LOW COMPLEXITY RECEIVER DESIGN FOR SPACE-TIME-FREQUENCY CODED MIMO-OFDM SYSTEM

Abstract

Multi-antenna communication systems with Orthogonal Frequency Division Multiplexing modulation (MIMO-OFDM) have the potential to play an important role in the design of the next generation broadband wireless communication systems. With Space-Time-Frequency (STF) coding, we can improve the diversity advantage over Space-Time (ST) coding by capitalizing the multipath diversity. Hence, STF coded MIMO-OFDM system can achieve diversity gain equivalent to that of ST coded MIMO-OFDM system with less number of antennas only. To design a portable personal station with less cost and less power requirements, one must design a low complexity receiver for a MIMO-OFDM system. The conventional subcarrier based space processing is optimal in performance. However, such an approach is quite complex, because multiple Discrete Fourier Transform (DFT) blocks, each per receive antenna are required to be used. This includes considerable complexity. In this dissertation work, we have used a pre-DFT processing scheme at the receiver of STF coded MIMO-OFDM systems. With this scheme, the number of DFT blocks at the receiver can be reduced to any numbers from one to the number of receive antennas, thus enabling effective complexity and performance trade-off. Here we have used Group STF coding (GSTF) which poses less decoding complexity. Using the pre-DFT processing scheme, the number of input signals to the GSTF decoder can be reduced compared with the subcarrier based space processing. Therefore, a high dimensional MIMO system can be shrunk into an equivalently low dimension one. Due to the dimension reduction, the complexity of the decoder can be reduced.