DVB-S2 communication between two USRP B200 boards with GNU Radio Companion

[sycelott]

Hi! Thank you for reading this.

I'm having difficulties with DVB-S2 communication between two USRP B200 SDR boards that are connected with SMA cable.

For hardware set-up, I'm using Raspberry Pi 4 (4 GB) to execute GNU Radio Companion, and using USB 3.0 port and cable to connect RPi and USRP B200. And I connected a DC block at the Tx port, as described in USRP homepage manual for DVB-S2. (So, the sequence is RPi 4-USB 3.0-USRP (Tx)-DC block-SMA cable (1 m)-USRP (Rx)-USB 3.0-RPi 4)

I have attached my hardware set-up pictures below.

  

I am trying to send some sample video through DVB-S2 communication. And I got DVB-S2 GRC flowcharts from links below. I've attached the screenshots, too.

https://github.com/drmpeg/gr-dvbs2

https://github.com/drmpeg/gr-dvbs2rx

   

At last trial, it was successful with RF options setting like below:

-Constellation: QPSK

-Code rate: 2/5

-Center Freq.: 1 GHz

-1 Mbps (sample rate) * 2 sps (sample per symbol) = 2 Mbps (bandwidth)

-Tx relative gain: 40 dB

(Regarding the code rate and bandwidth, I could see the video was received with 0.8 Mbps data rate)

But the problem is:

-this connection is very unstable as it does often fail even when the RF setting is the same.

Error logs with DVB-S2 decoders

-I need to raise the data rate as high as possible, but it's too low for me now. As I know, USRP B200 support ~61.44 Msps, but when I require about above 4 Mbps bandwidth, the log shows Us (underflow) at Tx and Os (overflow) at Rx. I confirmed that the clock rate setting is fine with 56 MHz.

-So I tried using other constellations, code rate, sample rate combinations but they failed. And for 8PSK option, I put 3 into sps variable at the Rx side as 8PSK is 3 bits per sample, but Rx flowchart rejected and saying 'sps needs to be even integer >= 2'. And it was not allowed to use 16APSK or beyond constellations in this USRP or in this flowgraph.

I guess I am missing something.

Is there any way that I can make stable connection and raise up the data rate?

I would really appreciate if you could help me.