Performance analysis of the OFDM system on multipath rayleigh fading channels

Abstract

Wireless data transmission requires robust and spectrally efficient communication techniques for fading channels. Mobile communication channels suffer from impairments such as multipath propagation, multiplicative distortion, Doppler frequency shift, and noise. Orthogonal frequency division multiplexing (OFDM) is an attractive modulation technique in the fading channel environment. In the OFDM system on frequency-nonselective fading channels, Doppler spread destroys orthogonality between subchannels and introduces interchannel interference (ICI) similar to that resulting from frequency offset. ICI degrades the system performance and causes the error floor for coherent detection. The wideband channel transfer function can be modeled as frequency-selective fading channels [2,5]. Multipath propagation causes intersymbol interference (ISI) between consecutive symbols and introduces the error floor. In the OFDM system, the ISI problem can be overcome by the insertion of a guard interval between two OFDM blocks when the guard interval is longer than delay spread of the radio channel [13, 15]. In this dissertation, we analyze the performance of the OFDM system on multipath Rayleigh fading channels. It is well known that the performance of the OFDM system on frequency-nonselective Rayleigh fading channels is improved when the normalized Doppler frequency N $f_D$ $T_s$ is increased where N is the number of subchannels, $f_D$ the maximum Doppler frequency, and $T_s$ the sampling interval. In this dissertation, we derive eaxt expressions for the symbol error probability of the MMSE equalizer with ideal interleaving in the space diversity reception. The analysis results show that the symbol error probability of the MMSE equalizer is dependent on the number of subchannels N. The performance improvement with ideal interleaving for N=8192 is 14dB at symbol error rate (SER) of $10^{-3}$ compared with that of a single carrier system with coherent detection, i.e. N=1. The perfor...