基于OFDM技术的无线调制解调器的DSP算法实现研究
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摘要
本文对利用FM无线信道，采用编码正交频分复用（COFDM/FM）技术传送数据的调制解调器进行了分析研究，并完成了用数字信号处理器（DSP）实现的COFDM/FM调制解调器的系统方案。而TMS320C5402则作为目标数字信号处理核心，在TI公司的CCS2.0软件开发平台上完成调制解调器的主要功能和算法。
方案中，从数据文件中输入预定的原始二进制数据，这些数据经过RS编码、频域交织和格状编码调制，再经过星座映射形成了16QAM调制信号。合理安排数据的信道分配，其余点补零并进行串/并变换，然后加上循环前缀和保护间隔，这样多路16QAM副载波调制信号合成在一起形成了一帧COFDM频域信号。OFDM其产生和相关解调是通过快速傅立叶反变换与傅立叶变换（IFFT和FFT）实现的。接收端建议了一种新的同步算法。该同步算法是利用保护间隔所携带的信息完成符号定时同步和载波频率同步的最大似然估计算法，从而克服了利用导频符号导致带宽和功率资源的浪费的缺点。解调部分对应于TCM编码采用了Viterbi软判决译码，而后去交织，RS解码恢复原始的二进制数据，输出到数据文件中。上述为方案的大体流程，其中具体实现参数，比如交织深度、基准信号对应的信道的选取等一些参数要依具体应用而定，使系统性能达到最佳。
上述所有主要功能和算法均由软件编程实现，最终实现的是一种全数字可编程调制解调器，所以不用改动硬件就可以容易进行算法的升级改进，同时也便于移植。实验表明，用TMS320C5402配以少量的外围电路即可实现半双工的适用于现有FM标准信道的传信率不小于9600bit/s的无线用调制解调器。
This paper studies a new type of MODEM to transmit data over a mobile radio channel. It’s based on a new technology called COFDM, which means Coded Orthogonal Frequency Division Multiplexing. The whole system Of COFDM/FM MODEM is realized on digital signal processing (DSP). Concretely, TMS320C5402 is selected to be the core processor, and all the main functions and algorithms of the MODEM.is realized on the platform of CCS2.0,provided by TI company.
In the scheme, original binary data are received in the form of data files, then are treated by RS coding, interleaving in frequency field and the trellis coded modulation (TCM) to form the 16-QAM modulated signals.Then safeguard interval and cylic prefix are inserted to the modulated signals. Through careful arrangement of sub-channels for useful data and zero, a frame of COFDM signals is made up of many sub-channels with the form of 16-QAM. OFDM is realized by IFFT and coherent demodulation is by FFT. In the receiver, synchronization algorithm is based on safeguard interval and is completed by the algorithm of maximal likelihood (ML),which avoids the waste of bandwidth and power if pilots are used for synchronization. In demodulation part, the soft-decision Viterbi decoding algorithm is selected, so is deinterleaving and RS decoding. Some parameters such as the depth of interleaving and selection of sub-channels can be planned depending on the reality to achieve the optimization.
All the functions and algorithms are achieved by software, so it is an all-digital programmable MODEM. The experiments indicate that the half-duplexing MODEM suitable for the existing standard FM channel with about 9600b/s, can be achieved by a TMS320C5402 aided by few peripheral circuits.
方案中，从数据文件中输入预定的原始二进制数据，这些数据经过RS编码、频域交织和格状编码调制，再经过星座映射形成了16QAM调制信号。合理安排数据的信道分配，其余点补零并进行串/并变换，然后加上循环前缀和保护间隔，这样多路16QAM副载波调制信号合成在一起形成了一帧COFDM频域信号。OFDM其产生和相关解调是通过快速傅立叶反变换与傅立叶变换（IFFT和FFT）实现的。接收端建议了一种新的同步算法。该同步算法是利用保护间隔所携带的信息完成符号定时同步和载波频率同步的最大似然估计算法，从而克服了利用导频符号导致带宽和功率资源的浪费的缺点。解调部分对应于TCM编码采用了Viterbi软判决译码，而后去交织，RS解码恢复原始的二进制数据，输出到数据文件中。上述为方案的大体流程，其中具体实现参数，比如交织深度、基准信号对应的信道的选取等一些参数要依具体应用而定，使系统性能达到最佳。
上述所有主要功能和算法均由软件编程实现，最终实现的是一种全数字可编程调制解调器，所以不用改动硬件就可以容易进行算法的升级改进，同时也便于移植。实验表明，用TMS320C5402配以少量的外围电路即可实现半双工的适用于现有FM标准信道的传信率不小于9600bit/s的无线用调制解调器。
This paper studies a new type of MODEM to transmit data over a mobile radio channel. It’s based on a new technology called COFDM, which means Coded Orthogonal Frequency Division Multiplexing. The whole system Of COFDM/FM MODEM is realized on digital signal processing (DSP). Concretely, TMS320C5402 is selected to be the core processor, and all the main functions and algorithms of the MODEM.is realized on the platform of CCS2.0,provided by TI company.
In the scheme, original binary data are received in the form of data files, then are treated by RS coding, interleaving in frequency field and the trellis coded modulation (TCM) to form the 16-QAM modulated signals.Then safeguard interval and cylic prefix are inserted to the modulated signals. Through careful arrangement of sub-channels for useful data and zero, a frame of COFDM signals is made up of many sub-channels with the form of 16-QAM. OFDM is realized by IFFT and coherent demodulation is by FFT. In the receiver, synchronization algorithm is based on safeguard interval and is completed by the algorithm of maximal likelihood (ML),which avoids the waste of bandwidth and power if pilots are used for synchronization. In demodulation part, the soft-decision Viterbi decoding algorithm is selected, so is deinterleaving and RS decoding. Some parameters such as the depth of interleaving and selection of sub-channels can be planned depending on the reality to achieve the optimization.
All the functions and algorithms are achieved by software, so it is an all-digital programmable MODEM. The experiments indicate that the half-duplexing MODEM suitable for the existing standard FM channel with about 9600b/s, can be achieved by a TMS320C5402 aided by few peripheral circuits.
引文
【 1 】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
【 2 】Hirosaki B,”An orthogonally multiplexed QAM system using the discrete Fourier transform”,IEEE Trans.Comm,Vol.COM-29,July,1981
【 3 】Hirosaki B,”A 19.2kbit/s voiceband data modem based on orthogonally multiplexed QAM techniques”,IEEE Trans.Comm.Vol COM-29 July 1981
【 4 】L.J Cimini,”Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing”,IEEE Trans.Comm.Vol COM-33 July 1985
【 5 】E.F.Casas and C.Leung,”OFDM for data communication over mobile radio FM channels-part 1:analysis and experimental results”,IEEE Trans.Comm.Vol COM-39 May.1991
【 6 】J.Proakis,”Digital Communications”,Prentice-Hall,3rd edition,1995.
【 7 】G.Ungerboeck,”Channel coding with multilevel/phase signals”,IEEE Trans.Infomation theory..Vol.IT-28,No.1,Jan 1982
【 8 】P.M.Petrovic,”Digitized speed transmission at VHF Using existing FM mobile radios”,IEEE Trans. Vehicu,vol.VT-31,No.2 May 1982
【 9 】 Rohit Negi and John Cioffi，“Pilot tone selection for channel estimation in a mobile OFDM system”，IEEE Transactions on Consumer Electronics，Vol．44，No.3，August 1998
【 10 】郑晨光 “基于DSP的COFDM/FM无线信道调制解调器的实现研究”，天津大学硕士学位论文,2000年1月
【 11 】Warner and Cyril，“OFDM/FM frame synchronization for mobile radio data communication”，IEEE Trans . Vehicu，vol．VT- 42，No.3，August 1993
【 12 】 William Y.Zou and Yiyan Wu，“COFDM：An overview”，IEEE Trans . Broadcasting,vol . 41, No.1,March 1995
【 13 】 G.Ungerboeck，“Channel Coding with multilevel/phase signals”，IEEE Transactions on Information Theory，Vol．IT-28，No.1，January 1982
【 14 】William Y.Zou and Yiyan Wu，“Orthogonal frequency division multiplexing: A multi-carrier modulation scheme”， IEEE Transactions on Consumer Electronics，Vol.41，No.3，August 1995
【 15 】王匡,姚庆栋,秦二龙 “正交频分复用技术的应用”，广播与电视技术，1995年第12期(Vol.22 No.12)
【 16 】张兆杨,高磊 “COFDM原理及在数字电视传输中的应用”，电视技术，1995年第10期
【 17 】潘武,刘序明,许希斌,姚彦 “正交频分复用技术在宽带通信中的应用”,移动通信技术,1997年第3期
【 18 】Donghoon Lee and Kyungwhoon Cheun，“A new symbol timing recovery algorithm for OFDM system”， IEEE Transactions on Consumer Electronics，Vol.43，No.3，August 1997
【 19 】Dong-Kyu Kim ,Sang-Hyun Do, Hyun-Kyu Lee，“Performance evaluation of the frequency detectors for orthogonal frequency division multiplexing”， IEEE Transactions on Consumer Electronics，Vol.43，No.3，August 1997
【 20 】宋爱平 “利用模拟调频电台传输高速数据和数字话”,电子技术应用,1986.11-12
【 21 】王重玮,陈健 “数据通信用调制解调器中的DSP技术”,电子技术,1998年第3期
【 22 】原进红,匡镜明 “时间色散信道中格形编码的正交频分复用(TC-OFDM)技术”,通信学报,1998年2月第19卷第2期
【 23 】Masafurni Ragiwara and Masao Nakagawa，“DSP type novel phase synchronizer with the method of least squares”， IEEE Transactions on Consumer Electronics，Vol.35，No.4，November 1989
【 24 】G.Ungerboeck，“Trellis coded modulation with redundant sets - PartⅠ: Introduction and Part Ⅱ:State of Art”，IEEE Communication．Mag，1987，25(2) :5～21
【 25 】李光球,梁慧君,姚庆栋 “格状编码调制”，广播与电视技术,1995年第8期(Vol.22 No.8)
【 26 】王匡,姚庆栋 “格状编码调制的维特比译码算法” ,广播与电视技术, 1996年第1期(Vol.23 No.1)
【 27 】Viterbi A.J.,“ Error Bounds for Convolutional Codes and an Asymp-
totically Optimum Decoding Algorithm”, IEEE Trans.Inform.Theory, Vol.IT-13, 1967:260～269
【 28 】周军,韩晓莉 “Viterbi译码及其DSP算法研究”,通信与广播电视,1999年第2期
【 29 】Texas Instruments Inc.《Viterbi Decoding Techniques in the
TMS320C54X Family》
【 30 】Texas Instruments Inc.《TMS320C54X User’s Guide》
【 31 】Magnus Sandell et al,”On Syncronization in OFDM Systems Using the Cyclic Prefix”,Div. Of Signal Processing, Lulea University of Technology,Sweden
【 32 】 Magnus Sandell et al, “ML Estimation of Timing and Frequency Offset in Multicarrier Systems”,Research report, Div. Of Signal Processing, Lulea University of Technology, Sweden
【 33 】樊昌信等, 《通信原理》,国防工业出版社,1988
【 34 】丁玉美,高西全,彭学愚, 《数字信号处理》, 西安电子科技大学出版社, 1995
【 35 】徐平平，宋铁成，叶芝慧等译《数字通信－基础与应用》第二版，电子工业出版社，2002.9
【 2 】Hirosaki B,”An orthogonally multiplexed QAM system using the discrete Fourier transform”,IEEE Trans.Comm,Vol.COM-29,July,1981
【 3 】Hirosaki B,”A 19.2kbit/s voiceband data modem based on orthogonally multiplexed QAM techniques”,IEEE Trans.Comm.Vol COM-29 July 1981
【 4 】L.J Cimini,”Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing”,IEEE Trans.Comm.Vol COM-33 July 1985
【 5 】E.F.Casas and C.Leung,”OFDM for data communication over mobile radio FM channels-part 1:analysis and experimental results”,IEEE Trans.Comm.Vol COM-39 May.1991
【 6 】J.Proakis,”Digital Communications”,Prentice-Hall,3rd edition,1995.
【 7 】G.Ungerboeck,”Channel coding with multilevel/phase signals”,IEEE Trans.Infomation theory..Vol.IT-28,No.1,Jan 1982
【 8 】P.M.Petrovic,”Digitized speed transmission at VHF Using existing FM mobile radios”,IEEE Trans. Vehicu,vol.VT-31,No.2 May 1982
【 9 】 Rohit Negi and John Cioffi，“Pilot tone selection for channel estimation in a mobile OFDM system”，IEEE Transactions on Consumer Electronics，Vol．44，No.3，August 1998
【 10 】郑晨光 “基于DSP的COFDM/FM无线信道调制解调器的实现研究”，天津大学硕士学位论文,2000年1月
【 11 】Warner and Cyril，“OFDM/FM frame synchronization for mobile radio data communication”，IEEE Trans . Vehicu，vol．VT- 42，No.3，August 1993
【 12 】 William Y.Zou and Yiyan Wu，“COFDM：An overview”，IEEE Trans . Broadcasting,vol . 41, No.1,March 1995
【 13 】 G.Ungerboeck，“Channel Coding with multilevel/phase signals”，IEEE Transactions on Information Theory，Vol．IT-28，No.1，January 1982
【 14 】William Y.Zou and Yiyan Wu，“Orthogonal frequency division multiplexing: A multi-carrier modulation scheme”， IEEE Transactions on Consumer Electronics，Vol.41，No.3，August 1995
【 15 】王匡,姚庆栋,秦二龙 “正交频分复用技术的应用”，广播与电视技术，1995年第12期(Vol.22 No.12)
【 16 】张兆杨,高磊 “COFDM原理及在数字电视传输中的应用”，电视技术，1995年第10期
【 17 】潘武,刘序明,许希斌,姚彦 “正交频分复用技术在宽带通信中的应用”,移动通信技术,1997年第3期
【 18 】Donghoon Lee and Kyungwhoon Cheun，“A new symbol timing recovery algorithm for OFDM system”， IEEE Transactions on Consumer Electronics，Vol.43，No.3，August 1997
【 19 】Dong-Kyu Kim ,Sang-Hyun Do, Hyun-Kyu Lee，“Performance evaluation of the frequency detectors for orthogonal frequency division multiplexing”， IEEE Transactions on Consumer Electronics，Vol.43，No.3，August 1997
【 20 】宋爱平 “利用模拟调频电台传输高速数据和数字话”,电子技术应用,1986.11-12
【 21 】王重玮,陈健 “数据通信用调制解调器中的DSP技术”,电子技术,1998年第3期
【 22 】原进红,匡镜明 “时间色散信道中格形编码的正交频分复用(TC-OFDM)技术”,通信学报,1998年2月第19卷第2期
【 23 】Masafurni Ragiwara and Masao Nakagawa，“DSP type novel phase synchronizer with the method of least squares”， IEEE Transactions on Consumer Electronics，Vol.35，No.4，November 1989
【 24 】G.Ungerboeck，“Trellis coded modulation with redundant sets - PartⅠ: Introduction and Part Ⅱ:State of Art”，IEEE Communication．Mag，1987，25(2) :5～21
【 25 】李光球,梁慧君,姚庆栋 “格状编码调制”，广播与电视技术,1995年第8期(Vol.22 No.8)
【 26 】王匡,姚庆栋 “格状编码调制的维特比译码算法” ,广播与电视技术, 1996年第1期(Vol.23 No.1)
【 27 】Viterbi A.J.,“ Error Bounds for Convolutional Codes and an Asymp-
totically Optimum Decoding Algorithm”, IEEE Trans.Inform.Theory, Vol.IT-13, 1967:260～269
【 28 】周军,韩晓莉 “Viterbi译码及其DSP算法研究”,通信与广播电视,1999年第2期
【 29 】Texas Instruments Inc.《Viterbi Decoding Techniques in the
TMS320C54X Family》
【 30 】Texas Instruments Inc.《TMS320C54X User’s Guide》
【 31 】Magnus Sandell et al,”On Syncronization in OFDM Systems Using the Cyclic Prefix”,Div. Of Signal Processing, Lulea University of Technology,Sweden
【 32 】 Magnus Sandell et al, “ML Estimation of Timing and Frequency Offset in Multicarrier Systems”,Research report, Div. Of Signal Processing, Lulea University of Technology, Sweden
【 33 】樊昌信等, 《通信原理》,国防工业出版社,1988
【 34 】丁玉美,高西全,彭学愚, 《数字信号处理》, 西安电子科技大学出版社, 1995
【 35 】徐平平，宋铁成，叶芝慧等译《数字通信－基础与应用》第二版，电子工业出版社，2002.9