衰落信道下OFDM系统中I/Q不平衡的估计和补偿技术

摘要

为了研制低价格、低功耗、小尺寸的OFDM终端,零中频的接收机结构越来越倍受关注.但是相对于经典的超外差结构,在零中频结构的接收机中射频损伤将更为严重.首先介绍了由零中频接收机产生的I/Q不平衡在衰落信道下对性能的影响;为了克服I/Q不平衡的影响,设计了一种特殊前导训练符号,方便地估计和补偿I/Q不平衡在衰落信道下对性能的影响.为了进一步减小估计方差,又提出了一种基于低通滤波的自适应补偿方法.仿真表明以上方法大大提高了OFDM零中频接收机的性能.%The architecture of zero IF receivers that has the advantage of low-cost, low power dissipation and small from factor is gaining interest while developing OFDM terminal. However, zero IF architecture suffers from greater RF impairment comparing with classical heterodyne architectures. The effect of I/Q imbalance caused by zero IF OFDM receiver on the performance in fading channel is introduced firstly;Secondly, the particular structure of the training symbols is designed to combat the I/Q imbalance at baseband, which the effect of I/Q imbalance is estimated and compensated in fading channel conveniently. In order to reduce the variances of the estimates, the adaptive compensation algorithm based on the low-pass filter is proposed. The simulation results show that the above methods greatly improve the performance of the zero IF OFDM receiver.