Inside GNSS Media & Research

NOV-DEC 2018

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www.insidegnss.com N O V E M B E R / D E C E M B E R 2 0 1 8 InsideGNSS 47 or worse hazardous misleading infor- mation (HMI), xPE ≥ xAL. A c c o r d i n g t o t h e p r e v i o u s definitions, the probability of IE can be computed as shown in Eq. (12) and the related targets are shown in Table 7. Stanford diagrams are t he t y pi- cal tool used to analyze the integrity (see Additional Resources). Such plots are built by gathering data (i.e., xPL vs xPE) from all monitoring stations for the entire observation period (i.e., one month). Some examples are shown in Figure 21. GPS-EGNOS.KPI-4: Continuity of Service e continuity of service of a system is the capability of the system to perform its function without unscheduled inter- ruptions during the intended operation (ICAO). According to ICAO Doc-9849, this metric is computed as one minus the continuity risk. The continuity risk (CR) is defined as the ratio between the total number of continuity events using a time-sliding window of 15 seconds, and the num- ber of samples with valid and available APV-I or LPV-200 solutions. A single continuity event (CE) occurs if the system is available at the start of the intended operation and it becomes not available within the next 15 seconds. Such performance shall be obtained under fault-free conditions. Table 8 lists the continuity of service targets coming from our two ICAO documents, i.e., 1 – 8 × 10 –6 per 15 sec- onds for both the APV-I and LPV-200 procedures. Furthermore, according to the statement reported in App. G, §2.6 of ICAO Doc-9849, an acceptable observa- tion period for this kind of analysis shall be larger than 22 days, e.g., at least one month. e procedure adopted to compute the continuity of service is illustrated within App. G of ICAO Doc-9849. is FIGURE 20 GPS/EGNOS service availability (from a BLUEGNSS monthly report) February 2018 HSA % 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 110 100 90 80 70 60 50 February 2018 HSA % 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 110 100 90 80 70 60 50 (a) APV-I horizontal service availability (c) LPV-200 horizontal service availability February 2018 VSA % 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 110 100 90 80 70 60 50 VSA % February 2018 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 110 100 90 80 70 60 50 (b) APV-I vertical service availability (d) LPV-200 vertical service availability used for the intended operation (or phase of flight). In other words, the integrity includes the ability of a system to provide timely warning (an alert) to users when the sys- tem itself cannot be used to carry out the desired procedure (I. Konaktchiev and C. Butzmuehlen). An APV-I or LPV-200 integrity event (IE) occurs when the navigation system error is greater than or equal to the cor- responding protection level for APV-I or LPV-200 and no alert is emitted within the time-to-alert (TTA) period (ICAO). Position domain safety index (xSI, x = H, horizontal, or V, vertical) is defined as the ratio between xPE and the related xPL at the i-th epoch, i.e., xSI i = xPE i / xPL i . • If xSI < 1, no anomaly occurred, i.e., normal operation (NO), xPL < xAL. or system unavailable (SU), xPL ≥ xAL. • Conversely, xSI ≥ 1 indicates mis- leading information (MI), xPE < xAL, Procedure Approach Target References APV-I 1 – 8×10 -6 per 15 sec ICAO LPV-200 (Cat. 1) 1 – 8×10 -6 per 15 sec Table 8 Continuity of service targets Station ID CR (%) Availability (%) Time (s) Continuity (%) LIML-MB01 0.0000 100.0000 2417557.0 100.0000 LGKO-TW01 0.0032 99.9981 2417066.0 99.9968 LMML-TW01 0.0267 99.9748 2414736.0 99.9733 LCLK-AS01 0.0140 99.9493 2412152.0 99.9860 Table 9 APV-I/LPV-200 horizontal continuity of service (from a BLUEGNSS monthly report)

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