Developments such as machine-to-machine communications and multimedia services are placing growing demands on high-speed reliable transmissions and limited wireless spectrum resources. Although multiple-input multiple-output (MIMO) systems have shown the ability to provide reliable transmissions in fading channels, it is not practical for single-antenna devices to support MIMO system due to cost and hardware limitations. Cooperative communication allows single-antenna devices to share their spectrum resources and form a virtual MIMO system where their quality of service (QoS) may be improved via cooperation. Most cooperative communication solutions are based on fixed spectrum access schemes and thus cannot further improve spectrum efficiency. In order to support more users in the existing spectrum, we consider dynamic spectrum access schemes and cognitive radio techniques in this dissertation. Our work includes the modelling, characterization and optimization of QoS-constrained cooperative networks and cognitive radio networks. QoS constraints such as delay and data rate are modelled. To solve power control and channel resource allocation problems, dynamic power control, matching theory and multi-armed bandit algorithms are employed in our investigations. In this dissertation, we first consider a cluster-based cooperative wireless network utilizing a centralized cooperation model. The dynamic power control and optimization problem is analyzed in this scenario. We then consider a cooperative cognitive radio network utilizing an opportunistic spectrum access model. Distributed spectrum access algorithms are proposed to help secondary users utilize vacant channels of primary users in order to optimize the total utility of the network. Finally, a noncooperative cognitive radio network utilizing the opportunistic spectrum access model is analyzed. In this model, primary users do not communicate with secondary users. Therefore, secondary users are required to find vacant channels on which to transmit. Multi-armed bandit algorithms are proposed to help secondary users predict the availability of licensed channels. In summary, in this dissertation we consider both cooperative communication networks and cognitive radio networks with QoS constraints. Efficient power control and channel resource allocation schemes have been proposed for optimization problems in different scenarios.

As redes de sensores sem fio (wsns) têm ganhado cada vez mais espaço no monitoramento e controle de processos na indústria. Dentro destas redes, os dispositivos são alimentados por baterias, e a comunicação é feita por radiofrequência. Por conta disto, os rádios dos dispositivos são responsáveis por consumir boa parte da energia armazenada nas suas baterias, e a comunicação dos dispositivos está sujeita à interferência provinda de outras redes e do maquinário industrial. Para sanar estes problemas podem ser empregadas técnicas de controle de potência de transmissão (cpt). Existem diversas técnicas de cpt na literatura, visando os mais diversos objetivos, desde economia de energia e redução de interferência, até controle da topologia da rede. Este trabalho apresenta uma proposta de emprego de (cpt) em uma rede de sensores sem fio através da utilização de controladores proporcionais-integrais (pi). Juntamente com a técnica proposta, são apresentados um procedimento para projeto dos controladores e alguns algoritmos desenvolvidos para o caso ideal e para os casos com saturação dos níveis de potência disponíveis. Este trabalho se diferencia dos trabalhos encontrados na literatura por apresentar uma técnica de controle linear e que depende apenas de informações já disponíveis em cada dispositivo cuja potência será ajustada. Deste modo, esta técnica pode ser empregada em conjunto com protocolos industriais mais restritivos quanto às informações que podem ser trocadas nas mensagens. Além disso, esta técnica reduz ainda mais o consumo e a interferência por evitar transmissões desnecessárias. A proposta apresentada foi validada através de simulações e de um experimento com dispositivos WirelessHART reais, apresentando bons resultados e provando que é possível controlar a potência sem a necessidade das informações extras. / Wireless sensor networks (wsns) are being increasingly adopted in monitor and control tasks in the industry. The devices within these networks are battery-powered, and they communicate through radio frequency. Therefore the radios of the devices account for the most of the consumption of the energy stored in the batteries, and the devices’ communication is subject to interference from other networks and industrial machinery. Transmission power control (tpc) techniques can be employed to cope with these problems. There are several tpc techniques in the literature, aiming at a wide range of objectives, from energy saving and interference reduction, to network topology control. This work presents the proposal of a (tpc) technique in a wireless sensor network that works by employing proportional-integral (pi) controllers. Besides the technique itself, a procedure is presented to design the controllers along some algorithms developed to the ideal case, and the case when there is saturation in the available power levels. This work, unlike the other works found in the literature, presents a linear technique that depends only on information that is already available in each device whose power needs to be adjusted. Therefore, the proposed technique can be employed together with more restrictive industrial protocols that limit the information that can be exchanged in the messages. Besides, it further reduces the power consumption and the interference by avoiding unnecessary transmissions. The proposal was validated through simulations and an experiment using real WirelessHART devices, presenting good results and proving that it is possible to adjust the transmission power without necessarily using the extra information.

The general trends in the past decade of increasing solar cell efficiency, decreasing PV system costs, increasing government incentive programs, and several other factors have all combined synergistically to reduce the barriers of entry for PV systems to enter the market and expand their contribution to the global energy portfolio. The shortcomings of current inverter functions which link PV systems to the utility network are becoming transparent as PV penetration levels continue to increase. The solution this thesis proposes is an approach to control the inverters real and reactive power output to help eliminate the problems associated with PV systems at their origin and in addition provide the grid with ancillary support services. The design, modeling, and analysis of a grid-tied PV system was performed in the PSCAD software simulation environment. Results indicate that in the presence of grid disturbances the smart inverter can react dynamically to help restore the power system back to its normal state. A harmonic analysis was also performed indicating the inverter under study met the applicable power quality standards for distributed energy resources.

<p>Power control is one of the technologies used to utilize the radio resources as efficient as possible in WCDMA. The transmission power is adjusted to transmit with the lowest power level possible while the required received signal quality is maintained. Since there are large variation in channel quality over time, the power has to be adjusted to compensate for these variations. During moments of bad channel conditions a high transmission power has to be used which will to a greater extent interfere with other users in the system. </p><p>To solve this problem a concept called transmission timing was proposed. The basic idea is that the transmitter avoids data transmission during the short periods of bad channel conditions caused by fast fading. Higher bit rates can be used to compensate for this when the channel conditions are good. </p><p>In this thesis the performance of transmission timing applied to uplink data transmissions is evaluated. This is accomplished through a theoretical analysis as well as simulations of a cellular system using transmission timing. Lowered transmission power is achieved and thus lowered interference is induced. Simulations showed that the transmission power can be lowered by up to 1.6 dB compared to ordinary continuous transmission with equal average data rate. These results are however strongly dependent on the used radio environment. It is also showed that transmission timing provides increased system stability in case of rapid changes in the load situation.</p>

In recent years, a number of power control concepts have been studied and implementedeither in simulation or in practice for different communication systems. It is still the case that a great deal of research is being conducted within the area of energyefficient power control mechanisms for future wireless communication networksystems. However, only a limited amount of practical work has been implemented onreal test beds environment. The main goal of this thesis is to propose and develop newprototype Transmit Power Control Mechanisms (TPCM) on WARP (Wireless Open-Access Research Platform) boards for point-to-point communications, which are to bedeveloped and tested in an indoor environment. This work mainly focuses on the automaticpower control nodes, transmission and reception over-the-air. In this thesis, wehave designed and developed TPCM to adjust the power levels on a transmitter nodeby following the feedback (ACK) approach. In this case, the destination (receiver)node always sends the feedback (ACK) to transmitter node during every successfultransmission of message signal and the main focus is on a reduction in the packetloss rate (PLR), an increase in the packet reception rate (PRR) and the capacity ofthe nodes. In this real work, we have developed and measured the results based ontwo functions namely, with and without packet window function power control mechanisms. According to the measurements section, both with and without function powercontrol mechanisms proved to have better performances for different tunable parameters.If both functions are compared, then the with window function power controlmechanism was shown to produce better performances than the without windowpower control mechanism and it also converged faster than the without window function.If consideration was given to controlling a reduction in packet loss rate, thenthe with widnow function offered higher performances than those without the windowfunction. In this regard, it was found that the with window function has acheived amaximum packet reception rate than that for the without window function for differenttunable parameters. In relation to the power consumption scenario, it was determinedthat the without window fuction proved to produce energy saving performances thanthe with window function. There are several interesting aspects of the transmit powercontrol mechanisms highlighted in the results and discussion chapter.

The objective of this research is to investigate the power-control problem and analyze the network capacity in cognitive radio (CR) networks. For CR users or Secondary users (SUs), two spectrum-access schemes exist: namely, spectrum underlay and spectrum overlay. Spectrum overlay improves the spectrum utilization by granting SUs the authority to sense and explore the unused spectrum bands provided by PUs. in this scheme, designing effective spectrum-sensing techniques in PHY layer is the major concern. Spectrum underlay permits Sus to share the same spectrum bands with PUS at the same time and location. In this scheme, designing robust power control algorithms that guarantee the QoS of both primary and secondary transmissions is the main task. In this thesis, we first investigate the power-control problems in CR networks. Especially, we conduct two research works on power control for CDMA and OFDMA CR networks. Being aware of the competitive spectrum-access feature of SUs, the non-cooperative game theory, as a standard mathematics, is used to study the power-control problem. Note that game-theoretical approaches provide distributed solutions for CR networks,, which fits the needs of CR networks. However, it requires channel state information (CSI) exchange among all SUs, which will cause great overheads in the large network deployment. To gain better network scalability and design more robust power-control algorithm for any hostile radio-access environments, we propose a reinforcement-learning-based repeated power-control game that solve the problem for the first time. The left part of the dissertation is to study the throughput capacity scaling of the newly arising cognitive ad hoc networks (CRAHNs). Stimulated by the seminal work of Gupta and Kumar, the fundamental throughput scaling law for large-scale wireless ad hoc networks has become an active research topic. This research is of great theoretical value for wireless ad hoc networks. Our proposed research studies it in the scenario of CRAHNs under the impact of PU activity. It is a typical and important network scenario that has never been studied yet. We do believe this research has its unique value, it will have an impact to the research community.

Wireless Mesh Networking is envisioned as an economically viable paradigm and a promising technology in providing wireless broadband services. The wireless mesh backbone consists of fixed mesh routers that interconnect different mesh clients to themselves and to the wireline backbone network. In order to approach the wireline servicing level and provide same or near QoS guarantees to different traffic flows, the wireless mesh backbone should be quality-of-service (QoS) aware. A key factor in designing protocols for a wireless mesh network (WMN) is to exploit its distinct characteristics, mainly immobility of mesh routers and less-constrained power consumption. In this work, we study the effect of varying the transmission power to achieve the required signal-to-interference noise ratio for each link and, at the same time, to maximize the number of simultaneously active links. We propose a QoS-aware routing framework by using transmission power control. The framework addresses both the link scheduling and QoS routing problems with a cross-layer design taking into consideration the spatial reuse of the network bandwidth. We formulate an optimization problem to find the optimal link schedule and use it as a fitness function in a genetic algorithm to find candidate routes. Using computer simulations, we show that by optimal power allocation the QoS constraints for the different traffic flows are met with more efficient bandwidth utilization than the minimum power allocations.

The goal of this Master's thesis was to solve resource allocation problems in wireless networks through the implementation of a lightweight simulation platform. The spectrum and power resources of wireless networks have to be efficiently used to accommodate the growing number of wireless terminals and the massive increase of data transferred by their applications. The major problem that needs to be tackled is interference, which significantly limits the performance of wireless systems. In this thesis, the resource allocation of interest was the joint problem of scheduling and power control with Quality of Service (QoS) constraints. The Signal-to-Interference-plus-Noise Ratio (SINR) was used to quantify QoS. This thesis studied the recently proposed mixed-integer linear programming (MILP) formulation of the problem. Due to the scheduling component, the problem is inherently combinatorial and NP-hard, therefore computationally expensive and difficult to solve in tractable time. A simulation platform was implemented in order to automate and facilitate the solving process.As a starting point, wireless channels and channel modeling issues were studied. Then, the platform was implemented to simulate random instances of multi-cellular wireless networks, with several mobile stations per cell, and generate the corresponding channels. Finally, the platform was extended to use the GNU Linear Programming Kit (GLPK) API in order to optimally solve the aforementioned formulated problem for various inputs of generated channels.Tests of the simulation platform were performed to check the consistency of the results. Indeed, the output results satisfied the initial expectations regarding the SINR constraints and the formulation. Moreover, they were produced in reasonable time. An analysis of the output results was presented.This thesis resulted in a configurable and lightweight simulation platform which is able to solve the MILP-formulated resource allocation problem. The simulation platform is basic and does not cover all the aspects of multi-cellular wireless networks and wireless channels. Due to its modularity, it can be extended in a future project.

Power control is one of the technologies used to utilize the radio resources as efficient as possible in WCDMA. The transmission power is adjusted to transmit with the lowest power level possible while the required received signal quality is maintained. Since there are large variation in channel quality over time, the power has to be adjusted to compensate for these variations. During moments of bad channel conditions a high transmission power has to be used which will to a greater extent interfere with other users in the system. To solve this problem a concept called transmission timing was proposed. The basic idea is that the transmitter avoids data transmission during the short periods of bad channel conditions caused by fast fading. Higher bit rates can be used to compensate for this when the channel conditions are good. In this thesis the performance of transmission timing applied to uplink data transmissions is evaluated. This is accomplished through a theoretical analysis as well as simulations of a cellular system using transmission timing. Lowered transmission power is achieved and thus lowered interference is induced. Simulations showed that the transmission power can be lowered by up to 1.6 dB compared to ordinary continuous transmission with equal average data rate. These results are however strongly dependent on the used radio environment. It is also showed that transmission timing provides increased system stability in case of rapid changes in the load situation.

Wireless Mesh Networking is envisioned as an economically viable paradigm and a promising technology in providing wireless broadband services. The wireless mesh backbone consists of fixed mesh routers that interconnect different mesh clients to themselves and to the wireline backbone network. In order to approach the wireline servicing level and provide same or near QoS guarantees to different traffic flows, the wireless mesh backbone should be quality-of-service (QoS) aware. A key factor in designing protocols for a wireless mesh network (WMN) is to exploit its distinct characteristics, mainly immobility of mesh routers and less-constrained power consumption. In this work, we study the effect of varying the transmission power to achieve the required signal-to-interference noise ratio for each link and, at the same time, to maximize the number of simultaneously active links. We propose a QoS-aware routing framework by using transmission power control. The framework addresses both the link scheduling and QoS routing problems with a cross-layer design taking into consideration the spatial reuse of the network bandwidth. We formulate an optimization problem to find the optimal link schedule and use it as a fitness function in a genetic algorithm to find candidate routes. Using computer simulations, we show that by optimal power allocation the QoS constraints for the different traffic flows are met with more efficient bandwidth utilization than the minimum power allocations.