Wireless Communication - Zigbee, Bluetooth - IIIT

Wireless Communication -
Zigbee, Bluetooth
Amarjeet Singh
February 19, 2012

Logistics
Sample exam paper on the course website
Derived from mid term exam of last year – will give you an idea
of what can be asked in the exam
Will create projects for those who did not get it since all topics were
over
Will create the presentation schedule for students by this weekend
2

Revision from last class - I
UART
What are specific example interfaces?
RS-232:
How do you make a minimum interface (with/without
handshaking)?
How will you support RS-232 with UART in your microcontroller?
RS-422:
How is it different from RS-232?
How is it extended to support multi-device bus?
Infrared:
How is it different from RS-232?
What bit-encodings are used in infrared?
3

Revision from last class - II
USB:
What does a USB packet contain?
What are different types of token packets?
What are different types of handshake packets?
What are different types of data transfers supported?
How is bandwidth distribution done in USB across different
types of transfers?
4

Range
IEEE 802 Wireless Space
WWAN
WMAN
IEEE 802.22
IEEE 802.20
WiMax
IEEE 802.16
WLAN
WPAN
ZigBee
802.15.4
15.4c
Bluetooth
802.15.1
WiFi
802.11
802.15.3
802.15.3c
0.01 0.1 1 10 100 1000
Data Rate (Mbps)

IEEE 802.15.4
Approved by IEEE in 2003 with revision in 2006 for
Wireless Sensor Networks
Specifies only 2 OSI layers - Physical (PHY) and
Medium Access Control (MAC)
Only direct, single hop communication possible
Two types of devices are defined:
RFD - Reduced Functionality Device
Contains limited features
Can only communicate to FFD
Requires little power, memory and processing
resources
FFD - Full Functionality Device
Full set of features - capable to act as network
coordinator
Communicate to both FFD and RFD
Higher power, memory and processing resources

IEEE 802.15.4 Data Transfer Models
Star:
Network Nodes (FFDs, RFDs) are connected to a
coordinator node (FFD)
Peer-to-peer:
FFDs can communicate to all devices in
transmissions range
RFDs can talk to FFDs they are associated with

IEEE 802.15.4 Physical Layer
Available in 3 frequency bands
Frequency
(MHz)
Number of
channels
2450 16 250
Data rates
(kbps)
915 10 40, 250
868 1 20,100
Unlicensed
Availability
Worldwide
America, Australia
Europe
2.4 GHz is most commonly used
Available worldwide without license
Typical device (0 dB power) can transmit up to 200 meters
outside and 30 meters inside

IEEE 802.15.4 MAC Layer
Key MAC layer responsibilities are:
Data framing: Data to be sent is encapsulated in MAC frame
that is passed to RF transceiver
Device addressing: Each device identified by 64-bit long MAC
address
Channel Sense Management (CSMA-CA): Device scans
preconfigured channels and chooses one with least activity
“listen before send” principle for managing access to single
physical channel among multiple devices
Device Association/Disassociation: Upon higher layer requests,
MAC layer enters/leaves network

Zigbee Specification
Two lowest layers (PHY and
MAC) are equal to those in IEEE
802.15.4
Higher layers in Zigbee stack are
specified to allow efficient
communication within entire
network and on the application
level
Routing mechanisms on network
layer allow multi-hop data
transmission, selection of best
suitable path and rerouting
Application framework provides
interface to enable simultaneous
execution of multiple applications

Zigbee Node Types
Coordinator: Only mandatory node type in the network; Acts as root
node and performs multiple network management activities
Only FFD in 802.15.4 terminology can act as network
coordinator
Router: A 802.15.4 FFD node not acting as network coordinator;
Used to extend network coverage area beyond transmission range of
single device; Increase network reliability by creating additional data
routing paths
End device: Correspond to RFD in 802.15.4; Can directly
communicate with a single coordinator/router
Node addressing: Each node that joins the zigbee network gets a 16
bit network address (How many bits was the MAC address?)
Communication at network level is performed based on this
address; Direct communication between two neighboring devices is
based on MAC address

Zigbee Network Topologies
Extends IEEE 802.15.4 transfer models by specifying tree and mesh
topologies
Star Topology: Corresponds to 802.15.4 star topology
Do you need a network layer in this case?
Tree Topology: Based on 802.15.4 peer-to-peer model
Routers/Coordinators can have child nodes
Direct communication possible in terms of parent-child
Hierarchical routing without alternate paths
Star Topology
Tree Topology
What will happen if a link fails in tree network?

Zigbee Network Topologies
Mesh Topology: Based on 802.15.4 peer-to-peer model
Routers/Coordinators can have child nodes
Direct communication possible between any FFD (coordinator/router)
in transmission range
End device can only communicate with its parent
Optimum and dynamic routing with alternate paths
Mesh Topology

ZigBee Mesh Networking

ZigBee Mesh Networking

ZigBee Mesh Networking

ZigBee Mesh Networking

ZigBee Mesh Networking

Zigbee Application Operation - I
Each application instance running on a node is a
unique network entity where messages can
originate/terminate
Termed as endpoint and has a unique address
Each node can have up to 240 endpoints - A
endpoint is identified by network address of the
node and its endpoint address on the node
Endpoint 0 reserved for Zigbee Device Object
(ZDO)
This application has multiple roles - defines
type of node (coordinator, router, end-point),
initializes the node and participates in
network creation

Zigbee Application Operation - II
Binding: Process of establishing a relationship between nodes that can
communicate e.g. in Home Automation, which switches control which lights
Binding between two applications is specified by:
Network address and endpoint of application where data is generated
Network address and endpoint of receiving application
Stored in a binding table (can be stored locally or on the coordinator
node)
Binding types:
One-to-one
One-to-many
Many-to-one
Can you think of application scenarios in light
control for different binding types?

Zigbee Operation - I
Network is initialized by the coordinator who pre-configures a number of
network properties :
Network Depth - Maximum number of hops from coordinator to the
farthest end-device
What is the network depth of star topology?
Maximum number of child devices allowed per router
Maximum number of child routers

Zigbee Operation - II
Forming a zigbee network by the coordinator
Search for a suitable radio channel
Start the network assigning a PAN ID to the network - can be predetermined
or obtained dynamically
Assigns itself the network id of 0x0000
Ready to respond to queries from other devices
Join process by other nodes:
Search for network: Scan the available channels and find operating
networks (separated by their PAN IDs)
Select parent: from (possibly) multiple routers and coordinator in
range
Send join request
Accept or reject join request (by the coordinator/routers)

Zigbee Operation - III
Message propagation:
Message contains two destination addresses - Address of final
destination, Address of next hop node
Are any of these obvious for any network topology?
Route discovery mechanism
Route discovery broadcast is sent by parent router of source end
device - Contains the network address of destination end device
All routers receive the broadcast
Parent router of destination end device replies back to parent router of
source end device
As the reply traverses back, the hop count and signal quality measure
for each hop are recorded - Each router in the path can build a routing
table containing best path to destination end device
Eventually each router in the path will have entry in the routing table

Zigbee Network Reliability
Zigbee employs a range of techniques for reliable communication
Channel Selection: On initialization, channels with least activity are
selected
CSMA-CA (Listen Before Sending): Before transmitting, node listens to
the channel to check if it is clear
Data coding: Applies a coding mechanism ensuring higher probability
of successful transmission even in case of simultaneous transfer
Acknowledgements: Receiving device acknowledges the successful
receipt of a message; retransmission if ack is not received in time
Route discovery: In mesh network, possibility of finding an alternate
route if the default route is down
Several mechanisms to ensure security:
Access control lists: Only pre-defined nodes can join the network
128-bit AES based Encryption
Message freshness timers: Timed-out messages are rejected,
preventing message replay attacks
Can you give an example of replay attack?

Radio Characteristics Comparison
ZigBee technology relies
upon IEEE 802.15.4, which
has excellent performance
in low SNR environments

Advanced Metering Application

Building/Home Automation

Bluetooth Characteristics (I)
Short range radio links intended to replace cables
No line of sight required unlike IrDA
Short range: 0-30 feet (10 meters) with power consumption of 4
dBm (2.5 mW)
Distance can be increased by amplifying the power
Operates in the unlicensed band at 2.4 GHz also used by other
devices such as 802.11, garage door openers, microwave etc.
Higher probability of interference
Bluetooth channel is divided into time slots each 625 uS in length
Devices hop through these timeslots making 1600 hops per
second

Bluetooth Characteristics (II)
Uses 79 channels in the frequency range 2.402 - 2.480 GHz
Uses Frequency Hop Spread Spectrum (FHSS) to avoid
interference
Transmitter hops between available frequencies according to specified
algorithm
Transmitter operates in sync with receiver
A short burst of data is transmitted on a narrowband
Transmitter then tunes to another frequency and transmits again -
capable of hopping its frequency over a given bandwidth several times a
second
Requires much wider bandwidth than required to transmit the same
information using one carrier frequency

Bluetooth Characteristics (III)
Supports two kinds of links
Asynchronous Connectionless (ACL) for data transmission
Synchronous Connection Oriented (SCO) for audio/video
Maximum effective rate around 700 kbps in asymmetric ACL link
Symmetric ACL allows data rates of around 400 kbps

Piconets
Nodes can assume the role of master or slave
One or more slaves can connect to a master, forming a piconet
The master sets the hopping pattern for the piconet, and all
slaves must synchronize to that pattern: All units share the same
channel
Maximum of 7 slaves controlled by a master (How many
address bits are required?)
Bluetooth radios are symmetric - same device can act as both
master and slave
Slaves are not allowed to talk to each other directly
Other operational states (low power)
Parked: Device does not participate in the piconet,
synchronized to the master and can be quickly reactivated
Standby: Device does not participate in the piconet,
occasionally monitoring, not synchronized

Operational States
Operational States
A piconet
Master
S
SB
SB
Slave
Parked*
M
P
Standby*
S
* Low power states
S
SB
S

Forming a Piconet (I)
• Initially, devices know only about themselves
• No synchronization
• Everyone monitors in standby mode (performs inquiry or page
scan for 10 ms every 1.28 seconds
• Power consumption in standby mode is reduced by over 98%
• All devices have the capability of serving as master or slave
D
E
F
A
H
C
B
G
• Devices in this illustration are in the same mode but are not
synchronized or coordinated - listening at different times and on
different frequencies

Forming a Piconet (II)
• Unit establishing the piconet automatically becomes the master
• It sends an inquiry to discover other devices out there
• Inquiry procedure: Enables a device to discover which devices are
in range and determine the addresses and clocks for devices
• Paging procedure: Establishes an actual connection; only
bluetooth device address is required to setup the connection
• Master and slave exchange packet using channel access code
and master clock
• Addressing
• Active devices are assigned a 3-bit active member address
(AMA)
• Parked devices are assigned an 8-bit parked member address
(PMA)
• Standby devices do not need an address

Inquiry
Note that a device can
be “Undiscoverable”
D
F
H
G
M
N
O
J
E
I
A
K
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Q
10 meters

States
standby
disconnected
detach
inquiry
page
connecting
Transmit
AMA
Connected
AMA
active
Park
PMA
Hold
AMA
Sniff
AMA
low power

Connecting to a Piconet
• Device in standby listens periodically
• If a device wants to establish a
piconet, it sends an inquiry,
broadcast over all wake-up carriers
• It will become the master of the
piconet
• If inquiry was successful, device
enters page mode
• Devices in standby may respond to
the inquiry with its device address
• It will become a slave to that
master
standby
Transmit
AMA
Park
PMA
inquiry
Hold
AMA
page
Connected
AMA
Sniff
AMA

Page and Connect States
• After receiving a response from
devices, the master can connect to
each device individually
• An AMA is assigned
• Slaves synchronize to the hopping
sequence established by the
master
standby
inquiry
page
• In active state, master and slaves
listen, transmit and receive
• A disconnect procedure allows
devices to return to standby mode
Transmit
AMA
Park
PMA
Hold
AMA
Connected
AMA
Sniff
AMA

Low Power States
• Sniff state
• Slaves listen to the piconet at a
reduced rate
• Master designates certain slots to
transmit to slaves in sniff state
standby
• Hold state
• Only internal timer is running
• Slave stops ACL transmission, but
can exchange SCO packets
Transmit
AMA
inquiry
page
Connected
AMA
• Park state
• Slave releases its AMA
• Still FH synchronized and wakes up
periodically to listen to beacon
Park
PMA
Hold
AMA
Sniff
AMA

Scatternets (I)
• Piconets with overlapping coverage use different hopping
sequences
• Collisions may occur when multiple piconets use the same
carrier frequency at the same time
• Higher probability of collision with more piconets
• Devices can participate in multiple piconets simultaneously,
creating a scatternet
• A device can only be the master of one piconet at a time
• A device may serve as master in one piconet and slave in
another
• A device may serve as slave in multiple piconets

Scatternets (II)
D
F
H
G
M
N
O
J
E
I
A
K
C
B
L
P
Q