2006 IEEE Ninth International Symposium on Spread Spectrum Techniques and Applications

Design, Simulation and Hardware Implementation of a DigitalTelevision System: System Overview

(Invitedpaper)

Jose M. C. Brito, Luciano L. Mendes, Fabbryccio A. Cardoso, Carlos A. F. Rocha and Dalton S. Arantes

Abstract - In the year 2005 the Brazilian government The main motivations that guided the development of thesupported many research consortia in order to develop an present DTV system are:advanced Digital Television System employing the most recenttechnologies for multimedia broadcasting. One of the . The SBTVD (Sistema Brasileiro de TV Digital -

proposals for the physical layer of this system was entitled . .Innovative Modulation for the Brazilian Digital TV System Brazilian Digital Television System) should have(MI-SBTVD). The MI-SBTVD Project includes high characteristics that facilitate the integration of services,performance error correcting codes, transmit spatial diversity such as e-mail and other multimedia services, in order toand multi-carrier modulation. The aim of this paper is to mitigate the so-called "digital divide".present an overview of this Innovative Modulation System. * The system should have high digital capacity, allowingThe building blocks of the system, its characteristics and most the transmission of High Definition TV (HDTV) orrelevant innovations are presented. The performance of the multiple programs in Standard Definition TV (SDTV).whole system under different channels is compared with the * The system should provide mobile phone reception usingperformance of the present-day Digital Television standards. in-band transmission. Signals for fixed reception and

Keywords - Digital Television, Channel Coding, OFDM mobile reception should co-exist through the same 6Modulation, Spatial Diversity, SBTVD. MHZ channel. This requirement is important since it

allows the broadcasters to develop new business modelsfor Digital Television.

I. INTRODUCTIONThe currently available Digital Television standards have This paper is organized as follow. Section 2 presents a

been conceived with technologies of the 90's. Since then, short introduction to the current Digital Televisionhowever, several important contributions have been standards; Section 3 presents the characteristics of theproposed for the new generations of digital wireless current system developed for the SBTVD; Section 4 showssystems. When these techniques are applied to the present- the performance of the proposed system under differentday Digital Television standards, a system with significantly channels and, finally, Section 5 presents our conclusions.higher capacity and robustness can be obtained. II CHARACTERISTICS OF THE CURRENT DTVAdvanced channel coding, modulation systems with STANDARDS

spatial diversity and efficient video compression techniquesare the key points to achieve higher capacity in a Digital In this section we discuss the three Digital TelevisionTelevision system. This paper presents the most relevant standards available today, the ATSC (Advanced Televisiontechnical innovations that were used in the implementation system Committee) developed in USA, the DVB-T (Digitalof the proposed wireless communication system for DTV Video Broadcasting - Terrestrial) developed in Europe andbroadcasting. The system is quite flexible and several the ISDB-T (Integrated Services Digital Broadcasting -different configurations allow transmission for indoor, Terrestrial) developed in Japan. The main characteristics ofoutdoor and mobile reception. The innovations reside these standards are presented in the next subsections.mainly on the Low Density Parity Code (LDPC) and the A. ATSCSpace-Time Code (STC) to allow transmission diversity. The ATSC standard has been developed by a group of

Jose M. C. Brito and Luciano L. Mendes are with the National Institute of companies called Grand Alliance. This standard wasTelecommunications - INATEL, Santa Rita do Sapucai, MG, Brazil adopted in USA in 1994 and its main characteristics are(brt dfeb, luinl(dnatel.br). Fabbryccio A. C. M. Cardoso and presented in Table I [1].Dalton S. Arantes are with the State University of Campinas - UNICAMP, ATSC does not support hierarchical transmission, aCampinas, SP, Brazil (cads DeoJeuiMapb, datn~ o fauesuprebytewothrsadd. Th signa tofee.unicam br). Carlos A. F. Rocha is with the Federal Univ. of Santa fetrsuptdbyhewotertaad.TesinloCatarina, UFSC, Florianopolis, SC, Brazil (auei.&eufsc.br). This work noise ratio threshold for acceptable quality is around 15 dBwas supported by FINEP - Financiadora de Estudos e Projetos and by in AWGN (Additive White Gaussian Noise) channel. NoFAPESP - Fundacao de Amparo a Pesquisa do Estado de Sao Paulo. other standard presents better performance in AWGN

0-7803-9780-0/06/$20.00 ©2006 IEEE 193

channel but, on the other hand, the performance of the configuration that allows reception in presence of largereceiver under dynamic multipath channel is compromised, Doppler spread.since the ATSC has not been designed for mobile reception. C. ISDB-T

TABLE I-CHARACTERISTICS OF THE ATSC STANDARD.ChAratE I ISDB-T has been developed in Japan and adopted in thisCharactertstcs country in 1999. This standard has been based on DVB-T,Inner Code -VTCM 2/3 but some features have been added in order to improve theOuter Code Reed Solomon (207,187,10) performance, especially for mobile reception. The flexibilityBandwidth 6MHz of ISDB-T has also increased, due to a new concept forTotal Symbol rate 10,76 Mbauds hierarchical transmission based on frequency segmentation.Data bit rate 19,28 Mbps In this case, the total 6MHz channel is divided in 13

B. DVB-T independent segments that can be dynamically grouped totransmit up to 3 different data streams. Table III presentsDVB-T standard has been developed in Europe to attend the main characteristics of ISDB-T standard [5].

the requirements of all the European countries. Thus, theflexibility of the system has been an initial requirement of TABLE III - CHARACTERISTICS OF THE ISDB-T STANDARD.the project. The main characteristics of the DVB-T are Characteristicspresented in Table II [2]. Multiplex COFDM (2k, 4k and 8k)

Modulation DQPSKQPSK, 16QAM or 64QAMThe main reason for the use of Coded Orthogonal Inner code Convolutional 1/2, 2/3, 5/6, 7/8Frequency Division Multiplexing is the robustness of this Outer code Reed Solomon (204,188,8)scheme under frequency selective channels. If the total time Bandwidth 6MHzdelay spread of the channel is shorter than the guard time Guard Time interval 1/4, 1/8, 1/16 and 1/32interval, then the received signal will not suffer intersymbol Data bit rate per segment Min: 280.8kbps - Max: 1.79Mbpsinterference (IIS). COFDM is also used in other high data III. CHANNEL CODING AND MODULATIONrate digital standards, such as Wi-MAX [3] and Wi-Fl [4]. SYSTEM FOR THE MI-SBTVDDue to the robustness of the COFDM technique under This section presents the main characteristics of themultipath channels, DVB-T can be used in Single channel coding and modulation system that have beenFrequency Networks (SFN). proposed for the SBTVD, called MI-SBTVD. The main

innovations are the LDPC for inner code and STC (SpaceTABLE II -Characteristics OF THE DVB-T STANDARD. Time Coding) for transmission diversity. Since LDPC is

Multiplex COFDM (2k and 8k) such a highly efficient error correction code, it is possible toModulation QPSK, 16QAM or 64QAM obtain performance close to Shannon's theoretical limit [6].Inner code Convolutional 1/2, 2/3, 5/6, 7/8 STC is a technique introduted by Alamouti in 1998 that usesOuter code Reed Solomon (204,188,8) up to two transmission antennas and multiple receivingBandwidth 6MHz, 7MHz or 8MHz antennas to obtain space-time diversity. This scheme isGuard Time interval 1/4,1/8,1/16 and 1/32 highly robust against Doppler spread, which makes theData bit rate (6MHz) Min: 3.73Mbps - Max: 23.7Mbps system very efficient for mobile reception.DVB-T allows hierarchical transmission of up to 2 data Figure 1 presents the block diagram of the transmitter

streams, which can be used for different applications. This while Figure 2 presents the block diagram of the receiver.flexibility offers new business models for the TV The outer code is the same Reed Solomon (204,188,8)broadcasters. One option is to use one data stream to used in DVB-T and ISDB-T. The inner code is a LDPCbroadcast video and audio while the other may transmit data with codeword length equal to 9792 and code rates 1/2, 2/3,associated with the scene. This allows an interactivity of the 5/6 and 7/8. The same band segmentation used in ISDB-Tuser with the scene. Another application is to use one data has also been adopted here to allow higher flexibility for thestream to broadcast SDTV while the other is used to broadcasters, while the modulations are QPSK, 16QAM andtransmit the enhanced layer for the HDTV signal. Thus, the 64QAM. This set of modulations allows the broadcasters tousers that are capable to receive both streams can watch the define the trade-off between system throughput andprogram in HDTV, while the users that can receive only the robustness. The matrix interleaver between the inner andSDTV stream watch the program in standard definition. outer codes improves the performance of the RS decoder.DVB-T also presents some problems that must be The STC associated with OFDM results in a robust

addressed. OFDM technique results in high Peak to system for mobile and selective channels. The use of twoAverage Power Ratio (PAPR), which means that the power transmission antennas provides diversity gains of order 2amplifiers must operate with a high back-off in order to when the receiver has only one antenna, which is anavoid signal clipping. This back-off reduces the efficiency interesting scenario for mobile reception. Table IVof the amplifier and increases the overall cost of the summarizes the main characteristics of the proposed system.transmitter. One solution to mitigate this problem is to use The overall performance of the system will be presentedsignal pre-distortion to avoid high power peaks. The intenxScioadthsluonppsdinhspprperformance of DVB-T under mobile channels does not will be compared with the currently available standards.seem satisfactory, because apparently there is no

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TABLE IV - CHARACTERISTICS OF THE MI-SBTVD. Data bit rate per segment Min: 280.8kbps - Max: 1.79MbpsCharacteristics | Diversity scheme STC-OFDM

Multiplex COFDM (2k and 8k) Interleaver Matrix- 4, 8 or 12 LDPC wordsModulation QPSK, 16QAM or 64QAM Number of streams up to 3Inner code LDPC 9792 - 1/2, 2/3, 5/6, 7/8Outer code Reed Solomon (204,188,8)Bandwidth 6MHzGuard Time interval 1/4, 1/8, 1/16 and 1/32

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FiV.gANALYSISurFeSYSTEM PERFORMANCE both systems present almost the same performance. It isIand ANALYSIS OF SYSTEM PERFOR1\4ANCE important to emphasize, however, that the results obtain forThe performance of the system has been analyzed for the ATSC standard are measured, while the results for the

different channel models by simulation, including AWGN MI-SBTVD are simulated.and Brazil A to e [7]. These channels represent different 0' CI AWGNp>S.reception conditions, such as indoor and outdoor reception. 10Figure 3 presents the performance of the system in __ __ _ __ _______

AWGN channel for different combinations of modulation 10.-2and code rate. From this figure it is possible to conclude that ¢ 6Q-3 _ _ _ =

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the system can operate with a carrier to noise ratio equal to . C15.4 dB for 64-QAM and code rate 3/4. With this _ __4configuration it is possible to achieve 19Mbps of data rate, QPSKmac R:

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higher bit rate with 16QAM and code rate 1/2. From Figure'5 it is possible to conclude that, for Brazil-AFhigurc4hcompares the performance of the proposed channel and for a given BER, the MI-SBTVD requires a

system with ATSC standard in AWGN channel. Notice that CRwihi Bsalrta htfrteID-.Ti

195

indicates that ISDB-T requires 4 times the power required On the other hand, the receiver has to be implemented inby MI-SBTVD to achieve the same video quality. This large ASIC to take advantage of a large production scale and togain in efficiency resulted from the joint action of STC- have an industrial price compatible with currently availableOFDM and LDPC. This gain increases even further when a commercial set-top-boxes. However, the prototype tomore adverse channel is used. This fact can be verified in provide a proof of concept for the proposed system has beenFigure 6 for Brazil-B channel and in Figure 7 for Brazil-E 100channel. MI-SBTV-

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Figure 4- Performance of ATSC and MI-SBTVD in Brazil-B channel.AWGN channel.

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TABLE V - VIRTEX IV'S RESOURCE UTILIZATION SUMMARY FOR decoderDEMODULATION AND SYNCHRONIZATION CIRCUITRY.

Used Available Utilization Figure 8-Receiver layout.# Occupied Slices 13063 15360 85%I# BRAM(FIFO16) -94 1192 480o# DSP48s 47 192 - 240o.......TABLE VI- VIRTEX IV'S RESOURCE UTILIZATION SUMMARY FOR

DECODER LDPC CIRCUITRY. _____

I______________________ Used Available Utilization# Occupied Slices -10467 15360 -680o# BRAM(FIFO106) 191 192 4°990# DSP48s 0 192 0%0

TABLE VII- STRATIX II'S RESOURCE UTILIZATION SUMMARY FORRS, DESCRAMBLER AND TRANSPORT STREAM RECOVERY.

____________________ ~~Used Available Utilization# ALUTs 2580 48,352 50o

# Tota RAMk bits 1,025, 920 2,544,192 620A

#Teciot9r bits 022840% Figure 9 - Transmitter assembly with two antennas for the#fDSPtblock 9asbitsembled0 sing 2880vMI-SBTVD lab prototype.TABLE VIII- STRATIX II'S RESOURCE UTILIZATION SUMMARY FOR.............

__________________design TRANSMITTER. ..........eI____________________ ~~Used Available Utilization# ALUTs 42,863 48,352 88%# Total RAM bits 1,579,392 2,544,19262% ......................

# DSP block 9 bits 80 288 270o.............

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