Use this URL to cite or link to this record in EThOS:
Title: Integrating device-to-device communications in 5G cellular networks
Author: Vlachos, Christoforos
ISNI:       0000 0004 7427 9884
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2018
Availability of Full Text:
Access from EThOS:
Access from Institution:
The evolution of wireless networks towards 5G dictates the integration of a mul-titude of heterogeneous radio access technologies to the traditional macro-cell systems. Equipping the network with numerous small cell nodes, such as fem-tocell and picocell base stations (BSs), implies a spectrum efficient and network performance improving solution to support the rapidly increasing user demands. However, this can be proven to be a cost-inefficient method that increases the capital and operational expenditures of the network operators as well as the power consumption, especially in low-traffic network conditions where a number of BSs should be switched-off. To this end, device-centric solutions that leverage the potentials stemming from the proximity, mobility and increased dynamics of user devices should be considered. To this end, direct, proximity-based Device-to-Device (D2D) communication, where two close-ranged user equipments (UEs) are able to exchange data by bypassing the BS, is expected to play predominant role in improving the overall network welfare and ease part of the traffic developed on the BSs side. This thesis focuses on the soft integration of inband D2D communications in emerging cellular networks where D2D-enabled devices utilize the licensed spec-trum. In the introductory part of the thesis we highlight the merits that this communication paradigm can offer in terms of spectrum utilization, energy sav-ing, delay reduction and data rate improvement. We also provide an overview of the D2D use cases that enable opportunities for new services, its potential in improving the overall network performance as well as its offloading capability that can ease the traffic employed along the network. In the sequel, we proceed with our proposed methodology that aims at easing the coexistence of cellular and D2D users in emerging cellular networks. One of the main contributions of the thesis is the optimization of cell association for D2D UEs (DUEs). Cell association for D2D communications is an unexplored area and a rather fertile ground for research. Following the conventional motif, a user device would preferably couple with a high power macro cell BS that provides the user with the highest signal power. However, with the advent of D2D com-munications, this could be proven to be highly inefficient for users that want to communicate directly and are associated with different BSs because BS intercom-munication complexity and access delay is introduced. To this end, we propose a number of optimization formulations for D2D-based cell association that takes into consideration not only the nature of the inband D2D communications (un-derlay or overlay), but also performance-hindering factors such as user density, interference and so on. Other than the throughput enhancing and power saving attributes of the proposed framework, notable resource efficiency improvement is achieved. Indicatively, for both underlay and overlay D2D communications, more than 12% and 45% radio resource utilization mitigation is ensured compared to baseline methods. On top of optimizing cell association for D2D communications, we further investigate the problem of resource allocation in different D2D underlaying cellu-lar network scenarios where DUEs are permitted to reuse the cellular resources and, therefore, high levels of interference need to be prevented. By consider-ing different deployment scenarios, we propose a set of low-complexity heuristic algorithms with the aim to achieve high data rate performance for D2D com-munications with respect to meeting the cellular users’ quality of service (QoS) requirements. The proposed algorithms are evaluated in high-traffic networking scenarios where D2D communications underlay relay-enabled cellular networks. In aggregate, more than 10% of sum throughput performance is achieved against various resource allocation techniques. In the sequel, we explore the dynamics of virtualizing the radio resources for efficient sharing as, nowadays, we are witnessing higher network heterogeneity and the emergence of multiple stakeholders with the overarching need to significantly reduce deployment costs and achieve a sustainable network operation. Network virtualization has emerged as a promising technique to overcome the complexity of current network operation as well as facilitate inter-operators’ sharing. There-fore, disruptive approaches to manage radio and network-virtualized resources are expected to be a catalyst element of future mobile network architectures. Despite the fact that a number of solutions for radio access network (RAN) virtualization emerged over the last few years, it is worth pointing out that little attention has been placed on issues related to D2D virtualization. Therefore, based on the integration of an inter-tenant controller that enables the radio resource sharing between multiple operators, we devise a set of efficient algorithms to optimize the throughput performance of D2D communications in virtualized environments as well as reduce the utilization levels of the allocated radio resources. More than 12% of sum-rate performance improvement compared to legacy, intra-tenant ap-proaches where the radio resources are assigned based on which device initiates the communication per case. Finally, a summary of the research outcomes along with some future directions for D2D communications concludes this thesis.
Supervisor: Friderikos, Vasilis ; Aghvami, Abdol-Hamid Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available