← Back

Featured Examples

Impact of LEO Altitude Variation on SNR and Path Loss

The experiment examines how altitude affects signal in each frequency band. The scenario is set to rural. The experiment is run for two frequency bands of interest (S and K), with the channel set to DL. The altitude range spans from 300km to 2100km. Transmitting and receiving antenna powers and characteristics are the equal for each altitude.

To simulate this example in NetSim, Open NetSim, Select Examples ->Non Terrestrial Network -> Impact of LEO Altitude Variation on SNR and Path Loss then click on the tile in the middle panel to load the example as shown in below screenshot.

Figure-1: List of scenarios for the example of Impact of LEO Altitude Variation on SNR and Path Loss

The following network diagram illustrates what the NetSim UI displays when you open the example configuration file.

Figure-2: Network set up for studying the Impact of LEO Altitude Variation on SNR and Path Loss

Settings done in example config file for S band

1. Set the satellite properties as follows. To configure, click on Satellite. On the right side, expand the property panel, go to the Physical Layer of Interface_2 (Service Link), and set the following properties:

Simulation Properties	Values
Satellite > Interface_2 (Service link) properties
EIRP Density (dBW/MHz)	34
Antenna Aperture Radius (m)	1
Pathloss (dBm)	Free Space
Additional Loss (dB)	0
Noise Figure	7
Central Frequency (GHz)	2.185
Bandwidth (MHz)	20
Shadow Fading	None
Outdoor Model	Rural
UE	Handheld
Altitude (km)	300, 600, 1200, 1500, 1800, 2100
gNB> Interface_4 (Feeder link) properties
Carrier Configuration	S Band n256

Table-1: Input Parameters for Link Budget Simulation Across Multiple Satellite Altitudes

2. Enable NTN UE Beam association log by clicking on plots/logs tab on the right side of the panel.

Figure-3: Enable NTN UE Beam Association log

Pathloss and SINR calculation for 600km

We consider the satellite co-ordinates as \((0,\ 0,\ 600)\) km, and the UE co-ordinates as \((0,\ 0)\ \)km. The elevation angle is calculated as arctan of the ratio of the satellite altitude to the distance between the satellite and the UE in the XY place.

\[\alpha = \tan^{- 1}\left( \frac{Z_{sat}}{\sqrt{\left( X_{UE} - X_{sat} \right)^{2} + \left( Y_{UE} - Y_{Sat} \right)^{2}}} \right)\ = \tan^{- 1}\left( \frac{600}{0} \right) = 90{^\circ}\]

The slant height used in NetSim is per 38.811, equation 6.6-3, i.e.

\[d = \sqrt{R_{E}^{2}\sin^{2}(\alpha) + h_{o}^{2} + 2h_{o}R_{E}} - R_{E}\sin(\alpha)\]

For a link between a ground station and a LEO satellite operating at 600 km with elevation angle \(\alpha = 86.59{^\circ}\).

\[d = \sqrt{\left( 6.371 \cdot 10^{6} \right)^{2} \cdot \sin^{2}(90{^\circ}) + \left( 6 \cdot 10^{5} \right)^{2} + 2 \cdot \left( 6 \cdot 10^{5} \right)\left( 6.371 \cdot 10^{6} \right)} - 6.371 \cdot 10^{6}\sin(90{^\circ})\]

\[d = 600\ km\]

The free space pathloss \(PL_{FS}\ \)for a channel with \(f_{c} = 2.185\ GHz\), or \(\lambda = \frac{c}{f} = 0.15m,\ \)and \(d = 600\ km\) is

\[ \begin{align}\begin{aligned}{PL_{FS} = 20\log_{10}{\left( \frac{4\pi d}{\lambda} \right) =}20\log_{10}\left( \frac{4\pi\left( 600 \times 10^{3} \right)\left( 2.185 \times 10^{9} \right)}{3 \times 10^{8}} \right) = 154.8\ dB }\\{CNR = EIRP + G_{Tx\ } + Rx\frac{G}{T} - k - PL_{FS} - PL_{SM} - PL_{AD} - B}\end{aligned}\end{align} \]

\[CNR = 48.01 + 0 + ( - 31.62) - ( - 228.6) - (154.8) - 2 - 73.01\]

\[= 15.18\ dBm\]

Results:

After the simulation, open the NTN UE Beam Association.csv under logs section from simulation results window and observe the SNR and pathloss value.

Figure-4: Opening NTN UE Beam Association log from simulation results window

Figure-5: SNR and Pathloss value from NTN UE Beam Association log

Figure-6: Impact of Satellite Altitude on Signal-to-Noise Ratio (SNR) and Pathloss in a Rural Outdoor Scenario.

Settings done in example config file for K band

1. Set the satellite properties as follows. To configure, click on Satellite. On the right side, expand the property panel, go to the Physical Layer of Interface_2 (Service Link), and set the following properties:

Simulation Properties	Values
Satellite > Interface_2 (Service link) properties
EIRP Density (dBW/MHz)	4
Antenna Aperture Radius (m)	0.25
Pathloss Model	Free Space
Additional Loss (dB)	0
Noise Figure	1.2
Carrier Configuration	K Band n510
Channel Frequency (GHz)	18.75
Bandwidth (MHz)	200
Shadow Fading	None
Outdoor Model	Rural
UE	VSAT
Rx Antenna Gain (dB)	35
Altitude	300, 600, 1200, 1500, 1800, 2100

Table-2: Simulation settings

2. Enable NTN UE Beam association log by clicking on plots/logs tab on the right side of the panel.

3. Run simulation for 10 seconds.

Pathloss and SINR calculation for 600km

We consider the satellite co-ordinates as \((0,\ 0,\ 600)\) km, and the UE co-ordinates as \((0,\ 0)\ \)km. The elevation angle is calculated as arctan of the ratio of the satellite altitude to the distance between the satellite and the UE in the XY place.

\[\alpha = \tan^{- 1}\left( \frac{Z_{sat}}{\sqrt{\left( X_{UE} - X_{sat} \right)^{2} + \left( Y_{UE} - Y_{Sat} \right)^{2}}} \right)\ = \tan^{- 1}\left( \frac{600}{0} \right) = 90{^\circ}\]

The slant height used in NetSim is per 38.811, equation 6.6-3, i.e.

\[d = \sqrt{R_{E}^{2}\sin^{2}(\alpha) + h_{o}^{2} + 2h_{o}R_{E}} - R_{E}\sin(\alpha)\]

For a link between a ground station and a LEO satellite operating at 600 km with elevation angle \(\alpha = 86.59{^\circ}\).

\[d = \sqrt{\left( 6.371 \cdot 10^{6} \right)^{2} \cdot \sin^{2}(90{^\circ}) + \left( 6 \cdot 10^{5} \right)^{2} + 2 \cdot \left( 6 \cdot 10^{5} \right)\left( 6.371 \cdot 10^{6} \right)} - 6.371 \cdot 10^{6}\sin(90{^\circ})\]

\[d = 600\ km\]

The free space pathloss \(PL_{FS}\ \)for a channel with \(f_{c} = 18.75\ GHz\), or \(\lambda = \frac{c}{f} = 0.15m,\ \)and \(d = 600\ km\) is

\[ \begin{align}\begin{aligned}{PL_{FS} = 20\log_{10}{\left( \frac{4\pi d}{\lambda} \right) =}20\log_{10}\left( \frac{4\pi\left( 600 \times 10^{3} \right)\left( 20 \times 10^{9} \right)}{3 \times 10^{8}} \right) = 173.47\ dB }\\{CNR = EIRP + G_{Tx\ } + Rx\frac{G}{T} - k - PL_{FS} - PL_{SM} - PL_{AD} - B}\end{aligned}\end{align} \]

\[CNR = 27.01 + 0 + 9.17 - ( - 228.6) - (173.47\ ) - 2 - 83.01\]

\[= 8.3\ dBm\]

Observe the SNR and pathloss value from NTN UE Beam Association log.

Figure-7: SNR and Pathloss value from NTN UE Beam Association log

Figure-8: Impact of Satellite Altitude on Signal-to-Noise Ratio (SNR) and Pathloss in a Rural Outdoor Scenario.

The Ka band, which operates at higher frequencies, experiences greater path loss as can be seen from the example numerical calculation provided. In downlink transmissions, the SNR values for the S-band and K-band cases are comparable. However, in downlink transmissions, the SNR values are comparable between the S-band and K-band cases. Although the K-band scenario has higher path loss and lower IERP input, the use of V-SAT antennas with a receiver gain of 35 dBi compensates for these effects, whereas the S-band scenario uses simulated handheld UEs with NIL receiver gain.

SNR Variation Across Outdoor Scenarios with Varying Transmit Power

To simulate this example in NetSim, Open NetSim, Select Examples ->Non Terrestrial Network -> SNR Variation Across Outdoor Scenarios with Varying Transmit Power then click on the tile in the middle panel to load the example as shown in below screenshot.

Figure-9: List of scenarios for the example of SNR Variation Across Outdoor Scenarios with Varying Transmit Power

The following network diagram illustrates what the NetSim UI displays when you open the example configuration file

Figure-10: Network set up for studying the SNR Variation Across Outdoor Scenarios

Settings done in example config file for Dense urban and Rural scenarios

1. Set the satellite properties as follows. To configure, click on Satellite. On the right side, expand the property panel, go to the Physical Layer of Interface_2 (Service Link), and set the following properties:

Simulation Properties	Values
Satellite > Interface_2 (Service link) properties
Antenna Aperture Radius (m)	1.5
Pathloss Model	Free Space
Noise Figure	1.2
Channel Frequency (GHz)	18.75
Bandwidth (MHz)	400
Shadow Fading	Log Normal
Additional Loss(dB)	0
Clutter Loss	Enabled
LOS probability	0 (NLOS)
UE	VSAT
Rx Antenna Gain (dB)	35
EIRP Density (dBW/MHz)	33.63, 36.64, 38.40, 39.65, 40.61, 41.41, 42.08, 42.66, 43.17, 43.63
Tx Power (dBm)	40.00, 43.01, 44.77, 46.02, 46.98, 47.78, 48.45, 49.03, 49.54, 50.00
gNB> Interface_4 (Feeder link) properties
Carrier Configuration	K Band n510

Table-3: Simulation settings

2. Enable NTN UE Beam association log by clicking on plots/logs tab on the right side of the panel.

Figure-11: Enable NTN UE Beam Association log

3. Run Simulation for 10 seconds.

Results

After the simulation, open the NTN UE Beam Association.csv under logs section from simulation results window and observe the SNR value.

Figure-12: Opening NTN UE Beam Association log from simulation results window

Figure-13: SNR value from NTN UE Beam Association log

Clutter loss enabled and NLOS

Figure-14: Effect of EIRP Density on Signal-to-Noise Ratio (SNR) in Rural and Dense Urban

If we consider 49.65 as Tx antenna gain, and calculate the Tx power based on that,

\[EIRP\ \lbrack dBW\rbrack = \ P_{tx}\lbrack dBm\rbrack - 30 + G_{Tx}\ \lbrack dBi\rbrack\]

\[59.65 = \ P_{tx}\lbrack dBm\rbrack - 30 + 49.65\]

\[P_{tx}\lbrack dBm\rbrack = 40\]

Figure-15: Effect of Transmit Power on Signal-to-Noise Ratio (SNR) in Rural and Dense Urban

SNR and Pathloss variation with varying elevation angles

In this experiment, a satellite at an altitude of 600km is deployed to measure pathloss and SNR values for different elevation angles. Changing the UE position, but keeping its altitude from ground fixed, aims at simulating how the signal might be affected as a UE moves towards the beam center. The test is performed in DL on the S band. The simulations are performed for every scenario. The results show how dramatically the elevation angle affects the signal, with SNR values that experience an immediate degradation when going from communicating with a satellite that is perfectly positioned to one that is slightly shifted. Elevation angle however, is not the only factor that changes, since the altitude from ground of the satellite is kept the same throughout the test, the distance between the communicating nodes is increasing with the diminishing of the elevation angle.

To simulate this example in NetSim, Open NetSim, Select Examples ->Non-Terrestrial Network -> SNR and Pathloss variation with varying elevation angles then click on the tile in the middle panel to load the example as shown in below screenshot.

Figure-16: List of scenarios for the example of SNR and Pathloss variation with varying elevation angles

The following network diagram illustrates what the NetSim UI displays when you open the example configuration file.

Figure-17: Network set up for studying the SNR and Pathloss variation with varying elevation angles

Settings done in example config file for sample

Elevation Angle	90	80	70	60	50	40	30	20	10
Slant height km	600	608.73	634.63	685.51	758.0	884.05	1072.8	1401.9	1995.58

Table-4: Slant Height vs. Elevation Angle in Satellite Geometry

Results:

Based on the UE position, the Elevation Angle and Slant Height (km) will change, these values can be observed from NTN UE Beam Association log.

Figure-18: Slant height and Elevation angle in NTN UE Beam Association log

Figure-19: Impact of Elevation Angle on Signal-to-Noise Ratio (SNR) and Pathloss in a Satellite Link

3GPP 38.821 Set 1 system level simulation

Introduction

This simulation is based on the Set 1 Reference Scenario from 3GPP TR 38.821, which provides guidelines for evaluating the performance of Non-Terrestrial Networks (NTN) with Low Earth Orbit (LEO) satellites. In this setup, the satellite uses a transparent payload, meaning it acts as a relay, passing signals between the ground gateway and the User Equipment (UE).

Objective

The goal is to measure the distributions and percentiles of SINR and throughput across multiple spot beams, with each beam containing multiple UEs.

Part1: Network Scenario

The following network diagram illustrates what the NetSim UI displays when you open the example configuration file.

Figure-20: 19 beams arranged in a hexagonal layout; S-band, LEO orbit; total 190 UEs (10 UEs per beam) connected via a transparent satellite relay with full buffer DL traffic

Simulation Setup

To create this scenario, we have:

• Set the Grid length to 450 × 200

• Dropped 19 beams in a hexagonal grid layout.

• Randomly placed 10 UEs in each beam (total of 190).

• Set the Band to S-band and Frequency reuse to FR1.

• Selected LEO 600 from the orbit options to configure a Low Earth Orbit at 600 km altitude.

• Simulation time is set to 30 seconds.

Parameter configuration

Evaluation parameters
Satellite Orbit	LEO 600
Satellite altitude	600 km
EIRP (dBW/MHz)	34
Noise Figure (dB)	7
Antenna aperture (m)	1
Band	S
Frequency	2 GHz (S Band)
Bandwidth (MHz)	30 per beam
Scheduling Type	Round robin
Traffic	Full buffer DL
RU%	100%
Elevation angle	Beam centres are at elevation angle \(90{^\circ}\). The UE’s elevation angle would depend on its location within the beam.
Antenna pattern	Bessel function per section 6.4.1 of TR 38.811. All UEs are not at the Nadir point and hence antenna gains need to be computed.
Additional loss(dB)	0
Clutter loss (dB)	0
UE density	10 UEs per spot beam
UE mobility	No mobility
Antenna temperature (k)	290
UE RX Antenna Gain (dB)	0

Table-5: System simulation parameters

Application properties

• Created a CBR application between Wired Node 9 to all UEs from the set traffic tab in the ribbon on top. Click on the created application, and in the right-side property panel, set the packet size to 1460B and Interarrival time to 584 μs, keeping the other application properties as default. This creates a generation rate of 20 Mbps ensuring full buffer at each UE.

Application settings
Packet size(B)	1460
Inter arrival time (\(\mathbf{\mu s)}\)	584
Generation rate (Mbps)	20

Table-6: Application properties

• The NTN Radio measurement log, NTN Resource allocation log and Application packet flow log files must be enabled from the design window.

• Log files can be enabled by clicking on the icon in Configure Reports > Plots > Network Logs option as shown below

Figure-21: Enabling the Log files

• Run simulation for 30s, after the simulation completes ,go to results window click on logs options and open NTN Radio Measurement Log.csv, note down the SINR, and from the Application packet flow log note down the Throughput for each application.

Figure-22: Results window

Results and Discussion

The results of the simulation are shown using CDF plots for SINR, UE Throughput and Beam throughput.

• To generate CDF of throughput plot, the Throughput column from the Application packet flow log file was considered, and the CDF of throughput was plotted.

Figure-23: CDF of downlink throughput per UE; LEO satellite network using S-Band with 19 beams and 10 UEs per beam

Throughput percentile metrics
5th percentile	1.62 Mbps
50th percentile	6.49 Mbps
95th percentile	10.85 Mbps

Table-7: Throughput percentile metrics.

To generate CDF of SINR plot, the SINR column from the radio measurement log file was considered, and the CDF of SINR was plotted

Figure-24:CDF of SINR ; LEO; S-Band; 10UEs per beam; 19 beams

Throughput percentile metrics
5th percentile	-0.40 Mbps
50th percentile	9.50 Mbps
95th percentile	14.66 Mbps

Table-8: SINR percentile metrics

To generate CDF of per beam throughput plot, the throughput for each application was taken from the results window. The number of UEs associated with each beam was obtained from the resource allocation log file, and the CDF of throughput per beam was then plotted.

Figure-25: CDF of Per-Beam Throughput

Throughput percentile metrics
5th percentile	45.39 Mbps
50th percentile	57.27 Mbps
95th percentile	69.97 Mbps

Table-9: Per-Beam Throughput percentile metrics.

The SINR CDF shows how the signal quality changes based on the user’s location within a beam. UEs near the beam center usually have better SINR, while edge UEs see lower values due to reduced antenna gain.

The throughput CDF shows how throughput is distributed among UEs. The scheduling is Round Robin scheduling and all UEs have full buffer traffic. UEs with higher SINR achieve slightly better throughput.

The per-beam throughput CDF shows how sum throughput varies across beams. Each beam has the same bandwidth and number of UEs, but performance depends on SINR which depends on UE location within the beam. Due to randomness in the UE positions we see a distribution in the per beam throughputs.

Satellite capacity:

• Satellite capacity = 1127.54 Mbps (Sum throughput of all 190 UEs)

Area Traffic capacity:

• Number of beams = 19

• Beam radius, \(R\) = 55.13 km

• Area per beam (A)= \(\frac{3\sqrt{3\ \ }}{2}\ R^{2} = \frac{3\sqrt{3\ \ }}{2}(55.13)^{2} = 7887.1\ km^{2}\)

• Total coverage area =\(\ 7887.1\ km^{2} \times 19 = \ 149854.9\) \(km²\)

• Area Traffic Capacity

\[\frac{1127.54\ Mbps}{149854.9\ km^{2}} = 0.007526\ \times 1000\ kbps/km^{2}\mathbf{= \ 7.526\ kbps/k}\mathbf{m}^{\mathbf{2}}\mathbf{\ .}\]

Average Spectral efficiency:

• Channel Bandwidth = 30 MHz

• Number of TRxPs = 19

• Average spectral Efficiency

\[\frac{Aggregate\ Throughput(bps)}{Bandwidth\ (Hz) \times Number\ of\ TRxPs} = \frac{1127.54 \times 10^{6}}{30 \cdot 10^{6} \times 19} = \mathbf{1.98\ \ bits/s/Hz/TRxP}.\]

Part-2: Peak Throughput and Spectral Efficiency Evaluation

In this simulation scenario, 1 UE is placed at the nadir point, and the full system bandwidth of 30 MHz is allocated to that single user. The maximum number of Physical Resource Blocks (PRBs) supported by 30 MHz at numerology μ = 0 is 160 PRBs. A full buffer downlink traffic model is used, with a generation rate of 125 Mbps.

Network Scenario

The following network diagram illustrates what the NetSim UI displays when you open the example configuration file.

Figure-26: Network Scenario

Simulation Setup

To create this scenario, we have:

• Set the Grid length to 120\(\ \times\) 40 km

• Dropped a single beam in a hexagonal grid layout.

• Placed the UE at the center of the beam footprint.

• Set the Band to S-band and Frequency reuse to FR1.

• Selected LEO 600 from the orbit options to configure a Low Earth Orbit at 600 km altitude.

• Simulation time is set to 50 seconds.

Parameter configuration

Evaluation parameters
Satellite Orbit	LEO 600
Satellite altitude	600 km
Slant height	600 km
EIRP (dBW/MHz)	34
Noise Figure (dB)	7
Antenna aperture (m)	1
Band	S
Frequency	2 GHz (S Band)
Bandwidth (MHz)	30 per beam
Scheduling Type	Round robin
Traffic	Full buffer DL
RU%	100%
Elevation angle(°)	90
Antenna pattern	Bessel function per section 6.4.1 of TR 38.811.
Pathloss( dB)	154
Additional loss( dB)	0
Clutter loss (dB)	0
UE density	1 UE
UE mobility	No mobility
Antenna temperature (k)	290
UE TX power (dBm)	23
UE RX Antenna Gain (dB)	0

Table-10: Simulation parameters.

Application Properties

• Created a CBR application between Wired Node 9 to all UE 11 from the set traffic tab in the ribbon on top. Click on the created application, and in the right-side property panel, set the packet size to 1460B and Interarrival time to 93.44 \(\mu s\), keeping the other application properties as default. This creates a generation rate of 125 Mbps ensuring full buffer at each UE.

Application settings
Packet size(B)	1460
Inter arrival time (\(\mathbf{\mu s)}\)	93.44
Generation rate (Mbps)	125

Table-11: Application settings

Theoretical Spectral Efficiency Computation

As per Annex 1 of the ITU-2020-NTN framework, the theoretical peak spectral efficiency is given by:

\[{SE}_{p} = \frac{v_{Layers}{.Q}_{m}.f.R_{\max}\frac{N_{PRB}^{BW,u}*12}{T_{s}^{u}}(1 - OH)}{BW\ }\]

• The NTN code block log file must be enabled from the design window. MCS value can be observed from the code block log file.

• Log file can be enabled by clicking on the icon in Configure Reports > Plots > Network Logs option as shown below

Figure-27: Enabling the NTN Radio measurements log file.

Where:

• Number of layer, \(\nu = 1\)

• Modulation order\(\ \left( Q_{m} \right) = 6\)

• Coding rate\(\ (R) = 0.852\ \)

• Numerology\(\ (\mu) = 0\)

• Overhead, OH\(\ = \ 0.14\ \)

• Bandwidth \(= 30\ MHz\).

• \(N_{PRB}^{BW,\mu}\ \)is the maximum Resource Block (RB) allocation in UE supported maximum bandwidth BW\(\ \)in a given band\(\ \)with numerology \(\mu\).

• \(T_{s}^{\mu}\)is the average OFDM symbol during in a subframe for numerology\(\ \mu,\ i.e.\ T_{s}^{\mu} = \frac{10^{- 3}}{14*2^{\mu}}\).

\[T_{s}^{u} = \frac{10^{- 3}}{14*2^{\mu}}\ \ = \frac{0.001}{14} = 0.00007143\]

\[\frac{N_{PRB}^{BW,u}*12}{T_{s}^{u}}(\ 1-OH)\ = \frac{160 \times 12 \times (1 - 0.14)}{0.00007143} = 23.11 \times 10^{6}\]

\[{SE}_{p} = \frac{1 \times 6 \times 0.852 \times 23.11 \times 10^{6}}{30 \times 10^{6}} = \frac{5.112 \times 23.11}{30} = \mathbf{3.94} \mathbf{b/s/Hz}\]

Results and discussion

From the simulation results:

• Achieved throughput = 105.92 Mbps

• MCS Index = 19

• Modulation = 64-QAM

• Coding rate (R) = 0.852

• Bandwidth \(= 30\ MHz\).

• Observed Spectral Efficiency (SE) =\(\frac{Achieved\ Throughput(bps)\ }{Bandiwdth(Hz)} =\) \(\frac{105.92\ \times 10^{6}\ }{30 \times 10^{6}} = 3.53\ bits/sec/Hz\)

Simulation Results
Throughput (Mbps)	\[105.92\]
MCS	\[19\]
Spectral efficiency (bits/s/Hz)	\[\mathbf{3.53\ }\]

Table+12: Simulation results

Thus, the theoretical peak spectral efficiency as per the ITU-2020-NTN Annex 1 formula is 3.94 bits/sec/Hz, while the observed spectral efficiency from the simulation is 3.53 bits/sec/Hz. This small gap reflects practical network conditions such as protocol overhead, scheduling inefficiencies, and real-time radio impairments.