Listen Before Talk in Wireless Communication | Advantages and disadvantages of LBT

This page covers Listen Before Talk (LBT) algorithm used in wireless communication. It mentions benefits or advantages of Listen Before Talk (LBT) and drawbacks or disadvantages of Listen Before Talk (LBT).

What is LBT (Listen before Talk) ?

It has been implemented to overcome limitations of ALOHA technique. ALOHA was first packet based network in which transmitters transmit the data immediately without any channel sensing. If collision occurs, the transmitter tries re-transmission again. ALOHA works efficiently up to 10% utilization of the radio frequency channels.

When devices use LBT protocol, they listen to radio channel first. The device transmits data if it finds the channel idle i.e. no transmission in the air. If it detects any activity on channel, it waits for random period of time and re-transmits the data.

WiFi uses LBT technique along with other advanced signal processing techniques to determine when to use the radio spectrum. It is used in LTE-U (Long Term Evolution Unlicensed) and LTE LAA (Licensed Assisted Access) Networks.

There are two algorithms by which it is determined whether channel is already occupied or not.
• Carrier sensing
• Energy detection

Benefits or advantages of Listen Before Talk (LBT)

Following are the benefits or advantages of Listen Before Talk (LBT).
➨It alleviates problems of hidden nodes.
➨It avoids collisions in the air when multiple wireless transmitters intending to transmit at the same time.
➨It utilizes radio channel efficiently better than ALOHA protocol.
➨There is very low requirements to re-transmit the data.

Drawbacks or disadvantages of Listen Before Talk (LBT)

Following are the drawbacks or disadvantages of Listen Before Talk (LBT).
➨Self powered devices can not support this feature.
➨It uses critical time resources over the air as algorithm requires transmitters to sense for some time period and act accordingly to transmit or wait for random period of time till channel is idle.
➨It is significantly complex to implement due to requirements of computer processor and accurate time synchronization.

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