宽带无线通信系统下行同步和小区搜索技术研究
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摘要
随着互联网的快速发展,宽带无线通信已经成为了通信界的热点。OFDM技术能够有效的对抗多径效应,消除符号间干扰,并且具有很高的频谱利用率,已经成为宽带无线通信系统的首选技术。作为宽带无线通信系统的代表,802.16E系统采用了OFDM技术作为其物理层基础。本文主要研究了802.16E系统的小区搜索和下行同步过程。
OFDM系统有两个方面的同步要求,符号定时同步和载波频率同步。本文对基于PN序列自相关特性的符号定时同步算法进行了理论分析,总结了影响该算法性能的因素并对该算法进行了改进。本文对Moose频域频偏估计算法和利用OFDM符号循环前缀的时域频偏估计算法的性能进行了分析,得到了这两种算法频偏估计误差的概率分布函数,并且给出了采用连续传输和分组传输的OFDM系统的频偏估计方案,并分析了其性能。
本文详细分析了802.16E帧前导符号的特点,给出了802.16E小区搜索和下行同步的完整算法流程,包括帧检测,粗符号定时和粗频偏估计,整数倍频偏估计与小区识别,精细定时同步和精细频偏估计,并且通过仿真验证了这些算法的性能。本文讨论了802.16E系统异频组网和同频组网两种组网模式。在同频组网模式下,由于来自相邻小区的干扰,在小区边缘传统帧检测算法失效。针对这一问题,本文给出了几种解决方案,通过仿真和性能分析验证了它们在同频组网模式下的有效性。最后,本文提出了频域同步跟踪算法,该算法可以有效地避免小区/扇区干扰对同步跟踪的影响。
With the rapid development of Internet, telecommunication industry pays more and more attention to broadBand wireless communication. At present, OFDM technology is preferred in broadBand wireless communication system, for the advantages that it can effectively combat the multi-path effect, eliminate internal symbol interferences, and it has high frequency efficiency. The 802.16E standard, representative of broadBand wireless system, chooses OFDM as its PHY layer framework. This paper mainly focuses on downlink synchronization and cell search scheme of 802.16E system.
There are two main aspects about OFDM synchronization technologies: symbol timing synchronization and carrier frequency synchronization. In this paper, the performance of symbol timing synchronization algorithm based on auto-correlation characteristic of PN sequence is analyzed theoretically, factors that affect its performance are summarized, and we propose an improved algorithm to better its performance. For carrier frequency synchronization techniques, we study performance of classical Moose carrier frequency offset estimation algorithm and time domain frequency estimation algorithm based on CP. After that, we propose carrier frequency synchronization schemes about continual OFDM system and packet OFDM system.
In this paper, the characteristics of 802.16E preamble are presented. We propose whole cell search and downlink synchronization scheme for 802.16E system including frame detection, coarse timing synchronization and coarse frequency offset estimation, integer frequency offset estimation and cell index identification, fine timing synchronization and fine frequency offset estimation. And these algorithms are validated by simulation. After that, two network organization mode called same frequency network mode and different frequency network mode are presented. In same frequency network mode, the classical frame detection algorithm is noneffective in cell edge. Several algorithms are proposed to solve this problem. Simulation and analysis prove that they are efficient in this case. At last a frequency tracking algorithm is proposed to avoid impact of interference from adjacent cell/sector.
OFDM系统有两个方面的同步要求,符号定时同步和载波频率同步。本文对基于PN序列自相关特性的符号定时同步算法进行了理论分析,总结了影响该算法性能的因素并对该算法进行了改进。本文对Moose频域频偏估计算法和利用OFDM符号循环前缀的时域频偏估计算法的性能进行了分析,得到了这两种算法频偏估计误差的概率分布函数,并且给出了采用连续传输和分组传输的OFDM系统的频偏估计方案,并分析了其性能。
本文详细分析了802.16E帧前导符号的特点,给出了802.16E小区搜索和下行同步的完整算法流程,包括帧检测,粗符号定时和粗频偏估计,整数倍频偏估计与小区识别,精细定时同步和精细频偏估计,并且通过仿真验证了这些算法的性能。本文讨论了802.16E系统异频组网和同频组网两种组网模式。在同频组网模式下,由于来自相邻小区的干扰,在小区边缘传统帧检测算法失效。针对这一问题,本文给出了几种解决方案,通过仿真和性能分析验证了它们在同频组网模式下的有效性。最后,本文提出了频域同步跟踪算法,该算法可以有效地避免小区/扇区干扰对同步跟踪的影响。
With the rapid development of Internet, telecommunication industry pays more and more attention to broadBand wireless communication. At present, OFDM technology is preferred in broadBand wireless communication system, for the advantages that it can effectively combat the multi-path effect, eliminate internal symbol interferences, and it has high frequency efficiency. The 802.16E standard, representative of broadBand wireless system, chooses OFDM as its PHY layer framework. This paper mainly focuses on downlink synchronization and cell search scheme of 802.16E system.
There are two main aspects about OFDM synchronization technologies: symbol timing synchronization and carrier frequency synchronization. In this paper, the performance of symbol timing synchronization algorithm based on auto-correlation characteristic of PN sequence is analyzed theoretically, factors that affect its performance are summarized, and we propose an improved algorithm to better its performance. For carrier frequency synchronization techniques, we study performance of classical Moose carrier frequency offset estimation algorithm and time domain frequency estimation algorithm based on CP. After that, we propose carrier frequency synchronization schemes about continual OFDM system and packet OFDM system.
In this paper, the characteristics of 802.16E preamble are presented. We propose whole cell search and downlink synchronization scheme for 802.16E system including frame detection, coarse timing synchronization and coarse frequency offset estimation, integer frequency offset estimation and cell index identification, fine timing synchronization and fine frequency offset estimation. And these algorithms are validated by simulation. After that, two network organization mode called same frequency network mode and different frequency network mode are presented. In same frequency network mode, the classical frame detection algorithm is noneffective in cell edge. Several algorithms are proposed to solve this problem. Simulation and analysis prove that they are efficient in this case. At last a frequency tracking algorithm is proposed to avoid impact of interference from adjacent cell/sector.
引文
[1]IEEE Standard for Local and metropolitan area networks,Part16:Air Interface for Fixed and Mobile BroadBand Wireless Access Systems,IEEE 802.16E-2005 and IEEE 802.16-2004/2005,Feb.2006.
[2]Tejas Bhatt;Vishwas Sundaramurthyl;Jianzhong Zhang and Dennis McCain;Initial Synchronization for 802.6e Downlink.Signals,Systems and Computers,2006.ACSSC '06.Fortieth Asilomar Conference on Oct.29 2006-Nov.1 2006 Page(s):701-706
[3]WiMAX Forum Mobile System Profile,WiMAX Forum,vl.2,Sep,2006.
[4]Yasamin Mostofi,Donald C.Cox,Mathematical Analysis of the Impact of Timing Synchronization Errors on the Performance of an OFDM System.IEEE Transaction on Communication,Vol.54,no.2,February 2006
[5]M.Speth,S.Fechtel,G.Fock,H.Meyr,Optimum receiver design for OFDM-based broadBand transmission.Ⅱ.A case study,IEEE Transaction.on Communication.,Vol.49,Issue.4,April 2001.
[6]Method,apparatus and computer program product providing synchronization for OFDMA downlink signal.United States Patent 20070280098.
[7]Symbol Synchronization at the BPSK-OFDM Receiver.2007 IEEE.
[8]Van de Beek J.Sandell M.,Isaksson M.,and Borjesson,ML Estimation of time and frequency offset in OFDM systems,IEEE Transaction on Signal Processing,Vol.45,pp.1800-1805,jul.1997.
[9]Matic D.;Petrochilos N.;Trindade A.;OFDM synchronisation based on the phase rotation of sub-carriers Vehicular Technology Conference Proceedings,2000.VTC 2000-Spring Tokyo.2000IEEE 51st,Page(s):1260-1264 Volume 2
[10]Timothy M.Schmidl;Cox,D.C.;Robust Frequency and Timing Synchronization for OFDM,IEEE Transaction on Communication,Volume 45,no.12,December 1997
[11]Tufvesson F;Edfors O;Faulkner M.;Time and Frequency synchronization for OFDM using PN-Sequence Preambles Proceedings of IEEE Vehicular Technology Conference,Amsterdam,The Betherlands,1999.19(22):2203-2207
[12]P.H.Moose,A technique for orthogonal frequency division multiplexing frequency offset correction,IEEE Transactions on Communications,vol.42,pp.2908-2914,October 1994.
[13]尹长川,罗涛,乐光新 多载波宽带无线通信技术,北京邮电大学出版社,2004.7
[14]Yang B,Letaief K,Cheng R,and Cao Z.Timing recovery for OFDM transimission,IEEE Journal on Selected Areas in Communication,Vol.18,pp.2278-2291,Nov.2000
[15]Morelli M.and Mengali U,An inproved frequency offset estimator for OFDM applications,IEEE Communication.Letter,Vol.3,pp.75-77,Mar.1999
[16]Cai L,Xu Y,Luo H,Song W,Zheng B,Cell search and Frequency Synchronization for Beyond 3G".IEEE 6~(th)CAC symp on Emerging Technologies:Mobile and Wireless Communicaton,Vol.1,pp.45-48,2004
[17]H-K,Song,Y.H.You,J.H.Paikand and Y.S.Cho,Frequency offset synchronization and channel estimation for OFDM-based transmission,IEEE Communication Letters,Mar 2000,pp 95-95
[18]Speth M.Frame Synchronization of OFDM systems in frequency selective fading channels
[19]Luise M and Reggiannini R.Carrier frequency acquisition and tracking for OFDM systems,IEEE Transaction on Communication,Nove 1996,44(11):1590-1598
[20]Keukjoon Bang,Namshin Cho,A Coarse Frequency Offset Estimation in an OFDM system Using the Concept of the Coherence Phase Bandwidth,IEEE Transaction on Communication Vol 49,No.8,Aug 2001
[21]佟学俭,罗涛,OFDM移动通信技术原理与应用,人民邮电出版社,2003.6
[22]王文博,郑侃“宽带无线通信OFDM技术”人民邮电出版社 2003年11月
[23]J.Heiskala,J.Terry,OFDM Wireless LANs:A Theoretical and Practical Guide,1 St edition,Sams,2001.
[24]J.-J.van de Beek,M.Sandell,M.Isaksson,and P.Borjesson,Low-Complex Frame Synchronization in OFDM Systems,in Proc.of ICUPC,pp.982-986,Nov 1995
[25]A.Reid,J.Son,Joint Synchronization using Semi-analytic Root likelihood Polynomials for OFDM Systems,submitted to IEEE Intl.Conf:on Acoustics,Speech and Signal Processing(ICASSP),Honolulu,Hawaii,April 2007
[26]L.J.Cimini,Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing,IEEE Trans.Commun.,vol.COM-33,no.7,pp.665-675,Jul.1985.
[27]T.M.Schmidl,Synchronization algorithms for wireless data transmission using orthogonal frequency division multiplexing(OFDM),Ph.D.dissertation,Stanford Univ.,Stanford,CA,1997.
[28]J.Van de Beek,M.Sandell,and M.Isaksson,Low-complex frame synchronization in OFDM systems,in Proc.4th IEEE Int.Conf.Universal Pets.Commun.,1995,pp.982-986.
[29]B.Yang,K.Letaief,and R.Cheng,Timing recovery for OFDM transmission,J.Sel.Areas Commun.,vol.18,no.11,pp.2278-2291,Nov.2000.
[30]M.Speth,F.Classen,and H.Meyr,Frame synchronization of OFDM systems in frequency selective fading channels,in Proc.47th IEEE Veh.Technol.Conf.,vol.3,1997,pp.1807-1811.
[31]Y.Mostofi,D.Cox,and A.Bahai,Effect of frame synchronization errorson pilot-aided channel estimation in OFDM:Analysis and solution,in Proc.5th Int.Symp.Wireless Pers.Multimedia Commun.,Oct.2002,pp.1309-1313.
[2]Tejas Bhatt;Vishwas Sundaramurthyl;Jianzhong Zhang and Dennis McCain;Initial Synchronization for 802.6e Downlink.Signals,Systems and Computers,2006.ACSSC '06.Fortieth Asilomar Conference on Oct.29 2006-Nov.1 2006 Page(s):701-706
[3]WiMAX Forum Mobile System Profile,WiMAX Forum,vl.2,Sep,2006.
[4]Yasamin Mostofi,Donald C.Cox,Mathematical Analysis of the Impact of Timing Synchronization Errors on the Performance of an OFDM System.IEEE Transaction on Communication,Vol.54,no.2,February 2006
[5]M.Speth,S.Fechtel,G.Fock,H.Meyr,Optimum receiver design for OFDM-based broadBand transmission.Ⅱ.A case study,IEEE Transaction.on Communication.,Vol.49,Issue.4,April 2001.
[6]Method,apparatus and computer program product providing synchronization for OFDMA downlink signal.United States Patent 20070280098.
[7]Symbol Synchronization at the BPSK-OFDM Receiver.2007 IEEE.
[8]Van de Beek J.Sandell M.,Isaksson M.,and Borjesson,ML Estimation of time and frequency offset in OFDM systems,IEEE Transaction on Signal Processing,Vol.45,pp.1800-1805,jul.1997.
[9]Matic D.;Petrochilos N.;Trindade A.;OFDM synchronisation based on the phase rotation of sub-carriers Vehicular Technology Conference Proceedings,2000.VTC 2000-Spring Tokyo.2000IEEE 51st,Page(s):1260-1264 Volume 2
[10]Timothy M.Schmidl;Cox,D.C.;Robust Frequency and Timing Synchronization for OFDM,IEEE Transaction on Communication,Volume 45,no.12,December 1997
[11]Tufvesson F;Edfors O;Faulkner M.;Time and Frequency synchronization for OFDM using PN-Sequence Preambles Proceedings of IEEE Vehicular Technology Conference,Amsterdam,The Betherlands,1999.19(22):2203-2207
[12]P.H.Moose,A technique for orthogonal frequency division multiplexing frequency offset correction,IEEE Transactions on Communications,vol.42,pp.2908-2914,October 1994.
[13]尹长川,罗涛,乐光新 多载波宽带无线通信技术,北京邮电大学出版社,2004.7
[14]Yang B,Letaief K,Cheng R,and Cao Z.Timing recovery for OFDM transimission,IEEE Journal on Selected Areas in Communication,Vol.18,pp.2278-2291,Nov.2000
[15]Morelli M.and Mengali U,An inproved frequency offset estimator for OFDM applications,IEEE Communication.Letter,Vol.3,pp.75-77,Mar.1999
[16]Cai L,Xu Y,Luo H,Song W,Zheng B,Cell search and Frequency Synchronization for Beyond 3G".IEEE 6~(th)CAC symp on Emerging Technologies:Mobile and Wireless Communicaton,Vol.1,pp.45-48,2004
[17]H-K,Song,Y.H.You,J.H.Paikand and Y.S.Cho,Frequency offset synchronization and channel estimation for OFDM-based transmission,IEEE Communication Letters,Mar 2000,pp 95-95
[18]Speth M.Frame Synchronization of OFDM systems in frequency selective fading channels
[19]Luise M and Reggiannini R.Carrier frequency acquisition and tracking for OFDM systems,IEEE Transaction on Communication,Nove 1996,44(11):1590-1598
[20]Keukjoon Bang,Namshin Cho,A Coarse Frequency Offset Estimation in an OFDM system Using the Concept of the Coherence Phase Bandwidth,IEEE Transaction on Communication Vol 49,No.8,Aug 2001
[21]佟学俭,罗涛,OFDM移动通信技术原理与应用,人民邮电出版社,2003.6
[22]王文博,郑侃“宽带无线通信OFDM技术”人民邮电出版社 2003年11月
[23]J.Heiskala,J.Terry,OFDM Wireless LANs:A Theoretical and Practical Guide,1 St edition,Sams,2001.
[24]J.-J.van de Beek,M.Sandell,M.Isaksson,and P.Borjesson,Low-Complex Frame Synchronization in OFDM Systems,in Proc.of ICUPC,pp.982-986,Nov 1995
[25]A.Reid,J.Son,Joint Synchronization using Semi-analytic Root likelihood Polynomials for OFDM Systems,submitted to IEEE Intl.Conf:on Acoustics,Speech and Signal Processing(ICASSP),Honolulu,Hawaii,April 2007
[26]L.J.Cimini,Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing,IEEE Trans.Commun.,vol.COM-33,no.7,pp.665-675,Jul.1985.
[27]T.M.Schmidl,Synchronization algorithms for wireless data transmission using orthogonal frequency division multiplexing(OFDM),Ph.D.dissertation,Stanford Univ.,Stanford,CA,1997.
[28]J.Van de Beek,M.Sandell,and M.Isaksson,Low-complex frame synchronization in OFDM systems,in Proc.4th IEEE Int.Conf.Universal Pets.Commun.,1995,pp.982-986.
[29]B.Yang,K.Letaief,and R.Cheng,Timing recovery for OFDM transmission,J.Sel.Areas Commun.,vol.18,no.11,pp.2278-2291,Nov.2000.
[30]M.Speth,F.Classen,and H.Meyr,Frame synchronization of OFDM systems in frequency selective fading channels,in Proc.47th IEEE Veh.Technol.Conf.,vol.3,1997,pp.1807-1811.
[31]Y.Mostofi,D.Cox,and A.Bahai,Effect of frame synchronization errorson pilot-aided channel estimation in OFDM:Analysis and solution,in Proc.5th Int.Symp.Wireless Pers.Multimedia Commun.,Oct.2002,pp.1309-1313.