Effects of narrowband interference and nonlinear amplifier in companded OFDM with application to 802.11n WLAN

It is a well known fact that orthogonal frequency division multiplexing (OFDM) suffers from high peak to average power ratio (PAPR). The nonlinear distortion introduced by an OFDM signal through practical amplifiers can further degrade the system performance. Due to the limited bandwidth in the radio frequency spectrum, it is impossible that wireless communication systems can operate in an environment which is free from all interference such as narrowband interference (NBI). Hence, it is important to understand how an OFDM system performs when it is subject to NBI interference. In this paper, we analyze the performance of a M-ary quadrature amplitude modulation (M-QAM) OFDM system which is subject to nonlinear high power amplifiers (HPAs) and NBI in a Rayleigh fading channel. In order to reduce the nonlinear distortion caused by HPAs, we propose a new companding technique to reduce the PAPR and a novel receiver structure to minimize the degradation effects from the decompander when the OFDM system operates in Rayleigh fading channel. For the purpose of simulation, we extend the analytical model to be in compliance with the IEEE 802.11n standard. The theoretical results are verified with the simulation.