[Discuss-gnuradio] ofdm decoder problem on USRP2

[Guanbo Zheng]

Hi,

I am trying to build the OFDM decoder on GRC based on the FTW 802.11a/g encoder.

At the USRP2 receiver, after CFO compensation, I want to see the QPSK constellation.

Basically, the process is:
bit stream ---- ofdm mod ---- usrp2 sink
usrp2 source -- timing offset comp --- CFO comp ---- ofdm demod ----- constellation sink

Before ofdm_demod, the signal spectrum observed in USRP2_fft is good as far as I know.

But after OFDM demod block, I can not receive anything. No data output!  :(

I read some threads by Veljko, regarding to the parameter setting of OFDM demod block.

But I am not sure about the number of tones, SNR. 

Where can I find the definition of this block? What is the meaning of S and Time out?
By the way, my setup environment is ubuntu 9.04 + gnuradio 3.2.2.

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Regards,
Guanbo