Nonregenerative Cellular Two-Way Relaying With Large-Scale Antenna Arrays.

In this paper, we consider a cellular two-way relay channel (cTWRC) where multiple mobile stations (MSs) exchange information with a base station (BS) via a relay station (RS). Both the BS and the RS are equipped with a very large-scale antenna array, whereas each MS is equipped with a small number of antennas. We investigate two zero-forcing (ZF)-based nonregenerative relaying schemes for cTWRCs, namely, signal-alignment-based ZF (SA-ZF) and antenna-selection-based ZF (AS-ZF). We focus on analyzing the impact of large antenna arrays on the performance of these low-complexity nonregenerative relaying protocols, and we derive closed-form asymptotic expressions for the signal-to-interference-plus-noise ratio (SINR) and the achievable sum rate when the numbers of antennas at the BS and the RS go large simultaneously. We show that with large-scale antenna arrays, ZF-based relaying can achieve the sum-rate capacity of the cTWRC, either when the RS is located much closer to the BS than to the MSs or when the number of antennas at the BS far exceeds that at the RS. We further show that, with large-scale antenna arrays, the transmit power of the BS and each MS can be made inversely proportional to the number of relay antennas while maintaining a given achievable rate for each end node. Numerical results are provided to verify our analysis. [ABSTRACT FROM AUTHOR]