APPARATUS FOR DERIVING SYNCHRONIZING PULSES FROM PULSES IN A SINGLE CHANNEL PCM COMMUNICATIONS SYSTEM

• US 3,701,894 A
• Filed: 09/11/1970
• Issued: 10/31/1972
• Est. Priority Date: 09/11/1970
• Status: Expired due to Term

• Current Assignee: Christopher Carl, Edward C. Posner, Lucien A. Couvillon, Richard M. Goldstein, Richard R. Green
• Original Assignee: Christopher Carl, Edward C. Posner, Lucien A. Couvillon, Richard M. Goldstein, Richard R. Green
• Inventors: Carl, Christopher, Couvillon, Lucien A., Goldstein, Richard M., Posner, Edward C., Green, Richard R.
• Primary Examiner(s): Felix D. Gruber
• Application Number:
  US05/070,967
• Time in Patent Office: 781 Days
• Field of Search: 178/69.5R 179/15BS,170.2 325/325 340/146.1D 235/181,150.51,150.52,150.53,156,160
• US Class Current: 708/422
• CPC Class Codes: H04L 2007/047 using a sine signal or unmodulated carrier
• CPC Class Codes: H04L 7/0337 Selecting between two or more discretely delayed clocks or selecting between two or more discretely delayed received code signals
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04L 7/043 Pseudo-noise [PN] codes variable during transmission synchronisation of spread spectrum receivers H04B1/69

Abstract

A method and apparatus is disclosed for bit synchronization of a received PCM communications signal, without requiring a separate synchronization channel in the communications signal by digital correlation of the received square-wave signal with a predetermined number of phase displaced replicas of its expected form. Each phase displaced replica is correlated with the input signal to determine which phase displaced replica produces the largest correlation signal. In carrying out the correlation of the square-wave signal with a given phased displaced replica, the two levels of the replica corresponding to the +1 and -1 binary values of the input signal are employed as sign signals to control the arithmetic addition or subtraction of the input signal binary values to the contents of an accumulator. The binary values of the input signal are produced by means for sampling and converting the input signal into +1 and -1 values. A plurality of samples of the input signal are thus accumulated during each cycle of a number of input signal cycles to develop a correlation value.

Claims

1. Apparatus for correlating a cyclic square-wave input signal with a replica of said input signal comprising timing means for producing synchronized periodic sample commands and clock pulses, converting means responsive to said sample commands for obtaining an arbitrary number of successive samples per cycle of said input signal and converting each sample to digital form, said digital form consisting of binary signals having two voltage levels representing binary values of plus one and minus one for the two levels of said input square-wave signal, means for generating said replica, said replica having two voltage levels corresponding to binary values of said input signal samples, said two voltage levels of said replica representing plus and minus signs corresponding to signs of said binary values of plus one and minus one of said input signal samples when converted to digital form, and means responsive to said clock pulses for accumulating in digital form a sequence of binary values of said input signal samples produced by said converting means over a number of cycles of said input signal to form a correlation value by arithmetically adding or subtracting the binary value of a given sample to the accumulation of binary values of previous samples under control of said replica according to whether said replica is at the time representing a plus or a minus sign, arithmetically adding when representing a plus sign and arithmetically subtracting when representing a negative sign, whereby after said number of cycles have been sampled, and the binary values thereof have been thus accumulated, said correlation value is proportional to the degree said replica is in phase with said input signal.

2. Apparatus for correlating a cyclic square-wave input signal with a plurality of phase-displaced versions of a replica of said input signal comprising timing means for producing synchronized periodic sample commands and clock pulses, converting means responsive to said sample commands for converting a number of successive samples per cycle of said input signal to digital form, said digital form consisting of binary signals having two voltage levels representing binary values of plus one and minus one for the two levels of said input square-wave signals, means for generating a plurality of phase displaced versions of said replica, each phase displaced version having two voltage levels corresponding to voltage levels of said input signal, said two voltage levels of each phase displaced version presenting plus and minus signs corresponding to signs of said binary values of plus one and minus one of said input signal samples converted to digital form, and means responsive to said clock pulses for accumulating in digital form a sequence of binary values of said input signal samples produced by said converting means over a number of cycles of said input signal to form a separate correlation value for each phase-displaced version of said replica by arithmetically adding or subtracting the binary value of a given sample to the accumulation of binary values of previous samples under control of separate phase displaced versions for each separate correlation value according to whether each separate phase displaced version is at the time representing a plus or a minus sign, by arithmetically adding when representing a plus sign and arithmetically subtract when representing a negative sign, whereby after said number of cycles have been sampled, and the binary values thereof have been thus accumulated, each correlation value is proportional to the degree that each of the separate phase displaced versions of said replica is in phase with said input signal.

3. Apparatus as defined in claim 2 wherein said accumulating means comprises a plurality of adder-subtracters, each connected to receive binary values from said converting means, and a plurality of registers, a given register connected to a given adder-subtracter for a given correlation value to be formed by accumulating said binary values, said given register being connected to receive the output of said given adder-subtracter, and to transmit to said given adder-subtracter the correlation value stored for addition or subtraction of a sample value received from said converting means under control of the sign of a given phase displaced version from said generating means.

4. Apparatus as defined in claim 2 wherein said accumulating means comprises a single adder-subtracter and a recirculating register of sufficient length to store in series said plurality of correlation values, said register being connected to receive the output of said single adder-subtracter, and to transmit to said adder-subtracter in sequence said correlation values for addition or subtraction of each binary value received from said converting means, each binary value being added or subtracted to each correlation value stored according to the sign of a different phase displaced version of said replica.