Capacity increase of the current land mobile satellite (LMS) communication systems is highly desirable to cater for more data-centric applications such as broadcasting. Since the Multiple-input Multiple-output (MIMO) offers high spectral efficiency without additional bandwidth and transmit power, its implementation in the LMS system has been widely investigated in terms of channel characterisation, channel modelling and coding algorithms. However, the aspect of receive antenna design and its performance evaluation has not yet been considered even though it has enormous impacts on the system performance. This thesis presents a study on designing a novel dual circularly polarised receive antenna system for the LMS MIMO system that utilises the printed quadrifilar helix antenna (PQHA) and also the required performance evaluation methods. The PQHA was miniaturised using two new methods, which are the element folding and combination of element folding and meandering where more than 50% size reduction can be achieved. These miniaturised PQHAs were combined to create a variety of dual circularly polarised arrays such as the dual circularly polarised single folded PQHA (SFPQHA) horizontal array and folded meandered PQHA (FMPQHA) vertical array. For evaluating the branch power ratio of these arrays, a newly derived formulation of the mean effective gain (MEG) in a Ricean fading channel that incorporates the polarisation of the line-of-sight (LoS) component and the corresponding antenna gain has been proposed. Further evaluation of these arrays as the receive antenna in this system was carried out using measurement campaigns. Results show that both arrays provide substantial capacity increase when compared to a single link system in both LoS and NLoS channels. A more comprehensive study on the effect of antenna properties was conducted using a newly, developed channel model that integrates the array characteristics with the propagation channel. This modelling approach allows for a performance comparison between the designed SFPQHA array and other antennas to be easily implemented, which is very useful in the process of designing MIMO antennas.

A mobile ad hoc network (MANET) is a self-organised wireless network where mobile nodes can communicate with each other without the need of any existing network infrastructure or centralised administration. There are no dedicated routing devices and each node has to rely on others to cooperatively provide forwarding services to ensure global connectivity. In an open MANET, different nodes may have different authorities and different goals. To conserve their own resources, some nodes may choose not to cooperate while still using the network to forward their packets. Uncooperative or misbehaving nodes can significantly degrade the performance of a MANET. Most previous works to mitigate the effects of misbehaving nodes focus on data forwarding. However, dropping control packets is a better strategy for the selfish nodes to avoid themselves from being requested to forward data packets. In this thesis, a new scheme is proposed to detect free-riding nodes which exhibit such a strategy. In the detection scheme, each node operates in promiscuous mode and monitors the activities of its neighbouring node. All nodes in the network are expected to contribute to the network on the continual basis within each predefined time frame. Those which fail will undergo a suspicious checking procedure to test for the suspicious behaviour. Detection alone is not enough to deal with free-riding nodes. To encourage the nodes to be cooperative, three variations of punishment schemes are proposed. The schemes punish free-riding nodes by isolating them and refusing them services.

GPS receivers in challenging signal reception areas can find it difficult to maintain continuous signal lock for the up-to 30 seconds needed to obtain the broadcast ephemeris from the satellites. It can take many minutes for receivers to obtain the ephemeris parameters from enough satellites to obtain a position fix. As well as users expecting a rapid time-to-first-fix (TTFF) when performing a warm start, the advent of the E-911 legislature in the USA also provides motivation for rapid TTFF with accurate positions. In this thesis, a scalable orbit prediction algorithm is developed to calculate an extended ephemeris of GPS satellites of up to 7 days on a mobile device to within an accuracy of 20 m rms (radial). The algorithm numerically integrates force models from a set of initial conditions, position and velocity, determined solely from the broadcast ephemeris. Forces used include Earth gravity models of varying resolution, third-body gravity effects, solar radiation pressure, relativity, and solid Earth tides. Adding these forces improves the ephemeris accuracy at the cost of the execution time, so research is undertaken to produce ephemeris data quickly whilst maintaining similar accuracy. An orbit determination algorithm is developed that uses a least-squares technique to optimise the computed orbit over multiple sets of previously observed broadcast ephemeris data. This modifies the estimate of the initial conditions made available to the orbit predictor, which then provides a modified ephemeris which has a substantially lower root-mean-square error. The algorithm again uses a suite of force models, and only broadcast ephemeris orbit data was utilised, no other satellite ephemeris is required. Studies determining the effect of modifying the a priori weights and the number of sets of ephemeris data used for observations are undertaken and results demonstrated on a HTC TyTN II mobile device. The orbit determination technique presented in this thesis is novel, in that it utilises only broadcast ephemeris parameters previously acquired by a single GPS receiver to modify the initial position and velocity for the orbit prediction algorithm. Previous techniques used either empirical modelling or least squares techniques to modify empirical parameters of the orbit prediction algorithm.

Radio spectrum is becoming increasingly scarce as more and more devices go wireless. Meanwhile, studies indicate that the assigned spectrum is not fully utilised. Cognitive radio (CR) technology is envisioned to be a promising solution to address the imbalance between spectrum scarcity and spectrum underutilisation. It improves the spectrum utilisation by reusing the unused or underutilised spectrum owned by incumbent systems (primary systems). With the introduction of CR networks, two types of interference originating from CR networks are introduced. They are the interference from CR to primary networks (CR-primary interference) and the interference among spectrum-sharing CR nodes (CR-CR interference). The interference should be well controlled and managed in order not to jeopardise the operation of the primary network and to improve the performance of CR systems. This thesis investigates the interference in CR networks by modelling and mitigating the CR-primary interference and analysing the CR-CR interference channels. Firstly, the CR-primary interference is modelled for multiple CR nodes sharing the spectrum with the primary system. The probability density functions of CR-primary interference are derived for CR networks adopting different interference management schemes. The relationship between CR operating parameters and the resulting CRprimary interference is investigated. It sheds light on the deployment of CR networks to better protect the primary system. Secondly, various interference mitigation techniques that are applicable to CR networks are reviewed. Two novel precoding schemes for CR multiple-input multipleoutput (MIMO) systems are proposed to mitigate the CR-primary interference and maximise the CR throughput. To further reduce the CR-primary interference, we also approach interference mitigation from a cross-layer perspective by jointly considering channel allocation in the media access control layer and precoding in the physical layer of CR MIMO systems. Finally, we analyse the underlying interference channels among spectrum-sharing CR users when they interfere with each other. The Pareto rate region for multi-user MIMO interference systems is characterised. Various rate region convexification schemes are examined to convexify the rate region. Then, game theory is applied to the interference system to coordinate the operation of each CR user. Nash bargaining over MIMO interference systems is characterised as well. The research presented in this thesis reveals the impact of CR operation on the resulting CR-primary network, how to mitigate the CR-primary interference and how to coordinate the spectrum-sharing CR users. It forms the fundamental basis for interference management in CR systems and consequently gives insights into the design and deployment of CR networks.

These days, most of the mobile phones are smart enough with computer like intelligence and equipped with multiple communication technologies such as Bluetooth, wireless LAN, GPRS and GSM. Different communication medium on single device have unlocked the new horizon of communication means. Modern mobile phones are not only capable of using traditional way of communication via GSM or GPRS; but, also use wireless LANs using access points where available. Among these communication means, Bluetooth technology is very intriguing and unique in nature. Any two devices equipped with Bluetooth technology can communicate directly due to their unique IDs in the world. This is opposite to GSM or Wireless LAN technology; where devices are dependent on infrastructure of service providers and have to pay for their services. Due to continual advancement in the field of mobile technology, mobile ad-hoc network seems to be more realised than ever using Bluetooth. In traditional mobile ad-hoc networks (MANETs), before information sharing, devices have partial or full knowledge of routes to the destinations using ad-hoc routing protocols. This kind of communication can only be realised if nodes follow the certain pattern. However, in reality mobile ad-hoc networks are highly unpredictable, any node can join or leave network at any time, thus making them risky for effective communication. This issue is addressed by introducing new breed of ad-hoc networking, known as opportunistic networks. Opportunistic networking is a concept that is evolved from mobile ad-hoc networking. In opportunistic networks nodes have no prior knowledge of routes to intended destinations. Any node in the network can be used as potential forwarder with the exception of taking information one step closer to intended destination. The forwarding decision is based on the information gathered from the source node or encountering node. The opportunistic forwarding can only be achieved if message forwarding is carried out in store and forward fashion. Although, opportunistic networks are more flexible than traditional MANETs, however, due to little insight of network, it poses distinct challenges such as intermittent connectivity, variable delays, short connection duration and dynamic topology. Addressing these challenges in opportunistic network is the basis for developing new and efficient protocols for information sharing. The aim of this research is to design different routing/forwarding techniques for opportunistic networks to improve the overall message delivery at destinations while keeping the communication cost very low. Some assumptions are considered to improved directivity of message flow towards intended destinations. These assumptions exploit human social relationships analogies, approximate awareness of the location of nodes in the network and use of hybrid communication by combining several routing concept to gain maximum message directivity. Enhancement in message forwarding in opportunistic networks can be achieved by targeting key nodes that show high degree of influence, popularity or knowledge inside the network. Based on this observation, this thesis presents an improved version of Lobby Influence (LI) algorithm called as Enhanced Lobby Influence (ELI). In LI, the forwarding decision is based on two important factors, popularity of node and popularity of node’s neighbour. The forwarding decision of Enhanced Lobby Influence not only depends on the intermediate node selection criteria as defined in Lobby Influence but also based on the knowledge of previously direct message delivery of intended destination. An improvement can be observed if nodes are aware of approximate position of intended destinations by some communication means such as GPS, GSM or WLAN access points. With the knowledge of nodes position in the network, high message directivity can be achieved by using simple concepts of direction vectors. Based on this observation, this research presents another new algorithm named as Location-aware opportunistic content forwarding (LOC). Last but not least, this research presents an orthodox yet unexplored approach for efficient message forwarding in Bluetooth communication environment, named as Hybrid Content Forwarding (HCF). The new approach combines the characteristics of social centrality based forwarding techniques used in opportunistic networks with traditional MANETs protocols used in Bluetooth scatternets. Simulation results show that a significant increase in delivery radio and cost reduction during content forwarding is observed by deploying these proposed algorithms. Also, comparison with existing technique shows the efficiency of using the new schemes.

The research activities over the three years were presented in this thesis. The work centred on the use of multiple spatial elements for Ultra wide band wireless system in order to increase the throughput, and for wireless range requirement applications, increases the coverage area. The challenges and problems of this type of implementation are identified and analysed when considered at the physical layer. The study presents a model design that integrates the multiple antenna configurations on the short range wireless communication systems. As the demand for capacity increases in Wireless Personal Area Networks (WPAN); to address this issue, the framework of the Wi-Media Ultra Wide Band (UWB) standard has been implemented in many WPAN systems. However, challenging issues still remain in terms of increasing throughput, as well as extending cellular coverage range. Multiple Input Multiple Output (MIMO) technology is a well-established antenna technology that can increase system capacity and extend the link coverage area for wireless communication systems. The work started by carrying out an investigation into integrated MIMO technology for WPANs based on the Wi-Media framework using Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM). It considered an extensive review of applicable research, the potential problems posed by some approaches and some novel approaches to resolve these issues. The proposed ECMA-368 standard was considered, and a UWB system with a multiple antenna configuration was undertaken as a basis for the analysis. A novel scheme incorporating Dual Circular 32 - QAM was proposed for MB-OFDM based systems in order to enhance overall throughput, and could be modified to increase the coverage area at compromise of the data rate. The scheme was incorporated into a spatial multiplexing model with measured computational complexity and practical design issues. This way the capacity could be increased to twice the theoretical levels, which could pay the way to high speed multi-media wireless indoor communication between devices. Furthermore, the range of the indoor wireless network could be increased in practical wireless sensor networks. The inherent presence of spatial and frequency diversity that is associated with this multiple radiators configuration enlarge the signal space, by introducing additional degrees of freedom that provide a linear increase in the system capacity, for the same available spectrum. By incorporating the spatial elements with a Dual Circular modulation that is specified within the standard, it can be shown that a substantial gain in spectral efficiency could be possible. A performance analysis of this system and the use of spatial multiplexing for potential data rates above Gigabit per second transmission were considered. In this work, a model design was constructed that increases the throughput of indoor wireless network systems with the use of dual radiating elements at the both transmitter and receiver. A simulation model had been developed that encapsulate the proposed design. Tests were carried out which investigate the performance characteristics of various spatial and modulation proposals and identifies the challenges surrounding their deployments. Results analysis based on various simulation tests including the IEEE802.15.3a UWB channel model had shown a lower error rate performance in the implementation of the model. The proposed model can be integrated in commercial indoor wireless networks and devices with relatively low implementation cost. Further, the design used in future work to address the current challenges in this field and provides a framework for future systems development.

In the current frequency allocation scheme, the radio spectrum is found to be heavily underutilized in time, frequency and space dimensions or any of their combination. To improve spectrum utilization, the unused contiguous or non-contiguous portion of the radio spectrum (spectrum hole) can be accessed opportunistically using cognitive radio technology provided it is interference free to the local users of the network. To reliably detect the spectrum holes, which is necessary to limit the interference, cognitive radio is required to have high time and frequency resolutions to detect radio technologies (e.g. GSM 900, 2.4 GHz WLAN) at the packet level in the transmitted channel to avoid misinterpretation of occupancy states in time and frequency. In addition, having high sensitivity and instantaneous dynamic range can enable cognitive radio to detect weak received signals and their detection in the presence of strong received signals. Besides these requirements, a large sensing bandwidth can increase the chances to find spectrum holes in multiple radio technologies concurrently. A chirp channel sounder receiver has been developed according to the aforementioned requirements with a bandwidth of 750 MHz to provide reliable detection of received signals in two frequency ranges; 1) 250 MHz to 1 GHz, 2) 2.2 GHz to 2.95 GHz. The developed receiver is capable of finding spectrum holes having a duration of 204.8 μs and a transmitted channel bandwidth up to 200 kHz. To explore the spectrum holes in the space dimensions, six chirp channel sounder receivers have been developed to form a homogeneous test-bed, which can be deployed and controlled independently. To experimentally validate the ability of the built receiver, short term spectrum occupancy measurements have been conducted to monitor 2.4 GHz WLAN traffic from a real wireless network to quantify the spectrum utilization and duration of spectrum holes in the time domain. It has been found that the radio spectrum is underutilized and empirical distribution of the duration of the spectrum hole can be modelled using lognormal and gamma distributions for prediction using a two state continuous time semi-Markov model. To experimentally validate the receiver’s capabilities in both the supported frequency ranges, long term spectrum occupancy measurements with 750 MHz sensing bandwidth have been performed and received signals have been detected at frame or packet level to quantify spectrum utilization. It has been found that the radio spectrum is highly underutilized at the measurement location and exhibits significant amount of spectrum holes in both time and frequency. To experimentally validate the functionalities of the homogeneous test-bed, short term spectrum occupancy have been performed to monitor 2.4 GHz WLAN traffic from a real wireless network. The experiment has been conducted using multiple receivers to quantify the amount of cooperation individual or multiple cognitive radio users can provide for reliable detection of spectrum holes in time, frequency and space. It has been found that the space dimension influences strongly the statistics of cooperation parameters.

A linear / stepped frequency modulated continuous wave (FMCW) signal has for a long time been used in radar and channel sounding. A novel FMCW waveform known as “Gated FMCW” signal is proposed in this thesis for the suppression of strong undesired signals in microwave radar applications, such as: through-the-wall, ground penetrating, and medical imaging radar. In these applications the crosstalk signal between antennas and the reflections form the early interface (wall, ground surface, or skin respectively) are much stronger in magnitude compared to the backscattered signal from the target. Consequently, if not suppressed they overshadow the target’s return making detection a difficult task. Moreover, these strong unwanted reflections limit the radar’s dynamic range and might saturate or block the receiver causing the reflection from actual targets (especially targets with low radar cross section) to appear as noise. The effectiveness of the proposed waveform as a suppression technique was investigated in various radar scenarios, through numerical simulations and experiments. Comparisons of the radar images obtained for the radar system operating with the standard linear FMCW signal and with the proposed Gated FMCW waveform are also made. In addition to the radar work the application of FMCW signals to radio propagation measurements and channel characterisation in the 60 GHz and 2-6 GHz frequency bands in indoor and outdoor environments is described. The data are used to predict the bit error rate performance of the in-house built measurement based channel simulator and the results are compared with the theoretical multipath channel simulator available in Matlab.

In this thesis I present my work in the field of SDR (Software Defined Radio) and concurrent systems. This work is part of the hybrid SDR Platform project, which distributes the signal processing between the Central Processing Unit of the PC (Personal Computer) and a dedicated signal processor. The PC side of the platform is the controller and the human interface of the system. It is a translator between the wishes of the user and the dedicated signal processor. As it is purely software we labelled it SP (Software Platform). The dedicated signal processor, together with the analogue RF (Radio Frequency) front-end and high speed signal converters is the HP (Hardware Platform). My share of this endeavour was the development of the SP (Software Platform) of the SDR Platform. The concept of the SDR Platform is to not limit the user to a specific HP (Hardware Platform). In real-time signal processing, the signal processing algorithms execute concurrently. To implement the algorithms I chose to use Communicating Sequential Processes, which with its processes and channels resembles block diagrams, visualising signal processing chains. The SP itself is a concurrent system as well, thus I use CSP (Communicating Sequential Processes) as the basis for the SP. The SP consists of the management and the exchangeable SM (Software Module) part. To exchange a SM it is first necessary to terminate the process network representing it. One way of terminating process networks is to spread a termination message (poison) through it, informing every process about the termination. I extended the graceful termination technique, by introducing a second type of poison. I developed a proof of concept implementation, JCSP-Poison, which is based on JCSP. I show the CSP models of these channels as well as verifying that the JCSP implementation of them works correctly. I developed KCSP (Kernel Communicating Sequential Processes), which is an add on to an OS kernel, providing a CSP environment. KCSP allows developers to develop device drivers following the CSP principles.

Wireless communication has been the major part of the wireless industry that have grown very fast and captured the attention of many researchers. it has evolved from different generations and the current 3G Long Term Evolution (LTE) is the main focus in this project. LTE is an emerging and promising technology that aims at providing broadband ubiquitous Internet access and improving multimedia services. This is achieved through streamlining the system for packet services, since LTE is an all Internet Protocol (IP) based network. The fact that 3G LTE is a packet based network brings about some improvements in the form of higher bit rates, lower latencies, etc. However, several technical challenges are expected to arise when voice traffic is transmitted over LTE network. Voice transmission over 3G LTE has brought major concerns due to the fact that voice traffic, similar to any other real-time traffic, is affected by technical issues such as end-ta-end delay or latency, jitter, and packet loss which adversely affect the Quality of Service (QoS). This has led to the development of different scheduling and resource allocation schemes with the aim of improving the QoS of voice traffic when transmitted over a 3G LTE network. This research, studies how cross-layered scheduling and resource allocation techniques can improve the QoS of voice traffic when transmitted over 3G LTE network. This research proposes a novel cross-layer scheduling and resource allocation algorithm in order to improve the performance gains and QoS of voice when transmitted over a 3G LTE Network. The novelty of the proposed algorithm is that it projects the voice packet scheduling and resource allocation problem as a constrained optimization problem in contrast to the existing techniques. This optimization problem is formulated using the transmission rate and channel state information at the physical layer as well as the queuing state information such as the queue length at the Medium Access Control (MAC) layer. The a1gorithmic implementation of the obtained solution is provided and this research also investigates the performance, mobility, complexity, and fairness issues of the proposed cross-layer scheduling algorithm under different conditions such as, VoIP delay, packet loss, etc.