Re: [Discuss-gnuradio] IEEE 802.11 Transceiver Module - Timing offset at receiver side

[Qurat-Ul-Ann Akbar]

I have been doing this for a long time now and I have changed all these parameters that you just mentioned in order to understand whats going on. I have changed both the transmitter and receiver gain and set different values but gain is not changing the SNR for some reason. It only works till 2.5 Mhz and at higher sampling rates data is not decoded at all. It does detect the correlation and start of frames in sync_Short block but data is not decoded probably because of high noise. I have also used different DC offset values and that doesn't help either. The antennas are placed within each other's LOS and I dont think interference should be a problem. And if you have used Vert2450 antennas then I really dont understand whats the problem. 

On Sun, Jun 4, 2017 at 11:47 AM, Bastian Bloessl <address@hidden> wrote:

On 06/04/2017 05:35 PM, Qurat-Ul-Ann Akbar wrote:

Then what could be the problem for a low SNR. The average power I see at the receiver is -100 to -120 db and the signal is too distorted within noise.

This can have many reasons (including gain, interference, DC offsets, LO leakage, etc etc.) I think it will take some more effort from your side to find out what's going wrong.

You might find lots of helpful information on
- wime-project.net/installation/
- the GNU Radio Wiki
- the mailing list archive
- Stack overflow

And I watched your video on YouTube in which you were showing a demo of the WiFi receiver. In that video you had big antennas and I don't think those were Vert 2450.

If the video shows larger dipoles with cables, they were ECOM9-5500. Again, I don't believe that the antennas are your problem. I used the transceiver successfully with many different antennas, including the Vert 2450 that you are using.

Best regards,
Bastian

On Jun 4, 2017 11:21 AM, "Bastian Bloessl" <address@hidden <mailto:address@hidden>> wrote:



    On 06/04/2017 05:16 PM, Qurat-Ul-Ann Akbar wrote:

        I understand. But you didnt connect them directly to the USRP.
        You used some cable to connect the two and had a stand for your
        antenna. Can you tell me which cable was that ?


    I have no idea what you are talking about. When I used the Vert
    antennas, I connected them directly to the USRP.

    If you experience low SNR you'll probably not improve things if you
    add cables between the SDR and the antenna. I doubt that the antenna
    or cables are your problem.

    Best,
    Bastian




        On Jun 4, 2017 11:13 AM, "Bastian Bloessl" <address@hidden

        <mailto:address@hidden> <mailto:address@hidden
        <mailto:address@hidden>>> wrote:

             Hi,


             On 06/04/2017 04:25 PM, Qurat-Ul-Ann Akbar wrote:

                 Thank you for the explanation. Can you tell me which
        antennas
                 did you use for your experiments when you wrote your paper?
                 Because I think a major problem with my receiver is a
        very low
                 SNR because everything works fine with simulations.
        Currently I
                 am using Vert 2450 antenna with my USRP N210.


             I used the same setup with the Vert 2450 antennas.

             Best,
             Bastian






                 On Sun, Jun 4, 2017 at 12:33 PM, Bastian Bloessl
                 <address@hidden <mailto:address@hidden>
        <mailto:address@hidden <mailto:address@hidden>>
                 <mailto:address@hidden <mailto:address@hidden>
        <mailto:address@hidden <mailto:address@hidden>>>> wrote:

                      Hi,

                      On 6/3/2017 9:11 PM, Qurat-Ul-Ann Akbar wrote:

                          Hello,

                          How is the timing offset being handled in the
        802.11
                 module. I
                          see that the sync_long block does frequency offset
                 correction
                          and the frame_equalizer block does the phase
        correction
                 but I
                          dont understand where is the timing offset being
                 handled. Can
                          anyone tell me which algorithm is being used
        to do that?


                      The Sync Long block correlates the signal with the
        known
                 pattern of
                      the long preamble to derive how the FFTs have to
        be aligned
                 in time.

                      Best,
                      Bastian


    --     Dipl.-Inform. Bastian Bloessl
    CONNECT Center
    Trinity College Dublin

    GitHub/Twitter: @bastibl
    https://www.bastibl.net/

--
Dipl.-Inform. Bastian Bloessl
CONNECT Center
Trinity College Dublin

GitHub/Twitter: @bastibl
https://www.bastibl.net/