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 non-coherent discriminator detection at the destination node. A semi-analytical 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.
['Qi Yang', 'Paul Ho']
Cooperative Transmission with Continuous Phase Frequency Shift Keying and Phase-Forward Relays