How to Implement Network Waveform in NS2

To implement a network waveform in NS2 has needs to adding or expanding the simulation to model diverse waveforms used for interaction among nodes. A waveform in the concept of wireless communication that usually refers to the physical layer (PHY) signal that denotes data transmission, that involves features like modulation, bandwidth, and channel characteristics. Waveforms play a vital role in the design of wireless communication systems, and modelling them can help to mimic their effects on network performance. Below is the guide on how to implement the network waveform in NS2:

Step-by-Step Guide to Implementing a Custom Network Waveform in NS2

To execute a network waveform in NS2, we will mainly need to expand the physical layer (PHY) to replicate the behaviour of a waveform, which can include:

  • Modulation schemes: Describe how bits are mapped to physical waveforms (e.g., BPSK, QPSK, OFDM).
  • Bandwidth and frequency: Specify the channel bandwidth and the frequency range used by the waveform.
  • Signal-to-noise ratio (SNR): To design on how different waveforms perform in changing levels of noise and interference.
  • Bit error rate (BER): Regulate how different waveforms impact the likelihood of bit errors during transmission.
  1. Extend the Physical Layer to Support Waveforms

In NS2, the physical layer is liable for replicating the transmission of packets across the wireless medium. We can adjust or expand the existing PHY layer to model different waveforms by integrating numerous modulation schemes, bandwidth, and frequency characteristics.

Modify or Create a Custom PHY Class

In NS2, the PHY layer is usually managed by classes like Phy/WirelessPhy (for wireless communication). We can expand this class to mimic the behaviour of different waveforms.

Here is an instance of how we can describe a custom waveform by prolonging the WirelessPhy class in C++.

Example C++ Code for a Custom Waveform:

class CustomWaveformPhy : public WirelessPhy {

public:

CustomWaveformPhy();

void sendDown(Packet* p);  // Handle transmission of packets

double calculateBER(double snr);  // Calculate bit error rate based on SNR

protected:

double modulationEfficiency;  // Define how efficient the modulation is

double bandwidth;              // Bandwidth of the waveform

double frequency;              // Carrier frequency of the waveform

};

// Constructor to initialize the waveform’s characteristics

CustomWaveformPhy::CustomWaveformPhy() : WirelessPhy(), modulationEfficiency(2.0), bandwidth(20.0e6), frequency(2.4e9) {

// Example: QPSK modulation (Efficiency = 2 bits per symbol), 20 MHz bandwidth, 2.4 GHz frequency

}

// Send packet down to the physical layer

void CustomWaveformPhy::sendDown(Packet* p) {

// Calculate SNR for the transmission based on the environment

double snr = calculateSNR(p);

// Calculate the Bit Error Rate (BER) based on the SNR and modulation scheme

double ber = calculateBER(snr);

// Simulate packet loss based on BER

if (random() < ber) {

// Drop packet due to errors

Packet::free(p);

} else {

// Transmit the packet successfully

WirelessPhy::sendDown(p);

}

}

// Calculate BER based on SNR (example: for QPSK modulation)

double CustomWaveformPhy::calculateBER(double snr) {

// Use a formula for BER based on the modulation scheme (QPSK in this case)

return 0.5 * erfc(sqrt(snr / 2.0));  // Example for QPSK

}

  1. Define Modulation Schemes and Waveform Parameters

In the custom physical layer class, we can describe diverse modulation schemes like BPSK, QPSK, or OFDM by modifying the performance metrics such as modulation efficiency, signal-to-noise ratio (SNR), and bit error rate (BER).

  • Modulation Efficiency: The number of bits transmitted per symbol like QPSK has an efficiency of 2 bits/symbol.
  • SNR: Signal-to-noise ratio regulates the quality of the signal in a noisy environment.
  • BER: Bit error rate is the probability that a transmitted bit will be received incorrectly.

Example of Modulation Parameters:

if (modulationScheme == “BPSK”) {

modulationEfficiency = 1.0;  // BPSK: 1 bit per symbol

} else if (modulationScheme == “QPSK”) {

modulationEfficiency = 2.0;  // QPSK: 2 bits per symbol

} else if (modulationScheme == “OFDM”) {

modulationEfficiency = 4.0;  // OFDM: Can vary, e.g., 4 bits per symbol

}

  1. Handle Packet Loss and Errors Based on Waveform Characteristics

Packet errors and losses relays on the modulation scheme and the signal quality. We can mimic this behaviour by estimating the bit error rate (BER) based on the SNR and deciding whether to drop the packet based on the BER.

For instance, we can use the erfc() function (complementary error function) to design the BER for diverse modulation schemes such as QPSK.

  1. Simulate Different Waveforms

Once the custom waveform PHY class is defined, we can replicate different waveforms by changing the modulation scheme, bandwidth, and frequency.

For instance, we can mimic the BPSK or QPSK with various bandwidths (e.g., 20 MHz, 40 MHz) or mimic OFDM with different subcarrier configurations.

  1. Create a Tcl Script for Simulation

Once the custom waveform is executed in the physical layer can mimic network communication with the new waveform using a Tcl script. Here’s a sample Tcl script that uses the custom waveform for interaction between two nodes.

Example Tcl Script for Custom Waveform Simulation:

# Create a simulator

set ns [new Simulator]

# Create two nodes

set node1 [$ns node]

set node2 [$ns node]

# Set up custom PHY (CustomWaveformPhy) for nodes

$node1 set phy_ [new Phy/CustomWaveformPhy]

$node2 set phy_ [new Phy/CustomWaveformPhy]

# Set up UDP agents and traffic

set udp1 [new Agent/UDP]

set udp2 [new Agent/UDP]

$ns attach-agent $node1 $udp1

$ns attach-agent $node2 $udp2

# Connect the agents and traffic

$ns connect $udp1 $udp2

# Start simulation traffic

set cbr [new Application/Traffic/CBR]

$cbr set packetSize_ 512

$cbr set interval_ 0.05

$cbr attach-agent $udp1

$ns at 1.0 “$cbr start”

# Run the simulation

$ns run

In this example:

  • CustomWaveformPhy is used as the physical layer for both nodes.
  • UDP agents are configures to create traffic among the nodes that is transmitted using the custom waveform.
  1. Evaluate the Network Performance

After executing and running the simulation with custom waveform, we can evaluate the performance based on parameters such as:

  • Packet delivery ratio (PDR): How successfully packets are delivered across the network.
  • Throughput: The amount of data transmitted over the network in a given time.
  • End-to-end delay: The time taken for data to travel from the source to the destination.
  • Energy efficiency: If we mimic an energy-aware networks, we can assess on how different waveforms impacts energy consumption.

We can extract these parameters from NS2’s trace files and use them to assess how well the custom waveform performs in different network conditions.

  1. Extend to More Complex Waveforms (OFDM, MIMO)

If we need to execute more advanced waveforms such as OFDM or MIMO, we can expand the physical layer further:

  • OFDM: Execute subcarrier modulation and parallel transmission over multiple frequency bands.
  • MIMO: To design multiple antennas and mimic on how they impact the transmission and reception of packets.

We clearly share the information about how to implement and envision the results for network waveform that is used to interact among nodes and enhance network performance that were executed using the ns2 simulation tool.  Additional specific details regarding the network waveform will also be providing.

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