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

Efisiensi Daya Protokol Quantize and Forward Pada Sistem Komunikasi Kooperatif Multi-relay

One of effective diversity techniques to combat fading on wireless channel is a cooperative communication system in which a source sends information through several relays and then forward it to a destination. A cooperative communication system has shown increased the system performance and reduced the energy consumption. However, it depends on the used relay mechanism that is relay protocols such as quantize and forward (QF) and amplify and forward (AF). In the previous research, energy efficiency of AF relay has investigated for a single-relay cooperative system, but multi-relay is more practical. Therefore, this research focuses on power efficiency in multi-relay cooperative communication system using QF protocol. The research method used is mathematical analysis and computer simulation for outage probability and power efficiency in the multi-relay QF. Simulation result found that multi-relay QF system could provide a high power efficiency, but the efficiency is reduced when the distance ratio increases. Power efficiency can be increased by adding the number of relays in the system. A comparison of power efficiency for QF and AF protocols has simulated, in which power efficiency of multi-relay QF is higher than that of multi-relay AF at distance ratio and power transmit. Thus, multi-relay QF system can provide high performance and power efficiency in the cooperative communication system

Energy-Harvesting in Cooperative AF Relaying Networks Over Log-Normal Fading Channels

Energy-harvesting (EH) and wireless power transfer are increasingly becoming a promising source of power in future wireless networks and have recently attracted a considerable amount of research, particularly on cooperative two-hop relay networks in Rayleigh fading channels. In contrast, this paper investigates the performance of wireless power transfer based two-hop cooperative relaying systems in indoor channels characterized by log-normal fading. Specifically, two EH protocols are considered here, namely, time switching relaying (TSR) and power splitting relaying (PSR). Our findings include accurate analytical expressions for the ergodic capacity and ergodic outage probability for the two aforementioned protocols. Monte Carlo simulations are used throughout to confirm the accuracy of our analysis. The results show that increasing the channel variance will always provide better ergodic capacity performance. It is also shown that a good selection of the EH time in the TSR protocol, and the power splitting factor in the PTS protocol, is the key to achieve the best system performance

On the Performance Analysis of WPT-based Dual-Hop AF Relaying Networks in α-μ Fading

In this paper, a two-hop amplify-and-forward relaying system, where an energy-constrained relay node entirely depends on the energy scavenged from the source signal, is investigated. This paper analyzes the performance of the energy-harvesting (EH) protocols, namely, ideal relaying receiver (IRR), power-splitting relaying (PSR) and time-switching relaying (TSR), over independent but not identically distributed (i.n.i.d.) α-μ fading channels in terms of the ergodic capacity and ergodic outage probability (OP). We derive exact unified and closed-form analytical expressions for the performance metrics with the aforementioned protocols over i.n.i.d. α-μ channels. Three fading scenarios, such as Weibull, Nakagami-m and Rayleigh channels, are investigated. Provided simulation and numerical results validate our analysis. It is demonstrated that the optimal EH time-switching and power-splitting factors of the corresponding TSR and PSR protocols are critical in achieving the best system performance. Finally, we analyzed the impact of the fading parameters α and μ on the achievable ergodic OP

Physical layer secrecy by power splitting and jamming in cooperative multiple relay based on energy harvesting in full-duplex network

In this article, we investigated the secrecy performance of a three-hop relay network system with Power Splitting (PS) and Energy Harvesting (EH). In the presence of one eavesdropper, a signal is transferred from source to destination with the help of a relay. The source signal transmits in full-duplex (FD) mood, jamming the relay transfer signals to the destination. The relay and source employ Time Switching (TS) and Energy Harvesting (EH) techniques to obtain the power from the power beacon. In this study, we compared the Secrecy Rate of two Cooperative Schemes, Amplify and Forward (AF) and Decode and Forward (DF), for both designed systems with the established EH and PS system. The Secrecy Rate was improved by 50.5% in the AF scheme and by 44.2% in the DF scheme between the relay and eavesdropper at 40 m apart for the proposed system in EH and PS. This simulation was performed using the Monto Carlo method in MATLAB

Performance Analysis in Full-Duplex Relaying Systems withWireless Power Transfer

Energy harvesting (EH) technology has become increasingly attractive as an appealing solution to provide long-lasting power for energy-constrained wireless cooperative sensor networks. EH in such networks is particularly important as it can enable information relaying. Different from absorbing energy from intermittent and unpredictable nature, such as solar, wind, and vibration, harvesting from radio frequency (RF) radiated by ambient transmitters has received tremendous attention. The RF signal can convey both information and energy at the same time, which facilitates the development of simultaneous wireless information and power transfer. Besides, ambient RF is widely available from the base station, WIFI, and mobile phone in the current information era. However, some open issues associated with EH are existing in the state-of-art. One of the key challenges is rapid energy loss during the transferring process, especially for long-distance transmission. The other challenge is the design of protocols to optimally coordinate between information and power transmission. Meanwhile, in-band full-duplex (IBFD) communication have gained considerable attraction by researchers, which has the ability to improve system spectral efficiency. IBFD can receive information and forward information at the same time on the same frequency. Since the RF signal can be superimposed, the antenna of the IBFD system receives the RF signal from both desired transmitter and local transmitter. Due to the short distance of the local transmission signals, the received signal power is much larger than the desired transmission signals, which results in faulty receiving of the desired signals. Therefore, it is of great significance to study the local self-interference cancellation method of the IBFD system. In the recent state-of-art, three main types of self-interference cancellations are researched, which are passive cancellations, digital cancellations, and analog cancellations. In this thesis, we study polarization-enabled digital self-interference cancellation (PDC) scheme in IBFD EH systems which cancels self-interference by antenna polarization (propagation domain) and digital processing (digital domain). The theme of this thesis is to address the following two questions: how the selfinterference would be canceled in the IBFD EH system and how to optimize key performances of the system to optimal system performances. This thesis makes five research contributions in the important area of IBFD relaying systems with wireless power transfer. Their applications are primarily in the domains of the Internet of Things (IoT) and 5G-and-beyond wireless networks. The overarching objective of the thesis is to construct analytical system models and evaluate system performance (outage probability, throughput, error) in various scenarios. In all five contributions, system models and analytical expressions of the performance metrics are derived, followed by computer simulations for performance analysis

Design methods for optimal resource allocation in wireless networks

Wireless communications have seen remarkable progress over the past two decades and perceived tremendous success due to their agile nature and capability to provide fast and ubiquitous internet access. Maturation of 3G wireless network services, development of smart-phones and other broadband mobile computing devices however have motivated researchers to design wireless networks with increased capacity and coverage, therefore un-leaching the wireless broadband capabilities. In this thesis, we address two very important design aspects of wireless networks, namely, interference management and control through optimal cross-layer design and channel fading mitigation through relay-assisted cooperative communications. For the former, we address, in the context of wireless network design, the problem of optimally partitioning the spectrum into a set of non-overlapping channels with non uniform spectrum widths and we model the combinatorially complex problem of joint routing, link scheduling, and spectrum allocation as an optimization problem. We use column generation decomposition technique (which decomposes the original problem into a master and a pricing subproblem) for solving the problem optimally. We also propose several sub-optimal methods for efficiently solving the pricing subproblems. For the latter problem, we study the joint problem of relay selection and power allocation in both wireless unicast and multicast cooperative cellular networks. We employ convex optimization technique to model this complex optimization problem and use branch and bound technique to solve it optimally. We also present sub-optimal methods to reduce the problem complexity and solve it more efficiently

Performance Analysis of Train Communication Systems

Trains are considered as a highly efficient transport mode which generate significant challenges in terms of their communication systems. For improved safety, to cope with the expected rapid increase in traffic, and to meet customer demands, an enhanced and reliable communication system is required for high-speed trains (HSRs). Mobile phone and laptop users would like to make use of the non-negligible time that they spend commuting but current HSR communication systems have a foreseeable end to their lifetime and a reliable, efficient, and fast communication replacement system has become essential. Encouraged by the use of existing power line networks for communication purposes, this research investigates the possibility of developing a train communication system based on the use of overhead line equipment (OLE). The ABCD transfer line model is developed to represent the transfer function of the OLE channel and is evaluated using computer simulations. The simulations of the OLE system used are based on orthogonal frequency division multiplexing as the chosen modulation scheme. Within the train, for the provision of broadband services, developing a reliable communication system which is a combination of power line communication and optical wireless communication services using visible light communication (VLC) is considered. Mathematical methods were developed for these networks to assess the overall capacities and outage probabilities of the hybrid systems. Derivation of such analytical expressions offered opportunities to investigate the impact of several system parameters on the performance of the system. To assess the possibility of improving the performance of the proposed integrated systems, their performance in the presence of different relaying protocols has been comprehensively analyzed in terms of capacity and outage probability. This thesis studied the outage probability and energy per bit consumption performance of different relaying protocols over the VLC channel. Accurate analytical expressions for the overall outage probability and energyper-bit consumption of the proposed system configurations, including the single-hop and multi-hop approaches were derived. It was found that the transfer function of the OLE channel can be represented by the two-port network model. It was also revealed that transmission over OLE is negatively affected by the speed of the train, frequency, and length of the OLE link. In train, relay-based communication systems can provide reliable connectivity to the end-user. However, choosing an optimal system configuration can enhance system performance. It was also shown that increasing relay numbers on the network contributes to the total power consumption of the system

Performance analysis of relay-aided wireless communication systems

Relay-aided networks have been proved to be cost-efficient solutions for wireless communications in respect of high data rates, enhanced spectrum efficiency and improved signal coverage. In the past decade, relaying techniques have been written into standards of modern wireless communications and significantly improve the quality of service (QoS) in wireless communications. In order to satisfy exponentially increased demands for data rates and wireless connectivities, various novel techniques for wireless communications have been proposed in recent years, which have brought significant challenges for the performance analysis of relaying networks. For the purpose of more practical investigations into relaying systems, researchers should not only analyse the relays employing novel techniques but also attach more importance to complex environments of wireless communications. With these objectives in mind, in this thesis, in-depth investigations into system performance for relay-assisted wireless communications are detailed. Firstly, the theoretic reliability of dual-hop amplify-and-forward (AF) systems over generalised η-μ and κ-μ fading channels are investigated using Gallager’s error exponents. These two versatile channel models can encompass a number of popular fading channels such as Rayleigh, Rician, Nakagami-m, Hoyt and one-sided Gaussian fading channels. We derive new analytical expressions for the probability distribution function (pdf) of the end-to-end signal-to-noise-ratio (SNR) of the system. These analytical expressions are then applied to analyse the system performance through the study of Gallager’s exponents, which are classical tight bounds of error exponents and present the trade-off between the practical information rate and the reliability of communication. Two types of Gallager’s exponents, namely the random coding error exponent (RCEE) and the expurgated error exponent, are studied. Based on the newly derived analytical expressions, we provide an efficient method to compute the required codeword length to achieve a predefined upper bound of error probability. In addition, the analytical expressions are derived for the cut-off rate and ergodic capacity of the system. Moreover, simplified expressions are presented at the high SNR regime. Secondly, the performance of a dual-hop amplify-and-forward (AF) multi-antenna relaying system over complex Gaussian channels is investigated. Three classical receiving strategies, i.e. the maximal-ratio combining (MRC), zero-forcing (ZF) and minimum mean square error (MMSE) are employed in the relay to mitigate the impact of co-channel interference (CCI), which follows the Poisson point process (PPP). We derive the exact analytical expressions of the capacities for this system in the infinite-area interference environment and the asymptotic analytical expressions for the lower bounds of capacities in the limited-area interference scenario. By computing the numerical results and the Monte Carlo simulation, we can observe the effect of relay processing schemes under different interference regimes. In the end, the non-orthogonal multiple access (NOMA) technique is introduced to relaying systems, which exploits multiplexing in the power domain. Order statistics are applied in this part to analyse the performances of ordered users. The randomness of both channel fading and path loss are taken into consideration. In addition to the exact analytical expressions, asymptotic expressions at high-SNR regimes are provided, which clearly show the effects of NOMA techniques using at relaying systems