Impulse Noise

Impulse noise describes random occurrences of energy spikes or irregular pulses of short duration, broad spectral density, and relatively high amplitude. These disturbances are usually distributed evenly over the useful passband of a transmission system.

Impulse noise can be caused by voltage spikes in equipment, voltage changes in adjacent pairs in a copper cable, tones generated for electrical signalling, maintenance and test procedures, lightning flashes and a wide variety of other phenomena.

Because of its intermittent nature, it is much harder to detect and analyse than traditional interference; its fast burst characteristic defies traditional troubleshooting methods. However, modern high-end bench-type oscilloscopes can help see, capture and analyse impulse noises during field tests.

Such bursty, high frequency impulses cause packet and pixel loss – video and audio – and degrade or freeze services like IPTV or over-the-top video services like Netflix. DSL services are affected differently by repetitive electrical impulse noise (REIN), prolonged electrical impulse noise (PEIN), short impulse noise event (SHINE) and electromagnetic interference (EMI). The sources of these various noise types are all different. Such noise energy can cause bad voice quality, pixelization on IPTV, and DSL not synchronising.

Both linear and non-linear techniques can be used for noise reduction. The linear approach, a noise reduction formula is applied to all pixels in an image linearly, without classifying the pixels into noisy and non-noisy types. Non linear noise reduction is a two-step process comprising noise detection and noise replacement, where noisy pixels are replaced by an estimated value.