On Wed, Feb 16, 2011 at 1:50 PM, Thomas Nitsche
<address@hidden> 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