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Basics of Wireless Networking Neil Tang 1/21/2009

Basics of Wireless Networking Neil Tang 1/21/2009. Outline. Wireless Communication Basics Wireless Networks Interference Model IEEE 802.11 MAC Protocols. Wireless Communications.

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Basics of Wireless Networking Neil Tang 1/21/2009

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  1. Basics of Wireless Networking Neil Tang1/21/2009 CS541 Advanced Networking

  2. Outline • Wireless Communication Basics • Wireless Networks • Interference Model • IEEE 802.11 MAC Protocols CS541 Advanced Networking

  3. Wireless Communications • There is no physical link in wireless networks. Signals are transmitted on a certain frequency, propagate in the space and are captured by the receiver tuned to the same frequency. • Wireless communication is normally broadcast communication, i.e., all nodes within the transmission range of a particular node can receive the transmitted packets. • Transmissions in a common neighborhood will interfere with each other. If the Signal-to-Interference-Noise-Ratio (SINR) in the receiver is large enough, a packet can be correctly decoded. CS541 Advanced Networking

  4. Wireless Networks • Single-hop wireless networks: cellular network, wireless LAN. • Multihop wireless networks: mobile ad hoc network, wireless mesh network, wireless sensor network. CS541 Advanced Networking

  5. Interference Model • Primary Interference: A B C A B C A B C CS541 Advanced Networking

  6. Interference Model • Protocol Model (for the fixed transmission power case): a A B b C D CS541 Advanced Networking

  7. Interference Model • PhysicalModel (for the variable transmission power case): CS541 Advanced Networking

  8. MAC Protocol – 802.11 • Basic architecture: Infrastructure mode and ad hoc mode • MAC protocol: CSMA/CA (MACA) CS541 Advanced Networking

  9. Basic Architecture AP Infrastructure mode Ad hoc mode CS541 Advanced Networking

  10. Hidden Terminal Problem A B C Transmission Range Node A and C are hidden terminals. CS541 Advanced Networking

  11. Exposed Terminal Problem A B D C Transmission Range Node A and B are exposed terminals. CS541 Advanced Networking

  12. 802.11 • Distributed Coordination Function (DCF) : Simple protocol with no centralized control. • Point Coordination Function (PCF): APs control medium access and provide collision-free communications. Bandwidth (timeslots) will be carefully allocated to nodes which has signed up for transmission. CS541 Advanced Networking

  13. DCF Basic Idea: CSMA/CA (MACA) • Request-To-Send (RTS) and Clear-To-Send (CTS) are used to reserve space and time for transmission. • Both physical and virtual carrier sensing are used to determine the time for transmission. Network Allocation Vector (NAV) is used for virtual carrier sensing. • For each transmitted data frame, an ACK frame will be sent back to from the sender. Stop-and-wait protocol are used to provide reliability. CS541 Advanced Networking

  14. DCF CS541 Advanced Networking

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