Digital Radio and TV Systems Part 1 V. 2
Course at FH Technikum Wien
DI Peter Knorr How it all began
1924 first radio transmission in Austria
25.07.2014 Digital Radio and TV Systems Part I Seite 2 How it all began
1955 first television transmission in Austria
25.07.2014 Digital Radio and TV Systems Part I Seite 3 How it all began
1972 colour television in Austria
25.07.2014 Digital Radio and TV Systems Part I Seite 4 How we developed digital TV
2006 – 2011 analog switch off – start of digital terrestrial television DVB-T in Austria
25.07.2014 Digital Radio and TV Systems Part I Seite 5 Next generation of digital television
2013 start of second generation of digital terrestrial television DVB-T2 in Austria
25.07.2014 Digital Radio and TV Systems Part I Seite 6 Digitalization of Broadcast in 2014
25.07.2014 Digital Radio and TV Systems Part I Seite 7 Definitions
Broadcast is a point to multipoint system
25.07.2014 Digital Radio and TV Systems Part I Seite 8 Definitions
Mobile Communication is a point to point system
25.07.2014 Digital Radio and TV Systems Part I Seite 9 Analog TV (Do you remember ?)
Ghosting Weak signal Electrical Transmitter (Multi path) Interference Interference
Source: www.rsm.govt.nz
25.07.2014 Digital Radio and TV Systems Part I Seite 10 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
25.07.2014 Digital Radio and TV Systems Part I Seite 11 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
25.07.2014 Digital Radio and TV Systems Part I Seite 12 Developing of a digital broadcasting system
But 1966 no processor power was available to realize this system
25.07.2014 Digital Radio and TV Systems Part I Seite 13 Developing of a digital broadcasting system
Video compression formats Audio compression formats
.1991 MPEG 1 .MPEG 1 Layer 1,2,3 (1989-1992)
.1994 MPEG 2 .AAC (1997), HE-AAC,
.2001 MPEG 4 (H.264) .Extended HE-AAC (2013)
.2013 H265 .Dolby Digital Audio AC-3 (1990)
MPEG = Moving Pictures Expert Group .Dolby Digital Plus (E-AC-3)
AAC = Advanced Audio Codec
25.07.2014 Digital Radio and TV Systems Part I Seite 14 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.
25.07.2014 Digital Radio and TV Systems Part I Seite 15 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 = 1.485 Gbit/s
Compression to MPEG2 (~ 2o Mbit) or MPEG4 (~ 10 Mbit)
Video elementary stream 1.5 …7 (15) Mbit/s
25.07.2014 Digital Radio and TV Systems Part I Seite 16 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 GOP (Group of Pictures) 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 Forward Prediction I-Frame B-Frame B-Frame P-Frame I-Frame motion-compensated difference Intra Bidirectional Bidirectional Predicted Intra Frame Predicted Predicted Picture Frame Backward Prediction Coded Picture Picture Coded information relative to previously Picture Picture decoded pictures
25.07.2014 Digital Radio and TV Systems Part I Seite 17
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
25.07.2014 Digital Radio and TV Systems Part I Seite 18 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
25.07.2014 Digital Radio and TV Systems Part I Seite 19 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
25.07.2014 Digital Radio and TV Systems Part I Seite 20 Multiplexing of Video, Audio and Data
270 Mbit/s SDI VIDEO 5 Mbit/s ENCODER
2 Mbit/s AUDIO AES/EBU 192 kbit/s 5,5 Mbit/s ENCODER MPEG2-TS MULTIPLEXER Data (Teletext …) 300 kbit/s
25.07.2014 Digital Radio and TV Systems Part I Seite 21 Multiplexing of more MPEG-TS
Video 1 Audio 1 Data 1 Encoder PID=Packet Identifier
Video 2 PID = 0 x 100 PID = 0 x 100 PID = 0 x 200 PID = 0 x 300 PID = 0 x 400 PID = 0 x 500 PID = 0 x 600 Audio 2 MPEG2-TS Transport Stream Multiplex Data 2 Encoder MPEG 2 - Multiplexer
Video 3
Audio 3
Data 3 Encoder
25.07.2014 Digital Radio and TV Systems Part I Seite 22 MPEG2-TS structure
Byte 1 = = 1 bit = 1 bit 13 bit 13 bit Reed Solomon Error Protection Packet Identifier PID Identifier Packet Packet Identifier PID Identifier Packet Sync Byte = 1 Byte Sync Byte Transport Error Indicator Sync Byte Sync Byte Transport Error Indicator RS (204,188)
Payload = 184 Byte Payload = 184 Byte
Header Header 4 Byte 4 Byte 188 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.
25.07.2014 Digital Radio and TV Systems Part I Seite 23 Synchronization problem
PCR interval all < 40 ms
MPEG2 MPEG2 Video, Audio Encoder Decoder Video, Audio PCR PCR MPEG 2 - TS 42 bit Counter Counter
STC – 27Mc
STC = System Time Clock Numerically 27 Mc 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.
25.07.2014 Digital Radio and TV Systems Part I Seite 24 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
25.07.2014 Digital Radio and TV Systems Part I Seite 25 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
25.07.2014 Digital Radio and TV Systems Part I Seite 26 DVB Project developed a transport systems for digital broadcasting
www.dvb.org Source: DVB Project
25.07.2014 Digital Radio and TV Systems Part I Seite 27 DVB and other digital television systems
www.dvb.org
25.07.2014 Digital Radio and TV Systems Part I Seite 28 At the end we need a standard
25.07.2014 Digital Radio and TV Systems Part I Seite 29 DVB Workflow
Integrated Circuit technology
Mathematical theory
Coding ETSI Prototype theory Standard test work
Digital processing techniques University and DVB Project
RF technology End production
25.07.2014 Digital Radio and TV Systems Part I Seite 30 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)
25.07.2014 Digital Radio and TV Systems Part I Seite 31 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
25.07.2014 Digital Radio and TV Systems Part I Seite 32 Signal processing before modulation
FEC 1 FEC 2 Outer Inner Coder Coder MPEG2 I TS Baseband Energy Reed Time Convolutional Puncturing Interface dispersal Solomon Interleaver Coder Q Encoding
Code Rate 1/2...7/8
25.07.2014 Digital Radio and TV Systems Part I Seite 33 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 Time Convolutional Coder Interleaver Coder
25.07.2014 Digital Radio and TV Systems Part I Seite 34 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: aaaabbbbccccddddeeeeffffgggg Interleaved: abcdefgabcdefgabcdefgabcdefg Transmission with a burst error: abcdefgabcd____bcdefgabcdefg Received code words after deinterleaving: aa_abbbbccccdddde_eef_ffg_gg
25.07.2014 Digital Radio and TV Systems Part I Seite 35
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 1960.
25.07.2014 Digital Radio and TV Systems Part I Seite 36 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)
25.07.2014 Digital Radio and TV Systems Part I Seite 37 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
25.07.2014 Digital Radio and TV Systems Part I Seite 38 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
25.07.2014 Digital Radio and TV Systems Part I Seite 39 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 !!
25.07.2014 Digital Radio and TV Systems Part I Seite 40 Bit Error Rate
FEC 1 FEC 2 Inner Outer Decoder Decoder MPEG2 DVB-S TS Viterbi Reed Front MPEG2 Decoder Solomon Decoder end Decoder
BER 25.07.2014 Digital Radio and TV Systems Part I Seite 41 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 25.07.2014 Digital Radio and TV Systems Part I Seite 42 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 25.07.2014 Digital Radio and TV Systems Part I Seite 43 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 25.07.2014 Digital Radio and TV Systems Part I Seite 44 Basics of digital Modulation . PM – Phase Modulation In PM, the angle of the carrier wave is varied by the incoming signal 25.07.2014 Digital Radio and TV Systems Part I Seite 45 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 25.07.2014 Digital Radio and TV Systems Part I Seite 46 Basics of digital Modulation Different forms of modulation in polar form Source: Agilent 25.07.2014 Digital Radio and TV Systems Part I Seite 47 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 25.07.2014 Digital Radio and TV Systems Part I Seite 48 Basics of digital Modulation Mapping for QPSK modulation BIT 1 BIT 0 I Q 0 0 +1 +1 0 1 -1 +1 1 0 -1 -1 1 1 +1 -1 I data bits Serial to I/Q Parallel Look-Up 01101.. Conversion Table Q 25.07.2014 Digital Radio and TV Systems Part I Seite 49 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. Source: Agilent transmitter receiver 25.07.2014 Digital Radio and TV Systems Part I Seite 50 Basics of digital Modulation Constellation points – constellation diagram – state diagram Each point is a “symbol” QPSK 16-QAM 64-QAM 2 bit per symbol 4 bit per symbol 6 bit per symbol 25.07.2014 Digital Radio and TV Systems Part I Seite 51 Basics of digital Modulation Any fast transition in a signal w ill 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” 25.07.2014 Digital Radio and TV Systems Part I Seite 52 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 25.07.2014 Digital Radio and TV Systems Part I Seite 53 Basics of digital Modulation DVB Modulation DVB-T QPSK, 16-QAM, 64-QAM DVB-T2 QPSK, 16-QAM, 64-QAM, 256-QAM DVB-S QPSK DVB-S2 QPSK, 8-PSK, 16-APSK, 32-APSK, DVB-C 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM DVB-C2 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, 1024-QAM, 4096-QAM DAB+ DQPSK DRM 16-QAM, 64-QAM DRM+ QPSK, 16-QAM 25.07.2014 Digital Radio and TV Systems Part I Seite 54 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 25.07.2014 Digital Radio and TV Systems Part I Seite 55 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) dB/10 10 = P1/P2 7/10 10 = P1/P2 0.7 10 = 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 ! 25.07.2014 Digital Radio and TV Systems Part I Seite 56 Time Domain vs. Frequency Domain Source: Agilent Technologies 25.07.2014 Digital Radio and TV Systems Part I Seite 57 Frequency Domain measurement Spectrum Analyzer 25.07.2014 Digital Radio and TV Systems Part I Seite 58 Time Domain measurement Oscilloscope 25.07.2014 Digital Radio and TV Systems Part I Seite 59 DVB-T 25.07.2014 Digital Radio and TV Systems Part I Seite 60 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 25.07.2014 Digital Radio and TV Systems Part I Seite 61 DVB-T Facts Standard: ETS 300 744 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 25.07.2014 Digital Radio and TV Systems Part I Seite 62 Channel Gaussian channel – direct line of sight between TX and RX (roof top antenna situation) 25.07.2014 Digital Radio and TV Systems Part I Seite 63 Channel Rice channel – a dominant line of sight between TX and RX 25.07.2014 Digital Radio and TV Systems Part I Seite 64 Channel Rayleight channel – no line of sight between TX and RX, many objects attenuate, reflect, refract and diffract the signal 25.07.2014 Digital Radio and TV Systems Part I Seite 65 DVB-T – Why we need a multicarrier transmission ? A (f) A (f) f f 8 MHz UHF Channel 8 MHz UHF Channel ANALOG TV Multicarrier All information Information spread in one carrier over many carriers DVB-T: Information distributed over thousands of subcarriers Solving fading problems 25.07.2014 Digital Radio and TV Systems Part I Seite 66 DVB-T – Multicarrier modulation Rather than carrying one data carrier on a single television frequency channel, COFDM works by splitting the digital data A (f) stream into a large number of slower digital streams, each of which digitally modulate a set of closely spaced adjacent subcarrier frequencies. f In the case of DVB-T, there are two choices for the number of carriers known f as 2K-mode or 8K-mode. These are Channel bandwidth actually 1,705 or 6,817 subcarriers that are approximately 4 kHz or 1 kHz apart. Each subcarrier is modulated. In this example with 16-QAM. 25.07.2014 Digital Radio and TV Systems Part I Seite 67 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 25.07.2014 Digital Radio and TV Systems Part I Seite 68 DVB-T – Multicarrier modulation Orthogonality condition: f = 1 / t 25.07.2014 Digital Radio and TV Systems Part I Seite 69 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. 25.07.2014 Digital Radio and TV Systems Part I Seite 70 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 25.07.2014 Digital Radio and TV Systems Part I Seite 71 DVB-T – Guard Interval The presence of ISI in the system introduces errors in the decision device at the receiver Output. 25.07.2014 Digital Radio and TV Systems Part I Seite 72 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. 25.07.2014 Digital Radio and TV Systems Part I Seite 73 DVB-T – Guard Interval COPY Source: Rohde&Schwarz 25.07.2014 Digital Radio and TV Systems Part I Seite 74 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 1/4 56 16,8 2k 224 1/8 28 8,4 2K 224 1/16 14 4,2 2K 224 1/32 7 2,1 8K 896 1/4 224 67,1 8K 896 1/8 112 33,6 8K 896 1/16 56 16,8 8K 896 1/32 28 8,4 25.07.2014 Digital Radio and TV Systems Part I Seite 75 DVB-T – Guard Interval f1 Example: GI = 224 µs (8K, ¼) 1 µs = 300m 300 x 224 = 67200m = 67,2 km f1 Receiver (RX) 25.07.2014 Digital Radio and TV Systems Part I Seite 76 DVB-T – MFN vs. SFN MFN = Multi Frequency Network SFN = Single Frequency Network f1 f2 f1 f1 f3 f1 MFN SFN 25.07.2014 Digital Radio and TV Systems Part I Seite 77 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 25.07.2014 Digital Radio and TV Systems Part I Seite 78 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) 25.07.2014 Digital Radio and TV Systems Part I Seite 79 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) 25.07.2014 Digital Radio and TV Systems Part I Seite 80 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 25.07.2014 Digital Radio and TV Systems Part I Seite 81 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 25.07.2014 Digital Radio and TV Systems Part I Seite 82 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 25.07.2014 Digital Radio and TV Systems Part I Seite 83 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 25.07.2014 Digital Radio and TV Systems Part I Seite 84 DVB-T – Pilots and TPS carrier 25.07.2014 Digital Radio and TV Systems Part I Seite 85 DVB-T – Carriers position 25.07.2014 Digital Radio and TV Systems Part I Seite 86 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. 25.07.2014 Digital Radio and TV Systems Part I Seite 87 DVB-T – Transmission After adding additional information to the datastream the modulator modulate the signal in COFDM. ) CC + RS ( Pilots Guard Interval TPS carrier info Coding DATA MIP packet COFDM Modulation (MPEG TS) Spectrum dvb-t signal 25.07.2014 Digital Radio and TV Systems Part I Seite 88 DVB-T – Spectrum and C/N (Carrier to noise) Bandwidth C/N Noisefloor 25.07.2014 Digital Radio and TV Systems Part I Seite 89 DVB-T – C/N vs. BER Required C/N for dvb-t transmission to achieve a BER = 2 . 10-4 after the Viterbi decoder 25.07.2014 Digital Radio and TV Systems Part I Seite 90 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.“ 25.07.2014 Digital Radio and TV Systems Part I Seite 91 „Cliff Effect“ in digital transmissions Source: IfN Braunschweig 25.07.2014 Digital Radio and TV Systems Part I Seite 92 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. 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 Source: Agilent quality. 25.07.2014 Digital Radio and TV Systems Part I Seite 93 DVB-T – MER MER – Modulation Error Ratio 25.07.2014 Digital Radio and TV Systems Part I Seite 94 DVB-T – Receiver RF Input Tuner Channel Inner A/D Demux Frontend FFT Estimation Demapping Interleaver MPEG2-TS De- Outer Outer Inner Srambler Decoder Interleaver Decoder Reed Viterbi Solomon Decoder 25.07.2014 Digital Radio and TV Systems Part I Seite 95 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: 1 (8MHz), 7/8 (7 MHz) Const1 6.75 E+6 bit/s = 6.75 * 10+6 bit/s Example: DVB-T in Vienna, Channel 24 = (CR 3/4, GI 1/4, 16-QAM) Net Data Rate = 0.921 * 0.75 * 4 * 0.8 * 1 * 6.75E+6 = 14920200 = 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, 25.07.2014 Digital Radio and TV Systems Part I Seite 96 DVB-T2 25.07.2014 Digital Radio and TV Systems Part I Seite 97 DVB-T2 Facts Constellation QPSK, 16-QAM, 64-QAM, 256 QAM FEC 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 1K, 2K, 4K, 8K, 16K, 32K Scattered Pilots 1%, 2%, 4%, 8% of total Continual Pilots 0,35% of total Bandwidth 1.7, 5,6,7,8 MHz Max. Bitrate 50,34 Mb/s Modulation COFDM Red: different to dvb-t 25.07.2014 Digital Radio and TV Systems Part I Seite 98 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 25.07.2014 Digital Radio and TV Systems Part I Seite 99 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 25.07.2014 Digital Radio and TV Systems Part I Seite 100 Shannon Law Source: R&S 25.07.2014 Digital Radio and TV Systems Part I Seite 101 Shannon Law Source: R&S 25.07.2014 Digital Radio and TV Systems Part I Seite 102 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 BCH LDPC Bit out Scrambler Coder Coder Interleaver 25.07.2014 Digital Radio and TV Systems Part I Seite 103 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. 25.07.2014 Digital Radio and TV Systems Part I Seite 104 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 25.07.2014 Digital Radio and TV Systems Part I Seite 105 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 25.07.2014 Digital Radio and TV Systems Part I Seite 106 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” 25.07.2014 Digital Radio and TV Systems Part I Seite 107 T2-MI interface Source: R&S 25.07.2014 Digital Radio and TV Systems Part I Seite 108 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 25.07.2014 Digital Radio and TV Systems Part I Seite 109 DVB-T2 Spectrum optimal DVB-T2 signal 25.07.2014 Digital Radio and TV Systems Part I Seite 110 DVB-T2 Spectrum weak DVB-T2 signal 25.07.2014 Digital Radio and TV Systems Part I Seite 111 Terrestrial DVB-T/T2 distribution 25.07.2014 Digital Radio and TV Systems Part I Seite 112 Reception problems 25.07.2014 Digital Radio and TV Systems Part I Seite 113 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 25.07.2014 Digital Radio and TV Systems Part I Seite 114 Antenna types for DVB-T/T2 reception Roof top antenna (Yagi) Indoor antennas 25.07.2014 Digital Radio and TV Systems Part I Seite 115 DVB-T/T2 transmit antennas 25.07.2014 Digital Radio and TV Systems Part I Seite 116 Digital Radio and TV Systems Part 2 V.1.1 Course at FH Technikum Wien DI Peter Knorr Seite 1 DVB-S 25.07.2014 Digital Radio and TV Systems Part II Seite 2 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 = 35780 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. 25.07.2014 Digital Radio and TV Systems Part II Seite 3 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 25.07.2014 Digital Radio and TV Systems Part II Seite 4 Satellite orbital position Example: .SES Astra .Longitude 19,2° East Vienna: .48° 12‘ N .16° 22‘ E 25.07.2014 Digital Radio and TV Systems Part II Seite 5 SES Satellite Fleet 25.07.2014 Digital Radio and TV Systems Part II Seite 6 Satellite footprint Source: SES 25.07.2014 Digital Radio and TV Systems Part II Seite 7 DVB-S Uplink - Downlink 25.07.2014 Digital Radio and TV Systems Part II Seite 8 Satellite Uplink Station 25.07.2014 Digital Radio and TV Systems Part II Seite 9 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. 25.07.2014 Digital Radio and TV Systems Part II Seite 10 Satellite transponder A satellite channel is called transponder, because it is a separate transceiver or repeater. 25.07.2014 Digital Radio and TV Systems Part II Seite 11 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 (10.7-12.75 GHz) collected by the dish, amplifies it, and downconverts the block of frequencies to a lower block of intermediate frequencies (IF = 950 2150 MHz). This downconversion allows the signal to be carried to the indoor satellite TV receiver using a relatively cheap coaxial cable. Source text: Wikipedia 25.07.2014 Digital Radio and TV Systems Part II Seite 12 Satellite parabol antenna types Source: Wikipedia 25.07.2014 Digital Radio and TV Systems Part II Seite 13 Azimuth - Elevation Azimuth Elevation ASTRA 19.2° Vienna: Azimuth =176°; Elevation = 34,64° 25.07.2014 Digital Radio and TV Systems Part II Seite 14 Elevation Elevation Offset satellite antenna 25.07.2014 Digital Radio and TV Systems Part II Seite 15 Elevation Elevation for location Vienna 25.07.2014 Digital Radio and TV Systems Part II Seite 16 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 …) 25.07.2014 Digital Radio and TV Systems Part II Seite 17 Free-space path loss c = Speed of light = 300 000 km/s = 3 x 108 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 = 36 000 km = 36 000 * 103 m f = 14 GHz = 14 x 109 Hz => λ= 3 x 108 / 14 x 109 = 0,0214 m F = 20 log (4 x 3,14 x 36 000 x 103 / 0,0214) = 206 dB (but this is without atmospheric attenuation calculations) 25.07.2014 Digital Radio and TV Systems Part II Seite 18 Attenuation on satellite links Atmospheric propagation degradation on satellite links • Cloud and fog • Rain attenuation • Oxygen attenuation • Water vapour • Atmospheric clouds 25.07.2014 Digital Radio and TV Systems Part II Seite 19 DVB-S Modulation QPSK Spectrum 25.07.2014 Digital Radio and TV Systems Part II Seite 20 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. 25.07.2014 Digital Radio and TV Systems Part II Seite 21 DVB-S Modulation Same data block diagram as DVB-T 25.07.2014 Digital Radio and TV Systems Part II Seite 22 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 * 0.8333 * 0.92 = 33.79 Mbit/sec. Symbolrate 22 Msymb./sec. = 44 Mbit/sec. (QPSK) means 10.21 Mbit/sec. for coding 25.07.2014 Digital Radio and TV Systems Part II Seite 23 DVB-S BER vs. Eb/No Example: Eb/N0 = C/N – 2,2 dB for QPSK, FEC = 5/6 25.07.2014 Digital Radio and TV Systems Part II Seite 24 Eb/No Eb/N0 (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 N0 = thermal noise in 1Hz of bandwidth R = system data rate BT= system bandwidth SNR = (Eb/N0) * (R/BT) 25.07.2014 Digital Radio and TV Systems Part II Seite 25 DVB-S2 25.07.2014 Digital Radio and TV Systems Part II Seite 26 DVB-S2 DVB-S 1994 DVB-S2 2003 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 25.07.2014 Digital Radio and TV Systems Part II Seite 27 DVB-S2 Modulation Phase modulation (consumer) . QPSK (consumer) . 8-PSK (consumer) . 16APSK (for commercial use) . 32APSK (for commercial use) 25.07.2014 Digital Radio and TV Systems Part II Seite 28 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) 1/2 2.5 1/2 1.3 3/5 9.1 2/3 4.3 3/5 2.3 2/3 8.8 3/4 5.3 2/3 3.1 3/4 9.1 5/6 6.4 3/4 4.1 5/6 9.6 7/8 7.1 4/5 4.7 8/9 10.9 5/6 5.3 9/10 11.2 8/9 6.3 9/10 7.3 25.07.2014 Digital Radio and TV Systems Part II Seite 29 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 25.07.2014 Digital Radio and TV Systems Part II Seite 30 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 25.07.2014 Digital Radio and TV Systems Part II Seite 31 Scrambling (used in all DVB systems) 25.07.2014 Digital Radio and TV Systems Part II Seite 32 Digital Radio and TV Systems Part 3 V.1.1 Course at FH Technikum Wien DI Peter Knorr Seite 1 DVB-C/C2 25.07.2014 Digital Radio and TV Systems Part III Seite 2 DVB-C/C2 25.07.2014 Digital Radio and TV Systems Part III Seite 3 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) 25.07.2014 Digital Radio and TV Systems Part III Seite 4 DVB-C SMATV: Satellite master antenna television distribution system TDT: Transparent digital transmodulation 25.07.2014 Digital Radio and TV Systems Part III Seite 5 DVB-C Prior to modulation, the I and Q signals shall be square- root raised cosine filtered. The roll-off factor is 0,15. Source: R&S 25.07.2014 Digital Radio and TV Systems Part III Seite 6 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 = 38.01 Mbit/sek. DVB-C net bit rate: ld(m) * symbol rate * 188/204 6 Bit/Symbol (64-QAM) * 6.9 Msymb./sek. * 188/204 = 38.15 Mbit/sek. 25.07.2014 Digital Radio and TV Systems Part III Seite 7 DVB-C Frequency Identification Channel 47 - 68 MHz Band I HF und VHF I C2 ... C4 87 - 108 MHz Band II VHF II FM 108 - 174 MHz Midband MB S2 ... S10 174 - 230 MHz Band III VHF III C5 ... C12 230 - 300 MHz Superband SB S11 ... S20 300 - 470 MHz Hyperband HB S21 ... S38 470 - 622 MHz Band IV UHF IV C21 ... C39 622 - 862 MHz Band V UHF V C40 ... C69 25.07.2014 Digital Radio and TV Systems Part III Seite 8 DVB-C Internet over cable infrastructure EuroDOCSIS DOCSIS = Data Over Cable Service Interface Specification 25.07.2014 Digital Radio and TV Systems Part III Seite 9 DVB-C Spectrum of DVB-C signals 25.07.2014 Digital Radio and TV Systems Part III Seite 10 DVB-C2 . Based on DVB-S2/T2 . COFDM with 4k Mode (4096 carrier), short guard intervals because of short reflections. . Subcarrier distance 2.232 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 25.07.2014 Digital Radio and TV Systems Part III Seite 11 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 25.07.2014 Digital Radio and TV Systems Part III Seite 12 DVB-C/C2 Signal level vs. analog TV Source: Fischer R&S 25.07.2014 Digital Radio and TV Systems Part III Seite 13 DVB-C2 25.07.2014 Digital Radio and TV Systems Part III Seite 14 Digital Radio and TV Systems Part 4 V.1.0 Course at FH Technikum Wien DI Peter Knorr Seite 1 DAB+ 25.07.2014 Digital Radio and TV Systems Part IV Seite 2 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). 25.07.2014 Digital Radio and TV Systems Part IV Seite 3 DAB ETSI Norm (February 1995) ETS 300 401 Radio Broadcasting Systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers 25.07.2014 Digital Radio and TV Systems Part IV Seite 4 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) 25.07.2014 Digital Radio and TV Systems Part III Seite 5 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 25.07.2014 Digital Radio and TV Systems Part III Seite 6 DAB additional frequencies in L-Band (1.4 GHz) 25.07.2014 Digital Radio and TV Systems Part III Seite 7 DAB Frequency planning Source: Komm Austria 25.07.2014 Digital Radio and TV Systems Part III Seite 8 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 25.07.2014 Digital Radio and TV Systems Part III Seite 9 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. 25.07.2014 Digital Radio and TV Systems Part III Seite 10 DAB DAB+ Source: Fraunhofer 25.07.2014 Digital Radio and TV Systems Part III Seite 11 DAB+ Audio format HE AAC+ v2 High efficiency advanced audio coding version 2 SBR (Spectral band replication) Transmitting guiding information such as the spectral envelope of the original input signal or additional Information to compensate for potentially missing high-frequency components. Source: EBU 25.07.2014 Digital Radio and TV Systems Part III Seite 12 DAB+ Source: EBU PS (Parametric stereo) In the encoder, only a Monaural downmix of the original stereo signal is coded after extraction of the Parametric Stereo data. Just like SBR data, these parameters are then embedded as PS side information in the ancillary part of the bit-stream. In the decoder, the monaural signal is decoded first. After that, the stereo signal is reconstructed, based on the stereo parameters embedded by the encoder. 25.07.2014 Digital Radio and TV Systems Part III Seite 13 DMB – Digital Multimedia Broadcasting DMB is a video and multimedia technology based an DAB(DAB+). It offer new services such mobile TV, traffic and safety information, interactive programmes, data information and other applications. . DMB is a broadcast technology and not a streaming technology meaning congestion is eliminated in the case of many simultaneous viewers (seen i.e. during the Olympics and FIFA World Cup) . DMB requires less power (battery usage) than streamed services . DMB requires less spectrum commitment than other mobile TV standards, which typically use 6-8 MHz blocks Source: worlddab.org 25.07.2014 Digital Radio and TV Systems Part III Seite 14 DMB – Digital Multimedia Broadcasting . Multimedia content to be delivered without the risk of network congestion . DMB also enables reception while moving at high speeds.(>300km/h) . Existing DAB transmitter networks can be to be adapted to carry these new services . Both DMB and DAB services to be accessed on the same receiver . DMB is an open International Standard . A wide range of TV and interactive services to be broadcast simultaneously on the same multiplex: − video services − DAB and DAB+ radio services − file downloading (podcasting) − electronic programme guide − slide show − broadcast website (BIFS) Source: worlddab.org 25.07.2014 Digital Radio and TV Systems Part III Seite 15 DAB Four audio modes are provided: . Mono . Dual channel (two mono) . Stereo . Joint stereo Audiobitrates: 16 – 384 kbit/sec. 25.07.2014 Digital Radio and TV Systems Part III Seite 16 DAB The DAB transmission system combines three channels . MSC (Main service channel) . FIC (Fast information channel) . Synchronization channel Each channel supplies data from different sources and these data are provided to form a transmission frame 25.07.2014 Digital Radio and TV Systems Part III Seite 17 DAB . MSC (Main service channel) – use to carry audio, PAD and data service components. The MSC is a time-interleaved data channel divided into a number of sub-channels which are individually convolutionally coded, with equal or unequal error protection . PAD (Programme Associated Data): text, label, name of the song, the artist and the genre of music, slide show 25.07.2014 Digital Radio and TV Systems Part III Seite 18 DAB FIC (Fast information channel) The FIC is limited in capacity but is capable of supplying information to a receiver faster than the main service channel allows. This is possible because the FIC is not subjected to the time interleaving part. Convolutional coding protection level is permanently fixed (CR = 1/3). In order to achieve an acceptable error performance, FIC information is repeated regularly. 25.07.2014 Digital Radio and TV Systems Part III Seite 19 DAB Synchronization channel – used internally within the transmission system for basic demodulator functions like AFC (automatic frequency control), AGC (automatic gain control) and a phase reference. 25.07.2014 Digital Radio and TV Systems Part III Seite 20 DAB 25.07.2014 Digital Radio and TV Systems Part III Seite 21 DAB - Frequency interleaving prevend fading causing burst errors Source: Mike Brookes 25.07.2014 Digital Radio and TV Systems Part III Seite 22 DAB - Transmission frame Source: ETSI 25.07.2014 Digital Radio and TV Systems Part III Seite 23 DAB - Transmission frame 25.07.2014 Digital Radio and TV Systems Part III Seite 24 DAB - MSC The MSC is made up of Common Interleaved Frames (CIFs). The CIF contains 55 296 bits. The smallest addressable unit of the CIF is the Capacity Unit (CU), comprising 64 bits. Therefore, the CIF contains 864 CUs. The MSC is divided into sub-channels. Each sub-channel shall occupy an integral number of consecutive CUs and is individually convolutionally encoded. Each sub-channel consist of audio service components and data elements. Gross bit rate: 864 CU * 64 bit = 55296 bit in 24ms 2.304 Mbit/sec. There are two transport modes in the MSC: . the stream mode (multiples of 8 kbit/s). Deliver data transparently from source to destination (audio) . packet mode for data service components 25.07.2014 Digital Radio and TV Systems Part III Seite 25 DAB – MSC 25.07.2014 Digital Radio and TV Systems Part III Seite 26 DAB - Modes Mode I: Is specially intented for single frequency network (SFN). Has a long guard interval for the absorption of multi- path reflections. Used in VHF band. Mode II: have a wider carrier spacing, better for mobil. Optimal for small SFN networks. Used in L-Band < 1.5 GHz Mode III: for satellite < 3 GHz 25.07.2014 Digital Radio and TV Systems Part III Seite 27 DAB - Modes Parameters Mode I II III Application SFN Terrestrial Satellite Frame duration ( Tf ) 96 ms 24 ms 24 ms Symbol duration ( Ts ) 1 ms 250 μs 125 μs Guard interval ( Tg ) 248 μs 62 μs 31 μs No. of symbols / frame (J) 76 76 153 No. Of carriers / symbol (N) 1536 384 192 Carrier spacing (fs ) 1 kHz 4 kHz 8 kHz Bandwidth (fw ) 1536 kHz 1536 kHz 1536 kHz Max. frequency (fm ) 250 MHz 1GHz 2GHz 25.07.2014 Digital Radio and TV Systems Part III Seite 28 DAB - Doppler effect Example: v = 100 km/h = 27,7m/sec. C = 3 * 108 m/s Christian F = 200 MHz = 200 * 106 Hz Doppler Δ f = 18,5 Hz 25.07.2014 Digital Radio and TV Systems Part III Seite 29 DAB Modulation ∏/4 DQPSK Example Mode I: COFDM Multicarrier 1536 carrier Carrier spacing 1 kHz 25.07.2014 Digital Radio and TV Systems Part III Seite 30 DAB Modulation ∏/4 DQPSK ∏/4-DQPSK Differential quaternary phase shift keying Source: Rohde&Schwarz 25.07.2014 Digital Radio and TV Systems Part III Seite 31 DAB Modulation ∏/4 DQPSK From symbol to symbol the carrier phase change 45 degree. Only +/- 45° and +/- 135° phase shift no 180° phase shift necessary Phase information from the PRS (Phase reference symbol) Source: Rohde&Schwarz Wikipedia 25.07.2014 Digital Radio and TV Systems Part III Seite 32 DAB Spectrum Source: Jim‘s Aerials 25.07.2014 Digital Radio and TV Systems Part III Seite 33 DAB Multiplex calculations DAB offer different error protections = UEP (unequal error protection) One frame has 864 CUs. Each service is transported in a SC (service channel) with a capacity of n CUs. It is possible that each subchannel has a specific error protection The sum of all SC must be < 864 CUs 25.07.2014 Digital Radio and TV Systems Part III Seite 34 DAB Multiplex calculations 25.07.2014 Digital Radio and TV Systems Part III Seite 35 DAB Applications Source: Rohde&Schwarz 25.07.2014 Digital Radio and TV Systems Part III Seite 36 DAB Applications Source: DAB Principles & Applications 25.07.2014 Digital Radio and TV Systems Part III Seite 37 DAB Applications MOT (Multimedia Object Transfer Protokoll) specifies a transmission protocol, which allows to broadcast various kinds of data using DAB. It is tailored to the needs of Multimedia services and the specific constraints given by the broadcasting characteristics of the DAB system. After reception this data can be processed and presented to the user (text, pictures, video or audio sequences) DLS (Dynamic Label Segment) Supplementary data services in text form (up to 128 characters) running alongside the DAB or DAB+ radio programme. Similar to RDS on FM radio. 25.07.2014 Digital Radio and TV Systems Part III Seite 38 DAB Applications IP over DAB Tunneling of IP datagrams over DAB. The tunnelling is to be done by encapsulating the IP datagrams into the MSC data groups. The IP tunnelling through DAB is unidirectional. TMC (Traffic Message Channel) The Traffic Message Channel (TMC) was originally designed for transport in the narrow-band Radio Data System (RDS) services in FM broadcast. DAB enables TMC messages to be carried in a much faster and bitrate- efficient way. DAB-TMC has a cycle time that is much shorter than RDS- TMC and the transmission is over the FIC channel. 25.07.2014 Digital Radio and TV Systems Part III Seite 39 DAB Applications TPEG (Transport Protocol Expert Group) . TPEG-RTM: Road Traffic Message Application . TPEG-PTI: Public Transport Information . RTM – Road Traffic Messages . TEC – Traffic Event Compact . TFP - Traffic Flow Prediction . PTI – Public Transport Information . PKI – Parking Information . SPI – Speed Limit Information . BSI – Bus Service Information . WEA – Weather . POI – Points of Interest . CTT – Congestion and Travel Time 25.07.2014 Digital Radio and TV Systems Part III Seite 40 DAB Applications PAD (Programme Associated Data) Used to describe data embedded into an audio stream such as DLS or Slideshow which is related to the programme being broadcast at that time. NPAD (Non Program Associated Data) Data – transmit together with the DAB ensemble 25.07.2014 Digital Radio and TV Systems Part III Seite 41