Submission

doc.: IEEE 802.11-15/0334r1

A Framework for MIMO Operation over mmWave Links

Slide 1 Alireza Tarighat, Broadcom

Authors:

Name Affiliation Address Phone Email

Alireza Tarighat Broadcom atarighat@broadcom.com

Payam Torab Broadcom ptorab@broadcom.com

Brima Ibrahim Broadcom brima@broadcom.com

Vipin Aggarwal Broadcom vaggarwa@broadcom.com

Vinko Erceg Broadcom verceg@broadcom.com

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Contents

• mmWave MIMO for NG60

• Possible MIMO scenarios• SVD multiplexing

• Multi-array beamforming

• Spatial aggregation

• Multi-array diversity

• Impact of phase noise on SVD multiplexing

• Conclusions

Slide 2 Alireza Tarighat, Broadcom

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Applicability of MIMO to mmWave

• A 2x2 mmWave system deploys 2 TX arrays and 2 RX arrays.• Each array may have N elements, but only two data feeds are available.

• Each array has a programmable phase shifter that can be leveraged to change the MIMO channel seen by the 2x2 system.• A major difference with sub-5GHz systems where omni elements are

used.

• Additional knob available through changing array patterns.

Slide 3 Alireza Tarighat, Broadcom

RF TRX

RF TRX

RF TRX

RF TRX

2x2 MIMO

2x2 MIMO

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)

• Form a 2x2 MIMO System

• Apply SVD with/without waterfilling

• Due to narrow beam patterns, the propagation will look like a LOS (AWGN) MIMO channel.

• Can we expect a significant multiplexing gain in LOS (AWGN) MIMO channels?

Slide 4 Alireza Tarighat, Broadcom

SVD

De-

Mul

tiple

xing

RF TRX

RF TRX 2-st

ream

D

ecod

er

SVD

Mul

tiple

xing

RF TRX

RF TRX

2-st

ream

Enc

oder

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)• Two example usage cases

• High cross-interference between the streams (LOS MIMO & AWGN MIMO scenarios)

• These two scenarios can be common in outdoor deployments.

Slide 5 Alireza Tarighat, Broadcom

Dev

ice

D

evic

e

Dev

ice

Dev

ice

LOS

Bloc

ker

Reflector Reflector

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)

SISO Capacity

Slide 6 Alireza Tarighat, Broadcom

1x1 y1

TX Power: P 𝐶𝑆𝐼𝑆𝑂 (𝑃 )=log(1+𝑃𝑁

)

March 9, 2015

x1 1𝑒 𝑗𝜙11

x2

1𝑒 𝑗𝜙22

𝑘𝑒 𝑗𝜙12

𝑘𝑒 𝑗𝜙21

y1

y2

𝐶𝑀𝐼𝑀𝑂= max𝐑 𝐱 :𝑻𝒓 (𝐑 𝐱 )=𝟐 𝑃

𝑙𝑜𝑔(det (𝐈+𝐇𝐑𝐱𝐇∗

𝑁))

𝐇𝐇∗=[ 1+𝑘2 𝑘 (𝑒 𝑗 (+𝜙11−𝜙21)+𝑒 𝑗 (+𝜙12−𝜙22))𝑘 (𝑒 𝑗 (−𝜙11+𝜙21)+𝑒 𝑗 (−𝜙12 +𝜙22 )) 1+𝑘2 ]

Line-of-Sight MIMO Capacity

Above can be realized through SVD when CSI is available at TX.

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)MIMO capacity will depend on the following value:

MIMO capacity without waterfilling:

MIMO capacity with waterfilling

Slide 7 Alireza Tarighat, Broadcom

𝐶𝑀𝐼𝑀𝑂=𝑙𝑜𝑔((1+ 𝑃𝑁

(1+k2 ))2

−2(𝑘 𝑃𝑁 )

2

(1+cos(+𝜙11−𝜙12+𝜙22−𝜙21)))

𝐶𝑀𝐼𝑀𝑂= max𝑃 𝑖 :∑ (𝑃 𝑖)≤ 2𝑃

∑𝑖

𝑙𝑜𝑔(1+𝑃 𝑖

2𝑃𝛾𝑖) Where , and are the eigenvalues of

𝜙𝑑=+𝜙11−𝜙12+𝜙22−𝜙21Phase delta (function of distance):

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

MIMO Capacity vs Phase Delta

Slide 8 Alireza Tarighat, Broadcom

0 20 40 60 80 100 120 140 160 1806

7

8

9

10

11

12

13

Cap

acity

(b/s

/Hz)

Phi Delta (deg)

P/N=15dB cross gain(k)=0dB

MIMO Capacity (1P per TX power)

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM) Phase delta=180deg (maximizes capacity)

K=0dB

Slide 9 Alireza Tarighat, Broadcom

-5 0 5 10 15 20 250

2

4

6

8

10

12

14

16

18

20

Cap

acity

(b/

s/H

z)

Single Link SNR (dB)

phase delta=180, cross gain(k)=0dB

SISO Capacity (1P TX power)

MIMO Capacity (2P total TX power)MIMO Capacity w/waterfilling (2P total TX power)

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM) Phase delta=0deg (minimizes capacity)

K=0dB

Slide 10 Alireza Tarighat, Broadcom

-5 0 5 10 15 20 250

2

4

6

8

10

12

Cap

acity

(b/

s/H

z)

Single Link SNR (dB)

phase delta=0, cross gain(k)=0dB

SISO Capacity (1P TX power)

MIMO Capacity (2P total TX power)MIMO Capacity w/waterfilling (2P total TX power)

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)

TX arrays spacing=15cm

RX arrays spacing=20cm

K=0dB

Short range (small # of elements)

Slide 11 Alireza Tarighat, Broadcom

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

2

4

6

8

10

12

14

16

18

Cap

acity

(b/

s/H

z)

Range (m)

TX spacing=0.15m, RX spacing=0.2m, cross gain(k)=0dB

SISO Capacity (1P TX power)

MIMO Capacity w/waterfilling (2P total TX power)

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 1: SVD Multiplexing (SM)

TX arrays spacing=15cm

RX arrays spacing=20cm

K=0dB

Long range (high # of elements)

Slide 12 Alireza Tarighat, Broadcom

0 10 20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

14

16

18

20

Cap

acity

(b/s

/Hz)

Range (m)

TX spacing=0.2m, RX spacing=0.3m, cross gain(k)=0dB

SISO Capacity (1P TX power)

MIMO Capacity w/waterfilling (2P total TX power)

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 2: Multi-Array Beamforming (MAB)

• Form a larger single array by phase-aligning the two arrays

• Transport a single stream at higher SNR• 2 TX arrays and 2 RX arrays: 9dB higher total SNR compared to SISO

case

Slide 13 Alireza Tarighat, Broadcom

Mul

ti-Ar

ray

Beam

form

ingRF TRX

RF TRX

1-st

ream

D

ecod

er

Mul

ti-Ar

ray

Beam

form

ing RF TRX

RF TRX

1-st

ream

Enco

der

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 2: Multi-Array Beamforming (MAB)

• Two example usage cases

• 9dB SNR gain compared to single array case (6dB from TX and 3dB from RX)

• At low SNR, scheme 2 outperforms scheme 1 without waterfilling

Slide 14 Alireza Tarighat, Broadcom

Dev

ice

D

evic

e

Dev

ice

Dev

ice

LOS

Bloc

ker

Reflector

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

SVD Multiplexing vs MAB

• Multi-array beamforming (MAB) provides 9dB SNR gain compared to a single array case (6dB from TX and 3dB from RX)

• At high SNR, SVD-M outperforms MAB in terms of capacity.

• At low SNR, MAB outperforms “SVD-SP w/o waterfilling” (with substantial delta)

• At low SNR, MAB outperforms “SVD-SP w waterfilling” (but with very marginal delta)

• Multi-Array Beamforming (MAB) is simple to support from standard perspective (11ad nearly sufficient to support it).

• It is more of an implementation choice.

Slide 15 Alireza Tarighat, Broadcom

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

SVD Multiplexing vs MAB

• SVD-Multiplexing can reach MAB performance at low SNR only with the help of waterfilling

Slide 16 Alireza Tarighat, Broadcom

0 20 40 60 80 100 120 140 160 1803.9

4

4.1

4.2

4.3

4.4

4.5

4.6

4.7spatial multiplexing (SM) with waterfilling vs. MAB (k=1, SNR=3dB)

phase delta (deg)

capa

city

(b/

s/hz

)

SVD-SM w/ waterfilling

MAB

0 20 40 60 80 100 120 140 160 1800

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1relative power in each spatial stream in SM with waterfilling (k=1, snr=10dB)

phase delta (deg)

fract

ion

of to

tal p

ower

2P

Strongest eigen-mode

Second eigen-mode

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 3: Spatial Aggregation (SA)

• SVD can be eliminated if sufficiently separated beams can be identified.

• Simplified TX and RX implementation

• May be defined as a baseline MIMO mandatory mode (while making SVD-Multiplexing optional)

Slide 17 Alireza Tarighat, Broadcom

RF TRX

RF TRX2-st

ream

En

code

r

Opti

onal

Inte

rfer

ence

-Ca

ncel

latio

nRF TRX

RF TRX

2-st

ream

D

ecod

er

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 3: Spatial Aggregation (SA)

• Example usage case

• SA is a subset of SVD-Multiplexing

• Use of interference cancellation in RX side is implementation and vendor choice.

Slide 18 Alireza Tarighat, Broadcom

Dev

ice

Dev

ice

Bloc

ker

Reflector

Reflector

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 4: Multi-Array Diversity (MAD)

• Transport the same streams across two arrays.

• A sub-optimal configuration to MAB when MAB is not applicable.• SNR is low for significant gain out of SVD-SM

• Link reliability/redundancy is a key metric

• Cross-interference between the multiple beams is relatively high

• 3dB diversity/energy combining gain compared to a single array case.

Slide 19 Alireza Tarighat, Broadcom

RF TRX

RF TRX

1-st

ream

En

code

r

Spati

al D

iver

sity

Co

mbi

ning

RF TRX

RF TRX

1-st

ream

D

ecod

er

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Scenario 4: Multi-Array Diversity (MAD)

• Example usage case• Simple reliability improvement

• Energy combining gain

Slide 20 Alireza Tarighat, Broadcom

Dev

ice

Dev

ice

Bloc

ker

Reflector

Reflector

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Summary of MIMO Scenarios

Mode Number of data streams

(Constellation-Level)

True MIMO Coding

Improved Merit of Figure

Some applicable usages

SVD Multiplexing (SM) -Closed Loop using CSI

Two Yes Throughput Backhaul capacity, adjacent arrays, high SNR, polarization multiplexing

Multi-Array Beamforming (MAB) Single No SNR Backhaul range, adjacent arrays, low SNR

Spatial Aggregation (SA)-Open Loop

Two No Throughput Indoor/Outdoor, polarization multiplexing when good separation available

Multi-Array Diversity (MAD) Single No SNR Indoor, distant arrays

Slide 21 Alireza Tarighat, Broadcom

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Phase Noise Impact on SVD Multiplexing

• Phase noise seen by the multiple streams may only be partially correlated• Cases that two different RFIC chips are deployed

• An SVD-based multiplexing will experience cross-stream interference due to uncorrelated phase noise• This effect is not seen in existing MIMO systems (such as 11ac where the

same LO is feeding the multiple streams)

• Simulation scenario:• Low-frequency “correlated phase noise” and high-frequency

“uncorrelated phase noise”

• Integrated phase noise (uncorrelated portion) of 5 deg (fairly pessimistic)

Slide 22 Alireza Tarighat, Broadcom

March 9, 2015

Submission

doc.: IEEE 802.11-15/0334r1

Phase Noise Impact on SVD Multiplexing

Slide 23 Alireza Tarighat, Broadcom

0 20 40 60 80 100 120 140 160 1803

4

5

6

7

8

9

Capacity degradation due to inter-stream interference from uncorr phase noise (5 deg rms)when using SVD based stream separation, SNR=10dB, cross-leakage=0dB

phase delta (deg)

capa

city

(b/

s/hz

)

MIMO, no pn, (1P per TX chain)

MIMO, with pn (1P per TX chain)SISO, no pn, (1P TX chain)

SISO, with pn, (1P TX chain)

March 9, 2015

Integrated uncorrelated phase noise = 5deg

Submission

doc.: IEEE 802.11-15/0334r1

Summary• All four “multi-radio” scenarios can be implemented using a

common PHY standard framework.

• Possible standard framework:• Ability to generate 2 to 4 independent streams (no cross coding)

• Enables two modes of operation: transport data streams over the same frequency channel (spatial aggregation) or over different frequency channels (carrier aggregation)

• Ability to apply some form of “SVD coding” to generate 2 to 4 coded data streams

• This “waveform generation” framework enables following usages: SVD multiplexing (LOS/AWGN MIMO), polarization multiplexing, multi-array beamforming, spatial aggregation, carrier aggregation, multi-array diversity.

Slide 24 Alireza Tarighat, Broadcom

Same channel Different channels

No TX cross-coding Spatial aggregation Carrier aggregation

TX cross-coding SVD multiplexing N/A

March 9, 2015