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					Information Transmission


           Trac D. Tran
         ECE Department
   The Johns Hopkins University
      Baltimore, MD 21218
                        Outline
   M-ary transmission and data rate
   Channel capacity
   Modulation
     Pulse modulation
     Amplitude modulation
     Frequency modulation
   Radio waves and radio frequencies
   Two-way data transmission with modems
   Cellular phone
       Inside a cell phone
       The cell approach
       From cell to cell
       Cell tower and antenna
       Digital cellular technologies: 1G, 2G, 3G & 4G!
      M-ary Transmission & Data Rate
           amplitude
            11  V3
             10  V2                                  threshold
                                                        levels
             01  V1
             00  V0
                                         time
   M-ary transmission
      M different signals in the transmission scheme
      Faster data transmission when M increases
      Problem: how to differentiate different signals with noise?
   Data rate D  R log 2 M bps

    signals transmitted or received per second
                   Channel Capacity
   Channel capacity C
                         s2 
           C  B log 2 1  2  bps
                         
                           n 

     channel bandwidth (bps)         signal-to-noise ratio
                                           s2 
Noiseless channel:  n  0  C  B log 2 1 
                     2
                                                     B log 2   
                                                0 
Noisy channel:     n   s2  C  B log 2 1  0  B log 2 1  0
                    2



   Example
     Telephone channel (3000Hz) with SNR=1,000
                     s2 
       C  B log 2 1  2   3000  log 2 1  1000  29,900 bps
                     
                       n 
                    Modulation
   Modulation
     Using higher-frequency sinusoids to carry signals
     More efficient transmission & allow multi-user sharing
   Pulse modulation
                                 Morse code,
                                 infrared remote control…
   Amplitude modulation
                                 AM radio stations,
                                 video part of TV signals…

   Frequency modulation
                                FM radio stations,
                                Audio part of TV signals,
                                Cell phones, cordless phones…
             Modulation Frequencies
   AM radio
      535 KHz – 1.7 MHz                    The Federal
   Citizens Band (CB) radio                Communications
      26.96 MHz – 27.41 MHz
                                            Commission (FCC)
   Cordless phones
      Early versions: 43 MHz – 49 MHz      manages & controls
      Current versions: 900 MHz, 2.4 GHz   frequency assignments
   FM radio
      88 MHz – 108 MHz
   TV stations
      54 MHz – 88 MHz, 174 MHz – 220 MHz
   Cellular phones
      824 MHz – 849 MHz, 1850 MHz – 1990 MHz (PCS)
   Global Positioning System (GPS)
      1227 MHz – 1575 MHz
   Others
      Garage door openers: ~40 MHz
      Baby Monitors: 49 MHz
                  Modem Transmission
   Frequency-shift keying (FSK)
     Uses analog sinusoids of different frequencies to carry digital signals



                   0        1        0       0        1
                         Transmit          Receive


                                                                    frequency
            300          1070 1270        2025 2225          3300
                        0 1                 0    1
   Phase-shift keying (PSK)
     Uses different phases of the same analog sinusoid to carry digital
      signals
               Cell Phones: Outside



                                     Motorola Razr     BlackBerry

Martin Cooper with
first cell phone 1973 DynaTAC 1983
                                            Samsung i8510




  Nokia N8    Samsung Galaxy S       HTC HD2         Apple iPhone 4
            Cell Phones: Inside




        front         back       LCD & keypad




microprocessor    flash memory   speaker, microphone
Inside the iPhone
    Cell Phone vs Walkie-Talkie vs CB
   Very similar conceptually
   Half-duplex
       Walkie-Talkie
       CB Radio
       Only one person can talk at a time
       Share the same modulating frequency for transmitting
        & receiving
   Full-duplex
       Cell phones!
       One modulating frequency for transmitting
       Another modulating frequency for receiving
       Both are simultaneously active
                   The Cell Approach
                                             Cellular telephone system is
                                              based on the principle of radio
                                              communication
                                             Coverage area is divided into
                                              hexagonal cells (each covers
                                              around 10 square miles)
                                             Non-adjacent cells can reuse
                                              the same frequencies
                                             Low-power transmitters: both
                         Cell Cluster
                                              phones & base stations
   Each carrier: 832 radio frequencies      Each city has a Mobile
   Duplex system: 395 voice channels         Telephone Switching Office
    & 42 control channels                     (MTSO)
   Each cell: 56 voice channels
         Cells & Tower Placements

                                             Cell cite
                                             Base station
                                             Cell tower




                                         Cell = Coverage Area
Mobile Tracking:
   How do we estimate the location of a certain cell phone?
Cell Splitting to Increase Traffic
From Cell to Cell
            System Identification (SID)
             code to check for available
             service
            MTSO uses the control
             channels to identify where
             the user is & assign
             frequencies
            MTSO handles the hand-off
             switching between cells
             based on signal strengths
            Everything happens within
             seconds or even less!
Cell Phone Tower
Cell Towers Everywhere!
          Digital Cellular Technologies
   FDMA: Frequency (1G)          TDMA: Time Division
    Division Multiple Access       Multiple Access (2G)




       CDMA: Code Division
        Multiple Access (3G)
                  3G & 4G Cellular Technology
             1G: analog cellular technology – FDMA
Past

             2G: digital cellular technology – TDMA, CDMA, PCS
             3G: third-generation digital cellular technology
               CDMA2000: based on 2G CDMA
               WCDMA: Wideband CDMA
Current




               TD-SCDMA: Time-division Synchronous Code-division
                Multiple Access
               potential transfer speeds of up to 3 Mbps (144 Kbps for 2G cell
                phones)
               video conferencing, streaming video, sending and receiving
                faxes, instantly downloading e-mail messages with attachments
             4G: fourth-generation digital cellular technology
               OFDMA: Orthogonal Frequency-Division Multiple Access
Future




               MIMO: Multiple Input Multiple Output
               Transfer speeds up to 1 Gbps
       Circuit-Switched Network
   Principle
     Several connections are time-multiplexed over one link
     A dedicated circuit is established during the complete
      duration of the connection




                           translation table
      Circuit-Switched Network
   Features
     Constant bit-rate, e.g. 64 kbps PCM channel
     Short transmission delay
     Small delay jitters
   Examples
     Public Switched Telephone Network (PSTN)
     Integrated Service Digital Network (ISDN)
   Suitable for real-time applications that requires constant
    bandwidth
     Audio streaming
     Constant-bit-rate compressed video (conferencing)
   Not efficient for bursty applications
     Data: file transfer, fax, email, web browsing…
     Variable-bit-rate compressed video
         Packet-Switched Network
   Principles
     Communication links are shared by multiple users
     Information encapsulated in packets
     Data packet
                          Header          Payload                    Trailer
        Header
            Packet length, packet number
            Source and destination routing information (IP addresses)
            Synchronization, transmission protocol
         Payload
            Packet body containing data to be transmitted
         Trailer or footer
            cyclic redundancy check: parity checking on the payload
     Connectionless
     Can have re-transmission request
        Packet-Switched Network
   Features
     Variable length packets
     Large transmission delay
     Large delay jitters
   Examples
     Local Area Network (LAN)
     Wide Area Network (WAN)
   Suitable for applications which require dynamic
    bandwidth
     Data download and upload: Internet!
     Variable-bit-rate compressed audio/video: VoIP!
   Problem with delay-sensitive applications
     Real-time video and audio communication (video conferencing)
Circuit- versus Packet-Switching
                Circuit-Switched   Packet-Switched
  Dedicated
                      Yes                No
  Connection
  Call Set-up         Yes                No

  Bandwidth          Fixed            Dynamic

  Fixed Route         Yes                No
  Network
                  Set-up time         Anytime
  Congestion
  Utilization
                  Time-based        Packet-based
  Charge

				
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posted:2/19/2011
language:English
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