A Study On The Performance Of Space Time Frequency Code For Cooperative Communication Systems

Quasi-orthogonal space time block codes (QOSTBC) can achieve spatial diversity gains over multiple-input multiple-output (MIMO) flat fading channels. However, the Maximum Likelihood (ML) decoding of QOSTBC requires joint detection of pairs of transmitted complex symbols. How to reduce its decoding complexity has received an interest in wireless communication field. Quasi-orthogonal space time frequency block codes (QOSTFBC) are designed by combining the QOSTBC with orthogonal frequency division multiplexing (OFDM) in frequency-selective fading channels. They are capable of fully exploiting spatial, temporal, and frequency diversities offered by the MIMO-OFDM systems. The low decoding complexity is also a key technology in their practical application. Cooperative communication system can exploit diversity gains by enabling single-antenna nodes to share their antennas. Applying the principles of QOSTBC to cooperative communication system generates the QOSTBC cooperative communication. The Nakagami distribution has received widespread application in wireless channel models. Therefore, this thesis investigates the low complexity decoding algorithm for QOSTBC over correlated Nakagami fading channels. This thesis uses QOSTBC and two-dimensional rotation matrix to design QOSTFBC, investigates the low complexity decoding algorithm for the QOSTFBC and the average symbol error rate (SER) performance of QOSTBC for cooperative communication system as well.Chapter1presents a brief review of QOSTBC, STFBC and space time block codes (STBC)/QOSTBC for cooperative communication systems.Chapter2investigates the decoding algorithm based on sorted QR decomposition(SQR) for QOSTBC with rectangular M-ary quadrature amplitude modulation (MQAM) over correlated Nakagami fading channels. The average SER performance of SQR-based decoding algorithm is compared with that of symbol-pair-wise ML decoding algorithm. The simulation results show that the average SER performance of SQR-based decoding algorithm for QOSTBC that can not achieve full diversity is near to that of ML decoding algorithm. For QOSTBC that can not achieve full diversity, its performance of SQR-based decoding algorithm is closer to ML decoding algorithm than that for full diversity QOSTBC.Chapter3designs full-rate QOSTFBC for2transmit antennas by using full-rate and full-diversity QOSTBC which is designed by incorporating two-dimensional rotation. The SQR-based decoding algorithm is employed to decode the QOSTFBC. The simulation results show that the performance of SQR-based decoding algorithm for QOSTFBC is slightly worse than that of ML decoding algorithm. Chapter4investigates the average SER performance of the closed-loop and open-loop QOSTBC cooperative communications with decode-and-forward protocol and MQAM modulation over Nakagami fading channels. By using relay-selection and phase-rotation methods to eliminate interference terms resulting from neighboring signals, the closed-loop QOSTBC for cooperative communication system can achieve symbol-wise ML decoding complexity. The SQR-based decoding algorithm is applied for the open-loop QOSTBC cooperative communications, and can allow for low complexity decoding of one real symbol at a time. The simulation results show that the average SER performance of the closed-loop QOSTBC cooperative communication is better than that of the open-loop QOSTBC cooperative communication.Chapter5is the conclusion of this thesis.