Improved OFDM transmission with DF relaying and power allocation for a sum power constraint

In this paper we consider an OFDM (orthogonal frequency division multiplexing) transmission scheme with a relay. Symbols sent by the source may or may not be retransmitted during a second time slot by the relay, which is assumed to be of the decode-and-forward (DF) type. For each relayed carrier the destination implements maximum ratio combining. Assuming perfect CSI (channel state information) knowledge the paper investigates the power allocation problem in order to maximize the rate offered by the scheme. Compared to [VDLZ08], the second time slot is better used. The source is allowed to transmit a new symbol during this second time slot when the relay is inactive. The optimization is performed for a sum power constraint. The theoretical analysis is illustrated by numerical results.