Advancements in broadband wireless networks and video compression tech- nologies have led to a tremendous increase in the demand for wireless multimedia services over recent years. Popular wireless transmission techniques enabling en- hanced throughput include orthogonal frequency division multiplexing (OFDM) while the recent video coding standard, namely the H.264/ AYC, enables up to twice the compression efficiency to be attained relative to previous video com- pression techniques. Regardless of these developments, the highly dynamic and unpredictable nature of wireless channels, along with the requirements for main- taining the quality of service (Q08) and seamless video playback for all users, impose severe constraints on the design of wireless multimedia systems. A video coding technique that has been developed for such environments is the scalable video coding (8YC), which allows parts of the encoded bitstream to be discarded in response to a drop in the channel quality. However, state-of-the-art resource allocation techniques for SYC transmission over the wireless medium suffer from high computational complexity. Low-complexity, sub-optimal alternatives, on the other hand, are not always adequate. Given the sparse nature of spectrum resources, and the paradigm shift in spectrum access with the advent of cognitive radio systems, it is evident that sub-optimal algorithms having large optimality gaps are not desired. In fact, such approaches would be in contradiction to the definition of spectrum efficient, cognitive radio systems. In this thesis, resource allocation schemes for the transmission of H.264 SYC over wireless networks are investigated. In particular, OFDM systems are consid- ered, including OFDM-based cognitive radio networks. Cross-layer optimisation techniques for fine grain scalable (FGS) video sequences are analysed. Although the problem is initially non-convex and has non-polynomial-time (NP) complex- ity, low complexity techniques are derived that lead to solutions very close to the optimal. Resource allocation schemes for coarse grain scalable (CGS) and medium grain scalable (MGS) sequences over OFDM-based cognitive systems are also investigated. As opposed to FGS, CGS/MGS do not allow an encoded bitstream to be truncated at random bit location. Consequently, new methods are derived that focus on this particular type of video coding. The presence of multiple antennas at the cognitive transmitter and their effect on the aggregate visual quality of all secondary users are also discussed. Furthermore, a joint call admission control (CAC) and resource allocation for the transmission of CGS and MGS video sequences over orthogonal frequency division multiple access (OFDMA) are analysed. This scheme considers the sce- narios where the available channel resources are not enough to support the video data of all users. Finally, rate-adaptation techniques for scalable video transmission over wire- less networks are presented. Rate-adaptation refers to the methods by which the encoding parameters of the video coding are adapted in response to the chan- nel conditions. Interestingly, it is shown that under a given channel condition, increasing the granularity of a scalable sequence lead to diminishing returns in terms of the rate achieved. Moreover, the transmission of scalable sequences over cognitive radio networks where perfect channel knowledge is not available is investigated. The effect of the granularity of the bitstream on the interference observed by incumbent users is also presented. It is shown that the probability of exceeding the interference threshold can be significantly reduced by proper specification of the video encoding parameters.

Next generation mobile networks envisage ubiquitous communications at very high data rates. This imposes a major challenge to connectivity and capacity for terrestrial urban mobile communications, where the radio propagation fading is extremely severe. An airbased wireless system is expected to improve the coverage, extend the range, enhance the connectivity and reduce the required transmit power when integrated into a terrestrial wireless network. Existing radio channel models for land mobile satellite systems generally consider mobiles moving along roads in open areas such as main highways with low building densities along the sides of the road. New statistical point-to-area radio channel models are required to predict coverage, including locations near buildings, taking into account the height of the air platform.

The fundamental principle of multiuser diversity states that it is possible to achieve a significant received energy gain in a multi user wireless communication system if channel resources are divided between users in an adaptive, dynamic and intelligent fashion. When every channel resource block is assigned to the user with the best channel quality at any time or frequency bin, the system-wide sum rate achieved can be significantly increased. There is a risk, though, that users with a weaker channel quality might starve for resources, as this approach prioritizes the stronger users. Therefore, it is of utmost important that some type of fairness control mechanism is used at the same time. Most of the work published in the relevant literature assumes that a central controller dictates the resource allocation process. Such an approach induces various costs though; all users have to transmit their channel quality information to the central controller and then the allocation decisions have to be fed back to them. In an inherently fast-varying wireless channel this generates a lot of overheads and makes the whole allocation process less efficient. In an attempt to minimize this cost and to remove the need for the existence of a central controller, this PhD work investigates the use of game theoretic concepts to achieve distributed resource allocation. Coalition formation is a game theoretic concept that allows individual entities to cooper- ate and perform a task more efficiently. By allowing users to form disjoint coalitions in a distributed fashion, this work tackles the problem of cooperative distributed resource allocation. Using the Nash Bargaining Solution as a means for enabling intra-coalition cooperation, individual users are able to exchange resource blocks and harvest the bene- fits of multiuser diversity, in a fashion that maintains a level of fairness similar to that of Proportional Fairness. For the purposes of this work, three different schedulers for resource allocation were de- veloped and are presented in this thesis. Two of them are based on the aforementioned game theoretic concepts, while the third is a hybrid between the Greedy scheduler and the game theoretic approach. Simulation results are presented and comparison to the widely adopted Proportional Fair scheduler is made. Additionally, the trade-offs between sum rate performance, fairness, complexity and overheads are investigated and the protocol used for the allocation process is presented.

The challenge of wirelessly streaming high quality video around the home is of considerable commercial interest. Consumers have access to ever-increasing quantities of audio-visual content and a growing choice of options for consuming that content, from large screen televisions to tablet-format mobile devices. Advances in consumer wireless technology (802.11n WiFi) and video compression (H.264/ AVe) make it possible to deliver High Definition (HD) video of good quality around the home over consumer-grade networks. However, multiple clients consuming content over the same network - a scenario becoming ever more typical in home environments - make the above streaming task more challenging. The trend of increasing spatial, temporal and dynamic range resolutions will most likely keep this problem relevant in the near future. In this thesis we propose methods for improving the quality of wirelessly streamed video in a 'home-theatre' scenario. This application assumes HD video resolutions and a viewer who is watching for entertainment purposes on a large display and expects little visible distortion to the content. We target a consumer electronics application where cost - and thus complexity - are important design features. Specifically, we examine two techniques which can be employed in this scenario: rate-adaptive streaming through Hy-pothetical Reference Decoder (HRD) parameter selection and spatiotemporal resolution scaling. The first of these techniques is motivated by the fact that designers of consumer electronics products which incorporate off-the-shelf components often have limited access to the internal parameters of those components. Adaptive streaming techniques which call for fine-grained control over compressed bit stream generation, for example, may not be usable. Instead, we propose a technique for meeting varying channel bandwidth constraints by adaptively specifying HRD parameters to an encoder. We implement the technique in a simulation which operates on a windowed basis, monitoring buffer conditions and specifying parameters for use in the upcoming window, and show that it is able to offer reduced video distortion by adapting to changes in the radio environment. The second technique involves the scaling of spatial and/or temporal resolution prior to compression at a target bit rate. With certain types of content and for certain bit rates, this results in improved perceptual video quality. We create a test set of content impaired id this way, then conduct a large subjective quality assessment of that content. We then use these results to evaluate the performance of a number of common objective video quality metrics. Finally, we present a classification-based method for selecting the appropriate level of spatiotemporal resolution scaling based on low-complexity features of the video.

This thesis investigates the feasibility of deploying mobile communication networks at the THz frequency range. Three areas were identified as the major issues on the way towards realising a functional THz mobile communication system: the high atmospheric attenuation levels and obstacle shadowing at the THz range, the deficiency in THz devices suitable for mobile telecommunications and the availability of reliable models for the analysis and design of THz radio networks.

In the forthcoming broadband wireless communications, channel equalisation and estimation solutions are required to be robust against frequency selective fading channels and have a low signal processing complexity. This thesis investigates iterative frequency-domain channel equalisation and estimation for single-carrier (SC) multi-input multi-output (MIMO) wireless communication systems, aiming to outperform iterative time-domain channel equalisation and estimation with a low complexity.

The motivation for the research was primarily to satisfy positional accuracy requirements for mobile phone handsets using terrestrial networks as specified by the United States (US) Federal Communications Commission (FCC) E-911 rules. The objective of the research was to improve location finding accuracy to support the emergency services and the stolen vehicle recovery service, in areas devoid of satellite coverage. Following a literature review, four novel location finding techniques were discovered and simulated. The first novel technique provides a means to achieve an accurate mobile time source (1 part in 107 ) in first generation cellular networks and thereby accurate positioning( < 100m). The second novel technique achieves improved base station timing accuracy (1 part in 107 ) using the , Network Time Protocol (NTP) over OPRS. The third novel technique was found to enhance the accuracy and resolution (<100 m) of Timing Advance (TA) in second generation networks. The fourth novel technique takes the form of a receiver architecture capable of high resolution (0.1°), multipath, Direction of Arrival (DOA) determination within a third generation network. Localisation using triangulation is achievable to <100 m for practical 30 cell sizes. DOA accuracy in a 10 DE environment is approximately 1°, increasing to 2S in a 40 DE environment. Additionally, two novel methods of improving radio signal detection range were discovered and simulated. These enable location finding to be achieved within cellular networks where maximum communication range alone is insufficient for DOA triangulation purposes. The first method takes the form of a novel high gain (> 20 dBi) pseudo-Doppler antenna. The second method provides enhanced processing gain using a novel Error Correction Coding (ECC) post processing algorithm for hard decision decoded messages where signal re-transmission exists or can be requested. The results of the study revealed that improvements in location finding accuracy are possible in 1st 2nd and 3rd generation cellular radio networks without compromising the operation of legacy handsets or stolen vehicle tracking devices.

Opportunistic Spectrum Access (OSA) [1] promises tremendous gain in improving spectral efficiency. The main objective of OSA is to offer the ability of identifying and exploiting the under-utilised spectrum in an instantaneous manner in a wireless device, without any user intrusion. Hence, the initial requirement of any OSA device is the ability to perform spectrum sensing. Local narrow-band spectrum sensing has been quite well investigated in the literature. However, it is realised that existing schemes can hardly meet the requirements of a fast and accurate spectrum sensing particulariy in very low signal-to-noise-ratio (SNR) range without introducing high complexity to the system. Furthermore, increase in the spectrum utilisation calls for spectrum sensing techniques that adopt an architecture to simultaneously search over multiple frequency sub-bands at a time. However, the literature of sub-band spectrum sensing is rather limited at this time. The main contributions of this thesis is two-fold: First a clusterd-based differential energy detection for local sensing of multi- carrier based system is proposed. The proposed approach can form fast and reliable decision of spectrum availability even in very low SNR environment. The underlying initiative of the proposed scheme is applying order statistics on the clustered differential Energy Spectral Density (ESD) in order to exploit the channel frequency diversity inherent in high data-rate communications. Second contribution is three-fold: 1) re-defining the objective of the sub- band level spectrum sensing device to a model estimator, 2) deriving the optimal model selection estimator for sub-band level spectrum sensing for fixed and variable number of users along with a sub-optimal solution based on Bayesian statistical modelling and 3) proposing a practical model selection estimator with relaxed sample size constraint and limited system knowledge for sub-band spectrum sensing applications in Orthogonal Frequency-Division Multiple Access (OFDMA) systems. The result obtained showed that through exploitation of the channel frequency selectivity the performance of the stat-of-the-art spectrum sensing techniques can be significantly improved. Furthermore, by modelling the sub-band level spectrum sensing through model estimation allows for new spectrum sensing approach. It was proved both analytically and through simulations that the proposed approach have significantly extended to state-of-the-art spectrum sensing. Key words: Differential, energy detection, low signal-to- noise ratio (SNR), multi- carrier, opportunistic spectrum access, spectrum sensing.

This thesis deals with the adaptation of the forward link of DVB-S2IRCS systems to mobile satellite systems providing services to nomadic vehicular satellite receiving terminals such as fast trains and maritime vessels. The work undertaken focuses on the adaptation of ACM and SNR estimation to mobile satellite environments. Error-based SNR estimation is revisited and extended to enable accurate SNR estimation in mobile satellite channels. The proposed algorithm employs un-coded DVB-S2 pilot symbols and provides improved estimation accuracy and stability in the presence of Rice fading, rain attenuation and short term shadowing events from the estimation process. The use of accurate Rice factor estimates as input to the SNR estimator is noted as a key requirement and, although Rice factor estimation in itself is outside the context of this thesis, references of candidate solutions are provided in the penultimate chapter. Adaptive Threshold Adjustment is employed to mitigate the need for fixed predefined switching thresholds in ACM. The proposed ATA algorithm builds on existing approaches and provides improved threshold stability, convergence time and overall performance through the use of conditional adjustment. Performance comparisons for both of the above algorithms are provided against algorithms found in the literature. The SNR estimator is shown to outperform a moment based estimator by up to one order of magnitude in terms of estimation MSE, depending on the Rice factor and average signal SNR. The proposed ATA algorithm is shown to improve throughput as compared to continuous threshold adjustment by up to 1.8% in static fading conditions depending on the average received E/No. In the presence of rain attenuation this throughput improvement rises to a maximum of 2.5% for a specific MCS, and 1.24% on average throughput. Finally, system level analyses indicate that the system throughput improvements achieved through the use of ACM in mobile satellite environments can be comparable to those already demonstrated in fixed satellite environments.

This thesis investigates the coexistence of heterogeneous cognitive radio systems, with directional user antennas. The coexistence scenarios of High Altitude Platform-Terrestrial systems and multiple terrestrial systems are examined. Spectrum etiquettes and the game theoretical assignment techniques are applied to improve the coexistence performance. Two spectrum etiquettes called CINR and INR based, for use on the downlink of coexisting systems have been developed. The Interaction Probability has been developed to quantify the interaction level. The mitigating interaction techniques have also been discussed. The use of game theory with novel multivariable payoff functions has been applied to formulate the non-cooperative multistage spectrum sharing games as an alternative assignment technique. Path Gain Ratio (PGR) is used as a parameter to determine the cost/benefits of specific transmit power levels. Payoff functions have been shown as a way to control the users’ behaviour and to represent the requirements of the related parties such as the systems, users, and regulator(s). Coexistence without any power control is feasible with the help of user directional antennas and operating with low rate modulation. Although both spectrum etiquettes enhance the performance, the spectrum sharing games outperform them. The spectrum sharing games reach the Nash Equilibrium (NE) with a high percentage depending on the number of players in a game and the interference level but it is shown that users not reaching the Nash Equilibrium still have adequate performance.