On Wed, Feb 16, 2011 at 1:50 PM, Thomas Nitsche <nitsc...@in.tum.de> wrote:
> Hi, > we are doing some research here on decoding 802.11g using GNURadio. As far > as i know there is code available for transmission of 802.11g frames on > CGRAN but no receiver code. Is there any work going on for the receiver side > right now? Is it theoretically possible to decode a signal received with the > USRP N210? The bandwidth provided by the gigabit ethernet connection should > be sufficient in contrast to the USRP1 USB connection, or am i wrong? > Thomas, Yes, the N210 will handle the bandwidth of 802.11g. > I had a look at the (generic) GNURadio OFDM mod/demod code but its kind of > hard to understand whats going on there. I have reused the ofdm-sync-pm code > to generate seemingly helpful frequency offset values from the 802.11 short > training sequence. I also extracted timing information by correlating with > the known short sequence. However i am not sure if this synchronization is > accurate enough for at least a few fft blocks. > > Is there anything like: > > fine timing/frequency correction, > Yes, provided by the ofdm_sync block in ofdm_receiver.py. > sampling offset correction, > Yes, also provided by the ofdm_sync block in ofdm_receiver.py. channel estimation or > Yes, in ofdm_frame_acq in ofdm_receiver.py. > code for using pilot tone subcarriers > No. That's one of the biggest gaps in the current implementation. > in the generic GNURadio ofdm implementation that could be reused for a > 802.11g receiver? What is with the code for extracting infos from the > subcarriers? Would it be easier to rewrite it from scratch or can some of > the gnuradio code be reused? > > Thanks for any information you can provide, > Thomas It should be a place to start, but it'll probably take some work (though hopefully less than starting from scratch). For getting the subcarriers, you probably want to look at the gr_ofdm_frame_sink block. Tom >
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