This information is then transmitted through air with the help of a transmitter and received at the other end through a receiver and demodulated. Since both transmission and reception of the signals has to be carried out at the same point, therefore a device known as an 'Access Point' (AP) is used which is a simple transmitter/receiver or transceiver. By assigning different frequencies to different users many users can access the network simultaneously without interfering. As is evident, the access to a wireless network can be gained only if the users are having devices which have wireless facility. These devices such as notebook computers and tablet PC's are widely available in the market and their prices have fallen by large amounts in recent times making them affordable.
Depending on the designing technology used WLAN's are mainly of three types. 'Narrowband wireless LAN's', 'Spread Spectrum wireless LAN's' and 'Infrared wireless LAN's'. Narrowband WLAN's, as is understood from the name, use narrowband signal for communication. Therefore the speeds achieved are low in this case but the problem of interference is greatly reduced as is the case with narrowband signals. The problem of low speeds is solved by the Spread Spectrum WLAN's which use wideband signals. The drawback of this technology is that the number of users accessing an access point is lesser and the security is also weaker than Narrow band WLAN's. However, in spite of these drawbacks it is the most widely used technology. The infrared WLAN's don't find many uses as the speeds as well as the range in this case is very low. Infrared WLAN's are used only when the devices and access points are placed close to each other and when they are in the line of sight. The requirement of devices to be in the line of sight is because RF signals cannot pass through opaque objects.
Development and Implementation of a WLAN
The leading authority involved in the specification and ratification of technology related standards is the 'Institute of Electrical and Electronics Engineers' (IEEE) (BECTA, 2005). Presently there are three wireless standards originated from IEEE. They are IEEE 802.11a, 802.11b and 802.11g.
It is the most widely used wireless network standard. It is used by most public wireless 'hotspots' (Khayat, 2002) . 802.11b standard was ratified by IEEE in 1999. The main features of this standard are as given below.
It operates in 2.4 GHz spectrum.
It has nominal data transfer rate of 11 Mbps and a practical rate of about 4-7 Mbps.
It offers three non-overlapping channels.
These features are adequate for most data transfer applications and for accessing internet but might be inadequate for multimedia access. It might also face problems when users in large number access the network from a single access point. The frequency of operation, i.e., 2.4 GHz, coincides with the spectrum used by cordless phones, microwave ovens, etc. Therefore the interference problems are more likely to occur.
It was rated by IEEE in 1999. The main features of this standard are as given below.
It uses 5 GHz frequency spectrum.
It has a nominal data transfer rate of 54 Mbps with a practical rate