Software Tools Simplify GPS Testing

Aug. 13, 2008
This flexible test software tool can be combined with modular PXI instruments to perform a large array of single-satellite and multisatellite GPS receiver measurements.

Global Positioning System (GPS) receivers have been guiding travelers for some time, and now they are guiding drivers of many new cars and even pedestrians by means of embedded circuits in cellular telephones. Of course, with this rapid spread of GPS receivers comes a corresponding need for efficient testing of both stand-alone GPS receivers and units embedded into other devices. For that purpose, the NI GPS Toolkit for Labview from National Instruments ( provides an easy-to-use and flexible measurement solution when teamed with software-programmable PXI test instruments. The test system allows newly generated and previously recorded waveforms to be combined to create realistic GPS operating environments for testing new designs in the lab or exercising units on the production line.

The firm has developed a full line of modular test instruments based on the PCI eXtensions for Instrumentation (PCI) format, an open specification governed by the PXI Systems Alliance ( PXI is supported by more than 70 companies with more than 1500 PXI products.

For the purpose of GPS radio and system testing, National Instruments offers its NI PXIe-5672 RF vector signal generator to create test signals from 250 kHz to 2.7 GHz with 16-b resolution, 20-MHz real-time bandwidth, and output range of -145 to +10 dBm; it also supplies the companion NI PXI 5661 RF vector signal analyzer with frequency range of 9 kHz to 2.7 GHz and corresponding 20-MHz realtime bandwidth; the analyzer features 80-dB spurious-free dynamic range (SFDR), 14-b resolution, and sampling rate of 100 MSamples/s. By adding the NI PXI-5690 low-noise two-channel preamplifier (100 kHz to 3 GHz, 30 dB fixed gain on one channel, -10 to +20 dB programmable gain on the other channel), test engineers use the analyzer to capture and record actual GPS signals with natural impairments.

The GPS Toolkit for LabVIEW provides the programmability for these PXI instruments to perform single-satellite and multi-satellite GPS testing (see figure). By using the NI LabVIEW software to create waveforms for simulation of as many as 12 satellites, the GPS Toolkit for LabVIEW when teamed with the appropriate PXI instruments can perform such single-satellite GPS receiver measurements as noise figure and sensitivity, and such multisatellite GPS tests as sensitivity, dynamic position accuracy, and time to first fix (TTFF).

The NI GPS Toolkit for LabVIEW can be combined with the NI Modulation Toolkit for LabVIEW, NI TestStand test management software, and modular PXI instruments, to assemble a low-cost production test station. Because software is used to define the functionality of the test system, the same basic PXI setup can be used to test GPS systems as well as other wireless devices, such as GSM and WCDMA cellular telephones, WiFi and Bluetooth wireless networking devices, and digital-video-broadcast (DVB) equipment. P&A: $1999 and up (NI GPS Toolkit for LabVIEW). National Instruments, 11500 North Mopac Expressway, Building B, Austin, TX 78759-3504; (512) 683-0100, (800) 258-7022, Fax: (800) 683-9300, E-mail: [email protected], Internet:

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