Análise de desempenho de receptores GMSK para o Global Open CoLlecting Data System (GOLDS)

Abstract

The Global Open CoLlecting Data System (GOLDS) is a satellite environmental data collection system proposed as an evolution the Brazilian Environmental Data Collecting System (SBCDA). The SBCDA signal is modeled with Phase Shift Keying (PSK) modulation and without channel encoding. One of the main problems of the SBCDA is inter-user interference. As the available bandwidth for reception is small, it is recommended that the frequency band occupied by the signals from Data Collection Platforms (PCD) be compact. In this context, with the aim of improving the spectral efficiency of PCD signals, GOLDS proposes the use of Gaussian Minimum Shift Keying (GMSK) modulation. Hence, the objective of this work is to evaluate synchronization and demodulation techniques for GMSK signals used in the GOLDS system. Three signal models were evaluated, and synchronization and demodulation techniques were presented to compose the receiver, followed by simulations to verify the system’s performance. The results showed an improvement in signal detection since inter-signals interference was reduced with the implementation of GMSK modulation. The MSK-type linear demodulator for the pre-coded GMSK signal demonstrated satisfactory performance for the system. As for timing and phase synchronization, some methods available in the literature were evaluated. Joint phase and timing estimation for MSK signals showed better performance for the GOLDS system.