Re: [Discuss-gnuradio] OFDM status

[Dominik Auras]

Hi!

> I kicked the can down the road with Matt Ettus and Tom Rondeau.  We have 
> spent two weeks on this total and others are welcome to contribute.  We 
> need to have the argument: How do we specify the constellations? How do 
> we map carrier usage (which are pilots, clocks, etc.)?

To open a discussion on that topic, here is my first proposition:

We create a generic OFDM mapper block. It should treat every occupied
carrier as a proper channel. I think of something like:

gr_make_io_signature (nchannels, nchannels, sizeof(unsigned char))

The input streams are unpacked bytes, containing 1 to 8 bits. In front
of the mapper, connect several packed_to_unpacked blocks and some
stream_to_streams. A parameter to the mapper block is a channel list
that assigns a modulation type to every subchannel.

The mapper's task is, in this model, to map chunks to symbols
independently for each subchannel. Additionally, it periodically outputs
known symbols that help synchronisation in the receiver(s).

Maybe a new packed_to_unpacked block can be created that fulfills two
tasks; to unpack and to split the input. I think of a block taking a
packed byte stream as input and outputting several unpacked byte streams
with different pack-sizes per output stream.

In the receiver, we do the inverse thing. Information exchange
transmitter <-> receiver could be done through a network (for a testing
platform).

By this, we can benefit of the OFDM's main advantage - to use the
optimal modulation to every subchannel. In the background, there can be
a control application that evaluates SNRs, receives them from the
clients (for first try: through network) and assigns modulation etc.

We can also insert pilot channels - simply connect a "pilot block" to a
subchannel input. This may help on synchronization and channel
estimation.

And it allows a new use case: 1 to N transmission, with one transmitter
and several receivers.

This system will allow to evaluate new algorithms for subcarrier
assignment, channel estimation, synchronization etc.

Greetings,
Dominik




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Re: [Discuss-gnuradio] OFDM status

[Robert McGwier]

http://www.gnuradio.org/trac/browser/gnuradio/branches/developers/n4hy

is the trac and


svn co http://gnuradio.org/svn/gnuradio/branches/developers/n4hy/ofdm

gets you the source.  I am merging the trunk into this about every 50 
revisions unless I see major progress on mblock,  usrp,  etc that is of 
immediate relevance.  Once we get a single instance running on hardware 
and over the air with some speed and reliability,  I will suggest that 
we be allowed to merge this into the trunk and we can all play.



I kicked the can down the road with Matt Ettus and Tom Rondeau.  We have 
spent two weeks on this total and others are welcome to contribute.  We 
need to have the argument: How do we specify the constellations? How do 
we map carrier usage (which are pilots, clocks, etc.)?


In order to be really credible,  we need mblock and we need the part 
that is running on the usrp because we need RSSI, it needs to be inband 
so we can do the gain management that is imperative for OFDM to work 
with its crest factor issues.




Bob



Kuntal Majumdar wrote:

Hello,

Who is doing the OFDM project? May I get some info on that, because my 
thesis project is on the same and  I would love help in this regard.


Thanks a lot.

Regards,
Kuntal


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Re: [Discuss-gnuradio] OFDM status

[Kuntal Majumdar]

Hello,

Who is doing the OFDM project? May I get some info on that, because my thesis 
project is on the same and  I would love help in this regard.

Thanks a lot. 

Regards,
Kuntal




 

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[Discuss-gnuradio] OFDM status

[Brett L. Trotter]

What is the current status of the OFDM project? Is it such that I could
give it a try using a tunnel.py type setup over a shared wireline - or
at least over two separate RX/TX wires?

Last I heard the receiver and transmitter were working but not over the air.


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