US 3,943,285 AGranted

Multiplexed data modem

AssigneeMilgo Electronic Corporation

InventorsRobert Gordon Ragsdale, Henry Howard Parrish

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Abstract

A data modem that operates to permit the concurrent high speed transmission/reception of digital data over two independent data links or systems, is disclosed. Data bits concurrently applied to a transmitting modem from two independent data sources are interlaced to form a stream of data bits that are effectively grouped as data words to be differentially phase modulated. Modulated data may be transmitted over ordinary voice grade telephone lines to a distant receiver modem at effectively twice the bit rate of the individual data sources. Successive groups of six interlaced data bits are divided into two groups of three bits which are uniquely identified by having a selected phase angle added to or subtracted from the differential phase angle for alternate groups of three bits. The selectively added phase angle is detected at a receiving modem to identify the respective groups of three bits and thereby permit accurate distribution of demodulated data bits to the respective data utilization terminals corresponding to the two data sources.

Claims23

Dependent claims

A data transmission system having a transmitter for transmitting data over a single transmission link as a differentially phase modulated carrier modulated at a given baud rate with digital data provided from two independent data sources each emitting data bits at one and one half times said baud rate, and a receiver for demodulating the differentially phase modulated signal received over said link, the improvement which comprises:

means at said transmitter operative at said given baud rate for differentially phase modulating successive three bit groups with bits in each group received from both of said independent data sources;
means at said transmitter connected to said modulating means and operative once for every other three bit group for modifying by a predetermined phase angle the differentially modulated phase angle associated with successive three bit groups, which modifying angle is capable of being detected at the receiver to properly segregate each three bit group from an otherwise randomly appearing stream of data bits represented in the received line signal;
means at said receiver for compensating, once each alternate baud time, the differentially phased signal received over said link with a predetermined modifying angle of the same amount as used at the transmitter;
and
means at said receiver responsive to the appearance of said predetermined modifying angle during demodulation for segregating said three bit groups into the form originally emitted by the two data sources at said transmitter.

2 more elements

Dependencies are inferred from the claim text.