How to Implement Dynamic Spectrum Access in OMNeT++

To implement the Dynamic Spectrum Access (DSA) in OMNeT++ has encompasses making a cognitive radio network where secondary users (SUs) can dynamically assess available spectrum devoid of interfering with primary users (PUs) who have priority access. This access is critical for enhancing spectrum utilization, specifically in situations where spectrum resources are rare.

Steps to Implement Dynamic Spectrum Access in OMNeT++

Install OMNeT++ and INET/Simu5G Framework:
- Make sure that OMNeT++ and the INET framework or Simu5G for 5G networks are installed. INET offer essential tools for mimicking wireless networks, containing cognitive radio capabilities.
Define the Network Topology:
- Make a network topology using a .ned file that contains primary users (PUs) with secure spectrum access and secondary users (SUs) that necessary to dynamically discovery and use available spectrum.
Implement Spectrum Sensing Mechanism:
- Improve a mechanism for secondary users to sense the spectrum and identify which frequency bands are presently unused by primary users. It can encompass methods such as energy detection, matched filtering, or cyclostationary feature detection.
Implement Spectrum Allocation and Management:
- Execute algorithms for spectrum allocation where SUs dynamically choose and switch among frequency bands depends on the sensing results. We can comprise decision-making strategies such as centralized, distributed, or hybrid approaches.
Simulate Various Scenarios:
- Form scenarios where primary users occupy several parts of the spectrum over time, and secondary users should adapt to these modifies by dynamically accessing available spectrum.
Configure the Simulation Environment:
- Use the .ini file to configure parameters like specific algorithms for DSA, channel occupancy by PUs, sensing accuracy, and spectrum availability.
Run the Simulation and Analyse Results:
- Implement the simulation and evaluate the performance of the dynamic spectrum access mechanism. Important metrics comprise spectrum utilization efficiency, interference levels, detection accuracy, and complete network throughput.

Example: Implementing Basic Dynamic Spectrum Access in OMNeT++

Define the Network Topology in a .ned File

// DynamicSpectrumAccessNetwork.ned

package networkstructure;

import inet.node.inet.WirelessHost;

import inet.node.inet.Router;

network DynamicSpectrumAccessNetwork

{

parameters:

int numPUs = default(2); // Number of primary users

int numSUs = default(3); // Number of secondary users

submodules:

primaryUser[numPUs]: WirelessHost {

@display(“p=100,100”);

numApps = 1;

app[0].typename = “PrimaryUserApp”;

}

secondaryUser[numSUs]: WirelessHost {

@display(“p=300,200”);

numApps = 1;

app[0].typename = “SecondaryUserApp”;

}

connections:

// Wireless communication is modeled, so no fixed connections are necessary

}

Implement the Spectrum Sensing Mechanism

Make a C++ class for the secondary user application that contains a simple spectrum sensing algorithm.

#include <omnetpp.h>

#include <inet/applications/base/ApplicationBase.h>

using namespace omnetpp;

using namespace inet;

class SecondaryUserApp : public ApplicationBase

{

protected:

double currentFrequency;

double sensingThreshold;

virtual void initialize(int stage) override;

virtual void handleMessageWhenUp(cMessage *msg) override;

void senseSpectrum();

public:

virtual int numInitStages() const override { return NUM_INIT_STAGES; }

};

Define_Module(SecondaryUserApp);

void SecondaryUserApp::initialize(int stage)

{

ApplicationBase::initialize(stage);

if (stage == INITSTAGE_APPLICATION_LAYER) {

currentFrequency = par(“initialFrequency”).doubleValue();

sensingThreshold = par(“sensingThreshold”).doubleValue();

// Schedule initial spectrum sensing

scheduleAt(simTime() + uniform(1, 2), new cMessage(“senseSpectrum”));

}

void SecondaryUserApp::handleMessageWhenUp(cMessage *msg)

{

if (strcmp(msg->getName(), “senseSpectrum”) == 0) {

senseSpectrum();

scheduleAt(simTime() + uniform(1, 2), msg); // Re-schedule spectrum sensing

} else {

delete msg;

}

void SecondaryUserApp::senseSpectrum()

{

EV << “Sensing the spectrum for available channels.” << endl;

// Example: Simple energy detection for spectrum sensing

bool channelOccupied = uniform(0, 1) < sensingThreshold; // Simplified sensing logic

if (channelOccupied) {

EV << “Channel occupied. Searching for another frequency.” << endl;

currentFrequency = uniform(2.4e9, 2.5e9); // Switch to a new frequency

} else {

EV << “Channel available. Using frequency: ” << currentFrequency << ” Hz” << endl;

// Implement communication on the current frequency

}

Implement Spectrum Allocation and Management

Implement the SecondaryUserApp class or make a separate class to manage spectrum allocation based on the sensing results.

void SecondaryUserApp::allocateSpectrum()

{

EV << “Allocating spectrum dynamically.” << endl;

// Example: Select a frequency based on sensing results

if (currentFrequency > sensingThreshold) {

EV << “Selected frequency: ” << currentFrequency << ” Hz” << endl;

// Set the transmission parameters based on the selected frequency

getParentModule()->getSubmodule(“wlan”)->par(“carrierFrequency”) = currentFrequency;

} else {

EV << “No suitable frequency found. Retrying…” << endl;

// Retry or wait for a better opportunity

}

Configure the Simulation in the .ini File

# omnetpp.ini

[General]

network = networkstructure.DynamicSpectrumAccessNetwork

sim-time-limit = 300s

# Primary user settings

*.primaryUser[*].wlan.mac.maxQueueSize = 1000;

*.primaryUser[*].wlan.phy.transmitter.power = 10mW;

*.primaryUser[*].mobility.bounds = “500m 500m”;

# Secondary user settings

*.secondaryUser[*].wlan.mac.maxQueueSize = 1000;

*.secondaryUser[*].wlan.phy.transmitter.power = 2mW;

*.secondaryUser[*].mobility.bounds = “500m 500m”;

*.secondaryUser[*].app[0].initialFrequency = 2.45e9; # Initial frequency in Hz (2.45 GHz)

*.secondaryUser[*].app[0].sensingThreshold = 0.7; # Threshold for detecting channel occupancy

Explanation of the Example

Network Topology (DynamicSpectrumAccessNetwork.ned):
- The network contains of primary users (PUs) and secondary users (SUs). The PUs must fixed spectrum access, as the SUs dynamically find and use available spectrum.
Spectrum Sensing Mechanism (SecondaryUserApp.cc):
- The SecondaryUserApp module comprises an elementary spectrum sensing algorithm that identifies whether a channel is engaged by a PU. If the channel is engaged, the SU switches to a necessary frequency.
Spectrum Allocation (SecondaryUserApp.cc):
- The spectrum allocation process dynamically allocates a frequency to the SU based on the outcomes of the spectrum sensing. The SU then uses this frequency for communication.
Simulation Configuration (omnetpp.ini):
- The .ini file configures primary frequencies, detecting thresholds, and other parameters for both primary and secondary users.

Running the Simulation

Compile the project in OMNeT++ IDE and run the simulation.
Use OMNeT++’s tools to monitor how secondary users dynamically access the spectrum and prevent interference with primary users. Attention on metrics such as spectrum utilization, interference levels, and complete network performance.

Extending the Example

Advanced Sensing Techniques: Execute more sophisticated spectrum detecting methods such as matched filtering or cyclostationary feature detection to enhance sensing accuracy.
Cooperative Spectrum Sensing: Allow several SUs to cooperate in detecting the spectrum and distributing their observations to enhance the reliability of spectrum access decisions.
Centralized vs. Distributed Spectrum Management: Compare centralized and distributed methods to spectrum management, where a central controller assigns spectrum against individual SUs creating independent decisions.
Machine Learning-Based Spectrum Allocation: Incorporate machine learning algorithms to guess spectrum availability and improve the spectrum allocation process.
Multi-Channel Access: Expand the execution to manage multi-channel access, where SUs can use numerous frequency bands concurrently.

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