In a Nutshell

A Link Budget is the accounting of all gains and losses from the transmitter to the receiver. Whether designing a 50km wireless bridge or a high-speed fiber link, engineers must ensure the signal arrives with enough power to be distinguished from noise. This article provides a step-by-step master class in link budget mathematics.

The Fundamental Equation

The beauty of Using decibels (dB) is that the complex physics of wave propagation reduces to simple addition and subtraction.

PRX=PTX+GTX−LTX−LPath−LRX+GRXP_{RX} = P_{TX} + G_{TX} - L_{TX} - L_{Path} - L_{RX} + G_{RX}

Step-by-Step Example: Wireless Link

Imagine a 5GHz Wireless Bridge over 5 km:

  1. Radio Output: 20 dBm (100 mW).
  2. Cable Loss: -2 dB.
  3. Antenna Gain: +23 dBi.
  4. Path Loss (FSPL): -120 dB (Calculated for 5km at 5GHz).
  5. Receiving Antenna Gain: +23 dBi.
PRX=20−2+23−120−2+23=−58 dBmP_{RX} = 20 - 2 + 23 - 120 - 2 + 23 = -58 \text{ dBm}

Optical Link Budgets

In Fiber, we focus on Attenuation per kilometer (dB/km) and Connector Loss.

Margin=(PTX−SensRX)−(α⋅L+N⋅Lc+S⋅Ls)\text{Margin} = (P_{TX} - \text{Sens}_{RX}) - (\alpha \cdot L + N \cdot L_c + S \cdot L_s)
  • α: Fiber attenuation (e.g., 0.35 dB/km for 1310nm).
  • L: Distance in km.
  • L_c: Connector loss (typically 0.5 dB each).
  • L_s: Splice loss (typically 0.1 dB each).

Conclusion

A link budget is a promise from the engineer to the hardware. If the budget is balanced with a healthy margin, the data will flow. If not, physics will win every time.

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Technical Standards & References

REF [1]
A. Kumar (2021)
Link Budget Analysis for Outdoor Wireless
Published: International Journal of Wireless
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REF [2]
Gerd Keiser (2013)
Optical Fiber Communications
Published: McGraw-Hill
VIEW OFFICIAL SOURCE
Mathematical models derived from standard engineering protocols. Not for human safety critical systems without redundant validation.

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