直接序列扩频系统的线性调频干扰抑制技术研究
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摘要
扩展频谱通信技术(简称扩频通信)是一种新兴的高科技通信技术，具有大容量、抗干扰、低截获率以及可实现码分多址(CDMA)等优点，在军事和民用通信系统中都得到了广泛的应用，并成为下一代移动通信的技术基础。扩频通信系统中，直接序列扩频(Direct Sequence Spread Spectrum，DSSS)技术的应用最为普遍，与窄带通信系统相比，DSSS系统有着很强的抗干扰能力，其干扰容限取决于系统的扩频增益(带宽)，但由于频谱资源有限，各类扩频系统的增益受带宽的限制不可能任意地提高，因此当外部干扰的强度超过了系统的干扰容限时，系统的性能将会急剧下降。在强干扰环境中，应考虑在系统中施以干扰抑制措施，以提高系统的接收性能。目前，干扰抑制领域的研究成果大多集中在窄带干扰的抑制上，而近年来，宽带非平稳干扰引起人们越来越多的重视，所以本文以典型的非平稳信号——线性调频(LFM)信号为干扰模型，重点研究DSSS系统对LFM干扰的抑制能力及相应的抗干扰技术。
本文首先对DSSS通信系统中的各种时频域干扰抑制方法进行了简要的概述，然后详细分析了DSSS系统自身对LFM干扰的抑制能力，得出了干扰各参数对系统误码率性能的影响；在此基础上，提出了基于离散Chirp-Fourier变换(Discrete Chirp-Fourier Transform，DCFT)的LFM干扰自适应干扰抑制方法，并把该方法用于DSSS系统的接收机中，在DCFT域实现干扰信号的检测、参数估计和抑制，性能分析表明，本文提出的自适应干扰抑制方法可获得较好的误码率性能，克服了其它变换域算法对强干扰抑制效果不佳的缺点。由于Chirp-Fourier变换可由一维FFT快速实现，和其它基于二维时频分析工具的滤波算法相比，本文提出的算法降低了计算的复杂度，实现更为简便。
Spread spectrum communication is a sort of new high-tech communication technique, it has a number of internal advantages, such as large capacity, interference immunity, low probability of intercept, code division multiple access (CDMA) etc, which make it get broad applications in civilian as well as military environments, and become the technical groundwork of next generation mobile communications. Compared with narrowband communication systems, DSSS systems have remarkable interference suppressing ability, whose interference tolerance depends on systemic spreading gain (bandwidth). On account of the restriction of frequency resource, various DS system spreading gains can't be improved arbitrarily. Therefore, when outside interference might be more powerful than accepted tolerance, it is necessary to introduce corresponding interference suppressing measures for improving system performance. At present, most of the research achievements concentrate on suppressing narrowband interference. In recent years, the
effect of broadband non-stationary interference on spread spectrum systems gets more and more attention, of which general type is linear frequency modulated (LFM) interference, so in this thesis we concentrate on performance analysis of DSSS systems' immunity to LFM interference and corresponding suppressing measures.
In this thesis, first the interference suppressing measures in time-frequency(t-f) domain in DSSS communication systems are summarized; then a detailed analysis of the interference suppressing ability of DSSS systems without any suppressing measures is carried out, the closed form of bit-error-rate (BER) is educed, and the simulation of BER changing with the interference parameters are simulated; at last, an novel adaptive interference suppressing algorithm based on discrete Chirp-Fourier transform is proposed and the interference detection, estimation and suppression are carried out in DCFT domain.. The performance analyses have shown that the proposed algorithm distinctly can obtain the better BER performance and overcomes the shortcoming of other transform domain algorithms that are disable to powerful interference. Because
Chirp-Fourier transform can be implemented by FFT, comparing with other filtering algorithms based two-dimensional t-f tool, it is easy in computation and simple in implementation.
本文首先对DSSS通信系统中的各种时频域干扰抑制方法进行了简要的概述，然后详细分析了DSSS系统自身对LFM干扰的抑制能力，得出了干扰各参数对系统误码率性能的影响；在此基础上，提出了基于离散Chirp-Fourier变换(Discrete Chirp-Fourier Transform，DCFT)的LFM干扰自适应干扰抑制方法，并把该方法用于DSSS系统的接收机中，在DCFT域实现干扰信号的检测、参数估计和抑制，性能分析表明，本文提出的自适应干扰抑制方法可获得较好的误码率性能，克服了其它变换域算法对强干扰抑制效果不佳的缺点。由于Chirp-Fourier变换可由一维FFT快速实现，和其它基于二维时频分析工具的滤波算法相比，本文提出的算法降低了计算的复杂度，实现更为简便。
Spread spectrum communication is a sort of new high-tech communication technique, it has a number of internal advantages, such as large capacity, interference immunity, low probability of intercept, code division multiple access (CDMA) etc, which make it get broad applications in civilian as well as military environments, and become the technical groundwork of next generation mobile communications. Compared with narrowband communication systems, DSSS systems have remarkable interference suppressing ability, whose interference tolerance depends on systemic spreading gain (bandwidth). On account of the restriction of frequency resource, various DS system spreading gains can't be improved arbitrarily. Therefore, when outside interference might be more powerful than accepted tolerance, it is necessary to introduce corresponding interference suppressing measures for improving system performance. At present, most of the research achievements concentrate on suppressing narrowband interference. In recent years, the
effect of broadband non-stationary interference on spread spectrum systems gets more and more attention, of which general type is linear frequency modulated (LFM) interference, so in this thesis we concentrate on performance analysis of DSSS systems' immunity to LFM interference and corresponding suppressing measures.
In this thesis, first the interference suppressing measures in time-frequency(t-f) domain in DSSS communication systems are summarized; then a detailed analysis of the interference suppressing ability of DSSS systems without any suppressing measures is carried out, the closed form of bit-error-rate (BER) is educed, and the simulation of BER changing with the interference parameters are simulated; at last, an novel adaptive interference suppressing algorithm based on discrete Chirp-Fourier transform is proposed and the interference detection, estimation and suppression are carried out in DCFT domain.. The performance analyses have shown that the proposed algorithm distinctly can obtain the better BER performance and overcomes the shortcoming of other transform domain algorithms that are disable to powerful interference. Because
Chirp-Fourier transform can be implemented by FFT, comparing with other filtering algorithms based two-dimensional t-f tool, it is easy in computation and simple in implementation.
引文
[1] Milstein. Interference rejection techniques in spread spectrum communications. Proceedings of the IEEE, 1988, 76(6): 657～671.
[2] L. Garth, R. Vijayan and H. V. Poor. A new approach to interference suppression in spread spectrum system. MILCOM'91, IEEE, 1991, 17(4): 1～5.
[3] L. R. Rusch and H. V. Poor. Narrowband interference suppression in CDMA spread spectrum communications. IEEE Trans. on Communo, 1994, 42(4): 1969～1979.
[4] J. Yoon and J. F. Doherty. A fast receiver for interference suppression in DS-CDMA system. MILCOM'99, IEEE, 821～825.
[5] U. Madhow and M. Honig. MMSE interference suppression for DSSS CDMA. IEEE Trans. on Commun., 1994, 42(12): 3178～3187.
[6] W. R. Wu and F. F. Yu. New nonlinear algorithms for estimating and suppressing narrowband interference in DS spread spectrum systems. IEEE Trans. on commun., 1996, 44(4): 508～515.
[7] J. D. Laster and J. H. Reed. Interference rejection in digital wireless communications. IEEE SP. Magazine, 1997, 37～61.
[8] 李冲泥，胡光锐．多分辨重叠变换在扩频通信系统抗干扰中的应用，电子学报， 2000，28(4)：17～19．
[9] 王坤杰，周祖成等．直扩通信中非线性窄带干扰抑制滤波器的性能分析．电子学报，1998，26(2)：77～79．
[10] 仇佩亮，郑数生，姚庆栋．扩频通信中干扰抑制的非线性滤波技术．通信学报，1995，16(2)：20～28．
[11] 唐瑜，李乐民．扩频通信中稳健自适应抗干扰技术的研究．通信学报，1998，19(7)：36～43．
[12] A. Jeffrey, S. Young and J. Lehnet. Analysis of DFT-based frequency excision algorithms for Direct-Sequence Spread Spectrum communications. IEEE Trans. on Commun., 1998, 46(8): 1076～1087.
[13] C. N. Li, G. R. Hu and M. J. Liu. Narrowband interference excision in spread spectrum systems using self-orthogonalizing transform-domain adaptive filters. IEEE Journal
on selected areas in communications. 2000, 18(3): 403～406.
[14] S. G. Glisic, et al. Rejection of frequency sweeping signal in DS spread spectrum systems using complex adaptive filters. IEEE Trans. on commun., 1999, 43(1): 136～145.
[15] 张贤达，保铮著．非平稳信号分析与处理(第一版)．北京：国防工业出版社，1998．
[16] M. Amin and X. Ouyang. Suppression of nonstationary interference in direct sequency spread spectrum communications using the Short Time Fourier Transform. Editor, L. Debnath, Wavelet Transforms and Time-Frequency Signal Analysis, 1998, 214～241.
[17] X. Ouyang and M. Amin. Performance analysis of the DS/SS communications receiver implementing a short time Fourier transform interference excision system. IEEE International Symposium on Time-Frequency and Time Scale Analysis, Pittsburgh: 1998, 393～396.
[18] X. Ouyang and M. Amin. Time-Frequency concentration measures for nonstationary interference excision in DS/SS communications. Proceedings of IEEE Sarnoff symposium on Advanced in Wired and Wireless communications, College of New Jersey, Trenton, NJ: 1998, 246～249.
[19] X. Ouyang and M. Amin. Short-time Fourier transform receiver for non-stationary interference excision in DSSS communications. IEEE Trans. on SE, 2001, 49(4): 851～863.
[20] M. Amin. Interference mitigation in spread spectrum communication systems using time-frequency distributions. IEEE Trans. on SP., 1997, 45(1): 90～101.
[21] C. Wang and M. Amin. Performance analysis of instantaneous frequency based interference excision techniques in spread spectrum communications. IEEE Trans. on SP., 1998, 46(1): 70～82.
[22] M. Amin, C. Wang and A. Lindsey. Optimum interference excision in spread spectrum communications using open-loop adaptive filters, IEEE Trans. on SP., 1999, 47(7): 1966～1976.
[23] S. Barbarossa and A. Scaglione. Adaptive time-varying cancellation of wideband
interferences in spread-spectrum communications based on time-frequency distributions. IEEE Trans. on SP., 1999, 47(4): 957～965.
[24] S. Lach, M. Amin and A. Lindsey. Broadband non-stationary interference excision for spread spectrum communications using time-frequency synthesis, Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing. Sealtle, WA: 1998, 3257～3260.
[25] S. Lach and M. Amin. Multiple component interference excision in spread spectrum communication using Wigner distribution synthesis technique, Proceedings of IEEE Sarnoff symposium on Advances in Wired and Wireless communications. College of New Jersey, Trenton, NJ: 1998, 179～182.
[26] S. Lach, M. Amin and A. R. Lindsey. Broadband interference excision for software-radio spread spectrum communications using time-frequency synthesis. IEEE Journal on Selected Areas in Communications, 1999, 17(4): 160～170.
[27] M. Amin and G. Mandapati. Nonstationary interference excision in spread spectrum communications using projection filtering methods. Proceedings of the ASILOMAR Conference on Signals, systems and Computers. Pacific Grove, CA: 1998, 827～831.
[28] R. Ramineni, M. Amin and A. Lindsey. Suppression of FM interference in DSSS communication systems using projection techniques. Proceedings of the ASILOMAR Conference on Signals, systems and Computers. Pacific Grove, CA: 1999, 1063～1066.
[29] R. Ramineni, M. Amin and A. Lindsey. Performance analysis of subspace projection techniques for interference excision in DSSS communications. Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing. Turkey: 2000, 294～297.
[30] R. Ramineni, M. Amin and A. Lindsey. Analysis of nonstationary interference excision in spread spectrum communications using orthogonal projections. Proceedings of IEEE Sarnoff symposium on Advanced in Wired and Wireless communications. College of New Jersey, Trenton, NJ: 1999, 290～293.
[31] Akay and F. Boudreaux-Bartels. Broadband interference excision in spread-spectrum
communication systems via fractional Fourier transforms. Proceedings.of the 31st Asilomar Conference on Signals, Systems and Computers. Pacific Grove, California: 1998, 832～837.
[32] Y. Q. Dong, R. Tao and S. Y. Zhou et al. The fractional Fourier analysis of multicomponent LFM signal. Chinese Journal of Electronics, 1999, 8(3): 326～329.
[33] 沈允春编著，扩谱技术(第一版)，北京：国防工业出版社，1995：235～270．
[34] A. Papoulis. Probablity Randon Variables and Stochastic Process. New York: Mc. GrawHill, 1965.
[35] 邱永红，甘仲民，潘亚汉．软件仿真在扩频通信系统中的应用研究．系统仿真学报，1999, 11(6)：461～464．
[36] X. G. Xia. Discrete Chirp-Fouriour transform and its application to chirp rate estimation. IEEE Trans. on SE, 2000, 48(11): 3122～3133.
[37] 孙泓波，郭欣，顾红等．修正离散Chirp-Fourier变换及其在SAR运动目标检测中的应用．电子学报，2003，31(1)：25～28．
[38] T. A. C. M. Classen and W. F. G. Mecklenbrauker. The Wigner distribution-A tool for time-frequency signal analysis: Part Ⅱ: Discrete time signals. Phillips Jour.Research., 1980, 35(6): 276～300.
[39] S. R. Lach, M. G. Amin and A.R.Lindsey. Broadband interference excision for sofuware-radio spread-spectrum communication using time-frequency distribution systhesis. IEEE Journal on Selected Areas In Communications, 1999, 17(4): 160～170.
[40] J. C. Wood and D. T. Barry. Radon Transformation of time-frequency distribution for analysis of multi-component signal. IEEE Trans. on SP., 1994, 42(11): 3166～3177.
[41] M. S. Wang, A. K. Chan and C. K. Chui. Linear frequency-modulated signal detection using Radon-ambiguity transform. IEEE Trans. on SP., 1998, 46(3): 571～586.
[42] T. J. Abatzoglou. Fast maximum likelihood joint estimation of frequency and frequency rate. IEEE Trans. on AES, 1986, 22(6): 708～715.
[2] L. Garth, R. Vijayan and H. V. Poor. A new approach to interference suppression in spread spectrum system. MILCOM'91, IEEE, 1991, 17(4): 1～5.
[3] L. R. Rusch and H. V. Poor. Narrowband interference suppression in CDMA spread spectrum communications. IEEE Trans. on Communo, 1994, 42(4): 1969～1979.
[4] J. Yoon and J. F. Doherty. A fast receiver for interference suppression in DS-CDMA system. MILCOM'99, IEEE, 821～825.
[5] U. Madhow and M. Honig. MMSE interference suppression for DSSS CDMA. IEEE Trans. on Commun., 1994, 42(12): 3178～3187.
[6] W. R. Wu and F. F. Yu. New nonlinear algorithms for estimating and suppressing narrowband interference in DS spread spectrum systems. IEEE Trans. on commun., 1996, 44(4): 508～515.
[7] J. D. Laster and J. H. Reed. Interference rejection in digital wireless communications. IEEE SP. Magazine, 1997, 37～61.
[8] 李冲泥，胡光锐．多分辨重叠变换在扩频通信系统抗干扰中的应用，电子学报， 2000，28(4)：17～19．
[9] 王坤杰，周祖成等．直扩通信中非线性窄带干扰抑制滤波器的性能分析．电子学报，1998，26(2)：77～79．
[10] 仇佩亮，郑数生，姚庆栋．扩频通信中干扰抑制的非线性滤波技术．通信学报，1995，16(2)：20～28．
[11] 唐瑜，李乐民．扩频通信中稳健自适应抗干扰技术的研究．通信学报，1998，19(7)：36～43．
[12] A. Jeffrey, S. Young and J. Lehnet. Analysis of DFT-based frequency excision algorithms for Direct-Sequence Spread Spectrum communications. IEEE Trans. on Commun., 1998, 46(8): 1076～1087.
[13] C. N. Li, G. R. Hu and M. J. Liu. Narrowband interference excision in spread spectrum systems using self-orthogonalizing transform-domain adaptive filters. IEEE Journal
on selected areas in communications. 2000, 18(3): 403～406.
[14] S. G. Glisic, et al. Rejection of frequency sweeping signal in DS spread spectrum systems using complex adaptive filters. IEEE Trans. on commun., 1999, 43(1): 136～145.
[15] 张贤达，保铮著．非平稳信号分析与处理(第一版)．北京：国防工业出版社，1998．
[16] M. Amin and X. Ouyang. Suppression of nonstationary interference in direct sequency spread spectrum communications using the Short Time Fourier Transform. Editor, L. Debnath, Wavelet Transforms and Time-Frequency Signal Analysis, 1998, 214～241.
[17] X. Ouyang and M. Amin. Performance analysis of the DS/SS communications receiver implementing a short time Fourier transform interference excision system. IEEE International Symposium on Time-Frequency and Time Scale Analysis, Pittsburgh: 1998, 393～396.
[18] X. Ouyang and M. Amin. Time-Frequency concentration measures for nonstationary interference excision in DS/SS communications. Proceedings of IEEE Sarnoff symposium on Advanced in Wired and Wireless communications, College of New Jersey, Trenton, NJ: 1998, 246～249.
[19] X. Ouyang and M. Amin. Short-time Fourier transform receiver for non-stationary interference excision in DSSS communications. IEEE Trans. on SE, 2001, 49(4): 851～863.
[20] M. Amin. Interference mitigation in spread spectrum communication systems using time-frequency distributions. IEEE Trans. on SP., 1997, 45(1): 90～101.
[21] C. Wang and M. Amin. Performance analysis of instantaneous frequency based interference excision techniques in spread spectrum communications. IEEE Trans. on SP., 1998, 46(1): 70～82.
[22] M. Amin, C. Wang and A. Lindsey. Optimum interference excision in spread spectrum communications using open-loop adaptive filters, IEEE Trans. on SP., 1999, 47(7): 1966～1976.
[23] S. Barbarossa and A. Scaglione. Adaptive time-varying cancellation of wideband
interferences in spread-spectrum communications based on time-frequency distributions. IEEE Trans. on SP., 1999, 47(4): 957～965.
[24] S. Lach, M. Amin and A. Lindsey. Broadband non-stationary interference excision for spread spectrum communications using time-frequency synthesis, Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing. Sealtle, WA: 1998, 3257～3260.
[25] S. Lach and M. Amin. Multiple component interference excision in spread spectrum communication using Wigner distribution synthesis technique, Proceedings of IEEE Sarnoff symposium on Advances in Wired and Wireless communications. College of New Jersey, Trenton, NJ: 1998, 179～182.
[26] S. Lach, M. Amin and A. R. Lindsey. Broadband interference excision for software-radio spread spectrum communications using time-frequency synthesis. IEEE Journal on Selected Areas in Communications, 1999, 17(4): 160～170.
[27] M. Amin and G. Mandapati. Nonstationary interference excision in spread spectrum communications using projection filtering methods. Proceedings of the ASILOMAR Conference on Signals, systems and Computers. Pacific Grove, CA: 1998, 827～831.
[28] R. Ramineni, M. Amin and A. Lindsey. Suppression of FM interference in DSSS communication systems using projection techniques. Proceedings of the ASILOMAR Conference on Signals, systems and Computers. Pacific Grove, CA: 1999, 1063～1066.
[29] R. Ramineni, M. Amin and A. Lindsey. Performance analysis of subspace projection techniques for interference excision in DSSS communications. Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing. Turkey: 2000, 294～297.
[30] R. Ramineni, M. Amin and A. Lindsey. Analysis of nonstationary interference excision in spread spectrum communications using orthogonal projections. Proceedings of IEEE Sarnoff symposium on Advanced in Wired and Wireless communications. College of New Jersey, Trenton, NJ: 1999, 290～293.
[31] Akay and F. Boudreaux-Bartels. Broadband interference excision in spread-spectrum
communication systems via fractional Fourier transforms. Proceedings.of the 31st Asilomar Conference on Signals, Systems and Computers. Pacific Grove, California: 1998, 832～837.
[32] Y. Q. Dong, R. Tao and S. Y. Zhou et al. The fractional Fourier analysis of multicomponent LFM signal. Chinese Journal of Electronics, 1999, 8(3): 326～329.
[33] 沈允春编著，扩谱技术(第一版)，北京：国防工业出版社，1995：235～270．
[34] A. Papoulis. Probablity Randon Variables and Stochastic Process. New York: Mc. GrawHill, 1965.
[35] 邱永红，甘仲民，潘亚汉．软件仿真在扩频通信系统中的应用研究．系统仿真学报，1999, 11(6)：461～464．
[36] X. G. Xia. Discrete Chirp-Fouriour transform and its application to chirp rate estimation. IEEE Trans. on SE, 2000, 48(11): 3122～3133.
[37] 孙泓波，郭欣，顾红等．修正离散Chirp-Fourier变换及其在SAR运动目标检测中的应用．电子学报，2003，31(1)：25～28．
[38] T. A. C. M. Classen and W. F. G. Mecklenbrauker. The Wigner distribution-A tool for time-frequency signal analysis: Part Ⅱ: Discrete time signals. Phillips Jour.Research., 1980, 35(6): 276～300.
[39] S. R. Lach, M. G. Amin and A.R.Lindsey. Broadband interference excision for sofuware-radio spread-spectrum communication using time-frequency distribution systhesis. IEEE Journal on Selected Areas In Communications, 1999, 17(4): 160～170.
[40] J. C. Wood and D. T. Barry. Radon Transformation of time-frequency distribution for analysis of multi-component signal. IEEE Trans. on SP., 1994, 42(11): 3166～3177.
[41] M. S. Wang, A. K. Chan and C. K. Chui. Linear frequency-modulated signal detection using Radon-ambiguity transform. IEEE Trans. on SP., 1998, 46(3): 571～586.
[42] T. J. Abatzoglou. Fast maximum likelihood joint estimation of frequency and frequency rate. IEEE Trans. on AES, 1986, 22(6): 708～715.