Performance of a VSF-OFCDM system using a symbol relocated scheme during retransmission

A symbol-relocated (SR) scheme has been proposed for variable spreading factor orthogonal frequency code-division multiplex systems to achieve frequency diversity during retransmission. The performance has been evaluated for two combining schemes of hybrid auto repeat request, namely chase combining and incremental redundancy. The results show that the proposed SR scheme achieves significant improvement in terms of system throughput over conventional schemes. This effect is more significant for chase combining because the rotated mechanism is more effective when the same packet is transmitted during the retransmission. It is also found that the SR scheme is not sensitive to Doppler frequency variation, which makes it an attractive candidate for fast-fading channels. Further investigation also suggests the suitability of an SR scheme for smaller spreading factors (in the frequency domain) and larger coding rates.