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TKU HSNL LRTKU HSNL LR--WPAN WPAN -- 11
IEEE 802.15.4IEEE 802.15.4MAC and PHY Specifications MAC and PHY Specifications
for LRfor LR--WPANsWPANs
中央大學通訊系 許獻聰
E-mail: stsheu@ce.ncu.edu.tw
TKU HSNL LRTKU HSNL LR--WPAN WPAN -- 22
Outline
1. IEEE 802.15.4 Architecture and Overview2. IEEE 802.15.4 PHY3. IEEE 802.15.4 MAC
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1. 802.15.4 Architectureand Overview
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IEEE 802.15 Working Group
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Applications
• Sensors & actuators• Interactive toys• Smart badges• Health monitoring• Computing peripherals• Remote control• Home Automation• Automatic Meter Reading
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New Trend of Wireless Technology
• Most Wireless industry focus on increasing increasing high data throughputhigh data throughput
• A set of applications requiring simple wireless connectivity, relaxed throughputrelaxed throughput, very low very low power, short distancepower, short distance and inexpensiveinexpensive– Industrial – Agricultural– Vehicular– Residential– Medical
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Wireless MarketsSH
OR
T
<
RA
NG
ER
AN
GE
>
LON
G
LOW < DATA RATEDATA RATE > HIGH
PANPAN
LANLAN
TEXT GRAPHICS INTERNET HI-FI AUDIO
STREAMINGVIDEO
DIGITALVIDEO
MULTI-CHANNELVIDEO
Bluetooth1
Bluetooth 2ZigBee
802.11b
802.11a/HL2 & 802.11g
Reference from ZigBee Alliance Inc.
TKU HSNL LRTKU HSNL LR--WPAN WPAN -- 88
Wireless Technologies
Reference from ZigBee Alliance Inc.
10
100
1,000
10,000
10 100 1,000 10,000 100,000
Bandwidthkbps
GSM
802.11a/g
GPRS EDGE 20002003-4
2005
Bluetooth
3G
HiperLAN/2Bluetooth 2.0
RangeMeters
802.11bZigBee
WiMediaBluetooth 1.5
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WLAN vs WPAN
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Wireless Applications
ZigBeeLOW DATA-RATE RADIO DEVICES
HOME AUTOMATION
CONSUMER ELECTRONICS
TVVCRDVD/CDremote
securityHVAClightingclosures
PC & PERIPHERALS
TOYS & GAMES
consolesportables
educational
PERSONAL HEALTH CARE
INDUSTRIAL & COMMERCIAL
monitorssensors
automationcontrol
mousekeyboardjoystick
monitorsdiagnostics
sensors
Reference from ZigBee Alliance Inc.
TKU HSNL LRTKU HSNL LR--WPAN WPAN -- 1111
Architecture
•• ZigBeeZigBee AllianceAlliance– 45+ companies: semiconductor
mfrs, IP providers, OEMs, etc.– Defining upper layers of protocol
stack: from network to application, including application profiles
– First profiles published mid 2003•• IEEE 802.15.4 Working GroupIEEE 802.15.4 Working Group
– Defining lower layers of protocol stack: MAC and PHY
– draft D18 (will be finalized 2003)
ZIGBEE STACKZIGBEE STACK
APPLICATIONAPPLICATION CustomerCustomer
IEEEIEEE802.15.4802.15.4
ZigBeeZigBeeAllianceAlliance
SILICONSILICON
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What is unique about wireless PAN (WPAN)?
•• Wireless Personal Area Networks (Wireless Personal Area Networks (WPANsWPANs))– short distance– small (ultra low complexity)– low duty-cycle (<0.1%)– power efficient (the most important factor)(the most important factor)– inexpensive (ultra low cost) solutions.
• Typically operating in the Personal Operating Personal Operating Space (POSSpace (POS)) of 10 meters10 meters.
• Supporting starstar and peerpeer--toto--peerpeer topologies– controlled by the PAN coordinatorPAN coordinator
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WPAN Features
• Media access is contention based.– Using carrier sense multiple access with collision carrier sense multiple access with collision
avoidance (CSMA/CA)avoidance (CSMA/CA) MAC protocol– Similar to IEEE 802.11 CSMA/CA protocol, but not the same
• Provide the optional SuperframeSuperframe structurestructure– The PAN coordinator periodically allocates guaranteed time guaranteed time
slotsslots (GTS)(GTS) to low latency devices• Dynamic device addressing
– Two kinds of address of a device–– 1616--bit Short Addressbit Short Address–– 6464--bit Extended Addressbit Extended Address
•• Fully acknowledged protocolFully acknowledged protocol for transfer reliability.
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Device Classes in WPAN
• There are two different device types :–– A full function device (FFD)A full function device (FFD)–– A reduced function device (RFD)A reduced function device (RFD)
• The FFD can operate in three modes serving–– DeviceDevice–– CoordinatorCoordinator–– PAN coordinatorPAN coordinator
• The RFD can only operate in a mode serving:–– DeviceDevice
•• Coordinator provides Coordinator provides synchronization informationsynchronization information to to other devicesother devices
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FFD vs RFD
• Full function device (FFD)–– AnyAny topology– Network coordinator capable– Talks to any other device
• Reduced function device (RFD)– Limited to starstar topology– Cannot become a network coordinator– Talks only to a network coordinator– Very simple implementation
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Network Topologies
•• Star and Peer2Peer TopologiesStar and Peer2Peer Topologies
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Network Topologies
•• Star network Star network formationformation:– An FFD may establish its own network and become the PAN
coordinator.– All star networks operate independently.– Choosing a PAN identifier, which is not currently used by any
other network within the radio sphere of influence.– Both FFDs and RFDs may join the network.
•• PeerPeer--toto--peer network peer network formationformation:– Each device is capable of communicating with any other
device.– One FFD device will be nominated as the PAN coordinator.
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Network Topologies
•• Star TopologyStar Topology– In star topology, data may be exchanged only
between the coordinator (FFD) and a device (FFD or RFD).
•• PeerPeer--Peer TopologyPeer Topology– In a peer-to-peer topology,data may be exchanged
between any two devices (FFDs).
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Star Topology
Full Function Device (FFD)Reduced Function Device (RFD)Communications Flow
Master/slave
NetworkNetworkcoordinatorcoordinator
Master/slave
NetworkNetworkcoordinatorcoordinator
TKU HSNL LRTKU HSNL LR--WPAN WPAN -- 2020
Star Topology
•• Home ApplicationHome Application
FFDRFD
RFD
RFD
FFD
FFD
RFD
FFDRFD
RFD
RFD
FFD
FFD
RFD
PAN coordinatorPAN coordinator
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Peer-Peer Topology
Communications FlowFull Function Device (FFD)
Point to pointPoint to point Tree
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Cluster Tree Topology
• Only one PAN coordinator• No detail yet
PAN coordinatorPAN coordinatorCluster HeadCluster Head
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Combined Topology (Cluster Star)
Peer2Peer Communications FlowStar Communications Flow
Full Function Device (FFD)Reduced Function Device (RFD)
Room 1Room 2
Room 3
Room 4
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Cluster Tree Establishment
• The PAN coordinatorPAN coordinator forms the first cluster by establishing itself as the cluster head (CLH)cluster head (CLH) with a cluster identifier (CID) of zerocluster identifier (CID) of zero.
• Choosing an unused PAN identifierunused PAN identifier (PANID)(PANID) and broadcasting broadcasting beaconbeacon framesframes to neighboring devices.
• A candidate device receiving a beacon frame may request to join the network at the CLH.
• If the PAN coordinator permits the device, it will add the new device as a child device in its Access Control List (ACL).
• The newly joined device will add the CLH as its parent in its ACL, and begin transmitting periodic beacons.
• Other candidate devices may then join the network at that device. A larger network (PAN) is possible by forming a mesh of multiple neighboring clusters.
• The PAN coordinator may instruct a device to become the CLH of a new cluster adjacent to the first one.
• Other devices gradually connect and form a multi-cluster network structure.
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Device Addressing
• All devices have IEEE addresses (64-bits)• Short addresses (16-bit) can be allocated• Addressing modes:
– Network + device identifier (star)– Source/destination identifier (peer-peer)– Source/destination cluster tree + device identifier
(cluster tree)
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2. 802.15.4 Physical Layer
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PHY Specifications
• The standard specifies twotwo PHYs :–– 868 MHz/915 MHz868 MHz/915 MHz direct sequence spread
spectrum (DSSS) PHY (11 channels)(11 channels)»» 11 channel (20Kb/s)(20Kb/s) in European 868MHz band»» 1010 channels (40Kb/s)(40Kb/s) inin 915 (902-928)MHz ISM band
–– 2450 MHz2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels)(16 channels)
»» 1616 channels (250Kb/s)(250Kb/s) in 2.4GHz band
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Operating Frequency Range
• A total of 27 channels, numbered 0 to 26, are available across the three frequency bands.
• 16 channels are for 2450 MHz, 10 are for 915 MHz an 1 is for 868 MHz.
BANDBAND COVERAGECOVERAGE DATA RATEDATA RATE CHANNEL(S)CHANNEL(S)
2.4 GHz ISM Worldwide 250 kbps 16
868 MHz Europe 20 kbps 1
915 MHz ISM Americas 40 kbps 10
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3. 802.15.4 MAC Layer
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Protocol Layer
PHY LAYER2.4 GHz 915MHz 868 MHz
MAC LAYERMAC LAYER
DATA LINK LAYER
NETWORK LAYERStar/Cluster/Mesh
APPLICATION INTERFACE
APPLICATIONS
Silicon
ApplicationZigBee Stack
Customer
IEEE802.15.4
ZigBeeAlliance
SECURITY
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IEEE 802.15.4 feature
•• Extremely low costExtremely low cost
•• Ease of installationEase of installation
•• Reliable data transferReliable data transfer
•• Short range operationShort range operation
•• Reasonable battery lifeReasonable battery life
Simple but flexible flexible protocol
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General Frame Structure
•• FourFour Types of Frames StructureTypes of Frames Structure:–– Beacon FrameBeacon Frame - used by coordinator
–– Data FrameData Frame - used for all transfers of data
–– Acknowledgment FrameAcknowledgment Frame - used for confirming successful frame reception
–– MAC CommandMAC Command Frame Frame - used for handling all MAC peer entity control transfers
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Superframe Structure
• The LR-WPAN allows the optional use of a superframestructure.
• The format of the superframe is defined by the coordinator.• The superframe is bounded by network beacons, is sent by the
coordinator and is divided into 16 equally sized slots.• The beacon frame is transmitted in the first slot of each
superframe.• If a coordinator does not wish to use a superframe structure it
may turn off the beacon transmissions.• The beacons are used to synchronize the attached devices, to
identify the PAN, and to describe the structure of the superframes.
• Any device wishing to communicate during the contentionaccess period (CAP) between two beacons shall compete with other devices using a slotted CSMA-CA mechanism.
• All transactions shall be completed by the time of the next network beacon.
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Superframe Structure• The superframe can have an active and an inactive portion. During
the inactive portion the PAN enters a low power mode.• The PAN coordinator may dedicate portions of the active
superframe to some devices/applications. These portions are called guaranteed time slots (GTSs).
• The GTSs comprise the contention free period (CFP). • The PAN coordinator may allocate up to 7 of these GTSs and a
GTS may occupy more than one slot period. (Note:all slots may beallocated for CFP.)
• All contention based transactions shall be complete before the CFP begins. Also each device transmitting in a GTS shall ensure that its transaction is complete before the time of the next GTS or the end of the CFP.
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Superframe Structure• The structure of this superframe is described by the
values of macBeaconOrder ((BOBO)) and macSuperframeOrder ((SOSO)).– The macBeaconOrder describes the interval at which the
coordinator shall transmit its beacon frames. – The macSuperframeOrder describes the length of the active
portion of the superframe, which includes the beacon frame.
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Data Transfer Model
q There are three typesthree types of data transfer transactions.1) Device -> Coordinator2) Coordinator -> Device3) Device (coordinator) -> Device (coordinator)
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Data Transmissions
(1)(1) Data transferred from device to coordinatorData transferred from device to coordinator– In a beaconbeacon--enableenable network, device finds the beaconbeacon to
synchronize to the superframe structure. Then using slotted CSMA/CAslotted CSMA/CA to transmit its data.
– In a non beaconnon beacon--enableenable network, device simply transmits its data using unslottedunslotted CSMA/CACSMA/CA
Communication to a coordinatorIn a beaconbeacon--enabled networkenabled network
Communication to a coordinatorIn a nonnon beaconbeacon--enabled networkenabled network
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Data Transmissions
(2) Data transferred from coordinator to device(2) Data transferred from coordinator to device– In a beaconbeacon--enable networkenable network, the coordinator indicates in
the beacon that the data is pendingpending. Device periodically listens to the beacon and transmits a MAC command MAC command requestrequest using slotted CSMA/CAslotted CSMA/CA if necessary.
– In a non beaconnon beacon--enable networkenable network, a device transmits a MAC command requestMAC command request using unslottedunslotted CSMA/CACSMA/CA. If the coordinator has its pending data, the coordinator transmits data frame using unslottedunslotted CSMA/CACSMA/CA. Otherwise, coordinator transmits a data frame with zero lengthzero lengthpayloadpayload.
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Data Transmissions (Indirect mode)
Communication from a coordinator in a non beaconnon beacon--enabled networkenabled network
Communication from a coordinatorIn a beaconbeacon--enabled networkenabled network
• indirect transmissionindirect transmission
pending listpending list
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Indirect transmissions
• Since the standard favors very low cost devices that, in general, will be battery powered, transactions can be instigated from the devices themselves rather than from the coordinator.– either coordinator indicates in its beacon when messages
are pending for devices– or devices polls the coordinator to determine if they have any
messages pending. – Such transfers are called indirect transmissionsindirect transmissions.
• For each transaction sent, if another exists for the same device, the coordinator sets its frame pending pending subfieldsubfield to 1, indicating the additional pending data. – Like ‘more data’ flag used in IEEE 802.11
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Pending Address Field
maximal 7 addressesmaximal 7 addresses
Beacon Frame
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Peer-to-Peer Data Transfers
• In order to do this effectively, the devices wishing to communicate will either need to be receiving constantly or they will need to synchronize with each other.
• The device simply transmits its data using unslottedCSMA-CA. Other measures need to be taken in order to achieve synchronization.
• Incomplete approach
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Frame Transmission
• If the source address (SA) field is not present, the originator of the frame shall be assumed to be the PAN coordinator.
• If the destination address (DA) field is not present, the recipient of the frame shall be assumed to be the PAN coordinator.
• If both SA and DA addresses are present, the MAC shall compare the destination and source PAN identifiersdestination and source PAN identifiers– If the PAN identifiers are identical, the intra PAN subfield of
the frame control field shall be set to 1 and the source PAN identifier shall be omitted from the transmitted frame.
» Save bandwidth, only carry the destination PAN identifier– If the PAN identifiers are different, the intra PAN subfield of
the frame control field shall be set to 0 and both destination and source PAN identifier fields shall be included in the transmitted frame.
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Frame reception and rejection
1. The frame typeframe type subfield shall not contain an illegal frame type.2. If the frame type indicates that the frame is a beacon framebeacon frame,
the source PAN identifiersource PAN identifier shall match macPANIdmacPANId unless macPANId is equal to 0xffff0xffff,, in which case the beacon frame shall be accepted regardless of the source PAN identifier.
3. If a destination PAN identifierdestination PAN identifier is included in the frame, it shall match macPANIdmacPANId or shall be the broadcast PAN identifier broadcast PAN identifier (0xffff)(0xffff).
4. If a short DAshort DA is included in the frame, it shall match either macShortAddressmacShortAddress or the broadcast address (0xffff)broadcast address (0xffff). Otherwise, it shall match aExtendedAddressaExtendedAddress.
5. If only SA fieldsonly SA fields are included in a data or MAC command frame, the frame shall only be accepted if the device is a PAN coordinator and the source PAN identifier matches macPANIdmacPANId.
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