1. Proposed Resolution to CID 12194
June 2013
doc.: IEEE /xxxxr0
Jan 2018
Proposed Resolution to CID 12194
Date:
Authors:
kaiying lv (ZTE)

2. Background Jan 2018 12194 kaiying Lv 230 2 27.9.3 295 60
Multiple SR PPDUs from different STAs may interfere the reception of SRP PPDU. Mechanism to reduce the interference needs to be considered.
Please clarify it

3. Jan 2018
Issue
An OBSS STA that meets SRP-based spatial reuse conditions is permitted to contend the medium over the on-going PPDU. Whereas, SR PPDUs from multiple OBSS STAs may seriously interfere the on-going reception at AP side as shown below
Fig 1 SRP-based spatial reuse with multiple SR transmissions

4. June 2013
Jan 2018
Analysis
A more stringent requirement, e.g increase the margin to allow lower acceptable interference level than usual, can mitigate the aforementioned interference issue by reducing Tx power of all spatial reuse transmissions
However, it will have a negative impact on the spatial reuse feature:
The reliability of all spatial reuse transmissions will be weakened
The number of disabled spatial reuse transmissions will increase since allowed Tx power is under the required link budget
Within a TXOP, it is less practical to converge to a tradeoff between the interference level and performance of spatial reuse transmission

5. June 2013
Dec 2017
Proposal
We propose a random spatail reuse to resolve the interference issue by statistically limiting the number of concurrent transmissions over the same PPDU rather than purely depending on reducing the Tx power
In the random spatial reuse, performing spatial reuse or not will be determined based on the comparison result of a local random value and an informed threshold. Wherein the threshold can be
Carried in the HE-SIG-A of an HE TB PPDU
A dynamic value provided by AP

6. LDPC Extra Symbol Segment
June 2013
Dec 2017
Changes to Draft 2.0
Add an SR Threshold field into the HE-SIG-A2 (see Fig 2) of HE TB PPDU and the Common Info field of Trigger frame (see Fig 3)
An exemplary encoding scheme is specified in Table 1
Table 1 Threshold field Encoding
TXOP
(B0-B6)
SR THRESHOD
(B7-B9)
RESERVED
(B10-B15)
CRC
(B16-B19)
TAIL
(B20-B25)
SR THREHOLD Value
Meaning
Value 0 indicate that the threshold is 0 1
Value 1 indicates that the threshold is 0.2 2
Value 2 indicates that the threshold is 0.4 3
Value 3 indicate that the threshold is 0.6 4
Value 4 indicatets that he threshold is 0.8
5-8
reserved
Fig 2 HE-SIG-A2 field of HE TB PPDU
STBC
(B26)
LDPC Extra Symbol Segment
(B27)
...
SR THRESHOLD
(B54-B56)
RESERVED
(B63)
Fig 3 Common Info field in Trigger frame

7. Changes to Draft 2.0 (Cont.)
Dec 2017
Changes to Draft 2.0 (Cont.)
Proposed operations regarding SRP-based spatial reuse
When receiving a trigger frame or an HE TB PPDU from an OBSS, a STA shall compare the SR THRESHOLD with a local value randomly generate within the range [0,1)
Spatial reuse shall be allowed when the local random value is equal to or greater than the SR THRESHOLD; Otherwise, it shall be not perform spatial reuse even though related conditions shown in Draft 2.0 is satisfied

8. Dec 2017
Summary
The presentation suggests the random spatial reuse as a comment resolution of the CID 12194

9. Dec 2017
Straw Poll
Do you agree to adopt the random spatial reuse as the resolution of CID ? Y N A

10. Dec 2017
Reference
[1]IEEE P802.11ax/D2.0, October 2017