What are the channel coefficients

[g.hadzhiyanev]

Hi, everyone

Does anyone have Idea what do channel coefficients (by channel estimation) mean?
As far as I understand when we have h=[1 0 0 0 0] , we have no ISI. When we have ISI for example h=[0.7 0.8 0.4 -0.5 0.03].
But what is the exact meaning of the numbers?

Thanks

 

[zorro]

They are the discrete-time impulse response of the channel.
Ideally, one transmitted symbol gives an output only in one symbol time without interfering other symbols, i.e. the response is ...0 0 0 1 0 0 0 ...
In you example, the symbol spreads over several time slices at the receiver with amplitudes 0.7, 0.8, ....
regards

Z

 

[g.hadzhiyanev]

So the position of the number in the vector shows in which timeslot a symbol spreads, and the number with how much of amplitude. Did I get it right? And furthermore does that mean that the channel estimation should always be done before demodulation? Otherwise the results for the channel impulse responses would be complex or I am wrong?

 

[zorro]

So the position of the number in the vector shows in which timeslot a symbol spreads, and the number with how much of amplitude. Did I get it right?

Yes.

And furthermore does that mean that the channel estimation should always be done before demodulation?

No. It is like you mention in the following.

Otherwise the results for the channel impulse responses would be complex or I am wrong?

Right. Channel estimation, as well as equalization can be done after demodulation, i.e. in baseband. Baseband equivalent channel is complex.
Regards

Z