Unit III Basic concepts of Wireless Sensor Networks (WSN) Unit III Prof. Prashant Lahane

Transcription

1 Unit III Basic concepts of Wireless Sensor Networks (WSN) 1

2 Wireless Sensor Network A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. - Wikipedia 2

3 Digital I/O ports Analog I/O Ports Motes & Wireless Sensor Networks Radio Transceiver External Memory Microcontroller D/A A/D Sensor Sensor A very low cost low power computer- on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. It performs tasks, processes data and controls the functionality of other components in the sensor node. Monitors one or more sensors. A Radio Link to the outside world. Are the building blocks of Wireless Sensor Networks (WSN). 3

4 WSN Overview (Cont.) CPU The Microcontroller Unit (MCU) is the primary choice for innode processing. Power consumption is the key metric in MCU selection. The MCU should be able to sleep whenever possible, like the radio. Memory requirements depend on the application ATmega128L and MSP430 are popular choices 4

5 Example Microcontrollers Texas Instruments MSP bit RISC core, 4 MHz Up to 120 KB flash 2-10 KB RAM 12 ADCs, RT clock Atmel ATMega 8-bit controller, 8 MHz Up to 128KB Flash 4 KB RAM 5

6 Communication Device Medium options Electromagnetic, RF Electromagnetic, optical Ultrasound bit stream Radio Transceiver radio wave 6

7 Transceiver Characteristics Service to upper layer: packet, byte, bit Power consumption Supported frequency, multiple channels Data rate Modulation Power control Communication range etc. 7

8 Transceiver States Transceivers can be put into different operational states, typically: Transmit Receive Idle ready to receive, but not doing so Sleep significant parts of the transceiver are switched off Tx Idle Sleep 8 Rx

9 Wakeup Receivers When to switch on a receiver is not clear Contention-based MAC protocols: Receiver is always on TDMA-based MAC protocols: Synchronization overhead, inflexible Desirable: Receiver that can (only) check for incoming messages When signal detected, wake up main receiver for actual reception Ideally: Wakeup receiver can already process simple addresses Not clear whether they can be actually built, however 9

10 WSN Overview (Cont.) Sensors The power efficiency of the sensors is also crucial, as well as their duty cycle. MEMS(micro electro-mechanical system) techniques allow miniaturization(manufacture ever smaller mechanical, optical and electronic products and devices). 10

11 Main categories Sensors Passive, omnidirectional Examples: light, thermometer, microphones, hygrometer, Passive, narrow-beam Example: Camera Active sensors Example: Radar Important parameter: Area of coverage Which region is adequately covered by a given sensor? 11

12 IWING-MRF Motes Digital sensor connectors Analog/Digital sensor connectors Radio transceiver USB Connector (for reprogramming and power) 8-bit AVR Microcontroller External battery connector Morakot Saravanee, Chaiporn Jaikaeo, Intelligent Wireless Network Group (IWING), KU 12

13 Characteristics of WSN Requirements: small size, large number, and low cost. Constrained by Energy, computation, and communication Small size implies small battery Low cost & energy implies low power CPU, radio with minimum bandwidth and range Ad-hoc deployment implies no maintenance or battery replacement To increase network lifetime, no raw data is transmitted 13

14 WSN Overview (Cont.) Distinguishing Features WSNs are ad hoc networks (wireless nodes that selforganize into an infrastructure less network). Sensing and data processing are essential WSNs have many more nodes and are more thickly deployed Hardware must be cheap; nodes are more prone to failures WSNs operate under very strict energy constraints WSN nodes are typically static. The communication scheme is many-to-one (data collected at a base station) rather than peer-to-peer 14

15 WSN Overview (Cont.) Lifetime Nodes are battery-powered. Nobody is going to change the batteries. So, each operation brings the node closer to death. "Lifetime is crucial! To save energy: Sleep as much as possible. Acquire data only if crucial. Use data synthesis and compression. Transmit and receive only if necessary. Receiving is just as costly as sending. 15

16 WSN Overview (Cont.) Scalability and Reliability WSNs should self-configure and be robust to topology changes (e.g., death of a node) maintain connectivity: can the Base Station reach all nodes? ensure coverage: are we able to observe all phenomena of interest? Maintenance Reprogramming is the only practical kind of maintenance. It is highly desirable to reprogram wirelessly. 16

17 WSN Overview (Cont.) Data Collection Centralized data collection puts extra burden on nodes close to the base station. Clever routing can ease that problem Clustering: data from groups of nodes are compound before being transmitted, so that fewer transmissions are needed. Often getting measurements from a particular area is more important than getting data from each node. Security and authenticity should be guaranteed. However, the CPUs on the sensing nodes cannot handle fancy encryption schemes. 17

18 WSN Overview (Cont.) Power Supply AA batteries power the vast majority of existing platforms. They dominate the node size. Alkaline batteries offer a high energy density at a cheap price. The discharge curve is far from flat, although. Lithium coin cells are more compact and boast a flat discharge curve. Rechargeable batteries: Who does the recharging? Solar cells are an option for some applications. Fuel cells may be an alternative in the future. Energy scavenging techniques are a hot research topic (mechanical, thermodynamical, electromagnetic). 18

19 WSN Overview (Cont.) Radio Commercially-available chips Available bands: 433 and 916MHz, 2.4GHz ISM bands Typical transmit power: 1 milliwatt =0 decibal milliwatt(dbm). Power control Sensitivity: as low as -110dBm Narrowband (FSK) or Spread Spectrum communication. DS-SS (e.g., ZigBee) or FH-SS (e.g., Bluetooth) Relatively low rates (<100 kbps) save power. 19

20 Ad Hoc Wireless Networks It is decentralized type of wireless network. Each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity. Large number of self-organizing static or mobile nodes that are possibly randomly deployed. Near(est)-neighbor communication. Sensor Networks and Sensor-Actuator Networks are a prominent example. 20

21 Wireless Sensor Networks Formed by hundreds or thousands of motes that communicate with each other and pass data along from one to another Research done in this area focus mostly on energy aware computing and distributed computing 21

22 Types of Sensors 1. Acoustic, sound, vibration a. Geophone (converts ground movement (displacement) into voltage) b. Hydrophone(listening to underwater sound) c. Microphone (converts sound in air into an electrical signal) 2. Automotive, transportation a. Radar gun (to detect the speed of other objects) b. Parking sensors (to alert the driver of unseen obstacles during parking military exercises) c. Speedometer 22

23 Types of Sensors 4. Electric current, electric potential, magnetic, radio 5. Environment, weather, moisture, humidity 6. Flow, fluid velocity 7. Ionizing radiation, subatomic particles 8. Navigation instruments 9. Position, angle, displacement, distance, speed, acceleration 10.Optical, light, imaging, photon 11.Pressure, Force, density, level 23

24 Sensor Network Architecture The two basic kinds of sensor network architecture Layered Architecture Clustered Architecture 24

25 1 Layered Architecture A layered architecture has a single powerful base station, and the layers of sensor nodes around it correspond to the nodes that have the same hop-count to the BS. In the in-building scenario, the BS acts an access point to a wired network, and small nodes form a wireless backbone to provide wireless connectivity. The advantage of a layered architecture is that each node is involved only in short-distance, low-power transmissions to nodes of the neighboring layers. 25

26 Figure 1 Layered architecture 26

27 Unified Network Protocol Framework (UNPF) UNPF is a set of protocols for complete implementation of a layered architecture for sensor networks UNPF integrates three operations in its protocol structure: Network initialization and maintenance MAC protocol Routing protocol 27

28 Network initialization and maintenance The BS broadcasts its ID using a known CDMA code on the common control channel. All node which hear this broadcast then record the BS ID. They send a beacon signal with their own IDs at their low default power levels. Those nodes which the BS can hear form layer one BS broadcasts a control packet with all layer one node IDs. All nodes send a beacon signal again. The layer one nodes record the IDs which they hear (form layer two) and inform the BS of the layer two nodes IDs. Periodic beaconing updates neighbor information and change the layer structure if nodes die out or move out of range. 28

29 MAC protocol During the data transmission phase, the distributed TDMA receiver oriented channel (DTROC) assignment MAC protocol is used. Two steps of DTROC : Channel allocation : Each node is assigned a reception channel by the BS, and channel reuse is such that collisions are avoided. Channel scheduling : The node schedules transmission slots for all its neighbors and broadcasts the schedule. This enables collision-free transmission and saves energy, as nodes can turn off when they are not involved on a send/receive operation. 29

30 2 Clustered Architecture A clustered architecture organizes the sensor nodes into clusters, each governed by a cluster-head. The nodes in each cluster are involved in message exchanges with their clusterheads, and these heads send message to a BS. Clustered architecture is useful for sensor networks because of its inherent suitability for data fusion. The data gathered by all member of the cluster can be fused at the cluster-head, and only the resulting information needs to be communicated to the BS. The cluster formation and election of cluster-heads must be an autonomous, distributed process. 30

31 Figure 2 Clustered architecture 31

32 WSN Applications Building Automation Sensors and Robots Healthcare Military surveillance Environmental/Habitat monitoring Inventory tracking Evolution of Sensor Hardware Platform 32

33 Building Automation Application Measuring temperature and humidity Controlling heating, ventilation, air-conditioning unit, shades blinds and lighting Controlling access and providing security etc. 33

34 Sensors Applications Low-power microscopic sensors with wireless communication capability Miniaturization of computer hardware Intelligence Micro Electro-Mechanical Structures (MEMS) Sensing Low-cost CMOS-based RF Radios Wireless Communications 34

35 Sensors Applications Even though wireless sensors has limited resources in memory, computation power, bandwidth, and energy. With small physical size Can be embedded in the physical environment. Support powerful service in aggregated form (interacting/collaborating among nodes) 35

36 Robot Application A ring of robots to fight fires. Robots that are connected to communicate with each other by Wireless Sensor Network to fight the fire by sensing the fire and locate it to make a ring shape around it and each Fire Fighter Robot will fight fire from one direction so that the fire will be easily stopped. 36

37 37

38 Healthcare Applications In Medical health care field, WSN are used with embedded systems to monitor the health of the patients in the hospital Or outside the hospital through the internet. 1) Wireless pulse Oximeter sensor 2) Wireless muscle movements monitor 38

39 Wireless pulse Oximeter sensor Devices collect the heart pulse rate and the Oxygen saturation and send these data over a short range(100m) Wireless Network to any number of receiving devices, including PDAs, laptops, or ambulance-based terminals which in turn can display the receiving data and record them. The device can alarms if data fall out of specific parameter. Easy to wear like hand watch. 39

40 Wireless movements monitor This device can monitoring the limb movements and muscle activity when they exercise. Sensor nodes in all the muscles of the body to create a network and send all the recorder info to the master. Master sends the info to the device that monitor. 40

41 41 Prof. Prashant Lahane Unit III

42 Military Applications Shooter Localization Perimeter Defense (Oil pipeline protection) Insurgent Activity Monitoring (MicroRadar) Sensors measuring: electromagnetic energy / signals, light, pressure, sound explosions Also: chemical, biological and explosive vapor; presence of people or objects Use of WSNs can reduce uncertainty: where enemy forces will be deployed; their role OTW (Other than War): Areas at risk of natural disaster; location of population to be protected 42

43 Military Applications. 43

44 What is RFID? RFID = Radio Frequency IDentification. An ADC (Automated Data Collection) technology that: uses radio-frequency waves to transfer data between a reader and a movable item to identify, categorize, track.. Is fast and does not require physical sight or contact between reader/scanner and the tagged item. Performs the operation using low cost components. Attempts to provide unique identification and backend integration that allows for wide range of applications. Other ADC technologies: Bar codes, OCR(optical character Reorganization ). 44

45 Ethernet RFID system components RFID Reader RFID Tag RF Antenna Network Workstation 45

46 RFID systems: logical view 11 ONS Server Internet Product Information (PML Format) 12 Antenna Write data to RF tags 1 Items with RF Tags RF Antenna Reader Read Manager Transaction Data Store Application Systems EDI / XML Trading Partner Systems Tag/Item Relationship Database 9 10 Tag Interfaces RFID Middleware Other Systems 46

47 RFID tags: Smart labels A paper label with RFID inside an antenna, printed, etched or stamped... and a chip attached to it on a substrate e.g. a plastic foil Source:

48 Some RFID tags 48 Source:

49 RFID tags Tags can be attached to almost anything: Items, cases or pallets of products, high value goods vehicles, assets, livestock or personnel Passive Tags Do not require power Draws from Interrogator Field Lower storage capacities (few bits to 1 KB) Shorter read ranges (4 inches to 15 feet) Usually Write-Once-Read-Many/Read-Only tags Cost around 25 cents to few dollars Active Tags Battery powered Higher storage capacities (512 KB) Longer read range (300 feet) Typically can be re-written by RF Interrogators Cost around 50 to 250 dollars 49

50 Tag block diagram Antenna Power Supply Tx Modulator Rx Demodulator Control Logic (Finite State machine) Memory Cells Tag Integrated Circuit (IC) 50

51 RFID tag memory Read-only tags Tag ID is assigned at the factory during manufacturing Can never be changed No additional data can be assigned to the tag Write once, read many (WORM) tags Data written once, e.g., during packing or manufacturing Tag is locked once data is written Similar to a compact disc or DVD Read/Write Tag data can be changed over time Part or all of the data section can be locked 51

52 Reader functions: Remotely power tags RFID readers Establish a bidirectional data link Inventory tags, filter results Communicate with networked server(s) Can read tags per second Readers (interrogators) can be at a fixed point such as Entrance/exit Point of sale Readers can also be mobile/hand-held 52

53 Some RFID readers 53 Source:

54 Reader anatomy Digital Signal Processor (DSP) Network Processor Power Supply 915MHz 13.56MHz Radio Radio 54

55 RFID application points Assembly Line Wireless Handheld Applications Bill of Lading Material Tracking Shipping Portals 55

56 RFID applications Manufacturing and Processing Inventory and production process monitoring Warehouse order fulfillment Supply Chain Management Inventory tracking systems Logistics management Retail Inventory control and customer insight Auto checkout with reverse logistics Security Access control Counterfeiting and Theft control/prevention Location Tracking Traffic movement control and parking management Wildlife/Livestock monitoring and tracking 56

57 Smart groceries Add an RFID tag to all items in the grocery. As the cart leaves the store, it passes through an RFID transceiver. The cart is rung up in seconds. 57

58 Smart cabinet Reader antennas placed under each shelf 1. Tagged item is removed from or placed in Smart Cabinet 2. Smart Cabinet periodically interrogates to assess inventory 3. Server/Database is updated to reflect item s disposition Passive read/write tags affixed to caps of containers 4. Designated individuals are notified regarding items that need attention (cabinet and shelf location, action required) 58 Source: How Stuff Works

59 Smart fridge Recognizes what s been put in it Recognizes when things are removed Creates automatic shopping lists Notifies you when things are past their expiration Shows you the recipes that most closely match what is available 59

60 Smart groceries enhanced Track products through their entire lifetime. 60 Source: How Stuff Works

61 Some more smart applications Smart appliances: Closets that advice on style depending on clothes available. Ovens that know recipes to cook pre-packaged food. Smart products: Clothing, appliances, CDs, etc. tagged for store returns. Smart paper: Airline tickets that indicate your location in the airport. Smart currency: Anti-counterfeiting and tracking. Smart people?? 61

62 RFID advantages over bar-codes No line of sight required for reading Multiple items can be read with a single scan Each tag can carry a lot of data (read/write) Individual items identified and not just the category Passive tags have a virtually unlimited lifetime Active tags can be read from great distances Can be combined with barcode technology 62

63 Overview of RFID Outline Reader-Tag; Potential applications RFID Technology Internals RF communications; Reader/Tag protocols Middleware architecture; EPC standards RFID Business Aspects Security and Privacy Conclusion 63

64 RFID communications Power from RF field Reader Antenna Reader->Tag Commands Reader Tag->Reader Responses Tags RFID Communication Channel 64

65 RFID communication Host manages Reader(s) and issues Commands Reader and tag communicate via RF signal Carrier signal generated by the reader Carrier signal sent out through the antennas Carrier signal hits tag(s) Tag receives and modifies carrier signal sends back modulated signal (Passive Backscatter also referred to as field disturbance device ) Antennas receive the modulated signal and send them to the Reader Reader decodes the data Results returned to the host application 65

66 Antenna fields: Inductive coupling IC or microprocessor Transceiver Tag Reader antenna RFID Tag antenna 66

67 Antenna fields: Propagation coupling IC or microprocessor Transceiver Tag Reader antenna RFID Tag antenna 67

68 Frequency Ranges Typical Max Read Range (Passive Tags) Tag Power Source Operational frequencies LF 125 KHz Shortest 1-12 Generally passive tags only, using inductive coupling HF MHz Short 2-24 Generally passive tags only, using inductive or capacitive coupling UHF MHz Medium 1-10 Active tags with integral battery or passive tags using capacitive storage, E-field coupling Microwave 2.45 GHz & 5.8 GHz Longest 1-15 Active tags with integral battery or passive tags using capacitive storage, E-field coupling Data Rate Slower Moderate Fast Faster Ability to read near metal or wet surfaces Applications Better Moderate Poor Worse Access Control & Security Identifying widgets through manufacturing processes or in harsh environments Ranch animal identification Employee IDs Library books Laundry identification Access Control Employee IDs supply chain tracking Highway toll Tags Highway toll Tags Identification of private vehicle fleets in/out of a yard or facility Asset tracking 68

69 Reader->Tag power transfer Reader Antenna Tag Reader Separation distance d Q: If a reader transmits Pr watts, how much power Pt does the tag receive at a separation distance d? A: It depends- UHF (915MHz) : Far field propagation : Pt 1/d 2 HF (13.56MHz) : Inductive coupling : Pt 1/d 6 69

70 Limiting factors for passive RFID 1. Reader transmitter power Pr (Gov t. limited) 2. Reader receiver sensitivity Sr 3. Reader antenna gain Gr (Gov t. limited) 4. Tag antenna gain Gt (Size limited) 5. Power required at tag Pt (Silicon process limited) 6. Tag modulator efficiency Et 70

71 RFID Summary Strengths Advanced technology Easy to use High memory capacity Small size Opportunities Could replace the bar code End-user demand for RFID systems is increasing Huge market potential in many businesses Weaknesses Lack of industry and application standards High cost per unit and high RFID system integration costs Weak market understanding of the benefits of RFID technology Threats Ethical threats concerning privacy life Highly fragmented competitive environment 71 Prof. Prashant Lahane Unit III