MATRUSRI ENGINEERING COLLEGE�(An Autonomous Institution)�DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

SUBJECT NAME: WIRELESS SENSOR NETWORKS(PE 518 EC)

FACULTY NAME: Dr. M.NARESH

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WIRELESS SENSOR NETWORKS(PE 518 EC)

COURSE OBJECTIVES:

• To make students understand the basics of wireless sensor network.
• To understand the concept of networking in WSN.
• To introduce the hardware and software platforms and tool in WSN.

COURSE OUTCOMES:

• To understand deployment strategies , challenges and technologies for WSN.
• To understand network architecture.Study suitable protocols and radio hardware.
• Describing the communication, energy efficiency computing, storage and transmission.
• Establishing the infrastructure and simulation.
• Explain the concept of security, and attacks in WSN and Introduction to 5G

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LESSON PLAN:

UNIT –II: Architectures

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INTRODUCTION:�

UNIT-II: Architectures

OUTCOMES:

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Build foundation for WSN by presenting challenges of wireless networking at various protocol layers

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A Wireless Sensor Network is one kind of wireless network includes a large number of circulating, self-directed, minute, low powered devices named sensor nodes called motes.

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These networks certainly cover a huge number of spatially distributed, little, battery-operated, embedded devices that are networked to caringly collect, process, and transfer data to the operators, and it has controlled the capabilities of computing & processing. Nodes are the tiny computers, which work jointly to form the networks.

CONTENTS:� 2.1. SINGLE-NODE ARCHITECTURE - HARDWARE COMPONENTS,� 2.2. ENERGY CONSUMPTION OF SENSOR NODES,� 2.3. OPERATING SYSTEMS AND EXECUTION ENVIRONMENTS � 2.4. NETWORK ARCHITECTURE - SENSOR NETWORK SCENARIOS, � 2.5. OPTIMIZATION GOALS AND FIGURES OF MERIT, GATEWAY CONCEPTS.�

OUTCOMES

Build foundation for WSN by presenting challenges of wireless networking at various protocol layers

UNIT-II: Architectures

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CONTENTS:� 2.1. SINGLE-NODE ARCHITECTURE - HARDWARE COMPONENTS,��

OUTCOMES:

Study about architectures of wireless sensor networks

MODULE-I

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2.1. Single-node architecture - hardware components

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• Controller A controller to process all the relevant data, capable of executing arbitrary code.

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• Memory Some memory to store programs and intermediate data; usually, different types of memory are used for programs and data.

• Sensors and actuators The actual interface to the physical world: devices that can observe or

control physical parameters of the environment.

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• Communication Turning nodes into a network requires a device for sending and receiving information over a wireless channel

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2.1. Single-node architecture - hardware components

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• The sensor node is a multi-functional, energy efficient wireless device. The applications of motes in industrial are widespread.

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• A collection of sensor nodes collects the data from the surroundings to achieve specific application objectives.

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• The communication between motes can be done with each other using transceivers. In a wireless sensor network, the number of motes can be in the order of hundreds/ even thousands.

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• In contrast with sensor networks, Ad Hoc networks will have fewer nodes without any structure.

Power supply As usually no tethered power supply is available, some forms of batteries are necessary to provide energy. Sometimes, some form of recharging by obtaining energy from the environment is available as well (e.g. solar cells).

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Each of these components has to operate balancing the trade-off between as small an energy consumption as possible on the one hand and the need to ful-fil their tasks on the other hand.

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For example, both the communication device and the controller should be turned off as long as possible.

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2.1. Single-node architecture - hardware components

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Hardware Components:

• Power supply
• Microcontrollers vs Microprocessors, FPGAs and ASIC
• Memory
• Communication devices
• Sensors & Actuators

- Passive omni- directional sensors

- Passive narrow- beam sensors

- Active sensors

- Actuators

Memory

The memory component is fairly straightforward. Evidently, there is a need for Random Access Memory (RAM) to store intermediate sensor readings, packets from other nodes, and so on.

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While RAM is fast, its main disadvantage is that it loses its content if power supply is interrupted. Program code can be stored in Read-Only Memory (ROM) or, more typically, in Electrically Erasable Programmable Read-Only Memory (EEPROM) or flash memory (the later being similar to EEPROM

but allowing data to be erased or written in blocks instead of only a byte at a time).

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2.1. Single-node architecture - hardware components

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Communication device:

Choice of transmission medium

• The communication device is used to exchange data between individual nodes. In some cases, wired communication can actually be the method of choice and is frequently applied in many sensor Network like settings (using field buses like Profi-bus, LON, CAN, or others).

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• The communication devices for these networks are custom off-the-shelf components.

Transceivers

• For actual communication, both a transmitter and a receiver are required in a sensor node. The essential task is to convert a bit stream coming from a microcontroller (or a sequence of bytes or frames) and convert them to and from radio waves.

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• For practical purposes, it is usually convenient to use a device that combines these two tasks in a single entity. Such combined devices are called transceivers.

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• Usually, half-duplex operation is realized since transmitting and receiving at the same time on a wireless medium is impractical in most cases (the receiver would only hear the own transmitter anyway).

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2.1. Single-node architecture - hardware components

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Transceiver tasks and characteristics

To select appropriate transceivers, a number of characteristics should be taken into account. The most important ones are:

• Service to upper layer
• Power consumption and energy efficiency
• Carrier frequency and multiple channels
• State change times and energy
• Data rates
• Modulations

• Coding
• Noise figure The noise figure
• Gain
• Power efficiency
• Receiver sensitivity
• Range
• Blocking performance
• Out of band emission
• Carrier sense and RSSI
• Frequency stability and Voltage range

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2.1. Single-node architecture - hardware components

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A fairly common structure of transceivers is into the Radio Frequency (RF) front end and the baseband part:

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• The radio frequency front end performs analog signal processing in the actual radio frequency band, whereas

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• The baseband processor performs all signal processing in the digital domain and communicates with a sensor node’s processor or other digital circuitry.

. TRANSCEIVER OPERATIONAL STATES:�MANY TRANSCEIVERS CAN DISTINGUISH FOUR OPERATIONAL STATES :��TRANSMIT IN THE TRANSMIT STATE, THE TRANSMIT PART OF THE TRANSCEIVER IS ACTIVE AND THE ANTENNA RADIATES ENERGY.��RECEIVE IN THE RECEIVE STATE THE RECEIVE PART IS ACTIVE.��

2.1. Single-node architecture - hardware components

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Idle A transceiver that is ready to receive but is not currently receiving anything is said to be in an idle state.

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Sleep In the sleep state, significant parts of the transceiver are switched off.

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There are transceivers offering several different sleep states, see reference for a discussion of sleep states for IEEE 802.11 transceivers. These sleep states differ in the amount of circuitry switched off and in the associated recovery times and startup energy

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2.1. Single-node architecture - hardware components

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Sensors and actuators

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Without the actual sensors and actuators, a wireless sensor network would be beside the point

entirely.

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But as the discussion of possible application areas has already indicated, the possible range of sensors is vast.

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It is only possible to give a rough idea on which sensors and actuators can be used in a WSN

Sensors

• Sensors can be roughly categorized into three categories

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• Passive, omni-directional sensors

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• Passive, narrow-beam sensors

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• Active sensors

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2.1. Single-node architecture - hardware components

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Power supply of sensor nodes

For untethered wireless sensor nodes, the power supply is a crucial system component. There are essentially two aspects: First, storing energy and providing power in the required form;

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second, attempting to replenish consumed energy by “scavenging” it from some node-external power source over time.

Storing power is conventionally done using batteries. As a rough orientation, a normal AA battery stores about 2.2–2.5 Ah at 1.5 V.

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Storing energy: Batteries

• Traditional batteries
• Capacity
• Capacity under load
• Self-discharge
• Efficient recharging, Relaxation, Unconventional energy stores and DC–DC Conversion

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2.1. Single-node architecture - hardware components

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Energy scavenging

Some of the unconventional energy stores described above – fuel cells, micro heat engines, radioactivity

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– convert energy from some stored, secondary form into electricity in a less direct and easy to use way than a normal battery would do. The entire energy supply is stored on the node itself – once the fuel supply is exhausted, the node fails.

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To ensure truly long-lasting nodes and wireless sensor networks, such a limited energy store is unacceptable. Rather, energy from a node’s environment must be tapped into and made available

to the node – energy scavenging should take place.

A MEMS device for converting vibrations to electrical energy, based on a variable capacitor .Reproduced by permission of IEEE

CONTENTS:� 2.2. ENERGY CONSUMPTION OF SENSOR NODES� 2.3. OPERATING SYSTEMS AND EXECUTION ENVIRONMENTS �

OUTCOMES:

To understand the concepts of energy scavenging and operating systems of WSN

MODULE-2

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2.2 Energy Consumption of Sensor Nodes

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At time t1, the decision whether or not a component (say, the microcontroller) is to be put into sleep mode should be taken to reduce power consumption from Pactive to Psleep.

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If it remains active and the next event occurs at time tevent, then a total energy of Eactive = Pactive(tevent − t1) has be spent uselessly idling.

Putting the component into sleep mode, on the other hand, requires a time τdown until sleep mode has been reached; as a simplification, assume that the average power consumption during this phase is (Pactive + Psleep)/2.

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Then, Psleep is consumed until tevent. In total, τdown(Pactive + Psleep)/2 + (tevent − t1 − τdown)Psleep energy is required in sleep mode as opposed to (tevent − t1)Pactive when remaining active.

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2.2 Energy Consumption of Sensor Nodes

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Microcontroller energy consumption

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Basic power consumption in discrete operation states:

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Intel Strong ARM

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The Intel Strong ARM ,In normal mode, all parts of the processor are fully powered.

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Power consumption is up to 400 mW.

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• In idle mode, clocks to the CPU are stopped; clocks that pertain to peripherals are active. Any interrupt will cause return to normal mode. Power consumption is up to 100 mW.

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• In sleep mode, only the real-time clock remains active. Wakeup occurs after a timer interrupt and takes up to 160 ms. Power consumption is up to 50 μW.

Energy per operation with dynamic power scaling on an Intel Strong ARM SA-1100

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2.3 Operating systems and Execution Environments

1. Embedded operating systems: The traditional tasks of an operating system are controlling and protecting the access to resources (including support for input/output) and managing their allocation to different users as well as the support for concurrent execution of several processes and communication between these processes.

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• 2.Programming paradigms and application programming interfaces (concurrent programming):

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- Process-based concurrency

- Event- based programming

- Interfaces to the operating

systems

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2.3 Operating systems and Execution Environments

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Event based programming model:

Such an event handler can interrupt the processing of any normal code, but as it is very simple and short, it can be required to run to completion in all circumstances without noticeably disturbing other code

Event handlers cannot interrupt each other (as this would in turn require complicated stack handling procedures) but are simply executed one after each other.

CONTENTS:� 2.4. NETWORK ARCHITECTURE - SENSOR NETWORK SCENARIOS, � 2.5. OPTIMIZATION GOALS AND FIGURES OF MERIT, GATEWAY CONCEPTS �

OUTCOMES:

MODULE-3

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To Discuss About network architecture and optimization goals with the figure of Merit Concepts

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2.4. Network architecture - sensor network scenarios

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Three types of sinks in a very simple single-hop sensor network

Types of Sources and sinks:

-Single hop versus Multi hop

From the basics of radio communication and the inherent power limitation of radio communication follows a limitation on the feasible distance between a sender and a receiver. Because of this limited distance, the simple, direct communication between source and sink is not always possible,

specifically in WSNs, which are intended to cover a lot of ground (e.g. in environmental or agriculture applications) or that operate in difficult radio environments with strong attenuation

.MULTI HOP NETWORK:��

2.4. Network architecture - sensor network scenarios

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To overcome such limited distances, an obvious way out is to use relay stations, with the data packets taking multi hops from the source to the sink.

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This concept of multi-hop networks is particularly attractive for WSNs as the sensor nodes themselves can act as such relay nodes, foregoing the need for additional equipment

Depending on the particular application, the likelihood of having an intermediate sensor node at the right place can actually be quite high

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2.4. Network architecture - sensor network scenarios

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Multiple sources and/or multiple sinks

In many cases, there are multiple sources and/or multiple sinks present. In the most challenging case, multiple sources should send information to multiple sinks, where either all or some of the information has to reach all or some of the sinks. Figure illustrates these combinations.

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2.4. Network architecture - sensor network scenarios

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Three types of Mobility

• Node mobility
• Sink mobility
• Event mobility

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Communication protocols for WSNs will have to render appropriate support for these forms of

mobility.

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In particular, event mobility is quite uncommon, compared to previous forms of mobile

or wireless networks.

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A mobile sinks moves through a mobile sensor network as a information being retrieves on its behalf

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2.5. Optimization goals and figures of merit, gateway concepts

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For all these scenarios and application types, different forms of networking solutions can be found.

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The challenging question is how to optimize a network, how to compare these solutions, how to decide which approach better supports a given application, and how to turn relatively imprecise optimizing goals into measurable figures of merit? While a general answer appears impossible considering the large variety of possible applications, a few aspects are fairly evident

1. Quality of service

- Event detection/reporting probability

- Event classification error

- Event detection delay

- Missing reports

- Approximation accuracy

- Tracking accuracy

2. Energy efficiency

- Energy/correctly received

- Energy/reported event

- Delay

- N/w Life time

3. Scalability

4. Robustness

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Area of sensor nodes detecting an event-an elephant-that moves through the network along with the event source

2.5. Optimization goals and figures of merit, gateway concepts

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2.5. Optimization goals and figures of merit, gateway concepts

Need for Gate ways

For practical deployment, a sensor network only concerned with itself is insufficient. The network rather has to be able to interact with other information devices,

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for example, a user equipped with a PDA moving in the coverage area of the network or with a remote user, trying to interact with the sensor network via the Internet (the standard example is to read the temperature sensors in one’s home while traveling and accessing the Internet via a wireless connection). Figure shows this networking scenario.

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2.5. Optimization goals and figures of merit, gateway concepts

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1. WSN to Internet communication

A sensor node wants to deliver an alarm message to some Internet host.

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The first problem to solve is akin to ad hoc networks, namely, how to find the gateway from within the network.

Basically, a routing problem to a node that offers a specific service has to be solved, integrating routing and service discovery

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2.5. Optimization goals and figures of merit, gateway concepts

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2. Internet to WSN communication

The case of an Internet-based entity trying to access services of a WSN is even more challenging .

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This is fairly simple if this requesting terminal is able to directly communicate with the WSN, for example, a mobile requester equipped with a WSN transceiver, and also has all the necessary protocol components at its disposal

In this case, the requesting terminal can be a direct part of the WSN and no particular treatment is necessary

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2.5. Optimization goals and figures of merit, gateway concepts

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3. WSN tunneling

In addition to these scenarios describing actual interactions between a WSN and Internet terminals, the gateways can also act as simple extensions of one WSN to another WSN.

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The idea is to build a larger, “virtual” WSN out of separate parts, transparently “tunneling” all protocol messages between

these two networks and simply using the Internet as a transport network.

This can be attractive, but care has to be taken not to confuse the virtual link between two gateway

nodes with a real link; otherwise, protocols that rely on physical properties of a communication

link can get quite confused.

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Assignment Question

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1. Write short notes on Berkeley Motes.
2. Explain single node architecture.
3. Explain Gateway concepts.
4. Explain network architecture and sensor network scenarios.
5. What is the function of controller in sensor node architecture.

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Short answer questions

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Questions & Answers

Questions & Answers

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Long answer questions