Flexible Design for $α$-Duplex Communications in Multi-Tier Cellular Networks

Backward compatibility is an essential ingredient for the success of new technologies. In the context of in-band full-duplex (FD) communication, FD base stations (BSs) should support half-duplex (HD) UEs without sacrificing the foreseen FD gains. This paper presents flexible and tractable modeling framework for multi-tier cellular networks with FD-BSs and HD-UEs. The presented model is based on stochastic geometry and accounts for the intrinsic vulnerability of uplink transmissions. To this end, we propose location-aware and fine-grained duplexing design, which allows partial overlap between uplink and downlink spectrum, to maximize the network transmission rate. The results show that FD-UEs are not necessarily required to harvest rate gains from FD-BSs. In particular, the results show that adding FD-UEs to FD-BSs offers a maximum of 8% rate gain over FD-BSs and HD-UEs case, which is a marginal gain compared to the burden required to implement FD transceivers at the UEs' side. To this end, we shed light on practical scenarios where HD-UEs operation with FD-BSs outperforms the operation when both the BSs and UEs are FD. Finally, we propose a location dependent mixed FD/HD strategy for the UEs that efficiently operates FD cellular networks when the UEs' FD receivers have different efficiencies.