How to Implement Uplink Synchronization in NS2
To implement uplink synchronization in NS2, has need to mimic the process in which mobile nodes synchronize their transmissions with a base station to prevent interference and signal overlap in a cellular-like network. Uplink synchronization is especially pertinent in systems such as LTE and 5G, in which multiple users transmit to a base station, and timing needs to be adapted to make sure signals reach the base station at the same time.
NS2 doesn’t natively support the cellular uplink synchronization as seen in LTE; however we can estimate this behaviour by controlling the timing of packet transmissions from mobile nodes to the base station.
Here’s a step-by-step guide to implementing uplink synchronization in NS2:
Step-by-Step Implementation:
- Basic Setup: Base Station and Mobile Nodes
Initially, configure the simulation environment with a base station (eNodeB) and multiple mobile nodes (UEs). We will describe wireless links among the base station and the mobile nodes to replicate uplink communication.
# Create an NS2 simulator instance
set ns [new Simulator]
# Create trace file to log the simulation
set tracefile [open “uplink_sync_trace.tr” w]
$ns trace-all $tracefile
# Create a base station (eNodeB)
set base_station [$ns node]
# Create mobile nodes (UEs)
set ue1 [$ns node]
set ue2 [$ns node]
set ue3 [$ns node]
# Define wireless duplex links between base station and mobile nodes
# Assuming 1Mb bandwidth and 10ms delay
$ns duplex-link $base_station $ue1 1Mb 10ms DropTail
$ns duplex-link $base_station $ue2 1Mb 10ms DropTail
$ns duplex-link $base_station $ue3 1Mb 10ms DropTail
- Simulate Uplink Synchronization with Timing Advance
In LTE, Timing Advance (TA) is used to modify the transmission timing of user equipment (UE) because that all signals from diverse UEs arrive at the base station in sync. To replicate this in NS2, we can establish latency according to the distance of the UE from the base station, and modify packet transmission times consequently.
# Define a procedure to adjust the timing advance
proc adjust_timing_advance {ue distance} {
global ns
set ta [expr $distance / 1000.0] ;# Simple formula to calculate timing advance based on distance
$ns at $ta “$ue set_transmit_time” ;# Adjust the transmit time of the UE
}
proc set_transmit_time {} {
# This procedure simulates the UE adjusting its transmission timing
# based on timing advance calculated earlier
puts “Uplink transmission synchronized.”
}
# Apply timing advance to UEs based on their distances from the base station
adjust_timing_advance $ue1 500 ;# Simulate UE1 located 500 meters away
adjust_timing_advance $ue2 800 ;# Simulate UE2 located 800 meters away
adjust_timing_advance $ue3 1200 ;# Simulate UE3 located 1200 meters away
- Create Uplink Traffic for Each UE
Next, generate the traffic sources and sinks to replicate uplink data transmissions from the UEs to the base station. We can use UDP for traffic generation to mimic data transfer in the uplink.
# Create UDP agents for uplink traffic
set udp1 [new Agent/UDP]
set udp2 [new Agent/UDP]
set udp3 [new Agent/UDP]
# Attach the UDP agents to the UEs
$ns attach-agent $ue1 $udp1
$ns attach-agent $ue2 $udp2
$ns attach-agent $ue3 $udp3
# Create traffic sources (CBR) for each UE
set cbr1 [new Application/Traffic/CBR]
$cbr1 attach-agent $udp1
$cbr1 set packetSize_ 512
$cbr1 set rate_ 100Kb ;# Uplink rate for UE1
set cbr2 [new Application/Traffic/CBR]
$cbr2 attach-agent $udp2
$cbr2 set packetSize_ 512
$cbr2 set rate_ 150Kb ;# Uplink rate for UE2
set cbr3 [new Application/Traffic/CBR]
$cbr3 attach-agent $udp3
$cbr3 set packetSize_ 512
$cbr3 set rate_ 200Kb ;# Uplink rate for UE3
# Create sinks at the base station to receive the uplink traffic
set null1 [new Agent/Null]
$ns attach-agent $base_station $null1
$ns connect $udp1 $null1
set null2 [new Agent/Null]
$ns attach-agent $base_station $null2
$ns connect $udp2 $null2
set null3 [new Agent/Null]
$ns attach-agent $base_station $null3
$ns connect $udp3 $null3
- Simulating Synchronization Behavior
To replicate the synchronization behaviour, we can coordinate the initial times of the traffic sources (CBR) according to the calculated timing advance for each UE. This will replicate uplink synchronization, in which signals from diverse UEs reach the base station at the same time.
# Simulate synchronized uplink transmission by starting traffic at calculated times
# UE1 starts uplink transmission
$ns at 1.0 “$cbr1 start”
$ns at 5.0 “$cbr1 stop”
# UE2 starts uplink transmission after adjusting for timing advance
$ns at 1.0 “$cbr2 start”
$ns at 5.0 “$cbr2 stop”
# UE3 starts uplink transmission after adjusting for timing advance
$ns at 1.0 “$cbr3 start”
$ns at 5.0 “$cbr3 stop”
- Monitoring and Tracing
To monitor the impacts of uplink synchronization, we can allow queue tracing to log the traffic and timing of transmissions at the base station. This will support you to learn on how packets from diverse UEs arrive at the base station.
# Enable queue tracing for uplink transmissions
$ns trace-queue $ue1 $base_station [open “queue1.tr” w]
$ns trace-queue $ue2 $base_station [open “queue2.tr” w]
$ns trace-queue $ue3 $base_station [open “queue3.tr” w]
# Run the simulation
$ns at 6.0 “finish”
# Define finish procedure
proc finish {} {
global ns tracefile
$ns flush-trace
close $tracefile
exit 0
}
# Start the simulation
$ns run
- Post-Simulation Analysis
After the simulation, we can evaluate the trace files to see if the uplink synchronization worked as expected. Look at the times when the packets from diverse UEs arrive at the base station and validate for synchronization.
Here, we clearly understood the basic implementation procedures for uplink synchronization that were securely implemented using the ns2 tool. We also outline additional information about how the uplink synchronization performs in diverse simulation tool.
Keep in touch with ns2project.com as we execute your Uplink Synchronization projects in ns2 tool and continue network performance monitoring. We work on LTE and 5G related projects for you.