Lecture 12
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The document discusses several topics related to digital broadcasting systems including: 1. DAB architecture and DVB container which are used for digital audio/video broadcasting over different mediums. 2. Unidirectional distribution systems which have limitations due to asymmetric bandwidth but can optimize transmissions through techniques like cyclic repetition. 3. Digital Audio Broadcasting (DAB) standards which use COFDM to transmit multiple audio and data services over radio frequencies with high quality and robustness.
Lecture 12
- 1. Broadcast Systems Unidirectional distribution systems DAB architecture DVB Container High-speed Internet
- 2. Typical Client Server Application Client IBM Server Sends a data request Server sends a huge volume of data
- 3. Unidirectional distribution systems Asymmetric communication environments bandwidth limitations of the transmission medium depends on applications, type of information examples wireless networks with base station and mobile terminals client-server environments (diskless terminal) cable TV with set-top box information services (pager, SMS) Special case: unidirectional distribution systems high bandwidth from server to client (downstream), but no bandwidth vice versa (upstream) problems of unidirectional broadcast systems a sender can optimize transmitted information only for one group of users/terminals functions needed to individualize personal requirements/applications
- 4. Typical Personalized Services – Broadcast Services A user might need a filter as a personal requirement. Starting time of news Disable all rated movie channels Disable all movie channels after 10.00pm As for the broadcast system goes, the broadcast takes place irrespective of the target user. MAIN ISSUE : Sender still has the control on when to send and what to send. HOW TO CIRCUMVENT THIS?
- 5. Cyclic Repetition In normal radio kind of broadcast, the receiver gets the packets if it tunes to the channel. Else, it will not. But in specific situations where the sender has to listen to the program (for ex., emergency weather announcement), data pattern has to be repeated.
- 6. Unidirectional distribution service provider service user sender receiver receiver receiver . . . unidirectional distribution medium A A A A A A A B B B B optimized for expected access pattern of all users individual access pattern of one user
- 7. Structuring transmissions - broadcast disks Sender cyclic repetition of data blocks different patterns possible (optimization possible only if the content is known) Receiver use of caching cost-based strategy: what are the costs for a user (waiting time) if a data block has been requested but is currently not cached application and cache have to know content of data blocks and access patterns of user to optimize A B C A B C flat disk A A B C A A skewed disk A B A C A B multi-disk
- 8. Broadcast Patterns Flat Disk : All blocks are repeated at equal intervals Average waiting time to receive the data is the same. Skewed Disk : Some important blocks are repeated several times in a sequence Will ensure that even if some blocks are corrupted, users will not miss the data Multi-Disk : Distribute evenly so that blocks occur at higher frequency Pattern should occur cyclically.
- 9. Broadcast Patterns The sender can optimize the broadcast patterns and design the sequence based on the type of programs. If an user has a prior knowledge of the access patterns, his waiting time is drastically reduced.
- 11. Digital Audio Broadcasting Why has this come up? higher fidelity more stations and more resistance to noise co-channel interference and multipath stronger error correction coding *** If the bit rates used are less, the performance can be worse than FM
- 12. Digital Audio Broadcasting A DVB receiver must support the following modes Mode I for Band III, Earth Mode II for L-Band, Earth and satellite Mode III for frequencies below 3 GHz, Earth and satellite Mode IV for L-Band, Earth and satellite
- 13. Digital Audio Broadcasting SERVICES Primary services, like main radio stations Secondary services, like additional sports commentaries Data services Electronic Programme Guide (EPG) Collections of HTML pages and digital images (Known as 'Broadcast Web Sites') Slideshows, which may be synchronised with audio broadcasts Video Java Platform Applications IP tunneling Other raw data
- 14. DAB: Digital Audio Broadcasting Media access COFDM (Coded Orthogonal Frequency Division Multiplex) SFN (Single Frequency Network) 192 to 1536 subcarriers within a 1.5 MHz frequency band Frequencies first phase: one out of 32 frequency blocks for terrestrial TV channels 5 to 12 (174 - 230 MHz, 5A - 12D) second phase: one out of 9 frequency blocks in the L-band (1452- 1467.5 MHz, LA - LI) Sending power: 6.1 kW (VHF, Ø 120 km) or 4 kW (L-band, Ø 30 km) Date-rates: 2.304 Mbit/s (net 1.2 to 1.536 Mbit/s) Modulation: Differential 4-phase modulation (D-QPSK) Audio channels per frequency block: typ. 6, max. 192 kbit/s Digital services: 0.6 - 16 kbit/s (PAD), 24 kbit/s (NPAD)
- 15. Orthogonal Frequency Division Multiplex (OFDM) Parallel data transmission on several orthogonal subcarriers with lower rate Amplitude f subcarrier: SI function= Maximum of one subcarrier frequency appears exactly at a frequency where all other subcarriers equal zero superposition of frequencies in the same frequency range k 3 f t c sin(x) x
- 16. OFDM II Properties Lower data rate on each subcarrier less ISI interference on one frequency results in interference of one subcarrier only no guard space necessary orthogonality allows for signal separation via inverse FFT on receiver side precise synchronization necessary (sender/receiver) Advantages no equalizer necessary no expensive filters with sharp edges necessary better spectral efficiency (compared to CDM) Application 802.11a, HiperLAN2, DAB, DVB, ADSL
- 17. Real environments ISI of subsequent symbols due to multipath propagation Symbol has to be stable during analysis for at least T data Guard-Intervall (T G ) prepends each symbnol (HIPERLAN/2: T G = 0.8 µs; T data = 3.2 µs; 52 subcarriers) (DAB: T data = 1 ms; up to 1536 subcarriers) fade out fade in impulse response OFDM symbol OFDM symbol OFDM symbol t analysis window OFDM symbol T data OFDM symbol OFDM symbol
- 18. Examples for DAB coverage
- 19. DAB transport mechanisms MSC (Main Service Channel) carries all user data (audio, multimedia, ...) consists of CIF (Common Interleaved Frames) each CIF 55296 bit, every 24 ms (depends on transmission mode) Hence Bit Rate is 55296/.024 = 2.304 Mbps ` CIF contains CU (Capacity Units), 64 bit each FIC (Fast Information Channel) carries control information consists of FIB (Fast Information Block) each FIB 256 bit (incl. 16 bit checksum) defines configuration and content of MSC Stream mode transparent data transmission with a fixed bit rate Packet mode transfer addressable packets
- 20. Transmission frame synchronization channel SC main service channel FIC MSC null symbol phase reference symbol data symbol data symbol data symbol . . . . . . symbol T u frame duration T F guard interval T d L 0 0 1 2 L-1 1 L fast information channel FIC
- 21. DAB sender Trans- mitter Trans- mission Multi- plexer MSC Multi- plexer ODFM Packet Mux Channel Coder Audio Encoder Channel Coder DAB Signal Service Information FIC Multiplex Information Data Services Audio Services Radio Frequency FIC: Fast Information Channel MSC: Main Service Channel OFDM: Orthogonal Frequency Division Multiplexing 1.5 MHz f carriers
- 22. DAB receiver Packet Demux Audio Decoder Channel Decoder Independent Data Service Audio Service Controller Tuner ODFM Demodulator User Interface FIC Control Bus (partial) MSC
- 23. Audio Coding Goal audio transmission almost with CD quality robust against multipath propagation minimal distortion of audio signals during signal fading Mechanisms fully digital audio signals (PCM, 16 Bit, 48 kHz, stereo) MPEG compression of audio signals, compression ratio 1:10 redundancy bits for error detection and correction burst errors typical for radio transmissions, therefore signal interleaving - receivers can now correct single bit errors resulting from interference low symbol-rate, many symbols transmission of digital data using long symbol sequences, separated by guard spaces delayed symbols, e.g., reflection, still remain within the guard space
- 24. Bit Rate Management a DAB ensemble combines audio programs and data services with different requirements for transmission quality and bit rates the standard allows dynamic reconfiguration of the DAB multiplexing scheme (i.e., during transmission) data rates can be variable, DAB can use free capacities for other services the multiplexer performs this kind of bit rate management, therefore, additional services can come from different providers maximum bit rate per multiplex of 1152 kbit/s.
- 25. Example of a reconfiguration D1 D2 D3 D4 D5 D6 D7 D8 D9 Audio 1 192 kbit/s PAD Audio 2 192 kbit/s PAD Audio 3 192 kbit/s PAD Audio 4 160 kbit/s PAD Audio 5 160 kbit/s PAD Audio 6 128 kbit/s PAD DAB - Multiplex D1 D2 D3 D4 D5 D6 D7 D8 D9 Audio 1 192 kbit/s PAD Audio 2 192 kbit/s PAD Audio 3 128 kbit/s PAD Audio 4 160 kbit/s PAD Audio 5 160 kbit/s PAD Audio 7 96 kbit/s PAD DAB - Multiplex - reconfigured Audio 8 96 kbit/s PAD D10 D11
- 26. Dynamic Reconfiguration Possibilities The channels need not be fixed before hand. Dynamic reconfiguration is very much possible. In the fig, there are six audio channels and nine data channels. Each audio channel as a Program Associated Data (PAD) At the transmitter, if the system comes to know that there are two additional data packets D10 & D11 and then Channel 3 does not need 192 Kbps bit rate, it can reconfigure to 128 kbps and use the additional BW available for the additional DATA.
- 27. Multimedia Object Transfer Protocol The DAB frames have to support the high end receivers that support extended graphics as well as the existing receivers that support simple one-line displays. This brought in the need for the MOT standards.
- 28. MOT standard Protocol MOT Object : Header Core : 7 Byte - Size of header, Size of Body and type of object. Header Core Header Extension Body
- 29. MOT standard Protocol MOT Object : Header Extension : Repetition distance (as explained earlier – skewed, flat disk etc related) Segmentation info Priority Body: Contains data as described by the header fields .
- 30. Digital Video Broadcasting (DVB) 1991 foundation of the ELG (European Launching Group) goal: development of digital television in Europe 1993 renaming into DVB (Digital Video Broadcasting) goal: introduction of digital television based on satellite transmission cable network technology later also terrestrial transmission
- 31. Digital Video Broadcasting (DVB) SDTV EDTV HDTV Multimedia PC DVD, etc. Terrestrial Receiver Cable Multipoint Distribution System Satellites DVB Digital Video Broadcasting Integrated Receiver-Decoder DVB-S DVB-C DVB-T
- 32. DVB DVB transmits MPEG-2 container high flexibility for the transmission of digital data no restrictions regarding the type of information DVB Service Information specifies the content of a container NIT (Network Information Table): lists the services of a provider, contains additional information for set-top boxes SDT (Service Description Table): list of names and parameters for each service within a MPEG multiplex channel EIT (Event Information Table): status information about the current transmission, additional information for set-top boxes TDT (Time and Date Table): Update information for set-top boxes
- 33. Transport Stream
- 34. DVB Container multimedia data broadcasting MPEG-2/DVB container single channel high definition television MPEG-2/DVB container HDTV multiple channels standard definition MPEG-2/DVB container SDTV multiple channels enhanced definition MPEG-2/DVB container EDTV
- 35. Example: high-speed Internet access Asymmetric data exchange downlink: DVB receiver, data rate per user 6-38 Mbit/s return channel from user to service provider: e.g., modem with 33 kbit/s, ISDN with 64 kbit/s, DSL with several 100 kbit/s etc.
- 36. DVB Internet Options DVB-S adapter PC Internet TCP/IP leased line service provider information provider satellite provider satellite receiver
- 37. Convergence of broadcasting and mobile comm. Definition of interaction channels Interacting/controlling broadcast via GSM, UMTS, DECT, PSTN, … Example: mobile Internet services using IP over GSM/GPRS or UMTS as interaction channel for DAB/DVB mobile terminal DVB-T, DAB (TV plus IP data) GSM/GPRS, UMTS (IP data) MUX Internet TV broadcaster ISP mobile operator TV data broadcast interaction channels
- 38. Classification DVB-C (Cable) EN 300 800 Digital Video Broadcasting (DVB); DVB interaction channel for Cable TV distribution systems (CATV) DVB-DSNG (Digital Satellite News Gathering) EN 301 210 TR 101 211 Guidelines EN 201 222 DVB-MC (Multipoint Microwave Video) EN 300 749 Digital Video Broadcasting (DVB); DVB framing structure, channel coding and modulation for MMDS systems below 10 GHz DVB-MS (Multipoint Microwave Video) EN 300 748 Digital Video Broadcasting (DVB); DVB framing structure, channel coding and modulation for MVDS at 10 GHz and above DVB-S (Satellite) EN 301 421 Digital Video Broadcasting (DVB); Modulation and Coding for DBS satellite systems at 11/12 GHz ETR 101 198 Implementation of BPSK modulation for DVB-S DVB-SFN (Single Frequency Networks) TS 101 190 Megaframe for Single Frequency Networks DVB-SMATV (Single Master Antenna TV) EN 300 473 Digital Video Broadcasting (DVB); DVB Satellite Master Antenna Television (SMATV) distribution systems
- 39. Classification DVB-T (Terrestrial TV) EN 300 744 Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television (DVB-T) TR 101 190 Implementation Guidelines for DVB-T Terrestrial Digital Communication Networks ETS 300 813 Digital Video Broadcasting (DVB); DVB interfaces to Plesiochronous Digital Hierarchy (PDH) networks ETS 300 814 Digital Video Broadcasting (DVB); DVB interfaces to Synchronous Digital Hierarchy (SDH) networks ETS 300 818 Broadband Integrated Services Digital Network (B-ISDN); Asynchronous Transfer Mode (ATM); Retainability performance for B-ISDN switched connections
- 40. HDTV Resolution Analog TVs : 525 lines for the NTSC with an upfate rate of 25 to 30 frames per second HDTVs have a Resolution of 1920 x 1080 ………… Much better than the analog TV resolution Tyoical Data Rates of DVB : 5-30 MBPS
- 41. Profiles for Data Broadcasting Data Pipe : Asynchronous end-end delivery of data (directly inserted in MPEG-2 transport packets) Data Streaming : Can be synchronized with other streams – audio/video, data and clock generation at receiver end possible. Multi-protocol Encapsulation : Transport of arbitrary network protocols on top of MPEG-2 Transport Stream., support for MAC address, unicast, multicast and broadcast. Object Corousels : Periodic transmission of Objects : Compatible with CORBA
- 42. Summary of MPEG-2 Compression Capability
- 43. Comparison