IEEE 802.15.3 High Rate WPAN - MAC functionalities & Power Save Mode - 2004.Mobile Network Lab.정상수, 한정애
Contents Introduction – General descriptionMAC – Medium Access Control- Piconet Management
- Association & Disassociation
- Channel Access & Channel Time Management
- Synchronization & Acknowledgement
- Power Management
Introduction(1) - 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
- 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 - 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- If association is denied, sends a responds with a reason code
DEV sends second association request using newly assigned DEVIDPNC broadcasts beacon containing DEV association informationDEVID (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)
- 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 - 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
- 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
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 onePNC 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
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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