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Broadcast Systems_ DAB_ DVB

VIEWS: 12 PAGES: 24

									Broadcast Systems, DAB, DVB

        Name: CHEN, Hanliu
     hchen101@site.uottawa.ca
          March 13, 2006
Overview
   Introduction to broadcast system
   DAB and DVB introduction
   Broadcast data scheduling technique
   Indexing technique
   Summary
    Broadcast system
Wireless broadcast data delivery:
    to disseminate information to a large user community in a wireless
    asymmetric communication environment.

Asymmetric communication environment:
   Systems are designed to deliver data from a few servers to a large number of
    mobile clients, but there is significantly more “downlink” bandwidth from servers
    to clients than in the opposite or “uplink” direction. Also, clients have low power
    reserves, while servers have plenty of power.
   Example:
        news feeds and traffic information systems
        cable TV with set-top box


Special case: unidirectional distribution systems
   high bandwidth from server to client “downlink”, but no bandwidth vice versa
    “uplink”.
Broadcast or point-to-point access
Two fundamental information delivery methods for wireless data applications:
   Point-to-point access: A logical channel is established between the
    client and the server.
   Broadcast: Data are sent simultaneously to all users in the broadcast
    area. It is up to the client to select the data it wants.

Why broadcast?
   Broadcast satisfies arbitrary number of users: A single broadcast of a data item can
    satisfy all the outstanding requests for that item at the same time.

   Broadcast satisfies the wireless environment: Mobile wireless environments are
    characterized by asymmetric communication. Data broadcast can take advantage of the
    large downlink capacity when delivering data to clients.

   Implemented without any additional cost: A wireless communication system
    essentially employs a broadcast component to deliver information. e.g. Server sends broadcast
    information to find the cell-phone user.
     DAB and DVB
   Digital Audio Broadcasting – In      Digital Video Broadcasting – In
    service 1996                          operation in Jan 2001 Australia
                                          and Europe
   Specifications:
        Transmits 6-10 CD quality       Specifications:
         audio channels (data-rate:           Transmits MPEG-2
         2.304 Mbit/s)                         compressed video (same
        1.5 MHz bandwidth                     format as used for DVD
                                               players)
        192 - 1536 carriers
         depending on frequency               Data rates up to 31 Mbps
        Transmit with OFDM signal            will replace the current
                                               analog system by around
                                               2008
                                              sufficient to support High
                                               Definition Television.
                                              Transmit OFDM signal
Physical layer of DAB and DVB - OFDM
   5 subcarriers
   sinc (sin(x)/x) frequency
    response → overlap in the
    frequency domain
   The thick black line: the
    combined response
   Circles: signal seen by the
    receiver
   Receiver (FFT): Discrete
    frequency samples → the
    peaks                         Advantages of OFDM:
   Orthogonality → no ICI        Strong multipath tolerance: no ISI
                                  Spectrally Efficient
                                  Each sub-carrier is independent: no ICI
           DAB Transmitter
                    Service
                    Information     FIC
                    Multiplex
                    Information
                                           Trans-
                                           mission
                                            Multi-                  Trans-
                                                         OFDM
                                           plexer                   mitter
Audio     Audio     Channel
Services Encoder     Coder
                                  MSC
                                  Multi-                          Radio Frequency
                                  plexer
Data       Packet   Channel
                                           FIC: Fast Information Channel
Services    Mux      Coder
                                           MSC: Main Service Channel
                                           OFDM: Orthogonal Frequency Division Multiplexing
DAB Receiver
                              (partial)
                               MSC
                 OFDM                     Channel    Audio    Audio
Tuner                                                         Service
               Demodulator                Decoder   Decoder


                    FIC
                                                              Independent
                                                              Data
                                                    Packet    Service
                                                    Demux
 Control Bus
                      Controller




                                   User Interface
    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

  DVB-S Satellites                                           SDTV
                                                             EDTV
       Multipoint                   Integrated               HDTV
       Distribution              Receiver-Decoder
         System
 DVB-C Cable                                                 Multimedia PC

   Terrestrial
   Receiver
DVB-T                 B-ISDN, ADSL,etc. DVD, etc.
Three Types of broadcast delivery systems
    Push-based broadcast:
    The users cannot place requests directly to the server. The broadcast schedule
     should be determined based solely on the access probabilities.

    The push-based model has already played an important role in our daily lives (e.g., the
     television programs) but, scheduling problem


    On-Demand (Pull-based) broadcast:
    The user can send a request to the server to tell what it is waiting for through a
     uplink channel.

    Hybrid broadcast:
    A combination of Push-based and Pull-based broadcast.
Two Critical Issues in Wireless Broadcast System

   Access efficiency: It concerns how fast a request is satisfied.
    Solution: Scheduling Technique
   Power conservation: It concerns how to reduce a mobile client’s
    power consumption when it is accessing the data it wants.
    Solution: Indexing Technique

    Two basic performance metrics used to measure access efficiency and
    power conservation for a broadcast system:
   Access time: The time elapsed between the moment when a query is issued
    and the moment when it is satisfied.
   Tune-in time: The time a mobile client stays active to receive the requested
    data items.
Data Scheduling
   Key issue: how the server organize the data in the broadcast in
    order that the clients can access the information efficiently in
    terms of the latency (access time) and the tune in time.

   Three categories:
        Push-based scheduling (e.g. flat broadcast, probabilistic-based
         broadcast, broadcast disks, optimal scheduling, etc.)
        Pull-based scheduling (e.g. for equal-size items, for variable-size
         items, energy-efficient scheduling, etc.)
        Hybrid scheduling (adaptive scheduling)
     Push-based Data Scheduling
                                           Probabilistic-Based Broadcast
    Flat Broadcast: all data
                                       

    items are broadcast in a round-        selects an item i for inclusion in
    robin manner. The access time          the broadcast program with
    for every data item is the same.       probability fi.
                                                                      qi
                                                       fi 
                                                              
                                                                  N
                                                                           qj
   The simplest broadcast scheme.                                j 1


   Poor performance in terms of          Improved performance for
    average access time when data          skewed data access.
    access probabilities are skewed.      it may have an arbitrarily large
                                           access time for a data item.
                                          Furthermore, this scheme
                                           shows inferior performance to
                                           other algorithms for skewed
                                           broadcast
         Push-based Data Scheduling
   Broadcast Disks:

1) Order the pages from the hottest to
   coldest.
2) Partition the list of pages into multiple
   ranges.
3) Choose the relative frequency of
   broadcast for each of the disks.
4) Split each disk into a number of chunks.
5) Create the broadcast program by
   interleaving the chunks of each disk.       rel_feq(1)=4, rel_feq(2)=2, rel_feq(3)=1
                                               LCM(4,2,1)=4
                                               num_chunk(1)=1, num_chunk(2)=2, num_chunk(3)=4
           Push-based Data Scheduling
   Empty slot problem:
    when it is not possible to evenly
    divide the number of pages (in a
    disk) into the required number
    of chunks.
   Complementary approach:
                                           After complementary
    to move some pages which are located   approach
    near the end of a broadcast cycle to
    those empty slots which occur before
    those pages.
            Pull-based Data Scheduling

    For equal-size items:                                 For variable-size items:
A.   First-Come-First-Served (FCFS)                 A.      Preemptive-Longest-Wait First
                                                            (PLWF): preemptive version of the LWF
B.   Most-Requests-First (MRF)                              algorithm.
C.   Most-Requests-First-Low                        B.      Shortest-Remaining-Time-First
     (MRFL): essentially the same as MRF,                   (SRTF)
     but it breaks ties in favor of the item with   C.      Longest-Total-Stretch-First
     the lowest request probability.
                                                            (LTSF): the stretch of a pending
D.   Longest-Wait-First (LWF)                               request = the time the request has been
                                                            in the system so far / its service time.
                                                    D.      MAX algorithm:       A deadline is
                                                            assigned to each arriving request, and it
                                                            schedules for the next broadcast the item
                                                            with the earliest deadline.

                                                         deadline=arrival time + service time * Smax
Hybrid Data Scheduling
    Motivation:

1.   Push-based data broadcast cannot adapt well to a large database
     and a dynamic environment.

2.   Pull-based data broadcast consumes more uplink bandwidth and
     energy of the mobile clients. When the uplink channel is congested,
     the latency will be extremely high.

     Thus, adaptive data broadcast scheduling combined with
     both push and pull based scheduling is needed!
           Hybrid Data Scheduling
    Two issues of adaptive scheduling:
1.   Where and how to get the request from the
     clients.
2.   Balance the bandwidth allocation between
     push-based and pull based deliveries.

    Mechanism:
•    Feedback manager: monitors the incoming feedback
     and interest patterns of the documents in the current
     broadcast program. estimates the number of feedback and
     client requests that should be collected for the server to
     summarize interest patterns with a desired precision.
•    Request manager:         deals with the sampled clients’
     requests incrementally based on the approximate response
     mechanism.                                                   Adaptive scheduling architecture
•    Broadcast scheduler:        generates new broadcast
     programs with the adaptive feedback.
Indexing Technique
   Key issue: how to reduce the power consumption of mobile clients in
    broadcast environment?
   Basic idea: allowing the mobile users to predict the arrival time of a
    requested data item, so that a mobile user may stay with power saving
    mode and only selectively tune in the broadcast channels when the
    data of interest actually arrives.
   Indexing techniques:
•   The hash technique
•   The index tree technique
•   The signature technique
•   The hybrid index approach: a combination of index tree and signature technique
•   The unbalanced index tree technique
•   Multiattribute indexing
Indexing technique
      NP-hard problem

      Indexing with scheduling technique:
e.g.
1.     The   Index Tree Technique with Flat Broadcast
2.     The   Index Tree Technique with the Broadcast Disks
3.     The   Signature Technique with Flat Broadcast
4.     The   Signature Technique with the Broadcast Disks
Summary

   Access efficiency and power consumption of the mobile clients are the
    main problems in wireless broadcast environment. Thus, scheduling
    and indexing techniques are important to deal with the two problems.

   The conclusion is that, by current technologies, no specific scheduling
    or indexing technique is the best solution for all broadcast systems.
    The scheduling and indexing technique should be carefully chosen
    according to various system requirements.
          Question and Answer
   Question 1:
      What are the three types of broadcast models?
      Answer:
      Push based broadcast; On-demand (or pull based) broadcast; Hybrid
    broadcast.
   Question 2:
     Scheduling and indexing techniques are very important in wireless
    broadcast system, why?
     Answer:
     In wireless data system, access efficiency and power conservation are
    two critical issues. Scheduling technique provides more access efficiency,
    which concerns how fast a request is satisfied. Indexing technique helps
    reduce a mobile client’s power consumption when it is accessing the data
    it wants.
           Question and Answer
   Question 3:
    The broadcast disk contains a multiplex of data from different disks onto the same
    broadcast channel. The multiplex can be weighted in order to separate between fast disks
    and slow disks. A cycle of broadcast disks is shown in the following figure. The disks with
    the same frequencies are shown in the same color chunks, e.g. disk 1 in black, disk 2, 3 in
    grey, and disk 4, 5, 6, 7, 8, 9, 10, 11 in white. What is the frequency relation between the
    black, grey and white?
    Answer:
    F (black): F (grey): F (white) = 4: 2: 1.
Thank you!

								
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