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Demodulation of Differential Phase Shifted Keyed Signals

IP.com Disclosure Number: IPCOM000080013D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 39K

IBM

Related People

Spragins, JD: AUTHOR

Abstract

This is a method for uniquely determining the differential phase shift delta phi between the i-1 sample of a sinusoidal carrier of frequency f and the i/th/ sample. The method comprises the steps of registering the time of occurrence of the carrier zero axis crossing (ZAC) every N/2f seconds, N being a fixed integer. If during the i/th/ -1 sample, a reference zero axis crossing occurs at time t(0), then the phase measurement for the i/th/ sample must be taken with reference to time t/0/ + N/2f.

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Demodulation of Differential Phase Shifted Keyed Signals

This is a method for uniquely determining the differential phase shift delta phi between the i-1 sample of a sinusoidal carrier of frequency f and the i/th/ sample. The method comprises the steps of registering the time of occurrence of the carrier zero axis crossing (ZAC) every N/2f seconds, N being a fixed integer. If during the i/th/ -1 sample, a reference zero axis crossing occurs at time t(0), then the phase measurement for the i/th/ sample must be taken with reference to time t/0/ + N/2f.

In a four-phase system in which the differential phase measure delta phi = +/- 45 degrees, +/- 135 degrees, in order to select one of the four phases, two bits of information are needed to uniquely define each phase. One bit of the pertinent information is the positional adjacency of that zero axis crossing occurring closest in time to t(0) + N/2f. The second bit of information is the match or mismatch of the sign of the slope of the zero axis crossing, taken at t(0) and the instant zero axis crossing. More particularly, one bit of information is whether the zero axis crossing occurs either before or after this reference time (t(0) + N/2f), while the second bit is whether the sign of the instant zero axis crossing is the same or different as the sign of the zero axis crossing taken at t(0).

The detection criteria may be represented in the following tabular form, in which a numeral (1) represents the occurrence of the...