Development of an experimental telemetry system

This article presents the design and implementation of a communications system to receive information about the status, height, speed, temperature or any other type of variable of interest from vehicles such as balloons or experimental rockets. In a first iteration, the system was designed to achieve transmission distances in the order of dozens kilometers but leaving some margin to extend the operating range to up to 100 km in line of sight. At the beginning of the project different factors such as the use of a frequency band suitable for this type of applications, the modulation scheme to use and a data protocol were analyzed. Subsequently, the most appropriate commercial devices to implement each of the system blocks were selected. With these components a first prototype of the telemetry board was built and the necessary tests to verify the correct performance of it were conducted. Finally, the design and implementation of the flight hardware was carried out and the final tests that fully validated the proposed design were performed.Facultad de Ingenierí

A Bayesian Technique for Real and Integer Parameters Estimation in Linear Models and its Application to GNSS High Precision Positioning

A novel Bayesian technique for the joint estimation of real and integer parameters in a linear measurement model is presented. The integer parameters take values on a finite set, and the real ones are assumed to be a Gaussian random vector. The posterior distribution of these parameters is sequentially determined as new measurements are incorporated. This is a mixed distribution with a Gaussian continuous part and a discrete one. Estimators for the integer and real parameters are derived from this posterior distribution. A Maximum A Posteriori (MAP) estimator modified with the addition of a confidence threshold is used for the integer part and a Minimum Mean Squared Error (MMSE) is used for the real parameters. Two different cases are addressed: i) both real and integer parameters are time invariant and ii) the integer parameters are time invariant but the real ones are time varying. Our technique is applied to the GNSS carrier phase ambiguity resolution problem, that is key for high precision positioning applications. The good performance of the proposed technique is illustrated through simulations in different scenarios where different kind of measurements as well as different satellite visibility conditions are considered. Comparisons with state-of-the-art ambiguity solving algorithms confirm performance improvement. The new method is shown to be useful not only in the estimation stage but also for validating the estimates ensuring a predefined success rate through proper threshold selection.Facultad de Ingenierí

A New Tracking Loop Scheme for High Dynamics Real-Time GNSS Receivers with Hardware Correlators

In this paper the implementation of one-delay carrier tracking loops in GNSS receivers that utilized hardware correlators is proposed. The previously adopted two-delay solutions were justified in the necessity of providing a phase reference to the correlator before the beginning of the correlation interval. However, this constraint can be relaxed by utilizing other phase reference and compensating the resulting correlation value accordingly after its computation. The proposed one-delay loop implementation is particularly useful for high dynamics conditions and therefore the UFA-PLL structure associated with an optimal digital loop filter was adopted for the analysis presented in this work. The optimum digital loop filter structures, previously derived for the case of two-delay carrier tracking loops, are updated under the one-delay condition. The obtained results are quite similar, with the novelty that the extra pole present in the former solution is not present any more. Two particular cases are analyzed by simulation to determine the pull-out performance and the associated tracking thresholds. First, a loop with correlation time of T = 10ms is shown to be able to track acceleration steps of 20g with similar performance than the previously obtained using two-delay implementations with T = 5ms and the same 75.6Hz bandwidth. In this case, doubling the correlation time imply a great reduction in the computational burden. Secondly, the same pull-out performance is shown in two T = 10ms loops, one with two delays and 37.8Hz bandwidth and the other with one delay and 19.8Hz bandwidth. In this case, half bandwidth imply half variance of the estimated phase, which is equivalent to an improvement of 3dB in the signal to noise ratio.Facultad de Ingenierí

A Bayesian Technique for Real and Integer Parameters Estimation in Linear Models and its Application to GNSS High Precision Positioning

A novel Bayesian technique for the joint estimation of real and integer parameters in a linear measurement model is presented. The integer parameters take values on a finite set, and the real ones are assumed to be a Gaussian random vector. The posterior distribution of these parameters is sequentially determined as new measurements are incorporated. This is a mixed distribution with a Gaussian continuous part and a discrete one. Estimators for the integer and real parameters are derived from this posterior distribution. A Maximum A Posteriori (MAP) estimator modified with the addition of a confidence threshold is used for the integer part and a Minimum Mean Squared Error (MMSE) is used for the real parameters. Two different cases are addressed: i) both real and integer parameters are time invariant and ii) the integer parameters are time invariant but the real ones are time varying. Our technique is applied to the GNSS carrier phase ambiguity resolution problem, that is key for high precision positioning applications. The good performance of the proposed technique is illustrated through simulations in different scenarios where different kind of measurements as well as different satellite visibility conditions are considered. Comparisons with state-of-the-art ambiguity solving algorithms confirm performance improvement. The new method is shown to be useful not only in the estimation stage but also for validating the estimates ensuring a predefined success rate through proper threshold selection.Facultad de Ingenierí

Diseño del sistema de comunicaciones para el nanosatélite de la Universidad Nacional de La Plata

El en el marco del proyecto de la Universidad Nacional de La Plata (UNLP), que lleva adelante el Centro Tecnológico Aeroespacial (CTA) de la Facultad de Ingeniería, para desarrollar el primer Cubesat (nanosatélites compuestos por unidades cúbicas de 10 cm de lado [1]) universitario de nuestro país [2], se propone el diseño del sistema de comunicaciones para el mismo.Facultad de Ingenierí

Multi-antenna GNSS Receiver Tracking Algorithm for Vehicles With Unconstrained Three-dimensional Motion

An algorithm for GNSS GPS/GLONASS receivers is presented that allows the receiver to seamlessly combine the inputs from multiple antennas during signal tracking in order to keep full sky visibility at all times. This algorithm has applications for both aeronautical and space applications in all kinds of vehicles with unconstrained three-dimensional motion capabilities: high maneuverability jet aircraft, rockets, satellites, unmanned aerial vehicles (UAVs), etc. The algorithm presented here keeps track of the received signal-to-noise ratios (SNR) and carrier phase on each of the antennas. For each set of correlation values the receiver selects the input antenna with the best SNR in order to do navigation message decoding and ranging. This fast-switching antenna selection process allows the receiver to stay synchronized with the incoming satellite signal for as long as at least one of the antennas of the set is within line-of-sight of the transmitting satellite. Distributing enough antennas throughout the fuselage of a vehicle, this algorithm will ensure that the receiver does not lose synchronization with the GNSS signals even during threedimensional maneuvers like spins and attitude changes. This algorithm was implemented on a four-antenna GNSS receiver prototype hardware, and tested using a GNSS signal simulator. During these tests the multi-antenna tracking algorithm performed successfully. The results of some of these tests are presented in this paper.Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

Diseño de un transmisor de telemetría doble banda para CubeSats

El presente trabajo consiste en el diseño de un transmisor para nanosatélites de baja órbita y bajo costo atractivo para proyectos universitarios y de investigación. En particular, se busca lograr un sistema de comunicaciones apto para el estándar CubeSat cuyo costo se encuentra en el orden de los miles de dólares en el mercado actual. Debe considerarse que el costo total de un nanosatélite de este tipo se estima en los cientos de miles de dólares, en franco contraste con las centenas de millones de dólares que cuestan las misiones satelitales tradicionales. El transmisor debe cumplir con diversos requerimientos como bajo consumo de potencia, suficiente velocidad de transmisión de datos para enviar toda la información del CubeSat hacia la estación terrena, capacidad de recibir comandos desde la estación que permitan modificar su funcionamiento, operar en bandas de frecuencia que no requieran licencias de uso exclusivo y ser construido con componentes comerciales adaptados para el uso espacial. En el trabajo se presenta el diseño de un transmisor capaz de operar tanto en UHF (banda de radioaficionados en 434 MHz) como también en banda S (banda en 2.4 GHz para aplicaciones Industriales, Científicas y Médicas) en el caso que se requiera mayor tasa de transmisión y por lo tanto mayor ancho de banda. Además, se realiza el cálculo de enlace subyacente para ambos casos y se define el tipo de modulación y protocolo de comunicaciones a utilizar. Una vez fijados todos los requerimientos y parámetros del enlace, se propone un diseño final del transmisor basado en componentes comerciales de bajo costo.Facultad de Ingenierí

Digital DS-CDMA detection in impulsive noise: base band vs. band-pass nonlinear processing

In the context of DS-CDMA detection, a digital base-band model for the received signal after chip-matched filtering, is often adopted. Nonlinear treatment of these samples for robust detection in impulsive environments has been already proposed. In this paper we study the advantages of band-pass nonlinear detection schemes for DS-CDMA receivers, over those in base-band. We consider for both schemes i) an impulsive noise model with independent α-stable distributed sequences and ii) a hard-limiter as memoryless nonlinearity. Probability of error and asymptotic relative efficiency expressions are given, with simulations that validate them. Results shown that band-pass nonlinear detection is preferable.Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

Likelihood Map Waveform Tracking Performance for GNSS-R Ocean Altimetry

Ocean altimetry with Global Navigation Satellite Systems signals (GNSS) signals is a remote sensing technique that measures the height of the sea surface through the difference in path length of the direct and reflected signal. Code altimetry estimates this parameter by tracking the code delay after performing correlations with a GNSS signal replica. It is of limited precision due to the low signal-to-noise ratio (SNR) and narrow bandwidth of the ocean-reflected GNSS signal. However, the potential advantages of the GNSS-R systems such as high temporal resolution and spatial coverage are a motivation to improve its altimetric precision. In this article, we present a performance assessment of the Likelihood Map Waveform tracking technique, a method based on Maximum Likelihood Estimation theory that exploits the available reflected power in a more efficient way than the single tracking point methods. We use a modification of the theoretical optimal solution that achieves a better performance than previous methods. We estimate it, in terms of SNR gain, using Monte Carlo method with a detailed stochastic model of the signal, and with actual signals from the Cyclone Global Navigation Satellite System. The gain values obtained were between 1.64 and 3.66 dB in the theoretical analysis, and between 1.69 and 2.62 dB with the real data, confirming the potential of the proposed approach.Facultad de IngenieríaInstituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

A Bayesian Technique for Real and Integer Parameters Estimation in Linear Models and its Application to GNSS High Precision Positioning

A novel Bayesian technique for the joint estimation of real and integer parameters in a linear measurement model is presented. The integer parameters take values on a finite set, and the real ones are assumed to be a Gaussian random vector. The posterior distribution of these parameters is sequentially determined as new measurements are incorporated. This is a mixed distribution with a Gaussian continuous part and a discrete one. Estimators for the integer and real parameters are derived from this posterior distribution. A Maximum A Posteriori (MAP) estimator modified with the addition of a confidence threshold is used for the integer part and a Minimum Mean Squared Error (MMSE) is used for the real parameters. Two different cases are addressed: i) both real and integer parameters are time invariant and ii) the integer parameters are time invariant but the real ones are time varying. Our technique is applied to the GNSS carrier phase ambiguity resolution problem, that is key for high precision positioning applications. The good performance of the proposed technique is illustrated through simulations in different scenarios where different kind of measurements as well as different satellite visibility conditions are considered. Comparisons with state-of-the-art ambiguity solving algorithms confirm performance improvement. The new method is shown to be useful not only in the estimation stage but also for validating the estimates ensuring a predefined success rate through proper threshold selection.Facultad de Ingenierí