How to Calculate Network Channel Capacity in NS2

To calculate the network channel capacity indicates the maximum rate at which information can be transferred through a communication channel devoid of errors. It is commonly computed with the help of Shannon’s capacity formula that considers the bandwidth of the channel and the signal-to-noise ratio (SNR).

Shannon’s Capacity Formula

The Shannon Capacity CCC of a channel is given by:

C=B×log⁡2(1+SNR)C = B \times \log_2(1 + \text{SNR})C=B×log2​(1+SNR)

Where:

  • CCC is the channel capacity in bits per second (bps).
  • BBB is the bandwidth of the channel in Hertz (Hz).
  • SNR\text{SNR}SNR is the Signal-to-Noise Ratio (linear, not in dB).

Steps to Calculate Network Channel Capacity in NS2

To compute the channel capacity in NS2, you need the SNR (Signal-to-Noise Ratio) and channel bandwidth. Here’s how you can set up your simulation in NS2 and estimate the channel capacity.

  1. Set Up the Wireless Network in NS2

Start by developing the ns2 simulation with nodes communication through a wireless channel. We need to set up parameters like transmission power, noise power and distance amongst the transmitter and receiver to estimate the SNR.

Example TCL Script to Set Up a Wireless Network:

# Create a new simulator object

set ns [new Simulator]

# Configure wireless channel and nodes

set val(chan)           Channel/WirelessChannel   ;# Wireless channel

set val(prop)           Propagation/TwoRayGround  ;# Propagation model

set val(netif)          Phy/WirelessPhy           ;# PHY layer (physical layer)

set val(mac)            Mac/802_11                ;# MAC layer

set val(ll)             LL                        ;# Link Layer

set val(ant)            Antenna/OmniAntenna       ;# Antenna model

# Create base station and user nodes

set node0 [$ns node]   ;# Base station node

set node1 [$ns node]   ;# User node

# Set up a wireless link between nodes

$ns at 1.0 “$node0 setdest 100 100 10”

$ns at 2.0 “$node1 setdest 200 200 5”

In this setup, two nodes are linked over a wireless channel. Node 0 acts as a base station, and Node 1 is a user node interacting with it.

  1. Set Transmission Power and Noise Power

In NS2, you can build the transmission power for the nodes using the Pt_ parameter. Additionally, you need to state the noise power of the environment to compute the SNR.

Setting Transmission Power and Noise Power:

# Set transmission power (in Watts)

$node0 set Pt_ 0.2818   ;# Transmission power of node0 (carrier) in Watts

# Set noise power (example value)

set noise_power 1e-9    ;# Noise power in Watts (1 nW)

  1. Calculate Signal-to-Noise Ratio (SNR)

You can use transmission power, path loss, and noise power to calculate the SNR. The path loss is based on the distance amongst the nodes and the propagation model.

TCL Script to Calculate SNR:

# Function to calculate received power and SNR

proc calculate_snr {tx_power distance frequency noise_power} {

# Constants

set c 3.0e8    ;# Speed of light in m/s

set Gt 1.0     ;# Transmitter antenna gain

set Gr 1.0     ;# Receiver antenna gain

# Calculate wavelength (lambda = c / frequency)

set lambda [expr $c / $frequency]

# Calculate path loss using Free Space Path Loss model

set path_loss_factor [expr ($lambda / (4 * 3.1416 * $distance)) ** 2]

# Calculate received power (in Watts)

set received_power [expr $tx_power * $Gt * $Gr * $path_loss_factor]

# Calculate SNR (linear scale)

set snr_linear [expr $received_power / $noise_power]

return $snr_linear

}

# Example usage for SNR calculation

set tx_power 0.2818       ;# Transmission power in Watts

set distance 150          ;# Distance between nodes (in meters)

set frequency 2.4e9       ;# Frequency in Hz (e.g., 2.4 GHz for Wi-Fi)

# Calculate SNR (linear)

set snr_linear [calculate_snr $tx_power $distance $frequency $noise_power]

puts “Calculated SNR (linear): $snr_linear”

This script estimates the SNR in terms of the transmission power, distance, and noise power. It returns the SNR in linear scale.

  1. Calculate Channel Capacity Using Shannon’s Formula

Once you have the SNR and channel bandwidth, you can measure the channel capacity using Shannon’s Capacity Formula.

TCL Script to Calculate Channel Capacity:

# Function to calculate channel capacity using Shannon’s formula

proc calculate_channel_capacity {bandwidth snr_linear} {

# Shannon’s Capacity Formula: C = B * log2(1 + SNR)

set capacity [expr $bandwidth * log(1 + $snr_linear) / log(2)]  ;# log base 2

return $capacity

}

# Example bandwidth and SNR

set bandwidth 20e6       ;# Channel bandwidth in Hz (20 MHz)

set capacity [calculate_channel_capacity $bandwidth $snr_linear]

puts “Calculated Channel Capacity: $capacity bps”

This function computes the channel capacity in bits per second (bps) using Shannon’s formula. For instance, if the bandwidth is 20 MHz and the SNR (linear) is 10, it calculates the all-out theoretical data rate that can be accomplished on that channel.

  1. Log Channel Capacity During the Simulation

If you want to observe the channel capacity dynamically during the simulation, you can log the capacity at regular intervals and see how it varies.

Example TCL Script to Log Channel Capacity:

# Function to log channel capacity at regular intervals

proc log_channel_capacity {bandwidth tx_power distance frequency noise_power} {

global ns

set snr_linear [calculate_snr $tx_power $distance $frequency $noise_power]

set capacity [calculate_channel_capacity $bandwidth $snr_linear]

puts “Time: [$ns now], Channel Capacity: $capacity bps”

# Re-schedule this procedure to run after 1 second

$ns at [expr [$ns now] + 1.0] “log_channel_capacity $bandwidth $tx_power $distance $frequency $noise_power”

}

# Start logging channel capacity every 1 second

$ns at 1.0 “log_channel_capacity $bandwidth $tx_power $distance $frequency $noise_power”

This script will log the channel capacity at 1-second intervals, allowing you to track how the channel capacity evolves during the simulation.

  1. Consider Channel Variability

In real networks, the channel conditions alter because of factors like mobility, fading, and intrusion. You can extend the model by launching fading or interference to calculate the channel capacity under more dynamic conditions.

In this above process, we have delivered the complete guide on how to approach the estimation of network channel capacity using ns2 simulator and their evaluation and samples snippets to help you understand it. If you need any information about this calculation, we will provide them.

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