Multilevel Modulation Techniques for Millimeter Guided Waves

The quaternary and higher-order modulation techniques which are described are extensions of the binary modulation technique previously discussed by the authors. 1 The earlier system uses binary differentiallycoherent phase-shift-keyed (B-FMDCPSIv) modulation, a form of modulation in which the frequency of the carrier is increased or decreased once during each time slot in such a manner that the phase (the time integral of the frequency shift) is changed by ± 9 0 ° relative to the phase of the previous time slot. Experimental repeaters were built which could regenerate, with a 10 -9 error rate, a signal which had been attenuated by an amount equivalent to 15 miles of waveguide. In this repeater the incoming millimeter-wave signals from circular waveguide were passed through band- and channel-demultiplexing filters, down-converted, amplified, differentially phase-detected, and regenerated (utilizing timing information self-contained in the signal) to obtain a polar baseband representation of the information. This baseband signal was used to drive an IF voltage-tuned oscillator, the output of which was amplified, up-converted, passed through 33