Answer 4—A data scrambler is a digital circuit that takes a stream of information (usually in bit-serial form) and produces in a reversible way a different datastream that has been randomized. For example, long strings of ones and zeros get turned into pseudorandom-looking sequences.

Why would you want to do this? Usually, long-distance communication systems (both wired and wireless) want to randomize the statistics of the data bits so that timing recovery is more reliable. There are commonly used data scrambling circuits—from 2 to 16 bits long—used for this purpose. See, for example, any of several ITU-T specifications. The corresponding descrambling logic at the receiver end has well-known characteristics with regard to error propagation, and FEC algorithms, if used, are designed to take this into account.

Contributor: David Tweed