> "The problem we are overcoming is the USB data rate bottleneck, which is
> limited to 32 MBps. Although this bit rate is high enough for many
> applications of gnuradio, for an 802.11b receiver it is not sufficient,
> because of the signal's bandwidth. The RF bandwidth of an 802.11b signal is
> 11 MHz. The minimum possible sampling rate (due to the Nyquist sampling
> criteria) is 22 Msamples/sec. Assuming a resolution of 8 bits for each I and
> Q sample, we require 2*22M = 44 MBps through the USB, which is clearly over
> the limit. Because of these limits, the current gnuradio receiver
> implementation of 802.11b (credit to BBN) reduced the signal bandwidth to 4
> MHz prior to sending it through the USB. Effectively, the sub-sampled signal
> arrives at the PC with very low SNR. Typically, 802.11b packets transmitted
> at the 1 Mbps rate can be received, but only at short range."
This is not true. Remember when you have complex samples the sample rate IS the
bandwidth. So 802.11b can be covered with 11 Msps 8-bit I and Q or 22 MByte/s.
So in 8-bit mode the 16 Msps standard USRP configuration can capture the signal.
I had done this previously though I modified my oscillator to be 44 MHz instead
of 64 MHz because (a) the 4x symbol rate interpolation was easier and (b) to
ease the datarate over the USB. I was able to demodulate all the 802.11b modes
including the 11 mbps packets.
-Clark
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