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The aims of this work were three-fold, to investigate the patterns of food intake exhibited by carp (Cyprinus carpio) feeding on an operant regime, to investigate the role of the nucleus posterior thalamicus (NPTh) in the control of food intake, and to investigate the role of gut peptides in the control of food intake. A range of techniques were employed in pursuit of these objectives. Behavioural studies were used to investigate feeding patterns, and to assess the effects of small electrolytic lesions placed in the region of the NPTh. Histological and physiological techniques were employed to investigate the cellular morphology of the NPTh and its relationship with both hindbrain and telencephalon. Pharmacological and behavioural techniques were employed to obtain a dose response characteristic for the peripheral administration of bombesin and its effect on food intake. Animals held individually and feeding on an operant regime showed no indication that they were feeding in bouts. Satiety was seen to increase exponentially or logarithmically over the course of a feeding session. Small lesions of the NPTh caused a highly significant and variable period of anorexia or hypophagia. On recovery of feeding behaviour in lesioned animals, satiety was seen to increase in a linear fashion over the course of a feeding session. Histologically the cell bodies within the NPTh are seen to be morphologically homogenous. Physiologically it is probable that the NPTh efferent fibres are of small diameter and unmyelinated, projecting to the vagal and facial lobes of the medulla. There is some evidence that the NPTh operates as a single unit providing the same function in both internal and external chemosensory systems. The hypothesis is advanced that the NPTh has a role in the determination of palatability in both internal and external chemosensory systems. Intra-peritoneal administration of the peptide bombesin was shown to reduce food intake in animals feeding on an operant regime, in a dose dependent manner. This result is very similar to the effects of bombesin administration seen in the higher vertebrates. A further result of bombesin administration demonstrated in these experiments is the appearance of a bout feeding pattern, effects of bombesin administration on the micro-structure of food intake have not been reported in other species.

In the beginning there was a spark. A spark that could magically create a second remote spark at some distance away without any interconnecting wires or visible medium. It is interesting to think what the early pioneers of radio; Hertz, Tesla, Marconi and Edison would make of the modern mobile phone that now sits comfortably in everyone's pocket. The mobile phone and the cellular network have been truly life changing technologies. From the early analogue systems to the latest 4G LTE multi-band developments. Bandwidth is a limited resource and there are theoretical limits as to how much data can be accommodated within a finite allocated band. With the evolution of cellular radio, new use cases have been created which demand greater data capacity with faster download times and lower latency. LTE 4G for all its engineering improvements in areas such as modulation, error correction and diversity is not capable of meeting the future requirements of some of the emerging technologies such as vehicle to vehicle communications, internet of things, industrial automation and immersive virtual reality. The next generation of mobile, 5G - 'new radio' is expected to address these requirements with a step increase in channel capacity, up to 1000 times greater than 4G, with sub millisecond latency. A singular basestation antenna and a singular mobile antenna is not capable of providing such a quantum leap in performance, hence, 5G is designed to use antennas arrays in a multiple in, multiple out (MIMO) configuration. Antenna arrays are one of the key enablers of 5G new radio. Antenna arrays have been exploited for a number of years but they have a major drawback, cross coupling, which is known as mutual coupling. For MIMO, all the antenna elements need to be de-correlated (isolated) and high levels of mutual coupling can reduce the channel capacity. This thesis investigates mutual coupling in antenna arrays. It explains the load pull effect on power amplifiers and how the output vectors of an antenna array are influenced by neighbouring elements and their excitations. It shows how far field radiation patterns are distorted by the presence of mutual coupling using a bespoke custom designed 5 channel transmitter. There is detailed correlation analysis between elements in an array with different spacing and topologies. This research addresses the issue of mutual coupling at source with passive circuitry introduced into the antenna array to counter the element cross-talk by means of a radically novel analogue Vector Cancellation network that employs a bandpass filter and coupler/splitter. Cancellation of the mutual coupling is achieved by replicating the arrays coupling response in antiphase, thus destructively interfering with the inherent antenna mutual coupling. Several different configurations of network using both lumped components, and microstrips were analysed. In a coupled microstip design (measured), the coupling was reduced by greater than 23 dB over the whole antenna bandwidth with improved radiation efficiency and measured average reduction in load pull due to antenna coupling from over 50 Ω to 4 Ω. This can be scaled up to multidimensional antenna arrays which would reduce the load pull effects on the amplifiers, decrease spectral growth, increasing efficiency and improving beam steering.

5G communications are exploiting millimetre wave (mmWave) spectrum designed to provide a high data rate and low latency. Applications with vehicular communications are subject to many challenges due to the dynamic channel characteristics, which should be addressed whilst developing the hardware. Therefore, the need to understand the impact of motion on the communications bearer necessities unlocking the parameters causing antenna's depointing. The vibrations produced from moving on uneven roads induce a Doppler power spectrum which causes a change of the composite amplitude and phase of the antenna's radiation pattern. This will degrade the fidelity of the link and the information caring capacity. Therefore, this thesis presents several measurement methodologies to characterise a mmWave vehicular channel and unlock one more parameter that characterises a vehicular channel by investigating the reflectivity that causes phase changes and the antenna's vibration resulting from a vehicle's suspension variations and causing antenna's depointing. The unlocked parameter is the micro-Doppler shift which is not limited to applications of the Radar Cross-Section. The contributions to the design methodologies include: • Investigation of the system functions in conjunction with the condensed parameters that characterise a vehicular channel by performing novel outdoor measurements to reflect simple V2V or V2I communication channels using the 26 GHz phased array antenna at the transmitter and a horn antenna at the receiver. • Develop novel theoretical and geometrical models that reflect mmWave vehicular communication channel with vibrations to investigate the gain sensitivity and the observed micro-Doppler shift with the Doppler power spectrum considering the antennas' heights and beamwidths. • Validate the theoretical model by performing novel reflectivity measurements in the Anechoic chamber. A narrow beamwidth shows a significant impact of suspension variations rather than a wider one for a height of 5G base station for macro-cell operating at mmWave over a maximum distance the system's dynamic range could cope. A metal reflector changes the phase response and induces a micro-Doppler shift whilst it moves. Furthermore, a 2.6휆 vertical displacement due to vibration of the receiver's antenna with 17° − 23° beamwidth results in a 2 dB difference in the average amplitude of the Doppler power spectrum.

Localisation in wireless communication systems is an important topic that has many applications. Accurate geolocation in urban environments is a well understood challenge and Global Navigation Satellite System (GNSS) based technologies like GPS yield poor accuracy in non-line-of-sight (NLOS) scenarios. Use of multiple GNSS systems improves location accuracy but is still affected by urban canyons. Mobile network-based schemes offer an alternative, particularly when antenna arrays are deployed. Massive antenna arrays in Massive Multiple-Input-Multiple-Output (Massive MIMO) present an opportunity because of the possibility to use inexpensive, low-power and low-precision components with greatly reduced complexity/cost, in addition to Massive MIMO being a core component of 5G. This thesis reviews the problem of localisation in urban environments and investigates the techniques that are relevant towards achieving localisation in next generation wireless systems. It evaluates the NLOS problem and proposes schemes that use machine leaning techniques in the form of Least-Squares Support Vector Machines (LSSVMs), to address the challenges. It also investigates Direction of Arrival (DOA) estimation, which is a step towards localisation, using the Bristol Massive MIMO testbed. The proposed location specific approach presented in this thesis is a new framework which is shown to achieve a best case NLOS identification accuracy of greater than 98 percent. This result exceeds reported accuracies for existing NLOS identification techniques. Another proposed direct localisation approach achieves an 80th percentile probability location accuracy of 10 metres without utilising NLOS identification and mitigation. DOA estimation experiments demonstrate the possibility of performing estimation using subsets of antennas on a single base station antenna array. An outdoor experiment demonstrated a best case DOA RMSE of 2 degrees achieved for 3 different User Equipment (UE) positions. Overall, the results in this thesis demonstrate techniques that can be employed to solve the intermediate challenges towards device localisation and can contribute to the design and operation of next-generation systems. Significant benefits for mobile wireless systems can be derived from localisation. New handover strategies, new dynamic resource, power and pilot allocation schemes that take advantage of the location information, can also be developed.

Multi-user multiple input multiple output (MU-MIMO) technologies exploit the spatial do- main to serve multiple users on the same time-frequency resource, achieving unrivalled spectral efficiencies. This thesis investigates and proposes novel signal processing-based solutions to practical challenges associated with two MU-MIMO technologies that are expected to play a key role in future wireless systems - massive MIMO and distributed MIMO cloud radio access networks (C-RAN). The first part of this thesis addresses the problem of peak-to-average-power ratio (PAPR) reduction, for improving the operating power efficiency of the large number of power amplifiers used in massive MIMO transmitters. It begins by using Bussgang's theory to derive a statistical signal model for the distortion introduced by conventional clipping-based PAPR reduction. This model is then used to develop a practical and effective PAPR reduction scheme that uses spatial filtering to eliminate the effects of clipping distortion from the signals received by the users, and can incorporate active constellation extension for improved performance. The remainder of the thesis focuses on lossy data compression for MIMO C-RAN - reducing the quantity of signal data such that low capacity fronthaul connections can be used. For the massive MIMO uplink, transform coding is shown to be effective at exploiting the inherent sparsity in the received signals to achieve efficient data compression. This transform coding approach is then adapted for distributed MIMO, using jointly optimised rate allocations to account for correlations between the signals received at different remote receivers. The final part of the thesis shows that distributed dimension reduction can be applied to distributed MIMO to produce a reduced dimension MIMO system that preserves many of the benefits provided by deploying a large number of antennas. Combined with simple scalar quantization, this represents an efficient fronthaul data compression/reduction strategy for both the distributed MIMO uplink and downlink.

In order to deliver the high capacity and throughput goals for 5G and beyond wireless connectivity, the effective use of Millimetre Wave (mmWave) spectrum is necessary. When compared to sub-6GHz spectrum, these higher frequencies incur greater attenuation due to path loss and blockages, necessitating the use of directional antennas at both ends of the communications link. These are most likely to be implemented by means of an antenna array and beamformer in a highly integrated form within the RF transceiver. In such compact devices, antenna connectors are typically not available, thus negating the use of connective testing methodologies. Further, the mmWave operational environments synonymous with 5G New Radio (NR), are known to be highly dynamic in both spatial and temporal domains, hence the need for effective low cost mmWave Over-the-Air (OTA) testing for both product development, optimisation and compliance testing. The novel millimetre wave OTA architecture described herein, importantly facilitates the excitation of the Device Under Test (DUT) from multiple dynamic angles of illumination, thus representing realistic operating conditions for 5G NR, as well as the handover operation between multiple access points (APs). The method exploits the reflective properties of the ellipse, overcoming the pin-point focal regions by means of multiple discrete plane reflectors configured onan ellipsoidal frame. The evolved architecture offers a test zone commensurate with integrated mmWave antennas and beamformers as well as compliance with the testing specifications of the 3GPP standardisation body. The research presented is based on theoretical analysis and raytracing to develop the highly novel solution, culminating with a series of practical measurements. The technique developed offers a low-cost novel solution for testing devices operating at mmWaves frequencies (e.g. 28 GHz) with screen size of up to 7 inches (≈18 cm). The laboratory-based prototype offers multi-source excitation and a test zone volume of 20 cm by 20 cm by 20cm. The main advantage of this method is that the multiple signals illuminating the DUT can be generated from a single location by an individual two-dimensional (2D) phase antenna arrayconformed by multiple sub-arrays. To mimic real link conditions the feeder antenna must be connected to a base station emulator in order to stimulate the DUT with the test signals. Ifrequired, an optional channel emulator can create temporal, and frequency fading conditions. With a 2D array facet, it is possible to electronically beam steer the signals in both azimuth and elevation from the source point. The signals will be redirected by means of one or more reflectors towards the DUT, thereby creating a 3D spatially addressable stimulus. This architecture can be readily enhanced to improve the characteristics of the test zone through the use of specially shaped reflector, active reflectarrays or active metasurfaces.

This thesis relates to the subject of propagation modelling for cellular radio communications. Since current generations of cellular radio are forecast to be incapable of delivering the data traffic expected by consumers, new 5G radio specifications have been put forward which have stringent latency, data rate, density and mobility requirements. To meet these requirements new technologies have been proposed such as mmWave and MIMO. To obtain a sufficient understanding of wireless radio channel behaviour to design these new systems well, channel models are required that handle their idiosyncrasies. This thesis discusses propagation modelling theory in Chapter 2, and shows how a ray tracing model can be used to design communication systems in Chapter 3. In Chapter 4, a new ray launching tool, designed to be an experimental platform for investigating models of propagation phenomena, is documented. In Chapter 5, diffuse scattering and diffraction models are implemented and evaluated against measured data. Chapter 6 describes techniques for the optimisation of ray tracing tools, and a new ray tracing tool is implemented as part of this work. Chapter 7 is devoted to the radio channel in situations in which there is mobility.

Machine to Machine (M2M) communications are a rapidly expanding subset of the Internet of Things (IoT). Example scenarios include small wireless sensor networks, which may only transmit small amounts of data a few times a day; being constrained by a finite and small battery life. This thesis examines the use of 4G (LTE) mobile communications for M2M, and how power consumption may be optimised. Whilst 4G may not be the most efficient way to communicate, the network ubiquity makes ease of deployment a highly attractive option. With this low efficiency, every possible technique should be considered to recover system efficiency, and increase battery life. The approach to this problem involves analysis of LTE signals, measurement and modelling of power consumption in real devices, and evaluation of candidate hardware techniques to improve efficiency. Hardware in the loop methods are used extensively, based on simulated and live networks to verify benefit. For LTE signals, correlation is observed between the signal envelope, and degrees of freedom within the system, such as bandwidth and modulation scheme. This allows the operating point of the power amplifier to be altered to reflect the current signal characteristics without the need to continually monitor the envelope, enabling low cost efficiency enhancement. Energy consumption of LTE modems was measured and modelled for a variety of use cases to produce information aimed at selecting appropriate transmission profiles. In order to remain energy competitive with other long range systems, LTE modems should be used in a high latency mode, accepting an increase in cold start time. Load modulation and dynamic power supply technologies are investigated for low speed modulation based only on MAC layer information in order to increase system efficiency. Improvements of up to ten percentage points in Power Added Efficiency across a reasonable range of output power values have been demonstrated.

We tend to assume that pervasive wireless connectivity exists everywhere, and with new applications such as Virtual Reality, Autonomous Driving and the Internet of Things, this with require a 1000-fold increase in capacity by 2020 based on cellular capacity in 2016. This increase now presents significant challenges to wireless system designers. The majority of consumer wireless technologies currently operate using spectrum between 380MHz and 6GHz. Given the favourable propagation for cellular communications, wireless local area networking (Wi-Fi), terrestrial television broadcasting and radar, this spectral spot has become extremely crowded, and mechanisms to enhance the spectrum effficiency are thus needed. Massive multiple-input, multiple-output (Ma-MIMO) enables efficient utilization of the limited radio resources providing significant capacity improvement by multiplexing more simultaneous users within the same radio resource by means of spatial domain signal processing. This thesis evaluates the practicality of using Ma-MIMO in real-world scenarios and identifies solutions to operational deployments as they are uncovered. At the time this work commenced, only a few real-time evaluations had been conducted and the majority of the theoretical papers were not validated. The work in this thesis presents the per-cell spectral efficiency (SE) of 145.6 bits/s/Hz achieved with a 128-antenna Ma-MIMO testbed and introduces the challenges and the limitation factors that were revealed when delivering this level of spectrum efficiency enhancement. Here, the Ma-MIMO channel robustness is evaluated through various indoor and outdoor field trials, and the improved channel robustness was then exploited to design a simple uplink closed loop power control scheme. This thesis also introduces novel adaptive user grouping algorithms to further enhance the Ma-MIMO advantages for different applications. The algorithms presented address the interference caused by the multiple simultaneous user channel vectors in the same frequency time domain as well as errors due to hardware impairments. This can be achieved by means of a novel error vector magnitude (EVM) prediction method proposed herein. Importantly, all the proposed algorithms and approaches in this thesis have been evaluated experimentally by means of a software-defined radio Ma-MIMO testbed.

Many wireless communications systems require access to multiple frequency bands in compact form factors. The capability of an antenna to achieve high efficiency and wide bandwidth is linked to its physical size. Efficient wide-band antennas can be too large for compact multi-band systems in the low UHF range (300-1000 MHz). Electrically small antennas (ESAs) can work around the spectrum requirements if they are frequency agile, but efficiency degradation associated with the tuning mechanism is often overlooked. There is also no consistent approach to reporting the performance enhancement over an integrated bandwidth from the efficiency perspective, upon which the user experience ultimately depends. Three topical tuning mechanisms have been investigated in the UHF band, each underpinned by identification of candidate technologies from the literature, design of a frequency agile demonstrator antenna, and measurement of the input response, 3D radiation pattern and realised efficiency. First, the ability of an RF-MEMS reconfigurable impedance matching network to preserve system efficiency has been challenged. Improved impedance matching in both free-space tuning and hand effect detuning scenarios was achieved, but the radiation performance of the whole system highlighted that previously undocumented losses given by emerging RF MEMS capacitors should not be overlooked when assessing tuner deployment in communication systems. Second, a Co2Z magneto-dielectric substrate material was found to offer profound miniaturisation (novel material achieved frequency reduction of 6.4× compared to Duroid RT5880) and susceptibility to magnetic biasing (frequency tuning 32% for S11 < -3 dB). The measured efficiency was found to be around 1% for this iteration of the material. Nonetheless, the miniaturisation and tuneability aspects warrant ongoing review for use in applications that are miniaturisation-critical, since the novel material offers significant board area savings as well as radiation pattern stability. Third, an improved novel approach to quantifying 'tuneability' in compact narrow band antennas (including electrically small antennas) has been formulated, emphasising the perspective of combined realised efficiency and frequency agility. Favouring efficiency aspects in the new approach increases relevance to power consumption, battery life, data rates and carbon emissions at the network level. Metrics for bandwidth of assured efficiency, average efficiency and integrated efficiency-bandwidth product have been given, reducing the commonplace over-reliance on tuneable S11 in isolation as a predictor of tuning performance. Demonstration of the approach has been given by application to a set of fixed-frequency/varactor-tuneable loop ESAs. The improved approach provides a platform for objective, quantified performance grading of a diverse range of antenna tuning technologies in future work, alleviating the problem of identification and grouping of tuning technologies by application. This in turn could reduce wasted design effort as well as promoting efficiency as a design concern in tuneable antenna solutions.