Frame synchronization in speech predictive encoded communication system

Claim 2

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a predetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system periodically sampling the amplitude of voice signals on each circuit of said plurality of voice circuits, comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, a method of frame synchronization including the step of transmitting frame synchronization information in an unused time slot only during periods of underflow.

Claim 3

In a digital communications system as recited in Claim 1, said system receiving the digitally encoded transmission frame over the transmission path, storing previously transmitted digitally encoded samples from prior sampling frames, and substituting for the samples stored respective transmitted present samples, said method of frame synchronization further including the steps of detecting an underflow condition in the received transmission frame, looking for the frame synchronization information in an unused time slot, and generating a synchronization pulse when the frame synchronization information is detected.

Claim 4

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a predetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system including meanms for periodically sampling the amplitude of voice signals on each circuit, means for comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and means for generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, the improvement comprising means at the transmitting station for detecting an underflow condition and means responsive to said underflow detecting means for controlling said transmission generating means to include frame synchronization information in an unused time slot during periods of underflow.

Claim 5

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a predetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system including meanms for periodically sampling the amplitude of voice signals on each circuit, means for comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and means for generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, the improvement comprising means at the transmitting station for detecting an underflow condition and means responsive to said underflow detecting means for controlling said transmission generating means to include frame synchronization information in an unused time slot during periods of underflow.

Claim 6

In a digital communications system as recited in claim 3, said system further including means at said receiving station for receiving the digitally encoded transmission frame over the transmission path, means for storing previously transmitted digitally encoded samples from prior sampling frames, and means for substituting for the samples stored respective transmitted present samples, the improvement further comprising means at said receiving station for detecting an underflow condition in a received transmission frame and means responsive to said receiving underflow detecting means for detecting frame synchronization information in an unused time slot of the received transmission frame and generating a synchronization pulse when the frame synchronization information is detected.

Claim 7

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a perdetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system periodically sampling the amplitude of voice signals on each circuit of said plurality of voice circuits comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, receiving the digitally encoded transmission frame over the transmission path, storing previously transmitted digitally encoded samples from prior sampling frames, and substituting for the samples stored respective transmitted present samples, a method of frame synchronization including the steps of transmitting frame synchronization information in an unused time slot only during periods of underflow, detecting an underflow condition in the received transmission frame, iteratively searching for the frame synchronization information in the received transmission frame, alternately changing the direction of the search for the frame synchronization information with each iteration and generating a synchronization pulse when the frame synchronization information is detected.

Claim 8

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a perdetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system periodically sampling the amplitude of voice signals on each circuit of said plurality of voice circuits comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, receiving the digitally encoded transmission frame over the transmission path, storing previously transmitted digitally encoded samples from prior sampling frames, and substituting for the samples stored respective transmitted present samples, a method of frame synchronization including the steps of transmitting frame synchronization information in an unused time slot only during periods of underflow, detecting an underflow condition in the received transmission frame, iteratively searching for the frame synchronization information in the received transmission frame, alternately changing the direction of the search for the frame synchronization information with each iteration and generating a synchronization pulse when the frame synchronization information is detected.

Claim 9

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a predetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system including means for periodically sampling the amplitude of voice signals on each circuit, means for comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and means for generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, means at said receiving station for receiving the digitally encoded transmission frame over the transmission path, means for storing previously transmitted digitally encoded samples from prior sampling frames and means for substituting for the samples stored respective transmitted present samples, the improvement comprising, means at the transmitting station for detecting an underflow condition, means responsive to said underflow detecting means for controlling said transmission generating means to include frame synchronization information in an unused time slot during periods of underflow, means at said receiving station for detecting an underflow condition in a received transmission frame, iterative means at said receiving station for iteratively searching for the frame synchronization information in the received transmission frame, means controlling said iterative means for alternately changing the direction of the search in the received transmission frame for the frame synchronizatiion information with each iteration, and means for detecting frame synchronization information in an unused time slot of the received transmission frame and generating a synchronization pulse when the frame synchronization information is detected.

Claim 10

In a digital communications system wherein information from a plurality of voice circuits at a transmitting station may be transmitted at a minimum bit rate to a receiving station via a transmission path by transmitting information from a predetermined number less than said plurality of voice circuits over the transmission path during any given frame, said system including means for periodically sampling the amplitude of voice signals on each circuit, means for comparing for each of said circuits a present amplitude sample with a prior amplitude sample which had been transmitted to the receiving station, and means for generating a transmission frame comprising a digital representation of those amplitude samples which differ from the corresponding prior amplitude samples by a predetermined amount, said transmission frame exhibiting an underflow when less than said predetermined number of samples are transmitted, means at said receiving station for receiving the digitally encoded transmission frame over the transmission path, means for storing previously transmitted digitally encoded samples from prior sampling frames and means for substituting for the samples stored respective transmitted present samples, the improvement comprising, means at the transmitting station for detecting an underflow condition, means responsive to said underflow detecting means for controlling said transmission generating means to include frame synchronization information in an unused time slot during periods of underflow, means at said receiving station for detecting an underflow condition in a received transmission frame, iterative means at said receiving station for iteratively searching for the frame synchronization information in the received transmission frame, means controlling said iterative means for alternately changing the direction of the search in the received transmission frame for the frame synchronizatiion information with each iteration, and means for detecting frame synchronization information in an unused time slot of the received transmission frame and generating a synchronization pulse when the frame synchronization information is detected.

Claim 11

In a digital communications system as recited in claim 6 wherein said iterative means comprises a first counter counting at a rate equal to the bit rate in the received transmission frame, address counter means, means for comparing the outputs of said first counter and said address counter means and providing an enabling input to said frame synchronization detecting means when a comparison is found to exist, and means for incrementing said address counter means until a synchronization pulse is generated.

Claim 12

In a digital communications system as recited in claim 7 wherein said address counter means comprises an address register having outputs connected to said comparing means, second counter for counting in a positive direction, third counter for counting in a negative direction, said means for alternately changing the direction of search controlling said incrementing means to alternately increment said second and third counters and further being operative to alternately read the contents of said second and third counters into said address register.

Claim 13

In a digital communications system as recited in claim 6 wherein receiving frame synchronization detecting means comprises correlation means for comparing the digital information in a predetermined unused time slot in the received transmission frame with a unique code word identifying the frame synchronism information and counting the errors representing a failure of corresponding bits in the digital information and the code word to match, means for comparing the errors counted with a predetermined number representing allowable errors and controlling the generation of said synchronization pulse.

Claim 14

In a digital communications system as recited in claim 9 wherein said iterative means includes pulse generating means enabled by said error comparing means when the number of counted errors exceeds said predetermined number of allowable errors.