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Mobile Computing COE 446

Network PlanningTarek Sheltami

KFUPMCCSECOE

http://faculty.kfupm.edu.sa/coe/tarek/coe446.htm

Principles of Wireless NetworksK. Pahlavan and P. Krishnamurth

Outline Infrastructure networks topology Infrastructure-less networks

topology Infrastructure vs ad hoc networks Cell concept

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Wireless Network Topology1. 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

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Wireless Network Topology2. 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

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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

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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

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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

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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

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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

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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

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Example 5.4 pp. 230-231

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