This dissertation examines the design and application of network coding (NC) strategies to enhance the performance of communication networks. With its ability to combine information packets from different, previously independent data flows, NC has the potential to improve the throughput, reduce delay and increase the power efficiency of communication systems in ways that have not yet been fully utilized given the current lack of processing power at relay nodes. With these motivations in mind, this dissertation presents three main contributions that employ NC to improve the efficiency of practical communication systems. First, the integration of NC and erasure coding (EC) is presented in the context of wired networks. While the throughput gains from utilizing NC have been demonstrated, and EC has been shown to be an efficient means of reducing packet loss, these have generally been done independently. This dissertation presents innovative methods to combine these two techniques through cross-layer design methodologies. Second, three methods to reduce or limit the delay introduced by NC when deployed in networks with asynchronous traffic are developed. Also, a novel opportunistic approach of applying EC for improved data reliability is designed to take advantage of unused opportunities introduced by the delay reduction methods proposed. Finally, computationally efficient methods for the selection of relay nodes and the assignment of transmit power values to minimize the total transmit power consumed in cooperative relay networks with NC are developed. Adaptive power allocation is utilized to control the formation of the network topology to maximize the efficiency of the NC algorithm. This dissertation advances the efficient deployment of NC through its integration with other algorithms and techniques in cooperative communication systems within the framework of cross-layer protocol design. The motivation is that to improve the performance of communication systems, relay nodes will need to perform more intelligent processing of data units than traditional routing. The results presented in this work are applicable to both wireless and wired networks with real-time traffic which exist in such systems ranging from cellular and ad-hoc networks to fixed optical networks.

This dissertation presents adaptation techniques that can achieve high spectral efficiency for single user multiple-input multiple-output (MIMO) systems. Two types of adaptation techniques, adaptive modulation and adaptive powe allocation, are employed to adapt the rate and the transmit power to fading channels. We start by investigating the adaptive modulation subject to a certain bit-error-ratio (BER) constraint, either instantaneous BER constraint or average BER constraint. The resulting average spectral efficiencies are obtained in closed-form expressions. It turns out that, by employing the average BER constraint, we can achieve the optimal average spectra efficiency at the cost of prohibitive computational complexity. On the other hand, instantaneous BER constraint leads to inferior performance with little computational complexity. In order to achieve comparable performance to the average BER constraint with limited complexity, a non-linear optimization method is proposed. To further enhance the average spectra efficiency, adaptive power allocation schemes are considered to adjust the transmit power across the temporal domain or the spatial domain, depending on the specific situation. Provided the closed-form expressions of the average spectral efficiency, the optimal MIMO coding scheme that offers the highest average spectral efficiency under the same circumstances can be identified. As we take into account the effect of imperfect channel estimation, the adaptation techniques are revised to tolerate interference introduced by the channel estimation errors. As a result, the degradation with respect to the average spectral efficiency is in proportion to signal-to-noise ratio (SNR). In order to facilitate fast development and verification of the adaptation schemes proposed for various MIMO systems, a reconfigurable Link Layer Simulator (LiLaS) which accommodates a variety of wireless/wireline applications is designed in the environment of MATLAB/OCTAVE. The idea of the simulator is originated from Software Defined Radio (SDR) and evolved to suit Cognitive Radio (CR) applications. For the convenience of modification and reconfiguration, LiLaS is functionally divided into generic blocks and all blocks are parameterized. / QC 20100812

In this thesis, novel designs for adaptive power amplifiers, capable of maintaining excellent performance at dissimilar signal parameters, are presented. These designs result in electronically reconfigurable, single-ended and Doherty power amplifiers (DPA) that efficiently sustain functionality at different driving signal levels, highly varying time domain characteristics and wide-spread frequency bands. The foregoing three contexts represent those dictated by the diverse standards of modern communication systems. Firstly, two prototypes for a harmonically-tuned reconfigurable matching network using discrete radio frequency (RF) microelectromechanical systems (MEMS) switches and semiconductor varactors will be introduced. Following that is an explanation of how the varactor-based matching network was used to develop a high performance reconfigurable Class F-1 power amplifier. Afterwards, a systematic design procedure for realizing an electronically reconfigurable DPA capable of operating at arbitrary centre frequencies, average power levels and back-off efficiency enhancement power ranges is presented. Complete sets of closed-form equations are outlined which were used to build tunable matching networks that compensate for the deviation of the Doherty distributed elements under the desired deployment scenarios. Off-the-shelf RF MEMS switches are used to realize the reconfigurability of the adaptive Doherty amplifiers. Finally, based on the derived closed-form equations, a tri-band, monolithically integrated DPA was realized using the Canadian Photonics Fabrication Centre (CPFC??) GaN500 monolithic microwave integrated circuit (MMIC) process. Successful integration of high power, high performance RF MEMS switches within the MMIC process paved the way for the realization of the frequency-agile, integrated version of the adaptive Doherty amplifier.

In this thesis, I study fluctuations and rare events of time-additive observables of discrete-time Markov chains on finite state spaces. The observable of interest is the mean node connectivity visited by a random walk running on instances of an Erdős-Rényi (ER) random graph. I implement and analyze the Adaptive Power Method (APM) which converges to the driven process, a biased random walk defined through a control parameter that simulates trajectories corresponding to rare events of the observable in the original dynamics. The APM demonstrates good convergence and accurately produces the desired quantities from a single trajectory. Due to the bulk-dangling-chain structure in the ER graph, the driven process seems to undergo a dynamical phase transition (DPT) for infinitely large graphs, meaning the behavior of the trajectories changes abruptly as the control parameter is varied. Observations show that the random walk visits two distinct phases, being de-localized in the bulk or localized in the chain. Through two simpler models capturing the bulk-dangling-chain property of the ER graph I study how the DPT occurs as the graph size increases. I observe that the trajectories of the driven process near the transition show intermittent behavior between the two phases. The diverging time scale of the DPT is found to be the average time that the random walk spends in a phase before it transitions to the other one. On the ER graph the trajectories are also intermittent but the form of the time scaling remains open due to computational limits on the graph size.

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The aim of this thesis is to explore the possibility of a dual-purpose electric vehicle. The vehicle should be able to be used for both commuting and racing. It also aims to describe different power limiting methods and their effect on performance. Lastly it hopes to see if the Swedish laws, as written today are reasonable. An electric longboard has been constructed for this purpose and several tests have been performed. A list of goals were set up for the board prototype. These included power output, running time, and that the board should have an audible warning device. The findings demonstrated that all tested power limiting methods worked and that the “Simple power limiting” method provided quickest movement over a fixed distance. Most of the goals were met by the prototype and the board’s two modes worked as planned. While the law is reasonable it can be improved to cover the diversity of electric vehicles. Further work may include better measurements and implementation of a dual microcontroller system. / Syftet med detta arbete är att testa möjligheten med ett två-läges personligt fordon. Fordonenet ska kunna användas för både pendling och tävling. Arbetet har även testat olika energilimeteringsmetoder samt undersökt hur dessa metoder påverkar prestandan. Arbetet har även försökt besvara frågan om det svenska lagarna, som det är skrivna idag, är lämpliga. En elektrisk longboard har konstruerats och flera test utförts. Ett antal målsättningar har definerats för prototypen. Dessa inkluderar: effekt, körtid och att brädan bör ha en ringklocka. Resultaten visar att alla metoder fungerade och att “Simple power limiting” var den som gav snabbast rörelse över den bestämda sträckan. Det flesta av målen nåddes av prototypen och brädans två lägen fungerade som tänkt. Dagens lagar är rimliga men kan förbättras för att täcka mångfalden av elektriska fordon. Framtida arbete kan inkludera bättre mätningar och implementation av ett system med två mikrokontroller.

The aim of this thesis is to explore the possibility of adual-purpose electric vehicle. The vehicle should be ableto be used for both commuting and racing. It also aims todescribe different power limiting methods and their effecton performance. Lastly it hopes to see if the Swedish laws,as written today are reasonable. An electric longboard hasbeen constructed for this purpose and several tests havebeen performed.A list of goals were set up for the board prototype. Theseincluded power output, running time, and that the boardshould have an audible warning device.The findings demonstrated that all tested power limitingmethods worked and that the “Simple power limiting” methodprovided quickest movement over a fixed distance. Most ofthe goals were met by the prototype and the board’s twomodes worked as planned. While the law is reasonable itcan be improved to cover the diversity of electric vehicles.Further work may include better measurements and implementationof a dual microcontroller system. / Syftet med detta arbete är att testa möjligheten med etttvå-läges personligt fordon. Fordonenet ska kunna användasför både pendling och tävling. Arbetet har även testat olikaenergilimeteringsmetoder samt undersökt hur dessa metoderpåverkar prestandan. Arbetet har även försökt besvarafrågan om det svenska lagarna, som det är skrivna idag, ärlämpliga. En elektrisk longboard har konstruerats och fleratest utförts.Ett antal målsättningar har definerats för prototypen. Dessainkluderar: effekt, körtid och att brädan bör ha en ringklocka.Resultaten visar att alla metoder fungerade och att “Simplepower limiting” var den som gav snabbast rörelse över denbestämda sträckan. Det flesta av målen nåddes av prototypenoch brädans två lägen fungerade som tänkt. Dagens lagarär rimliga men kan förbättras för att täcka mångfaldenav elektriska fordon. Framtida arbete kan inkludera bättremätningar och implementation av ett system med två mikrokontroller.