Capacity Region and Scheduling for Non-Orthogonal Duplex

Existing wireless mobile networks configure the uplink (UL) and downlink (DL) resources based on the orthogonal duplex principle, which has significantly evolved from the static frequency/time division duplex (FDD/TDD) to the semi-dynamic TDD in 4G and the fully-dynamic TDD in 5G. Fueled by the successful realizations of full duplex (FD) transmission, non-orthogonal duplex (NOD) emerges as an attractive candidate technique for future networks to improve the bidirectional throughput. In this paper, we investigate the performance limit of the NOD scheme, which imports the FD mode on the basis of fully-dynamic TDD. We first focus on a single-cell scenario by assuming no cooperation among cells, and strive to characterize the bidirectional capacity region by finding the capacity-optimal transmission mode scheduling policy. We obtain the optimal policies for the systems with and without modulation and coding scheme (MCS), respectively, where the policies are based on the instantaneous channel gains and the distribution of channels. We proceed to develop a scheduling policy that only relies on the instantaneous channel and queue information, and extend it to the multicell multiuser scenario with coordinated scheduling. Numerical and simulation results demonstrate the great potential of the NOD scheme in increasing bidirectional capacity and reducing the queuing delay.