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Femtocells Access Points (FAP) are low power, plug and play home base stations which are designed to extend the cellular radio range in indoor environments where macrocell coverage is generally poor. They offer significant increases in data rates over a short range, enabling high speed wireless and mobile broadband services, with the femtocell network overlaid onto the macrocell in a dual-tier arrangement. In contrast to conventional cellular systems which are well planned, FAP are arbitrarily installed by the end users and this can create harmful interference to both collocated femtocell and macrocell users. The interference becomes particularly serious in high FAP density scenarios and compromises the ensuing data rate. Consequently, effective management of both cross and co-tier interference is a major design challenge in dual-tier networks. Since traditional radio resource management techniques and architectures for single-tier systems are either not applicable or operate inefficiently, innovative dual-tier approaches to intelligently manage interference are required. This thesis presents a number of original contributions to fulfill this objective including, a new hybrid cross-tier spectrum sharing model which builds upon an existing fractional frequency reuse technique to ensure minimal impact on the macro-tier resource allocation. A new flexible and adaptive virtual clustering framework is then formulated to alleviate co-tier interference in high FAP densities situations and finally, an intelligent coverage extension algorithm is developed to mitigate excessive femto-macrocell handovers, while upholding the required quality of service provision. This thesis contends that to exploit the undoubted potential of dual-tier, macro-femtocell architectures an interference awareness solution is necessary. Rigorous evidence confirms that noteworthy performance improvements can be achieved in the quality of the received signal and throughput by applying cognitive methods to manage interference.

A Wireless Sensor Network (WSN) is composed of numerous spatially distributed, low cost, low power and multifunctional sensor nodes which can be used to monitor the surrounding environment. In mobile networks, the sensed data collected by the sensor nodes may move out of the area where it has been gathered (area of origin) with its carrying node. A problem may arise in this situation: when requesting the historical information of a specific area, it is possible that none of the nodes currently located in such area can provide the required information. This thesis addresses the issue of retaining data it its area of origin in an energy-constrained, infrastructure-less mobile Wireless Sensor Network. The concept of this “Data Hovering” has been defined in which the location-based data hovers in its area of origin by transmission between network nodes. Based on this concept, several policies need to be defined as well as considering the constraints of WSN including limited energy and limited transmission bandwidth. The existing related work has then been investigated by examining how it proposed to define the Data Hovering policies, in order to explore the limitations. It has been found that the existing approaches are not well suited to mobile WSN, due to the unique characteristics of WSN. In this thesis, an autonomous Data Hovering algorithm consisting of defined policies has been designed to improve the data retention (data availability) and the quality of the retained data which ensures that the retained data represents different information. The defined Data Hovering algorithm has been implemented in a network simulator and a baseline with simple policies has also been selected in order to be compared with the defined policies. The evaluation in terms of data availability, data quality and energy consumption has then been carried out to analyze the behaviours of the defined algorithm. Finally, the potential future work has been suggested.

This thesis considers the performance of OFDM in a non-linear satellite channel and mechanisms for overcoming the degradations resulting from the high PAPR in the OFDM signal in the specific satellite architecture. It was motivated by new S-DMB applications but its results are applicable to any OFDM system via satellites. Despite many advantages of OFDM, higher PAPR is a major drawback. OFDM signals are therefore very sensitive to non-linear distortion introduced by the power amplifiers and thus, significantly reduce the power efficiency of the system, which is already crucial to satellite system economics. Simple power amplifier back-off to cope with high OFDM PAPR is not possible. Two transmitter based techniques have been considered: PAPR reduction and amplifier linearization.

Mission-critical applications are potential future applications of wireless sensor networks (WSNs). These applications require that data delivery must be timely, reliable and energy-efficient. Most existing WSNs cannot support this mission-critical data delivery as they focus solely on the energy efficiency. A few recent studies improve data delivery performance but still fail to give strict performance guarantees. This thesis closes the outlined research gap by proposing novel solutions for timely, reliable and energy efficient data transport. The required performance is achieved by employing a tailor-made TDMA-based medium access control (MAC) protocol at the core of the wireless sensor network. In addition, two fundamentally different approaches for constructing such MAC protocols have been developed. The first approach called node-to-node framework employs a MAC protocol that provides timely data delivery between neighboring nodes and is used in conjunction with an analytical tool, called Sensor Network Calculus (SNC), to determine and ensure the maximum delivery time. The second approach called end-to-end framework uses a MAC protocol with a network-wide transmission schedule to calculate and guarantee the maximum delivery time. Both frameworks also utilize reliability control schemes and energy saving mechanisms to achieve the overall performance goal. This thesis details the design, implementation and evaluation of both frameworks. The evaluation results clearly demonstrate that the frameworks outperform existing approaches and efficiently enable the support of mission-critical applications. These results therefore emphasize that the presented research is necessary to overcome limitations of current WSNs. Furthermore, this thesis presents a performance comparison between the frameworks in order to gain knowledge of their relative merits and limitations. An insightful guideline for selecting a suitable framework to best serve a given deployment scenario is consequently provided.

Emergency Message (EM) dissemination in Vehicular Ad hoc Networks (VANETs) has attracted significant attention in Intelligent Transportation System (ITS) in recent years. Such dissemination mechanisms mostly rely on licensed Dedicated Short Range Communications (DSRC) systems such as IEEE 802.11p and IEEE PI609.1-4 standards. By timely broadcasting of emergency messages (EMs), drivers can avoid potentially dangerous accidents and experience a safer driving environment. As the result, a concern of the number of accidents is also reduced. Thus, an efficient broadcast protocol is required in this scenario. In this thesis, designs of robust broadcast protocols are considered for Emergency Message Dissemination in VANETs. It presents four innovative contributions. Firstly, a literature review as well as challenges and issues of the protocols designed for EM dissemination application are presented. Secondly, Priority-based Routing Protocol (PRP) and its reliability enhancement (PRP-RE) have been proposed as broadcast protocols for different types of EM disseminations, providing; 1) fully distributed broadcast protocol; 2) different Quality of Services (QoS) for different types of EMs: 3) maximum message dissemination distance per hop; and 4) high communication reliability. Thirdly, a more efficient and robust multi-hop broadcast protocol for time-critical EM disseminations is proposed as Trinary Partitioned Black-Burst based Broadcast Protocol (3P3B). A mini-DIPS in MAC sub-layer is introduced to give the time-critical EMs the highest priority access to the communication channel compared to other EMs. In addition, a trinary partitioning is designed to iteratively partition the communication area into small sectors, allowing only the furthest possible vehicle to perform EM forwarding. Therefore. 3P3B can increase dissemination speed and reduce contention period jitter. The performance evaluation results demonstrate that 3P3B outperforms benchmarks of the existing broadcast protocols in VANETs in terms of average message dissemination speed, message progress, communication delay, and packet delivery ratio. Finally, 3P3B-DTN is proposed based on an enhancement of 3P3B to deal with communications in a disruptive network with an introduction of EM store, carry, and forward to maximize packet delivery ratio while minimizing end-to-end delay. The performance evaluation results show that 3P3BDTN achieves higher packet delivery ratio than 3P3B even when the network is disrupted with a trade-off of higher end-to-end delay and overhead for those EMs, which would be lost otherwise.

The past decade has witnessed great strides in the networking field . New technologies such as fibre optics and ATM have made it possible to build networks with speeds ranging from hundreds of megabits to gigabits per second. There has been a. rapidly growing class of I/O intensive applications, such as those manipulating multiple media, made possible by the dramatic increase in hardware performance, and decreasing costs of computer hardware. Increasing network bandwidth is not leading to commensurate improvement in performance of end-user applications. The bottleneck lies within the end-hosts (workstations and servers) and is partly due to a lack of integration between the host network interface and the operating system. In addition, most current operating systems do not support I/O intensive applications well because they cannot transfer voluminous amounts of data efficiently. This is because improvements in memory performance have not kept pace with improvements in processor performance. The aim of this work is to improve operating system support for continuous media in the context of high-speed networks. An ATM host-interface has been built to enable both multimedia. and traditional data streams To be handled on general purpose operating systems. New process and memory models that provide a better integration of the operating system with the network interface are presented . This is achieved by using a memory mapped network interface. In order to evaluate the real-time performances of current operating systems, the effects of context switch times and interrupt latencies have been investigated. New data streaming styles are proposed to reduce or eliminate these overheads. The viability of the different techniques has been demonstrated by implementations and performance measurements. It is shown that with a careful integration of the operating system and the network interface it is possible to minimise or eliminate conventional overheads resulting from data copying, interrupt servicing and context switches.

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Recent years have witnessed a vast technological progress in the area of Quality of Service (QoS), mainly due to the emergence of multimedia networking and computing. QoS measurement and analysis have long been of interest to the networking research community. The major goals of this thesis are of two fold: Firstly, to investigate the effect of the QoS parameters on the overall QoS experienced by wireless networks. Secondly, to utilise the results in developing efficient mechanisms for intrusive and non-intrusive assessments of the performance of wireless ad hoc networks as well as the measurement of the available QoS for audio and videoconferencing applications over the IEEE 802.11 standard. To evaluate the network performance and the overall QoS of multimedia applications, new fuzzy logic and distance measure assessment approaches were developed taking into account the QoS parameters requirements of each application. The developed approaches essentially include measuring the main QoS parameters (delay, jitter and packet loss) and use them as input to the measurement systems, which combine them and produce an output that represents the instantaneous QoS. The devised approaches showed how the QoS can be measured without a need for complicated analytical mathematical models. In this study, several techniques were devised for estimating QoS. Firstly, a probe-based assessment method (active technique) was developed. In this method, special artificial monitoring packets were injected into the network. The overall QoS and its parameters were estimated by collecting statistics from these packets. It was possible to make reasonable inferences about the delay, throughput, packet losses and the overall average QoS using different probe rates. This technique showed some limitations for measuring the jitter. In addition, the rate of the monitoring packets played an essential role in the precision, level of resolution of estimated results and negatively impacted the network performance. Secondly, to overcome some of the drawbacks of the probing-based method, a new assessment technique was, subsequently, devised based on passive monitoring standard sampling methods. Unlike the active technique, the new method has the advantage of not adding an extra load to the network. In addition, it is not like the typical passive methods, which require the transfer and calculations of the whole captured data. Generally, all sampling schemes provided satisfactory measures of the overall QoS and its parameters and produced very acceptable bias and Relative Standard Error (RSE) result. Systematic sampling provided the most accurate estimates compared to the stratified and random approaches. In addition, after sample fraction of 2%, the estimated overall QoS bias from the actual QoS became constant and equal to -0.5% and RSE was less than 0.005 using both fuzzy and distance assessment systems. Thirdly, in order to overcome some negative aspects of inaccuracy and biasness caused by sampling techniques, a new scheme was proposed to correct these results to be closer to the actual traffic measurements. The new approach does not disturb the network performance (as in active methods), neither depends on the whole traffic (as in passive methods), nor bias the actual results (as in the standard sampling technique). Similarly, systematic sampling showed the best performance. Sample fractions, using the systematic sampling, greater than 2% gave an overall estimated QoS identical to the actual QoS because the obtained relative error was nearly constant and approximately close to zero using both assessment systems. The measured QoS can be used to optimise the received quality of the multimedia services along with the changing network conditions and to manage the utilisation of the network available resources especially for ad hoc networks. Overall, the findings of this study contribute to a method for drawing a realistic picture of the wireless multimedia networks QoS and provide a firm basis and useful insights on how to effectively design future QoS solutions.