Synchronizing circuit for modems in a data communications networ

Details Synchronizing circuit for modems in a data communications networ Synchronizing circuit for modems in a data communications networ

1974-10-18

1976-05-04

Libman, George H.

Telegraphy

Systems

Printing

178 695R, 325 60, H04B 100, H04L 700

Patent

active

039551415

ABSTRACT:
A modem with transmitter and reciever sections. Incoming digital data signals produce successive coordinate signals to define successive transmission points representing a given digital value and to modulate quadrature carrier signals. The coordinate signals have unit values of 0, 1, 2.707, 3 and 5 and together control the amplitude and phase of the modulated carrier signals. The receiver section uses received coordinate signals, after they are properly conditioned, to select a decision region which corresponds to a transmission point to produce the digital data signals. The decision regions have rectilinear boundaries on a Cartesian coordinate system at unit values 0, 1.25, 2 and 4 and each region is either rectangular or non-rectangular. Digital synchronism between separate modems is maintained by transmitting coordinate signals corresponding to a framing point which is separate from the transmission points, but which has the same digital value as a transmission point. Certain decision regions defined by the receiver use the receipt of the modulated carrier signals corresponding to a framing point to initiate a synchronizing operation.

REFERENCES:
patent: 3303284 (1967-02-01), Lender
patent: 3619503 (1971-11-01), Ragsdale
patent: 3736507 (1973-05-01), Wolejsza et al.

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