the frequency spectrum of ISI

[vicelina]

Hi all

I have a question on the effect of ISI. As far as my understanding, the cause of ISI is due to the fact that symbol in time domain spreads, so it interferences with its neighbours, therefore causing the receiver makes incorrect decision.

However, this is what I don't understand. According to another material, it says in the frequency domain, we need to guarantee that the fourier transform of the sampled response is flat, why? what does it really mean please?

[charan langton]

ISI can be caused by many things, infact it is the general name of all distortions in time domain. The ripple or non-flatness of the frequency response will cause some distortion and this can be said to cause ISI.

The non flat frequency response says that various frequencies are being distorted differently and that usually means signal distortion. Phase distortion also comes into the picture too, which is of course also part of the spectrum but much harder to characterize.

Charan Langton