Optimization of TT and C Carrier Tracking Loop in Dynamic Environments

Abstract

Carrier tracking is essential for a TT&C (Telemetry, Tracking and Command) system, the main functions of which are high accuracy ranging and velocity measurement, and the total carrier tracking error is mostly comprised of the thermal noise error and dynamic stress error. For TT&C carrier tracking loop design, loop bandwidth adjustment is the principal strategy to improve the loop performance in the most instances. Narrow bandwidth can reduce the thermal noise error but increase the dynamic stress error, while wide bandwidth will improve the dynamic performance of the loop but increase the thermal noise error. Therefore, there is involvement of a tradeoff between the two opposing consideration. Based on the analysis of spacecraft dynamic characteristic and the error characteristic of carrier tracking loop, an optimal loop bandwidth which can yield the minimum error in specified carrier-to-noise ratio and dynamic stress is derived. Then, an estimation method extracting the carrier-to-noise ratio and spacecraft dynamic real time form the carrier tracking loop itself is developed. By detecting the carrier-to-noise ratio and spacecraft dynamic, the loop parameter is adjusted adaptively to minimize the carrier tracking error. The simulation result shows that the algorithm is efficient to improve precision of the carrier tracking loop in the high dynamic circumstance.