Digital Radio and TV Systems Part 1 V.2

Transcription

1 Digital Radio and TV Systems Part 1 V.2 Course at FH Technikum Wien DI Peter Knorr

2 How it all began 1924 first radio transmission in Austria Digital Radio and TV Systems Part I Seite 2

3 How it all began 1955 first television transmission in Austria Digital Radio and TV Systems Part I Seite 3

4 How it all began 1972 colour television in Austria Digital Radio and TV Systems Part I Seite 4

5 How we developed digital TV analog switch off start of digital terrestrial television DVB-T in Austria Digital Radio and TV Systems Part I Seite 5

6 Next generation of digital television 2013 start of second generation of digital terrestrial television DVB-T2 in Austria Digital Radio and TV Systems Part I Seite 6

7 Digitalization of Broadcast in Digital Radio and TV Systems Part I Seite 7

8 Definitions Broadcast is a point to multipoint system Digital Radio and TV Systems Part I Seite 8

9 Definitions Mobile Communication is a point to point system Digital Radio and TV Systems Part I Seite 9

10 Analog TV (Do you remember?) Ghosting (Multi path) Weak signal Electrical Interference Transmitter Interference Source: Digital Radio and TV Systems Part I Seite 10

11 Technical requirements for a new terrestrial digital TV system: Bandwidth (use of existing TV channels in VHF and UHF) Simulcast with analog signals without interference Robustness against multipath reception Single frequency network Portable and fixed reception Digital Radio and TV Systems Part I Seite 11

12 Technical requirements for a new terrestrial digital radio system: Bandwidth (use of existing channels in VHF) Robustness against multipath reception (also in mobile situations) Single frequency network Mobile, portable and fixed reception Digital Radio and TV Systems Part I Seite 12

13 Developing of a digital broadcasting system But 1966 no processor power was available to realize this system Digital Radio and TV Systems Part I Seite 13

14 Developing of a digital broadcasting system Video compression formats 1991 MPEG MPEG MPEG 4 (H.264) 2013 H265 MPEG = Moving Pictures Expert Group Audio compression formats MPEG 1 Layer 1,2,3 ( ) AAC (1997), HE-AAC, Extended HE-AAC (2013) Dolby Digital Audio AC-3 (1990) Dolby Digital Plus (E-AC-3) AAC = Advanced Audio Codec Digital Radio and TV Systems Part I Seite 14

15 Why is data reduction (compression) of digital signals necessary? A digital standard definition video signal (SDTV) has a data rate of 270 Mbit/s (SDI format = CCIR 601)) A digital HDTV signal has a data rate > 1 Gbit/s (HD-SDI format) An uncompressed digital audio signal has a data rate of approx. 1.5 Mbit/s (Audio-CD) This high bit rates can be transported between cameras and studios only on short distances or via fibre optic (dark fibre technology). A transport via broadcasting or mobile systems is only possible if the signals are data reduced Digital Radio and TV Systems Part I Seite 15

16 Data reduction (compression) of digital video signals Source: uncompressed video signal SD = 270 Mbit/s (CCIR 601) Compression to MPEG2 / 4 Video Elementary stream 2-15 Mbit Source: uncompressed HD video signal HD-SDI = Gbit/s Compression to MPEG2 (~ 2o Mbit) or MPEG4 (~ 10 Mbit) Video elementary stream (15) Mbit/s Digital Radio and TV Systems Part I Seite 16

17 Data reduction (compression) of digital video signals MPEG Video Compression (Encoding): Analysis of moving parts and fix parts of pictures Group of picture (GOP) I, B and P frames An I frame indicates the beginning of a GOP. The I frames contain the full image and do not require any additional information to reconstruct it. P and B frames contains motion-compensated difference information relative to previously decoded pictures I-Frame Intra Frame Coded Picture B-Frame B-Frame Bidirectional Bidirectional Predicted Predicted Picture Picture GOP (Group of Pictures) P-Frame Predicted Picture I-Frame Intra Frame Coded Picture Forward Prediction Backward Prediction Digital Radio and TV Systems Part I Seite 17

18 Data reduction (compression = Encoding) of digital audio signals Source: uncompressed audio signal form studio AES/EBU= 2 Mbit/s or Audio-CD ~ 1.5 Mbit/s Encoded audio bit rates: MPEG, AAC: 16,32,64,128,160,192,256,384 kbit/s Dolby Digital AC3: 448 kbit/s Digital Radio and TV Systems Part I Seite 18

19 Data reduction (compression) of digital audio signals MPEG-2 Audio compression (Encoding): Audio compression by using Psycho Acoustic Model of Human Ear. Perceptual Coding = Irrelevancy Reduction + Redundancy Reduction It is found that the ear has a certain threshold of hearing. Below this the signals are inaudible. Source: Wikipedia Digital Radio and TV Systems Part I Seite 19

20 Data reduction (compression) of digital audio signals MPEG-2 Audio Compression (Encoding): Frequency Masking: If a strong sound is present on one frequency (Masker) then weaker sounds close to it may not be heard because the threshold of hearing is modified Source: Wikipedia Digital Radio and TV Systems Part I Seite 20

21 Multiplexing of Video, Audio and Data 270 Mbit/s SDI VIDEO ENCODER 5 Mbit/s 2 Mbit/s AES/EBU Data (Teletext ) AUDIO ENCODER 300 kbit/s 192 kbit/s MULTIPLEXER 5,5 Mbit/s MPEG2-TS Digital Radio and TV Systems Part I Seite 21

22 Multiplexing of more MPEG-TS Video 1 Audio 1 Data 1 Encoder PID=Packet Identifier Video 2 Audio 2 Data 2 Encoder MPEG2- Multiplexer PID=0x100 PID=0x200 PID=0x300 PID=0x400 PID=0x500 PID=0x600 PID=0x100 MPEG2-TS Transport Stream Multiplex Video 3 Audio 3 Data 3 Encoder Digital Radio and TV Systems Part I Seite 22

23 MPEG2-TS structure Sync Byte = 1 Byte Transport Error Indicator = 1 bit Packet Identifier PID 13 bit Sync Byte = 1 Byte Transport Error Indicator = 1 bit Packet Identifier PID 13 bit Reed Solomon Error Protection RS (204,188) Payload = 184 Byte Payload = 184 Byte Header 4 Byte 188 Byte Header 4 Byte 188 Byte 204 Byte Transport stream specifies a container format encapsulating packetized elementary streams, with error correction and stream synchronization features for maintaining transmission integrity when the signal is degraded Digital Radio and TV Systems Part I Seite 23

24 Synchronization problem PCR interval all < 40 ms Video, Audio MPEG2 Encoder PCR PCR MPEG2 Decoder Video, Audio 42 bit MPEG 2 - TS Counter Counter STC 27Mc STC = System Time Clock 27 Mc Numerically Controlled Oscillator PCR, or Program Clock Reference, is fundamental to the timing recovery mechanism for MPEG2 transport streams. PCR values are embedded into the adaptation field within the transport packets of defined PIDs Digital Radio and TV Systems Part I Seite 24

25 Additional Data in the MPEG-TS MPEG-2 Program Specific Information PAT Program Association Table (list of all programs in the TS) PMT Program Map Table (contain information about programs) CAT Conditional Access Table DVB SI Service Information NIT Network Information Table (info about name, RF parameter) SDT Service Descriptor Table BAT Bouquet Association Table (info about all services) EIT Event Information Table (Event info, EPG - program guide) TDT Time & Date Table (current time and date in UTC) TOT Time Offset Table (local time offset) RST Running Status Table (running status, delays..) ST Stuffing Table Digital Radio and TV Systems Part I Seite 25

26 DVB Project The DVB Project is an Alliance of about 200 companies, originally of European origin but now worldwide. Its objective is to agree specifications for digital media delivery systems, including broadcasting. It is an open, private sector initiative with an annual membership fee, governed by a Memorandum of understanding (MoU). The Members of the DVB project develop and agree specifications which are then passed to the European standards body for media systems, the EBU / CENELEC / ETSI Joint Technical Committee, for approval. The specifications are then formally standardised by either CENELEC or, in the majority of cases, ETSI. Source: DVB Project Digital Radio and TV Systems Part I Seite 26

27 DVB Project developed a transport systems for digital broadcasting Source: DVB Project Digital Radio and TV Systems Part I Seite 27

28 DVB and other digital television systems Digital Radio and TV Systems Part I Seite 28

29 At the end we need a standard Digital Radio and TV Systems Part I Seite 29

30 DVB Workflow Integrated Circuit technology Mathematical theory Coding theory Digital processing techniques University and DVB Project work ETSI Standard Prototype test RF technology End production Digital Radio and TV Systems Part I Seite 30

31 Basics of digital signal processing Why broadcast needs digital transmission: Solve problems with multipath reception and other interference Better signal (picture and audio) quality and more robustness More information capacity (more TV or Radio programs over one channel) Band width Power consumption (really? discussion), RF power, rack space Higher data security (encryption systems easier to integrate) User friendly (EPG, Scan, Data Services, Recording PVR, OTA Update) Digital Radio and TV Systems Part I Seite 31

32 Basics of Coding Encode source information, by adding additional information, sometimes referred to as redundancy, that can be used to detect, and perhaps correct errors in transmission. The more redundancy we add, the more reliably we can detect and correct errors, but the less efficient we become at transmitting the source data Digital Radio and TV Systems Part I Seite 32

33 Signal processing before modulation MPEG2 TS Baseband Interface Energy dispersal FEC 1 Outer Coder Reed Solomon Encoding Time Interleaver FEC 2 Inner Coder Convolutional Coder Puncturing I Q Code Rate 1/2...7/ Digital Radio and TV Systems Part I Seite 33

34 Signal processing before modulation DVB-T and DVB-S use 2 coding algorithms : Block Code = Reed Solomon Code Convolutional Coding and Scrambling and Interleaving Scrambler Reed Solomon Coder Time Interleaver Convolutional Coder Digital Radio and TV Systems Part I Seite 34

35 Signal processing before modulation Scrambler (energy dispersal) Use an algorithm that converts an input string into a seemingly random output string of the same length, thus avoiding long sequences of bits of the same value; in this context, a randomizer is also referred to as a scrambler. Time Interleaver Interleaving is widely used for burst error correction Example: Error-free code words: Interleaved: Transmission with a burst error: Received code words after deinterleaving: aaaabbbbccccddddeeeeffffgggg abcdefgabcdefgabcdefgabcdefg abcdefgabcd bcdefgabcdefg aa_abbbbccccdddde_eef_ffg_gg Digital Radio and TV Systems Part I Seite 35

36 Basics of Coding Block Code Reed Solomon Reed-Solomon might well be the most implemented algorithm. Barcodes use it; every CD, DVD, RAID6, and digital tape device uses it; so do digital TV Reed-Solomon belongs to a family of error-correction algorithms known as BCH (Bose- Chaudhuri-Hocquenghem-Codes). It s part of the FEC (Forward Error Correction) group. Reed-Solomon was introduced by Irving S. Reed and Gustave Solomon of MIT Labs in Polynomial Codes Over Certain Finite Fields, which was published in the Journal of the Society for Industrial and Applied Mathematics in Digital Radio and TV Systems Part I Seite 36

37 Basics of Coding Reed Solomon code In DVB Reed Solomon Code ( Outer Coder ) can correct 8 Byte Errors or 58 continue bit errors in a codeword. In the MPEG-TS the RS-Coder add additional 16 checkbytes to the 188 Databyte RS (204,188) Digital Radio and TV Systems Part I Seite 37

38 Basics of Coding Convolutional Coder (inner coding) Convolutionally encoding the data is accomplished using a shift register and associated combinatorial logic that performs modulo-two addition. The Convolutional code is used over a noisy channel The encoder is very simple to implement But the decoding is quite complex The basic code rate is ½ (called Mother Code ) The Viterbit algorithm is currently used for decoding Modulo two Digital Radio and TV Systems Part I Seite 38

39 Basics of Coding Convolutional Coder (inner coding) with puncturing Puncturing is the process of removing some of the parity bits after encoding with an error correction code. A pre-defined pattern of puncturing is used in the encoder. Then, the inverse operation, known as depuncturing, is implemented by the decoder Source: rohde&schwarz Digital Radio and TV Systems Part I Seite 39

40 Bit Error Rate The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. For example: 1 bit error in 100 transferred bits = 1/100 = 0.01 = 1E-2 = 1 * 10-2 The BER is 1E-2 Normally at the receiver input the BER is around 1E-2 The first FEC Decoder (Viterbi) should reach a BER at 2E-4 at the output. Than the Reed Solomon Decoder can reach a BER of 1E-11 called QEF (Quasi Error Free) 1 bit error during a period of 1 hour!! Digital Radio and TV Systems Part I Seite 40

41 Bit Error Rate MPEG2 TS DVB-S Front end FEC 1 Inner Decoder Viterbi Decoder FEC 2 Outer Decoder Reed Solomon Decoder MPEG2 Decoder BER<E-2 BER<2E-4 than QEF is possible BER<1E-11 QEF 1 error/hour Digital Radio and TV Systems Part I Seite 41

42 Basics of digital Modulation To transmit a signal over the air, there are three main steps: A pure carrier is generated at the transmitter The carrier is modulated with the information to be transmitted At the receiver the signal modifications or changes are detected and demodulated There are only three characteristics of a signal that can be changed over time: Amplitude Phase Frequency Digital Radio and TV Systems Part I Seite 42

43 Basics of digital Modulation AM Amplitude Modulation In AM, the amplitude of a high-frequency carrier signal is varied in proportion to the instantaneous amplitude of the modulating signal Source: Wikipedia Digital Radio and TV Systems Part I Seite 43

44 Basics of digital Modulation FM Frequency Modulation In FM, the amplitude of the modulating carrier is kept constant while its frequency is varied by the modulating signal Digital Radio and TV Systems Part I Seite 44

45 Basics of digital Modulation PM Phase Modulation In PM, the angle of the carrier wave is varied by the incoming signal Digital Radio and TV Systems Part I Seite 45

46 Basics of digital Modulation Amplitude and Phase Modulation together Polar Display A simple to view amplitude and phase is with the polar diagram. The carrier becomes a frequency and phase reference and the signal is interpreted relative to the carrier. Both are uses in digital communication systems. Source: Agilent Digital Radio and TV Systems Part I Seite 46

47 Basics of digital Modulation Different forms of modulation in polar form Source: Agilent Digital Radio and TV Systems Part I Seite 47

48 Basics of digital Modulation In digital communication, modulation is often expressed in terms of I and Q. This is a rectangular representation of the polar diagram. The I axis lies on the zero degree phase reference, and the Q axis is rotated by 90 degrees. Source: Agilent Digital Radio and TV Systems Part I Seite 48

49 Basics of digital Modulation Mapping for QPSK modulation BIT 1 BIT 0 I Q data bits Serial to Parallel Conversion I/Q Look-Up Table I Q Digital Radio and TV Systems Part I Seite 49

50 Basics of digital Modulation Why use I and Q? Digital modulation is easy to accomplish with I/Q modulators. Most digital modulation maps the data to a number of discrete points on the I/Q plane. These are know as constellation points. transmitter receiver Source: Agilent Digital Radio and TV Systems Part I Seite 50

51 Basics of digital Modulation Constellation points constellation diagram state diagram Each point is a symbol QPSK 2 bit per symbol 16-QAM 4 bit per symbol 64-QAM 6 bit per symbol Digital Radio and TV Systems Part I Seite 51

52 Basics of digital Modulation Any fast transition in a signal will require a wide occupied bandwidth. Filtering of rectangular pulses allows the transmitted bandwidth to be reduced without losing the content of the digital data. In DVB we use a so called Raised Cosine Filter Digital Radio and TV Systems Part I Seite 52

53 Basics of digital Modulation Modulation format Theoretical bandwidth efficiency limits QPSK 2 bit/second/hz 8PSK 3 bit/second/hz 16 QAM 4 bits/second /Hz 32 QAM 5 bits / second /Hz 64 QAM 6 bits / second / Hz But these figures cannot be achieved since they require perfect modulators, demodulators, filter and transmisssion paths. In real case of QPSK we need around 1,3Hz/Symbol A Symbolrate of 6 Msymb./sec. needs approx. 7,8 Mc Bandwidth Digital Radio and TV Systems Part I Seite 53

54 Basics of digital Modulation DVB DVB-T DVB-T2 DVB-S DVB-S2 DVB-C DVB-C2 DAB+ DRM DRM+ Modulation QPSK, 16-QAM, 64-QAM QPSK, 16-QAM, 64-QAM, 256-QAM QPSK QPSK, 8-PSK, 16-APSK, 32-APSK, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, 1024-QAM, 4096-QAM DQPSK 16-QAM, 64-QAM QPSK, 16-QAM Digital Radio and TV Systems Part I Seite 54

55 db Definition The decibel (db) is a logarithmic unit used to express the ratio between two values. The decibel confers a number of advantages, such as the ability to conveniently represent very large or small numbers, and the ability to carry out multiplication of ratios by simple addition and subtraction. For RF applications we use following formular: db = 10 * Log (Power Output / Power Input) Example: Power Output: 100 Watt Power Input: 50 Watt db = 10 * Log ( 100 / 50 ) = 10 * Log (2) = 3 db Digital Radio and TV Systems Part I Seite 55

56 db Definition Other example: A DVB-T transmitter needs 7 db less power for the same reception performance as an analog transmitter db = 10 Log (P1/P2) 10 db/10 = P1/P2 10 7/10 = P1/P = P1/P2 = 5.01 Normally a strong analog TV transmitter had 20 kw. The same performance (reception) is possible with an 4 kw DVB-T Transmitter! Digital Radio and TV Systems Part I Seite 56

57 Time Domain vs. Frequency Domain Source: Agilent Technologies Digital Radio and TV Systems Part I Seite 57

58 Frequency Domain measurement Spectrum Analyzer Digital Radio and TV Systems Part I Seite 58

59 Time Domain measurement Oscilloscope Digital Radio and TV Systems Part I Seite 59

60 DVB-T Digital Radio and TV Systems Part I Seite 60

61 DVB-T Facts Constellation QPSK, 16-QAM, 64-QAM FEC CC + Reed Solomon Code Rate 1/2, 2/3, 3/4, 5/6, 7/8 Guard Intervall 1/4, 1/8, 1/16, 1/32 FFT Size 2K, 8K Scattered Pilots 8% of total Continual Pilots 2,6% of total Bandwidth 5,6,7,8 MHz Max. Bitrate 31,66 Mb/s Modulation COFDM Digital Radio and TV Systems Part I Seite 61

62 DVB-T Facts Standard: ETS Digital Video Broadcasting; Framing structure, channel coding and modulation for digital Terrestrial television (DVB-T) Modulation: COFDM = Coded Orthogonal Frequency Division Multiplex = multicarrier transmission C = Forward Error correction O = Orthogonal (no cross talk between carriers) FDM = information distributed over many subcarriers Digital Radio and TV Systems Part I Seite 62

63 Channel Gaussian channel direct line of sight between TX and RX (roof top antenna situation) Digital Radio and TV Systems Part I Seite 63

64 Channel Rice channel a dominant line of sight between TX and RX Digital Radio and TV Systems Part I Seite 64

65 Channel Rayleight channel no line of sight between TX and RX, many objects attenuate, reflect, refract and diffract the signal Digital Radio and TV Systems Part I Seite 65

66 DVB-T Why we need a multicarrier transmission? A (f) A (f) f f 8 MHz UHF Channel 8 MHz UHF Channel ANALOG TV All information in one carrier Multicarrier Information spread over many carriers DVB-T: Information distributed over thousands of subcarriers Solving fading problems Digital Radio and TV Systems Part I Seite 66

67 DVB-T Multicarrier modulation Rather than carrying one data carrier on a single television frequency channel, COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulate a set of closely spaced adjacent subcarrier frequencies. A (f) In the case of DVB-T, there are two choices for the number of carriers known as 2K-mode or 8K-mode. These are actually 1,705 or 6,817 subcarriers that are approximately 4 khz or 1 khz apart. f Channel bandwidth f Each subcarrier is modulated. In this example with 16-QAM Digital Radio and TV Systems Part I Seite 67

68 DVB-T Multicarrier modulation Orthogonality condition: An OFDM signal consists of a number of closely spaced modulated carriers. Although the sidebands from each carrier overlap, they can still be received without the interference that might be expected because they are orthogonal to each another. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. Source: rohde&schwarz Digital Radio and TV Systems Part I Seite 68

69 DVB-T Multicarrier modulation Orthogonality condition: f = 1 / t Digital Radio and TV Systems Part I Seite 69

70 DVB-T Multicarrier modulation But how we can produce thousands of orthogonal subcarriers? In principle we need n I/Q modulators but this is not possible to realize. The IFFT (Inverse Fast Fourier Transform) at the transmitter side solve this problem. So we use numerical mathematic in a high integraded processor Digital Radio and TV Systems Part I Seite 70

71 DVB-T Multicarrier modulation Before we produce thousand of subcarriers we add a FEC to the datastream. (OFDM COFDM) Each of the subcarriers transmit only a small part of the overall datastream. DEMUX: Serial to parallel conversion and interleaving Each of this bits packets goes to the mapper MAPPER: mapping for each subcarrier in Real- and Imaginary number (produce complex symbols in the Frequency Domain). Two lists with thousands of Real- and Imaginary numbers are the inputs for the IFFT IFFT: Transfer of the subcarrier (in the complex plane) from the Frequency Domain in the Time Domain. Filtering, I/Q-Modulation and D/A Conversion. A RF Modulator bring the signal on the RF Frequency Digital Radio and TV Systems Part I Seite 71

72 DVB-T Guard Interval The presence of ISI in the system introduces errors in the decision device at the receiver Output Digital Radio and TV Systems Part I Seite 72

73 DVB-T Guard Interval The purpose of the guard interval is to introduce immunity to propagation delays, ISI (Intersymbol Interference),echoes, reflections and frequency selective fading, to which digital data is normally very sensitive. In COFDM, the beginning of each symbol is preceded by a guard interval. As long as the echoes fall within this interval, they will not affect the receiver's ability to safely decode the actual data, as data is only interpreted outside the guard interval. Guard Interval is a proportion of the time there is no new data transmitted. This guard interval reduces the transmission capacity. In fact during the guard interval we transmit a small part of the next symbol Digital Radio and TV Systems Part I Seite 73

74 DVB-T Guard Interval COPY Source: Rohde&Schwarz Digital Radio and TV Systems Part I Seite 74

75 DVB-T Guard Interval Each frame consists of 68 DVB-T COFDM symbols Four frames constitute one Superframe Each symbol is composed of two parts: useful part and guard interval(1/4, 1/8, 1/16, 1/32). Guard interval avoids ISI between symbols. The choice of the guard interval depends on the maximum transmission distance. MODE Symbol Guard Guard max. distance Duration (µs) Interval Interval (µs) in km 2K 224 1/ ,8 2k 224 1/8 28 8,4 2K 224 1/ ,2 2K 224 1/32 7 2,1 8K 896 1/ ,1 8K 896 1/ ,6 8K 896 1/ ,8 8K 896 1/ , Digital Radio and TV Systems Part I Seite 75

76 DVB-T Guard Interval f1 Example: GI = 224 µs (8K, ¼) 1 µs = 300m 300 x 224 = 67200m = 67,2 km f1 Receiver (RX) Digital Radio and TV Systems Part I Seite 76

77 DVB-T MFN vs. SFN MFN = Multi Frequency Network SFN = Single Frequency Network f1 f2 f1 f1 f3 f1 MFN SFN Digital Radio and TV Systems Part I Seite 77

78 DVB-T SFN (Single Frequency Network) In order to set up one SFN network, three conditions have to be fulfilled. DVB-T Transmitters belonging to one SFN cell shall radiate: over the same frequency at the same time the same OFDM symbols The first condition is easy to satisfy because all DVB-T transmitter will be configured once to the required broadcast frequency. The next two conditions imply to provide transmitter with extra information: Synchronization Transmission parameters This is specifically the task of the Single Frequency Network (SFN) adapter. SFN adapter will add to the TS stream all the information required by the transmitter Digital Radio and TV Systems Part I Seite 78

79 DVB-T SFN Adapter MIP Packet Synchronization and transmission information sent to the transmitter are stored into one TS packet called MIP packet. DVB normalized ist PID to 0x15. MIP = Megaframe Initialization Packet The MIP Packet consist of: Synchronization parameters (network delay, STS = Synchronization Time Stamp) Transmission parameter (bandwidth, FFT Mode, constellation, guard interval, code rate) Optional functions data (tx time offset, tx frequency offset, tx cell ID) Digital Radio and TV Systems Part I Seite 79

80 DVB-T SFN (Single Frequency Network) But how is synchronization achieved? When talking about transmitters synchronization, two main synchronization criteria have to be taken into account: 1. Temporal synchronization: DVBT-Transmitters broadcasting synchronously, at the same time. SFN adapter/mip inserter aim to provide synchronization information to transmitters based on one common clock reference: GPS 2. Frequency synchronization: Transmitters broadcast exactly the same set of subcarriers. The accuracy of 10 MHz (derived from 1PPS from the GPS signal) will guarantee any transmitter belonging to one SFN cell to broadcast exactly the same set of subcarriers (same frequency, no frequency shift) Digital Radio and TV Systems Part I Seite 80

81 DVB-T Pilot carriers In order to simplify the reception of the signal being transmitted on the terrestrial TV channel, additional signals are inserted in each block. Pilot signals are used during the synchronization and equalization phase, while TPS signals (Transmission Parameters Signalling) send the parameters of the transmitted signal and to unequivocally identify the transmission cell. The receiver must be able to synchronize, equalize, and decode the signal to gain access to the information held by the TPS pilots. The receiver analyse the pilot carriers (scattered and continual pilots) contained in the signal and calculate from these the linear distortion. After that a channel estimation is possible. The pilots are BPSK modulated at a boosted power level, 16/9 times greater than that used for the data and TPS symbols Digital Radio and TV Systems Part I Seite 81

82 DVB-T Pilots Continual pilots Fixed position in spectrum Fixed position in constellation diagram Used for automatic frequency control (AFC) They are located on the real axis (0 or 180 degrees) and have a defined amplitude The continual pilots are boosted by 3 db compared with the average signal power Digital Radio and TV Systems Part I Seite 82

83 DVB-T Pilots Scattered pilots Variable position in spectrum Fixed position in constellation diagram sweeping over spectrum Used for channel estimation & correction They are located also on the I axis at 0 or 180 degrees and have the same amplitude as the continual pilots Each scattered pilot jumps forward by three carrier positions in the next symbol Digital Radio and TV Systems Part I Seite 83

84 DVB-T TPS carrier TPS carrier Fixed position in spectrum BPSK modulation Transmission parameter signaling (TPS) Fast information channel from TX to RX about the current transmission parameter. All the TPS carriers in one symbol carry the same information. They are all either at 0 degrees or all at 180 degrees on the I axis. The TPS carriers keep the receiver informed about Mode (2K or 8K) Length of the guard interval (1/4, 1/8, 1/16, 1/32) Type of modulation (QPSK, 16QAM, 64QAM) and Code Rate Use of hierachical coding Digital Radio and TV Systems Part I Seite 84

85 DVB-T Pilots and TPS carrier Digital Radio and TV Systems Part I Seite 85

86 DVB-T Carriers position Digital Radio and TV Systems Part I Seite 86

87 DVB-T Type of transmitter for digital terrestrial television Transmitter transmit the signal over a defined RF channel f1 input ASI or IP (via microwave link, fiber or satellite) Transposer receive the signal from another TX on f1 and transmit the same signal on an another RF channel f2 Gap-Filler receive the signal from another TX on f1 and transmit the same signal on the same channel f1. A problem is the isolation between input/output antenna. Limitation of the output power at around 100W Digital Radio and TV Systems Part I Seite 87

88 DVB-T Transmission After adding additional information to the datastream the modulator modulate the signal in COFDM. DATA (MPEG TS) Coding (RS+CC) Guard Interval MIP packet Pilots TPS carrier info COFDM Modulation Spectrum dvb-t signal Digital Radio and TV Systems Part I Seite 88

89 DVB-T Spectrum and C/N (Carrier to noise) Bandwidth C/N Noisefloor Digital Radio and TV Systems Part I Seite 89

90 DVB-T C/N vs. BER Required C/N for dvb-t transmission to achieve a BER = after the Viterbi decoder Digital Radio and TV Systems Part I Seite 90

91 DVB-T Cliff Effect in digital transmissions If an error level exceeds the number of errors that can be corrected by the FEC design, then the system will fail dramatically. This leads to a behavior often dubbed the "cliff effect - a step function in performance that occurs when errors exceed the critical level. When the error level is below that critical level for which the FEC can compensate, a transmission will seem relatively error free, even in the presence of a large number of errors. Then, all of a sudden, things may go drastically wrong if the critical level is exceeded, the performance "falls off the cliff Digital Radio and TV Systems Part I Seite 91

92 Cliff Effect in digital transmissions Source: IfN Braunschweig Digital Radio and TV Systems Part I Seite 92

93 DVB-T MER MER Modulation Error Ratio which is an indicator of noise, interferences or distortions on DVB-T/T2 signals and is a figure of merit. Source: Agilent A good MER at the transmitter site should have a MER>35 db. MER, beside BER (C/N), is the primary parameter in a DVB transmission system as it provides information on transmission quality Digital Radio and TV Systems Part I Seite 93

94 DVB-T MER MER Modulation Error Ratio Digital Radio and TV Systems Part I Seite 94

95 DVB-T Receiver RF Input Tuner Frontend A/D FFT Channel Estimation Demux Demapping Inner Interleaver MPEG2-TS De- Srambler Outer Decoder Outer Interleaver Inner Decoder Reed Solomon Viterbi Decoder Digital Radio and TV Systems Part I Seite 95

96 DVB-T Net Data Rate Net Data Rate = 188/204 * Code Rate * log2 (m) * 1/(1+guard) * channel * const1 m: 5/6, 7/8 Guard: 1/4, 1/8, 1/16, 1/32 Channel: Const1 1 (8MHz), 7/8 (7 MHz) 6.75 E+6 bit/s = 6.75 * bit/s Example: DVB-T in Vienna, Channel 24 = (CR 3/4, GI 1/4, 16-QAM) Net Data Rate = * 0.75 * 4 * 0.8 * 1 * 6.75E+6 = = 14.9 Mbit/sek. 4(QPSK), 16(16QAM), 64 (64QAM) log2(m): 2(QPSK), 4(16QAM), 6 (64QAM) Code Rate: 1/2, 2/3, 3/4, Digital Radio and TV Systems Part I Seite 96

97 DVB-T Digital Radio and TV Systems Part I Seite 97

98 DVB-T2 Facts Constellation FEC QPSK, 16-QAM, 64-QAM, 256 QAM LDPC + BCH Code Rate 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 7/8 1/4, 19/256, 1/8, 19/128, 1/16, 1/32, Guard Intervall 1/128 FFT Size Scattered Pilots Continual Pilots Bandwidth Max. Bitrate Modulation 1K, 2K, 4K, 8K, 16K, 32K 1%, 2%, 4%, 8% of total 0,35% of total 1.7, 5,6,7,8 MHz 50,34 Mb/s COFDM Red: different to dvb-t Digital Radio and TV Systems Part I Seite 98

99 DVB-T vs. DVB-T2 Better coding systems based on DVB-S2 Outer FEC: BCH Coding Inner FEC: LDPC Coding Rotated constellation More parameters (GI, CR, FFT Size, Pilots) PLP Technology Future Extension Frames (FEF) Transmission for mobile and stationary receivers Improved SFN performance BCH=Bose-Chaudhuri-Hocquenghem LDPC=Low Density Parity Check Code Digital Radio and TV Systems Part I Seite 99

100 DVB-T vs. DVB-T2 DVB-T2 uses the same error correction coding as used in DVB-S2 and DVB-C2 => LDPC and BCH coding. The number of carriers, guard interval sizes and pilot signals can be adjusted, so that the overheads can be optimised for any transmission channel. DVB-T2 can offer a much higher data rate than DVB-T OR a much more robust signal Digital Radio and TV Systems Part I Seite 100

101 Shannon Law Source: R&S Digital Radio and TV Systems Part I Seite 101

102 Shannon Law Source: R&S Digital Radio and TV Systems Part I Seite 102

103 Coding DVB-T2 with the new coding 30% more net data rate is possible Additional we can use MPEG4 (half data rate to MPEG2). Example: DVB-T with ~ 15 Mbit to DVB-T2 with ~ 30 Mbit in Baseband Scrambler BCH Coder LDPC Coder Bit Interleaver out Digital Radio and TV Systems Part I Seite 103

104 QEF DVB-T2 If the received signal is above the C/N threshold, the Forward Error Correction (FEC) technique adopted in the System is designed to provide a "Quasi Error Free" (QEF) quality target. The definition of QEF adopted for DVB-T2 is "less than one uncorrected error-event per transmission hour at the level of a 5 Mbit/s single TV service decoder", approximately corresponding to a Transport Stream Packet Error Ratio PER < 10-7 before the de-multiplexer Digital Radio and TV Systems Part I Seite 104

105 Rotated constellation Rotation of constellation diagram gives different projection points on I and Q axis for each constellation point instead of same projection point in case of non-rotated diagram. This can be used for soft decision Source: Enensys, R&S Digital Radio and TV Systems Part I Seite 105

106 PLP A PLP (Physical Layer Pipe ) is a logical channel that may carry one or multiple services. Each PLP can have a different bit rate and error protection parameters. For example, it's possible to split SD and HD services to different PLPs Source: Enensys Digital Radio and TV Systems Part I Seite 106

107 Pilots in DVB-T2 Edge pilots Continual pilots Scattered pilots (8 different pilot pattern PP1-PP8) Frame closing pilots P2 pilots Purpose of pilot insertion Channel estimation (and equalisation) Synchronisation Common Phase Error correction As a form of padding Digital Radio and TV Systems Part I Seite 107

108 T2-MI interface Source: R&S Digital Radio and TV Systems Part I Seite 108

109 T2-MI interface (T2 Gateway) BB frames, PLP => payload packed in BB frames and transmitted via PLPs L1 signaling => DVB-T2 setup configuration data (e.g. FEC, interleaver, modulation of different PLPs Timestamp => used for SFN synchronization FEF => Additional frame structure to transmit other T2 profiles (e.g. T2-Lite) AUX => I/Q data, T2-MI packet type IA => used for configuration of individual transmitters T2-MI packets are encapsulated into DVB/MPEG transport stream packets using data piping Digital Radio and TV Systems Part I Seite 109

110 DVB-T2 Spectrum optimal DVB-T2 signal Digital Radio and TV Systems Part I Seite 110

111 DVB-T2 Spectrum weak DVB-T2 signal Digital Radio and TV Systems Part I Seite 111

112 Terrestrial DVB-T/T2 distribution Digital Radio and TV Systems Part I Seite 112

113 Reception problems Digital Radio and TV Systems Part I Seite 113

114 RF attenuation in buildings distance between the transmitting aerial and the building height of the transmitting aerial above the ground the type of electromagnetic wave propagation the construction and the width of the building the number and the height of the floors layers of the glass surfaces Digital Radio and TV Systems Part I Seite 114

115 Antenna types for DVB-T/T2 reception Roof top antenna (Yagi) Indoor antennas Digital Radio and TV Systems Part I Seite 115

116 DVB-T/T2 transmit antennas Digital Radio and TV Systems Part I Seite 116

117 Digital Radio and TV Systems Part 2 V.1.1 Course at FH Technikum Wien DI Peter Knorr Seite 1

118 DVB-S Digital Radio and TV Systems Part II Seite 2

119 DVB-S A geostationary orbit is a circular orbit directly above the earth's equator approximately 35,780 km above ground. Condition: gravitional force = centripetal force D = km The geostationary orbit where the satellites are in is also called the Clarke Belt, named after Arthur C. Clarke. He was a British scientist who first proposed the idea of the geostationary orbit used by today's satellites Digital Radio and TV Systems Part II Seite 3

120 DVB-S Geostationary orbit difficult to achieve more launch performance needed no service to polar regions (highest latitude 71 ) satellite first inserted in inclined elliptical transfer orbit Orbital perturbations (Sun, Moon, radiation pressure of the sun) Coverage by GEO Digital Radio and TV Systems Part II Seite 4

121 Satellite orbital position Example: SES Astra Longitude 19,2 East Vienna: N E Digital Radio and TV Systems Part II Seite 5

122 SES Satellite Fleet Digital Radio and TV Systems Part II Seite 6

123 Satellite footprint Source: SES Digital Radio and TV Systems Part II Seite 7

124 DVB-S Uplink - Downlink Digital Radio and TV Systems Part II Seite 8

125 Satellite Uplink Station Digital Radio and TV Systems Part II Seite 9

126 Polarisation An electromagnetic wave consists of electric field magnetic field Polarisation is the orientation of the electric (E) vector in an electromagnetic wave, frequently horizontal or vertical Digital Radio and TV Systems Part II Seite 10

127 Satellite transponder A satellite channel is called transponder, because it is a separate transceiver or repeater Digital Radio and TV Systems Part II Seite 11

128 LNB Low Noise Block Converter The LNB is a combination of low-noise amplifier, frequency mixer, local oscillator and IF amplifier. It receives the microwave signal from the satellite ( GHz) collected by the dish, amplifies it, and downconverts the block of frequencies to a lower block of intermediate frequencies (IF = MHz). This downconversion allows the signal to be carried to the indoor satellite TV receiver using a relatively cheap coaxial cable. Source text: Wikipedia Digital Radio and TV Systems Part II Seite 12

129 Satellite parabol antenna types Source: Wikipedia Digital Radio and TV Systems Part II Seite 13

130 Azimuth - Elevation Azimuth Elevation ASTRA 19.2 Vienna: Azimuth =176 ; Elevation = 34, Digital Radio and TV Systems Part II Seite 14

131 Elevation Elevation Offset satellite antenna Digital Radio and TV Systems Part II Seite 15

132 Elevation Elevation for location Vienna Digital Radio and TV Systems Part II Seite 16

133 Signal level vs. modulation DVB-T/T2 distance < 100km, high power TX, channel estimation possible Modulation in Amplitude + Phase (256-QAM) DVB-C/C2 distance ~ some km, Line-amplifier (high signal level), channel characteristic constant Modulation in Amplitude + Phase (4096-QAM) DVB-S/S2 distance 36000km Downlink, channel unknown because of weather conditions (rain, clouds) only Phase modulation (QPSK, 8PSK ) Digital Radio and TV Systems Part II Seite 17

134 Free-space path loss c = Speed of light = km/s = 3 x 10 8 m/s Frequency f in Hz Wavelenght λ in m C = λ. f Free space path loss in vacuum F: F = 20 log (4 π d / λ) Unit: db Example for satellite receive path: d = km = * 10 3 m f = 14 GHz = 14 x 10 9 Hz => λ= 3 x 10 8 / 14 x 10 9 = 0,0214 m F = 20 log (4 x 3,14 x x 10 3 / 0,0214) = 206 db (but this is without atmospheric attenuation calculations) Digital Radio and TV Systems Part II Seite 18

135 Attenuation on satellite links Atmospheric propagation degradation on satellite links Cloud and fog Rain attenuation Oxygen attenuation Water vapour Atmospheric clouds Digital Radio and TV Systems Part II Seite 19

136 DVB-S Modulation QPSK Spectrum Digital Radio and TV Systems Part II Seite 20

137 Amplifier back off In case of digital modulation it is not possible to operate an amplifier at saturation. A backoff at about 3dB or more is necessary to reach the linear range. This is done to avoid that the intermodulation products originating from the input carrier signal raise over a certain level, causing excessive interference in the adjacent bands Digital Radio and TV Systems Part II Seite 21

138 DVB-S Modulation Same data block diagram as DVB-T Digital Radio and TV Systems Part II Seite 22

139 DVB-S Net data rate Formular: Net data rate = Symbolrate * 2 (QPSK) * FEC * (1/RS) Example: Astra satellite channel 117 Symbolrate = 22 Msymb./sec. FEC = 5/6, RS (204,188) 1/RS = 0.92 Net data rate = 22 * 2 * * 0.92 = Mbit/sec. Symbolrate 22 Msymb./sec. = 44 Mbit/sec. (QPSK) means Mbit/sec. for coding Digital Radio and TV Systems Part II Seite 23

140 DVB-S BER vs. Eb/No Example: Eb/N0 = C/N 2,2 db for QPSK, FEC = 5/ Digital Radio and TV Systems Part II Seite 24

141 Eb/No Eb/N 0 (the energy per bit to noise power spectral density ratio) is an important parameter in digital communication. It is a normalized signal-to-noise ratio (SNR) measure, also known as the "SNR per bit". It is especially useful when comparing the bit error rate (BER) performance of different digital modulation schemes without taking bandwidth into account. Eb = Energy required per bit of information N 0 = thermal noise in 1Hz of bandwidth R = system data rate BT= system bandwidth SNR = (Eb/N 0 ) * (R/BT) Digital Radio and TV Systems Part II Seite 25

142 DVB-S Digital Radio and TV Systems Part II Seite 26

143 DVB-S2 DVB-S 1994 DVB-S New optimized FEC (LDPC + BCH coding) used in DVB-S2. Later exactly the same coding in DVB-T2 and DVB-C2 30% higher data rates than in DVB-S Designed for Broadcast and commercial use like DSNG Digital Radio and TV Systems Part II Seite 27

144 DVB-S2 Modulation Phase modulation (consumer) QPSK (consumer) 8-PSK (consumer) 16APSK (for commercial use) 32APSK (for commercial use) Digital Radio and TV Systems Part II Seite 28

145 Robustness DVB-S vs. DVB-S2 Minimum C/N - Fall of the Cliff Test results from Rohde&Schwarz - HUMAX DVB-S2 ST DVB-S DVB-S2, QPSK DVB-S2, 8PSK CR C/N (db) CR C/N (db) CR C/N (db) 1/ / / / / / / / / / / / / / / / / / / Digital Radio and TV Systems Part II Seite 29

146 Conditional Access (CA) To protect a DVB transmission, the DVB standard integrates into its broadcasting infrastructure an access control mechanism, commonly known as Conditional Access, or CA. To avoid confusion, the DVB-CA specification uses the terms scrambling and descrambling to mean the encrypting and decrypting of TV contents Digital Radio and TV Systems Part II Seite 30

147 Scrambling (used in all DVB systems) Free to air (no scrambling) Free to view (scrambled but after registration free) Pay TV (scrambled with monthly costs) Systems: with Smard Card Cardless Digital Radio and TV Systems Part II Seite 31

148 Scrambling (used in all DVB systems) Digital Radio and TV Systems Part II Seite 32

149 Digital Radio and TV Systems Part 3 V.1.1 Course at FH Technikum Wien DI Peter Knorr Seite 1

150 DVB-C/C Digital Radio and TV Systems Part III Seite 2

151 DVB-C/C Digital Radio and TV Systems Part III Seite 3

152 DVB-C No concatenated codes (DVB-T, DVB-S) Only Reed Solomon no convolutional coder (no channel estimation necessary because of robust channel characteristic cable) Digital Radio and TV Systems Part III Seite 4

153 DVB-C SMATV: Satellite master antenna television distribution system TDT: Transparent digital transmodulation Digital Radio and TV Systems Part III Seite 5

154 DVB-C Prior to modulation, the I and Q signals shall be squareroot raised cosine filtered. The roll-off factor is 0,15. Source: R&S Digital Radio and TV Systems Part III Seite 6

155 DVB-C Main target: It should be possible to receive a Mux from a satellite transponder with e.g a bandwidth of 33 MHz and transfer the TS stream direct without conversion into a cable RF channel with a bandwidth of 8 MHz. Satellite: QPSK, 27.5 Msymb./sek., FEC= ¾ Net bit rate = Mbit/sek. DVB-C net bit rate: ld(m) * symbol rate * 188/204 6 Bit/Symbol (64-QAM) * 6.9 Msymb./sek. * 188/204 = Mbit/sek Digital Radio and TV Systems Part III Seite 7

156 DVB-C Frequency Identification Channel MHz Band I HF und VHF I C2... C MHz Band II VHF II FM MHz Midband MB S2... S MHz Band III VHF III C5... C MHz Superband SB S11... S MHz Hyperband HB S21... S MHz Band IV UHF IV C21... C MHz Band V UHF V C40... C Digital Radio and TV Systems Part III Seite 8

157 DVB-C Internet over cable infrastructure EuroDOCSIS DOCSIS = Data Over Cable Service Interface Specification Digital Radio and TV Systems Part III Seite 9

158 DVB-C Spectrum of DVB-C signals Digital Radio and TV Systems Part III Seite 10

159 DVB-C2 Based on DVB-S2/T2 COFDM with 4k Mode (4096 carrier), short guard intervals because of short reflections. Subcarrier distance khz FEC with LDPC like T2/S2 Multiple TS and GS (generic streams) Single and multiple PLP Modulation QSPK 4096 QAM Variable coding and modulation Digital Radio and TV Systems Part III Seite 11

160 DVB-C2 3 type of interleaver (bit, time and frequency) Pilots like T2 (edge, continual and scattered) Broadband signals possible (e.g. 32 MHz) Sony DVB-C2 Demodulator chip Digital Radio and TV Systems Part III Seite 12

161 DVB-C/C2 Signal level vs. analog TV Source: Fischer R&S Digital Radio and TV Systems Part III Seite 13

162 DVB-C Digital Radio and TV Systems Part III Seite 14

163 Digital Radio and TV Systems Part 4 V.1.0 Course at FH Technikum Wien DI Peter Knorr Seite 1

164 DAB Digital Radio and TV Systems Part IV Seite 2

165 DAB / DAB+ History: Digital radio is one of the 'older' forms of new digital media. Research Project Eureka-147 (1987) Digital Audio Broadcasting (DAB) The MPEG-1 Audio Layer II ("MP2") codec was created as part of the EU147 project DAB was the first standard based on orthogonal frequency division multiplexing (OFDM) modulation technique, which since then has become one of the most popular transmission schemes for modern wideband digital communication systems. First DAB digital radio broadcasts in September 1995 (BBC, NRK) Digital Radio and TV Systems Part IV Seite 3

166 DAB ETSI Norm (February 1995) ETS Radio Broadcasting Systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers Digital Radio and TV Systems Part IV Seite 4

167 DAB Problems with FM Multipath fading (reflections from buildings, vehicles); very large variations in signal strength over distances of ~ 1m Interference (from equipment, vehicles and other radio stations) Digital Radio and TV Systems Part III Seite 5

168 DAB / DAB+ The Eureka 147 system comprises three main elements Source Coding: MUSICAM Audio Coding = MP2 ( by Philips, IRT, CCETT ) Masking Pattern Universal Sub-band Integrated Coding And Multiplexing Since 2011 DAB+ with a new audio compression format: HE AAC+ V2 Transmission coding & multiplexing Channel Coding: Convolution, Puncturing, Freq & Time interleaving COFDM Modulation Digital Radio and TV Systems Part III Seite 6

169 DAB additional frequencies in L-Band (1.4 GHz) Digital Radio and TV Systems Part III Seite 7

170 DAB Frequency planning Source: Komm Austria Digital Radio and TV Systems Part III Seite 8

171 DAB Receiving side Home receivers (Hifi tuners, kitchen radios, clock radios, portable stereo systems) Car radios Portable receivers, mobile phones, tablets PC-based receivers (USB device) Monitor receivers for network monitoring Fixed portable mobile Indoor = Outdoor Digital Radio and TV Systems Part III Seite 9

172 DAB DAB+ An upgraded version of the DAB system was released in February 2007, which is called DAB+. DAB is not forward compatible with DAB+, which means that DAB-only receivers will not be able to receive DAB+ broadcasts. DAB+ is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide high quality audio with as low as 64kbit/s. Reception quality will also be more robust on DAB+ than on DAB due to the addition of Reed-Solomon error correction coding Digital Radio and TV Systems Part III Seite 10

173 DAB DAB+ Source: Fraunhofer Digital Radio and TV Systems Part III Seite 11