Graduation Year

2017

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Huseyin Arslan, Ph.D.

Committee Member

Richard Gitlin, Sc.D.

Committee Member

Thomas Weller, Ph.D.

Committee Member

Dimitry Goldgof, Ph.D.

Committee Member

Mohamed Abdallah, Ph.D.

Keywords

Cognitive Radio, Filtered Multitones, Game Theory, Heterogeneous Networks, Scheduling

Abstract

The usage of the wireless communication technologies have been increasing due to the benefits they provide in our daily life. These technologies are used in various fields such as military communication, public safety, cellular communication. The current systems might not be sufficient to meet the increasing demand. Therefore, the new solutions such as the usage of smart antennas have been proposed to satisfy this demand. Among different solutions, cognitive heterogeneous networks (HetNets) have been recently introduced as a promising one to meet the high user demand. In cognitive Hetnets, there are secondary base stations (SBSs) with secondary users (SUs) and primary base stations (PBSs) with primary users (PUs) in a given area without any coordination between SBS-SBS and SBS-PBS.

Due to the physical coexistence of SBSs and the lack of available spectrum, interference caused by the SBSs becomes a significant issue. Therefore, there is a need for the techniques that allow users to share the same spectrum while maintaining the required performance level for each user by adopting interference mitigation techniques. In this dissertation, we focus on resource allocation, interference coordination/mitigation and channel control techniques in 4G and beyond systems.

As resource allocation techniques, we propose two studies. In the first study, we present the random subcarrier selection algorithm which is that each SU selects a specific number of subcarriers determined by its needs. In comparison where, at each iteration of the game, the SU searches all the subcarriers to maximize its payof, our algorithm is based on selecting the subcarriers randomly and checks only those subcarriers that achieve higher payof. In the second study, we utilize the reconfigurable antennas (RAs) which allows wireless devices to alter their antenna states determined by different radiation patterns to maximize received signal strength, and present the joint subcarrier and antenna state selection algorithm. SU selects the subcarriers whose capacity values are the highest among the available ones. Since SUs employ RAs, i.e., multiple antenna states, they obtain the reports for all subcarriers from each antenna states, and select the state with the subcarriers which provide the highest capacity gain.

As interference coordination/mitigation technique, we propose a game theoretical partially overlapping filtered multitone (POFMT) scheme. Partially overlapping is performed in both frequency and space domains. While intentional carrier frequency shift is introduced in frequency, RAs are utilized to achieve partially overlapping in space domain. Within a game theoretical framework, when SUs search for the frequency shift ratio, they also select the antenna state to increase the system utility.

We also combine the resource allocation technique with POTs and present the game theoretical resource allocation with POFMT. To achieve the resource allocation, an SBS slides a group of consecutive subcarriers through all available ones and computes the utility for each selected subcarriers. It picks the consecutive ones which give the highest capacity result. Our results show that our algorithms reach Nash equilibrium and increase the system gain substantially in terms of the corresponding utility.

As channel control technique, we propose a wireless channel control using spatially adaptive antenna arrays. This technique simultaneously utilizes beam-steering and spatial adaptation to enhance the wireless channel gain and system capacity. While the interference is reduced via beam-steering feature of proposed antenna, the wireless channel can be controlled by spatially moving the antenna in one axis. Simulated realized gain patterns at various array positions and phase shifter states are subsequently utilized in link and system level simulations to demonstrate the advantages of the proposed concept. It is shown that the system gain can be increased with the spatial adaptation capability of the antenna.

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