Re: [Discuss-gnuradio] small polyphase channelization application

[tom x]

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 <address@hidden> wrote:

On Wed, Feb 24, 2016 at 8:01 PM, tom x <address@hidden> 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 <address@hidden> wrote:

On Sat, Feb 20, 2016 at 12:43 AM, tom x <address@hidden> 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