ISI is similar to aliasing distortion?

[pardis123]

Hi Folks,
I was reading Intersymbol interference (ISI) definition and I'm wondering if ISI (defined in time domain) is similar to Aliasing distortion, or folding distortion(defined in Freq. domain).

Thanks in advance

 

[MacGyverS2000]

Is this homework?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[pardis123]

Hello Dan,
Does it have to be a homework to be answered?
No, I'm a system engineering intern & I have some questions regarding the fundamental things.That's why I registered in this forum.

Pardis

 

[zappedagain]

ISI is its own type of distortion. I like to think of it as the history of what went through the channel affecting then channel performance. For example, nost binary data is randomly 1 or 0 so the average is typically 0.5 (half and half), but if you get a long string of 1s (1111111111111) or 0s it can mess up the channel because the average value starts shifting away from 0.5. It gets a lot more complicated than that as you get into the communication theory.

Hope that helps,

Z

 

[pardis123]

Thanks alot Zappedagain

can I look at it in this way:
we have just one analog signal x(t) which is sampled respecting nyquist theorem.then these discrete values enter to the chanel hc(t).
then, we're in the end side of channel. if we look at our output signal in freq. domain: X(f)is convolved with a train of delta dirac signals and then the results multiplied with the Channel freq. response Hc(f).
the frequency shape of Hc(f)is very important in order that we don't face up Aliasing and signal be retreivable.
now, look at it in time domain,
the same sampled signal that has discrete voltages in the time domain enters the channel. the shape of channel in time domain is important in order that we can retrieve these time samples of the original signal.
--------------------------------------------
Zappedagain, i don't quite understand your point of view.
why are you looking at the input signals to the channel as a random variable and their probability?
even for a deterministic signal, if the channel time-shape is very large, we'll have ISI.
thanks
Pardis

 

[zappedagain]

P,

Sorry for the slow reply. I'm treating it as a digital channel, and the bits are randomly one or zero. A lot of the channel models take this into account. Another analogy is that if you AC couple the signal it will be symmetric about 0V. Some channels (aka modulation techniques) take this into account and add bits to keep it from shifting one way or the other.

Does it make sense to think of your 'channel time-shape' as the frequency response of the channel? If you try to pass faster data you'll get (low pass) distortion.