According to Nyquist bandwidth constraint for transmission without ISI (INTERSYMBOL INTERFERENCE) , the minimum system bandwidth should be R/2 symbols /sec, where R symbols /sec is the transmission rate.
If this is correct then i want to know that if this channel cannot support full transmission rate then do we use this model ??
I mean here system bandwidth is less than the transmission rate.

 

It appears to me that bandwidth should always be larger than the transmission rate to play safe. Because the symbol will spread when the bandwidth is lower than the highest frequency component in the transmission signal and consequently cause ISI. This applies to analog signal.


Some correction to your Nyquist bandwidth constraint, which applies to digital signal, the theoretical minimum required system bandwidth to detect Rs[symbols/s] without ISI is Rs/2[Hz] ....

Plz take note that the bandwidth is in Hz , not symbols/sec, the meaning of this two units make a hell of difference.