|How to use GPS record + replay to speed up your research|
Is there a way to fully test GPS applications without leaving your lab? Have you ever wished you could show how a GPS device would actually operate in the field, without moving from your test bench or lecture hall?
The LabSat GPS recorder, replayer and simulator will answer these questions. Read on to find out how record and replay technology could assist your research and teaching, and how to choose the best system for your needs.
What is GPS record and replay?
GPS record and replay allows you to record GPS data from a live antenna and replay it later. This allows you to gather the raw data once, and then replay it into devices under test for research or teaching an unlimited number of times, showing the actual behaviour of the GPS device in the field. You could show how a system would operate in New York’s Times Square whilst sitting in a research lab in Cambridge.
Why was GPS Record and Replay Developed?
For Racelogic, designers of high accuracy GPS data loggers for automotive testing and motorsport, demands for more and more accuracy meant they needed to continually improve the test methods they used to develop their products.
There were three options that could be used to test GPS devices:
Live sky …testing equipment in the field was useful for obtaining real world data, but the dynamic nature of satellite constellations meant tests were time intensive and not repeatable.
Design something more suitable... something that could record live GNSS signals and replay these into devices under test, offering the blend of realism and repeatability that they needed at an affordable price.
So, in 2008 LabSat was developed, with the ability to record raw GPS RF signals from a live antenna to be replayed at a later date. Users could now easily record a journey and replay this on the bench with identical results.
Racelogic then added the ability to create a scenario from scratch, and soon had five units in constant use. From the positive feedback of their R&D engineers, it was clear that LabSat could be helpful to other companies developing GPS products, at a lower cost than anything else available.
LabSat is now used in several industries, spanning mobile phones, defence, automotive electronics, education, and research institutions. For example, Nokia and Blackberry use LabSat for testing smartphones; Mercedes Benz, Bosch and Continental use it to test in-car navigation solutions whilst Northropp Grumman (makers of the B-2 Stealth bomber) and BAE systems use LabSat to test the latest defence technology.
So how does record and replay work? Here’s a demonstration:
GPS + GLONASS
With a full constellation, GLONASS is becoming increasingly important, and there is a need to use these signals in device development. LabSat 2 is capable of recording, replaying, and simulating GLONASS-L1 and GPS-L1 data simultaneously.
Choosing your sample rate
When choosing a record and replay system you need to think about the type of sampling you need when recording signals. For most applications such as navigation system testing, 1-bit sampling provides a good recording with typically around 1dB of signal loss.
The standard LabSat works with 1-bit sampling which produces file sizes of around 1.1Gbytes for 10 minutes recording. For higher fidelity recording, useful for receiver sensitivity tests, multipath capture and low signal level playback, LabSat 2 records at 2-bits for both GPS and GLONASS or 4-bits for a single constellation. This produces files of 4.4 GB for 10 minutes recording.
Sometimes pure data isn’t enough. Synchronised video footage is useful for seeing real world conditions; a brief glitch in position can be puzzling until you watch the video and see a large truck passing close by. Standard cameras don’t work well as they quickly go out of sync with the data.
Uniquely, LabSat can interface with Racelogic’s Video VBOX, which uses a high speed internal GPS engine to time stamp each video frame.
The Video VBOX is placed inside the vehicle with the LabSat during the test drive and the video is recorded alongside the RF data. When replayed on the bench, the time-stamped video is perfectly synchronised with the replayed GPS data.
Because Video VBOX is also a data logger, you can record many other signals at the same time and overlay these graphically on the video.
Many GPS applications also integrate with other technologies to improve quality in heavily built up areas. However, researching and testing combined GPS and external data is complex and time consuming.
Therefore, it’s important to be able to record and replay external data. LabSat conversion modules are available for analogue, CAN, RS232, RS422, and RS485 serial streams, to record external data perfectly synchronised with the GNSS data.
Testing your systems in remote locations
Racelogic’s SatGen software creates static or dynamic scenarios anywhere in the world. It allows you to create a data file which can be replayed on a LabSat and means you can simulate almost any kind of test anytime and anywhere.
LabSat Prices - up to 50% Discount for Education
With prices starting from $10,000, LabSat is the most affordable GNSS RF recorder and replayer available. Discounts of up to 50% are available for educational establishments.
Racelogic recently recorded a webinar on how to use GNSS record and replay to make your GNSS testing faster and more effective. Essential for anyone who researches and teaches GPS applications, it’s available here.