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TEDS Direct Access is a new extension to the TEDS part of the ETSI TETRA Release 2 standard. Simply put, it is a mechanism that enables dedicated data devices to register directly on the TEDS data carrier


without the need for a complete change of technology or hardware in the network is an obvious advantage. To take an example, let us imagine that one cell needs


to deliver 100 kbit/s of traffic. A traditional TETRA 1 cell would need from eight to ten TETRA transceiver radios – together with support such as electricity supply, battery back-ups, cooling, and the space that these transceivers need – plus, of course, 200–250 kHz of spectrum. In contrast, the same traffic could be delivered by a single TEDS 50 kHz carrier on QAM 64 modulation. TEDS would also require just one-fifth of the transmission and spectrum, one-tenth of the hardware and space, and even less electricity. Significant savings!


And even more... TEDS Direct Access is a new extension to the TEDS part of the ETSI TETRA Release 2 standard. Simply put, it is a mechanism that enables dedicated data devices to register directly on the TEDS data carrier. Without TEDS Direct Access, every TETRA radio terminal registers on the Main Control Channel. According to the service it requires, it is directed to traffic channels (TCH) for voice calls, to packet data channels (PDCH) for packet data transfer, or to the TEDS channel for high speed data. Tis mechanism is called TETRA Conventional Access. TEDS Direct Access and Conventional Access are complementary methods. Each method answers the needs of different operational scenarios. TEDS Conventional Access is necessary for TEDS-capable handportables, for example, which would be used mainly for voice. Direct Access, in contrast, is ideal for dedicated TEDS data radios. Using TEDS Direct Access, a radio will register not on


the TETRA MCCH but directly on the TEDS carrier. As long as the TEDS service is available, the radio will perform cell re-selection from one TEDS carrier to another, without ever visiting the conventional TETRA side. It may seem a small difference, but this mechanism can deliver great results. nQuality of service: because the dedicated TEDS data radios do not use the MCCH, the TEDS data services are independent from voice services and have separate Quality of Service (QoS). In other words, voice services will not suffer, however much TEDS data traffic is in the system – and vice versa. If there is congestion on either side, only the overloaded service has to be adjusted.


nCost-efficient dedicated data networks: Direct Access helps in building extremely cost efficient, dedicated TEDS data networks. If only narrowband or wideband data needs to be delivered, all carriers in the network can be TEDS data carriers.


nMore scalability for cell sizes: if a network has only a few voice users but needs extreme data capacity, TEDS


Issue 3 May 2011 TE TRA TODAY


Case in point: radio network for data transmission only T


Direct Access makes it possible to build extra wide coverage, low-capacity cells for voice and smaller, high- capacity cells for data. As the adoption of TEDS expands, more benefits from


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Direct Access will be discovered. For example, ETSI’s TC- TETRA is currently studying the potential of voice services over QAM (TEDS) channels, since this would yield better spectrum efficiency. TETRA and TEDS will continue to evolve for years and years to come.


EDS Direct Access is a great opportunity for a TETRA network owner who only needs data, or is only allowed to use data. (For example, the existing analogue trunked network may not yet be amortized, and the frequency regulator has thus granted the network owner a licence for data only.) Building a dedicated data network based on TEDS Direct Access has


several benefits for such an owner. All carriers in the base stations can be dedicated to TEDS, therefore yielding maximal data capacity. But the network itself is still a complete TETRA network, and so voice services can be introduced in the same network if the owner develops the need or gets permission for voice. What’s more, it may be possible to activate voice services on a base


station area over a remote connection (this depends on the technical details of the network).


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