COMMUNICATIONS SYSTEM WITH FREQUENCY AND TIME DIVISION TECHNIQUES

United States Patent

[in 3,573,379

[72] Inventors

Donald W. Schmitz;

Benjamin Chandler Shaw, Granada Hills,

Calif.

803,867

Mar. 3,1969

Apr. 6,1971

The Bendix Corporation

[54] COMMUNICATIONS SYSTEM WITH FREQUENCY AND TIME DIVISION TECHNIQUES 17 Claims, 9 Drawing Figs.

[52] U.S. CI 179/15,

179/2.5

[51] Int. CI H04j3/12

[50] FieldofSearch 179/15,15

(SSB), 15 (ASYNC), 15 (MM), 2 (DP), 2.5,15

(SIG)

[56] References Cited

UNITED STATES PATENTS

3,239,761 3/1966 Goode... 179/15X

(Async)

3,261,922 7/1966 Edson 179/2X(DP)

3,485,953 12/1969 Norberg 179/15(Async)

Primary Examiner—Ralph D. Blakeslee
Attorneys—Robert C. Smith and Plante, Arens, Hartz, Hix and
Smith

ABSTRACT: A communication system for a substantial number of subscribers is shown having random access capabilities without the requirement for the usual central exchange. The system uses a frequency division scheme for separating the several communication information channels. The individual subscriber units are interconnected as by means of one or more wires which are also connected to a master clock which continually generates time division digital information consisting of a plurality of pulses and unused time spaces (ones and zeros) including binary circuit code information and synchronizing pulses. A relatively limited band width is required for carrying this control information which is substantially displaced in frequency from the band containing the several communication information channels. These channels are generated by means of a frequency synthesizer in each of the subscriber units, each of which continually monitors the digital control information to determine whether its address is being called and the circuit code representing the channel of the incoming call. Similarly, outgoing calls are initiated by picking up a headset at the subscriber unit which causes an unused channel to be selected, inserting its circuit code into the digital stream and causing the frequency synthesizer in responding to this code to generate the corresponding carrier frequency. The audio information is then converted to single side band (or other) modulation of the particular carrier frequency signal.

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