search

bastibl / gr-ieee802-15-4

IEEE 802.15.4 ZigBee Transceiver
https://www.wime-project.net
GNU General Public License v3.0
270 stars 87 forks source link

What is the influence of "Select an even decimation to ensure that a halfband filter is enabled."warning? #36

Closed GJHLCX closed 6 years ago

GJHLCX commented 6 years ago

Hi bastibl, First of all, I'm very grateful for the code 'gr-ieee802-15-4' you contributed. I met a problem when using it. After running the grc code, i got this warning:

[INFO] [UHD] linux; GNU C++ version 5.4.0 20160609; Boost_105800; UHD_3.11.0.1-37-g2c9087d1 [INFO] [USRP2] Opening a USRP2/N-Series device... [INFO] [USRP2] Current recv frame size: 1472 bytes [INFO] [USRP2] Current send frame size: 1472 bytes [WARNING] [CORES] The requested decimation is odd; the user should expect CIC rolloff. Select an even decimation to ensure that a halfband filter is enabled. decimation = dsp_rate/samp_rate -> 25 = (100.000000 MHz)/(4.000000 MHz)

What is the influence of "Select an even decimation to ensure that a halfband filter is enabled."warning? Does this warning affect the time synchronization in chips (in ieee802.15.4 PHY, symbol to chip ) ?

Thanks, Jionghong

bastibl commented 6 years ago

That's an issue of older SDRs like the N210. It means that the spectrum might not be perfectly flat for some sample rates. I don't think that it will cause performance issues, but you can easily work around this by setting the sample rate to 5M and add a resampler directly after the SDR that resamples 5M -> 4M.