Out of line of sight

from Wikipedia, the free encyclopedia
First Fresnel zone above the hilly terrain of a radio link, with line of sight

The term non-line of sight , English: Non-line-of-sight , NLOS for short , is used in communications technology for radio transmission without direct visual contact between the transmitter and receiver .

When there is no line of sight, there is therefore an obstacle in the first Fresnel zone . In the case of a communication path outdoors, the obstacle can be e.g. B. be a house , forest or mountain . Most wireless connections are NLOS connections.

A well-known example of a non-line of sight connection is the connection between a mobile phone and a cellular base station ( Base Transceiver Station ). Examples of wireless transmission standards within closed rooms are WLAN and DECT (for the connection between handset and base station on cordless telephones).

An obstacle in the first Fresnel zone of a radio link causes the signal to be attenuated, which shortens the range or increases transmission errors ( BER ). There are the following options to counteract this:

  • Increase transmission power
  • Use antennas with a higher antenna gain
  • increase the input sensitivity of the receiver
  • Interposition of a repeater or a relay station to increase the signal strength again.
    The use of a repeater or relay station can also be used to prevent the NLOS connection by z. B. is built on the mountain top. There is then a direct line of sight (LOS) from the transmitter to the relay station and from the relay station to the receiver.

A variation of the transmission frequency would also have an influence on the attenuation of the obstacle, but this is not practically possible due to the frequencies defined and controlled by the regulatory authority. Furthermore, a change in frequency also causes different free space attenuation .

Regardless of the obstacle, the laws of wave propagation and free space attenuation apply to communication . Furthermore, multipath propagation and interference are to be expected. All these factors must be taken into account when developing a communication concept or when installing a radio transmission link.

literature

  • Gordon L. Stüber: Principles of Mobile Communication. 3rd edition, Springer Science + Business Media LLC, New York 2011, ISBN 978-1-4614-0363-0 .
  • Stephan Sand, Armin Dammann, Christian Mensing: Positioning in Wireless Communications Systems. John Wiley & Sons Ltd, Chichester 2014, ISBN 978-0-4707-7064-1 .
  • Aditya K. Jagannatham: Principles of Modern Wireless Communication Systems. Mc Graw Hill Education, New Delhi 2016, ISBN 978-1-259-02957-8 .

See also

Web links