CMMB系统物理层算法研究
摘要
在众多应用领域中,手机电视是一个广受关注且正处于快速发展阶段的行业,手机电视也将以其小型化、便携性以及丰富的媒体内容而获得人们的认可和青睐。手机电视标准中比较成熟的有由广电总局推出的CMMB标准,其已经成为手机电视的行业标准。本文主要研究CMMB物理层主要模块的算法。
本文首先讨论CMMB发射机物理层过程的各个模块；并分析无线移动广播信道特点,指出信道频率选择性衰落和快衰落对无线接收信号的影响,并总结几种适用于手机电视的无线广播信道模型。
本文针对CMMB中高度结构化的LDPC码,首先推导基于LU分解的快速LDPC码编码算法,并提出基于最小列权重和行权重乘积的稀疏矩阵LU分解算法。在考虑CMMB接收终端电池电量和运算速度受限的前提下,提出适用于手机终端的LDPC码译码算法。
本文提出针对CMMB帧结构的帧同步算法和频率同步算法。提出的基于预处理方式的帧同步算法利用CMMB帧结构中的两个相同的频域伪随机序列来获得帧同步,能在低信噪比和高频偏情况下正常工作。提出的频率同步算法包括基于训练序列的时域小数倍频偏粗估计算法、基于训练序列的频域滑动相关整数倍频偏估计算法和基于连续导频的频域小数倍频偏细估计算法。
本文提出适用于CMMB接收终端的信道估计方案。考虑到手机终端电量和运算能力有限,本文在导频子载波处的信道响应通过LS算法估计,在数据子载波处的信道响应通过DFT内插得到。本文还对CMMB中导频分布不均匀的问题给出解决方案。
Mobile television is one of the modern technological trends expected to rev-olutionize conventional provisioning of broadcast services, and represents an emerging hotbed for multimedia applications because it brings traditional televi-sion services and on-demand audiovisual content to mobile devices. Among var-ious mobile television technologies is China Mobile Multimedia Broadcasting (CMMB), a mature industrial standard developed by the CMMB work group, an organization initiated by China's State Administration of Radio, Film, and Tele-vision. This thesis mainly studies efficient physical layer algorithms for CMMB.
The thesis first discusses main modules of CMMB physical layer, analyzes characteristics of wireless mobile radio channels, and exploits the effects that frequency-selective fading or fast fading channels could exert on wireless sig-nals. Also several wireless channel models suitable for the CMMB are summa-rized. The transform process for encoding highly structured LDPC in CMMB based on rapid LU decomposition is derived and the strategy of min-col-prod LU decomposition of sparse matrix is given. Considering the CMMB receiv-ing terminals'constrained capacity of energy and capability to calculate, a low complexity LDPC decoding algorithm is put forward. Frame synchronization and frequency synchronization algorithms taking advantage of the two identi-cal frequency-domain pseudo-random sequences in the frame structure are pro-posed. The algorithms can function reliably under the condition of both low SNR and high frequency offset. Once again, taking into account that the mobile terminal power consumption and computing power is limited, specific channel estimation algorithm is developed. Channel responses at pilot sub-carriers are es-timated through the method of LS and channel responses at the data sub-carriers are obtained through DFT interpolation. The thesis also addresses the uneven distribution of pilot sub-carriers in an OFDM symbol.
本文首先讨论CMMB发射机物理层过程的各个模块；并分析无线移动广播信道特点,指出信道频率选择性衰落和快衰落对无线接收信号的影响,并总结几种适用于手机电视的无线广播信道模型。
本文针对CMMB中高度结构化的LDPC码,首先推导基于LU分解的快速LDPC码编码算法,并提出基于最小列权重和行权重乘积的稀疏矩阵LU分解算法。在考虑CMMB接收终端电池电量和运算速度受限的前提下,提出适用于手机终端的LDPC码译码算法。
本文提出针对CMMB帧结构的帧同步算法和频率同步算法。提出的基于预处理方式的帧同步算法利用CMMB帧结构中的两个相同的频域伪随机序列来获得帧同步,能在低信噪比和高频偏情况下正常工作。提出的频率同步算法包括基于训练序列的时域小数倍频偏粗估计算法、基于训练序列的频域滑动相关整数倍频偏估计算法和基于连续导频的频域小数倍频偏细估计算法。
本文提出适用于CMMB接收终端的信道估计方案。考虑到手机终端电量和运算能力有限,本文在导频子载波处的信道响应通过LS算法估计,在数据子载波处的信道响应通过DFT内插得到。本文还对CMMB中导频分布不均匀的问题给出解决方案。
Mobile television is one of the modern technological trends expected to rev-olutionize conventional provisioning of broadcast services, and represents an emerging hotbed for multimedia applications because it brings traditional televi-sion services and on-demand audiovisual content to mobile devices. Among var-ious mobile television technologies is China Mobile Multimedia Broadcasting (CMMB), a mature industrial standard developed by the CMMB work group, an organization initiated by China's State Administration of Radio, Film, and Tele-vision. This thesis mainly studies efficient physical layer algorithms for CMMB.
The thesis first discusses main modules of CMMB physical layer, analyzes characteristics of wireless mobile radio channels, and exploits the effects that frequency-selective fading or fast fading channels could exert on wireless sig-nals. Also several wireless channel models suitable for the CMMB are summa-rized. The transform process for encoding highly structured LDPC in CMMB based on rapid LU decomposition is derived and the strategy of min-col-prod LU decomposition of sparse matrix is given. Considering the CMMB receiv-ing terminals'constrained capacity of energy and capability to calculate, a low complexity LDPC decoding algorithm is put forward. Frame synchronization and frequency synchronization algorithms taking advantage of the two identi-cal frequency-domain pseudo-random sequences in the frame structure are pro-posed. The algorithms can function reliably under the condition of both low SNR and high frequency offset. Once again, taking into account that the mobile terminal power consumption and computing power is limited, specific channel estimation algorithm is developed. Channel responses at pilot sub-carriers are es-timated through the method of LS and channel responses at the data sub-carriers are obtained through DFT interpolation. The thesis also addresses the uneven distribution of pilot sub-carriers in an OFDM symbol.
引文
[1]张豪.对CMMB用户市场的初步研究[J].电视技术,2009(001)：56-57.
[2]汪云.CMMB商业运营一触即发[J].中国数字电视,2009(001)：43-43.
[3]Zhou J, Ou Z, Rautiainen M, et al. Digital Television for Mobile Devices [J]. IEEE MultiMedia,2009, 16(1):60-71.
[4]CMMB研究工作组.CMMB100问[M].北京：国家广播电影电视总局,2008.
[5]杨海生.对CMMB重新认识[J].中国数字电视,2009(1)：52-53.
[61 CMMB研究工作组.GY／T 220.1—2006.移动多媒体广播第1部分：广播信道帧结构、信道编码和调制[S].北京：国家广播电影电视总局,2005.
[7]Haykin S, Moher M. Modern wireless communication [M]. Prentice Hall,2004.
[8]Rappaport T. Wireless communications:principles and practice [M]. Prentice Hall PTR Upper Saddle River, NJ, USA,2001.
[9]Proakis J, Salehi M. Digital communications [M]. McGraw-Hill New York,1995.
[10]Jakes W, Cox D. Microwave mobile communications [M]. Wiley-IEEE Press,1994.
[11]Ross S. Introduction to probability models [M]. Academic Pr,2006.
[12]彭曦.基于CMMB的信道估计算法研究[学位论文].杭州市：浙江大学,2008.
[13]Gallager R. Low-density parity-check codes [J]. Information Theory, IRE Transactions on,1962,8 (1):21-28.
[14]Chung S, Forney Jr G, Richardson T, et al. On the design of low-density parity-check codes within 0.0045 dB ofthe Shannon limit [J]. IEEE Communications letters,2001,5 (2):58-60.
[15]Neal R. Sparse matrix methods and probabilistic inference algorithms [J]. IMA program on codes, systems and graphical models,1999.
[16]邓建民.低密度码编译码技术的研究[学位论文].北京市：北京邮电大学,2003.
[17]王彬.结构化LDPC码的构造及在CMMB中的应用研究[学位论文].南京市：南京航空航天大学,2007.
[18]Tanner R. A recursive approach to low complexity codes [J]. IEEE Transactions on Information The-ory,1981,27 (5):533-547.
[19]Chen J, Dholakia A, Eleftheriou E, et al. Reduced-complexity decoding of LDPC codes [J]. IEEE Transactions on Communications,2005,53 (8):1288.
[20]Richardson T, Urbanke R. The capacity of low-density parity-check codes under message-passing decoding [J]. IEEE Transactions on Information Theory,2001,47 (2):599-618.
[21]Schmidl T, Cox D. Robust frequency and timing synchronization for OFDM [J]. IEEE Transactions on Communications,1997,45 (12):1613-1621.
[22]刘喆.基于CMMB系统的帧同步与符号同步技术的研究[学位论文].上海市：上海交通大学,2008.
[23]Classen F, Meyr H. Frequency Synchronization Algorithms for OFDM Systems suitable for Com-munication over Frequency Selective Fading Channels [C]. In:Anon. Vehicular technology:44th Conference:Papers,1994:1655.
[24]Moose P. A technique for orthogonal frequency division multiplexingfrequency offset correction [J]. IEEE Transactions on Communications,1994,42 (10):2908-2914.
[25]van de Beek J, Sandell M, Borjesson P. ML estimation of time and frequency offset in OFDM systems [J]. IEEE Transactions on Signal Processing,1997,45 (7):1800-1805.
[26]Nogami H, NAGASHIMA T. A frequency and timing period acquisition technique for OFDM systems [J]. IEICE Transactions on Communications,1996,79 (8):1135-1146.
[27]Edfors O, Sandell M, van de Beek J, et al. OFDM channel estimation by singular value decomposition [J]. IEEE Transactions on Communications,1998,46 (7):931-939.
[28]宋伯炜.OFDM无线宽带移动通信系统中信道估计与均衡技术研究[学位论文].上海市：上海交通大学,2005.
[29]Van de Beek J, Edfors O, Sandell M, et al. On channel estimation in OFDM systems [C]. In:Anon. IEEE Vehicular Technology Conference,1995:815-815.
[30]Yang B, Cao Z, Letaief K, et al. Analysis of low-complexity windowed DFT-based MMSE channel estimator for OFDM systems [J]. IEEE Transactions on Communications,2001,49 (11):1977-1987.
[31]Gardner F, Co G, Alto P. Interpolation in digital modems. Ⅰ. Fundamentals [J]. IEEE Transactions on Communications,1993,41 (3):501-507.
[32]Gardner F. Interpolation in Digital Modems-Part Ⅱ:Implementation and Performance [J]. IEEE Transactions on communications,1993,41 (6):998-1008.
[33]Akram M. Pilot-based Channel Estimation in OFDM Systems [Dissertation]. Denmark:Technical University of Denmark,2007.
[34]Haykin S. Adaptive filter theory [M]. Prentice hall,2002.
[35]Hoeher P, Kaiser S, Robertson P, et al. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering [C]. In:Anon. IEEE International Conference On Acoustics Speech and Signal Pro-cessing,1997:1845-1848.
[36]Morelli M, Mengali U. A comparison of pilot-aided channel estimation methods for OFDMsystems [J]. IEEE Transactions on signal processing,2001,49 (12):3065-3073.
[37]唐恬.正交频分复用系统的信道估计研究[学位论文].北京市：北京邮电大学,2007.
[38]Edfors O, Sandell M, Van De Beek J, et al. Analysis of DFT-based channel estimators for OFDM [J]. Wireless Personal Communications,2000,12 (1):55-70.
[2]汪云.CMMB商业运营一触即发[J].中国数字电视,2009(001)：43-43.
[3]Zhou J, Ou Z, Rautiainen M, et al. Digital Television for Mobile Devices [J]. IEEE MultiMedia,2009, 16(1):60-71.
[4]CMMB研究工作组.CMMB100问[M].北京：国家广播电影电视总局,2008.
[5]杨海生.对CMMB重新认识[J].中国数字电视,2009(1)：52-53.
[61 CMMB研究工作组.GY／T 220.1—2006.移动多媒体广播第1部分：广播信道帧结构、信道编码和调制[S].北京：国家广播电影电视总局,2005.
[7]Haykin S, Moher M. Modern wireless communication [M]. Prentice Hall,2004.
[8]Rappaport T. Wireless communications:principles and practice [M]. Prentice Hall PTR Upper Saddle River, NJ, USA,2001.
[9]Proakis J, Salehi M. Digital communications [M]. McGraw-Hill New York,1995.
[10]Jakes W, Cox D. Microwave mobile communications [M]. Wiley-IEEE Press,1994.
[11]Ross S. Introduction to probability models [M]. Academic Pr,2006.
[12]彭曦.基于CMMB的信道估计算法研究[学位论文].杭州市：浙江大学,2008.
[13]Gallager R. Low-density parity-check codes [J]. Information Theory, IRE Transactions on,1962,8 (1):21-28.
[14]Chung S, Forney Jr G, Richardson T, et al. On the design of low-density parity-check codes within 0.0045 dB ofthe Shannon limit [J]. IEEE Communications letters,2001,5 (2):58-60.
[15]Neal R. Sparse matrix methods and probabilistic inference algorithms [J]. IMA program on codes, systems and graphical models,1999.
[16]邓建民.低密度码编译码技术的研究[学位论文].北京市：北京邮电大学,2003.
[17]王彬.结构化LDPC码的构造及在CMMB中的应用研究[学位论文].南京市：南京航空航天大学,2007.
[18]Tanner R. A recursive approach to low complexity codes [J]. IEEE Transactions on Information The-ory,1981,27 (5):533-547.
[19]Chen J, Dholakia A, Eleftheriou E, et al. Reduced-complexity decoding of LDPC codes [J]. IEEE Transactions on Communications,2005,53 (8):1288.
[20]Richardson T, Urbanke R. The capacity of low-density parity-check codes under message-passing decoding [J]. IEEE Transactions on Information Theory,2001,47 (2):599-618.
[21]Schmidl T, Cox D. Robust frequency and timing synchronization for OFDM [J]. IEEE Transactions on Communications,1997,45 (12):1613-1621.
[22]刘喆.基于CMMB系统的帧同步与符号同步技术的研究[学位论文].上海市：上海交通大学,2008.
[23]Classen F, Meyr H. Frequency Synchronization Algorithms for OFDM Systems suitable for Com-munication over Frequency Selective Fading Channels [C]. In:Anon. Vehicular technology:44th Conference:Papers,1994:1655.
[24]Moose P. A technique for orthogonal frequency division multiplexingfrequency offset correction [J]. IEEE Transactions on Communications,1994,42 (10):2908-2914.
[25]van de Beek J, Sandell M, Borjesson P. ML estimation of time and frequency offset in OFDM systems [J]. IEEE Transactions on Signal Processing,1997,45 (7):1800-1805.
[26]Nogami H, NAGASHIMA T. A frequency and timing period acquisition technique for OFDM systems [J]. IEICE Transactions on Communications,1996,79 (8):1135-1146.
[27]Edfors O, Sandell M, van de Beek J, et al. OFDM channel estimation by singular value decomposition [J]. IEEE Transactions on Communications,1998,46 (7):931-939.
[28]宋伯炜.OFDM无线宽带移动通信系统中信道估计与均衡技术研究[学位论文].上海市：上海交通大学,2005.
[29]Van de Beek J, Edfors O, Sandell M, et al. On channel estimation in OFDM systems [C]. In:Anon. IEEE Vehicular Technology Conference,1995:815-815.
[30]Yang B, Cao Z, Letaief K, et al. Analysis of low-complexity windowed DFT-based MMSE channel estimator for OFDM systems [J]. IEEE Transactions on Communications,2001,49 (11):1977-1987.
[31]Gardner F, Co G, Alto P. Interpolation in digital modems. Ⅰ. Fundamentals [J]. IEEE Transactions on Communications,1993,41 (3):501-507.
[32]Gardner F. Interpolation in Digital Modems-Part Ⅱ:Implementation and Performance [J]. IEEE Transactions on communications,1993,41 (6):998-1008.
[33]Akram M. Pilot-based Channel Estimation in OFDM Systems [Dissertation]. Denmark:Technical University of Denmark,2007.
[34]Haykin S. Adaptive filter theory [M]. Prentice hall,2002.
[35]Hoeher P, Kaiser S, Robertson P, et al. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering [C]. In:Anon. IEEE International Conference On Acoustics Speech and Signal Pro-cessing,1997:1845-1848.
[36]Morelli M, Mengali U. A comparison of pilot-aided channel estimation methods for OFDMsystems [J]. IEEE Transactions on signal processing,2001,49 (12):3065-3073.
[37]唐恬.正交频分复用系统的信道估计研究[学位论文].北京市：北京邮电大学,2007.
[38]Edfors O, Sandell M, Van De Beek J, et al. Analysis of DFT-based channel estimators for OFDM [J]. Wireless Personal Communications,2000,12 (1):55-70.