OFDM modulator and pilots

Hello,

I’m trying to add pilots to an OFDM modulation, is it possible with
OFDM_mod
block?
How I can “boost” energy of pilot in OFDM signal?

Regards,
Marcin
http://szelest.org

On Tue, Aug 10, 2010 at 9:53 AM, Marcin Szelest
[email protected] wrote:

Hello,

I’m trying to add pilots to an OFDM modulation, is it possible with OFDM_mod
block?
How I can “boost” energy of pilot in OFDM signal?

Regards,
Marcin
http://szelest.org

Yes, this is possible. There is a subcarrier mask concept in the
modulator and demodulator block that you should be able to use. Right
now, it specifies if a carrier is in use or not (e.g., data or
nothing). There are some hooks in there to add pilot tones pretty
easily to the modulator. Actually using them in the demodulator is
where you’ll have to focus most of your attention.

Tom

Tom

After reading gr_ofdm_insert_preamble.cc it looks like the pilots are
sent
periodically after every few payload symbols on all frequency bins. Is
it
like what I have shown attached ? If yes, then how may payload symbols
are
sent between two pilots ?

Another related question is: Who sets the parameters for the work
function
in this block ? particularly noutput_samples.

Srinivas
WINLAB, Rutgers University, NJ

On Fri, Aug 27, 2010 at 12:19:53PM -0400, Srinivas wrote:

Another related question is: Who sets the parameters for the work function
in this block ? particularly noutput_samples.

Srinivas,

The parameters passed to work are determined by the GR runtime system.
Their values depend on a lot of things, including free space in the
upstream and downstream buffers, the return values from forecast;
various settings such as history and output_multiple.

Eric

On Fri, Aug 27, 2010 at 12:19 PM, Srinivas [email protected]
wrote:

Tom

After reading gr_ofdm_insert_preamble.cc it looks like the pilots are sent
periodically after every few payload symbols on all frequency bins. Is it
like what I have shown attached ? If yes, then how may payload symbols are
sent between two pilots ?
Another related question is: Who sets the parameters for the work function
in this block ? particularly noutput_samples.
Srinivas
WINLAB, Rutgers University, NJ

No, that’s a slight mistake in terminology. What you are pointing out
are the “preamble” symbols that are used to set the initial
synchronization (phase, timing, and frequency). I thought you were
asking about “pilots,” which are specific subcarriers sent along in a
payload symbol that contain known data and are used for channel
estimation (equalizer settings) throughout a packet transmission. In
other words, the sync preambles are used to get the initial channel
estimation and pilots can be used to track channels that change
between preambles.

If you were talking about preambles, you should be able to use
insert_preambles, which takes a list of symbols so you can use as many
as you’d like. If you want to use pilots, you have to work with the
gr_ofdm_mapper_bcv and gr_ofdm_frame_acquisition to make use of the
subcarrier map.

Hope that clears it up.

Tom

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