二维扩展频谱技术研究
摘要
直接序列扩展频谱技术(DSSS)是第三代移动通信系统的核心技术，本文主要讨论的二维扩展频谱技术(2D-CDMA)就是直接序列扩展频谱技术与多载波码分多址技术(MC-CDMA)的结合，它是移动通信领域中一种新兴的扩频多址方式。
2D-CDMA将正交频分复用技术(OFDM)应用于CDMA中，使之同时具有这两者的优点。它先将原始数据流复制成多路并行数据，经频域扩频和时域扩频，再调制到互相正交的子载波上传输。这一技术能有效地抗多径干扰引起的符号间串扰(ISI)，并具有频率分集的优点，在移动通信领域中具有广阔的应用前景。
本文提出了一个较为完整的二维扩展频谱系统的总体模型，并通过对接收机和发射机的数学分析阐明了二维扩展频谱系统的基本原理。
通信系统的性能直接决定了它是否具有实际应用价值，本文重点分析了2D-CDMA在加性白高斯噪声(AWGN)信道和瑞利衰落信道中的性能，分析结果表明二维扩展频谱系统有较强的抗瑞利衰落的能力。
由于采用了多载波技术，系统具有频率分集的能力，所以本文将不同的合并方式应用于这一系统，得到了各自的性能，并对之作了比较。
最后本文对系统中的核心部分，即信道估计器作了深入的研究，分析了基于导频符号的一些信道估计方法，它们是线性插值估计、基于DFT的估计和基于变换域的估计。并且对不同的估计方法作了仿真，结果表明基于变换域的信道估计器要略优于另外两种方法。
Direct sequence spread spectrum (DSSS) technology is the central technology for the third generation mobile communication systems. In this paper, we discuss the two-dimensional spread spectrum technology (2D-CDMA), which is the combination of DSSS and multi-carrier code division multiple access (MC-CDMA). This is a novel spread spectrum multiple access method in mobile communication.
2D-CDMA applies orthogonal frequency division multiplexing (OFDM) into CDMA, thus has advantages of both of them. It copies the original data stream to several parallel data streams, spreads them in both time and frequency domain, then modulates them to orthogonal sub-carriers for transmission. This technology will have brilliant future for its efficiency in canceling ISI and its advantage of frequency diversity.
A whole model of 2D-CDMA is presented in this paper and it function is showed by mathematical analysis of its transmitter and receiver.
It is the performance of the communication system that determines its application value. Therefore, the performance of 2D-CDMA in both AWGN and Rayleigh fading channel is analyzed and the results show that this technology has the ability to counteract Rayleigh fading.
Frequency diversity is a main advantage of this system, because of the employment of multi-carrier. This paper applies different combination methods into the system and gets their performance comparison.
At the end of this paper, we focus on the channel estimator. Several estimation methods, such as linear Interpolation estimation, estimation based on DFT and estimation based on transform domain, are analyzed and simulated. The computer simulation results show that the estimator based on transform domain is better than the other two.
2D-CDMA将正交频分复用技术(OFDM)应用于CDMA中，使之同时具有这两者的优点。它先将原始数据流复制成多路并行数据，经频域扩频和时域扩频，再调制到互相正交的子载波上传输。这一技术能有效地抗多径干扰引起的符号间串扰(ISI)，并具有频率分集的优点，在移动通信领域中具有广阔的应用前景。
本文提出了一个较为完整的二维扩展频谱系统的总体模型，并通过对接收机和发射机的数学分析阐明了二维扩展频谱系统的基本原理。
通信系统的性能直接决定了它是否具有实际应用价值，本文重点分析了2D-CDMA在加性白高斯噪声(AWGN)信道和瑞利衰落信道中的性能，分析结果表明二维扩展频谱系统有较强的抗瑞利衰落的能力。
由于采用了多载波技术，系统具有频率分集的能力，所以本文将不同的合并方式应用于这一系统，得到了各自的性能，并对之作了比较。
最后本文对系统中的核心部分，即信道估计器作了深入的研究，分析了基于导频符号的一些信道估计方法，它们是线性插值估计、基于DFT的估计和基于变换域的估计。并且对不同的估计方法作了仿真，结果表明基于变换域的信道估计器要略优于另外两种方法。
Direct sequence spread spectrum (DSSS) technology is the central technology for the third generation mobile communication systems. In this paper, we discuss the two-dimensional spread spectrum technology (2D-CDMA), which is the combination of DSSS and multi-carrier code division multiple access (MC-CDMA). This is a novel spread spectrum multiple access method in mobile communication.
2D-CDMA applies orthogonal frequency division multiplexing (OFDM) into CDMA, thus has advantages of both of them. It copies the original data stream to several parallel data streams, spreads them in both time and frequency domain, then modulates them to orthogonal sub-carriers for transmission. This technology will have brilliant future for its efficiency in canceling ISI and its advantage of frequency diversity.
A whole model of 2D-CDMA is presented in this paper and it function is showed by mathematical analysis of its transmitter and receiver.
It is the performance of the communication system that determines its application value. Therefore, the performance of 2D-CDMA in both AWGN and Rayleigh fading channel is analyzed and the results show that this technology has the ability to counteract Rayleigh fading.
Frequency diversity is a main advantage of this system, because of the employment of multi-carrier. This paper applies different combination methods into the system and gets their performance comparison.
At the end of this paper, we focus on the channel estimator. Several estimation methods, such as linear Interpolation estimation, estimation based on DFT and estimation based on transform domain, are analyzed and simulated. The computer simulation results show that the estimator based on transform domain is better than the other two.
引文
[1.1] A.J.Viterbi, CDMA Principles of Spread Spectrum Communication, Reading Wesley, 1995
[1.2] Ramjee Pradad., Shinsuke Hara, An Overview of Multicarrier CDMA, Proc. Of IEEE ISSSTA, 1996, ppp107-114
[1.3] 朱近康．扩展频谱技术及其应用．中国科学技术大学出版社，1993年1月第1版
[1.4] 查光明，熊贤祚．扩频通信．西安电子科技大学出版社，1990年12月
[1.5] S.Kondo, L.B.Milstein,Performance of multicarrier DS CDMA systems, IEEE Trans. Commun. Vol.44, Feb, 1996.
[2.1] R.Prasad. CDMA for wireless personal communications. London: Artech House Boston, 1996
[2.2] S.Hara.and R.Prasad. Overview of multicarrier CDMA. IEEE Communication Magazine,Dec. 1997,35(12): pp.126～133
[2.3] Hongnian Xing and Rinne,J.The performance analysis of a two dimensional CDMA system for frequency selective channels. GLOBECOM 1998.IEEE,Vol 5,1998 pp.2537～2542
[2.4] Lei Xiao and Qinglin Liang. A novel MC-2D-CDMA communication system and its detection methods. ICC 2000 pp.1223～1227.June 18-22,2000,New Orleans,USA
[2.5] L.C.Cimini,Jr., Analysis and simulation of a digital mobile channel using orthogonal frequency-division melplexing. IEEE Trans. Commun. Vol.33,No.7, pp.665～675,July 1985.
[2.6] M.Alard and R.Lassale,"Principles of modulation and channel coding for digital broadcasting for mobile receivers.",EBU Tech. Review, No.224, pp.3～25, Aug.1987
[2.7] Won Gi Jeon, Kyung Hi Chang, and Yong Soo Cho, An equalization technique for OFDM and MC-CDMA in a time-varying multipath fading channels. IEEE Trans. Commun. Vol.38, No.7, pp.2559～2532,July 1995
[3.1] E.A. Sourour and M. Nakagawa, Performance of orthogonal multicarrier CDMA in a multipath fading channel, IEEE Trans. Commun. Vol 44, No. 3, pp. 356-367, March 1996.
[3.2] V.M. Dasilva and E.S. Soura, Multicarrier orthogonal CDMA signals for quasi-synchronous communication systems, IEEE Journal on Selected Areas in Communications, Vol. 12, No. 5, pp. 842-852, June 1994.
[3.3] D.A. Pados and S.N.Batalama, Low-complexity blind detection of DS/CDMA signals: Auxiliary-Vector Receivers, IEEE Trans. Commun., Vol 45(12), pp. 1586-1594, Dec, 1997
[3.4] S.Kaiser, OFDM-CDMA versus DS-CDMA: performance evaluation for fading
channels, ICC' 95, Vol. 3, pp1722-1726,1995
[3.5] K. Fazel, Performance of convolutionally coded CDMA/OFDM in a frequency-time selective fading channel and its near-far resistance, ICC'94, Vol.3, pp1438-1442,1994
[4.1] J.Chow, J.Ciffi, J.Bingham, Equalizer training algorithms for multicarrier modulation systems, ICC'93, 35.2,pp760-764,1993
[4.2] H. Sari, G.. Karam, and I. Jeanclaude, Channel equalization and carrier synchronization in OFDM systems, presented at the 1993 Tirrenia Int. Workshop on Digital Communications, Sep. 1993, Tirrenia (Pisa),Italy
[4.3] O.van de Viel and L.Vandendorpe, Adaptive equalization structures for multitone CDMA systems, Proceedings of PIMRC'94, pp. 253-257,1994
[4.4] H.Sari, G. Karam, I. Jeanclaude, Frequency-domain equalization of mobile radio and terrestrial broadcast channels, Proc. Of GLOBECOM'94, San Francisco, USA, pp. 1-5, Oct. 1994
[4.5] J. Rinne and M. Renfors, A combined equalization scheme for orthogonal frequency division multiplexing systems in channels with multipath propagation and phase noise, Proc. Of FINSIG'95, Espoo, Finland, pp.40-44, June 1995
[4.6] M.D. Courville, P. Duhamel, P. Madec, and J. Palicot, Blind equalization of OFDM systems based on the minimization of a quadratic criterion, in Proc. 1996 IEEE Int. Conf. On commun., ICC'96, Jun. 23-27,1996,Dallas TX, pp. 1318-1322
[5.1] J.van de Beek, et al. On channel estimation in OFDM systems, IEEE International Vehicular Technology Conference, pp. 815～819, Chicago,USA, 1995
[5.2] O.Edfors, et al. OFDM channel estimation by singular value decomposition, Proc. IEEE 46th Vehicular Technology Conference, Atlanta, GA,USA,Apr. 1996, pp. 923-927
[5.3] J.Rinne and M. Renfors, Channel estimation in OFDM systems utilizing pilots, Proc. 1996 IEEE, Nordic Signal Processing symposium, Espoo, Finland, Sept. 1996, pp. 187-190
[5.4] F.Tufvesson and T. Maseng. Pilot assisted channel estimation for OFDM in Mobile cellular systems, Proc. VTC'97, pp. 1639-1643.Arizona, USA. May 97
[5.5] P. Hoeher, s. Kaiser, P. Robertson. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering, Proceedings ICASSP'97, pp. 1845-1848.Munich, Germany, Apr. 1997
[5.6] J.K.Cavers, An analysis of pilot symbol assisted modulation for rayleigh fading channels, IEEE Trans. Vehic. Tech. Vol.40, No. 4, pp.686-693,Nov.1991
[5.7] John G. Proakis, Digital communications, third edition, McGraw-Hill,USA 1995
[5.8] W. Jakes, Microwave Mobile communications, Wiley-Interscience, USA, 1974
[5.9] M. Julia Fernandez-Getino Garcia, et al. Efficient pilot patterns for channel estimation in OFDM systems over HF channels, VTC'99. July 1999
[5.10] M.J. Fernandez-Getino Garcia,J.m. Paez-Borrallo and S. Zazo, Novel pilot patterns for channel estimation in OFDM mobile systems over frequency
selective fading channel. Proc. PIMRC'99,Vol. 2,pp.363-367.Osaka, Japan,Sept. 12-15 1999
[5.11] R.Nilsson, O.Edfors,M.Sandell, P.O. Borjesson. An analysis of two-dimensional pilot-symbol assisted modulation for OFDM. Proc. ICUPC'97, San diego, USA, Oct. 12-16, 1997
[5.12] Classen, F. et al., Channel estimation units for an OFDM system suitable for mobile communication, ITG-Fachberichte, No. 135, pp.457-466, Sept. 1995
[1.2] Ramjee Pradad., Shinsuke Hara, An Overview of Multicarrier CDMA, Proc. Of IEEE ISSSTA, 1996, ppp107-114
[1.3] 朱近康．扩展频谱技术及其应用．中国科学技术大学出版社，1993年1月第1版
[1.4] 查光明，熊贤祚．扩频通信．西安电子科技大学出版社，1990年12月
[1.5] S.Kondo, L.B.Milstein,Performance of multicarrier DS CDMA systems, IEEE Trans. Commun. Vol.44, Feb, 1996.
[2.1] R.Prasad. CDMA for wireless personal communications. London: Artech House Boston, 1996
[2.2] S.Hara.and R.Prasad. Overview of multicarrier CDMA. IEEE Communication Magazine,Dec. 1997,35(12): pp.126～133
[2.3] Hongnian Xing and Rinne,J.The performance analysis of a two dimensional CDMA system for frequency selective channels. GLOBECOM 1998.IEEE,Vol 5,1998 pp.2537～2542
[2.4] Lei Xiao and Qinglin Liang. A novel MC-2D-CDMA communication system and its detection methods. ICC 2000 pp.1223～1227.June 18-22,2000,New Orleans,USA
[2.5] L.C.Cimini,Jr., Analysis and simulation of a digital mobile channel using orthogonal frequency-division melplexing. IEEE Trans. Commun. Vol.33,No.7, pp.665～675,July 1985.
[2.6] M.Alard and R.Lassale,"Principles of modulation and channel coding for digital broadcasting for mobile receivers.",EBU Tech. Review, No.224, pp.3～25, Aug.1987
[2.7] Won Gi Jeon, Kyung Hi Chang, and Yong Soo Cho, An equalization technique for OFDM and MC-CDMA in a time-varying multipath fading channels. IEEE Trans. Commun. Vol.38, No.7, pp.2559～2532,July 1995
[3.1] E.A. Sourour and M. Nakagawa, Performance of orthogonal multicarrier CDMA in a multipath fading channel, IEEE Trans. Commun. Vol 44, No. 3, pp. 356-367, March 1996.
[3.2] V.M. Dasilva and E.S. Soura, Multicarrier orthogonal CDMA signals for quasi-synchronous communication systems, IEEE Journal on Selected Areas in Communications, Vol. 12, No. 5, pp. 842-852, June 1994.
[3.3] D.A. Pados and S.N.Batalama, Low-complexity blind detection of DS/CDMA signals: Auxiliary-Vector Receivers, IEEE Trans. Commun., Vol 45(12), pp. 1586-1594, Dec, 1997
[3.4] S.Kaiser, OFDM-CDMA versus DS-CDMA: performance evaluation for fading
channels, ICC' 95, Vol. 3, pp1722-1726,1995
[3.5] K. Fazel, Performance of convolutionally coded CDMA/OFDM in a frequency-time selective fading channel and its near-far resistance, ICC'94, Vol.3, pp1438-1442,1994
[4.1] J.Chow, J.Ciffi, J.Bingham, Equalizer training algorithms for multicarrier modulation systems, ICC'93, 35.2,pp760-764,1993
[4.2] H. Sari, G.. Karam, and I. Jeanclaude, Channel equalization and carrier synchronization in OFDM systems, presented at the 1993 Tirrenia Int. Workshop on Digital Communications, Sep. 1993, Tirrenia (Pisa),Italy
[4.3] O.van de Viel and L.Vandendorpe, Adaptive equalization structures for multitone CDMA systems, Proceedings of PIMRC'94, pp. 253-257,1994
[4.4] H.Sari, G. Karam, I. Jeanclaude, Frequency-domain equalization of mobile radio and terrestrial broadcast channels, Proc. Of GLOBECOM'94, San Francisco, USA, pp. 1-5, Oct. 1994
[4.5] J. Rinne and M. Renfors, A combined equalization scheme for orthogonal frequency division multiplexing systems in channels with multipath propagation and phase noise, Proc. Of FINSIG'95, Espoo, Finland, pp.40-44, June 1995
[4.6] M.D. Courville, P. Duhamel, P. Madec, and J. Palicot, Blind equalization of OFDM systems based on the minimization of a quadratic criterion, in Proc. 1996 IEEE Int. Conf. On commun., ICC'96, Jun. 23-27,1996,Dallas TX, pp. 1318-1322
[5.1] J.van de Beek, et al. On channel estimation in OFDM systems, IEEE International Vehicular Technology Conference, pp. 815～819, Chicago,USA, 1995
[5.2] O.Edfors, et al. OFDM channel estimation by singular value decomposition, Proc. IEEE 46th Vehicular Technology Conference, Atlanta, GA,USA,Apr. 1996, pp. 923-927
[5.3] J.Rinne and M. Renfors, Channel estimation in OFDM systems utilizing pilots, Proc. 1996 IEEE, Nordic Signal Processing symposium, Espoo, Finland, Sept. 1996, pp. 187-190
[5.4] F.Tufvesson and T. Maseng. Pilot assisted channel estimation for OFDM in Mobile cellular systems, Proc. VTC'97, pp. 1639-1643.Arizona, USA. May 97
[5.5] P. Hoeher, s. Kaiser, P. Robertson. Two-dimensional pilot-symbol-aided channel estimation by Wiener filtering, Proceedings ICASSP'97, pp. 1845-1848.Munich, Germany, Apr. 1997
[5.6] J.K.Cavers, An analysis of pilot symbol assisted modulation for rayleigh fading channels, IEEE Trans. Vehic. Tech. Vol.40, No. 4, pp.686-693,Nov.1991
[5.7] John G. Proakis, Digital communications, third edition, McGraw-Hill,USA 1995
[5.8] W. Jakes, Microwave Mobile communications, Wiley-Interscience, USA, 1974
[5.9] M. Julia Fernandez-Getino Garcia, et al. Efficient pilot patterns for channel estimation in OFDM systems over HF channels, VTC'99. July 1999
[5.10] M.J. Fernandez-Getino Garcia,J.m. Paez-Borrallo and S. Zazo, Novel pilot patterns for channel estimation in OFDM mobile systems over frequency
selective fading channel. Proc. PIMRC'99,Vol. 2,pp.363-367.Osaka, Japan,Sept. 12-15 1999
[5.11] R.Nilsson, O.Edfors,M.Sandell, P.O. Borjesson. An analysis of two-dimensional pilot-symbol assisted modulation for OFDM. Proc. ICUPC'97, San diego, USA, Oct. 12-16, 1997
[5.12] Classen, F. et al., Channel estimation units for an OFDM system suitable for mobile communication, ITG-Fachberichte, No. 135, pp.457-466, Sept. 1995