Adoption of smart mobile devices (smartphones, wearables, etc.) is rapidly growing. There are already over 2 billion smartphone users worldwide [1] and the percentage of smartphone users is expected to be over 50% in the next five years [2]. These devices feature rich sensing capabilities which allow inferences about mobile device user’s surroundings and behavior. Multiple and diverse sensors common on such mobile devices facilitate observing the environment from different perspectives, which helps to increase robustness of inferences and enables more complex context detection tasks. Though a larger number of sensing modalities can be beneficial for more accurate and wider mobile context detection, integrating these sensor streams is non-trivial. This thesis presents how multimodal sensor data can be integrated to facilitate ro- bust and energy efficient mobile context detection, considering three important and challenging detection tasks: indoor localization, indoor-outdoor detection and human activity recognition. This thesis presents three methods for multimodal sensor inte- gration, each applied for a different type of context detection task considered in this thesis. These are gradually decreasing in design complexity, starting with a solution based on an engineering approach decomposing context detection to simpler tasks and integrating these with a particle filter for indoor localization. This is followed by man- ual extraction of features from different sensors and using an adaptive machine learn- ing technique called semi-supervised learning for indoor-outdoor detection. Finally, a method using deep neural networks capable of extracting non-intuitive features di- rectly from raw sensor data is used for human activity recognition; this method also provides higher degree of generalization to other context detection tasks. Energy efficiency is an important consideration in general for battery powered mo- bile devices and context detection is no exception. In the various context detection tasks and solutions presented in this thesis, particular attention is paid to this issue by relying largely on sensors that consume low energy and on lightweight computations. Overall, the solutions presented improve on the state of the art in terms of accuracy and robustness while keeping the energy consumption low, making them practical for use on mobile devices.

The following various multiple access schemes based on CDMA are investigated: Hybrid OCA-FD/SC-CDMA: Whereas conventional FD/SC-CDMA schemes do not permit adjacent carrier spectra to overlap, this scheme overlaps adjacent carrier spectra intentionally. Even though interference arises from adjacent carrier, higher chance of multipath diversity and spectrally efficiency is achieved in comparison with conventional FD/SC-CDMA. It will be shown that OCA compensates for capacity loss incurred by subdivision of available spectrum for frequency division multiplexing, and also achieves even higher capacity for chip waveforms with smooth spectral shape at no extra system complexity while merits of FD/CDMA such as lower complexity and higher diversity gain for noncoherent reception are still fully exploited. In terms of capacity, for flat fading channel and rectangular pulse cut off at mainlobe-null in frequency domain, FD/SC-CDMA combined with OCA schemes gives roughly 56% gain in comparison with SC-CDMA and conventional FD/SC-CDMA. For frequency selective channel and noncoherent reception, even higher gain is achievable. Hybrid slow frequency hopping (SFH)/SC-CDMA: Overlapped carrier allocation (OCA) schemes can be applied to hybrid SFH/SC-CDMA. In power controlled systems, SFH/SC-CDMA is known to be much worse than pure DS-CDMA in terms of capacity. Introduction of OCA to SFH/SC-CDMA improves capacity significantly, and consequently it becomes comparable to pure DS-CDMA whilst merits of frequency hopping such as strong immunity to near/far effect is preserved. FD/MC-CDMA: In this scheme, available spectrum is subdivided into multiple discrete subspectra, and they are interleaved. Then diversity gain becomes equal to that of ordinary MC-CDMA frequency diversity. As a result of less subcarriers than ordinary MC-CDMA, equaliser becomes less complicated. Guard interval imposed to overcome timing synchronisation error and intersymbol interference helps to suppress inter-subcarrier interference. Successive subcarriers are apart by multiple of the chip rate, and so inter-subcarrier interference is reduced or nearly rejected. In FD/MC-CDMA, longer guard interval instead of windowing is more effective. SFH/MC-CDMA: This scheme replaces hardware implementation of frequency hopping with simple coding technique. Hence frequency hopping gives no extra hardware complexity unlike SFH/SC-CDMA. Even fast frequency hopping can be simply implemented. Likewise in FD/MC-CDMA, frequency diversity is fully exploited. In the absence of nonlinear distortion, FD/MC-CDMA outperforms other multiple access schemes under consideration in terms of capacity, hardware complexity, and flexibility of resource management in single rate and multi-rate applications. In practice, power-limited mobile terminals can not afford to impose sufficient output backoff on power amplifier, and consequently nonlinearity generates intermodulation products (IMP). IMP's degrade signal-to-noise ratio and make synchronisation even more difficult. Unlike narrow-band OFDM, intermodulation products become noise-like after despreading at the receiver, and so cross-talk does not happen. Flexibility in pulse shape, carrier frequency, and the width of spectrum makes performance analysis more troublesome.

Mobile Satellite Communication Systems are the best, and probably the only solution to a full 'global communication coverage'. Despite the intense scrutiny and inherent difficulties in gaining acceptance by the telecommunications market and the recent switch back towards GEO satellites, mobile satellite systems in non-geostationary LEO (500-2000km) and MEO (10000-12000km) constellations still remain an attractive solution in an integrated satellite/terrestrial scenario as they offer lower delays and lower power requirements than GEO satellites (35800km). Since Quality of Service (QoS) and service availability are major subscriber concerns, the investigation of factors which influence them are of central importance to the design of such systems. In non-GEO mobile satellite systems both the QoS and the service availability are very much dependant on the changing dynamics of the constellation and on the time varying nature of the propagation environment. Motivated by the above issues, we present, analyse and evaluate the coverage and availability of first generation constellation proposals in terms of LOS and bit-error-rate (QoS) requirements. Handover management is also identified as an important issue affecting the QoS and therefore handover strategies and mechanisms for various satellite constellations are presented and analysed. Based on the statistical but predefined nature of the constellation dynamics as well as the influence of the propagation channel and its dependence on the constellation design we propose two new channel adaptive handover algorithms in an effort to reduce the handover signalling whilst maximising at the same time the QoS as perceived by the user in terms of reduced call dropping rate for a typical circuit mode telephone call. Finally, as the current trend of the telecommunication services is towards the provision of packet oriented services, we focus the final part of this study on the performance investigation, in terms of throughput versus delay characteristics, on the provision of GPRS-like services over mobile satellite systems and compare GEO and non-GEO delivery. It is concluded, based on the MAC protocol proposed in the last chapter, that depending on the type of traffic and on the network load, the LEO approach doesn't always give superior performance in terms of delay characteristics to that of a MEO. The results and findings presented in this thesis can be used as a reference for optimising and designing future mobile satellite systems. Key words: Availability, QoS, handover, MAC protocols, satellite channel.

Satellites will play an indispensable role in the deployment of commercial networks to meet an increasing demand for supporting multimedia services at high data rates. Next generation satellite systems, operating at high frequency bands offer large bandwidth and are able to provide broadband services. To interface satellite links with existing terrestrial networks for providing communication access to a variety of users directly, several performance issues need to be addressed. Current thesis presents a technically viable satellite-integrated network model that is efficient in carrying broadband services to users over a wide scattered area. Accurate prediction of attenuation level is necessary for a reliable network model to operate with required service availability. Long term rainfall data has been analysed to characterise attenuation level at a selected region such as Dhaka. It is shown that rainfall is highly seasonal and attenuation level is quite high during monsoon. However, the seasonal behaviour of rainfall can be exploited to improve the link availability. Radar and rain gauge measurements at Sparsholt are also used to find rain cell size distribution, which is an important factor in site diversity implementation to combat severe rain fade. It is found that convective rain cell has extension in the region of 10 km. The network model is designed with dimensioning the effective bandwidth to support a number of users over the satellite link by taking into account the multimedia traffic characteristics. Concatenated coding, a robust coding scheme is implemented to improve the link quality at a level required to deliver broadband services. The ITU-T performance objectives of 7.5×10 for CLR and 1.4×10 for CER over satellite links are met at a required Eb/No of 2.95 dB and 2.88 dB respectively. Different enhancement mechanisms for optimum TCP performance are implemented to combat the large propagation delay associated with a satellite link. It is revealed through the simulation that TCP performance over a satellite link is as efficient as terrestrial links with these enhancement mechanisms Finally, the overall performance of the designed network is evaluated through link budget analysis and simulation. An innovative downlink power control strategy has been implemented to maintain the link during the rainiest months. The interference level due to high power satellite transmission in the designed system is also calculated to protect other existing communication links sharing the same frequency bands. A feasible broadband network designed with characterising propagation as well as networking issues will efficiently deliver broadband communication services to a large population promptly and in a cost-effective manner. Such a network solution will be in the realm of current R & D towards broadband satellite networks.

Mobile communication systems have continued to evolve beyond the currently deployed Third Generation (3G) systems with the main goal of providing higher capacity. Systems beyond 3G are expected to cater for a wide variety of services such as speech, data, image transmission, video, as well as multimedia services consisting of a combination of these. With the air interface being the bottleneck in mobile networks, recent enhancing technologies such as the High Speed Downlink Packet Access (HSDPA), incorporate major changes to the radio access segment of 3G Universal Mobile Telecommunications System (UMTS). HSDPA introduces new features such as fast link adaptation mechanisms, fast packet scheduling, and physical layer retransmissions in the base stations, necessitating buffering of data at the air interface which presents a bottleneck to end-to-end communication. Hence, in order to provide end-to-end Quality of Service (QoS) guarantees to multimedia services in wireless networks such as HSDPA, efficient buffer management schemes are required at the air interface. The main objective of this thesis is to propose and evaluate solutions that will address the QoS optimization of multimedia traffic at the radio link interface of HSDPA systems. In the thesis, a novel queuing system known as the Time-Space Priority (TSP) scheme is proposed for multimedia traffic QoS control. TSP provides customized preferential treatment to the constituent flows in the multimedia traffic to suit their diverse QoS requirements. With TSP queuing, the real-time component of the multimedia traffic, being delay sensitive and loss tolerant, is given transmission priority; while the non-real-time component, being loss sensitive and delay tolerant, enjoys space priority. Hence, based on the TSP queuing paradigm, new buffer managementalgorithms are designed for joint QoS control of the diverse components in a multimedia session of the same HSDPA user. In the thesis, a TSP based buffer management algorithm known as the Enhanced Time Space Priority (E-TSP) is proposed for HSDPA. E-TSP incorporates flow control mechanisms to mitigate congestion in the air interface buffer of a user with multimedia session comprising real-time and non-real-time flows. Thus, E-TSP is designed to provide efficient network and radio resource utilization to improve end-to-end multimedia traffic performance. In order to allow real-time optimization of the QoS control between the real-time and non-real-time flows of the HSDPA multimedia session, another TSP based buffer management algorithm known as the Dynamic Time Space Priority (D-TSP) is proposed. D-TSP incorporates dynamic priority switching between the real-time and non-real-time flows. D-TSP is designed to allow optimum QoS trade-off between the flows whilst still guaranteeing the stringent real-time component’s QoS requirements. The thesis presents results of extensive performance studies undertaken via analytical modelling and dynamic network-level HSDPA simulations demonstrating the effectiveness of the proposed TSP queuing system and the TSP based buffer management schemes.

Network simulations often output a log file, which must be parsed to understand the details of the simulation. Visualizations of these simulations are used to make debugging and analysis easier, and there are many visualizers that will display the simulation in 2D. Those in 3D do not fully utilize 3D graphics operations to visualize asimulation. This thesis explores the ways 3D graphics can be used to further enhance a visualization. To do this, it introduces a new network simulator and a visualizer, consisting of an analyzer, which collects statistics about a simulation, and a renderer, which leverages an existing program package for rendering.

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M.Ing. / In general, error control coding is absolutely necessary for reliable data transmission. However, the performance of error control codes depends on the statistical structure of the error process on the communication channel. The mobile radio channel, which has been investigated, is subject to path loss effects, a variety of noise effects and interferences and various types of scattering and multipath fading. All these effects contribute to the error processes on the radio channel when transmitting data over it. Any meaningful analytical description of the error process in terms of the characteristics of the individual physical causes of errors are difficult to undertake. Consequently, alternative ways of modelling real communication. channels are being presented. It is more convenient to include the above mentioned perturbations in a discrete inner communication channel consisting of the modem, radio equipment and the mobile radio medium, which are then modelled with a discrete partitioned Markov chain. The partitioned Markov chain inner channel models also give a more accurate description of a real communication channel than does a binary symmetric channel model. However, in order to model a communication channel, the complete statistical structure of the bit error sequence on the channel must be known. In the first instance the memory effective recording of the error sequence of discrete inner communications channels has been considered. This has led to an implementation, where a portable recording system has been developed for mobile .radio channels or any other communication channel with a data rate of up to 4800 bits per second. Programs have been developed to determine all the important statistical distributions which are necessary to be able to model the channel. A channel modelling system has been developed, which fits a channel model to the real channel and then determines the important statistical distributions of the channel model to enable comparison with the real channel. The channel modelling system is versatile and can be used with any future communication system. A number of different mobile VHF and UHF inner channels have been investigated experimentally and the associated discrete models have been developed. In addition to the above mentioned discrete inner communications channels, some "outer channels" have been developed. The "outer channels" comprise of an inner channel and the block error detection, correction and misdetection events, associated with the code words of an error control system. It has been shown that the underlying statistical structure of these events on a discrete renewal inner channel can be represented with outer channel models, i.e. simple partitioned Markov processes, similar to the inner channel models. Analytical procedures to determine the parameters of these outer channel models are being presented. The inner channel parameters and the characteristics of the error control event have been used to develop the outer channel models, i.e. the simple partitioned Markov chains, representing the underlying statistical structure of the block error detection, decoding error in error correction and misdetection (undetected error) events of a block code on the discrete renewal inner channel. Finally it is shown that these outer channel models can be used to evaluate error control codes and systems. Forward-error control and automatic-repeat-request systems have been evaluated and compared with each other.

The last decade has seen an explosion in the growth and use of the Internet. Rapidly evolving network and computer technology, coupled with the exponential growth of services and information available on the Internet, is heralding in a new era of ubiquitous computing. Hundreds of millions of people will soon have pervasive access to a huge amount of information, which they will be able to access through a plethora of diverse computational devices. These devices are no longer isolated number crunching machines; rather they are on our desks, on our wrists, in our clothes, embedded in our cars, phones and even washing machines. These computers are constantly communicating with each other via LANs, Intranets, the Internet, and through wireless networks, in which the size and topology of the network is constantly changing. Over this hardware substrate we are attempting to architect new types of distributed system, ones that are able to adapt to changing qualities and location of service. Traditional theories and techniques for building distributed systems are being challenged. In this new era of massively distributed computing we require new paradigms for building distributed systems. This thesis is concerned with how we structure distributed systems. In Part I, we trace the emergence and evolution of computing abstractions and build a philosophical argument supporting mobile code, contrasting it with traditional distribution abstractions. Further, we assert the belief that the abstractions used in traditional distributed systems are flawed, and are not suited to the underlying hardware substrate on which contemporary global networks are built. In Part U, we describe the experimental work and subsequent evaluation that constitutes the first steps taken to validate the arguments of Part I.

Recent years have witnessed a tremendous growth of research and development to provide mobile users with "seamless" communication through wireless media. Service provision in mobile networks is closely intertwined with network mobility management and therefore efficient management of subscriber mobility remains a challenging and an important area of research. This thesis examines management of signalling traffic in mobile networks and packet network design approaches, with specific contributions relating to i) reduction of network database signalling costs in GSM; ii) minimization of mobility signalling over the air-interface based a new technique for subscriber location management; iii) an efficient network design technique for packet communication networks with application to GPRS, based on a novel hybrid GA-Heuristic approach. A novel location management technique is proposed to reduce signalling costs in the core network, by reducing the rate of HLR-related transactions. By intelligent distribution of the HLR related signalling over a number of VLRs, the HLR is prevented from being a potential bottleneck and a single point of failure in the signalling network. Based on the analytical model developed, it is demonstrated that within the call-to-mobility range considered, the total network signalling cost as well as location management costs can be significantly reduced, compared to current strategy adopted in GSM, To address location management signalling in the access network, a number of dynamic schemes are considered and compared with the proposed adaptive multilayer technique. Through detailed simulations under various scenarios, the superiority of the proposed scheme, in terms of significant savings in the total signalling traffic (i.e. location update and paging) and ease of implementation, compared to other techniques is demonstrated . The location management scheme of GSM is used as baseline for comparisons. Finally, efficient design of packet communication networks, with application to GPRS backbone architecture, is addressed. To meet the cost and traffic requirements whilst ensuring that the delay and reliability constraints are also satisfied, a hybrid GA-heuristic approach is developed as an alternative to purely GA based and heuristic-only approaches. Under a common set of parameters, the performance of various techniques are compared and it is shown that the hybrid approach is capable of producing solutions that are superior to other typical network design methods.