Linear Transceiver Design in Nonregenerative Relays With Channel State Information

This paper deals with the design of nonregenerative relaying transceivers in cooperative systems where channel state information (CSI) is available at the relay station. The conventional nonregenerative approach is the amplify and forward (A&F) approach, where the signal received at the relay is simply amplified and retransmitted. In this paper, we propose an alternative linear transceiver design for nonregenerative relaying (including pure relaying and the cooperative transmission cases), making proper use of CSI at the relay station. Specifically, we design the optimum linear filtering performed on the data to be forwarded at the relay. As optimization criteria, we have considered the maximization of mutual information (that provides an information rate for which reliable communication is possible) for a given available transmission power at the relay station. Three different levels of CSI can be considered at the relay station: only first hop channel information (between the source and relay); first hop channel and second hop channel (between relay and destination) information, or a third situation where the relay may have complete cooperative channel information including all the links: first and second hop channels and also the direct channel between source and destination. Despite the latter being a more unrealistic situation, since it requires the destination to inform the relay station about the direct channel, it is useful as an upper benchmark. In this paper, we consider the last two cases relating to CSI. We compare the performance so obtained with the performance for the conventional A&F approach, and also with the performance of regenerative relays and direct noncooperative transmission for two particular cases: narrowband multiple-input multiple-output transceivers and wideband single input single output orthogonal frequency division multiplex transmissions