Challenges Imposed by User's Mobility in Future HetNet: Offloading and Mobility Management

The users' mobility imposes challenges to mobility management and, the offloading process, which hinder the conventional heterogeneous networks (HetNets) in meeting the huge data traffic requirements of the future. In this thesis, a trio-connectivity (TC), which includes a control-plane (C-plane), a user-plane (U-plane) and an indication-plane (I-plane), is proposed to tackle these challenges. Especially, the I-plane is created as an indicator to help the user equipment (UE) identify and discover the small cells in the system prior to offloading her from the overloaded cells e.g. macro cells, to the cells with abundant resources e.g. small cells. In order to show the advantages of the proposed TC structure, a comparison between the TC and the dual-connectivity (DC) is presented in this thesis, in terms of uplink energy efficiency (ULEE) and energy consumption. Furthermore, the complexity of mobility management is addressed in this thesis as the HetNets will have to handle a large number of UEs and their frequent handoffs due to very dense small-footprint small cells. Considering an accurate mobility framework is essential not only to find the potential offloading to the small cells but also to show the mobility impact on the quality of service (QoS). This thesis presents a framework to model and derive the coverage of small cells, the cell sojourn time and the handoff rate in a multi-tier HetNet by taking into account the overlap coverage among the small cells. The results show the effects of a number of parameters, including the density and the transmit power of the small cells and the power control factor, on the system performance. They also show that the TC can outperform the DC in dense HetNets in terms of energy efficiency and energy consumption

Mobility Management in Small Cell Networks

The cell sojourn time and the handoff rate are considered as the main parameters in the mobility management of the cellular systems. In this paper, we address the mobility management in a two-tier heterogeneous network (HetNet) and propose a framework to study the impact of different system parameters on the handoff rate and the small cell sojourn time. In the proposed framework, the overlapping coverage among the small cells and the number of overlaps on the path of a reference user equipment (UE) are derived to obtain the actual time that the reference UE spends in each small cell during its movement from the starting point to the destination point. The results show the accuracy of the analysis in this paper in comparison to the analysis when ignoring the impact of the overlaps. The results also show the importance of considering the overlaps among the small cells in dense HetNets

The Optimum Rate of Inter-Frequency Scan in Inter-Frequency HetNets

Inter-frequency scan (IFS) is a process carried out by the terminals to discover the small cells (SCs) in the interfrequency heterogeneous networks (HetNets) prior to offload them to the discovered SCs. The IFS has a great impact on the quality of service, the energy efficiency and the spectral efficiency in the cellular systems. In this paper, a framework is presented to model and evaluate the impact of IFS on the system performance by using the stochastic geometry. The energy efficiency is derived as performance metric to obtain the optimum value of the IFS rate (optimum number of scans per unit time) by taking into consideration the trade-off in the offloading process between the power consumption and exploiting the system resources efficiently. Considering the energy consumption for performing IFSs along with the energy consumption for maintaining the uplink transmission will help to find the optimum value of IFS rate that achieves the best energy efficiency. The analysis and results show that the optimum IFS rate depends on different system parameters such as SCs’ density, terminal’s speed and the transmit power of the SCs (SCs’ coverage)

Trio-Connectivity for Efficient Uplink Performance in Future Mobile HetNets

The technical challenges, e.g. the mobility management and the offloading process, hinder the conventional cellular systems to meet the huge data traffic requirements of the next generation mobile communications. The traditional system (e.g dual-connectivity (DC)) has been proposed to improve the mobility management, however, it will inherit the big trade-off in the offloading process between the energy consumption for the small cell (SC) discovery (SCD) process and the efficiency of utilizing the system resources (e.g. frequency and signaling). In this paper, we present a framework to model the potential offloading opportunities as well as the offloading loss when a typical user equipment (UE) performs the inter-frequency (IRF) scan periodically. The proposed framework also studies the impact of the SCD on the energy efficiency. To improve the system performance and reduce the power consumption at the UEs, a new scheme, trio-connectivity (TC), is proposed in this paper to tackle the aforementioned challenges. The TC includes three planes: control-plane (C-plane), user-plane (U-plane) and indication-plane (I-plane). The I-plane works as an indicator to help the UE to identify and discover the SCs in the system prior to offloading. The role of the I-plane is to keep the SCD on one frequency channel regardless of the number of frequency channels in the system. In the proposed offloading mechanism, some of the energy consumption is transferred from the UE to the network. By using the proposed framework, UE energy efficiency and system energy efficiency as well as the total energy consumption are derived as performance metrics to compare between the TC and the DC. The results show that the TC can outperform the DC in dense cellular systems

Impact of Small Cells Overlapping on Mobility Management

The mobility management will be more complex and will have a great impact on the quality of service (QoS) in the future cellular networks, as these networks will have to handle a huge number of user equipment (UEs) and their frequent handoffs due to very dense short-footage small cells. This paper presents a framework to model and derive the coverage of small cells, the cell sojourn time and the handoff rate in multi-tier small cell networks. The distribution of the small cells around a reference UE’s path is studied by taking into consideration the overlaps among the small cells. Two types of handoff rates are introduced to estimate the load managed by different cells, where inter-frequency handoff (IRH) rate and intra-frequency handoff (IAH) rate represent the fraction of handoffs managed by the first tier and the other tiers, respectively. Our analysis shows that ignoring the overlaps among the small cells affects the accuracy of the results ignificantly. The simulation results validate the accuracy of the analytical results and also show the impact of different parameters such as the small cell density, the number of tiers and the size of the small cells on the small cell sojourn time, the macro cell sojourn time and the handoff rate

Towards joint communication and sensing (Chapter 4)

Localization of user equipment (UE) in mobile communication networks has been supported from the early stages of 3rd generation partnership project (3GPP). With 5th Generation (5G) and its target use cases, localization is increasingly gaining importance. Integrated sensing and localization in 6th Generation (6G) networks promise the introduction of more efficient networks and compelling applications to be developed