Interference Models

CIR based Interference

Per TR 38.821 section 6.1.3.1 the Carrier-to-noise-and-interference ratio (CNIR) of transmission link between satellite and UE can be derived by carrier-to-noise ratio (CNR) and carrier-to-interference ratio (CIR) as follows

\[CNIR\ \lbrack dB\rbrack = - 10\log_{10}\left( 10^{- 0.1CNR\ \lbrack dB\rbrack} + 10^{- 0.1CIR\ \lbrack dB\rbrack} \right)\]

Link Budget Calculations: Example 4 LEO 600 and LEO 1200

Case 1:

Assuming a CIR of 5 dB, and using the CNR obtained from the earlier section we get

\[CNR\ \lbrack dB\rbrack = \ - 10\log_{10}{\left( 10^{- 0.1 \times ( - 1.6)} + 10^{- 0.1 \times 5} \right) = \ - 2.46\ dB}\]

Case 2:

Assuming a CIR of 5 dB, and using the CNR obtained from the earlier section we get

\[CNIR\ \lbrack dB\rbrack = - 10\log_{10}\left( 10^{- 0.1CNR\ \lbrack dB\rbrack} + 10^{- 0.1CIR\ \lbrack dB\rbrack} \right)\]

\[= \ - 10\log_{10}\left( 10^{- 0.1 \times ( - 4.62)} + 10^{- 0.1 \times 5} \right) = \ - 5.07\ dB\]

Simulation Parameters	LEO 600Km	LEO 1200Km
CNR	4.36	-4.66
CIR	5	5
CNIR	1.66	-5.11

Table-1: NR, CIR, and CNIR Comparison for LEO 600 km and 1200 km

Interference power calculations for CIR based Interference

\[Interference\ \lbrack mW\rbrack = Noise\lbrack mW\rbrack\ \times \left( \frac{CNR\ \lbrack mW\rbrack\ }{CNIR\ \lbrack mW\rbrack} - 1 \right)\]

\[Interference\ \lbrack dB\rbrack = 10 \times \log_{10}\left( Interference\ \lbrack mW\rbrack \right)\]

Case 1:

Assuming a CNR of 4.36 dB, and using the CNIR of 1.66 dB obtained from the earlier section we get

\[Interference\ \lbrack mW\rbrack = 10^{0.1\ \times \ - 99.05}\ \times \left( \frac{10^{0.1\ \times \ 4.36}\ }{10^{0.1\ \times \ 1.66}} - 1 \right)\]

\[Interference\ \lbrack mW\rbrack = 1.073\ \times 10^{- 10}\]

\[Interference\ \lbrack dB\rbrack = 10 \times \log_{10}\left( 1.073\ \times 10^{- 10}\ \right) = \ - 99.69\ dB\]

Case 2:

Assuming a CNR of -4.62 dB, and using the CNIR of -5.07 dB obtained from the earlier section we get

\[Interference\ \lbrack mW\rbrack = 10^{0.1\ \times \ - 99.05}\ \times \left( \frac{10^{0.1\ \times \ - 4.66}\ }{10^{0.1\ \times \ - 5.11}} - 1 \right)\]

\[Interference\ \lbrack mW\rbrack = 1.3439\ \times 10^{- 11}\]

\[Interference\ \lbrack dB\rbrack = 10 \times \log_{10}\left( 1.3439\ \times 10^{- 11}\ \right) = \ - 108.71\ dB\]

Exact geometric interference: In NTN systems, geometric interference arises when multiple beams sharing the same channel ID overlap, leading to co-channel interference at user terminals. The level of interference is influenced by the number of beams and the configured frequency reuse factor. In FR1, interference occurs from all available beams, whereas in FR3, it is limited to beams using the same channel ID