addressing lte multi-channel beamforming apps · pdf file–mimo, carrier aggregation...

Addressing Multi-Channel Synchronization for MIMO and Beamforming Test

Sheri DeTomasi

Keysight Technologies

© Keysight

Technologies 2015

Page Page Agenda © Keysight

Technologies 2015 2

Overview of Multi-Antenna Techniques

Multi-Antenna Test Challenges

Calibration of a Multi-Antenna System

Measurement Examples

© Keysight

Technologies 2015

Page

The Data Challenge

© Keysight

Technologies 2015 3

Internet

Email

Navigation

Texting

Music

Safety alerts

Youtube

TV

Social networking

Video/Photo Sharing

Games

Cloud

Imaging

Banking

•More connected devices

•Expanded coverage

•Explosion of mobile data

Page

How do wireless service providers keep up with the Data Demand?

Make better use of spectrum

Combine carriers with carrier

aggregation

Wider channel bandwidths

Denser modulation techniques

Multi-antenna techniques

Heterogeneous networks

© Keysight

Technologies 2015 4

Page

Comparing Wireless Standards

Cellular Wireless LAN

LTE LTE-Advanced 5G 802.11n 802.11ac

Peak

Data Rate

(DL/UL)

300 Mbps/

75 Mbps

1 Gbps/

500 Mbps

Being Defined

• Higher freq

• Higher mod

• Wider BW

• Massive MIMO

600 Mbps

(40 MHz, 4 streams)

6.9 Gbps

(160 MHz, 8 streams,

256 QAM)

Tx Bandwidth Up to 20 MHz Up to 100 MHz 20 MHz mandatory, 40

MHz optional

20 MHz, 40 MHz, 80

MHz to 160 MHz,

80+80 MHz

Modulation Types QPSK, 16QAM, 64QAM

(256 QAM in small cell)

BPSK, QPSK,

16QAM, 64QAM

BPSK, QPSK,

16QAM, 64QAM,

256 QAM (opt)

MIMO DL

Technology

UL

up to 4x4 Up to 8x8

N/A Up to 4x4 1 mandatory 1 mandatory, 2 to 8

layers opt

Beamforming Up to dual layer (DL) Up to 8 layer (DL) Up to 4 Tx

beamforming

Up to 8 layers Tx

beamforming

© Keysight

Technologies 2015 5

Multi-Antenna techniques are a key technology used to get

higher spectral efficiency and increase peak data rates

Page

Enhanced Multi-Antenna Techniques

– Use of multiple antennas to improve spectral efficiency - increase

overall capacity and the data rate through multiple antennas

© Keysight

Technologies 2015 6

Page

Enhanced Multi-Antenna Techniques

Path diversity

– Improves robustness

Spatial multiplexing

– Improves spectral efficiency

and throughput

Spatial multiplexing with

Beamsteering

– Increases signal robustness

w/the added advantage of the

improved throughput through

spatial multiplexing MIMO

© Keysight

Technologies 2015 7

MIMO

Transmit Diversity Receive Diversity

Space-time block

coding (STBC)

X1, X2

-X2, X1*

y1, y2

MIMO (4x2)

Matrix

X1

X2

y1

y2

Multi-user MIMO

4 streams, 3 users

Transmit Beamforming

Spatial division

multiplexing

Page

How does Beamsteering Work? – Use multiple antennas to electronically steer a single data stream

– Used in radar, sonar, seismology, electronic warfare, wireless

communications, radio astronomy, acoustics

– Takes advantage of multi-antenna interference to control directionality

– Multi-antenna signals are weighted relatively in both magnitude and phase to

produce spatial selectivity

• Constructive (in-phase) interference power gain in desired directions

• Destructive (out-of-phase) interference power nulling in other directions

© Keysight

Technologies 2015 8

-90 deg

-60 deg

-30 deg

0 deg

+30

deg

+60

deg

+90

deg | | | |

N Antenna Elements

Correlated co-polarized 0.5 wavelength

separation

Direction of

constructive

interference

gain

Direction of

destructive

interference

nulling

Antenna array geometry along with

relative per antenna element

mag/phase weightings determine

constructive/destructive interference pattern

Page Page





Agenda © Keysight

Technologies 2015 9

Page

Advantages and Challenges with Beamforming

Advantages

– Improved user experience through better

signal quality

• Beamforming selectivity

• Increases the signal to noise ratio

• Coherent signal gain

– Increase cell capacity with MU-MIMO

Challenges

– Requires more antennas

– Phase alignment of RF carrier is critical in

beamforming: < 1 deg at RF frequency

– Often requires multiple, highly synchronized

instruments in test

© Keysight

Technologies 2015 10

Common Issues

Single User MIMO

Multi-User MIMO

Page

Enhanced Multi-Antenna Designs

•Complexity of connecting multiple synchronized instruments •Control of relative phase, time and frequency of multiple channels •Calibration of the measurement system at the device under test

Complicated test setup for higher order MIMO including beamforming

• Analyzing multi-antenna beamforming signals with up to 8x8 MIMO

• Simultaneous UL & DL measurements

Visualizing and validating the MIMO signal at the RF antenna

• Test equipment cost & size

• Time consuming tests

• Development while standards evolving

Cost and footprint

© Keysight


Test Challenges

Page

Complicated Test Set-up

– Carrier aggregation with

carriers in different frequency

bands

– Multi-standard radios

– Diversity where antennas are

in different frequency bands

– Spatial multiplexing MIMO up

to 8x8

– Beamsteering

© Keysight


Need for multiple test channels

• Is channel testing done

sequentially or in parallel?

• What level of time

synchronization is needed?

• Do you need phase coherent

channels?

• Calibration of the measurement

system at the device under test

Considerations for Test

Equipment

Page

Critical Multi-Channel Synchronization Parameters

© Keysight


Time Alignment

– Use clock synchronization & triggering to

ensure waveform playback and waveform

captures start synchronously on all channels

– MIMO, carrier aggregation

Phase Coherence

– Two signals are coherent if they if they have a

constant relative phase at all instances in time

– Coherence is then a statistical property

between signals

– Beamforming

Page

Multi-Channel Time Synchronization

© Keysight


Example using PXI 10 MHz CLK

– One unit designated master,

synchronizes with multiple slaves

– Master uses one PXI trigger line to send

to all slave units

– Slaves each use one PXI trigger line to

send to master unit

– When all channels are armed, master

can signal a trigger event and all units

start on next 10MHz clock edge after

trigger event

– A common clock reference provides

time alignment but not phase coherence

Slave Module

D Q

DQ

Sync State

MachineRef10

Master Trigger Module

D1

D2

D3

…

Dn

Q

DQ

Ref10

Sync State

Machine

Slave Module

D Q

DQ

Sync State

MachineRef10

. . .

PXI_TRIGGER (Master)

PXI_TRIGGER (Slave N)

PXI_TRIGGER (Slave 1)

PXI_CLK10

PXIe_DSTARCm

All modules readyPXIe_DSTARB[m..p]

~ ~~ ~

~ ~~ ~

~ ~~ ~

~ ~~ ~

~ ~~ ~

~ ~~ ~

Module n is Trigger

Module

PXIe_DSTARCn

PXIe_DSTARCp

First Module

Ready

Trg Module

Ready

Last Module

Ready

All Ready seen

at Trg Module

Rdy seen at Sync

State Machine

Trg Module

asserts BP Trg

Trg seen at

modules

All modules assert

not ready

Trg seen at all

Sync SMs

1 2 3 4 5 6 7 8 9

PXI_CLK 10

PXI Trig 1

PXI Trig 2

PXI Trig 3

All modules ready

Page

Considerations for Phase Coherence

Two signals are coherent

if they if they have a

constant relative phase

at all instances in time

However, each signal

generation and

measurement channel

has its own phase noise

© Keysight


Phase Matching Issues

– Use a single, shared LO for all channels to achieve

True Phase Coherence

– All channels will have a constant, relative phase error

– Calibration is critical to remove any fixed phase offset

between channels

Solution

Page

Source Simplified Block Diagram

© Keysight


Example of 2 phase coherent channels

Modulator 2

Controller

Synthesizer

Modulator 1 Source output 1

Output signal

1

Download & definition

Frequency reference

Reference oscillator

Local oscillator

90° Σ RA

M

Output signal

2 90° Σ

RA

M

Level control

Source output 2

Level control

4 LO

outputs

Page

Analyzer Simplified Block Diagram

© Keysight


Example of 2 phase coherent channels

Downconverter 2 Digitizer 2

Controller

Synthesizer Frequency reference

Downconverter 1 Digitizer 1

RF input

attenuator

Pre-selector, or

low-pass filter

IF gain

Mixer

IF filter

Input

signal

1

Analog-digital

converter

Results & display

Input

signal

2

Reference

oscillator Local

oscillator

Page

Synchronization across Multiple Chassis

© Keysight


Extending PXI 10 MHz CLK to a second chassis

10 MHz10 MHz OCXO Out

10 MHz Ref In

100 MHz Out

/10PLL

10 MHz OCXO Reference Module

System Master

100 MHz In

Sync

10 MHz

Sync over TRIG

Slave Digitizer

100 MHz In

Sync

10 MHz

Sync over TRIG

TTL TRIGs

10 MHz

10 MHz Ref In

100 MHz Out

/10PLL

10 MHz OCXO Reference Module

Group Master

100 MHz In

Sync

10 MHz

Sync over TRIG

Slave Digitizer

100 MHz In

Sync

10 MHz

Sync over TRIG

TTL TRIGs

100 MHz

Chassis 1, Master

Chassis 2, Slave

External SMB Splitter

Equal Length SMB Cables

Example Two Chassis Receiver Configuration, two receivers per Chassis

– Front panel connections

between master in each chassis

– Common 10 MHz reference

shared via front panel

– Alignment of 10 MHz reference

required

– Within each chassis, backplane

triggers used

– Provides synchronous

frequency and timing but need

more for phase coherency

Page Page Agenda © Keysight






Page

Calibration of Phase Coherent Measurement Systems

© Keysight


Why is this important?

– Even when using a shared LO, there

will be some static time and phase

skew between instrument channels in

the measurement system

– Time and phase variations due to

cables, connectors, and signal

conditioning

Correcting out these offsets will ensure

that any measured differences is due to

the signal/device under test and not the

test equipment Corrected

using Keysight LTE-A

Multi-Channel Reference

Solution Tools

Uncorrected

Page

Calibration of Phase Coherent Signal Generation System

The End Goal – Perfectly Aligned in Time

and Phase – Determine channel to channel time and

phase differences and apply corrections

– Apply known signal to all channels and

measure each channel relative to master

source

– Collect BB time and phase differences

between channels

– Repeat for each frequency, amplitude, and

sample rate

– Apply time and phase corrections to multi-

channel phase coherent measurements

– Keysight has helpful tools to automate this

process and allows for integration of deltas

for design verification

© Keysight


Page

Multi-Channel Calibration Methods

Traditional Source

Calibration

• New Patent-Pending Multi-

Channel Calibration Method

– Automated for faster tests

– Less HW & SW lowers the cost

– For best results minimize cable length, keep cable

lengths the same, and select high quality splitter,

connectors, and cables.

New Source

Calibration

© Keysight


Analyzer

Calibration

VSG 1

VSG 2

VSG 3

VSG 4

4-

chan

Scope

VSG 1

VSG 2

VSG 3

VSG 4

VSA 1

4 Way

combiner

VSA 2

VSA 3

VSA 4

VSA

4 Way

Splitter VSG

Page

Tips for True Phase Coherent Measurement Systems

1. Use common LO Source

2. Use phase stable LO

3. Use low phase noise LO

4. Use reference clock synchronization to ensure

waveforms and acquisitions start at the same time

5. Calibrate out any time and phase skew between

generator channels or between analyzer channels

6. Calibrate out any losses and mismatches due to cables

and connectors

© Keysight


Minimize Phase Variations and Calibrate

Page Page





Agenda © Keysight


Page

Test Challenge: Complicated Test Setup

© Keysight


LTE-Advanced Multi-Channel Reference Solution

Signal Studio

N7624B & N7625B for

LTE/LTE-A FDD & TDD

89600 VSA & WLA Software

(Optional X-Series measurement

applications for SISO analysis)

Multi-Channel

Configuration &

Correction Utilities

So

ftw

are

H

ard

ware

Device

under test

Available Configurations

• Analyzers, sources or both

• 2, 4, or 8 channels

• Time synchronized or

phase coherent

• Chassis, controller, cables

• V2802A LO distribution

Test stimulus

from VSGs Signal to be

analyzed by VSAs

Accelerate LTE-A designs and gain deeper insight faster

http://cp.home.agilent.com/agilent7/s7viewers/flash/genericzoom.swf?logo2=false&serverUrl=/agilent7/is/image/&contentRoot=/agilent7/skins/&locale=en&config=Agilent/AGILENT-IMGSET&image=Agilent/PROD-1594835-IS

Page

Test Challenge: Visualization & Validation of Signals

© Keysight


Spectrum measurements like SEM, OBW, power, spurs,

ACPR

Isolation/cross-channel skew crosstalk, time alignment error

(TAE)

MIMO and beamforming measurements with beamforming

weightings per antenna

Modulation quality with EVM per layer

LTE/LTE-A FDD/TDD UL & DL, WLAN including 802.11ac

M9391A VSAs provide up to 8

LO locked phase coherent, time

aligned analyzers, 160 MHz BW

eNB

Test Challenge: Characterizing the full set of

LTE/LTE-A tests, including 8x8 MIMO, cross

channel measurements and multi-antenna

beamforming, which typically includes 4 or 8

antenna elements

Solution 89600 VSA Software

Page

Testing the Receiver Side

Signal Studio

– Support for the latest WLAN and cellular

multi-channel signals including 802.11ac and

LTE-Advanced TDD and FDD

– Select transmission mode including diversity,

spatial multiplexing, beamforming up to 8x8

MIMO and carrier aggregation

– Define, generate and export waveform files

© Keysight


LO Distribution

– MIMO signal generation solutions that can be used

with RF fading simulators

– Can be combined with carrier aggregation

Test Challenge: Ability to generate complex MIMO and

beamforming signals that have relative phase, time and

frequency characteristics to adhere that the latest wireless

standards

Solution

Up to 8x8 LO locked phase coherent,

time aligned generators, 160 MHz BW

or

or

Page

From Simulation to Manufacturing

– Model new LTE/LTE-A and

WLAN 802.11ac MIMO designs

– Verify interpretations of the

standard

– Rapid proto-typing and

integrated measurements

– Use in design simulation,

verification and testing

– New 5G libraries available

© Keysight


IP Reference Libraries 4G LTE-Advanced, LTE

3G HSPA+, WCDMA, EDGE, GSM

WLAN 802.11ac/n/a/b/g

WPAN 802.11ad, 802.15.3c

Test Equipment RF Sources & Analyzers

AWG & Digitizers

Scopes, Logic, Modular

Test Software I/O Lib, ComExpert

89600 VSA

Signal Studio

3rd Party

LTE design flow

Page

Case Study – Xidian University, China

Need 8x8 system with wide

bandwidth and phase coherent

channels

Key Test Challenges:

– Complexity and size of integrating 8

sources and 8 analyzers

– Phase coherency between channels to test

beamforming

– Characterizing wireless communications

Solution provides:

– Compact size

– Automatic routing of triggers

– Reduced complexity

© Keysight


Application: Research Verification

8x8 implementation

• 8 PXI VSGs, 6 GHz, 160 MHz

• 8 PXI VSAs, 6 GHz, 160 MHz

• MATLAB

• 89601B VSA SW

• 4 PXI Chassis with 1 embedded controller plus LO

distribution unit (not shown)

Page

Keysight Solution for MIMO Throughput Test

© Keysight


LTE/LTE-A 4x4 MIMO waveform generation, EVM, throughput test

Throughput test

PXIe VSG M9381A DUT PXIe VSA M9391A

SystemVue Software to create

LTE-A FDD or TDD channel &

capture measurements via 89600

VSA software

LTE-A Multi-Channel Reference Solution

• PXI chassis w/ embedded controller

• 4 M9381A PXI VSGs

• 4 M9391A PXI VSAs

• Configuration & Correction Tools

Page

Configuration and Calibration Demo

© Keysight


Signal Studio

N7624B & N7625B for

LTE/LTE-A FDD & TDD

89600 VSA & WLA Software

(Optional X-Series measurement

applications for SISO analysis)

Multi-Channel

Configuration &

Correction Utilities

So

ftw

are

H

ard

ware

Device

under test

Available Configurations

• Analyzers, sources or both

• 2, 4, or 8 channels

• Time synchronized or

phase coherent

• Chassis, controller, cables

• V2802A LO distribution

Test stimulus

from VSGs

Signal to be

analyzed by VSAs

Accelerate LTE-A designs and gain deeper insight faster

http://cp.home.agilent.com/agilent7/s7viewers/flash/genericzoom.swf?logo2=false&serverUrl=/agilent7/is/image/&contentRoot=/agilent7/skins/&locale=en&config=Agilent/AGILENT-IMGSET&image=Agilent/PROD-1594835-IS

Page

Summary

© Keysight


Newer carrier aggregation, spatial multiplexing, beamforming applications require tightly synchronized, phase-coherent channels for accurate test

Channel-to-Channel phase and time alignment and calibration is critical in the multi-antenna measurement system

Keysight provides in-depth signal generation & analysis solutions for advanced technology & research

Page

Optional Calibration and Repair Service Plans

Signal

Generators

RF Module Development

RF Proto RF Chip/module

Design

Simulation

BTS and Mobile

BB Chipset Development

L1/PHY

FPGA and ASIC

Conformance

RF and BB

Design

Integration

L1/PHY

System

Design

Validation

System Level

RF Testing BTS

or

Mobile Protocol Development

L2/L3

DigRF v4

Pre-Conformance

Network Deployment

Manufacturing

89600 VSA/WLA For Signal Analyzers, Scopes, LA

SystemVue and ADS

3D EM Simulation SystemVue (BB) ADS/GG (RF/A)

Scopes and

Logic Analyzers

Baseband

Generator and

Channel Emulator

Signal Studio

Software

RF Handheld Analyzers Manufacturing

Test

Battery Drain

Characterization

Signal Analyzers

PXI Modular

Solutions

3-year repair warranty coverage on all instruments

LTE UE Signalling, RF, Protocol and

Functional Test Power Measurement

Systems for RF and

Protocol Conformance

© Keysight


LTE / LTE-Advanced Design and Test Solutions

http://www.agilent.com/find/ThreeYearWarranty

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addressing lte multi-channel beamforming apps · pdf file–mimo, carrier aggregation...

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