Multiplex communications – Wide area network – Packet switching
Patent
1981-10-02
1983-08-16
Brigance, Gerald L.
Multiplex communications
Wide area network
Packet switching
364724, 179 84VF, H04J 312
Patent
active
043995365
ABSTRACT:
A digital multifrequency (MF) receiver for use in telephone switching systems is disclosed. Input MF signals in a PCM (pulse code modulation) format are detected by simultaneously computing the convolution of the digital input signal with discrete portions of the impulse response of a narrow bandpass filter. The convolution functions are performed by multiplication or log addition circuitry with adder and accumulator apparatus. A 10-millisecond PCM sample comprising 80 discrete samples of an input signal is simultaneously applied to four convolution circuits, each of which applies a different portion of the impulse response of a bandpass filter, also comprising 80 samples, to the input signal as it is received. The complete impulse response signals are applied to the convolution circuits but out-of-phase with impulse response signals as applied to the remainder of the convolution circuits. When four such circuits are used, a quadrature is established and the amplitude of the desired signal is computed at 2.5 millisecond intervals by computing the square root of the sum of the squares of adjacent convolution circuits.
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"Digital MF Receiver Technique", GTE Automatic Electric Journal, vol. 15, No. 7, May 1977, pp. 317-325, Jeffrey P. Mills, Ph.D.
Bell Telephone Laboratories Incorporated
Brigance Gerald L.
Padden F. W.
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