Performance Analysis of Time Reversal Space Time Block Codes in Nakagami Fading Channel

Abstract

ABSTRACT The demand of improved spectrum efficiency, link reliability and coverage of wireless networks is increasing constantly. Meeting this demand is challenging since wireless communications systems are subjected to the effect of fading. Fading is most challenging phenomena in wireless communication to establish a reliable communication between transmitter and receiver. Use of multiple antennas along with appropriate signalling and receiver techniques in space-time wireless technology offers a powerful tool for improving the wireless performance. Multiple antennas when used with appropriate space-time coding (STC) techniques can achieve huge performance gains in multipath fading wireless links. Space-time block codes have a most attractive feature of the linear decoding/detection algorithms and thus become the most popular among different STC techniques. Space-time coding involves the transmission of multiple copies of the data. This helps to compensate for the channel problems such as fading and thermal noise. However, Spacetime block codes (STBC) can obtain full transmit diversity gain in slow-fading environment. But it is not the case for STBC in fast-fading channel. In fast-fading, channel is no longer constant over a period of time. As a result of rapid time variation of the channel, the orthogonality of STBC is lost. This will cause error in decoding and hence the system performance is degraded. So, simple STBC transmit diversity scheme is capable of maximizing the diversity over frequency flat MIMO channel. For high data rate service, most channels cannot be considered frequency-flat anymore but are dispersive, causing inter-symbol interference. This frequency selectivity of the channel destroys the orthogonality of the transmitted STBC streams. Space-time coding for frequency-selective fading environments has attracted great attention. TR-STBCs (Time Reversal Space Time Block Codes) extend STBCs transmission over frequency selective channels by encoding together conventionally ordered and time reversed contiguous blocks of symbols. First of all, BER performance of TR-STBC is evaluated for two transmitter and one receiver antenna and then compared with performance of STBC. Generally, multipath fading amplitude distribution is modelled with Rayleigh channel. But, when fading is severe, Rayleigh model fails to characterize the exact channel characteristics. So, a more accurate model, named Nakagami-m model may use to represent the channel. iv The BER performance of TR-STBC is simulated in Nakagami-m fading channel. A low complexity zero forcing receiver is evaluated to mitigate the effect of fading. The BER performance of TR-STBC is compared with classical zero forcing receiver. For Rayleigh fading (m=1) proposed scheme gives performance similar to the classical zero forcing. For slow fading (m>1) the BER performance of proposed scheme is improved. But for (m<1), its BER performance degrades.