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Link Budget Equation

#link budget #system design #EIRP #path loss #margin #wireless link

Link Budget Equation

The link budget accounts for all gains and losses in a wireless communication system to determine if adequate signal strength reaches the receiver. This is the master equation for RF system design.

P_r = P_t + G_t - L_t - L_{fs} - L_m + G_r - L_r

Alternative Forms

Link Margin

M = P_r - S_{min}

Margin above minimum required signal level

EIRP Form

P_r = EIRP - L_{path} + G_r - L_r

Using Effective Isotropic Radiated Power

Input Variables

Transmit Power (P_t)

dBm

Power output from transmitter(Range: -30 – 60 dBm)

Transmit Antenna Gain (G_t)

dBi

Gain of transmitting antenna(Range: -10 – 50 dBi)

Transmit Losses (L_t)

Cable and connector losses at transmitter(Range: 0 – 20 dB)

Frequency (f)

MHz

Operating frequency(Range: 1 – 300000 MHz)

Distance (d)

Link distance(Range: 0.001 – 100000 km)

Miscellaneous Losses (L_m)

Fading margin, polarization loss, etc.(Range: 0 – 30 dB)

Receive Antenna Gain (G_r)

dBi

Gain of receiving antenna(Range: -10 – 50 dBi)

Receive Losses (L_r)

Cable and connector losses at receiver(Range: 0 – 20 dB)

Receiver Sensitivity (S_{min})

dBm

Minimum signal level for reliable reception(Range: -120 – -30 dBm)

Results

Received Power (P_r)

—

Link Margin (M)

—

Free Space Path Loss (L_fs)

—

EIRP (EIRP)

—

📖 Example: 10 km Point-to-Point Link at 5.8 GHz

Design a reliable 10 km wireless backhaul link

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