In the cooperative networks, in order to combat the 50% spectrum efficiency loss of the half-duplex limit imposed on most of the mobile terminals, this thesis studies the high efficiency two-path model and proposes the selective two-path model to recover the efficiency loss and explore the diversity. In the two-path succussive relay cooptative transmission, the 50% loss in data rate can be well avoided because the source can continuously transmit to two relays alternatively. Due to the concurrent transmission from source and relays, however, inter-relay interference may significantly damage the performance. Various practical interference cancellation algorithms are introduced in the thesis. Two practical relay protocols for the two-path model are studied: the amplify-forward protocol and decode-forward protocol. With the application of these two protocols, the interference emerges with different effects towards the final received signal. As demonstrated in the simulation parts, we show that the proposed algorithms can suppress the interference effectively, thus achieve satisfied performance without the sacrifice of other resources, e.g. time, frequency or space. " With the help of information theoretical tools, the analysis of the proposed selective two-path model proves that it can achieve diversity order of M if there are M potential relay candidates. Such diversity is obtained without the reduction of spectrum efficiency. The selective two-path model can combat the fading of wireless channels and improve the robustness of the system without the cost of power or bandwidth. With the recovered 50% spectrum efficiency, such model can be used in the cooperative networks which require high data rate and spectrum efficiency, for example, cellular networks or wireless sensor networks.

The unique contribution of this thesis is a resource allocation solution capable of handling mixed media applications within the constraints of a 60 GHz wireless network. The challenges of multimedia wireless transmission include high bandwidth requirements, delay intolerance and wireless channel availability. A performance analysis for a 60 GHz wireless network using the IEEE 802 .1S.3c protocol considers the impact of variable rate traffic on network throughput. The impact of network size on the optimal contention access period and superframe duration of the 802.1S.3c MAC layer is identified. A series of optimization techniques applied to the resource allocation problem are explored and compared against the criteria of execution time/network overhead and ability to support applications with both convex and non-convex utility functions. The Particle Swarm Optimization (PSO) method • emerges as the best solution for quality-rate optimized network utility maximization (NUM). A new channel time allocation PSO (CTA-PSO) is proposed with network-l inked swarm size, an increased diversity function and a learning method based on the personal best, Pbest, results of the swarm. CTA-PSO demonstrates improved Convergence speed while maintaining the QoS improvement of the NUM. A novel PTV utility function is also proposed in this work to describe the relationship between allocated channel time and the user perceived quality of the transmission. A further extension to CT A-PSG overcomes the issue of link blockage due to the short wavelength at 50 GHz. CTA-PSO demonstrates improved performance compared with resource allocation on the basis of fixed bandwidth allocation to individual services 50 that pre-planning of network resources is not required. The multimedia resource allocation solution presented in this thesis provides a practical solution for real time wireless networks.

This thesis contributes to the development and characterization of millimetre-wave personal area networks (WPANs) in the 60 GHz frequency band. Single-carrier and multi carrier transmission techniques are considered in the implementation of a 64.8 GHz WPAN capable of achieving a reliable indoor link. Thus, single-carrier with frequency domain equalization (SC- FDE) and orthogonal frequency-division multiplexing (OFDM) communication schemes were designed and implemented to mitigate the multi path fading of the 60 GHz indoor channels. As a result, a complete millimetre-wave transceiver operating at 64.8 GHz, with up to 100 Mh/s data-rate utilizing 16-QAM modulation scheme is realized. The re-programmability offered by field-programmable gate arrays (FP GAs) along with their capability of performing real-time digital signal processing has been exploited. A FPGA-based platform is employed to prototype the hardware implementation of the baseband digital signal processing modules of the proposed 64.8 GHz millimetre-wave transceiver. The design and the construction of the complete baseband transceiver is based on a software-defined radio (SDR) concept, which was achieved by a software and hardware implementation of different functional modules of the digital baseband transceiver. The baseband transceiver has been successfully interfaced with a 64.8 GHz radio system which was built using commercially available discrete RF modules. The back- to-back performance of both baseband transceiver and the 64.8 GHz WPAN has been validated. The performance of the implemented transceiver has been characterized in different transmission scenarios, within different environments, and with line-of-sight and non-line-of-sight conditions. This characterization has been performed by measuring the bit-error rate (BER) against signal-to-noise ratio (SNR) in different communication scenarios. The work presented in this thesis shows that a 64.8 GHz WPAN can be successfully implemented with either SC-FDE or OFDM communication scheme. Also, the advantage of SC-FDE and its ability to be a prominent alternative to the OFDM in multi path channels is presented.

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E-business systems provide the infrastructure whereby parties interact electronically via business transactions. At peak loads, these systems are susceptible to large volumes of transactions and concurrent users and yet they are expected to maintain adequate performance levels. Over provisioning is an expensive solution. A good alternative is the adaptation of the system, managing and controlling its resources. We address these concerns by presenting a model that allows fast evaluation of performance metrics in terms of measurable or controllable parameters. The model can be used in order to (a) predict the performance of a system under given or assumed loading conditions and (b) to choose the optimal configuration set-up for certain controllable parameters with respect to specified performance measures. Firstly, we analyze the characteristics of E-business systems. This analysis leads to the analytical model, which is sufficiently general to capture the behaviour of a large class of commonly encountered architectures. We propose an approximate solution which is numerically efficient and fast. By mean of simulation, we prove that its accuracy is acceptable over a wide range of system configurations and different load levels. We further evaluate the approximate solution by comparing it to a real-life E-business system. A J2EE application of non-trivial size and complexity is deployed on a 2-tier system composed of the JBoss application server and a database server. We implement an infrastructure fully integrated on the application server, capable of monitoring the E-business system and controlling its configuration parameters. Finally, we use this infrastructure to quantify both the static parameters of the model and the observed performance. The latter are then compared with the metrics predicted by the model, showing that the approximate solution is almost exact in predicting performance and that it assesses the optimal system configuration very accurately.

Peer-to-Peer (P2P) networks have become prevalent recently, thanks in large part to the publicity surrounding file-sharing networks, but P2P is evolving to encompass a wide- ranging set of applications. For many of these, a resource discovery mechanism is an essential basic service, but the properties of P2P networks make provision of this a nontrivial task. Solutions proposed have included central indexes, flooding and message forwarding, but the most promising appears to be the use of Distributed Hash Tables (DHTs). DHTs have been used to provide data lookup within logarithmic message costs whilst only requiring maintenance of limited amounts of routing state. One of the most widely known DHTs is Chord, which provides lookup in typically O(log n) hops across the network, where n is the number of nodes in the structure. Understanding that this message cost is proportional to the network size, our contribution is ROME (Reactive Overlay Monitoring and Expansion), a set of processes which run on top of the Chord DHT to provide control over network size. Every node acts as an autonomous agent in order to react to node underload and overload events, trying to maximise capacity utilisation and only increase the size of the ring when existing capacity is inadequate. Through simulation and calculation we show ROME can reduce the hop counts in networks where available node capacity exceeds workload, closely converging with that of Chord where capacity and workload become equal.

Mobile ad hoc networks (MANETs) have gained increasing attention from industry for their potential applications. MANETs allow devices to communicate in areas with no pre-existing communication infrastructure. In MANETs, node mobility leads to dynamic changes in network topologies and fluctuations in network available bandwidth. The lack of infrastructural support means that communication nodes need to collaborate among themselves functioning as routers (intermediate nodes) for other nodes. This places additional processing and communication loads onto the communication nodes and opens up doors to more active attacks by intermediate nodes. It is also worth noting that mobile nodes are typically battery powered, and they are more restrictive in terms of storage space and processing capabilities than their wired counterpart. These MANET features indicate that achieving QoS in MANETs should be done in the most cost-effective manner. In this thesis, a novel Adaptive Trust-aware Location-based (ATL-QoS) framework is proposed. The ATL-QoS framework can harvest fluctuating available bandwidth in the underlying network to deliver high priority traffic in various network conditions. The novelty of the framework lies in that it uses single path and multiple path deliveries and packet duplication over multiple path, in an adaptive manner, in an attempt to increase high priority traffic delivery with minimum bandwidth overhead costs. The framework handles low and high priority traffic in a differential manner. To implement these ideas, two novel ATL-QoS components are designed: (1) a Trust-Aware Dynamic Location-based (improved version) (TADLV2) multiple path discovery protocol and (2) a path Selection, traffic Allocation, and path Verification (SAV) solution. The TADLV2 protocol is designed to discover multiple path between a pair of communication nodes with minimum bandwidth overheads, we first designed TADL protocol and then an improved version of TADL, TADLV2. The SAV solution is designed to increase high priority traffic delivery success. These ATL-QoS framework ideas are implemented and evaluated using the NS-2 simulation and compared against the most relevant protocol in the literature. The simulation study shows that ATL-QoS outperforms the relevant protocol in terms of reducing routing overheads and increasing packet delivery ratios. These enhancements making ATL-QoS more effective in providing QoS.

Today two major technological forces drive the telecommunication era: the wireless cellular systems and the Internet. As these forces converge, the demand for new services, increasing bandwidth and ubiquitous connectivity continuously grows. The next-generation mobile systems will be based solely or in a large extent, on the Internet Protocol (IP). This thesis begins by addressing the problems and challenges faced in a multimedia, IP-based Wireless LAN environment. The ETSI HiperLAN/2 system has been mainly selected as the test wireless network for our theoretical and simulation experiments. Apart from the simulations, measurements have been taken from real life test scenarios, where the IEEE 802.11 system was used (UniS Test-bed). Furthermore, a brief overview of the All-IP network infrastructure is presented. An extension to the conventional wireless (cellular) architecture, which takes advantage of the IP network characteristics, is considered. Some of the trends driving the 3G and WLANs developments are explored, while the provision of quality of service on the latter for real-time and non-real-time multimedia services is investigated, simulated and evaluated. Finally, an efficient and catholic Q0S framework is proposed. At the same time, the multimedia services should be offered in a seamless and uninterrupted manner to users who access the all-IP infrastructure via a WLAN, meeting the demands of both enterprise and public environments anywhere and anytime. Thus providing support for mobile communications not only in terms of terminal mobility, as is currently the case, but also for session, service and personal mobility. Furthermore, this mobility should be available over heterogeneous networks, such as WLANs, IJMTS, as well as fixed networks. Therefore, this work investigates issues such as, multilayer and multi-protocol (SIP-Mobile IP-Cellular IP) mobility management in wireless LAN and 3G domains. Several local and global mobility protocols and architectures have been tested and evaluated and a complete mobility management framework is proposed. Moreover, integration of simple yet efficient authentication, accounting and authorisation mechanisms with the multimedia service architecture is an important issue of IP-based WLANs. Without such integration providers will not have the necessary means to control their provided services and make revenue from the users. The proposed AAA architecture should support a robust AAA infrastructure providing secure, fast and seamless access granting to multimedia services. On the other hand, a user wishing a service from the All-IP WLAN infrastructure needs to be authenticated twice, once to get access to the network and the other one should be granted for the required service. Hence, we provide insights into these issues by simulating and evaluating pre-authentication techniques and other network authentication scenarios based on the wellknown IEEE 802.lx protocol for multimedia IP-based WLANs.

As the need for faster, safer and more efficient healthcare delivery increases, medical consultants seek new ways of implementing a high quality telemedical system, using innovative technology. Until today, teleconsultation (the most common application of Telemedicine) was performed by transferring the patient from the Accidents and Emergency ward, to a specially equipped room, or by moving large and heavy machinery to the place where the patient resided. Both these solutions were unpractical, uneconomical and potentially dangerous. At the same time wireless networks became increasingly useful in point-of-care areas such as hospitals, because of their ease of use, low cost of installation and increased flexibility. This thesis presents an integrated system called MedLAN dedicated for use inside the A&E hospital wards. Its purpose is to wirelessly support high-quality live video, audio, high-resolution still images and networks support from anywhere there is WLAN coverage. It is capable of transmitting all of the above to a consultant residing either inside or outside the hospital, or even to an external place, thorough the use of the Internet. To implement that, it makes use of the existing IEEE 802.11b wireless technology. Initially, this thesis demonstrates that for specific scenarios (such as when using WLANs), DICOM specifications should be adjusted to accommodate for the reduced WLAN bandwidth. Near lossless compression has been used to send still images through the WLANs and the results have been evaluated by a number of consultants to decide whether they retain their diagnostic value. The thesis further suggests improvements on the existing 802.11b protocol. In particular, as the typical hospital environment suffers from heavy RF reflections, it suggests that an alternative method of modulation (OFDM) can be embedded in the 802.11b hardware to reduce the multipath effect, increase the throughput and thus the video quality sent by the MedLAN system. Finally, realising that the trust between a patient and a doctor is fundamental this thesis proposes a series of simple actions aiming at securing the MedLAN system. Additionally, a concrete security system is suggested, that encapsulates the existing WEP security protocol, over IPSec.