Evaluation of Sigma-Delta-over-Fiber for High-Speed Wireless Applications

Future mobile communication networks aim to increase the communication speed,\ua0provide better reliability and improve the coverage. It needs to achieve all of these enhancements, while the number of users are increasing drastically. As a result, new base-station (BS) architectures where the signal processing is centralized and wireless access is provided through multiple, carefully coordinated remote radio heads are needed. Sigma-delta-over-fiber (SDoF) is a communication technique that can address both requirements and enable very low-complexity, phase coherent remote radio transmission, while transmitting wide-band communication signals with high quality. This thesis investigates the potential and limitations of SDoF communication links as an enabler for future mobile networks.In the first part of the thesis, an ultra-high-speed SDoF link is realized by using state-of-the-art vertical-cavity surface-emitting-lasers (VCSEL). The effects of VCSEL characteristics on such links in terms of signal quality, energy efficiency and potential lifespan is investigated. Furthermore, the potential and limitations of UHS-SDoF are evaluated with signals having various parameters. The results show that, low-cost, reliable, energy efficient, high signal quality SDoF links can be formed by using emerging VCSEL technology. Therefore, ultra-high-speed SDoF is a very promising technique for beyond 10~GHz communication systems.In the second part of the thesis, a multiple-input-multiple-output (MIMO) communication testbed with physically separated antenna elements, distributed-MIMO, is formed by multiple SDoF links. It is shown that the digital up-conversion, performed with a shared local-oscillator/clock at the central unit, provides excellent phase coherency between the physically distributed antenna elements. The proposed testbed demonstrates the advantages of SDoF for realizing distributed MIMO systems and is a powerful tool to perform various communication experiments in real environments.In general, SDoF is a solution for the downlink of a communication system, i.e. from central unit to remote radio head, however, the low complexity and low cost requirement of the remote radio heads makes it difficult to realize the uplinks of such systems. The third part of this thesis proposes an all-digital solution for realizing complementary uplinks for SDoF systems. The proposed structure is extensively investigated through simulations and measurements and the results demonstrate that it is possible realize all-digital, duplex, optical communication links between central units and remote radio heads.In summary, the results in this thesis demonstrate the potential of SDoF for wideband, distributed MIMO communication systems and proposes a new architecture for all-digital duplex communication links. Overall, the thesis shows that SDoF technique is powerful technique for emerging and future mobile communication networks, since it enables a centralized structure with low complexity remote radio heads and provides high signal quality

Novas arquiteturas para transmissores digitais flexíveis e de banda larga

Next generation of wireless communication (5G) devices must achieve higher data rates, lower power consumption and better coverage by making a more efficient use of the RF spectrum and adopting highly exible radio architectures. To meet these requirements, the development of new radio devices will be far more complex and challenging than their predecessors. The future of radio communications have a twofold evolution, being one the low power consumption and the other the adaptability and intelligent use of the available resources. Conventional approaches for the radio physical layer are not capable to cope with the new demand for multi-band, multi-standard radio signals and present an inefficient and expensive solution for simultaneous transmission of multiple and heterogeneous radio signals. Digital radio transmitters have been presented as a solution for a newer and more exible architecture for future radios. All-digital transmitters use a completely digital implementation of the entire radio datapath from the baseband processing to the digital RF up-conversion. This concept bene ts from the use of highly integrated hardware together with a strong radio digitalization, motivated by the exibility and high performance from cognitive and software defi ned radio. However, such devices are still far from a massive deployment in most of communication scenarios due to some limiting factors that hinder their use. This PhD thesis aims to the development of novel radio architectures and ideas based on all-digital transmitters capable of improving the adaptability and use intelligently the available resources for software de ned and cognitive radio systems. The focus of this thesis is on the improvement of some of the common limitations for all-digital transmitters such as power efficiency, bandwidth, noise-shaping and exibility while using efficient and adaptable digital architectures. In the initial part of the thesis a review of the state-of-the-art is presented showing the most common digital transmitter architectures as well as their major bene ts and key limitations. A comparative analysis of such architectures is made considering their power and spectral efficiency, exibility, performance and cost. Following this initial analysis, the work developed on the course of this PhD is presented and discussed. The initial focus is on the improvement of all-digital transmitters bandwidth trough the study and use of parallel processing techniques capable of greatly improve common bandwidth values presented in the state-of-the-art. The presented work has resulted in several publications where FPGA-based architectures use parallel digital processing techniques to improve the system's bandwidth by a factor higher than 10. Other fundamental contribution of this thesis is focused on the pulsedtransmitters coding efficiency. In this section of the thesis, a method is presented showing the reduction of the quantization noise created by low amplitude resolution digital transmitters using multiple combined pulsedtransmitters to cancel the noise in speci c frequencies. This work has resulted in two main publications that showed how to increase the coding efficiency of the pulse-transmitters as well as the overall efficiency of the transmission system. Lastly, new-noise shaping methods are presented in order to develop new and more exible architectures for all-digital transmitters. The methods presented use new quantization processes that allow for the shaping of the quantization noise produced in pulsed-transmitters while using very simple and adaptable architectures. With these new techniques, it is possible to adjust the noise frequency distribution and deliberately change the noise shape in order to change some of the transmitter's characteristics such as central frequency or bandwidth. The work presented on this thesis has shown promising improvements to the all-digital transmitters' state-of-the-art, either in simulations and laboratory prototype measurements. It has contributed to advance the state-of-the-art in agile and power efficient all-digital RF transmitters with multi-mode and multi-channel capabilities and the improvement of the transceiver's bandwidth enabling the development of true software de ned and cognitive radio systemsA próxima geração de comunicações sem os (5G) exigirá taxas de transmissão mais elevadas, maior efi ciência energética e uma melhor cobertura fazendo um uso mais efi ciente do espectro de radiofrequência e adotando o uso de arquiteturas rádio mais flexíveis. Para cumprir tais requisitos, o desenvolvimento de novos dispositivos rádio será substancialmente mais complexo do que nas gerações anteriores. O futuro das comunicações rádio depende maioritariamente de dois fatores; o baixo consumo de potência e o uso inteligente dos recursos e tecnologias disponíveis. As abordagens convencionais para a camada física dos sistemas rádio não são as mais adequadas para lidar com a necessidade de dispositivos multi-banda e que usem múltiplos standards, por serem soluções inefi cientes e demasiado caras para esse efeito. Os transmissores rádio completamente digitais têm vindo a ser apresentados na literatura como uma solução inovadora e mais flexível para a implementação dos futuros sistemas de rádio. Os transmissores completamente digitais apresentam uma implementação da cadeia de processamento rádio, desde a banda-base até à conversão para RF, completamente constituída por lógica digital. Este conceito tira partido da vasta integração alcançada nas arquiteturas digitais, juntamente com a flexibilidade proveniente da digitalização das arquiteturas rádio que já se encontra em curso com a evolução dos rádios cognitivos e definidos por software. No entanto, devido a algumas limitações inerentes à tecnologia, este tipo de transmissores ainda não é amplamente utilizado na maioria dos sistemas. Esta tese de doutoramento propõe e avalia novas arquiteturas para transmissores completamente digitais, bem como novas técnicas de processamento de sinal que possam beneficiar das tecnologias de implementação existentes (e.g. FPGAs) por forma a construir novos transmissores digitais de forma eficiente e flexível. O objetivo desta tese é reduzir as limitações atuais ainda presentes neste tipo de transmissores, nomeadamente as relacionadas com a eficiência, largura de banda, cancelamento de ruído e falta de flexibilidade. Na parte inicial desta tese é realizada a revisão do estado da arte das diversas topologias de transmissores digitais bem como as suas principais vantagens e limitações técnicas. É também feita uma análise comparativa das diversas técnicas apresentadas em termos da sua eficiência energética, flexibilidade, desempenho e custo. De seguida, é apresentado o trabalho desenvolvido no contexto desta tese de doutoramento, seguindo-se uma discussão focada na resolução das atuais limitações deste tipo de transmissores. A primeira parte foca-se no uso de técnicas de processamento paralelo de sinal, por forma a suportar sinais de largura de banda mais elevada que os reportados no atual estado da arte. O trabalho desenvolvido e publicado baseia-se no uso de arquiteturas implementadas em FPGA que contribuíram para um aumento da largura de banda num fator de aproximadamente dez vezes. Outra das contribuições fundamentais desta tese consiste no aumento da eficiência do sistema através da melhoria da eficiência de codificação do sinal pulsado produzido. Com base no uso de múltiplos transmissores pulsados, e apresentado um esquema de combinação construtiva e destrutiva de sinais para a redução do ruído de quantização proveniente das técnicas de processamento de sinal pulsado usadas. Este trabalho resultou em duas importantes publicações que mostram que a melhoria da eficiência de codificação do sinal pode ser utilizada de forma a obter uma maior eficiência energética do transmissor. Por ultimo, são apresentadas diversas técnicas para a conversão dos sinais banda-base em sinais RF pulsados. As propostas apresentadas permitem o uso de uma arquitetura de hardware simplista, mas configurável por software, o que a torna bastante flexível. Com o uso desta arquitetura e possível alterar em pleno funcionamento a frequência central bem como a largura de banda e resposta do conversor pulsado. O trabalho apresentado nesta tese demonstra alguns dos melhoramentos no estado da arte para transmissores r adio completamente digitais, baseando os resultados obtidos não apenas em simulações mas também na implementação e medidas realizadas sobre protótipos laboratoriais. O trabalho desenvolvido no âmbito desta tese contribuiu com avanços na implementação de transmissores ageis, eficientes, com maior largura de banda e capazes de transmissão em múltiplas bandas com recurso a múltiplos protocolos, abrindo caminho para o desenvolvimento de novos rádios cognitivos e definidos por softwareFCT, FSEPrograma Doutoral em Engenharia Eletrotécnic

Linear Operation of Switch-Mode Outphasing Power Amplifiers

Radio transceivers are playing an increasingly important role in modern society. The ”connected” lifestyle has been enabled by modern wireless communications. The demand that has been placed on current wireless and cellular infrastructure requires increased spectral efficiency however this has come at the cost of power efficiency. This work investigates methods of improving wireless transceiver efficiency by enabling more efficient power amplifier architectures, specifically examining the role of switch-mode power amplifiers in macro cell scenarios. Our research focuses on the mechanisms within outphasing power amplifiers which prevent linear amplification. From the analysis it was clear that high power non-linear effects are correctable with currently available techniques however non-linear effects around the zero crossing point are not. As a result signal processing techniques for suppressing and avoiding non-linear operation in low power regions are explored. A novel method of digital pre-distortion is presented, and conventional techniques for linearisation are adapted for the particular needs of the outphasing power amplifier. More unconventional signal processing techniques are presented to aid linearisation of the outphasing power amplifier, both zero crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear regions of the amplifiers. In combination with digital pre-distortion the techniques will improve linearisation efforts on outphasing systems with dynamic range and bandwidth constraints respectively. Our collaboration with NXP provided access to a digital outphasing power amplifier, enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural modelling and linearisation efforts. The collaboration resulted in a bench mark for linear wideband operation of a digital outphasing power amplifier. The complimentary linearisation techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in both simulated and practical outphasing test benches. Initial results are promising and indicate that the benefits they provide are not limited to the outphasing amplifier architecture alone. Overall this thesis presents innovative analysis of the distortion mechanisms of the outphasing power amplifier, highlighting the sensitivity of the system to environmental effects. Practical and novel linearisation techniques are presented, with a focus on enabling wide band operation for modern communications standards

Earth imaging with microsatellites: An investigation, design, implementation and in-orbit demonstration of electronic imaging systems for earth observation on-board low-cost microsatellites.

This research programme has studied the possibilities and difficulties of using 50 kg microsatellites to perform remote imaging of the Earth. The design constraints of these missions are quite different to those encountered in larger, conventional spacecraft. While the main attractions of microsatellites are low cost and fast response times, they present the following key limitations: Payload mass under 5 kg, Continuous payload power under 5 Watts, peak power up to 15 Watts, Narrow communications bandwidths (9.6 / 38.4 kbps), Attitude control to within 5°, No moving mechanics. The most significant factor is the limited attitude stability. Without sub-degree attitude control, conventional scanning imaging systems cannot preserve scene geometry, and are therefore poorly suited to current microsatellite capabilities. The foremost conclusion of this thesis is that electronic cameras, which capture entire scenes in a single operation, must be used to overcome the effects of the satellite's motion. The potential applications of electronic cameras, including microsatellite remote sensing, have erupted with the recent availability of high sensitivity field-array CCD (charge-coupled device) image sensors. The research programme has established suitable techniques and architectures necessary for CCD sensors, cameras and entire imaging systems to fulfil scientific/commercial remote sensing despite the difficult conditions on microsatellites. The author has refined these theories by designing, building and exploiting in-orbit five generations of electronic cameras. The major objective of meteorological scale imaging was conclusively demonstrated by the Earth imaging camera flown on the UoSAT-5 spacecraft in 1991. Improved cameras have since been carried by the KITSAT-1 (1992) and PoSAT-1 (1993) microsatellites. PoSAT-1 also flies a medium resolution camera (200 metres) which (despite complete success) has highlighted certain limitations of microsatellites for high resolution remote sensing. A reworked, and extensively modularised, design has been developed for the four camera systems deployed on the FASat-Alfa mission (1995). Based on the success of these missions, this thesis presents many recommendations for the design of microsatellite imaging systems. The novelty of this research programme has been the principle of designing practical camera systems to fit on an existing, highly restrictive, satellite platform, rather than conceiving a fictitious small satellite to support a high performance scanning imager. This pragmatic approach has resulted in the first incontestable demonstrations of the feasibility of remote sensing of the Earth from inexpensive microsatellites

The Telecommunications and Data Acquisition Report

Tracking and ground-based navigation; communications, spacecraft-ground; station control and system technology; capabilities for new projects; networks consolidation program; and network sustaining are described

The Design of Low Power Ultra-Wideband Transceiver

Ph.DDOCTOR OF PHILOSOPH

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression

The effects of some typical and atypical neuroleptics on gene regulation : implications for the treatment of schizophrenia

The mechanisms by which antipsychotics (neuroleptics) produce their therapeutic effects in schizophrenia are largely unknown. Although neuroleptic efficacy is attributed to central dopamine D2 and/or serotonin 5-HT2 receptor antagonism, clinical improvements in schizophrenia are not seen until two or three weeks after daily neuroleptic administration. The mechanisms underlying the neuroleptic response must therefore occur downstream from initial receptor blockade and be a consequence of chronic neurotransmitter receptor blockade. The goal of the present study was to use neuroleptics with varied dopamine vs. serotonergic receptor blocking profiles to elucidate some of these intracellular post receptor mechanisms. Since the final steps of both dopamine and serotonin synthesis require the enzyme aromatic L-amino acid decarboxylase (AADC), the effects of neuroleptics on AADC gene (mRNA) expression were examined in PC12 cells and compared to their effects on the synthetic enzyme tyrosine hydroxylase (TH) and ' c-fos' (an early immediate gene [IEG]) mRNA. The neuroleptics examined did not significantly regulate AADC mRNA in PC12 cells, and only haloperidol upregulated TH and 'c-fos' mRNA. Later studies in rats showed that acute neuroleptic administration increased ' c-fos' mRNA, whereas the immunoreactivity of a related IEG (delta FosB) was increased upon chronic treatment. These studies and a subsequent dose response study demonstrated that upregulation of both 'c-fos' mRNA and delta FosB immunoreactivity was most prominent in dopaminergic projection areas including the striatum and nucleus accumbens. Because it has been suggested that neuroleptic treatment might prevent neurodegeneration in schizophrenia, the effects of neuroleptics on the mRNA expression of neuroprotective target genes of delta FosB were examined both ' in vivo' and 'in vitro'. These genes included brain-derived neurotrophic factor (BDNF), the neuroprotective enzyme superoxide dismutase (SOD), and the low affinity nerve growth factor receptor (p75). While dopamine D2 blockade unfavorably regulated BDNF and p75 mRNA, 5-HT 2 blockade either had no effect on or favorably regulated BDNF, SOD, and p75 mRNA. Thus, although little about the contribution of serotonergic blockade in the neuroleptic response was determined, dopaminergic blockade regulated IEG's and several of their target genes. Future studies will be needed to understand the role of 5-HT2 receptor blockade in the neuroleptic response