Next Generation Very High Throughput: 802.11ac WLAN MIMO ... · MIMO Transmitter Design With 802.11ac needing higher performance designs, every part of the transmit and receive chain

© 2012 Agilent Technologies

Wireless Communications

Greater insight. Greater confidence. Accelerate next-generation wireless.

Next Generation Very High Throughput: 802.11ac WLAN MIMO

Design & Test Challenges Presented by: Greg Jue and Jake Sanderson, Agilent Technologies



2 © 2012 Agilent Technologies



Agenda

• Market Drivers and Resulting Design & Test Challenges

• Quick Review: What is MIMO?

• MIMO Simulation Case Study

• MIMO Transmitter Hardware EVM Testing

• Advanced Modeling: 802.11ac Digital Pre-distortion (DPD)

• MIMO Receiver Design and Testing




3

802.xx A Family of Wireless

Standards

VHT 802.11ac/ad






New Applications for WLAN

Growth of high-definition video and desire for wireless connections is

driving need for higher data rates for applications such as:

• Wireless display

• Distribution of video/media content throughout the home or office

• Rapid file upload/download (sync devices, movie kiosks)

Example data rates:

Application Data Rate (Mbps)

Interactive videoconferencing 0.38 to 0.5

Internet video streaming 2.5 to 8

HDTV 19.4 to 25

Blu-Ray 40

Uncompressed video, “good” quality

(8-bits/color, 1920x1080p, 24 fps, 4:2:2)

796

Uncompressed video, “best” quality

(10-bits/color, 1920x1080p, 60 fps, 4:4:4)

3730






Enhancements for 802.11ac

• Wider channels

• Higher-order modulation

• MIMO: More spatial streams and antennas (up to 8)

• Multi-user MIMO

•

5

Feature Mandatory Optional

Channel bandwidth 20 MHz, 40 MHz, 80 MHz 160 MHz, 80+80 MHz

FFT size 64, 128, 256 512

Data subcarriers / pilots 52 / 4, 108 / 6, 234 / 8 468 / 16

Modulation types BPSK, QPSK, 16QAM, 64QAM 256QAM

MCS supported 0 to 7 8 and 9

Spatial streams and MIMO 1 2 to 8 Tx beamforming, STBC

Multi-user MIMO (MU-MIMO)

Operating mode / PPDU format Very high throughput / VHT

Data rates: 1.56 Gbps (80 MHz, 4 Tx, MCS9) “reasonable” case

6.93 Gbps (160 MHz, 8 Tx, MCS9, short GI) best case






802.11ac Design & Test Challenges

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

Channel

A/D

IQ Mod Impairments

LO Phase Noise

Filter Impairments

PA Linearity

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:

• Transmitter Design - LO phase noise needed to meet EVM for 256QAM vs. 64QAM

- PA linearity, IQ modulator, mixer, filter impairments

- PA digital pre-distortion?

• Transmitter MIMO Hardware Performance - RF MIMO EVM - how to generate and analyze R&D test signals (two or

more spatial streams, different bandwidths, different modulation orders…)

- Debug IQ and IF stages?

- Crosstalk and timing issues

• Receiver Hardware Performance - Coded BER performance of RF hardware…baseband HW available?

- Rx sensitivity and LO phase noise to meet BER for 256QAM vs. 64QAM






802.11ac MIMO System Design & Test Minimizing System Integration Risks…

MIMO Receiver

Design

PA Nonlinearities

/ Digital Pre-Distortion

MIMO Transmitter

Testing & Debug MIMO Receiver

Testing & Debug

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

RF Channel

A/D

MIMO Transmitter

Design

With 802.11ac needing higher

performance designs, every

part of the transmit and receive

chain becomes critical to the

link budget

So how to decide the optimum

balance, without over-

designing?

How are design requirements

impacted for 64QAM vs.

256QAM? ..for 80 MHz vs.

160MHz?...for SISO vs. MIMO?






Agenda





• Advanced Modeling: 802.11ac DPD





Transmit

Antennas

Receive

Antennas

SISO

The Radio

Channel

MISO

Single Input Single Output

Multiple Input Single Output

(Transmit diversity)

Receive

Antennas

Transmit

Antennas

MIMO

The Radio

Channel

SIMO

Single Input Multiple Output

(Receive diversity)

Multiple Input Multiple Output

(Multiple data streams)

MIMO: Increased Capacity

(and Test Complexity)

9






Diversity

Improve robustness

Spatial Expansion

(Transmit Diversity)

Receive Diversity

Multiple Antenna Techniques in

802.11ac

Space-time block

coding (STBC)

X1, X2

-X2, X1*

y1, y2

Spatial division multiplexing

(direct mapping) Multi-user MIMO

Transmit Beamforming

Spatial multiplexing

Improve user throughput

Multi-user Increase system

efficiency

MIMO

MIMO (4x2)

Matrix

4 streams, 3 users X1

X2

y1

y2

Downlink only

Up to 4 users

Up to 4 streams/user

Total 8 streams max






Agenda












802.11ac MIMO Transmitter Design

Design Considerations:

• LO phase noise needed for 64QAM vs. 256QAM?

• IQ modulator, mixer, and filter impairments?

• PA linearity?

• 80 MHz vs. 160 MHz bandwidth?






802.11ac MIMO Simulation Results

160 MHz 256 QAM






802.11ac MIMO Simulation Results

160 MHz 64 QAM

How do the design consideration change for 64 QAM, or maybe for 80 MHz bandwidth ??






Section Summary: MIMO Transmitter Design

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

Channel

A/D

IQ Mod Impairments

LO Phase Noise

Filter Impairments

PA Linearity

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:

• Transmitter Design Performance - LO phase noise needed to meet EVM for 256QAM vs. 64QAM







SystemVue Instrument Support Create MIMO Test Signals and Scenarios

DOWNLOAD

TO AWGs






Agenda










Notes: MIMO simulation & download is run from a math script instead of a single

controller UI, in order to set the master/slave configuration after the AWG download

Master 81180

Slave 81180

802.11ac MIMO Transmitter Testing Generate 5.8 GHz 160 MHz MIMO waveforms

18




802.11ac MIMO Hardware Testing 5.8 GHz 160 MHz 2x2 MIMO Transmitter test setup

19




Test Results- Waveform Time

Synchronization Multi-channel oscilloscope used for MIMO

wideband analysis

20

13 GHz Digital

Oscilloscope




Test Results- 5.8 GHz 160 MHz

2x2 MIMO Demod Equalizer trained by Preamble, Pilots, and Data for better EVM

21

13 GHz Digital

Oscilloscope +

89600 VSA SW





2x2 MIMO Demod Equalizer trained by Preamble only

22

13 GHz Digital

Oscilloscope +

89600 VSA SW






D/A PA FGPA/DSP

Digital oscilloscope with

VSA software (IQ, IF, RF) Digital oscilloscope with VSA

software for 2 or 4 channel

RF MIMO analysis

IF RF Analog

(IF or IQ)

Copyright Agilent Technologies 2010

D/A PA

Two or Four

RF MIMO

Transmitters

PA

PA

Troubleshooting IQ, IF, and

RF Issues




802.11ac MIMO Hardware Testing 3x3 MIMO with Wideband PXI MIMO Signal Analyzer

N5182B MXG Channel 1


• MXG Signal Generators with up

to 160 MHz modulated bandwidth

• Wideband MIMO PXI VSA

• 800 MHz IF BW

89600B VSA software, Opt BHJ

W1461BP SystemVue Environment

W1917EP WLAN library with 802.11ac

24






2x2 MIMO Demod PXI Wideband VSA Results

25 October 2011

Wideband

MIMO PXI VSA

With 89600

VSA software






Section Summary 802.11ac MIMO Transmitter Testing

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

Channel

A/D

IQ Mod Impairments

LO Phase Noise

Filter Impairments

PA Linearity

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:










Agenda










Advanced Modeling: 802.11ac DPD

Digital Pre-Distortion Problem Statement

Conflicting requirements

How to handle signals with high PAPR, while driving the PA to operate

with high PAE, while also having low signal distortion?

High

PAE

Signals

with high

PAPR

High

Spectral

Efficiency

Higher

Drive

levels

High

Distortion

levels

“Back off”

the drive

levels




29

High DC-RF

Efficiency High

Crest

Factor

High

Spectral

Efficiency

Increase

Drive

levels

Causes high

distortion

levels

Higher

Throughput

rates for

subscribers

CFR

DPD

CFR

DPD

Wideband DPD webcast

Sept 1, 2011

Copyright 2011 Agilent Technologies







• W1917 WLAN library can

generate signals for Agilent

W1716 DPD module

• DPD extends RF performance

and helps increase battery life

thru higher efficiency

• DPD requires 3-5x the signal

bandwidth of the PA

• Integrated crest factor reduction

(CFR)

• Agilent provides an open system

for wideband RX/TX modeling

October 2011







October 2011





Advanced Modeling: Sweep Power, watch EVM, ACP

Input waveform: • IEEE 802.11ac, 5 GHz WLAN

• No CFR (PAPR is 8.7dB)

• Bandwidth = 80MHz system

• 4x Oversampling rate=320 MHz

Device Under Test: • WLAN “FCE” model extracted from

Agilent GoldenGate RFIC simulator

EVM with DPD

EVM w/o DPD

ACLR with DPD

Lower/Upper ACLR

w/o DPD

Output < 0 dBm

DPD offers little benefit

0 < Output < +16.5 dBm

DPD offers significant benefit

+16.5 dBm < Output PA is not correctable

EVM vs. Output Power ACP vs. Output Power

Page 32






Section Summary: Digital Pre-Distortion

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

Baseband DPD algorithms

And PA Modeling

A/D

IQ Mod Impairments

LO Phase Noise

Filter Impairments

PA Linearity

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:

• Transmitter MIMO Performance Required for Higher Order Modulation - PA digital pre-distortion?






Agenda










WLAN 802.11ac Receiver Design

35

WLAN 802.11ac coded BER/FER measurements with AWGN channel

Re

Im

C2

Fc

CxEnv

E1

ModOUT

QUAD

OUT

FreqPhaseQ

IAmp

FCarrier=5e+9Hz [FCarrier]

InputType=I/Q

Modulator

Power=0.1W [SignalPower]

Frequency=5e+9Hz [FCarrier]

O1

TEST

REF

BitsPerFrame=8192 [User0_MPDUDataLength(1)*8]

StartStopOption=Samples

B2

Noise

Density

NDensity=-64.044dBm [NDensity]

NDensityType=Constant noise density

AWGN

WLAN_11ac _Receiver

Cons te l la tion

SigAftM atrix

ChCodedBits

M SDU

input

ShortGI=NO

SpatialMappingMatrix=1 [[1]]

SpatialMappingScheme=DirectMapping

ReInitialize=YES

ScrambleSeed=1;0;1;1;1;0;1 [[1, 0, 1, 1, 1, 0, 1]]User3_MPDUMACHeader=0;0;0;0;0;0;0;0 [[0,0,0,0,0,0,0,0]]

User3_MPDUDataLength=1024;1024;1024;1024;1024;1024;1024;1024 [[1024,1024,1024,1024,1024,1024,1024,1024]]

User2_MPDUMACHeader=0;0;0;0;0;0;0;0 [[0,0,0,0,0,0,0,0]]


User1_MPDUMACHeader=0;0;0;0;0;0;0;0 [[0,0,0,0,0,0,0,0]]


User0_MPDUMACHeader=0 [User0_MPDUMACHeader]

User0_MPDUDataLength=1024 [User0_MPDUDataLength]NumMPDUPerUser=1 [NumMPDUPerUser]

AggregatedMPDU=1 [AggregatedMPDU]

CodingType=0;0;0;0 [[0,0,0,0]]FrameFormat=DataFrames

STBC=NO

N_SS=1;1;1;1 [[1,1,1,1]]NumUsers=1

IdleInterval=12e-6s

MCS=2 [MCS]OversampleRatio=x2 [OversampleRatio]

Bandwidth=BW 40 MHz [Bandwidth]NumRx=1

WLAN_11ac_Receiver_1

WLAN_11ac _Sourc e

UE0_ChCodedBits

UE0_Cons te l lation

SigAftSpatia lM apSeg1

SigAftSpatia lM apSeg0

Output_IQSeg1

Output_IQSeg0

UEs Bi ts

WindowingLength=2ShortGI=NO

SpatialMappingScheme=DirectMappingScrambleSeed=1;0;1;1;1;0;1 [[1, 0, 1, 1, 1, 0, 1]]

User0_MPDUMACHeader=0 [User0_MPDUMACHeader]

User0_MPDUDataLength=1024 [User0_MPDUDataLength]NumMPDUPerUser=1 [NumMPDUPerUser]

AggregatedMPDU=1 [AggregatedMPDU]

CodingType=0 [[0]]STBC=NO

N_SS=1 [[1]]

NumUsers=1

TransmissionMode=MultiUser

IdleInterval=12e-6s

MCS=2 [MCS]

OversampleRatio=x2 [OversampleRatio]

Bandwidth=BW 40 MHz [Bandwidth]

NumTx=1

WLAN_11ac_Source_1

1 1 0 1 0

DataPattern=PN15

B1

OutputTiming=EqualToInput

N=8192 [User0_MPDUDataLength(1)*8]D1

802.11acparameterized

Coded TX source

802.11acparameterized

Reference RX

BER/FER

tester






WLAN 802.11ac Receiver Design System-level interference scenarios

Add Interferers, Fading

RF nonlinearities

Phase noise

ADC/DAC

Filtering, and more

Interference

NoiseDensity

NDensity=-173.975dBm

NDensityType=Constant noise density

Receiver_Thermal_Noise


N=32768 [User0_MPDUDataLength(1)*8]

D1

Re

Im

C2

ModOUT

QUADOUT

Freq

PhaseQ

IAmp


InputType=I/Q

Modulator



O1

1 1 0 1 0

DataPattern=PN15

B1

Env

OutputFc=Min

A1

Order=5

PassAtten=3

PassBandwidth=80e6Hz

FCenter=5e+9Hz [FCarrier]

F3 {BPF_Butterworth@Data Flow Models}

Fc

CxEnv

E1

WLAN_11ac_Receiver

Const ellat ion

SigAf t M at r ix

ChCodedBit s

M SDU

input

IdleInterval=12e-6s

MCS=8 [MCS]



NumRx=1


WLAN 11ac measurementsNon-adjacent Channel Rejection

Amplifier

NoiseFigure=0

Gain=-68 [-48-SignalPower_dBm]

GainUnit=dB

RF_Gain

Spectrum Analyzer

ResBW=100e3Hz

Start=12e-6s

Mode=ResBW

Spectrum

WLAN_11ac_Sour ce

U E0_ChCodedBit s

U E0_Const ellat ion

S igAf t Spat ialM apSeg1


O ut put _I Q Seg1

O ut put _I Q Seg0

UEsBit s


IdleInterval=12e-6s

MCS=8 [MCS]



NumTx=1

WLAN_11ac_Source_1

Desired Signal

802.11ac, Fc=5.16GHz, BW=80MHz

802.11ac, Fc=5.00GHz, BW=80MHz

1 1 0 1 0

DataPattern=PN15

B3

Re

Im

C1


Frequency=5.16e+9Hz [FCarrier+2*80e6]

O2

ModOUT

QUADOUT

Freq

PhaseQ

IAmp

FCarrier=5.16e+9Hz [FCarrier+2*80e6]

InputType=I/Q

Modulator1

Amplifier

NoiseFigure=0

Gain=-61 [-48-SignalPower_dBm+7]

GainUnit=dB

RF_Gain1

WLAN_11ac_Sour ce

U E0_ChCodedBit s

U E0_Const ellat ion



O ut put _I Q Seg1

O ut put _I Q Seg0

UEsBit s


IdleInterval=0s

MCS=0 [[0]]



NumTx=1

WLAN_11ac_Source_2

802.11ac Reference RX

TEST

REF



B2

AWGN

Interferer Signal for BER Test




WLAN 802.11ac Receiver Design: 802.11ac BER Example

37

Sweep Eb/No parameter

In BER simulation




WLAN 802.11ac Receiver Design: 802.11ac BER Example

38

BER vs Eb/No Result




39

WLAN 802.11ac Receiver

Hardware Testing: BER Example Detailed Connections

Ref Out

IQ data via LAN

SystemVue running

on PXI controller

89600 VSA software

running

on PXI controller

Wideband PXI MIMO

Signal Analyzer

N5182A MXG





Hardware Testing: Signal generation

40

ModOUT

QUADOUT

FreqPhase

Q

IAmp


InputType=I/Q

Modulator

Re

Im

C2

1 1 0 1 0

DataPattern=PN15

B1

WLAN_11ac_Source

UE0_ChCodedBits

UE0_Constellation

SigAftSpatialMapSeg1

SigAftSpatialMapSeg0

Output_IQSeg1

Output_IQSeg0

UEsBits

MCS=2 [MCS]


IdleInterval=12e-6s



NumTx=1

WLAN_11ac_Source_1



O1

Fc

CxEnv

E1

WLAN_11ac_EVM

TimeStep=25e-9 [1/SampleRate]

NumTx=1

Bandwidth=BW40MHz [Bandwidth]

TrackTiming=YES

TrackPhase=YES

TrackAmplitude=YES

SymbolTimingAdjust=-3.125

SubcarrierSpacing=312.5e3Hz

MeasurementInterval=53 [Nsym]

MeasurementOffset=0

SearchLength=1e-3s

GuardIntervalSel=Auto Detect Guard

FramesToAverage=4

AverageType=RMS (Video)

Start=0s

MirrorSpectrum=NO

W1

ESG4438C Downloader

AutoScale=YES

PrimAddress='141.121.94.223

HWAvailable=YES

S3

802.11ac source IP download directly to MXG





Hardware Testing: Signal Capture and Analysis

41

TEST

REF



B2

Re

Im

R2

1 1 0 1 0

DataPattern=PN15

B1


N=8192 [User0_MPDUDataLength(1)*8]

D1

DeModI

Amp

Freq

PhaseQ


OutputType=I/Q

D2

WLAN_11ac_Receiver

Constellation

SigAftMatrix

ChCodedBits

MSDU

input

MCS=2 [MCS]

IdleInterval=12e-6s



NumRx=1


123


S1

123

StartStopOption=Time

S2

Fc

CxEnv

E1

WLAN_11ac_EVM

TimeStep=12.5e-9 [1/SampleRate]

NumTx=1

Bandwidth=BW40MHz [Bandwidth]

TrackTiming=YES

TrackPhase=YES

TrackAmplitude=YES

SymbolTimingAdjust=-3.125

SubcarrierSpacing=312.5e3Hz

MeasurementInterval=53 [Nsym]

MeasurementOffset=0

SearchLength=1e-3s

GuardIntervalSel=Auto Detect Guard

FramesToAverage=4

AverageType=RMS (Video)

Start=0s

MirrorSpectrum=NO

W1

Spectrum Analyzer

SegmentTime=1e-3s [Stop_Time - Start_Time + Time_Spacing]

Start=0s [Start_Time]

Mode=TimeGate

S3 {SpectrumAnalyzerEnv@Data Flow Models}

VSA_89600B_Source

gap

out

VSATrace=B

OutputType=Timed (Envelope/Real Baseband)

VSATitle='Simulation output

V1

802.11ac receiver IP demodulates,

BER calculated

89600 VSA

software

Captures IQ

data from PXI

analyzer




Hardware Test Results: BER and EVM results

42

BER and EVM results in tabular form






Section Summary:

MIMO Receiver Design and Testing

RF Rx Coding

Algorithms

(Simulated)

D/A

Bits In Decoding

Algorithms

(Simulated)

Bits Out

Measure RF

Receiver

Components

A/D

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:

• Receiver BER Performance - Coded BER performance of RF hardware…baseband HW available?


Receiver Test

Signal






Summary:

802.11ac Design & Test Challenges

Tx Rx Coding

Algorithms

D/A

Bits In Decoding

Algorithms Bits Out

Channel

A/D

IQ Mod Impairments

LO Phase Noise

Filter Impairments

PA Linearity

Rx Sensitivity

LO Phase Noise

Filter Impairments

Considerations:

• Transmitter Design - LO phase noise needed to meet EVM for 256QAM vs. 64QAM


- PA digital pre-distortion?





• Receiver Hardware Performance - Coded BER performance of RF hardware…baseband HW available?





Additional Resources Webcasts

45

• Introduction to 802.11ac WLAN Technology and Testing

Webcast

• http://www.home.agilent.com/agilent/eventDetail.jspx?cc=US&lc

=eng&ckey=2067515&nid=-11143.0.00&id=2067515

• Innovations in EDA: High Performance Digital Pre-Distortion

(DPD) for Wideband Systems

• http://www.home.agilent.com/agilent/redirector.jspx?action=ref&l

c=eng&cc=US&nfr=-

34867.0.08&ckey=2021229&cname=AGILENT_EVENT

• Accelerate 802.11ac/ad system-level design & verification for

next-generation WLAN

• http://www.home.agilent.com/agilent/eventDetail.jspx?cc=US&lc

=eng&ckey=2112408&nid=-52844.3383972.08&id=2112408

http://www.home.agilent.com/agilent/eventDetail.jspx?cc=US&lc=eng&ckey=2067515&nid=-11143.0.00&id=2067515




http://www.home.agilent.com/agilent/redirector.jspx?action=ref&lc=eng&cc=US&nfr=-34867.0.08&ckey=2021229&cname=AGILENT_EVENT











Additional Resources Articles and Application Notes

46

• Tackling MIMO Design and Test Challenges for 802.11ac WLAN

– Microwave Journal

• http://www.microwavejournal.com/articles/17140-tackling-mimo-

design-and-test-challenges-for-802-11ac-wlan

• Wideband Digital Pre-Distortion with Agilent SystemVue and PXI

Modular Instrument

• http://cp.literature.agilent.com/litweb/pdf/5990-8883EN.pdf

• Accelerate Development of Next Generation 802.11ac Wireless

LAN Transmitters-Overview

• http://cp.literature.agilent.com/litweb/pdf/5990-9872EN.pdf

• Agilent’s WLAN 802.11ac Test and Design Home Page

• http://www.agilent.com/find/80211ac

http://www.microwavejournal.com/articles/17140-tackling-mimo-design-and-test-challenges-for-802-11ac-wlan





















http://cp.literature.agilent.com/litweb/pdf/5990-8883EN.pdf








http://www.agilent.com/find/80211ac




Thank You!

47




Documents

Next Generation Very High Throughput: 802.11ac WLAN MIMO ... · MIMO Transmitter Design With 802.11ac needing higher performance designs, every part of the transmit and receive chain