Signal velocity

The signal rate is that rate at which a signal propagates. A signal, ie a change of a state can propagate as a wave packet or as a wave front, for example. The time at which a certain location is a unique signal can be detected, is used to define this rate of diffusion. This time is subject to both the restriction of a good signal -to-noise ratio and an associated uncertainty, and is thus dependent not only on the shape of the signal, but also on the signal level.

Wherein electromagnetic waves, such as light, the signal speed is identical with the group velocity; excepting the case that the wave propagates in a lossy medium. A deviation between the two speeds is particularly pronounced in the vicinity of the absorption of the medium frequencies, see for example Hertzian dipole. Also, the tunnel effect, shows a similar behavior. In these cases, can exceed the speed of light in vacuum c is the group velocity, but the signal speed - with the ultimate information is transmitted - is always less than or equal to c. This is the case, since the signal at any time, it would have increased in the vacuum, can be used to detect information, since it is not attenuated and thus would be more than the weakened at any point.