How to Implement TSCH Sensors Communication in NS2

To implement Time-Slotted Channel Hopping (TSCH) sensors communication in NS2 has needs to expanding the default MAC layer protocols in NS2. TSCH is part of the IEEE 802.15.4e standard and is usually used in low-power, high-reliability communication networks like wireless sensor networks (WSNs) and industrial Internet of Things (IoT). TSCH improves interaction by using time-slotted access to the medium integrated with channel hopping to enhance reliability and minimize interference.

Here’s a guide to deploy TSCH-based communication for sensor networks in NS2:

Step-by-Step Implementation:

  1. Understand the Key Concepts of TSCH
  • Time-Slotted Communication: Time is divided into slots, and each node transmits only during its allocated slots.
  • Channel Hopping: Nodes interact on various channels for each time slot that diminish interference and multipath fading.
  • Scheduling: A key feature of TSCH is the schedule, that describes defines and where (on which frequency) each node should transmit and receive.
  • Superframes: A sequence of time slots is organized into super frames that repeat periodically.
  1. Extend the MAC Layer in NS2

While NS2 does not have a native TSCH implementation, we will need to expand the MAC layer. The steps include:

  • Adjusting the IEEE 802.15.4 MAC layer or generating a new MAC layer to support time slots and channel hopping.
  • Managing slot allocation, synchronization, and hopping among frequencies according on predefined schedules.

Key Files to Modify:

  • MAC Layer: We will need to adapt the MAC layer to contain time-slot and channel-hopping functionalities. The MAC layer in NS2 is usually located in mac/mac-802_15_4.cc and mac/mac-802_15_4.h if we are extending from the existing IEEE 802.15.4 protocol.
  • Packet Handling: we will also need to adjust how packets are managed to make sure that they are sent and received only in their distributed time slots.
  1. Time Slot Allocation and Superframe Setup
  • Superframe Structure: Describe a superframe structure in MAC protocol that consists of multiple time slots.
  • Time Slot Assignment: Each node should be distributed particular slots for transmission and reception. This can be completed using a predefined schedule or dynamically during the simulation.
  • Synchronization: Nodes must be synchronized to make sure they follow the same schedule.

Example code to define a superframe and time slots:

// Define superframe parameters

int numSlots = 10;  // Number of time slots in a superframe

int slotDuration = 10;  // Duration of each time slot in milliseconds

// Function to check if it’s the node’s time slot for transmission

bool isMyTimeSlot(int currentSlot, int nodeId) {

// Simple static assignment: nodeId determines the time slot

return (currentSlot % numSlots) == nodeId;

}

  1. Implement Channel Hopping

Channel hopping is a vital feature of TSCH. In each time slot, the nodes interacts on a different frequency to prevent interference.

  • Frequency List: Describe a set of frequencies that will be used for hopping.
  • Hopping Pattern: Execute a hopping sequence, in which each time slot uses a different channel.

Example hopping pattern code:

// Define frequency channels for hopping

int frequencies[] = {11, 12, 13, 14, 15};  // IEEE 802.15.4 channels

// Function to get the frequency for the current time slot

int getFrequencyForSlot(int slotNumber) {

return frequencies[slotNumber % (sizeof(frequencies) / sizeof(frequencies[0]))];

}

We will need to adjust the packet transmission function to use the proper frequency for each time slot.

  1. Handle Synchronization

TSCH needs a tight synchronization among nodes to make sure they transmit and receive at the correct times. We can execute synchronization mechanisms by sending beacons or using existing clock synchronization protocol such as RPL or IEEE 802.15.4 beaconing.

Example synchronization logic:

// Synchronize nodes based on a global time reference

void synchronizeNodes(int globalTime) {

// Adjust node’s local clock to match the global time

nodeClock = globalTime;

}

  1. Implement Packet Scheduling and Handling

Adapt how packets are queued and transmitted to make sure they are sent during the proper time slot. We can add logic to the MAC layer to manage the queue and validate whether it’s the proper time to transmit according to the slot schedule.

Example:

// Transmit packet only in the correct time slot

void MacTSCH::sendPacket() {

int currentSlot = getCurrentSlot();

if (isMyTimeSlot(currentSlot, nodeId)) {

// It’s our slot, send the packet

transmit(packet);

} else {

// Wait for the next time slot

scheduleNextSlot();

}

}

  1. Tcl Script for TSCH Simulation

In the Tcl simulation script, configure the nodes and setup the MAC layer to use the custom TSCH protocol. We can also describe traffic generation and node mobility.

Example Tcl script:

# Create the simulator instance

set ns [new Simulator]

# Create nodes

set node1 [$ns node]

set node2 [$ns node]

# Define a wireless channel for communication

set wireless_channel [new Channel/WirelessChannel]

# Configure MAC to use the TSCH protocol

$node1 set mac_ [new Mac/TSCH]

$node2 set mac_ [new Mac/TSCH]

# Attach agents and traffic sources

set udp1 [new Agent/UDP]

set udp2 [new Agent/UDP]

$ns attach-agent $node1 $udp1

$ns attach-agent $node2 $udp2

# Set up CBR traffic source

set cbr [new Application/Traffic/CBR]

$cbr set packetSize_ 100

$cbr set rate_ 1Mb

$cbr attach-agent $udp1

# Schedule packet transmission

$ns at 1.0 “$cbr start”

# Run the simulation

$ns run

  1. Performance Evaluation
  • Throughput: Evaluate the throughput in each time slot.
  • Latency: Assess how time-slot allocation and hopping impacts end-to-end delay.
  • Packet Delivery Ratio: validate on how many packets successfully reach their destination, particularly in the presence of interference or mobility.
  1. Advanced Features
  • Dynamic Scheduling: Execute dynamic scheduling techniques in which nodes negotiate or modify their time slots according on traffic conditions or priorities.
  • Energy Efficiency: While TSCH is used in low-power networks, incorporate power-saving mechanisms, like switching nodes to low-power states when they are not scheduled to transmit or receive.

In the above following procedures is often support to execute the Time-Slotted Channel Hopping in ns2 that enhance reliability and minimize interference. We also provide additional information regarding TSCH sensor communication performance in other simulation scenarios.

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