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MU-MIMO

TECHNICAL

CHALLENGESWLPC Phoenix 2016

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AGENDA

• MU-MIMO Benefits

• MU-MIMO Technology

• MU-MIMO Demonstration & Analysis

• Challenges & Conclusion

• Appendix – Wireshark MU-MIMO capture in more details

MU-MIMO is a new technology that improves spectrum utilization promising higher

practical throughputs and better user Quality of Experience. However there are

strong challenges in achieving effective implementation. This session will detail

these through demonstration and analysis of current commercial MU-MIMO APs

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11AC BEAMFORMING

• 11ac introduces Explicit method – Beamforming

• First time - client provides channel information

• Beamforming gain may allow higher MCS, especially mid-range

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BENEFITS

• MU-MIMO gives better spectrum utilization – higher throughputs

• Better client QoE

Lower Latency & Jitter

• Not straight forward as the diagram!

1x1

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MU-MIMO TECHNOLOGY

Complex to beamform

signal

11ac defined MU-MIMO

more effective clearer

environments

MIMO with multipath

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MU-MIMO TECHNOLOGY

1. MU-MIMO client

2. Sounding process

3. Grouping

4. MU DS Transmissions

5. BAs/BARs

Major differences

between chipsets!

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MU-MIMO QUESTIONSCategory Decision

Sounding

When should the AP sound?

Which clients does the AP sound?

How many clients does the AP sound?

How often should it sound those clients?

Sound the client for MU or SU beamforming?

Grouping

Who does the AP group?

How many clients are grouped?

How many groups?

TransmissionsWhen/how often does the AP do MU-MIMO Transmissions?

Use SU or MU beamforming?

On Mobility/TxFailure

Should the AP reduce the MCS for that client?

Should the AP transmit the data using SU?

How many failed transmissions/How far should the AP reduce the MCS before no longer performing MU-MIMO for that client?

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MU-MIMO GROUPING

Feedback Angles, SNR, DeltaSNR

Non-Orthogonal Clients

Close/Far Clients

Client MIMO level

? 2x2, 1x1, 1x1 client

? 4x 2x2

Client Access Category & QoS

Best Effort, Video..

How many groups? How many clients?

Same client in multiple groups

100 clients – 62 MU Groups – 248 pos.

Nature of Client Traffic

High/Low, TCP/UDP

Updates to client group assignment?

Static/Dynamic…

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VALUE

How do you know that MU-MIMO is happening?

Value in Scalable, Configurable, Repeatable, Independent

test environment, that provides Operation Visibility

under variety Traffic Models with QoE metrics

& can be Automated

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MU-MIMO TEST CONFIGURATION

Control Laptop

Wi-Fi & Ethernet Blade

Ethernet

In-cable RF

Linksys EA8500

Should be in a Chamber

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HOW IN-CABLE?

Handles all 4

simultaneous

users from

independent

“locations”

MU-MIMO Group

Any of 500 simulated

clients at any instance

MAC CPU

PHY FPGA

Signal

Chain

Know exactly the Vk for each client

Can see all information as in-cable connection

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MU-MIMO SCALING

• >10 clients see

drop off MU-MIMO

gains

• Reverts to SU

Clients only

0

100

200

300

400

500

600

700

800

900

1000

2 3 4 7 10 15

MU-Clients vs. UDP Forwarding Rate

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WIRESHARK

VHT NDP Announcement wlan.fc.type_subtype == 21

Action Frame(CBR) wlan.fc.type_subtype == 14

BF Report Poll wlan.fc.type_subtype == 20

Group ID Management wlan.vht.action == 1

MU-MIMO Data ixveriwave.VHT_GRPID < 63 &&

ixveriwave.VHT_GRPID > 0 && udp

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MU-MIMO PERFORMANCE (LATEST)

Highest 3 client performance, peaking 980Mbps

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CHALLENGES

1. AP Intelligence

• AP must make more decisions – non-deterministic/prioritization

• Unique solutions

2. Increased computational requirements

• Stressful on both Clients & APs

• Clients take Reference & respond within 16us SIFS – beyond a lot of clients today

• If AP looks at Orthogonality of each combination before transmission…

3. Channel Degradation

• Time since sounding – channel changes & degrades

• Especially sensitive in MU-MIMO

4. Sounding overhead

• As clients scale, how often & many do you sound?

• 10% -> Every 15ms with 1.5ms Sounding

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MU-MIMO CONCLUSION

• MU-MIMO promises!

• Success of MU-MIMO – in Intelligence

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MU-MIMO CAPTURE DETAILS IXIA – EA8500

…

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NDPA

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CBR

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CBR POLL

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MU-MIMO DATA

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MU-MIMO DATA BA

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MU-MIMO DATA BAR