Spectral efficiency

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Spectral efficiency , also known as bandwidth efficiency , is a term used in communications technology and describes the relationship between the data transmission rate (in bits / second) and the bandwidth of the signal (in Hertz ). Spectral efficiency is an important parameter for digital modulation methods .

The maximum possible spectral efficiency at which error-free transmission is possible in principle is limited by the signal-to-noise ratio ( Shannon-Hartley theorem ). The more the spectral efficiency is increased for a given signal noise , the more complex methods for forward error correction are required. With spectral efficiencies above the Shannon limit, transmission errors cannot be avoided even with channel coding methods; a reliable transmission is therefore not possible in principle.

With a sufficiently high signal-to-interference power ratio, the spectral efficiency can assume values ​​of over 1 bit / s per Hz bandwidth. For example, a modem over a telephone line with a bandwidth of approx. 3500 Hz can achieve a data transmission rate of 33,600 bit / s. The spectral efficiency in this case is 33,600 bit / s / 3,500 Hz ≈ 10 bit / s per Hz. The highest spectral efficiency in radio-based communication is currently (February 2018) offered by the LTE-Advanced R10 standard with 30 bit / s per Hz.

dimension

The unit bit / s / Hz can be shortened to bit, which is correct but not intuitive. Therefore, the unabridged, more understandable form is often used.

Examples

The following table shows some gross bit rates, i.e. H. including the bits for error detection and channel coding, specified per Hz bandwidth:

modulation Spectral efficiency / bit / s / Hz
FSK 1
BPSK 1
QPSK 2
8- PSK 3
16- QAM 4th

literature

  • John G. Proakis, Masoud Salehi: Communication Systems Engineering . 2nd Edition. Prentice Hall, Upper Saddle River NJ 2002, ISBN 0-13-095007-6 .
  • Martin Werner: communications engineering. An introduction to all courses, 7th edition, Vieweg + Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0905-6 .
  • Andres Keller: Broadband cables and access networks. Technical principles and standards. Springer-Verlag, Berlin / Heidelberg 2011, ISBN 978-3-642-17631-9 .
  • Volker Jung, Hans-Jürgen Warnecke (Hrsg.): Handbook for telecommunications. Springer Verlag, Berlin / Heidelberg 1998, ISBN 978-3-642-97703-9 .

Web links