doc.: IEEE 802.11-15/1321r0

Submission

Reducing Explicit MIMO Compressed Beamforming Feedback Overhead for 802.11ax

November 2015

Slide 1

Date: 2015-11-08

Authors:

Kome Oteri (InterDigital)

Name Affiliations Address Phone email Kome Oteri

InterDigital

Communication Inc.

9710 Scranton Road,

San Diego, CA, 92121

858 210 4826 Kome.oteri@interdigital.com

Hanqing Lou

Rui Yang

Joe Levy

Robert Olesen

doc.: IEEE 802.11-15/1321r0

Submission

Outline

• Introduction• Extension Schemes• New Schemes• Conclusion

Kome Oteri (InterDigital)Slide 2

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

Introduction• In this contribution, we discuss possible methods to reduce explicit MIMO

compressed beamforming feedback overhead in 802.11ax. • 802.11ac supports explicit MIMO compressed beamforming feedback with

• (4,2) or (6,4) bits to quantize angle (ϕ, ψ) for single user, and• (7,5) or (9,7) bits to quantize angle (ϕ, ψ) for multi-user.– For 802.11ax, the following has been agreed to [1]:

• The amendment shall define a mechanism to reduce the MIMO compressed beamforming feedback overhead. [MU Motion 25, September 17, 2015, see [2]]

• We discuss two groups of schemes:– Extension Schemes: Extension of 802.11ac feedback schemes. We discuss

six schemes.– New Schemes: New (to 802.11) MIMO compressed beamforming

feedback schemes. We discuss two schemes.• Our goal is to narrow down possible schemes for further study and design.

Kome Oteri (InterDigital)Slide 3

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

Extension Schemes• Extending the current beamforming feedback may be done by

1. Large Ng: • Increase the tone grouping size {Ng} during feedback [3][4]

2. ϕ Only Feedback: • Feedback ϕ only in N x 1 transmission and assume a fixed ψ [5]

3. Variable Angle Quantization: • Use different quantization levels for different Given’s rotation angles (ϕi, ψi).

4. Differential Given’s Rotation: • Feedback time or frequency difference in Given’s Rotation angles.

5. Multi-resolution/Multi-stage feedback • Identify frequency band(s)/Resource Units (RU(s)) based on scalar feedback

(e.g. SNR) and feed back full CSI for desired frequency band /RU(s).

6. Time Domain Channel Feedback• Feed back time domain channel

November 2015

Kome Oteri (InterDigital)Slide 4

doc.: IEEE 802.11-15/1321r0

Submission

Extension Scheme (1)1. Large Ng: Increase the tone grouping size {Ng} during feedback

• Minimum size has already been increased to 2 [3]• Maximum size may be increased to 16 with little impact on performance

for some scenarios [4]

November 2015

Kome Oteri (InterDigital)Slide 5

doc.: IEEE 802.11-15/1321r0

Submission

Extension Scheme (2)2. ϕ Only Feedback: Feed back ϕ only in N x 1 transmission and assume a

fixed ψ [5]– 802.11ah supports feedback of angles only with single data stream transmissions.

The values of ψ are fixed [5, 24.3.10.2]

– Reduction in overhead is shown in the tables below (methodology in appendix)

– We may keep the overhead the same and increase bϕ. (Table 1 and 2)

– We may reduce the overhead by keeping bϕ the same and changing bψ (Table 1 and 3)

November 2015

Kome Oteri (InterDigital)Slide 6

doc.: IEEE 802.11-15/1321r0

Submission

Extension Schemes (3)3. Variable Angle Quantization : Use different quantization levels for

different Given’s rotation angles (ϕi, ψi).– Angle ψ may vary over the distribution; for example range of ψ1 is greater than

range of ψ7 for 8 x 1 system shown below.

– To quantize the angles after Givens rotation, we may use different ranges for different angles or groups of angles. • For each angle or groups of angles, the range

November 2015

Slide 7 Kome Oteri (InterDigital)

doc.: IEEE 802.11-15/1321r0

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Extension Schemes (4)4. Differential Given’s Rotation : Feed back time or frequency difference in

Given’s Rotation angles– Send differential information between Given’s rotation angles of ‘baseline’ channel and

next channel in time [6] or frequency– May use scalar difference (subtraction) or vector difference (range/null space overlap).

November 2015

Slide 8

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

radians

F(x

)

Empirical CDF

Channel B+D+E

Channel B only

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

radians

F(x

)

Empirical CDF

Channel B+D+E

Channel B only

is approximately distributed within the range of

is approximately distributed within the range of

Kome Oteri (InterDigital)

Givens decomp.

H(k)

H(k+4) Givens decomp.

Original quantization

Differential quantization

{f(k), y(k)}

{f(k+4), y(k+4)} {df, dy}

+-

doc.: IEEE 802.11-15/1321r0

Submission

Extension Schemes (5)5. Multi-Resolution/Multi-Stage Feedback : Identify desired band/RU based

on scalar feedback (e.g. SNR) then feed back full CSI for specific RU(s).– This is an example of a scheme enabling a feedback granularity of less than

20 MHz [1]– The table below shows total feedback per transmission per user, i.e. the

amount of feedback needed from a user to enable a successful transmission: • Can save 90% overhead per user per

November 2015

Kome Oteri (InterDigital)Slide 9

Overhead savings is compared with 242 tone RU caseTotal Feedback/Tx/User = 2 bytes* No. RUs + No. subcarrier per RU * VHT BF report (bytes)

Additional details in Appendix

Typical RUs

DC RU

Total RUs

Feedback Typical RU

Feedback DC RU

SNR Feedback (2 bytes)

Total Feedback

(Typical RU)

Total Feedback (DC RU)

Total Feedback

Total Feedback

/user /transmission

Overhead Savings (%)

SU, 8x4, 26 tone RU (Bytes) 8 1 9 202 202 18 1616 202 1836 204.00 87.73%

SU, 8x4, 242 tone RU (Bytes) 1 0 1 1660 202 2 1660 0 1662 1662.00 N/A

doc.: IEEE 802.11-15/1321r0

Submission

Extension Schemes (6)

6. Time domain channel feedback: Feed back time domain channel– Number of significant taps may be much less than the number of tones

and may result in feedback overhead savings.– However, may need to feed back U, S and V of time domain channel U to

enable transformation of the channel to the frequency domain. i.e. one additional matrix.

– May also need to indicate position of tap– As such, there may be a trade-off between increasing the feedback per tap

and the number of taps fed back.

November 2015

Kome Oteri (InterDigital)Slide 10

doc.: IEEE 802.11-15/1321r0

Submission

New Feedback Schemes

7. Multiple component feedback: splits feedback into multiple components [7]– One component has a larger size and is fed back at longer intervals. – One component is smaller and is sent back at shorter intervals. – The combination of both may reduce the overall feedback– Examples include

• Feed back long term / short term information• Feed back wideband / sub-band information

8. Codebook-based feedback: Feed back codeword from a well designed codebook [8]– Overall feedback may reduce based on the size of the codebook.

November 2015

Slide 11 Kome Oteri (InterDigital)

doc.: IEEE 802.11-15/1321r0

Submission

Summary (Pros and Cons)

November 2015

Kome Oteri (InterDigital)Slide 12

doc.: IEEE 802.11-15/1321r0

Submission

Conclusions

• Multiple schemes may be used to reduce the explicit MIMO compressed beamforming Feedback Overhead for 802.11ax– They include six schemes that are simple extensions of 802.11ac

feedback schemes. – They include two new (to 802.11) MIMO compressed

beamforming feedback schemes.• The performance of these methods should be studied and a

combination of them adopted in 802.11ax

Kome Oteri (InterDigital)Slide 13

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

References

1. 11-15-0132-09-00ax-spec-framework

2. 11-15-1129-01-00ax-feedback-overhead-in-dl-mu-mimo

3. 11-15-1071-02-00ax-tone-grouping-factors-and-ndp-format-for-802-11ax

4. 11-15-1320-00-00ax-Maximum-tone-grouping-for-802_11ax-feedback

5. IEEE P802.11ah™/D2.0 Amendment 6: Sub 1 GHz License Exempt Operation

6. Porat, R.; Ojard, E.; Jindal, N.; Fischer, M.; Erceg, V., "Improved MU-MIMO performance for future 802.11 systems using differential feedback," in Information Theory and Applications Workshop (ITA), 2013 , vol., no., pp.1-5, 10-15 Feb. 2013

7. Chaiman Lim; Taesang Yoo; Clerckx, B.; Byungju Lee; Byonghyo Shim, "Recent trend of multiuser MIMO in LTE-advanced," in Communications Magazine, IEEE , vol.51, no.3, pp.127-135, March 2013

8. Love, D.J.; Heath, R.W.; Lau, V.K.N.; Gesbert, D.; Rao, B.D.; Andrews, M., "An overview of limited feedback in wireless communication systems," in Selected Areas in Communications, IEEE Journal on , vol.26, no.8, pp.1341-1365, October 2008.

Kome Oteri (InterDigital)Slide 14

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

Straw Poll #1

Do you agree with the following?• The amendment shall define a mechanism to reduce the MIMO

compressed beamforming feedback overhead.– The amendment may consider methods that extend the compressed

beamforming feedback ideas in 802.11ac

Y/ N/ A

Kome Oteri (InterDigital)Slide 15

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

Straw Poll #2

Do you agree with the following?• The amendment shall define a mechanism to reduce the MIMO

compressed beamforming feedback overhead.– The amendment may consider new ideas that are different from the

compressed beamforming feedback ideas in 802.11ac

Y/ N/ A

Kome Oteri (InterDigital)Slide 16

November 2015

doc.: IEEE 802.11-15/1321r0

Submission

Additional Material

November 2015

Kome Oteri (InterDigital)Slide 17

doc.: IEEE 802.11-15/1321r0

Submission

Multi-Resolution/Multi-Stage Feedback Overhead

November 2015

Kome Oteri (InterDigital)Slide 18

Typical RUs

DC RU

Total RUs

Feedback Typical RU

Feedback DC RU

SNR Feedback (2 bytes)

Total Feedback

(Typical RU)

Total Feedback (DC RU)

Total Feedback

Total Feedback

/user /transmission

Overhead Savings (%)

SU, 2x1, 26 tone RU (Bytes) 8 1 9 42 42 18 336 42 396 44.00 60.00%

SU, 4x1, 26 tone RU (Bytes) 8 1 9 57 57 18 456 57 531 59.00 77.13%

SU, 8x1, 26 tone RU (Bytes) 8 1 9 87 87 18 696 87 801 89.00 83.91%

SU, 8x2, 26 tone RU (Bytes) 8 1 9 129 129 18 1032 129 1179 131.00 86.34%

SU, 8x4, 26 tone RU (Bytes) 8 1 9 202 202 18 1616 202 1836 204.00 87.73%

SU, 2x1, 52 tone RU (Bytes) 4 1 5 49 42 10 196 42 248 49.60 54.91%

SU, 4x1, 52 tone RU (Bytes) 4 1 5 79 57 10 316 57 383 76.60 70.31%

SU, 8x1, 52 tone RU (Bytes) 4 1 5 139 87 10 556 87 653 130.60 76.38%

SU, 8x2, 52 tone RU (Bytes) 4 1 5 223 129 10 892 129 1031 206.20 78.50%

SU, 8x4, 52 tone RU (Bytes) 4 1 5 367 202 10 1468 202 1680 336.00 79.78%

SU, 2x1, 106 tone RU (Bytes) 2 1 3 67 42 6 134 42 182 60.67 44.85%

SU, 4x1, 106 tone RU (Bytes) 2 1 3 132 57 6 264 57 327 109.00 57.75%

SU, 8x1, 106 tone RU (Bytes) 2 1 3 262 87 6 524 87 617 205.67 62.81%

SU, 8x2, 106 tone RU (Bytes) 2 1 3 442 129 6 884 129 1019 339.67 64.58%

SU, 8x4, 106 tone RU (Bytes) 2 1 3 752 202 6 1504 202 1712 570.67 65.66%

SU, 2x1, 242 tone RU (Bytes) 1 0 1 108 42 2 108 0 110 110.00 N/A

SU, 4x1, 242 tone RU (Bytes) 1 0 1 256 57 2 256 0 258 258.00 N/A

SU, 8x1, 242 tone RU (Bytes) 1 0 1 551 87 2 551 0 553 553.00 N/A

SU, 8x2, 242 tone RU (Bytes) 1 0 1 957 129 2 957 0 959 959.00 N/A

SU, 8x4, 242 tone RU (Bytes) 1 0 1 1660 202 2 1660 0 1662 1662.00 N/A

Overhead savings is compared with 242 tone RU caseTotal Feedback/Tx/User = 2 bytes* No. RUs + No. subcarrier per RU * VHT BF report (bytes)

doc.: IEEE 802.11-15/1321r0

Submission

Overhead Calculation Details

• VHT Compressed Beamforming frame is utilized for CSI feedback.

Frame Size = MAC Header size + VHT Compressed BF frame Action field size• VHT Compressed Beamforming frame action field format

• VHT Compressed BF Report– Average SNR per stream– Angles compressed from V matrices per Ng subcarriers

• Number of angles reported depend on the size of V matrices.• Number of bits for and , and , are determined by VHT MIMO Control field.

November 2015

Kome Oteri (InterDigital)Slide 19