Design of a Fully Digital GMSK Demodulator for Telemetry Space Link / Projeto de Demodulador Completamente Digital para Enlace de Telemetria Espacial

Antonio Macilio Pereira de Lucena, Paulo Daving Lima de Oliveira, Francisco de Assis Tavares Ferreira da Silva


This paper presents the design of a coherent GMSK demodulator, with fully digital architecture, aimed at high speed (10 Mbps) space telemetry applications in which the absolute Doppler offset may reach up to 200 kHz. All functional modules that compose the demodulator are described through block diagrams and mathematical equations. The calculations for the determination of several design parameters are presented. The carrier phase and the symbol timing recovery modules are distinct from those found in the literature for this application and, therefore, original mathematical analysis for the project of such modules are performed. The performance of the proposed GMSK demodulator is evaluated via computational simulation. Besides the bit error rate under several operating conditions, the variance of the estimated parameters by the symbol and carrier synchronizers are measured and compared with theoretical bounds. The main results from computational simulations are presented and demonstrate remarkable performance of the designed demodulator.



GMSK; Demodulator; Telemetry; Fully digital; Space communications.


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