Electronic Design

GPS Satellite Signal Generation Simplifies Nav Receiver Testing

GPS technology is everywhere today, from your dashboard to your cell phone. According to ABI Research, more than 550 million GPS cell-phone handsets will be shipped in 2012, and more than 1 billion GPS receiver chips will be shipped in 2013. But before all of those products roll off the assembly line, someone has to implement a practical test for them. Considering all the variables involved in the satellite-based system, controlling test conditions can be a real chore.

The GPS Toolkit from National Instruments is a software accessory for the company’s popular LabVIEW program. In conjunction with NI’s PXIe-5672 or PXI-5671 RF vector signal generators, it can simulate up to 12 simultaneous GPS satellite signals with varying conditions (see the figure). The generator produces the standard coarse acquisition (C/A) codes in the L1 band (1.57542 GHz).

This combination of hardware and software is ideal for both design validation and production testing of GPS receivers. It also slashes test time to a fraction of what was previously required. The test setup can operate in single-satellite or multi-satellite mode. In single mode, the receiver simply measures the carrier-to-noise ratio. In the multi-mode or automatic mode, the receiver can achieve a position fix on the simulated satellites.

Common measurements include programmable power levels down to –145 dBm, power accuracy of better than ±1.0 dB down to –127 dBm, accuracy of receiver location, and time to first fix (TTFF). Users also can specify the receiver location and velocity, and the algorithms will automatically determine the optimal satellites for that location. Satellites are selected based on user-specified almanac and ephemeris information that describes satellite position, velocity, and altitude as historical data.

Stored in a binary file format, the created waveforms contain up to 12.5 minutes of non-repeating GPS satellite data. Users can stream GPS signals continuously from disk with the NI VSG. Additionally, users can simulate receiver mobility via Doppler shift (X, Y, or Z axis velocity) and set the receiver’s latitude, longitude, and altitude. Users also have manual control of satellite pseudo-range, Doppler, and power level.

Available now, the GPS Toolkit costs $1995.

National Instruments


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