Performance comparison of orthogonal complex MIMO STBC with ML decoding and soft decision decoding

Multiple input multiple output (MIMO) systems have become extremely popular transmission technique due to their improved capacity and reliability. Orthogonal complex space time block code (O-STBC) due to its single symbol decodability is a widely used MIMO technology. These codes are traditionally decoded by maximum likelihood (ML) decoder. Use of popular channel codes like low density parity check (LDPC) codes, Turbo codes etc. in conjunction with these orthogonal codes further increases error resiliency. But the use of codes like LDPC, Turbo codes necessitates soft decision decoding of the MIMO codes. The soft decision algorithm directly transfers soft information to the channel code decoder. This work computes the soft decision decoded values of the no zero entry four antenna code given by Tarokh et. al. It also presents a comparative study of bit error rate (BER) performances between ML decoding and soft decision decoding concatenated with LDPC as error correcting code, of a 4 antenna O-STBC. BER performance of STBC for four transmit antenna are also studied from the perspective of zero entries in the code matrix. This study is important because the STBCs with zero entries have a worse peak to average power ratio (PAPR) than the STBCs with no zero entries. Here, the LDPC code of IEEE 802.16 WiMAX standard has been used with the MIMO STBC system. Use of this LDPC gives much improved performance for the combined LDPC-STBC model.