IEEE Taekyoung Kwon

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 … ZigBee LOW DATA-RATE RADIO DEVICES HOME AUTOMATION CONSUMER ELECTRONICS TV VCR DVD/CD remote security HVAC lighting closures PC & PERIPHERALS mouse keyboard joystick TOYS & GAMES PETs gameboys educational PERSONAL HEALTH CARE monitors diagnostics sensors INDUSTRIAL & COMMERCIAL monitors sensors automation control

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

PHY DSSS 250 Kbps at 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

PHY: Packet structure Preamble Start of Packet Delimiter PHY Header PHY Service Data 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 Octets0-127 Octets

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

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

Constants

PIB attributes

PHY revisited Receiver sensitivity: -85 dBm at 2.4GHz dB = 10 log p/p_ref dBm = 10 log p/1mW LQI –Word file – How about a? –UWB –Any more parameter?

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. ligh t switch) Repetitive low latency data –Allocation of time slots (e.g. mouse)

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 PAN Coordinator

MAC: peer-to-peer Full function deviceCommunications 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 rooms of a hotel and each room has a star network for control.

General frame format 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 Indirect transmission

Communication in non-beacon mode (from coordinator to device) unslotted CSMA-CA Indirect transmission

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 * 2 n where 0  n  14 Network beacon Contention period Beacon extension period 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 2GTS 1 Guaranteed Time 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 * 2 BO macSuperframeOrder (SO) –Length of active portion of the superframe Superframe duration (SD) –SD = aBaseSuperframeDuration * 2 SO 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 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 format DSN

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 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 service Originator MAC Recipient MAC MCPS-DATA.request Data frame MCPS-DATA.confirm MCPS-DATA.indication Acknowledgement (if requested) Channel access Originator Recipient

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 PIB attributes

IEEE future? Some revision in b –Resolve ambiguities –Reduce complexities GTS as optional –Consider other available frequencies China

–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 IEEE 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 ) 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