**How to Calculate Network Outage probability in NS2**

To calculate the Network Outage Probability in ns2 has a numerous steps to follow and it is the important parameter in wireless communication systems that signify the probability which the system’s performance (typically based on signal-to-noise ratio (SNR) or throughput) falls below a specific threshold, interpretation communication unreliable or impossible. In NS2, we can estimate the outage probability by measuring on how usually the SNR or data rate for a given user drops below a predefined threshold in the course of the simulation.

**Key Concepts for Outage Probability**

**Outage Probability (P_out)**: The fraction of time in the course of that the network performance (e.g., SNR, data rate) is below a specific threshold.

Pout=Number of Outage EventsTotal Number of EventsP_{\text{out}} = \frac{\text{Number of Outage Events}}{\text{Total Number of Events}}Pout=Total Number of EventsNumber of Outage Events

**SNR Threshold**: The minimum acceptable SNR essential for successful communication.**Data Rate Threshold**: The minimum essential data rate for reliable communication.

**Steps to Calculate Network Outage Probability in NS2**

**Set up the Wireless Network in NS2**

Design the wireless network in which the each user interacts with a base station. We will track the **SNR** or **data rate** in the course of the simulation to detect the outage events (when the SNR or data rate drops below the threshold).

**Example Setup:**

# Define base station and user nodes

set bs [$ns node] ;# Base station

set ue1 [$ns node] ;# User 1

set ue2 [$ns node] ;# User 2

# Set up wireless links

$ns wireless-link $ue1 $bs 54Mb 10ms

$ns wireless-link $ue2 $bs 54Mb 10ms

In this setup, **base station (bs)** interacts with multiple users (UEs), and we need to estimate the outage probability for each UE.

**Define Outage Thresholds**

Describe an **SNR threshold** or a **data rate threshold** below that the network is deliberated in an outage state. For instance, we can set an SNR threshold at 10 dB or a data rate threshold at 1 Mbps.

# Define SNR or data rate thresholds for outage events

set snr_threshold 10 ;# SNR threshold in dB

set data_rate_threshold 1e6 ;# Data rate threshold in bps (1 Mbps)

**Calculate Signal-to-Noise Ratio (SNR)**

The **SNR** for each user is a key factor for defining network outages. In NS2, we can calculate the SNR for each user in terms of transmission power, path loss, and noise. The SNR can be estimated using the following formula:

SNR (dB)=10×log10(Received PowerNoise Power)\text{SNR (dB)} = 10 \times \log_{10} \left( \frac{\text{Received Power}}{\text{Noise Power}} \right)SNR (dB)=10×log10(Noise PowerReceived Power)

We can describe a function in NS2 to estimate the SNR in terms of network conditions:

**TCL Script to Calculate SNR:**

# Function to calculate SNR for a given transmission power, path loss, and noise power

proc calculate_snr {tx_power path_loss noise_power} {

# SNR (linear scale) = Received power / Noise power

set snr_linear [expr $tx_power / ($path_loss * $noise_power)]

# Convert SNR to dB

set snr_dB [expr 10 * log10($snr_linear)]

return $snr_dB

}

# Example usage

set tx_power 1.0 ;# Transmission power in Watts

set path_loss 0.5 ;# Path loss factor

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

set snr_ue1 [calculate_snr $tx_power $path_loss $noise_power]

puts “SNR for User 1: $snr_ue1 dB”

This script estimates the **SNR** for each user in terms of the transmission power, path loss, and noise power. We can utilize this function in the course of the simulation to track the SNR and compare it with the threshold to identify outages.

**Monitor Data Rate (Throughput)**

In some cases, we need to estimate **outage probability** in terms of the user’s **data rate** (throughput). To estimate the data rate, count the number of bytes received by each user and divide by the total simulation time.

**AWK Script to Calculate Data Rate:**

awk ‘{

if ($1 == “r” && $4 == “tcp”) { # Only consider received TCP packets

if ($3 == 1) { # Packets received by User 1

ue1_total_bytes += $6; # $6 is the packet size in bytes

}

}

} END {

simulation_time = 100.0; # Replace with actual simulation time in seconds

ue1_throughput_bps = ue1_total_bytes * 8 / simulation_time; # Throughput in bps for User 1

print “Throughput for User 1: ” ue1_throughput_bps ” bps”;

}’ out.tr

This script estimates the throughput for **User 1** by counting the size of received packets and dividing by the total simulation time.

**Calculate Outage Probability**

Now, we can estimate the **outage probability** by relating the SNR or throughput against the defined threshold. If the SNR or throughput drops below the threshold, it is measured an **outage event**.

**AWK Script to Calculate Outage Probability:**

awk ‘{

if ($1 == “r” && $4 == “tcp”) { # Only consider received TCP packets

if ($3 == 1) { # Packets received by User 1

ue1_total_bytes += $6; # $6 is the packet size in bytes

}

}

} END {

simulation_time = 100.0; # Replace with actual simulation time in seconds

ue1_throughput_bps = ue1_total_bytes * 8 / simulation_time; # Throughput in bps for User 1

# Define the data rate threshold (in bps)

data_rate_threshold = 1e6; # 1 Mbps

# Calculate the outage probability

if (ue1_throughput_bps < data_rate_threshold) {

outage_events++;

}

# Outage probability = Number of outage events / Total simulation time

outage_probability = outage_events / simulation_time;

print “Outage Probability for User 1: ” outage_probability;

}’ out.tr

This script:

- Computes the throughput for
**User 1**. - Compares the throughput with the
**data rate threshold**to identify outages. - Calculates the
**outage probability**according to the number of outage events.

**Log and Analyse Outage Probability Over Time**

To monitor how the **outage probability** changes through the simulation, we can estimate the outage events at regular intervals such as every second.

**AWK Script for Time-Windowed Outage Probability:**

awk ‘{

if ($1 == “r” && $4 == “tcp”) {

interval = int($2); # Group events by time intervals (in seconds)

if ($3 == 1) {

ue1_total_bytes[interval] += $6; # Sum packet sizes for UE1 per interval

}

}

} END {

for (interval in ue1_total_bytes) {

ue1_throughput_bps = ue1_total_bytes[interval] * 8; # Throughput for UE1 in bits

# Define the data rate threshold (in bps)

data_rate_threshold = 1e6; # 1 Mbps

# Check if the throughput is below the threshold

if (ue1_throughput_bps < data_rate_threshold) {

outage_events++;

}

}

# Outage probability = Number of outage events / Number of intervals

outage_probability = outage_events / NR;

print “Time Interval: ” interval ” s, Outage Probability: ” outage_probability;

}’ out.tr

This script will print the **outage probability** for each time interval, enable them to track how often the user experiences outages in the course of the simulation.

**Outage Probability Based on SNR**

If we prefer to estimate the **outage probability** in terms of **SNR** instead of throughput, we can adjust the script to utilize the estimated SNR rather than data rate:

if (snr_ue1 < snr_threshold) {

outage_events++;

}

In this case, **SNR** is estimated at each packet reception, and an outage is counted whenever the **SNR** falls below the threshold.

By following these procedures, we can calculate the Network Outage Probability in an NS2 simulation tool and evaluated the network’s performance. Let me know if you need further clarification or assistance!

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