How to Implement Network Demodulation in NS2

To implement the Network Demodulation using NS2 that needs to incorporating or replicating the demodulation process as portion of the physical layer of the wireless network model. These simulation NS2 doesn’t natively support thorough modulation and demodulation at the signal processing level such as a devoted communication system simulator like MATLAB or Simulink. But, we can mimic the demodulation impacts using the abstraction of the packet error models or by expanding the simulation environment NS2 to encompass simple demodulation mechanisms. To receive implementation guidance, please provide us with the details of your project. We are fully equipped with the necessary resources to assist you in your endeavours.

Here’s a guide to execute it within NS2:

Step-by-Step Implementation:

Understanding Network Demodulation

Demodulation is the procedure of extracting the original data signal from a modulated carrier wave. In the framework of NS2, we won’t model the particular signal-level operations however we can replicate the impacts of various modulation schemes by modeling packet loss, signal-to-noise ratio (SNR), or bit error rates (BER), which based on the modulation scheme.
We can consider a particular modulation scheme such as BPSK, QPSK, QAM and modify the parameters like SNR or BER consequently.

Approach for Implementing Demodulation

As NS2 doesn’t directly mimic signal modulation/demodulation, we can replicate its impacts using the given methods:

Packet Error Rate (PER) or Bit Error Rate (BER): Replicate the packet loss rely on the modulation techniques, as each modulation scheme has a various BER for a given SNR.
Extended Error Models: We can change the NS2’s error models to emulate various BERs under distinct modulation schemes.

Basic Steps for Demodulation Simulation in NS2

We can execute a basic version of demodulation in NS2 by altering the packet reception or dropping rates depends on the chosen modulation technique.

Modify WirelessPhy to Simulate Demodulation

To mimic the demodulation, we can make or change the Phy/WirelessPhy layer withinNS2, and we use a conditional method in which packet reception (or dropping) is according to the signal quality.

Step-by-Step Implementation

Step 1: Create or Modify WirelessPhy to Include BER Based on Modulation Scheme

Extend WirelessPhy Layer We require to change the wireless-phy.tcl script to contain BER computations according to the chosen modulation scheme.

Open the ~/ns-2.35/tcl/lib/wireless-phy.tcl file and append the parameters for various modulation schemes.

# Adding modulation scheme parameters to WirelessPhy class

set Phy/WirelessPhy/BPSK_ber 0.00001 ;# Example BER for BPSK

set Phy/WirelessPhy/QPSK_ber 0.0001 ;# Example BER for QPSK

set Phy/WirelessPhy/QAM_ber 0.001 ;# Example BER for 16-QAM

# Function to compute packet error based on BER and packet size

proc calc_packet_error { modulation packet_size } {

switch $modulation {

“BPSK” {

set ber [Phy/WirelessPhy set BPSK_ber]

}

“QPSK” {

set ber [Phy/WirelessPhy set QPSK_ber]

}

“QAM” {

set ber [Phy/WirelessPhy set QAM_ber]

}

default {

set ber 0.001 ;# Default BER if modulation is unknown

}

# Calculate probability of packet error

set packet_error_prob [expr 1.0 – pow((1.0 – $ber), $packet_size * 8)]

return $packet_error_prob

}

Step 2: Modify Packet Reception Logic to Use Demodulation

In the similar file (wireless-phy.tcl), change the packet reception logic to drop packets rely on the computed error rate.

# Modify the reception logic

proc Phy/WirelessPhy::recv {packet} {

# Get packet size

set packet_size [$packet size]

# Choose a modulation scheme (you can dynamically change it or set it in the TCL script)

set modulation “QPSK” ;# Example modulation scheme used

# Calculate packet error based on the modulation scheme

set error_prob [calc_packet_error $modulation $packet_size]

# Simulate packet loss based on the calculated error probability

set random_val [expr rand()]

if {$random_val < $error_prob} {

# Drop the packet

drop $packet

return

}

# If packet is not dropped, continue to the upper layer

$self up-target $packet

}

Step 3: Update the TCL Simulation Script

We will require to write a TCL script, which replicate a network situation with various modulation schemes and demodulation effects.

# Create a simulator instance

set ns [new Simulator]

# Create trace and nam files for output

set tracefile [open demodulation.tr w]

set namfile [open demodulation.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define network topology

set topo [new Topography]

$topo load_flatgrid 500 500 ;# Simulation area: 500×500 meters

# Create the General Operations Director (GOD)

set god_ [create-god 10] ;# 10 nodes

# Set parameters for wireless physical layer

set Phy/WirelessPhy/BPSK_ber 0.00001

set Phy/WirelessPhy/QPSK_ber 0.0001

set Phy/WirelessPhy/QAM_ber 0.001

# Define node configuration parameters

set opt(chan) Channel/WirelessChannel

set opt(prop) Propagation/TwoRayGround

set opt(netif) Phy/WirelessPhy

set opt(mac) Mac/802_11

set opt(ifq) Queue/DropTail/PriQueue

set opt(ll) LL

set opt(ant) Antenna/OmniAntenna

set opt(x) 500

set opt(y) 500

# Set number of nodes

set opt(nn) 10 ;# Number of nodes

# Create nodes and set initial positions

for {set i 0} {$i < $opt(nn)} {incr i} {

set node_($i) [$ns node]

$node_($i) random-motion 1 ;# Enable random motion for nodes

}

# Configure traffic and mobility

proc start_traffic {} {

global ns node_ opt

# Create UDP agents and attach them to nodes

for {set i 0} {$i < $opt(nn)} {incr i} {

set udp_($i) [new Agent/UDP]

set null_($i) [new Agent/Null]

$ns attach-agent $node_($i) $udp_($i)

$ns attach-agent $node_($i) $null_($i)

# Generate CBR traffic

set cbr_($i) [new Application/Traffic/CBR]

$cbr_($i) set packetSize_ 512

$cbr_($i) set interval_ 0.1

$cbr_($i) attach-agent $udp_($i)

# Connect the UDP agents for communication between nodes

$ns connect $udp_($i) $null_($i)

}

# Start the traffic

$ns at 1.0 “start_traffic”

# Run the simulation

$ns at 100.0 “finish”

# Finish procedure

proc finish {} {

global ns tracefile namfile

close $tracefile

close $namfile

$ns halt

}

# Run the simulation

$ns run

Explanation of the Script

Modulation Scheme: These three modulation schemes are described: BPSK, QPSK, and 16-QAM. Each has a corresponding BER.
Error Calculation: The calc_packet_error function estimates the probability of a packet being fell rely on the modulation scheme’s BER and the packet size.
Packet Reception: The recv function replicates the packet reception and drops packets probabilistically depends on the error rate.
TCL Script: The TCL script configures a basic wireless network including 10 nodes, generates traffic, and mimics packet loss because of the demodulation errors rely on the selected modulation scheme.

Running the Simulation

We can save the altered wireless-phy.tcl file and the TCL script (demodulation.tcl).
Run the simulation using:

ns demodulation.tcl

Analysing the Results

Estimate the trace file (demodulation.tr) to monitor how the demodulation process effects packet delivery, after running the simulation.
We can look for:
- Packet Loss: Evaluate the packet drops triggered by the modulation scheme and BER.
- Throughput: Verify how the various modulation schemes effects the network throughput.

Further Enhancements

Dynamic Modulation Switching: We can execute the dynamic modulation switching depends on the SNR or channel conditions.
Advanced Modulation Schemes: Replicate more difficult modulation schemes by changing BER rely on real-world communication models.
Link Adaptation: Execute the link adaptation in which nodes are modify their modulation scheme actively according to the channel conditions such as switching from BPSK to QPSK for better link quality.

The above procedure are about how to execute the Network Demodulation and we understand on how to approach it in NS2. We will be presented much more information and ideas concerning this topic in another manual.