E/N ratio
In the transmission of a pulse of an electromagnetic wave representing a bit, the ratio of (a) the energy in each bit, E, to (b) the noise energy density per hertz, N.
Note: E is usually expressed in joules per bit and N is usually expressed in watts per hertz. Thus, the E/N ratio is hertz-seconds per bit. A joule is a watt-second and a hertz is a cycle per second. Thus, the E/N ratio is actually cycles per bit. However, if a cycle is a bit, then the E/N ratio is dimensionless. [From Weik ’89]