A 27-MHz frequency shift keying wireless system resilient to in-band interference for wireless sensing applications

A 27-MHz wireless system with binary frequency shift keying (BFSK) modulation at 400-kHz is reported. The receiver has been designed to handle in-band interference corrupting the BFSK signal with the use of complex filters and amplitude comparison method. The BFSK modulation is carried out with a voltage-controlled oscillator before up-converting with a 27-MHz local oscillator. The bipolar junction transistors (BJT-based) power amplifier with 30% efficiency pumps 220 mW into a spiral antenna. The inductive-degenerated low-noise amplifier with a voltage of more than 30 dB amplifies an incoming signal before feeding into a mixer for complex direct down conversion. With deliberate Gaussian interference injection, the minimum ratios between the signal with interference and the interference only at the distance of 2.5, 10 and 15 m are 3.3, 8.5 and 11.5 dB, respectively at a maximum data rate of 20 kbps. Without any interference included, the system can achieve a data rate of 40 kbps at the maximum transmission distance of 15 m. Conceptually agreed with the presented bit-error-rate (BER) analysis, the BER measurements with Gaussian and single-tone/two-tone in-band interferences also confirm superiority offered by the amplitude comparison method where the signal-to-noise ratio is at 1 dB for BER=10-3 at 10 kbps (10 dB better than the phase detection counterpart)

IoT for measurements and measurements for IoT

The thesis is framed in the broad strand of the Internet of Things, providing two parallel paths. On one hand, it deals with the identification of operational scenarios in which the IoT paradigm could be innovative and preferable to pre-existing solutions, discussing in detail a couple of applications. On the other hand, the thesis presents methodologies to assess the performance of technologies and related enabling protocols for IoT systems, focusing mainly on metrics and parameters related to the functioning of the physical layer of the systems

Development of an integrated silicon photonic transceiver for access networks

Debido a la imparable aparición de dispositivos móviles multifunción junto con aplicaciones que requieren cada vez más un mayor ancho de banda en cualquier momento y en cualquier lugar, las futuras redes de acceso deberán ser capaces de proporcionar servicios tanto inalámbricos como cableados. Es por ello que una solución a seguir es el uso de sistemas de comunicaciones ópticas como medio de transporte de señales inalámbricas en enlaces de radio sobre fibra. Con ello, se converge a un dominio óptico reduciendo y aliviando el cuello de botella entre los estándares de acceso inalámbrico y cableado. En esta tesis, como parte de los objetivos establecidos en el proyecto europeo HELIOS en el que está enmarcada, se han investigado y desarrollado los bloques funcionales básicos necesarios para realizar un transceptor fotónico integrado trabajando en el rango de longitudes de onda milimétricas, y haciendo uso de los formatos de modulación más robustos y que mejor se adaptan al ámbito de aplicación considerado. El trabajo que se presenta en esta tesis se puede dividir básicamente en tres partes. La primera de ellas ofrece una descripción general de los beneficios del uso de la fotónica en silicio para el desarrollo de enlaces inalámbricos a velocidades de Gbps, así como el estado del arte de los transceptores desarrollados por los grupos de investigación más activos y punteros para satisfacer las necesidades de mercado, cada vez más exigentes. La segunda parte se centra en el estudio y desarrollo del transmisor integrado de onda milimétrica. Primero realizamos una breve introducción teórica tanto del funcionamiento de los dispositivos que forman parte del transmisor, como a los formatos de modulación existentes, centrando la atención en la modulación por desplazamiento de fase (PSK) que es la que se va a utilizar en el desarrollo de los dispositivos implicados, y más concretamente en la modulación (diferencial) de fase en cuadratura ((D)QPSK). También se presentan los bloques básicos que integran nuestro transmisor y se fijan las especificaciones que deben cumplir dichos bloques para conseguir una transmisión libre de errores. El transmisor está compuesto por un filtro/demultiplexor encargado de separar dos portadoras ópticas separadas una frecuencia de 60 GHz. Una de estas portadoras es modulada al pasar por un modulador DQPSK basado en una estructura de dos MachZehnders (MZs) anidados, para ser nuevamente combinada con la otra portadora óptica que se ha mantenido intacta. Una vez combinadas, éstas son fotodetectadas para ser transmitidas inalámbricamente. En la tercera parte de esta tesis, se investiga el uso de un esquema de diversidad en polarización junto a un receptor DQPSK integrado para la demodulación de la señal recibida. El esquema de diversidad en polarización está formado básicamente por dos bloques: un separador de polarización con el objetivo de separar la luz a la entrada del chip en sus dos componentes ortogonales; y un rotador de polarización. En lo que se refiere al receptor DQPSK propiamente dicho, se ha investigado y optimizado cada uno de los bloques funcionales que lo componen. Éstos son básicamente un divisor de potencia termo-ópticamente sintonizable basado en un interferómetro MZ, en serie con un interferómetro MZ que introduce un retardo de duración de un bit en uno de sus brazos, para obtener una correcta demodulación diferencial. El siguiente bloque que forma parte de nuestro receptor DQPSK es un 2x4 acoplador de interferencia multimodal actuando como un híbrido de 90 grados, cuyas salidas van a parar a dos fotodetectores balanceados de germanio. Las contribuciones principales de esta tesis han sido: ¿ Demostración de un filtro/demultiplexor con tres grados de sintonización con una relación de extinción superior a 25dB. ¿ Demostración de un rotador con una longitud de tan sólo 25µm y CMOS compatible. ¿ Demostración de un modulador DPSK a una velocidad máxima de 20 Gbit/s. ¿ Demostración de un demodulador DQPSK a una velocidad máxima de 20 Gbit/s.Due to the relentless emergence of multifunction mobile devices with applications that require increasingly greater bandwidth at anytime and anywhere, future access networks must be capable of providing both wireless and wired services. The use of optical communications systems as transport medium of wireless signals over fiber radio links is a steady solution to be taken into account. This will make possible a convergence to an optical domain reducing and alleviating the bottleneck between wireless access standards and current wired access. In this thesis, as part of the objectives of the European project HELIOS in which it is framed, we have investigated and developed the basic functional blocks needed to achieve an integrated photonic transceiver working in the range of millimetre wavelengths, and using robust modulation formats that best fit the scope considered. The work presented in this thesis can be basically divided into three parts. The first one provides an overview of the benefits of using silicon photonics for the development of wireless links at rates of Gbps, and the state of the art of the transceivers reported by the most important research groups in order to meet the increasingly demanding needs¿ market. The second part focuses on the study and development of millimetre-wave integrated transmitter. First we provide a brief theoretical introduction of the operation principles of the devices involved in the transmitter such as a modulation formats, focusing on the phase shift keying (PSK) which is the one that will be used, particularly the (differential) quadrature phase shift keying ((D) QPSK). We also present the building blocks involved in our transmitter and we set the specifications that must be met by these devices in order to achieve an error-free transmission. The transmitter includes a filter/demultiplexer which must separate two optical carriers 60 GHz separated. One of these optical carriers is modulated by passing through a DQPSK Mach-Zehnder-based modulator (MZM) by arranging two MZMs in a nested configuration. Using a combiner, the modulated optical signal and the un-modulated carrier are combined and photodetected to be transmitted wirelessly. In the third part of this thesis, we investigate the use of a polarization diversity scheme with an integrated DQPSK receiver for demodulating of the wireless signal. The polarization diversity scheme basically consists of two blocks: a polarization splitter in order to separate the random polarization state of the incoming light into its two orthogonal components, and a polarization rotator. Regarding the DQPSK receiver itself, all the functional blocks that comprise it have been investigated and optimized. It basically includes a thermo-optically tunable MZ interferometer power splitter, in series with a MZ interferometer that introduces, in one of its arms, a delay of one bit length in order to obtain a correct differential demodulation. The next building block of our DQPSK receiver is a 2x4 multimode interference coupler acting as a 90 degree hybrid, whose outputs are connected to two balanced germanium photodetectors. The main contributions of this thesis are: ¿ Demonstration of a filter/demultiplexer with three degrees of tuning and an extinction ratio greater than 25dB. ¿ Demonstration of a polarization rotator with a length of only 25¿m and CMOS compatible. ¿ Demonstration of a DPSK modulator at a maximum rate of 20 Gbit/s. ¿ Demonstration of a DQPSK demodulator to a maximum rate of 20 Gbit/s.Aamer, M. (2013). Development of an integrated silicon photonic transceiver for access networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31649TESI

All-optical processing systems based on semiconductor optical amplifiers

Doutoramento em Engenharia ElectrotécnicaNesta tese investigam-se e desenvolvem-se dispositivos para processamento integralmente óptico em redes com multiplexagem densa por divisão no comprimento de onda (DWDM). O principal objectivo das redes DWDM é transportar e distribuir um espectro óptico densamente multiplexado com sinais de débito binário ultra elevado, ao longo de centenas ou milhares de quilómetros de fibra óptica. Estes sinais devem ser transportados e encaminhados no domínio óptico de forma transparente, sem conversões óptico-eléctrico-ópticas (OEO), evitando as suas limitações e custos. A tecnologia baseada em amplificadores ópticos de semicondutor (SOA) é promissora graças aos seus efeitos não-lineares ultra-rápidos e eficientes, ao potencial para integração, reduzido consumo de potência e custos. Conversores de comprimento de onda são o elemento óptico básico para aumentar a capacidade da rede e evitar o bloqueio de comprimentos de onda. Neste trabalho, são estudados e analisados experimentalmente métodos para aumentar a largura de banda operacional de conversores de modulação cruzada de ganho (XGM), a fim de permitir a operação do SOA para além das suas limitações físicas. Conversão de um comprimento de onda, e conversão simultânea de múltiplos comprimentos de onda são testadas, usando interferómetros de Mach-Zehnder com SOA. As redes DWDM de alto débito binário requerem formatos de modulação optimizados, com elevada tolerância aos efeitos nefastos da fibra, e reduzida ocupação espectral. Para esse efeito, é vital desenvolver conversores integramente ópticos de formatos de modulação, a fim de permitir a interligação entre as redes já instaladas, que operam com modulação de intensidade, e as redes modernas, que utilizam formatos de modulação avançados. No âmbito deste trabalho é proposto um conversor integralmente óptico de formato entre modulação óptica de banda lateral dupla e modulação óptica de banda lateral residual; este é caracterizado através de simulação e experimentalmente. Adicionalmente, é proposto um conversor para formato de portadora suprimida, através de XGM e modulação cruzada de fase. A interligação entre as redes de transporte com débito binário ultra-elevado e as redes de acesso com débito binário reduzido requer conversão óptica de formato de impulso entre retorno-a-zero (RZ) e não-RZ. São aqui propostas e investigadas duas estruturas distintas: uma baseada em filtragem desalinhada do sinal convertido por XGM; uma segunda utiliza as dinâmicas do laser interno de um SOA com ganho limitado (GC-SOA). Regeneração integralmente óptica é essencial para reduzir os custos das redes. Dois esquemas distintos são utilizados para regeneração: uma estrutura baseada em MZI-SOA, e um método no qual o laser interno de um GC-SOA é modulado com o sinal distorcido a regenerar. A maioria dos esquemas referidos é testada experimentalmente a 40 Gb/s, com potencial para aplicação a débitos binários superiores, demonstrado que os SOA são uma tecnologia basilar para as redes ópticas do futuro.This thesis investigates and develops all-optical processing devices for wavelength division multiplexing networks (DWM) of the future. The ultimate goal of optical networks is to transport and deliver a densely multiplexed spectrum, populated by ultra-high bit rate signals over hundreds or thousands of kilometers of optical fiber. Such signals should be transported and routed transparently in the optical domain, without recurring to optic-electro-optic (OEO) conversions, avoiding its limitations and costs. Semiconductor optical amplifier (SOA) based technology is a promising building block due to its inherent ultra-fast and efficient non-linear effects, potential for integration, low power consumption and cost. Wavelength converters are the basic optical functionality to increase the network throughput and avoid wavelength blocking. Methods to increase the operation bandwidth of cross-gain modulation (XGM) converters are studied and experimentally assessed to enable operation beyond the physical constraints of SOA. Single and multi-wavelength conversion exploiting crossphase modulation (XPM) in Mach-Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is tested. High bit rate DWDM networks require optimized modulation formats with enhanced tolerance to fiber impairments and reduced spectral tolerance. As a consequence, it is crucial to develop all-optical modulation formats between legacy on-off-keying networks and networks employing advanced modulation formats. An all-optical format converter between optical double sideband (ODSB) and optical vestigial sideband (OVSB) based on SOA self-phase modulation is proposed and thoroughly characterized by simulations and experimental tests. A converter, which uses a mix of XGM and XPM to allow simultaneous pulse and modulation format conversion to the carrier suppressed format, is proposed. The interface between ultra-high bit rate transport networks and lower bit rate access networks requires optical pulse format conversions between return-tozero (RZ) and non-return-to-zero (NRZ). Two different structures are proposed and investigated. The first is based on detuned filtering of XPM converted signal; while the second uses the dynamics of the internal laser of a gainclamped SOA. All-optical regeneration is one of the most sought functionalities to reduce network costs. Regeneration is achieved in this work through two simple setups: a MZI-SOA based structure, and a method in which the internal laser from a GC-SOA is modulated with the input distorted signal. Most applications are experimentally validated at 40 Gb/s, with potential for even higher bit rates, demonstrating that SOA can be one of the key elements for the next generation of optical networks

Radar Detection, Tracking and Identification for UAV Sense and Avoid Applications

Advances in Unmanned Aerial Vehicle (UAV) technology have enabled wider access for the general public leading to more stringent flight regulations, such as the line of sight restriction, for hobbyists and commercial applications. Improving sensor technology for Sense And Avoid (SAA) systems is currently a major research area in the unmanned vehicle community. This thesis overviews efforts made to advance intelligent algorithms used to detect, track, and identify commercial UAV targets by enabling rapid prototyping of novel radar techniques such as micro-Doppler radar target identification or cognitive radar. To enable empirical radar signal processing evaluations, an S-Band and X-Band frequency modulated, software-defined radar testbed is designed, implemented, and evaluated with field measurements. The final evaluations provide proof of functionality, performance measurements, and limitations of this testbed and future software-defined radars. The testbed is comprised of open-source software and hardware meant to accelerate the development of a reliable, repeatable, and scalable SAA system for the wide range of new and existing UAVs

Advances in Optical Amplifiers

Optical amplifiers play a central role in all categories of fibre communications systems and networks. By compensating for the losses exerted by the transmission medium and the components through which the signals pass, they reduce the need for expensive and slow optical-electrical-optical conversion. The photonic gain media, which are normally based on glass- or semiconductor-based waveguides, can amplify many high speed wavelength division multiplexed channels simultaneously. Recent research has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions. Advances in Optical Amplifiers presents up to date results on amplifier performance, along with explanations of their relevance, from leading researchers in the field. Its chapters cover amplifiers based on rare earth doped fibres and waveguides, stimulated Raman scattering, nonlinear parametric processes and semiconductor media. Wavelength conversion and other enhanced signal processing functions are also considered in depth. This book is targeted at research, development and design engineers from teams in manufacturing industry, academia and telecommunications service operators

Noise-based Transmit Reference Modulation:A Feasibility Analysis

Wireless sensor networks (WSNs) receive huge research interest for a multitude of applications, ranging from remote monitoring applications, such as monitoring of potential forest fires, floods and air pollution, to domestic and industrial monitoring of temperature, humidity, vibration, stress, etc. In the former set of applications, a large number of nodes can be involved which are usually deployed in remote or inaccessible environments. Due to logistic and cost reasons, battery replacement is undesired. Energy-efficient radios are needed, with a power-demand so little that batteries can last the lifetime of the node or that the energy can be harvested from the environment. Coherent direct-sequence spread spectrum (DSSS) based radios are widely employed in monitoring applications, due to their overall resilience to channel impairments and robustness against interference. However, a DSSS rake receiver has stringent requirements on precise synchronization and accurate channel knowledge. To obviate the complexity of a coherent DSSS receiver, particularly for low data rate sensor networks, a DSSS scheme that has fast synchronization and possibly low power consumption, is much desired. In this regard, this thesis studies a noncoherent DSSS scheme called transmit reference (TR), which promises a simple receiver architecture and fast synchronization. In traditional TR, the modulated information signal is sent along an unmodulated reference signal, with a small time offset between them. In this thesis, we present and investigate a variant of TR, called noise-based frequency offset modulation (N-FOM), which uses pure noise as the spreading signal and a small frequency offset (instead of a time offset) to separate the information and reference signals. The detection is based on correlation of the received signal with a frequency-shifted version of itself, which collects the transmitted energy without compromising the receiver simplicity. Analytical expressions on performance metrics, supplemented by simulation results, improve understanding of the underlying mechanisms and provide insights into utility of N-FOM in low-power WSNs. In point-to-point line-of-sight (LOS) communication, it was observed that the communication scheme has a minimal utility. The energy-detector type of receiver mixes all in-band signals, which magnifies the overall noise. Particularly, the self-mixing of the transmitted signal also elevates the noise level, which increases with a further increase in the received signal energy. Therefore, for a fixed set of system parameters, the performance attains an asymptote with increasing transmission power. The phenomenon also establishes a non-monotonic relation between performance and the spreading factor. It was observed that a higher spreading factor in N-FOM is beneficial only in a high-SNR regime. After developing an understanding of the performance degrading mechanisms, few design considerations are listed. It is found that a suitable choice of the receiver front-end filter can maximize the SNR. However, the optimal filter depends on received signal and noise levels. A practically feasible – albeit suboptimal – filter is presented which gives close to the optimal performance. Next, timing synchronization is considered. The implications of synchronization errors are analyzed, and a synchronization strategy is devised. The proposed synchronization strategy has little overhead and can be easily implemented for symbol-level synchronization. The N-FOM LOS link model is extended to assess the performance degradation due to interference. Performance metrics are derived which quantify the effects of multiple-user interference, as well as that from external interferers, such as WiFi. Since the correlation operation mixes all in-band signals, the total interfering entities are quadratically increased. The research shows the vulnerability of N-FOM to interference, which makes it optimistic to operate in a crowded shared spectrum (such as the ISM 2.4\,GHz band). We also observe an upper limit on the number of mutually interfering links in a multiple access (MA) network, that can be established with an acceptable quality. The scheme is further investigated for its resilience against impairments introduced by a dense multipath environment. It is observed that despite the noise enhancement, the N-FOM system performs reasonably well in a non-line-of-sight (NLOS) communication. The detection mechanism exploits the multipath channel diversity and leads to an improved performance in a rich scattering environment. An analytical expression for outage probability is also derived. The results indicate that a healthy N-FOM link with very low outage probability can be established at a nominal value of the received bit SNR. It is also found that the choice of the frequency offset is central to the system design. Due to multiple practical implications associated with this parameter, the maximum data rate and the number of usable frequency offsets are limited, particularly in a MA NLOS communication scenario. The analysis evolves into a rule-of-thumb criterion for the data rate and the frequency offset. It is deduced that, due to its limited capability to coexist in a shared spectrum, N-FOM is not a replacement for coherent DSSS systems. The scheme is mainly suited to a low data rate network with low overall traffic, operating in an interference-free rich scattering environment. Such a niche of sensor applications could benefit from N-FOM where the design goal requires a simple detection mechanism and immunity to multipath fading

Optical fibre communication over a noisy partially coherent channel

As global IP traffic grows unceasingly, optical networks demand for technology upgrades in order to keep the feared “capacity crunch” away. The most celebrated technologies of coherent detection and wavelength-division multiplexing (WDM), widely deployed in long-haul links, are gaining ground in access networks, which is particularly challenging due to the shared-cost requirements, leading to denser channel spacings and the use of cheaper devices that tend to be noisier. In order to make the most of this technology combination, it is crucial to have a model of the channel that accurately describes all the present sources of noise. Traditionally, the most used model has been the additive white Gaussian noise (AWGN) channel, which, although only accounting for a linear contribution of complex noise and being insensitive to rotational phenomena, has shown its validity in numerous studies, as well as in commercial equipment. In this thesis, however, it is observed that the adoption of coherent detection and WDM, with lower-grade semiconductor lasers showing a moderate linewidth, yields scenarios where a phase-sensitive model becomes a must. The partially coherent AWGN (PCAWGN) channel is a popular choice that fulfils this need, but its high complexity due to non-trivial functions involved, deprives it from being suitable in high-speed digital circuits. The main goal of this thesis is to describe a reduced-complexity approximation in polar coordinates, accurate enough to find its applicability in modern systems. Furthermore, this works explores some possible end-to-end applications, like channel capacity estimation or symbol detection, assessing its performance by means of extensive simulations. Lastly, the emerging field of complex modulation of directly modulated lasers is revisited, with a special interest in how the proposed approximation can help to improve the performance of previously reported techniques, as well as proposing a new way to design spiral-shaped constellations aimed to maximise the channel capacity