To simulate Satellite Communication projects using NS2 has includes to design a satellite networks in which the communication occurs among the earth station (ground terminals) and one or more satellites. NS2 does not have built-in support for satellite communication; however we can still replicate it by customizing metrics like propagation delay, high altitude positioning, and adding custom protocols for satellite-specific features.
Here’s how we can simulate Satellite Communication projects in NS2 by prolonging the simulator to signify the satellite link, ground stations, and the distinct features of satellite networks like long propagation delay.
Steps to Simulate Satellite Communication Projects in NS2
- Basic Concepts in Satellite Communication
- Satellites: Satellites perform as relay stations that receive signals from an uplink station, process the signal (amplify and/or modulate it), and retransmit it back to the downlink station.
- Ground Stations: Earth-based terminals that transmit and receive signals to/from satellites.
- Propagation Delay: One of the key contexts of satellite communication is the large propagation delay triggered by the distance among the satellite and the ground station (up to ~250 ms round-trip delay for GEO satellites).
- Bandwidth and Link Capacity: Satellite links usually have high bandwidth, however with higher latency related to terrestrial networks.
- Extending NS2 for Satellite Communication
To simulate Satellite Communication in NS2, we need to:
- Model satellites as high-altitude nodes.
- Configure ground stations that interact with the satellites.
- Replicate the uplink and downlink with proper latency.
- Set up TCP/UDP agents for data transmission among ground stations through the satellite.
- Basic Satellite Communication Simulation Setup in NS2
Example: Simulating a Simple Satellite Communication Link
In this sample, we will simulate a simple satellite communication system with two ground stations (one for uplink and one for downlink) and a satellite that transmits traffic among them. We will utilize a TCP connection to replicate data transmission.
# Create NS2 simulator instance
set ns [new Simulator]
# Define the ground station (uplink) and satellite node
set ground_station_uplink [$ns node]
set satellite [$ns node]
set ground_station_downlink [$ns node]
# Set satellite position (to simulate height)
$satellite set X_ 0.0
$satellite set Y_ 0.0
$satellite set Z_ 35786.0 ;# Geostationary orbit (35786 km)
# Set ground station positions (these can be anywhere on earth)
$ground_station_uplink set X_ 100.0
$ground_station_uplink set Y_ 100.0
$ground_station_uplink set Z_ 0.0
$ground_station_downlink set X_ 200.0
$ground_station_downlink set Y_ 200.0
$ground_station_downlink set Z_ 0.0
# Create uplink and downlink duplex links
# Set large propagation delay to simulate long distance (300 ms delay for GEO)
$ns duplex-link $ground_station_uplink $satellite 100Mb 150ms DropTail
$ns duplex-link $satellite $ground_station_downlink 100Mb 150ms DropTail
# Set up TCP agents for uplink station (sender) and downlink station (receiver)
set tcp_sender [new Agent/TCP]
set tcp_receiver [new Agent/TCPSink]
$ns attach-agent $ground_station_uplink $tcp_sender
$ns attach-agent $ground_station_downlink $tcp_receiver
# Connect TCP sender and receiver through the satellite
$ns connect $tcp_sender $tcp_receiver
# Set up FTP application to simulate data transfer over the satellite link
set ftp [new Application/FTP]
$ftp attach-agent $tcp_sender
# Start the FTP transfer at 1.0 second
$ns at 1.0 “$ftp start”
$ns at 5.0 “$ftp stop”
# Enable tracing for analysis
set tracefile [open satellite_trace.tr w]
$ns trace-all $tracefile
# Define finish procedure to end the simulation
proc finish {} {
global ns tracefile
$ns flush-trace
close $tracefile
exit 0
}
# End the simulation after 6 seconds
$ns at 6.0 “finish”
$ns run
Explanation:
- Nodes (Ground Stations and Satellite): Three nodes denoted the ground station uplink, satellite, and ground station downlink.
- Satellite Position: The satellite is positioned in geostationary orbit (~35,786 km above the Earth).
- Uplink and Downlink Links: Duplex links with a high bandwidth (100 Mbps) and a large propagation delay (150 ms) indicate the satellite links.
- TCP Connection: A TCP connection is configure among the ground stations, and FTP traffic replicates data transmission between them via the satellite.
- Tracing: The simulation creates a trace file for performance evaluation (satellite_trace.tr).
- Introducing Mobility for Low Earth Orbit (LEO) Satellites
For Low Earth Orbit (LEO) satellites, the satellite position is not fixed, and the satellites move next of kin to the Earth’s surface. To replicate LEO satellites in NS2, we can establish mobility models in which the satellite moves in the course of the simulation.
Example: Simulating a Moving LEO Satellite
# Set up mobility for the LEO satellite (moving in orbit)
$satellite setdest 0.0 10000.0 7.5 ;# Move to new position (10000 km) at 7.5 km/s (typical LEO speed)
This command replicates a LEO satellite moving in its orbit at a speed of 7.5 km/s, that is usual for LEO satellites.
- Advanced Satellite Communication Features
5.1. Handover between Multiple Satellites
For satellite constellations such as LEO constellations like Starlink, handover happens when a ground station switches from one satellite to another as they move in and out of range. We can replicate this handover in NS2 by enthusiastically associating the ground station to different satellites in the period of the simulation.
# At time 5.0, switch to another satellite (handover)
$ns at 5.0 “$ns connect $tcp_sender $tcp_receiver_via_new_satellite”
5.2. Multicast Communication via Satellites
Multicast communication is usually utilized in satellite systems to transmit the same data to multiple ground stations. We can replicate multicast communication in NS2 by set up the multiple receivers for the same data stream.
# Connect one sender to multiple receivers (multicast via satellite)
$ns connect $tcp_sender $tcp_receiver1
$ns connect $tcp_sender $tcp_receiver2
5.3. Delay-Tolerant Networking (DTN) in Satellite Systems
Satellite networks usually utilize Delay-Tolerant Networking (DTN) to manage the large delays and potential disturbances in communication. We can replicate DTN in NS2 by incorporate custom protocols that buffer data at the satellite and ground stations.
- Performance Analysis for Satellite Communication
Key parameters in satellite communication that contain:
- Propagation Delay: The time taken for data to travel from the ground station to the satellite and back.
- Throughput: The rate of successful data transfer over the satellite link.
- Packet Loss: The percentage of packets lost because of signal degradation or handover among satellites.
- Handover Delay: The delay established when switching among satellites in a constellation.
Example: Parsing Trace File for Throughput
We can utilize AWK or Python scripts to parse the trace file and estimate the throughput or other parameters.
awk ‘{ if ($1 == “r” && $4 == “AGT” && $7 == “tcp”) count++; } END { print “Packets received: “, count; }’ satellite_trace.tr
This AWK script counts the number of TCP packets successfully received at the ground station through the satellite.
- Visualizing Satellite Communication in NAM
We can envision the satellite communication simulation using NAM (Network Animator) to track the packet flow and satellite mobility:
# Enable NAM trace file for visualization
set namfile [open satellite_comm.nam w]
$ns namtrace-all $namfile
# Open NAM after the simulation ends
proc finish {} {
global ns namfile
$ns flush-trace
close $namfile
exec nam satellite_comm.nam &
exit 0
}
We can then execute the following command to envision the satellite communication:
nam satellite_comm.nam
We presented the fundamental approaches that support you to simulate the satellite communication using ns2 tool. Further specific details will be added later in another manual.
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