正交频分复用系统峰均比抑制问题研究

发布时间：2018-01-17 22:15

本文关键词：正交频分复用系统峰均比抑制问题研究　出处：《西安电子科技大学》2014年博士论文　论文类型：学位论文

【摘要】：正交频分复用(OFDM)技术因其高频谱效率、强抗多径能力及低复杂度等诸多优点,被广泛采纳为多种无线通信系统的物理层标准。该技术的一个主要缺陷就是信号幅度具有较大的波动范围,即峰均比过大。当信号峰值超过放大器线性工作范围时,会产生非线性失真,降低系统性能。为了提高系统性能,需要降低放大器的工作电平,将OFDM信号容纳在放大器线性区范围内,而这会严重降低功率放大器的功率效率。在无线通信网络中,迫切需要减少能源消耗以降低系统运营成本,这要求尽可能提高功率放大器的功率效率。因此,对OFDM系统来说,放大器功率效率和系统性能之间的矛盾就变得更为尖锐。本文从信号处理出发,就如何有效降低OFDM信号峰均比以提升放大器功率效率进行了研究,具体的研究工作和创新性成果如下:1.针对压扩变换处理在降低OFDM信号峰均比时会产生压扩失真,造成系统性能恶化的问题,以提升OFDM系统的误码率性能为出发点,就压扩变换对OFDM信号造成的非线性影响进行了数学推导和理论分析,提出了压扩函数的通用设计准则。并基于提出的通用设计准则提出了两种失真最小化的压扩变换技术:分段线性压扩技术和分段指数压扩技术。通过合理设计压扩参数,分段线性压扩技术和分段指数压扩技术均能在有效抑制峰均比的同时减少压扩失真,提升系统误码率性能,获得良好的误码率和峰均比抑制性能折中。此外,通过合理选择压扩函数的分段点,分段线性压扩技术和分段指数压扩技术均具有很高的设计灵活度,可以满足更多的系统需求。2.针对理想载波注入技术复杂度过高的问题,提出了一种基于有序搜索的载波注入技术。该技术通过利用非线性失真频域信号包含的信号调整信息,确定载波搜索顺序,将理想载波注入技术中星座点-载波二维联合搜索问题简化为星座点/载波一维分步搜索问题,从而将载波注入技术的复杂度从随载波数目指数增长变为随载波数目线性变化,大大降低了载波注入技术的复杂度。此外,该技术通过分析各等效星座点对峰均比抑制的作用,减小了等效星座点数目,在实现峰均比有效抑制的同时进一步降低了该技术的复杂度。3.针对进一步提高放大器功率效率,减少系统能耗的问题,提出了一种基于归一化相关系数准则的载波预留OFDM信号预处理技术。该技术从最大化接收端信噪比的角度出发,利用放大器输入输出信号的归一化相关系数来衡量放大器对OFDM信号的非线性影响。通过最大化该归一化相关系数,该技术可有效降低放大器非线性失真对OFDM信号的影响,进而可以在提高放大器功率效率的同时提高系统性能。
[Abstract]:Orthogonal Frequency Division Multiplexing (OFDM) technology has many advantages, such as high spectral efficiency, strong anti-multipath ability and low complexity. It is widely adopted as the physical layer standard of many wireless communication systems. One of the main defects of this technology is that the signal amplitude has a large fluctuation range. When the peak value of the signal exceeds the linear range of the amplifier, it will produce nonlinear distortion and reduce the system performance. In order to improve the system performance, it is necessary to reduce the operating level of the amplifier. The OFDM signal is contained in the linear range of the amplifier, which will seriously reduce the power efficiency of the power amplifier. In wireless communication networks, there is an urgent need to reduce energy consumption in order to reduce the operating costs of the system. Therefore, for OFDM system, the contradiction between amplifier power efficiency and system performance becomes more sharp. This paper starts from signal processing. How to effectively reduce the PAPR of OFDM signal to improve the power efficiency of the amplifier is studied. The specific research work and innovative results are as follows: 1. Aiming at the problem of compression and spread distortion caused by the compression and spread transform processing when the PAPR of OFDM signal is reduced, the system performance will deteriorate. In order to improve the BER performance of OFDM system, the nonlinear effect of Companding transform on OFDM signal is derived and analyzed theoretically. In this paper, a general design criterion for the compression spread function is proposed, and based on the general design criterion, two techniques for minimizing distortion are proposed. Piecewise linear and piecewise exponential compression techniques. Both piecewise linear and piecewise exponential compression techniques can effectively reduce peak-to-average ratio (PAPR) and reduce spread distortion, improve the BER performance of the system, and achieve a good compromise between PAPR and PAPR suppression performance. By reasonably selecting the segmental points of the expansion function, the piecewise linear compression expansion technique and the piecewise exponential compression expansion technique have high design flexibility. It can meet more system requirements. 2. Aiming at the problem of high complexity of ideal carrier injection technology. In this paper, a carrier injection technique based on ordered search is proposed, which determines the sequence of carrier search by using the signal adjustment information contained in the nonlinear distortion frequency domain signal. The joint search problem of constellation point and carrier in ideal carrier injection technology is simplified to a constellation point / carrier one-dimensional step search problem. Thus, the complexity of carrier injection technology is changed from exponential increase with the number of carriers to linear change with the number of carriers, which greatly reduces the complexity of carrier injection technology. This technique reduces the number of equivalent constellation points by analyzing the effect of each equivalent constellation point to PAPR suppression. In order to improve the power efficiency of amplifier and reduce the energy consumption of the system, the complexity of this technique is further reduced while the PAPR is effectively suppressed. In this paper, a carrier reserved OFDM signal preprocessing technique based on normalized correlation coefficient criterion is proposed, which is based on maximizing the signal-to-noise ratio (SNR) of the receiver. The normalized correlation coefficient of the input and output signal of the amplifier is used to measure the nonlinear effect of the amplifier on the OFDM signal, and the normalized correlation coefficient is maximized. This technique can effectively reduce the influence of amplifier nonlinear distortion on OFDM signal, and then improve the power efficiency of amplifier at the same time improve the system performance.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN929.53

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