Spectrum sharing systems for improving spectral efficiency in cognitive cellular network

Since spectrum is the invisible infrastructure that powers the wireless communication, the demand has been exceptionally increasing in recent years after the implementation of 4G and immense data requirements of 5G due to the applications, such as Internet-of-Things (IoT). Therefore, the effective optimization of the use of spectrum is immediately needed than ever before. The spectrum sensing is the prerequisite for optimal resource allocation in cognitive radio networks (CRN). Therefore, the spectrum sensing in wireless system with lower latency requirements is proposed first. In such systems with high spatial density of the base stations and users/objects, spectrum sharing enables spectrum reuse across very small regions. The proposed method in this Thesis is a multi-channel cooperative spectrum sensing technique, in which an independent network of sensors, namely, spectrum monitoring network, detects the spectrum availability. The locally aggregated decision in each zone associated with the zone aggregator (ZA) location is then passed to a decision fusion centre (DFC). The secondary base station (SBS) accordingly allocates the available channels to secondary users to maximize the spectral efficiency. The function of the DFC is formulated as an optimization problem with the objective of maximizing the spectral efficiency. The optimal detection threshold is obtained for different cases with various spatial densities of ZAs and SBSs. It is further shown that the proposed method reduces the spectrum sensing latency and results in a higher spectrum efficiency. Furthermore, a novel power allocation scheme for multicell CRN is proposed where the subchannel power allocation is performed by incorporating network-wide primary system communication activity. A collaborative subchannel monitoring scheme is proposed to evaluate the aggregated subchannel activity index (ASAI) to indicate the activity levels of primary users. Two utility functions are then defined to characterize the spectral efficiency (SE) and energy efficiency (EE) as a function of ASAI to formulate a utility maximization problem. The optimal transmit power allocation is then obtained with the objective of maximizing the total utility at the SBS, subject to maximum SBS transmit power and collision probability constraint at the primary receivers. Since optimal EE and SE are two contradicting objectives to obtain the transmit power allocation, the design approach to handle both EE and SE as a function of common network parameter, i.e., ASAI, is provided which ultimately proves the quantitative insights on efficient system design. Extensive simulation results confirm the analytical results and indicate a significant improvement in sensing latency and accuracy and a significant gain against the benchmark models on the rate performance, despite the proposed methods perform with lower signalling overhead

Spectrum sharing systems for improving spectral efficiency in cognitive cellular network

Since spectrum is the invisible infrastructure that powers the wireless communication, the demand has been exceptionally increasing in recent years after the implementation of 4G and immense data requirements of 5G due to the applications, such as Internet-of-Things (IoT). Therefore, the effective optimization of the use of spectrum is immediately needed than ever before. The spectrum sensing is the prerequisite for optimal resource allocation in cognitive radio networks (CRN). Therefore, the spectrum sensing in wireless system with lower latency requirements is proposed first. In such systems with high spatial density of the base stations and users/objects, spectrum sharing enables spectrum reuse across very small regions. The proposed method in this Thesis is a multi-channel cooperative spectrum sensing technique, in which an independent network of sensors, namely, spectrum monitoring network, detects the spectrum availability. The locally aggregated decision in each zone associated with the zone aggregator (ZA) location is then passed to a decision fusion centre (DFC). The secondary base station (SBS) accordingly allocates the available channels to secondary users to maximize the spectral efficiency. The function of the DFC is formulated as an optimization problem with the objective of maximizing the spectral efficiency. The optimal detection threshold is obtained for different cases with various spatial densities of ZAs and SBSs. It is further shown that the proposed method reduces the spectrum sensing latency and results in a higher spectrum efficiency. Furthermore, a novel power allocation scheme for multicell CRN is proposed where the subchannel power allocation is performed by incorporating network-wide primary system communication activity. A collaborative subchannel monitoring scheme is proposed to evaluate the aggregated subchannel activity index (ASAI) to indicate the activity levels of primary users. Two utility functions are then defined to characterize the spectral efficiency (SE) and energy efficiency (EE) as a function of ASAI to formulate a utility maximization problem. The optimal transmit power allocation is then obtained with the objective of maximizing the total utility at the SBS, subject to maximum SBS transmit power and collision probability constraint at the primary receivers. Since optimal EE and SE are two contradicting objectives to obtain the transmit power allocation, the design approach to handle both EE and SE as a function of common network parameter, i.e., ASAI, is provided which ultimately proves the quantitative insights on efficient system design. Extensive simulation results confirm the analytical results and indicate a significant improvement in sensing latency and accuracy and a significant gain against the benchmark models on the rate performance, despite the proposed methods perform with lower signalling overhead

Terminal cooperation in next generation wireless networks: aerial and regional access networks

Throughout the years, progress of humankind has depended on the power of communication and over the decades, the ways of communication has witnessed mammoth changes. Specifically wireless communication in the last decade has completely revolutionized the way we communicate with each other. Smartphones have become an ubiquitous part of our life. With most operators throughout the world deploying fourth generation wireless communication systems, peculiar use cases and scenarios are being envisioned such as public safety networks, aerial networks, etc. to be addressed by the next generation wireless systems. Moreover, as urban areas are becoming saturated commercial network operators are looking for business cases to move towards the untapped regional areas. However, to deploy networks in regional areas economically, novel technologies and architectures need to be developed and investigated. In this thesis, we study the novel concept of terminal cooperation in the context of next generation wireless communication systems especially looking into aerial and regional access networks. In the first part of the thesis, we investigate the physical radio channel for device-to-device (D2D) communication which would help in enabling terminal cooperation in wireless networks. Specifically, we propose propagation model for D2D in rural areas using 922 MHz and 2466 MHz, a channel model for vehicular communications using 5.8 GHz and a propagation model for D2D using millimetre wave frequencies. In the second part of the thesis, we evaluate the coverage performance of aerial access networks using different technologies and develop algorithms to enhance the coverage using terminal cooperation in regional access networks. Specifically, we evaluate the performance of two different technologies, LTE and WiFi, in aerial access networks. We propose game-theoretic algorithms to enable terminal cooperation to enhance coverage in regional access networks and perform system level simulation to evaluate the proposed algorithms. In the last part of this thesis, we analyse and develop techniques to enhance energy efficiency in aerial access networks using terminal cooperation. Specifically, we propose a clustering algorithm called EECAN which improves the energy efficiency of the terrestrial nodes accessing the aerial base-station, a clustering algorithm based on Matern Hardcore Point Process which allows us to optimize cluster head spacing analytically and we further enhance this algorithm by including impairments introduced by the wireless channel. Throughout this thesis, we verify and validate our analytic results, algorithms and techniques with Monte-Carlo simulations of the considered scenarios. Most of the work presented in this thesis was published in-part or as a whole in conferences, journals, book-chapters, project reports or otherwise undergoing a review process. These publications and reports are highlighted in the course of the thesis. Lastly, we invite the reader to enjoy exploring this thesis and we hope that it will add more understanding to this promising new technology of terminal cooperation in aerial and regional access networks

Fairness and resource allocation in device-to-device wireless regional area network

With the rapid development in wireless devices, applications and networks, radio frequencies have become scarce resources. Therefore, it is critical to make efficient use of the radio frequencies. A promising way to solve this problem is the use of cognitive radio (CR). In CR, radio frequencies are allocated to licensed users, also called primary users (PUs) and these frequencies can be reused by unlicensed users, also called secondary users (SUs) without affecting the PUs. This way, the spectrum utilization can be increased significantly. Cognitive radio networks (CRNs) are the networks using CR technology, based on which the IEEE 802.22 working group has developed three standards and there are several other on-going projects. IEEE 802.22 aims at wireless regional area networks (WRANs) and broadband services in rural areas. TV channels are employed due to their underutilization in rural areas and good performance for long distance communication. A cellular architecture is adopted with large cells (up to a radius of 100\,km). Each cell has a base station (BS) and multiple customer premises equipment (CPE). IEEE 802.22 is a significant milestone in CRN standardization. However, WRANs have severely limited capacity due to their single operating channel, point-to-multipoint topology and the requirement for regular quiet periods (QPs) to do spectrum sensing. Moreover, the spectrum sharing amongst CPEs is not addressed by IEEE 802.22, and this influences the channel utilization directly. This thesis explores ways to enhance the network capacity by spectrum allocation. Another critical issue is also identified and addressed regarding resource allocation problems, which is the fairness issue. Many resources can be found in wireless networks, e.g., bandwidth, frequencies and energy, and their use influences the performance of the network significantly. For example, unfair spectrum allocation may lead to starvation in access opportunities of some CPEs and inefficient spectrum usage. Fairness has a different connotation depending on the context; consequently, it is difficult to answer questions such as what is fairness, how to measure it and how to achieve it. Hence, before addressing the WRAN capacity constraints, the fairness issues applicable to wireless networks in general are addressed in this thesis. This has resulted in two main research topics in this thesis. The first part deals with fairness in wireless networks. Within this part, definitions and different perspectives of fairness are discussed. To achieve fairness, an Observe-Plan-Do-Check-Act (OPDCA) based fairness process is proposed. Then, the existing fairness indices in resource allocations are examined. From this analysis we conclude that these indices are not sufficient and advanced indices are needed in the domain of wireless networks. Hence, based on the OPDCA framework, a general model of fairness indices is proposed and analyzed. The network capacity limitation of WRANs is addressed in the second part of this thesis. Device-to-device (D2D) communication is a promising method to increase the capacity of the cellular architecture, leading to the concept of device-to-device WRAN (D2DWRAN). There are three main ideas in D2DWRANs: D2D communication, channel reuse and the use of multiple operating channels. D2D communication enables intra-cell CPE-to-CPE communication and makes channel reuse possible. For links that are far from each other, the same channel can be used simultaneously, if there is transmission power control. With channel reuse, the utilization of radio frequencies can be increased significantly. One step further, to maximize the use of available channels, multiple operating channels are envisaged in D2DWRANs both in the downstream (BS to CPE) and upstream (CPE to BS) directions. These three ideas require new protocols and strategies. Hence, based on the existing standards of IEEE 802.22, relevant issues and proposed solutions in this thesis are: the D2DWRAN OFDMA system, the channel management of multiple channels, the spectrum sharing problem, the self-coexistence amongst cells and the QP scheduling. These proposals provide the basis for designing D2DWRANs that have a significantly higher capacity compared to the existing IEEE 802.22 network proposals, which is also confirmed by simulation results.Software and Computer TechnologyElectrical Engineering, Mathematics and Computer Scienc