Thanks to the use of satellite technology, mobile personal telecommunications systems are able to provide communications simultaneously anywhere on the Earth's surface. The implementation of such systems raises several regulatory issues: after a brief explanation of the technical characteristics of different satellite systems in the first chapter, the second chapter will introduce the principles of space law relevant to satellite communications, with particular attention to the provisions which the development of global satellite telecommunication system could infringe. In the third chapter, there will be place for further analysis of international regulations established in the framework of the International Telecommunication Union and the World Trade Organisation, dealing more specifically with satellite telecommunications. The discipline established by the former organisation aims to the optimal management of the orbit and spectrum resources, particularly controversial because of the divergence of interests and exigencies of the member countries, whereas the latter intervened in the liberalisation of the telecommunication services, with the purpose to create an open environment for their diffusion. Furthermore, telecommunication activities are subjected to national regulation. The domestic discipline pertaining to global mobile satellite telecommunication services will be analysed in the fourth chapter, with particular attention to the U.S. Federal Communication Commission regulations and to the developments of Italian legislation in the light of the recent European initiatives in the field. National authorisation requirement conditions, in spite of the international effort toward regulatory harmonisation and liberalisation, are the key elements in the deployment of global mobile telecommunications services. National authorities should not continue to function solely on the basis of their national considerations, but be more flexible and open to cooperation, a

The allocation of resources among various project, units. or users is accomplished through the use of a systematic mechanism called resource allocation. The types of resources vary, depending upon the system under consideration. For instance, frequency spectrum and transmitter power might be the resources needed to allocate in an efficient manner on a cellular network system, so that the number of mobile users attended is maximized. On a Grid computing system, one needs to allocate resources such as processors, memory, disk space, and so on, in order that computational tasks run in the most efficient manner. In order to evaluate resource allocation techniques performances, we first need to evaluate whether a particular resource allocation problem can be cast in the mathematical formu-lation we are exploring. We also need to decide which mechanism will be used, or if a new one needs to be constructed to solve the particular formulation. Finally, we need to evaluate whether the solution obtained is better than those obtained from other techniques that might express and solve the allocation problem in different ways. In this dissertation, we propose a new resource allocation technique for a system described only by a formulation known as the Multichoice Multidimensional Knapsack Problem, or MMKP. We also propose and evaluate resource allocation techniques on two other sys¬tems: a cellular network and a Grid computing system; in this regard, the resource alloca¬tion problem is not expressed as an MMKP, although the formulations used are particular cases of the MMKP. The MMKP formulation is not applied because its use would not have allowed us to make a fair performance comparison with other more commonly used allo¬cation techniques. However, we believe that as more complex tasks are demanded from systems where resource allocation mechanisms are needed, an MMKP formulation could more suitably represent the allocation problem. Numerical results indicate that the resource allocation techniques explored in this work present a better performance than previous techniques. Numerical results also indicate that the use of the proposed techniques and the use of suitable optimization criteria can be used to achieve a number of resource allocation goals.

The delay tolerant networks (DTNs) is characterized by frequent disconnections and long delays of links among devices due to mobility, sparse deployment of devices, attacks, and noise, etc. Considerable research efforts have been devoted recently to DTNs enabling communications between network entities with intermittent connectivity. Unfortunately, mobile devices have limited energy capacity, and the fundamental problem is that traditional power-saving mechanisms are designed assuming well connected networks. Due to much larger inter-contact durations than contact durations, devices spend most of their life time in the neighbor discovery, and centralized power-saving strategies are difficult. Consequently, mobile devices consume a significant amount of energy in the neighbor discovery, rather than in infrequent data transfers. Therefore, distributed energy efficient neighbor discovery protocols for DTNs are essential to minimize the degradation of network connectivity and maximize the benefits from mobility. In this thesis, we develop sleep scheduling protocols in the medium access control (MAC) layer that are adaptive and distributed under different clock synchronization conditions: synchronous, asynchronous, and semi-asynchronous. In addition, we propose a distributed clock synchronization protocol to mitigate the clock synchronization problem in DTNs. Our research accomplishments are briefly outlined as follows: Firstly, we design an adaptive exponential beacon (AEB) protocol. By exploiting the trend of contact availability, beacon periods are independently adjusted by each device and optimized using the distribution of contact durations. The AEB protocol significantly reduces energy consumption while maintaining comparable packet delivery delay and delivery ratio. Secondly, we design two asynchronous clock based sleep scheduling (ACDS) protocols. Based on the fact that global clock synchronization is difficult to achieve in general, predetermined patterns of sleep schedules are constructed using hierarchical arrangements of cyclic difference sets such that devices independently selecting different duty cycle lengths are still guaranteed to have overlapping awake intervals with other devices within the communication range. Thirdly, we design a distributed semi-asynchronous sleep scheduling (DSA) protocol. Although the synchronization error is unavoidable, some level of clock accuracy may be possible for many practical scenarios. The sleep schedules are constructed to guarantee contacts among devices having loosely synchronized clocks, and parameters are optimized using the distribution of synchronization error. We also define conditions for which the proposed semi-asynchronous protocol outperforms existing asynchronous sleep scheduling protocols. Lastly, we design a distributed clock synchronization (DCS) protocol. The proposed protocol considers asynchronous and long delayed connections when exchanging relative clock information among nodes. As a result, smaller synchronization error achieved by the proposed protocol allows more accurate timing information and renders neighbor discovery more energy efficient. The designed protocols improve the lifetime of mobile devices in DTNs by means of energy efficient neighbor discoveries that reduce the energy waste caused by idle listening problems.

This thesis investigates the problem of interaction of electromagnetic radiation with human tissues. A Finite Difference Time Domain (FDTD) code has been developed to model a cellular phone radiating in the presence of a human head. In order to implement the code, FDTD difference equations have been solved in a computational domain truncated by a Perfectly Matched Layer (PML). Specific Absorption Rate (SAR) calculations have been carried out to study safety issues in mobile communication.

Information access suffers tremendously in wireless networks because of the low correlation between content transferred across low-bandwidth wireless links and actual data used to serve user requests. As a result, conventional content access mechanisms face such problems as unnecessary bandwidth consumption and large response times, and users experience significant performance degradation. In this dissertation, we analyze the cause of those problems and find that the major reason for inefficient information access in wireless networks is the absence of any user-activity awareness in current mechanisms. To solve these problems, we propose three user-activity aware strategies for mobile information access. Through simulations and implementations, we show that our strategies can outperform conventional information access schemes in terms of bandwidth consumption and user-perceived response times.

Mobile computing devices like handhelds are becoming ubiquitous and so is computing embedded in cyber-physical systems like cameras, smart sensors, vehicles, and many others. Further, the computation and communication resources present in these settings are becoming increasingly powerful. The resulting, rich execution platforms are enabling increasingly complex applications and system uses. These trends enable richer execution platforms for running ever more complex distributed applications. This thesis explores these opportunities (i) for cooperative mobile platforms, where the combined resources of multiple computing devices and the sensors attached to them can be shared to better address certain application needs, and (ii) for distributed platforms where opportunities for cooperation are further strengthened by virtualization. The latter offers efficient abstractions for device sharing and application migration that enable applications to operate across dynamically changing and heterogeneous systems without their explicit involvement. An important property of cooperative distributed platforms is that they jointly and cooperatively provide and maintain the collective resources needed by applications. Another property is that these platforms make decisions about the resources allocated to certain tasks in a decentralized fashion. In contrast to volunteer computing systems, however, cooperation implies the commitment of resources as well as the commitment to jointly managing them. The resulting technical challenges for the mobile environments on which this thesis is focused include coping with dynamic network topology, the runtime addition and removal of devices, and resource management issues that go beyond resource usage and scheduling to also include topics like energy consumption and battery drain. Platform and resource virtualization can provide important benefits to cooperative mobile platforms, the key one being the ability to hide from operating systems and applications the complexities implied by collective resource usage. To realize this opportunity, this thesis extends current techniques for device access and sharing in virtualized systems, particularly to improve their flexibility in terms of their ability to make the implementation choices needed for efficient service provision and realization in the mobile and embedded systems targeted by this work. Specifically, we use middleware-based approaches to flexibly extend device and service implementations across cooperative and virtualized mobile platforms. First, for cooperating platforms, application-specific overlay networks are constructed and managed in response to dynamics at the application level and in the underlying infrastructure. When virtualizing these platforms, these same middleware techniques are shown capable of providing uniform services to applications despite platform heterogeneity and dynamics. The approach is shown useful for sharing and remotely accessing devices and services, and for device emulation in mobile settings.

<p>SIP is receiving much attention these days and it seems to be the most promising candidate as a signaling protocol for the current and future IP telephony services. Realizing this, there is the obvious need to provide a certain level of quality comparable to the traditional telephone service signalling system. Thus, we identified the major costs of SIP, which were found to be delay and security. This thesis discusses the costs of SIP, the solutions for the major costs, and the development of a low cost SIP application. The literature review of the components used to develop such a service is discussed, the networks in which the SIP is used are outlined, and some SIP applications and services previously designed are discussed. A simulation environment is then designed and implemented for the instant messaging service for wireless devices. This environment simulates the average delay in LAN and WLAN in different scenarios, to analyze in which scenario the system has the lowest costs and delay constraints.</p>

During the last decade, the demand for ubiquitous data access and spontaneous data exchange has increased significantly and with predictions to grow even further in the future. To satisfy such increasing demand, new protocols, standards and products addressing wireless networking have emerged. Mobility often implies the need for easy and fast deployment without any prior notice or any underlying infrastructure and with little or no administrative effort. This kind of self-organising mobile network is called an ad hoc network (AHN) or mobile ad hoc network (MANET). A mobile ad hoc network (MANET) is an attractive solution when it is not feasible to set up a fixed network infrastructure due to time or monetary constraints, eg. historical, and disaster sites or military operations. Another application field is in spontaneous self-organisation of mobile entities, such as for logistics, traffic control and conference. / This thesis is mainly focused on performance analysis and performance improvement of ad hoc networks. Based on these themes, we identify that congestion is one of the most important factors degrading the performance of ad hoc networks. We then propose a multi-path routing protocol with load balance policy which reduces the network congestion and hence improves the network performance significantly. The protocol is also shown, using simulation, to achieve a lower average end-to-end packet delay. We also propose a comprehensive theoretical framework modelling the overheads, congestions, connection throughput and average packet delay. The theoretical framework is shown to be consistent with the simulation results. It is also important to emphasise that the framework allows us to select routes that guarantee a better performance. They can also indicate in the first place whether for a particular network, using multi-path routing will bring any improvement. Next, we carry out a literature review on the performance of TCP in ad hoc networks. Despite its good performance in wired networks, TCP has been shown to perform very badly in ad hoc networks. It is mainly caused by high packet loss rate due to link breakage and channel errors. We propose a new coding technique which reduces the packet loss rate and thus improves the network performance. We also study the impact of wireless channels in ad hoc networks. The study leads to an innovative cross layer design, employing the predictability of the Rayleigh wireless channel, to improve the performance of ad hoc networks. In order to study the cross layer design analytically, we propose new comprehensive theoretical models for the IEEE 802.11 medium access control protocol (MAC) and the Rayleigh channel. BY combining these two models, we are able to analyse the cross layer design in detail. It is expected that this framework will motivate future theoretical studies of ad hoc networks. / Thesis (PhDTelecommunications)--University of South Australia, 2005.

Thesis (MEngineering)--University of South Australia, 2001

Success of Wireless Sensor Networks (WSN) largely depends on whether the deployed network can provide desired area coverage with acceptable network lifetime. In hostile or harsh environments such as enemy territories in battlefields, fire or chemical spills, it is impossible to deploy the sensor nodes in a predeter- mined regular topology to guarantee adequate coverage. Random deployment is thus more practical and feasible for large target areas. On the other hand, random deployment of sensors is highly susceptible to the occurrence of coverage holes in the target area. A potential solution for enhancing the existing coverage achieved by random deployments involves the use of mobility capable sensors that would help fill the coverage holes. This thesis seeks to address the problem of determining the current coverage achieved by the non-deterministic deployment of static sensor nodes and subsequently enhancing the coverage using mobile sensors. The main contributions of this dissertation are the design and evaluation of MAPC (Mobility Assisted Probabilistic Coverage), a distributed protocol for ensuring area coverage in hybrid wireless sensor networks. The primary contribution is a pragmatic approach to sensor coverage and maintenance that we hope would lower the technical barriers to its field deployment. Most of the assumptions made in the MAPC protocol are realistic and implementable in real-life applications e.g., practical boundary estimation, coverage calculations based on a realistic sensing model, and use of movement triggering thresholds based on real radio characteristics etc. The MAPC is a comprehensive three phase protocol. In the first phase, the static sensors calculate the area coverage using the Probabilistic Coverage Algorithm (PCA). This is a deviation from the idealistic assumption used in the binary detection model, wherein a sensor can sense accurately within a well defined (usually circular) region. Static sensors execute the PCA algorithm, in a distributed way, to identify any holes in the coverage. In the second phase, MAPC scheme moves the mobile nodes in an optimal manner to fill these uncovered locations. For different types of initial deployments, the proposed movement algorithms consume only 30-40% of the energy consumed by the basic virtual force algorithm. In addition, this thesis addresses the problem of coverage loss due to damaged and energy depleted nodes. The problem has been formulated as an Integer Linear Program and implementable heuristics are developed that perform close to optimal solutions. By replacing in-operational nodes in phase three, MAPC scheme ensures the continuous operation of the WSN. Experiments with real mote hardware were conducted to validate the boundary and coverage estimation part of the MAPC protocol. Extensive discrete event simulations (using NS2) were also performed for the complete MAPC protocol and the results demonstrate that MAPC can enhance and maintain the area coverage by efficiently moving mobile sensor nodes to strategic positions in the uncovered area.