What is the minimum bandwidth required for ISI free transmission if the modulation used is 32 QAM?

0 down vote favorite 1 If the bit rate of the digital communication system is 'R' Kbps & the modulation used is 32-QAM, what is the minimum bandwidth required for ISI free transmission? My understanding & analysis so far: QAM (a digital-to-analog conversion technique) is a combination of ASK & PSK. The idea behind QAM is to alter two characteristics (amplitude & phase) instead of just one to improve the bit rate. From literature (Data Communications & Networking by Forouzan), the minimum bandwidth required for QAM is same as that of ASK/PSK. BW for Binary ASK is given by B = (1+d)S, where S is the signal rate. For 32-QAM bandwidth is:- B = S = (bit rate)/(bits per signal element) = R/5 KHz (for 32-QAM no. of symbols per signal element is log2(32) = 5) read less