airports
Right: passengers alight from one of the airport’s shuttle buses to board their aircraft. A TETRA radio mounted overhead in the bus links the driver to the dispatcher
behaviour of the new system, which caused difficulty for some users. One of these was the call establishment time in the TETRA network. “On the old system, you could press and talk”, Michael Zaddach explains. “Now, you have 400 milliseconds before the call establishes itself. Tat was a huge problem the first time.” With the digital radios, if a user pressed the PTT key and began speaking immediately, his first word or two would be lost while the connection was being made. “Now, it’s no longer a problem because all the users have adapted to the new system. “We had some problems also with the transfer of
features from the old system to the new one. Group call, for example, is different in the behaviour of the system. So we’ve had to adapt the users to the behaviour of the new system. It’s a question of training. We had many trainings for these different user groups to make them familiar with the new system.” “As a little bit of an example, we had ground handling”, puts in Robert Wondra. “Tere is one central dispatcher and in the analogue times he would always use group call. But the single [person-to-person] call in TETRA is more effective, because the processes are changed.” With the person-to-person facility, he says, users can call each individually, without interrupting other colleagues by breaking in on their loudspeakers. “It now comes in as a private call by the radio and he looks at the display and he can decide whether to break into his telephone call and then call the radio. Tey can decide whether to call back immediately or in half a minute.” One especially demanding group of users was the pushback teams, who roll each aircraft back from the gate as it begins its departure. “Tese people need a direct connection to the apron controller in the tower, and if the apron controller says ‘Stop!’, they have to immediately stop”, says Michael Zaddach. “With the 400 milliseconds I mentioned, they had at first huge problems. Tey told us they can’t use this system!” Part of the difficulty, Robert Wondra explains, was that
the apron controllers also use conventional air-band radios, and the difference in feel between the two systems was very noticeable. “Te same person has to use air-to-ground to
talk to the pilots on the aeroplane and the next he has to talk with the pusher with TETRA.” “But now it works perfectly”, adds Michael Zaddach. “Tey adapted to this feature and it works perfectly. But the first time it was really heavy weather – 400 ms is not so much, but our apron controllers are very special.”
Base stations Te TETRA infrastructure at the airport is now very extensive. Five Motorola TETRA base stations linked to
Pushing back: drivers in this workgroup initially had difficulty with the TETRA radios because of the longer call set- up time. But with growing familiarity they have fully adjusted to it
30 TE TRA TODAY Issue 1 November 2010 - February 2011
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