Estimation and compensation of clipping noise in OFDMA systems

We propose an efficient and low-complexity scheme for estimating and compensating clipping noise in OFDMA systems. Conventional clipping noise estimation schemes, which need all demodulated data symbols, may become infeasible in OFDMA systems where a specific user may only know his own modulation scheme. The proposed scheme first uses equalized output to identify a limited number of candidate clips, and then exploits the information on known subcarriers to reconstruct clipped signal. Simulation results show that the proposed scheme can significantly improve the system performance.

I. Introduction

High peak-to-average power ratio (PAPR) is a well-known problem in orthogonal frequency-division multiplexing (OFDM) systems. As the multi-user version of OFDM, orthogonal frequency-division multiple access (OFDMA) has severer PAPR problem because of significantly increased number of subcarriers. Numerous solutions [1] have been investigated for the problem in OFDM systems. As one simple solution, clipping, and in particular, soft clipping reduces the magnitude of large signals to a predefined threshold while leaving their phase unchanged. Clipping noise introduced by the magnitude distortion degrades the system performance. Some approaches have been investigated to mitigate the noise, including decision aided reconstruction [2], iterative clipping noise estimation [3], and over-sampling based clipping noise reconstruction [4].