Resource allocation for cooperative relaying

The delay-limited capacity of the half-duplex relay channel is analyzed for several cooperative protocols under a long-term average total transmit power constraint. It is assumed that the source and the relay have access to partial channel state information in the form of channel amplitudes. Nonorthogonal amplify-and-forward (NAF), compress-and-forward (CF) and opportunistic decode-and-forward (ODF) protocols are compared with optimal resource allocation, i.e., at each channel state, the source and the relay transmit with the minimum total power allocation required to achieve the target rate. A hybrid opportunistic protocol is proposed in which CF or ODF with optimal resource allocation is chosen at each channel state. Numerical results demonstrate that, while the hybrid protocol offers the best delay-limited capacity, ODF follows the hybrid scheme closely for a wide range of relay locations and average power constraints. We also consider various low complexity protocols such as fixed time allocation and the estimate-andforward (EF) protocol in order to analyze the trade-off between the system complexity and delay-limited capacity.