Cognitive Massive MIMO Relay Networks

The sum rate performance of cognitive multi-user massive multiple-input multiple-output (MIMO) relay networks is investigated. Specifically, a secondary relay network is underlaid in the same cell of a primary multi-user network. Both primary and secondary networks are allowed to share the same frequency spectrum. Hence, the transmit power of the secondary relay network is constrained such that the interference inflicted at the primary network due to the secondary concurrent transmissions does not exceed a predefined interference temperature. Under the aforementioned system set-up, the asymptotic signal-to-interference-plus-noise ratio and achievable sum rate expressions are derived for two specific antenna configurations at the relay, secondary and primary base-stations. Our asymptotic analysis reveals that the secondary relay network can be operated at its peak average transmit power level without degrading the performance of the primary network whenever the numbers of antennas at the relay, secondary and primary base-stations are allowed to grow without bound while keeping fixed ratios among them. Consequently, the asymptotic performance metrics for both primary and secondary networks become independent of the corresponding interference temperature. Furthermore, the intra-cell co-channel interference inflicted at the secondary network due to the primary network and vice-versa can be asymptotically mitigated. Therefore, massive MIMO technology can be exploited for successful deployments of cognitive relay networks with underlay spectrum sharing.