Transceiver architectures and sub-mW fast frequency-hopping synthesizers for ultra-low power WSNs

Wireless sensor networks (WSN) have the potential to become the third wireless revolution after wireless voice networks in the 80s and wireless data networks in the late 90s. This revolution will finally connect together the physical world of the human and the virtual world of the electronic devices. Though in the recent years large progress in power consumption reduction has been made in the wireless arena in order to increase the battery life, this is still not enough to achieve a wide adoption of this technology. Indeed, while nowadays consumers are used to charge batteries in laptops, mobile phones and other high-tech products, this operation becomes infeasible when scaled up to large industrial, enterprise or home networks composed of thousands of wireless nodes. Wireless sensor networks come as a new way to connect electronic equipments reducing, in this way, the costs associated with the installation and maintenance of large wired networks. To accomplish this task, it is necessary to reduce the energy consumption of the wireless node to a point where energy harvesting becomes feasible and the node energy autonomy exceeds the life time of the wireless node itself. This thesis focuses on the radio design, which is the backbone of any wireless node. A common approach to radio design for WSNs is to start from a very simple radio (like an RFID) adding more functionalities up to the point in which the power budget is reached. In this way, the robustness of the wireless link is traded off for power reducing the range of applications that can draw benefit form a WSN. In this thesis, we propose a novel approach to the radio design for WSNs. We started from a proven architecture like Bluetooth, and progressively we removed all the functionalities that are not required for WSNs. The robustness of the wireless link is guaranteed by using a fast frequency hopping spread spectrum technique while the power budget is achieved by optimizing the radio architecture and the frequency hopping synthesizer Two different radio architectures and a novel fast frequency hopping synthesizer are proposed that cover the large space of applications for WSNs. The two architectures make use of the peculiarities of each scenario and, together with a novel fast frequency hopping synthesizer, proved that spread spectrum techniques can be used also in severely power constrained scenarios like WSNs. This solution opens a new window toward a radio design, which ultimately trades off flexibility, rather than robustness, for power consumption. In this way, we broadened the range of applications for WSNs to areas in which security and reliability of the communication link are mandatory

Feed-forward linearisation of a directly modulated semiconductor laser and broadband millimetre-wave wireless over fibre systems.

This thesis is concerned with reduction of non-linear distortion in a directly modulated uncooled semiconductor laser using feed-forward compensation and investigating the performance of broadband millimetre-wave wireless over fibre systems. One of the key elements that determine the performance in a fibre optic link is the linearity of the optical source. Direct modulation of an uncooled semiconductor laser diode is a simple and cost effective solution. However, the distortion and noise generated by the laser limit the achievable dynamic range and performance in a system. Feed-forward linearisation is demonstrated at 5 GHz, the highest operating frequency reported, with 26 dB third order intermodulation distortion suppression and simultaneous noise reduction leading to enhanced spurious free dynamic range of 107 dB (1Hz). The effectiveness of feed-forward in a multi-channel system is investigated. Laser non-linearity can cause spectral re-growth and interchannel distortion that can completely mask the adjacent channel. A significant 11 dB interchannel distortion suppression and 10.5 dB power advantage is obtained compared to the non-linearised case. These results suggest that feed-forward linearisation arrangement can make a practical multi-channel or multi-operator wireless over fibre system. In the second part of this thesis the first experimental transmission of wireless data over fibre with remote millimetre-wave local oscillator delivery using a bi-directional semiconductor optical amplifier in a full duplex system with 2.2 km coarse wavelength division multiplexing fibre ring architecture is demonstrated. The use of bi-directional SOAs in place of unidirectional erbium doped fibre amplifier or unidirectional SOAs, together with the use of CWDM and optical distribution of the local oscillator signal allow substantial reduction in overall complexity and cost. Successful transmission of data over 12.8 km fibre is achieved with clear and well defined constellations and eye diagrams as well as 10.5% and 7.8 % error vector magnitude values for the downlink and uplink directions, respectively. The thesis also presents an implementation and performance of a millimetre-wave gigabit wireless over fibre system. CWDM devices such as uncooled laser diodes and passive components are used for the first time in a gigabit system allowing cost savings compared to dense WDM. This makes such solutions more attractive for millimetre-wave access systems. Optically modulated gigabit wireless data signals to and from the base stations are distributed at 5 GHz and up-converted using a remotely delivered LO source. Eye diagrams and bit error rate are measured to assess the system performance

Vigilancia tecnológica: Estudio sectorial. Sector de las tecnologías de la información y comunicación: Tecnologías inalámbricas

las Tecnologías Inalámbricas dentro del sector de las Tecnologías de la Información y la Comunicación (TIC). Se ha abordado este sector al tratarse de uno de los sectores preferentes en la política de la Junta de Andalucía. El objetivo del Estudio es el de proporcionar una amplia información al sector TIC de Andalucía sobre todo lo que concierne a las tecnologías inalámbricas, haciendo hincapié en la información tecnológica y científica relacionada. En concreto, la vigilancia tecnológica está centrada en las siguientes tecnologías inalámbricas, que se han considerado más relevantes: < Tecnologías 3G y emergentes < Tecnologías WiFi < Tecnologías WiMax < Tecnologías Bluetooth < Tecnologías ZigBee < Tecnologías RFID En primer lugar, tras presentar de forma resumida los principales conceptos de la Vigilancia Tecnológica, se realiza un análisis exhaustivo de aquella información que es más relevante para el tejido empresarial andaluz. A continuación se señalan tendencias tecnológicas, normativa y legislación vigente que afecta a dicho campo sectorial. Para concluir el estudio, se incluye un Anexo técnico donde se describen en detalle aquellas tecnologías en las que se ha enfocado el estudio de vigilancia tecnológica

An Ultra-Low Power Predistortion-based FHSS Transmitter

In the new era of personal communications, the energy available for a wireless node is the limiting factor. Furthermore wireless links should be robust even in the harsh indoor environment where fading, attenuation and interferences can be severe. Spread-Spectrum techniques are largely used to have a robust link, while Frequency-Hopping (FH) is the most suitable for low data-rate applications. Unfortunately state-of-the-art FH systems are still far too complex and too power hungry to be implemented in a self contained wireless node. The proposed architecture simplifies considerably the hardware requirements for the hopping synthesizer achieving a current consumption of only 900 ,µA (excluding the output buffer) from a 1.8 V power supply

An 1mA Ultra-low Power FHSS TX Front-end Utilizing Direct-modulation with Digital Pre-distortion

This paper deals with the system and circuit-level aspects of an ultra-low-power robust wireless node for an asymmetric wireless link. A single building block TX front-end for a frequency hopping spread spectrum (FHSS) transmitter implemented in silicon-on-anything (SOA) bipolar technology is presented. It is realized with a directly modulated RF cascoded Colpitts power voltage-controlled oscillator (VCO), a frequency locked loop for center frequency calibration, and a digital pre-distortion algorithm for accurate frequency bins synthesis. The TX front-end draws only 1 mA at -18 dBm output power. By combining digital system techniques for frequency hopping and merging the VCO and the power amplifier (PA), a robust solution is obtained for indoor ultra-low-power wireless links. The proposed pre-distortion concept allows reduction of the hardware complexity, while the combination of a cascode output buffer and a common-collector Colpitts VCO allows us to reduce the complete FHSS front-end to a single building block that directly drives the antenna through a balun. A dedicated digital algorithm on the receiver side reduces the center frequency offset from a maximum value of 8.2 MHz to less than 8 ppm avoiding the use of any crystal on the transmitter side. Precision in the hopping synthesis is obtained by employing a ST-DFT based demodulator with differential encoding and an offset sending technique. The novel FHSS-predistortion concept has been verified by realizing a full wireless link that achieves a bit error rate better than 1.1% at -25 dBm output power while transmitting across an 8 meters indoor non-line-of-sight (NLOS) path

An 1mA Ultra-low Power FHSS TX Front-end Utilizing Direct-modulation with Digital Pre-distortion

This paper deals with the system and circuit-level aspects of an ultra-low-power robust wireless node for an asymmetric wireless link. A single building block TX front-end for a frequency hopping spread spectrum (FHSS) transmitter implemented in silicon-on-anything (SOA) bipolar technology is presented. It is realized with a directly modulated RF cascoded Colpitts power voltage-controlled oscillator (VCO), a frequency locked loop for center frequency calibration, and a digital pre-distortion algorithm for accurate frequency bins synthesis. The TX front-end draws only 1 mA at -18 dBm output power. By combining digital system techniques for frequency hopping and merging the VCO and the power amplifier (PA), a robust solution is obtained for indoor ultra-low-power wireless links. The proposed pre-distortion concept allows reduction of the hardware complexity, while the combination of a cascode output buffer and a common-collector Colpitts VCO allows us to reduce the complete FHSS front-end to a single building block that directly drives the antenna through a balun. A dedicated digital algorithm on the receiver side reduces the center frequency offset from a maximum value of 8.2 MHz to less than 8 ppm avoiding the use of any crystal on the transmitter side. Precision in the hopping synthesis is obtained by employing a ST-DFT based demodulator with differential encoding and an offset sending technique. The novel FHSS-predistortion concept has been verified by realizing a full wireless link that achieves a bit error rate better than 1.1% at -25 dBm output power while transmitting across an 8 meters indoor non-line-of-sight (NLOS) path