tx/rx radio synchronization

[wblair2]

Hi again,

I now have both tx and rx running, but am having trouble getting them to synchronize when using SDRs. I am running both tx and rx on a single machine, with two Ettus X300 radios connected and have them connected with an SMA cable with 30dB attenuation. My tx and rx syntax is:

./bin/dvbs2_tx \
--sim-stats \
--rad-tx-subdev-spec "A:0" \
--rad-ip-addr 192.168.50.2 \
--rad-tx-rate 10e6 \
--rad-tx-freq 1000.0e6 \
--rad-tx-gain 12 \
--rad-threaded \
-F 8 \
--src-type USER_BIN --src-path ./example.ts \
--mod-cod QPSK-S_3/5

./bin/dvbs2_rx \
--sim-stats \
--rad-threaded \
--rad-rx-subdev-spec "A:0" \
--rad-ip-addr 192.168.40.2 \
--rad-rx-rate 10e6 \
--rad-rx-freq 1000.0e6 \
--rad-rx-gain 3 \
-F 16 \
--snk-path output_stream_fifo.ts \
--mod-cod QPSK-S_3/5 \
--dec-implem NMS \
--dec-ite 10 \
--dec-simd INTER

I am not getting any underflows or overflows, and the SNR seems good, but am getting lots of bit errors and no video playback. The output of tx and rx is attached. When the SNR goes negative is when I stopped the transmitter, to confirm the receiver is getting the tx signal properly. txout.txt rxout.txt

I confirmed them working in simulation without bit errors and successful video playback using the dvbs2_tx_rx executable:

./bin/dvbs2_tx_rx \
-F 8 \
--src-type USER_BIN --src-path ./example.ts \
--snk-path output_stream_fifo.ts \
--mod-cod QPSK-S_3/5 \
--dec-implem NMS \
--dec-ite 10 \
--dec-simd INTER

Any suggestions for things to try or change?

Also, I was wondering how to tell what the symbol rate is? I'm guessing it's half of the sample rate based on the output saying the oversample factor is two, but wanted to double check. I am attempting also to run tx wirelessly to this dvbs2 receiver box and need to set the symbol rate as a receiver parameter, but have been unsuccessful - the gtmedia shows signal power but is unable to decode.

Thanks again!