Testing the operation and performance of a GPS receiver can be a time-consuming and complicated process. To achieve this effort, some receiver manufacturers and system integrators use a combination of receiving live sky GPS signals with an outside antenna as well as receiving signals produced from a GPS simulator.
While you may think that it is easy enough to just go out and put up an antenna to receive the GPS signals from the live sky, you need to ask yourself what it is that you are actually evaluating. Are you evaluating a position solution that contains the effects of local variations such as antenna shading due to placement of the antenna in relation to an existing structure? Are you seeing some effects of multipath being induced to the receiver solution? Is the placement of the antenna causing a larger than expected error? Will you get different navigation results by testing at different times of day? How do you test your receiver under dynamic conditions that contain vehicle motion? Due to the volatility of the GPS constellation, a satellite simulator provides you with repeatable and customizable test conditions.
A GPS simulator must model all transmission paths, anomalies, satellite motion, and user motion to provide you with the ability to control all aspects of the GPS signal to accomplish repeatable testing under known environmental conditions. A GPS simulator should also be capable of allowing you to define a specific time, date, and almanac to be utilized during the simulation, thus enabling you to reproduce the same GPS constellation characteristics as seen from a live-sky antenna for a specific time and location.
You can also use a GPS simulator to assist with the evaluation of new software builds for receivers, characterize a receiver, or evaluate multiple GPS receivers under identical operating conditions. A few simulators also provide the ability to drive an inertial interface, to assist with aircraft avionics integration and testing in a dynamic environment without leaving the laboratory for expensive flight testing.
Using a GPS simulator provides you with the ability to evaluate some operational specifications like time-to-first-fix, time-to-subsequent-fix, low signal-to-noise ratios, receiver loss of RF, reacquisition after signal loss, tracking of rising and setting SVs, and more.
Some GPS simulators also allow you to define and simulate multipath signals. The ability to define the characteristics of multipath signals provides you with a very precise and repeatable signal source to accurately measure and quantify the effects of multipath signals on carrier-phase measurements and receiver performance. This allows you to accurately characterize multiple types of GPS receivers, enabling you to select the appropriate receiver for use in different types of applications and operating environments.
John F. Clark is vice president, engineering, for CAST Navigation, LLC. He has more than 25 years of experience in the GPS industry, and has worked at CAST since 1991.
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The CRASAR response team included sUAS pilots Justin Adams of Constellation Consulting Group, David Merrick and Laura Hart of Florida State University Center for Disaster Risk Policy, Jon McBride of Rocky Mountain Unmanned Systems, and Robin Murphy of Texas A&M University. Funding was provided in part through research grants from an insurance partner and the National Science Foundation.
“This eruption is especially impactful because of its location,” said Esri’s Public Safety Lead, Ryan Lanclos. “That makes the CRASAR’s use of drones and mapping technologies, and the near real-time situational awareness it provides of people, homes, businesses and infrastructure during this disaster, a resource first responders will be able to turn to time and again.”
CRASAR’s deployment to Hawaii marked a number of firsts for technology applied to disaster response. To interact with the same GIS mapping and imaging technologies responders used on the scene at Kilauea Volcano Lower East Rift Zone, visit this page.