Addressing Multi-Channel Synchronization for MIMO and Beamforming Test Sheri DeTomasi Keysight Technologies © Keysight Technologies 2015 Agenda © Keysight Technologies 2015 Overview of Multi-Antenna Techniques Multi-Antenna Test Challenges Calibration of a Multi-Antenna System Measurement Examples © Keysight Technologies 2015 Page 2 The Data Challenge Internet Email Navigation Texting Music Safety alerts Youtube TV Social networking Video/Photo Sharing Games • More connected devices • Expanded coverage Cloud Imaging Banking • Explosion of mobile data © Keysight Technologies 2015 Page 3 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 Page 4 Comparing Wireless Standards Cellular Peak Data Rate (DL/UL) Modulation Types Beamforming LTE-Advanced 300 Mbps/ 75 Mbps Up to 20 MHz Tx Bandwidth MIMO Technology LTE Wireless LAN 802.11n 802.11ac 1 Gbps/ 500 Mbps 600 Mbps (40 MHz, 4 streams) 6.9 Gbps (160 MHz, 8 streams, 256 QAM) Up to 100 MHz 20 MHz mandatory, 40 MHz optional 20 MHz, 40 MHz, 80 MHz to 160 MHz, 80+80 MHz BPSK, QPSK, 16QAM, 64QAM BPSK, QPSK, 16QAM, 64QAM, 256 QAM (opt) QPSK, 16QAM, 64QAM (256 QAM in small cell) 5G Being Defined • Higher freq • Higher mod • Wider BW • Massive MIMO DL up to 4x4 Up to 8x8 UL N/A Up to 4x4 1 mandatory 1 mandatory, 2 to 8 layers opt Up to dual layer (DL) Up to 8 layer (DL) Up to 4 Tx beamforming Up to 8 layers Tx beamforming Multi-Antenna techniques are a key technology used to get higher spectral efficiency and increase peak data rates © Keysight Technologies 2015 Page 5 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 Page 6 Enhanced Multi-Antenna Techniques Transmit Diversity Receive Diversity Space-time block coding (STBC) Path diversity X1, X2 – Improves robustness y1, y2 -X2, X1* Spatial multiplexing – Improves spectral efficiency and throughput Spatial division multiplexing MIMO y1 X1 Spatial multiplexing with Beamsteering 4 streams, 3 users y2 X2 – Increases signal robustness w/the added advantage of the improved throughput through spatial multiplexing MIMO Multi-user MIMO Transmit Beamforming MIMO (4x2) Matrix © Keysight Technologies 2015 Page 7 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 Direction of destructive interference nulling 0 deg Direction of constructive interference gain +30 deg -30 deg -60 deg Antenna array geometry along with relative per antenna element mag/phase weightings determine constructive/destructive interference pattern +60 deg -90 deg |||| N Antenna Elements Correlated co-polarized 0.5 wavelength separation +90 deg © Keysight Technologies 2015 Page 8 Agenda © Keysight Technologies 2015 Overview of Multi-Antenna Techniques Multi-Antenna Test Challenges Calibration of a Multi-Antenna System Measurement Examples Page 9 Advantages and Challenges with Beamforming Common Issues Advantages – Improved user experience through better signal quality • Beamforming selectivity • Increases the signal to noise ratio Single User MIMO • 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 Multi-User MIMO © Keysight Technologies 2015 Page 10 Enhanced Multi-Antenna Designs Test Challenges Complicated test setup for higher order MIMO including beamforming •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 Visualizing and validating the MIMO signal at the RF antenna • Analyzing multi-antenna beamforming signals with up to 8x8 MIMO • Simultaneous UL & DL measurements Cost and footprint • Test equipment cost & size • Time consuming tests • Development while standards evolving © Keysight Technologies 2015 Page 11 Complicated Test Set-up Need for multiple test channels – 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 Considerations for Test Equipment • 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 © Keysight Technologies 2015 Page 12 Critical Multi-Channel Synchronization Parameters 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 © Keysight Technologies 2015 Page 13 Multi-Channel Time Synchronization Example using PXI 10 MHz CLK Master Trigger Module Q D Slave Module Slave Module Ref10 – One unit designated master, synchronizes with multiple slaves Sync State Machine ... D1 D2 D3 … Dn – Master uses one PXI trigger line to send to all slave units Q Ref10 D Sync State Machine Ref10 Q D Q D Q PXI_TRIGGER (Slave 1) PXI_TRIGGER (Slave N) 1 2 First Module Ready 3 Last Module Ready 4 5 6 Rdy seen at Sync State Machine 7 8 Trg seen at modules 9 All modules assert not ready PXI_CLK10 ~ ~ ~ ~ PXIe_DSTARCm ~ ~ PXI_CLK 10 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ PXIe_DSTARCp ~ ~ PXI Trig 2 ~ ~ PXIe_DSTARCn ~ ~ PXI Trig 1 PXI Trig 3 – A common clock reference provides time alignment but not phase coherence Q Sync State Machine PXI_TRIGGER (Master) – 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 D All modules ready PXIe_DSTARB[m..p] All modules ready Module n is Trigger Module Trg Module Ready All Ready seen at Trg Module Trg Module asserts BP Trg © Keysight Technologies 2015 Trg seen at all Sync SMs Page 14 Considerations for Phase Coherence Phase Matching Issues Two signals are coherent if they if they have a constant relative phase at all instances in time Solution – 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 However, each signal generation and measurement channel has its own phase noise © Keysight Technologies 2015 Page 15 Source Simplified Block Diagram Example of 2 phase coherent channels Modulator 1 Source output 1 Level control RA M Output signal 1 Σ 90° Modulator 2 Download & definition Source output 2 Level control Controller RA M 90° 4 LO outputs Output signal 2 Σ Frequency reference Reference oscillator Local oscillator Synthesizer © Keysight Technologies 2015 Page 16 Analyzer Simplified Block Diagram Example of 2 phase coherent channels Downconverter 1 Digitizer 1 Mixer Analog-digital converter Input signal 1 RF input attenuator Pre-selector, or low-pass filter IF gain IF filter Downconverter 2 Digitizer 2 Input signal 2 Results & display Controller Local oscillator Synthesizer Reference oscillator Frequency reference © Keysight Technologies 2015 Page 17 Synchronization across Multiple Chassis Extending PXI 10 MHz CLK to a second chassis Example Two Chassis Receiver Configuration, two receivers per Chassis – Front panel connections between master in each chassis Chassis 1, Master 10 MHz OCXO Out 10 MHz OCXO 100 MHz 10 MHz Ref In Reference Module PLL /10 100 MHz In System Sync Master 10 MHz Sync over TRIG 10 MHz TTL TRIGs 100 MHz Out – Common 10 MHz reference shared via front panel 10 MHz 100 MHz In Slave Sync Digitizer Sync over TRIG – Alignment of 10 MHz reference required Chassis 2, Slave – Within each chassis, backplaneExternal SMB Splitter triggers used 10 MHz OCXO 10 MHz Ref In Equal Length SMB Cables – Provides synchronous frequency and timing but need more for phase coherency Reference Module PLL /10 100 MHz In Group Sync Master 10 MHz Sync over TRIG 10 MHz TTL TRIGs 100 MHz Out 10 MHz 100 MHz In Slave Sync Digitizer Sync over TRIG © Keysight Technologies 2015 Page 18 Agenda © Keysight Technologies 2015 Overview of Multi-Antenna Techniques Multi-Antenna Test Challenges Calibration of a Multi-Antenna System Measurement Examples Page 19 Calibration of Phase Coherent Measurement Systems 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 Uncorrected Corrected using Keysight LTE-A Multi-Channel Reference Solution Tools © Keysight Technologies 2015 Page 20 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 multichannel phase coherent measurements – Keysight has helpful tools to automate this process and allows for integration of deltas for design verification © Keysight Technologies 2015 Page 21 Multi-Channel Calibration Methods Traditional Source Calibration VSG 1 VSG 2 VSG 3 New Source Calibration VSG 1 4chan Scope VSG 4 • New Patent-Pending MultiChannel Calibration Method VSG 2 4 Way combiner VSA VSG 3 VSG 4 Analyzer Calibration VSA 1 – Automated for faster tests – Less HW & SW lowers the cost – VSG 4 Way Splitter VSA 2 VSA 3 For best results minimize cable length, keep cable lengths the same, and select high quality splitter, connectors, and cables. VSA 4 © Keysight Technologies 2015 Page 22 Tips for True Phase Coherent Measurement Systems Minimize Phase Variations and Calibrate 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 Page 23 Agenda © Keysight Technologies 2015 Overview of Multi-Antenna Techniques Multi-Antenna Test Challenges Calibration of a Multi-Antenna System Measurement Examples Page 24 Test Challenge: Complicated Test Setup LTE-Advanced Multi-Channel Reference Solution Software Accelerate LTE-A designs and gain deeper insight faster Multi-Channel Configuration & Correction Utilities Signal Studio N7624B & N7625B for LTE/LTE-A FDD & TDD 89600 VSA & WLA Software (Optional X-Series measurement applications for SISO analysis) Hardware 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 Device under test Signal to be analyzed by VSAs © Keysight Technologies 2015 Page 25 Test Challenge: Visualization & Validation of Signals 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 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 eNB 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 © Keysight Technologies 2015 Page 26 8x2 BF modulation analysis example MIMO/BF – Downlink 89600 VSA SW © Keysight Technologies 2015 Page 27 Testing the Receiver Side 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 LO Distribution Solution or or Signal Studio – Support for the latest WLAN and cellular multi-channel signals including 802.11ac and LTE-Advanced TDD and FDD Up to 8x8 LO locked phase coherent, time aligned generators, 160 MHz BW – MIMO signal generation solutions that can be used with RF fading simulators – Select transmission mode including diversity, spatial multiplexing, beamforming up to 8x8 MIMO and carrier aggregation – Define, generate and export waveform files – Can be combined with carrier aggregation © Keysight Technologies 2015 Page 28 From Simulation to Manufacturing LTE design flow – Model new LTE/LTE-A and WLAN 802.11ac MIMO designs – Verify interpretations of the standard – Rapid proto-typing and integrated measurements IP Reference Libraries – Use in design simulation, verification and testing 4G LTE-Advanced, LTE 3G HSPA+, WCDMA, EDGE, GSM WLAN 802.11ac/n/a/b/g WPAN 802.11ad, 802.15.3c – New 5G libraries available Test Software Test Equipment I/O Lib, ComExpert 89600 VSA Signal Studio 3rd Party RF Sources & Analyzers AWG & Digitizers Scopes, Logic, Modular © Keysight Technologies 2015 Page 29 Case Study – Xidian University, China Application: Research Verification 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 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) © Keysight Technologies 2015 Page 30 Keysight Solution for MIMO Throughput Test LTE/LTE-A 4x4 MIMO waveform generation, EVM, throughput test Throughput test PXIe VSG M9381A DUT SystemVue Software to create LTE-A FDD or TDD channel & capture measurements via 89600 VSA software PXIe VSA M9391A LTE-A Multi-Channel Reference Solution • PXI chassis w/ embedded controller • 4 M9381A PXI VSGs • 4 M9391A PXI VSAs © Keysight Tools • Configuration & Correction Page 31 Technologies 2015 Configuration and Calibration Demo Software Accelerate LTE-A designs and gain deeper insight faster Multi-Channel Configuration & Correction Utilities Signal Studio N7624B & N7625B for LTE/LTE-A FDD & TDD 89600 VSA & WLA Software (Optional X-Series measurement applications for SISO analysis) Hardware 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 Device under test Signal to be analyzed by VSAs © Keysight Technologies 2015 Page 32 Summary 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 © Keysight Technologies 2015 Page 33 Thank You !!! Questions and Answers © Keysight Technologies 2015 Copyright © 2014 Agilent. All rights reserved Page 34 LTE / LTE-Advanced Design and Test Solutions 89600 VSA/WLA Signal Studio Software For Signal Analyzers, Scopes, LA SystemVue and ADS Signal Analyzers Signal Generators 3D EM Simulation SystemVue (BB) ADS/GG (RF/A) Baseband Generator and Channel Emulator RF Module Development RF Proto Design Simulation RF Chip/module BTS and Mobile BB Chipset Development L1/PHY RF and BB Design Integration L1/PHY DigRF v4 FPGA and ASIC Protocol Development L2/L3 LTE UE Signalling, RF, Protocol and Functional Test Scopes and Logic Analyzers PXI Modular Solutions RF Handheld Analyzers Battery Drain Characterization Pre-Conformance System Design Validation System Level RF Testing Conformance Manufacturing BTS or Mobile Power Measurement Network Deployment Manufacturing Test Systems for RF and Protocol Conformance 3-year repair warranty coverage on all instruments Optional Calibration and Repair Service Plans © Keysight Technologies 2015 Page 35