Massive MIMO Aided Multi-Pair Relaying with Underlaid D2D Communications

Device-to-device (D2D) communication underlaying a cellular infrastructure is an important technique, e.g. to offload traffic, but has a limit of short range, which can be overcome via relaying. In such context, the coexistence of D2D and multi-pair communications in massive MIMO aided relaying is considered in this paper. The direct D2D transmission reuses the source-to-relay spectrum in the first hop, which leads to a rate loss at the destination users, due to the amplify-and-forward relaying. To evaluate this loss, a closed-form deterministic equivalent of the end-to-end (e2e) signal to interference-plus-noise ratio (SINR) is derived. Moreover, in case of failed direct transmissions, D2D receivers can perform the detection in the second hop, based on the signal forwarded by the relay. The associated deterministic D2D SINR equivalent is also derived. The asymptotic analysis indicates that the transmit power of source users can be made inversely proportional to the number of relay antennas, such that non-vanishing e2e rate at the destination users and relay assisted D2D rate exist. Simulations validate the analytical results and the feasibility of supporting underlaid D2D transmissions when deploying multi-pair relaying with massive MIMO.