How to Implement Network HetNets Allocation in NS2

To implement the Heterogeneous Networks (HetNets) in NS2 that refers to deployment of various kinds of access networks, like macrocells, small cells such as picocells, femtocells, and Wi-Fi networks, in a unique environment to enhance the capacity, coverage, and network efficiency. In the simulation NS2 (Network Simulator 2), we can replicate the HetNets by using several network kinds with various ranges, bandwidths, and characteristics, and mimic traffic allocation over these networks. In the HetNets, traffic allocation refers to allocating user devices to various kinds of networks like macrocells vs. small cells that rely on the factors such as load balancing, signal strength, or user requirements.

Steps to Implement HetNets Allocation in NS2

  1. Understand the Components of HetNets

In the network HetNets, we will normally have:

  • Macrocells: High-power base stations which cover a large area.
  • Small Cells: Low-power base stations like picocells, femtocells that conceal a smaller areas and they are deployed to maximise the capacity in high-demand areas.
  • Wi-Fi Access Points: Deliver extra wireless access in the particular areas.
  • User Devices: Devices which are connect to the obtainable networks according to various criteria like signal strength, available bandwidth, or network load.
  1. Set up NS2 Environment

Make certain that NS2 is installed and properly set up in the system. If not, we can install NS2, follow these steps:

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

  1. Design the HetNet Topology

In a usual HetNet, we might have:

  • A macrocell covering the whole area.
  • Numerous small cells are presenting an additional coverage in the dense areas.
  • Wi-Fi access points to offload data traffic.
  • User devices which connect to these networks actively depend on the predefined criteria.

3.1. Create Nodes for the HetNet

In the NS2, we make the nodes are signifying the macrocell, small cells, Wi-Fi access points, and user devices.

Example OTcl Script to Create HetNet Nodes:

# Create a simulator object

set ns [new Simulator]

# Open the NAM trace file

set nf [open out.nam w]

$ns namtrace-all $nf

# =======================

# Macrocell Base Station

# =======================

set macrocell [$ns node]

# =======================

# Small Cells

# =======================

set smallcell1 [$ns node]

set smallcell2 [$ns node]

# =======================

# Wi-Fi Access Points

# =======================

set wifi1 [$ns node]

set wifi2 [$ns node]

# =======================

# User Devices

# =======================

set user1 [$ns node]

set user2 [$ns node]

set user3 [$ns node]

set user4 [$ns node]

# ==========================

# Define Connections

# ==========================

# Macrocell to core network

set core [$ns node]

$ns duplex-link $macrocell $core 1Gb 5ms DropTail

# Small cells to core network

$ns duplex-link $smallcell1 $core 1Gb 2ms DropTail

$ns duplex-link $smallcell2 $core 1Gb 2ms DropTail

# Wi-Fi to core network

$ns duplex-link $wifi1 $core 100Mb 10ms DropTail

$ns duplex-link $wifi2 $core 100Mb 10ms DropTail

# Users connected to different access points

$ns duplex-link $user1 $macrocell 100Mb 20ms DropTail

$ns duplex-link $user2 $smallcell1 100Mb 10ms DropTail

$ns duplex-link $user3 $smallcell2 100Mb 10ms DropTail

$ns duplex-link $user4 $wifi1 50Mb 15ms DropTail

In this setup:

  • Macrocell, small cells, and Wi-Fi access points are connected to a core network.
  • User devices are allocated to various kinds of access points that signifying dynamic traffic allocation in the HetNet.
  1. Simulate Dynamic Allocation in HetNets

In the network HetNets, user devices can dynamically switch among the networks according to several criteria like signal strength, load, or data rate. We can replicate this dynamic allocation using traffic generation including agents and applications such as TCP and UDP.

4.1. Generate Traffic for HetNets

Replicate the traffic among user devices and these connected networks such as macrocell, small cells, Wi-Fi.

Example OTcl Script for Traffic Generation:

# Create a TCP agent and attach it to user 1 (connected to macrocell)

set tcp1 [new Agent/TCP]

$ns attach-agent $user1 $tcp1

# Create a TCP sink and attach it to the core network

set sink1 [new Agent/TCPSink]

$ns attach-agent $core $sink1

# Connect the TCP agent to the sink

$ns connect $tcp1 $sink1

# Create a CBR (Constant Bit Rate) application to generate traffic over the TCP connection

set cbr1 [new Application/Traffic/CBR]

$cbr1 attach-agent $tcp1

$cbr1 set packetSize_ 1000   ;# Set packet size to 1000 bytes

$cbr1 set rate_ 50Mb         ;# Set the traffic rate to 50 Mbps

# Start sending traffic from user 1 (macrocell) to the core

$ns at 1.0 “$cbr1 start”

# Create UDP traffic from user 2 (connected to smallcell1)

set udp2 [new Agent/UDP]

$ns attach-agent $user2 $udp2

set sink2 [new Agent/Null]

$ns attach-agent $core $sink2

$ns connect $udp2 $sink2

# Generate UDP traffic from user 2 (smallcell1) to the core

set cbr2 [new Application/Traffic/CBR]

$cbr2 attach-agent $udp2

$cbr2 set packetSize_ 800    ;# Set packet size to 800 bytes

$cbr2 set rate_ 30Mb         ;# Set the traffic rate to 30 Mbps

$ns at 2.0 “$cbr2 start”

# Create traffic for users connected to Wi-Fi access points

set udp3 [new Agent/UDP]

$ns attach-agent $user4 $udp3

set sink3 [new Agent/Null]

$ns attach-agent $core $sink3

$ns connect $udp3 $sink3

# Generate UDP traffic from user 4 (Wi-Fi1) to the core

set cbr3 [new Application/Traffic/CBR]

$cbr3 attach-agent $udp3

$cbr3 set packetSize_ 600    ;# Set packet size to 600 bytes

$cbr3 set rate_ 20Mb         ;# Set traffic rate to 20 Mbps

$ns at 3.0 “$cbr3 start”

# End the simulation after 10 seconds

$ns at 10.0 “finish”

proc finish {} {

global ns nf

$ns flush-trace

close $nf

exit 0

}

$ns run

In this script:

  • TCP traffic is produced among the user1 and the core network through the macrocell.
  • UDP traffic is generated among user2 and the core network through the smallcell1.
  • Generated UDP traffic among user4 and the core network through the Wi-Fi.
  1. Dynamic Network Selection for HetNets

To mimic dynamic allocation, we can execute various user performances or network selection criteria. It can be based on:

  • Signal Strength: User devices are connect to the network including the strongest signal.
  • Network Load: Users are assigned to the network with the least congestion.
  • Data Rate Requirements: Users are assigned to networks depends on their data rate requirements.

We can replicate this by dynamically switching users among the networks while simulation.

5.1. Simulate Network Switching Based on Load

We can describe dynamic behaviour to move users among various networks while simulation. For example, we can move user1 from the macrocell to a small cell according to the network load.

Example of Dynamic Network Switching:

# After 5 seconds, switch user 1 from macrocell to smallcell2 due to network load

$ns at 5.0 “$ns duplex-link-delete $user1 $macrocell”

$ns at 5.0 “$ns duplex-link $user1 $smallcell2 100Mb 10ms DropTail”

This dynamic switch will detach the user1 from the macrocell and reconnect them to smallcell2 while simulation.

  1. Enable Trace Files and Visualize the Simulation

We can permit the trace file generation to apprehend the performance metrics and also we visualize the traffic in NAM (Network Animator).

6.1. Enable Trace Files:

# Create a trace file to record simulation data

set tracefile [open “out.tr” w]

$ns trace-all $tracefile

This method will support you to know how to execute the Network HetNets Allocation in the simulation tool NS2 and also we will present the more insights in another manual.

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