Digital multi-level multi-phase modulation communication system
AssigneeNippon Electric Co., Ltd.
InventorsYasuharu Yoshida, Yoshimi Tagashira, Seijiro Yokoyama
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Abstract
A digital multi-level multi-phase modulation system utilizes quaternary differential encoding and decoding of only the first two of N digital signal trains. A decision circuit is used to examine the frame pulses in one of the first two signal trains and in at least one of the remaining signal trains and generates output signals which can be used in a gate circuit to resolve the phase-lock ambiguity of the recovered carrier and thereby reproduce the original N signal trains.
Claims8
A digital multi-level multi-phase modulation communication system having a transmitting section and a receiving section, wherein said transmitting section includes:
- first means for performing quarternary differential encoding on the first two trains of N digital signal trains (N is an integer of 4 or more), a frame pulse being included in at least three of said N digital signal trains, to generate a first pair of digital signals;
- and
- second means for generating a modulated wave by performing multi-level multi-phase modulation on a carrier with a first set of digital signals comprising the remaining (n-2) trains of said N digital signal trains and said first pair of digital signals;
- and wherein said receiving section includes:
- third means for performing coherent detection and multi-level decision on said modulated wave to recover said carrier and generate a second set of digital signals and a second pair of digital signals corresponding to said remaining (N-2) trains of said N digital signal trains and said first pair of digital signals respectively;
- fourth means for performing quaternary differential decoding on said second pair of digital signals to generate said first two trains of digital signal;
- fifth means for generating a frame synchronization output signal and establishing frame synchronism by means of the output signal from said fourth means;
- sixth means responsive to the output of said fifth means for extracting frame pulses corresponding to said frame pulses included in said remaining (N-2) trains of said N digital signal trains and in the output signal of said fourth means;
- seventh means responsive to the output of said sixth means for generating a control signal representing the phase-locking state of the carrier recovered in said third means;
- and
- eighth means responsive to said control signal for converting said second set of digital signals into the same trains as said remaining (N-2) trains of said N digital signal trains.
Dependencies are inferred from the claim text.