How to Implement Network Channel Sensing in NS2
To implement the Network Channel Sensing using NS2, which encompasses simulating the capacity of nodes such as secondary users in cognitive radio networks to identify whether a network channel is being used by key users or is free for the communication. It is specifically significant in cognitive radio and wireless networks that spectrum sensing permits dynamic access to underutilized spectrum. Now, we follow the given procedure to execute the Network Channel Sensing in NS2:
Step-by-Step Implementation:
- Understand the Concept of Network Channel Sensing
In network channel sensing, these nodes are periodically scan the network channels to verify whether they are engaged or free. It is generally complete via mechanisms like:
- Energy detection: Computing the power levels on a channel.
- Pilot-based detection: Identifying the existence of a known signal (pilot signal).
- Cooperative sensing: Numerous nodes collaborate to sense a channel and share the outcomes.
- Set up Multiple Channels in NS2
Primarily, describing several channels in the simulation. If we are functioning with a wireless network, every node will have access to a number of channels, which they can detect.
# Create NS2 simulator instance
set ns [new Simulator]
# Define channels (example: 3 channels)
set channels [list 1 2 3]
- Implement Channel Sensing Logic
Every single node wants to periodically sense the channels. We can make a process to replicate the channel sensing mechanism. This process will verify whether a channel is engaged (e.g., by a primary user) or free.
- a) Energy-Based Channel Sensing
One simplest way to emulate the channel sensing is by verifying the power or activity on a channel (energy detection).
# Define a global variable to represent channel status (0: free, 1: busy)
set channel_busy(1) 0
set channel_busy(2) 0
set channel_busy(3) 0
# Simulate the energy detection mechanism
proc sense_channel {channel_id} {
global channel_busy
# Check if the channel is busy or free
if { $channel_busy($channel_id) == 1 } {
puts “Channel $channel_id is busy.”
return 0 ;# Channel is busy
} else {
puts “Channel $channel_id is free.”
return 1 ;# Channel is free
}
}
This function verifies the status of each channel. In this situation, channel_busy is a global variable, which tracks whether a channel is engaged.
- b) Simulating Primary User Activity
To replicate primary users engaging channels, we can write a function, which periodically allocates a busy status to particular channels. For example, we can mimic primary user traffic that creates channels busy for particular periods.
proc primary_user_activity {channel_id duration} {
global channel_busy
# Mark the channel as busy
set channel_busy($channel_id) 1
puts “Primary user is occupying channel $channel_id”
# Release the channel after the duration
after $duration “set channel_busy($channel_id) 0; puts \”Channel $channel_id is now free\””
}
# Simulate primary user activity on channels
$ns at 5.0 “primary_user_activity 1 5000” ;# Primary user occupies channel 1 at time 5s for 5s
$ns at 10.0 “primary_user_activity 2 8000” ;# Primary user occupies channel 2 at time 10s for 8s
This function replicates primary user activity by marking a channel as busy for a indicated duration.
- Perform Channel Sensing Periodically
These nodes should periodically sense the available channels. We can mimic it by making a function, which acts sensing at regular intervals.
proc periodic_sensing {node_id interval} {
global channels
foreach ch $channels {
set result [sense_channel $ch]
if { $result == 1 } {
puts “Node $node_id: Channel $ch is available for use.”
} else {
puts “Node $node_id: Channel $ch is busy.”
}
}
# Schedule the next sensing event
after $interval “periodic_sensing $node_id $interval”
}
# Start periodic sensing for node 1 every 2 seconds
$ns at 1.0 “periodic_sensing 1 2000”
In this code, periodic_sensing verifies the status of every channel at regular intervals (interval in milliseconds). The node records whether each channel is engage or free.
- Schedule Transmission Based on Channel Sensing Results
When a node senses that a channel is free, it can start the transmission on that channel. The transmission logic can be combined into the sensing procedure.
proc transmit_on_free_channel {node_id} {
global channels
foreach ch $channels {
if { [sense_channel $ch] == 1 } {
puts “Node $node_id is transmitting on channel $ch.”
# Simulate transmission (you can add more logic here)
return $ch ;# Return the selected channel
}
}
return -1 ;# No channel available
}
In this specimen, transmit_on_free_channel is used to detect channels and choose a free channel for transmission. If no free channel is found then it returns -1.
- Simulate Traffic and Transmission
When the channel sensing and selection mechanism is executed, replicate network traffic and schedule transmissions actively depends on the sensing results.
# Attach UDP agent to node and create traffic flow
set udp [new Agent/UDP]
$ns attach-agent $n1 $udp
set null [new Agent/Null]
$ns attach-agent $n2 $null
$ns connect $udp $null
# Start transmission on a free channel
set selected_channel [transmit_on_free_channel 1]
if { $selected_channel != -1 } {
puts “Node 1 is using channel $selected_channel”
set cbr [new Application/Traffic/CBR]
$cbr set packetSize_ 1000
$cbr set interval_ 0.05
$cbr attach-agent $udp
$ns at 2.0 “$cbr start”
} else {
puts “No available channel for Node 1 at this time.”
}
The above code mimics UDP traffic from the nodes node n1 to node n2. The transmission begins only if a free channel is found while sensing.
- Logging and Tracing Sensing and Transmission
We can record the outcomes of channel sensing and transmission by using NS2’s trace functionality.
set tracefile [open “channel_sensing_trace.tr” w]
$ns trace-all $tracefile
# Log the sensing results
proc log_sensing {node_id channel result} {
global tracefile
if { $result == 1 } {
puts $tracefile “Node $node_id sensed channel $channel as free.”
} else {
puts $tracefile “Node $node_id sensed channel $channel as busy.”
}
}
We can use this process to record sensing results for future analysis.
- Analyse Sensing Performance
We can estimate the outcomes by reviewing the trace files or using a visualization tool such as xgraph, after running the simulation. Important performance metrics to assess contain:
- Channel utilization: Percentage of time channels were used.
- Accuracy of sensing: How successfully the sensing mechanism senses channel availability.
- Throughput: Amount of data effectively transmitted.
- Delay: Time among sensing and successful transmission.
We conducted a detailed procedure on the Network Channel Sensing, with implementation and analysed via the simulation platform NS2. We will explore deeper into this concept through the use of appropriate simulation tools.
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