Best-effort cooperative communication without dedicated relays

Traditional decode-and-forward cooperation systems consider dedicated relays, while instead we consider wireless transceivers that cooperatively relay signals in addition to primary communication missions. A system that transmits the additional signal using a best-effort transmission policy within the original transmission energy constraint is considered. To maintain the original energy budget we consider the feasibility of reallocating energy from pilot signals toward the relaying service when channel conditions are stationary. Under the best-effort delivery policy, the node is not obligated to devote energy for relaying signals, nor does it provide a guarantee of signal quality to retransmissions. Instead the relay sacrifices energy at its own discretion, prioritizing the primary communication mission. Using the best-effort delivery policy, we derive an optimal power allocation rule that maintains a fixed symbol error rate for the relay's primary transmission, and further demonstrate cooperative communication gains using the proposed delivery method.