Performance Evaluation of High-Rate Space-Time Block-Coded Wireless Systems Working Under Nakagami Fading Channel

Abstract

Fading is one of the most challenging phenomena in wireless communication when a reliable communication path has to be established between transmitter and receiver. Fading is more prominent when there is no line-of-sight component, moreover it is more prominent in case of urban and suburban cities. Generally, the multipath fading amplitude distribution is modelled with Rayleigh probability distribution function (PDF). But when the fading is more severe, the Rayleigh model fails to characterize the exact channel characteristics. Therefore, a more accurate model, named m-Nakagami model may be employed to characterize the channel. However, Inter symbol interference (ISI), an another important issue that is again a matter of concern when frequency-selective fading case is considered. Frequency-selective fading is defined when signal bandwidth is greater than channel bandwidth. Thus, Frequency-selective fading causes ISI. The equalization is one of the methods that invert the effects of channel. Orthogonal frequency division multiplexing (OFDM) may be the other useful technique which can be employed to mitigate the effect of ISI. Generally, in OFDM, each subcarrier undergoes flat fading since its bandwidth is smaller than the coherence bandwidth. OFDM converts frequency-selective channel into a number of flat fading channels by using cyclic prefix, but sub-bands of OFDM are disclosed to deep fading and may cause complete loss of sub-band information. To deal with this problem Space-time block coding is applied in OFDM, however it also introduces redundancy. By affixing CP at beginning of OFDM symbol block, the linear convolution associated with channel impulse response become a circular convolution, so inter-block interference is precluded. In this thesis, we have made an effort to study space-time block coded (STBC) and high-rate STBC working under different fading wireless channels. We have presented simulation results which demonstrates that in mobile environment at lower value of SNR for (slow fading) effective throughput is high in case of both high-rate STBC as well as full-rate STBC when compared to (Rayleigh fading) and effective throughput is low for when compared to for both systems. Secondly, simulation results demonstrate that at high values of SNR (e.g. 6dB to 20dB) proposed low complexity zero forcing (ZF) receiver gives better effective throughput for the values of and for effective throughput is between and . Whereas at lower values of SNR (e.g. 0dB to 6dB) proposed receiver achieves better effective throughput for the values of .