Design and Simulation of Adaptive Phase Locked Loop Based BPSK Demodulator for Satellite Communication

In deep space missions, performance requirements of a satellite communication system are much more stringent as signal delay is of order of tens of minutes. Coherent receivers are therefore by default used in the onboard satellite system because of their superior performance. Main building block of coherent receiver system is Phase Locked Loop (PLL). Loop filter bandwidth of a PLL controls the performance of a receiver system. Designing a system with constant PLL bandwidth, results in sub optimal receiver system in varying input signal strength and relative dynamics scenario. The way out of the problem is an adaptive PLL based receiver, where PLL parameters are constantly updated based on the signal strength and relative dynamics measurements. The paper proposed the adaptive PLL based receiver system as a solution to meet the challenging requirements of satellite communication particularly in deep space missions. Adaptive PLL system constantly adjusted its parameters with present signal condition and relative dynamics scenario. Different receiver configurations based on the adaptive PLL systems are discussed in the paper. Application of adaptive PLL in Binary Phase Shift Keying (BPSK) demodulator is studied in detail. Paper describes the modelling of BPSK demodulator for conventional PLL and Automatic Gain Control filter (AGCF)-PLL based on the acquisition time. Carrier acquisition time is the most important parameter in satellite communication, so the impact of changing loop gain in adaptive system on carrier acquisition time is deliberated and analyzed in detail. One of the basic requirements of Adaptive PLL system is measurement of Signal to Noise (SNR) and relative dynamic, as based on these two measured values, algorithm calculates the new value of PLL parameters. SNR Measurement methods are evaluated based on implementation aspects. Relative dynamics comprises of relative acceleration and relative jerk, for relative jerk measurement, 3rd order PLL system is designed and simulated. Phase error and lock signal behavior are evaluated for relative acceleration and jerk conditions. Simulation results of developed systems are compared with conventional systems. It was found that the adaptive gain PLL works better than the conventional PLL in challenging and unknown conditions.