7News from Rohde & Schwarz Number 161 (1999/I )

The breakthrough has finally been made– that would be the right description forthe present status of TETRA (terrestrialtrunked radio). Field trials like those inDenmark or the Schengen three-nation

field trial have yielded positive results,while others (eg Berlin/Brandenburgpolice) are still in progress. High speechquality and data transmission at max-imized frequency economy are clear

advantages over other standards. Tech-nically superior functions such as PDO(packet data optimized – for pure datatransmission) or DMO (direct mode operation – direct connection betweenmobiles without a base station) arewaiting to be introduced. On top ofthis, competition between manufacturersof terminal equipment has meanwhilebrought about acceptable prices formobile and base stations.

To qualify for operation, terminal equip-ment has to pass the type-approval testto TBR35 (technical basis for regula-tion), which consists of two parts. In thefirst part RF parameters are tested withthe aid of the Rohde & Schwarz TETRASimulator TS8940 [1], and in the second part signalling procedures (ofthe protocol) are checked with TETRAProtocol Test System TS1240 (FIG 1).

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TETRA Protocol Test System TS1240

Type-approval tests of TETRAmobile radiosDuring the past year, TETRA has been firmly establishing itself to take over from the analog MPT1327 standard in wireless communication. About 25 projectsare presently running in Europe and overseas. Any application based on analogsystems is a potential market for TETRA. To ensure reliable communication – particularly for police, fire brigades and emergency services – not only RF parameters but also signalling procedures have to be tested in type approval ofthe transceivers, and this is where TETRA Protocol Test System TS1240 comes in.

FIG 1 TETRA Protocol Test System TS1240 tests signalling procedures of TETRA mobiles in development and production. Photo 43 144/2

8 News from Rohde & Schwarz Number 161 (1999/I )

TETRA status and specifications

Details of TETRA status [2]:

Phase 1 (completed in the first half of1997) defines network and air inter-face requirements as well as security requirements for PDO and V&D (voiceplus data), plus standards and require-ments for conformance tests at the airinterface and stage one of the supple-mentary services.

Phase 2 (completed in the second halfof 1997) describes the air interface ofthe DMO and the SDL (specification description language) model, validationand test suites for edition 1 of TBR35,voice codec requirements and testingas well as three security algorithms.

Phase 3 (shortly to be completed) de-fines the SDL model, validation and testsuites for DMO and the SDL model aswell as the validation for PDO and thesecond and third stages of the supple-mentary services, for the TETRA SIMcard, the intersystem interface (ISI) forindividual call and mobility manage-ment, edition 2 of TBR35, and the PSTNgateway.

Phase 4 (in progress) defines the com-pletion of the ISI group call and shortdata service, ISDN gateway, updates

of V&D test suites and a test of the V&Dand PDO air interfaces.

TETRA operates in the frequency band380 to 440 MHz; an extension to

900 MHz is planned. Other featuresof TETRA are:• high spectral efficiency,• 25 kHz channel spacing with four

timeslots per physical channel (TDMA),

• π/4 DQPSK modulation (symbolrate 18 ksym/s),

• voice and data transmission pos-sible,

• simplex, semi-duplex and duplex operation supported,

• encryption (air interface, end-to-end).

Description of protocol tester

TETRA Protocol Test System TS1240consists of the universal Protocol TestUnit PTW30 and Digital Radiocom-munication Tester CMD91. The centralunit PTW30 is based on a controllerwith hardware enhancements, ie a DSPcard and an I/Q interface card. Radio-

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FIG 3Test System TS1240

offers tools like PCO (top) and

MSC for analysis of test results.

Stack 1 Stack 0

Shortcut...

...

...

L3

L2

L1

Beam

Block 0

LLME

FIG 2TETRA protocol concept: block,stack, layer (L1, L2,L3) and beam

9News from Rohde & Schwarz Number 161 (1999/I )

communication Tester CMD91 servesas an RF output stage in the transmitand receive directions. Data exchangebetween PTW30 and CMD91 is in theform of digital I/Q data, while devicesettings are serially transmitted.

All functions required for the protocoltest of TETRA terminal equipment areimplemented in the test system soft-ware:

Because of the time-critical require-ments of the TETRA protocol stack, a realtime operating system – LynxOS –is used. This Unix derivative is com-patible with Posix and SystemV.

The TETRA protocol engine contains all processes, data and interfaces required to control the TETRA protocolstack (FIG 2). One possible operatingmode of TS1240 is simulation of abase station for testing a TETRA mobilephone after registration via the air inter-face. Another operating mode allowsthe setting up of a direct connectionfrom a higher layer (eg via Ethernet) toan external controller, where a singlelayer has been started as a DUT (virtual type approval).

A modern graphical user interface(GUI) is implemented offering the usualwindows. The simulation manager enables selection and setting of the desired simulation mode. PCO (point of control and observation betweenlogical layers) and MSC (message sequence chart representing data trans-mitted between TS1240 and DUT in decoded form across all layers) areamong the means available for resultanalysis. FIG 3 illustrates the interactionbetween the modules.

The test cases defined by ETSI (Euro-pean Telecommunications Standards Institute) are in a language particularlysuitable for protocol tests: TTCN (treeand tabular combined notation, in thecase of TETRA with ASN.1 notation).This language allows fast and con-venient conversion of test cases into executables. This coding is implement-

ed in Test System TS1240 in two steps(FIG 4). First the supplied TTCN compil-er translates the code into C language.Secondly, C is translated into execut-ables using system libraries. With theaid of a test case selector, one or moretest cases can be conveniently selectedand started via the graphical interface,the verdicts being clearly displayed intabular form. Trace files generated during program run permit detailedanalysis down to command level.

Tests not covered by ETSI test cases canbe implemented by creating their ownscenario. For this TS1240 hardwareand software are available via functioncalls (open programming platform). Ascenario executor permits the programsto be executed in realtime or line byline.

TETRA Protocol Test System TS1240 isideal for the development and testing ofTETRA signalling procedures and ableto translate TTCN test cases publishedby ETSI into executables. TS1240 fea-tures all attributes of a modern protocoltester, following in the steps of a longtradition of Rohde & Schwarz protocoltesters for mobile radio standards.

Detlef Willam

REFERENCES

[1] Schneider, H.-J.; Tiwald, W.: TETRA TestSystems TS8940 – Type-approval tests of TETRA base and mobile stations to TBR35.News from Rohde & Schwarz (1997) No. 153, pp 4–6

[2] Brian, O.: The road ahead – The future for the TETRA Project. TETRA InternationalConference, London (1998)

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Features of TETRA Protocol Test System TS1240Implementation to standard of TETRA protocol stack (layer 1 and 2)

TTCN test cases executable to TBR35

All protocol layers implemented per software

TETRA air interface implemented

Open platform concept for programming of scenarios

Graphical user interface

Reader service card 161/04

FIG 4 Two-stage implementation of ETSI test cases in TETRA Test System TS1240

.gr .mp .c .h .o

.exe

.make

Syntax check

TTCN Editor TTCN Compiler

Simulator Library System specific part

LT interface Protocol Library

C Compiler