PSK-Based Space Time Modulation for Two-User Two-Way Massive MIMO Relay Systems

In this letter, we consider a two-way relay system in which there are two source nodes with each having a single antenna and one relay node equipped with a large number of antennas. It is assumed that each node has no channel information. For such a relay system, we systematically design a pair of absolutely additively uniquely decomposable phase-shift keying (PSK) constellations such that when any linear combination of two PSK signals with positive weight coefficients is received, each individual PSK signal can be uniquely decoded. With this, a novel distributed space-time modulation scheme is proposed for the system. We prove that when the number of antennas at the relay node grows to infinite, two user PSK symbols and large scale coefficients can be uniquely determined in a noise-free case. In a noisy case, a minimum Riemannian distance detector is developed for efficiently and effectively estimating both the channel coefficients and the transmitted signals.