The document discusses the hardware components and architecture of sensor nodes. It describes the main components as the controller module, memory module, communication module, sensing modules, and power supply module. The controller is the core and processes data from sensors. Memory stores programs and data. The communication device allows nodes to exchange data wirelessly. Sensors interface with the physical environment. Power is stored and replenished through batteries or energy scavenging from the environment. TinyOS was developed as an operating system for sensor networks since traditional OSes were not suitable due to constraints like limited memory and power.

1. T.Y.B.Sc.C.S
Chapter 2 : Sensor Node Hardware and Network
Architecture
By
Mrs.Vidhi Khedekar
Assistant Professor,
Dnyandeep College of Science and Commerce,
Morvande-Boraj,Khed.

2.  Agenda:
1. What is Single-node architecture?
2. What are the hardware components & design constraints?
3. Introduction to TinyOS and nesC.

3.  A sensor is a device that detects and responds to some type of input from the physical
environment.
 The specific input could be light, heat, motion, moisture, pressure, or any one of a great number
of other environmental phenomena.
 The output is generally a signal that is converted to human-readable display at the sensor
location or transmitted electronically over a network for reading or further processing.
Example:
 In a mercury-based glass thermometer, the input is temperature. The liquid contained expands
and contracts in response, causing the level to be higher or lower on the marked gauge, which is
human-readable.
Sensor node:
 A sensor node, also known as a mote, is a node in a sensor network that is capable of performing
some processing, gathering sensory information and communicating with other connected nodes
in the network.
 A mote is a node but a node is not always a mote.

4.  Main Architecture of Sensor Node:
The main architecture of sensor node includes
following components:
 Controller module
 Memory module
 Communication module
 Sensing modules
 Power supply module

5. Main components of a WSN node :
 Controller-
 Processes all relevant data
 Capable of executing arbitrary code
 Communication device(s) -
 Device for sending and receiving data over a wireless channel
 Sensors/actuators -
 The actual interface to the physical world;
 Devices that can observe or control physical parameters of the environment.
 Memory -
 Stores data and programs
 Often different types of memory are used for programs and data
 Power supply -
 Some form of batteries to provide energy
 Sometime recharging by obtaining energy from the environment,
e.g. solar cells

6.  Controller-
 The controller is the core of a wireless sensor node, it process all relevant data, capable of
executing arbitrary code.
 It has to execute various programs, hence it is a Central Programming Unit (CPU) of the node.
 These,
-Collects data from the sensors
-Process the collected data
-Decides when and where to send the data
-Receives data from the other sensor nodes
-Decides on the actuator’s behavior

7.  Microcontroller:
◦ For the sensor nodes mostly microcontroller are used
◦ It is a general purpose processor, optimized for embedded applications, low power consumption
◦ Examples
 Intel StrongARM
- High-end processor often used in PDAs
- SA-1100 model: 32-bit RISC core, running @206MHz
 Texas Instruments MSP 430
- Intended for usage in embedded applications
- 16-bit RISC core, up to 4 MHz, 2-10 kB RAM, several DACs, RT clock
 Digital signal processor(DSPs)
- These are familiar because of their architecture and instruction set for processing large amount
of vector data
 FPGA(Field Programmable Gate Arrays)
- Flexible, can be reprogrammed to adapt to a changing set of requirements.
- But take time and energy.
 ASIC(Application Specific Integrated Circuit)
- These are used only when peak performance is needed
- Ex: High speed routers and switches

8.  Memory is required to store the programs and intermediate data; usually different types of
memory are used for program and data.
 RAM (Random Access Memory)
- To store intermediate sensor readings, packets from other nodes and so on.
- Is fast, but looses content if power supply is interrupted
 ROM (Read-Only Memory)
- To store fixed programs; not writeable
 EEPROM (Electrically Erasable Programmable)or Flash Memory
- Programs are stored
- Enables overwriting of data
- Can be used as intermediate storage if RAM is insufficient or if the RAM’s power supply should
be turned-off
- BUT: long read/write access delays, high energy requirement

9.  To turn nodes into a network a device is required for sending and receiving information over the
wireless channel.
 Communication device is used to exchange data between individual nodes.
 Choices of transmission medium:
 Wireless communication chooses any one of the following as transmission medium
- Radio frequencies(most used in WSN)
- Optical communication
- Ultra sound
- Magnetic inductance(less used)
 Among the above Radio Frequency(RF) is best because it provides,
-Long range
-High data rates
-Acceptable error rates at reasonable energy expenditure
-Does not require line of sight between sender and receiver

10.  - Both a transmitter and a receiver are required in a sensor node
- For practical purposes these two tasks are often combined in one entity, the so called transceiver
- It convert a bit stream coming from a microcontroller(or a sequence of bytes or frames) and
convert them to and from radio waves.
- A range of low cost transceiver is commercially available.
- It includes all the circuitry required for transmitting and receiving modulation, demodulation,
amplifiers, mixers, filters and so on.
- Usually it uses half duplex mode because transmitting and receiving at the same time is
impractical in the wireless medium
Bit Stream Radio Waves
Radio
Transceiver

11.  Transceivers can be put into different operational states:
 Transmit
- In this state transceiver is active and the antenna radiates energy
 Receive
- In this state receive part is active
 Idle
- In this state transceiver ready to receive but currently no receiving
 Sleep
- Significant parts of the receiver are switched off
 A fairly common structure of transceivers is into the Radio Frequency (RF) front end and the
baseband part:
- The radio frequency front end performs analog signal processing in the actual radio frequency
band.
- The baseband processor performs all signal processing in the digital domain and communicates
with a sensor node’s processor or other digital circuitry.

12.  Some important elements of an RF front ends architecture are:
- The Power Amplifier (PA) accepts up converted signals from the IF or baseband part and
amplifies them for transmission over the antenna.
- The Low Noise Amplifier (LNA) amplifies incoming signals up to levels suitable for further
processing without significantly reducing the SNR.

13.  The actual interface to the physical world: The devices that can observe or control physical
parameters of the environment.
 Sensors can be roughly categorized into three categories:
 Passive, omnidirectional sensors
 These sensors can measure a physical quantity at the point of the sensor node without actually
manipulating the environment by active probing -In this sense, they are passive.
 Passive, narrow-beam sensors
 These sensors are passive as well, but have a well-defined notion of direction of measurement.
 A typical example is a camera, which can “take measurements” in a given direction, but has to be
rotated if need be.
 Active sensors
 This last group of sensors actively probes the environment.
 For example, a sonar or radar sensor or some types of seismic sensors, which generate shock waves
by small explosions.
 Actuator:
 a device that converts an electrical signal to a physical output
 to open or close a switch or a relay or to set a value in some way. Whether this controls a motor, a
light bulb, or some other

14. There are essentially two aspects:
◦ First, storing energy and providing power in the required form;
◦ Second, attempting to replenish(refill) consumed energy by “scavenging” it from some node-external
power source over time.
1.Storing energy :Batteries
 Traditional batteries: The power source of a sensor node is a battery, eighter non-
rechargeable(Primary) or rechargeable (Secondary).
 Upon these batteries the requirements are
o Capacity
o Capacity under load
o Self-discharge
o Efficient recharging
o Relaxation
o DC-DC conversion: Unfortunately, batteries alone are not sufficient as a direct power source for a
sensor node.
 One typical problem is the reduction of a battery’s voltage as its capacity drops. Consequently, less
power is delivered to the sensor node’s circuits, – a node on a weak battery will have a smaller
transmission range than one with a full battery.

15.  For this energy scavenging is used which is the process of recharging the battery with energy
gathered from the environment like solar cells or vibration-based power generation.
1. Photovoltaics
◦ The well-known solar cells can be used to power sensor nodes
2. Temperature gradients
◦ Differences in temperature can be directly converted to electrical energy.
3. Vibrations
◦ General form of mechanical energy is vibrations.
4. Flow of air/liquid
◦ Another often-used power source is the flow of air or liquid in wind mills or turbines.
◦ The challenge here is again the miniaturization, but some of the work on millimeter scale.

16. • Why was TinyOS needed?
• Introduction to TinyOS
• Goals/Objectives behind TinyOS
• Requirements of WSN for Operating System
• TinyOS as a Solution
• TinyOS Model
▫ Data Model
▫ Thread Model
▫ Programming Model
▫ Component Model
▫ Network Model
• Example Application

17.  Problems with traditional OS
◦ Multithreaded Architecture not useful
◦ Large Memory Footprint
◦ Does not help to conserve energy and power
 Requirements for Wireless Sensor Networks
◦ Efficient utilization of energy and power
◦ Small Footprint
◦ Should support diversity in design and usage
◦ More emphasis on Concurrent execution

18.  TinyOS began as a collaboration between University of California, Berkeley and Intel Research.
 It is a free open source operating system designed for wireless sensor networks.
 It is an embedded operating system written in NesC
 It features a component based architecture.
TinyOS as a Solution
• Component based architecture allows frequent changes while still keeping the size of code
minimum.
• Event based execution model means no user/kernel boundary and hence supports high
concurrency.
• It is power efficient as it makes the sensors sleep as soon as possible.
• Has small footprint as it uses a non-preemtable FIFO task scheduling.

19. • Static Memory Allocation
▫ No Heaps or any other dynamic
structures used.
▫ Memory requirements determined
at compile time.
This increases the runtime efficiency.
• Global variables
▫ Allocated on per frame basis.
• Local Variables
▫ Saved on the stack
▫ Defined in the function/method

20. • Power-Aware Two-levels Scheduling
▫ Long running tasks and interrupt events
▫ Sleep unless tasks in queue, wakeup on event
• Tasks
▫ Time-flexible, background jobs
▫ Atomic with respect to other tasks
▫ Can be preempted by events
• Events
▫ Time-critical, shorter duration
▫ Last-in first-out semantic (no priority)
▫ Can post tasks for deferred execution

21.  Separation construction/composition
 Construction of Modules
◦ Modules implementation similar to C coding
◦ Programs are built out of components
◦ Each component specifies an interface
◦ Interfaces are “hooks” for wiring components
 Composition of Configurations
◦ Components are statically wired together
◦ Increases programming efficiency (code reuse) an runtime efficiency (static defs.)

22.  Components should use and provide bidirectional interfaces.
 Components should call and implement commands and signal and handle events.
 Components must handle events of used interfaces and also provide interfaces that must implement
commands.
Component Model : Hierarchy
 Commands
◦ Flow downwards
◦ Non Blocking requests
◦ Control returns to caller
 Events
◦ Flow upwards
◦ Post task, signal higher level events, call lower level cmds
◦ Control returns to signaler
 To avoid cycles
◦ Events can call commands
◦ Commands can NOT signal events