OFDM系统调制解调的理论研究与硬件实现
摘要
未来宽带无线通信为了实现宽带、随时随地以任何方式进行信息交流的目标,要求具有高质量、高可靠性、高传输速率的移动通信技术。正交频分复用(OFDM)多载波调制解调系统,具有抗多径干扰能力强,频谱利用率高,可以与MIMO技术、不同的多址接入方式相结合,可使信道容量到达最优,所以基于OFDM的多载波调制解调系统越来越得到广泛的应用。
本文首先讨论了无线通信信道相关特性及OFDM的基本理论知识。衰落,多径及多普勒频移这些特性使无线信道变得复杂,文中对此进行了分析。然后对OFDM系统的基本原理以及各组成部分功能进行了讨论,并对OFDM的时域波形及频域波形进行了Matlab仿真,最后给出一个OFDM系统的基本实现框图。
其次,本文对OFDM系统涉及到的关键技术进行了详细的分析论述,具体讨论了OFDM系统同步问题,信道估计和如何减小峰均比的问题。主要介绍和分析了国内外在这些方面的很多研究成果,并针对每一个问题给出了相应的多种解决方案。
最后,本文讨论了OFDM系统电路设计和硬件实现方案。在OFDM系统设计部分,详尽分析了选用器件的原则与器件基本特性,讨论了电路实现上的一系列问题,给出基于OFDM技术的无线传输系统的基本结构,并根据系统的应用环境以及实际的需求确定了该OFDM系统的参数指标及帧结构。介绍了发送端和接收端系统结构后,讨论了OFDM系统硬件实现所涉及到的关键算法,给出综合图及VHDL仿真结果,最后给出了整个系统的实现,并对整个系统的性能进行分析。
全文详细论述了OFDM系统从基本概念到实际电路设计所遇到的相关概念和问题。
In order to obtain the goal of communicating information by broadband with any manner, in any place and at any moment, the future wireless communication requires the characteristics of high quality, high reliability and high transmitting rate. OFDM system is a very promising technology since it has many advantages, such as its high-efficient spectrum and ICI interference avoidance. It can also easily connect with MIMO and access technologies like FDMA, TDMA, and CDMA. Because different subcarriers can adopt different coding and modulation methods, the capacity of the channel is able to reach the optimum value.
Firstly, the paper discusses characters of the wireless channel and the basic theoretics of OFDM. Multi-path fading, Doppler frequency excursion make the wireless channel complex. They are going to be analyzed in this paper. Then the paper analyzes the basic theoretics of OFDM and the function of every module in OFDM system, and simulates the wave and spectrum of OFDM signal with MATLAB software. At last, the block diagram of OFDM system is put forward.
In the following chapters, the paper discuses the key technologies of OFDM system. The key technologies are the synchronization, channel estimation, and PAPR problems. This paper mainly introduces and analyzes the domestic and overseas researches and gives some methods to resolve every problem.
Finally, the paper designs the hardware structure of OFDM system. In the design of OFDM system part, the paper presents rules to choose the appropriate chips and the specialitis of them, then discusses the existed problems. The frame of OFDM system is designed according to application system requirements. After considering the sender and receiver parts, the paper gives the key algorithms of the hardware design, and gives the RTL synthesized figure and timing simulative figure. At last, this paper discusses the hardware structure of this system, and analyzes the performance of it.
The paper discusses OFDM system in detail, and introduces problems that may be encountered when implementing the system.
本文首先讨论了无线通信信道相关特性及OFDM的基本理论知识。衰落,多径及多普勒频移这些特性使无线信道变得复杂,文中对此进行了分析。然后对OFDM系统的基本原理以及各组成部分功能进行了讨论,并对OFDM的时域波形及频域波形进行了Matlab仿真,最后给出一个OFDM系统的基本实现框图。
其次,本文对OFDM系统涉及到的关键技术进行了详细的分析论述,具体讨论了OFDM系统同步问题,信道估计和如何减小峰均比的问题。主要介绍和分析了国内外在这些方面的很多研究成果,并针对每一个问题给出了相应的多种解决方案。
最后,本文讨论了OFDM系统电路设计和硬件实现方案。在OFDM系统设计部分,详尽分析了选用器件的原则与器件基本特性,讨论了电路实现上的一系列问题,给出基于OFDM技术的无线传输系统的基本结构,并根据系统的应用环境以及实际的需求确定了该OFDM系统的参数指标及帧结构。介绍了发送端和接收端系统结构后,讨论了OFDM系统硬件实现所涉及到的关键算法,给出综合图及VHDL仿真结果,最后给出了整个系统的实现,并对整个系统的性能进行分析。
全文详细论述了OFDM系统从基本概念到实际电路设计所遇到的相关概念和问题。
In order to obtain the goal of communicating information by broadband with any manner, in any place and at any moment, the future wireless communication requires the characteristics of high quality, high reliability and high transmitting rate. OFDM system is a very promising technology since it has many advantages, such as its high-efficient spectrum and ICI interference avoidance. It can also easily connect with MIMO and access technologies like FDMA, TDMA, and CDMA. Because different subcarriers can adopt different coding and modulation methods, the capacity of the channel is able to reach the optimum value.
Firstly, the paper discusses characters of the wireless channel and the basic theoretics of OFDM. Multi-path fading, Doppler frequency excursion make the wireless channel complex. They are going to be analyzed in this paper. Then the paper analyzes the basic theoretics of OFDM and the function of every module in OFDM system, and simulates the wave and spectrum of OFDM signal with MATLAB software. At last, the block diagram of OFDM system is put forward.
In the following chapters, the paper discuses the key technologies of OFDM system. The key technologies are the synchronization, channel estimation, and PAPR problems. This paper mainly introduces and analyzes the domestic and overseas researches and gives some methods to resolve every problem.
Finally, the paper designs the hardware structure of OFDM system. In the design of OFDM system part, the paper presents rules to choose the appropriate chips and the specialitis of them, then discusses the existed problems. The frame of OFDM system is designed according to application system requirements. After considering the sender and receiver parts, the paper gives the key algorithms of the hardware design, and gives the RTL synthesized figure and timing simulative figure. At last, this paper discusses the hardware structure of this system, and analyzes the performance of it.
The paper discusses OFDM system in detail, and introduces problems that may be encountered when implementing the system.
引文
1 ETSI-European Telecommunications Standards Institute. Radio broadcasting systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receiver. Valbonne, France, 1995: 1~14
2 EN 300 744. Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television. Valbonne, France, 1997: 1~201
3 U. Reimers. Digital video broadcasting. IEEE Commun Mag. 1998: 104~110
4 T. Pollet, M. V. Sladel, M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise. IEEE Trans. Commun. . 1995, (43), pp.191~193
5 Peter Hoeher. A Statistical Discrete-Time Model for the WSSUS Multipath Channel. IEEE Transactions on Vehicular Technology. 1992, 41(4): 461~468
6王文博,郑侃.宽带无线通信OFDM技术.人民邮电出版社. 2003, 11(1): 7~21
7徐志军,徐光辉. CPLD/FPGA的开发与应用.电子工业出版. 2002: 12~16
8张乃通,徐玉滨等.移动通信系统.哈尔滨工业大学出版社, 2001: 1~150
9佟学俭. OFDM移动通信技术原理与应用.人民邮电出版社. 2000: 1~200
10 J. J. van de Beek, M. Sandell, and P. O. Borjesson. ML Estimation of Time and Frequency Offset in OFDM Systems. IEEE Trans. On Signal Processing. 1997, (45): 1800~1805
11 Timothy M. Schmidl and D. C. Cox. Robust Frequency and Timing Synchronization for OFDM. IEEE Trans. on Commun.. 1997, (45): 1613~1621
12 M. Morelli and U. Mengali. An improved frequency offset estimator for OFDM applications. IEEE Communications Letters. 1999, (3): 75~77
13 Y. H. Kim, I. Song, S. Yoon, and S. R. Park. An efficient frequency offset estimator for OFDM systems and its performance characteristics. IEEE Transactions on Vehicular Technology. 2001, (50): 1307~1312
14 H. Minn, V. K. Bhargava, and K.Ben Letaief. A robust timing and frequency synchronization for OFDM systems. IEEE Transactions on Wireless Comruunications. 2003, (2): 822~839
15 Y Li. Pilot-symbol-aided channel estimation for OFDM in wireless systems. IEEE Transactions on Vehicle Technology. 2000, 49(4): 1207~1215
16 P Hoeher, S Kaiser, I Robertson. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering[A]. Proceedings of IEEE ICASSP'97[C]. 1997: 1845~1848
17 O Edford, M Sandell, J J van de Beek. OFDM channel estimation by singular value decomposition[J]. IEEE Transactions on Communication. 1998, 46(7): 931~939
18 Y Zhao. A Countermeasure Against Frequency Offset in Orthogonal Frequency Division Multiplexing Communication Systems[A]. IEEE Transactions on Communication. 2005, 26(7): 822~827
19 Gao C, Ming Zhao, Shidong Zhou, Yan Yao. Blind channel estimation algorithm for MIMO-OFDM systems[J]. Electronics Letters. 2003, 39(19): 1420~1422
20 David T. Harvati, Rodger E.Ziemer. Orthogonal frequency division multiplexing performance in delay and Doppler spread channels. Vehicular Technology Conference, 1997 IEEE. 1997, (3): 1644~1647
21 O Edford, M Sandell, J J van de Beek. Analysis of DFT-based channel estimators for OFDM[A]. Research Report Of Signal Processing[R], Lulea University of Technology. 1996: 359~380
22 M J F Garcia, J M Paez-Borrallo, S Zazo. DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems[A]. Proceedings of IEEE VTC'01 Spring[C]. 2001:810~814
23 Yuping Zhao, Aiping Huang. A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transform-domain processing[A]. Proceedings of IEEE VTC'97[C], Phoenix, USA. 1997: 2089~2093
24 Jianhua Liu, Jian Li. Parameter Estimation and Error Reduction for OFDM-Based WLANs[J]. IEEE Transactions on Mobile computing. 2004, 3(2): 152~163
25 Coleri S, Ergen M, Puri A, Bahai A. Channel estimation techniques based on pilot arrangement in OFDM systems[J]. IEEE Transactions on Broadcasting. 2002,48(3):223~229
26 Changho Suh, Hwangt C-S, Hokyu Choi. Comparative study of time-domain and frequency-domain channel estimation in MIMO-OFDM systems[A]. 14th IEEE Proceedings on PIMRC 2003 [C]. 2003, (2): 1095~1099
27 Vineet Srivastava, Chin Keong Ho, Patrick Ho, Wang Fung. Robust MMSE Channel Estimation in OFDM Systems with Practical Timing Synchronization[J]. WCNC 2004/IEEE Communications Society. 2004: 146~158
28 Song Tiecheng, You Xiaohu, Shen Lianfeng, Song Xiaojin. Adaptive Channel Estimation Based on Pilot Signals and Transform-Domain Processing in SISO OFDM and MIMO OFDM systems. Journal of Southeast University(English Edition). 2005, 21(3):249~253
29 Tellambura. Computation of the continuous-time PAPR of an OFDM signal with BPSK subcarriers. Communications Letters, IEEE. 2001, 5(5): 185~187
30 Golay, M. Complementary Series. Information Theory. IEEE Transactions on Communication. 1961,7(2): 82~87
31 Davis J.A., Jedwab J. Peak-to-mean power control and error correction for OFDM transmission using Golay sequences and Reed-Muller codes. Electronics Letters. 1997, 33(4): 267~268
32 Xiaodong Li, Ritcey, J.A. M-sequence for OFDM peak-to-average power ratio reduction and error correction. Electronics Letters. 1997, 33(7): 554~555
33 Muller, S.H., Huber, J.B. A Comparison of Peak Power Reduction Schemes for OFDM. Global Telecommunications Conference, IEEE. 1997, (1): 211~215
34 Krongold, B.S., Jones, D.L. PAPR reduction in OFDM via active constellation extension Broadcasting. IEEE Transactions. 2003, 49(3): 258~268
35顾晴茹,周玉洁. OFDM系统中高速FFT处理器的FPGA实现.信息技术. 2005(12): 70~73
36程佩青.数字信号处理教程.清华大学出版社. 2001: 138~184
37 Ma Jose Canet, Felip Vicedo, Vicen Almenar. Fpga implemention of an if transceiver for OFDM-based wlan. IEEE Transactions on Communication. Jul 2004, 26(7): 227~232
38廖巨华,陈岚.基于改进FFT算法的OFDM调制解调模块设计.微电子学与计算机. 2005(6): 57~61
39求是科技. VHDL应用开发技术与工程实践.人民邮电出版社. 2005:42~204
40 Esteban O. Garcia, Rene Cumplido, Miguel Arias. Pipelined CORDIC design on FPGA for a digital sine and cosine waves generator. IEEE Transactions on Communication. Jul 2005, 46(7): 931~935
41王凯,葛建华,梁锡林. OFDM调制中高速FFT处理器的设计与实现.中国有线电视. 2006 (01): 57~62
42 Joaquín García, RenéCumplido. On the design of an FPGA-Based OFDM modulator for IEEE 802.16-2004. Proceedings of the 2005 International Conference on ReConFig. 2005: 253~256
43 Moisès Serra, Pere Martí, Jordi Carrabina. Implementation of a Channel Equalizer for OFDM Wireless LANs. Proceedings of the 15th IEEE RSP’04. 2004: 1125~1132
44陈海建,李式巨,叶红.基于DSP的高速无线局域网OFDM关键技术实现.电子设计应用. 2003.7: 84~89
45张冠华,陆余良,邓小鹏等.软件无线电的兴起对未来移动通信的影响.计算机与通信. 1999.10:8~12
46 F. Adachi and K. Takeda. Bit Error Rate Analysis of DS-CDMA with Joint Frequency-Domain Equalization and Antenna Diversity Combining. IEICE Trans. Commun., 2004,E87-B(12): 2991–3002.
47张鑫、李颖、魏急波.基于软件无线电的OFDM传输系统基带电路设计.通信与计算机. 2003(10): 46~48
48吴远达,李景文.直接中频采样及数字相干检波的研究.电子学报. 1994(10): 51~56
49 R. Van Nee and R. Prasad, OFDM for Multimedia Communications, Artech House, 2000: 36~41
2 EN 300 744. Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television. Valbonne, France, 1997: 1~201
3 U. Reimers. Digital video broadcasting. IEEE Commun Mag. 1998: 104~110
4 T. Pollet, M. V. Sladel, M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and wiener phase noise. IEEE Trans. Commun. . 1995, (43), pp.191~193
5 Peter Hoeher. A Statistical Discrete-Time Model for the WSSUS Multipath Channel. IEEE Transactions on Vehicular Technology. 1992, 41(4): 461~468
6王文博,郑侃.宽带无线通信OFDM技术.人民邮电出版社. 2003, 11(1): 7~21
7徐志军,徐光辉. CPLD/FPGA的开发与应用.电子工业出版. 2002: 12~16
8张乃通,徐玉滨等.移动通信系统.哈尔滨工业大学出版社, 2001: 1~150
9佟学俭. OFDM移动通信技术原理与应用.人民邮电出版社. 2000: 1~200
10 J. J. van de Beek, M. Sandell, and P. O. Borjesson. ML Estimation of Time and Frequency Offset in OFDM Systems. IEEE Trans. On Signal Processing. 1997, (45): 1800~1805
11 Timothy M. Schmidl and D. C. Cox. Robust Frequency and Timing Synchronization for OFDM. IEEE Trans. on Commun.. 1997, (45): 1613~1621
12 M. Morelli and U. Mengali. An improved frequency offset estimator for OFDM applications. IEEE Communications Letters. 1999, (3): 75~77
13 Y. H. Kim, I. Song, S. Yoon, and S. R. Park. An efficient frequency offset estimator for OFDM systems and its performance characteristics. IEEE Transactions on Vehicular Technology. 2001, (50): 1307~1312
14 H. Minn, V. K. Bhargava, and K.Ben Letaief. A robust timing and frequency synchronization for OFDM systems. IEEE Transactions on Wireless Comruunications. 2003, (2): 822~839
15 Y Li. Pilot-symbol-aided channel estimation for OFDM in wireless systems. IEEE Transactions on Vehicle Technology. 2000, 49(4): 1207~1215
16 P Hoeher, S Kaiser, I Robertson. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering[A]. Proceedings of IEEE ICASSP'97[C]. 1997: 1845~1848
17 O Edford, M Sandell, J J van de Beek. OFDM channel estimation by singular value decomposition[J]. IEEE Transactions on Communication. 1998, 46(7): 931~939
18 Y Zhao. A Countermeasure Against Frequency Offset in Orthogonal Frequency Division Multiplexing Communication Systems[A]. IEEE Transactions on Communication. 2005, 26(7): 822~827
19 Gao C, Ming Zhao, Shidong Zhou, Yan Yao. Blind channel estimation algorithm for MIMO-OFDM systems[J]. Electronics Letters. 2003, 39(19): 1420~1422
20 David T. Harvati, Rodger E.Ziemer. Orthogonal frequency division multiplexing performance in delay and Doppler spread channels. Vehicular Technology Conference, 1997 IEEE. 1997, (3): 1644~1647
21 O Edford, M Sandell, J J van de Beek. Analysis of DFT-based channel estimators for OFDM[A]. Research Report Of Signal Processing[R], Lulea University of Technology. 1996: 359~380
22 M J F Garcia, J M Paez-Borrallo, S Zazo. DFT-based channel estimation in 2D-pilot-symbol-aided OFDM wireless systems[A]. Proceedings of IEEE VTC'01 Spring[C]. 2001:810~814
23 Yuping Zhao, Aiping Huang. A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transform-domain processing[A]. Proceedings of IEEE VTC'97[C], Phoenix, USA. 1997: 2089~2093
24 Jianhua Liu, Jian Li. Parameter Estimation and Error Reduction for OFDM-Based WLANs[J]. IEEE Transactions on Mobile computing. 2004, 3(2): 152~163
25 Coleri S, Ergen M, Puri A, Bahai A. Channel estimation techniques based on pilot arrangement in OFDM systems[J]. IEEE Transactions on Broadcasting. 2002,48(3):223~229
26 Changho Suh, Hwangt C-S, Hokyu Choi. Comparative study of time-domain and frequency-domain channel estimation in MIMO-OFDM systems[A]. 14th IEEE Proceedings on PIMRC 2003 [C]. 2003, (2): 1095~1099
27 Vineet Srivastava, Chin Keong Ho, Patrick Ho, Wang Fung. Robust MMSE Channel Estimation in OFDM Systems with Practical Timing Synchronization[J]. WCNC 2004/IEEE Communications Society. 2004: 146~158
28 Song Tiecheng, You Xiaohu, Shen Lianfeng, Song Xiaojin. Adaptive Channel Estimation Based on Pilot Signals and Transform-Domain Processing in SISO OFDM and MIMO OFDM systems. Journal of Southeast University(English Edition). 2005, 21(3):249~253
29 Tellambura. Computation of the continuous-time PAPR of an OFDM signal with BPSK subcarriers. Communications Letters, IEEE. 2001, 5(5): 185~187
30 Golay, M. Complementary Series. Information Theory. IEEE Transactions on Communication. 1961,7(2): 82~87
31 Davis J.A., Jedwab J. Peak-to-mean power control and error correction for OFDM transmission using Golay sequences and Reed-Muller codes. Electronics Letters. 1997, 33(4): 267~268
32 Xiaodong Li, Ritcey, J.A. M-sequence for OFDM peak-to-average power ratio reduction and error correction. Electronics Letters. 1997, 33(7): 554~555
33 Muller, S.H., Huber, J.B. A Comparison of Peak Power Reduction Schemes for OFDM. Global Telecommunications Conference, IEEE. 1997, (1): 211~215
34 Krongold, B.S., Jones, D.L. PAPR reduction in OFDM via active constellation extension Broadcasting. IEEE Transactions. 2003, 49(3): 258~268
35顾晴茹,周玉洁. OFDM系统中高速FFT处理器的FPGA实现.信息技术. 2005(12): 70~73
36程佩青.数字信号处理教程.清华大学出版社. 2001: 138~184
37 Ma Jose Canet, Felip Vicedo, Vicen Almenar. Fpga implemention of an if transceiver for OFDM-based wlan. IEEE Transactions on Communication. Jul 2004, 26(7): 227~232
38廖巨华,陈岚.基于改进FFT算法的OFDM调制解调模块设计.微电子学与计算机. 2005(6): 57~61
39求是科技. VHDL应用开发技术与工程实践.人民邮电出版社. 2005:42~204
40 Esteban O. Garcia, Rene Cumplido, Miguel Arias. Pipelined CORDIC design on FPGA for a digital sine and cosine waves generator. IEEE Transactions on Communication. Jul 2005, 46(7): 931~935
41王凯,葛建华,梁锡林. OFDM调制中高速FFT处理器的设计与实现.中国有线电视. 2006 (01): 57~62
42 Joaquín García, RenéCumplido. On the design of an FPGA-Based OFDM modulator for IEEE 802.16-2004. Proceedings of the 2005 International Conference on ReConFig. 2005: 253~256
43 Moisès Serra, Pere Martí, Jordi Carrabina. Implementation of a Channel Equalizer for OFDM Wireless LANs. Proceedings of the 15th IEEE RSP’04. 2004: 1125~1132
44陈海建,李式巨,叶红.基于DSP的高速无线局域网OFDM关键技术实现.电子设计应用. 2003.7: 84~89
45张冠华,陆余良,邓小鹏等.软件无线电的兴起对未来移动通信的影响.计算机与通信. 1999.10:8~12
46 F. Adachi and K. Takeda. Bit Error Rate Analysis of DS-CDMA with Joint Frequency-Domain Equalization and Antenna Diversity Combining. IEICE Trans. Commun., 2004,E87-B(12): 2991–3002.
47张鑫、李颖、魏急波.基于软件无线电的OFDM传输系统基带电路设计.通信与计算机. 2003(10): 46~48
48吴远达,李景文.直接中频采样及数字相干检波的研究.电子学报. 1994(10): 51~56
49 R. Van Nee and R. Prasad, OFDM for Multimedia Communications, Artech House, 2000: 36~41