| Summary: | This paper proposes a heterogeneous network topology, where the backhaul links are supported by massive multiple-input multiple-output systems with full-duplex (FD) modes. Communication is achieved in two phases. In the first phase, we equip macro cell (MC) base station (BS) with massive receive antennas and few transmit antennas and all small cell (SC) BSs with massive receive antennas and a single transmit antenna. In the second phase, a circulator switches the massive receive antennas into transmit antennas and transmit antennas into receive antennas. Under the assumption of imperfect channel state information and large antenna regime, closed-form expressions have been derived for the uplink/downlink achievable sum-rate. From the results, we check that the strength of self-interference (SI) and SC-to-SC interference which occur due to FD operation depends largely on the number of SCs. By increasing the number of SCs, achievable sum-rates also increase but require more antennas to overcome the deleterious effects of the SI and SC-to-SC interference. Based on our analytical results, a hybrid FD/half-duplex system is proposed according to the interferences and the number of antennas. Furthermore, using our system model, it is shown that the transmit power of the MC BS and the SC BSs can be scaled down proportionally to the massive number of receive antennas (first phase) and the massive number of transmit antennas (second phase) and still achieve a required rate.
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