To simulate MIMO (Multiple-Input Multiple-Output) systems using NS2 (Network Simulator 2), which needs important changes or extensions NS2 does not natively support MIMO functionalities like several antennas and spatial multiplexing. But, we can replicate the MIMO system in NS2 by estimating its behaviour using the following strategies:
- Model High-Bandwidth Channels: Since MIMO improves throughput by using numerous spatial streams, we can be mimicked high-bandwidth wireless links in NS2 to estimate the effects of MIMO.
- Modify the PHY Layer: MIMO operates at the physical layer, thus we may require to expand or change the physical layer within NS2 to replicate numerous antennas and spatial diversity.
- Use Custom Propagation Models: MIMO performance can be affected by propagation environments (e.g., urban or rural), thus launching more advanced propagation models can better denote MIMO’s real-world performance.
- Implement MIMO Behavior via Custom Models: A few users prolong NS2 with custom C++ modules or use an NS2-MIMO patch (if available) to integrate MIMO behaviour.
The following is a technique to simulate MIMO-like behaviour using higher bandwidth, lower latency, and by modelling the effect of several antennas on link performance.
Steps to Simulate MIMO Projects in NS2
- Install NS2: If NS2 is not already installed then we can install it on a Linux system using the below command:
sudo apt-get install ns2
Verify the installation by typing:
ns -version
- Extend or Patch NS2 for MIMO: Even though there is no built-in MIMO support in NS2, we can approximate the MIMO behaviour by changing the bandwidth, delay, and propagation models of the wireless communication system. We can also seek community-developed MIMO patches for NS2 or write own C++ modules to prolong its functionality.
- Create a MIMO-Like Scenario Using a Tcl Script: Below is a basic Tcl script to replicate a high-throughput, low-latency wireless system, which approximates a MIMO system by maximizing bandwidth and changing packet sizes.
Example Tcl Script for Simulating MIMO-Like Behavior in NS2
# Create a new NS2 simulator object
set ns [new Simulator]
# Open trace and NAM files for logging
set tracefile [open mimo_out.tr w]
$ns trace-all $tracefile
set namfile [open mimo_out.nam w]
$ns namtrace-all-wireless $namfile 500 500
# Define the wireless channel and propagation model
set val(chan) Channel/WirelessChannel ;# Channel type
set val(prop) Propagation/TwoRayGround ;# Propagation model
set val(netif) Phy/WirelessPhy ;# Wireless PHY model
set val(mac) Mac/802_11 ;# Use 802.11 MAC protocol
set val(ifq) Queue/DropTail/PriQueue ;# Interface Queue
set val(ll) LL ;# Link Layer
set val(ant) Antenna/OmniAntenna ;# Antenna model
set val(ifqlen) 50 ;# Interface Queue length
set val(nn) 2 ;# Number of nodes (MIMO Tx and Rx)
set val(x) 500 ;# X dimension of the simulation area
set val(y) 500 ;# Y dimension of the simulation area
set val(bw) 500Mb ;# Higher bandwidth for MIMO (approximated)
set val(delay) 2ms ;# Lower delay to simulate MIMO low-latency
# Define the network topology
set topo [new Topography]
$topo load_flatgrid $val(x) $val(y)
# Configure the simulation with MIMO-like parameters
$ns node-config -llType $val(ll) \
-macType $val(mac) \
-ifqType $val(ifq) \
-ifqLen $val(ifqlen) \
-antType $val(ant) \
-propType $val(prop) \
-phyType $val(netif) \
-channelType $val(chan) \
-topoInstance $topo \
-agentTrace ON \
-routerTrace ON \
-macTrace ON
# Create the MIMO nodes (transmitter and receiver)
set node_(0) [$ns node] ;# MIMO Transmitter
set node_(1) [$ns node] ;# MIMO Receiver
# Set initial positions for the nodes
$node_(0) set X_ 100.0
$node_(0) set Y_ 100.0
$node_(1) set X_ 400.0
$node_(1) set Y_ 400.0
# Define the high-throughput link between nodes to simulate MIMO behavior
$ns duplex-link $node_(0) $node_(1) $val(bw) $val(delay) DropTail
# Define traffic flow using UDP and CBR (Constant Bit Rate) to simulate MIMO data rate
set udp [new Agent/UDP]
$ns attach-agent $node_(0) $udp
set null [new Agent/Null]
$ns attach-agent $node_(1) $null
$ns connect $udp $null
# Create CBR traffic to simulate high-throughput MIMO-like traffic
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 1024 ;# Larger packet size for MIMO
$cbr set interval_ 0.001 ;# Higher data rate (1000 packets per second)
$cbr attach-agent $udp
# Schedule the traffic
$ns at 1.0 “$cbr start”
$ns at 5.0 “$cbr stop”
# Simulation ends at 6 seconds
$ns at 6.0 “finish”
# Define the finish procedure to close trace files and run NAM
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam mimo_out.nam &
exit 0
}
# Run the simulation
$ns run
Explanation of the Tcl Script:
- Simulator Object:
- The set ns [new Simulator] command initializes the NS2 simulator object.
- Wireless Channel Configuration:
- The WirelessChannel is described, and the TwoRayGround propagation model is utilized for realistic path loss in wireless communication.
- We can substitute the propagation model according to the needs (e.g., Shadowing Model for urban environments).
- MIMO-Like Bandwidth and Latency:
- To mimic the high data rates and low latency of a MIMO system, the bandwidth (val(bw)) is set to 500 Mbps, and the delay (val(delay)) is minimized to 2 ms.
- Nodes and Traffic Model:
- Two wireless nodes are made: node_(0) signifies the MIMO transmitter, and node_(1) denotes the MIMO receiver.
- UDP traffic is made with CBR (Constant Bit Rate) application, using larger packet sizes (1024 bytes) and a higher transmission rate (1 ms intervals) to mimic high-throughput MIMO communication.
- Simulation End:
- The simulation stops after 6 seconds, and the finish approach closes the trace files and runs NAM for visualization.
- Run the Simulation:
We can save the script as mimo_simulation.tcl and run it using NS2:
ns mimo_simulation.tcl
After the simulation finishes then we can open the Network Animator (NAM) to visualize the simulation:
nam mimo_out.nam
- Analyzing the Results:
- The trace file (mimo_out.tr) logs packet-level events like transmission, reception, and routing decisions. We can investigate this trace file using AWK scripts or other tools to extract parameters such as:
- Throughput
- Packet delivery ratio
- End-to-end delay
- Packet loss
- Example AWK script to calculate Throughput:
BEGIN {
total_packets = 0;
start_time = 0;
end_time = 0;
}
{
if ($1 == “r” && $4 == “AGT”) {
total_packets++;
if (start_time == 0) {
start_time = $2;
}
end_time = $2;
}
}
END {
duration = end_time – start_time;
throughput = (total_packets * 1024 * 8) / (duration * 1000); # kbps
printf(“Throughput: %.2f kbps\n”, throughput);
}
Extending the Simulation:
- MIMO Diversity Gains: Launches modifications in link quality to model the diversity gains offered by MIMO using numerous antennas.
- Adaptive Modulation and Coding: Execute adaptive bandwidth or coding techniques to simulate the behaviour of MIMO in changing wireless environments.
- MIMO Propagation Models: We can make or incorporate propagation models, which better replicate the effects of MIMO, like enhanced signal quality in multipath environments.
- Channel Fading: Launch fading models (e.g., Rayleigh fading) to replicate real-world conditions, which influences MIMO communication.
By using above simulation method with necessary instance for MIMO Projects that were simulated and analysed within NS2 simulation environment. We are available to offer detailed explorations and in-depth insights if requested.
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