UWB for multi-gigabit/s communications beyond 60 GHz

The recently allocated 71–76 GHz and 81–86 GHz bands provide an opportunity for realizing Line Of Sight (LOS) links for directional point-to-point “last mile” applications. An efficient use of this spectrum may allow wireless to finally “catch up” with wires, leading to systems such as “multi-Gigabit wireless Ethernet,” and “wireless fiber.” However, the transmission at such a frequency range is characterized by several additional challenges compared to lower frequency bands, from both technological and propagation point of view, which makes difficult to use them efficiently. In this scenario, IR (Impulse Radio) UWB (Ultra Wide Band) technology might offer some more degrees of freedom for the design of a highly integrated and low cost transceiver. This work has at its core the design and BER (Bit Error Rate) performance evaluation of an IR-UWB architecture based on an 85 GHz up-conversion stage of train of Gaussian pulses having duration lower than 1 ns. Finally, we compare performance of this architecture with the ones of a more traditional continuous wave communications system with FSK (Frequency Shift Keying) modulation. Simulation results show that BER performance, in presence of RF non-linearities, for an IR-UWB transceiver architecture operating at 85 GHz (with same data rate and bandwidth) are better than a coherent BFSK scheme working in a similar scenario. Finally, some conclusions are reported, pointing out the UWB antenna design and the future works related to the modeling of the channel at frequencies beyond 60 GHz and the implementation of the test bed

Spectral and Energy Efficient Communication Systems and Networks

In this thesis, design and analysis of energy- and spectral-efficient communication and cellular systems in micro wave and millimeter wave bands are considered using the following system performance metrics: i) Energy efficiency; ii) Spectral efficiency; iii) Spatial spectral efficiency; iv) Spatial energy efficiency, and v) Bit error rate. Statistical channel distributions, Nakagami-m and Generalized-K, and path loss models, Line of Sight (LOS) and Non-Line of Sight (NLOS), are used to represent the propagation environment in these systems. Adaptive M-QAM and M-CPFSK communication systems are proposed to enhance their efficiency metrics as a function of Signal-to-Noise Ratio (SNR) over the channel. It is observed that in the adaptive M-QAM system energy efficiency can be improved by 0.214 bits/J whereas its spectral efficiency can be enhanced by 40%, for wide range of SNR compared to that of conventional M-QAM system. In case of adaptive M-CPFSK system, spectral and energy efficiencies can be increased by 33% and 76%, respectively. A framework for design and analysis of a cellular system, with omni and sectorized antenna systems at Base Station (BS), using its efficiency metrics and coverage probability is presented assuming wireless channel is Nakagami-m fading coupled with path loss and co-channel interference. It is noted that sectorized antenna system at BS enhances energy and spectral efficiencies by nearly 109% and 1.5 bits/s/Hz, respectively, compared to conventional omni antenna system. A Multi-User MIMO cellular system is then investigated and closed-form expressions for its uplink efficiency metrics are derived for fading and shadowing wireless channel environment. It is observed that increasing number of antennas in MIMO system at BS can significantly improve efficiency metrics of cellular system. Finally, a framework for design and analysis of dense mmWave cellular system, in 28 and 73 GHz bands, is presented for efficient utilization of spectrum and power of the system. The efficiency metrics of the system are evaluated for LOS and NLOS links. It is observed that while 28 GHz band is expedient for indoor cellular systems, the 73 GHz band is appropriate for outdoor systems

Millimeter-wave and terahertz optical heterodyne photonic integrated circuits for high data rate wireless communications

The data rate of wireless communications systems has been increasing because of the new applications that today’s society are applying. The prospective data rate for wireless communications in the marketplace will be 100 Gbps within 10 years. Therefore, to enable such data rates the use of millimetre and terahertz (THz) waves, whose frequencies range from 100 GHz to 1 THz, for broadband wireless communications is very suitable and efficient. At frequencies above 100 GHz, GaAs and InP based devices and integrated circuits (ICs) have been key players in THz communications research, because of high cut-off and maximum frequencies of transistors. In fact, the photonics-based transmitter has become more effective to achieve higher data rates of over 20 Gbps. This could be realized thanks to the availability of telecom-based high-frequency components such as lasers, modulators and photodiodes (O-E converters). The use of optical fiber cables enables us to distribute high-frequency RF signals over long distances, and makes the size of transmitter frontends compact and light. Regarding the photonics-based receiver, photodiode is the photonic component best suited to be a signal downconverter. It is used an enveloped detector, so an easy modulation format such as on-off keying shifting (OOK) can be used to recover the transmitted data. Most common optical continuous wave (CW) signal generator is based on an optical heterodyning, using a dual-wavelength optical source. In this technique, two optical wavelengths λ1 and λ2 are mixed on a photodiode or a photoconductor to generate an electrical beat note with its frequency being determined by the difference of the two optical wavelengths. There are different solutions to implement the dual wavelength source. The most straightforward source involves combining the light from two independent different single-frequency semiconductor lasers. The most straightforward approach to implement these signal generation schemes is to assemble the required discrete components. However, the optical fiber connections that are required introduce many problems, including path length variations due to thermal variations. A novel approach, that is becoming readily available nowadays, is to use photonic integration techniques. Photonic integration allows placing all of the required components onto a single chip. This has several advantages, starting from eliminating fiber coupling losses among the different components. Besides, a reduced size of the components gives a result a cost-effective solution.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Tadao Nagatsuma.- Secretario: Horacio Lamela Rivera.- Vocal: Íñigo Molina Fernánde

On-chip mode-locked microwave photonic integrated circuits

Mención Internacional en el título de doctorLa generación de frecuencias cada vez más elevadas, llegando al rango de ondas Milimétricas (mmW, de 30 a 300 GHz) y ondas de Terahertz (THz, 300-3000 GHz) es una forma de hacer frente a la creciente necesidad de ancho de banda en las comunicaciones inalámbricas que utilizan técnicas de modulación simples. Los resultados experimentales recientes han informado tasas de datos de hasta 48 Gbps en una frecuencia portadora de 300 GHz que demuestra que una solución rentable para hacer frente a los anchos de banda requeridos en las comunicaciones inalámbricas es aumentar la frecuencia de la onda portadora en la región de ondas milimétricas y más allá. Las dificultades para generar, amplificar y modular las señales en estas frecuencias se han superado mediante la combinación de lo mejor de dos mundos, electrónica y fotónica, resultando en un nuevo campo comúnmente referido hoy en día como fotónica de microondas. Un sistema de fotónica de microondas usualmente incluye un sintetizador de frecuencia óptica (OFS) y un convertidor opto-electrónico (OEC). El OFS es especialmente diseñado para entregar una señal óptica que cuando es convertida al dominio eléctrico por el OEC genera una señal eléctrica de alta frecuencia. Actualmente, la mayoría si no son todos los reportes de enlaces de comunicación inalámbrica que operan por encima de 100 GHz emplean generación fotónica de la frecuencia portadora. Generalmente, hay dos principales técnicas de generación de señal fotónica comúnmente usadas, fuentes pulsadas y fuentes heterodinas. Uno de los méritos de las fuentes pulsadas sobre las heterodinas es que para la misma potencia óptica se alcanza mayor potencia eléctrica emitida (aproximadamente 7 dBm por encima). Por lo tanto, las fuentes pulsadas son una opción atractiva para ser implementada como un generador de portadora con el nuevo enfoque de la integración fotónica. En el marco de este trabajo, hemos desarrollado un nuevo tipo de fuentes fotónicas basadas en la técnica de generación de señal pulsada, la cual puede ser fabricada mediante una fundición genérica en un circuito integrado fotónico. Nuestras soluciones son estructuras de láser mode-locked integradas en chip, diseñadas usando bloques de construcción genéricos de una plataforma de tecnología de integración fotónica en indio-fósforo. Nosotros hemos diseñado y caracterizado nuevas estructuras de láser mode-locked integradas en chip usando reflectores de interferencia multimodo, los cuales nos permiten ubicar los dispositivos en cualquier lugar dentro del chip, haciendo la señal óptica disponible para el resto de componentes en el chip, y permitiendo las subsecuentes operaciones de procesamiento de señal fotónica dentro del chip (modulación, filtrado óptico, multiplicación de la tasa de repetición, etc.). Nosotros hemos publicado un láser ―colliding pulse mode-locked‖ integrado en chip trabajando a una tasa de repetición de 70 GHz y un nuevo láser ―multiple colliding pulse mode-locked‖ integrado en chip operando a una tasa de repetición de 100 GHz. Como valor añadido, las características de rendimiento de las nuevas estructuras de láser mode-locked integradas en chip permiten ser utilizadas como una fuente pulsada en enlaces inalámbricos en banda-E y banda-F. La estructura de láser ―colliding pulse mode-locked‖ integrada en chip trabajando a una taza de repetición de 70 GHz se ha utilizado para demostrar el enlace inalámbrico en banda-E, mientras que la estructura de láser ―multiple colliding pulse mode-locked‖ integrada en chip funcionando a una frecuencia de 100 GHz fue usada para demostrar el enlace inalámbrico en banda-F.The generation of increasingly higher frequencies, reaching the Millimeter (MMW, 30 to 300 GHz) and Terahertz-wave (THz, 300 to 3000 GHz) range is one way to address the increasing need for bandwidth in wireless communications using simple modulation techniques. Recent experimental results have reported data rates up to 48 Gbps on a 300 GHz carrier frequency demonstrating that a cost effective solution to cope with the required bandwidths in wireless communications is to increase the carrier wave frequency into the millimeter wave region and beyond. The difficulties to generate, amplify and modulate signals at these frequencies have been overcome by combining the best of two worlds, electronics and photonics, arising a new field commonly referred nowadays as microwave photonics. A microwave photonic system usually involves an optical frequency synthesizer (OFS) and an opto-electronic converter (OEC). The OFS is specifically designed to deliver an optical signal that when is converted to the electrical domain by the OEC generates a high frequency electrical signal. Currently, most if not all of the reported wireless communication links operating above 100 GHz employ photonic generation of the carrier frequency. Generally, there are two main photonic signal generation techniques commonly used, pulsed sources and heterodyning sources. One of the merits of pulsed sources over heterodyning ones is that for the same optical power achieves a higher electrical emitted power (about 7 dBm above). Thus, pulsed sources are an attractive option to be implemented as a carrier generator with the novel approach of photonic integration. In the frame of this work, we have developed a new kind of photonic sources based on the pulsed signal generation technique, which can be fabricated within a generic foundry in a photonic integrated circuit. Our solutions are on-chip mode-locked laser structures, designed using generic building blocks from an indium-phosphide photonic integration technology platform. We have designed and characterized novel on-chip mode-locked laser structures using multimode interference reflectors, which enable us to locate the devices anywhere on the chip, making the optical signal available to the rest of the components on the chip, and allowing subsequent photonic signal processing operations within the chip (modulation, optical filtering, repetition rate multiplication and so on). We have reported an on-chip colliding pulse mode-locked laser working at 70 GHz repetition rate and a novel on-chip multiple colliding pulse mode-locked laser operating at 100 GHz repetition rate. As an added value, the performance characteristics of the novel on-chip mode-locked laser structures allow them to be used as a pulsed source in E-band and F-Band wireless link demonstrations. The on-chip colliding pulse mode-locked laser working at 70 GHz repetition rate has been used to demonstrate E-band wireless link while the on-chip multiple colliding pulse mode-locked laser operating at 100 GHz repetition rate was used to demonstrate the F-Band wireless link.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: John Mcinerney.- Secretario: Horacio Lamela Rivera.- Vocal: Erwin Bent