GPS World, September 2013

GNSS DESIGN Galileo and BeiDou can be seen that the gain changed around 02 dB This example shows the sensitivity of the system to changes in environmental conditions Usually the measurement system is temperature stabilized and controlled and the system will not change during data acquisition But every control system can be broken or an element changes its behavior For this reason the calibration is performed at least at the beginning and at the end of a satellite path maximum 8 hours Measurement Results Here we present selected results from the European Galileo and the Chinese BeiDou navigation systems Galileo FM3 and FM4 In October 2012 the third and fourth operational Galileo satellites FM3 and FM4 were launched into orbit Signal transmissions started in November and in December respectively Both satellites provide fully operational signals on all three frequency bands E1 E5 and E6 The measurement data of both satellites were captured in December 2012 shortly after the beginning of the signal transmission FIGURE 8 on page 40 shows the spectra of both satellites for El E5 and E6 bands The quality of the transmitted signals seems to be good but for the El signal of FM4 satellite minor deformations of the spectra are visible FIGURE 9 THE OPENING FIGURE shows the results of the IQ constellations both for FM3 and FM4 concerning each transmitted signal band The constellations and consequently the modulation quality of each signal are nearly perfect for the FM3 satellite The IQ constellation diagrams of FM4 show minor deformations in each band What impact these imperfections create for future users has yet to be analyzed Both satellites were at the time of measurement campaign still in the in orbit test phase and did not transmit the final CBOC signal in the E1 band It could be expected that especially the signals of the FM4 will be adjusted to become more perfect BeiDou M6 BeiDou satellites transmit navigation signals in three different frequency bands all are located adjacent to or even inside currently employed GPS or Galileo frequency bands The center frequencies are for the B1 band 15611 MHz B3 band 126852 MHz and B2 band 120714 MHz In 2012 China launched six satellites two inclined geostationary space vehicles and four medium Earth orbit ones concluding in September M5 and M6 and October 2012 IGSO6 There have been further BeiDou launches in 2013 but these satellites signals are not analyzed here FIGURE 10 page 40 displays calibrated measurement results from the Beidou M6 satellite The spectra of the B2 and B3 band of the Beidou M6 satellite are clean and show no major deformation Within the B1 spectra some spurious results especially on top of the side lobes are obvious This behavior has to be investigated more in detail to determine their origin The IQ diagrams which visualize the modulation quality show also no major deformation Only within the B3 signal a marginal compression of the constellation points can be seen which points to a large signal operation at the beginning of the saturation of the amplifier of the satellite Conclusion Reviewing the quality of the presented measurements signal DQDO VLV DQG YHUL FDWLRQ RQ 166 VDWHOOLWHV WKH XVH RI WKH 30 meter high gain antenna offers excellent possibilities and results Regarding the calibration measurements of the antenna gain and measurement system the variances are in the range of measurement uncertainty of the equipment The sensitivity of the measurement system concerning ambient conditions was exemplarily shown based on the gain drift caused by a temperature drift But the solution is simple stabilize the ambient conditions or perform calibration in a short regular cycle to detect changes within the system behavior to be able to correct them Based on this absolute calibration a first impression of the signal quality of Galileo FM3 and FM4 and the BeiDou M6 satellites were presented using spectral plots and IQ diagrams Only minor distortion could be detected within the Galileo FM4 and Beidou M6 signal these distortions may be negligible for most users Concerning FM4 and FM3 both satellites were in the in orbit test phase during the data acquisition The signal quality may have been changed during their stabilization process in orbit or the signals have been adjusted in the meantime Thus it would be interesting and worthwhile to repeat the measurements and perform detailed analysis to assess the final NVS TECHNOLOGIES AG GPS GLONASS GALILEO ƚŚŝƐ ŝƐ ŽŶĞ ŽĨ ƚŚŽƐĞ ƌĂƌĞ ƟŵĞƐ ƚŚĂƚ ƚŚĞ ƌƵůĞƐ ŽĨ ƚŚĞ ŐĂŵĞ ĂƌĞ ĐŚĂŶŐĞĚ ďǇ ŽŶĞ ŽĨ ŝƚƐ ƉůĂǇĞƌƐ onetalent gnss com NV08C SERIES GNSS RECEIVERS PRECISE POSITION NAVIGATION TIMING Compact Robust Professional Highly Integrated All Inclusive YƵŝĐŬ ƚŽ DĂƌŬĞƚ ŶƚĞŐƌĂƟŽŶ Raw Data Carrier Code Phase Doppler 10Hz Update Rate 1PPS 15ns GPS World September 2013 www gpsworld com 38