How to Implement Network Spectrum Allocation in NS2

To implement network spectrum allocation in NS2 has needs to mimic on how spectrum resources are allocated to different users or nodes in a wireless network. Spectrum allocation make sure that multiple nodes can interact without interfering with each other, especially in multi-user systems such as cognitive radio networks (CRNs), 5G, or dynamic spectrum access (DSA) systems. The main objective is to replicate efficient utilization of the available spectrum though reducing interference.

Here’s a step-by-step procedure to execute network spectrum allocation in NS2.

Key Concepts in Spectrum Allocation:

1. Frequency Bands: Diverse frequency channels are available, and they must be assigned to different nodes.
2. Dynamic Spectrum Access (DSA): Nodes can enthusiastically access unused portions of the spectrum, that usually seen in cognitive radio networks.
3. Interference Avoidance: Make sure that two nearby nodes don’t use the same frequency band at the same time.
4. Quality of Service (QoS): Allocation based on bandwidth requirements, delay, and reliability.

Step-by-Step Guide to Implement Network Spectrum Allocation in NS2

1. Define the Available Spectrum

We need to describe the spectrum like available frequency bands and handle on how nodes access these resources. This contain to generate a set of frequency bands (or channels) and allocating them to different nodes.

Example: Define Frequency Bands

We can generate a list of available channels (frequencies) and handle them enthusiastically during the simulation.

class SpectrumManager {

public:

SpectrumManager(int numBands);

int allocateBand();     // Allocate a frequency band to a node

void releaseBand(int band);  // Release the band when no longer in use

protected:

vector<int> availableBands;  // List of available bands

vector<bool> isBandAllocated;  // Track if a band is allocated

};

// Constructor to initialize the number of bands

SpectrumManager::SpectrumManager(int numBands) {

availableBands.resize(numBands);

isBandAllocated.resize(numBands, false);

for (int i = 0; i < numBands; i++) {

availableBands[i] = i;  // Example: frequency bands 0 to numBands-1

}

}

// Allocate a band that is not currently in use

int SpectrumManager::allocateBand() {

for (int i = 0; i < availableBands.size(); i++) {

if (!isBandAllocated[i]) {

isBandAllocated[i] = true;  // Mark the band as allocated

return availableBands[i];   // Return the allocated band

}

}

return -1;  // Return -1 if no bands are available

}

// Release a band when it is no longer in use

void SpectrumManager::releaseBand(int band) {

if (band >= 0 && band < isBandAllocated.size()) {

isBandAllocated[band] = false;  // Free the band

}

}

In this sample, the SpectrumManager class handles a list of frequency bands and assigned them to nodes as desirable.

2. Modify the Physical Layer to Support Frequency Bands

The physical layer in NS2 needs to be adjusted to manage frequency-based communication. Each node should be able to transmit and receive on a particular frequency band (or channel).

Extend the Physical Layer to Support Dynamic Band Selection:

We can expand the WirelessPhy class to permits nodes to work on certain frequency bands. This contains to choose a frequency band during transmission and reception.

Example C++ Code to Modify WirelessPhy:

class SpectrumAwarePhy : public WirelessPhy {

public:

SpectrumAwarePhy();

void setFrequencyBand(int band);  // Set the frequency band for this node

bool canReceive(Packet *p);       // Check if the node can receive a packet on the current band

protected:

int currentBand;  // The current frequency band in use by this node

};

// Constructor to initialize the frequency band

SpectrumAwarePhy::SpectrumAwarePhy() : WirelessPhy(), currentBand(-1) {

}

// Set the frequency band for this node

void SpectrumAwarePhy::setFrequencyBand(int band) {

currentBand = band;

}

// Check if the node can receive the packet (same band)

bool SpectrumAwarePhy::canReceive(Packet *p) {

int packetBand = getPacketBand(p);  // Extract the frequency band from the packet

return packetBand == currentBand;   // Only receive if the bands match

}

In this instance, the SpectrumAwarePhy class make sure that the node only receives packets that are transmitted on its allocated frequency band.

3. Implement Dynamic Spectrum Allocation

Dynamic spectrum access (DSA) permits nodes to enthusiastically choose a frequency band according to the availability, interference, or quality of service (QoS) requirements. We can execute DSA by intermittently scanning for available bands and reallocating spectrum as needed.

Dynamic Spectrum Allocation Process:

1. Scan for Available Bands: Nodes occasionally validates that bands are free.
2. Select a Band: A node chooses a band based on interference, signal strength, or QoS requirements.
3. Reallocate Spectrum: When a node finishes transmission, it releases the band for others to use.

Example of Dynamic Spectrum Allocation in the PHY Layer:

void SpectrumAwarePhy::dynamicSpectrumAllocation() {

int bestBand = -1;

double bestSignalQuality = -1.0;

// Scan for the best available band

for (int band = 0; band < numBands; band++) {

double signalQuality = measureSignalQuality(band);

if (signalQuality > bestSignalQuality && !isBandOccupied(band)) {

bestSignalQuality = signalQuality;

bestBand = band;

}

}

// Switch to the best band

setFrequencyBand(bestBand);

}

// Function to check if a band is occupied by another node

bool SpectrumAwarePhy::isBandOccupied(int band) {

// Example implementation to check if another node is using the same band

return bandManager.isBandAllocated(band);

}

4. Incorporate Interference Management

Spectrum allocation also needs to deliberate interference management. When multiple nodes transmit on the same or overlapping frequency bands, interference occurs. We can mimic interference by validating the signal-to-interference-plus-noise ratio (SINR) for each transmission.

Example of SINR Calculation:

double SpectrumAwarePhy::calculateSINR(Packet *p) {

double receivedPower = getSignalPower(p);  // Signal power of the current packet

double interferencePower = calculateInterferencePower(p);  // Interference from other transmissions

double noisePower = getNoisePower();

return receivedPower / (interferencePower + noisePower);  // SINR calculation

}

The SINR is used to regulate whether a packet can be successfully received. If the SINR falls below a threshold, the packet is likely to be misplaced because of interference.

5. Handle Spectrum Reallocation

When a node no longer needs its allocated frequency band (e.g., after completing transmission), it should release the band so that other nodes can use it.

Example of Releasing a Frequency Band:

void SpectrumAwarePhy::releaseBand() {

bandManager.releaseBand(currentBand);

currentBand = -1;  // Reset the band assignment

}

6. Integrate Spectrum Allocation with NS2 Simulation

After executing the spectrum allocation mechanism in the PHY layer, we can incorporate it into NS2 by adjusting the Tcl script to configure the spectrum manager, allocate frequency bands to nodes, and mimic the dynamic spectrum access.

Example Tcl Script for Spectrum Allocation Simulation:

# Create a simulator

set ns [new Simulator]

# Create nodes

set node1 [$ns node]

set node2 [$ns node]

set node3 [$ns node]

# Set up the spectrum manager and allocate bands dynamically

set spectrumManager [new SpectrumManager 10]  # 10 frequency bands available

# Set the PHY layer to support dynamic spectrum access

$node1 set phy_ [new Phy/SpectrumAwarePhy]

$node2 set phy_ [new Phy/SpectrumAwarePhy]

$node3 set phy_ [new Phy/SpectrumAwarePhy]

# Allocate frequency bands to nodes dynamically

$node1 setFrequencyBand [$spectrumManager allocateBand]

$node2 setFrequencyBand [$spectrumManager allocateBand]

# Create UDP agents and traffic

set udp1 [new Agent/UDP]

set udp2 [new Agent/UDP]

set udp3 [new Agent/UDP]

$ns attach-agent $node1 $udp1

$ns attach-agent $node2 $udp2

$ns attach-agent $node3 $udp3

# Create traffic sources and sinks

set cbr1 [new Application/Traffic/CBR]

$cbr1 set packetSize_ 512

$cbr1 set interval_ 0.05

$cbr1 attach-agent $udp1

$ns at 1.0 “$cbr1 start”

# Run the simulation

$ns run

7. Analyse Spectrum Utilization and Performance

Once the simulation is done, we can measure on how effectively the spectrum is used by evaluating:

• Spectrum Utilization: The percentage of available spectrum being used at any given time.
• Packet Delivery Ratio (PDR): The ratio of successfully delivered packets to the total number of transmitted packets.
• Throughput: The total amount of data transmitted successfully via the network.
• Interference Levels: Assess the effect of interference on packet loss and communication quality.

In the above manual, we demonstrate the comprehensive procedures to implement and execute the network spectrum allocation that has key concepts, implementation procedures explanation were given to executed in ns2 tool. Additional specific details regarding the network spectrum allocation will be provided.

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