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negative effect by 44Mhz sampling rate conversion?

    Question

  • Hi everyone,

     

    Recently, I am having measurement study on 802.11a signals using SORA. A problem doing this is, when I estimate SNR from relative constellation error (RCE), it never reaches 25 dB while RSSI based SNR exceeds 40dB. Likewise, when I directly read the signals generated by demod11 just after conversion process (using TestConv11A() ), it has about 23dB SNR, which is somewhat low considering that the signals are not transmitted through real wireless channel. Plotting the receiver process signals, I could see some noises are included in the signals. Probably noises are added in the receiver processing. 

    Then I found when I changed the sampling rate 44Mhz to 40Mhz, such processing noise significantly decreases, and RCE based SNR exceeds 30dB. So I concluded 44Mhz sampling rate conversion is the main source of the noise inflation. But in real measurement, as I have only XCVR2450 that requires 44Mhz sampling, I cannot use 40Mhz sampling rate. How can I avoid such an inherent noise and improve reception probability in real measurement?

     

    Thanks in advance.

     

    Sangki Yun





    Friday, June 10, 2011 1:54 AM

Answers

  • Hi Sangki,

     

    You are right. The resampling will cause some performance loss.

    The sampling rate is provided by a fixed oscillistor, so you cannot change it using software. You can change, of course, the oscillistor, to change the sampling frequency.

    If you only need Sora to Sora communication and want no resampling, you can directly feed 40MHz baseband signal to RCB. That is fine for Sora to Sora communication, as long as the sender and the receiver match.

     

    Thanks,

    - Kun

    Sunday, June 12, 2011 1:36 PM

All replies

  • Hi Sangki,

     

    You are right. The resampling will cause some performance loss.

    The sampling rate is provided by a fixed oscillistor, so you cannot change it using software. You can change, of course, the oscillistor, to change the sampling frequency.

    If you only need Sora to Sora communication and want no resampling, you can directly feed 40MHz baseband signal to RCB. That is fine for Sora to Sora communication, as long as the sender and the receiver match.

     

    Thanks,

    - Kun

    Sunday, June 12, 2011 1:36 PM
  • I see.

    Can I avoid the problem if I use WARP transceiver?

     

    Thank you,

    Sangki Yun

    Thursday, June 16, 2011 12:26 AM
  • Hi Sangki,

    If you have a 40MHz sampled RF, you don't need the resampling filter to communicate to a standard WIFI card.

    At any rate, if you only want to experiment Sora to Sora communicate, you may also simply remove the filter, depending on what you want to do.

    Thanks,

    - Kun

    Friday, June 24, 2011 6:01 AM