Measurement of path parameter of digital TV radio transmitters

By Vladimir Bogdanov, Lev Polosin, Sergej Tretiyak

Review contents:

Digit is on a horizon The standardization of the digital TV broadcasting transmitter features Digital and digital-analog (hybrid) TV-transmitters Transmitters for digital terrestrial TV broadcasting Low-power DVB-repeaters from ELTI Company Spot: filling gaps in DVB-T networks with digital repeaters NEC transmitters for digital TV Transmitters of Rohde & Schwarz for broadcasting Radio broadcasting transmitters of Technosystem and Screen Service Italia Transmitters of Thales Broadcast & Multimedia for digital television broadcasting Measurement of path parameter of digital TV radio transmitters

In European DVB system of the digital TV the methods of the measurement of the parameters and parameters of TV transmitters are specified in “The manual to measurements in DVB systems” TR101290. In all digital DVB broadcasting system an input and output signal is a transport MPEG-2 stream, but methods of the TV signal transmission for each system are different.

In accordance with this the set of controlling parameters, recommended by TR101290, includes two groups: the first is intended to control a transport MPEG-2 stream and is general for all delivery facilities, the second is intended to control the channel equipment and takes into account the specifics of the different TV program transmission system (air, cable and satellite).

Control of transport MPEG-2 stream parameters

Control of a digital transport stream provides the analysis of its structure and syntax. The the parameters of the structure and syntax of the digital transport stream are integrated in three groups.

The first group contains the base set of parameters for continuous monitoring, required for confident decoding of the transport stream:

• Loss of transport stream synchronizing (TS sync loss). This indicator will be discarded after successful receiving of five consequent sync bytes, and is established after skipping of two sync bytes. If indicator is installed, the rest parameters are not measured;
• Error of the sync byte receiving (Sync byte error). This indicator is established if immediately after receiving of the next package (188 bytes) the sync byte do not discovered. Checking of this parameter is necessary, since many decoders use this byte for switching of their own circuits, but do not check its location;
• Error of the program-association table (PAT error). This indicator is established if package with PAT table does not appeared during 0.5 second, or package with identifier 0×0000 does not contain the identifier of the tables 0×00, showing the beginning of PAT section, or its field of the control of encoding is not equal to 00;
• Error of count continuity (Continuity count error). This indicator is established under wrong sequence of packages, including when finding missed or repeated (more often, than twice) packages;
• Error of the program-map table (PMT error). This indicator is established if package with table RMT for each identifier in table PAT does not appeared during 0.5 second, or packages with this identifier does not contain the identifier of the tables 0×02, or their field of the checking of the encryption is not equal to 00;
• Error in determination of the package identification (PID error). This indicator is established if for received identifier of the package PID the elementary stream is absent.

The second group includes the parameters for continuous and periodic monitoring.

• Error in transport package (Transport error). This indicator is established according to meaning of the package headline field of the transport error pointer. If indicator is established then for this package the rest parameters will not measure. It is recommended also count both the total number of packages with errors, and for each elementary stream separately. The values of identifiers of error packages and results of the measurement shall be fixed and saved;
• Error of the cyclic-redundance checking of all tables (CRC error). This indicator is established if corresponding table contains any error. The other indicators for this table do not established;
• Error in transmission of the sync signal of the master generator (PCR error). This indicator is established if an interval between time stamps is more than 40 ms;
• Error of the inadmissible leaving of the frequency of the sync signal (PCR accuracy error). This indicator is established if during adjusting of master generator the error on phase more than 500 ns is discovered;
• Error of the pre-selection time stamp (PTS error). This indicator is established if pre-selection time stamp are absent in stream more than 700 ms;
• Error of the conditional access table (CAT error). This indicator is established if the absence of the conditional access table is discovered.

The third group comprises some parameters, required in special case only.

All parameters are binary indicators. If an indicator is active, a transport stream contains a corresponding error.

Parameter control of DVB systems

The manual TR101290 defines both general main parameters for different systems of the TV signal transmission, as well specific parameters for air, cable and satellite systems. Also on different stages of the production and application of digital TV-transmitter the different parameters can be subjected to measurement. A part of parameters, recommended by TR101290, is included in drafts of national standards for corresponding equipment and from metrological side provides its issue. The other part, basically, can be used under exploitation of the transmitter. When a transmitter is checked as a path link during exploitation the minimum list of necessary parameters are the following:

• Measurement of BER (the bit-error rate) before Reed-Solomon and Viterbi decoders (for DVB-T and DVB-S);
• Analysis of I- and Q-signal with display of modular constellations and with measurement of modulation parameters (MER, EUM, STE and etc.).

The checking of the transmitter of any DVB system is possible according the scheme given on the figure. Herewith a measuring demodulator should be corresponded to the applied system (DVB-T, DVB-S or DVB-C).

The scheme of the parameter control of digital television radio transmitter

The generator of digital measuring signals forms the necessary signals in format of the transport stream MPEG-2. Measuring demodulator realizes demodulation of a signal and provides the measurement of DVB parameters. Its output signal is a transport stream MPEG-2, which is subjected to the analysis by means of the transport stream analyzer.

It is a possibility to carry out the measurements in process of the program transmission too. Herewith instead of the generator signal is used the signal of the TV-program source, and in this case an analyzer can additionally checking the signal at the transmitter input.

Below is the main specification to devices, which are shown on scheme (the requirements to measuring demodulator are stated in DVB-T version):

Generator of the digital transport stream

• MPEG-2 transport stream forming in accordance with ISO/IEC 13818 (ITU-T H222.0);
• Forming of “zero-packages” and pseudorandom sequence in accordance with the TR101290;
• In accordance with working mode of the DVB transmitter, a possibility of inclusion of the PSI and SI tables in transport stream and installation of the table NIT content;
• Stability of the frequency: 10^-6;
• Availability of the interfaces ASI and SPI;
• Possibility of the installation of the transport stream rates in accordance with the DVB transmitter working mode.

Analyzer of the transport stream (TS)

• Analysis of the MPEG-2 TS in real time scale;
• Analysis of the TS with different length (188/204 bytes);
• Determination of actual rate of multiplexed transport MPEG-2 stream;
• Determination of TS error in accordance with priority groups according to the TR 101290;
• Logging of TS check results;
• Mode of the TS monitoring;
• Viewing of the programs inside TS;
• Measurement of the phase jitter of the program chosen by user from TS according to the document TR 101290.

Interfaces

• Synchronous parallel in accordance with standard EN 50083-9 (TS Parallel);
• Asynchronous serial in accordance with standard EN 50083-9 (signal receiving rate is 270 Mbit/s) (TS ASI);
• The measuring digital TV demodulator DVB-T;
• Frequency range of input signal is from 170 to 230 MHz and from 470 to 862 MHz;
• Bandwidth for channel is 8 MHz, 7.61 MHz;
• Possibility of the recognition and automatic adjusting in working mode of digital TV-radio transmitter with display of the transmitter working modes: OFDM dimensionality is 2K/8K; the applied modulation types are QPSK, 16QAM, 64QAM; the guard space values are 1/4, 1/8, 1/16, 1/32; the digital stream rate is in the range from 4.98 to 31.67 Mbit/s;
• Measurement of the bit error rate (BER): to Viterbi decoder, from 10^-2 to 10^-4, after Vitterby decoder is 10^-7;
• Measurement of the modulation parameters with display of the I/Q diagram: MER (modulator error rate), EVM (the value of the error vector), STEM (the average value of system error of constellation points), STED (deviation of system error of constellation points), AI (amplitude disbalance), QE (quadrature error), PJ (phase jitter);
• Availability of the output of demodulated transport digital stream on SPI and ASI interfaces.

When performing the measurements of digital television transmitters it is used the measuring devices, designed by NTK-18 FGUP NIIT (“Scientific-research institute of the television”), or similar technical means.

The devices for measuring of parameters of digital broadcasting TV, produced by NTK-18 FGUP NIIT

Name of measuring device Indication of measuring device type, number of the certificate about its approve as means of the measurement

Analyzer of digital television transport stream ATP-1, Certificate of Russian Gosstandart #14730/2, is registered in State Register of measuring means #24762-03

Generator of digital television test signal G-420, Certificate of Russian Gosstandart #11611/2, is registered in State Register of measuring means #22442-02

Measuring digital television demodulator DVB-T DCT-1, is produced from IV quarter of 2004 year.

Auxiliary measuring facilities for checking of digital path parameters in analog presentation:

TV monitoring analyzer ATM-2, Certificate of Russian Gosstandart #3370, is registered in State Register of measuring means #17243-98

Audio channel meter IZK, Certificate of Russian Gosstandart #5894, is registered in State Register of measuring means #17971-98

Note. The auxiliary measuring facilities can be used for checking of through digital path. There the generator forms the traditional measuring signals of the analog TV in digital format, but auxiliary measuring facilities are connected to path output and provide the analysis of signal in analog presentation.

Features of the analyzer of the digital TV transport stream ATP-1

The analyzer ATP-1

The analyzer of the transport MPEG-2 stream ATP-1 is intended for correctness checking of formed transport MPEG-2 stream according to standard ISO/IEC 13818-1 in real time scale (monitoring), for viewing of system information and TS composition, determination of TS rate and phase jitter of programmer tacts. The analysis of the transport stream is carried out in accordance with the document TR 101290. The results of the analysis are displayed on built-in LCD-display and are stored in permanent memory of the unit.

Name of measuring device	Indication of measuring device type, number of the certificate about its approve as means of the measurement
Analyzer of digital television transport stream	ATP-1, Certificate of Russian Gosstandart #14730/2, is registered in State Register of measuring means #24762-03
Generator of digital television test signal	G-420, Certificate of Russian Gosstandart #11611/2, is registered in State Register of measuring means #22442-02
Measuring digital television demodulator DVB-T	DCT-1, is produced from IV quarter of 2004 year.
Auxiliary measuring facilities for checking of digital path parameters in analog presentation:
TV monitoring analyzer	ATM-2, Certificate of Russian Gosstandart #3370, is registered in State Register of measuring means #17243-98
Audio channel meter	IZK, Certificate of Russian Gosstandart #5894, is registered in State Register of measuring means #17971-98

Information displayed on LCD has a multi-level menu structure that provides its lighter and suitable perception. ATP-1 can work autonomous and remotely (from personal computer). In the case of remote imaging of data, the operator gets more detailed and pictorial information about checking transport MPEG-2 stream with broader tuning possibility. Software is shell, executed as 32-bit Windows-application. For functioning in remote mode it is necessary a personal computer, compatible with IBM, not below Pentium class with free RS-232C interface.

The operating and indication controls are laceted on front panel of the analyzer. On back panel are located the input and output connectors, the connector for connection of the remote control cable, the connector of the connection of the network voltage, the fuses and the earth link.

The features of the ATP-1 are as follows:

• Analysis of the MPEG-2 TS in real time scale;
• Through pass of transport MPEG-2 stream from any single interface to all interfaces;
• Analysis of the TS with different length (188/204 bytes);
• Determination of actual rate of multiplexed transport MPEG-2 stream;
• Determination of effective rate of each program of multiplexed transport MPEG-2 stream and each PID separately;
• Determination of TS error in accordance with priority groups according to the TR 101290;
• Logging of TS check results (up to 255 recordings);
• Mode of the TS monitoring;
• Adjustment of analysis parameters;
• Analysis of the system information tables (SI/PSI) of the transport MPEG-2 stream;
• Viewing of the programs inside TS (up to 16 programs with 8 components in each of them);
• Measurement of the phase jitter of the program chosen by user from TS;
• Operational mode with output on PC display the current information on TS, errors, PID, PCR, with possibility of more detail processing (with interface RS-232C, optionally);
• Multi-layered structure of menu;
• Maximum rate of the input transport stream is 54 Mbit/s;
• The interfaces: synchronous parallel in accordance with EN 50083-9 (TS Parallel), asynchronous serial in accordance with EN 50083-9 (the rate of the signal receiving is 270 Mbit/s) (TS ASI), parallel port LPT (technological), serial port RS-232C;
• Indication: 6 LEDs and LCD-display with four lines.

The features of the television test signal generator G-420

G-420

The generator of TV test signal G-420 provides:

• Forming of the transport MPEG-2 stream, containing the test dynamic tables and scenes for express-test;
• Forming of “zero-packages” and pseudo random sequences in accordance with the document TR101290;
• Forming of the test lines in active part of frame for checking of digital paths in accordance with “Temporary norms…”;
• Forming of the multi-programmed stream;
• Adjustment of an the transport stream rate within the range from 2 to 216 Mbit/s with the 200 bits/s accuracy;
• Possibility of the inclusion the PSI and SI tables in transport stream;
• Possibility of the editing of the table NIT content;
• Possibility of the setting of the transport stream parameters: program_number (service_id), program_map_ PID, elementary_PID;
• Availability of interfaces ASI and SPI;
• Forming of uncompressed digital stream in SDI (video) and AES/EBU (audio) formats;
• Possibility of the signal composition change and adding of new signals under connection with computer.

NTK-18 FGUP NIIT is designed the methods of the measurements of the digital TV radio transmitter parameters by means of above mentioned measuring equipment.

Material is provided by NTK-18 FGUP NIIT