WLC16-5: BER Analysis of STBC with Packet Combining in MIMO Rayleigh Fading Channels: LLR-Based Approach

Adopting a log-likelihood ratio (LLR) based approach, we analyze the bit error rate (BER) performance of orthogonal space-time block coding (STBC) using M-ary quadrature amplitude modulation (M-QAM) along with packet combining triggered by automatic repeat request (ARQ) retransmission over multiple-input multiple-output (MIMO) Rayleigh fading channels. Specifically, considering the 16-QAM case of study, we provide an exact formula for the aggregate LLR distribution in the case the STBC codeword can be transmitted twice, and derive an exact expression for the BER. For higher number of retransmissions, an approximation of the error function, erf(.), is used to derive the LLR distributions and the system´s ensuing BER. The proposed BER analytical model is validated through simulations considering transmission over additive white Gaussian noise (AWGN) and MIMO Rayleigh fading channels, for different STBC mappings, different values of combined transmissions, and possible constellation rearrangement (CoRe).