Patent
1977-04-22
1978-12-26
Olms, Douglas W.
179 15RW, 325 38A, H04J 700
Patent
active
041317610
ABSTRACT:
A multilevel mainstream of digital signals, organized in a recurrent frame, is monitored at a transmitting end by a pulse generator GP1 which emits a marking pulse whenever that mainstream has a modulable waveform, i.e. a symbol represented by either the lowest or the highest amplitude level. A waveform generator GF controlled by pulse generator GP1 produces a bipolar signal 19 whose pulses are to be superimposed upon the modulable waveforms coinciding with the occurrences of the marking pulses, the superimposition being carried out in an analog adder S1 which extends the amplitude excursion of the mainstream signal beyond its limiting level. The mainstream frame is divided into a plurality of subframes during the first of which the bipolar signal 19 is a frame-alignment word with an invariable first part and a variable second part, the latter specifying the number of clock cycles -- corresponding to the number of mainstream symbols -- elapsed between the start of the frame and the appearance of the first modulable waveform. In subsequent subframes, the bipolar signal 19 carries message bits from one or more supplementary signal channels. At a receiving end, a threshold circuit CD emits confirmation pulses 24 upon detecting any modulable waveform in the incoming composite signal stream and further emits demodulation pulses 25 if that waveform is amplitude-modulated beyond the normal highest or lowest level. From these two pulse sequences 24, 25 a comparator CF1 determines, during a first subframe, whether the fixed part of an incoming alignment word has a predetermined configuration whereupon a second comparator CF2 checks, with the aid of a counter CL2 stepped by extracted clock pulses and a shift register R2 controlled by that counter, whether the variable second part of that alignment word corresponds to the number of elapsed clock cycles. Upon verification of alignment, counter CL2 is enabled by a logic network LA to allow the readout of demodulation pulses 25 during the following subframes as a replica of the supplementary message bits. Otherwise, logic network LA initiates an alignment search until the requisite synchronism is achieved.
REFERENCES:
patent: 3612770 (1971-10-01), Zegers et al.
patent: 3970798 (1976-07-01), Epenoy et al.
patent: 4002846 (1977-01-01), Barbier
CSELT - Centro Studi E Laboratori Telecomunicazioni
Olms Douglas W.
Ross Karl F.
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