Mobility

A user in a wireless system can be anything that utilises the wireless network. People are one of the most common types of users. Users of wireless networks tend to be mobile, that is, constantly moving from one place to another. Mobility (seamless connection) is one of the most prominent benefits of deploying a wireless network.

The media access control (MAC) in the IEEE 802.11 network allows for two operating modes: the ad hoc mode and the infrastructure mode. In the infrastructure mode users are connected together and to the network through an AP. A handoff (roaming) occurs when a mobile user moves from the coverage of one AP to another. In the process of a handoff, the client should be able to detect the new APs and switch across, based on signal strength measurement. For this process to happen without disconnection, the coverage of neighbouring APs must overlap [13, 18, 31, 32, 68, 92] when more than one AP is used. Of course, this might generate interference. However, by restricting the network with non- overlapping channels, the neighbouring APs can operate without mutual interference [60, 63, 69].

Using our model, in the planning of wireless LANs, potential users/test points are dis- tributed in the demand areas to provide a means for calculating the loss or strength of the

signal at these points. The number and coordinates of these potential users are set by the design specifications, while the number of APs and their locations are not known and are to be found by the program. Once the number and placement are found, they are supposed to be installed permanently. It is assumed that in order to save the cost deployment, after the APs are installed, their number and placement will not change. For this reason, the APs will be static in their placement. Although the APs are static, they have to cover users, wherever they move in the demand areas and at all times. In order to make the whole design space a demand area, it is sufficient to distribute the potential users/test points to all parts of the coverage area. In doing this, the demand areas will be extended and overlapping of APs will occur. We show our procedure through the following case study.

Figure 5.13 shows that when Pt= 15 dBm and Rth= -55 dBm (plmax= 70 dB), four APs are found to cover the demand areas in the F-building. As can be seen in this figure, user1 on the left is covered only by AP2 because the path loss to this AP is 68.07 dB, which is less than 70 dB. Calculated path loss indicates that the coverage of this user is ensured if she/he moves along the path shown with solid line. It should be noted that this is not the only path where this user can move. In fact, this user can move to anywhere that other potential users are located. Calculated path loss shows that when this user moves to position 8, she/he is not covered by any of the nearest APs such as AP1, and AP3. The path loss from this user to AP1 is 81.74 dB, which is higher than the maximum path loss of 70 dB. This, of course, is due to the 3 walls that are between them.

Figure 5.13: User1 cannot access the network at position 8

In order to make users mobile along the path shown with dashed line, it is required to make this area a demand area by distributing test points. Figure 5.14 shows that the number of APs is increased to five, since the size of demand area is increased. Therefore, users can

Effect of Parameters of WLAN 5.2. Conclusion

Figure 5.14: Mobility of users is ensured in designated demand areas

If coverage of the users in all parts of the F-building is required, then the entire building should be made as demand area. This can happen when test points are distributed in whole design space, as shown in Figure 5.15. As can be seen in this figure, the number of required APs is increased to six.

Figure 5.15: Mobility of users can be ensured when the whole building is made as demand area

5.2

Conclusion

In this chapter we discussed that wireless LAN deployment involves recognising and taking into account the effect of the parameters of the WLAN.

Through case studies, we showed how to use our model to find the effect of these para- meters on deployment cost, coverage, capacity, processing time, and mobility. To provide mobile users with what they need, the number of APs should be increased. However, this increases deployment costs, processing time, and number of handoffs. In order to save on the cost of deployment, coverage can be provided for a subset of areas. This limits the mobility of users and mobility is an important issue in WLAN. To make users mobile, the coverage of neighbouring APs should overlap. This can happen when the entire design area

In the next chapter, we will describe the features and operation of a software that we have developed to assist network designers in planning wireless LANs. This software uses the optimisation model and algorithm presented in Chapters 3 and 4.

Chapter 6

Software for Planning Wireless LAN

Systems

For a network designer to be able to analyse different system configuration scenarios, and to evaluate the trade-offs between the coverage, capacity, deployment costs, and the quality of service very quickly, and accurately, an interactive software tool is required [23–25, 32, 61]. Coverage prediction made by these tools will provide immediate feedback on system performance [7, 77].

In Chapter 3 we developed and presented an optimisation model to find the minimum number of APs in order to save on the cost of deployment. In Chapter 4 we extended the model to enhance the physical security of the network by moving the APs away from unsafe areas and exterior walls. A global optimisation algorithm was used to solve the optimisation problems.

We have developed a software based on the proposed optimisation model and algo- rithm. This software can assist network designers in planning and evaluating wireless LAN systems quickly for small and large design areas.

The aim of this chapter is to explain the features and operation of this software.

6.1

Overview of the Features

The developed software allows a network designer to provide coverage for a building in- cluding obstacles. The main features of the software are listed below:

• The minimum number of APs is determined, saving on the cost of deployment. • The placement of APs in the building is found.

• The APs can be placed away from unsafe areas in order to maximise their security. • The loss of signal throughout the design area is calculated to ensure that the quality

of coverage is above a given threshold value.

• The designer is able to calculate the coverage distance of an AP, the distance between two terminals, and the distance between a test point and an AP.

• The APs are moved away from unsafe areas in order to enhance the physical security of the network.

• Coverage can be provided for the subsets of area in the building to save on the cost of deployment.

• Designer is provided with visual feedback.

• Output is generated in different formats for documentation purposes.