1. Nyquist’s theorem: D = 2BLog2K
Provides an absolute maximum that cannot be achieved in practice.
Engineers have observed that a real communication system is subject to small amount of background interference called noise, and that such noise makes it impossible to achieve the theoretical maximum rate.
B = bandwidth (2B for the RS-232 that uses two values of voltage data)
K = Possible values of voltages
D = Maximum date rate in bits per second
Shannon’s theorem: C = BLog2(1 +S/N)
Shannon extended Nyquist’s work to specify the maximum data rate that can be achieved over a transmission system that introduces noise.
C = Is the effective limit on the channel capacity in bits per second
S = Average signal power
N = Average noise power
B = Bandwidth