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

In this paper, a symbol relocated (SR) scheme has been proposed for variable spreading factor orthogonal frequency code division multiplexing (VSF-OFCDM) systems to achieve frequency diversity during retransmission. The performance has been evaluated for two combining schemes of hybrid auto repeat request (ARQ) namely chase combining and incremental redundancy. The results show that the proposed SR scheme achieves significant improvement in terms of system throughput over the 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 SR scheme is not sensitive to Doppler frequency variation, which makes SR scheme an attractive candidate for fast fading channels. Further investigations also suggest the suitability of the SR scheme for smaller spreading factors (in frequency domain) and larger coding rates.