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Geoinformatics_04-2009
article mr. fotis karamitsos (www.autoandsociety.com) frequenting frequencies gnss update on march 24 the modernization of gps finally entered a new era. on that day, at 4:34, another gps iir-m satellite was launched from cape canaveral (usa), this time with the l5 demonstration payload on board. the l5 demonstration payload is needed to comply with international telecommunication union requirements and will pave the way for the third generation of gps. the start of the transmission for the new l5 signal was on april 10 around noon (utc time). by huibert-jan lekkerkerk he launch of the l5 demonstration payload has been delayed quite a few times over the last few years (see also earlier editions of this series). with the new l5 frequency (1176.45 mhz) a new, third civil signal will be transmitted as well, the other two civil signals being the l1 c/a code and the l2c code. from gps iii onwards, all gps space vehicles will include an operational l5 signal. with this third frequency, the accuracy of gps should increase and be available for high-end, surveygrade receivers to better cope with ionospheric delays as well as increase carrier-phase gps performance such as in rtk gps. another advantage of the l5 demonstration payload is that researchers and manufacturers have the ability to test combined gps / galileo receivers on two common frequencies (l1 and l5 / e5a). if, that is, satellites from both constellations transmitting that signal are available at the same time. so far only giove-b and the new gps iir-m (20) satellite have this capability. t the last edition of this series we wrote about the launch of new satellites, predicting that the improvements had begun. and they have: almost three months later there are still 19 operational satellites with an additional one undergoing maintenance at the time of writing. the bad news is that users who bought their receiver a while ago may have faced an unpleasant surprise. on march 11, the glonass authorities decided to change the operating frequencies on two pairs of satellites. those who bought their glonass or gps / glonass receivers quite recently shouldn t have a problem even though there was no advance warning at all. older receivers may have experienced some problems after that date. glonass, in contrast to gps, uses frequency division multiplexing (fdma) where every satellite is assigned its own frequency and channel. during the munich satellite navigation summit, however, the russians were still positive about changing glonass from an fdma system to code division multiplexing (cdma), the multiplexing system used by both gps and galileo. glonass those who purchased a glonass receiver in the past can now start enjoying the full merits of an additional system. over the last few years we have had to note repeatedly that the number of satellites was falling. in galileo there is still little progress on galileo. during the munich satellite navigation summit, fotis karamitsos, director of the european june 2009 34
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