Non‐coherent transmission for two‐way relaying systems with relay having large‐scale antennas

Abstract

Without channel state information at the users and relay node, a non-coherent transmission scheme for the two-way relaying systems is investigated in this study. At the relay node, the authors first detect the uplink data with non-coherent maximum likelihood receiver by fully utilising the large receiving freedom of relay's large-scale antennas. Channel estimations can also be obtained by treating the detected uplink data as pilot symbols. Then, the relay node forwards the detected data by using beamforming. To assure the reliable detection of the users' transmitted symbols non-coherently, the authors propose a transmitting constellation design with the idea of searching an optimal angle for rotating one user's constellation. Specially, for M-PSK constellations, they derive the optimal rotation angle, which is highly consistent with the exhaustive searching results. In addition, they also analyse the lower bound of channel estimations in terms of normalised mean square error (NMSE). From simulation results, the proposed non-coherent transmission scheme achieves considerable error performance, and the NMSE lower bounds of channel estimations are also tight when the number of relay's antennas approaches to be large.