Abstract:A novel grouping method is proposed for LDSTBC(Layered Differential Space-Time Block Code) over frequency selective channels, relying on mutual orthogonality between subcarriers of different users in OFDMA(Orthogonal Frequency-Division Multiple Access) systems. At the transmitter, LDSTBC combined with OFDM is applied . At the receiver, the group suppression based on subcarrier selection matrices is used, then the traditional decoding method for DSTBC is used for each layer. Compared with SVD the improved approach only needs one receive antenna so the complexity of the receiver decreases remarkably. Simulation results show that the performance of the improved method is better than the one based on SVD.