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Beyond S-Parameters

© Agilent Technologies, Inc. 2007

© Copyright 2008 Agilent Technologies, Inc.

WiMAX®

Wave 2 Testing --

MIMO & STC

“WiMAX,” “Mobile WiMAX” and “WiMAX Forum”are trademarks of the WiMAX Forum

June, 2008

Beyond S-Parameters

© Agilent Technologies, Inc. 2007Page M6- 2

Aerospace and Defense Symposium 2007This Presentation:

• Physical Layer Aspects of Wave 2 -- Brief Summary

• MIMO & Space Time Coding -- Brief Summary

• Using Simulations & VSA to Understand Interactions, Trade-offs

– Crosstalk

– Frequency response problems

– Frequency/timing error

• Wave 2 Signal Generation & Analysis Solutions

– Signal generation software, hardware

– Signal analysis software, hardware

• Protocol Test & Manufacturing Test Solutions

• Learn More

– Make measurements yourself with trial/demonstration modes

– References, Resources

Beyond S-Parameters


Aerospace and Defense Symposium 2007Learn by Making Measurements

• 89601A VSA Software, Free Demo License,

N7615B Signal Studio, Free Simulation Mode

– Recorded signals provided: perform any kind of vector analysis or demodulation

– Simulated hardware

– Tutorials

– Troubleshooting help

– Example displays

• VSA & Signal Generators

14-day Free Trial Licenses

– Connect to hardware

– Generate, download & play back signals

• Tech Overviews, Demo

Guides

Beyond S-Parameters


Aerospace and Defense Symposium 2007WiMAX Wave 2 Overview

Beyond S-Parameters


Aerospace and Defense Symposium 2007New Features in Wave 2

• Adaptive Modulation and Coding (AMC)

– DL/UL AMC 2x3 zones

• Beamforming

• Matrix A & Matrix B

– Space Time Coding (STC)

– 2x2 MIMO with vertical encoding

• Uplink collaborative spatial multiplexing

• Effective CINR measurement using pilots

• IO-BF (beamforming) profile

– DL-PUSC and AMC 2x3 with dedicated pilots

– UL-PUSC without subchannel rotation

– Uplink sounding

Beyond S-Parameters


Aerospace and Defense Symposium 2007WiMAX MIMO/STC Implementations

DLMatrix A(2x1 STC)

DLMatrix B(2x2 MIMO)

MIMOchannel

MISOchannel

ULCollaborative

SpatialMultiplex(2x2 MIMO)

Concept

• One data stream sent twice, for

improved robustness. Allows use

of more efficient modulation

formats for any given SNR.

• Two separate data streams sent

simultaneously on same channel.

Matrix decoder separates them in

the receiver, doubles the thruput.

• Two separate data streams sent

simultaneously on same channel,

as above. But they’re from two

separate transmitters in two

separate handsets.

2 TX

2 TX

1 TX

1 TX

2 RX

2 RX

1 RX

Note: WiMAX MIMO allows 1, 2 or 4 TX antennas.

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO & STC Overview

Beyond S-Parameters


Aerospace and Defense Symposium 2007

MIMO – the art of getting from

THIS to THIS

Increased capacity from a

given spectrum occupancy

Conceptual

Beyond S-Parameters


Aerospace and Defense Symposium 2007Why MIMO?

• MIMO is a Capacity Enhancement Scheme

– Evading the “Shannon” limit!

– Capacity can be traded for more range or other benefits

• CDMA, OFDM, etc. are Multiplexing Schemes

– Dividing capacity among users, frequencies

– Better operation in impaired conditions

– Shannon still applies!

CDMA Example:

Dividing Capacity by Code

OFDM Example:

Dividing Capacity by Carrier

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO Exposed - The 2 x 2 Instance

Tx1

Tx2

Rx1

Rx2

x1

x

2

h11

h12

h21

h22

LinearChannel

x1 h

11+ x

2 h

21

x1 h

12+ x

2 h

22

x1

x2

x1

x2

H-1

(DSP)

The real channel (complicated)

Solving the equations

The channel for one OFDM sub-

carrier during the course of a packet

Beyond S-Parameters


Aerospace and Defense Symposium 20072-Channel Thought Experiment

• Two signal generators generate 1 MHz spaced multi-tone signals

• Signals identified with each source by adding a 500 kHz offset to one of them

• Two antennas connected to a dual input signal analyzer

• Movements in the environment near the antennas show how the four independent radio paths (color coded) can be identified

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO/STC Signal Creation

DataStream

XX MB/sec

IFFT

IFFT

TX0

TX1

En-coder

......

YY MB/sec

YY MB/sec

Bits

(1,0,1,1…)

Constellation

Points

(a+jb, c+jd…)

OFDM

Symbols

(waveform)

Beyond S-Parameters


Aerospace and Defense Symposium 2007Variations on the Theme

DataStream

2X MB/sec

IFFT

IFFT

TX0

TX1

StreamParser

X MB/sec

X MB/sec

• STBC (Alamouti) encoder creates 2 different

versions of the same bitstream, for robustness.

• Example: WiMAX Matrix A

• Note: numerous STBC schemes exist, and can be

used along with any of the below techniques.

• Vertical encoding splits the original bitstream

into two half-rate bitstreams, for throughput.

• Example: WiMAX Matrix B

• Example: 802.11n Direct Map modes

• Horizontal encoding accepts 2 bitstreams and

keeps them as separate TX chains, typically for

separate users.

• Example: WiMAX Matrix B

DataStream

IFFT

IFFT

TX0

TX1

STBCEn-

coderX MB/sec

X MB/sec

X MB/sec

DataStreamX MB/sec

IFFT

IFFT

TX0

TX1

X MB/sec

Y MB/sec

DataStreamY MB/sec

En-coder

DataStream(s)

X MB/sec

IFFT

IFFT

TX0

TX1

X MB/sec

X MB/sec

En-code

SS

• Spatial Spreading encoding accepts 2 encoded

bitstreams, and spreads them onto 2 TX chains,

(e.g. a+b, a-b) for improved diversity.

• Example: 802.11n Spatial Spreading modes

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO/STC – Data & Spatial Streams, Channels

DataStream(s)

IFFT

IFFT

TX0

TX1

Bits

(1,0,1,1…)

Constellation

Points

(a+jb, c+jd…)

OFDM

Symbols

(waveform)

En-coder

SS

Spatial Streams

(aka Layers)

relate to the

original data

payload.

TX Chains

(aka Antennas)

relate to the

actual transmitted

signals.

Ant0

Ant1

Ant0

Ant1

RX0

RX1

Matrix

De-

coder

H00

H01

H10

H11

Channel Matrix

Individual freq response

curves for each TX-RX path.

Spatial

Stream(s)

OFDM

De-

mod

Data

Stream(s)

Beyond S-Parameters


Aerospace and Defense Symposium 2007WiMAX STC/MIMO Signals at the PHY Layer

. . .

. . .

Symbol n Symbol n+2Symbol n+1

TX 0

TX 1

Data subcarriers overlap, pilots don’t... data subcarrier

pilot subcarrier

Observing a single pilot frequency over time….TX1 TX1 TX1 TX1 TX1 TX1

TX0 TX0 TX0 TX0 TX0 TX0

Observing a single data subcarrier over time….TX1 TX1 TX1 TX1 TX1 TX1 TX1 …

+TX0 +TX0 +TX0 +TX0 +TX0 +TX0 +TX0

Matrix A = 2 versions of same dataMatrix B = 2 different data streams

CSM = 2 different handsets

Beyond S-Parameters


Aerospace and Defense Symposium 2007WiMAX STC/MIMO Signals at the PHY Layer

. . .

. . .

Symbol n Symbol n+2Symbol n+1

TX 0

TX 1

Data subcarriers overlap, pilots don’t...data subcarrier

pilot subcarrier

Constellation as transmitted...

Data subcarriers add,create a “constellationof constellations”.

...as received.

Pilots never overlap

Pilots

TX 0 or TX 1 TX 0 plus TX 1 crosstalk

Data

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO--WiMAX vs. IEEE802.11n

• Preamble used for channel

estimation only

• Preamble on Tx0 only

• Many pilots, used for

demodulation reference and

MIMO matrix calculation

• Pilots move, not on every

symbol in a slot

• “Direct mapped” MIMO, no

spatial spreading (yet)

• Preamble used for channel

estimation, MIMO matrix

calculation

• Preamble on Tx0 and Tx1

• Few pilots, used for

demodulation reference only

• Pilots static, present for every

symbol

• “Direct mapped” and spatially

spread modes (a+b, a-b, etc.)

WiMAX 802.11n

Beyond S-Parameters


Aerospace and Defense Symposium 2007Verifying STC/MIMO Signals -- Downlink

Matrix B (MIMO)Transmitter MIMO

channel

• RF metrics of indiv. or both TX’s• Validate combined PHY format• Cross-TX metrics (time, power, etc.)

• RF metrics of indiv. TX• Validate PHY format of indiv. TX

• MIMO channel matrix (1 or 2 chan)

Matrix A (STC)Transmitter MISO

channel

• RF metrics of indiv. TX• Validate PHY format of indiv. TX


• MISO channel matrix

What to measure and where?

Beyond S-Parameters


Aerospace and Defense Symposium 2007VSA for STC/MIMO

Input Chan. 0RX0

RX1Input Chan. 1

Matrix

Decoder

OFDM

Demod

TX0 + TX1 signal

(+ chan. response)

Chan

Estim.TX0 + TX1 signal

(+ chan. response)

Input Channel 1

Input Channel 2

Matrix A Analysis Stream

Matrix B Stream 1

Matrix B Stream 2

� Use Matrix Decoder


pilot-based EQ(decoder ON)

Preamble/pilot/data – based EQ (decoder OFF) OFDM Measurement Results MIMO Ch Freq Resp. (pilots only)

Eq Chan Freq Resp.

Conceptual Model

Beyond S-Parameters


Aerospace and Defense Symposium 2007Using Simulations & VSA to Understand Measurement Results, Interactions, Trade-offs

WiMAX MIMO Simulation Case Study

Beyond S-Parameters


Aerospace and Defense Symposium 2007Simulation Examples to Measure

• Transmitter0 Transmitter1 Crosstalk

– “Good” 41 dB

– “Not so good” 35 dB

– “Not good enough” 29 dB

• Transmitter Frequency Response Defect

– 2 MHz bandpass filter

• Simulation Output Stream Fed to 89600 VSA “Instance”

Operating Inside Simulation

– Same measurements, user interface as when connected to hardware

– Insert VSA at nearly any point; verify simulation is doing what is intended

Beyond S-Parameters


Aerospace and Defense Symposium 2007Modeling Crosstalk In ADS

Beyond S-Parameters


Aerospace and Defense Symposium 2007Crosstalk Results -- 41 dB

89600 VSA

Beyond S-Parameters



Beyond S-Parameters



Beyond S-Parameters


Aerospace and Defense Symposium 2007Matrix Decoder, Crosstalk, RCT

• RCT Measurements Are Made Without Matrix Decoder

– Effects of crosstalk are included in measurement

– Crosstalk can cause RCT limit fail

– Error due to crosstalk can hide other errors

• Measure Both Ways to Understand Error Contribution of Crosstalk

Matrix

Decoder

OFDM

Demod

Chan

Estim.

Input Channel 1

Input Channel 2


Matrix B Stream 1

Matrix B Stream 2



pilot-based EQ(decoder ON)

OFDM Meas Results

Beyond S-Parameters


Aerospace and Defense Symposium 2007Crosstalk 29 dB With Matrix Decoder

Matrix decoder removes crosstalk in the channel and in the device

Beyond S-Parameters


Aerospace and Defense Symposium 2007Crosstalk Obscures Another Impairment

Measurement Without Matrix Decoder

Beyond S-Parameters


Aerospace and Defense Symposium 2007Crosstalk Obscures Another Impairment

Measurement With Matrix Decoder

Characteristic V-shapederror vector spectrum

Beyond S-Parameters


Aerospace and Defense Symposium 2007Modeling Frequency Response Defect in ADS

• 2 MHz Bandpass Filter

• Centered on Channel

• Transmitter 1 Only

• Example for Illustration

Only

– Not realistic, but effects and measurement results are easier to understand

Beyond S-Parameters


Aerospace and Defense Symposium 2007Measurement Results Ch 1 Direct Connection

Low EVM

No crosstalk

Beyond S-Parameters


Aerospace and Defense Symposium 2007Measurement Results Ch 2 Direct Connection

EVM very high;Demod successfuldue to pilots

Note filter effectsin Ch2 spectrum

Beyond S-Parameters


Aerospace and Defense Symposium 2007Channel Freq. Response, MIMO Signal Quality

Channel 1Channel 2

0 dB = 1 1 = Ideal

Beyond S-Parameters


Aerospace and Defense Symposium 2007MIMO “Condition Number”A Quantitative Measure of MIMO Quality

• Not a Demodulation Operation

• Does Not Require Matrix Decoder

• Calculated from Equalizer Channel

Frequency Responses

– One condition number value for each

subcarrier; log or linear format

– Condition number is a standard measure

of how ill-conditioned a matrix is

• Ratio of Matrix Max Singular Value to the Min Singular Value

– Value is always real, and always greater than or equal to one.

– Larger values indicate a more ill-conditioned matrix

• If the condition number is larger than the SNR of the signal, it is

likely that MIMO separation of the multiple data streams will not

work correctly

0 dB = 1

Beyond S-Parameters


Aerospace and Defense Symposium 2007Wave 2 Signal Generation & Analysis Solutions

Beyond S-Parameters


Aerospace and Defense Symposium 2007Signal Generation Software and Hardware

N7615B Signal Studio for 802.16 WiMAX software

N5182A MXG, E4438C ESG, or E8267D PSG Signal Generators

DUT

WiMAX

waveform

LAN or GPIB

Analog or digital baseband or RF WiMAX signal

Beyond S-Parameters


Aerospace and Defense Symposium 2007Signal Studio New Features (Version 2.0.0.0)

• Matrix A waveforms for DL-PUSC zone

• Matrix B waveforms for DL-PUSC zone

• Collaborative spatial multiplexing for uplink PUSC zone

• Increase maximum waveform length to 64 Msamples

• Create DL and UL HARQ allocations and sub-bursts (not full support of HARQ)

• Support uplink sounding type A

• Dedicated pilots for DL-PUSC and DL-AMC zones

• Subchannel rotation on/off for UL-PUSC zone

Beyond S-Parameters


Aerospace and Defense Symposium 2007Signal Studio New Features: Fading

• Software incorporates fading effects in waveform with ITU Pedestrian A/B and Vehicular A/B channel models, including WiMAX 2x2 MIMO channel models

– Create waveforms on Tx side (points A0 or A1) for use with external fader, or signals on Rx side with fading (points B0 or B1) for input to receiver under test

– Fading support for UL collaborative MIMO (2 MS’s with 2 fading models)

– Intended for MIMO receiver verification or troubleshooting. Not a replacement for real-time fading for conformance or system testing, but provides big cost savings compared to buying a real-time fader, for situations where a repeating signal is okay.

– N5115B Baseband Studio for Fading can provide real-time fading for up to 2 channels only (e.g. for STC/matrix A). For real-time fading of 2x2 MIMO, use external RF fader.

Rx

Tx0

Tx Tx1Data

Chan H00

Chan H01

Chan H10

Chan H11

ΣΣΣΣ

ΣΣΣΣ

Rx0

Rx1

A0

B1A1

B0

Rx

Tx0

Tx Tx1Data

Tx0

Tx Tx1Data

Chan H00

Chan H01

Chan H10

Chan H11

ΣΣΣΣΣΣΣΣ

ΣΣΣΣΣΣΣΣ

Rx0Rx0

Rx1Rx1

A0

B1B1A1

B0B0

Desktop PC

N5101A PCI Cards

N5115B Baseband Studio for Fading SW

Digital

I/Q data

RF Out

Beyond S-Parameters


Aerospace and Defense Symposium 2007Baseband Synchronization

– For STC/MIMO, need to synchronize baseband generators to start waveform

playback simultaneously in both sources

– Signal Studio will automatically download waveforms, set up triggering, and initiate waveform playback in 2 ESGs, 2 PSGs, or 2 MXGs

– New in MXG version A.01.20 firmware: synchronize up to 16 MXGs with

baseband trigger repeatability < 1 ns and fine delay adjustment

10 MHz OUT

10 MHz IN

PATT TRIG IN

EVENT 2

PATT TRIG IN

E4438C ESGs or

E8267D PSGsRF Output

10MHz OutEVENT 1

RF Output

10MHz OutREF IN

EVENT 1

PATT TRIG

Master

MXG

Slave

MXG(s)

RF Output

10MHz Out

REF IN

EVENT 1

PATT TRIG

1

2

Normal Arb trigger

Etc.

Beyond S-Parameters


Aerospace and Defense Symposium 2007Add Impairments to Signals

• Use I/Q adjustments menu in signal generators to add impairments such as I/Q skew, quadrature angle, gain imbalance, etc.

• Add real-time noise with option 403 (calibrated AWGN)

• New in MXG A.01.20 firmware: option for adding phase noise impairment (N5182A-432)

Beyond S-Parameters


Aerospace and Defense Symposium 2007Measurement Configurations--Analysis

Beyond S-Parameters


Aerospace and Defense Symposium 2007Signal Analysis Hardware, Software

89601A VSA

Software

PSA Spectrum Analyzer X Series Signal Analyzers

89640 VXI VSA

(802.16 OFDMA Application for MXA)

Logic Analyzers

Oscilloscopes

ADS Simulation Software

Beyond S-Parameters


Aerospace and Defense Symposium 2007VSA STC/MIMO - Conceptual Model

Input Chan. 0RX0

RX1

Signals after separationinto TX1 and TX2

Input Chan. 1

Signals as-received;

any cross-talk or channel

combining looks like

added noise.

Matrix

Decoder

OFDM

Demod

TX1 + TX2 signal

(+ chan. response)

Chan


(+ chan. response)

Displays



demod metrics

Beyond S-Parameters


Aerospace and Defense Symposium 2007VSA STC/MIMO - Conceptual Model

Input Chan. 0RX0

RX1Input Chan. 1

Matrix

Decoder

OFDM

Demod

TX1 + TX2 signal

(+ chan. response)

Chan


(+ chan. response)

Displays

Input Channel 1

Input Channel 2


Matrix B Analysis Stream 1

Matrix B Analysis Stream 2



pilot EQ traditional EQ (based on P, P+D, etc.)

demod metrics

MIMO Ch Freq Resp. (pilots only)1-4 overlaid traces, unaffected by settings. Inactive Ant traces usually noisy, can be turned off.

Chan Freq Response• Decoder ON:

Display H00 thru H41 using INPUT CHAN, TX ANT. • Decoder OFF:

Display H00 thru H41 using INPUT CHAN, TX ANT.

Beyond S-Parameters


Aerospace and Defense Symposium 2007Verifying STC/MIMO DL SignalsVSA Measurements What & Where?

Matrix A (STC)Transmitter


channel

MISOchannel

• RF metrics of indiv. TX (ant 0 only)• Validate PHY format of indiv. TX (ant 0 only)


• MISO channel responses• RF metrics of indiv. TX – pilot-based (ant 0 or 1)


• RF metrics of indiv. TX (ant 0 only)• Validate PHY format of indiv. TX (ant 0 only)

• MIMO channel responses (1 or 2 chan)• RF metrics of indiv. TX – pilot-based (ant 0 or 1)

Beyond S-Parameters


Aerospace and Defense Symposium 2007Verifying STC/MIMO Signals – Single Channel



channel

MISOchannel1

1

1

1

1-Ch. VSA

Test Configurations Analyzer Configurations

1 Use when: signals are well-isolated- e.g. hardwired to individual TX’s.- e.g. before MISO/MIMO channels.

To get:- individual TX metrics (EVM, power, flatness)- cross-chan. metrics (pilot-based)- RCT pass/fail tests (crosstalk-limited) - PHY format validation

1a

1a Use when: Matrix A signals in MISO channel.

To get:- composite TX metrics (EVM, power, flatness)- individual TX metrics (pilot-based)- PHY format validation- channel profile validation- STC payload stream recovery

Beyond S-Parameters


Aerospace and Defense Symposium 2007Verifying STC/MIMO Signals – Multi-Channel



channel

MISOchannel

2-Ch. VSA


Use when: signals are not well-isolated- e.g. crosstalk-limited is not good enough- e.g. downstream of MIMO channel

To get:- individual TX metrics (simultaneous)- composite TX metrics (simultaneous)- cross-chan. metrics (gain, phase, skew,

correlation, coherence, etc.)- channel matrix meas. (Hxx, matrix cond.)- beam-forming validation - channel fading validation- PHY format validation- MIMO payload stream recovery

2

2

2 2

Beyond S-Parameters


Aerospace and Defense Symposium 2007Verifying STC/MIMO Signals – Combined 1-Chan.



channel

MISOchannel

1-Ch. VSA + Combiner


Use when: economy is a concern- e.g. when pilot-based meas. are sufficient

To get:- individual TX metrics (pilot-based)- composite TX metrics (pilot-based)- cross-chan. metrics (limited)- PHY format validation

3

3

3 3

3

Beyond S-Parameters


Aerospace and Defense Symposium 2007

OFDM Frame Summary

OFDM Frame Summary from VSA

Preamble Power as RSSI,Preamble RCE, and Preamble PCINR R1 and R3

Statistic result summary:Mean, Peak Hold, & StdDev

RMS averaging = 10

Beyond S-Parameters


Aerospace and Defense Symposium 2007New VSA MIMO Measurements & Displays

• OFDM MIMO Info Trace

– DataScPwr – reports the power of the data subcarriers, referenced to RefScPwr

– RefScPwr – reports the power of the reference subcarriers

– PilotPwr – reports the power in the pilot pattern for the selected antenna

– PilotScPwr – reports the relative per-pilot subcarrier power, referenced to RefScPwr

– PilotRCE – reports the RCE of the pilot pattern for the selected antenna

• Condition number

• MIMO Equalizer Channel Frequency Response

Beyond S-Parameters


Aerospace and Defense Symposium 2007Protocol Test - E6651A Mobile WiMAX Test Set

• Base Station Emulation

• IP Traffic Support

• Network Entry

• RF Parameter measurements

• Wave 2 Support

– DL

– STC

– SM

– UL collaborative MIMO

• Measure UL Signals Without External Equipment

Beyond S-Parameters


Aerospace and Defense Symposium 2007Manufacturing TestN8300A Wireless Networking Test Set

• RF Parametric Test Set

• One Box Integrated Solution

– Source

– Receiver

• Standard-Compliant PHY Testing

• SCPI Interface

• Vector Signal Generation, Analysis

Beyond S-Parameters


Aerospace and Defense Symposium 2007Agilent WiMAX Solutions

Beyond S-Parameters


Aerospace and Defense Symposium 2007Learn by Making Measurements

• 89601A VSA Software, Free Demo License,

N7615B Signal Studio, Free Simulation Mode

– Recorded signals provided: perform any kind of vector analysis or demodulation

– Simulated hardware

– Tutorials

– Troubleshooting help

– Example displays

• VSA & Signal Studio Software

14-day free trial licenses

– Connect to hardware

– Generate & downloadsignals

Beyond S-Parameters


Aerospace and Defense Symposium 2007Resources

– Agilent WiMAX Portal: www.agilent.com/find/wimax

www.agilent.com/find/webcasts

– Agilent ADS: http://eesof.tm.agilent.com

– Application Notes:

• 89600 Series VSA Software for OFDMA Evaluation and Troubleshooting,

Self-Guided Demonstration, Literature No. 5989-2383EN

• “IEEE 802.16e WiMAX OFDMA Signal Measurements and

Troubleshooting” AN-1578 Literature No. 5989-2382EN

• Many others (fixed & mobile WiMAX, OFDM) - See portals

– Webcast / eSeminar (recorded): “Testing Mobile WiMAX Radios from Pre-Certification through Manufacturing” www.techonline.com

– RF Design magazine article on OFDM Troubleshooting by Bob Cutler: http://rfdesign.com/mag/radio_effects_physical_layer/

– Trial Versions 89601A VSA Software & N7615B Signal Studio for 802.16 WiMAX (Download or contact Agilent)

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