Re: [Discuss-gnuradio] Regarding on the new OFDM implementation.

[Martin Braun (CEL)]

Hi Alex,

On Wed, May 15, 2013 at 12:13:16PM -0500, Alex Zhang wrote:
> It is excited to see the new OFDM implementation has been merged and test in
> the GNURadio master branch. Several Questions:
> 
> 1. What are the main changes from the old design?

The biggest differences are the increased modularity and
configurability.
Before, you couldn't really change the flow graphs much. These new OFDM
blocks can be configured in many ways, and if one individual element (it
might be the synchronization, or the equalizer, or whatever) needs to be
changed, it's as easy as exchanging blocks. You can also test and
re-arrange the flow graphs in GRC as a result of this.

The new blocks operate on a frame-by-frame basis. For this, we used the
new tagged_stream_blocks (in fact, these were triggered by the OFDM
code).

> 2. Seems it support NC-OFDM as the user can arrange the carriers? And how is
> the gain of dB between the occupied carriers and vacant carriers?

You can arrange the carriers however you want (this also makes your
second question irrelevant), which is one of the new features. Right
now, you can't change them adaptively, though.

> 3. How about the data rate which is the supported by the new design? 

We're lacking proper benchmarks. As usual, there wouldn't be a
definitive answer to this question as it depends on too many things.

What's still lacking are support for frame-by-frame FEC and better
equalizers. Also, there's only one detection and synchronisation
algorithm implemented (Schmidl & Cox). However, the infrastructure
allows easy adding of such blocks.

MB

-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

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