A New Algorithm for Peak/Average Power Reduction in OFDM Systems

We present a new method (MMSE-threshold) for peak/average power reduction. This technique is derived from a constellation shaping algorithm, where the constellation points with lower average energy are selected from a larger set of points. There are multiple choices available to select the points with lower peak energy for a given sequence of data bits, and this flexibility is used to reduce the peak to average power ratio (PAPR). Subsequently, this selection algorithm, which is formulated in terms of a zero-one quadratic problem, is optimized by the semidefinite programming algorithm (SDPA). Simulation results show that the PAPR of SDPA is noticeably better than MMSE-Threshold, while the complexity of MMSE-Threshold is smaller than that of SDPA. MMSE-Threshold is compared with alternative techniques reported in the literature. We show that, while we obtain a PAPR that is similar or better than those of the compared techniques, the complexity of MMSE-Threshold is low. In addition, the MMSE-threshold method results in about 1 dB shaping gain (reduction in the average energy) with less than 1% rate loss for PAPR reduction.

I. Introduction

The orthogonal frequency division multiplexing (OFDM) method, a form of multi-carrier multiplexing technique, is used in many wireless standards. This technique partitions a high frequency selective wide band channel into a group of non selective narrow band sub-channels. This makes the system robust against large delay spreads by preserving orthogonality in the frequency domain. The OFDM signal, which is the superposition of a large number of modulated sub-channels, usually exhibits a high instantaneous peak with respect to its average value [1], [2]. This is often cited as the major drawback of OFDM systems and is quantified by a parameter called peak to average power ratio (PAPR), defined as peak power of the OFDM signal to average power of the OFDM signal.