How to Implement OFDMA Coexistence in NS2
To implement Orthogonal Frequency-Division Multiple Access (OFDM) Coexistence in NS2 has series of steps to follow that includes mimicking the coexistence of multiple networks or user devices that allocates the same frequency spectrum efficiently. OFDMA is usually used in 4G LTE and 5G for multi-user access, in which the available spectrum is divided into subcarriers, and different subcarriers are shared to different users. In coexistence scenarios, OFDMA permits numerous types of wireless networks or user devices to perform without causing significant interference to each other.
Although NS2 does not natively support OFDMA, we can simulate the contexts of OFDMA coexistence by manually distributing the resources such as subcarriers, bandwidth to different users or networks, and by customizing the transmission patterns and interference models. If you face any doubts in implementation then you can reach us out we are ready to help you.
Here is the procedure to implement the OFDMA coexistence in NS2:
Steps to Implement OFDMA Coexistence in NS2
- Set up NS2 Environment
If NS2 is not already installed, we can install it as follows:
wget https://sourceforge.net/projects/nsnam/files/latest/download -O ns-allinone-2.35.tar.gz
tar -xzvf ns-allinone-2.35.tar.gz
cd ns-allinone-2.35
./install
Make sure that NS2 is functioning properly by running a simple simulation.
- Understand the Key Concepts of OFDMA
In OFDMA, the frequency spectrum is divided into smaller subcarriers, and different subcarriers are allocated to various users or networks. The primary goals of OFDMA coexistence are:
- Resource Allocation: Efficiently distribute frequency subcarriers to multiple users or networks.
- Interference Management: Diminish interference among the coexisting users or networks using the same spectrum.
- Dynamic Allocation: Dynamically modify the allocation of subcarriers according to the network conditions or user requirements.
In NS2, we can emulate these characteristics by handling the bandwidth and traffic patterns manually for various users or networks.
- Design a Network Topology for OFDMA Coexistence
For OFDMA coexistence, we will design a scenario in which the multiple user devices (UEs) associated to a base station, and the base station allocates different subcarriers (or frequency blocks) to each UE. This can signify various users sharing the same channel without interfering with each other.
3.1 Create Nodes for Base Station and User Devices
# Create a simulator object
set ns [new Simulator]
# Open a NAM trace file for visualization
set nf [open out.nam w]
$ns namtrace-all $nf
# Base Station (BS)
set bs [$ns node] ;# Represents the base station handling OFDMA
# User Devices (UEs)
set ue1 [$ns node] ;# User Equipment 1
set ue2 [$ns node] ;# User Equipment 2
set ue3 [$ns node] ;# User Equipment 3
# Define Links
# Base station connects to the core network (e.g., internet)
set core [$ns node]
$ns duplex-link $bs $core 10Gb 1ms DropTail ;# Base station to core network
# UEs connect to the base station (representing wireless links with OFDMA)
$ns duplex-link $ue1 $bs 100Mb 10ms DropTail ;# UE1 connected to the base station
$ns duplex-link $ue2 $bs 100Mb 10ms DropTail ;# UE2 connected to the base station
$ns duplex-link $ue3 $bs 100Mb 10ms DropTail ;# UE3 connected to the base station
Here, we have three user devices (UEs) connected to a base station (BS), that mimics a multi-user scenario in which the same frequency band is shared using OFDMA.
- Simulate Resource Allocation (Subcarrier Allocation) in OFDMA
In OFDMA, the base station distributes subcarriers to each user dynamically. In NS2, we can mimic this by allotting different amounts of bandwidth or describing diverse traffic patterns for each user.
4.1 Manual Resource Allocation
We can manually distribute bandwidth to each user by modifying the link characteristics.
# Allocate different subcarrier resources to different UEs
# UE1 gets 50Mb, simulating a higher number of subcarriers
$ns duplex-link $ue1 $bs 50Mb 10ms DropTail
# UE2 gets 30Mb, simulating a moderate number of subcarriers
$ns duplex-link $ue2 $bs 30Mb 10ms DropTail
# UE3 gets 20Mb, simulating a lower number of subcarriers
$ns duplex-link $ue3 $bs 20Mb 10ms DropTail
This allocation denotes various subcarrier assignments for different users, that permits us to mimic the resource sharing in an OFDMA environment.
- Simulate Traffic for Each User
To mimic traffic on these OFDMA channels, we can generate various kinds of traffic patterns using TCP or UDP agents.
5.1 Traffic Generation
Create TCP or UDP traffic for each user to mimic data transmission over the distributed subcarriers.
# Traffic for UE1 (higher bandwidth)
set tcp1 [new Agent/TCP]
$ns attach-agent $ue1 $tcp1
set sink1 [new Agent/TCPSink]
$ns attach-agent $core $sink1
$ns connect $tcp1 $sink1
# Create a CBR (Constant Bit Rate) application for UE1
set cbr1 [new Application/Traffic/CBR]
$cbr1 attach-agent $tcp1
$cbr1 set packetSize_ 1000 ;# Set packet size to 1000 bytes
$cbr1 set rate_ 40Mb ;# Traffic rate of 40 Mbps
# Start traffic for UE1 at time 1.0
$ns at 1.0 “$cbr1 start”
# Traffic for UE2 (moderate bandwidth)
set udp2 [new Agent/UDP]
$ns attach-agent $ue2 $udp2
set sink2 [new Agent/Null]
$ns attach-agent $core $sink2
$ns connect $udp2 $sink2
# Create a CBR application for UE2
set cbr2 [new Application/Traffic/CBR]
$cbr2 attach-agent $udp2
$cbr2 set packetSize_ 800 ;# Set packet size to 800 bytes
$cbr2 set rate_ 20Mb ;# Traffic rate of 20 Mbps
# Start traffic for UE2 at time 2.0
$ns at 2.0 “$cbr2 start”
# Traffic for UE3 (lower bandwidth)
set udp3 [new Agent/UDP]
$ns attach-agent $ue3 $udp3
set sink3 [new Agent/Null]
$ns attach-agent $core $sink3
$ns connect $udp3 $sink3
# Create a CBR application for UE3
set cbr3 [new Application/Traffic/CBR]
$cbr3 attach-agent $udp3
$cbr3 set packetSize_ 500 ;# Set packet size to 500 bytes
$cbr3 set rate_ 10Mb ;# Traffic rate of 10 Mbps
# Start traffic for UE3 at time 3.0
$ns at 3.0 “$cbr3 start”
In this setup:
- UE1 gets higher bandwidth (40 Mbps), simulating more subcarriers allocated to it.
- UE2 gets moderate bandwidth (20 Mbps).
- UE3 gets lower bandwidth (10 Mbps).
This permits us to mimic the resource allocation in an OFDMA-based system.
- Manage Interference in OFDMA Coexistence
Interference management is vital in OFDMA coexistence scenarios. In NS2, we can simulate interference by controlling the bandwidth, delay, and packet loss rates. For instance, we could establish cross-traffic or congestion on the base station to mimic interference.
6.1 Simulating Interference between Users
We can establish artificial interference or congestion by adjusting the packet loss rate or minimizing the available bandwidth for certain links.
# simulate interference by reducing the bandwidth for UE2 dynamically
$ns at 5.0 “$ns duplex-link-delete $ue2 $bs”
$ns at 5.0 “$ns duplex-link $ue2 $bs 10Mb 10ms DropTail” ;# Reduce bandwidth for UE2 at 5.0 seconds
This simulation will show you on how the base station can enthusiastically handles the resources and manage interference by adapting bandwidth or traffic priorities.
- Enable Trace Files and Visualization
Enable trace files and use NAM (Network Animator) to envision the traffic patterns, bandwidth allocation, and interference in the OFDMA network.
7.1 Enable Trace Files:
# Enable trace file for the simulation
set tracefile [open “out.tr” w]
$ns trace-all $tracefile
7.2 Run the Simulation and Visualize It in NAM:
Execute the simulation and view it in NAM:
ns your_script.tcl
nam out.nam
This permits to envision how traffic flows among the UEs and the base station, that mimics the OFDMA resource allocation.
- Analyse Performance
Once the simulation is complete, evaluate key performance metrics:
- Throughput: Evaluate on how much information is successfully transmitted for each user.
- Latency: Assess the latency for packets traveling among UEs and the core network.
- Interference: evaluate on how to minimize bandwidth or increasing packet loss impacts users.
We can extract this data from the trace files using tools like AWK or custom Python scripts.
- Future Enhancements
Here are a few enhancements to further develop the OFDMA coexistence simulation:
- Dynamic Resource Scheduling: Execute dynamic resource scheduling, in which subcarriers are reallocated according to real-time traffic needs or channel conditions.
- Adaptive Modulation and Coding (AMC): To mimic various modulation and coding schemes for each UE based on their channel conditions.
- Mobility: Add mobility to the user devices and mimic on how the base station reallocates resources as users move.
- QoS Management: Establish QoS policies to select particular traffic types such as URLLC, eMBB.
We had shown how successfully the OFDM coexistence will be implemented in ns2 tool that has contain to design a network topology then mimic the resource allocation after that emulate the traffic for each user to manage the interference and then evaluate the outcomes. We intended to provide more information regarding the OFDM coexistence.