A novel and realistic hybrid downlink-uplink coupled/decoupled access scheme for 5G HetNets

Cell association in present day heterogeneous networks (HetNets) is still based on the technique used by homogeneous cellular networks despite power and coverage area disparities of network nodes. In ongoing policy, both uplink (UL) and downlink (DL) associations are coupled based on DL characteristics, which introduces UL-DL asymmetry and cell load imbalances. Recently, decoupled cell association, also known as downlink-uplink decoupling (DUDe), has been introduced in 3rd Generation Partnership Project (3GPP) Release 12 to improve uplink performance, load balancing, and cell capacity. In DUDe, characteristics of both DL and UL channels can be considered. By using this concept, various theoretical UL or DL analytical decoupled access models have been proposed without giving their practical realization. In these frameworks, all network users are assumed to use DL-UL decoupled access without considering its practical utility. Existing solutions also ignore noise, which may lead to practical inaccuracies. This paper proposes a novel and realistic hybrid scheme in which coupled or decoupled cell associations can be selected depending upon user location and its advantages. Building upon this innovative approach, it has been established that decoupled access is chosen by few users and accordingly a two-tier analysis framework for these devices has been formulated. Simple closed-form solutions for user performance metrics without ignoring noise have been precisely derived, which relate user performance with HetNet densities. Devised distributions are employed to compare the performance of the decoupled case with the ongoing procedure of coupled access. A practical network design has been proposed, which requires minimum changes to the existing network. Results show that decoupling is viable in the 5G HetNet to achieve fairness, cell load balancing, and performance improvements.

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