IEEE 802.15.3High Rate WPAN

- MAC functionalities & Power Save Mode -

2004.

Mobile Network Lab.

정상수 , 한정애

Contents

• Introduction – General description• MAC – Medium Access Control

– Piconet Management– Association & Disassociation– Channel Access & Channel Time Managemen

t– Synchronization & Acknowledgement– Power Management

Introduction(1)

• Highrate WPAN overview– Goals

• Ad hoc networks

• Fast connection time

• QoS support

• Dynamic membership

• Efficient data transfer

• Power managemnet

Introduction(2)

– PNC (Piconet Coordinator) manages piconet– Timing is based on the superframe

• Beacon• CAP• CFP

– 2.4 GHz PHY• 4 channels (high density) or 3 channels (with 802.11

b) modes are available• Supports 5 data rates

– 11Mbps(QPSK), 22Mbps(DQPSK without coding), 33Mbps(16QAM), 44Mbps(32QAM), 55Mbps(64QAM)

Piconet Management

• Starting a Piconet– DEV uses passive scan

ning to detect piconet

– To start a piconet, DEV chooses the channel and broadcasts its beacon

Association

• DEV initiates association request during CAP or association MCTA

• PNC responds with DEVID– If association is denied, sends a responds with a reason code

• DEV sends second association request using newly assigned DEVID

• PNC broadcasts beacon containing DEV association information

• DEVID (Device ID)– Assigned in sequence– One associated DEV : One DEVID except PNC

Disassociation

• PNC sends a disassociation request to DEV with the reason code

• All DEVs should send frames to the PNC often enough to assure that the Association Timeout Period(ATP) is not reached

• If DEV cannot receive beacon for longer than ATP, the DEV shall consider itself disassociated

Channel Access• Channel time is divided into superframe with

– Beacon • Contains piconet synchronization parameter and IE (Informati

on Element)s

– CAP (Contention Access Period) • Optional. For command frames and non-stream data. Using CS

MA/CA with backoff scheme

– CFP (Contention Free Period) • For data stream. PNC assigns to DEV with each CTA (Channe

l Time Allocation)

• Contention based access– To minimize collision, first sense that medium is idle for a random length

time (backoff)

– When backoff counter is zero, DEV shall check whether there is enough time remaining in the CAP

– CCA(Clear Channel Assessment) of PHY is used to detect the channel

• Backoff procedure– The DEV first waits a BIFS duration

– Choose the random integer [0, (7, 15, 31, 63)]

– Backoff counter is decreased only when the medium is idle for the pBackOffSlot duration

– Whenever channel is busy, counter is suspended

– Backoff counter shall be suspended outside of the CAP and superframe

– If transmission fails, backoff counter shall be increased

• Contention Free Access– To enable power saving and QoS

– CTA• Private CTA – for dependent piconet

• Dynamic CTA – scheduled on a superframe by superframe basis

• Pseudo-Static CTA – only for isochronous stream. Allowed to transmit during CTA as long as the number of consecutive lost beacon is less then mMaxLostBeacons

• Channel time usage– DEV uses CTR(Channel Time Request) message to change their CTA

– PNC remember CTR until another CTR is received from the DEV

– Source DEV is expected to estimate the channel time to send a frame and SIFS (+ ACK + SIFS time if ACK is used)

– If a DEV did not receive the beacon, it can’t use CAP or MCTA or dynamic CTA except pseudo-static CTA

– PNC must respond to a CTR • DEV use information to adjust its parameter

• Management CTA– PNC can use MCTAs instead of CAP for command fra

mes

– Open MCTA • SrcID is BcstID. Any DEV can attempt to send a command fra

me to PNC

– Association MCTA • SrcID is UnassocID. Any DEV not associated to the piconet ca

n attempt to send a association request to PNC

– Access mechanism• Assigned MCTA - TDMA basis

• Open & Association MCTA - Slotted ALOHA

Synchronization & Fragmentation

• Synchronization– All DEV within a piconet must be synchronized to the PNC clock

– Each DEV resets its superframe clock to zero at the beginning of beacon preamble

• Fragmentation– All fragments shall be equal size except last fragment

– Fragment number field incremented by one

– If no-ACK policy is used, all fragment is discarded when a fragment is missing

– If Dly-ACK policy is used, it is responsibility of the destination DEV to deliver the frame in correct order to upper layer

Acknowledgement• No-ACK

– Assumes that the frame is successful– Used with broadcast and multicast frame

• Immediate ACK– If intended recipient correctly receives the frame, it sends the ACK frame

• Delayed ACK– With the negotiation between DEVs

• Source DEV sends frame with Dly-ACK request bit• Dest DEV sends Dly-ACK with setting max burst field

– If dest DEV want to decline the use of Dly-ACK, it shall reply with the Imm-ACK

– If the max burst value is 0, source DEV stops to transmission and reopen the Dly-ACK mechanism

– If Dly-ACK is not received when requested, the last data frame is repeated until the ACK frame is received.

• During the CAP, follows the backoff procedure

• During the CFP, when an ACK is expected but is not received during RIFS, retransmit the frame at the end of RIFS

• If retransmission occurred, there must be enough channel time

Retransmission

Power management

• DEV state – AWAKE, SLEEP

• DEV mode– ACTIVE, HIBERNATE, PSPS, SPS

Power management- PSPS mode

• System wake beacon – Announced by the PNC, determined by the PNC

– PNC shall announce the system wake beacon in the next wake beacon field

• PS set index equal to one• PNC allocates MCTAs

– For PSPS DEV may need to send command to the PNC

SPS mode

• SPS mode device– DEV may use SPS set determined by other DEV or det

ermines the beacon interval

– Other DEVs may use the information in PS status IE in beacon to learn when to transmit to an SPS DEV

– SPS mode allows synchronized data transfer of DEVs

• PNC shall create one PS status IE in the beacon for each SPS set

SPS CTR

HIBERNATE mode

• HIBERNATE mode – allows a DEV to conserve power for extended periods u

ntil DEV choose to listen for a beacon

– So, DEV may loose it’s synchronization of piconet

– To avoid being disassociated from the piconet, all DEVs in HIBERNTE mode must send at least one ACK frame to the PNC during their ATP

Reference

• IEEE 802, Part 15.3: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specification for High Rate Wireless Personal Area Networks (WPAN)