Receiver carrier-to-noise ratio monitoring based on improved cumulative SUM (CUSUM) method

As more and more country are concerned about the safty of the civil aviation, China began its research on the Ground Based Augmentation System. Because the approaching period is the most crucial phase which has much higher integrity risk than any other flight route, the Civil Aviation Adminstration of China (CAAC) has begun its research in integrity monitoring in civil aviation. For Category II and III operations, the integrity requirement is 200 times tighter than for Category I operations; Thus the monitors existen may be insufficient. The monitoring algorithms still needs improving. The importance of signal power level cam be learnt from the history events, such as the outage of PRN 19 on November 2, 1998. From the analysis afterward, the receiver Carrier-to-Noise ratio was used to determine the timing and duration of the outages. Signal power levels significantly below specified levels can increase ranging errors and may result in integrity risk. This paper introduced the existen signal power-receiver Carrier-to-Noise ratio(C/N₀) integrity monitoring mothod and analysed the disadvantage of this method. According to the similar integrity monitoring algorithms, this paper proposed to monitor the Signal power using the CUSUM charts algorithms. But, CUSUM charts perform not so good when the mean shift is very small. An improved CUSUM algorithm was introduced which can shorten the detection time when the mean shift is small, and performs as well as the large shift. From the theoretical simulation, the detection time using the improved CUSUM algorithm is half the detection time as the time using the nominal CUSUM algorithms when the mean shift is small. Besides the threotical simulation failure test was also done.