Terminology » LoRaWAN Link Budget Calculation with example

LoRaWAN Link Budget Calculation with example

Introduction : In wireless communication, the link budget represents the balance of gains and losses a signal experiences as it travels from a transmitter to a receiver. In the context of LoRaWAN, link budget analysis is crucial for determining achievable coverage, network capacity and device performance. By considering factors such as transmit power, antenna gains, path loss and receiver sensitivity, network designers can estimate the maximum communication range and ensure reliable connectivity.

What is Link Budget?

As mentione, it is the total gain and loss from transmitter to receiver. It helps in estimation of maximum range and to know whether the signal will be above the receiver sensivity or not. The Link Budget formula taking into consideration receiver sensitivity is as follows.

Link Budget (dB) = P_tx + G_t + G_r - L_sys - P_{rx_min}

Where, P_{rx_min} = receiver sensivity P_tx = Transmit power G_t , G_r = Transmit and receive antenna gain (dBi) L_sys = System Losses due to cables and connectors in dB

Step-1 : Determine Receiver Sensitivity (dBm)

P_{rx_min} = -174 + 10*log10(BW) + NF + SNR_min

Example Calculation : INPUTS : BW = 125 KHz, NF = 6 dB, SNR_min = -20dB (for SF12 as per table) OUTPUT : Receiver Sensivity (P_{rx_min})= -137 dBm

SF	SNR Limit (dB)
7	-7.5
8	-10
9	-12.5
10	-15
11	-17.5
12	-20

Table : Spreading Factor (SF) vs SNR Limit (dB)

Step-2 : Calculate Link Budget (dB)

Link_Budget = P_tx + G_t + G_r - L_sys - P_{rx_min}

Example Calculation :

INPUTs : P_tx = 14 dBm (EU868 limit), G_t = G_r = 2 dBi, L_sys = 2 dB

OUTPUT : LB = 14+2+2-2-(-137) = 153 dB

Step-3 : Calculate distance based on Path Loss Formula

Equate Path Loss to Link Budget and solve for distance (i.e. range) using free space path loss formula.

PL (dB) = 32.44 + 20*log10(Freq_MHz)+ 20*log10(d_km)

Example Calculation :

Set PL = Link_Budget to solve for distance (d_km) in above formula-3.

153 = 32.44 + 20log10(868) + 20 log10(d) => d = 10^3.09 = 1236 Km.

NOTE : This is ideal free space range of LoRaWAN ; in real urban/rural environments, additional fading, obstacles and duty cycle limits reduce range drastically. Practially we can have urban: 2–5 km , suburban: 5–15 km and rural / LoS: 15–30 km.

LoRaWAN Range Calculator

Check-out LoRaWAN Range Calculator Page

Conclusion: A well calculated link budget enables operators to optimize gateway placement, select appropriate spreading factors and balance energy consumption against coverage requirements.