Oversampling in OFDM

Hi,

I have a question related with the OFDM transmitter. What is the 
commonly method to increase the sampling rate ?

- Increasing the IFFT size and insert zero in the inpput ?
or
- Insert zero in the IFFT output and followed by interpolation filter ?

What is the trade-off ? anyone can help ?

Thanks.

Buzz

> Hi,
>
> I have a question related with the OFDM transmitter. What is the commonly 
> method to increase the sampling rate ?
>
> - Increasing the IFFT size and insert zero in the inpput ?
> or
> - Insert zero in the IFFT output and followed by interpolation filter ?
>
> What is the trade-off ? anyone can help ?
>
> Thanks.
>
> Buzz

To me this doesn't seem very straightforward to answer.

The first solution would be the easiest and cost less HW/SW, certainly if 
you optimize the IFFT by knowing that some (most?) of the inputs are 0.
However I would expect that the out-of-band suppression isn't very good with 
the first solution as you still keep the sinx/x of the all OFDM carriers 
between the extra inserted zeros.
The interpolation filter you can make as good/bad as you want.

Probably if you don't care about what is going on outside the OFDM band, 
doing the first would be best/cheapest you could also just use a very simple 
interpolation filter.

Intiutively I would think tha exploiting the very HW/SW efficient IFFT in 
some way woud be a good thing to do.

NL