How to Implement Dynamic Spectrum Access in NS2
To implement the Dynamic Spectrum Access (DSA) in NS2, which are vital components in a cognitive radio network with secondary users are granted to access unused spectrum in a devious method without interrupting with main users.
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You need to follow these provided steps below:
Step-by-Step Implementation:
- Understand Dynamic Spectrum Access (DSA) in NS2
In DSA, the network nodes (secondary users) must accomplish spectrum sensing, detecting existed channels, and then dynamically shift to these channels while evading interruptions with primary users. Executing DSA encompasses simulating spectrum sensing, spectrum distribution, and handover amongst various channels.
- Modify NS2 for Cognitive Radio Network (CRN) Simulation
NS2 does not have built-in support for cognitive radio or DSA, so you’ll need to alter it. Numerous extensions have been designed for NS2 to support CRN and DSA like:
- Cognitive Radio Cognitive Network (CRCN) simulator
- CogNS (an NS2 extension for cognitive radio)
These tools offer basic frameworks for accomplishing cognitive radio concepts in NS2.
- Install CRCN or CogNS for NS2
Start by installing the cognitive radio extension for NS2. Refer the below sample of how to set up CRCN:
- Download the CRCN patch from the official repository.
- Apply the patch to your NS2 installation.
- Recompile NS2 to add cognitive radio functionalities.
Once you have installed CRCN, you can begin using its cognitive radio modules that has spectrum sensing, dynamic spectrum access, and spectrum handoff.
- Define Spectrum Bands
In DSA, you will need to set up multiple spectrum bands (channels) that secondary users can dynamically switch among. In NS2, Simulate these several bands by altering the PHY (physical) layer.
set channels [list 1 2 3 4 5] ;# Define 5 spectrum bands for dynamic access
- Implement Spectrum Sensing
Spectrum sensing permits secondary users to identify either a particular channel is being used by a primary user. This can be accomplished by occasionally observing the channel to verify for behaviors.
proc sense_channel {channel_id} {
# Simulate sensing the channel (could be based on signal strength or packet reception)
if { [channel_busy $channel_id] == 1 } {
puts “Channel $channel_id is busy.”
return 0
} else {
puts “Channel $channel_id is free.”
return 1
}
}
In this code, channel_busy is a function that defines whether a channel is currently engaged by a primary user.
- Implement Spectrum Decision & Allocation
Once a secondary user senses the spectrum, it needs to decide which channel to use. This decision could be depends on various categories like signal quality, channel availability, or user priority.
proc allocate_channel {node_id} {
global channels
foreach ch $channels {
if { [sense_channel $ch] == 1 } {
puts “Node $node_id is switching to channel $ch”
return $ch
}
}
return -1 ;# No channel available
}
The function allocate_channel allows a node to shift to an existed channel.
- Dynamic Spectrum Handoff
If a primary user reclaims a channel that is presently being used by a secondary user, the secondary user must swing to a various channel. This process is called spectrum handoff.
proc spectrum_handoff {node_id current_channel} {
global channels
set new_channel [allocate_channel $node_id]
if { $new_channel != -1 } {
puts “Node $node_id is performing spectrum handoff from $current_channel to $new_channel.”
return $new_channel
} else {
puts “Node $node_id cannot find a new channel. Waiting…”
return $current_channel
}
}
The function spectrum_handoff performs the process of discovering and shifting to a new channel if the current one is reclaimed by a primary user.
- Simulation of Primary Users
Imitate primary users by designing nodes that once in a while transmit on certain channels. These nodes should have priority access to the spectrum.
proc primary_user_traffic {node_id channel_id} {
# Simulate traffic from a primary user on a given channel
puts “Primary user $node_id is using channel $channel_id.”
set channel_busy($channel_id) 1
# Transmission lasts for 5 seconds
after 5000 “set channel_busy($channel_id) 0”
}
This makes sure that when a primary user is transmitting, secondary users are forced to vacate the channel and perform a spectrum handoff.
- Logging and Results
You can use NS2’s tracing potentials to store the performance of your DSA implementation. This contains:
- Spectrum handoff events
- Channel consumption by secondary users
- Primary user intrusion avoidance
- Spectrum sensing precision
Example of tracing:
set tracefile [open “dsa_trace.tr” w]
proc log_handoff {node_id old_channel new_channel} {
global tracefile
puts $tracefile “$node_id performed handoff from $old_channel to $new_channel”
}
- Analyze Performance
Once the simulation is done, assess the outcomes in terms of:
- Channel utilization by secondary users
- Handoff delay because spectrum switching
- Interference avoidance with primary users
- Throughput or latency improvement for secondary users
Plot the results by using the trace file analysis or visualization tools like xgraph or MATLAB.
Example Simulation Code (TCL)
# Define channels and nodes
set channels [list 1 2 3 4 5]
set ns [new Simulator]
set tracefile [open “dsa_trace.tr” w]
# Define primary users
proc primary_user_traffic {node_id channel_id} {
puts “Primary user $node_id is using channel $channel_id.”
set channel_busy($channel_id) 1
after 5000 “set channel_busy($channel_id) 0”
}
# Define dynamic spectrum allocation for secondary users
proc allocate_channel {node_id} {
global channels
foreach ch $channels {
if { [sense_channel $ch] == 1 } {
puts “Node $node_id is switching to channel $ch”
return $ch
}
}
return -1
}
# Example of node 1 dynamically accessing spectrum
set channel1 [allocate_channel 1]
puts “Node 1 assigned to channel $channel1”
# Define handoff mechanism if a channel becomes busy
proc spectrum_handoff {node_id current_channel} {
global channels
set new_channel [allocate_channel $node_id]
if { $new_channel != -1 } {
puts “Node $node_id is performing handoff from $current_channel to $new_channel.”
return $new_channel
} else {
puts “Node $node_id cannot find a new channel. Waiting…”
return $current_channel
}
}
# Close the tracefile
close $tracefile
We had clearly understood the concept which is essential for the implementation regarding Dynamic Spectrum Access in the simulation set up with the help of ns2 simulator by installing the Cognitive Radio Cognitive Network (CRCN) simulator and CogNS into the network.