Re: [Discuss-gnuradio] OFDM modulator and pilots

[Tom Rondeau]

On Fri, Aug 27, 2010 at 12:19 PM, Srinivas <address@hidden> 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



> On Thu, Aug 26, 2010 at 11:58 AM, Tom Rondeau <address@hidden>
> wrote:
>>
>> On Tue, Aug 10, 2010 at 9:53 AM, Marcin Szelest
>> <address@hidden> 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
>>
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>
>
>
> --
> Srinivas
>
>