"Differential Detection of GMSK Signals Corrupted by AWGN and a Doppler Shift"

Abstract

The purpose of my research was to support the design of a DSP microprocessor-based receiver for a satellite communication system supervised by my thesis advisor, Dr. Costas Georghiades. Dr. Georghiades and his graduate students had already decided to use a two-bit differential detector as the demodulator for this receiver, and my research focused on characterizing the performance of this demodulator in processing GMSK signals corrupted by AWGN and a Doppler shift. I accomplished this by simulating a baseband GMSK modem using Alta Group's Signal Processing Workstation (SPW) software. I first simulated the performance of a two-bit differential detector when the signal-to-noise ratio (SNR) is varied. After I had determined that an SNR of 17.4 dB corresponded to a bit-error rate of 10-5, I simulated the performance of a two-bit differential with a Doppler shift present and the SNR fixed at 17.4 dB. Finally, the results of these simulations indicated that a two-bit differential detector is very sensitive to a Doppler shift. Thus, the receiver Dr. Georghiades and his graduates students are designing must include the capability to estimate and correct a Doppler shift.