Zigbee - Building Smart Homes

Electrical Engineering Department – NFC IET Multan

Building Smart HomesUsing Zigbee

Omer Ali

Structure

IntroductionConceptsArchitectureImplementationEvaluationReference

Electrical Engg Dept ZigBee – Building Smart Homes slide 2 of 56


Introduction

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


ZigBee Alliance - Members


and many more....


Concepts

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)




picture taken from [9]


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


Usage Scenarios

• Industrial & commercial

• Consumer electronics

• Toys & games

• PC & periphals

• Personal health care

• home/building automation


Just everything you can imagine for wireless sensor nodes or in general short range communications

ZigBee Frequency Bands


ZigBee Protocol Stack


IEEE 802 Model7 Application User Application <<ZigBee6 Presentation5 Session Application Profile Upper Layers4 Transport3 Network Network2 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

Protocol Stack



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)



Architecture

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


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


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


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


Addressing/Binding ZigBee Endpoints



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


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)



Beacon-Mode



Traffic-Modes

1. Non-Beacon mode:

• coordinator/routers have to stay

awake (robust power supply

needed)

• heterogeneous network

• asymmetric power



Topologies

Mesh-Topology



Topologies

Tree-Topology




Implementation

PHY layer

2400MHz Band specs

• 4 Bits per symbol• DSSS with 32 Bit chips• O-QPSK modulation• Sine halfwave impulses


Bitto

Symbol

QPSKMod.

Symbolto

Chip

Binary Data

Medium


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)


Diff.Encoder

BPSKMod.

Bitto

Chip

Binary Data

Medium

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 threshold2.Carrier sense only3.Carrier sense with energy above threshold


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)


table taken from [1]

MAC layer

Channel access specification

• Beacon/Nonbeacon• Define Superframe structure• Slotted/unslotted CSMA-CA


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


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


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


MAC layer

How far have we come?


0

1

2

4

3

5

6

7

Problem: How do 6 and 7 talk to coordinator 0?Solution: Routing (NWK Layer)

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


NWK layer

Distributed address assignment - Example

• Cm=2 ; Rm=2 ; Lm=2


Depth in network d Offset Value0 31 12 0

0

1

4

5

6

?2

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


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


NWK layer

Route discovery


RREQRREP

1 2 3

4

2

1

5

NWK layer

Routing

• Check if routing table entry exists• Initiate route discovery if possible• Hierarchical routing as fallback


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

Application Level



Application Level



Application Layer

Application Support Sub-layer (APS):

• interface to NWK-layer (offers general set of functions)• Data transmission, binding and security management



Application Level



Application Layer

Application Framework:

• Specifies Datatypes• Devices describe themselves by ZigBee descriptor:

– frequency band– power description– application flags– application version– serial number– manufacturer– ...


Application Layer

Supported Data-types


table taken from [1]

Application Level



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




Evaluation

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


Cons

• Not many end devices available yet

• Single point of failure (centralized architecture)

Gadget example

Pantech & Curitel P1 phone

• Only a prototype

• control electrical appliances

• Check temperature & humidity

• Sending messages in case of trespass




References

References


[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

http://www.tutorial-reports.com/wireless/zigbee

http://www.cens.ucla.edu/sensys03/sensys03-callaway.pdf

http://www.i4u.com/article2561.html

http://www.korwin.net/eng/infor/info_zb_01.asp


Thank you