Resource optimization in the decode-and-forward multiple relay-assisted channel

The half-duplex multiple relay-assisted channel is investigated, where the relays work under decode-and-forward (DF) in time/frequency orthogonal resources. Achievable rates are optimized with respect to the transmitted powers and with respect to the fraction oftimelbandwidth allocated to the relay-receive and the relay-transmit phases. Different transmission strategies associated to different complexities at the receivers are considered. For each case we take into account either the synchronous or asynchronous transmission of the terminals, depending on the availability of channel state information (CSI) in transmission from all links. We find that all the cases can be formulated as a unique convex problem, and we compare the achievable rates thus obtained. We finally derive under which conditions the use of two DF relays brings significant gains over the use of one