ZP may be seen as CP at all. (looking the padded zeros as a part of the
data block, ZP of the former OFDM symbol is CP of current OFDM symbol.)
So the difference is mainly arised from the parameters.
In your case, ZP-OFDM symbol  is shorter than CP-OFDM symbol.
That is all.

chaselweng wrote:
> Hi all....
> I just simulated the Zero-Padding OFDM and Cyclic-Prefix OFDM system...
> I found some difference between their power spectrum density...
> In CP-OFDM, the in-band ripple is larger than ZP-OFDM...
> But in out-of-band, the ZP-OFDM is larger than CP-OFDM....
> I just got the conclusion through simulation...
> How could i explain the phenomenon in physical or math. sense....
>
> Anyone can tell me how to formulate it as a math problem..!?
> (any recommend paper or book also good)...Thx a lot!!

Hi all....
I just simulated the Zero-Padding OFDM and Cyclic-Prefix OFDM system...
I found some difference between their power spectrum density...
In CP-OFDM, the in-band ripple is larger than ZP-OFDM...
But in out-of-band, the ZP-OFDM is larger than CP-OFDM....
I just got the conclusion through simulation...
How could i explain the phenomenon in physical or math. sense....

Anyone can tell me how to formulate it as a math problem..!?
(any recommend paper or book also good)...Thx a lot!!