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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.

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.