1. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 1 Authors: Transmission Mechanism in MU-MIMO Date: 2010-11-10

2. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 2 Abstract A detailed transmission mechanism for MU-MIMO are proposed in this contribution, including protective mechanism with CTS-to-Self and scheduled multiple RTS/CTS frame changes, MU-MIMO data transmission, scheduled ACK and exception handling.

3. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 3 Background Current data transmission mechanism was designed for SU-MIMO only –Tx STA sends RTS addressing one Rx STA with one RA field. –Rx STA addressed by the RA field responds with CTS. –Not all recipients’ neighbors can be protected. Challenges to MU-MIMO data transmission: –Define multiple recipients RTS/CTS protective mechanism. –Define MU-MIMO data selection method. –Define multiple recipients ACK scheduling. –Define retransmission rules. –Be compatible with legacy devices.

4. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 4 MU-MIMO Transmission Mechanism A short PPDU, e.g. CTS-to-Self is used to start MU-MIMO transmission and reserve the MAX transmission duration, including all RTS/CTSs, MU-MIMO data frames, scheduled ACKs and all xIFSs. Multiple RTS/CTS frame exchanges are used to reserve bandwidth for multiple recipients The RTS/CTSs for primary STAs will be arranged first. If no CTS is correctly received from any primary STA, the current MU-MIMO transmission is failed. If the remaining time within the TXOP duration is sufficient to complete an MU-MIMO transmission, AP may initiate a new transmission or retry the previous MU-MIMO transmission. AP may terminate the TXOP with a CF-END. Otherwise, if a CTS is not correctly received, AP should issue the next RTS, until RTS/CTS exchanges for all rest scheduled recipients are issued.

5. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 5 MU-MIMO Transmission Mechanism (cont.) MU-MIMO data streams are carried in a MU-MIMO data frame based on above reservation. Only data with successfully received CTS will be carried in the MU- MIMO data frame; Planned data without a successfully received CTS will be removed from the MU-MIMO data frame. Scheduled ACKs are used for each recipient to acknowledge the receiving of data carried in MU-MIMO data frame. A CF-END may be used to terminate a MU-MIMO transmission if the transmission is terminated before the duration reserved by CTS-to- Self.

6. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 6 MU-MIMO Transmission Mechanism Analysis A CTS-to-Self is used to reserve a long duration allowing MU-MIMO transmission through “duration” field AP checks scheduled recipient one by one by RTS/CTS exchanges The RTS(s) for primary STA(s) should be arranged firstly.

7. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 7 MU-MIMO Transmission Mechanism Analysis (cont.) If AP does not detect a valid CTS frame within one SIFS period plus a delta time (TBD) following the RTS transmission, AP shall initiate the next RTS/CTS frame exchange, or start MU-MIMO data frame transmission. The data for a scheduled recipient with unsuccessful RTS/CTS frame exchange will be removed from the transmitted MU-MIMO data frame.

8. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 8 The ACK(s) is (are) scheduled based on the stream information indicated in the Nsts field of MU-MIMO data frame. MU-MIMO Transmission Mechanism Analysis (cont.)

9. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 9 If one ACK is missed, the other STA(s) will send ACK at the scheduled time shown as below. MU-MIMO Transmission Mechanism Analysis (cont.)

10. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 10 MU-MIMO Transmission Mechanism Analysis (cont.) Only when any primary STA failed to receive MU-MIMO data, the AP will initiate retransmission. The retransmission could be: retransmitted MU-MIMO data frame which includes at least the data for a primary STA failed in previous MU-MIMO transmission, and the data for other STA(s) failed in previous MU- MIMO transmission, or retransmitted SU-MIMO data frame which includes the data for a primary STA failed in previous MU-MIMO transmission, or retransmitted MU-MIMO data frame which includes at least the data for a primary STA failed in previous MU-MIMO transmission, and the data for other STA(s) failed in previous MU- MIMO transmission, and new data for other STA(s) succeeded in previous MU-MIMO transmission

11. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Summary The proposed MU-MIMO transmission mechanism provides following advantages: –Avoiding hidden node problems in BSS and OBSS –Compatibility with legacy devices –Reuse of legacy RTS/CTS frame exchanges –Avoiding unexpected confliction during the gap when a CTS is missed –Efficient MU-MIMO transmission Sun Bo, ZTE CorpSlide 11

12. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Sun Bo, ZTE CorpSlide 12 References [1] Yun.Joo.Kim, et. al., “considerations-on-mu-mimo- protection-in-11ac” IEEE 802.11-10/335r01. [2] Allan Zhu, et. al, “txop-sharing-for-dl-mu-mimo-support” IEEE 802.11-10/1123r00 [3] Tian Kaibo, et. al, “Multiple CTSs in MU-MIMO transmission” IEEE 802.11-10/1067r00

13. doc.: IEEE 802.11-10/1244r1 Submission Nov.2010 Thank you! Sun Bo, ZTE Corp