BRNO UNIVERSITY OF TECHNOLOGY Faculty of Electrical Engineering and Communication Department of Radio Electronics

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2 BRNO UNIVERSITY OF TECHNOLOGY Faculty of Electrical Engineering and Communication Department of Radio Electronics Ing. Tomáš Kratochvíl, Ph.D. ANALYSIS OF TRANSMISSION DISTORTIONS IN DIGITAL TELEVISION DVB-T/H ANALÝZA PŘENOSOVÝCH ZKRESLENÍ DIGITÁLNÍ TELEVIZE DVB-T/H Short Version of Habilitation Thesis BRNO 2009

3 KEY WORDS digital television, digital video signal, source coding, channel coding, forward error correction, transmission channel model, transmission simulation, picture quality, mobile terminal, handheld receiver, interactive channel, digital terrestrial television, multipath reception, SFN echo, AWGN, fixed reception, portable reception, mobile reception, DVB-T, DVB-H KLÍČOVÁ SLOVA digitální televize, digitální videosignál, zdrojové kódování, kanálové kódování, dopředná chybová korekce, model přenosového kanálu, simulace přenosu, kvalita obrazu, mobilní terminál, kapesní přijímač, interaktivní kanál, pozemní digitální televize, vícecestné šíření, odraz SFN, AWGN, statický příjem, přenosný příjem, mobilní příjem, DVB-T, DVB-H THESIS IS AT DISPOSAL Department of Radio Electronics, FEEC BUT, Purkyňova 118, Brno, CZ-61200, Czech Republic Tomáš Kratochvíl, 2009 ISBN ISSN X

4 CONTENT CONTENT... 3 ABOUT AUTHOR INTRODUCTION Digital Video Broadcasting DVB Project European Standards DVB-T (Digital Video Broadcasting - Terrestrial) DVB-H (Digital Video Broadcasting - Handheld) DVB-T2 (Digital Video Broadcasting Terrestrial 2nd Generation) Multimedia Broadcasting and Interactivity Conclusions on DVB Evolution MOTIVATION Digital Terrestrial Television Transmission Technical Description of the DVB-T/H Transmitter Technical Description of the DVB-T/H Receiver Individual Parts of the Habilitation Thesis Simulation of the Error Protection and Baseband Transmission in DVB Application of the Error Protection and Baseband Transmission in DVB Analysis of the Error Protection and Baseband Transmission in DVB Testing of the DVB-H mobile terminals capabilities Analysis of the DVB-T/H digital terrestrial television transmission Behind the Habilitation Thesis Parts vol RESULTS AND COMMENTS Simulation of the Error Protection and Baseband Transmission in DVB Other works related to the 1 st part of the habilitation thesis Application of the Error Protection and Baseband Transmission in DVB Other works related to the 2 nd part of the habilitation thesis Analysis of the Error Protection and Baseband Transmission in DVB Other works related to the 3 rd part of the habilitation thesis Testing of the DVB-H Mobile Terminals Capabilities Other works related to the 4 th part of the habilitation thesis Analysis of the DVB-T/H Digital Terrestrial Television Transmission Other works related to the 5 th part of the habilitation thesis Behind the Habilitation Thesis Parts vol ACKNOWLEDGEMENTS REFERENCES CURRICULUM VITAE ABSTRACT ABSTRAKT

5 ABOUT AUTHOR Tomáš KRATOCHVÍL, Dipl. Eng., Ph.D. Department of Radio Electronics FEEC BUT Purkyňova 118 CZ Brno Czech Republic Tel: Fax: Author of the thesis was born in April 16, 1976 in Brno (Czech Republic). He graduated in Electronics and Communication at Brno University of Technology (BUT) in His diploma thesis topic was Vectorscope PAL/NTSC and the thesis was awarded by the Dean of the Faculty of Electrical Engineering and Communication (FEEC). He finished doctoral study in Electronics and Communication at BUT in His doctoral thesis topic was Transmission Distortion Analysis of Digital Video Signals. Since 2001 he is an assistant professor at Department of Radio Electronics, FEEC BUT. He submitted his habilitation thesis on topic Analysis of Transmission Distortions in Digital Television DVB-T/H in October His professional interest is focused on digital television and audio broadcasting and their processing and transmission of multimedia in digital broadcasting networks. His research and development is realized in theoretical and experimental evaluation of digital television transmission and its complex analysis in time and frequency domain. He is specialized in real transmission channels influence on error rates and picture quality in transmission of DVB (Digital Video Broadcasting). His pedagogical interest is focused on audio electronics and digital television technique. Since 2004 he is a guarantor of subject Audio Frequency Electronics in bachelor degree program and since 2006 he is a guarantor of subject Digital Television Systems in master degree program, both in Electronics and Communication at BUT. He is a lecturer in two courses on behalf of the BUT and its University of the Third Age educational program. He is a main author or co-author of 5 papers in international scientific journals, 18 international and 28 national papers in conference proceeding, 9 university textbooks and more than 20 syllabus. In he was supervisor of 6 projects of the Ministry of Education, Youth and Sport of the Czech Republic in creative works of students in doctoral study and innovation of the university education projects. In he was supervisor of the grant project Simulation and Analysis of the Digital Signal Transmission and Transmission Distortions in DTV and DVB Area of the Grant Agency of the Academy of Sciences of the Czech Republic. In he collaborated as a co-worker on grant project Qualitative Aspects of Audiovisual Information Processing in Multimedia Systems of the Czech Science Foundation. Since January 2008 he is a supervisor of the grant project Analysis and Simulation of the Transmission Distortions of the Digital Television DVB-T/H of the Czech Science Foundation. 4

6 1 INTRODUCTION The habilitation thesis deals with the DVB (Digital Video Broadcasting) standards for DTT (Digital Terrestrial Television) and its source and channel coding, signal processing, channel modulation and simulated transmission in laboratory environment. The thesis originally consists of 16 selected author s original scientific and research papers. The papers are divided into 5 related parts and each part is supplemented with short introduction, results and brief comments. There were analyzed and simulated various parts of the DVB-T (Terrestrial) and DVB-H (Handheld) transmission block diagram in baseband and radio frequency band as well. Before that a short introduction to DVB and especially terrestrial standards DVB-T and DVB-H (in the thesis and selected papers due to their common origin called DVB-T/H) is given. All presented works were done at Department of Radio Electronics, Brno University of Technology in last 5 years ( ). Some of the papers have been partially done by cooperation with respected colleagues and skilful students. 1.1 DIGITAL VIDEO BROADCASTING The DVB Project [1] [2] is the consortium of over 280 broadcasters, manufacturers, network operators, software developers, regulatory bodies and others in over 35 countries committed to designing open interoperable standards for the global delivery of digital media services. As DVB's name suggests, these include mainly broadcasting. Services using DVB standards are available not only European area with more than 200 million DVB receivers deployed [3]. Towards the end of 1991, broadcasters, equipment manufacturers and regulatory bodies in Europe came together to discuss the formation of a group that would oversee the introduction of DTV (Digital TV). The group, which became known as the European Launching Group (ELG), realized that a consensus-based framework, through which all of the key stakeholders could agree on the appropriate technologies to be used. A Memorandum of Understanding (MoU) was signed in September 1993 by all ELG participants, and the DVB Project was born. A key report from the Working Group on Digital Television was also central to setting out important concepts that would go on to shape the introduction of DTV not only in Europe. The DVB Project began the first phase of its work in 1993 [4]. The project s philosophy was as follows. The initial task was to develop a complete suite of digital satellite, cable and terrestrial broadcasting technologies in one pre-standardization body. Rather than having a one-to-one correspondence between a delivery channel and a program channel, the systems would be containers which carry any combination of image, audio or multimedia. They would thus be open and ready for LDTV (Low Definition), SDTV (Standard Definition), HDTV (High Definition) or any kind of new media which roll out over time. The work should result in ETSI (European Telecommunications Standards Institute) [5] standards for the physical layers, error correction, and transport for each delivery medium. It should also result in an ETSI report which outlines the baseband systems which are options for carriage. Wherever possible there should be commonality across the different delivery. Only when there was no other choice would there be differences between different delivery media DVB Project European Standards The first phase of DVB s work involved establishing standards to enable the delivery of DTV to the consumer via the traditional broadcast networks. Thus, the three key standards during this phase were DVB-S [6] for satellite networks, DVB-C [7] for cable networks and DVB-T [8] for terrestrial networks. In addition to these the whole range of supporting standards were required covering areas such as service information DVB-SI [9], subtitling DVB-SUB [10], interfacing DVB-ASI [11], etc. Interactive TV required the creation of a set of return channel standards and the MHP (Multimedia Home Platform) [12] [13]. 5

7 DVB then moved to embrace network convergence through the development of standards using innovative technologies that allow the delivery of DVB services over fixed and wireless telecommunications networks (e.g. DVB-H [14] for mobile TV, DVB-IPTV [15] [16]). The latest phase of DVB s work is a natural progression into areas such as a system for content protection and copy management DVB-CPCM [17], and looking at how DVB devices operate in the environment of the home network. Thus we have already seen the scope of DVB-H expanded into the S-band through DVB-SH [18] and publication of second generation standard DVB-S2 [19]. In 2008 is in progress the developments of next generation terrestrial DVB-T2 [20] and cable DVB-C2 [21] standards. Future work items may cover areas such open Internet TV and middleware for interactive services on IPTV and mobile TV. DVB Project produces specifications which are subsequently standardized in one of the European statutory standardization bodies, usually the ETSI. ETSI, the Centre for Electrotechnical Standards (CENELEC) and the European Broadcasting Union (EBU) have formed a Joint Technical Committee (JTC) to handle the DVB family of standards. ETSI official publications with relevant information about the DTV systems are [22]: - TR (Technical Report): typically a set of guidelines for the implementation of a more normative specification or standard. - TS (Technical Specification): a document which can contain normative text, i.e. mandatory text such as "shall". A DVB TS is generally a stepping stone to a more stable document. - ES (ETSI Specification): a document approved by the entire ETSI membership. It is a more stable document than either a TR or TS. - EN (European Standard): the highest ranking ETSI publication approved by the national standards organizations of Europe. - DVB BlueBooks: From time to time, DVB publishes documents following their approval by its Steering Board [2] - the BlueBooks DVB-T (Digital Video Broadcasting - Terrestrial) At the beginning of the 1990s, change was coming to the European satellite broadcasting industry, and it was becoming clear that the once state-of-the-art MAC (Multiplexed Analogue Components) systems would have to give way to all-digital technology. It became clear that satellite and cable would deliver the first broadcast digital television services. Fewer technical problems and a simpler regulatory climate meant that they could develop more rapidly than terrestrial systems. The DVB-T [8] [23] system for digital terrestrial television (DTT) was more complex because it was intended to cope with a different noise and bandwidth environment and multi-path. The system has several dimensions of receiver agility, where the receiver is required to adapt its decoding according to signaling. The key element is the use of OFDM (Orthogonal Frequency Division Multiplex). There are two modes: 2k and 8k carriers plus QAM (Quadrature Amplitude Modulation). The 8k mode can allow more multi-path protection, but the 2k mode can offer Doppler advantages where the receiver is moving. The DVB-T, in common with almost all modern terrestrial transmission systems, uses OFDM modulation. This type of modulation, which uses a large number of sub-carriers, delivers a robust signal that has the ability to deal with very severe channel conditions. The DVB-T has technical characteristics that make it a very flexible system: 3 modulation options (QPSK, 16-QAM, 64-QAM), 5 different FEC (Forward Error Correction) convolutional code rates, 4 Guard Interval options, a choice of 2k or 8k carriers and can operate in 6, 7 or 8 MHz channel bandwidths. Using different combinations of the above parameters a DVB-T network can be designed to match the requirements of the network operator, finding the right balance between robustness and capacity. Networks can be designed to deliver a whole range of services: SDTV, radio, interactive services, HDTV and, using multi-protocol encapsulation, even IP datacasting. 6

8 The use of OFDM modulation with the appropriate Guard Interval (GI) allows DVB-T to provide a tool for regulators and operators in the form of the Single Frequency Network (SFN). An SFN is a network where a number of transmitters operate on the same RF frequency. SFN can cover a country or be used to enhance in-door coverage using simple gap-filler. One final technical aspect of DVB-T worth mentioning is its capacity for Hierarchical Modulation [24]. Using this technique, two completely separate data streams are modulated onto a single DVB-T signal. A High Priority (HP) stream is embedded within a Low Priority (LP) stream. Broadcasters can thus target two different types of receiver with two completely different services. For example, DVB-H mobile TV services optimized for more difficult reception conditions could be placed in the HP stream, with DVB-T stationary HDTV services targeted to fixed antennas delivered in the LP stream. Whilst not originally designed to target mobile receivers, DVB-T performance is such that mobile reception is not only possible, but forms the basis of some commercial services. The use of a diversity receiver with two antennas gives a typical improvement of 5 db in the home and a 50% reduction in errors is expected in a car [23]. DVB-T is a complete solution for DTT, with the flexibility and capacity to deliver a whole range of services, in a range of channel bandwidths. It will continue to be the system of choice for the launch of new services for years to come, with consumers benefiting from the huge economies of scale that open standards bring to growing markets. For a number of countries, however, ASO is approaching in the next couple of years, and with it the release of valuable UHF spectrum. This transition will create a window of opportunity for the introduction of new technologies. DVB is now actively working on DVB-T2 [20] DVB-H (Digital Video Broadcasting - Handheld) A more flexible and robust digital terrestrial system DVB-H [25] has also recently been developed. The system is intended to be receivable on handheld receivers and thus includes features which will reduce battery consumption (Time Slicing function) and a compromise 4k OFDM mode, together with other measures. DVB-H services will also use more efficient video compression systems such as MPEG-4 AVC (Advanced Video Coding). The DVB-H is an extension of DVB-T with some backwards compatibility, i.e. it can share the same DVB-T multiplex. It uses a mechanism called Multi-Protocol Encapsulation (MPE), making it possible to transport data network protocols on top of MPEG-2 TS (Transport Stream). A FEC scheme is used in conjunction with this to improve the robustness and thus mobility of the signal. In addition to the 2k and 8k modes available in DVB-T, a 4k mode is added to DVB-H giving increased flexibility for network design. A short in-depth interleaver was introduced for 2k and 4k modes that lead to better tolerance against impulsive noise (helping to achieve a similar level of robustness to the 8k mode). The system was built on the proven mobile performance of DVB-T. Another essential element of DVB-H is Time Slicing, the main technique used to achieve the required power savings. Each individual TV service in a DVB-H signal is transmitted in bursts allowing the receiver to go into sleep mode, only waking up when the service to which it is tuned is transmitted. For handheld devices this can add up to very significant power savings in the frontend. For battery life and thermal balance this is a key functionality. Statistical multiplexing is also possible in DVB-H, ensuring optimum use of bandwidth to deliver services. DVB-H is designed for use in TV bands III, IV and V as well as L-band. The DVB-H standard [14] is fully specified and published. Some additional work is ongoing within the DVB Project revising the DVB-IPDC (Internet Protocol Datacast) [26] systems layers following extensive implementation experience. As with all elements of DVB-H the work is standardized as quickly as possible to facilitate implementers. DVB has also published a specification called DVB-SH (Satellite Handhelds) [27], introducing the option of using satellites operating in the S-band below 3GHz as part of the mobile TV chain. DVB-SH is also 7

9 designed to utilize the DVB-IPDC systems layer specifications and thus complements the DVB-H specification. The DVB-SH system and waveform specifications have been published as formal ETSI standards [18]. DVB-SH seeks to exploit opportunities in the higher frequency S-band, where there is less congestion than in UHF DVB-T2 (Digital Video Broadcasting Terrestrial 2 nd Generation) DVB-T2 [20] is a digital terrestrial transmission system designed for use in a post-analogue Switch-Off (ASO) environment. It introduces the latest modulation and coding techniques to enable highly efficient use of valuable terrestrial spectrum for the delivery of audio, video and data services to fixed, portable and mobile devices. DVB-T2 is not designed to replace existing DVB-T. Rather the two standards will coexist for many years. As with its predecessor, DVB-T2 uses OFDM modulation, with a large number of sub-carriers delivering a robust signal. Also in common with DVB-T, the new specification offers a range of different modes making it a very flexible standard. In the domain of error correction, DVB-T2 uses the same coding that was selected for DVB-S2. LDPC coding combined with BCH coding offers excellent performance in the presence of high noise levels and interference, resulting in a very robust signal. Several options are available in areas such as the number of carriers (new 1k, 4k, 16k and 32k modes), guard interval sizes (3 new options) and pilot signals, so that the overheads can be minimized for any target transmission channel. A new technique, called Rotated Constellations, provides significant additional robustness in difficult channels. Also, a mechanism is provided to separately adjust the robustness of each delivered service within a channel to meet the required reception conditions (e.g. indoor antenna/roof-top antenna). This same mechanism allows transmissions to be fitted such that a receiver can save power by decoding only a single program rather than a whole multiplex of programs. DVB-T2 also specifies a transmitter diversity method, known as Alamouti coding, which improves coverage in small scale SFN networks. Finally, DVB-T2 has defined a way that the standard can be compatibly enhanced in the future through the use of Future Extension Frames. The specification setting work is largely completed. The draft specification will be before the DVB Steering Board for approval at the end of June On approval it will be released as a DVB BlueBook [28] and sent to ETSI for publication as a formal standard. Vendors are already working on the design of DVB-T2 equipment, with the first prototypes expected by the end of In parallel, further work will be required within the DVB Project on the creation of implementation guidelines, validation testing, etc Multimedia Broadcasting and Interactivity Digital broadcasting has the capacity to deliver multimedia in addition to television programs. This can look like an electronic version of a magazine page or a web page. It is either independent of the television program or allied to it in some way. It can be one-way multimedia which displays pictures and information on screen - superimposed or separate or it can be two-way multimedia which uses a return path system [29] to the broadcaster, to allow the viewer to interact directly with the broadcaster. The delivery of one way material is usually arranged in a data carousel. This means that information is available in a repeating cycle. The receiver grabs the information the viewer has requested (via his controls) as it goes by. There can be a finite waiting time for broadcast multimedia whose length depends on luck and how much overall multimedia is being offered by the channel. The DVB Project agreed that it could not take any specific one of these as a DVB system, but needed an outside, new and open system. The system developed was MHP (Multimedia Home Platform) [30]. 8

10 1.2 CONCLUSIONS ON DVB EVOLUTION By any measure the DVB Project has been a success. More than 200 million devices around the world are receiving services that use DVB standards. Of these, about 100 million are satellite receivers and more than 60 million are receiving DVB-T signals. DVB-S/S2 forms the basis of digital satellite TV just about everywhere. DVB-C is the most commonly used system for digital cable TV. DVB-T has seen phenomenal growth in the last few years with services on air across Europe and in parts of Asia, with further launches to follow in Southeast Asia, Latin America and the EMEA (Europe, the Middle East and Africa) region. The economies of scale engendered by such success mean that the prices consumers have to pay for receivers are falling all the time. Newer services such as mobile TV based on DVB-H/DVB-SH and IPTV services based on DVB specifications are in their beginning. However, indications are that these too will benefit from the stability and flexibility that comes with all DVB standards. 2 MOTIVATION Selected papers presented in the habilitation thesis deals with author s gradual exploration of the DVB-T/H transmission chain performance. At the beginning of all works there were applied image processing blocks for the conversions and source coding of non-compressed digital images into transmission signals. These signals were protected against transmission errors by forward error protection codes established in DVB. Then simplified transmission channel model was applied in Matlab to explore efficiency of used codes and robustness of FEC coding. With the results of symbol- and bit-error rates before and after the correction an idea of according picture quality analysis has appeared. A standard procedure based on objective quality metrics evaluation was then applied on transmitted and decoded images. Then a research has been applied on available DSP platform to compare results from Matlab with ones from DSP. Recent works have been done using test and measurement hardware equipments from the Laboratory of the digital television that was built up at Department of Radio Electronics, Brno University of Technology. Complete DVB-T/H transmission chain from baseband generation across the digital modulation and laboratory RF transmission was set up to explore sensitivity of DVB-T/H signals on various transmission conditions. 2.1 DIGITAL TERRESTRIAL TELEVISION TRANSMISSION Simplified block diagram of DVB-T/H digital terrestrial transmission is shown in Fig. 1. The main blocks of the transmitter side are source encoder with multiplexer, channel encoder and transmitter. The main blocks of the receiver side and decoders are of course reversed. In the terrestrial transmission of digital television signals, according to the DVB-T/H standard, the most appropriate modulation method to cope with mentioned problems is COFDM modulation (Coded Orthogonal Frequency Division Multiplex). It means that OFDM modulation is preceded by channel coding FEC [31]. Payload carriers are mapped absolutely and they are not differentially coded. This requires channel estimation and correction for which numerous pilot signals are provided in DVB-T/H spectrum [32]. These are also used as test signals for channel estimation. Between the COFDM symbols a Guard Interval of defined, but often adjustable length, is maintained. Inside this Guard Interval, transient events due to echoes can decay which prevents ISI (Inter Symbol Interference). The Guard Interval must be longer than the longest echo delay time of the transmission system. Modulator of the DVB-T/H transmitter can cause I/Q modulation errors like amplitude imbalance, I/Q phase errors and lack of carrier suppression [33]. Noise AWGN (Additive White Gaussian Noise) is always present during all the processing. Then the signal is transmitted via terrestrial transmission link with multi-path reception with various echo paths caused by reflection, additive noise AWGN, narrow-band or wide-band interference sources and Doppler effects and its frequency shift in case of mobile reception. 9

11 Fig. 1 Block diagram of the DTT (Digital Terrestrial Television) transmission. In the ideal case, exactly one signal path arrives at the receiving antenna. The signal is then only attenuated to a greater or lesser extent and is merely subjected to noise AWGN. This channel with a direct view of the transmitter is called Gaussian channel and provides the best conditions of reception for the receiver. If multiple echoes are added to this direct signal path, the conditions of reception become much more difficult. This channel with a direct line of sight and a defined number of multiple echoes, which can be simulated as a mathematical channel model, is called a Ricean channel. If then the direct line of sight to the transmitter is also blocked, i.e. direct signal path, the channel is called Rayleigh channel. This represents the worst conditions of stationary reception [32]. The receiver side consists of classical TV tuner with low noise level, channel encoder and transport stream demultiplexer with selected program demultiplexing and source decoding. DVB-T/H signal carries a pilot signals which can be used as measuring signals for channel estimation and channel correction in the receiver. A FFT sampling window of the COFDM demodulator is not placed precisely over the actual COFDM symbol. This causes phase shift in all subcarriers or twisted constellation, compression or expansion of the constellation [33]. Measuring the amplitudes and phase distortion of the continual and scattered pilots enables the correction function for the channel to be calculated and the transmission distortion can be removed. A practical DVB-T/H receiver has only a few discrete components such as the tuner, SAW filter, the mixing oscillator for the IF band and a low-pass filter. DVB-T/H demodulator chip contains all modules of the COFDM demodulator after the A/D converter. Transport stream is fed into the MPEG-2 decoder where it is decoded back into video and audio signals Technical Description of the DVB-T/H Transmitter With reference to the Fig. 2 a short description of the signal processing blocks follows [33]. - Source coding and MPEG-2 multiplexing (MUX): compressed video, compressed audio and data streams are multiplexed into PSs (Program Streams). 10

12 Fig. 2 Block diagram of the DVB-T/H signal processing. - One or more PSs are joined together into an MPEG-2 TS (Transport Stream). This is the basic digital stream which is being transmitted and received by set-top box (STB). Allowed bit-rates for the transported data depend on a number of coding and modulation parameters and can range from about 5 to about 32 Mbit/s. - Splitter: two different TSs can be transmitted at the same time, using a technique called Hierarchical Modulation. It may be used to transmit, for example, a standard definition SDTV signal and a high definition HDTV signal on the same channel carrier. At the receiver, depending on the quality of the received signal, the STB may be able to decode the HDTV stream or, if signal strength lacks, it can switch to the SDTV one. In this way, all receivers that are in proximity of the transmission site can lock the HDTV signal, whereas all the other ones, even the farthest, may still be able to receive and decode an SDTV signal. - MUX adaptation and energy dispersal: the MPEG-2 TS is identified as a sequence of data packets of fixed length (188 bytes). With a technique called energy dispersal the byte sequence is decorrelated using PRBS (Pseudo Random Binary Sequence). - External encoder: a first level of error correction is applied to the transmitted data, using a Reed-Solomon RS (204, 188) block code, a code allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet. - External interleaver: convolutional interleaving is used to rearrange the transmitted data sequence, in such a way that it becomes more rugged to long sequences of errors. 11

13 - Internal encoder: a second level of error correction is given by a punctured convolutional code, which is often denoted in STB menu. There are five valid coding rates: 1/2, 2/3, 3/4, 5/6 and 7/8. - Internal interleaver: data sequence is rearranged again, aiming to reduce the influence of burst errors. This time, a block interleaving technique is adopted, with a pseudo-random assignment scheme. This is really done by two separate interleaving processes, one operating on bits and another one operating on groups of bits. - Mapper: the digital bit sequence is mapped into a base band modulated sequence of complex symbols. There are three valid modulation schemes: QPSK, 16-QAM and 64-QAM. - Frame adaptation: the complex symbols are grouped in blocks of constant length (1512, 3024 or 6048 symbols per block). A frame of 68 blocks length is generated and a superframe is built by 4 frames. - Pilot and TPS signals: in order to simplify the reception of the signal being transmitted on the terrestrial radio channel, additional signals are inserted in each block. Pilot signals are used during the synchronization and equalization phase, while TPS signals (Transmission Parameters Signaling) send the parameters of the transmitted signal and to identify the transmission parameters. The receiver must be able to synchronize, equalize, and decode the signal to gain access to the information held by the TPS pilots. Thus, the receiver must know this information beforehand, and the TPS data is only used in special cases, such as changes in the parameters, resynchronizations, etc. - OFDM Modulation: the sequence of blocks is modulated according to the OFDM technique, using 2048, 4096, or 8192 carriers (2k, 4k, 8k mode, respectively). Increasing the number of carriers does not modify the payload bit rate, which remains constant. - Guard Interval insertion: to decrease receiver complexity, every OFDM block (symbol) is extended, copying in front of it its own end (cyclic prefix). The width of such Guard Interval can be 1/32, 1/16, 1/8, or 1/4 that of the original blocks length. Cyclic prefix is required to operate Single Frequency Networks, where there may exist an ineliminable interference coming from several sites transmitting the same program on the same carrier frequency. - DAC and front-end: the digital signal is transformed into an analog signal, with a digital-toanalog converter (DAC), and then modulated to radio frequency (VHF, UHF) by the RF frontend. The occupied bandwidth is designed to accommodate each single DVB-T/H signal into 5, 6, 7, or 8 MHz wide channels. The base band sample rate provided at the DAC input depends on the channel bandwidth Technical Description of the DVB-T/H Receiver The receiver adopts techniques which are dual to those ones used in the transmitter [32] [34]: - Front-end and ADC: the analog RF signal is converted to base-band and transformed into a digital signal, using an analog-to-digital converter (ADC). - Time and frequency synchronization: the digital base band signal is searched to identify the beginning of frames and blocks. Any problems on the frequency of the components of the signal are corrected too. The property that the guard interval at the end of the symbol is placed also at the beginning is exploited to find the beginning of a new OFDM symbol. On the other hand, continual pilots (whose value and position is determined in the standard and thus known by the receiver) determine the frequency offset suffered by the signal. This frequency offset might have been caused by Doppler shift, inaccuracies in either the receiver clock etc. - Guard interval disposal: the cyclic prefix is removed. Autocorrelation is used to derive synchronization information. Since in the guard interval, the end of the next symbol is repeated before each present symbol, the autocorrelation function will supply an identification signal in the area of the guard interval and in the area of symbols. 12

14 - OFDM demodulation: The data stream is split into two data streams by a switch (odd samples and even samples in branches). These streams are offset from one another by half of the sampling clock cycle. To eliminate this offset the branches are filtered (interpolation) and delayed. Data streams are then fed to a complex mixer which is supplied with carriers by a numerically controlled oscillator (NCO). The receiver must also be locked to the transmitted frequency by means of Automatic Frequency Control (AFC). This is done by the evaluation of continual pilots after FFT. - Frequency equalization: the pilot signals equalize the received signal. DVB-T/H signal carries a pilot signals which can be used as measuring signals for channel estimation and channel correction in the receiver. Measuring the amplitudes and phase distortion of the continual and scattered pilots enables the correction function for the channel to be calculated. - Demapping: TPS information is error-protected and is needed by the demapper following the channel correction and also by channel decoder. The data stream is available and is provided for channel decoding. - Internal deinterleaving: data sequence is rearranged again, aiming to reduce the influence of burst errors (reverse to Internal interleaving). - Internal decoding: It uses the Viterbi algorithm. Locations where bits have been punctured are carried by TPS. - External deinterleaving: convolutional deinterleaving is used to rearrange the transmitted data sequence (reverse to External interleaving). - External decoding: a Reed-Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes. Otherwise packet is marked as wrong packet. - MUX adaptation: With a technique energy dispersal, the byte sequence is decorrelated again. The descrambler is the same as in transmitter side. The MPEG-2 TS is identified as a sequence of data packets and selected program can be decoded. - Succeeds MPEG-2 demultiplexing and source decoding, decompression and DAC. 2.2 INDIVIDUAL PARTS OF THE HABILITATION THESIS As this was previously mentioned, the habilitation thesis deals with 16 selected original and previously published scientific and research papers of the author (see page 33). All papers are divided into 5 related parts and each part is supplemented with short comments and brief conclusions in the next chapter. All presented works were done at Department of Radio Electronics, Brno University of Technology in last 5 years ( ). This short overview of all the parts should explain author s motivation to work on individual parts Simulation of the Error Protection and Baseband Transmission in DVB The 1 st part of the thesis deals with the papers [35] [40] [42] from years ( ). This part deals with the transmission simulation model applied in Matlab that covers selected phenomena of baseband coding of digital images and conversions from transmitted images to transmitted signals. Error protection secured by FEC was included. Using the simulation model the influence of the transmission errors on error rates and transmitted images and efficiency of FEC can be evaluated. There was implemented simplified transmission channel model in baseband based on design of the digital filters. For the evaluation of transmitted pictures quality there was implemented system in Matlab. Note: Some of the topics have been partly included in PhD thesis of the author. All the papers presented in this part have been published before author s PhD thesis submission Application of the Error Protection and Baseband Transmission in DVB The 2 nd part of the thesis deals with the papers [55] [56] from years ( ). 13

15 Previously introduced transmission simulation model was applied on DSP evaluation board. In advance, there was included MPEG-2 source encoder for one video stream. Also there was applied standard FEC protection against transmission errors. This way the simulation model in Matlab was verified. Results of influence of the transmission errors on bit-error rates and transmitted compressed video can be evaluated. The transmission channel model in baseband was applied with the same intention as before. Note: Although this topic partly deals with PhD thesis of the author, finally it has not been included in submitted PhD thesis. Thus, there is opportunity to include it into the works within the habilitation thesis with appropriate introduction in previous first part Analysis of the Error Protection and Baseband Transmission in DVB The 3 rd part of the thesis deals with the papers [59] [60] [61] [62] from years ( ). Using the transmission simulation model applied in Matlab and of course DSP. Results of transmission errors influence on bit-error rates and transmitted non-compressed images and compressed video were analyzed. In this part the transmission channel model in baseband is analyzed and discussed. There was analyzed influence of variable normalized cut-off frequency of the channel on error rates and according picture quality. Standard methods of picture quality evaluation based on picture differencing method were applied. Note: Some of the topics have been partly included in PhD thesis of the author. All the papers presented in this part have been published after author s PhD thesis submission Testing of the DVB-H mobile terminals capabilities The 4 th part of the thesis deals with the papers [69] [70] from year This part deals with the DVB-H standard that was established in This type of digital video broadcasting for handheld terminals was experimentally tested during the Invex 2005 exhibition in Brno and with successful trial in Prague in 2006 (Czech Republic). There was opportunity to test all three terminals from the trial and their capability to work in all the RF bands, modulations and modes of broadcasting. In advance there was possibility to test all three terminals during the GSM procedures using the BTS configuration Analysis of the DVB-T/H digital terrestrial television transmission The 5 th part of the thesis deals with the papers [72] [73] [74] [75] [76] from The last part deals with the DVB-T/H digital video broadcasting in variously defined transmission conditions. There was tested influence of various types of fading profiles, SFN echoes and used Hierarchical Modulation on transmitted digital terrestrial television signal. The results of bit-error rates, modulation errors and according digital video quality evaluation are presented in the papers. Final work presents experimental assessment of interferences influence on transmitted digital terrestrial television. All the results were achieved using the test and measurement devices from Laboratory of the digital television, Brno University of Technology. 2.3 BEHIND THE HABILITATION THESIS PARTS VOL. 1 At this point author should explain his deep interest on digital television topics which are closely related to the habilitation thesis and especially all his works in last 5 years. After the works on PhD thesis in years ( ) 1 and various grant and development projects works in years ( ), author has become in 2005 a guarantor of a new master study course Digital Television Systems. The task for new guarantor was to prepare 13 technical lectures 1 PhD thesis were unfortunately submitted in

16 and 8 practical laboratory measurements on topics of the digital television and DVB standards especially. The course has successfully started in winter term of academic year 2006/2007 in Czech language and in academic year 2008/2009 in English language. Fortunately, there was built up in years ( ) a new Laboratory of the digital television at Department of Radio Electronics, Brno University of technology. This laboratory was financially supported by the development project of the Ministry of Education, Youth and Sport of the Czech Republic in 2003 for the laboratory test and measurement equipments. Further devices were obtained from the author s or respected colleagues research and grant projects on topics of digital television in following years. Finally, in 2008 author obtained post doctoral grant project from Czech Science Foundation, research project no. 102/08/P295 Analysis and Simulation of the Transmission Distortions of the Digital Television DVB-T/H ( ). This project is on topics of DVB-T/H transmission and analysis of the transmission parameters influence on transmitted digital terrestrial television signals. 3 RESULTS AND CONCLUSIONS Paper reprints of all 16 author s selected papers, divided into 5 related parts, are contained at the end of the habilitation thesis. All the reprints present previously reviewed and published papers from international journals and international conferences only (except [76]). Full paper versions are inserted in exact layout as they were published in printed journals and conference proceedings. Partial details from the papers are not mentioned in this chapter. Rather most relevant results and brief conclusions on all individual parts are given. In advance, each individual part is completed with related works such as student s bachelor and diploma thesis which were supervised by the author at Brno University of Technology. 3.1 SIMULATION OF THE ERROR PROTECTION AND BASEBAND TRANSMISSION IN DVB The first part of the thesis deals with the simulation of FEC (Forward Error Correction) protection against transmission errors in simulated DVB baseband transmission. Simulation model that covers selected image and signal processing in DVB standards was presented and applied in Matlab [35]. There are covered simplified RGB to YC B C R conversions [36], color image YC B C R samples multiplexing, FEC1 (Reed-Solomon code) and FEC2 (convolutional code) encoding with inserted interleaving. Simplified model of the transmission channel in baseband is used for the transmission with prospective errors. The model of the transmission channel in baseband is designed as a lowpass FIR (Finite Impulse Response) filter with defined attenuations in pass-band and stop-band and variable normalized cut-off frequency. A method used for design of such kind of model deals with the weighting of impulse response and with variable shape of the window function. The developed model for digital transmission channel simulation for baseband digital video signal transmission is the FIR filter with low-pass character and variable parameters and method of design [37]. Acceptable design methods for simulation in Matlab are weighting of the impulse response method, sampling of the frequency characteristic method and design by approximation of frequency characteristic with LS algorithm [38]. The pertubative signals influence on transmitted digital signal is substituted with one source of pertubative signal. This source is optionally added to useful signal. Additive pertubation may be modeled for, e.g. as AWGN. The next possibility of pertubative signal is the reflected and delayed signal and its influence on the transmitted digital signal.described philosophy, model for the simulation and analysis and software implementation was the partial solution of the grant project [38]. There are some general results for baseband digital transmission channel simulation and analysis of digital television transmission. The developed Matlab application for the 15

17 simulation and analysis uses functions of the Signal Processing, Image Processing and Communication Toolboxes of Matlab. It can be used for the illustrative modeling and experimental education of the digital television technique area. This work presents an open modular application that can be ensemble with the other transmission phenomena of the DVB standard signal processing (digital modulation techniques, transmission in RF band etc.) [39]. There are also mentioned enhancements of the model using the MPEG based image compression and digital modulations in RF band. After the simulation an objective check (symboland bit-error rates) and subjective check (picture quality evaluation) of transmission quality can be done according to the transmission simulation set up [40]. Then a simplified evaluation system called PQES (Picture Quality Evaluation System) was implemented in Matlab [41]. It contains well-arranged grafical user interface and it uses dialogs for reference and degraded picture (or couple of consequent frames in separate files) selection and evaluation of spectral and temporal characteristics of the pictures. The objective PQE (Picture Quality Evaluation) contains the feature extraction and picture differencing approach and directly enumerates measures that were presented in the paper [42]. The subjective PQE deals with applied algorithms of ITU-R BT.500 recommendation and respects an order of test pictures [43]. Picture differencing uses a matrix-based mathematical computation to process each picture or sequence of pictures [44]. The pixel-by-pixel reference between filtered version of the referenced and degraded pictures is used to determine an objective quality score. This method provides better objective picture quality measurement correlation with subjective results. The picture differencing measures contain evaluation of MSE (Mean Square Error), PSNR (Peak Signal to Noise Ratio), NK (Normalized Cross-Correlation), AD (Average Difference), SC (Structural Content), MD (Maximum Difference), LMSE (Laplacian MSE), NAE (Normalized Absolute Error) etc. [45] Perception based on objective evaluation presents PQS (Picture Quality Scale) [46] and perception based on subjective evaluation is quantified by MOS (Mean Opinion Score) [43]. Depending on the original picture, the test value and evaluation are not always correlated with the impression of quality of a subjective observation. To bring the objective picture quality test value closer to the subjectively perceived picture quality, other quantities in the moving picture must also be taken into consideration. Advantages of picture quality subjective testing are obtaining of valid results for conventional and compressed television systems and evaluation of scalar MOS that works over a wide range of still and motion picture applications. The disadvantages of subjective testing are in a wide variety of possible methods and test must be considered, many observers must be selected and it is very time consuming [43]. The advantage of the picture extraction method is that calculated characteristics may be sent through the transmission channel along with the compressed picture for objective scoring. The objective testing with picture differencing correlates best with subjective results. Combination of these methods gives the best results and correlation between subjective and objective scores but it is still not technology independent. Application of the HVS (Human Visual System) [44] and the JND image quality metric provides all the facilities required for a robust objective picture quality measurement method. It includes evaluation of dynamic and complex motion sequences (spatial analysis, temporal analysis and full color analysis) Other works related to the 1 st part of the habilitation thesis There were 2 diploma and 1 bachelor thesis, related to the topic of the 1 st part of the habilitation thesis, which were solved at Department of Radio Electronics, Brno University of Technology: - HRDINA, J. Simulation of the Digital Image Signal Transmission in Television Technique. Brno University of Technology, Faculty of Electrical Engineering and Communication, p. Diploma thesis supervisor Ing. Tomáš Kratochvíl [47], 16

18 - ŠIMÍČEK, P. Assessment of Picture Quality in Television Technique and Video Technique. Brno University of Technology, Faculty of Electrical Engineering and Communication, p. Bachelor thesis supervisor Ing. Tomáš Kratochvíl [48], - ŠEVČÍK, M. Simulation of the HVS Characteristics in Matlab. Brno (Czech Republic): Brno University of Technology, Faculty of Electrical Engineering and Communication, p. Diploma thesis supervisor Ing. Tomáš Kratochvíl, Ph.D. [49]. 3.2 APPLICATION OF THE ERROR PROTECTION AND BASEBAND TRANSMISSION IN DVB The second part deals with DSP (Digital Signal Processor) implementation of the source and channel coding in DVB standards. Baseband processing of video digitizer and MPEG based compression was applied on DSP development board MDS TM-13 IREF using commercial application libraries. Then the system was completed with software application on PC that allows source coded and MPEG-2 compressed video file provide against simulated transmission errors by FEC (Forward Error Correction) codes. Reed-Solomon symbol oriented correction code, interleaver for burst oriented correction and convloutional bit oriented correction code were applied with simulated transmission in baseband. Simplified transmission channel was modeled as a low-pass filter FIR with variable attenuation and normalized cut-off frequency. This complex simulation system was applied as a demonstration of error protection influence on transmitted digital video in experimental laboratory measurements in master study course Digital Television Systems. The MDS TM-13 IREF [50] is a PCI bus board for real time video, audio and telecommunications processing. It uses the 180 MHz Philips PNX-1300 DSP processor (later called Nexperia) that is 32 bit fixed and floating point VLIW processor with integrated video and audio interfaces. The development board provides video I/O in both CVBS and Y/C (S-video) formats, stereo audio I/O and telecommunications I/O through a modem interface and DAA (2 wire phone line). The Nexperia processor is programmed in C or C++ using an optimizing compiler and scheduler NDK (Nexperia Development Kit) that include operations for efficient real time video processing. The DSP also has a built image co-processor and variable length decoder (VLD) used in MPEG video compression. The architecture overview of the DSP and the comprehensive features overview of all parts are available in [51]. The development board operates with the video input and reads digital video data stream from an off-chip source into main memory. It accepts CCIR656-compliant device with 8-bit parallel 4:2:2 YUV (8 x 27 Mbps). The video output provides a digital YUV data stream to off-chip video subsystems vice-versa to video input. Gathering bytes from the separate YUV planes stored in SDRAM generates the output signal. The image coprocessor unit off-loads the CPU of cycleconsuming image processing tasks such as copying image from SDRAM to a host video frame buffer. The VLD unit operates as a memory-to-memory coprocessor to decode Huffman encoded MPEG-1 and MPEG-2 video data streams. More details are available in [50]. The Nexperia processor operates with the IADK (Integrated Application Development Kit) application libraries. These are basic input and output video and audio codecs [52]. In DSP application used libraries are available option to use with the MDS TM-13 IREF development board and it also contains MPEG encoders and decoders: - MPEG encoder and decoder Lib (ISO/IEC and ) provides a set of functions produce the MPEG-1 video streams from pictures separate from YUV (4:2:0) pixel data blocks, I and P frames support, variable/constant bit rate and free definition of quantizer. MPEG decoder accepts the MPEG-1 and MPEG-2 MP@ML. - MPEG program and transport stream demux Lib (ISO/IEC and ) extracts the stream of MPEG audio and video, recognizes the IDs of streams and corresponding PES (Packetized Elementary Stream) start codes and parses PES packets. The demultiplexer receives 17

19 a single MPEG-2 transport streams, scans the incoming PES, extract the PIDs (Packet Identifiers) of video and audio and starts to decoding the stream. Generally, the MPEG family standards are used as an effective tool for coding audio and video signals. The MPEG-1 and MPEG-2 may both reduce the temporal correlation, so that a greater coding efficiency is achievable. Used libraries present standard solution of multimedia and digital video compression. The principal of the channel coding in digital video transmission deals with the redundancy information that is added to the source-coded digital signal in the channel encoder. Two relevant methods of error protection in the transmission of digital video and digital television accords to standard DVB are FECs (forward error corrections) by block FEC1 (Reed-Solomon code) [53] and FEC2 (convolution code) [54] with interleaving. The RS code (FEC1) is symbol oriented code. The correction is not only in the error recognition and its replacement. Symbol with the error should be replaced. The convolution code (FEC2) is binary oriented and correction of binary errors is possible only with the bit inversion after the error localization. Efficiency of convolution code depends on the length of used shift register in coder and its content determines the state of coder. Viterbi algorithm of the decoder is wide-spread decoding technique of convolution codes. The experimental application of channel coding of multimedia digital video using DSP development board TM-13 IREF was presented in [55] [56] [57]. The DSP channel coding application provides the resistance against errors during the transmission of coded video data. These errors are occurred in transmission media and they are usually caused by any perturbation. Described transmission uses the model that makes definition of the random errors of digital data. The observer can evaluate the errors on the AV monitor screen in spatial area (visual information) and the subsequent subjective evaluation of video quality is possible offline. Due to block based compression the image artefacts are easy visible according to amount of errors that are imposed on transmitted packets of digital video stream [58] Other works related to the 2 nd part of the habilitation thesis There was a diploma thesis, related to the topic of the 2 nd part of the habilitation thesis, which was solved at Department of Radio Electronics, Brno University of Technology: - SLANINA, M. Implementation of Image Transmission and Channel Coding FEC in Area DVB. Brno University of Technology, Faculty of Electrical Engineering and Communication, p. Diploma thesis supervisor Ing. Tomáš Kratochvíl [57]. 3.3 ANALYSIS OF THE ERROR PROTECTION AND BASEBAND TRANSMISSION IN DVB The third part of the thesis deals with analysis of the error protection efficiency, channel coding application and characteristics of the transmission channel model in baseband DVB transmission. Results of achieved symbol- and bit- error rates and corresponding picture quality evaluation analysis are presented, including the evaluation of influence of the channel coding on transmitted RGB images and their noise rates related to MOS. Then the influence of the transmission channel parameters on error rates and picture quality in DVB baseband transmission was evaluated. The analysis included the evaluation of subjective picture quality influence on normalized cut-off frequency of the baseband channel, relative amplitude of additive noise and reflected signal. The last part introduces baseband channel with variable cut-off frequency and then two simulation experiments. The first was done with the DVB baseband processing and simulation in Matlab (1 st part of the thesis) applied to the set of test images with variable characteristics. The second was done with the real digital video captured, compressed and processed again according to DVB on PC and DSP (2 nd part of the thesis). The results of achieved error rates and according picture quality measures in dependence on the transmission channel cut-off were presented and compared. 18

20 The main objective criteria in digital data transmission are BER (bit error rate) and SER (symbol error rate). These rates evaluation allows in component analysis comparison of input and output samples values and their bits and symbols. The error rates can be properly evaluated as BER 1 before FEC2 decoding (rate without any error protection), BER 2 after the FEC2 decoding (digital transmission protected against bit errors), SER 1 before FEC1 decoding (symbol error rate without the symbol protection) and SER 2 after the FEC1 decoding (symbol error rate of full protected digital transmission). Picture differencing uses a matrix-based mathematical computation to process each picture or sequence of pictures. The pixel-by-pixel reference between filtered version of the reference and degraded pictures is used to determine the objective quality score. The picture differencing measures can contain evaluation of MSE (Mean Square Error), NMSE (Normalized MSE), SNR (Signal to Noise Ratio), PSNR (Peak SNR), etc. To bring the objective picture quality test value closer to the subjectively perceived picture quality, other quantities in the test picture must also be taken into consideration. These are spatial and spectral measures. The SFM (Spatial Frequency Measure) indicates the overall activity level in a picture, defined by row and column frequencies and in spectral domain the SAM (Spectral Activity Measure) that is defined as a measure of picture predictability. The evaluation deals with the DFT coefficients of picture and SAM has the dynamic range of [1, infinity) [59]. The aim of the analysis was to determine the influence of channel encoder parameters on achieved error rates and objective PQE metrics. Evaluated data were BER after the convolutional decoding and SER after the Viterbi decoding of the RS code. These rates were evaluated in [%], where error rate 0 % corresponds to absolutely errorless transmission and vice versa 100 % corresponds to absolutely errorneous transmission and lost of the data and corresponding picture. Subsequent objective PQE was based on the MSE, NMSE error metrics and PSR and PSNR [db] noise rates evaluation mainly. The first analysis evaluated the RS code and its parameters influence on transmitted signal and decoded pictures [59]. The second analysis evaluated the interleaving depth influence on transmitted signal and decoded pictures [59]. The third analysis evaluated the convolutional code and its rate parameters influence on transmitted signal and decoded pictures [59]. The fourth analysis evaluated the normalized cutoff frequency influence on transmitted signal and achieved BER and SER. The fifth postprocessing analysis evaluated picture quality based on the MSE, NMSE error metrics and SNR and PSNR [db] evaluation [60]. The sixth analysis evaluated the relative amplitude of additive noise influence on transmitted signal and achieved BER and SER. The seventh analysis evaluated the reflected signal (relative amplitude 30 %) delay influence on transmitted signal and achieved BER and SER [61]. The detailed analysis of the source, channel and link coding of the simulation model was done. Influence of the source encoder parameters on error rates is not too critical. The sampling format selection affects only the image resolution and only the parallel transmission multiplex causes increase of the BER and SER. Influence of RS coding and its application on error rates and picture quality is evident. It almost does not depend on RS parameters, but it is necessary to use it. Influence of used interleaving depth on results of error rates and picture quality is not too serious. The higher depth (more than 12 symbols) gives better results. Principal influence on error rates results has the convolutional code. Only the code with rate R = 1/2 gives excellent picture quality and other rates are worst than transmission without the convolutional protection. Only the RZ unipolar code is not convenient for the transmission because it produces enormous increase of BER. The best results give the RZ and NRZ bipolar codes. Effect of the noise perturbation in the model of the channel is visible in transmitted and decoded pictures when the relative amplitude of the perturbation is greater the 40% of the transmitted signal. The last analysis evaluated influence of the transmission channel cut-off parameter on achieved objective picture quality metrics based on picture differencing and transmission error rates 19