Doc.: IEEE 802.11-10/0584r0 Submission May 2010 Slide 1 Grouping Process for MU-MIMO Date:...
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doc.: IEEE 802.11-10/0584r0 Submission May 2010 Slide 1 Grouping Process for MU-MIMO Date: 2010-05-16 Authors: N am e C om pany A ddress Phone em ail Y ung-Szu Tu Ralink Technology 5F., No.36, Taiyuan St., JhubeiCity, H sinchu County 302, Taiw an +886-3- 560-0868 [email protected] Y en-Chin Liao [email protected] Cheng-H suan Wu cs_wu@ ralinktech.com.tw PeterLoc 20833 Stevens Creek Blvd, Suite 200, Cupertino CA 95014 +1-408- 807-0868 [email protected] Tom Paré +1-408- 725-8070 [email protected] H enry Lin [email protected]
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doc.: IEEE /0584r0 Submission MU problem set-up: 3 users May 2010 Slide 3 Composite channel: Received signal T. Paré et al., Ralink Technology
Transcript of Doc.: IEEE 802.11-10/0584r0 Submission May 2010 Slide 1 Grouping Process for MU-MIMO Date:...
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 1
Grouping Process for MU-MIMODate: 2010-05-16
Authors:
Name Company Address Phone email Yung-Szu Tu
Ralink Technology
5F., No.36, Taiyuan St., Jhubei City, Hsinchu County 302, Taiwan
+886-3-560-0868
Yen-Chin Liao [email protected]
Cheng-Hsuan Wu
Peter Loc 20833 Stevens Creek Blvd, Suite 200, Cupertino CA 95014
+1-408- 807-0868
Tom Paré +1-408-725-8070
Henry Lin [email protected]
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 2
Outline
• Typical problem definition
• MU solution details:– Optimal linear solution [1]– Single and multi-spatial stream users– Grouping algorithm
• Real-time implementation issues– Qualifying candidate groupings– Regrouping, adding/subtracting users from groups– Use of pre-coded NDP sounding packets for group management
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
MU problem set-up: 3 usersMay 2010
Slide 3
MU-AP
STA1
STA2
STA3
H1
H2
H3
• Composite channel:
• Received signalT. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
Finding the precoding matrices
May 2010
Slide 4
• Precoded MU transmission:
• Need to find V:
• Necessary condition:
• Two step problem1. Find appropriate Null spaces for each MU user i2. Find best Vi in the Null space for good reception at STAi
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 5
• Two conditions to satisfy:
1. Null space requirement:
2. Good Tx gain, can’t have:
Problem necessary conditions
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 6
Problem statement
• Constrained optimization problem:
• Maximize the transmission through the ith channel, subject to Null space constraint
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 7 T. Paré, Ralink Technology
Typical 3-user example
• AP: 8x8• Three users:
– STA1 and STA2: 2x2– STA3: 1x1
• MU Channel dimensions:
• Corresponding Nullspaces:– Find nullspaces using QR decomposition
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 8
Precoder for STA3: 1SS user
• Nullspace:• Assume linear solution:• Find a that maximizes Y3, where:
• Let:
• Optimal solution (2-norm):
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 9
Multi-stream Users: STA1,2
• Larger nullspace:• Solution form:• Find A (5X2) that maximizes Y1, where
• SVD solution to find optimal directions:
• Optimal solution (2-norm):
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 10
Grouping Algorithm: Iterative solution to find feasible groups
1. Gather Candidate
GROUP CSI
2. Form Nullspaces
Ni
3. Compute Precoding Matrices:
Vi
4. CHECK transmission:
|Hi*Vi| > THRESH
5. OK?
7. Remove user i from
group
6. i=i+1
No
Yes
8. Periodic/inital GRP sounding validation
9. Determine interference
between users
10. Remove offending
user
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 11
Observations
• 1SS vs multi-SS clients– Should 2SS be split up and treated individually?
• This could potentially penalize the 2SS device• Let AP decide number of SS for each multi-SS device• Client does not need to know details of spatial stream selection
• Incompatible pairs of users requires re-computation of nullspaces, precoders– Good: Solution for reduced set of clients improves– Bad: Could require many QR operations
• Include a mechanism to minimize/guarantee suitable groups are formed
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 12
• Design results in precoded MU channel:
• By design:– Off-diagonal terms are zero– Non-zero indicates interference between users
• MU-Sounding recommendation:– Include BF-NDP or precoded-NDP mode for direct
measure of MU channel
MU-Sounding Mode (1/3)
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 13
MU-Sounding Mode (2/3)• Possible MU-Sounding Formats
– Precoded-NDP– Staggered Precoded-LTF
• Feedback – BF-CSI
• Transparent to users– SINR metrics
• Reduced overhead• Per User interference level• Per STS interference level
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
• Benefits for MU operation– Validate initial Group Formation Algorithm
• Detect poor initial CSI, or• Practical imperfections in antenna/RF circuits• Assist MU MCS selection (similar to FLA in .11n)
– Provide specific info on particular interfering pairs• Streamline re-grouping process• Minimize QR re-computation process
– Detect changing channel conditions• Allow AP to maintain/schedule interference metrics• AP suspend, regroup and re-initiate MU operation
MU-Sounding Mode (3/3)
May 2010
Slide 14 T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
SINR report simulation
2x2 user:• SINR lower on 2nd SS• Less impact co-existing with 1SS STA
1x1 STA• Symmetric interference from 2x2 STAs
May 2010
Slide 15
18 20 22 24 26 28 3015
20
25
30
35
40Interference report from 2SS user
channel SNR
SIN
R d
B
STR1: from 2SS userSTR2: from 2SS userSTR1: from 1SS userSTR2: from 1SS user
18 20 22 24 26 28 3018
20
22
24
26
28
30
32Interference report from 1SS user
channel SNR
SIN
R d
B
STR1: from 1st 2SS userSTR1: from 2nd 2SS user
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
May 2010
Slide 16
• Group stages: Formation, validation, and maintanenceGroup maintenance process
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
Summary
May 2010
Slide 17
• Proposed MU-sounding mode (BF or Precoded NDP)– Direct Interference measure– Qualify candidate groupings– Assist MU link adaptation
• Periodic MU-Sounding– Staggered BF LTF, or periodic Precoded-NDP
• Real-time assessment of grouping validity– SINR feedback for reduced overhead
• Allow single user to belong to multiple groups– Streamlines group formation process– Allow groups to add/subtract users seamlessly
T. Paré et al. , Ralink Technology
doc.: IEEE 802.11-10/0584r0
Submission
• [1] Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, “Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels” IEEE Trans. Sig. Proc., vol. 52, pp. 461–471 , Feb. 2004
Reference
May 2010
Slide 18 T. Paré et al. , Ralink Technology
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