Transcript Document

IEEE 802.15.4
Taekyoung Kwon
802.15.4
• Wireless MAC and PHY layer
specifications for Low-rate Wireless
Personal Area Networks (LR-WPANs)
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Short distance
Little or no infrastructure
Small
Power-efficient
inexpensive
Application spaces
• Home Networking
• Automotive Networks
• Industrial Networks
• Interactive Toys
• Remote Metering
More specifically…
monitors
sensors
automation
control INDUSTRIAL &
CONSUMER
ELECTRONICS
COMMERCIAL
monitors
diagnostics
sensors
TV
VCR
DVD/CD
remote
ZigBee
LOW DATA-RATE
RADIO DEVICES
PC &
PERIPHERALS
PERSONAL
HEALTH CARE
PETs
gameboys
educational
TOYS &
GAMES
HOME
AUTOMATION
security
HVAC
lighting
closures
mouse
keyboard
joystick
Application topology
•Cable replacement - Last meter connectivity
•Virtual Wire
Mobility
•Wireless Hub
Ease of installation
•Stick-On Sensor
requirements
Thousands of sensors in a small space  Wireless
but wireless implies Low Power!
and low power implies Limited Range.
Of course all of these is viable if a Low Cost
transceiver is required
Basic characteristics
802.15.4 PHY
• DSSS
• 250 Kbps at 2.450 GHz (ISM)
– 16-ary quasi-orthogonal modulation
• 4 bit -> 1 symbol
– 32 chip sequence
• 1 symbol -> 32 chips
– O-QPSK
– 2.0Mchip/s
• 62.5ksymbol/s
* FEC
802.15.4 PHY: Packet structure
PHY Packet Fields
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Preamble (32 bits) – synchronization
Start of Packet Delimiter (8 bits)
PHY Header (7 bits) – PSDU length
PSDU (0 to 1016 bits) – Data field
Preamble
Start of
Packet
Delimiter
6 Octets
PHY
Header
PHY Service
Data Unit (PSDU)
0-127 Octets
802.15.4 PHY
service primitive
• user services provided by a layer are
implemented as a set of service primitives
• the primitive name includes details of its
type and identity of layer providing service
4 primitives
• For confirmed service, there are 4
primitives
request - entity wants service to do some work
indication - entity is informed about event
response - entity wants to respond to event
confirm - entity is to informed about its request
• For unconfirmed service, the first 2
primitives
4 primitives
802.15.4 PHY: primitives
PHY Data Service
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PD-DATA – exchange data packets between MAC and PHY
PHY Management Service
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PLME-CCA – clear channel assessment
PLME-ED - energy detection
PLME-GET / -SET– retrieve/set PHY PIB parameters
PLME-SET-TRX-STATE – enable/disable transceiver
details
details
Constants
PIB attributes
802.15.4 PHY revisited
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Receiver sensitivity: -85 dBm at 2.4GHz
dB = 10 log p/p_ref
dBm = 10 log p/1mW
LQI
– Word file
– www.rfdh.com
• How about 802.15.4a?
– UWB
– Any more parameter?
802.15.4 MAC
 Extremely low cost
 Ease of implementation
 Reliable data transfer
 Short range operation
 Very low power consumption
Simple but flexible protocol
Traffic types
• Periodic data
– Application defined rate (e.g. sensors)
• Intermittent data
– Application/external stimulus defined rate (e.g.
light switch)
• Repetitive low latency data
– Allocation of time slots (e.g. mouse)
802.15.4 MAC
MAC
• Full function device (FFD)
– Any topology
– Network coordinator capable
– Talks to any other device
• Reduced function device (RFD)
– Limited to star topology
– Cannot become a network coordinator
– Talks only to a network coordinator
– Very simple implementation
MAC: star topology
PAN
Coordinator
Master/slave
Full function device
Reduced function device
Communications flow
MAC: peer-to-peer
Point to point
Full function device
Cluster tree
Communications flow
MAC: combined topology
Clustered stars - for example,
cluster nodes exist between rooms
of a hotel and each room has a
star network for control.
Full function device
Reduced function device
Communications flow
General frame format
PHY Layer
MAC
Layer
Payload
Synch. Header
(SHR)
MAC Header
(MHR)
PHY Header
(PHR)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
MAC Service Data Unit
(MSDU)
MAC Protocol Data Unit (MPDU)
PHY Service Data Unit (PSDU)
MAC Footer
(MFR)
Data transfer model
• To a coordinator
• From a coordinator
• Between peer-to-peer entities
Communication in beacon mode
(from device to coordinator)
Slotted CSMA-CA
Communication in non-beacon
mode (from device to coordinator)
unslotted CSMA-CA
Communication in beacon mode
(from coordinator to device)
slotted CSMA-CA
Indirect
transmission
Communication in non-beacon
mode (from coordinator to device)
Indirect
transmission
unslotted CSMA-CA
How about peer-to-peer mode?
• In a peer-to-peer PAN, every device may
communicate with every other device in its
radio sphere of influence. In order to do this
effectively, the devices wishing to
communicate will need to either receive
constantly or synchronize with each other. In
the former case, the device can transmit data
using unslotted CSMA-CA mode. In the latter
case, other measures need to be taken in
order to achieve synchronization. Such
measures are beyond the scope of this
standard.
Superframe: CSMA-CA + TDMA
GTS 2
Total 16 slots
Contention Access
Period
GTS 1
Contention Free Period
15ms * 2n
where 0  n  14
Network beacon
Transmitted by network coordinator. Contains network information,
frame structure and notification of pending node messages.
Beacon extension
period
Space reserved for beacon growth due to pending node messages
Contention period
Access by any node using CSMA-CA
Guaranteed
Time Slot
Reserved for nodes requiring guaranteed bandwidth [n = 0].
up to 7 GTSes
Superframe structure
• macBeaconOrder (BO)
– Interval between beacons
• Beacon Interval (BI)
– BI = aBaseSuperframeDuration * 2BO
• macSuperframeOrder (SO)
– Length of active portion of the superframe
• Superframe duration (SD)
– SD = aBaseSuperframeDuration * 2SO
• aBaseSuperframeDuration = 16 * aBaseSlotDuration
• 0<=SO<=BO<=14
• If BO = SO = 15, no beacon -> unslotted CSMA-CA
Example of superframe
Inter-frame spacing (IFS)
Illustration (2.4GHz)
• A minimum size slot: 30 bytes
– 60 symbols, 0.96ms
• If MPDU’s size < 18 octet, SIFS = 6
octet
– Otherwise, LIFS = 20 octets
• aUnitBackoffPeriod = 10 octets
CSMA-CA
• CSMA-CA is not for beacon, ACK,
data frames in CFP
Unslotted version
macMinBE = 3
aMaxBE = 5
macMaxCSMABackoff = 4
MAC addressing
• All devices have IEEE addresses (64 bits)
• Short addresses (16 bits) can be allocated
• Addressing modes
– PAN identifier (16 bits)+ device identifier
(16/64 bits)
• 0xffff: PAN ID, short address
• Beacon frame: no destination address
General frame format
PHY Layer
MAC
Layer
Payload
Synch. Header
(SHR)
MAC Header
(MHR)
PHY Header
(PHR)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
MAC Service Data Unit
(MSDU)
MAC Protocol Data Unit (MPDU)
PHY Service Data Unit (PSDU)
MAC Footer
(MFR)
General MAC frame
Frame control field
Addressing mode
src
BSN
Beacon frame
Superframe spec.
DSN
Data frame format
ACK frame
MAC command frame
MAC commands
Association command
PAN ID Conflict
• Beacon frame is received by the PAN
coordinator with the same PAN ID
• PAN ID conflict notification command from
a device
– A beacon frame is received
– Same PAN ID, but coordinator has different
address
• Resolution
– Active scan and then select new PAN ID
– Coordinator realignment command
Orphan notification
• Loss of synchronization (data
transmission failure)
• Orphaning mechanism
– Orphan channel scan
• Orphan notification command
– Only the original coordinator will reply
with coordinator realignment command
• Or reset and try association again
Coordinator realignment
• Orphan notification command is
received by coordinator
• Any attribute of PAN configuration
changes
Header omitted
MAC primitives
MAC Data Service
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MCPS-DATA – exchange data packets between MAC and PHY
• MCPS-PURGE – delete the data packet in MAC queue
MAC Management Service
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MLME-ASSOCIATE/DISASSOCIATE – network association
MLME-SYNC / SYNC-LOSS - device synchronization
MLME-SCAN - scan radio channels
MLME-GET / -SET– retrieve/set MAC PIB parameters
MLME-START / BEACON-NOTIFY – beacon management
MLME-POLL - beaconless synchronization
MLME-GTS - GTS management
MLME-ORPHAN - orphan device management
MLME-RX-ENABLE - enabling/disabling of radio system
MLME-RESET MLME-COMM-STATUS -
MCPS service
MAC data service
Recipient
MAC
Originator
MAC
MCPS-DATA.request
Originator
Recipient
Channel
access
Data frame
Acknowledgement
(if requested)
MCPS-DATA.indication
MCPS-DATA.confirm
MLME-ASSOCIATE
• After issuing MLME-RESET
• Active or passive channel scan
– PAN descriptors
• Src PAN ID: 0xffff
MLME-BEACON-NOTIFY
• macAutoRequest
• beacon payload
MLME-SCAN
ED SCAN
• When a prospective PAN coordinator
to select a channel
• Measure peak energy in each
requested channel
• Discard every frame received while
scanning
• Return energy levels
active SCAN
• When FFD wants to locate any coordinator
within POS
– A prospective coordinator selects PAN ID
– Prior to device association
• Receive beacon frames only
– macPANId = 0xffff
• Send beacon request command
– Destination PAN ID = 0xffff
• Return PAN descriptors
passive SCAN
• No beacon request command
• Device to prior to association
• Receive beacon frames only
– macPANId = 0xffff
Orphan scan
• Device attempts to relocate its
coordinator
• For each channel, send orphan
notification command
– Dest PAN id, dest short addr = 0xffff
• Only the original coordinator will reply
• Receive coordinator realignment
command frame only
MLME-COMM-STATUS
• MLME communicates to the next
higher layer about transmission status
when transmission is not instigated
by .request primitive
• Two cases
– .response primitive
– Reception of a frame
MLME-START
MLME-SYNC
Logical channel, TrackBeacon
MLME-POLL
• For requesting data from a
coordinator (indirect transmission)
Starting a PAN
• An FFD performs active channel scan
• Decides own PAN ID, short address
• MLME-START
– Set PAN coordinator flag in beacon frame
• Beacon generation
– An FFD (not coordinator) can send beacon
– Same PAN ID as the coordinator
PAN start message flow (1/2)
PAN start message flow (2/2)
MAC constants
MAC constants
MAC constants
MAC PIB attributes
MAC PIB attributes
MAC PIB attributes
MAC PIB attributes
MAC PIB attributes
MAC PIB attributes
IEEE 802.15.4 future?
• Some revision in 802.15.4b
– Resolve ambiguities
– Reduce complexities
• GTS as optional
– Consider other available frequencies
• China
802.15.5
• 802.15.5
– to determine the necessary mechanisms that must
be present in the PHY and MAC layers of WPANs
to enable mesh networking
• Initial objectives
– Extension of network coverage without increasing
transmit power or receive sensitivity
– Enhanced reliability via route redundancy
– Easier network configuration
– Better device battery life due to fewer
retransmissions
mmWave interest group in 802.15
• IEEE 802.15 has formed an interest group to
explore the use of the 60 GHz band for
wireless personal area networks (WPANs).
This little-used band (as defined in FCC 47
CFR 15.255) provides 5 GHz of bandwidth
and avoids interference with nearly all
electronic devices, given the high attenuation
of these wavelengths by walls and floors, and
promises to allow more WPANs to occupy the
same building