How to Implement Cellular Network in ns2
To implement the cellular network in Network Simulator 2 (ns2) can be difficult because of the restrictions of ns2 in simulating latest cellular features. Yet, you can estimate a simple cellular network environment by configuring a structure that imitates the necessary elements of a cellular network like base stations (cells), mobile nodes (user equipment) and the interaction amongst them.
Follow the step-by-step guide on how to implement a basic cellular network in ns2.
Step-by-Step Implementation:
Step 1: Understand the Limitations
ns2 does not have built-in backing for cellular networks, particularly for latest standards like LTE or 5G. But, we can simulate a basic cellular network by generating several base stations and mobile nodes in which every base station indicates a cell and the mobile nodes travel amongst these cells.
Step 2: Create the Tcl Script
Below is a sample Tcl script to simulate a basic cellular network with three cells and mobile nodes travelling amongst these cells.
Example Tcl Script
# Create a simulator object
set ns [new Simulator]
# Define the topography object
set topo [new Topography]
$topo load_flatgrid 1000 1000
# Create the General Operations Director (GOD) for wireless simulations
create-god 3 # Number of cells
# Configure node settings for cellular network simulation
$ns node-config -adhocRouting DSDV \
-llType LL \
-macType Mac/802_11 \
-ifqType Queue/DropTail/PriQueue \
-ifqLen 50 \
-antType Antenna/OmniAntenna \
-propType Propagation/TwoRayGround \
-phyType Phy/WirelessPhy \
-channelType Channel/WirelessChannel \
-topoInstance $topo \
-agentTrace ON \
-routerTrace ON \
-macTrace ON
# Open trace and NAM files for recording the simulation
set tracefile [open cellular_out.tr w]
$ns trace-all $tracefile
set namfile [open cellular_out.nam w]
$ns namtrace-all-wireless $namfile 1000 1000
# Define a finish procedure to close files and end the simulation
proc finish {} {
global ns tracefile namfile
$ns flush-trace
close $tracefile
close $namfile
exec nam cellular_out.nam &
exit 0
}
# Create base stations (BS) as static nodes
set bs0 [$ns node]
set bs1 [$ns node]
set bs2 [$ns node]
# Set the positions for base stations (cells)
$bs0 set X_ 200.0
$bs0 set Y_ 500.0
$bs0 set Z_ 0.0
$bs1 set X_ 500.0
$bs1 set Y_ 500.0
$bs1 set Z_ 0.0
$bs2 set X_ 800.0
$bs2 set Y_ 500.0
$bs2 set Z_ 0.0
# Create mobile nodes (user equipment)
set ue0 [$ns node]
set ue1 [$ns node]
set ue2 [$ns node]
# Set initial positions for the mobile nodes
$ue0 set X_ 150.0
$ue0 set Y_ 550.0
$ue0 set Z_ 0.0
$ue1 set X_ 550.0
$ue1 set Y_ 550.0
$ue1 set Z_ 0.0
$ue2 set X_ 850.0
$ue2 set Y_ 550.0
$ue2 set Z_ 0.0
# Define node movements to simulate handover between cells
$ns at 10.0 “$ue0 setdest 500.0 550.0 5.0”
$ns at 20.0 “$ue0 setdest 800.0 550.0 5.0”
$ns at 10.0 “$ue1 setdest 200.0 550.0 5.0”
$ns at 20.0 “$ue1 setdest 800.0 550.0 5.0”
$ns at 10.0 “$ue2 setdest 500.0 550.0 5.0”
$ns at 20.0 “$ue2 setdest 200.0 550.0 5.0”
# Define traffic for the cellular network
# TCP Traffic from ue0 to ue2 through base stations
set tcp0 [new Agent/TCP]
$ns attach-agent $ue0 $tcp0
sink0 [new Agent/TCPSink]
$ns attach-agent $ue2 $sink0
$ns connect $tcp0 $sink0
set ftp0 [new Application/FTP]
$ftp0 attach-agent $tcp0
$ftp0 start
# UDP Traffic from ue1 to ue2 through base stations
set udp1 [new Agent/UDP]
$ns attach-agent $ue1 $udp1
set null1 [new Agent/Null]
$ns attach-agent $ue2 $null1
$ns connect $udp1 $null1
set cbr1 [new Application/Traffic/CBR]
$cbr1 attach-agent $udp1
$cbr1 set packetSize_ 512
$cbr1 set rate_ 1Mb
$cbr1 start 2.0
# Schedule the end of the simulation
$ns at 50.0 “finish”
# Run the simulation
$ns run
Step 3: Run the Tcl Script
Store the script with a .tcl extension, for instance, cellular_simulation.tcl. Then execute the script using the given command in the terminal:
ns cellular_simulation.tcl
Step 4: Visualize the Cellular Network Simulation
To visualize the network and the traffic, open the created NAM file using:
nam cellular_out.nam
This will show the base stations, mobile nodes, and the imitated traffic when the mobile nodes move amongst cells.
Script Explanation
- Base Stations (Cells): The base stations are static nodes indicating various cells in the network. Every base station is located at a particular position.
- Mobile Nodes: Mobile nodes denote user equipment (UE) that travel through the network. Their movements are stated to simulate handover amongst several cells.
- Traffic: It configures both TCP and UDP traffic amongst the mobile nodes to simulate data transfers in a cellular network. The traffic directs through the base stations when the mobile nodes move.
- Handover Simulation: The movement commands (setdest) recreate the handover procedure as mobile nodes travel from one cell (base station) to another.
Customization
- Increase Node Count: Simulate a more difficult cellular network by attaching more base stations.
- Adjust Mobility: Alter the mobility patterns to simulate multiple handover situations like quicker movements or various movement patterns.
- Different Traffic Types: Test with several kinds of traffic (such as video streaming) to mimic different use cases in the cellular network.
- Routing Protocols: Adjust the routing protocol to DSR or AODV to simulate various networking environments into the cellular network.
Limitations
- Simplified Model: It offers a simplified model of a cellular network. It does not contain several advanced mechanisms of latest cellular networks like LTE or 5G.
- No Real Handover Mechanism: The script only mimics handover by travelling nodes amongst base stations, yet it does not execute the real handover functionalities as found in latest cellular networks.
- Lack of Advanced Features: Functionalities like QoS management, real-time handover, and cellular-specific intrusion management are not modeled.
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