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WIRELESS MODEM

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Title: WIRELESS MODEM


1
WIRELESS MODEM
Senior Design EE 4512Spring 2000
2
Team Members
Shane Easterling
Ian Smith
Dr. James Fowler
(Advisor)
April Martin
Daniel Ling
3
Abstract
  • Design a wireless modem system using Direct
    Sequence Spread Spectrum
  • By using the spread spectrum technique we will be
    able to increase efficiency and security of the
    overall system
  • Once our project is completed it will allow users
    to connect to a base station from rooms and
    offices thus eliminating the use of wires

4
Motivation
  • The time taken to implement and design network
    infrastructure(such as a LAN network) is too time
    consuming and costly.
  • The ability to provide an offsite connection to a
    central office network
  • The ability to provide high speed connections at
    a fraction of the cost,
    compared to fiber optics, ISDN, and DSL
    installation

5
Objectives
  • Transmitter The transmitter must have an output
    power of 1 watt which is specified by the FCC
    for spread spectrum systems such as the one we
    are designing
  • Receiver The receiver must achieve a desired
    bit error rate of 1E-6. Only one error out of
    4.295 billion errors will be undetected.
    Therefore, the desired end-to-end bit error
    rate will be only 2.328E-14 .
  • Direct Sequence This device must stay within the
    frequency range of 902 to 928 MHz DSSS

6
Objectives
  • Throughput We want the system to have a raw
    data throughput of 128 Kbps.  
  • Range Our aim is to achieve a 3-mile distance of
    transmission, which is acceptable for our
    purpose which includes a use for small
    distances, such as, residential areas,
    university campuses, and businesses that would
    have a three mile parameter.
  • Power Usage The design will use a 12VDC wall
    adapter and a portable battery such as a normal
    laptop battery pack
  • Cost The component cost for our design will not
    exceed 150.00. The expected market price for
    the unit will be less than 400.00

7
Approach
  • Transmitter and Receiver
  • System view for simulation
  • Matlab
  • Calculations
  • Throughput
  • Gzip to determine worst case of a
    typical compress and uncompress files

8
Transmitter
9
Receiver
10
Why use DSSS
  • DSSS is defined as Direct Sequence Spread
    Spectrum
  • Unlike Frequency Hopping DS spreads the signal
    over the entire bandwidth
  • DS transmits continuously during bit intervals
    instead of just subintervals like Time Hopping
  • Low probability of intercept and interference
    immunity compared to TH and FH
  • Low transmit power density and simultaneous
    transmissions
  • For these reasons it has been used widely in the
    military

11
DSSS Model
12
Before and After Despreading
13
Test Specifications
  • Delete sample documenticons and replace with
    working document icons as follows
  • From Insert Menu, select Object...
  • Click Create from File
  • Locate File name in File box
  • Make sure Display as Icon is checked
  • Click OK
  • Select icon
  • From Slide Show Menu, Select Action Settings
  • Click Object Action and select Edit
  • Click OK

  • Circuit Modeling
  • Use to verify transmitter and receiver objectives
  • Software Testing
  • Using Gzip on a number of files to find the worst
    case compression ratio. Then figure out the
    bandwidth to support the device.
  • Class B Emission
  • Follow Code of Fed. Regulations to be sure
    frequency bands are 902 928MHz

14
Tests Specifications
15
Future Aspects
  • Delete sample documenticons and replace with
    working document icons as follows
  • From Insert Menu, select Object...
  • Click Create from File
  • Locate File name in File box
  • Make sure Display as Icon is checked
  • Click OK
  • Select icon
  • From Slide Show Menu, Select Action Settings
  • Click Object Action and select Edit
  • Click OK

  • Improve modem gain so it could be used at further
    distances from the base antenna
  • Make the overall product smaller using DSP
  • Improving the synchronization of both the
    transmitter and receiver


16
Summary
  • We plan to create a wireless modem system
    allowing a connection to PC and internet/LAN
  • By using DSSS the signal will be spread over a
    wide frequency band which is much wider than the
    minimum bandwidth required to transmit
    information
  • Allows teachers and workers easier means of
    giving presentations, or accessing information.

17
Acknowledgements
  • We would like to thank Dr. Fowler, our advisor,
    for all of his valuable input on our project.

18
References
  • 1 R.C. Dixon, Spread Spectrum Systems,
    John-Wiley Sons, 1984, page 7.
  •  
  • 2 K. Gilhousen, Qualcomm Inc., USENET newsgroup
    discussion.
  •  
  • 3 R.E. Ziemer and R.L. Peterson, Introduction
    to Digital Communication, New York, Macmillan,
    1985.
  • 4 R.E. Ziemer and R.L. Peterson, Introduction
    to Digital Communications, New York, Macmillan,
    1985.
  • 5 G.R. Cooper and C.D. McGillem, Modern
    Communications and Spread Spectrum, New York,
    Mc-Graw-Hill, 1986.
  • 6 R. Skang, J.F. Hjelmstad, Spread Spectrum in
    Communications, Short Run Press Ltd 1985.
  •  
  • 7 C. E. Cook, F. W. Ellersick, L. B. Milstein,
    D. L. Schilling, Spread Spectrum Communications,
    IEEE Press 1983.
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