HARQ with variable spreading factor for multicode MC-CDMA

A new hybrid automatic repeat request (HARQ) with variable spreading factor (VSF) suitable for multicarrier code division multiple access (MC-CDMA) is presented. A HARQ based on incremental redundancy strategy is considered. The throughput of MC-CDMA HARQ is a function of the frequency diversity gain, the coding gain and the inter-code interference. To effectively exploit the frequency diversity gain and the coding gain, the spreading factor is changed between the initial transmission and the succeeding retransmissions. It is shown by computer simulation that HARQ with VSF can provide better throughput performance than with fixed spreading factor.