Lecture 12
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Lecture 12 Lecture 12 Presentation Transcript

  • Broadcast Systems
    • Unidirectional distribution systems
    • DAB
      • architecture
    • DVB
      • Container
      • High-speed Internet
  • Typical Client Server Application Client IBM Server Sends a data request Server sends a huge volume of data
  • 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
  • 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?
  • 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.
  • 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 
  • 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
  • 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.
  • 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.
  •  
  • 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
  • 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
  • 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
  • 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)
  • 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
  • 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
  • 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
  • Examples for DAB coverage
  • 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
  • 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
  • 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
  • DAB receiver Packet Demux Audio Decoder Channel Decoder Independent Data Service Audio Service Controller Tuner ODFM Demodulator User Interface FIC Control Bus (partial) MSC
  • 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
  • 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.
  • 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
  • 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.
  • 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.
  • MOT standard Protocol
    • MOT Object :
    • Header Core : 7 Byte
    • - Size of header, Size of Body and type of object.
    Header Core Header Extension Body
  • 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 .
  • 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
  • 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
  • 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
  • Transport Stream
  • 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
  • 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.
  • DVB Internet Options DVB-S adapter PC Internet TCP/IP leased line service provider information provider satellite provider satellite receiver
  • 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
  • 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
  • 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
  • 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
  • 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
  • Summary of MPEG-2 Compression Capability
  • Comparison