Improving MIMO systems performances by concatenating LDPC decoder to the STBC and MRC receivers

Multiple-input multiple-output (MIMO) systems are commonly used in wireless communications to ensure high bit-rate and high capacity transmission. Space time block coding (STBC) is a technique used in MIMO to provide transmit diversity in communication over fading channels. Although STBC has full diversity gain, the coding gain need to be improved by using channel coding such as low density parity check (LDPC) codes or Turbo codes. This paper evaluates the performance of MIMO systems and the improvement obtained by concatenating LDPC codes. MIMO are based on spatially separated multiple transmitting and receiving antennas to provide diversity. This helps combatting the effect of multipath fading in wireless channels. For single-input multiple-output (SIMO) schemes, maximum ratio combining (MRC) receiver are used to handle redundantly the same information-bearing signal over two or more fading channel. The output of this receiver consist on soft decision metrics that can be fed to LDPC decoder for error correction. For MIMO and multiple-input single-output (MISO) systems, space time block codes (STBC) are used to generate orthogonal signals to avoid interference between signal streams. These signals are transmitted at slightly different times to benefit from temporal diversity. LDPC codes are used in conjunction with STBC to improve the error capability. This paper investigates diversity coding for MIMO systems combined with LDPC soft decoding. Performances of the proposed scheme in terms of bit error rates are reported.