Bit Rearrangement for MIMO Retransmissions

In this paper, we propose a new hybrid automatic repeat request (H-ARQ) scheme in MIMO. The proposed scheme performs bit-level exchanges and modifications every retransmission and covers all combinations of number of antennas and number of retransmissions in M-QAM. In order to obtain a better bitwise mapping scheme, we define two independent bitwise suboperations, which are called bit swapping and inversion (BSI) and bit shifting between antennas (BSA), and derive sets for BSI and BSA. The performance of the proposed scheme is evaluated through link simulations with a 3GPP long-term evolution (LTE) specification and is compared to previous H-ARQ schemes in MIMO. The results show that the proposed bitwise mapping scheme provides approximately 2 dB gain over the conventional scheme even at a high mobile speed.