Novel Packet Retransmission in OFDMA Systems Using Frequency Diversity

In this paper, the packet combining technique in the downlink OFDMA system is introduced in conjunction with frequency diversity to enhance the reliability of retransmissions and thus reduce the large time delay caused by retransmissions. The novel retransmission technique aims to reduce the maximum number of retransmissions for failed packets, while maximizing the throughput. A suboptimal algorithm is proposed, in which the retransmitted packets have higher priorities to be given resources than new packets. At the receiver, failed and retransmitted packets are combined before detection by using maximal ratio combining (MRC). It is shown that the proposed retransmission scheme can reduce the maximum packet delay significantly, while maintaining the maximum throughput of the conventional retransmission schemes.