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Low Collision EDCA

Date: Jan, 2012. Low Collision EDCA. Authors:. Date: 2012-01-16. Group in[2]. Date: Jan, 2012. STAs can be classified into several groups. Different group can also has different priority. Each group has its own { Q n ,T n }.

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Low Collision EDCA

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  1. Date: Jan, 2012 Low Collision EDCA Authors: Date: 2012-01-16 Liwen Chu Etc.

  2. Group in[2] Date: Jan, 2012 • STAs can be classified into several groups. Different group can also has different priority. Each group has its own {Qn,Tn}. • By setting different {Qn,Tn}values for different groups, AP can control the mainly transmission groups at a period of time. • Group with EDCA is a good method to harmonize with the large BSS.

  3. Group Definition There are two kind of STAs: group-access STAs and normal STAs. A normal STA does not belong to any group. A group-access STA may be allocated to a group. Before being allocated to a group, a group-access STA acts as a normal STA. Each group owns a group time slot. The AP select group number (the number of groups that are in the BSS), maximal STA numbers in each group, the STAs that are in each group, the start time, stop time of each group time slot, and time slot period. Date: Jan, 2012 AP Normal STA Group STAs Green group Blue group Purple group Red group

  4. Group Definition (Cont’d.) A group may include multiple STAs. There are two possible methods to specify a group: Group members are STAs with AIDs that are clustered. If such group definition is selected, then in group power saving, each bit in the Partial Virtual Bitmap field is assigned to an AID, and the Bitmap Control field is extended to 2 bytes, because the AIDs in the BSS may grow larger than 8*256 = 2048. Or, Group members are localized STAs (but AIDs may be scattered). The localized STAs in a group can help to avoid collisions from hidden nodes. a group member ID is allocated to each group member. If such group definition is selected, then in group power saving, each bit in the Partial Virtual Bitmap is then assigned to a group member ID. Date: Jan, 2012 AP Normal STA Group STAs Green group Blue group Purple group Red group

  5. Group Time Slot Definition The group time slot may be a beacon interval, multiple beacon intervals or fraction of a beacon interval. The benefit of a beacon interval-based time slot is that it is easy to harmonize with TIM-based power saving. Date: Jan, 2012 Time Slot Period TIM Group0 time slot Group1 time slot Group3 time slot Group4 time slot Group0 time slot Group1 time slot Group2 time slot Group5 time slot Group2 time slot

  6. Group Medium Access and Power Saving When a group-access STA is not included in any group, it still uses the normal medium access methods to contend for the medium in any time slot (no change to the EDCA rules). It also follows the normal power saving rules (PS-Poll, APSD, WNM-Sleep etc.). When such STAs acquire a TXOP, the TXOP may finish after the end of any group’s time slot. But the TBTT rules should be followed. A normal STA uses the normal medium access method to contend the medium in any time slot (no change to the EDCA rules). It also follows the normal power saving rules (PS-Poll, APSD, WNM-Sleep etc.). When a normal STA acquires a TXOP, the TXOP may finish after the end of any group’s time slot. But the TBTT rules should be followed. The current PS-Poll and APSD will be used by group member power saving in group’s time slot. A power-save group member sleeps at time slots of the other groups. Date: Jan, 2012

  7. Group Medium Access and Power Saving (cont’d.) The AP and normal STAs use the normal EDCA medium access method in any time slot. The group members (group access STAs) use the normal EDCA medium access methods to contend for the medium access right in a group’s time slot. When a group member acquires a TXOP, the TXOP must finish before the end of the group time slot. If a group is allocated to the AP, the time slot can be used for group-address frame transmission. The time slot will start at DTIM TBTT. A STA has the different medium access chance in another group’s time slot: One option is that STAs that belong to a group is in doze state in another group’s time slot. Date: Jan, 2012

  8. References Doc. #802.11-11/17r5, Proposed IEEE 802.11ah Use Cases. Doc. #802.11-11/1255r0, DCF Enhancements for Large Number of STAs. Doc. #802.11-04/899r0, STMicro MAC Partial Proposal Presentation. Date: Jan, 2012

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