OFDM信号峰均功率比的统计分布

PAR Statistical Distribution of the OFDM Signals

正交频分复用(OFDM)由于能有效对抗码间干扰而特别适用于无线环境下的高速传输,被普遍认为是下一代通信系统必不可少的技术。OFDM的一个主要缺点是峰均功率比特别高,而高的峰均比会对系统的设计带来很多问题。掌握了峰均比的统计分布,可以知道信号受高峰均比影响的严重程度,同时也是评价峰均比降低技术性能的参照。已有关于峰均比分布的分析均是针对所有载波都使用的情况,而在几乎所有的国际标准中都规定不用靠边沿的子载波,以便于信号的谱成形和避免邻近信道干扰。本文分析了这种情况下OFDM连续信号峰均比的渐近分布,结果表明,OFDM信号的峰均比是由实际采用的载波数和各载波的功率分配方案决定,而与FFT的点数N无关。

Orthogonal Frequency Division Multiplexing （OFDM） is specially suitable for high-speed wireless communication owing to resistance to inter-symbol interference, and is considered as a necessary technique for the next Generation （4G） communication system. The principal drawback of the OFDM systems is that the Peak-to-Average envelope power Ratio （PAR） of its signals may be very high. A high PAR may cause many problems in system design. The PAR distribution can tell us how serious the effect of the high PAR on the system is, and it is a baseline to evaluate the performance of the PAR-reduction technologies. But all the existed distribution approximations are developed by assuming that all the N subcarriers are used. In fact, almost in all the international standards that used OFDM technique, it is specified that some edge subcarriers are not used in order to shape the signal spectrum and to avoid the adjacent channel interference. A perfect approximation is derived for the PAR distribution for this case. Analysis result shows that the PAR distribution depends on the number of the actual used subcarriers and the scheme of the power allocation for each subcarriers, not on the number of the FFT points.