8/4/2015 Cpre 458/558: Real-Time Systems (G. Manimaran) 1 Wireless Communication in Industrial Networks Kavitha Balasubramanian Teaching Assistant, CprE.

04/19/2304/19/23 Cpre 458/558: Real-Time Systems (G. Manimaran)Cpre 458/558: Real-Time Systems (G. Manimaran) 11

Wireless Communication in Wireless Communication in Industrial NetworksIndustrial Networks

Kavitha BalasubramanianTeaching Assistant, CprE 458/558

04/19/2304/19/23 Cpre 458/558: Wireless Communication in Industrial NetworksCpre 458/558: Wireless Communication in Industrial Networks 22

AgendaAgenda

IntroductionIntroduction Existing Wireless StandardsExisting Wireless Standards Non real time applicationsNon real time applications Soft real-time applicationsSoft real-time applications Hard Real-time applicationsHard Real-time applications Techniques for improving reliabilityTechniques for improving reliability The FutureThe Future


IntroductionIntroduction

Immense development of wireless Immense development of wireless communication technology for consumer communication technology for consumer electronicselectronics

Also finding its way into industrial setupAlso finding its way into industrial setup Salient features of communication system Salient features of communication system

in industrial applicationin industrial application• Part of production facilityPart of production facility• Loss of production costly in comparison to the Loss of production costly in comparison to the

communication systemcommunication system• Focus on reliability, predictability and fault Focus on reliability, predictability and fault

tolerancetolerance


Introduction …Introduction …

How wireless is accepted?How wireless is accepted?• Technology should have clear benefits Technology should have clear benefits

and is reliable so as to justify and is reliable so as to justify investmentinvestment

• Globally accepted standards has led to Globally accepted standards has led to mass chip productionmass chip production

• Low prices for complex productsLow prices for complex products• Some of these are used in the industrySome of these are used in the industry

55

Motivation for wireless industrial networksMotivation for wireless industrial networks

Reduced installation, Reduced installation, reconfiguration and maintenance reconfiguration and maintenance costscosts

Easy access to machines for Easy access to machines for diagnostic or programming diagnostic or programming purposespurposes

Improved coverage of the factory Improved coverage of the factory floorfloor

Eliminates adverse effects due to Eliminates adverse effects due to damage of cablingdamage of cabling

Desire to save on cablingDesire to save on cabling

Globally accepted standards Globally accepted standards leading to mass production and leading to mass production and reduced pricesreduced prices

66

Industrial ApplicationsIndustrial Applications

Wireless Industrial Applications

time

Non Real -

Hard Real -Time

Remote ControlMachine Health Monitoring

System ConfigurationInternet Connectivity

Control LoopsMachine-to-machine communication

Events RegistrationMeasurements

Media-

Rea

lS

oft

time

77

WorkloadWorkload

Application Requirements

Meeting DeadlinesPredictability and ReliabilityGuaranteed packet delivery Guaranteed delivery timesPrioritizing messages

Message Characteristics

Periodic traffic with deadlinesAcyclic packets (alarms) with bounded latencyShort packets (order of kilobytes)

88

Industrial wireless network marketIndustrial wireless network marketS

HO

RT

<

R

AN

GE

>

L

ON

G

LOW < DATA RATE > HIGH

PAN

LAN

TEXT GRAPHICS INTERNET HI-FI AUDIO

STREAMINGVIDEO

DIGITALVIDEO

MULTI-CHANNELVIDEO

Bluetooth1

Bluetooth 2

ZigBee

802.11b

802.11a/HL2 & 802.11g

99

Existing protocols- comparisonExisting protocols- comparison

Feature 802.11 Bluetooth Zigbee

Interference from other devices

-- Avoided using frequency hopping

Dynamic channel selection possible

Optimized for Multimedia, TCP/IP and high data rate applications

Cable replacement technology for portable and fixed electronic devices.

Low power low cost networking in residential and industrial environment.

Energy Consumption High Low (Large packets over small networks)

Least (Small packets over large networks)

Voice support/Security Yes/Yes Yes/Yes No/Yes

Type of Network / Channel Access

Mobile / CSMA/CA and polling

Mobile & Static / Polling Mostly static with infrequently used devices / CSMA and slotted CSMA/CA

Bit error rate High Low Low

Real Time deadlines ??? ??? ???

1010

Challenges and Spectrum of SolutionsChallenges and Spectrum of Solutions

Wireless Challenges

AttenuationFadingMultipath dispersionInterferenceHigh Bit Error rateBurst channel errors

Application Requirements

Reliable deliveryMeet deadlinesSupport message priority

Antenna Redundancy

Cooperative diversity

ARQ

Error Correction Codes

Modulation Techniques

Transmitter Design

Existing SolutionsExisting Solutions


Existing Wireless StandardsExisting Wireless Standards 802.11802.11

• Oldest and most matureOldest and most mature• Spread spectrum techniques for PHY layerSpread spectrum techniques for PHY layer

Direct Sequence Spread spectrum with Differential Direct Sequence Spread spectrum with Differential Binary Phase Shift Keying or Differential Quadrature Binary Phase Shift Keying or Differential Quadrature Phase Shift KeyingPhase Shift Keying

Frequency Hopping Spread Spectrum with Gaussian Frequency Hopping Spread Spectrum with Gaussian Frequency Shift KeyingFrequency Shift Keying

• Split intoSplit into 802.11a – 5GHz ISM band, Up to 2 Mbps802.11a – 5GHz ISM band, Up to 2 Mbps 802.11b – 2.45GHz ISM band, Up to 11 Mbps802.11b – 2.45GHz ISM band, Up to 11 Mbps 802.11e – Supports QoS802.11e – Supports QoS

• Uses CSMA/CA MAC (contention based) with Uses CSMA/CA MAC (contention based) with dynamic packet length up to 4096 bytes longdynamic packet length up to 4096 bytes long


Existing Wireless Standards …Existing Wireless Standards … HiperLAN/2HiperLAN/2

• Support for soft real-time applications like Support for soft real-time applications like mediamedia

• Uses Time Division Duplex scheme (Contention Uses Time Division Duplex scheme (Contention free)free)

• Static packet length of 54 bytesStatic packet length of 54 bytes• Better suited for real-time applications because Better suited for real-time applications because

of time deterministic MACof time deterministic MAC• OFDM modulationOFDM modulation

Multicarrier modulation schemeMulticarrier modulation scheme Adapts bit-rate based on channel conditionsAdapts bit-rate based on channel conditions Handles performance reduction due to multipath Handles performance reduction due to multipath

fading radio channelsfading radio channels


Existing Wireless Standards …Existing Wireless Standards … BluetoothBluetooth

• Low-complexity low-cost solution for short-range Low-complexity low-cost solution for short-range wireless communicationswireless communications

• Intended for cable replacement and adhoc connections Intended for cable replacement and adhoc connections of consumer devicesof consumer devices

• Instead of creating protocols in all layers of the protocol Instead of creating protocols in all layers of the protocol stack for each application, profiles existsstack for each application, profiles exists

• Subset of protocols serving a certain applicationSubset of protocols serving a certain application• Uses FHSS with hopping frequency of 1600 hops/secUses FHSS with hopping frequency of 1600 hops/sec• Also supports soft real-time applications like multimediaAlso supports soft real-time applications like multimedia


Non real-time applicationsNon real-time applications Remote Control:Remote Control:

• Used for remote control of overhead cranesUsed for remote control of overhead cranes• Dependent on security Dependent on security • Uses long code words to initiate remote control actionUses long code words to initiate remote control action

Machine health monitoring:Machine health monitoring:• Accurate information about the status of a processAccurate information about the status of a process• Locally on demand or over a wireless network to a Locally on demand or over a wireless network to a

control roomcontrol room• For local information, use PDA or laptop that connects to For local information, use PDA or laptop that connects to

sensors or actuatorssensors or actuators• Plant equipped with access point for communication with Plant equipped with access point for communication with

the control room at the same timethe control room at the same time• Using Bluetooth is a cheap way of achieving local health Using Bluetooth is a cheap way of achieving local health

monitoringmonitoring


Non real-time applications …Non real-time applications … System Configuration and Information Exchange: System Configuration and Information Exchange:

• Information is downloaded to a target deviceInformation is downloaded to a target device• Higher demand for fault toleranceHigher demand for fault tolerance• Use File Transfer Protocol with secure deliveryUse File Transfer Protocol with secure delivery• Profiles in BTProfiles in BT

Object Exchange protocol includes a file transfer protocolObject Exchange protocol includes a file transfer protocol TCP/IP over Bluetooth transport protocolsTCP/IP over Bluetooth transport protocols

• Fault ToleranceFault Tolerance With Error detection/correction, there is a probability that the With Error detection/correction, there is a probability that the

errors go undetected (depends on type of coding method and the errors go undetected (depends on type of coding method and the code rate)code rate)

Repeat message a number of times and use majority votingRepeat message a number of times and use majority voting For small configuration changes, value is uploaded into the device For small configuration changes, value is uploaded into the device

and echoed back. A mismatch will initiate a re-transmissionand echoed back. A mismatch will initiate a re-transmission Configured device can echo the changed value a number of times – Configured device can echo the changed value a number of times –

if correct value is received all the times, there is a very little if correct value is received all the times, there is a very little chance that the configured value is wrong chance that the configured value is wrong


Non real-time applications …Non real-time applications … Internet Connectivity:Internet Connectivity:

• Used for surveillance, supervision and health monitoring Used for surveillance, supervision and health monitoring of devicesof devices

• Demands soft real-time guarantees if applications like Demands soft real-time guarantees if applications like voice and video need to be supportedvoice and video need to be supported

• E.g. Distributed supervision of heat and ventilation E.g. Distributed supervision of heat and ventilation systemsystem

• Heat/ventilation system has an embedded web servers Heat/ventilation system has an embedded web servers that runs scriptsthat runs scripts

• Personnel can supervise and configure the system using Personnel can supervise and configure the system using a PC with a web browsera PC with a web browser

• Can use 802.11 or BT depending on the bandwidth Can use 802.11 or BT depending on the bandwidth requirementsrequirements


Soft real-time applicationsSoft real-time applications

QoS Parameters include QoS Parameters include • deadline : delay constraints of the deadline : delay constraints of the

applicationapplication• probability of correct delivery within the probability of correct delivery within the

deadline: bit error rate of the deadline: bit error rate of the communication channelcommunication channel

• Jitter of the delayJitter of the delay


Soft real-time applications …Soft real-time applications …

Event Registration:Event Registration:• Time-stamp an event with high time Time-stamp an event with high time

resolutionresolution• Transmission of the event from device Transmission of the event from device

that registered the event is not so that registered the event is not so critical i.e. requires only a reasonable critical i.e. requires only a reasonable response time.response time.

• E.g. Events don’t control anything but E.g. Events don’t control anything but should be logged at the right timeshould be logged at the right time

• Requires clock synchronizationRequires clock synchronization


Soft real-time applications …Soft real-time applications … Measurement:Measurement:

• Measures a physical process, timestamp the sample Measures a physical process, timestamp the sample values and transmit sequence of values to the uservalues and transmit sequence of values to the user

• Present course of events in a correct way so that the Present course of events in a correct way so that the time stamps can reconstruct the processtime stamps can reconstruct the process

• Notion of global correct time is importantNotion of global correct time is important

• Requires clock synchronization; precision demands is Requires clock synchronization; precision demands is dictated by the granularity of the measured valuesdictated by the granularity of the measured values

• For e.g. Geological or industrial wireless sensor system For e.g. Geological or industrial wireless sensor system with sensors collecting data and transmitting them to with sensors collecting data and transmitting them to base station or control roombase station or control room

• No delay constraints in transmission but measures and No delay constraints in transmission but measures and timestamps done in real-time to reconstruct course of timestamps done in real-time to reconstruct course of events of the physical processevents of the physical process

• High accuracy and synchronized clocksHigh accuracy and synchronized clocks 802.11 : 150ms; BT: 20us802.11 : 150ms; BT: 20us


Soft real-time applications …Soft real-time applications … Media:Media:

• Applications like voice and video transferApplications like voice and video transfer• Delay and loss rate constraints based on comfort provided by Delay and loss rate constraints based on comfort provided by

application to the userapplication to the user• BT:BT:

Supports voice channelsSupports voice channels Range of 10mRange of 10m Establishes adhoc connections: As soon as 2 or 3 people are within the Establishes adhoc connections: As soon as 2 or 3 people are within the

range, a communication channel is establishedrange, a communication channel is established• HiperLAN/2:HiperLAN/2:

Supports guaranteed media streamsSupports guaranteed media streams Slow control loop:Slow control loop:

• Control loops used in process control of slow or non-critical operationsControl loops used in process control of slow or non-critical operations• Low sample rate which are not affected by a few samples being lostLow sample rate which are not affected by a few samples being lost• Delay constraint based on comfort demandsDelay constraint based on comfort demands• E.g. heat control and ventilation system E.g. heat control and ventilation system • No time stamping necessary but low jitter requirementNo time stamping necessary but low jitter requirement• HiperLAN/2 or IEEE 802.11e is suitableHiperLAN/2 or IEEE 802.11e is suitable


Hard real-time applicationsHard real-time applications Result presented too late is disastrous to the Result presented too late is disastrous to the

systemsystem One missed deadline will led to a disaster and One missed deadline will led to a disaster and

cannot be toleratedcannot be tolerated E.g. control loopsE.g. control loops

Most distributed real-time systems assume fault-Most distributed real-time systems assume fault-free operation of the processing unit and free operation of the processing unit and communication channel that is not truecommunication channel that is not true• Error probability cannot be neglected for wireless Error probability cannot be neglected for wireless

channel and its function cannot be guaranteed at all channel and its function cannot be guaranteed at all timestimes

• Errors are sporadic in nature for wireless while for wired, Errors are sporadic in nature for wireless while for wired, permanent errors caused by wire or connector damage permanent errors caused by wire or connector damage dominatesdominates


Hard real-time applications …Hard real-time applications … Parameters:Parameters:

• DeadlineDeadline• Probability to deliver within the deadlineProbability to deliver within the deadline

If we quantify the probability for If we quantify the probability for communication channels, we can analyze communication channels, we can analyze the error probability of the entire system the error probability of the entire system and then employ risk analysis methods for and then employ risk analysis methods for calculating failure characteristics of the calculating failure characteristics of the systemsystem

Problem: Quantify Probability to deliver Problem: Quantify Probability to deliver within the deadline for certain system within the deadline for certain system conditionsconditions


Techniques for improving reliability Techniques for improving reliability of wireless channelof wireless channel

Based on radio signalsBased on radio signals Transmitted wave interferes with the surrounding Transmitted wave interferes with the surrounding

environment creating multiple waves hitting the receiver environment creating multiple waves hitting the receiver antennaantenna

Waves delayed with respect to each otherWaves delayed with respect to each other For some conditions, there is destructive interference at the For some conditions, there is destructive interference at the

receiver antenna causing signal attenuation. This is called receiver antenna causing signal attenuation. This is called fadingfading

Fading causes bursts of errors in wireless channelFading causes bursts of errors in wireless channel Fast fading occurs when the transmitter or the receiver Fast fading occurs when the transmitter or the receiver

move fast. Slow fading occurs in stationery situations. move fast. Slow fading occurs in stationery situations. FEC: Add redundant information to the bit stream that helps FEC: Add redundant information to the bit stream that helps

receiver correct channel induced bit errors. Used for fast receiver correct channel induced bit errors. Used for fast fading channelsfading channels

ARQ: Retransmit entire packets of data when the receiver ARQ: Retransmit entire packets of data when the receiver cannot decode the packet. Used for slow fading channelscannot decode the packet. Used for slow fading channels



Soft decision decodingSoft decision decoding• Efficiency of decoding depends on chosen codewordEfficiency of decoding depends on chosen codeword• At receiver, the decoder tries to decode the code words At receiver, the decoder tries to decode the code words

into information symbolsinto information symbols• Separate symbols as much as possible to minimize Separate symbols as much as possible to minimize

probability that decoder interprets one symbol for probability that decoder interprets one symbol for another. These are called maximum distance codes. E.g. another. These are called maximum distance codes. E.g. Reed Solomon codes.Reed Solomon codes.

• In soft decision decoding, the distance between the code In soft decision decoding, the distance between the code word and symbols is calculated as the Euclidian distance word and symbols is calculated as the Euclidian distance rather than the hamming distance. No information is rather than the hamming distance. No information is discarded during the coding process.discarded during the coding process.

• Turbo coding is a recursive scheme that iterates a Turbo coding is a recursive scheme that iterates a number of cycles to enhance the probability of number of cycles to enhance the probability of successful decodingsuccessful decoding



Deadline dependent coding:Deadline dependent coding:• Uses FEC and ARQ to improve Bit Error Uses FEC and ARQ to improve Bit Error

RateRate• Have a number of re-transmissions Have a number of re-transmissions

before the deadline; retransmissions before the deadline; retransmissions have different coding rate depending on have different coding rate depending on the remaining time to the deadlinethe remaining time to the deadline

• Tradeoff between throughput and how Tradeoff between throughput and how much redundant information is needed much redundant information is needed to secure the communication linkto secure the communication link



From release time to deadline, there is a transmission time window. The From release time to deadline, there is a transmission time window. The aim is to transmit the information within this window and succeed with a aim is to transmit the information within this window and succeed with a certain probabilitycertain probability

Send predefined number of transmissions. Therefore no need to wait for Send predefined number of transmissions. Therefore no need to wait for ACK. Decoder keeps packet even if decoding fails and performs additional ACK. Decoder keeps packet even if decoding fails and performs additional processing such as majority voting. Use different codes for different processing such as majority voting. Use different codes for different packets to conserve energy.packets to conserve energy.• Fading nature of channel will give error bursts. ARQ isolates the error burstsFading nature of channel will give error bursts. ARQ isolates the error bursts• Decoder keeps information for future use enhancing the decoder efficiency.Decoder keeps information for future use enhancing the decoder efficiency.


Ultra wide-Band radioUltra wide-Band radio Transmitter sends Gaussian pulses with duration less than a Transmitter sends Gaussian pulses with duration less than a

nanosecond. This is called a Gaussian monocyclenanosecond. This is called a Gaussian monocycle

Monocycle is a wide bandwidth signal with center frequency Monocycle is a wide bandwidth signal with center frequency and bandwidth dependent on the width of the pulseand bandwidth dependent on the width of the pulse

Modulation done in time domain by introducing different Modulation done in time domain by introducing different delays between pulses for different symbolsdelays between pulses for different symbols

Signal not vulnerable to multipath fading to the same Signal not vulnerable to multipath fading to the same extent as signals with carrier frequencyextent as signals with carrier frequency

The bandwidth allows the transmitter to send at a very low The bandwidth allows the transmitter to send at a very low output power. Hence it does not interfere with already output power. Hence it does not interfere with already allocated bandsallocated bands

Fear of interference with GPS signals because of their Fear of interference with GPS signals because of their relatively low powerrelatively low power


The FutureThe Future Wireless Technologies will play an important role even in Wireless Technologies will play an important role even in

safety critical industrial applicationssafety critical industrial applications

First step is to implement non-critical applications and get First step is to implement non-critical applications and get wireless technology accepted in the industrial sectorwireless technology accepted in the industrial sector

For safety critical applications, more research is requiredFor safety critical applications, more research is required

New wireless technologies with higher throughput makes it New wireless technologies with higher throughput makes it possible to use complex coding schemes possible to use complex coding schemes

These coding schemes handle the insecure wireless media These coding schemes handle the insecure wireless media in a predictable and secure wayin a predictable and secure way

8/4/2015 Cpre 458/558: Real-Time Systems (G. Manimaran) 1 Wireless Communication in Industrial Networks Kavitha Balasubramanian Teaching Assistant, CprE.

Documents

industrial applications

wireless industrial

accepted standards

mass production

future slide

g slide

industry slide

communication system