Cluster-Based Transmit Diversity Scheme for MIMO OFDM Systems

For practical multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, it is important to develop transmit diversity schemes that are transparent to a receiver in that the receiver does not need to perform additional processing. In this paper, we examine one of the most widely-used receiver-transparent transmit diversity schemes - the cyclic delay diversity (CDD) scheme. It is shown that the CDD scheme effectively increases the delay spread of the channel and that the performance degrades under non-ideal channel estimation. As a remedy to the performance loss due to non-ideal channel estimation, a cluster-based transmit diversity scheme is proposed, which garners almost all the benefits of the CDD scheme without degrading the performance of a cluster-based channel estimation. The simulation results are provided in the realistic setting of IEEE 802.16e WiMAX systems.