# LC by pengtt

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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
   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
video part of TV signals…

   Frequency modulation
Audio part of TV signals,
Cell phones, cordless phones…
Modulation Frequencies
 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
 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

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

microprocessor    flash memory   speaker, microphone
Inside the iPhone
Cell Phone vs Walkie-Talkie vs CB
   Very similar conceptually
   Half-duplex
   Walkie-Talkie
   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)
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
   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
 Packet length, packet number
 Source and destination routing information (IP addresses)
 Synchronization, transmission protocol
 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
 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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