Uplink/Downlink Decoupled Access with Dynamic TDD in 5G HetNets

Dynamic time-division duplexing (TDD) enables flexible adjustments of uplink (UL) and downlink (DL) resources according to the instantaneous traffic load. However, it also brings new challenges in heterogeneous cellular networks (HetNets) because of the introduction of cross-link interference i.e., uplink to downlink interference and downlink to uplink interference. One step further in the optimization of HetNet, is the interdependency between UL and DL and how the association policies affect the system performance on both links in a way to mitigate the cross-link interference. In classical HetNets, coupled UL/DL access (CoUD) mode is adopted, where each user is associated in downlink and uplink with a single cell. However, the power imbalance between the macro cells and the small cells motivates the decoupling of both links. In the next generation HetNets, instead of being connected to a specific cell, a mobile user can independently receive the downlink traffic from one base station (BS) and transmit uplink traffic through another BS. This situation is referred to as decoupled uplink and downlink (DeUD) access. The optimization of a HetNet based system according to time-variant traffic loads necessitates finding a system level simulator where we can present the motivation and accurately assess the role of both decoupling and dynamic TDD techniques. In this paper, we resort to a system level simulator under which we develop a new module that investigates the dynamic TDD technique along with multiple association policies in a dense HetNet deployment. We create appropriate simulation environment that is relative to real scenarios i.e. simulations where multiple small cells are deployed in a heavy loaded HetNet system and under various traffic loads.