16 research outputs found
Elevation scanning laser/multi-sensor hazard detection system controller and mirror/mast speed control components
The electro-mechanical and electronic systems involved with pointing a laser beam from a roving vehicle along a desired vector are described. A rotating 8 sided mirror, driven by a phase-locked dc motor servo system, and monitored by a precision optical shaft encoder is used. This upper assembly is then rotated about an orthogonal axis to allow scanning into all 360 deg around the vehicle. This axis is also driven by a phase locked dc motor servo-system, and monitored with an optical shaft encoder. The electronics are realized in standard TTL integrated circuits with UV-erasable proms used to store desired coordinates of laser fire. Related topics such as the interface to the existing test vehicle are discussed
Modelling, simulation and control of photovoltaic converter systems
The thesis follows the development of an advanced solar photovoltaic power conversion
system from first principles. It is divided into five parts.
The first section shows the development of a circuit-based simulation model of a
photovoltaic (PV) cell within the 'SABER' simulator environment. Although simulation models
for photovoltaic cells are available these are usually application specific, mathematically intensive
and not suited to the development of power electronics. The model derived within the thesis is
a circuit-based model that makes use of a series of current/voltage data sets taken from an actual
cell in order to define the relationships between the cell double-exponential model parameters and
the environmental parameters of temperature and irradiance. Resulting expressions define a
'black box' model, and the power electronics designer may simply specify values of temperature
and irradiance to the model, and the simulated electrical connections to the cell provide the
appropriate I/V characteristic.
The second section deals with the development of a simulation model of an advanced PVaware
DC-DC converter system. This differs from the conventional in that by using an embedded
maximum power tracking system within a conventional linear feedback control arrangement it
addresses the problem of loads which may not require the level of power available at the
maximum power point, but is also able to drive loads which consistently require a maximum
power feed such as a grid-coupled inverter.
The third section details a low-power implementation of the above system in hardware.
This shows the viability of the new, fast embedded maximum power tracking system and also the
advantages of the system in terms of speed and response time over conventional systems.
The fourth section builds upon the simulation model developed in the second section by
adding an inverter allowing AC loads (including a utility) to be driven. The complete system is
simulated and a set of results obtained showing that the system is a usable one.
The final section describes the construction and analysis of a complete system in hardware
(c. 500W) and identifies the suitability of the system to appropriate applications
Airborne range and orbit determination design study- volumes i - iv final report
Airborne Range and Orbit Determination systems design, development, assembly, testing, and analysi
Recommended from our members
Signal Encoding and Digital Signal Processing in Continuous Time
This work investigates signal encoding in, and architectures of, digital signal processing systems that function in continuous time (CT). Unlike conventional digital signal processors (DSPs), which rely on a clock to dictate the sampling times of an analog-to-digital converter (ADC) and to provide the tap delay timing, CT DSPs function entirely in continuous time, without a sampling or a synchronizing clock. The samples of a CT DSP system are generated and processed only when some measure of the input signal crosses a predetermined threshold. The effective sampling rate and the dynamic power dissipation of a CT digital system automatically adapt to the activity of the input signal. The properties of signals sampled in continuous time are investigated in this thesis. A technique for reducing the effective sampling rate of a CT system is presented, in which the digital signal encoding is varied by adjusting the resolution according to a property of the input. A variable-resolution system leads to a decrease in the number of samples generated, a reduction in the power dissipation and a reduction in the effective chip area of a CT DSP, all without sacrificing in-band performance. The properties of several asynchronous signal-driven sampling techniques are analyzed and compared. The architecture and signal encoding of CT DSPs for signals in the lower gigahertz frequency range are investigated, with consideration of speed and accuracy limitations in the context of submicron CMOS technologies. A per-edge digital signal encoding technique is developed, which bypasses timing problems of processing high-speed digital signals; the properties of per-edge encoded signals are discussed. The design considerations of a low-resolution per-edge-encoded gigahertz-range CT DSP are discussed and an implementation for a possible application is detailed. A prototype chip has been fabricated in ST 65 nm CMOS technology, which has a compact processor core area of 0.073 mm^2. The implemented CT digital processor achieves SNDR of over 20 dB with 3 bits of resolution and a maximum usable -3 dB bandwidth of 0.8 GHz to 3.2 GHz. The processor can be configured as a one-tap to six-tap CT FIR filter and has an active power dissipation that varies from 0.27 mW to 9.5 mW, depending on the amplitude and frequency of the input signal
Quantifying, generating and mitigating radio interference in Low-Power Wireless Networks
Doctoral Programme in Telecommunication - MAP-teleRadio interference a ects the performance of low-power wireless networks (LPWN),
leading to packet loss and reduced energy-e ciency, among other problems. Reliability
of communications is key to expand application domains for LPWN. Since most LPWN
operate in the license-free Industrial Scienti c and Medical (ISM) bands and hence share
the spectrum with other wireless technologies, addressing interference is an important
challenge.
In this context, we present JamLab: a low-cost infrastructure to augment existing LPWN
testbeds with accurate interference generation in LPWN testbeds, useful to experimentally
investigate the impact of interference on LPWN protocols.
We investigate how interference in a shared wireless medium can be mitigated by performing
wireless channel energy sensing in low-cost and low-power hardware. For this
pupose, we introduce a novel channel quality metric|dubbed CQ|based on availability
of the channel over time, which meaningfully quanti es interference. Using data collected
from a number of Wi-Fi networks operating in a library building, we show that our metric
has strong correlation with the Packet Reception Rate (PRR). We then explore
dynamic radio resource adaptation techniques|namely packet size and error correction
code overhead optimisations|based on instantaneous spectrum usage as quanti ed by
our CQ metric.
To conclude, we study emerging fast fading in the composite channel under constructive
baseband interference, which has been recently introduced in low-power wireless
networks as a promising technique. We show the resulting composite signal becomes
vulnerable in the presence of noise, leading to signi cant deterioration of the link, whenever
the carriers have similar amplitudes.
Overall, our results suggest that the proposed tools and techniques have the potential
to improve performance in LPWN operating in the unlicensed spectrum, improving
coexistence while maintaining energy-e ciency. Future work includes implementation
in next generation platforms, which provides superior computational capacity and more
exible radio chip designs.A interferência de r adio afeta o desempenho das redes de comunicação sem o de baixo consumo - low-power wireless networks (LPWN), o que provoca perdas de pacotes, diminuição da e ciência energética, entre outros problemas. A contabilidade das comunicações e importante para a expansão e adoção das LPWN nos diversos domínios de potencial aplicação. Visto que a grande maioria das LPWN partilham o espectro radioelétrico com outras redes sem o, a interferência torna-se um desafio importante.
Neste contexto, apresentamos o JamLab: uma infraestrutura de baixo custo para estender a funcionalidade dos ambientes laboratoriais para o estudo experimental do desempenho das LPWN sob interferência. Resultando, assim, numa ferramenta essencial para a adequada verificação dos protocolos de comunicações das LPWN.
Para al em disso, a Tese introduz uma nova técnica para avaliar o ambiente radioelétrico e demostra a sua utilização para gerir recursos disponíveis no transceptor rádio, o que permite melhorar a fiabilidade das comunicações, nomeadamente nas plataformas de baixo consumo, garantindo e ciência energética. Assim, apresentamos uma nova métrica| denominada CQ - concebida especificamente para quantificar a qualidade do canal r adio, com base na sua disponibilidade temporal. Mediante dados adquiridos em v arias redes sem o Wi-Fi, instaladas no edifício de uma biblioteca universitária, demonstra-se que esta métrica tem um ótimo desempenho, evidenciando uma elevada correlação com a taxa de receção de pacotes. Investiga-se ainda a potencialidade da nossa métrica CQ para gerir dinamicamente recursos de radio como tamanho de pacote e taxa de correlação de erros dos códigos - baseado em medições instantâneas da qualidade do canal de radio.
Posteriormente, estuda-se um modelo de canal composto, sob interferência construtiva de banda-base. A interferência construtiva de banda-base tem sido introduzida recentemente nas LPWN, evidenciando ser uma técnica prometedora no que diz respeito à baixa latência e à contabilidade das comunicações. Na Tese investiga-se o caso crítico em que o sinal composto se torna vulnerável na presença de ruído, o que acaba por deteriorar a qualidade da ligação, no caso em que as amplitudes das distintas portadoras presentes no receptor sejam similares.
Finalmente, os resultados obtidos sugerem que as ferramentas e as técnicas propostas têm potencial para melhorar o desempenho das LPWN, num cenário de partilha do espectro radioelétrico com outras redes, melhorando a coexistência e mantendo e ciência energética. Prevê-se como trabalho futuro a implementação das técnicas propostas em plataformas de próxima geração, com maior flexibilidade e poder computacional para o processamento dos sinais rádio.This work was supported by FCT (Portuguese Foundation for Science and Technology) and by ESF
(European Social Fund) through POPH (Portuguese Human Potential Operational Program), under
PhD grant SFRH/BD/62198/2009; also by FCT under project ref. FCOMP-01-0124-FEDER-014922
(MASQOTS), and EU through the FP7 programme, under grant FP7-ICT-224053 (CONET)
The 25th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting
Papers in the following categories are presented: recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; international and transnational applications of precise time and time interval (PTTI) technology with emphasis on satellite laser tracking networks, GLONASS timing, intercomparison of national time scales and international telecommunication; applications of PTTI technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; application of PTTI technology to evolving military communications and navigation systems; and dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites