Recovery of frame alignment word having bits distributed in a digital transmission signal

Claim 1

A method of recovering a frame alignment word having bits distributed in a digital transmission signal, said frame alignment word having a predetermined number N of bits distributed in a frame of said digital signal, said frame being divided into M consecutive sectors, each of said sectors including first and second parts, said first part being a heading including a predetermined number of alignment bits, the heading bits of all said consecutive sectors in said frame placed end to end forming said frame alignment word, said second part being a bit packet corresponding to digital signal information, said method comprising taking bit groups from said digital signal at a sector frequency at which said sectors are transmitted in said digital signal, each of said bit groups having a number of digital signal consecutive bits equal to said number of bits in each heading, storing said taken bit groups to form a binary word having an increasing length up to a maximum length equal to that of said frame alignment word, comparing said stored binary word with each of N words composed of said frame alignment word and N-1 circular permutations thereof, determining when the comparison of a number of N bits results in an identity to indicate rank k of one of said circular permutations of said frame alignment word, and completing synchronization of said digital signal at the start of a k th sector after said comparison has indicated an identity.

Claim 2

A method of recovering a frame alignment word having bits distributed in a digital transmission signal, said frame alignment word having a predetermined number N of bits distributed in a frame of said digital signal, said frame being divided into M consecutive sectors, each of said sectors including first and second parts, said first part being a heading including a predetermined number of alignment bits, the heading bits of all said consecutive sectors in said frame placed end to end forming said frame alignment word, said second part being a bit packet corresponding to digital signal information, said method comprising taking bit groups from said digital signal at a sector frequency at which said sectors are transmitted in said digital signal, each of said bit groups having a number of digital signal consecutive bits equal to said number of bits in each heading, storing said taken bit groups to form a binary word having an increasing length up to a maximum length equal to that of said frame alignment word, comparing said stored binary word with each of N words composed of said frame alignment word and N-1 circular permutations thereof, determining when the comparison of a number of N bits results in an identity to indicate rank k of one of said circular permutations of said frame alignment word, and completing synchronization of said digital signal at the start of a k th sector after said comparison has indicated an identity.

Claim 5

A device for recovering a frame alignment word having bits distributed in a digital transmission signal, said frame alignment word having a predetermined number N of bits distributed in a frame of said digital signal, said frame being divided into M consecutive sectors having ranks 1,2 . . . (1-M), M, each of said sectors being divided into first and second parts, said first part being a heading including a predetermined number of alignment bits, the heading bits of all said consecutive sectors in said frame placed end to end forming said frame alignment word, said second part being a bit packet corresponding to digital signal information, said device comprising: a time base source for periodically deriving a sector frequency with which said sectors are transmitted in said digital signal and at a frame frequency, a sequence of signals determining M consecutive time slots, each of said time slots being equal in length to a sector, a first N-bit shift register controlled by said time base responsive to said digital signal and timed at said sector frequency for progressively storing bit groups taken from said digital signal, each of said bit groups having a number of digital signal consecutive bits equal to said number of bits in each heading, a second N-bit shift register having stored said frame alignment word and looped back on itself for deriving all N-1 circular permutations of said alignment word under the control of said time base, said circular permutations being of ranks 1 . . . k . . . (N-1), comparing means connected to said first and second shift registers and controlled by said time base source for comparing bit-by-bit a binary word derived from said first register with said alignment word and said circular permutations thereof, the binary word derived from said first register having an increasing length up to a maximum length equal to that of said frame alignment word, and storing means connected to said comparing means and controlled by said time base source for storing rank k of one of said circular permutations for which an identity is detected by said comparing means between contents of said first and second registers, the sector frequency of said time base source being inhibited by said comparing means once said identity is detected, said sector frequency being inhibited during one of said consecutive time slots positioned in rank M of said frame and remaining inhibited for a number of time slots equal to said rank k of said stored permutation whereby frame alignment is recovered.

Claim 6

A device for recovering a frame alignment word having bits distributed in a digital transmission signal, said frame alignment word having a predetermined number N of bits distributed in a frame of said digital signal, said frame being divided into M consecutive sectors having ranks 1,2 . . . (1-M), M, each of said sectors being divided into first and second parts, said first part being a heading including a predetermined number of alignment bits, the heading bits of all said consecutive sectors in said frame placed end to end forming said frame alignment word, said second part being a bit packet corresponding to digital signal information, said device comprising: a time base source for periodically deriving a sector frequency with which said sectors are transmitted in said digital signal and at a frame frequency, a sequence of signals determining M consecutive time slots, each of said time slots being equal in length to a sector, a first N-bit shift register controlled by said time base responsive to said digital signal and timed at said sector frequency for progressively storing bit groups taken from said digital signal, each of said bit groups having a number of digital signal consecutive bits equal to said number of bits in each heading, a second N-bit shift register having stored said frame alignment word and looped back on itself for deriving all N-1 circular permutations of said alignment word under the control of said time base, said circular permutations being of ranks 1 . . . k . . . (N-1), comparing means connected to said first and second shift registers and controlled by said time base source for comparing bit-by-bit a binary word derived from said first register with said alignment word and said circular permutations thereof, the binary word derived from said first register having an increasing length up to a maximum length equal to that of said frame alignment word, and storing means connected to said comparing means and controlled by said time base source for storing rank k of one of said circular permutations for which an identity is detected by said comparing means between contents of said first and second registers, the sector frequency of said time base source being inhibited by said comparing means once said identity is detected, said sector frequency being inhibited during one of said consecutive time slots positioned in rank M of said frame and remaining inhibited for a number of time slots equal to said rank k of said stored permutation whereby frame alignment is recovered.