  Full duplex (FD) communications has the potential to double the capacity of a
half duplex (HD) system at the link level. However, FD operation increases the
aggregate interference on each communication link, which limits the capacity
improvement. In this paper, we investigate how much of the potential doubling
can be practically achieved in the resource-managed, small multi-cellular
system, similar to the TDD variant of LTE, both in indoor and outdoor
environments, assuming FD base stations (BSs) and HD user equipment (UEs). We
focus on low-powered small cellular systems, because they are more suitable for
FD operation given practical self-interference cancellation limits. A joint UE
selection and power allocation method for a multi-cell scenario is presented,
where a hybrid scheduling policy assigns FD timeslots when it provides a
throughput advantage by pairing UEs with appropriate power levels to mitigate
the mutual interference, but otherwise defaults to HD operation. Due to the
complexity of finding the globally optimum solution of the proposed algorithm,
a sub-optimal method based on a heuristic greedy algorithm for UE selection,
and a novel solution using geometric programming for power allocation, is
proposed. With practical self-interference cancellation, antennas and circuits,
it is shown that the proposed hybrid FD system achieves as much as 94%
throughput improvement in the downlink, and 92% in the uplink, compared to a HD
system in an indoor multi-cell scenario and 54% in downlink and 61% in uplink
in an outdoor multi-cell scenario. Further, we also compare the energy
efficiency of FD operation.
