IN-ORBIT TESTING OF TDMA OCCUPIED CHANNELS

The expected introduction of new TDMA earth-stations in the EUTELSAT n etwork with a lower diameter antenna, together with the need to ensure the high quality of services are the two principal reasons why regula r review of the performance trend of TDMA links is becoming so vital. Such a review will allow overall optimization of the EUTELSAT TDMA sys tem by ensuring that the transponders are operated at their specified points, and will make it possible to be prepared in advance in the eve nt of a transponder gain drop to reconfigure the system with no loss o f traffic. To implement these tests, EUTELSAT at its IOT facilities ne ar Paris has installed a 'burst mode saturation analyser' (BMSA) devel oped by Hollis Electronics Company. The BMSA has been specially design ed as a stand-alone test system for testing TDMA channels in a burst m ode without interrupting the operational traffic. This paper describes how the BMSA operates and in particular how the system self synchroni zes in order to position the BMSA test burst correctly in the frame, a nd how the burst is allowed to vary in amplitude in order to character ize the channel under test. This paper also discusses how the BMSA is interfaced to the host IOT station and how the tight measurement accur acy in terms of absolute transmit e.i.r.p. and spacecraft IPFD have be en met. The paper concludes by comparing results obtained by classical CW test methods with this new burst method, The conclusions also disc uss the limitations of the system and suggest possible improvements.