How to Implement Network PAPR Mitigation in NS2

To implement Network Peak-to-Average Power Ratio (PAPR) Mitigation in NS2 has includes to replicate the approaches that minimize the PAPR in communication systems, especially in Orthogonal Frequency Division Multiplexing (OFDM) systems. PAPR mitigation is vital in wireless communication due to high PAPR that can minimize power efficiency and cause non-linear distortion in power amplifiers.

The below is brief procedure to implement the Network Peak-to-Average Power Ratio (PAPR) Mitigation in ns2:

Step-by-Step Implementation:

  1. Understanding PAPR and Its Importance
  • PAPR (Peak-to-Average Power Ratio): It is the ratio of the peak power of a signal to its average power. A high PAPR means that the signal has spikes of high power, that can overload the transmitter’s amplifier that leads distortion.
  • PAPR Mitigation: Approaches such as Clipping, Selective Mapping (SLM), Tone Reservation (TR), Partial Transmit Sequence (PTS), and Coding are used to minimize PAPR.
  1. Approach to Simulate PAPR Mitigation in NS2
  • Packet Transmission with PAPR Modeling: Execute PAPR modelling in the physical layer and mimic the transmission of packets with high PAPR.
  • PAPR Mitigation Techniques: Execute PAPR mitigation approaches such as clipping or selective mapping during packet transmission.
  • Evaluate PAPR Reduction: Assess the effects of PAPR mitigation on the transmission by monitoring parameters such as power efficiency or bit error rate (BER).
  1. Steps for Implementing PAPR Mitigation in NS2

Step 1: Modify the Physical Layer to Model PAPR

We need to adjust the physical layer (WirelessPhy) to design the PAPR and mimic its effects on transmission. The PAPR will be estimated for each transmitted packet.

Define PAPR Parameters in the Physical Layer

We need to describe key metrics to signify the PAPR and the threshold for mitigation.

# Define PAPR parameters

set WirelessPhy/papr_threshold 10  ;# Threshold for PAPR in dB

set WirelessPhy/clipping_ratio 0.8 ;# Clipping ratio for PAPR mitigation (e.g., 80%)

Function to Calculate PAPR

The PAPR is estimated as the ratio of the peak power to the average power. We will execute a function to estimate the PAPR for each packet.

# Function to calculate PAPR (Peak-to-Average Power Ratio)

proc calc_papr {signal} {

# Calculate the peak power

set peak_power [expr max($signal)]

# Calculate the average power

set avg_power [expr [avg($signal)]]

# Calculate PAPR (peak-to-average ratio)

set papr [expr 10 * log10($peak_power / $avg_power)]

return $papr

}

Step 2: Implement PAPR Mitigation Techniques

There are numerous approaches for PAPR mitigation. For simplicity, we will execute clipping as the prevention approaches. Clipping minimizes the peak power by a defined clipping ratio.

Clipping Function

# Function to mitigate PAPR using clipping

proc mitigate_papr_clipping {signal} {

set clipping_ratio [WirelessPhy set clipping_ratio]

# Clip the signal to the defined clipping ratio

foreach sample $signal {

if {$sample > $clipping_ratio} {

set sample $clipping_ratio

}

}

return $signal

}

Apply PAPR Mitigation before Transmission

We will adjust the packet transmission function to implement PAPR mitigation before routing the packet.

# Packet transmission function with PAPR mitigation

proc Phy/WirelessPhy::transmit_packet {packet} {

# Get the signal data from the packet

set signal [$packet data]

# Calculate the PAPR of the signal

set papr [calc_papr $signal]

puts “PAPR of the signal: $papr dB”

# If PAPR exceeds the threshold, apply PAPR mitigation

set papr_threshold [WirelessPhy set papr_threshold]

if {$papr > $papr_threshold} {

puts “Applying PAPR mitigation (Clipping)…”

set signal [mitigate_papr_clipping $signal]

}

# Transmit the packet with the mitigated signal

$self send_packet_with_signal $packet $signal

}

Send the Packet with the Mitigated Signal

This function will manage the actual transmission of the packet after implementing PAPR mitigation.

# Function to transmit the packet with the mitigated signal

proc Phy/WirelessPhy::send_packet_with_signal {packet signal} {

# Simulate the transmission of the packet using the mitigated signal

puts “Transmitting packet with mitigated PAPR…”

# Forward the packet to the upper layers

$self send_up $packet

}

Step 3: Define a TCL Simulation Script for PAPR Mitigation

In the TCL script, we will describe a basic wireless network with multiple nodes and allows the PAPR mitigation in the physical layer.

# Create a simulator instance

set ns [new Simulator]

# Define trace and nam files for output

set tracefile [open papr_mitigation.tr w]

set namfile [open papr_mitigation.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define the network topology

set topo [new Topography]

$topo load_flatgrid 1000 1000  ;# Simulation area: 1000×1000 meters

# Create the General Operations Director (GOD)

set god_ [create-god 5]  ;# 5 nodes in the network

# Define node parameters for wireless communication

set opt(chan)  Channel/WirelessChannel

set opt(prop) Propagation/TwoRayGround

set opt(netif) Phy/WirelessPhy

set opt(mac) Mac/802_11

set opt(ifq) Queue/DropTail/PriQueue

set opt(ll)  LL

set opt(ant) Antenna/OmniAntenna

set opt(x) 1000

set opt(y) 1000

# Create nodes and set initial positions

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

set node_($i) [$ns node]

set x [expr rand() * $opt(x)]

set y [expr rand() * $opt(y)]

$node_($i) set X_ $x

$node_($i) set Y_ $y

$node_($i) set Z_ 0.0

}

# Set up traffic generation

proc start_traffic {} {

global ns node_

# Create UDP agents and attach them to nodes

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

set udp_($i) [new Agent/UDP]

set null_($i) [new Agent/Null]

$ns attach-agent $node_($i) $udp_($i)

$ns attach-agent $node_($i) $null_($i)

# Generate CBR traffic (constant bit rate)

set cbr_($i) [new Application/Traffic/CBR]

$cbr_($i) set packetSize_ 512

$cbr_($i) set interval_ 0.1

$cbr_($i) attach-agent $udp_($i)

# Connect the UDP agent to the null agent

$ns connect $udp_($i) $null_($i)

}

}

# Start the traffic at 1 second

$ns at 1.0 “start_traffic”

# End simulation after 100 seconds

$ns at 100.0 “finish”

# End simulation procedure

proc finish {} {

global ns tracefile namfile

close $tracefile

close $namfile

$ns halt

}

# Run the simulation

$ns run

  1. Explanation of the Script
  • PAPR Calculation: The script estimates the PAPR for each transmitted signal using the ratio of the peak power to the average power.
  • Clipping: If the PAPR exceeds the threshold, the signal is clipped to minimize the peak power. This is one of the simplest PAPR mitigation approaches.
  • Packet Transmission: After implementing PAPR mitigation, the packet is routed using the mitigated signal.
  • Traffic Generation: CBR traffic is created among nodes, and PAPR mitigation is applied during each packet transmission.
  1. Running the Simulation
  1. Save the modified wireless-phy.tcl and the TCL script (papr_mitigation.tcl).
  2. Execute the simulation using:

ns papr_mitigation.tcl

  1. Analysing Results
  • After running the simulation, evaluate the trace file (papr_mitigation.tr) to monitor on how PAPR mitigation impacts the transmission.
  • Metrics to evaluate include:
    • PAPR Reduction: evaluate the reduction in PAPR after applying clipping or other approaches.
    • Packet Delivery Ratio: Assess how PAPR mitigation enhances packet delivery.
    • Power Efficiency: Evaluate on how much power efficiency enhance with PAPR mitigation.
  1. Further Enhancements
  • Selective Mapping (SLM): Execute a more advanced PAPR mitigation approaches such as SLM, in which different phase shifts are useful to the signal, and the one with the lowest PAPR is designated.
  • Tone Reservation (TR): Reserve some tones (subcarriers) to minimize PAPR without altering the original data.
  • BER Evaluation: Assess the impact of PAPR mitigation on the Bit Error Rate (BER) and overall transmission quality.

This technique will guide you through the implementation of Network Peak-to-Average Power Ratio (PAPR) Mitigation using ns2 tool and it contains the details regarding the how to setup the simulation, design the network and how to execute the process to perform the results with samples snippets. We intend to expand on how the Network PAPR Mitigation is performed in other simulation settings.

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