Near Optimal Combining Scheme for MIMO-OFDM HARQ with Bit Rearrangement

In this paper, we study the combining scheme for type I hybrid Automatic Repeat-reQuest (HARQ) in MIMO-OFDM system. A new pre-combining scheme based on hybrid QRMC detector is proposed. The proposed scheme is applied to HARQ with various bit rearrangement strategies. The significant gain has been obtained for both slow fading and fast fading channel comparing with the system using near optimal QRD-M detector as a bitwise post-combining scheme at the cost of increased storage requirement. The performance of various bit rearrangement strategies using the proposed combining method is evaluated and compared. It is shown that proper bit-rearrangement can greatly improve the system performance even in slow fading channel. The new combining scheme has flexible structure and can be applied to any bit rearrangement strategies.