基于认知无线电的预编码OFDM系统研究
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摘要
认知无线电(Cognitive Radio, CR)技术能够感知到无线通信环境中的“频谱空洞”,并且能够通过一定的方式充分利用这些频谱来提高频谱的利用效率。随着无线通信技术的发展、用户需求不断的增加,该技术解决了无线频谱资源紧张的局面。它是一种智能的无线通信系统,具有认知和重新配置能力,能够动态地改变认知用户的配置参数,不会对正在工作的授权用户造成干扰的情况下,合理利用空闲频谱进行通信。
正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术具有较高的频谱利用效率和较强的抗多径干扰能力,并且可以实现高速的数据传输,成为了4G通信的热点候选方案。另外,OFDM技术可以通过频率的组合或裁剪实现良好的频谱资源控制能力,并可以有效的利用频谱进行数据传输,这些都满足了实现认知无线电的技术要求。OFDM技术和认知无线电的结合可以缓解当前无线频谱资源紧张和分配不均的局面,实现无线频谱资源的合理分配和充分利用。
文章首先介绍了OFDM技术基本原理及其相关的技术知识；阐述了认知无线电的基本原理以及与OFDM技术相结合的优势；分析了自适应OFDM系统在认知无线电条件下提高频谱效率,最大化系统容量的性能；之后,又分析了零前缀OFDM系统的性能,并对NC-OFDM系统进行了仿真分析。最后,着重研究了所提出的基于认知无线电的预编码无循环前缀OFDM(无CP OFDM)系统。基于通过认知无线电技术感知到的无线频谱状态信息,控制OFDM用户实时地改变系统通信配置参数,包括调制方式、编码方式、频率及带宽和发射功率等,从而在数据传输时避免对授权用户造成干扰。另外,将这些配置参数预编码成伪随机序列与OFDM符号数据一起发送。这样可以省去专门用于传输通信配置参数的控制信令,从而提高了频谱利用效率,减小了传输功率,增加了系统容量。
Cognitive radio technology can aware the "spectrum hole" in wireless communication environment; and makes full use of the spectrum through a certain way to increase spectrum utilization efficiency. The technology solves the tense situation of radio spectrum resources as wireless communication technology development and the users demand increasing. As an intelligent wireless communication system it has the ability of cognition and reconfigure. It can rationally communicate using free spectrum with dynamic changing secondary users' configuration parameters, and doesn't cause interference to the working authorized users.
OFDM technology has high spectral efficiency and the ability of anti-multipath interference. It may achieve high speed data transmission as a hot candidate for 4G communication. In addition, OFDM technology achieves well control of spectrum resources through combination or cutting frequency, and effectively uses spectrum for data transmission, that meets the requirements of cognitive radio. The combination of OFDM and cognitive radio technology not only eases the situation of current short supply radio spectrum and uneven distribution, but also achieves rational allocation and fully utilizing of radio spectrum.
This paper first introduces the basic principle of OFDM technology and its related technical knowledge, and describes the basic principles of cognitive radio technology and the advantages combined with OFDM. In cognitive radio conditions, adaptive OFDM system can improve spectrum efficiency and maximize its system capacity. Then we analyses the system performance of ZP-OFDM and make simulation analysis of NC-OFDM system. In the last, it focuses on the precoded OFDM system without CP based on cognitive radio. Cognitive radio makes the user of OFDM real-time change communication configuration parameters including modulation, coding, frequency, bandwidth and transmission power etc according the perceived status of wireless spectrum, so as to avoid interference to the authorized users in data transmission. The system makes these configuration parameters precoded into a pseudo-random sequence and transmits it with OFDM symbols. In this way, the system eliminates the specific control signaling for the transmission of communication configuration parameters, also improves the spectrum utilization efficiency and reduces the transmission power to increase system capacity.
正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术具有较高的频谱利用效率和较强的抗多径干扰能力,并且可以实现高速的数据传输,成为了4G通信的热点候选方案。另外,OFDM技术可以通过频率的组合或裁剪实现良好的频谱资源控制能力,并可以有效的利用频谱进行数据传输,这些都满足了实现认知无线电的技术要求。OFDM技术和认知无线电的结合可以缓解当前无线频谱资源紧张和分配不均的局面,实现无线频谱资源的合理分配和充分利用。
文章首先介绍了OFDM技术基本原理及其相关的技术知识；阐述了认知无线电的基本原理以及与OFDM技术相结合的优势；分析了自适应OFDM系统在认知无线电条件下提高频谱效率,最大化系统容量的性能；之后,又分析了零前缀OFDM系统的性能,并对NC-OFDM系统进行了仿真分析。最后,着重研究了所提出的基于认知无线电的预编码无循环前缀OFDM(无CP OFDM)系统。基于通过认知无线电技术感知到的无线频谱状态信息,控制OFDM用户实时地改变系统通信配置参数,包括调制方式、编码方式、频率及带宽和发射功率等,从而在数据传输时避免对授权用户造成干扰。另外,将这些配置参数预编码成伪随机序列与OFDM符号数据一起发送。这样可以省去专门用于传输通信配置参数的控制信令,从而提高了频谱利用效率,减小了传输功率,增加了系统容量。
Cognitive radio technology can aware the "spectrum hole" in wireless communication environment; and makes full use of the spectrum through a certain way to increase spectrum utilization efficiency. The technology solves the tense situation of radio spectrum resources as wireless communication technology development and the users demand increasing. As an intelligent wireless communication system it has the ability of cognition and reconfigure. It can rationally communicate using free spectrum with dynamic changing secondary users' configuration parameters, and doesn't cause interference to the working authorized users.
OFDM technology has high spectral efficiency and the ability of anti-multipath interference. It may achieve high speed data transmission as a hot candidate for 4G communication. In addition, OFDM technology achieves well control of spectrum resources through combination or cutting frequency, and effectively uses spectrum for data transmission, that meets the requirements of cognitive radio. The combination of OFDM and cognitive radio technology not only eases the situation of current short supply radio spectrum and uneven distribution, but also achieves rational allocation and fully utilizing of radio spectrum.
This paper first introduces the basic principle of OFDM technology and its related technical knowledge, and describes the basic principles of cognitive radio technology and the advantages combined with OFDM. In cognitive radio conditions, adaptive OFDM system can improve spectrum efficiency and maximize its system capacity. Then we analyses the system performance of ZP-OFDM and make simulation analysis of NC-OFDM system. In the last, it focuses on the precoded OFDM system without CP based on cognitive radio. Cognitive radio makes the user of OFDM real-time change communication configuration parameters including modulation, coding, frequency, bandwidth and transmission power etc according the perceived status of wireless spectrum, so as to avoid interference to the authorized users in data transmission. The system makes these configuration parameters precoded into a pseudo-random sequence and transmits it with OFDM symbols. In this way, the system eliminates the specific control signaling for the transmission of communication configuration parameters, also improves the spectrum utilization efficiency and reduces the transmission power to increase system capacity.
引文
[1]. Haykin S. Cognitive Radio:Brain-Empowered Wireless Communications [J]. IEEE Journal on Selected Areas in Communications,2005,23(2):201-220.
[2]. Weiss T, Jondra F. Spectrum pooling:an innovative strategy for the enhancement of spectrum efficiency[C]. IEEE Communications Magazine,2004,42:8-14.
[3]. Capar F, Martoyo I, Weiss T, et al. Comparison of bandwidth utilization for controlled and uncontrolled channel assignment in a spectrum pooling system. In:Proc. of the IEEE 55th Vehicular Technology Conference VTC Spring 2002, Birmingham,2002:1069-1073.
[4]. Mitola J. Cognitive Radio:an integrated agent architecture for software defined radio. Doctor of Technology,2000.
[5]. Akyildiz I F, Lee W Y, Vuran M C, et al. Next generation dynamic spectrum access cognitive radio wireless networks:a survey. Computer networks journal (Elsevier),2006,1(50):2127-2159.
[6].尹长川,罗涛,乐光新.多载波宽带无线通信技术[M].北京邮电大学出版社,2004
[7]. R. W. Chang, Synthesis of Band-Limited Orthogonal Signals for multichannel Data Transmission, Bell Syst. Tech. J, Dec.1966, pp:1775-1796.
[8]. A. Peled, A. Ruiz, Frequency Domain Data Transmission Using Reduced Computational Complexity Algorithms, Proc. IEEE Int. Conf. Acoust Speech Signal Processing, Denver, 1980, pp.964-967.
[9]. J. A. C. Binham, Multicarrier Modulation for Data Transmission:An Idea Whose Time Has Come, IEEE Commun. Mag, May,1990, vol.28, no.5, pp.5-14.
[10]. W. Y. Zou, Y. Wu, COFDM-An Overview, IEEE Trans. Broadcasting, Mar.1995, vol.41, no. 1,pp.1-8.
[11]. B M Popovic, New complex space-time block coding for efficient transmit diversity, IEEE International Symposium on Spread Spectrum Techniques and Applications[C],2000,1:132-136.
[12]. L. J. Cimini, Jr, Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing[J], IEEE Trans. July 1985, Commun, vol.3, pp.665-675.
[13]. Zhendao Wang, Giannakis G.B. Wireless Multicarrier Communications:Where Fourier Meets Shannon [J]. IEEE Signal Processing Magazine,2000,17(3):29-48.
[14].袁泉,周鹏.认知无线电中一种基于OFDM技术的频谱资源控制方法研究[J].电信快报,2009,(4)：15-17.
[15]. Tao Qin, Cyril Leung, C., Fair Adaptive Resource Allocation for Multiuser OFDM Cognitive Radio Systems, Communications and Networking in China,2007. CHINACOM'07. pp:115-119.
[16].周小飞,张宏纲.认知无线电原理及应用[M].北京：北京邮电大学出版社,2007, 22-24..
[17]. Farhang-Boroujeny B., Kempter R, Multicarrier communication techniques for spectrum sensing and communication in cognitive radios; Communications Magazine, IEEE,2008, Volume 46, Issue 4, pp:80-85.
[18].李波,刘勤,李维英.认知无线电技术[J].中兴通讯技术,2006,12(2)：10-13.
[19]. Xianbin Wang, Ho, P., Jie Zhu, Radiation Footprint Minimization Using Encoded OFDM Pilots for Cognitive Radio Communications Vehicular Technology Conference,2008. VTC Sping 2008. pp:948-952.
[20].刘元,彭瑞,陈楚.认知无线电的关键技术和应用研究[J].通信技术,2007,40(7)50-52.
[21]. Shichang Zhang, Jun Wang, Shaoqian Li, A channel estimation method for NC-OFDM systems in cognitive radio context, Communication Systems,2008. ICCS 2008. pp:208-212.
[22]. Qianxi Lu, Wei Wang, Tao Peng, Wenbo Wang, Efficient Multiuser Water-filling Algorithm under Interference Temperature Constraints in OFDMA-based Cognitive Radio Networks, Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, 2007,pp:174-177.
[23]. Chen Yang, Zheng Zhou, Xuebin Sun, Yabin Ye, The Tradeoff between Channel Capacity and Out-of-Band Interference of Cognitive Radios, Communications and Information Technologies,2008. ISCIT 2008. pp:398-401
[24]. Chien-Hwa Hwang, Shih-Chang Chen, Primary Users Signal Detection in OFDM Based Cognitive Radios, Communications,2008. ICC'08. pp:663-667.
[25]. Xin Liu, Xuezhi Tan, The Spectrum Allocation Algorithm of Cognitive Radio Based on OFDM Wireless Communications, Networking and Mobile Computing,2008. WiCOM'08. pp:1-4.
[26]. Mwangoka J. W., Ben Letaief K, Zhigang Cao, Robust End-to-End Qos Maintenance in Non-Contiguous OFDM Based Cognitive Radios, Communications,2008. ICC'08.2905-2909.
[27]. Ziyuan Yang, Haixia Zhang, Dongfeng Yuan, Zhiquan Bai, Kyungsup Kwak, A Novel Nyquist Window for OFDM-based Cognitive Radio Systems, Cognitive Radio Oriented Wireless Networks and Communications,2008. Crowncom 2008.1-5.
[28].包路平,张元,OFDM技术在认知无线电中应用的研究[J],西安邮电学院学报,2007,.12(5)：54-57.
[29].张亮,赵林靖,胡婧等,基于认知无线电技术的802.22标准[J],无线电工程,2007,37(1),pp:9-11.
[30].陈东,李建东,李维英,马静,认知无线电环境下MIMO-OFDM系统的无线资源管理[J],电子学报,2007,Vol.35,pp：60-63.
[31]. Xianbin Wang, Yiyan Wu, Hsiao-Chun Wu. A New Adaptive OFDM System With Precoded Cyclic Prefix for Cognitive Radio [C]. IEEE International Conference on Communications,2008, ICC'08.2008:3642-3646.
[32]. S. Weinstein, P. Ebert.. Data transmission by frequency-division multiplexing using the discrete Fourier transform. IEEE Trans. on Comm., Oct.1971, (5):628-634.
[33]. J. Bingham. Multicarrier modulation for data transmission:An idea whose time has come. IEEE Comm. Mag.,1990,28(5):5-14.
[34].胡光书.数字信号处理—理论、算法与实现[M].北京：清华大学出版社,1997
[35]. Peled, A. Ruiz. Frequency domain data transmission using reduced computational complexity algorithms. Proc. IEEE INt. Conf. Acoust Speech Signal Processing, Denver, 1980:964-967.
[36]. T. S. Rappaport, Wireless Communications principles and practice Prentice-Hall, NJ,1996.
[37].杨大成,移动传播环境[M].北京：机械工业出版社,2003.
[38]. P. A. Bello. Characterization of randomly time-variant linear channels. IEEE Trans on Communications Systems.1963.11(12).360-393.
[39]. Richard van Nee, Ramjee Prasad. OFDM wireless multimedia communications. Boston, London:Artech House,2000.
[40].佟学检等.OFDM移动通信技术原理与应用[M].北京：人民邮电出版社,2003
[41]. Michele Morelli, Umberto Mengali, A Comparison of pilit-aided channel estimation method for OFDM systems, IEEE Transactions on signal processing, Volune 49, no.12, December 2001.
[42]. Muquet B, Wang Z, and Giannakis G B, et al. Cyclic prefixing or zero padding for wireless multicarrier transmissions? IEEE Trans. on Communications,2002,50(12):2136-2148.
[43]. D. Kimand G. L. Stuber. "Residual ISI cancellation for OFDM with applications to HDTV broadcasting" [J] IEEE Journal on Selected Areas in Communications,1998, vol.16:1590-1599.
[44]. Y. Li, H. Minn. Channel Estimation and Equalization in the Presence of Timing Offset in MB-OFDM Systems[J], IEEE GLOBECOM 2007,7:3389-3394.
[45].李长青,UWB-OFDM系统中若干关键技术的研究[D],北京,北京邮电大学博士论文,2006.
[46].宋鹏鹏,OFDM及其在蜂窝通信系统中的应用,西安,西安电子科技大学硕士论文,2002.
[47]. Keller T, Hanzo L. Adaptive modulation techniques for duplex OFDM transmission. [J] IEEE Transactions on Vehicular Technology,2000,49:1893-1906
[48]. Ye. S, Blum, R. S, Cimini, L.J, Adaptive modulation for variable-rate OFDM systems with imperfect channel information. Vehicular Technology Conference,2002. VTC Spring 2002. IEEE 55th, Volume:2,6-9 May 2002.767-771.
[49].Mitola J et al., Cognitive radio:Making software radios more personal, IEEE Pers. Commun, Aug.1999, vol.6, no.4, pp:13-18.
[50]. Mahmoud, H, Yucek. T, Arslan, H. OFDM for cognitive radio:merits and challenges. IEEE Wireless Communications.2009, pp:6-15.
[51]. Poston J D, Home W D. Discontiguous OFDM Considerations for Dynamic Spectrum Access in Idle TV Channels [C]. IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks,2005:607-610.
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[53]. Dong Li, Xianhua Dai, Han Zhang. Sidelobe Suppression in NC-OFDM using Phase Shift[C]. Wireless Communications, Networking and Mobile Computing,2008. WiCOM'08. International Conference.2008, pp:1-4.
[54]. Dong Li, Xianhua Dai, Han Zhang. Sidelobe Suppression in NC-OFDM using Constellation Adjustment [J]. IEEE Communications Letters.2009, pp:327-329.
[55].吕浚哲,张海林,何非,刘增基.无保护间隔的OFDM信道自适应均衡的一种新算法[J].电子学报,2002,30(7)：941-944.
[56]. Xianbin Wang, Ho P, Wu Y. Robust Channel Estimation and ISI Cancellation for OFDM Systems With Suppressed Features [J]. IEEE Journal on Selected Areas in Communications, 2005,23(5):963-972.
[57].李司坤,王宗欣.无CP的OFDM联合信道估计和干扰抵消[J].无线电工程,2008,38(1)：19-21
[2]. Weiss T, Jondra F. Spectrum pooling:an innovative strategy for the enhancement of spectrum efficiency[C]. IEEE Communications Magazine,2004,42:8-14.
[3]. Capar F, Martoyo I, Weiss T, et al. Comparison of bandwidth utilization for controlled and uncontrolled channel assignment in a spectrum pooling system. In:Proc. of the IEEE 55th Vehicular Technology Conference VTC Spring 2002, Birmingham,2002:1069-1073.
[4]. Mitola J. Cognitive Radio:an integrated agent architecture for software defined radio. Doctor of Technology,2000.
[5]. Akyildiz I F, Lee W Y, Vuran M C, et al. Next generation dynamic spectrum access cognitive radio wireless networks:a survey. Computer networks journal (Elsevier),2006,1(50):2127-2159.
[6].尹长川,罗涛,乐光新.多载波宽带无线通信技术[M].北京邮电大学出版社,2004
[7]. R. W. Chang, Synthesis of Band-Limited Orthogonal Signals for multichannel Data Transmission, Bell Syst. Tech. J, Dec.1966, pp:1775-1796.
[8]. A. Peled, A. Ruiz, Frequency Domain Data Transmission Using Reduced Computational Complexity Algorithms, Proc. IEEE Int. Conf. Acoust Speech Signal Processing, Denver, 1980, pp.964-967.
[9]. J. A. C. Binham, Multicarrier Modulation for Data Transmission:An Idea Whose Time Has Come, IEEE Commun. Mag, May,1990, vol.28, no.5, pp.5-14.
[10]. W. Y. Zou, Y. Wu, COFDM-An Overview, IEEE Trans. Broadcasting, Mar.1995, vol.41, no. 1,pp.1-8.
[11]. B M Popovic, New complex space-time block coding for efficient transmit diversity, IEEE International Symposium on Spread Spectrum Techniques and Applications[C],2000,1:132-136.
[12]. L. J. Cimini, Jr, Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing[J], IEEE Trans. July 1985, Commun, vol.3, pp.665-675.
[13]. Zhendao Wang, Giannakis G.B. Wireless Multicarrier Communications:Where Fourier Meets Shannon [J]. IEEE Signal Processing Magazine,2000,17(3):29-48.
[14].袁泉,周鹏.认知无线电中一种基于OFDM技术的频谱资源控制方法研究[J].电信快报,2009,(4)：15-17.
[15]. Tao Qin, Cyril Leung, C., Fair Adaptive Resource Allocation for Multiuser OFDM Cognitive Radio Systems, Communications and Networking in China,2007. CHINACOM'07. pp:115-119.
[16].周小飞,张宏纲.认知无线电原理及应用[M].北京：北京邮电大学出版社,2007, 22-24..
[17]. Farhang-Boroujeny B., Kempter R, Multicarrier communication techniques for spectrum sensing and communication in cognitive radios; Communications Magazine, IEEE,2008, Volume 46, Issue 4, pp:80-85.
[18].李波,刘勤,李维英.认知无线电技术[J].中兴通讯技术,2006,12(2)：10-13.
[19]. Xianbin Wang, Ho, P., Jie Zhu, Radiation Footprint Minimization Using Encoded OFDM Pilots for Cognitive Radio Communications Vehicular Technology Conference,2008. VTC Sping 2008. pp:948-952.
[20].刘元,彭瑞,陈楚.认知无线电的关键技术和应用研究[J].通信技术,2007,40(7)50-52.
[21]. Shichang Zhang, Jun Wang, Shaoqian Li, A channel estimation method for NC-OFDM systems in cognitive radio context, Communication Systems,2008. ICCS 2008. pp:208-212.
[22]. Qianxi Lu, Wei Wang, Tao Peng, Wenbo Wang, Efficient Multiuser Water-filling Algorithm under Interference Temperature Constraints in OFDMA-based Cognitive Radio Networks, Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, 2007,pp:174-177.
[23]. Chen Yang, Zheng Zhou, Xuebin Sun, Yabin Ye, The Tradeoff between Channel Capacity and Out-of-Band Interference of Cognitive Radios, Communications and Information Technologies,2008. ISCIT 2008. pp:398-401
[24]. Chien-Hwa Hwang, Shih-Chang Chen, Primary Users Signal Detection in OFDM Based Cognitive Radios, Communications,2008. ICC'08. pp:663-667.
[25]. Xin Liu, Xuezhi Tan, The Spectrum Allocation Algorithm of Cognitive Radio Based on OFDM Wireless Communications, Networking and Mobile Computing,2008. WiCOM'08. pp:1-4.
[26]. Mwangoka J. W., Ben Letaief K, Zhigang Cao, Robust End-to-End Qos Maintenance in Non-Contiguous OFDM Based Cognitive Radios, Communications,2008. ICC'08.2905-2909.
[27]. Ziyuan Yang, Haixia Zhang, Dongfeng Yuan, Zhiquan Bai, Kyungsup Kwak, A Novel Nyquist Window for OFDM-based Cognitive Radio Systems, Cognitive Radio Oriented Wireless Networks and Communications,2008. Crowncom 2008.1-5.
[28].包路平,张元,OFDM技术在认知无线电中应用的研究[J],西安邮电学院学报,2007,.12(5)：54-57.
[29].张亮,赵林靖,胡婧等,基于认知无线电技术的802.22标准[J],无线电工程,2007,37(1),pp:9-11.
[30].陈东,李建东,李维英,马静,认知无线电环境下MIMO-OFDM系统的无线资源管理[J],电子学报,2007,Vol.35,pp：60-63.
[31]. Xianbin Wang, Yiyan Wu, Hsiao-Chun Wu. A New Adaptive OFDM System With Precoded Cyclic Prefix for Cognitive Radio [C]. IEEE International Conference on Communications,2008, ICC'08.2008:3642-3646.
[32]. S. Weinstein, P. Ebert.. Data transmission by frequency-division multiplexing using the discrete Fourier transform. IEEE Trans. on Comm., Oct.1971, (5):628-634.
[33]. J. Bingham. Multicarrier modulation for data transmission:An idea whose time has come. IEEE Comm. Mag.,1990,28(5):5-14.
[34].胡光书.数字信号处理—理论、算法与实现[M].北京：清华大学出版社,1997
[35]. Peled, A. Ruiz. Frequency domain data transmission using reduced computational complexity algorithms. Proc. IEEE INt. Conf. Acoust Speech Signal Processing, Denver, 1980:964-967.
[36]. T. S. Rappaport, Wireless Communications principles and practice Prentice-Hall, NJ,1996.
[37].杨大成,移动传播环境[M].北京：机械工业出版社,2003.
[38]. P. A. Bello. Characterization of randomly time-variant linear channels. IEEE Trans on Communications Systems.1963.11(12).360-393.
[39]. Richard van Nee, Ramjee Prasad. OFDM wireless multimedia communications. Boston, London:Artech House,2000.
[40].佟学检等.OFDM移动通信技术原理与应用[M].北京：人民邮电出版社,2003
[41]. Michele Morelli, Umberto Mengali, A Comparison of pilit-aided channel estimation method for OFDM systems, IEEE Transactions on signal processing, Volune 49, no.12, December 2001.
[42]. Muquet B, Wang Z, and Giannakis G B, et al. Cyclic prefixing or zero padding for wireless multicarrier transmissions? IEEE Trans. on Communications,2002,50(12):2136-2148.
[43]. D. Kimand G. L. Stuber. "Residual ISI cancellation for OFDM with applications to HDTV broadcasting" [J] IEEE Journal on Selected Areas in Communications,1998, vol.16:1590-1599.
[44]. Y. Li, H. Minn. Channel Estimation and Equalization in the Presence of Timing Offset in MB-OFDM Systems[J], IEEE GLOBECOM 2007,7:3389-3394.
[45].李长青,UWB-OFDM系统中若干关键技术的研究[D],北京,北京邮电大学博士论文,2006.
[46].宋鹏鹏,OFDM及其在蜂窝通信系统中的应用,西安,西安电子科技大学硕士论文,2002.
[47]. Keller T, Hanzo L. Adaptive modulation techniques for duplex OFDM transmission. [J] IEEE Transactions on Vehicular Technology,2000,49:1893-1906
[48]. Ye. S, Blum, R. S, Cimini, L.J, Adaptive modulation for variable-rate OFDM systems with imperfect channel information. Vehicular Technology Conference,2002. VTC Spring 2002. IEEE 55th, Volume:2,6-9 May 2002.767-771.
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