Improvement of Quality of Service (QoS) in MISO-OFDM Systems Using Superposition Based Adaptive Modulation (SPAM) and Space Frequency Block Coding (SFBC) Technique

摘要

4G based wireless communication systems require high data rate with high QoS with minimal system complexity. In wireless environment, as the effect of multipath fading increases, Bit Error Rate (BER) also increases. To offer high data rate, the bandwidth has to be increased which is a limited resource. The best possible solution for obtaining high data rate is to combine Multi Input Multi Output (MIMO) with OFDM. To ameliorate the performance of MIMO-OFDM systems over multipath fading channels, we use the concept of SFBC which retrieves the orthogonality property of OFDM signals in frequency selective fading channels. In frequency selective fading environment, adaptive modulation gives better performance than fixed modulated systems but with increased decoding complexity. Adaptive modulation implemented with SPAM offers less decoding complexity. Adaptive modulation combined with diversity schemes still improves the reliability of the system. In this paper, SPAM based SFBC is proposed with OFDM to give better performance with less decoding complexity. From the Simulation results we can conclude that proposed system will have better performance compared to fixed modulated systems.