R: R: Re: around empty subcarrier in 802.11n implementation

Hi guys,
I’ve tried to follow the suggested procedure. I guess the problem is
inside the uhd driver I’m using (UHD_003.005.001), since the
set_rx_freq() gives the following error:
AttributeError: ‘uhd_usrp_source_sptr’ object has no attribute
‘set_rx_freq’
Or, maybe, the problem is the daughterboard, which is of type XCVR2450.
Is there another way to set dc offset?
Any hint will be greatly appreciated.
Francesca

----Messaggio originale----

Da: [email protected]

Data: 09/10/2013 10.52

A: [email protected]

Ogg: [Discuss-gnuradio] R: Re: around empty subcarrier in 802.11n
implementation

Thanks for your answer.
I’m a computer scientist, so I’m not so aware of what DC-offset exactly
means, but I’m going to try this tuning. I’ll let you know if I solve
the problem.
Best regards
Francesca

----Messaggio originale----

Da: [email protected]

Data: 08/10/2013 16.22

A: [email protected]

Ogg: Re: [Discuss-gnuradio] around empty subcarrier in 802.11n
implementation

Likely, if it’s the central tones, you’re looking at DC-offset (or the
removal thereof) interfering.

You can use offset tuning in the hardware to slide the DC offset outside
of your passband.

http://files.ettus.com/uhd_docs/manual/html/general.html#tuning-notes

on Oct 08, 2013, removed_email[email protected] [email protected] wrote:

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

On 10/09/2013 09:55 AM, [email protected] wrote:

‘set_rx_freq’
Francesca

Francesca


        ofdm_frame_acquisition. FEC is also included in the chain.
        poor snr values. So
        implementation.

Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Since you’re likely using the Gnu Radio interface that is a wrapper for
UHD, you’d use the set_center_freq() method.

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