Dissertations / Theses on the topic 'Energy harvesting relays'

Wireless communication has experienced tremendous growth over the past three decades. This led to the development of many novel technologies aimed at enhancing the system performance due to the limited availability of radio resources. Cooperative relaying is a promising technology which enhances transmission reliability using simple hardware. However, the extra power consumed for the process of information relaying may be an issue. Recent advances in wireless energy transfer have made it possible for self-sustainable relays that power themselves by capturing ambient energy wirelessly. In this thesis we focus on two technologies, namely, cooperative relaying which enhances the energy efficiency and reliability by allowing multi-hop communication with low power nodes, and Radio Frequency (RF) energy harvesting which obviates the need for a battery by capturing the ambient RF energy and using it as a source power. In the first part of the thesis, we study RF energy harvesting in a Decode-and-Forward (DF) Wireless Relay Network (WRN) in the presence of an interferer node. We consider the Time Switching Relaying (TSR) protocol, the Power Splitting Relaying (PSR) protocol and we propose a new hybrid TSR-PSR protocol. We derive expressions for the outage probability and throughput in the delay-sensitive transmission mode for the three relaying protocols, and compare their performances. For simplicity, we neglect the energy harvested from the interferer signal. In the second part, we study the general case in which we include the effect of harvesting energy from the interferer signal. Expressions for the outage probability and throughput in the delay-sensitive transmission mode are derived for the three relaying protocols. Numerical results are presented to illustrate the effect of including RF energy harvesting from the interferer. In the third part, we study shared and non-shared power allocation schemes for a two-hop DF WRN with multiple source-destination pairs. The pairs communicate via a single relay which harvests RF energy from the source transmissions in the presence of an interfering signal. The studied schemes are compared in terms of outage probability, throughput in the delay-sensitive transmission mode and fairness.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

Wireless communication networks are subject to exponential growth as a result of proliferation of smart phones, diverse wireless services and Internet of Things (IoT) applications. This extensive growth of wireless networks can significantly increase energy consumption, and escalating environmental pollution and energy costs have already created an urge for green communication. Therefore, we need to be proactive in designing environment friendly communication technologies and efficient resource allocation solutions, which will potentially drive the future generation of wireless communication. In this thesis, we focus on two promising communication technologies, namely cooperative relaying, which improves energy and spectral efficiency by providing spatial diversity, and energy harvesting technology, which can improve sustainability by utilizing renewable energy sources. The objective of this thesis is to address a number of key challenges in the design of efficient resource allocation techniques for wireless systems based on these two communication technologies. Firstly, we address the problem of energy efficiency maximization for downlink orthogonal frequency division multiple access (OFDMA)-based cooperative networks. The power and subcarrier allocation policies are jointly optimized with quality of service (QoS) provisioning. Afterwards, we investigate frequency reuse in OFDMA device-to-device (D2D) cooperative systems in which D2D pairs are classified based on the level of proximity with each other. We propose different scenarios of downlink communications and provide efficient frequency allocation techniques. Moreover, resource allocation algorithms with low complexity and signaling overhead are developed. Next, we focus on energy limitation of the relay nodes in cooperative systems. Using wireless energy harvesting to power the relay nodes, we propose an efficient resource allocation algorithm. As wireless energy harvesting technology is only effective for charging small nodes in communication systems, finally, we focus on the issue of charging the wireless nodes with renewable energy. We investigate the problem of resource allocation in energy harvesting systems considering the fact that the energy harvested from environment may not be enough to satisfy the QoS of all users due to its random nature. Two different utility functions are introduced and both offline and online schemes are devised to address this problem.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

In this thesis, I focus on the system design and performance analysis of wireless communication networks with radio frequency (RF) energy harvesting. Battery re-placement/recharging has always been a challenging issue in wireless communication networks, especially in large-scale networks like wireless sensor networks (WSNs). Recently, RF energy harvesting (EH) technology has been developed as a new viable solution to extend the lifetime of wireless networks via enabling wireless devices to harvest energy from RF signals. Inspired by this technique, wireless-powered communication networks (WPCNs) have attracted an upsurge of research interest. According to the protocols proposed in current literature, an EH user will exhaust all the energy it harvests straightway during this transmission block. This may be a sub-optimal solution, since this little amount of energy may not be able to contribute to an effective transmission. Therefore, in this thesis, I consider energy accumulation at each EH node by providing an energy storage (e.g. a rechargeable battery), so that it can an accumulate sufficient amount of harvested energy before transmission and wait to transmit in an appropriate time slot. To begin with, I first investigate wireless energy harvesting (WEH) technique in cooperative communication networks where the source and relay can both communicate with the destination. I refer to this kind of network as wireless-powered cooperative communication networks (WPCCNs). This WEH technique offers a new cooperation manner for wireless devices since the relay node is now able to harvest energy from the source’s information. In this thesis, I consider the relay as a wireless-powered node that has no external power supply; but it is equipped with an EH unit and a rechargeable battery so that it can harvest and accumulate energy from RF signals broadcast by the source. By fully incorporating the EH feature of the relay, an opportunistic relaying protocol was developed, termed accumulate-then-forward (ATF), for the considered WPCCN with a direct link. The discrete Markov chain is adopted to model the dynamic charging and discharging behaviors of the relay battery. Based on this, I derive a closed-form expression for the exact system outage probability of the proposed ATF protocol. Numerical results show that the ATF scheme can outperform the direct transmission one, especially when the amount of energy consumed by the relay for information forwarding is optimized. In order to further take advantage of the direct link between the source and destination, an incremental accumulate-then-forward (IATF) scheme was proposed to the considered WPCCNs. In the IATF protocol, the source sends its information to the destination via the direct link and requests the relay to cooperate only when it is necessary, such that the relay has more chances to accumulate energy. By modelling the charging/discharging behaviors of the relay battery as a finite-state Markov chain, I derive a closed-form expression for the system outage probability of the proposed IATF. Numerical results validate my theoretical analysis and show that the IATF scheme can significantly outperform the direct transmission scheme without cooperation and the ATF scheme. A comparison of these two schemes is also given to show examples of their advantages and disadvantages. One of the key features of WEH technique is one-to-many, where multiple EH nodes can harvest energy simultaneously from one single RF signal. The energy from broadcasted RF signals can thus be transferred to several EH nodes rather than only one EH node, which can increase the energy transfer efficiency of the whole communication network. Contrast to the single EH node previously, in the last chapter of this thesis, I investigate a WPCN with multiple EH nodes and focus on the multi-user scheduling problem. I assume a power beacon (PB) is deployed in WPCN dedicating to charge the EH nodes by broadcasting RF energy signals. With this PB-assisted WEH technique, the considered WPCN consists of a PB, an access point (AP) and multiple EH users attempting to transmit information toward the AP. In this thesis, I consider that only one EH user can be selected to forward its information, and the rest of the nodes will continue to harvest energy. In order to harvest energy effectively and transmit information efficiently, I proposed several types of multi-user scheduling schemes based on the availability of the channel state information (CSI), i.e. multi-user scheduling scheme without CSI, multi-user scheduling scheme using channel state information at the receiver (CSIR), and multi-user scheduling scheme using channel state information at the transmitter (CSIT). Two more Proportional Fairness scheduling schemes are proposed in order to achieve the fairness among all the EH users. Simulation results show that the availability of CSI can significantly improve the access outage probability, where the average probability of the user successfully connect to the AP is shown. Moreover, the fairness among different users can be dramatically improved by two Proportional Fairness schemes.

Abstract The rapid evolution of wireless networks to meet the requirements of explosive data traffic demand is escalating energy consumption beyond sustainable limits. Consequently, energy efficiency (EE) has emerged as a key performance indicator for future wireless networks to address the increasing concern over greenhouse gas emissions and sustainable economic growth. This thesis studies energy-efficient transmission strategies for multiantenna wireless systems. The aim is to develop linear beamforming techniques maximizing the bit-per-Joule EE metric, focusing on three appealing scenarios: a coordinated multicell system; a fronthaul-constrained cloud radio access network (C-RAN); and a multi-pair wireless-powered relaying system. The primary emphasis is on suboptimal but efficient optimization approaches which are attractive for practical implementation. The problem of achieving EE fairness in a multicell multiple-input single-output downlink system is studied first. Specifically, coordinated beamforming is designed to maximize the minimum EE among all base stations. Novel efficient iterative optimization methods solving the design problem in both centralized and decentralized fashions are proposed. In a downlink C-RAN with finite-capacity fronthaul links, the network-wide EE performance is explored via a joint design of beamforming and remote radio head-user association. A relatively realistic power consumption model including rate-dependent circuit power and nonlinear power amplifiers' (PA) efficiency is also considered. To gain an insight into the optimal performance of the design problem, an algorithm achieving globally optimal solutions is devised. Towards practical implementation, two efficient iterative suboptimal methods are proposed aiming at yielding near-optimal performance. Finally, a multi-pair amplify-forward relaying network is considered, in which energy-constrained relays adopting time-switching protocol harvest energy from the radio frequency signals transmitted by users. To maintain EE fairness among all user pairs, joint optimization of system parameters, such as users' transmit power, relay beamforming, and energy harvesting (EH) time, is studied. Impacts of rate-dependent circuit power, nonlinear PAs' efficiency and nonlinear EH circuits on the achievable performance are also addressed
Tiivistelmä Langattomat verkot ovat kehittyneet nopeasti räjähdysmäisesti kasvavan dataliikenteen mahdollistamiseksi, minkä seurauksena energiankulutus on kasvanut kestävän kehityksen rajat ylittävällä tavalla. Siksi energiatehokkuudesta (EE, energy efficiency) on tullut uusien langattomien verkkojen keskeinen suunnittelukriteeri vastauksena kasvavaan huoleen kasvihuonepäästöistä ja kestävästä talouskasvusta. Väitöskirjassa tutkitaan moniantennisten langattomien järjestelmien energiatehokkaita tiedonsiirtostrategioita. Tavoitteena on kehittää lineaarisia keilanmuodostustekniikoita, jotka maksimoivat energiatehokkuuden mitattuna bitteinä joulea kohden, keskittymällä kolmeen kiinnostavaan vaihtoehtoon, joita ovat koordinoitu monisolujärjestelmän lähetys laskevalla siirtotiellä, pilvipohjainen radioliityntäverkko (C-RAN, cloud radio access network), jossa laskentayksikön ja varsinaisen radiolähettimen välinen yhteys (fronthaul) on rahoitettu, ja usean parin relejärjestelmiin, joissa releet toimivat paristoilla. Työn pääpaino on alioptimaalisissa, mutta käytännöllisesti tehokkaissa optimointimenetelmissä. Pääpaino on alioptimaalisissa mutta tehokkaissa optimointitavoissa, jotka ovat kiinnostavia käytännön toteutuksen näkökulmasta. Ensiksi tarkastellaan tasapuolisen energiatehokkuuden saavuttamista monisoluisessa laskevan siirtotien moni-tulo yksi-lähtö (MISO, multiple-input single-output) -järjestelmässä. Koordinoitu keilanmuodostus on suunniteltu erityisesti maksimoimaan energiatehokkuuden minimitaso kaikilla tukiasemilla. Tarkemmin sanottuna pyritään maksimoimaan huonoin energiatehokkuus solmujen välillä, kun käytetään yhteistoiminnallista keilanmuodostusta. Muodostetun ongelman ratkaisemiseksi ehdotetaan edistyksellisiä iteratiivisia menetelmiä käyttämällä sekä keskitettyjä että hajautettuja ratkaisuja. Laskevan siirtosuunnan fronthaul-rajoitetussa C-RAN-järjestelmässä selvitetään verkonlaajuista energiatehokkuutta keilanmuodostuksen ja palvelevan tukiaseman yhteisoptimoinnilla. Tässä käytetään verrattain realistista tehonkulutusmallia, joka sisältää datanopeudesta riippuvan prosessointitehon ja epälineaarisen tehovahvistimen (PA, power amplifier) hyötysuhteen. Jotta saadaan käsitys ongelman optimaalisesta suorituskyvystä, siihen kehitetään globaalisti optimaalinen menetelmä. Lisäksi ehdotetaan kaksi käytännöllisempää iteratiivista menetelmää, jotka saavuttavat lähes optimaalisen suorituskyvyn. Lopuksi keskitytään monen parin vahvista-ja-välitä eteenpäin (AF. amplify and forward) verkkoon, jossa aikajakokytkentää käyttävät energiarajoitetut toistimet keräävät energiaa käyttäjien lähettämistä radiosignaaleista. Jotta saavutetaan EE:n oikeudenmukaisuus kaikkien parien välillä, parametrit, kuten käyttäjien lähetysteho, toistimen keilanmuodostus, ja energiankeräysaika suunnitellaan yhdessä. Tässä tutkitaan nopeusriippuvaisen piirin tehon, epälineaarisen tehovahvistimen hyötysuhteen ja epälineaaristen energiankeräyspiirien tehon vaikutusta suorituskykyyn

碩士
國立成功大學
電腦與通信工程研究所
103
Energy harvesting (EH) is an attractive solution to prolong the lifetime of wireless devices. As the replacement of traditional battery-powered relay nodes, EH relays extract energy from the signal of the source node and use the harvested energy to perform information relaying, enabling a self-sustainable cooperative network. To use the harvested energy efficiently which is limited due to the energy loss by wireless channel impairment and RF-DC conversion, it is important to properly schedule the two tasks for relays, namely information and EH, within a transmission block. In this thesis, we investigate block scheduling and relay selection problems in a cooperative networks with EH relays. In terms of block scheduling, we consider two variants of time division multiplexing, including partial time reuse and full-duplex scheduling. In terms of relay selection, we propose a relay selection scheme where selected max-max relay selection (S-MMRS) considers both the source-relay channel for EH and the relay-destination channel for information relaying in selecting the cooperating relay. To evaluate the performance of the proposed S-MMRS, we theoretically analyze the outage probability and the throughput and the simulation results are presented to verify the analysis accuracy and demonstrate the impact of system parameters to the proposed relay selection scheme.

碩士
國立中山大學
通訊工程研究所
103
In this thesis, we consider AF cooperative networks with multiple radio frequency energy-harvesting (RFEH) relays, and investigate power allocation and relay selection strategies to prolong the network lifetime since relays are battery-powered with limited energy. Through cooperation among multiple relays, reliability and transmission rate of cooperative networks are enhanced by exploiting spatial diversity. If relays rely on wireline power supplies, implementation cost must increase and mobility is lacked. Therefore, we consider relays apply RFEH technology to harvest energy by transferring ambient RF signal into electrical energy, so that they can be self-sustained. Consequently, the network lifetime can be further prolonged. In this thesis, we investigate relay selection strategies to choose one relay to forward messages while the others perform energy harvesting. Those selection strategies aim to minimize the loss of energy dissipation, reducing wasted energy and increase the average harvested energy, in order to prolong the network lifetime. In this thesis, we define network lifetime based on the outage performance of the network. Specifically, if outage probability of network is lower than a threshold, the system is treated as &;quot;well-functioned&;quot;, and the network lifetime is defined as the longest period in which network is well-functioned. From the expression of outage probability, network lifetime is related to the residual energy of relays.Compares with existing relay selection strategies which take Channel State Information(CSI),Residual Energy Information(REI), and/or Harvested Energy Information(HEI) into account, we proposed a novel relay selection scheme based on opportunity cost of each choice. Because the proposed scheme properly exploits CSI, REI, and HEI, the proposed scheme outperforms others with stringent outage requirement. Moreover, since all relay selection strategies require simply local CSI, REI, and HEI, they can be accomplished in a distributed manner through opportunistic carrier sensing without extra overhead.

碩士
國立成功大學
電腦與通信工程研究所
102
The use of energy harvesting (EH) nodes as cooperative relays is a promising and emerging solution for energy limited wireless systems, rendering the network self-sustaining with significantly prolonged lifetime. In this thesis, we consider multiple EH relay nodes harvesting energy from the radio frequency (RF) signal received from the source and use that harvested energy to forward the source information to the destination. Unlike conventional wireless nodes relied on fixed power supplies, EH relays may not be permanently available to assist the source transmission due to the limited energy conversion efficiency, the mismatch between the charging and discharging profiles, and the finite energy storage capacity. Our objective is to improve the reliability of EH relays by properly selecting one relay to perform data forwarding while the remaining relays perform energy harvesting. We propose the ``battery-aware relay selection (BARS)', which jointly considers the channel condition and the buffer status for relay selection. The outage probability of the proposed scheme is analyzed based on a Markov chain model. Simulations are performed to validate the analysis accuracy. The proposed scheme is compared with the ``CSI-based relay selection scheme', which selects the cooperating relay only based on the channel condition. Through numerical results, we show that the CSI-based scheme suffers error floor while the propose BARS scheme can achieve the full diversity order equal to the number of relays without the need of fixed power cables.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2020
In recent years, there has been an explosive growth in bandwidth-hungry wireless devices and applications which has, in turn, caused a strain on the provisions of the present electromagnetic spectrum. Several technologies have been studied and implemented in the quest to try and alleviate this growing scarcity of the spectrum. This work, therefore, tries to address some of these challenges by looking at spectrum utilisation techniques and how optimal they can be implemented to improve the spectral efficiency and overall system performance. This research seeks to investigate the sum-rate and outage performance of an energy harvesting cognitive massive multiple-input multiple-output (MIMO) multi-relay assisted network with underlay spectrum sharing. The secondary network is permitted to opportunistically access the licenced primary network frequency band provided that the intra-cell interference imposed on the primary base station due to concurrent secondary network transmissions does not exceed the pre-set interference temperature and hence maintain the quality-of-service (QoS) requirements of the primary network. The introduction of relays improves the system performance by increasing the network coverage and this research analyses the performance of the cognitive relay networks by looking at (i) the effect of primary user interference on the relay and subsequently relay selection, (ii) the outage probability of the secondary network being assisted by an amplify-and-forward (AF) relay and (iii) the impact of the number of relay antennas and the number of relays. The power-constrained secondary network nodes harvest energy from concurrent transmissions of the energy sufficient primary users. A time switching protocol is implemented in this work for energy harvesting and closed-form expressions for the harvested energy and achievable sum-rate are derived. To that end, this research seeks to quantify the trade-off between the achievable sum-rate of the network and the harvested energy. The primary base station and secondary destination employ zero-forcing detection and performance is investigated over Rayleigh fading
CK2021

碩士
國立中山大學
電機工程學系研究所
102
Due to rapid development of mobile communications, radio-frequency signals are surrounded in our environment. Besides conveying information, the ambient radio-frequency signal has gradually been utilized for energy harvesting. Radio Frequency energy harvesting begins from the fact that people gradually rely on mobile applications, such as communication apps., picturing software, and games, in their daily life. However, these applications are energy consuming. Although these devices can be charged through portable power bank, the energy stored in the power bank is still limited, which leads to inconvenience when the power bank is in outage. To provide further convenience, RF energy harvesting has been developed to avoid mobile devices suffering power outage by gathering energy from from the ambient radio frequency signals and transferring into electricity. Furthermore, simultaneously processing information and harvesting energy from the RF signal has been studied extensively in recent years. In this thesis, we will employ this technique in two-way amplify-and-forward relay system, where two users exchange information under assistance of an energy-harvesting relay node. Specifically speaking, transmission power of the relay node depends on the electrical energy harvested in previous phase. We assume that the relay node is equipped with two antennas, while the users are equipped with a single antenna. With perfect channel information, the relay node can coherently combines the signals received at two antennas, so that the relay node is able to gather more energy. In this thesis, we proposed a joint design of a precoding matrix and power-slitting ratios for the relay node to maximize the sum-rate of two users under a constraint that the transmission power of the relay node cannot exceed the harvested energy. However, this optimization problem is neither convex nor concave, and it can’t be solved by CVX tool. Thus, we divide the problem into two sub-problems to approach a locally-optimal solution of the precoding matrix and power-splitting ratios in an iterative manner. Specifically, we employ gradient algorithm to obtain power-splitting ratios with initial value obtained by exhaustively searching over a rough grid. Then, the beamforming matrix is obtained using power iteration algorithm. After several iterations, two subproblems get converged and we can find the set of suboptimal solutions. It shows through simulation results that the proposed scheme can effectively improve the spectrum efficiency of the system.

碩士
國立中央大學
通訊工程學系
103
Toward a green communication, the scheduling and the optimal power allocation are two key approaches to address the problem of inadequate resources in the future wireless communications. The existing schemes are based on fixed and stochastic energy and they didn’t take the energy causality constraints into account. In this work, we focus on the optimal power control schemes under the uncertainty of harvested energy, and we also consider both half-duplex and full-duplex protocols to transmit the data. In this research, we consider online case and offline case with an energy harvesting (EH) sources communicates with the destination via an EH decode-and-forward relay. In online case, we formulate the problem as a Markov decision process to find the best policies. In the offline case, we use optimal form to solve the problem and propose a suboptimal simplifying the complexity. The main contribution of this research is to find the optimal policies that maximize the throughput and minimize the outage probability under different situations.

碩士
國立中山大學
電信工程國際碩士學位學程
107
A system with two single-antenna users that want to exchange their data via a multi-antenna relay has been investigated in this work. After the two users send their data, the relay performs a signal processing so that the sum-rate is maximum. After deriving the SNR equation, we optimize three parameters to achieve the goal: phase rotating factor, precoder, and power splitting ratio. Since the joint optimization over these three variables is difficult, then we optimize them separately. The purpose of optimizing the phase rotating factor is to get the harvested power as high as possible that will be used for data broadcasting by the relay. We develop an iterative algorithm that has a low computational complexity and fast in convergence. Besides, we find a near optimum point that can be calculated analytically. The purpose of optimizing the precoder is to get the rate as high as possible. Since the conventional method finding the first derivation equals to zero cannot be implemented to find an optimum precoder, we finally use the gradient descent method that is developed with an initial point optimization that is close with the actual optimal point. We consider these three methods to find an optimal solution for the power splitting ratio. It has been analyzed that these three methods have their own positive and negative sides.

碩士
國立成功大學
電腦與通信工程研究所
107
In this thesis, we study the relay selection problem for a buffer-aided and energy harvesting cooperative system. A number of relays harvest energy from the source signal and one relay are selected to forward the source signal using the harvested energy. Since the harvested energy is often weak, the best practice is to accumulate the harvested energy by storing it into the rechargeable battery. With the aid of energy and data storage, both limited in size, an important question is how to determine the action of each relay, namely receiving data or forwarding the source signal. A relay selection scheme, called dual buffer relay selection (DBRS) is proposed considering the data buffer, energy buffer and channel status simultaneously. To evaluate the performance of DBRS, theoretical analysis based on Markov chain model is performed. Simulation results are presented to validate the analysis accuracy and get insights into the system performance subject to numerous key parameters.

碩士
國立中央大學
通訊工程學系
103
Cooperative Spectrum Sharing (CSS) is proposed as a solution for the inefficient utilization of the spectrum. In CSS of cognitive-radio networks, primary licensed user (PU) with poor channel condition (between its transmitter and receiver) can achieve a higher data rate by using a secondary unlicensed user (SU) as a relay. In return, the primary user possibly decides to lease part of its spectrum resource to secondary users in exchange for appropriate remuneration. The key point of CSS is how the PU and SU agree on the cooperative transmissions and resource allocations. In previous schemes, they are propose on the transmission policy with unconstrained energy. However, we focus on wireless sensor networks with energy harvesting and propose a method between PU and SU ‘s transmits policies in CSS. In our study, we formulate the problem as a Markov Decision Process (MDP) framework by which the channel states, battery conditions and harvested process are stochastic. Moreover, we also consider the condition without information of transition probability. In this case, we use the Q-learning algorithm to find the optimal transmission policies .Finally, we compare the performance of our scheme with others.

碩士
國立中央大學
通訊工程學系
107
This paper discusses the outage performance of full-duplex relay channel using amplify-and-forward(AF) relay protocol with energy harvesting(EH) and compare with its optimum one. Previous works almost focused on that destination treated the self-interference signal as interference only, so in that works they wanted to eliminate self-interference(SI) signal. We provide a system model with make self-interference signal assist information decoding at the destination. At the relay node, the received signals, including self-interference, are split according to a power ratio for information processing (IP) and energy harvesting, respectively. We derive an approximate, yet accurate, closed-form expression for the end-to-end outage probability and optimum one. In addition, the processing delay is larger than one in practice, the proposed close-form outage probability expression is still valid. Finally, we corroborate our theoretical results with simulations in different situations. The results indicate that the proposed system model with optimization can outperforms system with fixed power splitting method.

Wireless is everywhere. Smartphones, tablets, laptops, implantable medical devices, and many other wireless devices are massively taking part of our everyday activities. On average, an actively digital consumer has three devices. However, most of these wireless devices are small equipped with batteries that are often limited and need to be replaced or recharged. This fact limits the operating lifetime of wireless devices and presents a major challenge in wireless communication. To improve the perpetual energy operation of wireless communication systems, energy harvesting (EH) from the radio frequency (RF) signals is one promising solution to make the wireless communication systems self-sustaining. Since RF signals are known to transmit information, it is interesting to study when RF signals are simultaneously used to transmit information and scavenge energy, namely simultaneous wireless information and power transfer (SWIPT). In this thesis, we specifically aim to study the SWIPT in multiple-input multiple-output (MIMO) relay communication systems and in cognitive radio (CR) networks. First, we study the SWIPT in MIMO relay systems where the relay harvests the energy from the source and uses partially/fully the harvested energy to forward the signal to the destination. For both the amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols, we consider the ideal scheme where both the energy and information transfer to the relay happen simultaneously, and the practical power splitting and time switching schemes. For each scheme, we aim to maximize the achievable end-to-end rate with a certain energy constraint at the relay. Furthermore, we consider the sum rate maximization problem for the multiuser MIMO DF relay broadcasting channels with multiple EH-enabled relays, and an enhanced low complex solution is proposed based on the block diagonalization method. Finally, we study the energy and data performance of the SWIPT in CR network where either the primary receiver (PR) or the secondary receiver (SR) is using the antenna switching (AS) technique. When the PR is an EH-enabled node, we illustrate the incentive of spectrum sharing in CR networks. When the SR is an EH-enabled node, we propose two thresholding-based selection schemes: the prioritizing data selection scheme and the prioritizing energy selection scheme.

Resource allocation in wireless networks is one of the most studied class of problems. Generally, these problems are formulated as utility maximization problems under relevant constraints. The challenges posed by these problems vary widely depending on the nature of the utility function under consideration. Recently, the widespread prevalence of wireless devices prompted researchers and engineers to delve into the security issues of wireless communication. As compared to the wired medium, ensuring security for the wireless medium is more challenging mainly due to the broadcast nature of the transmission. But the ongoing research on physical layer security promises robust and reliable security schemes for wireless communication. Contrary to conventional cryptographic schemes, physical layer security techniques are impregnable as the security is ensured by the inherent randomness present in the wireless medium. In this thesis, we consider several wireless scenarios and propose secrecy enhancing resource allocation schemes for them in the first few chapters. We initially address the problem of secure transmission by following the conventional approach in the secrecy literature|secrecy rate maximization. Needless to say, in these chapters, secrecy rate is the utility function and the constraints are posed by the available power budget. Then we consider a pragmatic approach where we target the signal-to-noise ratio (SNR) of participating nodes and ensure information secrecy by appropriately constraining the SNRs of those nodes. In those SNR based formulations, SNR at the destination is the utility function and we are interested in maximizing it. In the last two chapters, we study two scenarios in a non-secrecy setting. In one of them, end-to-end data rate is the utility, whereas, in the other one, two utility functions|based on revenue generated|are defined for two rational agents in a game-theoretic setting. In the second chapter, we study parallel independent Gaussian channels with imperfect channel state information (CSI) for the eavesdropper. Firstly, we evaluate the probability of zero secrecy rate in this system for (i) given instantaneous channel conditions and (ii) a Rayleigh fading scenario. Secondly, when non-zero secrecy is achievable in the low SNR regime, we aim to solve a robust power allocation problem which minimizes the outage probability at a target secrecy rate. In the third, fourth and fifth chapters, we consider scenarios where the source node transmits a message to the destination using M parallel amplify-and-forward (AF) relays in the presence of a single or multiple eavesdroppers. The third chapter addresses the problem of the maximum achievable secrecy rate for two specific network models: (a) degraded eavesdropper channel with complex channel gain and (b) scaled eavesdropper channel with real-valued channel gains. In the fourth chapter, we consider the SNR based approach and address two problems: (i) SNR maximization at the destination and (ii) Total relay power minimization. In the fifth chapter, we assume that the relay nodes are untrusted and to counter them, we deliberately introduce artificial noise in the source message. For this model, we propose and solve SNR maximization problems for the following two scenarios: (i) Total power constraint on all the relay nodes and (ii) Individual power constraints on each of the relay nodes. In the sixth chapter, we address the problem of passive eavesdroppers in multi-hop wire-less networks using the technique of friendly jamming. Assuming decode-and-forward (DF) relaying, we consider a scheduling and power allocation (PA) problem for a multiple-source multiple-sink scenario so that eavesdroppers are jammed, and source-destination throughput targets are met. When channel state information (CSI) of all the node are available, we intend to minimize the total power consumption of all the transmitting nodes. In the absence of eavesdroppers CSI, we minimize vulnerability region of the network. In chapter seven, the problem of cooperative beamforming for maximizing the achievable data rate of two-hop amplify-and-forward (AF) network (in the absence of eavesdropper(s)) is considered. Along with an individual power constraint on each of the relay nodes, we consider a weighted sum power constraint. To solve this problem, we propose a novel algorithm based on the Quadratic Eigenvalue Problem (QEP) and discuss its convergence. In chapter eight, we study a Stackelberg game between a base station and a multi-antenna power beacon for wireless energy harvesting in a multiple sensor node scenario. Assuming imperfect CSI between the sensor nodes and the power beacon, we propose a utility function that is based on throughput non-outage probability at the base station. We find the optimal strategies for the base station and the power beacon that maximize their respective utility functions.

Resource allocation in wireless networks is one of the most studied class of problems. Generally, these problems are formulated as utility maximization problems under relevant constraints. The challenges posed by these problems vary widely depending on the nature of the utility function under consideration. Recently, the widespread prevalence of wireless devices prompted researchers and engineers to delve into the security issues of wireless communication. As compared to the wired medium, ensuring security for the wireless medium is more challenging mainly due to the broadcast nature of the transmission. But the ongoing research on physical layer security promises robust and reliable security schemes for wireless communication. Contrary to conventional cryptographic schemes, physical layer security techniques are impregnable as the security is ensured by the inherent randomness present in the wireless medium. In this thesis, we consider several wireless scenarios and propose secrecy enhancing resource allocation schemes for them in the first few chapters. We initially address the problem of secure transmission by following the conventional approach in the secrecy literature|secrecy rate maximization. Needless to say, in these chapters, secrecy rate is the utility function and the constraints are posed by the available power budget. Then we consider a pragmatic approach where we target the signal-to-noise ratio (SNR) of participating nodes and ensure information secrecy by appropriately constraining the SNRs of those nodes. In those SNR based formulations, SNR at the destination is the utility function and we are interested in maximizing it. In the last two chapters, we study two scenarios in a non-secrecy setting. In one of them, end-to-end data rate is the utility, whereas, in the other one, two utility functions|based on revenue generated|are defined for two rational agents in a game-theoretic setting. In the second chapter, we study parallel independent Gaussian channels with imperfect channel state information (CSI) for the eavesdropper. Firstly, we evaluate the probability of zero secrecy rate in this system for (i) given instantaneous channel conditions and (ii) a Rayleigh fading scenario. Secondly, when non-zero secrecy is achievable in the low SNR regime, we aim to solve a robust power allocation problem which minimizes the outage probability at a target secrecy rate. In the third, fourth and fifth chapters, we consider scenarios where the source node transmits a message to the destination using M parallel amplify-and-forward (AF) relays in the presence of a single or multiple eavesdroppers. The third chapter addresses the problem of the maximum achievable secrecy rate for two specific network models: (a) degraded eavesdropper channel with complex channel gain and (b) scaled eavesdropper channel with real-valued channel gains. In the fourth chapter, we consider the SNR based approach and address two problems: (i) SNR maximization at the destination and (ii) Total relay power minimization. In the fifth chapter, we assume that the relay nodes are untrusted and to counter them, we deliberately introduce artificial noise in the source message. For this model, we propose and solve SNR maximization problems for the following two scenarios: (i) Total power constraint on all the relay nodes and (ii) Individual power constraints on each of the relay nodes. In the sixth chapter, we address the problem of passive eavesdroppers in multi-hop wire-less networks using the technique of friendly jamming. Assuming decode-and-forward (DF) relaying, we consider a scheduling and power allocation (PA) problem for a multiple-source multiple-sink scenario so that eavesdroppers are jammed, and source-destination throughput targets are met. When channel state information (CSI) of all the node are available, we intend to minimize the total power consumption of all the transmitting nodes. In the absence of eavesdroppers CSI, we minimize vulnerability region of the network. In chapter seven, the problem of cooperative beamforming for maximizing the achievable data rate of two-hop amplify-and-forward (AF) network (in the absence of eavesdropper(s)) is considered. Along with an individual power constraint on each of the relay nodes, we consider a weighted sum power constraint. To solve this problem, we propose a novel algorithm based on the Quadratic Eigenvalue Problem (QEP) and discuss its convergence. In chapter eight, we study a Stackelberg game between a base station and a multi-antenna power beacon for wireless energy harvesting in a multiple sensor node scenario. Assuming imperfect CSI between the sensor nodes and the power beacon, we propose a utility function that is based on throughput non-outage probability at the base station. We find the optimal strategies for the base station and the power beacon that maximize their respective utility functions.