All Global Navigation Satellite Systems (GNSS), of which the US built and managed Global Positioning System (GPS) is the best known example, work by measuring the transmission-time delay from a satellite to the receiver. With a clear view of the sky and an unobstructed path to multiple satellites a modern GNSS receiver is able to calculate its position rapidly and accurately. However atmospheric propagation effects can alter the speed of the signals to an indeterminate degree, signals can be obscured by buildings or reflected off surfaces such as the sea, all of which will compromise the performance of the receiver, reducing accuracy, extending acquisition time or reducing sensitivity. Thorough evaluation of receiver performance requires that the impact of these various sources of impairment is assessed. An emerging technique for performing this testing is by Recording the RF signal for subsequent Playback in the lab.
- Complete evaluation requires real-world signals
- Real-world conditions are not repeatable making comparable trials difficult
- Record and Playback Systems (RPS) provide real-world, repeatable test conditions
Why Record and Playback
| Issue |
Repeatable testing using representative real-world signals. |
| Solution |
Spirent’s GSS6400 is a completely self-contained 2-bit GNSS Record and Playback System. |
| Benefits |
Using a Record & Playback System avoids the need to continually return to the field by providing representative GNSS signals in the lab and being able to repeatably reproduce the recorded RF wherever and whenever required. The GSS6400 provides 2-bit fidelity and OCXO stability in a self-contained affordable instrument. |
Recording the RF signals for subsequent Playback in the lab avoids the cost of repeated field trials and eliminates the uncertainty due to uncontrolled variability in live-sky trials.
One of the challenges in GNSS receiver evaluation is that conditions are always changing. The satellites constantly move and different antenna positions will be subject to different multipath fades and obscuration. Whether performing comparative testing of a variety of receivers or reviewing the impact of a software change during development it is impossible to exactly repeat a trial. Add to this the cost and time of performing field trials and the benefits of recording a sample of RF for repeatable trials conducted in the lab are clear.
What of simulation? Simulation allows absolute control of the test environment where individual sources of impairment can be added or removed at will. Simulation also allows the evaluation of signals not yet available from space or extremes of vehicle motion which may be expensive or difficult to trial. Indeed the generation of synthetic signals derived from mathematical models represents the ultimate in control. However, the generation of an environment that can be said to be truly representative requires expertise and could require verification to confirm that the combination of impairments is valid.
The Record and Playback approach allows an actual environment to be captured and replayed at will, complete with real-life propagation, fades and interference. It is by its nature representative of the real world and so complements simulation as a source of GNSS signals for test.
The GSS6400:
- Is simple to operate
- Provides repeatable test environments
- Represents real world conditions
- Makes collaboration easy with scenarios portable between units
On-Demand Webinars
GSS6400 Help Sheets
GSS6400 "How To" Help Sheet #1
This help sheet explains the use of the Built-in Attenuator in the GSS6400 Record Playback Systems
GSS6400 "How To" Help Sheet #3
This help sheet explains the Repeatability Test using the GSS6400 RPS (Static GPS Signals)
GSS6400 "How To" Help Sheet #4
This help sheet explains how to Extract a Section of Data from a Recorded File in the GSS6400 Record Playback Systems.
GSS6400 "How To" Help Sheet #6
This help sheet explains the use of FTP to Transfer Files Between GSS6400 and External Devices
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