Peng Li Fall2008 Ece5765 Introduction To Wireless Networks


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Peng Li Fall2008 Ece5765 Introduction To Wireless Networks

  1. 1. ECE, UMD Introduction to Wireless Network Peng Li
  2. 2. Motivation Why we use Wireless Network  Mobility  Ease of use  Installation Simplicity and Flexibility  Cost
  3. 3. Outline The elements in Wireless Network 1 Spread Spectrum 2 OFDM 3 Wireless Data Services 4 Summary 5
  4. 4. The elements in Wireless Network Data Format Wireless Network Network Structure Radio Signals
  5. 5. The elements in Wireless Network In terms of the OSI reference model  Data format controls several of high layers.  Network Structure includes the wireless network interface adapters and base stations that send and receive the radio signals.  Radio signal operates at physical layers.
  6. 6. Spread Spectrum What’s the modulation method for Radio signal in Wireless Network ?  AM ?  FM ?  PCM ?  Something else ? Spread Spectrum !
  7. 7. Spread Spectrum What’s Spread Spectrum ?  Spread spectrum is a family of methods for transmitting a single radio signal using a relatively wide segment of the radio spectrum.
  8. 8. Spread Spectrum Frequency-Hopping FHSS Spread Spectrum Direct-Sequence Spread DSSS Spectrum Orthogonal Frequency OFDM Division Multiplexing
  9. 9. OFDM What’s OFDM ?  OFDM is a combination of modulation and multiplexing.  OFDM is a special case of FDM (Frequency Division Multiplex).  The main concept in OFDM is orthogonality of the sub-carriers.
  10. 10. OFDM OFDM System Diagram
  11. 11. OFDM Benefits of OFDM  Very easy and efficient in dealing with multi-path  Robust again narrow-band interference
  12. 12. Wireless Data Services Wi-Fi Cellular Mobile Wireless Services WiMAX Bluetooth
  13. 13. Wireless Data Services Wi-Fi  It covers the various IEEE 802.11 technologies (including 802.11n, 802.11b, 802.11g, and 802.11a).
  14. 14. Wireless Data Services Wi-Fi Characteristics
  15. 15. Wireless Data Services Wi-Fi Type Frequency Modulation 802.11a 5 GHz OFDM 802.11b 2.4 GHz DSSS 802.11g 2.4 GHz OFDM
  16. 16. Wireless Data Services Cellular Mobile Wireless Services
  17. 17. Wireless Data Services WiMAX Worldwide Interoperability for Microwave Access, The technology is  based on the IEEE 802.16 standard (also called WirelessMAN).
  18. 18. Wireless Data Services Bluetooth  Bluetooth is an FHSS system that splits the radio signal into tiny pieces. It moves among 79 different frequencies 1,600 times per second in the same unlicensed 2.4 GHz range as 802.11b and 802.11g Wi-Fi services.
  19. 19. Summary  Connecting your computer to the Internet (or a local network) by radio offers several advantages over connecting the same computer through a wired connection.  First, wireless provides convenient access for portable computers; it’s not necessary to find a cable or network data outlet.  Second, it allows a user to make a connection from more than one location and to maintain a connection as the user moves from place to place.
  20. 20. ECE, UMD Q&A