Around empty subcarrier in 802.11n implementation

GNU Radio
1

Hi list,

I’m using gnuradio 3.6.0 together with USRPs N210 for implementing OFDM
802.11
n communications, just SISO for the moment (in the future it would be
MIMO). I
have properly modified parameters such as FFT size, number of occupied
tones
and so on. I have also included all preambles (STF, LTF…) and I have
accordingly modified the “correlate” and “calculate_equalizer” functions
in
ofdm_frame_acquisition. FEC is also included in the chain. In the
ofdm_frame_sink file I’ve added a function that computes SNR in a
per-carrier
basis.

Everything is working fine, I obtain about 80% of correct packets, but
I’ve
noticed from the snr plotting, that the carriers around the central
empty one
(3 subcarriers before and 3 subcarriers after) have very poor snr
values. So
I’ve investigated about this effect, and I’ve realized that the all
transmission errors are in those subcarriers and, in most cases, FEC is
able to
recover, but I would like to understand why this happens.

I conducted some searches in the web but unfortunately I didn’t find an
answer.
Let me know if you need some other information about my implementation.

Thanks for your attention
francesca

2

On Tue, Oct 8, 2013 at 9:52 AM, [email protected] [email protected] wrote:

Thanks for your attention
francesca

The USRPs do a good job at getting rid of the DC carrier, but there
are still issues around DC that are probably affecting you. The crude
but easy option is to try to make sure you are perfectly centered on
DC by some hand-tuning.

Tom

3

hey, I’m the beginner of gnu radio with usurp N210.

and, i want to do sth as u to receive 802.11n wifi signal and decode it.

can i ask u about how do u achieve it?

or do u know where can i get more informations?

thank u so much~ !