European Space Operations Centre

About: European Space Operations Centre is a government organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Orbit determination & Satellite. The organization has 309 authors who have published 331 publications receiving 10399 citations. The organization is also known as: ESOC.

Carrier phase synchronization for GMSK signals

Abstract: Several carrier phase recovery schemes for Gaussian minimum shift keying (GMSK) modulated signals are derived and analysed in terms of squaring loss and acquisition time. Two bandwidths are considered for the GMSK signal: BTb=0.5 and 0.25, following the recommendations of the Consultative Committee for Space Data Systems. Pre-encoding is assumed to remove the inherent differential encoding of the GMSK modulations. The carrier phase recovery schemes are derived from the approximate expression of the GMSK signal as an OQPSK signal or as the superposition of two OQPSK signals maximum a posteriori/maximum likelihood phase estimation is considered, with perfect clock reference; both non-data-aided and decision–directed schemes are analysed. Moreover, in the case of GMSK with BTb=0.25, an equalizer is also included in the synchronizer loop to remove inter-symbol interference. High and low signal to noise ratio (SNR) approximations are considered to simplify the structure of the synchronizers. It is shown that, for the considered BTb values, the complex synchronizers initially derived do not provide any improvements over their simplified versions; the introduction of the equalizer for GMSK with BTb=0.25 leads to a better performance. Moreover, it is shown that GMSK with BTb=0.5 has a better performance than unfiltered OQPSK, which is better than GMSK with BTb=0.25. The SNR values above which the high SNR approximation turns out to be convenient with respect to the low SNR approximation are also given. Copyright © 2002 John Wiley & Sons, Ltd.