Some basic questions

GNU Radio
1

Hi,
Could someone please answer following questions of mine :

  1. In
    pkt = ofdm_packet_utils.make_packet(payload, 1, 1, self._pad_for_usrp,
    whitening=True)

what is whitening?

  1. In gr.fft_vcc(fft_size,forward, window, shift=false)
    What is window vector?

  2. in ofdm_mod there is a portion of code having comments:
    Use freq domain to get doubled-up known symbol for correlation in time
    domain

Can you please explain this part.
Thank you in advance.
Cheers

2

Hi Jack,

Answer to question 1:

I believe the whitening option randomises the data bits so that the PAPR
(Peak-to-Average Power Ratio) is reduced.

Mike

3

On Mon, May 03, 2010 at 09:25:56PM +0000, jack william wrote:

Hi,
Could someone please answer following questions of mine :

  1. In
    pkt = ofdm_packet_utils.make_packet(payload, 1, 1, self._pad_for_usrp,
    whitening=True)

what is whitening?

It scrambles up your bits (makes them white in a stochastic sense).

  1. In gr.fft_vcc(fft_size,forward, window, shift=false)
    What is window vector?

A tapering window applied before the actual FFT (like a Hamming window)

  1. in ofdm_mod there is a portion of code having comments:
    Use freq domain to get doubled-up known symbol for correlation in time domain

This is part of OFDM timing synchronisation. You probably want to read
up on that topic if your interested (e.g., the paper on OFDM synch by
Schmidl & Cox).

Cheers
MB

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