【作者】 郝张红；

【导师】 唐友喜； 赵宏志；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2013， 博士

【摘要】 干扰是影响无线通信系统容量和通信质量的重要因素，直接序列扩频通信技术由于具有良好的抗干扰能力等特点，在军事通信和民用通信领域得到广泛的应用。但是，由于扩频增益的限制，直接序列扩频通信系统本身的抗干扰能力有限，如何在不增加扩频增益的前提下，进一步提高扩频通信系统的抗干扰能力，对于军事通信和民用通信都具有重大的意义。现有直接序列扩频通信系统抗干扰技术的研究通常假设干扰是时不变的，而在实际系统中，干扰具有时变特性。本文以时变干扰为研究对象，对CDMA系统中的时变单音干扰抑制、时变多音干扰抑制和时变多址干扰抑制进行了研究。首先，针对时变单音干扰场景，分析了CDMA系统在时变单音干扰下的误码率性能，推导了理论误码率公式，分析了多普勒频移对误码率性能的影响，并通过仿真验证了理论分析的正确性；并且针对时变单音干扰，提出了频域干扰估计时域对消算法，推导了干扰抑制后的理论误码率公式。分析和仿真结果表明，理论分析与仿真结果相吻合，所提算法的误码率性能由干扰功率和多普勒频移等因素决定。在加性白高斯信道中，当信噪比为10dB，扩频增益为16，多普勒频移为100Hz时，所提算法可以抑制30dB的单音干扰。其次，针对时变多音干扰场景，分析了CDMA系统在时变多音干扰下的误码率性能，推导了理论误码率公式，分析了多普勒频移对误码率性能的影响，并通过仿真验证了理论分析的正确性；并且针对时变多音干扰，提出了频域干扰检测抑制算法。分析与仿真结果表明，所提算法的误码率性能由干扰功率和多普勒频移等因素决定，在加性白高斯信道下，存在三个单音干扰，信噪比为10dB，扩频增益为16，多普勒频移为100Hz时，所提算法可以抑制20dB的多音干扰。最后，针对CDMA系统中的时变多址干扰，提出了频域干扰抑制合并算法，分析了所提算法在单载波CDMA系统中的误码率下限。所提算法不需要干扰用户和信道的先验信息。仿真结果表明，与频域最大比合并相比，所提的频域干扰抑制合并算法可以降低干扰对系统的影响。在一发两收，存在三个等功率干扰用户，扩频增益为16，误码率为10^-3时，所提算法输出的信噪比较频域最大比合并算法提高了2dB。本文研究了直接序列扩频通信系统中的时变干扰抑制技术，研究丰富了现有的干扰抑制方法，具有理论和实用价值，其结果可以应用于第三代和新一代无线通信系统中。更多还原

【Abstract】 Interference is the important factor that affects the capacity and quality of thecommunication system, direct sequence spread spectrum （DSSS） communicationsystem has been widely employed in military and civilian communications, for its goodanti-interference capability and other characteristics.However, the capability is relatedto the spreading gain, when the spreading gain is restricted, the anti-interferencecapability is limited. How to improve the anti-interference capability of DSSScommunication system is significant for military and civilian communications withoutthe increasing spreading gain.Existing activeinterference suppression methods used in DSSS considered that theinterferences are time-invariant. But in some practical scenarios, the interferences havethe characteristic of time-varying.In this paper, time-varying interferenceis studied，including the suppression of time-varying single tone jamming （STJ）, the suppression oftime-varying multitone jamming （MTJ）, and the suppression of time-varying multipleaccess interference （MAI） in CDMA systems.First, the BER performance of CDMA in the presence of time-varying STJ isanalyzed. The BER expression is derived and the effect of the Doppler shift on theperformance is discussed. The accuracy of the BER estimation evaluated by theexpression is verified by computer simulations. Furthermore, a frequency cancellationmethod is proposed to suppress the time-varying STJ. The BER expression is analyzedto assess the performance of the proposed method. Simulation results demonstrate theeffectiveness of the method in mitigating time-varying STJ and approaching theinterference-free performance limit over practical ranges of STJ power levels andmobility levels. Under the condition of AWGN channel, whenSNR （Signal-to-NoiseRatio） is10dB,the spreading gain is16, Doppler frequency is100Hz, JSR（Jamming-to-Signal power Ratio） is less than30dB, theSTJ can be suppressed by theproposed method.Second, the BER performance of CDMA in the presence of time-varying multi-tonejamming （MTJ） is analyzed. The BER expression is derived and the effect of the Doppler shift on the performance is discussed. The accuracy of the BER estimationevaluated by the expression is verified by computer simulations. Besides, a method offrequency domain interference detection is proposed to suppress the time-varying MTJ.The performance of the proposed method is validated by computer simulations, and thesimulation results show that the effectiveness of the proposed method inmitigatingtime-varying MTJ over practical ranges of MTJ power levels and mobilitylevels.Under the condition of AWGN channel,there are three STJ in the systems, SNR is10dB,the spreading gain is16, Doppler frequency is100Hz, JSR is less than20dB,theMTJ can be suppressed by the proposed method.Finally, a frequency domain interference rejection combining （FD-IRC） algorithm isproposed to suppress the time-varyingMAI for uplink CDMA systems. The theoreticalBER lower bound of the FD-IRC in cyclic prefix CDMA （CP-CDMA） is derived. Theproposed method doesn’t require any priori information about the interfering user andchannel. The simulation results show that the proposed method can improve theperformance of the system compared to frequency domain maximal ratio combining.When there are three interfering users in the system and each of them has the samepower as the desired user, at the BER value of10^-3, andthe spreading gain is16, theSNR of the proposed method is improved by2dB.The research in this thesis explores the problem of time-varyinginterferencesuppression techniques for DSSS systems, which extends the existingresearches and has theoretical and practical values. The research results can be appliedto the3G and next generation mobile communication systems.更多还原