宽带无线全双工MIMO-OFDM系统回波干扰抑制技术研究

发布时间：2018-05-01 04:23

本文选题：全双工系统 + 自干扰信号　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：本文研究宽带无线通信全双工(Full Duplex,FD)多输入输出(Multiple Input Multiple Output,MIMO)正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统回波自干扰抑制技术。针对现有FD系统实现技术的关键难点问题与不足,重点研究了两类宽带全双工系统回波自适应干扰抑制方法,包括被动式的自适应干扰抑制方法,以及基于空间波束成型(Beamforming)的主动式自适应干扰抑制方法。论文首先总结了现代无线全双工技术的发展演进及其存在关键难点问题;基于典型的MIMO-OFDM系统构架和数学模型,刻画了FD系统回波自干扰问题产生的原因、表现及其对系统性能的影响,阐述了全双工系统的相关理论基础;随后,重点介绍了各类信道条件下全双工系统可达系统容量的计算方法;进一步,分析评价了两种典型的全双工自干扰抑制方法,包括模拟域自干扰抑制及数字域自干扰抑制,通过选取其中具有代表性算法,对其技术优缺点,包括误码率、可达系统容量以及计算复杂度等方面进行了分析评价。以此为基础,鉴于现有FD系统大多基于单天线配置、回波自干扰抑制算法复杂度高以及多数算法未考虑非理想衰落信道对传输性能影响的缺陷,本文针对多天线宽带无线局域网(Wireless Local Area Network,WLAN)系统框架,首先提出了一种被动式的无线FD-MIMO-OFDM系统基带回波自干扰抑制方案,该方案结合天线物理隔离与模拟域回波抵消处理,在数字域利用归一化最小均方(Normalized Least Mean Squares,NLMS)学习算法自适应抵消自干扰信号;给出了该方案详尽的信号处理流程,从误码率性能、系统容量两个方面分析了该方案的可行性,理论推导了该系统可达系统容量。理论分析与仿真结果表明,该方案在采用间距为20cm的天线对时,可实现30dB左右的数字域基带抑制效果。自适应算法与理想无干扰半双工(Half Duplex,HD)MIMO系统相比,BER性能仅损失0.3-0.5dB,但其系统容量可达到理想HD-MIMO系统容量的1.5倍;而与理想自干扰抑制FD-MIMO系统相比,虽然该方案误码率有所增加,但其系统容量可达理想系统容量的80%;仿真结果验证了该方案的可行性及其优良性能。进一步,针对被动式抑制尚存在方式简单且抑制效果有限的问题,本文又将空域波束成型方法引入FD系统构架,提出了一种联合主动式抑制机制的无线FD-MIMO-OFDM系统回波自干扰抑制方案,从系统复杂度、误码率、系统容量三个方面分析了该方案的可行性。理论分析与仿真结果表明,在理想信道条件下,该方案可达系统容量为理想HD-MIMO系统的1.7倍;而在衰落信道条件下,该方案以信噪比牺牲0.3-0.5dB的代价,获得的可达系统容量为未采用空域波束成型FD-MIMO系统的1.2倍。
[Abstract]:In this paper, the echo self interference suppression technique for full Duplex (full Duplex) Multiple-Input-Output MIMO-OFDM (orthogonal Frequency Division Multiplexing OFDM) system for wideband wireless communication is studied. Aiming at the key problems and shortcomings of the current FD system implementation techniques, two kinds of adaptive interference suppression methods for wideband full-duplex systems are studied, including passive adaptive interference suppression methods. And the active adaptive interference suppression method based on spatial beamforming. Firstly, this paper summarizes the evolution of modern wireless full-duplex technology and its key and difficult problems, and describes the causes of echo self-interference problem in FD system based on typical MIMO-OFDM system architecture and mathematical model. Performance and its influence on the system performance, the theoretical basis of full-duplex system is expounded. Then, the calculation methods of the capacity of full-duplex system under various channel conditions are introduced. Two typical full-duplex self-interference suppression methods are analyzed and evaluated, including analog domain self-interference suppression and digital self-interference suppression. The capacity and computational complexity of the reachable system are analyzed and evaluated. Based on this, most of the existing FD systems are based on single antenna configuration, the complexity of echo self-interference suppression algorithm is high, and most of the algorithms do not consider the influence of non-ideal fading channel on transmission performance. In this paper, a passive baseband echo self-interference suppression scheme is proposed for multi-antenna wideband wireless Local Area network (WLAN) system, which combines antenna physical isolation with analog domain echo cancellation. In digital domain, the normalized Least Mean squares NLMS-based learning algorithm is used to adaptively cancel the self-interference signal, and the detailed signal processing flow is given. The feasibility of the scheme is analyzed from two aspects: error rate performance and system capacity. The reachable system capacity of the system is deduced theoretically. The theoretical analysis and simulation results show that the proposed scheme can achieve the baseband suppression effect in the digital domain of 30dB when the antenna pair with spacing of 20cm is adopted. Compared with the ideal half-duplex HD-MIMO system, the adaptive algorithm has a performance loss of 0.3-0.5 dB, but its system capacity is 1.5 times that of the ideal FD-MIMO system, although the bit error rate of the proposed scheme is higher than that of the ideal self-interference suppression FD-MIMO system. But the system capacity can reach 80% of the ideal system capacity, and the simulation results verify the feasibility of the scheme and its excellent performance. Furthermore, aiming at the problem that passive suppression still exists in simple way and limited suppression effect, the spatial beamforming method is introduced into the framework of FD system in this paper. An echo self-interference suppression scheme for wireless FD-MIMO-OFDM systems with combined active suppression mechanism is proposed. The feasibility of the scheme is analyzed from three aspects: system complexity, bit error rate and system capacity. Theoretical analysis and simulation results show that the system capacity of the proposed scheme is 1.7 times that of the ideal HD-MIMO system under ideal channel conditions, while in fading channel, the scheme sacrifices the cost of 0.3-0.5dB with SNR. The reachable system capacity is 1. 2 times that of the non-spatial beamforming FD-MIMO system.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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