Hi Andy!

Andy Ray ha scritto:
> A floating point FFT is likely to produce more accurate results than a
> fixed point FFT. That said you can make a fixed point FFT as accurate
> as you wish.

Perfect.
Then it's only a matter of studying the FFT theory.
The important thing is to understand that this block is not so critical
as it appeared.
And of course, if you can suggest some documentation it would be really
useful.

> For 802.11a, which I believe uses a maximum of 64QAM, I find it hard to
> believe that floating point is necessary. Basically a less accurate fft
> will add a little extra noise to your system. If it's small enough its
> not worth worrying about.

This is a really interesting point.
Can you suggest some text/documentation in order to understand a
systematic way to evaluate the noise due to the fixed-point
representation? Of course this noise must be somehow affected by the
number of bits we dedicate to the foxed-point representation. I think
an in-depth theory must be available in some book...

And another critical point... Even the DAC (after the ofdm modulator,
before the RF part of the transmitter) introduces noise, due to the
number of bits of its resolution. How can we quantify its effects?
Also here, this problem must have been already studied.


> There's also the QAM/BPSK/QPSK modulator/demodulator and data formatting
> for the MAC.
>
> The real magic in these modems, however, is the front end processing
> required to equalize the channel. Issues such as AGC, alignment and
> equalization are a real swine to get right and have a huge bearing on
> the quality of results (at least thats my take from implementing a
> couple of wireline modem standards).

I think we will consider these problems at a later stage.
As you have probably understood, we are really at the beginning of this
work and for the moment we are mostly acquiring information. The
complete project (a 802.11a transceiver) will take several months
(several years?). Unfortunately the people involved in my group lack of
the necessary expertise (but we are of course working to build it up).

Ciao,
Franco