Wireless Sensor Networks and MANETs Quiz

Unit 1: Wireless Sensor Networks (WSNs)

• Textbooks:
  • Protocols and Architectures for Wireless Sensor Network, Holger Kerl, Andreas Willig, John Wiley and Sons, 2005
  • Wireless Sensor Networks Technology, Protocols, and Applications, Kazem Sohraby, Daniel Minoli, and TaiebZnati, John Wiley & Sons, 2007
  • Mobile communications, Jochen Schiller, 2nd Edition, Addison wisely, Pearson Education, 2012

Sensor Definition

• Sensor: An electronic device that measures a physical quantity and converts it into a readable signal.

Introduction to Sensor Networks

• WSNs: Networks composed of sensor nodes.
• Sensor Nodes: Nodes capable of sensing and responding to surrounding physical phenomena (e.g., temperature, color, vibration).
• Network Formation: Collectively, multiple sensor nodes form a wireless sensor network (WSN).
• WSN Popularity: WSNs are popular due to diverse applications.

Wireless Sensor Networks

• Network Structure: Consists of numerous densely deployed sensor nodes within an area allowing collaboration.
• Data Transformation: Sensor measurements are transformed into digital signals for analysis.
• Data Transmission: Sensor nodes have limited transmission range and intermediate nodes act as relays.
• Data Transmission Pattern: WSNs use a multi-hop path to send data to sink nodes.

Why WSNs are Needed

• Comprehensive Coverage: Deploying numerous sensors and nodes over a large area provides a comprehensive understanding of the area's occurrences.
• Extended Monitoring: Provides richer sensing coverage across a larger area compared to a single sensor.

WSN Classifications

• Stationary WSNs: Fixed sensor nodes.
• Mobile WSNs: Sensor nodes that can move.

Basic Components of a Sensor Node

• Location Finding System: Used for determining the location of the sensor node.
• Sensing Unit: Contains the sensor for detecting a physical event or quantity.
• Analog-to-Digital Converter (ADC): Converts the physical signal into a digital format.
• Processing Unit: Processes data and controls other units within the node.
• Processor: Executes instructions for data processing.
• Storage: Stores data and instructions.
• Mobilizer: Enables movement if the node is mobile.
• Transceiver: Acts as a communication device for transmitting and receiving data.
• Power Unit: Provides power to the sensor node from external sources or traditional batteries.

Sensor Nodes (Sizes and Shapes)

• Different Types: Sensor nodes come in various sizes and shapes to fit specific application needs.
  • Xbow Mica Mote
  • Eco
  • Dots

Sensor Node Characteristics

• Multifunctional: The number of sensor nodes utilized depends on the application type.
• Short Transmission Range: Nodes have limited transmission distance.
• Operating System (OS): Nodes often utilize Tiny OS (or other similar systems).
• Battery Powered: Nodes typically run on batteries with limited operational life.

WSN Data Flow

• Sources: Sensor node devices collecting data.
• Sinks: Nodes responsible for receiving and processing data.

Event Detection (Examples)

• Multiple Objects: Detects multiple objects in a single space.
• Single Object: Detects a single object through a network of sensors.

Constraints on Sensor Nodes

• Compact Size: Sensor nodes are often smaller than a cubic centimeter.
• Low Power Consumption: Must use low power.
• Unattended Operation: Operate autonomously in locations without human intervention.
• Adaptable Environment: Sensors need to be adaptable to environments.
• Memory Limitations: Typically use flash memory for storage of code and RAM to store data.

Common WSN Challenges

• Scalability: Maintaining adequate service in large networks of nodes, with throughput decreasing as the number of nodes increases.
• Quality of Service (QoS): Guaranteeing bandwidth, latency, jitter, and packet loss parameters.
• Energy Efficiency: Nodes have limited battery life and require energy efficient communication techniques.
• Maintainability: Ability for the system to adapt to changing environmental conditions, failing nodes, new tasks.
• Programmability: Nodes need to be easily reprogrammed to handle evolving tasks and demands.
• Varying Densities: The number of nodes per unit area in a WSN can vary significantly.

WSN Advantages over Wired Networks

• Ease of Deployment: Easy and quick deployment to locations of interest at lower costs than wired networks.
• Extended Range: The ability to replace a single large-scale wired sensor with multiple smaller wireless sensors at the same cost.
• Fault Tolerance: The failure of a single node does not result in a total network outage or significant disruption to overall function as there are other nodes capable of collecting the data.
• Mobility: Ability of sensor nodes to be used in situations requiring mobile deployment.

Ideal WSN Features

• Attribute-based Addressing: Addresses sensors based on descriptive attribute-value pairs (e.g., temperature > 35°C, location= "Dadar").
• Location Awareness: Nodes constantly know their location.
• Time-critical Applications: Sensors must react quickly to environmental changes.
• Query Handling: Users should be able to ask for data from the network.

WSN Application Types

• Event Detection: Identifying specific events.
• Periodic Measurements: Taking measurements at specified intervals.
• Function Approximation: Estimating functions from sensor data.
• Tracking: Monitoring objects or phenomena.

Examples of WSN Applications and Measurements

• Forest Fire Detection: Measuring factors like temperature, humidity, and gases.
• Air Pollution Monitoring: Monitoring the concentrations of dangerous gases.
• Water Quality Monitoring: Measuring factors like temperature, turbidity, and pH.
• Land Slide Detection: Monitoring soil movements for early warning.
• Military Surveillance: Tracking the enemy, monitoring borders, detecting attacks.

Mobile Ad Hoc Networks (MANETs)

• Dynamic Network: Networks formed dynamically by mobile nodes via wireless links.
• No Centralized Infrastructure: Networks operate without fixed or centralized administration or base stations.
• Nodes in Motion: Mobile nodes can move freely.
• Adaptive Topology: Network topology changes frequently as nodes move.
• Internet Connectivity: Can connect to the wider internet.

Ad Hoc Networks Characteristics

• Peer-to-peer Communication: Networks operate on a peer-to-peer basis (e.g., node-to-node).
• Multi-hop Transmission: Data is transferred across multiple sensors called intermediate nodes.
• Store-and-Forward Transmission: Sensor nodes in the middle of data transmission temporarily store data packets so they can transmit the data at a later time towards their intended destination.

Ad Hoc Network Applications

• Tactical Networks: Military communications, automated battlefields.
• Emergency Services: Disaster recovery.
• Educational Settings: Virtual classrooms, conferences, lectures.
• Home and Entertainment Settings: Home/office wireless networks, personal area networking, multi-user games.
• Outdoor Internet Access: Allows for use in areas without traditional wired infrastructure.

WSN Challenges (Overview)

• Infrastructure Limitations: Developing new networks brings design challenges given the limited nature of wireless communications and the tendency for dynamic topologies.
• Dynamic Topology Issues: The dynamic changes in network topologies cause route changes and frequent network partitions leading to packet loss.
• Physical Layer Restrictions: Limited wireless range and broadcast transmission patterns contribute to packet loss during communication.
• Mobile Node Constraints: Limitations of the mobile nodes including limited battery life and capacities impact network performance.

Enabling Technologies for Wireless Sensor Networks

• Hardware Miniaturization: Reduced chip size increases efficiency and decreases costs.
• Processing and Communication: Improvements to processing power and communication capabilities.
• Sensing Equipment: Development of more accurate and efficient sensing equipment.

WSN Clustering

• Data Aggregation: Aggregation of data from multiple sources reduces the amount of data that needs to be transferred, decreasing transmission overhead and energy consumption.
• Cluster Nodes: Grouping sensor nodes into clusters improves network lifetime, optimizes energy management, reduces the load on base stations, and facilitates data routing/aggregation.
• Cluster Head (CH): Node that acts as a coordinator within a cluster, responsible for aggregation, processing, and transmission to the base station.
• Member Nodes (MN): Sensor nodes that contribute to the cluster, responsible for sensing data and forwarding data to the CH.

Clustering Parameters

• Cluster Count/Number of Clusters: The number of WSN clusters can be fixed or variable.
• Cluster Size Uniformity: Clusters can have equal or unequal sizes (even or odd).
• Inter-cluster Routing: Describes the mode of communication between clusters (i.e., single hop or multi-hop).
• Intra-cluster Routing: Describes the mode of communication between member nodes and cluster heads (i.e., single hop or multi-hop).

WSN Clustering Advantages

• Scalability: Ease of adding or removing nodes to the network.
• Data Aggregation: Efficiently reducing redundant data.
• Reduced Load: Reducing the load on the base station by aggregating data at various levels in the WSN structure.
• Improved Energy Efficiency: Reducing the energy used for transmission, aggregation, and other communication processes.
• Collision Avoidance: Ensuring that data from various clusters does not interfere with each other.
• Load Balancing: Distributing load across the network among various nodes to avoid exceeding their resources.
• Fault Tolerance: Enabling the quick recovery from failing sensor nodes by adjusting the clustering method.
• Ensuring QoS: Providing quality and non-redundant data to users.

Sensor Node Hardware and Network Architecture

• Controller: Processes data, manages sensors, and controls behavior.
• Memory: Stores programs, intermediate data and results.
• Sensors and Actuators: Interfaces with the physical environment.
• Communication Device: Enables communication via wireless channels (e.g., radio frequencies).
• Hardware Components (Overview): Includes Memory, Controller, Communication device, Sensors/actuators, and power supply.

Controller Overview

• Core Function: Controls data acquisition from sensors.
• Decision Making: Determines when and where data is transmitted.
• Actuator Control: Controls actuators in the physical environment.
• Program Execution: Executes operating systems, and applications.
• CPU (Central Processing Unit): Responsible for managing various program executions.

Microcontrollers (General Purpose Processors)

• Alternative to General Purpose Processors: Better suited for resource-constrained systems, such as wireless sensor nodes.
• Flexible Communication: Able to connect with other devices.
• Efficient Processing: Designed to perform specific, time-critical signal processing tasks.
• Low Power Consumption: Consumption is lower than general purpose processors.
• Sleep States: Able to reduce power consumption by entering sleep to put the entire controller or specific parts of the controller to sleep when they are not in use.

Microcontroller Example

• Intel StrongARM
• Texas Instruments MSP 430
• Atmel ATmega

Memory

• Random Access Memory (RAM): Used to store intermediate sensor readings, packets from other nodes, and more, but is volatile and loses its content if the power supply is disrupted.
• Read-Only Memory (ROM): Contains static programs that are not meant to change.
• Electrically Erasable Programmable Read-Only Memory (EEPROM): Stores program code and more, and different types of memory are usually used for programs and data.
• Flash Memory: Stores program code, data and can be used as intermediate storage of data when memory in RAM is insufficient or when the power supply of RAM needs to be temporarily shut down.

Communication Device

• Data Exchange: Enables communication between nodes.
• Choices: Radio frequencies, optical communication, and ultrasound, but Radio Frequency communication is the most used.
• High Data Rates: Enables faster transmission of large amounts of data.
• Long range: Enables communication over relatively extended distances.
• Acceptable Errors: Enables tolerance in communication errors.
• Reduced Energy Expenditure: Achieves communication without excessive energy expenditure.
• Wireless Communication Frequencies: WSNs often use frequencies about 433 MHz and 2.4 GHz (and other variations).

Transceivers

• Combined Function: Combines transmitting and receiving processes into a single unit.
• Bit Conversion: Converts bit streams from microcontrollers or byte/frame sequences into radio waves.
• Practical Use: Useful in a variety of applications to handle the full communication process related to WSNs.
• Half-Duplex Operation: Enables sequential sending and receiving to conserve bandwidth during communication.

Sensors and Actuators (Categories)

• Passive Omnidirectional Sensors: Detect physical quantities without intervening with the environment, self-powered.
• Passive Narrow-beam Sensors: Detect physical quantities in a specified direction (e.g., cameras).
• Active Sensors: Sensors that actively probe the environment using emitted energy (e.g., sonar, radar).

Power Supply

• Traditional Batteries: WSNs are often powered by traditional batteries as an initial energy source.
• Energy Scavenging: Provides an additional energy source; methods include solar power, ambient energy (e.g,, thermal, vibrations).

Operating Systems for WSNs

• Tiny OS: Developed at UC Berkeley, a free, open-source operating system designed for WSNs, that supports the NesC programming language.
• Other Supported Operating Systems: Contiki OS, Mantis OS, Nano-RK.

Additional Topics

• Quality of Service (QoS): Describes the performance of a network related to attributes like event detection and reporting probability, event classification, event detection delay, and missing reports (i.e., undelivered reports).
• Energy Efficiency: How much energy is used to send a bit of data.
• Scalability: Maintains performance despite increasing/decreasing the size of the network (related to system growth).
• Robustness: Maintains performance despite errors, failures, or losses in the network.
• Design Principles of WSNs: Outlines distributed organization principles, and in-network processing.
• Data Centricity: Focuses on data in networks and not on sensor nodes acting as the source of data. This is different from other communication models.
• Exploit Location Information: Locating sensors and devices within the network to improve network performance.
• Exploit Activity Patterns: Handling large amounts of data to improve efficiency during sensor activity.
• Exploit Heterogeneity: Handling varied needs and energy usage of varied sensor nodes/devices.
• Gateway Concepts: Enables the ability of WSNs to communicate via external devices for additional functionality and flexibility as part of a larger network (such as the internet), or to the greater community.