Power transfer balance

The link budget ( English budget link ) is in the communications engineering a measure of the quality of a transmission channel . The balance is given in the unit Bel (with positive or negative values) and calculated in a simple model by adding the transmission power , the receiver sensitivity , the antenna gain and the free space attenuation . Part of the power transfer balance is formed by the Friis transfer equation.

calculation

The power transmission balance describes the power received at the receiver ; powers are expressed in dBm in relation to the transmission power emitted by the transmitter minus various attenuation influences that describe the transmission channel . An exemplary power transfer balance can take the following form: ${\displaystyle P_{RX}}$ ${\displaystyle P_{TX}}$

${\displaystyle P_{RX}=\underbrace {P_{TX}+G_{TX}-L_{TX}} _{\mathsf {Senderparameter}}-\overbrace {L_{FS}-L_{M}} ^{\mathsf {Pfadverlust}}+\underbrace {G_{RX}-L_{RX}} _{\mathsf {Empf{\ddot {a}}ngerparameter}}}$

The directional properties of the receiving or transmitting antenna are entered as antenna gain with a positive sign, the remaining summands represent transmission losses, such as the attenuation of connecting cables on the receiving and transmitting side . The term represents the free space attenuation , this term is usually the largest in terms of value. All losses during propagation are summarized in the term path loss . In addition to the attenuation of free space, these are above all absorption losses when penetrating media ( atmosphere ), losses through diffraction and shading, and losses through diffraction at obstacles within the Fresnel zone (possibly occurring as fading ). All these losses occurring in addition to the free space attenuation are summarized here under . ${\displaystyle G_{RX}}$ ${\displaystyle G_{TX}}$ ${\displaystyle L_{RX}}$ ${\displaystyle L_{TX}}$ ${\displaystyle L_{FS}}$ ${\displaystyle L_{M}}$

The attenuation values ​​usually exceed several powers of ten, primarily due to the high free space attenuation. Power transmission balances with very large values ​​occur because of the great distances in interstellar communication systems or in earth-moon-earth communication. In the latter case, the free space attenuation is around 250 dB, which must be compensated for by antennas with a correspondingly large antenna gain, high transmission powers and very sensitive receivers.

See also

• Range (radio technology)

Web links

• IEV 713-02-10, link (power) budget
• Calculation of the link budget of a UMTS base station ( memento from September 19, 2011 in the Internet Archive )