NC-OFDM系统旁瓣抑制中的可变干扰抵消基函数设计

Variable Cancellation Basis for Side-Lobe Suppression in Non-contiguous OFDM Systems

在抑制非连续载波正交频分复用(Non-contiguous Orthogonal Frequency-Division Multiplexing,NC-OFDM)系统旁瓣的方法中,使用固定长度和矩形形状干扰抵消子载波的主动干扰抵消方法(Active Interference Cancellation,AIC)抑制深度不够,而其改进方法扩展AIC(Extended AIC)对数据子载波干扰又太大.本文发现插入在不同频段的干扰抵消子载波对旁瓣抑制的效果不同,并在此基础上提出对干扰抵消子载波按频率分组,不同组的干扰抵消子载波使用不同的长度与波形,从而提高对NC-OFDM信号旁瓣的抑制效果,同时减小了所引入的载波间干扰.仿真结果表明:采用本文提出的可变基函数方案,在达到-60d B的旁瓣抑制深度时,即使采用高阶的64-QAM符号映射(实验条件是误符号率为10-5),干扰抵消信号对数据子载波造成的载波间干扰也几乎可以忽略.

In non-contiguous orthogonal frequency-division multiplexing （NC-OFDM） based cognitive radio sys- tems,conventional active interference cancellation （AIC） and extended AIC （EAIC） schemes use the same rectangular waveform of the same length for all canceling carders （ CCs）, leading to the limitation of performance improvement of sidelobe suppression or inter-carrier interference （ICI） reduction. In this paper, a novel variable cancellation basis was proposed for side-lobe suppression in NC-OFDM cognitive radio systems based on the observation that CCs in different frequency have non-uniform attribution for sidelobe suppression. So, CCs are grouped by frequency locations and shaped with different waveforms of different lengths to satisfy good side-lobe suppression performance while reducing ICI at the same time. Numerical results show that, with the proposed CC scheme, NC-OFDM signal＇ s side-lobe can be suppressed to - 60 dB with negligible signal-to-noise ratio loss at a symbol error rate of 10 -5 with 64 quadratic-amplitude modulation symbol.