Post on 01-Jan-2016
description
IEEE 802.15.4
Taekyoung Kwon
802.15.4
• Wireless MAC and PHY layer specifications for Low-rate Wireless Personal Area Networks (LR-WPANs)– Short distance– Little or no infrastructure– Small– Power-efficient– inexpensive
Application spaces
• Home Networking
• Automotive Networks
• Industrial Networks
• Interactive Toys
• Remote Metering
More specifically…
ZigBeeLOW DATA-RATE RADIO DEVICES
HOME AUTOMATION
CONSUMER ELECTRONICS
TVVCRDVD/CDremote
securityHVAClightingclosures
PC & PERIPHERALS
mousekeyboardjoystick
TOYS & GAMES
PETsgameboys
educational
PERSONAL HEALTH CARE
monitorsdiagnostics
sensors
INDUSTRIAL &
COMMERCIAL
monitorssensors
automationcontrol
Application topology
•Cable replacement - Last meter connectivity
•Virtual Wire
•Wireless Hub
•Stick-On Sensor
Mobility
Ease of installation
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
PreambleStart ofPacket
Delimiter
PHYHeader
PHY ServiceData Unit (PSDU)
PHY Packet Fields• Preamble (32 bits) – synchronization • Start of Packet Delimiter (8 bits)• PHY Header (7 bits) – PSDU length• PSDU (0 to 1016 bits) – Data field
6 Octets 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 primitivesrequest - entity wants service to do some workindication - entity is informed about eventresponse - entity wants to respond to eventconfirm - entity is to informed about its request
• For unconfirmed service, the first 2 primitives
4 primitives
802.15.4 PHY: primitives
PHY Data Service• PD-DATA – exchange data packets between MAC and PHY
PHY Management Service• 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
• 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
Full function device
Reduced function device
Communications flow
Master/slave
PANCoordinator
MAC: peer-to-peer
Full function device Communications flow
Point to point Cluster tree
MAC: combined topology
Full function device
Reduced function device
Communications flow
Clustered stars - for example,cluster nodes exist between roomsof a hotel and each room has a star network for control.
General frame formatPayload
PH
Y L
ayer
MA
CLa
yer
MAC Header(MHR)
MAC Footer(MFR)
MAC Protocol Data Unit (MPDU)
MAC Service Data Unit(MSDU)
PHY Header(PHR)
Synch. Header(SHR)
PHY Service Data Unit (PSDU)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
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
Indirecttransmission
Communication in non-beacon mode (from coordinator to
device)
unslotted CSMA-CA
Indirecttransmission
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
15ms * 2n
where 0 n 14
Network beacon
Contention period
Beacon extensionperiod
Transmitted by network coordinator. Contains network information,frame structure and notification of pending node messages.
Space reserved for beacon growth due to pending node messages
Access by any node using CSMA-CA
GTS 2 GTS 1
GuaranteedTime Slot
Reserved for nodes requiring guaranteed bandwidth [n = 0].
Contention Access Period
Contention Free Period
up to 7 GTSes
Total 16 slots
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 = 5macMaxCSMABackoff = 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 formatPayload
PH
Y L
ayer
MA
CLa
yer
MAC Header(MHR)
MAC Footer(MFR)
MAC Protocol Data Unit (MPDU)
MAC Service Data Unit(MSDU)
PHY Header(PHR)
Synch. Header(SHR)
PHY Service Data Unit (PSDU)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
General MAC frame
Frame control field
Addressing mode
Beacon frame
Superframe spec.
BSN
src
Data frame formatDSN
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 primitivesMAC Data Service• MCPS-DATA – exchange data packets between MAC and
PHY• MCPS-PURGE – delete the data packet in MAC queue
MAC Management Service• 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 serviceOriginator
MACRecipient
MAC
MCPS-DATA.request
Data frame
MCPS-DATA.confirmMCPS-DATA.indication
Acknowledgement(if requested)
Channelaccess
Orig
inat
orR
ecipient
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-SYNCLogical 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