An Efficient Algorithm for Reducing the Peak Power in an AM-OFDM Signal

A. Walambe, M. Caggiano, J. Evans, and Z. Gajic (USA)




Techniques such as clipping, coding and scrambling have been used to reduce the high peak power in OFDM signals. These techniques suffer from impractical complexity when there are a large number of carriers, significant overhead in redundant transmissions or spectral leakage. They achieve modest reductions in signal Peak to Average Power Ratios (PAPR) in the range of 6.8 to 9.3dB. This paper presents a simple heuristic algorithm that relies on a mixture of clipping and phasing strategies to reduce the Peak to Mean Power Ratio (PMPR) of a 256-carrier, AM-OFDM signal, to typically less than 6.2dB and always less than 7.2dB. This superior reduction in signal peak power more than compensates for the inefficiency of amplitude modulation of the carriers in a peak power limited system. The relationship of the final carrier phases to the Newman phases, used for test signal generation, is highlighted.

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