Using IEEE's Zigbee Protocol to design a low power, noise efficient node for home automation. The presentation provides some of the key ingredients and working modes for the Zigbee Protocol. Many companies like (DiGi) built smart zigbee radios (commercially named: XBee) based on these protocol stacks, which now help reshaping wireless sensor networking and low power consumer electronics integration .

1. Electrical Engineering Department – NFC IET Multan
Building Smart Homes
Using Zigbee
Omer Ali

2. Structure
Introduction
Concepts
Architecture
Implementation
Evaluation
Reference
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Introduction

4. Introduction
What is ZigBee?
• • Specification of protocols for small, low-power radios
History
• May 2003: IEEE 802.15.4 completed
• December 2004: ZigBee specification ratified
• June 2005: public availability
ZigBee-Alliance
• Companies developing and promoting the standard
• 150+ members
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5. ZigBee Alliance - Members
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and many more....

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Concepts

7. Why do we need another WPAN standard?
Decreasing
• Power consumption
–ZigBee: 10mA <==> BT: 100mA
• Production costs
–In the beginning of 2005
–ZigBee: 1.1 $ <==> BT: 3 $
• Development costs
–Codesize ZB/codesize BT = ½
• Bit-error-rate (BER)
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8. Why do we need another WPAN standard?
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picture taken from [9]

9. Why do we need another WPAN standard?
Increasing
• Sensitivity
–ZigBee: -92dbm(0,63pW) <==> BT: -82dbm(6,2pW)
• flexibility
–No. of supported nodes
–ZigBee: 65536 (in a mesh) <==> BT: 7 (in a star)
• Security
–ZigBee: AES (128bit) <==> BT: SAFER (64/128bit)
• Latency requirements
–ZigBee: optional guaranteed time slot
• Range
–ZigBee: up to 75 m in LOS condition <==> BT: 10 m
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10. Usage Scenarios
• Industrial & commercial
• Consumer electronics
• Toys & games
• PC & periphals
• Personal health care
• home/building automation
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 Just everything you can imagine for wireless sensor
nodes or in general short range communications

11. ZigBee Frequency Bands
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12. ZigBee Protocol Stack
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IEEE 802 Model
7 Application User Application <<ZigBee
6 Presentation
5 Session Application Profile Upper Layers
4 Transport
3 Network Network
2 Data Link Data Link Logic Link Control (LLC) <<802.14.5
Media Access Control (MAC)
1 Physical Physical Physical
7Layer
ISO-OSI-Model
Simplified 5Layer
ISO-OSI-Model

13. Protocol Stack
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picture taken from [10]

14. ZigBee Profiles
Profiles:
Definition of ZigBee-Profiles
• describes a common language for exchanging data
• defines the offered services
• device interoperatbility across different manufacturers
• Standard profiles available from the ZigBee Alliance
• profiles contain device descriptions
• unique identifier (licensed by the ZigBee Alliance)
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Architecture

16. ZigBee Node-Types
ZigBee Coordinator (ZBC) (IEEE 802.15.4 FFD)
• only one in a network
• initiates network
• stores information about the network
• all devices communicate with the ZBC
• routing functionality
• bridge to other networks
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17. ZigBee Node-Types
ZigBee Router (ZBR) (IEEE 802.15.4 FFD)
• optional component
• routes between nodes
• extends network coverage
• manages local address allocation/de-allocation
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18. ZigBee Node-Types
ZigBee End Device (ZBE) (IEEE 802.15.4 RFD)
• optimized for low power consumption
• cheapest device type
• communicates only with the coordinator
• sensor would be deployed here
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19. Addressing/Discovering ZigBee Nodes
Addressing ZigBee Nodes:
• optimized unique 64 bit address (IEEE 802.15.4)
• 16 bit network address (65536 devices)
• 256 sub addresses for subunits
Device Discovery
• unicast (NWK id known), broadcast (NWK id unknown)
• ZBC-/ZBR-Response: IEEE address + NWK address + all known network addresses
Binding
• creating logical links between 2 or more end devices
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20. Addressing/Binding ZigBee Endpoints
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picture taken from [11]

21. Traffic-Types
1. Data is periodic
• application dictates rate
2. Data is intermittent
• application or stimulus dictates rate (optimun power savings)
3. Data is repetitive (fixed rate a priori)
• device gets guaranteed time slot
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22. Traffic-Modes
1. Beacon mode:
• beacon send periodically
• Coordinator and end device can
go to sleep
• Lowest energy consumption
• Pricise timing needed
• Beacon period (ms-m)
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picture taken from [1]

23. Beacon-Mode
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picture taken from [8]

24. Traffic-Modes
1. Non-Beacon mode:
• coordinator/routers have to stay
awake (robust power supply
needed)
• heterogeneous network
• asymmetric power
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picture taken from [1]

25. Topologies
Mesh-Topology
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picture taken from [7]

26. Topologies
Tree-Topology
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picture taken from [7]

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Implementation

28. PHY layer
2400MHz Band specs
• 4 Bits per symbol
• DSSS with 32 Bit chips
• O-QPSK modulation
• Sine halfwave impulses
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Bit
to
Symbol
QPSK
Mod.
Symbol
to
Chip
Binary Data
Medium
picture taken from [4]

29. PHY layer
868/915 MHz Band specs
• 1 Bit per symbol
• Differential encoding
• DSSS with 15 Bit Chips
• BPSK modulation
• RC impulses (roll-off = 1)
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Diff.
Encoder
BPSK
Mod.
Bit
to
Chip
Binary Data
Medium

30. PHY layer
General specs and services
• Error Vector Magnitude (EVM) < 35%
• -3dBm minimum transmit power (500µW)
• Receiver Energy Detection (ED)
• Link Quality Indication (LQI)
• Use ED & LQI to reduce TX-power
• Clear Channel Assessment (CCA) with 3 modes
1.Energy above threshold
2.Carrier sense only
3.Carrier sense with energy above threshold
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31. PHY layer
PHY Protocol Data Unit (PPDU) frame structure
• Frame to be sent via radio
• Preamble for chip and symbol synchronization
• Contains either data or data acknowlegement
• Packet size 8-127 Octets
• Contains MAC Protocol Data Unit (MPDU)
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table taken from [1]

32. MAC layer
Channel access specification
• Beacon/Nonbeacon
• Define Superframe structure
• Slotted/unslotted CSMA-CA
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33. MAC layer
Managing PANs
• Channel scanning (ED, active, passive, orphan)
• PAN ID conflict detection and resolution
• Starting a PAN
• Sending beacons
• Device discovery
• Device association/disassociation
• Synchronization (beacon/nonbeacon)
• Orphaned device realignment
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34. MAC layer
Transfer handling
• Transaction based (indirect transmission)
–Beacon indication
–Polling
• Transmission, Reception, Rejection, Retransmission
–Acknowleded
–Not acknowledged
• GTS management
–Allocation/deallocation
–Usage
–Reallocation
• Promiscous mode
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35. MAC layer
Frame security
• Provided security features
–Access control
–Data encryption
–Frame integrity
–Sequential freshness
• Avaiable security modes
–Unsecured mode
–ACL mode
–Secured mode
• Avaiable security suites
–AES-CTR
–AES-CCM
–AES-CBC-MAC
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36. MAC layer
How far have we come?
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0
1
2
4
3
5
6
7
Problem: How do 6 and 7 talk to coordinator 0?
Solution: Routing (NWK Layer)

37. NWK layer
Distributed address assignment
• Tree structure or self managed by higher layer
• 16Bit network space divided among child routers
• Child routers divide there space again for their children
• Depends on:
–Maximum child count per parent
–Maximum child-routers per parent
–Maximum network depth
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38. NWK layer
Distributed address assignment - Example
• Cm=2 ; Rm=2 ; Lm=2
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Depth in network d Offset Value
0 3
1 1
2 0
0
1
4
5
6
?2

39. NWK layer
Routing cost
• Metric to compare „goodness“ of routes
• Base: Link cost between 2 neighbors
• Path cost = sum of link costs along the path
• Link cost determination:
–Link quality indication from PHY
–Statistical measures
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40. NWK layer
Route discovery
• Find or update route between specific source and destination
• Started if no active route present in routing table
• Broadcast routing request (RREQ) packets
• Generates routing table entries for hops to source
• Endpoint router responds with Routing response (RREP) packet
• Routes generated for hops to destination
• Routing table entry generated in source device
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41. NWK layer
Route discovery
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RREQ
RREP
1 2 3
4
2
1
5

42. NWK layer
Routing
• Check if routing table entry exists
• Initiate route discovery if possible
• Hierarchical routing as fallback
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Route maintenance
• Track failed deliveries to neighbors
• Initiate route repair when threshold reached
• Careful with network load!
• In case of total connectivity loss:
– Orphaning procedure
– Re-association with network

43. Application Level
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picture taken from [11]

44. Application Level
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picture taken from [11]

45. Application Layer
Application Support Sub-layer (APS):
• interface to NWK-layer (offers general set of functions)
• Data transmission, binding and security management
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picture taken from [1]

46. Application Level
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picture taken from [11]

47. Application Layer
Application Framework:
• Specifies Datatypes
• Devices describe themselves by ZigBee descriptor:
–frequency band
–power description
–application flags
–application version
–serial number
–manufacturer
–...
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48. Application Layer
Supported Data-types
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table taken from [1]

49. Application Level
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picture taken from [11]

50. Application Layer
ZigBee defined Objects (ZDO):
• provides common function for applications
• Initializes APS, NWK-Layer and Security Service Specification
• offers services like device-/service-descovery, binding and security management
• assembles information about the network
• for ZBC/ZBR -> e.g. binding table
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picture taken from [1]

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Evaluation

52. Pros and Cons
Pros
• good extension of existing
standards
• supported by many companies
• low power consumption
• low cost
• easy implemented (Designer
concentrates on end application)
• flexible network structure
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Cons
• Not many end devices
available yet
• Single point of failure
(centralized architecture)

53. Gadget example
Pantech & Curitel P1 phone
• Only a prototype
• control electrical appliances
• Check temperature & humidity
• Sending messages in case of trespass
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picture taken from [9]

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References

55. References
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[1] ZigBee Specifications v1.0
[2] “Designing with 802.15.4 and ZigBee”, Presentation Slides, available on ZigBee.org
[3] “ZigBee Tutorial”, http://www.tutorial-reports.com/wireless/zigbee
[4] IEEE 802.15.4 Specification
[5] “Network Layer Overview”, Presentation Slides, Ian Marsden, Embedded Systems Show,
Birmingham, October 12th, 2006, 064513r00ZB_MG_Network_Layer_Overview.pdf, available
on ZigBee.org
[6] “Designing a ZigBee Network”, Presentation Slides, David Egan, Ember Corporation, ESS
2006, Birmingham, 064516r00ZG_MG_Network_Design.pdf, available on ZigBee.org
[7] “ZigBee Architecture Overview”, Presentation Slides, Oslo, Norway June 2005,
ZigBee_Architecture_and_Specifications_Overview.pdf, available on ZigBee.org
[8] “Low Power Consumption Features of the IEEE 802.15.4/ZigBee LR-WPAN Standard”,
http://www.cens.ucla.edu/sensys03/sensys03-callaway.pdf
[9] “ZigBee Home Automation Mobile from Pantech”, http://www.i4u.com/article2561.html
[10] “Basic Lecture - ZigBee” http://www.korwin.net/eng/infor/info_zb_01.asp
[11] “Introduction to the ZigBee Application Framework”, Presentation Slides, ZigBee Open
House, San Jose, June 15th, 2006, 053340r06ZB_AFG-Overview-ZigBee-Open-House.pdf,
available on ZigBee.org

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Thank you