Shannon's law

In telecommunication, a Shannon's law is a statement defining the theoretical maximum rate at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise, usually expressed in the form C = W log₂(1 + S /N ), where C is the channel capacity in bits per second, W is the bandwidth in hertz, and S /N is the signal-to-noise ratio in db.

Note: Error-correction codes can improve the communications performance relative to uncoded transmission, but no practical error correction coding system exists that can closely approach the theoretical performance limit given by Shannon's law.

Source: from Federal Standard 1037C and from MIL-STD-188