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

2. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks2 Agenda Introduction Introduction Existing Wireless Standards Existing Wireless Standards Non real time applications Non real time applications Soft real-time applications Soft real-time applications Hard Real-time applications Hard Real-time applications Techniques for improving reliability Techniques for improving reliability The Future The Future

3. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks3 Introduction Immense development of wireless communication technology for consumer electronics Immense development of wireless communication technology for consumer electronics Also finding its way into industrial setup Also finding its way into industrial setup Salient features of communication system in industrial application Salient features of communication system in industrial application Part of production facilityPart of production facility Loss of production costly in comparison to the communication systemLoss of production costly in comparison to the communication system Focus on reliability, predictability and fault toleranceFocus on reliability, predictability and fault tolerance

4. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks4 Introduction … How wireless is accepted? How wireless is accepted? Technology should have clear benefits and is reliable so as to justify investmentTechnology should have clear benefits and is reliable so as to justify investment Globally accepted standards has led to mass chip productionGlobally accepted standards has led to mass 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

5. 5 Motivation for wireless industrial networks Reduced installation, reconfiguration and maintenance costs Reduced installation, reconfiguration and maintenance costs Easy access to machines for diagnostic or programming purposes Easy access to machines for diagnostic or programming purposes Improved coverage of the factory floor Improved coverage of the factory floor Eliminates adverse effects due to damage of cabling Eliminates adverse effects due to damage of cabling Desire to save on cabling Desire to save on cabling Globally accepted standards leading to mass production and reduced prices Globally accepted standards leading to mass production and reduced prices

6. 6 Industrial Applications

7. 7 Workload Application Requirements Meeting Deadlines Predictability and Reliability Guaranteed packet delivery Guaranteed delivery times Prioritizing messages Message Characteristics Periodic traffic with deadlines Acyclic packets (alarms) with bounded latency Short packets (order of kilobytes)

8. 8 Industrial wireless network market SHORT LONGLOW HIGH PAN LAN TEXTGRAPHICSINTERNETHI-FI AUDIO STREAMING VIDEO DIGITAL VIDEO MULTI-CHANNEL VIDEO Bluetooth1 Bluetooth 2 ZigBee 802.11b 802.11a/HL2 & 802.11g

9. 9 Existing protocols- comparison Feature802.11BluetoothZigbee Interference from other devices --Avoided using frequency hopping Dynamic channel selection possible Optimized forMultimedia, 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 ConsumptionHighLow (Large packets over small networks) Least (Small packets over large networks) Voice support/SecurityYes/Yes No/Yes Type of Network / Channel Access Mobile / CSMA/CA and polling Mobile & Static / PollingMostly static with infrequently used devices / CSMA and slotted CSMA/CA Bit error rateHighLow Real Time deadlines???

10. 10 Challenges and Spectrum of Solutions Wireless Challenges Attenuation Fading Multipath dispersion Interference High Bit Error rate Burst channel errors Application Requirements Reliable delivery Meet deadlines Support message priority Existing Solutions

11. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks11 Existing Wireless Standards 802.11 802.11 Oldest and most matureOldest and most mature Spread spectrum techniques for PHY layerSpread spectrum techniques for PHY layer Direct Sequence Spread spectrum with Differential Binary Phase Shift Keying or Differential Quadrature Phase Shift Keying Direct Sequence Spread spectrum with Differential Binary Phase Shift Keying or Differential Quadrature Phase Shift Keying Frequency Hopping Spread Spectrum with Gaussian Frequency Shift Keying Frequency Hopping Spread Spectrum with Gaussian Frequency Shift Keying Split intoSplit into 802.11a – 5GHz ISM band, Up to 2 Mbps 802.11a – 5GHz ISM band, Up to 2 Mbps 802.11b – 2.45GHz ISM band, Up to 11 Mbps 802.11b – 2.45GHz ISM band, Up to 11 Mbps 802.11e – Supports QoS 802.11e – Supports QoS Uses CSMA/CA MAC (contention based) with dynamic packet length up to 4096 bytes longUses CSMA/CA MAC (contention based) with dynamic packet length up to 4096 bytes long

12. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks12 Existing Wireless Standards … HiperLAN/2 HiperLAN/2 Support for soft real-time applications like mediaSupport for soft real-time applications like media Uses Time Division Duplex scheme (Contention free)Uses Time Division Duplex scheme (Contention free) Static packet length of 54 bytesStatic packet length of 54 bytes Better suited for real-time applications because of time deterministic MACBetter suited for real-time applications because of time deterministic MAC OFDM modulationOFDM modulation Multicarrier modulation scheme Multicarrier modulation scheme Adapts bit-rate based on channel conditions Adapts bit-rate based on channel conditions Handles performance reduction due to multipath fading radio channels Handles performance reduction due to multipath fading radio channels

13. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks13 Existing Wireless Standards … Bluetooth Bluetooth Low-complexity low-cost solution for short-range wireless communicationsLow-complexity low-cost solution for short-range wireless communications Intended for cable replacement and adhoc connections of consumer devicesIntended for cable replacement and adhoc connections of consumer devices Instead of creating protocols in all layers of the protocol stack for each application, profiles existsInstead of creating protocols in all layers of the protocol stack 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

14. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks14 Non real-time applications Remote Control: Remote Control: Used for remote control of overhead cranesUsed for remote control of overhead cranes Dependent on securityDependent 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 control roomLocally on demand or over a wireless network to a control room For local information, use PDA or laptop that connects to sensors or actuatorsFor local information, use PDA or laptop that connects to sensors or actuators Plant equipped with access point for communication with the control room at the same timePlant equipped with access point for communication with the control room at the same time Using Bluetooth is a cheap way of achieving local health monitoringUsing Bluetooth is a cheap way of achieving local health monitoring

15. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks15 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 protocol Object Exchange protocol includes a file transfer protocol TCP/IP over Bluetooth transport protocols TCP/IP over Bluetooth transport protocols Fault ToleranceFault Tolerance With Error detection/correction, there is a probability that the errors go undetected (depends on type of coding method and the code rate) With Error detection/correction, there is a probability that the errors go undetected (depends on type of coding method and the code rate) Repeat message a number of times and use majority voting Repeat message a number of times and use majority voting For small configuration changes, value is uploaded into the device and echoed back. A mismatch will initiate a re-transmission For small configuration changes, value is uploaded into the device and echoed back. A mismatch will initiate a re-transmission Configured device can echo the changed value a number of times – if correct value is received all the times, there is a very little chance that the configured value is wrong Configured device can echo the changed value a number of times – if correct value is received all the times, there is a very little chance that the configured value is wrong

16. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks16 Non real-time applications … Internet Connectivity: Internet Connectivity: Used for surveillance, supervision and health monitoring of devicesUsed for surveillance, supervision and health monitoring of devices Demands soft real-time guarantees if applications like voice and video need to be supportedDemands soft real-time guarantees if applications like voice and video need to be supported E.g. Distributed supervision of heat and ventilation systemE.g. Distributed supervision of heat and ventilation system Heat/ventilation system has an embedded web servers that runs scriptsHeat/ventilation system has an embedded web servers that runs scripts Personnel can supervise and configure the system using a PC with a web browserPersonnel can supervise and configure the system using a PC with a web browser Can use 802.11 or BT depending on the bandwidth requirementsCan use 802.11 or BT depending on the bandwidth requirements

17. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks17 Soft real-time applications QoS Parameters include QoS Parameters include deadline : delay constraints of the applicationdeadline : delay constraints of the application probability of correct delivery within the deadline: bit error rate of the communication channelprobability of correct delivery within the deadline: bit error rate of the communication channel Jitter of the delayJitter of the delay

18. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks18 Soft real-time applications … Event Registration: Event Registration: Time-stamp an event with high time resolutionTime-stamp an event with high time resolution Transmission of the event from device that registered the event is not so critical i.e. requires only a reasonable response time.Transmission of the event from device that registered the event is not so critical i.e. requires only a reasonable response time. E.g. Events don’t control anything but should be logged at the right timeE.g. Events don’t control anything but should be logged at the right time Requires clock synchronizationRequires clock synchronization

19. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks19 Soft real-time applications … Measurement: Measurement: Measures a physical process, timestamp the sample values and transmit sequence of values to the userMeasures a physical process, timestamp the sample values and transmit sequence of values to the user Present course of events in a correct way so that the time stamps can reconstruct the processPresent course of events in a correct way so that the time stamps can reconstruct the process Notion of global correct time is importantNotion of global correct time is important Requires clock synchronization; precision demands is dictated by the granularity of the measured valuesRequires clock synchronization; precision demands is dictated by the granularity of the measured values For e.g. Geological or industrial wireless sensor system with sensors collecting data and transmitting them to base station or control roomFor e.g. Geological or industrial wireless sensor system with sensors collecting data and transmitting them to base station or control room No delay constraints in transmission but measures and timestamps done in real-time to reconstruct course of events of the physical processNo delay constraints in transmission but measures and timestamps done in real-time to reconstruct course of events of the physical process High accuracy and synchronized clocksHigh accuracy and synchronized clocks 802.11 : 150ms; BT: 20us 802.11 : 150ms; BT: 20us

20. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks20 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 application to the userDelay and loss rate constraints based on comfort provided by application to the user BT:BT: Supports voice channels Supports voice channels Range of 10m Range of 10m Establishes adhoc connections: As soon as 2 or 3 people are within the range, a communication channel is established Establishes adhoc connections: As soon as 2 or 3 people are within the range, a communication channel is established HiperLAN/2:HiperLAN/2: Supports guaranteed media streams Supports 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 systemE.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

21. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks21 Hard real-time applications Result presented too late is disastrous to the system Result presented too late is disastrous to the system One missed deadline will led to a disaster and cannot be tolerated One missed deadline will led to a disaster and cannot be tolerated E.g. control loops E.g. control loops Most distributed real-time systems assume fault- free operation of the processing unit and communication channel that is not true Most distributed real-time systems assume fault- free operation of the processing unit and communication channel that is not true Error probability cannot be neglected for wireless channel and its function cannot be guaranteed at all timesError probability cannot be neglected for wireless channel and its function cannot be guaranteed at all times Errors are sporadic in nature for wireless while for wired, permanent errors caused by wire or connector damage dominatesErrors are sporadic in nature for wireless while for wired, permanent errors caused by wire or connector damage dominates

22. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks22 Hard real-time applications … Parameters: Parameters: DeadlineDeadline Probability to deliver within the deadlineProbability to deliver within the deadline If we quantify the probability for communication channels, we can analyze the error probability of the entire system and then employ risk analysis methods for calculating failure characteristics of the system If we quantify the probability for communication channels, we can analyze the error probability of the entire system and then employ risk analysis methods for calculating failure characteristics of the system Problem: Quantify Probability to deliver within the deadline for certain system conditions Problem: Quantify Probability to deliver within the deadline for certain system conditions

23. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks23 Techniques for improving reliability of wireless channel Based on radio signals Based on radio signals Transmitted wave interferes with the surrounding environment creating multiple waves hitting the receiver antenna Transmitted wave interferes with the surrounding environment creating multiple waves hitting the receiver antenna Waves delayed with respect to each other Waves delayed with respect to each other For some conditions, there is destructive interference at the receiver antenna causing signal attenuation. This is called fading For some conditions, there is destructive interference at the receiver antenna causing signal attenuation. This is called fading Fading causes bursts of errors in wireless channel Fading causes bursts of errors in wireless channel Fast fading occurs when the transmitter or the receiver move fast. Slow fading occurs in stationery situations. Fast fading occurs when the transmitter or the receiver move fast. Slow fading occurs in stationery situations. FEC: Add redundant information to the bit stream that helps receiver correct channel induced bit errors. Used for fast fading channels FEC: Add redundant information to the bit stream that helps receiver correct channel induced bit errors. Used for fast fading channels ARQ: Retransmit entire packets of data when the receiver cannot decode the packet. Used for slow fading channels ARQ: Retransmit entire packets of data when the receiver cannot decode the packet. Used for slow fading channels

24. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks24 Techniques for improving reliability of wireless channel Soft decision decoding Soft 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 into information symbolsAt receiver, the decoder tries to decode the code words into information symbols Separate symbols as much as possible to minimize probability that decoder interprets one symbol for another. These are called maximum distance codes. E.g. Reed Solomon codes.Separate symbols as much as possible to minimize probability that decoder interprets one symbol for another. These are called maximum distance codes. E.g. Reed Solomon codes. In soft decision decoding, the distance between the code word and symbols is calculated as the Euclidian distance rather than the hamming distance. No information is discarded during the coding process.In soft decision decoding, the distance between the code word and symbols is calculated as the Euclidian distance rather than the hamming distance. No information is discarded during the coding process. Turbo coding is a recursive scheme that iterates a number of cycles to enhance the probability of successful decodingTurbo coding is a recursive scheme that iterates a number of cycles to enhance the probability of successful decoding

25. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks25 Techniques for improving reliability of wireless channel Deadline dependent coding: Deadline dependent coding: Uses FEC and ARQ to improve Bit Error RateUses FEC and ARQ to improve Bit Error Rate Have a number of re-transmissions before the deadline; retransmissions have different coding rate depending on the remaining time to the deadlineHave a number of re-transmissions before the deadline; retransmissions have different coding rate depending on the remaining time to the deadline Tradeoff between throughput and how much redundant information is needed to secure the communication linkTradeoff between throughput and how much redundant information is needed to secure the communication link

26. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks26 Techniques for improving reliability of wireless channel 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 certain probability 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 certain probability Send predefined number of transmissions. Therefore no need to wait for ACK. Decoder keeps packet even if decoding fails and performs additional processing such as majority voting. Use different codes for different packets to conserve energy. Send predefined number of transmissions. Therefore no need to wait for ACK. Decoder keeps packet even if decoding fails and performs additional processing such as majority voting. Use different codes for different 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.

27. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks27 Ultra wide-Band radio Transmitter sends Gaussian pulses with duration less than a nanosecond. This is called a Gaussian monocycle Transmitter sends Gaussian pulses with duration less than a nanosecond. This is called a Gaussian monocycle Monocycle is a wide bandwidth signal with center frequency and bandwidth dependent on the width of the pulse Monocycle is a wide bandwidth signal with center frequency and bandwidth dependent on the width of the pulse Modulation done in time domain by introducing different delays between pulses for different symbols Modulation done in time domain by introducing different delays between pulses for different symbols Signal not vulnerable to multipath fading to the same extent as signals with carrier frequency Signal not vulnerable to multipath fading to the same extent as signals with carrier frequency The bandwidth allows the transmitter to send at a very low output power. Hence it does not interfere with already allocated bands The bandwidth allows the transmitter to send at a very low output power. Hence it does not interfere with already allocated bands Fear of interference with GPS signals because of their relatively low power Fear of interference with GPS signals because of their relatively low power

28. 8/4/2015 Cpre 458/558: Wireless Communication in Industrial Networks28 The Future Wireless Technologies will play an important role even in safety critical industrial applications Wireless Technologies will play an important role even in safety critical industrial applications First step is to implement non-critical applications and get wireless technology accepted in the industrial sector First step is to implement non-critical applications and get wireless technology accepted in the industrial sector For safety critical applications, more research is required For safety critical applications, more research is required New wireless technologies with higher throughput makes it possible to use complex coding schemes New wireless technologies with higher throughput makes it possible to use complex coding schemes These coding schemes handle the insecure wireless media in a predictable and secure way These coding schemes handle the insecure wireless media in a predictable and secure way