I am Feng Xiang, a Marketing Engineer of Agilent Technologies, and I will talk about the measurement
challenges for DVB-T and DVB-T2 receivers. DVB-T is the most widely deployed
digital video standard and DVB-T2 is an enhancement system of it. In this video, I am going to
show you some examples of DVB-T2 receiver performance tests using Agilent instruments.
Our demo instruments include two signal generators MXG, one is used for DVB-T wanted signal and
the other is used for the interference signal. This demo also includes a commercial
DVB-T2 set-top box with a TV for video display, and a signal analyzer, MXA, to monitor signal.
The first thing I would like to do is give you an overview of the N7623B Signal Studio
for Digital Video. Under format, we can see the different standards supported.
In this example, we use a DVB-T2 signal and we can set parameters like bandwidth, PLPs,
modulating type, guard interval and so on. We are going to use the default setting with two PLPs,
which is a common use case. The stream file used here is a TS file and an MPEG2 TS file
can be loaded as payload, which can be installed on a hard disk of the PC or the MXG.
Now let's use a signal analyzer to measure the quality of the transmitted signal. On the signal analyzer,
we can see the rotated constellation of the DVB-T2 signal and the MER measured that is
about 48 dB. And we can view the video stream on the TV. The stream is played very smoothly.
Next let's add the AWGN to the DVB-T2 signal and implement the carrier to noise ratio performance
test in the Gaussian channel. Set the signal to noise ratio to a large value such as 25 dB
and then decrease the signal to noise ratio and monitor the display. By doing this,
We can see that when signal to noise ratio is decreased to 18.9 dB. The video stream is
frozen in the form of a mosaic. This is the carrier to noise ratio we want to measure.
We can also use the BER as the degradation criteria. In a multi-path environment,
we can add echoes to the signal by adjusting the Signal Studio software settings. For example,
we can add two echoes with the relative delay and the power level settings. And we can see
the channel impulse response from the MXA. For interference immunity test, an additional
signal generator is used to generate the interference signal. Then we combine it with the wanted
DVB-T2 signal and feed the combined the signal to the set-top box. Here we use a signal analyzer
to check the power difference and the frequency relationship of the interference and the wanted
signal. You can see the spectrum of the combined signals. In the following example, we execute
the performance test with two interference signals. The interference DVB-T2 signals are
in channels of N+2 and N+4 as defined in the performance test specs. The multi-carrier
feature of the N7623B Signal Studio software is used to generate waveform for the DVB-T2
signal and two channels. The frequency separation of these two channels is 16 MHz. To perform
the test, we use one MXG to generate the real-time DVB-T2 signal as the wanted signal. And another
MXG to play the waveform for the interfering signal. The frequency offset between these
two MXGs is three carrier bandwidths. Adjust each interferer level and wanted signal level
to -25 dBm. Next, decrease the wanted signal level until the video streaming is frozen.
Then record the power level difference. As we've shown you in the video Agilent has a complete solution
for testing digital video receivers, using the N7623B Signal Studio for Digital Video software
with the X-Series MXG signal generator. All of the tests defined
in the conformance test specifications can be fully supported.
For more information, please visit Agilent's website.