If you have access to the examples available in GNURadio package, please check:
\examples\digital\packet
Or
\example\digital\demod
The parameters are straight forward though.
Samples Per Symbol for your case is 2.
Filter Rollof Factor of 0.35 is fine.
Prototype Filter Size of 44 or 45 does the job.
Loop Bandwidth is the famous constant of 2*pi/100.
I use these values and the flowgraph seems to be fine. I hope they do the same for you.
Cheers.
Sent from Mail for Windows 10
From: Brian
Sent: 04 July 2017 19:12
To: Mojtaba Mansour Abadi
Subject: RE: [Discuss-gnuradio] Fwd: USRP Packet Decoder and Encoder
Thanks
How do I configure the fll band edge
From: Mojtaba Mansour Abadi
Sent: 04/07/2017 18:53
To: address@hidden
Subject: Re: [Discuss-gnuradio] Fwd: USRP Packet Decoder and Encoder
Hi Brian,
Good work you attached the flowgraphs.
My suggestion is to either
- add an FLL Band-Edge block before the Polyphase Clock Recovery block at Rx;
so your Rx side looks like this:
USRP Source -> FLL Band-Edge -> Polyphase Clock Recovery -> CMA Equalizer -> ...
Or
- Instead of low level blocks for modulation and demodulation, use PSK Mod and PSK Demod from GNURadio.
So the Tx looks like:
File Source -> Packet Encoder -> PSK Mod -> USRP Sink
And RX looks like:
USRP Source -> PSK Demod -> Repack Bits -> Packed to Unpacked -> Packed Decoder -> File Sink
Of course PSK Mod/Demod are deprecated but I found them to be quite robust and functional.
I hope it helps.
Cheers.
Sent from Mail for Windows 10
From: Brian Clark
Sent: 04 July 2017 18:34
To: address@hidden
Subject: [Discuss-gnuradio] Fwd: USRP Packet Decoder and Encoder
Hi All,
I have gone through my flow graph and can confirm that with no USRPs connected I can successfully transmit a file which includes encoding and QPSK modulation at the transmitter, and the reverse at the receiver. The attached flow graph is my file.
Moving on and using my successful flow graph I have now split this and introduces USRP radios. This is the second flowgraph, you will notice that I have disabled the transmitter side (the opposite is true on my other file on my transmitting usrp)
The results I have monitored include;
1. A file is created with 0B - even before the transmitter is turned on
2. The QT GUI Sink on the receiver appears to raise the noise floor to -40db (quite wide and not limited to the band). The transmitter shows a fairly well defined signal
3. At no point does there appear to be an output from the Demodulator
My Thoughts are now that the blocks are working, but there is a problem with the transmission of the signal over USRP. I have tested both USRP as a sinmple FM RXer and FM Txer successfully. Could this be a syncronisation problem? or a saturation one? This would lead to signal being received and the access code not present therefore no output present
---------- Forwarded message ----------
From: Brian <address@hidden>
Date: 4 July 2017 at 10:38
Subject: RE: [Discuss-gnuradio] USRP Packet Decoder and Encoder
To: Mojtaba Mansour Abadi <address@hidden>
Derek and Mojitaba,
Thanks for your comments. I am not in front of my machines at the moment but I did attempt a single flow graph without usrp and that worked well.
My usrp are connected via antenna and the rxer threshold is -120db with just noise and -40db with a signal.
I will try your suggestions and let you know if unsuccesful I will upload the grc files.
Thanks
Brian
From: Mojtaba Mansour Abadi
Sent: 04/07/2017 10:15
To: address@hidden
Subject: Re: [Discuss-gnuradio] USRP Packet Decoder and Encoder
Hi Brian,
From my experience, if packet decoder is not receiving any detectable preamble bit sequence there will be no output.
From your email I realised that you’re receiving noise-like signal if decoder is bypassed. So I also agree with Derek that either you probably are not receiving any signal or the modulation/demodulation procedure is not performed correctly.
Try your system back-to-back without any packetisation mechanism. Use a very short length vector source with couple of numbers as data. Make sure you are receiving the same sequence at the Rx side.
If you don’t. Try a loopback system without any USRPs and see if your data is received at the Rx side.
Cheers.
Sent from Mail for Windows 10
From: Derek Kozel
Sent: 04 July 2017 08:48
To: Brian
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] USRP Packet Decoder and Encoder
Hello Brian,
It will be difficult to provide useful advice without seeing your flowgraph. Does your file correctly get written if you bypass the actual radios and simply connect the transmitter and receiver flowgraphs together? If it does then you probably need to add synchronization to your receiver.
Another good check is to look at the received raw spectrum and ensure that the signal is being received at an appropriate power level. How do you have the two USRPs connected? Antennas or coax with an attenuator?
Regards,
Derek
On Mon, Jul 3, 2017 at 11:29 PM, Brian <address@hidden> wrote:
I have a flow graph that currently has a packet encoder at the transmitter and an encoder at the receiver.
I am attempting to send a file from one usrp to the other.
On investigating the output of the receiver it would not appear that it is processing anything possibly because of the access code but I have conformed they match and are suitably long and random.
The file I get out is 0bytes. If I bypass the decoder a large file is created, although large and unusable (noise)
Any advice on how to proceed will be gratefully received and a pre-configured tx and rx flow graph will be most welcome.
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