A method has been developed to measure the total effective noise power in a GPS receiver, including contributions from the system temperature, the antenna temperature, interference, lossy components, etc. A known level of noise is periodically injected before the preamplifier during normal tracking, with a switch set to a very low duty cycle, so that there is insignificant signal loss for the GPS signals being tracked. Alternately, a signal of known power may be injected.
The coupling port is fed with a switch that can be controlled from the receiver’s digital processing section. The switch can connect the coupling port to a noise or signal source at a known power level. The combined system noise is measured, and nearly continuous noise calibrations are made. The effect from injected noise/signals on the performance of the GPS receiver can be less than 0.01 dB of SNR loss. Minimal additional components are required. The GPS receiver is used to measure the SNRs required to solve for the noise level. Because this measurement is referenced to the preamplifier input, it is insensitive to variations in the receiver gain.
This work was done by Lawrence E. Young, Stephan Esterhuizen, and Dmitry Turbiner of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management NPO-47818
JPL
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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This Brief includes a Technical Support Package (TSP).
Method to Measure Total Noise Temperature of a Wireless Receiver During Operation
(reference NPO-47818) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing a novel method for measuring the total effective noise power in GPS receivers. This method accounts for various noise contributions, including system temperature, antenna temperature, interference, and losses from components. The research aims to enhance the understanding of noise characteristics in wireless receivers, which is crucial for improving their performance.
Key advantages of the proposed method include the ability to measure all noise sources, nearly continuous noise calibrations, and minimal impact on the GPS receiver's performance during calibration—resulting in less than 0.01 dB of signal-to-noise ratio (SNR) loss. The method requires minimal additional components and utilizes the GPS receiver itself to measure the SNRs necessary for determining the noise level. This approach is particularly beneficial as it is referenced to the preamplifier input, making it insensitive to variations in receiver gain.
The document presents equations that describe the relationship between received GPS power and noise temperatures. It outlines two measurement positions for SNR, providing equations that allow for the calculation of total noise temperature by relating the SNR measurements to the equivalent noise temperatures of the system and interference. The derived equations facilitate the analysis of how errors in measurements affect the overall noise temperature calculation.
The research was conducted at JPL under NASA sponsorship, emphasizing the importance of this work in the context of aerospace technology. The findings are expected to have broader implications beyond aerospace applications, potentially benefiting various fields that rely on wireless communication technologies.
Overall, this Technical Support Package serves as a comprehensive resource for understanding the methodology and significance of measuring noise in GPS receivers, highlighting its potential to improve receiver performance and reliability in various applications. The document also provides contact information for further inquiries related to the research and technology discussed.
