Framing system

Claim 1

A framing system for a digital signal having a frame which is made up of an n-bit long framing pattern and m-bit long information and a clock period of T seconds, said framing system comprising: counter means for counting clock pulses, modulo (n + m), and generating a framing pulse every time the count reaches a predetermined value K; correlation detector means for observing an n'-bit bit pattern (n' being a positive integer not larger than n) arrived thereat up to a given instant of observation and obtaining a correlation between the observed bit pattern and an n'-bit reference pattern to determine whether or not the observed pattern is coincident with the reference pattern; state control means for controlling said counter means in accordance with a state of the system; and means for determining as a first observation time one bit time which starts at a leading end of a framing pulse appearing at every (n + m)-T seconds, and defining a second observation time having a predetermined width the center of which is defined by the first observation time, each when the internal state of the state control means is an initial state, said means being constructed to reset said internal state to the initial state if an output of the correlation detector means indicates coincidence in the first observation time, and to immediately change the internal state into a hunting state under at least one of a condition wherein the output of the correlation detector means indicates uncoincidence predetermined N consecutive times in the first observation time and a condition wherein the output of the correlation detector means indicates coincidence even once in the second observation time, said means in the hunting state of the state control means continuously observing outputs of the correlation detector means and, upon detection of coincidence, immediately loading the predetermined value K in the counter means to generate a new framing pulse.