How to Calculate Network SNR and SINR in NS2

To calculate the Signal-to-Noise Ratio (SNR) and Signal-to-Interference-plus-Noise Ratio (SINR) in ns2 this has a vital parameters in wireless network simulations, as they quantify the quality of a wireless communication link.

SNR trials the ratio of the power of the chosen signal to the power of background noise.
SINR expands SNR by also allowing for interference from other signals, as long as a more realistic measure in environments in which multiple transmitters are present.

To calculate SNR and SINR in NS2 has to know the network setup, the metrics of the wireless channel, and the interference from other nodes.

Below are the approaches to calculate on how to achieve this in ns2:

Steps to Calculate SNR and SINR in NS2

Set up the Wireless Network

Initially, describe wireless network topology in NS2, has contain nodes, communication links, and traffic patterns.

# Create a new simulator object

set ns [new Simulator]

# Define the network parameters

set val(chan) Channel/WirelessChannel ;# Channel type

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

set val(netif) Phy/WirelessPhy ;# Network interface type

set val(mac) Mac/802_11 ;# MAC type

set val(ifq) Queue/DropTail/PriQueue ;# Interface queue type

set val(ll) LL ;# Link layer type

set val(ant) Antenna/OmniAntenna ;# Antenna model

set val(x) 500 ;# X dimension of the topography

set val(y) 500 ;# Y dimension of the topography

# Create the nodes

for {set i 0} {$i < 5} {incr i} {

set node($i) [$ns node]

$node($i) set X_ [expr rand() * $val(x)]

$node($i) set Y_ [expr rand() * $val(y)]

$node($i) set Z_ 0.0

}

# Define traffic sources, sinks, and connections as needed

Configure the Physical Layer Parameters

Set the physical layer bounds, that has transmission power, antenna gains, and other related metrics.

# Set transmission power (Pt_), antenna gains (Gt_ and Gr_), and receiver threshold (RxThresh_)

$ns node-config -phyType $val(netif) \

-antType $val(ant) \

-propType $val(prop) \

-channelType $val(chan) \

-txPower 0.2818 \

-rxPower 0.0 \

-txGain 1.0 \

-rxGain 1.0 \

-rxThresh 3.652e-10 \

-antHeight 1.5 \

-bandwidth 2e6 \

-freq_ 914e6

# Alternatively, set parameters individually for each node

foreach n [array names node] {

$node($n) set Pt_ 0.2818 ;# Transmission power in Watts

$node($n) set Gt_ 1.0 ;# Transmitter antenna gain

$node($n) set Gr_ 1.0 ;# Receiver antenna gain

$node($n) set freq_ 914e6 ;# Carrier frequency in Hz

$node($n) set L_ 1.0 ;# System loss

}

Enable Trace Files

Create trace files to log packet transmissions and receptions.

set tracefd [open “out.tr” w]

$ns trace-all $tracefd

Calculate SNR

The SNR can be estimated using the received power and the noise power.

Received Power (PrP_rPr) can be calculated using the Friis free-space equation:

Pr=Pt×Gt×Gr×(λ4πd)2×1LP_r = P_t \times G_t \times G_r \times \left( \frac{\lambda}{4\pi d} \right)^2 \times \frac{1}{L}Pr=Pt×Gt×Gr×(4πdλ)2×L1

Where:

PtP_tPt is the transmission power (Watts)
GtG_tGt is the transmitter antenna gain
GrG_rGr is the receiver antenna gain
λ\lambdaλ is the wavelength (meters)
ddd is the distance among transmitter and receiver (meters)
LLL is the system loss (dimensionless)

Noise Power (NNN) can be calculated using:

N=k×T×BN = k \times T \times BN=k×T×B

Where:

kkk is Boltzmann’s constant (1.38×10−23J/K1.38 \times 10^{-23} \text{J/K}1.38×10−23J/K)
TTT is the system temperature (Kelvin)
BBB is the bandwidth (Hz)

TCL Procedure to Calculate SNR:

proc calculate_snr {tx_node rx_node} {

global node

# Get node positions

set x1 [$node($tx_node) set X_]

set y1 [$node($tx_node) set Y_]

set x2 [$node($rx_node) set X_]

set y2 [$node($rx_node) set Y_]

# Calculate distance between nodes

set dx [expr $x2 – $x1]

set dy [expr $y2 – $y1]

set distance [expr sqrt($dx*$dx + $dy*$dy)]

# Physical parameters

set Pt [$node($tx_node) set Pt_] ;# Transmission power

set Gt [$node($tx_node) set Gt_] ;# Transmitter antenna gain

set Gr [$node($rx_node) set Gr_] ;# Receiver antenna gain

set L [$node($tx_node) set L_] ;# System loss

set freq [$node($tx_node) set freq_];# Carrier frequency

set c 3.0e8 ;# Speed of light

# Calculate wavelength

set lambda [expr $c / $freq]

# Calculate received power (Friis equation)

set numerator [expr $Pt * $Gt * $Gr * ($lambda / (4 * 3.1416 * $distance))**2]

set Pr [expr $numerator / $L]

# Noise power

set k 1.38e-23 ;# Boltzmann’s constant

set T 290 ;# System temperature in Kelvin

set bandwidth [$node($tx_node) set bandwidth]; # Bandwidth in Hz

set N [expr $k * $T * $bandwidth]

# Calculate SNR

set snr [expr $Pr / $N]

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

return $snr_dB

}

Usage Example:

# Calculate SNR between node 0 and node 1

set snr_dB [calculate_snr 0 1]

puts “SNR between node 0 and node 1: $snr_dB dB”

We can schedule this procedure to execute at certain times during the simulation.

Calculate SINR

In environments in which multiple transmitters are active, interference from other transmitters must be measured. The SINR encompasses the SNR by contains interference power.

SINR=PrI+N\text{SINR} = \frac{P_r}{I + N}SINR=I+NPr

Where:

PrP_rPr is the received power from the preferred transmitter.
III is the summation of interference power from other transmitters.
NNN is the noise power.

To calculate SINR, you need to:

Compute PrP_rPr as before.
Summation the interference power III from all other transmitters.
Compute the noise power NNN.

Modify the Procedure to Calculate SINR:

proc calculate_sinr {tx_node rx_node} {

global node

# Get node positions

set x_rx [$node($rx_node) set X_]

set y_rx [$node($rx_node) set Y_]

# Physical parameters

set Pt_desired [$node($tx_node) set Pt_]

set Gt_desired [$node($tx_node) set Gt_]

set Gr_desired [$node($rx_node) set Gr_]

set L_desired [$node($tx_node) set L_]

set freq [$node($tx_node) set freq_]

set c 3.0e8

set lambda [expr $c / $freq]

# Calculate distance between desired tx and rx

set x_tx [$node($tx_node) set X_]

set y_tx [$node($tx_node) set Y_]

set dx_desired [expr $x_rx – $x_tx]

set dy_desired [expr $y_rx – $y_tx]

set d_desired [expr sqrt($dx_desired*$dx_desired + $dy_desired*$dy_desired)]

# Calculate desired received power

set Pr_desired [expr ($Pt_desired * $Gt_desired * $Gr_desired * ($lambda / (4 * 3.1416 * $d_desired))**2) / $L_desired]

# Noise power

set k 1.38e-23

set T 290

set bandwidth [$node($tx_node) set bandwidth]

set N [expr $k * $T * $bandwidth]

# Calculate interference power from other transmitters

set interference_power 0.0

foreach n [array names node] {

if {$n != $tx_node && $n != $rx_node} {

# Get positions

set x_intf [$node($n) set X_]

set y_intf [$node($n) set Y_]

# Calculate distance between interfering node and receiver

set dx_intf [expr $x_rx – $x_intf]

set dy_intf [expr $y_rx – $y_intf]

set d_intf [expr sqrt($dx_intf*$dx_intf + $dy_intf*$dy_intf)]

# Get parameters

set Pt_intf [$node($n) set Pt_]

set Gt_intf [$node($n) set Gt_]

set Gr_intf [$node($rx_node) set Gr_]

set L_intf [$node($n) set L_]

# Calculate interfering received power

set Pr_intf [expr ($Pt_intf * $Gt_intf * $Gr_intf * ($lambda / (4 * 3.1416 * $d_intf))**2) / $L_intf]

# Sum interference power

set interference_power [expr $interference_power + $Pr_intf]

}

# Calculate SINR

set sinr [expr $Pr_desired / ($interference_power + $N)]

set sinr_dB [expr 10 * log10($sinr)]

return $sinr_dB

}

Usage Example:

# Calculate SINR between node 0 and node 1

set sinr_dB [calculate_sinr 0 1]

puts “SINR between node 0 and node 1: $sinr_dB dB”

This procedure computes the SINR by:

Calculating the received power from the chosen transmitter to the receiver.
Counting the received powers from all other transmitters to the receiver as interference.
Estimating the SINR using the formula.

Note: This calculation assumes that all routers are transmitting instantaneously and on the same frequency band, that are not always be the case in simulation. Adapt consequently for the certain scenario.

Schedule SNR and SINR Calculations during Simulation

To track SNR and SINR over time, we can schedule the calculation process at certain times.

# Function to log SNR and SINR over time

proc log_snr_sinr {tx_node rx_node interval} {

global ns

set snr_dB [calculate_snr $tx_node $rx_node]

set sinr_dB [calculate_sinr $tx_node $rx_node]

puts “Time: [$ns now], SNR: $snr_dB dB, SINR: $sinr_dB dB”

# Schedule next call

$ns at [expr [$ns now] + $interval] “log_snr_sinr $tx_node $rx_node $interval”

}

# Start logging SNR and SINR every 1 second

$ns at 0.0 “log_snr_sinr 0 1 1.0”

Log SNR and SINR to a File

We need to record the SNR and SINR values to a file for analysis.

# Open a log file

set snr_log [open “snr_sinr_log.txt” w]

proc log_snr_sinr_to_file {tx_node rx_node interval} {

global ns snr_log

set snr_dB [calculate_snr $tx_node $rx_node]

set sinr_dB [calculate_sinr $tx_node $rx_node]

puts $snr_log “Time: [$ns now], SNR: $snr_dB dB, SINR: $sinr_dB dB”

# Schedule next call

$ns at [expr [$ns now] + $interval] “log_snr_sinr_to_file $tx_node $rx_node $interval”

}

# Start logging SNR and SINR to file every 1 second

$ns at 0.0 “log_snr_sinr_to_file 0 1 1.0”

Consider Mobility and Changing Network Conditions

If the simulation has contained node mobility or dynamic changes in network conditions, the SNR and SINR values will variation over time. The scheduled logging will capture these fluctuations.

Analyse the Results

After the simulation:

Use the logged data to plot SNR and SINR over time.
Classify periods of low SNR or SINR that relate to poor link quality or high interference.
Evaluate the effect of network metrics on SNR and SINR.

Considerations

Channel Conditions: The propagation model such as TwoRayGround, Shadowing, Nakagami impacts the received power calculation. Adapt the calculations consequently if using a different model.
Interference Modelling: In NS2, interference is not always designed clearly. The above approaches assume that all other nodes are possible interferers routing on the same frequency and at the same time.
MAC Layer Effects: The MAC protocol such as CSMA/CA in 802.11 can avoid simultaneous transmissions, minimizing interference. Take this into account when inferring SINR outcomes.
Frequency Bands: If nodes perform on diverse frequencies, meddling cannot occur. Make sure that frequency metrics are set properly.

This setup will permit to calculate and evaluate the Signal-to-Noise Ratio (SNR) and Signal-to-Interference-plus-Noise Ratio (SINR) in ns2 simulation that provide the insights to regulate the network setup and the interference from other nodes. We will explore how the SNR-SINR clarifies within other simulation frameworks.

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