# Calculate SDR Sensitivity, Link Budget and Maximum Allowable Path Loss

Updated Oct 8, 2021

## Environment

### Hardware

• USRP-2954
• USRP Software Defined Radio Device
• PXI Vector Signal Transceiver

In RF/Wireless system design, it is required to calculate the System Link Budget between transmitter and receiver which requires to know transmitter power and receiver sensitivity. For Software Defined Radio such as NI-USRP and NI VST (Vector Signal Transceivers), the RF parameters are dynamically defined according to user requirements which are used to define the receiver sensitivity.

For RF/wireless system to operate stable, the RF propagation path loss must be lower than the Maximum Allowable Path Loss, by the amount of system link margin. Maximum Allowable Path Loss (MAPL) will define the distance between transmitter and receiver, the bigger the MAPL, the longer the distance which is related the RF propagation environment. RF propagation discussion is out of this article scope.

### Calculate USRP Sensitivity

1. The sensitivity is calculated with formula Sev = N_floor  + NF + 10xlog(BW) + SNR, N_floor  = kTB = -174dBm,
Where:
N_floor  is the system noise power in 1 Hz,  in room temperature, we call it noise floor,
k is Boltzmann's constant, k
= 1.38 × 10-23J K-1
T is the absolute temperature of the receiver also known as noise temperature, consider it equals to 290K at room temperature of 17C
B is the bandwidth of 1 Hz
1. Find USRP-2954 Noise Figure NF = 6dB, and consider BW = 1MHz, SNR = 5dB for 64QAM modulation with 5% BER,
2. Calculate the sensitivity using the formula given in step 1. Sev = -174 + 6 + 10xlog(1,000,000) + 5= -103dBm

### Calculate USRP System Link Budget

1. Find USRP-2954 transmitter power from data sheet: 17dBm
2. USRP-2954 receiver sensitivity is calculated above: -103dBm
3. Calculated system link budget with formula S_LB = Tx_pwr - Sev
S_LB = 17 - (-103) = 120dB

Where:
S_LB is the System Link Budget
Tx_pwr is the transmitter power

### Calculate Maximum Allowable Path Loss - MAPL

1. Define the link margin according to system design requirements, consider 18 dB
2. Get the system link budget calculated above: 120dB
3. Get Transmitter antenna gain, consider 12dB
4. Get the receiver antenna gain, consider 8dB
5. Calculated maximum allowable path loss (MAPL) with formula MAPL = S_LB + G_tx + G_rx - LKM
MAPL  = 120 + 12 + 8 - 18 = 122dB

Where:
G_tx: transmitter antenna gain, 