Theory of phaselock techniques as applied to aerospace transponders

Phaselock techniques as applied to aerospace transponder

High-dynamic GPS tracking

The results of comparing four different frequency estimation schemes in the presence of high dynamics and low carrier-to-noise ratios are given. The comparison is based on measured data from a hardware demonstration. The tested algorithms include a digital phase-locked loop, a cross-product automatic frequency tracking loop, and extended Kalman filter, and finally, a fast Fourier transformation-aided cross-product frequency tracking loop. The tracking algorithms are compared on their frequency error performance and their ability to maintain lock during severe maneuvers at various carrier-to-noise ratios. The measured results are shown to agree with simulation results carried out and reported previously

GPS Multipath Detection in the Frequency Domain

Multipath is among the major sources of errors in precise positioning using GPS and continues to be extensively studied. Two Fast Fourier Transform (FFT)-based detectors are presented in this paper as GPS multipath detection techniques. The detectors are formulated as binary hypothesis tests under the assumption that the multipath exists for a sufficient time frame that allows its detection based on the quadrature arm of the coherent Early-minus-Late discriminator (Q EmL) for a scalar tracking loop (STL) or on the quadrature (Q EmL) and/or in-phase arm (I EmL) for a vector tracking loop (VTL), using an observation window of N samples. Performance analysis of the suggested detectors is done on multipath signal data acquired from the multipath environment simulator developed by the German Aerospace Centre (DLR) as well as on multipath data from real GPS signals. Application of the detection tests to correlator outputs of scalar and vector tracking loops shows that they may be used to exclude multipath contaminated satellites from the navigation solution. These detection techniques can be extended to other Global Navigation Satellite Systems (GNSS) such as GLONASS, Galileo and Beidou.Comment: 2016 European Navigation Conference (ENC 2016), May 2016, Helsinki, Finland. Proceedings of the 2016 European Navigation Conference (ENC 2016

Optimum and suboptimum frequency demodulation

Optimum and suboptimum linear demodulators for telemetry communication syste

Ranging and tracking system for proximity operations, phase 1

A study task is reported which is directed towards developing a conceptual design of a small, lightweight range and range rate radar sensor system to meet NASA's requirements for accurate short-range and velocity measurements in an orbital environment. Within the context of the requirements, the short range implies system operation at 0 m to 1850 m (6000 ft) and accurate implies a range measurement to within 1 sigma accuracy of 0.20 m (0.67 ft) and a range rate (velocity) measurement to within 1 sigma accuracy of 0.01 m/sec (0.033 ft/sec)

Hardware simulation of Ku-band spacecraft receiver and bit synchronizer, volume 1

A hardware simulation which emulates an automatically acquiring transmit receive spread spectrum communication and tracking system and developed for use in future NASA programs involving digital communications is considered. The system architecture and tradeoff analysis that led to the selection of the system to be simulated is presented

Hardware simulation of KU-band spacecraft receiver and bit synchronizer, phase 2, volume 1

The acquisition behavior of the PN subsystem of an automatically acquiring spacecraft receiver was studied. A symbol synchronizer subsystem was constructed and integrated into the composite simulation of the receiver. The overall performance of the receiver when subjected to anomalies such as signal fades was evaluated. Potential problems associated with PN/carrier sweep interactions were investigated

Dark solitons in laser radiation build-up dynamics

We reveal the existence of slowly-decaying dark solitons in the radiation build-up dynamics of bright pulses in all-normal dispersion mode-locked fiber lasers, numerically modeled in the framework of a generalized nonlinear Schr\"odinger equation. The evolution of noise perturbations to quasi-stationary dark solitons is examined, and the significance of background shape and soliton-soliton collisions on the eventual soliton decay is established. We demonstrate the role of a restoring force in extending soliton interactions in conservative systems to include the effects of dissipation, as encountered in laser cavities, and generalize our observations to other nonlinear systems

Optical altimeter receiver systems study and design for a spaceborne laser altimeter

Design and specifications for optical altimeter receiver system