How to Calculate Network Signal to Noise Ratio in NS2

To calculate the Signal to Noise Ratio (SNR) in NS2, this is defined to the ratio of the received signal power to the noise power at the receiver. SNR is parameters in wireless networks to estimate the quality of a communication link, by way of a higher SNR specifies better signal clarity and lower interference from noise.

NS2 does not support directly compute SNR in its default setup. But, we can design and calculate SNR using NS2’s wireless propagation models by making an allowance for the received signal strength and noise power. NS2 delivers numerous propagation models such as TwoRayGround, FreeSpace that can be utilized to compute the received signal power, and the noise power can be well-defined based on system metrics such as bandwidth and temperature.

The following is the detailed approach to calculate the SNR in ns2:

Formula for SNR:

The Signal to Noise Ratio (SNR) is typically expressed in decibels (dB) and is calculated as:

SNR (dB)=10⋅log⁡10(PsignalPnoise)\text{SNR (dB)} = 10 \cdot \log_{10}\left(\frac{P_{signal}}{P_{noise}}\right)SNR (dB)=10⋅log10​(Pnoise​Psignal​​)

Where:

  • PsignalP_{signal}Psignal​ is the received signal power (in watts).
  • PnoiseP_{noise}Pnoise​ is the noise power (in watts).

Steps to Calculate SNR in NS2:

  1. Set Up the Wireless Propagation Model: Utilize a wireless propagation model such as TwoRayGround or FreeSpace to evaluation the received signal strength in terms  of the distance among the sender and receiver.
  2. Define Noise Power: Noise power can be well-defined based on metrics such as thermal noise, bandwidth, and temperature. For instance, thermal noise can be calculated using the formula:

Pnoise=k⋅T⋅BP_{noise} = k \cdot T \cdot BPnoise​=k⋅T⋅B

Where:

    • kkk is the Boltzmann constant (1.38×10−231.38 \times 10^{-23}1.38×10−23 J/K),
    • TTT is the system temperature (in Kelvin, typically 290 K),
    • BBB is the bandwidth (in Hz).
  2. Calculate SNR: For each received packet, compute the SNR based on the received signal strength and the predefined noise power.
  3. Log SNR in the Trace File: Adapt the NS2 code or simulation script to log the SNR at the receiver for each packet.

Example Tcl Script to Simulate SNR Calculation in NS2:

Here’s an sample Tcl script that configures a simple wireless network using the TwoRayGround propagation model. The SNR for received packets will be intended based on the signal strength and noise power.

# Create a new simulator instance

set ns [new Simulator]

# Set the simulation area and channel

set val(x) 500

set val(y) 500

# Define wireless channel and propagation model

set val(chan) Channel/WirelessChannel

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

# Define other parameters (noise power, etc.)

set noise_power 1e-10  ;# Noise power in watts (this can be calculated based on bandwidth and temperature)

# Create two nodes (sender and receiver)

set node0 [$ns node]

set node1 [$ns node]

# Set node positions

$node0 set X_ 50

$node0 set Y_ 100

$node0 set Z_ 0.0

$node1 set X_ 450

$node1 set Y_ 100

$node1 set Z_ 0.0

# Define the wireless link between nodes using the specified channel

set chan_1_ [new $val(chan)]

$ns node-config -adhocRouting AODV \

-llType LL \

-macType Mac/802_11 \

-ifqType Queue/DropTail/PriQueue \

-ifqLen 50 \

-antType Antenna/OmniAntenna \

-propType $val(prop) \

-topoInstance [new Topography] \

-channel $chan_1_ \

-agentTrace ON \

-routerTrace ON \

-macTrace ON

# Attach UDP agents to both nodes

set udp0 [new Agent/UDP]

set null0 [new Agent/Null]

$ns attach-agent $node0 $udp0

$ns attach-agent $node1 $null0

$ns connect $udp0 $null0

# Create a CBR traffic source to generate packets

set cbr0 [new Application/Traffic/CBR]

$cbr0 attach-agent $udp0

$cbr0 set packetSize_ 512

$cbr0 set rate_ 1Mb

# Start the traffic flow at 1 second and stop it at 5 seconds

$ns at 1.0 “$cbr0 start”

$ns at 5.0 “$cbr0 stop”

# Define a procedure to calculate and log the SNR

proc log_snr {signal_power noise_power} {

set snr_db [expr 10 * log10($signal_power / $noise_power)]

puts “SNR: $snr_db dB”

}

# Modify the wireless PHY layer to log SNR for received packets

$node1 set ragent_ [$node1 ragent]

$node1 ragent_ instproc recv {pkt} {

global noise_power

set signal_power [Phy/WirelessPhy getRxPower] ;# Received signal power

log_snr $signal_power $noise_power

$self recv $pkt

}

# Finish the simulation after 6 seconds

$ns at 6.0 “finish”

# Finish procedure to close the simulation

proc finish {} {

global ns

$ns flush-trace

exit 0

}

# Run the simulation

$ns run

Explanation of the Script:

  1. Propagation Model (TwoRayGround): The TwoRayGround propagation design is used to estimate the received signal power based on the distance among the nodes.
  2. Noise Power: The noise power is set physically as 1e-10 watts. We can adapt this value according to the bandwidth and temperature of the system.
  3. Logging SNR: The log_snr procedure estimate the SNR (in dB) for each received packet using the formula:

SNR (dB)=10⋅log⁡10(Received Signal PowerNoise Power)\text{SNR (dB)} = 10 \cdot \log_{10}\left(\frac{\text{Received Signal Power}}{\text{Noise Power}}\right)SNR (dB)=10⋅log10​(Noise PowerReceived Signal Power​)

  1. Modifying Packet Reception: The script adapts the features of the receiver (node1) to log the SNR when a packet is received. The received signal power is gotten using the getRxPower function (a placeholder here, nevertheless it should be well-defined or adapted in the NS2 PHY layer).
  1. Noise Power Calculation:

If we need to estimate the noise power more precisely, we can utilize the formula for thermal noise power:

Pnoise=k⋅T⋅BP_{noise} = k \cdot T \cdot BPnoise​=k⋅T⋅B

Where:

  • kkk is Boltzmann’s constant (1.38×10−231.38 \times 10^{-23}1.38×10−23 J/K),
  • TTT is the temperature in Kelvin (e.g., 290 K),
  • BBB is the bandwidth in Hz (e.g., 1 MHz = 10610^6106 Hz).

For example, for a bandwidth of 1 MHz and temperature of 290 K:

Pnoise=1.38×10−23×290×1×106=4.002×10−15 WP_{noise} = 1.38 \times 10^{-23} \times 290 \times 1 \times 10^6 = 4.002 \times 10^{-15} \, \text{W}Pnoise​=1.38×10−23×290×1×106=4.002×10−15W

  1. Post-Simulation Analysis:

After the simulation, we can evaluate the SNR values that were logged to measure the quality of the communication link at diverse times and distances.

Summary of Steps:

  1. Set up the wireless network with a propagation model such as TwoRayGround in NS2.
  2. Define noise power physically or based on system metrics such as bandwidth and temperature.
  3. Modify the receiver to log the received signal power and estimates the SNR for each received packet.
  4. Run the simulation and measure the SNR values to measure the quality of the wireless link.

In this process, we had covered the details from the simulation setup to the assessments of outcomes of the SNR and its computation in ns2. For further analysis we will help you with additional information of this process. To calculate the Signal to Noise Ratio (SNR) in NS2 tool it is advisable to get our professional help to get high results in your work.