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Wireless Communication Networks

Wireless Communication Networks. Tzu-Chieh Tsai Department of Computer Science National Cheng-Chi University. Outline. Background Introduction Cellular IEEE 802.11 CDPD Recent work: Mobile Police Information System. Introduction. Layers: physical layer data link layer

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Wireless Communication Networks

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  1. Wireless Communication Networks Tzu-Chieh Tsai Department of Computer Science National Cheng-Chi University

  2. Outline • Background Introduction • Cellular • IEEE 802.11 • CDPD • Recent work: Mobile Police Information System

  3. Introduction • Layers: • physical layer • data link layer • MAC(Medium Access Control sublayer) • Network layer: (Routing, etc) • Transport layer: (Flow control, etc) • Packet switching(store and forward) vs. circuit switching: dynamic bandwidth

  4. Introduction (Physical layer) • Transmit power vs. connectivity • multihop vs. single hop • multiuser and near-far problem • spatial reuse vs. transmit power A B C increase power A B C

  5. Introduction (Data link layer) • Two types of control are generally considered: • acknowledgement mechanisms (ARQ) • forward error correction (FEC) coding • Both ARQ and FEC are combined together to achieve an adequate level of link performance, usually.

  6. Introduction(MAC layer) • ALOHA • random access, simple • CSMA (Carrier Sense Multiple Access) • CSMA/CD is not applicable • TDMA (Time Division Multiple Access) • CDMA (Code Division Multiple Access)

  7. Introduction (Routing) • A vast amount of literature: Bellman-Ford, Dijkstra, distributed mobile routing(Corson and Ephremides 1995), and bandwidth routing (Gerla, 1986) • key issues: • how to choose an appropriate routing method, and how to spread minimum routing information to achieve efficient packet forwarding • how much mobility such a routing scheme can support

  8. Introduction (Flow control) • dynamics of packet radio and channel sharing provides challenges • admission control for a circuit assures that network resources will not be overtaxed; and flow control when available resources are limited • congestion control for connectionless traffic: detection of congestion by measuring delay • considerable research is still needed in this area

  9. Traffic(Application Requirement) • Traffic Type: • datagram (eg. email, file transfer): packet switching • 100% correctness • can suffer longer delay • bursty • time-bound traffic (eg. voice): circuit switching • delay is very sensitive • loss may be acceptance • connection-oriented • Different applications need different network protocol design

  10. 行動式警政資訊系統--網路協定部分 • Goal: Develop robust, but simple, implementable solutions • Protocols include: • Location tracking and routing: used for multihop routing and location management • QoS routing and MAC: used for time-bound traffic • Mobile IP concept

  11. Location Tracking and Routing 記錄: (timestamp) A MG 送hello: MGIP + Seq # + hop x, y, z number register 記錄: C B A MGIP Seq # (timestamp) hop = 1 register node=MG 替誰轉送= x, y, z (timestamp) a b x y z hop = 2 register node = A

  12. QoS routing and MAC • QoS (delay, bandwidth) information collection --> hard ! • scheduling • dynamics • MAC options: • IEEE 802.11 PCF (polling) • TDMA • QoS routing: spread traffic as far as possible (spatial reuse)

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