Performance Evaluation of Space-Frequency Block -Coded Detection Technique Based on MMSE Criterion Under Mobile Environment

Abstract

Depending on how rapidly the transmitted baseband signal changes as compared to the rate of change of the channel, a channel is classified either as a fast fading or slow fading channel. In a fast fading channel, the channel impulse response changes rapidly within the symbol duration. That is, the symbol period of the transmitted signal is greater than the coherence time of the channel. This causes frequency dispersion which is also called as a time selective fading due to Doppler spreading, which leads to signal distortion, while in the frequency domain, signal distortion due to fast fading increases with increasing Doppler spread relative to the bandwidth of the transmitted signal. In a fast fading channel, the use of space frequency block code (SFBC) is beneficial because symbol is transmitted on neighbouring sub carriers. SFBC has the better performance as compared to space-time block coding when channel is fast varying in nature, i.e., where the channel varies too quickly. While in slow varying channels, SFBC as well as space-time block-code (STBC) exhibit same performance. To reduce the fast fading distortion caused by high-speed mobility a single car r ier SFBC f requency domain equal izat ion (SC-SFBC FDE) system can be used for reliable communication. The SFBC system codes transmitted, using two antennas and over two adjacent subcarriers instead of two consecutive symbol intervals, is more robust against fast fading distortion in frequency nonselective fading environments. Therefore we have made an effort to study SC-SFBC FDE system working under frequency selective fading environment. We have presented first, an Alamouti-like scheme for combining SFBC with single-carrier frequency-domain equalization (SC-FDE) in wireless fading channels where channel response is not same for adjacent subcarriers. The matched filter at the receiver produces error floor in the bit error rate performance, which is compensated by the proposed design. This thesis focuses on the design of low complexity zero forcing (ZF) equalizer for the combining receiver for a communication system with two transmit antennas and one receive antenna. It is shown, through computer simulations that the proposed design of the equalizer outperforms the matched filter receiver for fast fading mobile environments, and also provides an advantage of lower computational complexity at the receiver than classical ZF equalizer. Further, the work deals with the detection of single carrier space frequency block coded (SCSFBC) in frequency selective wireless MIMO channel. Due to frequency-selectivity nature of channel the inter-symbol interference (ISI) occurs. In single carrier SFBC system, ISI is caused due to the loss of the „quasi-static‟ fading assumption caused due to frequency selectivity of wireless MIMO channel. In this article, we evaluate and propose the performance analysis of SC-SFBC FDE for interference cancellation receiver which mitigates the effect of ISI in frequency-selective MIMO channels.