Enhanced HARQ Using Prioritized Bit Selection and Rearrangement for WiMAX Systems

HARQ (hybrid automatic-repeat-request) enhances system throughput by improving SNR and gaining time diversity through retransmissions. To utilizing the coding gain, this paper classifies the priority of FEC coded bits and rearranges the bits for each retransmission at MSB (most significant bit) positions or LSB (less significant bit) positions of modulation symbols according to their priorities. In Addition to time diversity, the proposed HARQ gains frequency and spatial diversities. With the maximum retransmissions of two, numerical simulations show that the proposed scheme outperforms the conventional Chase Combining (CC) HARQ and Incremental Redundancy (IR) HARQ for WiMAX systems in terms of BLER (block error rate)and throughput with maximum SNR (signal-to-noise ratio) gains of 3.5 dB and 3 dB, respectively.