分布式空时编码系统同步问题研究
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摘要
随着无线通信需求的日益增长和实现技术的日新月异,无线通信技术向更高数据传输速率,更大系统容量,更高频谱利用率和更适合各种信道条件的方向发展。分布式系统由于能够在移动端只有单天线的情况下通过合作分集实现传统的多天线(MIMO)系统所能够带来的显著的分集增益而引起学者们越来越浓厚的研究兴趣。本文在采用合作分集的分布式系统中将空时编码引入,这种分布式空时编码系统是本文的主要研究方向。
本文首先提出并分析了分布式空时编码系统的物理层信号同步问题。物理层信号同步包括定时同步和频率同步。在分布式空时编码系统中,信号同步问题有它自身的独特性,这是由于分布式空时编码系统中存在多个节点或发送端,因此可能存在多个时钟偏差以及频率偏移,使得接收端无法同时进行定时同步和频率同步。
本文接下来将分布式空时分组编码与正交频分复用相结合建立起分布式空时分组编码正交频分复用系统(DSTBC-OFDM)。DSTBC-OFDM系统能抑制多个时钟偏差给系统性能带来的影响,这是因为正交频分复用技术本身对时钟偏差并不敏感。
如何抑制多个载波频率偏移给DSTBC-OFDM系统性能带来的严重影响是本文研究的关键问题。本文最后提出了一种简单的频域均衡技术来抑制多个载波频率偏移给系统性能带来的影响。仿真结果表明这种均衡技术在各分布式发送端间的载波频率之差较小时具有优异的性能,同时,通过把接收端的频率设置为各发送端频率的平均值可以获得更好的性能。
The world of wireless communications is rapidly evolving. New wireless technologies which improve the transmission rate, system capacity, spectrum efficiency of the wireless system and which are more adapted to channel conditions are continuing to emerge. Distributed system attracts more and more research interests because it can achieve the significant benefit of diversity as in traditional MIMO system through cooperative diversity when there is only one antenna at the mobile terminal. This thesis involves space-time coding into distributed system with cooperative diversity. The distributed space-time coded system is mainly investigated in this thesis.
The thesis first proposes and investigates the problem of synchronization of signal in physical layer in distributed space-time coded system. In distributed space-time coded system, the problem of synchronization is unique. Because there exists multiple nodes or transmitters in the distributed space-time coded system, there may exist multiple timing offsets and frequency offsets. Thus, it is impossible for the receiver to synchronize to multiple transmitters at the same time.
The thesis combines the distributed space-time coding with orthogonal frequency-division multiplexing to construct the DSTBC-OFDM system. The DSTBC-OFDM system can mitigate the influence of the multiple timing offsets, because OFDM is not sensitive to timing offsets.
How to mitigate the serious interference caused by the multiple carrier frequency offsets in DSTBC-OFDM system is the key problem in the thesis. Finally the thesis proposes a simple frequency domain equalization technology to mitigate the interference caused by the multiple carrier frequency offsets. The simulation results show that the equalization technique is quite effective when the carrier frequency difference between the distributed transmitters is small, and moreover, by setting the receiver’s frequency to the mean value of the transmitters’frequencies, a better performance can be obtained.
本文首先提出并分析了分布式空时编码系统的物理层信号同步问题。物理层信号同步包括定时同步和频率同步。在分布式空时编码系统中,信号同步问题有它自身的独特性,这是由于分布式空时编码系统中存在多个节点或发送端,因此可能存在多个时钟偏差以及频率偏移,使得接收端无法同时进行定时同步和频率同步。
本文接下来将分布式空时分组编码与正交频分复用相结合建立起分布式空时分组编码正交频分复用系统(DSTBC-OFDM)。DSTBC-OFDM系统能抑制多个时钟偏差给系统性能带来的影响,这是因为正交频分复用技术本身对时钟偏差并不敏感。
如何抑制多个载波频率偏移给DSTBC-OFDM系统性能带来的严重影响是本文研究的关键问题。本文最后提出了一种简单的频域均衡技术来抑制多个载波频率偏移给系统性能带来的影响。仿真结果表明这种均衡技术在各分布式发送端间的载波频率之差较小时具有优异的性能,同时,通过把接收端的频率设置为各发送端频率的平均值可以获得更好的性能。
The world of wireless communications is rapidly evolving. New wireless technologies which improve the transmission rate, system capacity, spectrum efficiency of the wireless system and which are more adapted to channel conditions are continuing to emerge. Distributed system attracts more and more research interests because it can achieve the significant benefit of diversity as in traditional MIMO system through cooperative diversity when there is only one antenna at the mobile terminal. This thesis involves space-time coding into distributed system with cooperative diversity. The distributed space-time coded system is mainly investigated in this thesis.
The thesis first proposes and investigates the problem of synchronization of signal in physical layer in distributed space-time coded system. In distributed space-time coded system, the problem of synchronization is unique. Because there exists multiple nodes or transmitters in the distributed space-time coded system, there may exist multiple timing offsets and frequency offsets. Thus, it is impossible for the receiver to synchronize to multiple transmitters at the same time.
The thesis combines the distributed space-time coding with orthogonal frequency-division multiplexing to construct the DSTBC-OFDM system. The DSTBC-OFDM system can mitigate the influence of the multiple timing offsets, because OFDM is not sensitive to timing offsets.
How to mitigate the serious interference caused by the multiple carrier frequency offsets in DSTBC-OFDM system is the key problem in the thesis. Finally the thesis proposes a simple frequency domain equalization technology to mitigate the interference caused by the multiple carrier frequency offsets. The simulation results show that the equalization technique is quite effective when the carrier frequency difference between the distributed transmitters is small, and moreover, by setting the receiver’s frequency to the mean value of the transmitters’frequencies, a better performance can be obtained.
引文
[1] IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems. IEEE, 2002,8.
[2] IEEE, Part 11:Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High Speed Physical Layer in the 5 GHz Band, IEEE Std 802.11a/D7.0, 1999.
[3] R. W. Chang. Synthesis of band-limited orthogonal signals for multichannel data transmission. Bell syst. Tech. J., 1966, 45(12) :1775-1796.
[4] T.M. Schmidl, D.C. Cox. Robust frequency and timing synchronization for OFDM. IEEE Transactions on Communications, 1997, 45(12) : 1613 -1621.
[5] S. Patel,; L. Cimini, B. McNair. Comparison of frequency offset estimation techniques for burst OFDM. Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th , 2002, 2 : 772 -776.
[6] V.K. Jones, G.C. Raleigh. Channel estimation for wireless OFDM systems. Global Telecommunications Conference, 1998. GLOBECOM 98 , 1998, 2. : 980 -985.
[7] A.A. Hutter, R. Hasholzner, J.S. Hammerschmidt. Channel estimation for mobile OFDM systems. Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50th , 1999,1.: 305 -309.
[8] M. Morelli, U. Mengali. A comparison of pilot-aided channel estimation methods for OFDM systems. IEEE Transactions on Signal Processing, 2001, 49(12): 3065 -3073.
[9] H. Chen, G.J. Pottie. An orthogonal projection-based approach for PAR reduction in OFDM. Communications Letters, IEEE , 2002, 6(5) : 169 -171.
[10] A.N. Barreto. Controlling the peak-to-average power ratio in OFDM-based wireless-LAN systems. Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th , 2002, 2: 762 -766.
[11] C. RoBing, V. Tarokh. A construction of OFDM 16-QAM sequences having low peak powers. IEEE Transactions on Information Theory, 2001, 47(5) : 2091 -2094.
[12] T. May, H. Rohling. Reducing the peak-to-average power ratio in OFDM radio transmission systems. IEEE Vehicular Technology Conference, 1998.,1998, 3.: 2474 -2478.
[13] J.A. Davis, J. Jedwab. Peak-to-mean power control in OFDM, Golay complementary sequences and Reed-Muller codes. 1998 IEEE International Symposium on Information Theory, 1998: 190.
[14] M. Speth, S.A. Fechtel, G. Fock, H. Meyr. Optimum receiver design for wireless broad-band systems using OFDM, I. IEEE Transactions on Communications, 1999, 47(11): 1668 -1677.
[15] G. J. Foschini. Layered space-time architecture for wireless communication in a fading environment when using multiple antennas. Bell Laboratiories Technical Journal, 1996,1(2):741-765.
[16] P. W. Wolniansky, G. J. Forshini, G. D. Golden, et al. V-BLAST:an architecture for realizing very high data rates over the rich-scattering wireless channel. Proc ISSSE-98, 1998.
[17] D. Agrawal, V. Tarokh, A. Naguib, N. Seshadri. Space-time coded OFDM for high data-rate wireless communication over wideband channels. IEEE Vehicular Technology Conference, 1998,3 : 2232 -2236.
[18] R. J. Piechocki, P. N. Flectcher, A. R. Nix, C. N. Canagarajah, and J. P. McGeehan. Performance evaluation of BLAST-OFDM enhanced Hiperlan/2 using simulated and measured channel data. Electron. Lett., 2001, 37(18) : 1137-1139.
[19] V. Tarokh, N. Seshachi, A. R. Calderbank. Space-time codes for high data rate wireless communications: performance analysis and code construction. IEEE Trans. Inform. Theory, 1998,44(2):744-765.
[20] Z.Liu, G.B.Giannakis, B.Muquet, and S. Zhou. Space-time coding for broadbandwireless communications. Wireless Commun. Mobile Comput., 2001, 1(1) : 33-53.
[21] A.F.Naguib, N.Seshadri and R.Calderband. Space-time coding and signal processing for high data rate wireless communications. IEEE Signal Processing Mag., 2000, 17(5) : 76-92.
[22] S. M. Alamouti. A simple transmit diversity technique for wireless communications. IEEE J. Select. Areas Commun., 1998, 16(8) : 1451-1458.
[23] S. Suthaharan, , A. Nallanathan and B. Kannan, Space-time coded MIMO-OFDM for high capacity and high data-rate wireless communication over frequency selective fading channels. International Workshop on Mobile and Wireless Communications Network, 2002, 2 : 424-428.
[24] A. Sendonaris, E. Erkip and B. Aazhang. User cooperation diversity, part Ⅰ, Ⅱ. IEEE Trans. Commun., 2003, 51(6) : 1927-1948.
[25] R.U. Nabar, H. Bolcskei and F.W. Kneubuhler. Fading relay channels: performance limits and space-time signal design. IEEE J. Select. Areas Commun., 2004, 22(13) : 1099-1109.
[26] G.J.Foschini and M.J.Gans. Layered space–time architecture for wireless communication in a fading environment when using multiple antennas. Bell Labs. Syst. Tech. J., 1996, 1 : 41-59.
[27] E. Telatar. Capacity of Multi-Antenna Gaussian Channels. AT&T-Bell Labs Internal Technical Memo, 1995, 6.
[28] R. Steele. Mobile Radio Communications. IEEE Press. New York, 1992.
[29] A. Nosratinia, T.E. Hunter, and A. Hedayat, Cooperative communication in wireless networks. IEEE Communications Magazine, 2004, 2 : 74-80.
[30] J. N. Laneman and G. W. Wornell. Distributed space–time-coded protocols for exploiting cooperative diversity in wireless networks. IEEE Trans. Inform. Theory, 2003, 49(3) : 2415-2425.
[31] I.Kalet, The multitone channel. IEEE trans. Commun.,1989, 37(2) : 119-124.
[32] T. Pollet, M. Van Bladel and M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise. IEEE Trans. Commun., 1995, 43(7) : 191-193.
[33] F. Classen and H. Meyr, Frequency synchronization algorithms for OFDM systems suitable for communication over frequency selective fading channels, IEEE Vehicular Technology Conference, 1994, 3(6) : 1655-1659.
[34] T.M. Schmidl,and D.C. Cox, Robust frequency and timing synchronization for OFDM, IEEE Transactions on Communications, 1997, 45(7) : 1613-1621.
[35] M. Morelli, and U. Mengali, An improved frequency offset estimator for OFDM applications, IEEE Communications Letters, 1999, 3(9) : 75-77.
[36] Van De Beek J.J., M. Sandell and P.O. Borjesson, ML estimation of time and frequency offset in OFDM systems, IEEE Transactions on Signal Processing, 1997, 45(2) : 1800-1805.
[37] Liu H and U. Tureli, A high-efficiency carrier estimator for OFDM communications, IEEE Communications Letters, 1998, 2-4(6) : 104-106.
[38] J. Mietzner, J. Eick and P. A. Hoeher. On distributed space-time coding techniques for cooperative wireless networks and their sensitivity to frequency offsets. 2004 ITG Workshop on Smart Antennas, 2004, 2 : 114-121.
[39] Tim Zhong Mingqian, A. B. Premkumar and A. S. Madhukumar. Performance investigation of STBC-OFDM systems with frequency offset and a semi-blind approach for the correction. in Proc. 2004 IEEE Vehicular Technology Conf. (VTC 59th), 2004, 4(13) : 1836-1839.
[40] Ding-Bing Lin, Ping-Hung Chiang and Hsueh-Jyh Li. Performance analysis of two-branch transmit diversity block-coded OFDM systems in time-varying multipath Rayleigh-fading channels. IEEE Trans. Vehicular Technology, 2005, 54(4) : 136-148.
[41] J. Ahn and H. S. Lee. Frequency domain equalization of OFDM signal over frequency nonselective Rayleigh fading channels. Electron. Lett., 1993, 29(1) :1476-1477.
[42] C. Muschallik. Improving an OFDM reception using an adaptive Nyquist windowing. IEEE Trans. Consumer Electron., 1996, 42(6) : 259-269.
[43] Yuping Zhao and S. G. Haggman. Intercarrier interference self-cancellation scheme for OFDM mobile communication systems. IEEE Trans. Commun., 2001, 49(4) : 1185-1191.
[44] Won Gi Jeon, Kyung Hi Chang and Yong Soo Cho. An equalization technique for orthogonal frequency-division multiplexing systems in time-variant multipath channels. IEEE Trans. Commun., 1999, 47(7) : 27-32.
[45] 王新梅, 肖国镇. 纠错码-原理与方法. 西安电子科技大学出版社, 2001.4
[46] Richard Van Nee and Ramjee Prasad OFDM for wireless Multimedia Communications, Artech House, Boston London, 2000.
[47] Masao Ikekawa and Ichiro Kuroda, Software Solutions for the Viterbi Algorithm, IEEE Signal Processing Society Workshop on VLSI Signal Processing, 1995.
[2] IEEE, Part 11:Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High Speed Physical Layer in the 5 GHz Band, IEEE Std 802.11a/D7.0, 1999.
[3] R. W. Chang. Synthesis of band-limited orthogonal signals for multichannel data transmission. Bell syst. Tech. J., 1966, 45(12) :1775-1796.
[4] T.M. Schmidl, D.C. Cox. Robust frequency and timing synchronization for OFDM. IEEE Transactions on Communications, 1997, 45(12) : 1613 -1621.
[5] S. Patel,; L. Cimini, B. McNair. Comparison of frequency offset estimation techniques for burst OFDM. Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th , 2002, 2 : 772 -776.
[6] V.K. Jones, G.C. Raleigh. Channel estimation for wireless OFDM systems. Global Telecommunications Conference, 1998. GLOBECOM 98 , 1998, 2. : 980 -985.
[7] A.A. Hutter, R. Hasholzner, J.S. Hammerschmidt. Channel estimation for mobile OFDM systems. Vehicular Technology Conference, 1999. VTC 1999 - Fall. IEEE VTS 50th , 1999,1.: 305 -309.
[8] M. Morelli, U. Mengali. A comparison of pilot-aided channel estimation methods for OFDM systems. IEEE Transactions on Signal Processing, 2001, 49(12): 3065 -3073.
[9] H. Chen, G.J. Pottie. An orthogonal projection-based approach for PAR reduction in OFDM. Communications Letters, IEEE , 2002, 6(5) : 169 -171.
[10] A.N. Barreto. Controlling the peak-to-average power ratio in OFDM-based wireless-LAN systems. Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th , 2002, 2: 762 -766.
[11] C. RoBing, V. Tarokh. A construction of OFDM 16-QAM sequences having low peak powers. IEEE Transactions on Information Theory, 2001, 47(5) : 2091 -2094.
[12] T. May, H. Rohling. Reducing the peak-to-average power ratio in OFDM radio transmission systems. IEEE Vehicular Technology Conference, 1998.,1998, 3.: 2474 -2478.
[13] J.A. Davis, J. Jedwab. Peak-to-mean power control in OFDM, Golay complementary sequences and Reed-Muller codes. 1998 IEEE International Symposium on Information Theory, 1998: 190.
[14] M. Speth, S.A. Fechtel, G. Fock, H. Meyr. Optimum receiver design for wireless broad-band systems using OFDM, I. IEEE Transactions on Communications, 1999, 47(11): 1668 -1677.
[15] G. J. Foschini. Layered space-time architecture for wireless communication in a fading environment when using multiple antennas. Bell Laboratiories Technical Journal, 1996,1(2):741-765.
[16] P. W. Wolniansky, G. J. Forshini, G. D. Golden, et al. V-BLAST:an architecture for realizing very high data rates over the rich-scattering wireless channel. Proc ISSSE-98, 1998.
[17] D. Agrawal, V. Tarokh, A. Naguib, N. Seshadri. Space-time coded OFDM for high data-rate wireless communication over wideband channels. IEEE Vehicular Technology Conference, 1998,3 : 2232 -2236.
[18] R. J. Piechocki, P. N. Flectcher, A. R. Nix, C. N. Canagarajah, and J. P. McGeehan. Performance evaluation of BLAST-OFDM enhanced Hiperlan/2 using simulated and measured channel data. Electron. Lett., 2001, 37(18) : 1137-1139.
[19] V. Tarokh, N. Seshachi, A. R. Calderbank. Space-time codes for high data rate wireless communications: performance analysis and code construction. IEEE Trans. Inform. Theory, 1998,44(2):744-765.
[20] Z.Liu, G.B.Giannakis, B.Muquet, and S. Zhou. Space-time coding for broadbandwireless communications. Wireless Commun. Mobile Comput., 2001, 1(1) : 33-53.
[21] A.F.Naguib, N.Seshadri and R.Calderband. Space-time coding and signal processing for high data rate wireless communications. IEEE Signal Processing Mag., 2000, 17(5) : 76-92.
[22] S. M. Alamouti. A simple transmit diversity technique for wireless communications. IEEE J. Select. Areas Commun., 1998, 16(8) : 1451-1458.
[23] S. Suthaharan, , A. Nallanathan and B. Kannan, Space-time coded MIMO-OFDM for high capacity and high data-rate wireless communication over frequency selective fading channels. International Workshop on Mobile and Wireless Communications Network, 2002, 2 : 424-428.
[24] A. Sendonaris, E. Erkip and B. Aazhang. User cooperation diversity, part Ⅰ, Ⅱ. IEEE Trans. Commun., 2003, 51(6) : 1927-1948.
[25] R.U. Nabar, H. Bolcskei and F.W. Kneubuhler. Fading relay channels: performance limits and space-time signal design. IEEE J. Select. Areas Commun., 2004, 22(13) : 1099-1109.
[26] G.J.Foschini and M.J.Gans. Layered space–time architecture for wireless communication in a fading environment when using multiple antennas. Bell Labs. Syst. Tech. J., 1996, 1 : 41-59.
[27] E. Telatar. Capacity of Multi-Antenna Gaussian Channels. AT&T-Bell Labs Internal Technical Memo, 1995, 6.
[28] R. Steele. Mobile Radio Communications. IEEE Press. New York, 1992.
[29] A. Nosratinia, T.E. Hunter, and A. Hedayat, Cooperative communication in wireless networks. IEEE Communications Magazine, 2004, 2 : 74-80.
[30] J. N. Laneman and G. W. Wornell. Distributed space–time-coded protocols for exploiting cooperative diversity in wireless networks. IEEE Trans. Inform. Theory, 2003, 49(3) : 2415-2425.
[31] I.Kalet, The multitone channel. IEEE trans. Commun.,1989, 37(2) : 119-124.
[32] T. Pollet, M. Van Bladel and M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise. IEEE Trans. Commun., 1995, 43(7) : 191-193.
[33] F. Classen and H. Meyr, Frequency synchronization algorithms for OFDM systems suitable for communication over frequency selective fading channels, IEEE Vehicular Technology Conference, 1994, 3(6) : 1655-1659.
[34] T.M. Schmidl,and D.C. Cox, Robust frequency and timing synchronization for OFDM, IEEE Transactions on Communications, 1997, 45(7) : 1613-1621.
[35] M. Morelli, and U. Mengali, An improved frequency offset estimator for OFDM applications, IEEE Communications Letters, 1999, 3(9) : 75-77.
[36] Van De Beek J.J., M. Sandell and P.O. Borjesson, ML estimation of time and frequency offset in OFDM systems, IEEE Transactions on Signal Processing, 1997, 45(2) : 1800-1805.
[37] Liu H and U. Tureli, A high-efficiency carrier estimator for OFDM communications, IEEE Communications Letters, 1998, 2-4(6) : 104-106.
[38] J. Mietzner, J. Eick and P. A. Hoeher. On distributed space-time coding techniques for cooperative wireless networks and their sensitivity to frequency offsets. 2004 ITG Workshop on Smart Antennas, 2004, 2 : 114-121.
[39] Tim Zhong Mingqian, A. B. Premkumar and A. S. Madhukumar. Performance investigation of STBC-OFDM systems with frequency offset and a semi-blind approach for the correction. in Proc. 2004 IEEE Vehicular Technology Conf. (VTC 59th), 2004, 4(13) : 1836-1839.
[40] Ding-Bing Lin, Ping-Hung Chiang and Hsueh-Jyh Li. Performance analysis of two-branch transmit diversity block-coded OFDM systems in time-varying multipath Rayleigh-fading channels. IEEE Trans. Vehicular Technology, 2005, 54(4) : 136-148.
[41] J. Ahn and H. S. Lee. Frequency domain equalization of OFDM signal over frequency nonselective Rayleigh fading channels. Electron. Lett., 1993, 29(1) :1476-1477.
[42] C. Muschallik. Improving an OFDM reception using an adaptive Nyquist windowing. IEEE Trans. Consumer Electron., 1996, 42(6) : 259-269.
[43] Yuping Zhao and S. G. Haggman. Intercarrier interference self-cancellation scheme for OFDM mobile communication systems. IEEE Trans. Commun., 2001, 49(4) : 1185-1191.
[44] Won Gi Jeon, Kyung Hi Chang and Yong Soo Cho. An equalization technique for orthogonal frequency-division multiplexing systems in time-variant multipath channels. IEEE Trans. Commun., 1999, 47(7) : 27-32.
[45] 王新梅, 肖国镇. 纠错码-原理与方法. 西安电子科技大学出版社, 2001.4
[46] Richard Van Nee and Ramjee Prasad OFDM for wireless Multimedia Communications, Artech House, Boston London, 2000.
[47] Masao Ikekawa and Ichiro Kuroda, Software Solutions for the Viterbi Algorithm, IEEE Signal Processing Society Workshop on VLSI Signal Processing, 1995.