Performance of MIMO space-time coded system and training based channel estimation for MIMO-OFDM system

Abstract

Multiple-input-multiple-output (MIMO) antenna architecture has the ability to increase capacity and reliability of a wireless communication system. Orthogonal frequency division multiplexing (OFDM) is another popular technique in wireless communication which is famous for the efficient high speed transmission and robustness to frequency selective channels. Therefore, the integration of the two technologies probably has the potential to meet the ever growing demands of future communication systems. Because of aforementioned merits of these two techniques, this thesis was about MIMO and MIMO-OFDM system, and it addressed two different issues. Firstly it has investigated the performance of MIMO-STBC system and surveyed the effect of imperfect channel estimation on performance of MIMO-OFDM system. Secondly, it has focused on training based channel estimation algorithm for MIMO-OFDM system. In the first part, BER of space-time block coded system (STBC) was calculated for different antenna configuration using simulation software. The results proved that the reliability of the wireless link increases as the number of transmits and received antenna increase. At the next stage of the project, the effect of channel estimation algorithm on performance of MIMO-OFDM system was investigated. The simulation results shown that imperfect channel estimation degrade the performance of the system significantly. At the final part of the research, channel estimation in MIMO-OFDM system has been discussed. The mathematical model of the system in frequency selective fading channel has been developed. Then the comparison analysis in terms of performance efficiency and computational complexity has been made for two different channel estimations algorithm namely LS (Least Square) and QR decomposition. It should be mentioned that reduction of computational complexity of the channel estimation and data detection algorithm is a major challenge for receiver design in MIMO-OFDM system, and complication of receiver design is mostly due to these algorithms. Therefore in this part QR decomposition algorithm has been investigated as a solution. For doing so, the performance analysis between QR decomposition and LS algorithm in terms of MSE (Mean Square Error) and BER (Bit Error Rate) has been done using simulations software. A complexity comparison between two algorithms has been made in terms of number of mathematical operation. The results have shown that the performance efficiency of these two algorithms are exactly the same as it expected while the computational complexity of the QRD is much less than LS algorithm. Finally it can be concluded that the application of QR decomposition can greatly reduces the complexity of channel estimation in MIMO-OFDM system