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)