A GaAs FET bandpass distributed amplifier under optical illumination has been in¨estigated from the small-signal equi¨alent circuit model, and the¨ariation of gain¨ersus frequency responses as a function of optically induced plasma density ha¨e been reported. ᮊ 1998John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 41᎐43, 1998. Key words: distributed amplifier; millimeter-wa¨e circuit; optical control; semiconductor plasma INTRODUCTIONThe direct optical illumination of microwave semiconductor devices has been an area of growing interest, since various RF control functions such as gain control of amplifiers, oscillator tuning, locking, and frequency modulation, as well as switching, mixing, limiting, and phase shifting, can be w x achieved 1, 2 . Optical control of microwave amplifiers can . be achieved in two different ways: 1 by direct injection of . light into the active device region, or 2 by indirect means, such as using a photodetector to convert the optical energy to electrical energy which then acts to change the gain of the device. The injection of light effectively provides an extra terminal to the device, which possesses inherent optical isolation, no decoupling structure being required. Many investigaw x w x tions have been carried out on GaAs FET 3 and HEMT 4 under optical illumination. In this paper, the active circuit which has been considered under direct optical illumination is the GaAs FET bandpass distributed amplifier. A distributed amplifier using MESFET was demonstrated by Jutzi w x 5 , and the concept was successfully applied to GaAs MESw x FET amplifier at microwave frequencies 6 .The fundamental physical mechanism arising in optical illumination of the MESFET is the generation of free carriers within the semiconductor material when irradiation energy is greater than or equal to the bandgap energy of the semiconductor material used for the device. Regions between gate and source and between gate and drain allow penetration of light, which is absorption in the active region and substrate. Due to the photovoltaic effects in the gate region and the active channel, there are changes in the parasitic resistances such as transconductance, gate-to-source capacitance, and drain-to-sourcergate-to-source resistances. The equivalent circuit and its parameters of a bandpass disw x tributed amplifier have been considered from 7 , and the change in equivalent circuit parameters due to the photow x voltaic and photoconductive effects are estimated from 3 . Finally, the variation of gain bandwidth under optical illumination has been quantitatively discussed. GaAs FET DISTRIBUTED AMPLIFIER UNDER OPTICAL ILLUMINATIONA schematic diagram of the bandpass distributed amplifier Ž . considered for the analysis is shown in Figure 1 a , and its small-signal equivalent circuit model under illumination is Ž . w x shown in Figure 1 b 7 . In the case of a bandpass distributed amplifier, the optimum number of devices decides the maximum gain, and it has been chosen as four.The change in transconductance of ...

Positioning a person or an object has become essential in many applications. It already exists solutions for outdoor positioning such as satellite based techniques (i.e. GPS) but indoor positioning still remains a great challenge for applications like sports monitoring, contextual visits of museum, Building Information Modeling (BIM) or automated drone missions. Classical approaches using radio communication such as WiFi, Bluetooth, ZigBee only give an accuracy of approximately 2.5 meters when the mobile is static, of course worse when moving. Recently some new radio communication chipsets have emerged based on Ultra Wide Band (UWB) communications. UWB allows accurate Time Of Flight (TOF) measurements, and thus distances estimations between nodes equipped with. A positioning algorithm named Best Anchor Selection for Trilateration (BAST) based on position prediction and noise estimation is proposed. Then a wearable, light and low power Wireless Sensor Network (WSN) prototype (named Zyggie) including an UWB chipset has been developed for algorithms comparison. Finally, an experimental testbed using real cases experiments shows that BAST can give from 1.26 up to 4.17 times better accuracy than low complexity state of the art algorithms when the mobile/person is in movement (e.g. tennis player).

Nowadays, there is a high demand for human and/or objects monitoring/localizing in the context of applications like Building Information Modeling (BIM), automated drone missions, contextual visits of museum or sports monitoring for instance. While for outdoor positioning accurate and robust solutions (i.e. GPS) exist for many years, indoor positioning is still very challenging. There is also a need of gesture/motion tracking systems that could replace video solutions. We propose in this paper a hardware/software platform named Zyggie that combines both Ultra Wide Band (UWB) technology and Received Signal Strength Indicator (RSSI) for low power accurate indoor positioning and Inertial Measurement Unit (IMU) utilization for motion tracking. Very few industrial/academic existing solutions can simultaneously perform indoor positioning and motion tracking and none of them can do both under low power, low cost and compacity constraints addressed by our platform. As Zyggie has the capability to estimate distances w.r.t other platforms in the environment and quaternions (which represents the attitude/orientation) users can test/enhance state of the art algorithms for positioning and motion tracking applications.

LoRa is popular for internet of things applications as this communication technology offers both a long range and a low power consumption. However, LoRaWAN, the standard MAC protocol that uses LoRa as physical layer, has the bottleneck of a high downlink latency to achieve energy efficiency. To overcome this drawback we explore the use of wake-up radio combined with LoRa, and propose an adequate MAC protocol that takes profit of both these heterogeneous and complementary technologies. This protocol allows an opportunistic selection of a cluster head that forwards commands from the gateway to the nodes in the same cluster. Furthermore, to achieve self-sustainability, sensor nodes might include an energy harvesting sub-system, for instance to scavenge energy from the light, and their quality of service can be tuned, according to their available energy. To have an effective self-sustaining LoRa system, we propose a new energy manager that allows less fluctuations of the quality of service between days and nights. Latency and energy are modeled in a hybrid manner, i.e., leveraging microbenchmarks on real hardware platforms, to explore the influence of the energy harvesting conditions on the quality of service of this heterogeneous network. It is clearly demonstrated that the cooperation of nodes within a cluster drastically reduces the latency of LoRa base station commands, e.g., by almost 90% compared to traditional LoRa scheme for a 10 nodes cluster.