This thesis focuses on the effect of variable time delay of multipath components on WCDMA mobiles. Most of the existing research treats the time delay as a constant factor when testing the mobile performance under multipath fading condition. In this thesis, three variable time delay functions (birth-death, sinusoidal and linear) which are generated due to the end user mobility are suggested as possible variable time delay condition to be studied and their effect on mobile receivers to be analysed.

No description available.

No description available.

No description available.

Recent years have witnessed widespread adoption of mobile devices. Whereas initial popularity was driven by voice telephony services, capabilities are now broadening to allow an increasing range of data orientated services. Such services serve to extend the range of sensitive data accessible through such devices and will in turn increase the requirement for reliable authentication of users. This thesis considers the authentication requirements of mobile devices and proposes novel mechanisms to improve upon the current state of the art. The investigation begins with an examination of existing authentication techniques, and illustrates a wide range of drawbacks. A survey of end-users reveals that current methods are frequently misused and considered inconvenient, and that enhanced methods of security are consequently required. To this end, biometric approaches are identified as a potential means of overcoming the perceived constraints, offering an opportunity for security to be maintained beyond pointof- entry, in a continuous and transparent fashion. The research considers the applicability of different biometric approaches for mobile device implementation, and identifies keystroke analysis as a technique that can offer significant potential within mobile telephony. Experimental evaluations reveal the potential of the technique when applied to a Personal Identification Number (PIN), telephone number and text message, with best case equal error rates (EER) of 9%, 8% and 18% respectively. In spite of the success of keystroke analysis for many users, the results demonstrate the technique is not uniformly successful across the whole of a given population. Further investigation suggests that the same will be true for other biometrics, and therefore that no single authentication technique could be relied upon to account for all the users in all interaction scenarios. As such, a novel authentication architecture is specified, which is capable of utilising the particular hardware configurations and computational capabilities of devices to provide a robust, modular and composite authentication mechanism. The approach, known as IAMS (Intelligent Authentication Management System), is capable of utilising a broad range of biometric and secret knowledge based approaches to provide a continuous confidence measure in the identity of the user. With a high confidence, users are given immediate access to sensitive services and information, whereas with lower levels of confidence, restrictions can be placed upon access to sensitive services, until subsequent reassurance of a user's identity. The novel architecture is validated through a proof-of-concept prototype. A series of test scenarios are used to illustrate how IAMS would behave, given authorised and impostor authentication attempts. The results support the use of a composite authentication approach to enable the non-intrusive authentication of users on mobile devices.

Nowadays, a commonly used wireless network (i.e. Wi-Fi) operates with the aid of a fixed infrastructure (i.e. an access point) to facilitate communication between nodes when they roam from one location to another. The need for such a fixed supporting infrastructure limits the adaptability of the wireless network, especially in situations where the deployment of such an infrastructure is impractical. In addition, Wi-Fi limits nodes' communication as it only provides facility for mobile nodes to send and receive information, but not reroute the information across the network. Recent advancements in computer network introduced a new wireless network, known as a Mobile Ad Hoc Network (MANET), to overcome these limitations. MANET has a set of unique characteristics that make it different from other kind of wireless networks. Often referred as a peer to peer network, such a network does not have any fixed topology, thus nodes are free to roam anywhere, and could join or leave the network anytime they desire. Its ability to be setup without the need of any infrastructure is very useful, especially in geographically constrained environments such as in a military battlefield or a disaster relief operation. In addition, through its multi hop routing facility, each node could function as a router, thus communication between nodes could be made available without the need of a supporting fixed router or an access point. However, these handy facilities come with big challenges, especially in dealing with the security issues. This research aims to address MANET security issues by proposing a novel intrusion detection system that could be used to complement existing prevention mechanisms that have been proposed to secure such a network. A comprehensive analysis of attacks and the existing security measures proved that there is a need for an Intrusion Detection System (IDS) to protect MANETs against security threats. The analysis also suggested that the existing IDS proposed for MANET are not immune against a colluding blackmail attack due to the nature of such a network that comprises autonomous and anonymous nodes. The IDS architecture as proposed in this study utilises trust relationships between nodes to overcome this nodes' anonymity issue. Through a friendship mechanism, the problems of false accusations and false alarms caused by blackmail attackers in global detection and response mechanisms could be eliminated. The applicability of the friendship concept as well as other proposed mechanisms to solve MANET IDS related issues have been validated through a set of simulation experiments. Several MANET settings, which differ from each other based on the network's density level, the number of initial trusted friends owned by each node, and the duration of the simulation times, have been used to study the effects of such factors towards the overall performance of the proposed IDS framework. The results obtained from the experiments proved that the proposed concepts are capable to at least minimise i f not fully eliminate the problem currently faced in MANET IDS.

No description available.

No description available.

Modem digital radio systems using high symbol rates are more susceptible to multipath interference than traditional systems. These systems need to adapt to the propagation environment in order to minimise transmission errors while minimising transmitted power and interference between systems. Mobile terminals will experience variations in the propagation environment as they move. Both fixed and mobile terminals will experience variations in the propagation environment as the environment changes with time. The extent and speed of environmental changes are necessary inputs to the design process for new radio systems. Previous reported measurements aimed at characterising the radio environment have been made over short durations of a few tens of milliseconds. In this thesis measurements over periods of up to 15 seconds are described and the results analysed to quantify longer term variations. The channel sounder developed at UMIST was used for the measurements and the environment was sampled over a number of paths in Manchester and Durham. The data from each 15 second measurement was split into two ensembles, one from the first 7.5 seconds and one from the remaining 7.5 seconds so that statistics from different times could be compared. The number of multipath components, the mean delay and the RMS delay spread were extracted for each 20 msec interval of each measurement. Cumulative Distribution Functions formed from the data from the two ensembles of each measurement showed differences between the ensembles. The results from Kolmogorov-Smirnof tests confirmed the differences for all three statistics. Attempts to model the variation of the statistics by fitting Normal and Weibull distributions to the data failed in most cases. PDFs of the RMS delay spread were multimodal suggesting that insufficient data was available. It has been concluded that there is temporal variation in the radio environment but that more measurement data will be needed for the variation to be characterised.

Wideband Code Division Multiple Access (WCDMA) is one of the technologies for third generation systems. In a CDMA system, all users interfere with each others, therefore the CDMA system is interference limited. The users, who suffer from a strong shadow effect or that are far away from the BS, need more power to reach it. In this case, the users may transmit at their maximum allowed power without satisfying their Quality of Service. Therefore, this would leave some mobiles in outage and also create too much interference to the neighboring cells. One-way to counter this problem and therefore to improve the capacity is to increase the number of BSs. But this solution cannot be efficient as it significantly increases the network infrastructure cost. Alternative techniques that involve less planning and are quick to deploy appear to be more advantageous. Relaying is one of these techniques and is growing in importance for future wireless systems. In this thesis, a new radio access network based on combinations of multi-hop and star-topology architectures is proposed. The main objective of this thesis is to demonstrate achievable capacity gains under various relaying criteria compared with no-relaying (conventional) cellular architecture. In this new architecture, some intermediate nodes (mobile or fixed) located between the originating terminal and the BSs are used for the purpose of retransmitting the original packets. We show that under specific criteria and conditions the multihop concept indeed yields capacity gains. A number of different scenarios are defined and their relative performances are fully evaluated using an accurate dynamic system-level simulator. The capacity gains are compared to the case of no relaying/hopping. To demonstrate the achievable capacity gains, we use UMTS FDD and TDD modes. The proposed concepts and criteria for relaying are generic enough to be used with current and future radio access technologies. The results show that under certain conditions an uplink capacity gain of 30-40% is readily achievable with the multihop architecture.