Performance of Space Time Trellis Codes Over Nakagami Fading Channels

Abstract

In this technological era thirst for capacity in wireless communication systems has been like sky-rocketing in world-wideday by day. This has been driven by increasing data rate requirements of cellular mobile systems, and demand for wireless internet and multimedia services. As the available radio spectrum is limited, higher data rates can only be achie ved by designing more efficient signaling techniques. The research in the field of space-time coding (STC) and multiple-input multiple-output(MIMO)systems has acquired an abundant interest in recent years. MIMO systems apply STC such as space-time block codes (STBC) and space-time trellis codes (STTC). STBC only provides diversity gain but not coding gain later to combat with this STTC were introduced which provide both diversity gain and coding gain with high throughput. STTC is performance criterion based codes, with different modulation techniques and using distribution of codes in constellation this code gives better performance without sacrificing bandwidth, power and other quantities for better transmission of data.Its performance is based on construction of codes, number of transmit and receive antenna and varies with fading channel characteristics. In this thesis the effect of STTC over fading in MIMO systems which employs the necessary mathematical analysis to consider the achieved capacity performance was analyzed. In this context, flat fading across time and frequency is considered ,furthermore, the case of spatial selective fading is examined by considering LOS propagat ion, with the Rician model and combines both Rician and Rayleigh model to form Nakagami model. It is shown that if number of states of trellis is increased there will be corresponding performance increased. I t is shown that if m-factor of Nakagami fading increases up to certain level it improves the performance of the system and if m=1 or Rician fading factor K=0 for special case it corresponds to equivalent Rayleigh fading channel’s response . Also, it is shown that if number of transmit antenna we re increased at base station for fixed receivers then the burden of increasing receiving antenna will be sort out and also increases throughput .Also for fast fading, 4-state QPSK Nakagami fading channel’s performance is better than corresponding Rician and Rayleigh fading channel’s performance. It is also derived that for slowly fading, 4-state QPSK Nakagami fading channel’s performance is worse than corresponding Rayleigh and Rician fading channel’s performance.