Wireless Networks

WIRELESS NETWORKS

WIRELESS LANs

The increased demands for mobility and flexibility in our daily life are demands that lead the development from wired LANs to wireless LANs (WLANs).

WLANS use electromagnetic radio waves to transport data between computers in a Local Area Network (LAN), without the limitations set by ―hard wired network cable or phone wire connection‖. Whilst simple optical links are commercially available, radio is presently more useful since it is not strictly restricted to line-of-sight paths.

Radio waves are often called radio carriers when they are used to carry information. The data to be transported is superimposed on the radio carrier by various modulation techniques which allow the data to be faithfully reconstructed at the receiving end. Once data is superimposed (modulated) onto the radio carrier, this combined ―radio channel‖ now occupies more than a single frequency since the frequency components or spectra of the modulating data add frequency bandwidth to the basic carrier (in direct proportion to its information content or bit rate). The frequency range which is needed to accommodate a radio signal with any given modulation bandwidth is called a channel. Radio receiver techniques can select one radio channel while efficiency rejecting signals on other frequencies. Many radio signals to and from many users can thereby co-exist in the same place and time without interfering with each other if the radio waves are transmitted at minimum necessary power within different radio channels.

ADVANTAGES OF WLAN OVER WIRED LAN

Flexibility : With in radio coverage nodes can communicate without further restriction.

Planning : Wireless ad hoc network allow communication without planning whereas wired network needs wiring plans.

Design : Wireless Network allows for the design of small independent devices.

Robustness : Wireless network can survive disaster. If the wireless devices survive people can communicate.

Cost : Adding additional users to a wireless network will be increase the cost. But where as with fixed network addition of an user will lead into unplugging and plugging. Wireless communications do not wear out.

DISADVANTAGES

QOS:

          Wireless offers lower quality than that of wired. The reasons are

          The lower bandwidth due to limitations in radio transmission.

          High error rate due to interference.

          Higher delay due to error correction and detection mechanisms.

PROPRIETARY SOLUTION :

          Many companies have  comeup  with  proprietary solutions offering standardized functionality.

          This is due to slow standardization procedures.

RESTRICTION :

          The wireless products need to comply with national regulations.

  WLAN are limited to low power senders and certain license free frequency hand which are not same world wide.

SAFETY AND SECURITY :

          The radio waves are used for data transmission. They will interfere with other equipment. Precaution have to be taken to prevent safety hazards.i

· As it is via radio transmissions eaves dropping is possible.

DESIGN GOALS

Global operation : While the product is being sold in all the countries, national and international frequency regulations should be considered.  

Low Power : Devices communicating via WLAN are also wireless devices. These devices run on battery power – while designing a WLAN these aspects should also be considered.  

License free Operation : The equipment must operate in a license free band such as 2.4 GHz ISM Band  

Robust      Transmission   Technology  :   WLAN   operate  under   difficult

conditions. As they are radio transmission many other electrical devices can interfere with them.  

Simplified Spontaneous Co-operation : WLAN should not require complicated startup routines , but should run spontaneously after power up.  

Easy to use : WLAN‘s are mad for simple use. They should be like plug and play.  

Protection of Investment : For transmission from wired to wireless, simple bridging should be enough to interoperate.  

Safety and Security : WLAN should be safe to operate. When low radiation are used. The network should consider user privacy and security.  

Transparency : Existing applications should continue to run over WLAN with trade off to higher delay and lower bandwidth.