In this paper, we first propose a modified adap- tive subcarrier allocation algorithm for a two-hop decode-and- forward OFCDM relay system and then its BER performance analysis is formulated and numerically evaluated via Monte- Carlo simulation. The effect of considering the CSI of source- base station and source-relay links are evaluated in a cooperative diversity system. Results show that the allocation of subcarriers based on source-relay link CSI provides better BER performance at higher Eb/No and at lower Eb/No, both the source-relay and source-base station links need to be considered. We also introduce a parameter called cooperative channel state information, C-CSI- (0 ≤ ν ≤ 1), that weighs in end-to-end SINR and hence impacts the subcarrier allocation in OFCDM systems. From our numeri- cal simulation, we notice that the cross-over Eb/No point (around which frequency spreading gives better performance than time spreading) moves towards the lower Eb/No when ν approaches 1; that is, when the subcarrier allocation is done giving more weight to source-base station link rather than the source-relay link. We also observe a relationship between the cross-over point (Eb/No in dB) and the C-CSI, which provides additional flexibility in operating environment for OFCDM systems.
['Sivasothy Senthuran', 'Alagan Anpalagan', 'Olivia Das', 'Sehrish Khan']
Effect of Cooperative CSI in Adaptive Subcarrier Allocation for OFCDM Based Decode-and-Forward Relay Systems