Link Budget

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.