Comparative Study of Open-Loop Transmit Diversity Schemes for Four Transmit Antennas in Coded OFDM Systems

The authors compare four open-loop transmit diversity schemes in a coded Orthogonal Frequency Division Multiplexing (OFDM) system with four transmit antennas, namely Cyclic Delay Diversity (CDD), Space-Time Block Code (STBC, Alamouti code is used) with CDD, Quasi-Orthogonal STBC (QO-STBC) and Minimum-Decoding-Complexity QOSTBC (MDC-QOSTBC). They show that in a coded system with low code rate, a scheme with spatial transmit diversity of second order can achieve similar performance to that with spatial transmit diversity of fourth order due to the additional diversity provided by the phase shift diversity with channel coding. In addition, they also compare the decoding complexity and other features of the above four mentioned schemes, such as the requirement for the training signals, Hybrid Automatic Retransmission reQuest (HARQ), etc.