Genetic Algorithm Based Nearly Optimal Peak Reduction Tone Set Selection for Adaptive Amplitude Clipping PAPR Reduction

In tone reservation (TR) based OFDM systems, the peak to average power ratio (PAPR) reduction performance mainly depends on the selection of the peak reduction tone (PRT) set and the optimal target clipping level. Finding the optimal PRT set requires an exhaustive search of all combinations of possible PRT sets, which is a nondeterministic polynomial-time (NP-hard) problem, and this search is infeasible for the number of tones used in practical systems. The existing selection methods, such as the consecutive PRT set, equally spaced PRT set and random PRT set, perform poorly compared to the optimal PRT set or incur high computational complexity. In this paper, an efficient scheme based on genetic algorithm (GA) with lower computational complexity is proposed for searching a nearly optimal PRT set. While TR-based clipping is simple and attractive for practical implementation, determining the optimal target clipping level is difficult. To overcome this problem, we propose an adaptive clipping control algorithm. Simulation results show that our proposed algorithms efficiently obtain a nearly optimal PRT set and good PAPR reductions.

I. Introduction

Orthogonal frequency division multiplexing (OFDM) is widely used in high-speed wireless communication systems because of its inherent robustness against multipath fading and resistance to narrow-band interference [1]. However, OFDM suffers from the high peak to average power ratio (PAPR) of the transmitted signal. This issue can cause serious problems including a severe power penalty at the transmitter. Conventional solutions to reduce the PAPR are to use a linear amplifier or to back-off the operating point of a nonlinear amplifier. But both these solutions result in a significant loss of power efficiency. Many methods have thus been proposed to reduce the PAPR by modifying the signal itself. The simplest one is clipping the OFDM signal below a PAPR threshold level [2], [3], but it degrades the bit-error-rate (BER) of the system and results in out-of-band noise and in-band distortion. Coding [4] is another technique. Although it can offer the best PAPR reductions, the associated complexity and data rate reduction limit its application. Selected mapping (SLM) technique [5] and the partial transmit sequence (PTS) [6] are based on multiple signal representation method. These methods [7], [9], [11], [12] improve the PAPR statistics of the OFDM signals, but side information may be transmitted from the transmitter to the receiver, which results in a loss of data throughput.