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What are wireless link characteristics?

Wireless LANs are very common and useful. All this communication is established over a wireless link which is also a great primary challenge to the wireless network. Another primary challenge is posed by the mobility i.e., the mobile phone users keep changing their position with respect to the network. WLANs are also prevalent at many homes and campuses.
Elements of a wireless network are:

  • Hosts i.e., PDAs or other wireless devices.
  • Base stations
  • Wireless link
  • Infrastructure mode

In this article we focus upon the third element i.e., the wireless links and their characteristics.

Wireless links are what that connect the base stations and mobiles. These links also serve as a backbone link. The access to these links is coordinated by the MAC protocol.
1. Varying data rates:
– The data rates in the wireless links vary with the distance of the transmission.
– They are thus totally different from their wired counterparts.

2. Varying signal strength:
– The signal strength also varies all along the transmission length.
– This is so because the attenuation of the radio wave occurs as it propagates through the media.
– In wired links the signal travels with very less attenuation no matter how long the distance is.
– But in wireless links the signal starts fading because it is exposed to the whole environment.
– All this happens in a short matter of time.
– This loss is called the path loss.

3. Interference:
– This occurs because of the occasional sharing of the standardized frequencies.
– Also, there are other devices such as the microwave ovens that may interfere with the transmission.
– When a bus is used i.e., in the wired links, the frequency is set and cannot be altered and so the data transmission is very secure.
– But this is not so in the case of the wireless links.
– In air there a number of signals propagating simultaneously.
– If frequency of our signal lies close to that of some other signal’s frequency then it is very probable that the interference will occur.

4. Multi-path propagation:
– The radio signal has a tendency to get reflected from the face of the objects and therefore the data frames arrive at different times at the destination.
– Because of this the same data packets are received by the destination host a number of times.

5. Hidden terminal:
– The problem of communicating over wireless links worsens further when there are too many senders and receivers.
– Consider 3 nodes A, B, C. Between A and C lies some great physical obstacle such as a hill, tall building, trees etc.
– Because of this, the signals from C cannot reach A directly.
– Therefore A and C are unable to hear each other.
– But A can hear B and B can hear C.
– This way both A and C are unaware of the interference that takes place at B.

6. Signal fading:
– If the nodes are located quite apart from each other, then the chances of the signal getting attenuated increases highly because the signal gets too far away from its source.

7. MAC problem:
– The channel is shared that gives rise to the standard MAC problem.
– As the two nodes might seek to transmit at the same time, the MAC would seek to avoid the collisions.

The base stations usually have connections with the wired network and are responsible for forwarding the data packets between the wireless and the wired networks that lie under its coverage area. The base station is changed by the mobile devices. Ad hoc mode is another element of the wireless networks. Here there is no client rather nodes transmit to the other nodes.

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