In this video, we will demonstrate creating GPS test signals for GPS receiver verification.
GPS receivers vary widely in capability and functionality. Written specifications for
individual GPS receivers are difficult to compare because there are no standardized
conformance tests as there are for other standards, such as the cellular formats. This means that
GPS receiver verification depends on testing with a reliable a repeatable GPS signal simulator.
The GPS signal must conform to real world scenarios and also include the capability
to include real life impairments.
The instruments used to create the GPS signals are the N5106A PXB baseband generator and
channel emulator and the N5182A MXG signal generator. The signal itself is created by
the N7609B signal studio for global navigation satellite systems software, running inside
the PXB. The GPS signals will be sent to a GPS receiver, the u-blox EVK-5H evaluation
kit and results from the receiver are viewed using the u-blox u-Center software. The configuration
for the system is shown here. The N7609B signal studio software creates the GPS baseband signal
in the PXB this digital baseband signal is then sent over the LVDS digital BUS to the
MXG signal generator where it is up-converted to the GPS RF frequency and sent to the GPS
receiver.
The GPS receiver sends its information to the u-blox evaluation software through a USB
interface. First, let us show how simple it is to create GPS signals using the N7609B
signal studio software. From the signal studio user interface, we have already set the GPS
L1 frequency of 1.57542 GHz on the MXG. We have also set the RF output power of the MXG
at -120 dBm From the GPS settings tab we can select a predefined scenario file. We then
click on play to begin the simulation. Information about the select-a-scenario is shown on the
lower half of the display. This information includes the satellites in view, the location,
time and date, and the scenario playback time. On the u-blox u-Center software, we see the
results of the GPS signal as it is acquired by the u-blox GPS receiver. The display shows
the acquisition of the individual satellites. Blue indicates that the GPS satellite has
been identified, but is not yet being used for a navigation fix. You can see that the
time has been determined. As the satellites turn green, indicating that they are now being
used for navigation information, we see that the u-Center software displays the time to
first fix (or TTFF) and the location given in longitude, latitude, and altitude.
Also shows are some accuracy calculations along with the HDOP and PDOP estimations.
Because this is a real time GPS signal, we can change the visibility and relative power
settings of the individual satellites while the signal is playing using the satellites
settings tab. Here, we can turn off the visibility of some of the satellites and lower the power
on others by 6 and 10 dB. The resulting signal is shown on the u-Center software. This concludes
our introduction to creating GPS signals using the N7609B signal studio for global navigation
satellite system software running in the N5106A PXB. In a separate video, we will continue
the demonstration by showing how to create custom scenarios and add impairments such
as multipath. For more information please contact your local Agilent Technologies representative
or go to the web at www.agilent.com/find/gps. Thank you.