802.11ac MAC Frame Length Indication

1. 802.11ac MAC Frame Length Indication Date: 2010-03-16 Authors: Slide 1 Jaewoo Park et al

2. Background • 11b STA • frame length in PLCP header • 16 bit PSDU length in microseconds • 11a/g STA • Frame length indication in L-SIG • 12 bit PSDU length in bytes • 11n STA • Frame length indication in HT-SIG • 16 bit PSDU length in bytes • How about VHT STA? • Frame length shouldbe indicated in VHT-SIG • Need to consider MU-MIMO cases Jaewoo Park et al

3. Frame lengthindication in VHT • Frame length indication • SU-MIMO • Frame length for single user should be indicated • MU-MIMO • Transmitter needs to specify the frame lengths for each user. • Need to consider frame length indication method in VHT-SIG Jaewoo Park et al

4. Frame end indication • Approaches for frame end indication • Frame length indication • Delimiter • Approaches • Using duration in VHT-SIG + Delimiter padding (suggested in [1]) • Using duration and per user length in VHT-SIG (our suggestion) [1] Yong Liu, et al, VHT Frame Padding, IEEE 802.11-10/0064r1 Jaewoo Park et al

5. MU-MIMO transmission end indication • Each STA participating in DL MU-MIMO transmission knows the end of the transmission • End time can be the reference for the ack protocols • Each STA’s ACK procedure can calculatethe ACK response time using the transmission end indication • Duration field in VHT-SIG can be used for MU-MIMO transmission end indication Jaewoo Park et al

6. Using Duration + Delimiter padding [1] • Duration is indicated using # of symbols • Duration field is assumed to be in VHT-SIG-A • The PHY in each STA notifies the maximum duration of user streams. • But, maximum duration does not provide MAC PDU length for each user • MAC frame is padded up to the last symbol • Frame padding is needed • MAC layer should find the mac data end by delimiter-matching • A New PSDU format is required • PHY decoder cannot decide the exact stop timing of the decoder • MAC notifies the PHY decoder to stop after it detects the EOF Jaewoo Park et al

7. Using Duration + Delimiter padding [1] • In VHT MAC, if length field is not included in VHT SIG, • PSDU forwarded to the MAC layer has MAC PDU and frame padding • PHY Layer cannot provide MPDU length information to MAC layer • Frame padding such as delimiter padding, MAC padding should be used to fill up to the maximum duration • In MAC Layer, MAC frame should be parsed to the end • EOF field can be used to indicate the real end of data Jaewoo Park et al

8. Using Duration + Frame length • Length fields for each user areincluded in VHT-SIG • The same PSDU format as11n can be used • No need to change the 11n MAC parsing function • Complex MAC padding scheme is not required • PHY decoder can stop immediately after the specified length • Power saving in PHY Layer compared to [1] • In padding scheme of [1], MAC notifies the PHY decoder to stop after it detects the EOF  possible delay after receiving actual data before the PHY decoder stops • Natural way to extend 11n to VHT MU-MIMO Jaewoo Park et al

9. SU-MIMO length VHT-SIG Common Info VHT-SIG user Info PSDU Length Reference Timing for Multi-user ACK protocol Duration MU-MIMO duration length VHT-SIG Common Info VHT-SIG Per-user Info PSDU length Concept of MAC frame length indication • Same PSDU format with 11n • Duration • specifiesthe end of MU-MIMO transmission & channel status • Length field per user • specifies the length of each user’s PSDU Jaewoo Park et al

10. Conclusions • In MU-MIMO, each STA participating in MU-MIMO transmission needs to know the end of the transmission • Using duration and per user length in VHT SIG: • Length fields for each user are included in VHT-SIG • Transmission end can be known to the receiver using the length indication • Natural way to extend 11n to VHT MU-MIMO • No need to change the 11n MAC parsing function • No change to the 11n PSDU format • Necessary to consider using duration and per user length for 802.11ac MAC frame end indication Jaewoo Park et al