Adaptive Inter-Loop Aiding for Performance Improvements in Low CNIR Environments

Abstract

Use of inter-loop aiding for improving tracking performance has been widely researched in recent years. However, most of the previously proposed aiding schemes rely on the assumption that the aiding loop remains unaffected by received interference. This paper argues that this may not always be the case. It is likely that the performance of the aiding loop may also degrade in the case where interference is received at the aiding carrier’s frequency resulting in performance degradation of both aiding and aided loops. This paper proposes an aiding scheme that offers performance improvements in case interference corrupts both frequencies. Also, an algorithm is proposed that continuously updates the aided loop bandwidth to keep its jitter at a minimum. A relationship between the quality of the aiding signal and its effects on the performance of the aided loop is analysed. An adaptive Kalman filter-based implementation of the aiding architecture is proposed to improve the quality of aiding estimates. This implementation offers an improved margin against received interference. Simulation and real data results are presented that show improvements of 7 and 5 dB-Hz in this margin by employing the proposed aiding scheme with and without an adaptive Kalman filter.