Proposal for enabling overlay FEC in GCR Block Ack March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Proposal for enabling overlay FEC in GCR Block Ack Date: 2011-03-15 Authors: Jochen Miroll, Saarland University Jochen Miroll

Motivation To enable optional Coded Block Ack for Groupcast March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Motivation To enable optional Coded Block Ack for Groupcast To reduce overhead of GCR polled Block Ack Jochen Miroll, Saarland University Jochen Miroll

Proposal Extend polled Block Ack by polled Coded Ack March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Proposal Extend polled Block Ack by polled Coded Ack After completing a GCR Data transmission, an AP or Mesh STA will transmit Unicast BlockAckReq frames to (a subset of) GCR STAs participating in the GCR stream. In Polled Coded Ack mode, the BlockAckReq contains an integer number k to be evaluated by the BlockAckReq addressed STA. Each STA receiving BlockAckReq frame will respond with Ack if the Coding Condition is met. The Coding Condition is met, if k frames of the preceding Block have been received. Each STA receiving BlockAckReq frame will remain silent if the Coding Condition is not met. Jochen Miroll, Saarland University Jochen Miroll

March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Issues How to handle moving the buffered frames from MAC to upper layers in GCR stream receiving STA? Use same mechanism as defined for 802.11 Block Ack and GCR Block Ack How to determine the Coding Condition? Coding Condition (as well as Block Ack block length e.g.) has to be determined by the AP or Mesh STA. Out of scope for TGaa. For overlay FEC, there is typically only systematic data and parity. Could be a good use for the DEI bit. Out of scope for TGaa. Multicast-Broadcast sequence numbers AP or Mesh STA needs to add the number of interim MC/BC frames to k Jochen Miroll, Saarland University Jochen Miroll

Advantages This enables overlay FEC support at the MAC layer. March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Advantages This enables overlay FEC support at the MAC layer. Overlay FEC is considered good practice for Multicast. The scheme consumes less medium time compared to GCR Block Ack Because Coded Block Ack BAR-ACK sequence is known from Delayed Block Ack, there will be no legacy client compatibility issue Jochen Miroll, Saarland University Jochen Miroll

Typical exchange with GCR polled Block Ack March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Typical exchange with GCR polled Block Ack Data Data Data BAR BAR AP … BA GCR Group Member 1 BA GCR Group Member 2 Not included as part of polled Ack GCR Group Member 3 Slide taken from Suri, Hart, 802.11-10/1179r0 Jochen Miroll, Saarland University Jochen Miroll

Typical exchange with polled Coded Ack March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Typical exchange with polled Coded Ack Data 1 Data 2 any mgmt Data k BAR BAR BAR Data k+1 (parity) AP … ACK GCR Group Member 1 Did not receive k+1 GCR Group Member 2 ACK GCR Group Member 3 Not included as part of polled Ack GCR Group Member 4 Slide adapted from Suri, Hart, 802.11-10/1179r0 Jochen Miroll, Saarland University Jochen Miroll

March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Straw Poll Should this scheme be adopted, extending the polled GCR Block Ack mechanism? Yes - 1 No - 7 Abstain - 4 Jochen Miroll, Saarland University Jochen Miroll

March 2011 Overlay FEC example Usage of erasure codes (Vandermond-Code, Reed-Solomon) Usage of „Virtual Interleaving“ (cf. ETSI) Result is a Block-of-packets FEC code that has: As input: a number of Bytes As output: a number of equal length packets (e.g. 1500 Bytes) The property: out of n packets, any k packets are sufficient to decode n k Redundancy Data Table Application Data Table Jochen Miroll, Saarland University

March 2011 Case 1: Packet loss This case addresses the problem that within a block of upto 64 frames (GCR Block Ack), loss may be uncorrelated among the receivers Jochen Miroll, Saarland University

Case 1: Packet loss, GCR … March 2011 D D D D D D D D D D D D D D D D doc.: IEEE 802.11-11/0293r1 March 2011 Case 1: Packet loss, GCR BAR start seq# Same seq# as before, need retransm. of all frames D D D D BAR BAR BAR BAR D D D D BAR BAR AP D D D BA D D D BA GCR1 D BA D D BA D D D GCR2 … D D D BA D D D GCR3 D D D BA D D D GCR4 Jochen Miroll, Saarland University Jochen Miroll

Case 1: Packet loss, coded GCR March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Case 1: Packet loss, coded GCR Did not get k Everyone has k upto now BAR start seq# Did you get k? Did not get k D D D D BAR P BAR P BAR BAR BAR BAR AP D D D P BA GCR1 D BA D D P P GCR2 D D D P BA GCR3 D D D P P BA GCR4 Jochen Miroll, Saarland University Jochen Miroll

Case 2: Frame seq# mix w/ single counter March 2011 Case 2: Frame seq# mix w/ single counter This case addresses the problem that within a block of upto 64 frames (GCR Block Ack), an arbitrary number of frames using the same single sequence number counter (Management and Broadcast/Multicast frames) may be scheduled intermediately Jochen Miroll, Saarland University

Case 2: Frame seq# mix w/ single counter March 2011 doc.: IEEE 802.11-11/0293r1 March 2011 Case 2: Frame seq# mix w/ single counter GCR as defined in P802.11aa D3.01, possible sequence (example) BAR start seq# BAR for one Data frame D,1 MC,2 MGMT,3 MC,4 … *,64 BAR … D,65 AP Proposed coded GCR, possible sequence (same example) BAR for all Data frames, AP asks each receiver individually for „how many“ plus number of intermediate (red or blue) BAR start seq# D,1 MC,2 MGMT,3 MC,4 … D,65 D,66 BAR AP The AP knows how many MGMT or MC frames it has sent to each receiver, so it may ask each for a different number k+x. Assumes those x frames are indeed received. Jochen Miroll, Saarland University Jochen Miroll

March 2011 Rate Adaptation Rate (MCS) adaptation based on immediate receiver feedback is possible in … Unicast GCR Block Ack Coded GCR Block Ack Yet, adding an overlay FEC onto a Groupcast transmission has to rely on receiver reports => Rate adaptation is out of scope for TGaa, but remains in the same way possible as in the above 1., 2. and 3. Jochen Miroll, Saarland University

March 2011 Motion Move to instruct the TGaa editor to incorporate normative text changes in 11/0294r1 into the P802.11aa Draft 3.01 Moved: Seconded: Result (Yes/No/Abstain): Jochen Miroll, Saarland University