GPS World - February 2008 - (Page 35)

Galileo | SYSTEM DESIGN & TEST The elements transmitted in the navigation message are the spacecraft group delay, BGD, the coefficients for the effective ionisation level, Az, and the ionospheric disturbance flags that can be monitored by the user to ensure that the ionospheric corrections are valid for his particular region. BGD and the Az coefficients transmitted enable the user to estimate the ionospheric delays through a simplified ionospheric delay model, NeQuick. The ionospheric module in the Orbit Determination and Timing System (ODTS) process provides the information described earlier. It runs every 48 hours (starting from 00:00 UTC) to generate the estimated vertical total electron content at each GESS location and epoch, the satellite and stations broadcast group delays, the Az coefficients, and the ionospheric disturbances flags. The following parameters have been analysed to ensure that the navigation message transmitted has a good accuracy: The GIOVE broadcast group delays and GESS group delays; The GPS group delays and the vertical total electron content (vTEC) determination at each GESS; The NeQuick model vTEC computation when the effective ionisation level Az is estimated from the three ionospheric coefficients transmitted; Iono disturbance flag analysis. GESS Group Delays. FIGURE 9 shows the GESS group delays stability over around 80 days in 2007. It can be seen that generally the stability is good, except for a couple of stations (GVES and GMAL) and for offset that have been traced to maintenance activity in the infrastructure. GPS Group Delay. As a second benchmark of the ionospheric module performance, the GPS group delays values Under 1 second Time To First Fix 50 channels, 1 million correlators SuperSense® -160 dBm sensitivity Under 50 mW power consumption Galileo-ready u-blox’ 5th generation has redefined the boundaries of GPS performance GPS for Mobile Terminals To experience u-blox 5 performance first-hand, come visit us at: your position is our focus Mobile World Congress 2008, Feb. 11-14, Barcelona, Spain CeBIT 2008, March 4-9, Hannover, Germany CTIA 2008, April 1-3, Las Vegas, NV, USA 5 u-blox 5 Chipsets Modules were compared to the IGS computed values from IONEX files, as shown in FIGURE 10. The values compared to about 0.25 ns RMS over 3 months. vTEC Computation. The NeQuick model calculates the TEC value between two locations as a function of time and solar activity. To take the solar activity into account, the NeQuick model will be driven by one effective ionisation level Az. The Az corresponds to the solar flux f10.7, which is a measure of the solar radio flux per unit frequency at a wavelength of 10.7 cm, near the peak of the observed solar radio emission. It represents a measure of diffuse, nonradiative heating of the coronal plasma trapped by magnetic fields over active regions, and is an excellent indicator of overall solar activity levels. The effective ionisation level Az parameter is analytically calculated in the IONO algorithm by combining three coefficients (a0, a1, and a2), which Single Chips www.u-blox.com www.gpsworld.com February 2008 | GPS World 35 http://www.u-blox.com http://www.gpsworld.com

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GPS World - February 2008 Contents Out in Front Expert Advice Galileo's Second Coming Soon UPS First to Use ADS-B European Industry Group Galileo Validation 2008 Antenna Survey Tsumani Detection by GPS Classifieds Advertisers Index Seen + Heard

GPS World - February 2008

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