Full-duplex technology has become an attractive solution for future 5th generation (5G) systems for accommodating\nthe exponentially growing mobile traffic demand. Full duplex allows a node to transmit and receive simultaneously in\nthe same frequency band, thus, theoretically, doubling the system throughput over conventional half-duplex systems.\nA key limitation in building a feasible full-duplex node is the self-interference, i.e., the interference generated by the\ntransmitted signal to the desired signal received on the same node. This constraint has been overcome given the\nrecent advances in the self-interference cancellation technology. However, there are other limitations in achieving the\ntheoretical full-duplex gain: residual self-interference, traffic constraints, and inter-cell and intra-cell interference. The\ncontribution of this article is twofold. Firstly, achievable levels of self-interference cancellation are demonstrated using\nour own developed test bed. Secondly, a detailed evaluation of full-duplex communication in 5G ultra-dense small\ncell networks via system level simulations is provided. The results are presented in terms of throughput and delay.\nTwo types of full duplex are studied: when both the station and the user equipments are full duplex capable and\nwhen only the base station is able to exploit simultaneous transmission and reception. The impact of the traffic profile\nand the inter-cell and intra-cell interferences is addressed, individually and jointly. Results show that the increased\ninterference that simultaneous transmission and reception causes is one of the main limiting factors in achieving the\npromised full-duplex throughput gain, while large traffic asymmetries between downlink and uplink further\ncompromise such gain.
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