Link budget

A link budget is an accounting of all of the <a href="/facts/Power_(physics)/mkaEyRnn">power</a> gains and losses that a communication <a href="/facts/Signal/41YqUJ8c">signal</a> experiences in a <a href="/facts/Telecommunication/vxoj1cxR">telecommunication</a> system; from a transmitter, through a <a href="/facts/Communication_channel/MtlxEShV">communication medium</a> such as <a href="/facts/Radio_wave/XmB6WPpF">radio waves</a>, <a href="/facts/Transmission_line/cYlqaPo3">cables</a>, <a href="/facts/Waveguide_(radio_frequency)/M60l8qrm">waveguides</a>, or <a href="/facts/Optical_fiber/5ruuIFbj">optical fibers</a>, to the receiver. It is an equation giving the received power from the transmitter power, after the attenuation of the transmitted signal due to propagation, as well as the <a href="/facts/Antenna_gain/ke1y0LcM">antenna gains</a> and <a href="/facts/Feedline/y9qa2CWa">feedline</a> and other losses, and <a href="/facts/Amplifier/pnRgxncC">amplification</a> of the signal in the <a href="/facts/Radio_receiver/5olDTxkg">receiver</a> or any <a href="/facts/Repeater/JTkWvTEP">repeaters</a> it passes through. A link budget is a design aid, calculated during the design of a communication system to determine the received power, to ensure that the information is received intelligibly with an adequate <a href="/facts/Signal-to-noise_ratio/qohClhyG">signal-to-noise ratio</a>. In most real world systems the losses must be estimated to some degree, and may vary. A <a href="/facts/Link_margin/q2E09wV8">link margin</a> is therefore specified as a safety margin between the received power and minimum power required by the receiver to acurately detect the signal. The link margin is chosen based on the anticipated severity of a communications drop out and can be reduced by the use of mitigating techniques such as <a href="/facts/Antenna_diversity/Q3gbLaWh">antenna diversity</a> or <a href="/facts/MIMO/1EXPB7Vl">multiple-input and multiple-output</a> (MIMO).
A simple link budget equation looks like this:

Received power (dBm) = transmitted power (dBm) + gains (dB) − losses (dB)
Power levels are expressed in (<a href="/facts/DBm/nIFIN7E7">dBm</a>), Power gains and losses are expressed in <a href="/facts/Decibel/0LyxAPXh">decibels</a> (dB), which is a <a href="/facts/Logarithm/QeXaV97q">logarithmic</a> measurement, so adding decibels is equivalent to multiplying the actual power ratios.

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Link budget