Examination Committee

Prof Chun LIANG, LIFS/HKUST (Chairperson)
Prof Khaled BEN LETAIEF, ECE/HKUST (Thesis Supervisor)
Prof Jianwei HUANG, Department of Information Engineering, The Chinese University of Hong Kong (External Examiner)
Prof Danny H K TSANG, ECE/HKUST
Prof Wai Ho MOW, ECE/HKUST
Prof Brahim BENSAOU, CSE/HKUST
 

Abstract

Given the 1000x capacity increase requirement for 5G networks, cell densification has been proposed as an important enabling technique. By deploying various types of small cells coexisting with conventional base stations (BSs), the network is evolving into a heterogeneous network (HetNet). Consequently, it brings formidable design challenges especially due to the irregular BS locations. Meanwhile, multiple-input multiple-output (MIMO) techniques have proven to be a powerful tool to boost the network performance, and it will continue to play a pivotal role in 5G networks. The combination of MIMO techniques and HetNets, while promising, brings additional difficulties in system analysis and design. This thesis explores two fundamental questions in MIMO HetNets: one is how the network densification will affect various performance metrics; the other is how MIMO techniques should be utilized to improve network performance.
 
The analytical framework is based on the random spatial model and a novel Toeplitz matrix representation, which provides highly tractable expressions. The results show that in single-tier networks, cell densification can improve success probability and area spectral efficiency (ASE), but it can increase energy efficiency only in certain conditions. In multi-tier MIMO HetNets, it is shown that cell densification may decrease the success probability. Meanwhile, the maximum success probability is achieved by activating only one tier of BSs, while the maximum ASE is achieved by activating all the BSs. Although the success probability can be improved by increasing the number of BS antennas, thanks to beamforming, it is fundamentally limited by intercell interference. Thus we propose an effective interference coordination scheme to improve the success probability, which outperforms existing methods. Furthermore, a joint jamming and interference nulling scheme is proposed to enhance the network secrecy. Numerical results show that the proposed scheme achieves significant performance gains, which reveals the importance of interference management in jamming assisted networks.