Performance enhancement solutions in wireless communication networks

In this dissertation thesis, we study the new relaying protocols for different wireless network systems. We analyze and evaluate an efficiency of the transmission in terms of the outage probability over Rayleigh fading channels by mathematical analyses. The theoretical analyses are verified by performing Monte Carlo simulations. First, we study the cooperative relaying in the Two-Way Decode-and-Forward (DF) and multi-relay DF scheme for a secondary system to obtain spectrum access along with a primary system. In particular, we proposed the Two-Way DF scheme with Energy Harvesting, and the Two-Way DF Non-orthogonal Multiple Access (NOMA) scheme with digital network coding. Besides, we also investigate the wireless systems with multi-relay; the best relay selection is presented to optimize the effect of the proposed scheme. The transmission protocols of the proposed schemes EHAF (Energy Harvesting Amplify and Forward) and EHDF (Energy Harvesting Decode and Forward) are compared together in the same environment and in term of outage probability. Hence, with the obtained results, we conclude that the proposed schemes improve the performance of the wireless cooperative relaying systems, particularly their throughput. Second, we focus on investigating the NOMA technology and proposing the optimal solutions (protocols) to advance the data rate and to ensure the Quality of Service (QoS) for the users in the next generation of wireless communications. In this thesis, we propose a Two-Way DF NOMA scheme (called a TWNOMA protocol) in which an intermediate relay helps two source nodes to communicate with each other. Simulation and analysis results show that the proposed protocol TWNOMA is improving the data rate when comparing with a conventional Two-Way scheme using digital network coding (DNC) (called a TWDNC protocol), Two-Way scheme without using DNC (called a TWNDNC protocol) and Two-Way scheme in amplify-and-forward(AF) relay systems (called a TWANC protocol). Finally, we considered the combination of the NOMA and physical layer security (PLS) in the Underlay Cooperative Cognitive Network (UCCN). The best relay selection strategy is investigated, which uses the NOMA and considers the PLS to enhance the transmission efficiency and secrecy of the new generation wireless networks.V této dizertační práci je provedena studie nových přenosových protokolů pro různé bezdrátové síťové systémy. S využitím matematické analýzy jsme analyzovali a vyhodnotili efektivitu přenosu z hlediska pravděpodobnosti výpadku přes Rayleighův kanál. Teoretické analýzy jsou ověřeny provedenými simulacemi metodou Monte Carlo. Nejprve došlo ke studii kooperativního přenosu ve dvoucestném dekóduj-a-předej (Two-Way Decode-and-Forward–TWDF) a vícecestném DF schématu s větším počtem přenosových uzlů pro sekundární systém, kdy takto byl získán přístup ke spektru spolu s primárním systémem. Konkrétně jsme navrhli dvoucestné DF schéma se získáváním energie a dvoucestné DF neortogonální schéma s mnohonásobným přístupem (Non-orthogonal Multiple Access–NOMA) s digitálním síťovým kódováním. Kromě toho rovněž zkoumáme bezdrátové systémy s větším počtem přenosových uzlů, kde je přítomen výběr nejlepšího přenosového uzlu pro optimalizaci efektivnosti navrženého schématu. Přenosové protokoly navržených schémat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou společně porovnány v identickém prostředí z pohledu pravděpodobnosti výpadku. Následně, na základě získaných výsledků, jsme dospěli k závěru, že navržená schémata vylepšují výkonnost bezdrátových kooperativních systémů, konkrétně jejich propustnost. Dále jsme se zaměřili na zkoumání NOMA technologie a navrhli optimální řešení (protokoly) pro urychlení datového přenosu a zajištění QoS v další generaci bezdrátových komunikací. V této práci jsme navrhli dvoucestné DF NOMA schéma (nazýváno jako TWNOMA protokol), ve kterém mezilehlý přenosový uzel napomáhá dvěma zdrojovým uzlům komunikovat mezi sebou. Výsledky simulace a analýzy ukazují, že navržený protokol TWNOMA vylepšuje dosaženou přenosovou rychlost v porovnání s konvenčním dvoucestným schématem používajícím DNC (TWDNC protokol), dvoucestným schématem bez použití DNC (TWNDNC protokol) a dvoucestným schématem v zesil-a-předej (amplify-and-forward) přenosových systémech (TWANC protokol). Nakonec jsme zvážili využití kombinace NOMA a zabezpečení fyzické vrstvy (Physical Layer Security–PLS) v podpůrné kooperativní kognitivní síti (Underlay Cooperative Cognitive Network–UCCN). Zde je zde zkoumán výběr nejlepšího přenosového uzlu, který užívá NOMA a bere v úvahu PLS pro efektivnější přenos a zabezpečení nové generace bezdrátových sítí.440 - Katedra telekomunikační technikyvyhově

Outage performance of underlay cognitive radio networks over mix fading environment

In this paper, the underlay cognitive radio network over mix fading environment is presented and investigated. A cooperative cognitive system with a secondary source node S, a secondary destination node D, secondary relay node Relay, and a primary node P are considered. In this model system, we consider the mix fading environment in two scenarios as Rayleigh/Nakagami-m and Nakagami-m/Rayleigh Fading channels. For system performance analysis, the closed-form expression of the system outage probability (OP) and the integral-formed expression of the ergodic capacity (EC) are derived in connection with the system's primary parameters. Finally, we proposed the Monte Carlo simulation for convincing the correctness of the system performance

Secrecy performance enhancement for underlay cognitive radio networks employing cooperative multi-hop transmission with and without presence of hardware impairments

In this paper, we consider a cooperative multi-hop secured transmission protocol to underlay cognitive radio networks. In the proposed protocol, a secondary source attempts to transmit its data to a secondary destination with the assistance of multiple secondary relays. In addition, there exists a secondary eavesdropper who tries to overhear the source data. Under a maximum interference level required by a primary user, the secondary source and relay nodes must adjust their transmit power. We first formulate effective signal-to-interference-plus-noise ratio (SINR) as well as secrecy capacity under the constraints of the maximum transmit power, the interference threshold and the hardware impairment level. Furthermore, when the hardware impairment level is relaxed, we derive exact and asymptotic expressions of end-to-end secrecy outage probability over Rayleigh fading channels by using the recursive method. The derived expressions were verified by simulations, in which the proposed scheme outperformed the conventional multi-hop direct transmission protocol.Web of Science212art. no. 21

Joint Spatial and Spectrum Cooperation in Wireless Network.

PhDThe sky-rocketing growth of multimedia infotainment applications and broadband-hungry mobile devices exacerbate the stringent demand for ultra high data rate and more spectrum resources. Along with it, the unbalanced temporal and geographical variations of spectrum usage further inspires those spectral-efficient networks, namely, cognitive radio and heterogeneous cellular networks (HCNs). This thesis focuses on the system design and performance enhancement of cognitive radio (CR) and HCNs. Three different aspects of performance improvement are considered, including link reliability of cognitive radio networks (CNs), security enhancement of CNs, and energy efficiency improvement of CNs and HCNs. First, generalized selection combining (GSC) is proposed as an effective receiver design for interference reduction and reliability improvement of CNs with outdated CSI. A uni- ed way for deriving the distribution of received signal-to-noise ratio (SNR) is developed in underlay spectrum sharing networks subject to interference from the primary trans- mitter (PU-Tx) to the secondary receiver (SU-Rx), maximum transmit power constraint at the secondary transmitter (SU-Tx), and peak interference power constraint at the PU receiver (PU-Rx), is developed. Second, transmit antenna selection with receive generalized selection combining (TAS/GSC) in multi-antenna relay-aided communica- tion is introduced in CNs under Rayleigh fading and Nakagami-m fading. Based on newly derived complex statistical properties of channel power gain of TAS/GSC, exact ergodic capacity and high SNR ergodic capacity are derived over Nakagami-m fading. Third, beamforming and arti cial noise generation (BF&AN) is introduced as a robust scheme to enhance the secure transmission of large-scale spectrum sharing networks with multiple randomly located eavesdroppers (Eves) modeled as homogeneous Poisson Point Process (PPP). Stochastic geometry is applied to model and analyze the impact of i BF&AN on this complex network. Optimal power allocation factor for BF&AN which maximizes the average secrecy rate is further studied under the outage probability con- straint of primary network. Fourth, a new wireless energy harvesting protocol is proposed for underlay cognitive relay networks with the energy-constrained SU-Txs. Exact and asymptotic outage probability, delay-sensitive throughput, and delay-tolerant through- put are derived to explore the tradeoff between the energy harvested from the PU-Txs and the interference caused by the PU-Txs. Fifth, a harvest-then-transmit protocol is proposed in K-tier HCNs with randomly located multiple-antenna base stations (BSs) and single antenna mobile terminals (MTs) modeled as homogeneous PPP. The average received power at MT, the uplink (UL) outage probability, and the UL average ergodic rate are derived to demonstrate the intrinsic relationship between the energy harvested from BSs in the downlink (DL) and the MT performance in the UL. Throughout the thesis, it is shown that link reliability, secrecy performance, and energy efficiency of CNs and HCNs can be signi cantly leveraged by taking advantage of multiple antennas, relays, and wireless energy harvesting

Hybrid satellite–terrestrial networks toward 6G : key technologies and open issues

Future wireless networks will be required to provide more wireless services at higher data rates and with global coverage. However, existing homogeneous wireless networks, such as cellular and satellite networks, may not be able to meet such requirements individually, especially in remote terrain, including seas and mountains. One possible solution is to use diversified wireless networks that can exploit the inter-connectivity between satellites, aerial base stations (BSs), and terrestrial BSs over inter-connected space, ground, and aerial networks. Hence, enabling wireless communication in one integrated network has attracted both the industry and the research fraternities. In this work, we provide a comprehensive survey of the most recent work on hybrid satellite–terrestrial networks (HSTNs), focusing on system architecture, performance analysis, design optimization, and secure communication schemes for different cooperative and cognitive HSTN network architectures. Different key technologies are compared. Based on this comparison, several open issues for future research are discussed

Physical-Layer Security in Cognitive Radio Networks

The fifth-generation (5G) communications and beyond are expected to serve a huge number of devices and services. However, due to the fixed spectrum allocation policies, the need for cognitive radio networks (CRNs) has increased accordingly. CRNs have been proposed as a promising approach to address the problem of under-utilization and scarcity of the spectrum. In CRNs, secondary users (SUs) access the licensed spectrum of the primary users (PUs) using underlay, overlay, or interweave paradigms. SUs can access the spectrum band simultaneously with the PUs in underlay access mode provided that the SUs’ transmission power does not cause interference to the PUs’ communication. In this case, SUs should keep monitoring the interference level that the PU receiver can tolerate and adjust the transmission power accordingly. However, varying the transmission power may lead to some threats to the privacy of the information transfer of CRNs. Therefore, securing data transmission in an underlay CRN is a challenge that should be addressed. Physical-layer security (PLS) has recently emerged as a reliable method to protect the confidentiality of the SUs’ transmission against attacks, especially for the underlay model with no need for sharing security keys. Indeed, PLS has the advantage of safeguarding the data transmission without the necessity of adding enormous additional resources, specifically when there are massively connected devices. Apart from the energy consumed by the various functions carried out by SUs, enhancing security consumes additional energy. Therefore, energy harvesting (EH) is adopted in our work to achieve both; energy efficiency and spectral efficiency. EH is a significant breakthrough for green communication, allowing the network nodes to reap energy from multiple sources to lengthen battery life. The energy from various sources, such as solar, wind, vibration, and radio frequency (RF) signals, can be obtained through the process of EH. This accumulated energy can be stored to be used for various processes, such as improving the users’ privacy and prolonging the energy-constrained devices’ battery life. In this thesis, for the purpose of realistic modelling of signal transmission, we explicitly assume scenarios involving moving vehicles or nodes in networks that are densely surrounded by obstacles. Hence, we begin our investigations by studying the link performance under the impact of cascaded κ−μ fading channels. Moreover, using the approach of PLS, we address the privacy of several three-node wiretap system models, in which there are two legitimate devices communicating under the threat of eavesdroppers. We begin by a three-node wiretap system model operating over cascaded κ − μ fading channels and under worst-case assumptions. Moreover, assuming cascaded κ − μ distributions for all the links, we investigate the impact of these cascade levels, as well as the impact of multiple antennas employed at the eavesdropper on security. Additionally, the PLS is examined for two distinct eavesdropping scenarios: colluding and non-colluding eavesdroppers. Throughout the thesis, PLS is mainly evaluated through the secrecy outage probability (SOP), the probability of non-zero secrecy capacity (Pnzcr ), and the intercept probability (Pint). Considering an underlay CRN operating over cascaded Rayleigh fading channel, with the presence of an eavesdropper, we explore the PLS for SUs in the network. This study is then extended to investigate the PLS of SUs in an underlay single-input-multiple-output (SIMO) CRN over cascaded κ-μ general fading channels with the presence of a multi-antenna eavesdropper. The impact of the constraint over the transmission power of the SU transmitter due to the underlay access mode is investigated. In addition, the effects of multiple antennas and cascade levels over security are well-explored. In the second part of our thesis, we propose an underlay CRN, in which an SU transmitter communicates with an SU destination over cascaded κ-μ channels. The confidentiality of the shared information between SUs is threatened by an eavesdropper. Our major objective is to achieve a secured network, while at the same time improving the energy and spectrum efficiencies with practical modeling for signals’ propagation. Hence, we presume that the SU destination harvests energy from the SU transmitter. The harvested energy is used to produce jamming signals to be transmitted to mislead the eavesdropper. In this scenario, a comparison is made between an energy-harvesting eavesdropper and a non-energy harvesting one. Additionally, we present another scenario in which cooperative jamming is utilized as one of the means to boost security. In this system model, the users are assumed to communicate over cascaded Rayleigh channels. Moreover, two scenarios for the tapping capabilities of the eavesdroppers are presented; colluding and non-colluding eavesdroppers. This study is then extended for the case of non-colluding eavesdroppers, operating over cascaded κ-μ channels. Finally, we investigate the reliability of the SUs and PUs while accessing the licensed bands using the overlay mode, while enhancing the energy efficiency via EH techniques. Hence, we assume that multiple SUs are randomly distributed, in which one of the SUs is selected to harvest energy from the PUs’ messages. Then, utilizing the gathered energy, this SU combines its own messages with the amplified PUs messages and forwards them to the destinations. Furthermore, we develop two optimization problems with the potential of maximizing the secondary users’ rate and the sum rate of both networks