Abstract

A Linear Feedback Shift Register (LFSR) is a standard parallel shift register with output taps on some of its stages. If the output taps are combined and fed back to the initial stage, on each clock cycle the shift register will change to a new state. By appropriate selection of the tap connections an n-stage LFSR can be made to cycle through all possible 2n-1 states before repeating the sequence. The output from any stage is called a maximal length pseudorandom sequence. Such a sequence has many of the statistical properties of a sequence of ideal random numbers, but obviously results from a very well defined process. Once a LFSR is known, its associated pseudorandom sequence can be described in full. The inverse problem of identifying the LFSR which generated a given pseudorandom sequence is far more difficult.

© 1985 Optical Society of America