NOMA-Aided Multi-Way Massive MIMO Relay Networks

We propose a novel transmission protocol for multiway relay networks (MWRNs) in which the number of timeslots required for full mutual multi-way data exchange among K user nodes can be reduced to just two from Γ(K - 1)/21 + 1 in the current state-of-the-art. The proposed MWRN adopts superposition-coded transmission, successive interference cancellation (SIC) reception, power-domain non-orthogonal multipleaccess (NOMA) and linear detection/precoding facilitated by massive multiple-input multiple-output (MIMO). First, the user nodes transmit their signals to a massive MIMO-enabled relay, where a linear detector based on maximal ratio combining criterion is used for signal reception. Next, the relay composes a superposition-coded signal for each user node and transmits towards the user nodes by using a linear precoder based on maximal ratio transmission criterion. User nodes perform SICbased decoding for retrieving symbols sent by the remaining K user nodes. Thus, our proposed MWRN protocol completes the full mutual multi-way data exchange among all users within two time-slots. We derive the achievable sum rate of it via the so-called worst-case Gaussian approximation and show that a significant spectral efficiency gain can be achieved over the existing MWRN counterparts.