Power saving for extending session lifetime is an important research subject in wireless sensor networks (WSNs). Recognizing the fact that Quality of Service can be deteriorated by insufficient transmit power, this work studies how to minimize power consumption while achieve a satisfactory QoS of data streams in WSNs. A cross-layer routing scheme is proposed to maximize session lifetime by adjusting individual transmit power on intermediate nodes. The thesis is divided into two major parts for analyzing our proposition. In the first part, we propose an efficient routing scheme with optimal power management and on-demand quality control for WSNs. When source node issues a QoS provision for route discovery, an adjustment of transmit power is computed for each pass-by node by taking into its individual wireless link account. Then, an optimal route associated with lowest power consumption and consistent QoS can be selected among all of the candidate routes. In the second part, by following the definition of QoS criterion in the first part, we further consider the problem of how to balance the needs on constraining end-to-end quality and prolonging lifetime in an established route. The problem can be interpreted as a non-linear optimization paradigm, which is then shown to be a max-min composite formulation. To solve the problem, we propose two methods, (1) route-associated power management (RAPM), and (2) link-associated power management (LAPM). Considering computation-restricted sensor nodes, the RAPM scheme is two-fold simplification; not only it can reduce power computation, but it also quickly determines the longest lifetime and proper transmit power for nodes. On the other hand, if computational cost is not a major concern in a sink node, the LAPM algorithm is more suitable than RAPM to solve the lifetime maximization problem, in terms of accuracy. Finally, we analyze the performance of these two methods. The results demonstrate that the LAPM scheme is very comparable to a heuristic approach.

Emerging body-wearable sensor devices for continuous health monitoring are severely energy constrained and yet required to offer high communication reliability under fluctuating channel conditions. This thesis aims at investigating the opportunities and challenges in the use of dynamic radio transmit power control for prolonging the lifetime of such devices. We first present extensive empirical evidence that the wireless link quality can change rapidly in body area networks, and a fixed transmit power results in either wasted energy (when the link is good) or low reliability (when the link is bad). We then propose a class of schemes feasible for practical implementation that adapt transmit power in real-time based on feedback information from the receiver. We show conservative, balanced, and aggressive adaptations of our scheme that progressively achieve higher energy savings of 14%-30% in exchange for higher potential packet losses (up to 10%). We also provide guidelines on how the parameters can be tuned to achieve the desired trade-off between energy savings and reliability within the chosen operating environment. Finally, we implement and profile our scheme on a MicaZ mote based platform, demonstrating that energy savings are achievable even with imperfect feedback information, and report preliminary results on the ultra-low-power integrated healthcare monitoring platform from our collaborating partner Toumaz Technology. In conclusion, our work shows adaptive radio transmit power control as a low-cost way of extending the battery-life of severely energy constrained body wearable devices, and opens the door to further optimizations customized for specific deployment scenarios.

The fuel economy of Fuel Cell Vehicles (FCVs) is affected by various factors such as the fuel cell efficiency, the regenerative energy capturing, the power control strategy, the vehicle driving patterns, the degree of hybridization between fuel cells and energy storage systems, and so on. In this thesis, a new power control strategy is proposed to improve fuel economy for hybrid FCVs considering the fuel cell efficiency and battery energy management. In order to show the power flows due to the proposed power control strategy and analyze the fuel economy, an overall vehicle simulation for three types of FCVs is implemented. The results show that the fuel economy can be improved by operating the fuel cell system within the specified high efficiency region and managing the state of charge (SOC) of the battery for absorbing regeneration energy effectively.

Downlink power control and beamforming designs in wireless system have been a recent research focus. To achieve reliable and efficient designs, good estimation of wireless channel knowledge is desired. However, the presence of uncertain channel knowledge due to constant changing radio environment will cause performance degradation in system designs. Thus the mismatches between the actual and presumed channel state information (CSI) may frequently occur in practical situations. Robust power control and beamforming were introduced considering the channel uncertainty. In this thesis, a new robust downlink power control solution based on worst-case performance optimization is developed. Our approach explicitly models uncertainties in the downlink channel correlation (DCC) matrices, uses worst-case performance optimization and guarantees that the quality of service (QoS) constraints are satisfied for all users using minimum amount of power. An iterative algorithm to find the optimum power allocation is proposed. The key in the iteration is the step to solve an originally non-convex problem to obtain worst-case uncertainty matrices. When the uncertainty is small enough to guarantee that the DCC matrices are positive semidefinite, we obtain a closed-form solution of this problem. When the uncertainty is large, we transform this intractable problem into a convex problem. Simulation results show that our proposed robust downlink power control using the approach of worst-case performance optimization converges in a few iterations and reduces the transmission power effectively under imperfect knowledge of the channel condition. / Thesis / Master of Applied Science (MASc)

In the present day, Ad Hoc wireless networks are quite convenient in a local area. But hidden terminal problems and exposed terminal problems exits in Ad Hoc networks. So how to avoid these problems and add channel bandwidth utilization efficiently in MAC (Medium Access Control) layer is a very critical topic. A number of MAC protocols have been presented to overcome these drawbacks, such as RTS / CTS ¡V based and busy tone ¡V based protocol. In this paper, we proposed a dynamic power control scheme, Adjustable Power Control Protocol (APC). APC is based on the concept of power level with broadcasted message. The basic idea is sender should not interfere with other hosts¡¦ going transmissions. Sender would use a suitable power level to send its data so as to overcome above problems. Our simulations show that the channel utilizations of APC is indeed increased in the same time.

Most mobile nodes are operated using batteries, protocols which conserve energy are of interest. The Dynamic Directional Power Control Protocol (DDPC) is a protocol that dynamically varies the energy used in directional transmission to increase the battery life of the transmitter without sacrificing connectivity with the receiver. The advantage of DDPC is that it takes into account the remaining battery power of a node before changing its transmission power. DDPC can achieve a higher network lifetime when compared to a network where nodes use a fixed transmit power level. Meanwhile DDPC dynamically reduces the energy consumed by a node in transmission. It can also reach nodes far from the transmitter by using directional antennas.

Since 2004, when the Long Term Evolution (LTE) was first proposed to be publicly available in the year 2009, a plethora of new characteristics, techniques and applications have been constantly enhancing it since its first release, over the past decade. As a result, the research aims for LTE-Advanced (LTE-A) have been released to create a ubiquitous and supportive network for mobile users. The incorporation of heterogeneous networks (HetNets) has been proposed as one of the main enhancements of LTE-A systems over the existing LTE releases, by proposing the deployment of small-cell applications, such as femtocells, to provide more coverage and quality of service (QoS) within the network, whilst also reducing capital expenditure. These principal advantages can be obtained at the cost of new challenges such as inter-cell interference, which occurs when different network applications share the same frequency channel in the network. In this thesis, the main challenges of HetNets in LTE-A platform have been addressed and novel solutions are proposed by using self-organising network (SON) management approaches, which allows the cooperative cellular systems to observe, decide and amend their ongoing operation based on network conditions. The novel SON algorithms are modelled and simulated in OPNET modeler simulation software for the three processes of resource allocation, mobility management and interference coordination in multi-tier macro-femto networks. Different channel allocation methods based on cooperative transmission, frequency reuse and dynamic spectrum access are investigated and a novel SON sub-channel allocation method is proposed based on hybrid fractional frequency reuse (HFFR) scheme to provide dynamic resource allocation between macrocells and femtocells, while avoiding co-tier and cross-tier interference. Mobility management is also addressed as another important issue in HetNets, especially in hand-ins from macrocell to femtocell base stations. The existing research considers a limited number of methods for handover optimisation, such as signal strength and call admission control (CAC) to avoid unnecessary handovers, while our novel SON handover management method implements a comprehensive algorithm that performs sensing process, as well as resource availability and user residence checks to initiate the handover process at the optimal time. In addition to this, the novel femto over macro priority (FoMP) check in this process also gives the femtocell target nodes priority over the congested macrocells in order to improve the QoS at both the network tiers. Inter-cell interference, as the key challenge of HetNets, is also investigated by research on the existing time-domain, frequency-domain and power control methods. A novel SON interference mitigation algorithm is proposed, which is based on enhanced inter-cell interference coordination (eICIC) with power control process. The 3-phase power control algorithm contains signal to interference plus noise ratio (SINR) measurements, channel quality indicator (CQI) mapping and transmission power amendments to avoid the occurrence of interference due to the effects of high transmission power. The results of this research confirm that if heterogeneous systems are backed-up with SON management strategies, not only can improve the network capacity and QoS, but also the new network challenges such as inter-cell interference can also be mitigated in new releases of LTE-A network.

[pt] Este trabalho examina várias técnicas de alocação de canais, e alocação de potência, baseados no parâmetro relação sinal ruído interferência. Os esquemas de controle de potência que utilizam este parâmetro, são resolvidos a partir da determinação do raio espectral de uma matriz obtida a partir da manipulação da matriz de ganhos de enlace. Foi provado que é possível resolver esta matriz por outro método baseado em determinantes, e também foi mostrado que este método permite se obter rapidamente uma alocação de canais factível. Além disso, várias técnicas de otimização da alocação de potência foram estudadas, ampliando a abordagem para uma visão completa do problema de alocação de potência. / [en] This work examines several techniques of allocation of canals, and allocation of power, based in the parameter relation signal noise interference. The projects of power control that use this parameter, are decided from the determination of the spectral ray of a matrix gotten from the manipulation of the matrix of profits of enlace. It was proven that it is possible to solve this matrix through another method based on determinative, and also was shown that this method allows to get a feasible allocation of canals quickly. Moreover, several techniques of otimization of the power allocation had been studied, extending the boarding for a complete vision of the problem of power allocation.

<p>In an optimal power control scheme for a Code Division Multiple Access (CDMA) system all mobile stations signals should arrive to the base station at equal power. If not, stronger singals may cause too much interference and block out weaker ones. Commonly used power control schemes utilizes the Signal to Interference Ratio (SIR) to design a Power Control Command (PCC) to adjust the transmit power of the mobile station. A significant problem within the conventional methods is the slow SIR recovery due to deep channel fades. Conventional methods base the PCC on the previous channel state when in fact, the channel state may have significantly changed when transmission occurs. These channel changes may cause the SIR to drop or rise drastically and lead to uncontrollable Multi Access Interference (MAI) resulting in power escalation and making the system unstable. In order to overcome power escalation and improve the recovery from deep fades a novel power control method has been developed. Based on Linear Quadratic Control and Kalman filtering for channel prediction this method designs the PCC based on the coming channel state instead of the current. This optimizes the PCC for the channel state where transmission occurs. Simulations show that this control scheme outperforms previous methods by making the impacts of the deep fades less severe on the SIR and also improves the overall SIR behaviour.</p>

In an optimal power control scheme for a Code Division Multiple Access (CDMA) system all mobile stations signals should arrive to the base station at equal power. If not, stronger singals may cause too much interference and block out weaker ones. Commonly used power control schemes utilizes the Signal to Interference Ratio (SIR) to design a Power Control Command (PCC) to adjust the transmit power of the mobile station. A significant problem within the conventional methods is the slow SIR recovery due to deep channel fades. Conventional methods base the PCC on the previous channel state when in fact, the channel state may have significantly changed when transmission occurs. These channel changes may cause the SIR to drop or rise drastically and lead to uncontrollable Multi Access Interference (MAI) resulting in power escalation and making the system unstable. In order to overcome power escalation and improve the recovery from deep fades a novel power control method has been developed. Based on Linear Quadratic Control and Kalman filtering for channel prediction this method designs the PCC based on the coming channel state instead of the current. This optimizes the PCC for the channel state where transmission occurs. Simulations show that this control scheme outperforms previous methods by making the impacts of the deep fades less severe on the SIR and also improves the overall SIR behaviour.