Massive MIMO Relay Networks With Underlay Spectrum Sharing

The achievable rates of multicell/multiuser massive multiple-input multiple-output (MIMO) relay networks with underlay spectrum sharing are investigated for imperfect/perfect channel state information (CSI). The transmit power constraints of the secondary user nodes and relays are derived. A max-min fairness optimal secondary transmit power control algorithm is formulated, and thereby, optimal power allocation coefficients and the maximum common achievable user rates are derived. The detrimental effects of intracell and intercell pilot contamination are studied for three pilot sequence designs (PSDs). Thereby, it is shown that for some PSDs and CSI assumptions, the secondary network can be operated at the peak average transmit power without degrading the performance of the primary network when the base-stations are equipped with massive MIMO. Consequently, the asymptotic achievable rates become independent of the primary interference temperature. For the worst-case scenario of full pilot reuse in the primary and secondary networks as well as in the co-channel cells, the achievable rates are severely degraded by intra-cell and inter-cell pilot contamination. Counter-intuitively, a significant portion of the achievable rate gains observed under the perfect CSI assumption can still be obtained by using a PSD with a fundamental trade-off between system performance and practical viability.