Range (radio technology)

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The range is the radio engineering at a radio connection the distance that the maximum between the transmitter and the receiver , so that even a possible communications must exist.

Basics of digital radio

The reliability of a modern radio system working with digital transmission methods depends on the bit error rate (BER) of the received bit stream . So that the error correction methods used by the radio system , such as forward error correction , can deliver a bit stream that is sufficiently error-free for the radio application, the bit error rate of the received, uncorrected bit stream must not be too high. The rule of thumb for easily understandable voice communication is a maximum permissible bit error rate of 0.1% (BER = 1E-3). So at most every 1000 bit may be incorrectly received, so that the error correction process in the receiving device can correct the bit error and an acceptable voice quality results.

For fast data transfers, the requirements for the maximum permissible bit error rate are significantly higher. As a rule of thumb for fast data transfers, a maximum permissible bit error rate of 0.001% (BER = 1E-6) applies.

The bit error rate (BER) depends on Eb / N0 and the digital modulation method used . Eb / N0 is to be understood as the normalized signal-to-noise ratio (SNR) and is also referred to as "SNR per bit".

Range of digital radio with sky waves

For reliable radio systems with a long range, electromagnetic waves from the frequency range 30 MHz to 90 GHz must be used. In this frequency range, the electromagnetic waves mainly spread out as space waves .

For modern digital radio in this frequency range, the signal-to-noise ratio under ideal radio conditions is:

depends on the following essential factors:

All these factors need to be link budget (Engl. "Link budget") are considered.

In general, the line of sight and thus the range of terrestrial radio is limited by the curvature of the earth . The formula for geodetic visibility can be used to calculate the maximum distance of the line of sight. As an alternative to the formula for visibility, the approximation formula for the radio horizon can be used.

If there is no line of sight between the transmitting and receiving antennas, other factors influence the range of modern digital radio:

  • Attenuation, multi-path reception and other influences from vegetation (for example: forest )
  • Attenuation, multi-path reception and other influences from the building (internal building: wall ) or object
  • Attenuation, multi-path reception and other influences from the earth's surface and water

Notes on the individual factors

Free space attenuation

The free space attenuation depends, among other things, on the transmission frequency. The free space attenuation is largely responsible for the range of a radio link. The further away the transmitter and receiver are from one another and the higher the transmission frequency , the greater the free space attenuation and the more the transmission signal is attenuated. The greater the distance to be bridged, the higher the transmission power of the transmitter or the sensitivity of the receiver must be.

Influences of the earth's atmosphere on radio waves

In the troposphere , the weather dampens or absorbs the radio signal through humidity , rain , snow and other weather influences. In addition to the troposphere, the ionosphere also influences the propagation of radio waves through attenuation , absorption , refraction , scintillation and depolarization .

Fading due to multi-path reception

If there is a line of sight between the transmitting and receiving antennas, the influence of multipath reception should be taken into account in the power transmission balance using the mathematical model "rice fading". If the line of sight between the transmitting and receiving antenna is missing, the influence of the multipath reception should be taken into account in the power transmission balance using the mathematical model "Rayleigh fading".

Frequency multiplexing , or a mixture of frequency - and time division multiplexing onset cellular standards or trunked radio systems with automatic, adaptive transmit power control (TPC) often reduce the transmit power for pure voice transmission, when the link margin (left margin)> 25 dB is. The 25 dB comes from "Rayleigh fading" with a bit error rate of 0.1% (BER = 1E-3).

Modern digital transmission methods are either immune to multi-path reception, such as COFDM . Or you can even use multi-path reception to improve radio reception, such as the rake receiver .

Receiver sensitivity

With very good receivers, the heat noise significantly limits the receiver's sensitivity. The greater the bandwidth of the radio signal to be received, the greater the noise power and the higher the noise voltage . The noise power has a direct influence on the signal-to-noise ratio.

See also

literature

  • Martin Werner: Telecommunications: An introduction to all courses. 7th edition, Vieweg + Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0905-6 .
  • Dennis Roddy: Satellite Communications third edition, McGraw-Hill, ISBN 0-07-137176-1 .

Web links

Individual evidence

  1. ↑ http://www.cdt21.com/resources/TechnicalArticle/article9.asp Circuit Design Inc. - Understanding the Quality of Radio System Communication
  2. ↑ https://fahrplan.events.ccc.de/camp/2011/Fahrplan/attachments/1864_satellite_communication.pdf Irmtraut Meister - Chaos Communication Camp 2011 - Introduction to satellite communication
  3. ↑ http://sss-mag.com/pdf/1mss.pdf Prof. Randy H. Katz - CS 294-7: Mobile Satellite Systems
  4. ↑ https://funkperlen.blogspot.ch/2017/11/wenn-baume-den-wellen-im-wege-haben.html Anton's Funkperlen - When trees stand in the way of the waves
  5. ↑ http://www.tele-satellite.com/TELE-satellite-0709/eng/feature.pdf Peter Miller - Ka-Band - the future of satellite communication?
  6. ↑ https://www.esa.int/Our_Activities/Telecommunications_Integrated_Applications/Satellite_frequency_bands ESA - Satellite frequency bands
  7. ↑ http://diru-beze.de/funksysteme/skripte/DiFuSy/Mobilfunk-Kanal_WS0405.pdf Prof. Dr. – Ing. Dietmar Rudolph - radio channel
  8. ↑ http://bigsemite.tripod.com/mcgraw.pdf Satellite Communications - Dennis Roddy - Third Edition