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