Coders and decoders from Tandberg Television Company

By Lavrshin

Review contents:

MPEG-2 coders and decoders MPEG-1/-2 coders from Canopus Orca coder from Doremi Labs Company Optibase card for MPEG-coding/decoding Professional MPEG-2 coder with IP MGW 2000 output. Main possibilities and applications MPEG Pinnacle Studio MovieBox USB coder Coding devices of the Streampress Encode Series Equipment for MPEG coding and decoding from Scopus Network Technologies company MPEG coders from Sigma Designs Company Professional decoders MPEG-1/MPEG-2 Stradis Coders and decoders from Tandberg Television Company MPEG-2 coders from lower price ranges

Introduction

The whole TV-signal possesses a certain redundancy. So, for instance, if the technical possibility to exclude all empty gap in spectrum of the videosignal is existed, that we can have the real spectrum with band 400 kHz only instead of 5 MHz, but at present such possibility is unknown. The simple analogue-to-digital transformation of the videosignal brings to increase of the occupied frequency band in tens, and so it is incompatible with existing communication link with bandwidth from 8 to 40 MHz.

Solve the task of the digital content transmission on communication channels has been able for the expert group on moving pictures (Moving Pictures Expert Group). The Tandberg Television Company took the active participation in functioning of this group, begun in 1992. In 1994 the International MPEG-2 standard was appeared. For HD-television (HDTV) MPEG-3 standard was intended, subsequently jointed with MPEG-2 and stopped its independent existence. At present over 300 production companies support the MPEG-2 standard and DVB principles that means compatibility of the equipment which produced by different companies and provides filling of 16 tables, provided by MPEG-2 standard, as well as introduction of all instructions, under which a receiver must this stream “to unpack” to MPEG-stream. Existed at the time of making the MPEG-2 standard the communication channels differed both by bandwidth and by degree to noiseproof. For satellite communication link under analogue transmission of the signal (FM) a bandwidth from 27 to 36 MHz was typical, but impulse signal/noise (S/N) at the input receiver 10.5 dB, so for digital satellite transmission the QPSK modulation was offered. Its use has allowed providing the hard communication at S/N ratio up to 6 dB. For cable networks a bandwidth 8 MHz was typical (in Europe, Asia, Africa and Australia), but S/N ratio at the input of analogue receiver was 46 dB (under amplitude modulation), so for digital transmission at cable networks QAM64 modulation is used, allowing at S/N ratio 24 dB at the input digital receiver to provide the reliable communication. The structured scheme of main station is given on the following figure. In spite of variety of the facilities for the signal spreading, the core and unchangeable section of the system is the compression devices and, certainly, the coders.

Coders from Tandberg Television

Tandberg Television produces the broad model row of TV coders (SD and HD). SD coders E5710 and E5720 use the method of the double “picture” passage and algorithm of the prediction of the motion vector. These operations provide the high quality of the picture even under low rates. As option, it is possibility to load of software, allowing working at minimum rates (down to 0.256 Mbit/s).

Most popular Tandberg Television’s coder models: E5710 (top) and E5720

In spite of it modest size, 1RU coder E5710 allows to compress one video- and two audio (the stereo) signals; it provided by data input RS-422 (from 64 to 2048 kbit/s) in base completing, as well as two free slots that allows to add two modules according to customer will. For instance, it is possible to use the multiplexor module and get the coder with possibility of re-multiplexing of additional digital streams DVB-ASI or to install the audio stereochannel modules as well. On front panel coder is found the two-line display and 6 control buttons, by means of which it is possible to set the coding modes. The main features of E5710coder are the following:

• Analog video input or SDI (10-bit ADC, PAL and NTSC);
• Audio inputs AES/EBU or analog (built-in 20-bit ADC);
• Coding in 4:2:0 MP@ML and 4:2:2 P@ML;
• Horizontal resolution: 720, 704, 640, 544, 480 and 352 pixels;
• 625 and 525 lines;
• GOP structure is configured over a wide range. The GOP value is from 1 to 12 (for 1 the structure looks as IIIIIIIIIIIII, for 12 — as IBBBPBBBPBBBI).

A logotype can be loaded in coder from computer. In the event of disappearing of the input signal advertising logo is swithed on, which also can be loaded from computer.

The coder E5714 version has built-in QPSK-modulator and output of L-range. Such coder is very suitable for signal transmission from place of event (DSNG). Only a connection with antenna SHF-block and a connection of the camera on input are required.

The coders of E5720 series differ from E5710 by twice height and have twice more varieties of the extension of the functional possibilities. The modules AC-3 5.1 can be installed under customer will. The front coder panel has 20 buttons and multiline liquid-cristal display, imaging input signal in the manner of live pictures.

Both coders can be used as independent blocks, as well as in composition of the compression system. In the last case the control system TDC or MEM is used, designed by Tandberg Television. The control system is connected with each of block via Ethernet or RS-232 interfaces and provides the back-up, as well as controlling of coding parameters.

Reflex System

Example of the Reflex system operation

The interesting decision of the company Tandberg Television, allowing spare the transponder band or place the greater amount of the programs, is a Reflex system. It provides the statistical multiplexing. The system of the statistical multiplexing gives the advantage to account that in one transport stream the several television programs are sent. For instance, translation of the tennis tournament from Wimbldon can require the significant resource since in this case the picture of the small tennis ball is sent, which with top speed flies through the whole court (up to 7 Mbit/s). At the same time, the transmission of weather forecast occupies about 2 Mbit/s. The task of the Reflex system consists in quick redistribution of the resource between different television programs.

Example of the bit rate reduction for three statistically multiplexed streams

The bit rates of the source digital programs are changed thereby that output multiplexed stream has strictly constant total rate in spite of the fact that each of television programs can change the bit rate within range from 1.5 to 10 Mbit/s. For change of stream rates, which come from the other sources, Tandberg Television uses BRC (the device of the bit rate change), controlling by the same Reflex system. As entering transport streams can emerge as signals, received from satellite, from ATM-network, so and signals from TV server. It is a possibility to apply some different modes of the Reflex system.

Circuit controlling the bit rates reduces the rate each of them thereby that on output is got a new statistical multiplexed stream with total rate with summed rate below than sum of the input stream rates. Be the events, when input stream contains the television programs with constant rate, and is required to reduce the rate to skip it via narrow-band channel. For decision of this task the same Reflex system can be used, which is given on the following figure.

Reduction of rate of the stream, containing programs with constant rates

In Russia enough often form the situations, when television companies require the certain parameters of their signal transmission. In this case the Reflex system can help also, allowing from statistical multiplexed stream to get the transport MPEG stream once again, in which each program occupies strictly determined constant rate.

Coder module for TT7115/TT7116

At the beginning of this article was mentionned that any coder can work as multiplexor. But company Tandberg Television does not stay on place, and the most interesting from the last decisions is a development of the coder card for multiplexor TT7115.

The coder module occupies one slot. Maximum number of slots within one frame is 10. This is the best technical decision for the case, when many coders are required. The module includes strictly coder of one videosignal, coders of two audio stereo signals and circuit of the information extraction of the framed interval. It provides the high quality of the coding in 4:2:0 MP@ML. The card of the module is provided with SDI input. The standards of the audio coding are Musicam and Dolby Digital AC3.

Coders for HD-television

HDTV is a priority direction of the development in USA and Australia. In USA ATSC standard is used, in Australia — DVB-T. In spite of difference in type of the applicable modulation, the core of the compression system is a coder. In common the processes of HDTV digitization and coding do not differ from that processes that take place in coder for SD-TV. The rate of input SDI-stream is 1485 Mbit/s. A short technical specification for HDTV E5821 coder is given below:

• SDI input (1485 Mbit/s);
• Audio input Dolby AC-3 5.1;
• Presentation 4:2:0 HMP@HML;
• Horizontal resolution 704 and 720 pixels;
• HDTV formats: 1080i/30, 1080i/29, 1080i/25, 720p/60, 720p/59.94, 480p/60, 480p/59.94;
• GOP structure is configured over a wide range. The size of GOP is from 1 to 12 (for 1 the structure looks as IIIIIIIIIIIII, for 12 — as IBBBPBBBPBBBI).

A logotype can be loaded in coder from computer. In the event of disappearing of the input signal advertising logo is swithed on, which also can be loaded from computer.

Other coding methods

Approximately at the same time, when committee DVB came to a conclusion about MPEG-4 inclusion (the part 10 in DVB), Tandberg Television company with Microsoft has offered the standard Windows Media 9 Series. This development more economical and provides the best quality under the same bandwidth. Unlike MPEG-4 encoding equipment Microsoft Media 9 Series is executed by hardware (EN5920 coder). The choice of such technical decision was made in accordance with Microsoft wishes. Future will show which standard win.

Tandberg Television decoders

There are decoders presenting itself an inexpensive device, intended for using in satellite, terrestrial and cable networks.

TT1220 satellite receiver

The satellite receivers TT1220 will convert input QPSK-signal in digital stream DVB/ASI, from which is extracted video- and audio information. The most popular model is a receiver with “Russian SECAM” option. The receiver can be supplied by additional stereoaudio output that allows to user to get from one transport stream the television and radio simultaneously. If receiving signal is locked by a system of the conditional access, there is beautiful possibility to use the module of the conditional access, got up it in slot on receiver back panel. It is possible to use the following systems of the conditional access: Betacrypt, Conax, Cryptoworks, Irdeto, Mediaguard, Nagravisio and Viaccess.

The receiver works in broad range of the input rates (from 0.75 to 45 Mbit/s). The front panel is provided with two-line display, and by means of 6 buttons it is possible to tune on receiving signal easy. Also there is jalousie on front panel, through which is realized forced ventilation of the receiver by means of built-in ventilator. The display is highlighted, so any adjustment can be to carry out even in the dark quite comfortably.

The advanced model is TT1260 receiver, which in addition to possibilities of TT1220 has also SDI, DVB/ASI, AES/EBU, RS-422 (from 64 to 2048 kbit/s) outputs, but the main thing that he works in presentation 4:2:2.

The receiver TT1220 of DVB-T standard differs from its satellite relative by HF part only. It supports all modulation types: QPSK, QAM16, QAM64. HF input — from 44 to 907 MHz, FEC from 1/2 to 7/8, and protective interval from 1/2 to 1/32.

Network decoders

These decoders are produced under ATM (STM-1), E1, E2, E3, DS3 standards. They have the standard options, similar as on satellite receiver.

Descramblers

When use the standard receiver a possibility is given to open only one TV or radio program. For increasing of available programs number the descramblers are used.

Tandberg descrambler

System of the conditional access	Descrambler type
Irdeto, Betacrypt	TT5010
Conax	TT5031
Mediaguard	TT5032
Nagravision	TT5033
Viaccess	TT5034
Cryptoworks	TT5035
Videoguard (NDS)	TT5020

Often by means of one smart-card it is possible to open the transport stream at whole, including radio and television. Depending on coding mode the number of required smart-cards is changed. For different types of the conditional access systems some different types of descramblers are used:

Material is provided by I.S.P.A.-Engineering Company