A Transmit Diversity Technique for OFDM System

Abstract: In current 4G systems growing demand of multimedia services and the growth of internet related contents lead to increasing interest to high speed communications. One indispensable problem of the wireless channel is fading, which can be mitigated by diversity. There are various coding methods to achieve high reliability for Multiple Input Multiple Output- Orthogonal Frequency Division Multiplexing (MIMO-OFDM) systems earlier. Recently, Space Time Block Codes (STBC) have gained much attention as an effective transmit diversity technique to provide reliable transmission with high peak data rates to increase the speed and performance of wireless communication systems. This paper presents the performance evaluation of OFDM system, in which fading is reduced by using diversity techniques along with coding methods under various fading channels such as Rician and Rayleigh fading channels. In this work, a performance criterion such as Bit Error Rate (BER) for low Signal to Noise Ratio (SNR) ranging from 10dB to 20dB is analyzed. The BER for OFDM system without including STBC is 1.776x10-3 and including STBC is 1.621x10-3 over Rician Channel. Whereas, over Rayleigh channel the BER for OFDM system without including STBC is 1.834x10-5 and including STBC, it is reduced to 6.345x10-6 for the same SNR of 14dB. Thus, OFDM system with STBC provide high data rate with good reliability.

Keywords: Wireless channel, MIMO, OFDM, BER, STBC, SNR, LoS