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Abstract

A suppressed carrier signal is offset quadrature phase shift key modulated so the reference carrier phase is stepped 90.degree. in the same direction in synchronism with sequential bits of a serial data stream and is further bi-phase modulated in response to the binary data source having first or second binary values. A coherent receiver responds to the suppressed carrier signal to establish an equivalent sequence of stepping reference phases at the carrier frequency. The reference phases synchronously rotate in 90.degree. increments in the same direction as the suppressed carrier reference, being permitted a four-fold initial phase ambiguity (0.degree., 90.degree., 180.degree., and 270.degree.). The rotating reference phase is compared in a bi-phase manner with the appropriate component of the suppressed carrier signal to derive sequential d.c. polarities indicative of the binary bit values during the sequential binary data bits.

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