08 TETRASUPPLEMENT


technologies designed for 3G and 4G public cellular use as they require wider bandwidths in which to operate, and more ‘guard bands’ either side to protect against interference. TEDS is therefore the optimal solution for private high speed data networks in narrow band spectrum. The higher data rates of TEDS provide many


advantages in the transport market. Lower latencies – i.e. faster transfer of data – makes TEDS more suitable for time critical data exchange, such as signalling information. The higher bandwidths enable more capacity – for example, if TEDS was used for location reporting, more positional updates could be sent from each vehicle allowing better location accuracy. It can also be used for pictures – either still pictures or medium quality video, for example for surveillance cameras at either fixed or on-board locations.


Direct Access TEDS The first release of TEDS (TETRA Release 2.0) required the TEDS data channels to be tethered to TETRA 1 cells, and behave similarly to single and multislot packet data channels. This means that when a terminal moves between cells, all


signalling takes place on the TETRA 1 control channels: this is known as Conventional Access. The next release of the TETRA standard, TETRA Release 2.1, which will be published later in 2011, introduces a new feature called Direct Access to TEDS. Direct Access allows the TEDS


Sectored TEDS DA cells with omnidirectional speech channels


data channels to be used directly as control channels: this will allow TEDS cells to break free from TETRA 1 cells and operate as standalone cells – or to give more flexibility in how TEDS is integrated into a TETRA network. In a Direct Access cell, a TEDS QAM data


channel acts as the Main Control Channel. This allows a mobile station to join a cell directly on the TEDS channel, which allows a much more efficient cell-to-cell handoff process as no time is wasted in moving through TETRA 1 conventional control channels. Voice calls are set up from the TEDS channel, moving the radios to


conventional TETRA 1 speech channels for the duration of a call, then returning them to the TEDS channel afterwards. It allows terminals to be far more data centric, and to move around a network remaining on TEDS channels where available, and this of course also reduces the load on the conventional TETRA 1 control channels which can continue to be used for voice centric terminals. This enhanced performance for data centric terminals will be a big advantage in transport applications, where much of the information sent over the radio is data, and voice calls between driver and dispatcher are infrequent. However, the integration between voice and data remains, so that voice calls can still be set up immediately, pre-empting data sessions in progress if necessary in an emergency. Direct access allows many useful scenarios


in planning a network, and will allow different densities of cells dedicated to high speed data compared with densities of cells carrying conventional speech and data. Channels can be shared between cells, and this will allow scenarios such as sectored TEDS data cells to increase data capacity at a cell site which


THE BEST OF TETRA TECHNOLOGY FOR PUBLIC TRANSPORT


Etelm 9 avenue des deux lacs - P.A de Villejust - 91971 Courtaboeuf cedex France Tél : +33 1 69 31 79 00 Contact : M. Jean Beharel Commercial Manager - Website : www.etelm.eu


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