An Introduction to Wireless Technology, Second Edition

safe power levels. Microwave ovens also operate in the 2.4 GHz ISM band and

are not seen as a health hazard.

5.9 Wireless LAN Applications

There are many existing applications where a wireless LAN could improve the

flexibility of the existing system. There are also new applications which could

not exist without the use of a wireless LAN.

5.9.1 Point of Sale (POS) Terminals

In supermarkets and department stores the layout of the display stands is

frequently changed to allow new articles to be displayed or to rearrange the

position of existing articles. One of the limiting factors is the position of POS

terminals. These terminals cannot be easily relocated or new ones installed, as

both a data connection (typically a LAN connection to a server) and a power

connection are required. The data connection is required as the server may

hold the price database and log each POS transaction. These transactions can

be fed to a warehouse application to maintain inventories by automatic

reordering. Power connections are generally available throughout a building,

but the data connections are found only at the locations which have been

planned at the initial installation. Laying new cables for an additional POS

terminal is expensive and sometimes not possible where cables would be

running across the floor or the building structure does not allow it. Installing a

WLAN connection between the POS terminal and the server can allow the

terminal to be placed anywhere on the shop floor that a power connection is

available. For example, during a sale this would enable a temporary POS

terminal to be installed very quickly. Temporary POS terminals could also be

set up outside the store in the summer selling seasonal goods such as

sunglasses.

POS data connections are quite suited to wireless transmission since as each

article is scanned, only a short key data record is sent to the server and the item

and price information returned is also contained in a short data record. The

transaction record then sent to the server is also a small amount of data.

Bandwidth considerations are not a problem as data rates are low. The

reliability of the wireless connection is of great importance so that customers are

not kept waiting and that they have confidence that their receipts are correct.

5.9.2 Replacement for Wired LAN

Another major application for WLANs is as an alternative to traditional wired

LANs. There may be a number of reasons why a traditional wired LAN is

unsuitable or too costly for installation in a particular building. The building

could be old and of historic significance, and the occupier may not be allowed to

modify the interior, cut holes, or install cable ducting. The building could also

have thick solid walls and interior partitions which would make it difficult to

install LAN cables. Some older buildings may also have materials such as

asbestos used in their construction, where it could pose a health hazard to make

holes to install LAN cables.

Even for newer buildings, there may be a cost saving by installing a wireless

LAN for new LAN installations.

114 An Introduction to Wireless Technology