TETRASUPPLEMENT 07


information services, on-board telemetry and more advanced applications such as video surveillance and safety critical signalling systems. Most applications will be built on top of the Internet Protocol (IP), and the open interfaces provided by TETRA terminals and systems are designed to simplify integration of these applications with TETRA. TETRA has always offered simple data


services as well as more extensive data bearer services – the Status and Short Data Services both provide very efficient means of sending small amounts of data, and SDS provides the foundation for services such as Vehicle Location, text messaging, user identification and running number assignment. The IP packet data services were later additions to TETRA and on the TETRA Release 1 platform offer single slot and multislot packet data – TETRA uses Time Division Multiplexing with four timeslots per carrier (radio frequency pair), and whereas a user would only be allocated one timeslot for speech communications, multiple slots can be assigned to data transfers, allowing a greater speed. The IP packet data service is an enabler for


applications where a data bearer is needed, such as the telemetry and signalling applications mentioned previously. However, it also enables


services internal to the TETRA radio – for example browsers using WAP (Wireless Application Protocol) which can provide access to information such as timetables or can be used for form filling for reports. Specialist data terminals such as PDAs and tablets have also been created around the TETRA data services to allow users to access organisational data while remaining within the secure boundaries of their own network.


MCCH: Main Control Channel


TEDS – the TETRA Advanced Data Service The TETRA Release 2 programme included a number of new features, of which the headline was the TETRA Advanced Data Service, TEDS. Other additions include extended operating range, primarily to improve air-to-ground operation, but also applicable to any land based application where the original 58km range limitation of TETRA was a problem. The TEDS high speed data service allows


higher data speeds through the use of more complex modulation schemes, in particular Quadrature Amplitude Modulation (QAM), and different channel bandwidths. The system is adaptive, and can be tailored to give the best data throughput by sending data in the best modulation scheme for each terminal according to the quality of its signal. The scheme can pack a lot of energy into each of the data bits, giving a relatively low throughput but excellent range, or when the range is less it can send more bits using the same transmitter energy, which raises the throughput. Wider bandwidths allow more bits to be transmitted, and the widest data channel supported by the current standard (150kHz) allows data speeds of up to 500kbps to be sent. First TEDS implementations are already on the market, concentrating on the 25 and 50kHz channel options due to the current difficulties in obtaining spectrum for wider bandwidth channels. TEDS, like TETRA, has been designed to fit


into existing spectrum by maintaining excellent adjacent channel performance – i.e. minimising the interference to neighbours in the next radio channels – so that it can be used in frequency spectrum shared with analogue and TETRA 1 services. This is a big advantage over


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