Addressing LTE Multi-channel beamforming apps · PDF file–MIMO, carrier aggregation...
Transcript of 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
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
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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
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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
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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
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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
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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
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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
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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
Overview of Multi-Antenna Techniques
Multi-Antenna Test Challenges
Calibration of a Multi-Antenna System
Measurement Examples
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
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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
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Technologies 2015 11
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
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Technologies 2015 12
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
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Critical Multi-Channel Synchronization Parameters
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Technologies 2015 13
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
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Technologies 2015 14
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
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Technologies 2015 15
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
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Technologies 2015 16
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
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Technologies 2015 17
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
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Technologies 2015 18
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
Technologies 2015 19
Overview of Multi-Antenna Techniques
Multi-Antenna Test Challenges
Calibration of a Multi-Antenna System
Measurement Examples
Page
Calibration of Phase Coherent Measurement Systems
© Keysight
Technologies 2015 20
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
Technologies 2015 21
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
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Technologies 2015 22
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
Technologies 2015 23
Minimize Phase Variations and Calibrate
Page Page
Overview of Multi-Antenna Techniques
Multi-Antenna Test Challenges
Calibration of a Multi-Antenna System
Measurement Examples
Agenda © Keysight
Technologies 2015 24
Page
Test Challenge: Complicated Test Setup
© Keysight
Technologies 2015 25
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
Page
Test Challenge: Visualization & Validation of Signals
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Technologies 2015 26
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
8x2 BF modulation analysis example MIMO/BF – Downlink
© Keysight
Technologies 2015 27
89600 VSA SW
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
Technologies 2015 28
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
Technologies 2015 29
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
Technologies 2015 30
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
Technologies 2015 31
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
Technologies 2015 32
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
Page
Summary
© Keysight
Technologies 2015 33
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
Copyright © 2014 Agilent. All rights reserved
Thank You !!!
Questions and Answers
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Technologies 2015 34
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Optional Calibration and Repair Service Plans
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LTE / LTE-Advanced Design and Test Solutions