Coverage Analysis of Dynamic TDD in Two-Tier Heterogeneous Ultra Dense Networks

Ultra dense network (UDN) is one of the key technologies to improve the network capacity by densely de-ployed small cells. As for the asymmetry and variations of future traffic, dynamic time division duplex (D-TDD) has been proposed as a promising solution to dynamically adjust the uplink (UL)/downlink (DL) configuration. In this paper, we propose a general and tractable analytical framework for the theoretical performance under D-TDD two-tier heterogeneous networks. We firstly model user equipment (UE) and base station (BS) as homogenous Poisson point process (HPPP). Then, by leveraging stochastic geometry and geometry relationship, we propose an analysis method based on geometry approximation and derive analytical expressions for the UL and DL coverage probability. To increase the accuracy of analysis, we consider the coupling between UEs and BSs, so that more accurate interference can be obtained. Our results show that the derived coverage probabilities match the simulation results quite well and suitable for heterogeneous UDN scenarios. In addition, a comparison of the coverage probabilities between D-TDD system and static TDD (S-TDD) system is also provided to show that compared with S-TDD system, D-TDD system sacrifices uplink coverage performance to obtain better downlink performance.