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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1/ 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。
In order to develop low cost, low power consumption, small size of the OFDM terminal, zero IF receiver structure more and more attention. However, compared with the classical superheterodyne structure, the radio frequency damage will be more serious in receivers with zero IF structure. Firstly, the influence of 1 / Q imbalance caused by zero-IF receiver on performance under fading channel is introduced. In order to overcome the influence of I / Q imbalance, a special preamble training symbol is designed to easily estimate and compensate I / Q imbalance in the fading channel on the performance impact. In order to further reduce the estimation variance, an adaptive compensation method based on low-pass filtering is proposed. Simulation shows that the above method greatly improves the performance of OFDM zero IF receiver.