How to Calculate Network Spectral Bandwidth in NS2

To calculate Network Spectral Bandwidth in ns2, which the communication networks represents to the frequency range in excess of which the network routes data. It is vital for defining how much data can be routed within a given time, and it impacts the overall channel capacity. In NS2, the spectral bandwidth is usually predefined when we configure the network simulation, specifically for wireless networks.

Though NS2 does not directly estimated spectral bandwidth, we can physically setting up and calculate it based on the channel bandwidth to define. Spectral bandwidth can be associated to the bandwidth of the communication channel and how much of the frequency spectrum is used for transmission.

The following are the techniques to calculate the Network Spectral Bandwidth in ns2:

Key Concepts:

  • Spectral Bandwidth (B): The range of frequencies used by a network for data transmission, often evaluated in Hertz (Hz) or Megahertz (MHz).
  • Channel Bandwidth: The frequency range over which data is routed usually configured for wireless communication systems in NS2.

How to Calculate or Set the Spectral Bandwidth in NS2

  1. Set up the Wireless Channel in NS2

The channel bandwidth in NS2 is usually defined in the wireless channel and the physical layer settings. We can set this bandwidth when generating the communication links among nodes.

Example TCL Script to Set Channel Bandwidth:

# Create a new simulator object

set ns [new Simulator]

# Configure wireless channel

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

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

set val(netif)          Phy/WirelessPhy           ;# Physical layer settings

set val(mac)            Mac/802_11                ;# MAC layer (e.g., 802.11)

set val(ifq)            Queue/DropTail/PriQueue   ;# Queue type

set val(ll)             LL                        ;# Link layer

set val(ant)            Antenna/OmniAntenna       ;# Omni-directional antenna

# Create base station and user nodes

set node0 [$ns node]

set node1 [$ns node]

# Define wireless link between nodes with bandwidth

# For example, assume the bandwidth is 20 MHz (20e6 Hz)

$ns duplex-link $node0 $node1 10Mb 10ms DropTail

In this setup:

  • The bandwidth of the link among node0 and node1 can be set explicitly. Here, 10 Mbps is well-defined as the data transmission rate, however we assume a spectral bandwidth of 20 MHz in the wireless environment.
  1. Manually Define the Spectral Bandwidth

If we want to explicitly calculate or set the spectral bandwidth, it is usually linked with the physical layer features in wireless systems such as Wi-Fi, LTE, or 5G. In wireless systems, the spectral bandwidth is usually predefined by the standard like 20 MHz for Wi-Fi, 1.4 MHz to 20 MHz for LTE.

To mimic a specific spectral bandwidth in NS2, we want to require metrics like frequency and channel width.

Example Setup for Wi-Fi or LTE Bandwidth:

For instance, if we are mimicking an 802.11 Wi-Fi system, the spectral bandwidth can be 20 MHz or 40 MHz relaying on the standard we are utilized. Also, in LTE, the bandwidth could change among 1.4 MHz and 20 MHz.

# Set the frequency and bandwidth for a wireless PHY layer

set phy [new Phy/WirelessPhy]

$phy set freq_ 2.4e9      ;# Frequency in Hz (2.4 GHz Wi-Fi)

$phy set bandwidth_ 20e6  ;# Bandwidth in Hz (20 MHz Wi-Fi)

In this setup:

  • freq_ is the center frequency (e.g., 2.4 GHz for Wi-Fi).
  • bandwidth_ is the spectral bandwidth of the channel (e.g., 20 MHz).
  1. Calculate Network Spectral Efficiency

Once we have defined the spectral bandwidth, we estimate the spectral efficiency (which is compared to how efficiently the bandwidth is used for data transmission). Spectral efficiency is usually expressed in bits per second per Hertz (bps/Hz) and is calculated as:

Spectral Efficiency=Channel Capacity (bps)Bandwidth (Hz)\text{Spectral Efficiency} = \frac{\text{Channel Capacity (bps)}}{\text{Bandwidth (Hz)}}Spectral Efficiency=Bandwidth (Hz)Channel Capacity (bps)​

This permits to control how efficiently the network is using the accessible spectral bandwidth.

Example TCL Script to Calculate Spectral Efficiency:

# Assume channel capacity has been calculated or set

set channel_capacity 54e6  ;# Example: Channel capacity in bits per second (54 Mbps)

# Assume spectral bandwidth is 20 MHz

set bandwidth 20e6         ;# Bandwidth in Hertz (20 MHz)

# Calculate Spectral Efficiency

set spectral_efficiency [expr $channel_capacity / $bandwidth]

puts “Spectral Efficiency: $spectral_efficiency bps/Hz”

In this example:

  • Channel Capacity is assumed to be 54 Mbps.
  • Bandwidth is set to 20 MHz.
  • The Spectral Efficiency will be estimated and printed in bps/Hz.
  1. Log and Analyse Spectral Bandwidth during Simulation

We can log the spectral bandwidth and related performance metrics such as capacity, efficiency in the course of the simulation. While the bandwidth is usually predefined, we can track it along the dynamic performance like throughput, capacity of the network.

Example TCL Script to Log Bandwidth and Spectral Efficiency:

# Function to log bandwidth and spectral efficiency during the simulation

proc log_bandwidth_and_spectral_efficiency {bandwidth channel_capacity} {

global ns

# Calculate Spectral Efficiency

set spectral_efficiency [expr $channel_capacity / $bandwidth]

puts “Time: [$ns now], Bandwidth: $bandwidth Hz, Spectral Efficiency: $spectral_efficiency bps/Hz”

# Re-schedule logging every 1 second

$ns at [expr [$ns now] + 1.0] “log_bandwidth_and_spectral_efficiency $bandwidth $channel_capacity”

}

# Start logging bandwidth and spectral efficiency

set bandwidth 20e6       ;# 20 MHz

set channel_capacity 54e6  ;# 54 Mbps (example)

$ns at 1.0 “log_bandwidth_and_spectral_efficiency $bandwidth $channel_capacity”

This logs the bandwidth and spectral efficiency at 1-second intervals in the course of the simulation.

In the given above steps are the concepts on how to calculate the network spectral bandwidth and how the frequency spectrum will used for transmission will also explained here that will executed in ns2 simulator too. We will provide insights into the calculation of the network spectral bandwidth in diverse simulation scenarios.

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