Bit Error Rate Analysis for an OFDM System with Channel Estimation in a Nonlinear and Frequency-Selective Fading Channel

Amir Ligata,Haris Gacanin,Miha Smolnikar,Mihael Mohorcic,Fumiyuki Adachi

doi:10.1155/2011/670637

Abstract

Orthogonal frequency division multiplexing (OFDM) is an effective technique for high-speed digital transmission over time-dispersive channels. However, for coherent detection, a reliable channel estimation (CE) is required. OFDM is characterized by its high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions that may affect the channel estimation accuracy leading to a bit error rate (BER) performance degradation. In this paper, we present closed-form BER expression for OFDM with a pilot-assisted CE in a nonlinear and frequency-selective fading channel. We discuss how, and to what extent, the nonlinear degradation affects the BER performance with the CE based on a time/frequency division-multiplexed (TDM/FDM) pilot. The analysis is based on a Gaussian approximation of the nonlinear noise due to both HPA amplitude limitation and quantization. We also evaluate the estimator's mean square error (MSE) with both TDM and FDM pilots. Our results show that pilot-assisted CE using FDM pilot is more sensitive to nonlinear distortions than the CE using a TDM pilot, since its pilot subcarriers are affected by nonlinear noise due to both the HPA and the quantization.

Highlights

In a terrestrial radio channel, the transmitted signal reaches the receiver through multiple propagation paths, which all have a different relative delay and gain
Orthogonal frequency division multiplexing (OFDM) is characterized by its high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions that may affect the channel estimation accuracy leading to a bit error rate (BER) performance degradation
Our results show that pilot-assisted channel estimation (CE) using FDM pilot is more sensitive to nonlinear distortions than the CE using a TDM pilot, since its pilot subcarriers are affected by nonlinear noise due to both the high-power amplifier (HPA) and the quantization

Summary

Introduction

In a terrestrial radio channel, the transmitted signal reaches the receiver through multiple propagation paths, which all have a different relative delay and gain. In a real implementation, in order to keep the system complexity and the power consumption low, it is desirable to keep the resolution of the DA/AD converters as low as possible [9, 10] It was shown, in [11], that the quantization requirements are higher at the receiver end, for severely frequencyselective channels. We present a theoretical analysis of an OFDM system with a pilot-assisted CE based on TDM and FDM pilots in a nonlinear and frequency-selective fading channel. The results show that the BER performance with pilot-assisted CE based on an FDM pilot is more sensitive to the nonlinear distortion a TDM pilot, since its pilot subcarriers are affected by nonlinear noise due to both the HPA and the quantization.

System Model

Performance Analysis

Numerical Results and Discussions

Conclusions