ieee 802.15.3 high rate wpan - mac functionalities & power save mode - 2004. mobile network lab....
TRANSCRIPT
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- 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
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