Link Budget
Prx = Ptx + Gtx − Ltx − FSPL + Grx − Lrx
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Formula
Description
A link budget accounts for all gains and losses in a wireless communication link to determine whether the received signal power is sufficient for reliable operation. Starting with the transmitter power, antenna gains add signal strength by focusing energy in a particular direction, while cable losses and free space path loss subtract from it. The result must exceed the receiver's sensitivity threshold by a fade margin (typically 10-20 dB) to ensure reliable operation under varying conditions such as rain, multipath, and interference.
Variables
- Prx — Received power (dBm)
- Ptx — Transmitter output power (dBm)
- Gtx — Transmit antenna gain (dBi)
- Ltx — Transmitter cable/connector losses (dB)
- FSPL — Free space path loss (dB)
- Grx — Receive antenna gain (dBi)
- Lrx — Receiver cable/connector losses (dB)
Practical Notes
Receiver sensitivity for common systems: WiFi -65 to -85 dBm, Bluetooth -70 to -90 dBm, LoRa -130 to -148 dBm, cellular LTE -100 to -120 dBm. Always include a fade margin of at least 10 dB for outdoor links and 20 dB for indoor or obstructed paths.
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