Block Diagonal Differential Space-Time-Frequency Codes for Four Transmit Antennas

For Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system with four transmit antennas, this paper presents a novel block diagonal differential space-time-frequency (DSTF) coded scheme with full diversity and rate one. It overcomes the rate loss of the traditional differential orthogonal space-time-frequency coded scheme for four transmit antennas. The coding and decoding method are described in detail. After analyzing the system error performance, this paper provides two measures to improve the system error performance. One measure is to design good codes which achieve large coding gain. Thus, linear constellation decimation (LCD) codes are imported. The optimal decimation factors are given in the Table 1 under different design parameters. Another measure is to select a good subcarrier grouping method. A grouping method is proposed that all groups have the same subcarrier spacing. By the derived rule of evaluating subcarrier grouping, the optimal subcarrier spacing is obtained by computer search under different channels. Simulation results are presented to illustrate the performance of block diagonal DSTF codes and the proposed subcarrier grouping method.