On Sat, Feb 20, 2016 at 12:43 AM, tom x <tomx4...@gmail.com> wrote: > Hi, > > I am working on an application to capture IEEE 802.15.4 traffic on > multiple channels simultaneously. (I will mention now that I am new to GNU > Radio and DSP.) I can successfully capture on one channel. I read the 2009 > paper "Multi-Channel IEEE 802.15.4 Packet Capture Using Software Defined > Radio", where L. Choong is able to capture traffic on four channels > simultaneously with four frequency translation and FIR filter blocks. I > have tried this approach with two channels but did not have success, most > likely because the parameters to my filters were incorrect. > > This mailing list's archives pointed me to the polyphase channelization > block, which I think can simplify this task. Here is a link to a picture of > my flow graph: > > http://i.imgur.com/sxQnEIw.png > > I am tuning the USRP to halfway between channel 25 and 26 (whose > corresponding frequencies are shown in the picture). Each channel is 2MHz > wide, and the center of each channel is separated by 5 MHz. With this in > mind, I set the USRP's bandwidth to 7MHz, which would contain channels 25 > and 26 (Is setting this parameter necessary? I would like to scale this > design up to four channels.) > The 'target_rate' is the width of a channel, so I am setting the frequency > cutoff to half of that, assuming the signal I want would be centered about > 0 Hz. I set the transition window to less than half of the sample rate, on > the advice of this blog: > http://blog.kismetwireless.net/2013/08/hackrf-pt-2-gnuradio-companion-and.html > . However, no packets are making it to the sinks, when I transmit on either > channel from a separate radio. Does anything about this set up jump out as > incorrect? I would appreciate any tips you could offer. > > Thanks, > Tom > >
Tom, This might help you out: http://www.trondeau.com/examples/2014/1/23/pfb-channelizers-and-synthesizers.html One issue is you're offsetting the frequency and shouldn't be. Channel 0 spans -B/2 to +B/2 (B being the bandwidth of the channel) and centered around 0. There should be images in the link (or the paper it references) that should show this. Tom
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