正交频分复用技术在无线接入中传输性能的研究
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摘要
无线通信技术的发展给人们的生活带来了极大的方便。无线多媒体通信是无线技术的发展方向，而高速的无线数据传输是实现多媒体通信的基础。正交频分复用技术(OFDM)在无线环境下具有很高的频谱利用率和很强的抗多径干扰能力，其优良的特性已经使得OFDM成为各种高速无线接入的核心技术。
掌握无线信道传播特性是OFDM技术应用的基础；同时，OFDM采用IFFT来产生频谱正交的子载波，高速的数字信号处理技术是OFDM技术实用化的前提。另一方面，OFDM技术仍存在信号的峰均值功率比(PAR)过大导致对系统的非线性失真敏感；码元同步错误破坏载波间的正交性等问题，有必要进行深入的研究。
本文从OFDM系统的工作原理出发，阐述了OFDM的FFT实现方法和循环扩展的物理作用，接着对OFDM系统的基本性能进行仿真并分析了结果。本文重点分析了使用循环扩展实现码元同步的原理，并且指出了在多径环境下存在的问题，提出了改进方案；OFDM信号峰均值比(PAR)过大是其应用的主要缺点，现有的各种解决方案并没有以一种系统的观点来对待这个问题，本文对此进行了分类，指出不同方案优缺点。
The development of wireless communication technology brings great facility to people's life. Wireless multimedia communication is the future of wireless communications, and high data rate is the basement of wireless multimedia communication. Orthogonal Frequency Division Multiplexing (OFDM) has better bandwidth efficiency and increased robustness to multipath fading and to interference than single carrier adaptive equalization modulation techniques in wireless environment, OFDM has became the core technology of kinds of high speed wireless access due to its better characteristic.
The properties of wireless access channel has great influence on OFDM systems performance, so it is the fundament knowledge of OFDM systems in application; on the other hand, OFDM use IFFT to produce orthogonal sub-carriers, high rate signal processing technology is very important. OFMD also have it disadvantages, for example, the big signal Peak-to-Average Power Ratio result in OFDM is very sensitive to system's non-linearity; symbol synchronization error will destroy orthogonal between sub-carriers.
This paper start from OFDM system work principle, describe the FFT realize method and Physical action of Cyclic Prefix of OFDM. Then simulating the OFDM basic property with simulate software and analysis the result. The emphasis of this paper is to analyze the principle of use Cycle Prefix to realize symbol synchronization, and point out it disadvantage in multipath propagation, we proposed a new schematic. The major drawback of OFDM is the large Peak-to-Average Power Ratio (PAR) of the transmit signal, Existing solutions do not attack this PAR issue in a systematic way however. We discuss and compare a broad range of such techniques and organize, and
point out its advantages and disadvantages.
掌握无线信道传播特性是OFDM技术应用的基础；同时，OFDM采用IFFT来产生频谱正交的子载波，高速的数字信号处理技术是OFDM技术实用化的前提。另一方面，OFDM技术仍存在信号的峰均值功率比(PAR)过大导致对系统的非线性失真敏感；码元同步错误破坏载波间的正交性等问题，有必要进行深入的研究。
本文从OFDM系统的工作原理出发，阐述了OFDM的FFT实现方法和循环扩展的物理作用，接着对OFDM系统的基本性能进行仿真并分析了结果。本文重点分析了使用循环扩展实现码元同步的原理，并且指出了在多径环境下存在的问题，提出了改进方案；OFDM信号峰均值比(PAR)过大是其应用的主要缺点，现有的各种解决方案并没有以一种系统的观点来对待这个问题，本文对此进行了分类，指出不同方案优缺点。
The development of wireless communication technology brings great facility to people's life. Wireless multimedia communication is the future of wireless communications, and high data rate is the basement of wireless multimedia communication. Orthogonal Frequency Division Multiplexing (OFDM) has better bandwidth efficiency and increased robustness to multipath fading and to interference than single carrier adaptive equalization modulation techniques in wireless environment, OFDM has became the core technology of kinds of high speed wireless access due to its better characteristic.
The properties of wireless access channel has great influence on OFDM systems performance, so it is the fundament knowledge of OFDM systems in application; on the other hand, OFDM use IFFT to produce orthogonal sub-carriers, high rate signal processing technology is very important. OFMD also have it disadvantages, for example, the big signal Peak-to-Average Power Ratio result in OFDM is very sensitive to system's non-linearity; symbol synchronization error will destroy orthogonal between sub-carriers.
This paper start from OFDM system work principle, describe the FFT realize method and Physical action of Cyclic Prefix of OFDM. Then simulating the OFDM basic property with simulate software and analysis the result. The emphasis of this paper is to analyze the principle of use Cycle Prefix to realize symbol synchronization, and point out it disadvantage in multipath propagation, we proposed a new schematic. The major drawback of OFDM is the large Peak-to-Average Power Ratio (PAR) of the transmit signal, Existing solutions do not attack this PAR issue in a systematic way however. We discuss and compare a broad range of such techniques and organize, and
point out its advantages and disadvantages.
引文
[1] 朱洪波 付海阳 吴志忠 唐宝民，无线接入网，第1版，2000年，人民邮电出版社，80—82页
[2] 赵亚红 李伟华 吴伟陵，正交多载波调制(OFDM)技术及其应用，电讯技术，2001年，第1期，92—93页
[3] 刘元安等，宽待无线接入和无线局域网，第1版，2000年，第一版，北京邮电大学出版社，95页
[4] G.C.Porter,"Error distribution and diversity performance of a frequency-differential PSK HF modem," IEEE Trans. Commun,Technol., vol. COM-13, pp.320-333,Sept. 1965.
[5] M. Beach, "Propagation and System Aspects", University of Bristol, Future Communication Systems course, April 1994.
[6] T.S. Rappaport, "Wireless Communications Principles & Practice", IEEE Press, New York, Prentice Hall, pp. 169-177, 1996.
[7] William Y. Zou, Yiyan Wu, "COFDM:AN OVERVIEW", IEEE Transactions on Broadcasting, VOL.41, NO. 1, March 1995.
[8] Proakis,J.G:"Digital Communications", McGraw Hill, New York, 1989
[9] 吴伟陵，移动通信中的关键技术，第1版，2000年，北京邮电大学出版社，235页
[10] R.R,. Mosier and R.G. Clabaugh, "Kineplex, a bandwidth-efficient binary transmission system," AIEE Trans., vol. 76, pp. 723-728, Jan. 1958.
[11] G. 卡尔霍恩，何英姿 等译，数字蜂窝移动通信，第1版，1997年，人民邮电出版社，222页
[12] 曲桦 李转年 韩俊刚，接入网与V5接口，第1版，1999年，人民邮电出版社，
[13] IEEE P802.11, Draft Standard for Wireless LAN, May 9,1997
[14] Radio Equipment and Systems (RES); High Performance Radio Local Area Network (HIPERLAN TYPE 1); Functional specification, ETS 300 652.May 1997.
[15] 樊昌信 等，通信原理，第5版，2001年，国防工业出版社
[16] Ye (Geoffrey) Li, "OFDM for Wireless Communications: Techniques for Capacity Improvement," International Conference on Communication Technology, ICCT'98 October 22-24,1998 Beijing, China
[17] J-J.van de Beek, M. Sandell, M. Isakson, P.O. Borjesson, "Low-complex frame synchronization in OFDM Systems" in Proc. of ICUPC'95, Tokyo, pp.928-986, 1995
[18] A. Palin, Symbol synchronization in DVB-T OFDM system, Master of Science Thesis, Tampere University of Technology, 1997
[19] M. Kuhn, "The Single Frequency Network of Deutsche Bundespost-Telekom" in Proc. of HDTV'93,Ottawa, October 26-28, 1993
[20] A. Palin, J. Pikkarainen, J.Rinne, "Improved Symbol Synchronization Method in OFDM System in Channels with Large Delay Spreads" in Proc. of CSDSP'98, Sheffield, England,pp.309-312, 1998
[21] Muller, S., Bauml, R., Fischer, R., Huber J., "OFDM with Reduced Peak-to-Average Power Ratio by Multiple Signal Representation," Annals of Telecommunications, Vol.52, No. 1-2, pp.58-67, February 1997
[22] Mestdagh, D., Spruyt, P., "A Method to Reduce the Probability of Clipping in DMT-Based Transceivers," IEEE Trans. On Comm., Vol.44, No 10,pp. 1234-1238, October 1996
[23] Gross, R., Veeneman D., "SNR and Spectral Properties for a Clipped DMT ADSL Signal," Proceedings SuperComm/ICC'94, New Orleans, LA, pp. 843-847, May 1994
[24] Tellambura, C., "Phase optimization criterion for reducing peak-to-average power ration in OFDM," Electronics Letters, Vol.43, No.2, pp. 169-170, January 1998
[25] Tellado, J., Cioffi, J., "Further Results on Peak-to-Average Ratio Reduction," T1E1.4: VDSL/ADSL, TIEI.4/98-225,August 1998
[26] Wilkinson, T., Jones, E., "Minimisation of the Peak to Mean Envelope Power Ratio of Multicarrier Transmission Schemes by Block Coding," Proceedings VTC'95, Chicago, IL, pp 25-28, July 1995
[27] Kamerman, A., Krishnakumar, A., "OFDM encoding with reduced crestfactor," Symp. On Comm.& Vehicular Tecnology. in the Benelux, Louvain-La-Neuve, Belgium, pp. 182-186, November 1994.
[28] Friese, M., "Multicarrier modulation with low peak-to average power ratio," Electronics Letters, Vol.32, No.8, pp.713-714, April 1996
[29] Ochiai, H., Inai, H., "Performance of Block Codes with Peak Power Reduction for Indoor Multicarrier Systems," Proceedings VTC'98, Ottwa, Canada, pp. 338-342, May 1998
[30] Li, X., Ritcey, J., "M-sequences for OFDM peak-to average power ratio reduction and error correction," Electronics Letters, Vol.33, No.7, pp. 554-555, March 1997
[31] Wulich, D., Goldfeld, L., "Reduction of Peak Factor in Orthogonal Multicarrier Modulation by Amplitude Limiting and Coding," IEEE Trans. on Comm., Vol.47, No.1, pp.18-21, January 1999
[32] Chow, J., Bingham, J., Flowers, M., "Mitigating Clipping Noise in Multi-carrier Systems," Proceedings ICC' 97, Montreal, Canada, pp. 715-719, June 1997
[33] Gatherer, A., Polley, M., "Controlling Clipping Probability in DMT Transmission," Proc, Conf. On Signals, Systems and Computers, Pacific Grove, CA, pp. 578-584, Nov. 1997
[34] Kin, D., Stuber, G., "Clipping Noise Mitigation for OFDM by Decision-Aided Reconstruction," IEEE Comm, Letters, Vol.3, No. 1, pp.4-6, January 1999
[35] Van Nee, R., De Wild, A., "Reducing the Peak-to-Average Power Ratio of OFDM," Proceedings VTC'98, Ottawa, Canada, pp.072-2076, May 1998
[36] Tellado, J., Cioffi, J., "Peak Power Reduction for Multicarrier Transmission," Proceedings Globecom'98, Sydney, Australia, November 1998
[37] Tellado, J., Cioffi, J., "Revisiting DMT's Peak-to-Average Ratio," VDSL ETSI/ANSI TM6:TD08, Antwerp, April 1998
[38] Yamauchi, K., Kakiuchi, S., Takebe, A., Sugitomo, M., "Digital Audio Broadcasting receiver development" International Broadcasting Conference IBC'95, Amsterdam, Netherlands, pp. 71-75, September 1995
[39] O'Neill, R., Lopes, L.B., "A study of novel OFDM transmission schemes for use in indoor environments" Proceedings VTC'96, Atlanta, GA, pp.909-913, April 1996
[40] Gyselinckx, B., Eberle, W., Engels, M., Schurgers, C., Thone, S., Vandenameele, P., Van der Perre, L., "A flexible architecture for future wireless local area networks" Proceedings of ICT'98-International Conference on Telecommunications, Chalkidiki, Greece, pp. 115-119, June 1998
[41] Nobles, P., Halsall, F., "OFDM for high bit rate data transmission over measured indoor radio channels" IEE Colloquuium on 'Radio LANs and MANs', London, UK, pp.5/1-5, April 1995.
[42] IEEE 802.11 a draft:http://grouper.ieee.org/groups/802/11/
[43] Van Eetvelt, P., Wade, G., Tomlinson, M., "Peak to average power reduction for OFDM schemes by selective scrambling," Electronics Letters, Vol.32, No.21, pp. 1963-1964, November 1996
[45] N. Yee, J, P., Linnartz, and G. Fettweis, "Multicarrier CDMA in Indoor Wireless Radio Nerworks," Proc. IEEE PIMRC'93, Yokohama, Japan, Sept, 1993, pp.109-13
[46] Kwang-Cheng Chen, and Shan-Tsung Wu, "A Programmable Architecture for OFDM-CDMA," IEEE Communications Magazine, Topics in Software and DSP in Radio, November 1999, pp.76-82
[47] IEEE Std 802.11a-1999, High-speed Physical Layer in the 5 GHZ Band, September, 1999
[48] IEEE P1394.1 Group Meeting, Rennes, "ETSI Project BRAN Hiperlan Type 2 for IEEE 1394 Applications System Overview", October, 1999
[2] 赵亚红 李伟华 吴伟陵，正交多载波调制(OFDM)技术及其应用，电讯技术，2001年，第1期，92—93页
[3] 刘元安等，宽待无线接入和无线局域网，第1版，2000年，第一版，北京邮电大学出版社，95页
[4] G.C.Porter,"Error distribution and diversity performance of a frequency-differential PSK HF modem," IEEE Trans. Commun,Technol., vol. COM-13, pp.320-333,Sept. 1965.
[5] M. Beach, "Propagation and System Aspects", University of Bristol, Future Communication Systems course, April 1994.
[6] T.S. Rappaport, "Wireless Communications Principles & Practice", IEEE Press, New York, Prentice Hall, pp. 169-177, 1996.
[7] William Y. Zou, Yiyan Wu, "COFDM:AN OVERVIEW", IEEE Transactions on Broadcasting, VOL.41, NO. 1, March 1995.
[8] Proakis,J.G:"Digital Communications", McGraw Hill, New York, 1989
[9] 吴伟陵，移动通信中的关键技术，第1版，2000年，北京邮电大学出版社，235页
[10] R.R,. Mosier and R.G. Clabaugh, "Kineplex, a bandwidth-efficient binary transmission system," AIEE Trans., vol. 76, pp. 723-728, Jan. 1958.
[11] G. 卡尔霍恩，何英姿 等译，数字蜂窝移动通信，第1版，1997年，人民邮电出版社，222页
[12] 曲桦 李转年 韩俊刚，接入网与V5接口，第1版，1999年，人民邮电出版社，
[13] IEEE P802.11, Draft Standard for Wireless LAN, May 9,1997
[14] Radio Equipment and Systems (RES); High Performance Radio Local Area Network (HIPERLAN TYPE 1); Functional specification, ETS 300 652.May 1997.
[15] 樊昌信 等，通信原理，第5版，2001年，国防工业出版社
[16] Ye (Geoffrey) Li, "OFDM for Wireless Communications: Techniques for Capacity Improvement," International Conference on Communication Technology, ICCT'98 October 22-24,1998 Beijing, China
[17] J-J.van de Beek, M. Sandell, M. Isakson, P.O. Borjesson, "Low-complex frame synchronization in OFDM Systems" in Proc. of ICUPC'95, Tokyo, pp.928-986, 1995
[18] A. Palin, Symbol synchronization in DVB-T OFDM system, Master of Science Thesis, Tampere University of Technology, 1997
[19] M. Kuhn, "The Single Frequency Network of Deutsche Bundespost-Telekom" in Proc. of HDTV'93,Ottawa, October 26-28, 1993
[20] A. Palin, J. Pikkarainen, J.Rinne, "Improved Symbol Synchronization Method in OFDM System in Channels with Large Delay Spreads" in Proc. of CSDSP'98, Sheffield, England,pp.309-312, 1998
[21] Muller, S., Bauml, R., Fischer, R., Huber J., "OFDM with Reduced Peak-to-Average Power Ratio by Multiple Signal Representation," Annals of Telecommunications, Vol.52, No. 1-2, pp.58-67, February 1997
[22] Mestdagh, D., Spruyt, P., "A Method to Reduce the Probability of Clipping in DMT-Based Transceivers," IEEE Trans. On Comm., Vol.44, No 10,pp. 1234-1238, October 1996
[23] Gross, R., Veeneman D., "SNR and Spectral Properties for a Clipped DMT ADSL Signal," Proceedings SuperComm/ICC'94, New Orleans, LA, pp. 843-847, May 1994
[24] Tellambura, C., "Phase optimization criterion for reducing peak-to-average power ration in OFDM," Electronics Letters, Vol.43, No.2, pp. 169-170, January 1998
[25] Tellado, J., Cioffi, J., "Further Results on Peak-to-Average Ratio Reduction," T1E1.4: VDSL/ADSL, TIEI.4/98-225,August 1998
[26] Wilkinson, T., Jones, E., "Minimisation of the Peak to Mean Envelope Power Ratio of Multicarrier Transmission Schemes by Block Coding," Proceedings VTC'95, Chicago, IL, pp 25-28, July 1995
[27] Kamerman, A., Krishnakumar, A., "OFDM encoding with reduced crestfactor," Symp. On Comm.& Vehicular Tecnology. in the Benelux, Louvain-La-Neuve, Belgium, pp. 182-186, November 1994.
[28] Friese, M., "Multicarrier modulation with low peak-to average power ratio," Electronics Letters, Vol.32, No.8, pp.713-714, April 1996
[29] Ochiai, H., Inai, H., "Performance of Block Codes with Peak Power Reduction for Indoor Multicarrier Systems," Proceedings VTC'98, Ottwa, Canada, pp. 338-342, May 1998
[30] Li, X., Ritcey, J., "M-sequences for OFDM peak-to average power ratio reduction and error correction," Electronics Letters, Vol.33, No.7, pp. 554-555, March 1997
[31] Wulich, D., Goldfeld, L., "Reduction of Peak Factor in Orthogonal Multicarrier Modulation by Amplitude Limiting and Coding," IEEE Trans. on Comm., Vol.47, No.1, pp.18-21, January 1999
[32] Chow, J., Bingham, J., Flowers, M., "Mitigating Clipping Noise in Multi-carrier Systems," Proceedings ICC' 97, Montreal, Canada, pp. 715-719, June 1997
[33] Gatherer, A., Polley, M., "Controlling Clipping Probability in DMT Transmission," Proc, Conf. On Signals, Systems and Computers, Pacific Grove, CA, pp. 578-584, Nov. 1997
[34] Kin, D., Stuber, G., "Clipping Noise Mitigation for OFDM by Decision-Aided Reconstruction," IEEE Comm, Letters, Vol.3, No. 1, pp.4-6, January 1999
[35] Van Nee, R., De Wild, A., "Reducing the Peak-to-Average Power Ratio of OFDM," Proceedings VTC'98, Ottawa, Canada, pp.072-2076, May 1998
[36] Tellado, J., Cioffi, J., "Peak Power Reduction for Multicarrier Transmission," Proceedings Globecom'98, Sydney, Australia, November 1998
[37] Tellado, J., Cioffi, J., "Revisiting DMT's Peak-to-Average Ratio," VDSL ETSI/ANSI TM6:TD08, Antwerp, April 1998
[38] Yamauchi, K., Kakiuchi, S., Takebe, A., Sugitomo, M., "Digital Audio Broadcasting receiver development" International Broadcasting Conference IBC'95, Amsterdam, Netherlands, pp. 71-75, September 1995
[39] O'Neill, R., Lopes, L.B., "A study of novel OFDM transmission schemes for use in indoor environments" Proceedings VTC'96, Atlanta, GA, pp.909-913, April 1996
[40] Gyselinckx, B., Eberle, W., Engels, M., Schurgers, C., Thone, S., Vandenameele, P., Van der Perre, L., "A flexible architecture for future wireless local area networks" Proceedings of ICT'98-International Conference on Telecommunications, Chalkidiki, Greece, pp. 115-119, June 1998
[41] Nobles, P., Halsall, F., "OFDM for high bit rate data transmission over measured indoor radio channels" IEE Colloquuium on 'Radio LANs and MANs', London, UK, pp.5/1-5, April 1995.
[42] IEEE 802.11 a draft:http://grouper.ieee.org/groups/802/11/
[43] Van Eetvelt, P., Wade, G., Tomlinson, M., "Peak to average power reduction for OFDM schemes by selective scrambling," Electronics Letters, Vol.32, No.21, pp. 1963-1964, November 1996
[45] N. Yee, J, P., Linnartz, and G. Fettweis, "Multicarrier CDMA in Indoor Wireless Radio Nerworks," Proc. IEEE PIMRC'93, Yokohama, Japan, Sept, 1993, pp.109-13
[46] Kwang-Cheng Chen, and Shan-Tsung Wu, "A Programmable Architecture for OFDM-CDMA," IEEE Communications Magazine, Topics in Software and DSP in Radio, November 1999, pp.76-82
[47] IEEE Std 802.11a-1999, High-speed Physical Layer in the 5 GHZ Band, September, 1999
[48] IEEE P1394.1 Group Meeting, Rennes, "ETSI Project BRAN Hiperlan Type 2 for IEEE 1394 Applications System Overview", October, 1999
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