LabSat

LabSat SatGen Software allows you to create a data file which can be replayed on a LabSat which is based on a user-generated trajectory file. This allows you to simulate almost any kind of test, at a set time and date, anywhere in the world.

For example, say you are based in the UK, but you have customers for your products in Australia. You can create a test scenario based around Melbourne and check that your equipment works under these conditions.

If your GPS equipment is used under very high dynamic conditions, you can create a scenario to check what happens to your product under these conditions. You could simulate an aircraft taking off and going into a vertical climb up to 30,000 feet, and then performing a high-g turn at this altitude, all without leaving your bench!

Creating your own scenario could not be easier. If you have an NMEA file which contains GGA data, then you can import this directly into the software or alternatively, you can start from scratch by creating a route in Google Earth, or build a route using simple user commands.

Creating a route in Google Earth is very easy, you simply create a path using the 'Add Path' tool. This is a standard tool available in the free version of Google Earth, and you can zoom in as far as you want to get fine detail or zoom out to cover long distances. You can have as many or as little points as you want, the software will automatically fill in the detail later on.

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The path is then exported as a Google Earth '.kml' file and imported directly into SatGen. These points are then interpolated and smoothed using preset limits on jerk rate, acceleration, cornering forces and top speed to produce a realistic trajectory file in an NMEA format (GGA messages).

This makes the definition of a scenario really quick and easy to do. It is quite feasible to define a complicated route through a city in just a few minutes, leaving the software to generate a fully realistic and driveable test.

Once the route and velocity profile has been defined, the software will then use this data to create a binary file which can be replayed on your LabSat. The creation of this file is automatic, but it is quite a complex task, and will therefore take a number of hours of processor time to complete, depending on the length of your scenario.

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The screenshot on the left shows the London '.kml' file after it has been imported into the software. All the gaps between the points have been filled in, and the corners rounded off so that no sudden movement unsettles the GPS.

Many aspects of the output can be adjusted; parameters such as maximum accelerations, jerk rates, stationary periods (for initial satellite lock), position smoothing levels and maximum speed, are all user configurable.

A complex driving scenario, around any place in the world would normally be a labour intensive process taking hours to build up using conventional Simulator software, but with SatGen you can generate complex trajectories in literally a couple of minutes!

Another method of defining a trajectory involves typing in simple commands in a text window, as shown on the left. Commands such as 'vel=100@100m' means change the currently velocity to 100km/h over 100 metres. You can specify initial position, time, heading and height, and then during the scenario you can change velocity, heading and height, either over a pre-defined distance or time.

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IQ file generation

The next stage is to create the IQ data file from the trajectory, time and date specified by the user. The input into this part of the software is a NMEA file (GGA data at up to 1000Hz), so this is what is output in the first stage of the trajectory generation. The process of converting the NMEA file into a binary file is completely automatic, on a quad core Intel 2.5GHz PC it is around 11s per second of scenario. A screenshot from this process is shown below.

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