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IEEE 802.15

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IEEE 802.15 Powered By Docstoc
					IEEE 802.15.3 High 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 Management 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 802.11b) 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 scanning 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 (Information Element)s

– CAP (Contention Access Period)
• Optional. For command frames and non-stream data. Using CSMA/CA with backoff scheme

– CFP (Contention Free Period)
• For data stream. PNC assigns to DEV with each CTA (Channel 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 frames – Open MCTA
• SrcID is BcstID. Any DEV can attempt to send a command frame to PNC

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

Retransmission
• 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

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 determines 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 until 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)


				
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