I am Mirin Lew, an applications engineer from Agilent Technologies, and today I would like
to speak with you about digital video signal generation solutions. There are a variety
of digital video standards being adopted in different regions around the world for various
transmission methods. The Agilent N7623B Signal Studio for Digital Video, along with the new
X-Series MXG signal generator, can generate signals for digital video receiver tests,
including performance and functional tests.
This solution supports most of the standards with waveform playback mode, including the
DVB series, ISDB-T, ATSC, J.83 Annex, DOCSIS, and the Chinese standards DTMB and CMMB. It
also supports several standards with real-time signal generation, including DVB-T/H/T2/C/S
and S2 and ISDB-T.
For waveform playback mode, the playback time can be up to one minute due to the large memory
in the MXG. For real-time signal generation, we can change some modulation parameters at
anytime, and the changes will take effect immediately.
Measurements defined in the conformance test specs, such as MBRAI, Nordage and D-Book can
be supported, including sensitivity, interference and performance testing under AWGN and multipath
environments.
I am going to show you Agilent’s latest solution for generating digital video signals
for receiver tests using a DVB-T signal as an example.
This solution uses Agilent’s N7623B Signal Studio for Digital Video software running
on a PC, together with an X-Series MXG or EXG signal generator. Our demo devices are
a commercial DVB-T dongle and a PXA signal analyzer. The output DVB-T signal from the
X-Series signal generator is connected to both the PXA signal analyzer and the DVB-T
dongle through a power divider.
This is the Signal Studio application for real-time digital video. Under format we can
see the different standards that are supported. We can select the signal format first, and
then set the parameters in the node below.
In this example we used a DVB-T signal, and we can set parameters like mode, bandwidth,
modulation type, guard interval and so on. In this example we are going to use default
values for most parameters, and set the modulation type to 64-QAM. The stream file used here
is a TS file or transport stream file. An MPEG2 TS file can be loaded as the payload,
which can be stored on the hard disk of the PC or the signal generator. Click the “State
On” button and the signal will be generated from the EXG.
Now let’s use the PXA to measure the quality of the transmitted signal and monitor the
parameter changes. On the PXA we can see the constellation graph of the DVB-T signal that
has been transmitted, and the MER can be up to 47 DB, and we can view the video stream
on the display software of the dongle receiver. The stream is now playing very smoothly.
Now in the N7623B software we will change the modulation type to 16QAM, and the change
of parameters will take effect immediately. We can see on the PXA that the constellation
graph has now changed to 16QAM, accordingly.
Next let’s add AWGN noise to the DVB-T signal and implement the carrier-to-noise performance
test in the Gaussian Channel. These settings are under the real-time AWGN setup under the
instrument node. Set the signal-to-noise ratio to a larger value, like 15 dB, and then turn
on the real-time AWGN.
Next, let’s decrease the signal-to-noise ratio by one dB at a time and monitor the
display. We can see that when the carrier-to-noise is decreased to 10dB the video stream is frozen.
This is the carrier-to-noise value that we want to measure. We can also use bit error
rate as a degradation criteria.
Besides the carrier-to-noise test on the Gaussian Channel, other conformance tests can also
be performed easily. For an interference test we can use another X-Series signal generator
to add the required interference signal, and for the multipath test, we can use the N5106A
PXB, which can add up to 24 paths with Doppler shift and some predefined channel profile.
As we have shown in this video, Agilent has the complete solution for testing digital
video receivers using the N7623B Signal Studio for Digital Video software, with the new X-Series
EXG or MXG signal generators. All of the tests defined in the conformance test specifications
can be fully supported.
For more information please visit Agilent’s website, and thank you for watching this video.