August 6, Mobile Computing COE 446 Network Planning Tarek Sheltami KFUPM CCSE COE Principles of Wireless Networks K. Pahlavan and P. Krishnamurth

Outline Infrastructure networks topology Infrastructure-less networks topology Infrastructure vs ad hoc networks Cell concept August 6, 20152

3 Wireless Network Topology 1. 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

August 6, 20154

5 Wireless Network Topology 2. 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

August 6, 20156

7 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

August 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

August 6, 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

August 6, 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

August 6, 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

August 6, 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

August 6, Example 5.4 pp

August 6,