Cognitive radio systems in LTE networks

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.The most important fact in the mobile industry at the moment is that demand for wireless services will continue to expand in the coming years. Therefore, it is vital to find more spectrums through cognitive radios for the growing numbers of services and users. However, the spectrum reallocations, enhanced receivers, shared use, or secondary markets-will not likely, by themselves or in combination, meet the real exponential increases in demand for wireless resources. Network operators will also need to re-examine network architecture, and consider integrating the fibre and wireless networks to address this issue. This thesis involves driving fibre deeper into cognitive networks, deploying microcells connected through fibre infrastructure to the backbone LTE networks, and developing the algorithms for diverting calls between the wireless and fibre systems, introducing new coexistence models, and mobility management. This research addresses the network deployment scenarios to a microcell-aided cognitive network, specifically slicing the spectrum spatially and providing reliable coverage at either tier. The goal of this research is to propose new method of decentralized-to-distributed management techniques that overcomes the spectrum unavailability barrier overhead in ongoing and future deployments of multi-tiered cognitive network architectures. Such adjustments will propose new opportunities in cognitive radio-to-fibre systematic investment strategies. Specific contributions include: 1) Identifying the radio access technologies and radio over fibre solution for cognitive network infrastructure to increase the uplink capacity analysis in two-tier networks. 2) Coexistence of macro and microcells are studied to propose a roadmap for optimising the deployment of cognitive microcells inside LTE macrocells in the case of considering radio over fibre access systems. 3) New method for roaming mobiles moving between microcells and macrocell coverage areas is proposed for managing spectrum handover, operator database, authentication and accounting by introducing the channel assigning agent entity. The ultimate goal is to reduce unnecessary channel adaptation

Throughput Maximization Using an SVM for Multi-Class Hypothesis-Based Spectrum Sensing in Cognitive Radio

A framework of spectrum sensing with a multi-class hypothesis is proposed to maximize the achievable throughput in cognitive radio networks. The energy range of a sensing signal under the hypothesis that the primary user is absent (in a conventional two-class hypothesis) is further divided into quantized regions, whereas the hypothesis that the primary user is present is conserved. The non-radio frequency energy harvesting-equiped secondary user transmits, when the primary user is absent, with transmission power based on the hypothesis result (the energy level of the sensed signal) and the residual energy in the battery: the lower the energy of the received signal, the higher the transmission power, and vice versa. Conversely, the lower is the residual energy in the node, the lower is the transmission power. This technique increases the throughput of a secondary link by providing a higher number of transmission events, compared to the conventional two-class hypothesis. Furthermore, transmission with low power for higher energy levels in the sensed signal reduces the probability of interference with primary users if, for instance, detection was missed. The familiar machine learning algorithm known as a support vector machine (SVM) is used in a one-versus-rest approach to classify the input signal into predefined classes. The input signal to the SVM is composed of three statistical features extracted from the sensed signal and a number ranging from 0 to 100 representing the percentage of residual energy in the node’s battery. To increase the generalization of the classifier, k-fold cross-validation is utilized in the training phase. The experimental results show that an SVM with the given features performs satisfactorily for all kernels, but an SVM with a polynomial kernel outperforms linear and radial-basis function kernels in terms of accuracy. Furthermore, the proposed multi-class hypothesis achieves higher throughput compared to the conventional two-class hypothesis for spectrum sensing in cognitive radio networks

Backscatter Communication: Design and Optimisation For Emerging Use-Cases

Backscatter communication (BackCom) holds significant potential to improve the pervasiveness and energy efficiency of future wireless networks, through its passive modulation and reuse of existing radiofrequency signals. In order to function as a key technology under the Internet of Things paradigm, issues relating to BackCom, such as its limited coverage and deployment flexibility, low data rates, and the difficulty of channel estimation, need to be addressed. To complement this, a wider range of use-cases and deployment scenarios also need to be established. This thesis focuses on addressing these issues inherent to BackCom, by exploring a series of system setups which push the boundaries in terms of coverage and flexible deployment, and then future-proofs BackCom through the study of the assistance from another emerging technology, the intelligent reflecting surface (IRS). The first half of the thesis focuses on the coverage and deployment flexibility of BackCom devices under conventional wireless communication settings. First, we study a novel use-case in which BackCom devices replace conventional, actively transmitting relays to assist an information transmission from a source to a destination. We introduce the decode-and-forward (DF) BackCom relaying scheme and perform a detailed bit error rate (BER) characterisation of the DF BackCom scheme alongside the amplify-and-forward (AF) BackCom 'reflection' scheme. The feasibility and practical range of the BackCom relay is demonstrated through a case study, and our findings indicate that with careful selection of relay parameters, the DF scheme can improve the functionality of BackCom relays through the decoding operation, while resulting in minimal BER differences compared to the AF 'reflection' scheme. Second, we study the coverage maximisation of bistatic BackCom systems in wide-area environmental monitoring applications through judicious power beacon (PB) placement. We propose a straightforward metric to characterise coverage, the guaranteed coverage distance (GCD), to overcome the complex shape of each PB's coverage area when the performance of the BackCom link is dependent on the strength of the energy transfer link. We find that a single-tier symmetric deployment of PBs performs favourably under a practical number (24 or less) of PBs, with a GCD of more than 100m being readily achievable. The second half of the thesis studies the incorporation of the IRS into BackCom systems, with the aim of improving BackCom performance. The IRS-assisted bistatic BackCom system is studied first, where we solve a transmit power minimisation problem at the carrier emitter involving the joint optimisation of the transmit and receive beamforming, the IRS phase shifts and the BackCom splitting coefficients. We present a unique signal model arising from this system, where a signal originating from the carrier emitter may be reflected by the IRS twice before reaching the reader, and account for this added complexity in our algorithm design. Our results indicate that transmit power savings of over 6 dB may be achieved with a moderately-sized IRS, which may be converted to nearly 50m of range increase. Then, we study the use of the IRS in an ambient BackCom system, with the goal of reducing direct-link interference and improving detection performance. We assume the absence of all ambient signal and channel knowledge, which is a practical assumption given the passively reflecting nature of both BackCom devices and IRSs. We propose a deep reinforcement learning (DRL)-based algorithm which maximises the backscatter channel difference (that is, the ratio of the energies of the direct-link interference and overall received signal) based on instantaneous signal samples, which may be converted to BER reductions. We find that the DRL approach with no channel knowledge can achieve a backscatter channel difference within 25% of that obtained using benchmarks with full channel knowledge

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

D11.2 Consolidated results on the performance limits of wireless communications

Deliverable D11.2 del projecte europeu NEWCOM#The report presents the Intermediate Results of N# JRAs on Performance Limits of Wireless Communications and highlights the fundamental issues that have been investigated by the WP1.1. The report illustrates the Joint Research Activities (JRAs) already identified during the first year of the project which are currently ongoing. For each activity there is a description, an illustration of the adherence and relevance with the identified fundamental open issues, a short presentation of the preliminary results, and a roadmap for the joint research work in the next year. Appendices for each JRA give technical details on the scientific activity in each JRA.Peer ReviewedPreprin

Optimising multiple antenna techniques for physical layer security

Wireless communications offer data transmission services anywhere and anytime, but with the inevitable cost of introducing major security vulnerabilities. Indeed, an eavesdropper can overhear a message conveyed over the open insecure wireless media putting at risk the confidentiality of the wireless users. Currently, the way to partially prevent eavesdropping attacks is by ciphering the information between the authorised parties through complex cryptographic algorithms. Cryptography operates in the upper layers of the communication model, bit it does not address the security problem where the attack is suffered: at the transmission level. In this context, physical layer security has emerged as a promising framework to prevent eavesdropping attacks at the transmission level. Physical layer security is based on information-theoretic concepts and exploits the randomness and the uniqueness of the wireless channel. In this context, this thesis presents signal processing techniques to secure wireless networks at the physical layer by optimising the use of multiple-antennas. A masked transmission strategy is used to steer the confidential information towards the intended receiver, and, at the same time, broadcast an interfering signal to confuse unknown eavesdroppers. This thesis considers practical issues in multiple-antenna networks such as limited transmission resources and the lack of accurate information between the authorised transmission parties. The worst-case for the security, that occurs when a powerful eavesdropper takes advantage of any opportunity to put at risk the transmission confidentiality, is addressed. The techniques introduced improve the security by offering efficient and innovative transmission solutions to lock the communication at the physical layer. Notably, these transmission mechanisms strike a balance between confidentiality and quality to satisfy the practical requirements of modern wireless networks

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin