Panorama

peak periods. Apart from the usual CRTC02 also has functionality for anyway. The required handover func- remedies like installation of microcells checking multiband mobile phones. tions between GSM900 and DCS1800 and allocation of additional frequen- These phones can be operated both are defined in GSM specifications. cies, the use of half-rate speech coding in the GSM900 and the DCS1800 CRTC02 provides two RF carriers that is another efficient means of increasing band. DCS1800 mobiles can thus use can be operated independently of each capacity. Here two mobiles share a the 900 MHz band for roaming in other both in the GSM900 and the time slot and use the individual bursts countries where no DCS1800 network DCS1800 band. The tester is thus alternately. Powerful hardware in the yet exists. This means that DCS1800 able to perform even these extremely mobile phone in conjunction with an network subscribers can now be called elaborate and complex tests. elaborate algorithm ensures approxi- worldwide. Frank Körber; Roland Steffen mately the same speech quality al- though only half the number of bits are In some countries a network operator transmitted. In addition to the required may use both bands – GSM900 and basic functions such as half-rate speech DCS1800. In these cases long-range and channel coding, the signalling soft- GSM frequencies can be used to cover ware must be considerably enhanced large areas while the short-range so that the network is informed that DCS1800 frequencies are more suit- the mobile phone supports the half- able in cities where, for reasons of rate mode and wants to make use of capacity, microcells are employed Reader service card 155/13 the benefits of a half-rate connection, which include lower charges for in- stance. Thanks to new software op- tions, also available for testers already supplied, CRTC02 is able to perform all the necessary tests.

Through further development of speech coders, speech quality can be im- proved in full-rate mode using the same number of bits. CRTC02 is now able to test these new enhanced full- FIG 2 rate speech coders with the associated Automatic test run signalling. with sequencer

DVB-T, the new terrestrial TV standard

In February 1997 the voting procedure first, and is expected to be taken up in all other DVB specifications, the terres- for the new terrestrial European Telecom- other parts of the world too. trial broadcasting standard is based munications Standard ETS 300 744 (in on the requirements of potential users. short DVB-T) ended with a unanimous The basic technical specifications vote*. Thus, within about two years, a were prepared by the European DVB * ETS 300 744: Digital broadcasting systems for basis has been created for the terres- Project and in particular by its Tech- television, sound and data services; Framing trial television of the future. This new nical Module, in which Rohde & structure, channel coding and modulation for standard will be applied in Europe Schwarz is taking an active part. Like digital terrestrial television. March 1997

News from Rohde & Schwarz Number 155 (1997/III) 31 Panorama

The DVB-T standard is envisaged to • Multiplex adaptation and energy dis- • Pilot and TPS signals (transmission fulfill the following requirements: persal: multiplex adaptation through parameter signalling): insertion of • Trade-off between transmission ca- appropriately standardized inter-- pilot carriers, some of which carry pacity and coverage range should faces, inversion of every eighth the transmission parameters in cod- be possible. sync byte, energy dispersal for ed form as modulation signals. • The implementation of large-area even power distribution in the trans- • OFDM (orthogonal frequency-divi- and local single-frequency networks mission channel. sion multiplex): calculation of IFFT should be possible. • Outer coder: coder with shortened with 2048 or 8192 carriers, with • The system should allow transmis- Reed-Solomon code (204,188, t = 8), 1705 or 6817 of which containing sion of data containers irrespective capable of correcting up to eight data or transmission parameters, of their actual contents (eg com- errored bytes in an MPEG2 trans- 1512 or 6048 being exclusively re- pressed video or audio data). port-stream packet. served for payload data. • The system should be robust and • Outer interleaver: interleaver with • Guard interval insertion: insertion allow adjacent-channel operation of a depth of I = 12 for dispersal of a guard interval for the OFDM analog and digital TV signals in a of burst errors to different packets signal, permissible intervals are densely occupied frequency band. so that higher probability of suc- 1/4, 1/8, 1/16 or 1/32 of symbol • The transmission standard should cessful error correction is achieved. duration. be available well in time to enable • Inner coder: punctured convolu- • Digital/analog conversion: conver- network operators wishing to adopt tional code with code rates of sion of digital into an analog signal. the standard to start operation still 1/2, 2/3, 3/4, 5/6 and 7/8. • Front end: conversion to output in 1997. channel, usually in UHF range.

To antenna

Program Transport MUX MUX MUX Video Outer Inner Frame Guard adaptation, Outer Inner coder inter- inter- Mapper adapta- OFDM interval D/A Front end energy coder coder leaver leaver tion insertion Splitter dispersal Audio 1 coder MUX 2 Outer Pilots & adaptation, Outer Inner inter- TPS Data n energy coder coder coder dispersal leaver signals

Functional block diagram of system (terrestrial channel adapter)

The DVB-T standard contains elements • Inner interleaver: combination of For the socalled hierarchical modula- of the standards for satellite and cable bit interleaving and symbol inter- tion, two sets of the forward error- transmission. The input signal, for in- leaving. correction blocks are required and stance, is defined in all cases as an • Mapper: allocation of information to the MPEG2 transport stream is split up MPEG2 transport stream. For error the individual carriers and constella- accordingly. protection too, well-proven techniques tion points; permissible modes are have been resorted to. In contrast to QPSK (quadrature phase-shift key- Rohde & Schwarz pre-series DVB-T other systems, a multicarrier transmis- ing), 16QAM and 64QAM (quad- modulators successfully passed their sion method was chosen for adaptation rature amplitude modulation), Gray first interoperability tests and are to the terrestrial transmission channel mapping. at present being used in laboratory with its multipath propagation. Chan- • Frame adaptation: providing syn- and field tests in cooperation with nel coder and modulator contain the chronization to frame structure of the customers. following functional blocks (FIG): signal. Dr Jürgen Lauterjung

32 News from Rohde & Schwarz Number 155 (1997/III)