LLR based analysis of LDPC codes concatenated with orthogonal STBC coded MIMO systems

Multiple input multiple output (MIMO) system is one of the most promising wireless technologies that can achieve wide coverage, high throughput and improved reliability. Low density parity check (LDPC) codes can achieve capacity near Shannon's limit with good error correcting performance. In this paper, we combined LDPC codes with orthogonal space time block codes (OSTBC) in MIMO systems. The performance of LDPC codes depends on the structure of the parity check matrix and decoding algorithms. In this paper, we analyzed the bit-error rate (BER) performance of different LDPC codes like Quasi Cyclic (QC) and random which differs in their parity check matrix structures. For low complexity decoding, log domain Sum Product Algorithm (log-SPA) is used which has messages in the form of log-likelihood ratios (LLR). Further, the approximate BER expressions are derived and verified for above mentioned system with different antenna configurations.