Peak-to-average Power Ratio of Orthogonal Frequency Division Multiplexing

Orthogonal frequency division multiplexing (OFDM) is successfully used in many wireless digital communication systems over multipath channels. One of the principal disadvantages of OFDM is the occurrence of high peak to average power ratios (PAR). Many PAR reduction techniques have been proposed in the literature. This report describes the PAR problem, PAR reduction methods and related issues. Performances of several PAR reduction techniques are compared. As high peaks are relatively rare, the PAR can be reduced simply by clipping high peaks. However, severe clipping introduces inband distortion and out of band radiation. Multiple signal representation techniques are effective in OFDM system with large number of subcarriers, which reduce the PAR with an increased complexity at the receiver. Although coding techniques limit the PAR 3 dB at most, coding rate is prohibitively low when number of carriers is increased beyond 32.