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DIGITAL TELEVISION IMPLEMENTATION SOLUTIONS

M A Aitken COMARK Communications, INC., USA, (a THOMCAST company)

ABSTRACT

The first UHF transmitter for “THE MODEL STATION PROJECT” has been installed in the U.S. This has provided equipment manufacturers and suppliers an opportunity to deal with some of the real challenges of deploying a digital broadcast television service. This project was formed for the purpose of designing, installing and operating the first full digital HDTV station in the U.S. In a similar US. context, involvement with the National Institute of Standards and Technology supported “HDTV BROADCAST TECHNOLOGY RESEARCH COLLABORATIVE” has allowed an understanding of many technology gaps that must be closed.

This paper will discuss some of the new technology opportunities and choices being made as a result of the increased awareness such activities make available to broadcasters and manufacturers.

INTRODUCTION

The digital era for broadcasters is certainly here. Every bit of news today confirms that reality. The announcements in the U.S. by the FCC about the ATSC (Advanced Television System Committee) standard for DTV (Digital Television), the FCC allocation of digital spectrum for Tv broadcasting and the wide variety of possible content in the form of pictures, sound and data open revolutionary new digital service opportunities. DVB’s aggressive deployment and adoption provide similar opportunities.

In this fast paced arena of television broadcasting, new products and services are required to meet the diverse needs of U.S. and international customers. These new broadcast transmission and distribution technologies are in various stages of development. The integration and implementation of these technologies, within the studio as well as the transmission site, demand a new level of understanding. What follows is a partial understanding of some of the available solutions.

NEW TRANSMISSION PRODUCTS

The industry has seen many new products being brought to the market. COMARK has introduced, what has become over the course of this year, a

new family of transmitters, the AdvantageTM series.

This UHF IOT (Inductive Output Tube) product has features and benefits which were developed in direct response to market driven wants and needs. Given some of the diverse power levels proposed and most likely to be implemented, the product range has grown to cover power requirements of 2.5kW average on the “IOW power” end up to power levels in excess of 1 OOkW average. This broad range of powers can be addressed by using both air-cooled and water-cooled IOT products available from a variety of manufacturers.

There is also a new generation of Solid State LDMOS products coming to market which will fill a portion of the lower power requirements for UHF broadcasters.

Control

The AdvantageTM series IOT transmitter offers a user friendly “Distributed Intelligence System Control”TM (DISC) approach to facility control, allowing for easy integration into the facility environment. The Man Machine Interface (MMI), which is GUI (Graphical User Interface) based, and the overall system architecture is shown in Figure I. This control approach is typical in most of the new broadcast transmitter products being offered today, Solid State and tube alike.

International Broadcasting Convention, 12-16 September 1997 Conference Publication No. 447, 0 IEE, 1997

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The MMI allows the use of a standardized interface to control the system, and the use of a GUI allows users to select pictures and depiction’s of that system with which one is familiar. Additionally, the enhancing capabilities of a CD drive and Modem in the MMI computer can be added. This can be used to supply context sensitive help and instructional materials with a wide variety of text and descriptive pictures to guide the user. (Schematics, Parts, Maintenance operations, etc.) Support personnel can Interactively assist users in operation and maintenance of their system.

Advantages of this system approach are;

1.

2.

3.

4.

5.

6.

Fiber optics eliminate complex and unreliable inter-wiring harnesses and connectors.

Measurements are designed to be accurate since they are developed inside intelligent nodes and are absolute and presented in digital code to the central controller.

No common mode signal problems. Each measurement is made at the voltage it is measuring.

Absolute records maintained on all measurements and adjustments.

Automatic calibrations from the central controller.

Adjustments to all operating parameters are made as digital commands to the intelligent nodes.

With the addition of a sophisticated touch screen display system and diagnostic software, it is possible for the operator to locally and remotely control and analyze major aspects of the system, and provide an active network environment for the needs of more complex systems (Figure 2). In many cases, factory support and repair or work arounds can be done without actually traveling to the transmitter site.

All Digital 8-VSB Exciter

The newly developed 8-VSB modulator must conform to all the recommendations put forth by the ATSC documents relating to the transmission characteristics of the D N signal. In this new generation of ATSC compliant DTV

product, special interest has been placed on the proper utilization of the inputted encoded GA transport stream. The modulator takes the GA input digital video data stream and performs data randomization and adds the Reed-Solomon error correction coding. The signal then goes through data interleaving and trellis coding. Segment and field sync are inserted into the signal along with the small pilot signal.

Digital VSB

The ATSC compliant modulator uses a company proprietary digital filtering technique to generate the side band shaping required for the 8-VSB signal. This Vestigial sideband characteristic is precise enough to eliminate the need for any additional analog SAW filter device (Figure 3). Digital filtering is required to ensure optimum DAP system performance (discussed below). The elimination of any analog process at this stage ensures that the digital signal at the DAP’s input is essentially error-free. The exciter also provides for converting the signal to its proper on-channel frequency. (Figure 4)

Digital Adaptive Predistortion (DAP)

This newly developed DTV Exciter incorporates a unique approach to signal pre-correction. Digital Adaptive Predistortion (DAPE) is an integrated function of this ATSC conforming D W Exciter, as well as future DVB-T products. The technology is an extension of long having been a leader in the field of pre-distorting the transmitted signal so that non-linearities generated in the transmitter (in-band and out-of-band) are canceled out. In a severely compressed system it is easy to depict the effect of proper linearization by looking at the resultant out- of-band products spectrally as in Figure 5.

The effect of this correction is to increase the available noise margin (SNR signal to noise ratio) within the system. SNR can be directly related to Error Vector Magnitude (EVM). SNR can be defined as the ratio of the average symbol power waveform over the average noise power. This average noise power may be anything that causes symbol deviation (additive noise, distortions, ISI, IM’s etc.) SNR takes into account both linear and nonlinear distortions of the in-band signal.

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This full DTV Exciter with DAPE automatically monitors any distortion in the final output signal and adapts its internal digital correction circuitry to compensate for transmitter non-linearity. It provides for precise digital correction of the various amplitude and phase distortions created by system level non-linearities, and provides operational performance not possible with analog and other digital correction techniques. Since the correction is adaptive, it does not require the operator to spend hours making maintenance adjustments. Instead the signal is insured to be good quality at all times without operator intervention, even at different power levels. The technology approach is essentially “Digital Feed Forward”. Figure 6 is illustrative of performance levels achievable with the application of DAPE with the severe compression corrected for as illustrated in Figure 5.

This proprietary technology eliminates the need for manual correction. It provides for full-time monitoring and adaptive correction of the entire RF system envelope. It provides effective correction for system variations of many kinds, such as:

1. Line voltage variations 2. Temperature variations 3. Amplifier device aging 4. Out-of-limits conditions

The ultimate measure of a transmitter‘s performance (quality) will be based on the effectiveness of this DAPE technology.

Designed as platforms which support world digital transmission standards, both ATSC as well as DVB-T at all power levels, these new series of transmitter products are finding world- wide applications. Air-cooled and water-cooled IOT devices are available from all of the major current tube suppliers, including EEV, TTE, and CPI (and perhaps Litton in the near future).

STUDIO FAClLlN ISSUES

In the US, companies are playing a major role in supplying new technologies and developments through its involvement with “The Model HDTV Station Project”, the David Sarnoff Research Center led “HDTV Broadcast Technology Team” and other interelated initiatives. All of these initiatives are aimed at providing the broadcast industry with the technologies, tools and understanding to implement the FCC adopted ATSC standard. As well, members of the ATSC organization will be bringing these technologies for demonstration to the world market for future acceptance.

“HDTV Broadcast Technology Team”

COMARK is a member, along with several other leading U.S. companies (Sarnoff, Thomson, Philips, IBM, MCI, Sun Microsystems, Advanced Modular, NBC), of a NlST Advanced Technology Program (ATP) which is a focused co-funded research and development effort. This effort has identified the “key” areas of technology development which are required for broadcasters to make DTV, specifically HDTV, a practical reality. The primary program objective is to develop the required integrated solutions for HDTV studio operations and distribution. These include;

0 Network pass-thru operations 0 Live production

Program preparation 0 Editing 0 Browsing 0 Archiving

Play-to-air control

It is the intent of this programs participants to be able to show a comprehensive system approach which will support multiple levels of compression and quality (20-300Mb/s). This shall be done within an architecture based upon “single” wire connectivity and an ATM based scaled system approach to switching.

Some of the novel features of such a system will be;

0 “Real Time” compressed bitstream splicing

0 Effects and logo insertion in the compressed domain

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0 “Single” wire “Plug’n’Play”

0

0

0 Advanced automated logging with

0 Open “Object Oriented” system

connectivity Seamless control of remote sites Editing and browsing of compressed video databases

flexible archiving

architecture

All of this will give broadcasters the required technologies which will allow the commercial development of cost effective tools for broadcasters.

In support of the need to commercialize many of the technologies required new companies are being formed. COMARK DIGITAL SERVICES (CDS) is one such example which is bringing multiple solutions to broadcasters implementing Digital Television. Early adopters will require the most cost effective solutions which can be offered. One possibility may be a fully compressed solution. An example of such an approach is shown in Figure 7.

“The Model HDTV Station Project”

WHD-TV, which resides at the NBC WRC-TV4 host station in Washington, D.C., represents the most broadly supported DTV effort in the U.S. It is here that the primary tools required by broadcasters are being brought together to prepare broadcasters for a new learning experience. DTV is HDTV and a whole lot more. What DTV brings to broadcasters is the ability to work within an extremely flexible digital architecture that will support a variety of simultaneous program streams. These streams may be HDTV with Dolby AC-3 surround sound, it may be HDTV plus one or two SDTV programs, or it may be several SDTV programs. Additionally, there may be interactive ads and catalogues, or data broadcasting. The fact is the mix of content is almost variably unlimited.

Both of these efforts, the NlST “HDTV Broadcast Technology Team” and “The Model HDTV Station Project” will provide broadcasters worldwide with a visible focus of activities that should provide a detailed level of understanding of the related requirements of specific technologies and products.

INTERNATIONAL

Customers around the world are looking for similar turnkey facility responsibilities. In Europe, for example, pilot network requests involve the supply of equipment from the broadcast studio (source control, MPEG compression, etc.), through primary transport stream distribution (including ATM interfacing, transport stream multiplexing and multi-site distribution), broadcast site transmission and secondary distribution (site feed and conversion, high power amplification) and reception. Along with the primary equipment being requested, the responsibility of many of these programs extends to the providing of full integration and commissioning services for the “Global Chain” represented in Figure 8.

The approach taken is aimed at satisfying a number of expectations as to the functional capabilities of the entire Digital Video Broadcasting (DVB) chain. These expectations are:

0

0

Multiple TV channel reception HDTV in 16x9 format Hi-Fi sound Regional program reception Broadband data channel services Electronic Program Guides (EPG) and information services Multi-program enhanced (EPG linked) recording Portable/Mobile reception

All of these expectations are aimed at being able to provide a wide variety of programming services and applications over a broad national network. Some of the available Digital Terrestrial Television applications will include:

Free over-the-air program channels Pay-n/ program channels

0 Pay-per-view Internet (and related) access and services

0 Interactive multimedia Software distribution

These dynamically varied offerings of services require that broadcast providers focus on

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content, and define the new business models which will generate revenues from these (and potentially other) business opportunities. This focus on generating revenues requires that a large amount of the system issues be provided by a systems integrator. It is this type of large scale systems integration broadcast technology providers must be offering. The ability to offer such services is derived from the expertise and knowledge being acquired from a number of front-line digital initiatives providers have been involved with in the past, and continue to be involved with today.

CONCLUSION

In the world market, the technologies and equipment being developed and sold extend across the entire broadcast spectrum, and continue to fit the diverse requirements of multiple world digital standards.

The reason for involvement in these and other digital activities is clear. World class providers are offering the broadcast industry the combined produdt and intellectual resources to ensure that broadcasters can offer continued leadership in a rapidly changing and evolving broadcast market. The business tasks alone are difficult. We are giving broadcasters the opportunity to focus on those core challenges, while leaving the technology challenges to proven systems providers.

Figure 1 MMI System Architecture

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Figure 2 System Level Network Environment

Figure 3 CQMARK Proprietary Digital 8-VSB Shaping

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System Controller

Transport Stream Input r

Interconnection Power Supply Board

Corrected IQ Signal - RF Signal

Output RF Signal

I 7

Transmitter

Reference IQ

Serial Digital IQ Signal

Figure 4 Exciter Block Diagram

f r i s c L 7 .dF GFlV 3 4 P MUR A -3.25 MHz

REF -5.0 d8m #ATTEN 10 dB -44.84 d%

CENTER 751.00 MHz SPAN 28. BB MHz SWP 6.7 eec +RES 0W 30 kHz #VSW 300 HE I

Figure 5 Uncorrected/Corrected Transmitter Output Spectrum

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1 TRFiCE 8 : D l 5ipactrul.i 8 Murk.er 704 320 312.5 Hz -50.43 d61.r

LosMus

10 dB

/ d i v

-1 30 dRPi

EV M = 3. 8663 %riSis x pk ut SYl'l 458

Mug Err = 2.7324 %rinis -10.212 PL pk Ut S Y P I 154 Phase E r r = 3.3100 de9 40.410 des pk. ut syl'i 462

F r e q E r r = -9.4222 kHz P i l o t L v l -0.533

17.267

640 10110001 11000100 656 1100lli0 01001000 672 01010100 10100101 688 l0lilli0 11000100 704 0 0 0 0 ~ 1 l0li0010

Figure 6 Vector Analysis of Output Spectrum

Digital Turnkey System

Local Video Playback Network Pass-through &

NTSC -

t

20

3

[------' I 20Mb's I -

RS-422 1 c o y i

20 Mbls -? \

STi

20 Mbls Compressed Tape (DVCR)

Figure 7 Pass-through Facility

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DVB-T GLOBAL CHAIN Production Center #1

Figure 8 DVB-T Global Chain