Cooperative Power Allocation Schemes and BER Performance in Decode-and-Forward OFCDM Based Relay Networks

In this paper, different power allocation schemes between the source and the cooperating relay nodes are analyzed and numerically evaluated for a two-hop decode-and-forward OFCDM based relay network. A cooperative power allocation ratio ¿ (=source power/total power) is defined and BER performance is evaluated for different values of ¿ in the relay network. It is shown that there exists an optimal power allocation ratio for different operating environment such as source-to-relay channel gains and time-frequency spreading factors. It is reported that (a) When all three channels (source-to-relay, source-to-destination and relay-to-destination) have equal gains, power ratio is found to be ¿ ¿ 0.8 (i.e., 80% and 20% of the total power is distributed among source and relay node respectively). The BER performance degrades at a faster rate when ¿ increases above the optimal value than the decrement at higher E_b/N_¿. (b) For a network with stronger source-to-relay link, the optimal ¿ remains invariant at higher E_b/N_¿ for equal channel gain case; however, the optimal power ratio moves toward lower value of ¿ at lower E_b/N_¿. (c) The optimal ¿ remains almost the same with different time-frequency spreading factors.