Wireless technology has revolutionized the world of communications, enabling ubiquitous connectivity and leading every year to several new applications and services embraced by billions of users. To meet the increasing demand for high data-rate wireless services, standardization bodies and vendors released a new generation of standard-based devices capable to offer wide area high-speed and high-quality wireless coverage. More recently, wireless sensor networks (WSNs) have captured the attention of the industry society to migrate substantial parts of the traditionally wired industrial infrastructure to wireless technologies. Despite the increasing appetite for wireless services, the basic physical resource of these systems, the bandwidth, is limited. Therefore, the design of efficient network control mechanisms for optimizing the capabilities of complex networks is becoming an increasingly critical aspect in networking. In this thesis, we explore the application of optimization techniques to resource allocation in wireless systems. We formulate the optimal network operation as the solution to a network utility maximization problem, which highlights how system performance can be improved if the traditionally separated network layers are jointly optimized. The advantage of such cross-layer optimization is twofold: firstly, joint optimization across layers reveals the true performance limits that can be achieved by practical protocols, and is hence useful for network design or performance analysis; secondly, distributed optimization techniques can be used to systematically engineer protocols and signalling schemes that ensure the globally optimal system operation. Within this framework, we consider several challenging problems. The first one considers the design of jointly optimal power and end-to-end rate allocation schemes in multi-hop wireless networks that adhere to the natural time-scales of transport and physical layer mechanisms and impose limited signalling overhead. To validate the theoretical development, we present a detailed implementation of a cross-layer networking stack for DS-CDMA ad-hoc networks in the network simulator ns-2. This implementation exercise reveals several critical issues that arise in practice, but are typically neglected in the theoretical protocol design. Second, we consider networks employing resource scheduling at the data link layer, and we develop detailed distributed solutions for joint end-to-end communication rate selection, multiple time-slot transmission scheduling and power allocation that achieve the optimal network utility. We show with examples how the mathematical framework can be applied to optimize the resource allocation in spatial-reuse time division multiple access (S-TDMA) networks and orthogonal frequency division multiple access (OFDMA) networks. We then make a slight shift in focus, and consider off-line cross-layer optimization to investigate the benefits of various routing strategies in multi-hop networks, and apply these results to a techno-economical feasibility study of cellular relaying networks. Finally, we consider the design of efficient resource scheduling schemes for deadline-constrained real-time traffic in wireless sensor networks. Specifically, we develop theory and algorithms for time- and channel-optimal scheduling of networks operating according to the recent Wireless HART standard. / QC20100726

The use of low cost fixed wireless relays has been proposed as a way to deploy high data-rate networks at an affordable cost. During the last decade, significant academic and industrial research has been dedicated to relays. Protocol architectures for cellular-relaying networks are currently considered for standardization as part of both IEEE 802.16 and 3GPP. Various relaying techniques have successfully been commercialized over the years. This dissertation concentrates on the particular case of large scale use of low cost relays, for which focus is put on signal processing and radio resource allocation, rather than on antenna and radio frequency (RF) design, or on network planning. A key question is how low relay cost is low enough for a relaying architecture to be viable from an economic point of view? We develop a framework for evaluating the viability of relaying solutions. The framework is based on a comparison between the relaying architectures and traditional single-hop cellular architectures. This comparative analysis is done from an operator perspective, and is formulated as a network-dimensioning problem. The associated investment decisions are based on financial measures (cost or profit) and taken under technical constraints (throughput, coverage, etc.).First, we consider a large number of traditional dimensioning scenarios, in which the radio network is design for a predefined traffic demand and target quality of service level. We show that the use of low cost relays can indeed be viable, but that the cost savings vary strongly from case to case and often are only modest. Due to the half-duplex nature of the low cost relays, these relays are best suited for providing coverage to guaranteed data-rates, at low end-to-end spectral efficiency, and in environments with strong shadow fading. The type of environment and the placement of relays are more important than the specific protocols and algorithms used in the network. Therefore, traditional network planning remains an essential and challenging task, which is unlikely to be replaced by large-scale (unplanned) use of relays.Second, we suggest a new direction of research in which the viability of relays is judged considering the entire life cycle of a radio network. We give several examples in which the temporary use of relays is economically viable, especially if the service uptake is slow or the uncertainty about the future demand is high. This is particularly relevant if the last-mile cost of a network is dominated by the backhaul transmission cost, and if relaying is implemented as a feature of an access point, rather than as a new device type. / QC 20100812

This thesis mainly studies the downlink of a wireless multiuser system, where the transmitter has limited knowledge about the communication channels of the users. Key techniques to improve the performance of such systems are, for instance, multiple antennas, multiuser diversity and orthogonal frequency-division multiple access (OFDMA). Common for these techniques is that, to exploit them fully, a cross-layer approach has to be adopted. This means that the scheduling and the signal designs are done jointly and based on parameters from several communication layers. Multiuser diversity can be used to significantly increase system throughput in wireless communication systems. The idea is to schedule users when they experience good channel conditions and let them wait when the channels are weak. In this thesis, several aspects of OFDMA systems that exploit multiuser diversity are investigated. An adaptive reduced feedback scheme for OFDMA is proposed. It significantly reduces the total feedback overhead while maintaining a multiuser diversity gain. The scheme uses clusters of sub-carriers as feedback units and feeds back information about the fading peaks only. It adapts to the number of users so that less feedback per user is required if there are many users in the system. With such a selective feedback scheme, there is a risk that the scheduler has no instantaneous channel quality information for some parts of the spectrum. Better uses for these sub-carriers are investigated. In addition, an alternative based on the the channel quality feedback of some uniformly spaced sub-carriers is proposed. The scheduler estimates the channel quality on the other sub-carriers. Channel-aware scheduling is necessary in order to exploit multiuser diversity. A modified proportional fair (PF) scheduler is proposed. It incorporates individual target bit-rates and delays and a tunable fairness level. An opportunistic beamforming scheme for clustered OFDMA is presented and evaluated. A key aspect of the opportunistic beamforming scheme is that it induces artificial frequency selectivity for users with relatively flat channels. Several aspects of the proposed system are evaluated by means of simulations. In the simulations, the clustered beamforming with the modified PF scheduler performs better than three comparison systems. The modified PF scheduler manages to divide the resources according to the user targets, while at the same time exploiting the multiuser diversity as well as the standard PF algorithm. In many scenarios, the largest gains from having multiple antennas at the basei station come from space-division multiple access (SDMA). In the downlink, this means that data is transmitted to several users simultaneously by using several beams. Opportunistic space-division OFDMA is proposed and evaluated. An enhancement that exploits temporal channel correlation is able to boost the throughput significantly. SDMA based on subspace packings is proposed and evaluated. A set of beamforming matrices (a subspace packing) is made a priori available at the base-station and at all users. In each block, one of the matrices is used for multi-beam transmission. The users pick and feed back the index of one preferred column (beam) from one of the matrices, and the corresponding SINR, which includes all potential inter-beam interference. This enables scheduling of spatially compatible users and accurate rate adaptation, with relatively little feedback. Three different subspace packings are considered and evaluated with simulations. For the i.i.d. Rayleigh fading channel, Grassmannian subspace packings were the best choice. Moreover, a method to further reduce the feedback for large packings is proposed and evaluated. It is based on the arrangement of beams in a graph and the feedback of a neighbor index. Numerical results show that the feedback can be significantly reduced with only small performance losses, even for relatively fast fading channels. / QC 20100819

Multimedia communications over packet networks, and in particular the voice over IP (VoIP) application, have become an integral part of society. However, the unreliable and heterogeneous nature of packet networks has led to a best-effort delivery of services. Delay, limitation of bandwidth, and packet-loss rate all affect the quality of service (QoS). In this thesis, we address two important network impairments in the design of robust multimedia communication systems: packet delay-variation and packet-loss. Paper A considers the mitigation of the effect of packet delay-variation for audio communications by introducing a buffer at the receiver side. A new adaptive playout scheduling approach is proposed to control the buffering length, or, equivalently, the packet playout deadlines, in response to varying network conditions. A Wiener process is used to model the fluctuation of the buffering length without any playout adjustment. The playout scheduling problem is then reformulated as a stochastic impulse control problem by taking the playout adjustment as the control signal. The proposed approach is shown to be the optimal solution to the new control problem. It is demonstrated experimentally that the proposed approach provides improved perceived conversional quality. Papers B, C and D address the packet-loss issue. Paper B focuses on the design of a low-complexity packet-loss concealment (PLC) method that is compatible with existing speech codecs for VoIP application. The new method is rigorously motivated based on the autoregressive (AR) speech model and the minimum mean squared error (MMSE) criterion. The effect of model estimation error on the prediction of the missing speech segment is also considered and an upper bound for the prediction error is derived. Both the theoretical and experimental results provide insight in the performance of the heuristically designed PLC methods. On the other hand, Paper C and D consider an active packet-loss-resilient coding scheme, namely multiple description coding (MDC). In general, MDC can be used for the transmission of any media data. Paper C derives a simple and accurate approximation of the rate-distortion lower bound of a particular multiple- description scenario and then demonstrates that the performance loss of some practical MD systems can be evaluated easily with the new approximation. Paper D studies the performance limit of a vector Gaussian multiple description scenario. An outer bound to the rate-distortion region is derived, and the outer bound is tight when the problem specializes to the scalar Gaussian case. / QC20100830

Wireless sensor networks have been proposed as a cost effective and easy to deploy alternative to traditional wired systems in a multitude of application scenarios ranging from industrial automation to healthcare monitoring. They are expected to enable an unparalleled number of new services that will bring countless benefits to society. However, low power communications of sensor nodes operating in unlicensed bands face several challenges and are easily corrupted by transmissions of other collocated wireless networks. This problem has recently raised reliability concerns which have been tremendously enhanced by the proliferation of wireless devices we have been witnessing during the last years in the few available regions of the spectrum. This dissertation studies how to achieve reliable communications by proposing different ways for the energy aware management of the radio interference problem. The use of wireless sensing technologies has been envisaged in a broad variety of settings: for this reason it is not possible to identify a unifying solution for the problem of interference, but rather it is necessary to tailor the design of communication schemes accounting for the specific communication paradigm adopted by sensors, the traffic pattern generated by the expected application, as well as for the channel conditions experienced by nodes. When packet transmissions are addressed to a single receiver, cognitive access schemes can be utilized and sensors can opportunistically select for their transmissions when to access a certain channel or which channel to access so as to avoid interference. We provide an energy aware design for communication schemes implementing these ideas and evaluate their energy performance by means of experiments using real hardware. Our results indicate that the first approach should be considered only for sporadic packet transmissions over channels presenting limited interfering activities; channel adaptation should instead be preferred for large bulks of data or when the risk of operating in heavily interfered frequency bands is high. We further propose and evaluate a novel adaptive frequency hopping algorithm: this algorithm has been shown to be very efficient in mitigating the negative effects of interference allowing at the same time to avoid the use of the energy costly spectrum sensing algorithms required by cognitive access schemes. However, none of these three approaches may be suitable for scenarios where packet transmissions are addressed to multiple receivers. To deal with the packet losses that nodes may experience over noisy or interfered channels we envisage the use of fountain codes and show how it is possible to engineer such a coding solution so as to reduce the complexity and overhead introduced by the encoding and decoding procedures. The resulting codes provide an efficient way for disseminating data over multi-hop wireless sensor networks. Results obtained in this dissertation can be of great utility for designers of sensor applications who can use them in order to select the most energy efficient way to achieve reliable interference-aware communications. / QC 20101124

Wireless Sensor Networks (WSNs) provide a way to bridge the gap between the physical and the virtual worlds. They promise unprecedented abilities to observe and understand large-scale, real-world phenomena at a fine spatial-temporal resolution. Their application in Developing Countries is evenmore interesting: they can help solve problems that affect communities. The number of potential applications in such an environment is huge: water monitoringand crop modeling are just two examples. This thesis will analyze the potential of WSNs in Developing Countries, and tackle three of the main problems that their deployment poses: 1. Power. Power consumption is an important issue in deployments. For WSN nodes this is a well-addressed issue. Most commercial solutions today assume that WSN gateways (the devices that provide the interface between the nodes and the network infrastructure) will encounter ideal scenarios in terms of power when deployed. In a Developing World scenario, the gateway must operate with bounded energy supplies. The gateway should have sufficient stored power to save sensed data with high probabilities of service interruptions due to power loss. 2. Connectivity. Network connectivity in many Developing Countries is unreliable. Data gathered by the sensor nodes (motes) must therefore be stored safely in the gateway and transferred when a network connection is available. WSN deployments can encounter different network topologies such as wired, wireless and mesh, and should be flexible enough to interact with each of them. A two layer architecture with long wireless links above a wireless sensor network is a practical alternative for providing connectivity in the access network. 3. Quality of WSN links. To implement reliable and robust sensor networks, we need to understand the variation of link quality and battery behavior in a real world environment. Low-power transmitters have a limited range, and it is important to understand communication patterns. Energy is the scarcest resource of WSN motes, and it determines the lifetime of WSNs. Motes are meant to be deployed in various environments, including remote and hostile regions; consequently, they must use little power and one need to make sure that all batteries last the same amount of time. Also, battery level has an impact on routing. There is still research to be carried out to make WSNs suitable for deploymen tin Developing Regions. Following the most recent developments of sensor networks, this thesis discusses what ICT4D researchers could do to accelerate the dissemination of this new technology and proposes prototype solutions for some of the three problems mentioned above. These include: • Efficient link quality models. Link quality models are important tools upon which the deployment of wireless sensor networks depends. They allow the selection of efficient working parameters that enable the information collected by sensor networks to be routed efficiently from WSN nodes to a sensor base station. Using two testbed WSNs based on two different technologies, we analyzed spatial and temporal behavior of link quality and derived good working parameters for sensor network deployments. These parameters have been used in related works to design new routing protocols for sensor networks. • Robust and flexible gateways. Building upon the assumption that a WSN gateway to be deployed in developing regions should be designed at low cost with battery backup to maintain a continuous supply of electric power in absence of power grid, we proposed in this thesis two low-cost solutions that 1) meet low-power consumption and high storage capabilities constraints 2) are based on web technologies and (3) allow long range deployment for information dissemination. These solutions are developed around two smart board systems. • Long wireless links. Besides power energy limitations, limited range is one of the main factors which has delayed large scale deployments of wireless sensor networks. Building upon the assumption that next generation sensor networks will be employed in multilayer network environments with a WiFi gateway network layered above islands of sensor networks, we presented the deployment of several long wireless links. These prototypes revealed that long distance links can be a practical, inexpensive alternative for connecting wireless sensor networks while providing access to Internet in Developing Countries. • Water quality management. We developed a water quality monitoring system to de deployed in Malawi. Water quality measurementadds another dimension to the issue of power consumption of the WSN system since one has to take into account the contribution of the energy consumed by the water quality sensors in the overall energy consumption of the water monitoring system. As low-power sensors for water quality are not yet commercially available, we proposed an energy consumption minimization strategy where a wake-up mechanism that triggers sleeping/wake-up modes is used to reduce energy consumption. / QC 20101207

No description available.

The purpose of this thesis is to discuss which policy tools government could use in order to help industries develop. Nowadays, the telecommunication industry is in the transitional stage in terms of the product life cycle. The characteristic of this stage is that the standard product has formed. Therefore, the research and development of the product focuses on the function, quality, customer satisfaction, and market acceptance in order to become the standard. In the meantime, there would be lots of enterprises launching the market. In order to meet the product development speed, the economic of scale becomes the competitive advantage, and the key issue would be the process innovation. According to the strategic group model developed by Amoco Co., this thesis divided the telecommunication industry into four strategic groups, which are the unique technique ability, low-cost advantage, market-oriented, and diversified strategic groups. Each strategic group has its own key successful factors, which point out how industry could innovate clearly. In addition, analyzing the national innovation system helps to find out which policy tools government could apply appropriately. The national innovation system includes government policies, and industrial innovation system, which consists of technology system and national environment. This thesis studies the national innovation system of Canada. Because the trend of telecommunication industry goes to the unified standard, we have to check the international status of Canada in order to understand her relationship and interaction with the world first. Furthermore, we would check the status quo of the Canadian industrial innovation system. According to the analysis of telecommunication industry and Canadian national innovation system, the major contribution of this thesis is to provide governments certain model to follow up. This model helps governments to take advantage of the limited resources and apply them to the adequate direction appropriately. On the other hand, enterprises could take advantage of this model as well. To sum up, this research provides certain model for both governments and enterprises to apply their limited resources in the adequate direction appropriately.

<p>A recent trend is to integrate sensing, communication, and computation into every aspect of our daily life, ranging from various user devices to physical environment. The goal is to give computer systems an awareness of the users and their situations, so that they can support their diverse interaction needs at anytime, any place. A major problem hindering achieving this promising goal is that the users usually play a passive role in these systems with little possibility to interfere with the processing. Additionally, there is no option for the user to prevent being monitored by the system.</p><p>This drawback stems from the lack of an independent and consistent user oriented viewpoint in current ubiquitous computing systems, which can easily result in the occurrence of user privacy invasion and misinterpretation of the user.</p><p>To overcome this problem, this thesis proposes a Person-Centric Context Aware System architecture, helping to preserve an independent representation for each individual user to different computer systems. The main idea embraced in this system architecture is that the users are the owners of their personal information, thus they should have the control of how their information will be used by others.</p><p>In the design of this system architecture, a number of important issues have been addressed with their corresponding solutions in terms of different system components. Among these issues, three are identified as the most crucial ones, and hence these issues have received most of our efforts to provide better solutions: Context Data Communication, Location Detection, and Communication Anonymity support. A prototype system constructed during the process of developing each specific solution is also presented. Together these comprise the main contributions of this thesis work. Finally, our concluding remarks are presented together with our planned future work, based on the current implementation of a Person-Centric Context Aware System.</p>

<p>This thesis addresses the problem of low-cost multicast delivery of multimedia content in future mobile networks. The trend towards reuse of existing infrastructure for cellular and broadcasting for building new systems is challenged, with respect to the opportunities for low cost service provision and scalable deployment of networks.</p><p>The studies outline significant potential of hybrid cellular-broadcasting infrastructure to deliver lower-cost mobile multimedia, compared to conventional telecom or broadcasting systems. Even with simple interworking techniques the achievable cost savings can be significant, at least under some specific settings.</p><p>The work starts with a foresight study shaped around four scenarios of the future, and continues with the introduction of a high-level framework for radio resource management in Ambient Networks. Two approaches on the hybrid system architecture are considered. The first one assumes different degrees of interworking between conventional cellular and broadcasting systems, in single and multi-operator environments. Second, is a broadcast only system where cellular sites are used for synchronized, complementary transmitters for the broadcasting site. In the first approach, the key issue is the multi-radio resource management, which is strongly affected by the degree of integration between the two networks. Two case studies deal with the problem of delivering, for lowest cost, a data item to a certain number of recipient users. A flexible broadcasting air interface, which offers several transmission data rates that can be dynamically changed, is demonstrated to significantly increase cost efficiency under certain conditions. An interesting result is that real-time monitoring of the user reception conditions is not needed, at least when multicast group is large. This indicates a high degree of integration between cellular and broadcasting networks may not by generally justified by visible cost savings.</p><p>Scalability of the hybrid infrastructure deployment is the main topic in the second approach. For a DVB-H type of network, the numerical evaluations show that achievement of economies of scale while increasing network capacity and coverage, by employing higher modulation and coding rate or installing new transmission sites, is difficult. Therefore, a technique based on application-layer forward error correction with Raptor codingA is suggested for enabling a flexible trading between system capacity, perceived coverage and delay, in the case of mobile users.</p>