Sai K. Kalyanaraman

Code tracking architecture influence on GPS carrier multipath

It is well known that carrier-phase multipath is one of the limiting error sources in high-precision differential GPS (Global Positioning System) applications. A thorough understanding of carrier-phase multipath is the first step in the course of mitigating its impact in high precision applications. Complete characterization of carrier-phase multipath error requires a fundamental theoretical description and mathematical modeling. However, the theory and models must be validated with real data. This paper documents the results of a study of the influence of GPS receiver code tracking architecture (coherent and noncoherent) on the carrier-phase multipath error, and provides a thorough validation of carrier-phase multipath theory. Validation is carried out for wide and narrow correlator spacing within coherent and noncoherent code tracking architectures by comparing bench test data to theoretical predictions. Prior to this effort, scant attention had been given to validating carrier-phase multipath theory against GPS data (Townsend et al., 1995). In addition, data collected for non-zero multipath phase rates is presented. The impact of GPS receiver architecture on the mitigation of phase-rate multipath was discussed.

Phase Compensation in GPS Array Processing using a Software Radio

Digital Beam Forming (DBF) and nulling are viable means of GPS array signal processing that enable multipath mitigation and provide protection against interference. However, as reported in the literature, nulling causes errors in the carrier phase and code phase measurements. Unlike single element GPS antennas (Fixed reception pattern antennas - FRPAs), multi element antenna arrays (Controlled Reception Pattern Antennas - CRPAs) exhibit significant distortions in their phase patterns. Correction for known anomalies in the individual element patterns mitigates the carrier phase error. Part of the carrier phase error arising from the application of non-trivial complex weights, implemented as part of the nulling action, can be compensated for in the carrier phase tracking and measurement domain in the baseband GPS receiver processing. Such an approach enabled by the use of a SW defined GPS radio will be demonstrated in the paper with results to support the theory.

Communication and navigation applications of nonlinear micro/nanoscale resonator oscillators

Micro/nanoscale resonator oscillators offer size, weight, and cost advantages to traditional quartz crystal oscillators. However, they typically cannot produce equivalent performance. Analyses and simulation are used to determine performance thresholds necessary for application of these devices in communication and navigation radios. Micro/nanoscale resonator oscillators have been created which use nonlinearities to improve their phase noise. These devices were used in actual radios to verify analyses and simulation. Measured results have shown radio performance equivalent to a 236 km communication range increase. A microscale oscillator was successfully used as a frequency reference in a navigation radio to acquire and track GPS.

Influence of GPS code tracking on multipath performance

Influence of GPS code tracking on multipath performance. It is well known that carrier-phase multipath is one of the limiting error sources in high-precision differential GPS applications. A thorough understanding of carrier-phase multipath is the first step in the course of mitigating its impact in high precision applications. Complete characterization of carrier-phase multipath error requires a fundamental theoretical description and mathematical modeling. However, the theory and models must be validated against real data. The purposes of This work are to study the influence of GPS receiver code tracking architecture on the carrier-phase multipath error, and to provide a thorough validation of carrier-phase multipath theory. Previous research published by the authors has served to validate carrier-phase multipath theory against bench test data, which was collected using wide (1.0 chip spacing) and narrow (0.1 chip spacing) correlator spacing for the case of the non-coherent code tracking architecture (Kalyanaraman and Braasch, 2003). Prior to (Kalyanaraman and Braasch, 2003) scant attention has been given to validating carrier-phase multipath theory against GPS data (Townsend et al., 1995). Current research efforts will validate carrier-phase multipath theory for wide and narrow correlator spacing within coherent code tracking architectures by comparing bench test data to theoretical predictions. In addition, data has been collected for nonzero multipath phase rates.