DEVELOPMENT OF A DIGITAL DIFFERENTIALLY COHERENT MINIMUM SHIFT KEYING DEMODULATOR
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Minimum Shift Keying (MSK) is a bandwidth and power efficient modulation scheme. These characteristics, combined with a sharp spectral roll-off and constant-amplitude envelope make MSK an attractive scheme for use in satellite links. MSK is one of a class of modulations that can be differentially detected. When compared to coherent demodulators, differentially coherent demodulators, while having slightly poorer performance, have reduced signal acquisition times and decreased circuit complexity, both attributable to the lack of carrier recovery systems. The differential demodulator, consisting primarily of a multiplier and a one-bit-period delay, lends itself to simple and low cost implementation. This thesis outlines the development of two versions of such a demodulator. The first is a standard linear demodulator utilizing a charge coupled device delay element and a four quadrant multiplier. The second demodulator includes a hard-limiter acting on the input signal and uses a shift register as the delay element and an exclusive-or gate for the multiplier. The performance of the two units is compared, and it is concluded that differential MSK demodulators can be realized using hard-limiting circuitry with little or no performance penalty as compared to linear differential demodulators.