int. usn workshop, hanyang & sunchon universities, korea, 14-16 february 2008 using zigbee and...

Int. USN Workshop, Hanyang & Sunchon Universities, Korea, 14-16 February 2008

Using ZigBee and 802.11 for Real-timeApplications

José Fonseca, Paulo Bartolomeu

[email protected]; [email protected]

mailto:[email protected]

mailto:[email protected]

Int. USN Workshop, Korea - 14/2/2008 - 2 -

0. Portugal


0. Aveiro

• Aveiro is a city with around 100,000 inhabitants.• Holds several important r&d centers in telecommunications:• PT – Inovação• Nokia – Siemens• NEC

• University with 15,000 students• 1,500 in Electronics and Telecommunications.• Two academic research centers in the field:• Instituto de Telecomunicações• IEETA

Aveiro


1. Introduction

• Recent application domains where wireless communications are becoming pervasive require real-time operation.

• We are interested in the following:• Assistive technologies.• Building automation.• Vehicular communications.• Industrial automation.

• Although some of these domains use proprietary approaches for wireless communications (e.g. assistive technologies), we believe in standard solutions.


2. Some examples of applications

• These two fields are our main target for research

• Assistive Technologies:• Patient monitoring (e.g. cardiac patients, Alzheimer patients, …)• Home and device automation for severely impaired people, e.g.

tetraplegic.• Health Smart Homes for ill or elderly people.

• Vehicular Communications:• Vehicle to vehicle (V2V) communications for safety and comfort

applications (hard braking, adaptive cruise control).• Infrastructure to vehicle (I2V) communications for safety and road

management (traffic light violations, road condition information, tolling, traffic information).


2. Some examples of applications (2)

• These two fields share some problems of the first two and are also of interest for us.

• Building Automation:• We believe that there is here lots of interest in wireless communications.• We are particularly interested in retrofitting private houses.

• Industrial Automation:• We have done extensive work in real-time networks (fieldbuses and

Ethernet).• We believe that the introduction of wireless interconnections between the

networks or replacing partially or totally the networks is an issue.• A wealth of real-time and dependability problems exist here.


3. Technologies that interest us

• Bluetooth• Assistive devices.

• Interfaces for tetraplegic people.• Specific applications.

• MIDI cable replacement.

• ZigBee and IEEE802.15.4• Assistive Technologies in general.

• Fall detectors, cardiac monitoring.• Home Automation.

• Retrofitting private homes (lights, doors, curtains, devices).• Homes for tetraplegic people (the B-Live System – Micro I/O)

• Building and Enterprise management applications.• Access control, Time attendance systems• Car parking management

• Industrial Automation


3. Technologies that interest us (2)

• IEEE802.11• IEEE802.11e is a promising standard for real-time communications.

• Industrial automation.• IEEE802.11p (WAVE) @ 5.9GHz.

• Still being closed.• A promising standard for vehicular communications.

• WiMax• Primarily designed for the “last mile” communications in developing

regions without cabled infrastructures.• Also promising for vehicular communications (a mobile version exists) due

to an enhanced range when compared with IEEE802.11.


4. R&D Partnerships

• Some Industrial Partners• Micro I/O – A Spin-off company of the University of Aveiro• BRISA – The largest portuguese motorway company with branches in the USA,

Poland, Brasil.• PT – In – The R&D branch of the largest portuguese telecommunications company

with branches in Brasil and several african countries.• Several companies under the InovaRia Consortium (a cluster of SMEs and PT – In,

in the field of information technologies and communications).• CMRRC – Rovisco Pais (Rehabilitation Center)• CERCITOP (Home Care and Daily Care Center)

• Some Academic Partners• IT – Instituto de Telecomunicações• University of Porto, Faculdade de Engenharia• ISEL / ISEC – Instituto Superior de Engenharia de Lisboa / Porto• Instituto Politécnico de Castelo Branco• CERTIC – Universidade de Trás-os-Montes e Alto Douro


5. Research in Bluetooth

• Objective: to use Bluetooth in time constrained applications, such as MIDI cable replacement (a widespread musical instruments interconnection standard).

• The focus was in performing measures of end-to-end delays in open environments subject to interferences, e.g. from Wi-Fi.

• The use of Bluetooth should be done without changing the standard modules available.

• So, the experimentation was done at various levels of the available Bluetooth stack.

• This line of research is stopped since 2006.


5. Research in Bluetooth (2)

• End-to-end delays were studied in:

• Serial Port Profile based links (based on v1.1 devices)• Slave transmissions: delays can reach the 500 ms threshold although

being, in average, smaller than 50ms.• Master transmissions: delays are smaller than 100ms being, in average,

smaller than 30 ms.

• ACL based links (based on v1.1 devices)• Slave transmissions: delays are, in average, smaller than 25ms with a

jitter of 10ms.• Master transmissions: delays are, in average, smaller than 20ms with a

jitter of 1ms.


5. Research in Bluetooth (3)

• Yet the Bluetooth example:• ACL Master-transmitting delays


6. Research in ZigBee / IEEE802.15.4

• Managing the system’s database:• Applications with safety critical requirements, e.g. industrial automation,

vehicular communications, assistive technologies, depend strongly on a uniform view of the system’s variables, shared by all nodes.

• In cabled based solutions, several fieldbuses rely on broadcast to simplify the process of achieving coherent data bases, but:

• Atomic broadcast is quite difficult to achieve even in those cabled broadcast buses (e.g. CAN).

• Broadcast is less problematic in small networks, e.g.• A single Bluetooth piconet• A star topology in 802.15.4


6. Research in ZigBee / IEEE802.15.4 (2)

• Broadcast can lead to significant worst case values in a large network.

• Example: the case of broadcast in a ZigBee mesh network:

• The timeliness of the broadcast mechanism must be evaluated.• It is complex to derive the worst case broadcast delay due to the multiple

routes that can be used during this process.• And due to the possibility of retransmissions when required due to

interferences (a model is required).• Worst case values seem rather long even in small networks.

• We were concerned with broadcast in ZigBee to facilitate some applications e.g. in health smart homes.



• Best-case delays • end-node to a router

• router to a router

• last hop of the path

• Worst-case delays • end-node to a router

• router to a router

• last hop of the path

End-to-end broadcast delays (theoretical analysis)



• End-to-end delay of a broadcast initiated by an end-node

• End-to-end delay of a broadcast initiated by a router




• Best case end-to-end delay

• Worst case end-to-end delay




End-to-end broadcast delays (practical assessment)

Percentage of lost messages as a function of the (Wi-Fi interference) load




Histograms of the delays bellow the 500ms threshold

1 byte (interference) payload 1472 bytes (interference) payload




Histogram of the delays above the 500ms threshold




Minimum and maximum delays vs. (interference) load



• Practical results are consistent with the theoretical analysis

• Best case delay is above the 20 ms threshold • Worst-case delay is bellow the 2.4 s limit.

• Delays become significantly large (above the 500 ms threshold) in environments exposed to disturbances

• In (almost) interference-free environments, delays are bellow the 100 ms limit

• Thus ZigBee broadcast communications seem adequate for building automation systems of reduced size when the network operates in free RF channels



• Achieving real-time traffic management in IEEE802.15.4:

• Solution: to use GTSs – Guaranteed Time Slots in the superframe structure of the beacon enabled mode

• Limited number of slots.• Slot allocation

• On-going work: Implementing a flexible real-time traffic management using the GTS mechanism based on the FTT – Flexible Time-Triggered communication model.



• Centralized synchronization:• Superframe structure;• FTT master = PAN coordinator (PC);• TT and ET traffic using CFP and CAP;• Real-time requirements (GTSs).

• Centralized traffic scheduling:• Communication requirements / message scheduler at PC;• On-line admission control to guarantee traffic timeliness.

• Master / multislave transmission• Synchronous traffic schedule conveyed in beacon frame (“GTS fields”);• GTS valid for current superframe.


7. Research in IEEE802.11

• IEEE 802.11e enables traffic with different QoSs:• Indeterminate number of collisions can occur among stations using

the highest quality of service.

• An improved traffic management mechanism is required.

• One of the solutions studied was a Virtual Token Passing Mechanism:• Established among RT stations, • Complemented by a traffic separation mechanism (TSm),• To guarantee that a RT station contending for the medium will win

the contention prior to any other standard (ST) station.


7. Research in IEEE802.11 (2)

• Analyzing and implementing IEEE802.11p

• Also known as:• Dedicated Short Range Communications (DSRC)• Wireless Access in Vehicular Environments (Wave)

• Operates in the 5.9 GHz band.

• On-going project starting now, developing a demonstrator for a vehicular safety application.

• Real-time traffic management will be studied, in principle taking into consideration master-slave architectures with the master at the base station.


8. Some issues regarding our work with WiMax

• WiMax: Worldwide Interoperability for Microwave Access, IEEE 802.16 (IEEE, 2008)

• Allows fixed and mobile access with Non-Line Of Sight (NLOS) reaching data rates of 40 Mbps in a 3Km to 10 Km cell, per channel.

• Development based on a Fujitsu WiMAX Development kit.

• Under evaluation the use of this technology for vehicular communications.

• Work funded by TELESAL Network, by PT Inovação, and by Instituto de Telecomunicações, under contract with the University of Aveiro, funded by BRISA, S.A


9. Some publications

• P. Bartolomeu, J.A. Fonseca, F. Vasques, “On the Timeliness of Broadcast Communications using ZigBee”, submitted to WFCS’2008, 7th IEEE Workshop on Factory Communication Systems, Dresden, Germany, May 20-23, 2008.

• P. Simao, V. Santos, J.A. Fonseca, “Time Attendance System with Multistation and Wireless Communications”, submitted to 12th Annual IEEE International Symposium on Consumer Electronics – ISCE’2008, Algarve, Portugal, April, 14-16th 2008.

• P. Bartolomeu, J.A. Fonseca, F. Vasques, “Challenges in Health Smart Homes”, ATDMCP - Ambient Technologies for Diagnosing and Monitoring Chronic Patients Workshop, part of the 2nd International Conference on Pervasive Computing Technologies for Healthcare 2008, Tampere, Finland 29 Jan 2008.

• P. Bartolomeu, J.A. Fonseca, V. Santos, A. Mota, V. Silva, M. Sizenando, “Automating Home Appliances for Elderly and Impaired People: The B-Live Approach”, DSAI'2007 – “Software Development for Enhancing Accessibility and Fighting Info-exclusion”, November, Vila Real, Portugal, 2007.

• R. Moraes, F. Vasques, P. Portugal, J.A. Fonseca, “VTP-CSMA: A Virtual Token Passing Approach for Real-Time Communication in IEEE 802.11 Wireless Networks”, IEEE Transactions on Industrial Informatics,Vol. 3, No. 3, August 2007.

• N. Ferreira, J.A. Fonseca, “Using Time-Triggered Communications over IEEE 802.15.4”, WIP, Proceedings 12th IEEE Conference on Emerging Technologies and Factory Automation, Patras – Greece, September 25-28, 2007.


9. Some publications (2)

• R. Moraes, F. Vasques, P. Portugal, and J.A. Fonseca, “Real-Time Communication in 802.11 Networks: The Virtual Token Passing VTP-CSMA Approach” Proceedings of the 31st IEEE Conference on Local Computer Networks (LCN), Tampa, Florida, USA, November 14-17, 2006.

• P. Bartolomeu, J.A. Fonseca, P. Rodrigues, L. Girão, “Evaluating the Timeliness of Bluetooth ACL connections for the Wireless Transmission of MIDI”, Proceedings of ETFA’06, 11th IEEE International Conference on Emerging Technologies and Factory Automation, Prague, Czech Republic, September 20-22, 2006.

• R. Moraes, F. Vasques, P. Portugal, and J.A. Fonseca, “An Enhanced Traffic Separation Mechanism to Support Real-Time Communication in IEEE 802.11e Networks”, Proceedings of the 24th Brazilian Symposium on Computer Networks (SBRC). Curitiba, Brazil, pp. 1075-1078, May 29 - June 2, 2006.

• R. Moraes, F. Vasques, P. Portugal, J. A. Fonseca, “A Traffic Separation Mechanism (TSm) allowing the coexistence of CSMA and real-time traffic in Wireless 802.11e Networks” WSEAS Transactions on Communications, vol. 5, no. 5, pp. 890-897, May 2006.

• R. Moraes, F. Vasques, P. Portugal, and J.A. Fonseca, “A new Traffic Separation Mechanism (TSm) in Wireless 802.11e Networks: A simulation study”, Proceedings of the 6th WSEAS International Conference on Robotics, Control and Manufacturing Technology (ROCOM '06), Hangzhou, China, pp. 107-112, April 16-18, 2006.

• P. Bartolomeu, J. A. Fonseca, P. Duarte, P. Rodrigues, L. Girão, “MIDI over Bluetooth”, ETFA’2005, 10th IEEE International Conference on Emerging Technologies and Factory Automation, September 19-22, 2005, Catania, Italy.


9. Conclusions

• We believe that wireless communications will have widespread use in applications that require real-time and dependable operation, e.g.:

• Assistive Technologies, Vehicular applications, Industrial Automation

• We think standard technologies are the most promising:• Price is lower and dissemination is easier.• Research and development tends to be more focused on them.

• Deterministic communications will hardly be achieved in the wireless domain, but:

• Several applications can live with lost samples (e.g. NCSs).• A reasonable probability of achieving response times within a certain

threshold is possible to be determined.• Improved MACs and other mechanisms can lead to better traffic

management, less influence of interferences, improved coherence in the distributed database, ...

int. usn workshop, hanyang & sunchon universities, korea, 14-16 february 2008 using zigbee and...

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