Equipment of the the IMOS Company

By Vladimir Bogdanov, Denis Kustov, Sergey Tretiyak

Review contents:
MPEG-2 and measurements TV Network Monitoring Equipment of the the IMOS Company Going digital with program insertion — challenges and solutions Innovative T&M system for MPEG-2 monitoring and analysis Systems from Snell & Wilcox for testing, estimation and checking of MPEG streams Video test and measurement equipment

Introduction

The digital TV in Russia takes the turns slowly, but confidently. Either as any new type of the issue to information, the digital TV, anyway, must pass the certain stage of its development. In common it is possible to select the following stages: choice of the most suitable standard of the information transfer as a whole, development of state standard, development of the canal equipment from devices of the digital information forming to receiving devices, development of checking and measuring equipment.

Unlike the Russian sphere of the telecommunications, where is basically used the foreign equipment, the digital TV in Russia can be based on its own equipment, since and overseas this direction is in development stage.

Work in this area is carried out by different Russian manufacturers. In particular, the development of DVB/MPEG-2 checking and measuring equipment is provided by scientific-research complex “IMOS” from Saint Petersburg.

Measurements in MPEG-2

Since for digital TV in Russia the European DVB specification have accepted, so all specifications, referring to DVB, including standards ISO/IEC 13818 (MPEG-2), is quite reasonable to take as base of state standard for communication channels and equipment. In Europe in the group of documents and specifications for digital TV the recommendation for measurements in DVB is included, which last version ETSI TR101.290 v1.2.1 “Digital Video Broadcasting: Measurement guidelines for DVB system” have issued in 2001. This recommendation contains in itself the ideas and prescriptions of measurements in MPEG-2, DVB-C, -S, -T. It is necessary to note the main idea of this recommendations specifically, i. e. a measuring equipment of the alike purpose, produced by different manufacturers, must give the correlated results of the measurements of the same parameter provided that measurement adjustments are same.

In section of the measurements in MPEG-2 transport stream the recommendation TR101.290 separates the measurements on check of syntax and structure and measurement of physical parameters of MPEG-2 stream.

Checking the structure and syntax is divided into three priority groups:

• First priority: the parameters required for confident decoding of the transport stream;
• Second priority: the parameters for continuous and periodic monitoring of the stream;
• Third priority: the parameters, which are necessary only in special cases.

The conditions and algorithms of estimation are determined for all parameters. The mistake is the execution of any condition for considered parameter.

Measurement of data rate and jitter is considered as measurement of physical parameters of MPEG-2 transport stream. For these parameters the profiles are incorporated, which define the correlations between quality and duration of the measurement. So, the most exact measurement will be the most slowly, and conversely.

The measurement of the rate of MPEG-2 transport stream is divided on five profiles. Depending to chosen profile it is possible to measure as constant, so and variable rates of MPEG-2 transport stream. The jitter subdivides on four components:

• Deflection of the frequency (PCR_FO): is defined as any difference between transmitted frequency of program beats and nominal clock rate;
• Drift (PCR_DR): is defined as the first derivative of the change the frequency and is measured on component of the low frequency program beats at differences between transmitted frequency of program beats and nominal frequency of beats;
• General jitter (PCR_OJ): is defined as change of radio frequency components and is measured by difference between transmitted frequency of program beats and nominal beat frequency;
• Accuracy PCR (PCR_AC): is defined as difference between transmitted value of PCR and value, which must be in transport stream, presented by byte index for its temporal actual position.

It is necessary to note the principle difference between measurements of PCR accuracy: from the one side, and frequency deflection, from another side — drift and the general jitter. In the first case the difference is calculated between transmitted PCR value and its actual temporal position in transport stream. In the second case the difference between transmitted PCR value and nominal value of the clock rate with provision of frequencies of the delimitation is calculated. All delimitation frequencies are straight on depended from one of four profiles chosen by user.

Besides, recommendation TR101.290 defines the types and parameters of test signal for checking of communication channels such as zero-packages and pseudorandom sequences, as well as test signals, containing different components of the program beat phase jitter for checking the measuring equipment.

Measuring equipment

In IMOS Company the works of three directions are conducted, referring to measurements in MPEG-2: development of MPEG-2 transport stream generator, MPEG-2 transport stream analyzer, as well as MPEG-2 picture quality analyzer. There are the development and production of generators G-410 and G-420 of digital measuring signals, as well as the MPEG-2 transport stream analyzer ATP-1. All these instruments have passed the certified test of Gosstandart RF for the reason of the type of the measurement means assignment, are enclosed in state register of the measurement means and approved for use in Russian Federation.

The generator G-420 is used for checking of TV broadcasting digital system parameters, using the digital stream compression in accordance with MPEG-2 standard and complied with the requirements of European DVB standard. Also, the generator is used for check of workability capacity of transmitters by standards DVB, ATSC, encoding video devices on signal in SDI format, audio MPEG-2 encoding devices, decoding MPEG-2 devices, digital communication paths and satellite channels.

G-410 and G-420 digital test signals generators

The generator G-420 provides more than 20 different MPEG-2 transport streams: dynamic tables, zero-packages, pseudorandom sequences 2K and 8K, test scenes, recommended ITU, special transport stream for checking of communication channels. Also, the generator produces the uncompressed signals in SDI format. Amongst MPEG-2 transport streams, which the generator are produced, there are multi-programmed as well. All MPEG-2 transport streams are provided with individual adjustments which are saved up to their change by user. The transport stream rate is adjusted within the range of 2…216 Mb/sec, the length of the package (188/204 bytes) is chosen, there are adjustments of the tables PAT, PMT and NIT. Any table SI/PSI, contained in transport stream, is possible both as include, so and exclude. Under connection to generator of such peripherals, as monitor, keyboard and mouse, an user can at own discretion to correct the streams, to enter the intentional errors, as well as to write the new streams. The generator can operate remotely, such as by an external personal computer and by corresponding software. Any group of adjustments can be saved in memory, but then it quickly extract. For autonomous functioning on faceplate of G-420 there are single-lined LCD and eight control buttons. LCD display the signal name loaded in memory or one of the adjustment parameter.

The following modes and issues are chosen by operating controls:

• Working generator modes: SETUP, MPEG or SDI;
• Formed signals. In MPEG mode: one of the dynamic tables; one of the test stream ITU; one of the pseudorandom sequences; the zero-packages. In SDI mode: dynamic table; one of the static tables (scenes); the signal of the test lines in active part of raster; the color bands;
• Audio signals (in AES/EBU mode);
• Transport stream rate (in MPEG mode);
• Channel number (in MPEG mode);
• Program number (in MPEG mode);
• Program identifier (PID) for PMT table of chosen program (in MPEG mode);
• Elementary stream (in MPEG mode);
• Type of the consequent coding of frame differences (in MPEG mode);
• Program identifier (PID) of the elementary stream (in MPEG mode).

In mode Setup it is possible to install the time lag, and as this time passes, on display the information on earlier chosen working mode is restored in that case if operating controls are in the rest.

The generator has portable and rack mount versions of the design.

The main features of the G-420 are as follows:

• Forming of the transport stream, containing the test dynamic tables and test video clips for express-analysis;
• Forming of zero-packages and pseudorandom sequences in accordance with recommendation TR101.290;
• Forming of multi-programmed transport stream;
• Possibility of the installation of the uncompressed transport stream within the range of 2…216 Mb/sec;
• Forming of uncompressed digital video stream in SDI format;
• Forming of uncompressed digital audio stream in AES/EBU format;
• Possibility of the intentional error introduction;
• Possibility of the editing of the signal composition by means of external PC;
• Recording of new test signals by user by external PC;
• Control convenience and simplicity of both with faceplate, and with peripherals (connecting keyboard and monitor).

The interfaces:

• Asynchronous serial (ASI) in accordance with EN 50083-9;
• Synchronous parallel (SPI) in accordance with EN 50083-9;
• Serial RS-422;
• Serial digital SDI and AES/EBU.

The generator G-410 is the simpler and cheaper version of the generator G-420.

The analyzer of the digital MPEG-2 transport stream ATP-1 is intended for checking of correctness of formed MPEG-2 transport stream according to the ISO/IEC 13818-1 standard in real time (monitoring), viewing of system information and composition of the transport stream, determination of the transport stream rate and phase jitter of program beats. The analysis of the transport stream is produced in accordance with recommendation TR 101.290. The results of the analysis are displayed on built-in LCD and are saved in permanent memory of the instrument. The information displayed on a screen, has a structure of multi-level menu that provides easy and convenient control.

ATP-1 transport stream analyzer

ATP-1 can work as autonomous, so and remotely (PC control). In the case of remote control the operator can get more minute and demonstrative information about checking MPEG-2 transport stream with more wide adjustment possibility.

Software is a shell, executed as 32-bit application for Windows. For functioning in remote mode should be provided a personal computer, compatible with IBM (Pentium or later model with free interface RS-232C).

The analyzer is manufactured in rack or mobile version. Operating controls and indicators are located on faceplate of the device. On backboard are located the following facilities: input and output connectors, connectors for remote control cable or power cable, as well as fuses and earth.

The main features of ATP-1 are as follows:

• Analysis of the MPEG-2 transport stream in real time;
• End-to-end passage of the MPEG-2 transport stream from any single input interface to all output interfaces;
• Determination of actual rate of multiplexed MPEG-2 transport stream;
• Determination of efficient rate of each program of multiplexed MPEG-2 transport stream and each type of the package (PID) separately;
• Reception of the transport stream with package of 188/204 bytes;
• Determination of transport stream error in accordance with three priority groups according to recommendation TR101.290;
• Logging of the transport stream checking results (up to 255 records);
• monitoring mode of the transport stream;
• Adjustment of analysis parameters;
• Analysis of the system information tables (SI/PSI) of the MPEG-2 transport stream;
• browsing of the program composition inside transport stream (up to 16 programs on 8 forming);
• Maximum speed of the transport stream is 54 MB/sec;
• Measurement of the program beat jitter tact of the program selected by user according to recommendation TR101.290;
• Measurement of the input transport stream rate according to recommendation TR101.290.

The interfaces:

• Synchronous parallel in accordance with EN50083-9 (TS Parallel);
• Asynchronous serial in accordance with EN50083-9 (TS ASI);
• Serial RS-232C.

Analyzer control:

• Six buttons on faceplate;
• Serial port RS-232C.

Indication:

• Six LEDs of the first priority in accordance with recommendation TR101.290;
• 4-line LCD-display.

At present the development of the picture quality analyzer AKI-1 is in progress. The main difficulty of design of this instrument is an achievement of high correlation between objective evaluation, got this instrument, and subjective assessment.

It is necessary to note some new projects of IMOS in joining of the satellite receiver with the transport stream analyzer in one case. There is an intention to create a mobile version of this unit provided by external controls from notebook and with display of the receiving information on its screen. Also the work to implement the transport stream parameter reliability checking in this analyzer is carried out.

Remote monitoring

The important working direction is the creation of the systems for remote monitoring of digital stream. The Recommendation TR101.290 on measurements in DVB system defines the nomenclature of analysis parameter at the level of MPEG-2 transport stream in DVB transmission system. The measuring procedures are determined as for regulate measurements (outside of service), so and in process of the program transmission (monitoring).

The ETSI specification TS102 032 v1.1.1 “Digital Video Broadcasting; SNMP MIB for test and measurement applications in DVB systems”, issued at April 2002, is dedicated to remote monitoring of digital streams. In this specification the information base MIB is determined, which must be created in any measuring facility, used in mode of the remote monitoring in accordance with TR101.290 recommendation. This specification will be applying in the first place in analyzer of the MPEG-2 transport stream ATP-1.

The Specification TS102 032 comprises whole administrative information required for functioning, and gives the description of database for all TR101.290 parameters, suitable for network measurements.

Though at present the recommended base MIB is exhausting, any time when TR101.290 has been complemented, the MIB must be complemented too. The access to this base is realized by means of SNMP protocol, which was chosen as the most-eligible for this case.

The information base MIB includes the results of the measurement in specified format. They can be inquired, accepted and analyzed by the network manager.

In reality the structure of MIB is a file with information, presented hierarchically. Each module in this structure is assigned by its unique object identification number (OID). This enables to equalize the priorities of different information, receiving from measuring instruments, containing MIB and integrating in the monitoring system of the technical status.

Also, to each parameter in MIB its own identification number is assigned. Thereby, the different measuring facilities, residing in monitoring mode, shall not be in conflict between them in network.

The component part of MIB is a table, giving the full presentation about measured parameters, supported by corresponding measuring facility.

MIB introduce some notions and determinations, providing structuring of the received measuring information. In particular, the determinations “Errors of the condition” and “Errors of the event” are entered. According to TR101.290 all disturbances during the monitoring process MIB divides into indicated two categories. The error of the condition can take such value as “standard” or “defect”, defined for any time point, but error of the event is defined as manifestation of the separate event. For “Error of the event” class is no evident way of the reception of the continuous checking of the condition (standard/defect), and instructions on this cause the TR101.290 does not give. However for the monitoring it is very advisable to carry out this condition checking continuously for any used test. Considering for this case decision is a determination of time, during which the information about the past event is saved.

By measuring facility the MIB provides a forming so named TRAPS that are messages, dispatching by instruments to the network manager. The inadmissibility of the system overfilling under transmission of such messages is the native restriction.

When MIB forming in any measuring facility it is necessary to take into account that this information base is originated rather as instrument for control of measuring results, then as control system for measuring instruments.

To realize the base in measuring instrument it is necessary to integrate in its structure an Ethernet-controller, which must include a server with assignment of an Internet individual address. Such equipment presents itself a new device class, functioning within the framework of Internet infrastructure.

Material is provided by IMOS Company