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 43 vided by the representative GPS receiver • is the probability • is the horizontal positioning accuracy • is the vertical positioning accuracy. e procedure to check the above requirements is briefly illustrated below. • e average positioning accuracy is compared to the glob- al average target. us, assuming M monitoring stations (placed in M different locations), each one able to provide a measurement of GPS accuracy (i.e., a pair per every j-th station), it is possible to compute the average accuracy as follows. • e worst positioning accuracy is compared to the worst location target. us, assuming M monitoring stations, each one provided with a pair of ( ), the worst accuracy is calculated as follows Figure 12 and Figure 13 show an example of positioning accu- racy plots in which the ICAO thresholds are never violated within the periods of interest. GPS.KPI-5: Continuity Continuity is the probability that the healthy SIS per satellite will continue to be healthy without unscheduled interruptions over a specified time interval. As indicated in Table 1, this metric is generally computed in terms of continuity breaks. us, this KPI becomes the prob- ability of losing the SIS availability due to unscheduled inter- ruptions. A continuity break event at the i-th epoch, namely E CB [prn, i], of the prn GPS satellite occurs only if the following condi- tion is true: where [H(prn)] i is the health status (GPS Interface Control Document) at the i-th epoch and !(.) is the not operator. us, the probability of continuity breaks can be computed as follows: where N CB is the number of continuity break events within the observation time (i.e., T = N day . 24 hr/day, where N day is the number of days) and for each prn belonging to a constellation of 32 GPS satellites. Table 5 reports the number of continuity breaks per day within the period of interest. No anomaly was detected. Day of February 1 2 3 4 5 6 7 MSF Number 0 0 0 0 0 0 0 Day of February 8 9 10 11 12 13 14 MSF Number 0 0 0 0 0 0 0 Day of February 15 16 17 18 19 20 21 MSF Number 0 0 0 0 0 0 0 Day of February 22 23 24 25 26 27 28 MSF Number 0 0 0 0 0 0 0 Table 5 Number of continuity breaks per day (from a BLUEGNSS monthly report) FIGURE 12 Positioning accuracy plots (from a BLUEGNSS monthly report) December 2017 HPE 95% (m) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 20 16 12 8 4 0 December 2017 VPE 95% (m) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 40 30 20 10 0 (a) HPE 95% vs. ICAO thresholds (b) VPE 95% vs. ICAO thresholds FIGURE 13 Positioning accuracy plots (from an Italian BLUEGNSS daily report) December 2017 HPE (m) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 20 16 12 8 4 0 December 2017 Abs. VPE (m) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 40 30 20 10 0 (a) HPE vs. ICAO thresholds (b) VPE vs. ICAO thresholds

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