Transcript ZigBee - University of Greenwich

ZigBee
and
IEEE 802.15.4
Lecture Overview
Technical overview
Applications / uses
Device Types
Protocols
Network topologies and communication models
AODV Routing
Network Technology
Richard Anthony
The University of Greenwich
The 802 Wireless Space
ZigBee is NOT intended to provide high bandwidth service of WLAN
ZigBee is NOT intended to provide moderate bandwidth wireless link over short range
(as Bluetooth does)
ZigBee IS intended to provide LOW bandwidth, robust connectivity at moderate range.
ZigBee IS ideally suited to sensing and control applications.
Network Technology
Richard Anthony
The University of Greenwich
General characteristics
Overall design goals
Low power, low cost, flexible wireless communication technology
Range
10 – 100M low power, up to 1000M high power
Data rates
20 kilobits/second to 250 kilobits/second
Transmission frequency
2.4 GHz in the Industrial, Scientific and Medical (ISM) radio band
Transmission power levels
1mW and 100mW
Communication structure / Topology
Ad-hoc, dynamic
Network Technology
Richard Anthony
The University of Greenwich
ZigBee extends IEEE 802.15.4
IEEE 802.15.4 defines the Physical layer and MAC layer for
ZigBee.
This gives a well-defined, standardised wireless link.
ZigBee adds a number of features to facilitate full wireless
networks for communities of devices:
Device discovery and neighbour associations
Device roles
Logical grouping (PAN ID)
Routing
….
Addressing
64-bit IEEE address – Unique address – ‘burned in’
16-bit Node-ID – Assigned when a node joins a network
Network Technology
Richard Anthony
The University of Greenwich
ZigBee extends IEEE 802.15.4
Various ZigBee modules available, some e.g. ‘EasyBee’ only
cover the wireless transmission and require the higher protocol
stack to be implemented in software.
– problematic for low-resourced sensor nodes
– potentially useful if only a simple point-point link is needed.
Network Technology
Richard Anthony
The University of Greenwich
ZigBee Network layer
 Performs routing (uses AODV see later)
 Determines if a neighbouring device belongs to the network.
 Discovers new neighbours (any role, so includes routers).
ZigBee Application layer (ZigBee system interface to end users).
Deals with Addressing !
 64-bit IEEE address – fixed
 16-bit Node ID – dynamically assigned
 Devices within a node identified by Endpoint Identifier (1 – 240)
Comprises components added by ZigBee spec (on top of IEEE
802.15.4 radio link spec), includes:
ZigBee Device Object (ZDO) responsible for defining role of a
device (Coordinator / End device) and for the discovery of new
(one-hop) devices and the identification of their offered services.
Application objects (application specific data objects).
Application support sublayer (APS) offers a well-defined interface
and control services. Serves as a bridge between the network
layer and the other components of the application layer: manages
binding tables – maps devices to the services offered by the
discovered devices.
Application domains targeted by ZigBee:
Application Profiles released
 Smart Energy 1.0
 Home Automation
 Health Care
 RF4CE – Remote Control
 Telecommunication services
Application Profiles in development
 Smart Energy 2.0
 Building Automation
 Retail Services
Network Technology
Richard Anthony
The University of Greenwich
Device Types
A ZigZee network comprises several different ‘types’ of device
(assigned roles)
Coordinator (C)
one
End Device (E)
one or more (FFD or RFD, see below)
Router
zero or more (FFD, see below)
(R)
Classes of devices:
Reduced-Functionality device (RFD)
Full-Functional device (FFD)
FFD nodes can form networks of any type (mesh, star, hybrid).
RFD nodes can only connect to a full function node.
Network Technology
Richard Anthony
The University of Greenwich
Device Types - Coordinator
The Coordinator is the logical equivalent of an access point in a
wireless network, in terms of device connectivity, or a master
node in Bluetooth,
The role of ‘Coordinator’ is a network-level role (i.e. for
establishing the network) and not necessarily an applicationlevel role.
The Coordinator can be the data sink for sensing applications,
and can issue commands in remote control applications.
However, a node does not have to be the Coordinator to carry
out such functions.
Network Technology
Richard Anthony
The University of Greenwich
Device Types – End device
End devices are the nodes deployed within a given application
to perform sensing and actuation.
These devices will often be optimised to use low power because
will often be placed in low-accessibility positions, or will possibly
be attached to mobile objects (consider a trolly in a hospital).
Most sensor applications fall natively into the RFD class, with
extended networks making use of both FFDs and network
coordinators to form bridges and links required by the network
topology.
Network Technology
Richard Anthony
The University of Greenwich
Device Types – Router
A Router is a device (class FFD) that will forward messages
between end devices and the coordinator.
A series of hops through several routers may be required.
End nodes may be configured to act as routers:
Routers also need to use low amounts of power
Routers may be simple sensor devices with low
processing resources - therefore need a simple and
robust routing strategy:
A modified form of AODV routing is used.
Network Technology
Richard Anthony
The University of Greenwich
Network topologies and communication models
Simple topologies
Wireless link to remote data source
Wireless sensing of an environment
A router is positioned to extend range
ZigBee Coordinator
ZigBee Router
ZigBee End Node
ZigBee End Node and Router
Network Technology
Richard Anthony
Wireless sensing of remote environment
The University of Greenwich
Network topologies and communication models
Mesh network topologies
Routers facilitate a mesh network
Multi-path connectivity provides robustness but adds complexity and overheads
Generic concept of a mesh connecting the end-devices to the Coordinator
Redundant links provide robustness
Network Technology
Richard Anthony
The University of Greenwich
Network topologies and communication models
Application-specific topologies
Sparsely sensed area
Sparsely sensed area
Densely sensed area # 1
Densely sensed area # 2
An example where environmental sensing is non-uniform.
The application could be, for example, security systems at an airport
Network Technology
Richard Anthony
The University of Greenwich
Network topologies and communication models
Topology / connectivity formation
Each node maintains Neighbour, Routing and Binding Tables
Coordinator is responsible for initialising, maintaining and controlling
the network.
An End device is said to ‘belong’ to a parent node
A parent node can be the coordinator or a router.
The End device polls to find a Parent node.
The parent node ‘discovers’ the end device by receiving these polls.
The parent node adds the end device to a Table
Network Technology
Richard Anthony
The University of Greenwich
ZigBee hardware - Modules
‘EasyBee’ provides the wireless
hardware and minimal ZigBee support
(need to implement the protocol stack
in software)
Antenna is a track on the PCB
‘ProBee’ module
supports almost entire
ZigBee Pro spec.
Various antenna
options
Antenna screws onto
here
Network Technology
Richard Anthony
The University of Greenwich
ZigBee hardware – Evaluation Board and Modules (1)
ProBee module on ZigBee evaluation board – with ‘chip’ antenna
Network Technology
Richard Anthony
The University of Greenwich
ZigBee hardware – Evaluation Board and Modules (2)
ProBee module on
ZigBee evaluation
board – with Dipole
antenna.
Network Technology
Richard Anthony
The University of Greenwich
Transmission Power
The standard ZigBee transmission power is approximately 1mW. This
power level can be driven directly from the ZigBee chips.
Advantages include:
 Very small physical module, no RF amplifier is needed
 No external antenna is needed, can be on-chip / on circuit board
 Very low power usage when transmitting.
 Usable range of about 10m to 100m depending on the environment,
antenna, and frequency band.
An amplifier can be added, boosting power to approximately 100mW.
This power level gives:
 Far greater range.
 Better SNR and performance in terms of dealing with obstacles.
 Shortens battery life or requires replenishable power source.
Network Technology
Richard Anthony
The University of Greenwich
Transmission Power – Range illustration
Image from http://www.rfm.com/products/apnotes/wp_zigbeepoweroptions.pdf
Network Technology
Richard Anthony
The University of Greenwich
Application-specific transmission power settings
Example – Livestock monitoring on a farm
Enclosure area # 2
Enclosure area # 1
Enclosure area # 3
Key
Low power (1mW) link used by small collar mounted devices with small battery
100mW link between fixed devices with (large battery, solar or mains power)
Network Technology
Richard Anthony
The University of Greenwich
Protocols – Multiplexing and Separation and coding
Channel
There are 16 ZigBee channels in the 2.4 GHz band.
Each channel requires 5 MHz of signal bandwidth (separation).
The 2.4 GHz band Each channel can transmit up to 250 kbit/s.
(actual data throughput < max specified bit rate due to packet
overhead and processing delays).
Coding
The radios use direct-sequence spread spectrum coding (DSSS)
Offset quadrature phase-shift keying (OQPSK) is used in the
2.4 GHz band (enables transmission of four bits per symbol).
Grouping
A ‘PAN ID’ enables logical grouping / separation of nodes.
- A 16-bit value which is used to uniquely define a PAN.
- Devices identify which networks to join based on their PAN ID.
Network Technology
Richard Anthony
The University of Greenwich
Protocols (Transmission options)
Each transmission can be sent secured or unsecured
Acknowledged: originator data is confirmed by recipient
Unacknowledged: no confirmation
Unicast: send to a specific recipient
Broadcast: send to all recipients
Multichannel: Originator attempts Tx using frequency reacquisition mechanism
Single channel: Originator attempts Tx on the expected channel
Network Technology
Richard Anthony
The University of Greenwich
Protocols (discovery)
Device discovery
Find other ZigBee devices that can be paired to.
Can be attempted repeatedly
- for fixed duration, or
- until sufficient number of responses received
Service discovery
Information is exchanged between a pair of devices:
Device capabilities: target / controller
mains / battery power
Vendor information
Application information (user-defined description of the device’s
functionality – e.g. Entrance foyer camera control)
Requested Device type (type of device requested through discovery,
e.g. a camera control console might search for PZT cameras)
Network Technology
Richard Anthony
The University of Greenwich
Routing – Ad hoc On-Demand Distance Vector (AODV)
Used in ZigBee’s network layer.
Achieves robust routing in highly dynamic networks (designed for wireless
sensor networks (WSN) and mobile ad hoc networks (MANETs).
Reactive - establishes a route to a destination on demand. (Internet routing
protocols are proactive; establishment of routing paths is a separate activity to
the transmission of packets over those paths. Paths set up in advance of being
needed; paths re-established automatically if topology changes.)
Establishes a mesh network through the use of broadcast communication.
A node broadcasts a route request to all of its neighbours.
The neighbours forward broadcast the request to their neighbours, etc. until the
destination is reached (this staged broadcast technique is termed ‘flooding’).
Destination receives multiple copies and determines the shortest path taken.
The route reply is unicast following the lowest cost path back to the source.
The source then updates its routing table for the destination address with the
next hop in the path and the path cost (number of hops).
Network Technology
Richard Anthony
The University of Greenwich
Routing – AODV in Operation
2
1
3b
2
3a
3b
3b
3a
4
1. End Device has data to send to sink,
passes message to its parent node.
2. Router broadcasts route request to its
neighbours.
3. Neighbouring routers forward
broadcast the route request (flood,
steps 3a and 3b nearly simultaneous).
4. (Assuming that ‘3a’ message arrives
first at the Coordinator) The route reply
is sent back – using the route.
Network Technology
Richard Anthony
3a
4
+Ve points: adaptive, robust
-Ve points: latency, overheads
The University of Greenwich