased by approximately 600 kbps compared to that using a fixed 1.25-MHz Pilot transmission bandwidth, i.e., only time domain Channel-dependent scheduling, owing to an increasing multiuser diversity effect in the frequency domain. We also show that the user throughput using the adaptive Pilot Channel transmission bandwidth scheme at a 5% cumulative distribution function is increased by approximately 35 and 30 % compared to that using a 5-MHz transmission for 16 and 32 UEs per cell, respectively, for the inter-site distance of 500 m.
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downlink transmission of broadband ofcdm systems part i hybrid detection
IEEE Transactions on Communications, 2005Co-Authors: Yiqing Zhou, Jiangzhou Wang, M SawahashiAbstract:The broadband orthogonal frequency and code division multiplexing (OFCDM) system with two-dimensional spreading (time and frequency domain spreading) is becoming a very attractive technique for high-rate data transmission in future wireless communication systems. In this paper, a quasianalytical study is presented on the downlink performance of the OFCDM system with hybrid multi-code interference (MCI) cancellation and minimum mean square error (MMSE) detection. The weights of MMSE are derived and updated stage by stage of MCI cancellation. The effects of Channel estimation errors and sub-carrier correlation are also studied. It is shown that the hybrid detection scheme performs much better than pure MMSE when good Channel estimation is guaranteed. The power ratio between the Pilot Channel and all data Channels should be set to 0.25, which is a near optimum value for the two-dimensional spreading system with time domain spreading factor (N/sub T/) of 4 and 8. On the other hand, in a slow fading Channel, a large value of the Channel estimation window size /spl gamma/N/sub T/, where /spl gamma/ is an odd integer, is expected. However, /spl gamma/=3 is large enough for the system with N/sub T/=8 while /spl gamma/=5 is more desirable for the system with N/sub T/=4. Although performance of the hybrid detection degrades in the presence of the sub-carrier correlation, the hybrid detection still works well even the correlation coefficient is as high as 0.7. Finally, given N/sub T/, although performance improves when the frequency domain spreading factor (N/sub F/) increases, the frequency diversity gain is almost saturated for a large value of N/sub F/ (i.e., N/sub F/ /spl ges/ 32).
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experiments on three step fast cell search algorithm employing common Pilot Channel for ofcdm broadband packet wireless access in forward link
Vehicular Technology Conference, 2004Co-Authors: Motohiro Tanno, Hiroyuki Atarashi, Kenichi Higuchi, M SawahashiAbstract:This paper presents laboratory and field experimental results on a three-step cell search algorithm employing the time-multiplexed common Pilot Channel (CPICH) for orthogonal frequency and code division multiplexing (OFCDM) broadband wireless access with a 100-MHz bandwidth. In the proposed three-step cell search method using a two-dimensional cell-specific scrambling code, the OFCDM symbol timing, packet frame timing and scrambling code group, and the scrambling code within the group are detected by taking advantage of the CPICH in the first, second, and third step, respectively (note that the packet data Channel (PDCH) is also used in the first step). The laboratory experimental results using a multipath fading simulator show that the cell detection probability of 90% is achieved within approximately 4 and 26 msec when the average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub b//N/sub 0/) of the PDCH is -2 and -5 dB, respectively, where the maximum Doppler frequency is 20 to 400 Hz and the root mean squared delay spread is 0.1 to 0.6 /spl mu/sec. Furthermore, field experimental results with the carrier frequency of 4.635 GHz show that the cell search time at the detection probability of 90% is approximately 10 msec in a course that is 800 to 1000 meters away from the cell site, even with the transmission power of the time-multiplexed CPICH (PDCH) of 0.06 W (0.13 W).
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investigation of optimum Pilot Channel structure for vsf ofcdm broadband wireless access in forward link
Vehicular Technology Conference, 2003Co-Authors: Yoshihisa Kishiyama, Noriyuki Maeda, Hiroyuki Atarashi, M SawahashiAbstract:This paper clarifies the optimum Pilot Channel structure in the broadband forward link for variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM) wireless access using two-dimensional spreading while taking into account the following factors that affect radio link performance: (1) Channel estimation accuracy for coherent detection, (2) the accuracy of the signal-to-interference power ratio (SIR) measurement for adaptive modulation and Channel coding and the reliability information of the received signals, (3) the configuration of simultaneously multiplexed orthogonal Pilot patterns, and (4) the impact on cell search, as well as flexibility in allocating transmission power resources. We show that although the time-multiplexed and code-multiplexed structure achieves almost the same Channel estimation accuracy, the code-multiplexed structure is more advantageous due to flexible multiplexing of the orthogonal Pilot patterns within one sub-carrier resulting from the accommodation of numerous OFCDM symbols in a frame. Assuming the use of an adaptive antenna array beam-forming transmitter where many orthogonal Pilot patterns are required, we clarify that the cod-multiplexed structure achieves more accurate SIR measurement compared to the time-multiplexed structure. Meanwhile, the time-multiplexed structure is advantageous in that it does not require an exclusive synchronization Channel for cell search. Consequently, we elucidate that the code-multiplexed structure is overall slightly superior to the time-multiplexed structure because the code-multiplexed Pilot Channel structure is advantageous in that it can flexibly share transmission power resources among other physical Channels, thereby resulting in increasing the number of orthogonal Pilot patterns and increasing the number of simultaneous packet Channels despite obtaining almost the identical merits of the time-multiplexed structure from the viewpoint of radio link performance.
Noriyuki Maeda - One of the best experts on this subject based on the ideXlab platform.
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performance of the delay profile information Channel based subcarrier transmit power control technique for ofdm fdd systems
Electronics and Communications in Japan Part I-communications, 2003Co-Authors: Noriyuki Maeda, Seiichi Sampei, Norihiko MorinagaAbstract:The convolutionally encoded OFDM (Orthogonal Frequency Division Multiplexing) scheme, is an effective approach that is superior in its robustness to frequency-selective fading and in assuring high transmission quality in a broadband wireless transmission system. However, since the burst length becomes shorter as the transmission speed becomes higher, there are problems of reduced coding gain due to lack of interleaving effect and of increased transmission power with increased bandwidth. These problems are particularly significant in the application to indoor environments in which the demand for high-speed transmission is high and the Doppler frequency is small. Hence, further improvement of receiver sensitivity and reduction of transmit power are indispensable. In this paper, a subcarrier transmit power control technique is proposed in which the delay profile information estimated using a Pilot Channel is reported to the message sender and the transmit power is controlled to make the receiving condition for each subcarrier constant based on the obtained delay profile information, so that the receiver sensitivity is improved by transmit power control. Further, the use of PNPA (Partial Non-Power Allocation), which suppresses excessive transmit power caused by the application of the subcarrier transmit power control, is considered. When the transmission characteristics of the proposed scheme are evaluated by computer simulation, it is confirmed that the error correcting capability can be improved drastically by the proposed scheme and that the transmit power can be reduced substantially. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 72–80, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1163
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performance of the delay profile information Channel based subcarrier transmit power control technique for ofdm fdd systems
Electronics and Communications in Japan Part I-communications, 2003Co-Authors: Noriyuki Maeda, Seiichi Sampei, Norihiko MorinagaAbstract:The convolutionally encoded OFDM (Orthogonal Frequency Division Multiplexing) scheme, is an effective approach that is superior in its robustness to frequency-selective fading and in assuring high transmission quality in a broadband wireless transmission system. However, since the burst length becomes shorter as the transmission speed becomes higher, there are problems of reduced coding gain due to lack of interleaving effect and of increased transmission power with increased bandwidth. These problems are particularly significant in the application to indoor environments in which the demand for high-speed transmission is high and the Doppler frequency is small. Hence, further improvement of receiver sensitivity and reduction of transmit power are indispensable. In this paper, a subcarrier transmit power control technique is proposed in which the delay profile information estimated using a Pilot Channel is reported to the message sender and the transmit power is controlled to make the receiving condition for each subcarrier constant based on the obtained delay profile information, so that the receiver sensitivity is improved by transmit power control. Further, the use of PNPA (Partial Non-Power Allocation), which suppresses excessive transmit power caused by the application of the subcarrier transmit power control, is considered. When the transmission characteristics of the proposed scheme are evaluated by computer simulation, it is confirmed that the error correcting capability can be improved drastically by the proposed scheme and that the transmit power can be reduced substantially. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 72–80, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1163
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investigation of optimum Pilot Channel structure for vsf ofcdm broadband wireless access in forward link
Vehicular Technology Conference, 2003Co-Authors: Yoshihisa Kishiyama, Noriyuki Maeda, Hiroyuki Atarashi, M SawahashiAbstract:This paper clarifies the optimum Pilot Channel structure in the broadband forward link for variable spreading factor-orthogonal frequency and code division multiplexing (VSF-OFCDM) wireless access using two-dimensional spreading while taking into account the following factors that affect radio link performance: (1) Channel estimation accuracy for coherent detection, (2) the accuracy of the signal-to-interference power ratio (SIR) measurement for adaptive modulation and Channel coding and the reliability information of the received signals, (3) the configuration of simultaneously multiplexed orthogonal Pilot patterns, and (4) the impact on cell search, as well as flexibility in allocating transmission power resources. We show that although the time-multiplexed and code-multiplexed structure achieves almost the same Channel estimation accuracy, the code-multiplexed structure is more advantageous due to flexible multiplexing of the orthogonal Pilot patterns within one sub-carrier resulting from the accommodation of numerous OFCDM symbols in a frame. Assuming the use of an adaptive antenna array beam-forming transmitter where many orthogonal Pilot patterns are required, we clarify that the cod-multiplexed structure achieves more accurate SIR measurement compared to the time-multiplexed structure. Meanwhile, the time-multiplexed structure is advantageous in that it does not require an exclusive synchronization Channel for cell search. Consequently, we elucidate that the code-multiplexed structure is overall slightly superior to the time-multiplexed structure because the code-multiplexed Pilot Channel structure is advantageous in that it can flexibly share transmission power resources among other physical Channels, thereby resulting in increasing the number of orthogonal Pilot patterns and increasing the number of simultaneous packet Channels despite obtaining almost the identical merits of the time-multiplexed structure from the viewpoint of radio link performance.
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broadband packet wireless access based on vsf ofcdm and mc ds cdma
Personal Indoor and Mobile Radio Communications, 2002Co-Authors: Hiroyuki Atarashi, Noriyuki Maeda, S Abeta, M SawahashiAbstract:This paper proposes broadband packet wireless access employing Variable Spreading Factor-Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) with two-dimensional spreading that prioritizes time domain spreading in the forward link and multi-carrier/DS-CDMA (MC/DS-CDMA) in the reverse link for the system beyond IMT-2000. Based on the wireless access scheme, we propose major radio air interfaces in the physical layer to achieve our target maximum throughput beyond 100 Mbps and 20 Mbps in the forward and reverse links, respectively. Furthermore, we present key technologies such as the adaptive radio link parameter control coupled with link adaptation, Pilot Channel assisted coherent detection in both links, adaptive antenna array beam forming transmitter and receiver, cell search, and Channel coding. Finally, simulation results elucidate that VSF-OFCDM using die proposed radio link parameters achieves a throughput above 100 Mbps at the average received signal energy per symbol-to-background noise power spectrum density ratio (Ea/No) of approximately 13 dB (101.5 MHz bandwidth, without antenna diversity reception, 12-path Rayleigh fading Channel). Furthermore, MC/DS-CDMA realizes a throughput above 20 Mbps at the average received Ea/No of approximately 8 dB (40 MHz bandwidth, with antenna diversity reception, 6-path Rayleigh fading Channel).
Mohammad Ghavami - One of the best experts on this subject based on the ideXlab platform.
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Pilot Channel assisted log likelihood ratio selective rake combining for low rate ultra wideband communications
IEEE Transactions on Communications, 2008Co-Authors: Xiaoli Chu, R D Murch, Junsheng Liu, Mohammad GhavamiAbstract:For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath compnents, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath Channels and in the presence of multi-user interference.
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Pilot Channel assisted log likelihood ratio selective combining for low rate ds uwb communications
International Conference on Communications, 2008Co-Authors: Xiaoli Chu, Mohammad Ghavami, R D MurchAbstract:In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for Rake receivers that will be used in long-range low-rate UWB communications targeted by the IEEE 802.15.4a specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output signal-to-noise ratio. Simulation results show that the proposed PCA-LLR-SC scheme is able to provide robust low-rate UWB communications in fast-fading multipath Channels.
Xiaoli Chu - One of the best experts on this subject based on the ideXlab platform.
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performance analysis of Pilot Channel assisted log likelihood ratio selective combining
Personal Indoor and Mobile Radio Communications, 2008Co-Authors: Xiaoli Chu, R D MurchAbstract:In this paper, we provide performance analysis for a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme that is designed to support robust long-range low-rate UWB communications targeted by the IEEE 802.15.4a. Including the loss of orthogonality between data and Pilot pulses caused by the UWB multipath Channel, a closed-form bit-error-rate expression is derived, and verified by comparisons with simulation results. Our analytical result shows its accuracy in performance evaluation for the PCA-LLR-SC scheme and confirms that PCA-LLR-SC is able to support robust low-rate UWB communications in fast-fading multipath Channels.
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Pilot Channel assisted log likelihood ratio selective rake combining for low rate ultra wideband communications
IEEE Transactions on Communications, 2008Co-Authors: Xiaoli Chu, R D Murch, Junsheng Liu, Mohammad GhavamiAbstract:For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath compnents, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath Channels and in the presence of multi-user interference.
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Pilot Channel assisted log likelihood ratio selective combining for low rate ds uwb communications
International Conference on Communications, 2008Co-Authors: Xiaoli Chu, Mohammad Ghavami, R D MurchAbstract:In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for Rake receivers that will be used in long-range low-rate UWB communications targeted by the IEEE 802.15.4a specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output signal-to-noise ratio. Simulation results show that the proposed PCA-LLR-SC scheme is able to provide robust low-rate UWB communications in fast-fading multipath Channels.
R D Murch - One of the best experts on this subject based on the ideXlab platform.
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performance analysis of Pilot Channel assisted log likelihood ratio selective combining
Personal Indoor and Mobile Radio Communications, 2008Co-Authors: Xiaoli Chu, R D MurchAbstract:In this paper, we provide performance analysis for a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme that is designed to support robust long-range low-rate UWB communications targeted by the IEEE 802.15.4a. Including the loss of orthogonality between data and Pilot pulses caused by the UWB multipath Channel, a closed-form bit-error-rate expression is derived, and verified by comparisons with simulation results. Our analytical result shows its accuracy in performance evaluation for the PCA-LLR-SC scheme and confirms that PCA-LLR-SC is able to support robust low-rate UWB communications in fast-fading multipath Channels.
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Pilot Channel assisted log likelihood ratio selective rake combining for low rate ultra wideband communications
IEEE Transactions on Communications, 2008Co-Authors: Xiaoli Chu, R D Murch, Junsheng Liu, Mohammad GhavamiAbstract:For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath compnents, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath Channels and in the presence of multi-user interference.
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Pilot Channel assisted log likelihood ratio selective combining for low rate ds uwb communications
International Conference on Communications, 2008Co-Authors: Xiaoli Chu, Mohammad Ghavami, R D MurchAbstract:In this paper, we propose a Pilot-Channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for Rake receivers that will be used in long-range low-rate UWB communications targeted by the IEEE 802.15.4a specification. The Pilot and data Channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the Channel estimation mean square error and maximizing the receiver output signal-to-noise ratio. Simulation results show that the proposed PCA-LLR-SC scheme is able to provide robust low-rate UWB communications in fast-fading multipath Channels.
