Downlink/uplink Decoupling Research Articles

Dynamic Channel Assignment for Downlink and Uplink Decoupling in Wireless Networks

The demand for wireless communication capacity continues to increase with the extensive usage of smartphones, tablets, and devices that are related to the Internet of Things (IoT). However, devices and base stations are diversified, and base stations of various sizes are mixed. In existing cellular networks, the transmission powers of the base stations are different. If the downlink received power from the base station that belongs to the device is maximum, the uplink received power from the device at the base station is not always the maximum. This study maximizes the power that is received from the device through downlink-uplink decoupling (DUDe). DUDe can improve the spectral efficiency by selecting the downlink base station and the uplink base station independently in a network with base stations with different transmission powers. This study focuses on two technologies, DUDe and the dynamic channel assignment (DCA). It proposes an association algorithm to solve the dynamic combinational optimization problem for uplink and downlink cellular networks separately using DUDe. When a user device arrives, it first connects to the base station that has the maximum capacity at that time. Subsequently, by using the base station assignment at that time as an individual, the proposed method performs a more optimal base station assignment with DCA by using a genetic algorithm. The computer simulations demonstrate that the proposed method can achieve up to a 140 % higher spectral efficiency than the existing DUDe in the fixed channel assignment (FCA).

X2-Based Signalling Mechanisms for Downlink Uplink Decoupling in Next Generation Communication Systems

Cell selection in cellular networks is an important aspect that impacts the quality of service. The traditional cell selection mechanism is based on downlink received power. Despite the dense deployment of macrocells, mobile network operators are still confronting the daunting challenge of providing capacity and coverage. Deployment of a large number of small cells has emerged as a promising solution towards addressing this problem. However, this success expands the heterogeneous cellular networks where there is a significant disparity in the transmit power of the different base station types. Downlink and Uplink Decoupling (DUDe) can improve efficiency by associating the downlink cell based on the downlink received power and the uplink based on the pathloss. While the higher layer signalling has not been proposed in detail for the DUDe mechanism yet, we aim to propose a solution for the problem. This work addresses four different signalling mechanisms to realise decoupled up/downlinks connections in the radio access network for the next-generation communication systems with handling mobility. Our proposed signalling mechanisms cover uplink decoupling, downlink coupling, downlink decoupling, and uplink coupling scenarios. We analyse the proposed signalling mechanisms using ns3 simulation and present the impact of applying the DUDe mechanism, which mainly shows improvements for the uplink. For the selected mobility scenario, delay and lost packets are reduced by 30% and 26%, respectively. Delay and lost packets are reduced by 36% and 27% for the fix location scenario, respectively. The improvements imply that it reaches particular demand considering next-generation communication systems, with a massive number of smart devices demanding high quality of service requirements.

Joint DL/UL Decoupled Cell-Association and Resource Allocation in D2D-Underlay HetNets

With the rise of data-hungry applications and the rapid development of the Internet-of-Things (IoT), 5G and device-to-device (D2D) communications come into being. While such technologies are designed to support massive data access to meet the ever-increasing demands, the complexity and heterogeneity of the network structure bring bigger challenges for interference management. As such, downlink/uplink decoupling (DUDe) has become an attractive approach, as it offloads user equipments (UEs) to small-cells (SCells) and creates a more benign environment for D2D communication. In this paper, we investigate the application of DUDe in D2D-underlay heterogeneous networks, and propose an efficient joint cell-association, subchannel allocation, and power control scheme for network sum-rate maximization. The proposed scheme includes a minimum path-loss based DUDe to decide the uplink (UL) serving base-station, and a greedy coloring scheme with modified Munkres algorithm to cluster the UEs, and allocate subchannels. Furthermore, the difference of convex functions based programming algorithm for power control is utilized to maximize the network sum-rate while satisfying the UE transmit power and data rate constraints. The results presented show that the proposed scheme can achieve superior performance to the coupled benchmarks.

Predicted Decoupling for Coexistence Between WiFi and LTE in Unlicensed Band

Wireless fidelity (WiFi) and long term evolution (LTE) coexistence system has attracted significant attention recently. However, most studies on coexistence only consider the issues about downlink performance and fairness between WiFi network and LTE network. In this paper, we take a comprehensive consideration of both the performance of WiFi and LTE, to propose a downlink/uplink decoupling (DUDe) scheme for the fairness of the coexistence system. Through the process of modeling construction, problem formulation with reformulation, solution and simulations, we illustrate that DUDe can achieve proportional fairness in terms of sum throughput and load balancing between uplink and downlink. In our decoupling model for coexistence between WiFi and LTE, resource allocation is under adaptive spectrum partitioning and users can access each network of WiFi and LTE. Moreover, to make our proposal more realistic, we adopt support vector machine (SVM) to predict the total number of users in WiFi and LTE coexistence system, where the predictive simulation shows its high prediction accuracy with low complexity. We further apply the prediction results to the optimization problem of DUDe. Simulation results manifest that the proposed DUDe scheme has better performance in terms of sum throughput. The sum throughput of DUDe scheme can come up to almost twice more than that of coupled association scheme. The result shows that DUDe can also achieve load balance between uplink and downlink in the coexistence system.

Dynamic Time Division Duplexing for Downlink/Uplink Decoupled Millimeter Wave-Based Cellular Networks

The upcoming 5G cellular network’s standard from 3GPP is expected to support the millimeter-wave (mmwave)-based small cell base stations (SCBSs) to increase the data rate and network capacity. Furthermore, the downlink/uplink decoupling (DUDe) has been proposed in 5G to compensate for the transmit power imbalance between the macro-base stations and SCBSs. In this letter, joint uplink and downlink scheduling and resource allocation in a dynamic time division duplex (TDD) system is formulated as an optimization problem. Given a generalized $\alpha $ -fair scheduler, the dynamic TDD and the user scheduling time fractions are derived for a relaxed problem. The derived dynamic TDD results are shown to be a function of the system load. Simulation results are presented, which match with the derived results and show 17% gain in throughput for certain scenarios.

Performance analysis of downlink and uplink decoupled access in clustered heterogeneous cellular networks

The performance of heterogeneous cellular networks (HCNs) is typically analyzed with the assumption that the users connect with the same base station in uplink and downlink. However, recent investigations have shown that downlink–uplink decoupling (DUDe) can provide network performance gains relative to the conventional coupled access. Many authors have evaluated HCN performance while assuming that the network users are distributed according to a homogeneous Poisson point process (HPPP). However, the HPPP cannot accurately model the uplink interference when the users are clustered in urban hotspots such as shopping malls and sports stadiums. This work investigates DUDe access for an HCN with user-clustering modeled by the Matern cluster process. We derive analytical expressions of the coverage probability and average throughput for DUDe access as well as the conventional coupled access. The results show that DUDe outperforms the coupled access scheme in terms of coverage and throughput. The user-clustering is also shown to benefit the coverage and throughput performance relative to the case of HPPP distributed users. The derived results are validated by Monte Carlo simulations.

Joint Load Balancing of Downlink and Uplink for eICIC in Heterogeneous Network

The 3GPP has proposed enhanced intercell interference coordination (eICIC) by making the macrocell silent in the almost blank subframes (ABSs) to mitigate interference for low-power base stations (BSs) in the downlink direction. However, two important challenges are introduced: 1) the underutilization for macrocell in ABS and 2) the optimal downlink association may not be optimal for uplink transmission, i.e., downlink/uplink decoupling (DUDe). In this paper, we first propose a novel method based on configuring uplink transmission in the macrocell in ABSs (UM-ABS) for eICIC to improve the efficiency of the ABS. Then, the UM-ABS and DUDe are formulated as an optimization problem of investigating the joint load balancing of downlink and uplink for eICIC in heterogeneous networks (HetNets) while considering different service classes. The problem is actually a mixed binary integer programming problem, which is difficult to solve. We provide a relaxed-rounding solution to the model. Numerical results illustrate that the proposed algorithm achieves superior performance in comparison to state-of-the-art methods in terms of system throughput and the rate gain for users.

Joint user association and resource partition for downlink-uplink decoupling inmulti-tier HetNets

Traditional cellular networks require the downlink (DL) and uplink (UL) of mobile users (MUs) to be associated with a single base station (BS). However, the power gap between BSs and MUs in different transmission environments results in the BS with the strongest downlink differing from the BS with the strongest uplink. In addition, the significant increase in the number of wireless machine type communication (MTC) devices accessing cellular networks has created a DL/UL traffic imbalance with higher traffic volume on the uplink. In this paper, a joint user association and resource partition framework for downlink-uplink decoupling (DUDe) is developed for a tiered heterogeneous cellular network (HCN). Different from the traditional association rules such as maximal received power and range extension, a coalition game based scheme is proposed for the optimal user association with DUDe. The stability and convergence of this scheme are proven and shown to converge to a Nash equilibrium at a geometric rate. Moreover, the DL and UL optimal bandwidth partition for BSs is derived based on user association considering fairness. Extensive simulation results demonstrate the effectiveness of the proposed scheme, which enhances the sum rate compared with other user association strategies.

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.