Thanks for your help. I reviewed the documents again and also looked at the energy detection example in this archive, which was similar to what I'm trying: http://gnuradio.squarespace.com/storage/examples/ucla2014/02-filters_and_filtering.tar.gz
I took the parameters to the 4 channel channelizer in energy_detect.grc and modified them until I got something like this: http://i.imgur.com/bsGd0H5.png I am only considering the first two channels for now. With 20 MHz of bandwidth divided between 4 channels, channel 0 will be centered at DC and the next channel is separated by 5 MHz, which is what I want. The problem now is that I'm still not getting packets, but will occasionally get a 'malformed packet'. I am wondering if anyone has any more suggestions for how to debug/solve this. THanks, Tom On Sat, Feb 27, 2016 at 6:45 PM, Tom Rondeau <t...@trondeau.com> wrote: > On Wed, Feb 24, 2016 at 8:01 PM, tom x <tomx4...@gmail.com> wrote: > >> Thanks for the reply, >> Could you please clarify what you mean by 'you're offsetting the >> frequency and shouldn't be'? >> I am tuning the frequency of the USRP, but other than that I am not sure >> what you mean. The channelizer flow graphs in the link set the Ch0: Center >> Freq field as well. >> Thanks, >> Tom >> > > > Take a look at the link and paper that I mentioned. It sounded like you > think that the channelization should be something like the following, > assuming a 4 channel channelizer: > > | ch2 | ch3 | ch0 | ch1 | > | | | > | | > -f/2 ------------ -f/4 ------------ 0 ------------ f/4 ------------ f/2 > > > When the channelization is really: > > ch2 | ch3 | ch0 | ch1 | ch2 > | | | | > -f/2 ------------ -f/4 ------------ 0 ------------ f/4 ------------ f/2 > > > So channel 0 spans DC. You had offset the channel from 0 to f/4. > > And because we're at complex baseband, channel 2 wraps around from +f/2 to > -f/2 > > Tom > > > >> On Sun, Feb 21, 2016 at 4:11 PM, Tom Rondeau <t...@trondeau.com> wrote: >> >>> 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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