Cooperative Transmission with Continuous Phase Frequency Shift Keying and Phase-Forward Relays

We propose in the paper the concept of phase forward (PF) as a possible relay strategy for cooperative communication involving CPFSK modulation in a "fast" fading environment. The technique enables the relay nodes to maintain constant envelop signaling without the need to perform decoding and signal regeneration. To further reduce complexity, we adopt noncoherent discriminator detection at the destination node. A semianalytical expression for the bit error probability (BEP) of this phase forward non-coherent CPFSK cooperative transmission scheme is derived in the paper. The analysis is general in the sense that it can accommodate different Doppler frequencies and signal-to-noise ratios in the various links. It was found that PF can provide a strong diversity effect, especially when the signal-to-noise ratio in the source-relay link is substantially stronger than those in the source-destination and the relay-destination links. Furthermore, from a BEP stand point, phase forward is better than conventional decode-and-forward (DF) under typical channel conditions. It can also attain the same performance as amplify-and-forward (AF) when fading is static. Finally, we found that the concept of PF applies equally well to PSK modulations.