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arXiv 1002.1447cs.ITmath.IT
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使用主动星座扩展的空时和空频编码OFDM系统的PAPR缩减

PAPR reduction of space-time and space-frequency coded OFDM systems using active constellation extension

Mahmoud Ferdosizadeh Naeiny, Farokh Marvasti

摘要:

主动星座扩展(ACE)是降低OFDM系统峰均功率比(PAPR)的技术之一。在该技术中,扩展星座点,使得PAPR最小化,但星座点的最小距离不减小。本文将一种迭代ACE方法推广到空间编码OFDM系统。所提出的方法是这样的峰均比降低同时在所有天线,而空间编码关系仍然成立。它将被证明,原来的ACE方法可以采用之前的空时分组码(STBC)。但是在空频块编码(SFBC)的情况下,已经提出了两种修改的技术。在第一种方法中,OFDM帧由若干子帧分隔,并且ACE方法被独立地应用于这些子帧以降低它们对应的PAPR。然后,基于SFBC关系对低PAPR子帧进行重组,以产生来自不同天线的发射信号。在第二种方法中,对于每次迭代,ACE被应用于具有最大PAPR的天线,并且其他天线的信号从该天线的信号生成。仿真结果表明,两种算法都是收敛的,但当天线数增加时,第二种方法的性能优于第一种方法。

英文摘要:

Active Constellation Extension (ACE) is one of techniques introduced for Peak to Average Power Ratio (PAPR) reduction for OFDM systems. In this technique, the constellation points are extended such that the PAPR is minimized but the minimum distance of the constellation points does not decrease. In this paper, an iterative ACE method is extended to spatially encoded OFDM systems. The proposed methods are such that the PAPR is reduced simultaneously at all antennas, while the spatial encoding relationships still hold. It will be shown that the original ACE method can be employed before Space Time Block Coding (STBC). But in case of Space Frequency Block Coding (SFBC), two modified techniques have been proposed. In the first method, the OFDM frame is separated by several subframes and the ACE method is applied to these subframes independently to reduce their corresponding PAPRs. Then the low PAPR subframes are recombined based on SFBC relationships to yield the transmitted signals from different antennas. In the second method, for each iteration, the ACE is applied to the antenna with the maximum PAPR, and the signals of the other antennas are generated from that of this antenna. Simulation results show that both algorithms converge, but the second method outperforms the first one when the number of antennas is increased.

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