Also available on the radio network is a telephone interconnect function with full two-way speech, enabling users to make and receive calls via the public telephone network.

In addition, there is now the possibility for mobile and portable radios to send and receive data, and some of the department’s customers on the airport are already using this. Opportunities exist, too, to benefit by integrating the TETRA system with the airport’s IT applications.

Implementing the network

Today’s radio system is the result of several years of work by the IT department. “We started the complete project in 2005 with the preparation of a requirements definition and the definition of the RFP [request for proposals]”, Zaddach continues. “Then we made a tender process and the contract, and we started the implementation of the central system in 2007.”

While the TETRA system was progressively being brought into use, the old analogue system continued running throughout, and remained in operation until the middle of last year. This lengthy period of parallel working allowed a gradual, steady migration of users, group by group. Careful planning was needed to map out the sequence of changeovers, because many user groups needed to communicate with other groups, and it was important to avoid making them carry the old radio as well as the new one.

“We wanted to make sure that we had no operational failure in this migration phase”, Zaddach says. “But now all the users are on the new system and it works very well.”

Users of the TETRA radios are spread across a whole range of airport operations, from staff inside the terminal buildings and facilities management people to apron personnel, airport control and winter services such as de?icing and snow removal on the runways and aprons – an important task in Munich, where winters are hard.

“We have some users who are very happy using the new system”, comments Robert Wondra, project manager for the TETRA programme. “For example, the terminal services. These are the people you see in the blue jackets. Before, they had analogue trunked radios weighing 450 grams – which was too heavy to put in their pockets and they had to hold it in their hands. But the new ones are 250 grams and it’s very easy to put it in a jacket pocket. Also, it gives full-duplex telephone calls, and they can switch it between loudspeaking and privacy.

“They changed at the end of 2007 and since then we have never heard from them!”

Some initial problems did come to light – a few technical hitches needed to be ironed out in the central system, but there were also factors such as the different 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. That 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. “There 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. They 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. “These 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. They 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. “The 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.”
(中国集群通信网 | 责任编辑：陈晓亮)