Know what is GNSS testing?

The most basic GNSS test, that is, the key characteristic test of the GNSS receiver, includes:

Time to First Fine Fix (TTFF)

This is also the amount of time, typically measured in seconds, that the receiver takes to report its calculated date, time, and location (pinpoint). The time is from when the receiver resets to when the receiver reports a fix. Different kinds of calibration can be performed from all receivers: cold start, warm start.

 

                                                                 (Beitian GNSS receiver BT-468)

When performing a cold start, the memory of the receiver is cleared, and the receiver must perform calculations without adding any saved files. Deletes information about constellation of satellites (old ephemeris), precise orbit and digital clock data for each satellite (ephemeris) and its date, time and position. Cold calibration in the receiver is generally not performed by switching off the switching power to the device, but by pushing a separate command to the receiver. Time to first pinpoint is greatest during cold calibration.

Warm reset (warm reset) generally turns off the power of the host computer, and then restarts it to execute. A warm restart keeps the old ephemeris content in memory and deletes the ephemeris and its date, time and position content, which allows the receiver to be pinpointed more efficiently than a cold calibration.

When GNSS reception is temporarily stopped (for example due to tunnel construction) and then gradually resumes, this is called a hot reset. The receiver saves all stored information (old ephemeris, ephemeris, date/time, position) and can quickly obtain precise positioning.

Precise Positioning Accuracy

Position accuracy testing usually involves operating the test for a period of time and collecting position deviations at regular intervals (for example: operating the test for one hour, then collecting observations every second).

On-time accuracy

The timing accuracy of the receiver can be known by using a time interval electronic counter or a digital oscilloscope. Like the positioning accuracy test, the measurement results must be collected every second for a period of time.

sensitivity

Receiver sensitivity is the lowest output power level a GNSS signal can have that a GNSS receiver can lock onto and keep track of. There are two key categories of sensitivity: capture and track.

Acquisition sensitivity is the output power level required by the receiver to lock onto the GNSS signal for the first time; tracking sensitivity is the output power level required by the receiver to maintain the tracking signal after acquisition. The signal must be acquired at a higher output power level than is required to maintain tracking.

GNSS bias

There are some uncontrollable factors in the environment that will affect these basic testing processes, so to obtain accurate conclusions, it is very important to test machine equipment in an environment that simulates real operation.

When the GNSS signal is transmitted from the satellite to the receiver, it will cross the troposphere and ionosphere. All mobile phone simulators selected for testing can set the air model and add deviations, so that the receiver machine can be tested in different deviation environments. equipment. Multipath also occurs when a signal originating from a communications satellite bounces off objects or the ground causing several radar echoes of the main signal to reach the receiver. The more frequently it happens. Some RF interference also occurs when there are FM transmitters nearby to affect the frequency of GNSS transmissions. Impacts can exist all the time or occur at will, so it is necessary to test the receiver characteristics of key operating machines around the road surface to prevent the impact of the resulting impact.