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Mobile Computing COE 446 Network Planning

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  1. Mobile Computing COE 446Network Planning Tarek Sheltami KFUPM CCSE COE Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

  2. Outline • Infrastructure networks topology • Infrastructure-less networks topology • Infrastructure vs ad hoc networks • Cell concept

  3. Wireless Network Topology • Infrastructure Network Topology: • There is fixed (wired) infrastructure that supports communication between MT and fixed terminals • It is often designed for large coverage areas and multiple BSs or APs • BSs/APs serves as the hub of the network • Any communication from one MT to another has to be sent through the BS/AP • The hub station usually controls the MT and monitors what each station is transmitting

  4. Wireless Network Topology • Infrastructure-less Network Topology: • Can operate without the need for a fixed infrastructure • Best suited for conference meetings, lectures, crowd control, search and rescue, disaster recovery, on-the-fly conferencing applications, and automated battlefields. Typically such applications do not have infrastructure or central administration available • Users have to cooperate in carrying messages through the network • Ad hoc Network = multihop network

  5. Comparison of Ad hoc and Infrastructure Network Topologies • Scalability: • To scale up a wireless infrastructure network, the number of BSs or APs is increased to expand the coverage area or to increase the capacity • In ad hoc networks, it depends on the routing protocol • Flexibility: • Operation of infrastructure networks is very expensive • Ad hoc network is very flexible • Controllability: • Infrastructure network centrally controlled and synchronized • In ad hoc networks there is no centralized administration • Therefore, infrastructure network is more controllable than ad hoc

  6. Comparison of Ad hoc and Infrastructure Network Topologies • Routing Complexity: • In ad hoc network, each node must act a router. There is a need for routing algorithms the directs the info to the appropriate next hop • This problem does not exist in infrastructure network • Coverage: • In WLANs, coverage of the network is an issue of concern • The max distance between two MTs is the max transmission range of MTs • In infrastructure network, two MTs communicate through BS/AP • The max distance is twice range of the coverage of a single wireless modem

  7. Comparison of Ad hoc and Infrastructure Network Topologies • Reliability: • Ad hoc network is resistance to failure • Infrastructure network are “single failure point network. If the AP/BS fail, the entire communication network is destroyed • Store and Forward Delay and Media Efficiency: • In infrastructure topology, data is transmitted twice. Once from the source to the BS/AP and once from BS/AP to the destination • The BS/AP should store the message and forward it later. This adds to the delay encountered by the data packets • Ad hoc may have several transmissions and several store and forward delays

  8. Cellular Topology • Cellular Concept • Deploying a large number of low-power BSs for transmission, each having a limited coverage area • The available capacity is multiplied each time a new BS is setup because the space spectrum is being reused several times in a given area • The fundamental principle of cellular concept is to divide the coverage area into a number of smaller areas, which are each served by its own BS • Radio channels are allocated to their smaller areas in an intelligent way to minimize the interference, provide adequate performance and cater to the traffic loads in the these areas • Each of these smaller areas is called cell

  9. Cellular Topology • Cellular Concept • Cells are grouped into clusters • Each cluster utilizes the entire available radio spectrum • The reason for clustering is that adjacent cell can not use the same frequency, so the frequency bands have to be split into chunks and distributed among the cell of a cluster • The distribution of the radio spectrum within a cluster should be done in a way to obtain the desired performance • The number of cells in a cluster is called the cluster size or frequency reuse factor

  10. Cellular Topology • Cellular Concept • The interference due to using the same frequency cells of different clusters is referred to as cochannel interference • The cell that use the same set of frequencies or channels are called cochannel cells • The interference from different frequency channel used with a cluster whose side-lobes over-lap is call adjacent channel interference • The allocation of channel within the cluster and between clusters must be designed to minimize both interferences

  11. Example 5.4 pp. 230-231