How to Implement Network Nearest Antenna Selection in NS2

To implement Network Nearest Antenna Selection in NS2, we need to replicate on how nodes choose the nearest antenna or base station/access point according to proximity or signal strength. This technique is usually used in cellular networks, wireless sensor networks, and wireless LANs. The main concept is to estimate the distance among nodes and antennas and enthusiastically connect the nodes to the nearest antenna as they move.

The below is a brief procedure to implement the Nearest Antenna Selection in NS2:

Step-by-Step Implementation:

  1. Understanding nearest Antenna Selection
  • Nearest Antenna Selection: Nodes (mobile users, sensors, etc.) choose the nearest antenna (access point or base station) to associate to base on their current position or signal strength.
  • Goal: The goal is to enhance connectivity by minimizing latency, enhancing signal strength, and reducing packet loss by make sure that nodes connect to the most optimal (nearest) antenna.
  1. Basic Steps for Implementation
  1. Define the Antennas (Base Stations): Place antennas (access points or base stations) at fixed positions in the network.
  2. Node Movement and Distance Calculation: execute a mechanism in which nodes move via the network and estimate the distance among the node and each antenna.
  3. Nearest Antenna Selection: Nodes choose the nearest antenna according to the distance or signal strength and re-evaluate the connection periodically.
  1. TCL Script to Implement nearest Antenna Selection

Step 1: Define Antennas in the Network

In the simulation, describe several antennas (or access points) at fixed positions. These antennas will serve as the connection points for the mobile nodes.

# Create a simulator instance

set ns [new Simulator]

# Create trace and nam files for output

set tracefile [open nearest_antenna_selection.tr w]

set namfile [open nearest_antenna_selection.nam w]

$ns trace-all $tracefile

$ns namtrace-all $namfile

# Define the network topology (e.g., 1000×1000 meters)

set topo [new Topography]

$topo load_flatgrid 1000 1000

# Create the General Operations Director (GOD)

set god_ [create-god 10]  ;# 10 nodes in the network

# Define the number of mobile nodes and antennas (base stations)

set opt(nn) 10      ;# Number of mobile nodes

set opt(antennas) 3 ;# Number of antennas

# Define fixed positions for antennas

for {set i 0} {$i < $opt(antennas)} {incr i} {

set antenna_($i) [$ns node]

set x [expr 300 * $i + 100]  ;# Spread antennas evenly in the x-direction

set y [expr 500]             ;# Position antennas at y = 500

$antenna_($i) set X_ $x

$antenna_($i) set Y_ $y

$antenna_($i) set Z_ 0.0

# Optionally mark antennas in NAM file for visualization

$ns at 0.1 “$antenna_($i) color red”

}

Step 2: Implement the Nearest Antenna Selection Logic

The core logic for choosing the nearest antenna is based on estimating the distance among the node and each antenna. Nodes enthusiastically connect to the nearest antenna based on proximity.

# Function to calculate Euclidean distance between two points (x1, y1) and (x2, y2)

proc calc_distance {x1 y1 x2 y2} {

return [expr sqrt(($x1 – $x2) * ($x1 – $x2) + ($y1 – $y2) * ($y1 – $y2))]

}

# Function for a node to select the nearest antenna based on distance

proc select_nearest_antenna {node} {

global antenna_ opt

set node_x [$node set X_]

set node_y [$node set Y_]

set nearest_antenna -1

set min_distance 100000  ;# Initialize with a large value

# Iterate through all antennas and calculate the distance

for {set i 0} {$i < $opt(antennas)} {incr i} {

set antenna_x [$antenna_($i) set X_]

set antenna_y [$antenna_($i) set Y_]

set distance [calc_distance $node_x $node_y $antenna_x $antenna_y]

if {$distance < $min_distance} {

set min_distance $distance

set nearest_antenna $i

}

}

# Connect the node to the nearest antenna (optionally change its destination)

if {$nearest_antenna != -1} {

# Mark the selected antenna in NAM for visualization (optional)

$node color blue

# Move the node towards the nearest antenna

set nearest_x [$antenna_($nearest_antenna) set X_]

set nearest_y [$antenna_($nearest_antenna) set Y_]

$node setdest $nearest_x $nearest_y 10.0  ;# Move with speed 10.0 m/s

}

}

Step 3: Periodically Check and Re-Evaluate the Nearest Antenna

To make sure nodes continuously associate to the nearest antenna as they move, the select_nearest_antenna function should be appealed periodically.

# Function to periodically move nodes and re-evaluate the nearest antenna

proc move_nodes_and_select_antenna {} {

global ns node_ opt

for {set i 0} {$i < $opt(nn)} {incr i} {

# Move the node to a random destination

set x [expr rand() * 1000]

set y [expr rand() * 1000]

$node_($i) setdest $x $y 10.0  ;# Set random destination with speed 10.0

# Recalculate and select the nearest antenna

$ns at 1.0 “select_nearest_antenna $node_($i)”

}

# Re-evaluate every few seconds

$ns at 5.0 “move_nodes_and_select_antenna”

}

# Initial call to move nodes and select antennas

$ns at 0.1 “move_nodes_and_select_antenna”

Step 4: Set Up Traffic Generation

To mimic traffic among the nodes and the antennas, we will generate agents for data transmission.

# Traffic generation for nodes

proc start_traffic {} {

global ns node_ opt

# Create UDP agents and attach them to nodes

for {set i 0} {$i < $opt(nn)} {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 node to the nearest antenna

set nearest_antenna [select_nearest_antenna $node_($i)]

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

}

}

# Start traffic at 2.0 seconds

$ns at 2.0 “start_traffic”

Step 5: End the Simulation

Describe the termination of the simulation and run the script.

# End simulation procedure

proc finish {} {

global ns tracefile namfile

close $tracefile

close $namfile

$ns halt

}

# Run the simulation

$ns at 100.0 “finish”

$ns run

  1. Explanation of the Script
  • Antennas: We position antennas (or base stations) at fixed points in the network, and nodes will occasionally connect to the nearest one.
  • Nearest Antenna Selection: The select_nearest_antenna function calculates the Euclidean distance among the node and each antenna. The node enthusiastically associates to the nearest antenna.
  • Node Movement: Nodes move to random locations, and the nearest antenna is re-measured intermittently.
  • Traffic Generation: The script creates CBR traffic among the nodes and the designated antennas using UDP agents.
  1. Running the Simulation
  • Save the TCL script as nearest_antenna_selection.tcl.
  • Execute the simulation using the command:

ns nearest_antenna_selection.tcl

  1. Analysing Results
  • Use the generated trace file (nearest_antenna_selection.tr) and the NAM output file (nearest_antenna_selection.nam) to envision and measure the simulation.
  • Metrics to evaluate include:
    • Packet Delivery Ratio: validate on how well the nodes deliver packets to the nearest antenna.
    • Latency: evaluate the delay triggered by connecting to distant antennas or frequent switching among antennas.
  1. Further Enhancements
  • Dynamic Signal Strength Evaluation: Rather than distance, execute nearest antenna selection based on real-time signal strength measurements.
  • Handoff Mechanisms: Execute handoff protocols to mimic the process of switching from one antenna to another when a node moves.
  • Energy Efficiency: In wireless sensor networks, measure the energy consumption of nodes when choosing antennas.

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