>
>> The FFT is relatively easy, using fixed-point arithmetic. No reason to
>> use floating point.
>
>
> Can you explain this to me? This is a critical point!
> I had a look at a master thesis of a guy here at the university...
> He wrote that a floating point representation is required (but he
> didn't write why).
> It would be much easier to operate with fixed-point numbers, but I
> should understand why...
>


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.

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.



>
>> Other parts of the system are more challenging.
>
>
> Do you mean the Viterbi decoder?
>


Viterbi is not such a hard thing to implement but it can be tricky to
get it performing properly.

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).