Centralized UL/DL Resource Allocation for flexible TDD Systems with Interference Cancellation

Flexible time division duplex (TDD) is expected to be one of the key technologies for 5G flexible air interface. The main benefit of flexible TDD is to allow for better radio resource utilisation based on instantaneous user traffic demands. To boost network capacity, one could thus utilise flexible TDD along with a dense deployment of small-cells. Flexible TDD systems can be designed to benefit from strong-interference cancellation of the cross-link interference along with advanced inter-cell coordination. In this paper, we propose a centralized coordination scheme with joint UL/DL user scheduling, rate and MIMO rank adaptation. To reduce the complexity of coordinated scheduling, we propose a cluster-based scheduling scheme where joint UL/DL selection and joint user scheduling is performed within a cluster. MIMO rank and rate adaptation is performed across the clusters using inter-cluster rate and rank adaptation. Simulation based results are evaluated in an outdoor urban micro scenario with bursty traffic and assuming realistic channel estimation. It is observed that the proposed flexible TDD scheme with joint UL/DL scheduling, interference cancellation and coordination provides over 120% gain in the 5th percentile and over 29% gain in the average end-to-end uplink throughput as compared to flexible TDD standalone scheduling without coordination. Our results show that successive interference cancellation receivers provide over 20% uplink throughput gain for flexible TDD systems as compared to IRC receivers. We also find that fully flexible TDD with interference cancellation significantly outperforms fully-synchronised TDD for different cell sizes.