Design and Development of Gaussian Minimum Shift Keying (GMSK) Demodulator for Satellite Communication

This paper discusses DSP based implementation of Gaussian Minimum Shift Keying (GMSK) demodulator using Polarity type Costas loop. The demodulator consists of a Polarity type Costas loop for carrier recovery, data recovery, and phase detection. Carrier has been recovered using a loop of center-frequency locking scheme as in M-ary Phase Shift Keying (MPSK) Polarity type Costas-loop. Phase unwrapping and Bit-Reconstruction is presented in detail. All the modules are first modeled in MATLAB (Simulink) and Systemview. After bit true simulation, the design is coded in VHDL and code simulation is done using QuestaSim 6.3c. The design is targeted to Virtex-4 XC4VSX35-10FF668 Xilinx FPGA (Field programmable gate array) for real time testing, which is carried out on Xtreme DSP development platform.