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IEEE 802.15.4 Low-Rate Wireless PAN (LR-WPAN). 1. Wireless Sensor Network Standards. IEEE 802.15.4 Low-Rate Wireless PAN ZigBee 6LoWPAN IEEE 1451 standards for connecting smart transducers to networks. Wireless Sensor Network Standards. - PowerPoint PPT Presentation
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IEEE 802.15.4 IEEE 802.15.4 Low-Rate Wireless PAN Low-Rate Wireless PAN (LR-WPAN)(LR-WPAN)
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Wireless Sensor Network Wireless Sensor Network StandardsStandards
IEEE 802.15.4 Low-Rate Wireless PAN
ZigBee
6LoWPAN
IEEE 1451standards for connecting smart transducers to
networks
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Wireless Sensor Network Wireless Sensor Network StandardsStandards
IEEE 802.15.4 PHY
IEEE 802.15.4 MAC (CPS)
ZigBee NWK
MAC (SSCS)802.2 LLC
6LowPAN
API Transport
ZA1 ZA2 … IA1 IA2 IAn
Transmission & reception on the physical radio channel
Channel access, PAN maintenance, reliable data
transport
Topology management, MAC management, routing, discovery protocol, security management
Application interface designed using
general profile
End developer applications, designed using application
profiles
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802.15.4 with Five Key Words802.15.4 with Five Key Words
Very low costVery low power consumptionLow complexityLow rateShort range
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Basic Radio CharacteristicsBasic Radio Characteristics
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Home Networking
Automotive Networks
Industrial Networks
Interactive Toys
Remote Metering
802.15.4 Applications Space802.15.4 Applications Space
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High-Level CharacteristicsHigh-Level Characteristics
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802.15.4 Architecture802.15.4 Architecture
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Device ClassesDevice Classes
Full function device (FFD)Any topologyNetwork coordinator capableTalks to any other device
Reduced function device (RFD)Limited to star topologyCannot become a network coordinatorTalks only to a network coordinatorVery simple implementation
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Network TopologyNetwork Topology
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Star
PANCoordinator
Point to point Cluster tree
Full function device
Reduced function device
LR-WPAN: LR-WPAN: Data RateData Rate
DSSSTx range: 10 ~ 75 m at 0 dBm (1 mW)
Band Symbol rate Modulation Bit rate channels
868 MHz 20 Ksps BPSK 20 Kbps 1
915 MHz 40 Ksps BPSK 40 Kbps 10
2.4 GHz 62.5 Ksps O-QPSK 250 Kbps 16
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MAC FeaturesMAC Features
Generating network beacons if the device is a coordinator
Synchronizing to beaconsPAN association, disassociationOptional acknowledged frame deliveryEmploying the CSMA/CA for channel access
mechanismGuaranteed time slot management
MAC management has 35 primitives RFD has 24 primitivescf. 131 primitives of 802.15.1 / Bluetooth
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Superframe StructureSuperframe Structure For some applications requiring dedicated bandwidth to achieve low latencies A superframe is divided in 16 time slots
CAP: • Slotted CSMA-CA channel access (beacon-enabled network)• Unslotted or standard CSMA-CA in networks (non beacon-enabled network)
CFP: Optionally, contention-free access using Guaranteed Time Slots (GTSs) in beacon-enabled netrwork
aBaseSuperframeDuration = 60 symbols/slot * 16 slots = 960 symbols 15.36 ms at 250 kbps, 24 ms at 40 kbs, 48 ms at 20 kbps
BO (Beacon Order) How often the PNC transmits a beacon, 0 ≤ BO ≤ 14 (15.36 ms ~ 251.65824 sec) 15 if non beacon
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Backoff periods of a device not related to that of any other deviceTherefore, synchronization is not required
CCA – Clear Channel Assessment to check if channel is busy or idle
Unslotted CSMA-CAUnslotted CSMA-CA
Another Device’s Transmission
2 1 0 8 7 6 5 4 3 2 1 0 BackoffNumber
Frame Transmission
Perform CCA, and finds channel busyBE=4 8 selected
Perform CCA, and finds channel idle
Frame arrivalBE=3 2 selected
aTurnaroundTime
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Slotted CSMA-CASlotted CSMA-CA
Backoff period boundaries aligned by the periodic beacon transmission
It also implies that they are aligned with superframe slot boundaries (for GTS) as Slot = n * aUnitBackoffPeriod
Frame Transmission
Another Device’s Transmission
2 1 0 8 7 6 5 4 3 2 1 0 BackoffNumber
Perform CCA, and finds channel busyBE=4 8 selected
Perform CCA, and finds channel idle
Frame arrivalBE=3 2 selected
BCNCW= 2 1 0
aTurnaroundTime
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Inter-frame SpacingInter-frame Spacing
Short frame: frame size <= aMaxSIFSFrameSize
Long frame: otherwise
Long frame ACK Short frame ACK
tack LIFS tack SIFS
Acknowledged transmission
Long frame Short frame
LIFS SIFS
Unacknowledged transmission
aTurnaroundTime tack (aTurnaroundTime (12 symbols) + aUnitBackoffPeriod (20 symbols))LIFS > aMaxLIFSPeriod (40 symbols)SIFS > aMacSIFSPeriod (12 symbols)
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MAC addressingMAC addressing
All devices have IEEE addresses (64 bits)Short addresses (16 bits) can be allocatedAddressing modes
PAN identifier (16 bits)+ device identifier (16/64 bits)
Beacon frame: no destination address
General Frame FormatGeneral Frame Format
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Payload
PHY Header(PHR)
Synch.Header(SHR) PHY Service Data Unit (PSDU)
PH
Y L
ayer
MA
CL
ayer MAC Header
(MHR)MAC Footer
(MFR)
MAC Protocol Data Unit (MPDU)
MAC Service Data Unit(MSDU)
General MAC Frame FormatGeneral MAC Frame Format
Octets:2 1 0/2 0/2/8 0/2 0/2/8 variable 2Destination
PAN identifier
Destination address
Source PAN
identifier
Source address
MAC payload
MAC footer
Frame check
sequence
MAC header
Addressing fields
Frame control
Sequence number
Frame payload
Bits: 0-2 3 4 5 6 7-9 10-11 12-13 14-15
Frame typeSequrity enabled
Frame pending
Ack. Req. Intra PAN ReservedDest.
addressing mode
ReservedSource
addressing mode
Frame control field
Beacon frameData frameAcknowledgement frameMAC command frame
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source PAN id is skipped
Destination in Beacon frame
Data Frame formatData Frame format
Provides up to 104 byte data payload capacity Data sequence numbering to ensure that all packets are tracked Robust frame structure improves reception in difficult conditions Frame Check Sequence (FCS) ensures that packets received are
without error
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Acknowledgement Frame FormatAcknowledgement Frame Format
Provides active feedback from receiver to sender that packet was received without error
Short packet that takes advantage of standards-specified “quiet time” immediately after data packet transmission
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MAC Command Frame FormatMAC Command Frame Format
Mechanism for remote control/configuration of client nodes
Allows a centralized network manager to configure individual clients no matter how large the network
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Beacon Frame formatBeacon Frame format
Client devices can wake up only when a beacon is to be broadcast, listen for their address, and if not heard, return to sleep
Beacons are important for mesh and cluster tree networks to keep all of the nodes synchronized without requiring nodes to consume precious battery energy listening for long periods of time
Minimum beacon PPDU length = 136 bits / 250 Kbps = 544 μsec
Bits: 0-3 4-7 8-11 12 13 14 15Beacon
orderSuperframe
orderFinal CAP
slotBattery life extension
ReservedPAN
coordinatorAssociation
permit
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MAC Data PrimitivesMAC Data Primitives
Primitive Request Confirm Indication Response
MCPS-DATA Required Required Required
MCPS-PURGEOptional for
RFDOptional for
RFD
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Data Transfer: no-beacon modeData Transfer: no-beacon mode
Originator
MAC Recipient
MAC
Data frame
Acknowledgment (if requested)
Originator higher layer
Recipient higher layer
MCPS-DATA.request
MCPS-DATA.indication
MCPS-DATA.confirm
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Device Coordinator
Coordinator Device
Indirecttransmission
Data Transfer: Beacon ModeData Transfer: Beacon Mode
Coordinator
MAC Device MAC
Data frame
Acknowledgment
Coordinator higher layer
Device higher layer
MCPS-DATA.request (indirect)
MCPS-DATA.indication
MCPS-DATA.confirm
Beacon frame
Data request
Acknowledgement
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Coordinator DeviceDevice Coordinator
Management ServiceManagement Service
Access to the PIBAssociation / disassociationGTS allocationMessage pending Node notificationNetwork scanning/startNetwork synchronization/search
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MAC Management PrimitivesMAC Management Primitives
Access to the PIB Association / disassociation GTS allocation Message pending
Node notification Network scanning/start Network
synchronization/search
Primitive Request Confirm Indication Response
MLME-GET Required Required
MLME-SET Required Required
MLME-ASSOCIATE Required Required Optional for RFD Optional for RFD
MLME-DISASSOCIATE Required Required Required
MLME-GTS Optional for RFD Optional for RFD Optional for RFD
MLME-BEACON-NOTIFY Required
MLME-POLL Required Required
MLME-COMM-STATUS Required
MLME-ORPHAN Optional for RFD Optional for RFD
MLME-SCAN Required Required
MLME-START Optional for RFD Optional for RFD
MLME-RX-ENABLE Required Required
MLME-SYNC Required
MLME-SYNC-LOSS Required
MLME-RESET Required Required
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AssociationAssociation
Device MAC
Coordinator MAC
Association request
Acknowledgment
Device higher layer
Coordinator higher layer
MLME-ASSOCIATE.request
MLME-ASSOCIATE.indication
MLME-ASSOCIATE.response
Acknowledgement
Association response
MLME-ASSOCIATE.confirm
aResponseWaitTime
MLME-COMM-STATUS.indication
Data request
Acknowledgment
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DisassociationDisassociation
= Originator
MAC Recipient
MAC
Disassociation notification
Acknowledgment
Originator higher layer
Recipient higher layer
MLME-DISASSOCIATE.request
MLME-DISASSOCIATE.indication MLME-DISASSOCIATE.confirm
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Data PollingData Polling Device MAC
Coordinator MAC
Data request
Acknowledgment (FP = 0)
Device higher layer
MLME-POLL.request
MLME-POLL.confirm
No data pending at the coordinator
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Device MAC
Coordinator MAC
Data request
Acknowledgment (FP = 1)
Device higher layer
MLME-POLL.request
MLME-POLL.confirm
Data
Acknowledgement
MCPS-DATA.indication
Data pending at the coordinator
ED SCANED SCAN
When a prospective PAN coordinator to select a channel
Measure peak energy in each requested channel
Discard every frame received while scanningReturn energy levels
Active ScanActive Scan
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Device MAC
Coordinator MAC
Beacon request
Device higher layer
MLME-SCAN.request
MLME-SCAN.confirm
ScanDuration Beacon
Set 1st Channel
CSMA
Set 2nd Channel
Beacon request
When FFD wants to locate any coordinator within POSA prospective coordinator
selects PAN IDPrior to device association
Receive beacon frames onlymacPANId = 0xffff
Send beacon request commandDestination PAN ID = 0xffff
Return PAN descriptors
Passive ScanPassive Scan
No beacon request command
Device to prior to association
Receive beacon frames onlymacPANId = 0xffff
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Device MAC
Coordinator MAC
Device higher layer
MLME-SCAN.request
MLME-SCAN.confirm
ScanDuration Beacon
Set 1st Channel
Set 2nd Channel
Orphan ScanOrphan Scan
Device attempts to relocate its coordinator
For each channel, send orphan notification commandDest PAN id, dest short
addr = 0xffff Only the original
coordinator will reply Receive coordinator
realignment command frame only
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= Coordinator
MAC Device MAC
Coordinator realignment
Orphan notification
Coordinator higher layer
MLME-ORPHAN.response
MLME-COMM-STATUS.indication
MLME-ORPHAN.indication
Differences from 802.11 WLANDifferences from 802.11 WLAN
Simpler PHYOne Tx rate per channelLow Tx power
Simpler MACNo virtual carrier-senseNo worry about hidden nodesNo RTS/CTS & No fragmentationNo continuous CCARelaxed timing requirement
Extensive power saving features
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Power Save MechanismsPower Save Mechanisms
Going to sleep state as often as possible by utilizing:Inactive mode in superframesBackoff periods when macRxOnWhenIdle is
reset.GTS for other devices
Extracting pending messages from coordinatorUsing data request commandMessage pending indicated in beacon frames
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LR-WPAN: Low Duty CycleLR-WPAN: Low Duty Cycle
Beacon interval(max) 960 symbols * 214 = 15,728,640 symbolsAt 250 Kbps, (min) 15.36 msec ~ (max) 251.65824
sec (over 4 min)
Beacon duty cycle544 μsec / 251.65824 sec = 0.000216% (lowest
possible)Non-beacon mode is also possible
Example: 0.1% duty cycle 10 mW active, 10 μW standby → 19.99 μW average
powerAAA battery with capacity of 750mAh, regulated to 1VBattery life: 37,519 hours ≈ 4.28 years
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LR-WPAN: LR-WPAN: Imperfect Time BasesImperfect Time Bases
“Ideal” beacon
reception time
“Ideal” beacon
transmission time
εTX TbeaconεTX Tbeacon
εRX TbeaconεRX Tbeacon
εTbeaconεTbeacon TC
receiver
transmitter
Uncertainty due to imperfect receiver time base
Uncertainty due to imperfect transmitter time base
[Guti03]
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LR-WPAN: LR-WPAN: Duty Cycle vs. CostDuty Cycle vs. Cost
Lowest possible duty cycle of a receiver is(2ε·Tbeacon + TC) / Tbeacon
Duty cycle is limited by the time base tolerance εNo matter how long Tbeacon is made
IEEE 802.15.4 is designed to supportTime base tolerance as great as ±40 ppm
(note) lowest duty cycle = 2.16 ppmUse of inexpensive reference crystals
Lower duty cycle requires more stable time baseIncreases the cost of time base
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IEEE 802.15.4aIEEE 802.15.4a Scope and Description:
Develop an alternate physical layer (PHY) for data communication with
• high precision ranging / location capability (1 meter accuracy and better)
• high aggregate throughput• and ultra low power• scalability to data rates• longer range• lower power consumption and cost.
The alternate PHY is an (optional) amendment to the current IEEE 802.15.4-2003 LR-WPAN standard.
802.15.4a became an official Task Group in March 2004; with its committee work tracing back to November 2002.
Current StatusThe baseline is two optional PHYs
• UWB Impulse Radio (operating in unlicensed UWB spectrum) • Chirp Spread Spectrum (operating in unlicensed 2.4GHz spectrum)
The UWB Impulse Radio will be able to deliver communications and high precision ranging.
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IEEE 802.15.4bIEEE 802.15.4b Scope and Description
Resolve ambiguities, provide corrections, removing unnecessary complexity, and define enhancements to the current IEEE 802.15.4-2003 standard. The revised standard will be backward compatible.
Enhancementssupport for distributing a shared time-baseSupport for group addressingExtensions of the 2.4GHz derivative modulation
• Yields higher data rates at the lower frequency bandsSupport of Beacon-Enabled Cluster Tree network.
• IEEE802.15.4 does not support while 15.4b doesProtection of broadcast and multicast frames possibleEasier setup of protection parameters possiblePossibility to vary protection per frame, using a single
keyOptimization of storage for keying material
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