Digital transmission systems, such as digital subscriber lines (DSL), radio, and coaxial cable are subject to transmission errors due to noise induced into the transmission media. Some noise, such as crosstalk and radio frequency interference, is relatively constant. Other noise sources including light dimmers, power supplies, light flashers, and gas discharge lighting systems (e.g., fluorescent lighting systems) produce impulse noise. Impulse noise produces noise of a brief duration, and is often quite severe during the brief interval. Some sources of impulse noise produce periodic impulses. Impulse noise often has a high amplitude that can overwhelm most methods to mitigate noise.
An impulse may occur during the rising edge of a sinusoid and a second impulse may occur during the falling edge. This causes a complex pattern involving two different intervals. Existing techniques do not fully address the impulse noise problems associated with complex periodic behavior such as patterns involving more than one repeating time period between impulses.