WirelessNetworks-UniversityofEngineeringand.ppt

How about wireless networks? Base Station Shared Channel Wireless users access the network by means of a shared channel Access capacity is inherently limited. Implication For wire-line systems, we can simply install new cables to increase capacity. For wireless systems, the channel can only be shared by the users. Capacity does not increase. Interference Multiuser Interference Radio signals of different users interfere with each other Self-Interference Multipath effect Phase-shifted images of the signal at the receiver interact and may cancel the entire signal, (i.e. destructive interference). Interference Management How to manage multiuser interference? i.e. how to share the channel? Multiple Access Problem FDMA, TDMA, CDMA, etc. Media Access Control Aloha, CSMA, etc. How to manage self-interference? Physical layer issue Equalization, coding, diversity, etc. These issues will NOT be considered in this course The 2nd challenge User Mobility Location Management Problem How does the network know where the intended recipient of a message is currently located? Cellular Scenario Where is 5008011? Send broadcast messages from every base station? Internet Scenario Dest. Net router Nhops interface 223.1.1 - 1 223.1.2 - 1 223.1.3 - 1 7 7 A B E Forwarding table in router Suppose A sends a datagram to E misc fields data The router sends the datagram to via interface What happens if E moves to elsewhere? B A S E F H J D C G I K M N L How to find a suitable path from source S to destination D? The 3rd challenge Device Limitation Resource Limitation Limited memory Limited computational power Small display Limited battery life This issue will NOT be considered at the moment but may be extended later Classification of Wireless Systems Personal communication systems Focus on voice communication Limited bit-rate data transmission Large-scale mobility and coverage Operate over licensed