Cooperative Protocols for a Source and an Occasional Nearby Relay

We consider a wireless network where a source is communicating with a remote destination, and where a relay terminal is occasionally present in the source´s vicinity without the source´s knowledge. Cooperative protocols based on decode-and-forward (DF) and quantize-and-forward (QF) are proposed which improve upon single-user performance when the relay is present, and do not degrade single-user performance in the relay´s absence. For DF, optimal correlation between the source´s and relay´s transmissions is investigated, and for QF, a scheme is suggested for incorporating partial side information without the relay terminal knowing the destination´s channel state.