1,721,097 research outputs found
Avalanche Microwave Noise Sources in Commercial 90-nm CMOS Technology
No full textThis paper presents a microwave noise source implemented in a commercial CMOS technology. The circuit is based on the avalanche noise generated by both the source-to-bulk and the drain-to-bulk junctions in reverse breakdown. Two sources of different junction area are fabricated using a standard NMOS transistor in 90-nm CMOS technology having a width of 5- and 20-μm, respectively. From the experimental characterization emerges that the breakdown voltage of the source/drain to bulk diodes is 12.4 V, whereas excess noise ratios (ENRs) of 20 dB (5-μm source) and of 25 dB (20-μm source) are observed at 24 GHz for a current density of about 0.14 mA per square micrometer. Finally, a theoretical explanation of the observed behaviors is proposed by means of an equivalent circuit. The developed noise source can be used in a CMOS system-on-chip (SoC) for a variety of applications ranging from the built-in self test (BIST) of the RF chain to the calibration of fully integrated microwave radiometric sensor
Avalanche noise diodes: A compact circuit model compatible with advanced CAD tools
No full textThis paper proposes, for the first time, a compact model for avalanche noise diodes that can easily be inserted in advanced CAD tools. The model is based on the theory of the Read type microwave avalanche diodes. It fully accounts for the electronic tuning of the avalanche frequency with the square root of the diode biasing current and is scalable with the device area. The equivalent circuit has been written for ADS of Keysight Technologies and is verified against published experiments. The modeled input impedance is within 20% of the measured one in the whole frequency band from DC to 40 GHz. Futhermore, the Excess Noise Ratio (ENR) of the diode can be predicted as a funtion of the avalanche current and is in good agreement with experiments. The developed model is useful for the simulation and the design of calibration circuits adopted by microwave radiometers, radio astronomy receivers and high reliability wireless apparatuses.ESPLABICLA
GNSS-Based Navigation for Lunar Missions
Get PDFNumerous applications, not only Earth-based, but also space-based, have strengthened the interest of the international scientific community in using Global Navigation Satellite Systems (GNSSs) as navigation systems for space missions that require good accuracy and low operating costs. Indeed, already used in Low Earth Orbits (LEOs), GNSS based-navigation GNSS-based navigation systems can maximize the autonomy of a spacecraft while reducing the costs of ground operations, allowing for budget-limited missions of micro- and nanosatellites. This is why GNSS is also very attractive for applications in higher Earth orbits up to the Moon, such as in Moon Transfer Orbits (MTOs). However, while GNSS receivers have already been exploited with success for LEOs, their use in higher Earth orbits above the GNSS constellation is extremely challenging, particularly on the way from the Earth to the Moon, characterized by weaker signals with wider gain variability, larger dynamic ranges resulting in higher Doppler and Doppler rates, critically lower satellite signal availability, and poorer satellite-to-user geometry. In this context, the first research objective and achievement of this PhD research is a feasibility study of GNSS as an autonomous navigation system to reach the Moon, and the determination of the requirements for the design of a code-based GNSS receiver for such a mission. The most efficient combinations of signals transmitted by the GPS, Galileo, and combined GPS-Galileo constellations have been identified by analyzing the theoretical achievable signal acquisition and tracking sensitivities, the resultant constellation availability, the pseudorange error factors, and the geometry error factor and accordingly the achievable navigation performance The results show that GNSS signals can be tracked up to Moon altitude, but not with the current GNSS receiver technology for terrestrial use. The second research objective and achievement is the design and implementation of a GNSS receiver proof-of-concept capable of providing GNSS observations onboard a space vehicle orbiting up to Moon altitude. This research work describes the hardware architecture, the high-sensitivity acquisition and tracking modules and the standalone single-epoch navigation performance of the developed GPS L1 C/A hard-ware receiver, named the WeakHEO receiver. Although they can still be collected, GNSS observations at Moon altitude, if not filtered, but simply used to compute a single-epoch least-squares solution, lead to a very coarse navigation accuracy, on the order of 1 to 10 km, depending on the number and type of signals successfully processed. Therefore, the third and main research objective and achievement is the design and implementation of a GNSS-based orbital filter (OF) determination unit, based on an extended Kalman filter (EKF) and an orbital forces model, able to significantly improve the achievable navigation performance and also to aid acquisition and tracking modules of the GNSS receiver. Simulation results of the OF performance when processing simulated GPS and Galileo observations, but also real GPS L1 C/A observations provided by the WeakHEO receiver (when connected in a hardware in the loop configuration to a full constellation GNSS radio frequency signal simulator), show a positioning accuracy at Moon altitude of a few hundred meters.ESPLA
Real-Time GNSS Software Receiver Optimized for General Purpose Microprocessors
No full textA satellite navigation system (like GPS) allows an user to determine its own position everywhere and anytime on Earth. The process of calculating the position is relatively simple (use of trilateration). The main issue is to obtain and decode the transmitted information and to estimate accurately the Time Of Arrival (TOA) of the signals as they lie below the thermal noise floor. A technique called spread-spectrum has been applied for the transmission of these signals that distributes a narrow-band signal over a large bandwidth with the help of spreading codes. In the receiver, these known sequences (one for every satellite) are re-generated and correlated with the incoming signal. As the satellites are moving, the signals undergo additionally a Doppler frequency shift that also has to be compensated in the receiver. These correlation processes require a huge number of opera- tions which make them difficult to be executed in software. Current microprocessors and mobile devices (like smartphones and mobile computers) offer more and more processing power and system resources. Therefore, the interest in software receivers increased during the last years as they offer a great level of flexibility and allow a low-cost implementation with few additional components. The aim of this thesis is to develop and implement a real-time software receiver on a general purpose microprocessor. This includes an extensive study of the current state-of-the-art and the development and the imple- mentation of a new signal processing baseband architecture. The require- ments and the performance are finally evaluated with simulated and real signals.ESPLA
Advanced Tracking Algorithm Designs for New Galileo Signals and Security Protection and Mitigation
No full text
Architecture of a Real-Time Platform Independant GPS L1 Software Receiver
Get PDFPersonal digital assistants or mobile phones applications are not anymore restricted to multimedia or wireless communications, but have been extended to handle Global Positioning System (GPS) functionalities. Consequently, the growing market of GPS capable mobile devices is driving the interest of software receiver solutions as they provide several advantages with respect to traditional hardware implementations. First, they share the same system resources such as the processor, embedded memory and power with other system units, reducing both the size and the costs of their integration. Second, they can be easily reprogrammed – via a firmware update – for incorporating the latest developments, such as the exploitation of the future satellites signals or some improved multipath mitigation techniques. Finally, they offer a more flexible solution for rapid research and development as compared to conventional hardware receivers where the chip design is fixed and obtained after a long integration process. With the increasing performance of modern processors, it becomes now feasible to implement in software a multi-channel GPS receiver operating in real-time. However, a major problem with the software architecture is the large computing resources required for the digital signal processing. Former studies have demonstrated that a straightforward transposition of traditional hardware based architectures into software would lead to an amount of integer operations which is not suitable for today's fastest computers. From this observation, several strategies have been proposed in the literature in order to reduce the complexity of the receiver operations. The first one relies on the utilization of advanced microprocessor instructions set which provides the capability of processing vectors of data by operating on multiple integer values at the same time. This results in significant gains in execution speed, but also severely limits the portability of the code, since the operations are tied to specific processors architectures. Another alternative consists in exploiting the native bitwise representation of the signal. The data bits are stored in separate vectors on which logical parallel operations can be performed. The objective is to take advantage of the universality, high parallelism, and speed of the bitwise operations for which a single integer operation translates into a few simple parallel logical relations. However, the inherent drawback of the bitwise processing is the lack of flexibility as the complexity becomes bit-depth dependent. This thesis has been carried out in the framework of a two-year industrial project (2007-2009) in collaboration with U-blox AG in Thalwil. It aimed to the realization of a multi-channel, platform-independent real-time GPS L1 software receiver. The main challenge of this project consisted in providing real-time performances while keeping the portability of the code to make the receiver suitable for any type of software implementation. In that sense, new techniques and algorithms have been developed for optimizing the processing chain in order to lower the processor load. The main idea consists in regrouping data which share the same characteristics, and process them in batches instead of sequentially. This way, it becomes possible to progressively reduce the data throughput and consequently the amount of operations to perform. A completely new receiver architecture has been proposed and validated through the realization of a functional prototype, thus demonstrating the feasibility of the concept.ESPLA
Parameter Estimation with GNSS-Reflectometry and GNSS Synthetic Aperture Techniques
No full textAside from intentional interference, multipath is the most significant error source for Global Navigation Satellite Systems (GNSS) receivers in many operational scenarios. In this thesis, we study the multipath estimation from two different perspectives: to retrieve useful information from it using GNSS-Reflectometry (GNSS-R) techniques; and to mitigate its effects or to estimate its direction-of-arrival (DOA) as well as the line-of-sight (LOS) signal¿s using synthetic aperture (SA) processing.
The first part of the thesis focuses on precision bounds for GNSS-R techniques for ground-based receivers, in scenarios where a single antenna simultaneously receives the LOS signal and a specular reflection. First, we derive the Cramér-Rao bound (CRB) of the receiver¿s height and the reflection coefficient, with the latter depending on the surface¿s electrical properties. More specifically, we propose a CRB derivation applicable to GNSS-R techniques that make use of the phase information and long observation times, such as the interference pattern technique (IPT). The derivation is based on the parameter transformation of the Fisher information matrix. We study the dependence of the computed CRB on the scenario and the receiver bandwidth. The CRB results for the simulated scenarios are consistent with the precision reported for many GNSS-R techniques used in these scenarios. The proposed CRB is meant to benchmark and compare new and existing techniques.
Besides the derived CRB, we propose an algorithm to obtain the maximum-likelihood (ML) estimator of the parameters of interest with the IPT: the segmented ML estimator (SML). The SML transforms a complex multivariate optimization problem into multiple simpler ones by dividing the parameter search space taking advantage of the cost function¿s particular structure. The SML is validated with simulated signal and asymptotically cross-validates the CRB results.
The second part of the thesis is devoted to the study of the SA processing of GNSS signals. The goal is to estimate the DOA of the signals received, and mitigate errors in the navigation solution caused by interfering signals, such as multipath. We start by deriving the CRB for the SA context, as a function of the antenna trajectory. This CRB considers the effect of the antenna complex gain, and we show in simulations that it is possible to achieve meaningful DOA estimation only by changing the antenna¿s orientation. We continue by proposing a development framework built upon a signal tracking architecture integrating SA processing. Before any SA processing, it is necessary to estimate and compensate any carrier phase contribution not related to the antenna motion. To do so, we propose two new sequential techniques based on the extended Kalman filter (EKF): EKF1 and EKF2. Also, we develop an open-loop version of the proposed SA tracking architecture, more robust than its closed-loop counterpart. Finally, we validate the proposed architecture and SA-based techniques with synthetic GPS signals at first, and then with real signals, recorded using an antenna mounted on a mechanical rotating arm. The obtained results validate the implemented techniques and show how the proposed SA architecture can ultimately mitigate the position bias error observed in environments with severe multipath interference.ESPLA
Analysis of Low Power, Low Data Rate Ultra Wideband Impulse Radio Systems
No full textDuring the last decade, ultra wideband (UWB) systems gained a large interest in the scientific world because of their suitability to realize among others communication systems with tremendous data rates and accurate indoor positioning and location systems. As a differing technology compared to classical narrowband radio transmission systems, UWB requires some novel approaches. Well established methods to develop and analyze narrowband transmission systems remain essentially valid but are not always well tailored or optimal to UWB systems. The need for novel approaches illuminates the reasons why there are still some uncovered topics in the literature, mainly related to the analyses of imperfections and perturbations during an UWB transmission. Consequently, this thesis attempts to cover some of these topics by theoretical studies, numerical simulations, as well as experimental verification.ESPLA
Real-time GNSS software receiver optimized for general purpose microprocessors
Get PDFThèse de doctorat : Université de Neuchâtel, 2010A satellite navigation system (like GPS) allows an user to determine its own position everywhere and anytime on Earth. The process of calculating the position is relatively simple (use of trilateration). The main issue is to obtain and decode the transmitted information and to estimate accurately the Time Of Arrival (TOA) of the signals as they lie below the thermal noise floor. A technique called spread-spectrum has been applied for the transmission of these signals that distributes a narrow-band signal over a large bandwidth with the help of spreading codes. In the receiver, these known sequences (one for every satellite) are re-generated and correlated with the incoming signal. As the satellites are moving, the signals undergo additionally a Doppler frequency shift that also has to be compensated in the receiver. These correlation processes require a huge number of operations which make them difficult to be executed in software. Current microprocessors and mobile devices (like smartphones and mobile computers) offer more and more processing power and system resources. Therefore, the interest in software receivers increased during the last years as they offer a great level of flexibility and allow a low-cost implementation with few additional components. The aim of this thesis is to develop and implement a real-time software receiver on a general purpose microprocessor. This includes an extensive study of the current state-of-the-art and the development and the implementation of a new signal processing baseband architecture. The requirements and the performance are finally evaluated with simulated and real signals
- …
