Re: [Discuss-gnuradio] Fwd: Re: Transmission error

[Rama V]

Hi all,

I have tried to send packets to the receiver from /digital/narrowband folder and it has mostly succeeded. The output I was able to get when I sent the following commands were

Sender: ./benchmark_tx.py -p 4 -M 2 -f 2.435000061G --tx-gain=28 -r 250000

Receiver: ./benchmark_rx.py -p 4 -f 2.435000061G --rx-gain=54 -r 250000

ok =  True  pktno = 1323  n_rcvd = 1303  n_right = 1294
ok =  True  pktno = 1324  n_rcvd = 1304  n_right = 1295
ok =  True  pktno = 1325  n_rcvd = 1305  n_right = 1296
ok =  True  pktno = 1326  n_rcvd = 1306  n_right = 1297
ok =  True  pktno = 1327  n_rcvd = 1307  n_right = 1298
ok =  True  pktno = 1328  n_rcvd = 1308  n_right = 1299
ok =  True  pktno = 1329  n_rcvd = 1309  n_right = 1300
ok =  True  pktno = 1330  n_rcvd = 1310  n_right = 1301
ok = False  pktno = 1331  n_rcvd = 1311  n_right = 1301

But there were a few packets where I have not received them correctly. I guess only 95% of them were efficient in transmitting.  I have tried changing the gain settings and what I observed was that if I decrease the gain from its normal value, the reception of packets are somewhat less efficient. Can I kindly know what I might be able to do in order to receive those packets in a more efficient way or is that what generally happens in a real world transmission? Thanks

Regards,

Dave

On Tue, Sep 22, 2015 at 1:02 PM, Marcus Müller <address@hidden> wrote:

Ok,

This is because I have changed my folder to /digital/ofdm, I have started to receive packets.

this means that you're using something *completely* different than before. It's simply a completely different transceiver system.

kindly advise if I need to figure out the combination settings till most of them receive properly?

Yes. You will need to figure out the optimum settings. Increase gain on the RX end, see if things get better or worse. Find an optimum for that. Do the same with the TX gain.

Because even though I did not set any sample rate, the transmitter sent the information.

As mentioned before multiple times: run the programs with "--help". They will show you what default settings they have.

Please help. Please excuse me if I am being naive in asking these.

It's alright to ask questions, but please remember to apply the things we tell you.

Best regards,
Marucs

On 22.09.2015 00:59, Rama V wrote:

Hi,
As advised, the problem has been solved to a little extent where I have got the below results by giving the commands as

Sender : ./benchmark_tx.py -f 2.435G --tx-gain=25

Receiver: ./benchmark_rx.py -f 2.435G --rx-gain 50

ok: True      pktno: 1971      n_rcvd: 1687      n_right: 358
ok: False      pktno: 1972      n_rcvd: 1688      n_right: 358
ok: False      pktno: 1973      n_rcvd: 1689      n_right: 358
ok: False      pktno: 1974      n_rcvd: 1690      n_right: 358
ok: True      pktno: 1975      n_rcvd: 1691      n_right: 359
ok: False      pktno: 1976      n_rcvd: 1692      n_right: 359
ok: True      pktno: 1977      n_rcvd: 1693      n_right: 360
ok: False      pktno: 1978      n_rcvd: 1694      n_right: 360
ok: True      pktno: 1979      n_rcvd: 1695      n_right: 361
ok: True      pktno: 1980      n_rcvd: 1696      n_right: 362
ok: False      pktno: 1981      n_rcvd: 1697      n_right: 362
ok: True      pktno: 1982      n_rcvd: 1698      n_right: 363
ok: False      pktno: 1983      n_rcvd: 1699      n_right: 363
ok: True      pktno: 1984      n_rcvd: 1700      n_right: 364
ok: False      pktno: 1985      n_rcvd: 1701      n_right: 364
ok: True      pktno: 1986      n_rcvd: 1702      n_right: 365
ok: False      pktno: 1987      n_rcvd: 1703      n_right: 365
ok: True      pktno: 1988      n_rcvd: 1704      n_right: 366

This is because I have changed my folder to /digital/ofdm, I have started to receive packets. But I guess this is only 50% efficient in receiving packets. Not all of them have been receiving properly. kindly advise if I need to figure out the combination settings till most of them receive properly? Because even though I did not set any sample rate, the transmitter sent the information. Please help. Please excuse me if I am being naive in asking these.

Regards,

Dave

On Mon, Sep 21, 2015 at 11:00 AM, Rama V <address@hidden> wrote:

Hi,

Thanks Marcus. I will do as you have advised and approach if any uncertainties.

Regards,

Dave

On Mon, Sep 21, 2015 at 10:16 AM, Marcus Müller <address@hidden> wrote:

Hi Dave,

you shouldn't be modifying the python files before you understand what they do exactly. Please revert your edits, because it will be impossible to help you if you don't use the same scripts as we do, obviously. We've talked about this[1].

So:

Sender : benchmark_tx.py -f 2.435G -r 250k
Receiver : benchmark_rx.py -f 2.435G

That's wrong! Now, your transmitter sends 250,000 bits per second, but your receiver expects 100.000 (the default value, which doesn't work with your hardware), so that's not good. Use the same setting for both benchmark_tx and benchmark_rx.

So all you say is I need to change and play with the sampling rates and --tx-amplitude  until the received packet becomes 'n_rcvd=1'

No. RF is not "hey, there's this correct setting, let's apply it everywhere"; you'll have to figure out which combination settings work best. Generally, I'd leave the  --tx-amplitude untouched, because 0.25 is a sane value for the digital samples; what you want is analog gain, not digital scaling.

You should really set a TX gain and a RX gain. Try around with a few different gain settings for RX and TX gain -- a good approach would be to set something like 25 dB TX gain, and around 50 dB RX gain, if you place your TX and RX antennas far enough from each other. Notice that I'm assuming you're using antennas, and no direct connection! If you're using a direct cable between TX and RX, please use an attenuator, because you might otherwise damage your hardware.

To find out how to change the gains, please read the output of
benchmark_tx.py --help
and of
benchmark_rx.py --help


Best regards,
Marcus


[1] http://lists.gnu.org/archive/html/discuss-gnuradio/2015-09/msg00124.html

On 21.09.2015 16:48, Rama V wrote:

I have tried the following commands in the terminal

Sender : benchmark_tx.py -f 2.435G -r 250k
Receiver : benchmark_rx.py -f 2.435G

But the data packets are not being sent correctly. I have been receiving the packets as ok=false. I have tried modifying benchmark  python scripts. Can I do the modification of those scripts or evrything needs to be given in the command line. Please excuse me as I am slightly unable to understand. Thanks

Regards,
Dave

On Sep 18, 2015 2:21 PM, "Rama V" <address@hidden> wrote:

Thanks for the reply Michael. I will look into that as you have advised. So all you say is I need to change and play with the sampling rates and --tx-amplitude  until the received packet becomes 'n_rcvd=1' and CRC check changes to 'ok=true' from the narrowband folder?

Regards,

Dave 

On Fri, Sep 18, 2015 at 12:40 PM, Michael Dickens <address@hidden> wrote:

Hi Dave - I'm thinking that you are confusing "--samples-per-symbol" for the sample rate. I think the option you're looking for is "-r". Look at the "--help" for those examples when you get a chance. - MLD

 

On Thu, Sep 17, 2015, at 02:01 PM, Rama V wrote:

Thank you very much Michael. I will follow up on your advice. I am sorry that I wasn't able to understand some parts in GNU RADIO and didn't specify enough information.  Regarding the question, I have been doing the benchmark in the digital/ narrowband/ folder. The exact commands I have been working on are

Sender: benchmark_tx.py -f 2.435G --tx-gain 25 --samples-per-symbol 250000

Receiver: benchmark_rx.py -f 2.435G

When I give 250kS/s, my laptop freezes. USRP is XCVR2450. So I started to give less Samples like 50kS/s so that they communicate with each other without errors. But I couldn't figure out the solution to that. So I just have a doubt whether I need to modify benchmark scripts or is it enough for the parameters I give in the command line. Thanks for the help. Please advice

 

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