PERFORMANCE EVALUATION OF SPACE TIME BLOCK CODED MC CDMA SYSTEM OVER FADING CHANNEL

Abstract

With the spread of wireless internet and continued dramatic increase in demand for all types of advanced wireless multimedia services, including conventional voice and data transmissions, we require broadband systems which maintain the quality of service regardless of the propagation environment and the available bandwidth. Space Time (ST) coding provides an effective transmit antenna diversity to combat fading in wireless channels. ST coding techniques integrate the antenna array spatial diversity and channel coding to provide significant capacity gains. However, wireless channels are frequency selective in nature. Multi-carrier modulation divides the available channel bandwidth into number of subcarriers which experience independent flat fading. Multi Carrier Code Division Multiple Access (MC-CDMA) combines multi-carrier modulation and frequency domain spreading which gives a wideband CDMA (Code Division Multiple Access). The space-time spreading improves the downlink performance providing maximal path diversity at the receiver without extra transmit power, or channel information. Therefore coupling space-time spreading with MC-CDMA, we can achieve- i) Directionality which creates high network capacity via space diversity ii) A transmit diversity gain which supports high performance at the receiver. iii) Increased capacity and performance via MC-CDMA ability to support both CDMA and frequency diversity. In this dissertation the MC CDMA system is coupled with ST coding and the performance of the ST block coded MC CDMA system is evaluated for the multi user situation. The channel state is assumed to be known at the receiver. A Multi User Detection (MUD) technique is used to improve the performance of the system in a multi user case.