A Selective HARQ Scheme Operating based on Channel Conditions for High Speed Packet Data Transmission Systems

A selective hybrid automatic repeat request (HARQ) scheme operating based on channel conditions for high speed packet data transmission systems is presented. This scheme exploits the channel condition identified by the channel quality indicator (CQI) to determine whether the retransmitted packet is directly decoded without soft combining or it is soft combined with the original packet and decoded. Since the channel condition is already measured and mapped to the CQI number by the receiver to report to the base-station for adaptive modulation and coding, additional increase of computational complexity at the receiver is not required for this scheme. The proposed selective HARQ scheme shows about two to three times performance improvement in terms of throughput because it takes the quality of retransmitted packets into account based on channel conditions before performing soft combining with the original packet with error.