1 of 30 LTE Base Station Testing Basics Emilio Franchy Senior Product Manager March 31 st , 2010
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LTE Base Station Testing Basics
Emilio Franchy Senior Product Manager
March 31st, 2010
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Agenda
LTE Technology Overview LTE Terms LTE vs. 3G Comparison LTE RF Measurements LTE Modulation Measurements LTE Over-the-Air (OTA) Measurements Question & Answer
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In the downlink, Orthogonal Frequency Division Multiplexing (OFDMA) is selected as the air-interface for LTE.
OFDMA communication systems do not rely on increased symbol rates in order to achieve higher data rates.
Transmission by means of OFDM is a particular form of multi-carrier modulation (MCM) i.e. a parallel transmission method which divides an RF channel into several narrower bandwidth subcarriers.
Sub-carrier typically 15 kHz Standard allows for other
values
LTE Basic Technologies – OFDMA
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What is OFDMA?
“Orthogonal Frequency Division Multiple Access”
Assigns different subcarriers & symbols to each user Can dynamically change
Each subcarrier is modulated with QAM or PSK LTE uses QPSK, 16 QAM, and 64 QAM BPSK for some control signals
PHICH, PUCCH
Allows many users to be supported At variable bit rate Scheduling many users With different quality of service Complex Time
Subcarrier
Different users
System Overhead
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LTE Physical Channel Names (Downlink) RS
Reference Signal Similar to Pilots in 802.11 Subcarrier varies with MIMO transmitter & Cell ID
P-SS, S-SS Primary & Secondary Synchronizing Signals Contains cell ID
PCFICH Physical Control Format Indicator Channel How many symbols are used for PDCCH
PBCH Physical Broadcast Channel
PHICH (not shown) Physical Hybrid ARQ Indicator Channel Sends Acknowledgements or Not Acknowledgements Part of Error Protection system for the uplink
PDCCH Physical Downlink Control Channel Who’s assigned to what resources?
PDSCH Physical Downlink Shared Channel Where all the user data goes
Time
Subcarrier
Shared
Shared
Shared
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LTE Frame Structure (FDD) Frame
10 ms Subframe
1 ms 10 per frame
Slot 500 us 2 per subframe, 20 per frame 7 or 6 symbols (normal or extended CP) Limited usefulness, as scheduling
limited to subframes
Subframe Frame 10 ms
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Resource Blocks Resource Block (RB)
12 subcarriers * 1 slot 1 slot = 0.5 ms 2 slots/subframe 10 subframes/frame 1 frame = 10 ms
Subframe
Subcarrier
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Compatible Bandwidths
Control Channels in center of channel BW
20 MHz BW
5 MHz BW
1.4 MHz BW
10 MHz BW
15 MHz BW
3 MHz BW
Tim
e
Frequency
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MIMO (2X2 examples) MIMO = Multiple Input, Multiple Output
MIMO (Transmit Diversity) Multi-beam antenna’s
Dual 2X2
(eNodeB Tx) 4X2 (UE Rx)
Quad 4X4
Data stream repeated
All signal paths
Increase coverage
MIMO (Spatial Multiplexing) Different data streams
Higher data rate
Relies on Multi-path
MIMO Tx Diversity
MIMO Spatial Multiplexing
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LTE terms similarity to 3G terms LTE CDMA W-CDMA
RS (Reference Signal) Pilot CPICH
P-SS (Primary Synchronizing Signals) Sync P-SCH
S-SS (Secondary Synchronizing Signals) NA S-SCH
PCFICH (Physical Control Format Indicator Channel) NA NA
PBCH (Physical Broadcast Channel) Paging BCCH
PHICH (Physical Hybrid ARQ Indicator Channel) NA NA PDCCH (Physical Downlink Control Channel ) Paging P/S-CCPCH & PICH
PDSCH (Physical Downlink Shared Channel) Traffic Traffic
EVM (Signal Quality) Rho EVM
Frequency Accuracy Freq Accy Freq Accy
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LTE Measurements vs. W-CDMA Measurements
RF Channel Spectrum Power vs. Time Spectral Emission Mask ACLR
Modulation Quality Resource Element Power Control & Traffic Channel Power Spectral Flatness Constellation
OTA Sync Signal Scan Channel Power Monitor
RF Channel Spectrum Power vs. Time Spurious Emission ACLR
Demodulator CDP (Code Domain Power)
Control & Traffic Channel Power Constellation
OTA Pilot Scan Multipath
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LTE Measurements vs. CDMA Measurements
RF Channel Spectrum Power vs. Time Operating Band Unwanted Emissions
(Spectrum Emission Mask) ACLR
Modulation Quality Resource Element Power Control & Traffic Channel Power Spectral Flatness Constellation
OTA Sync Signal Scan Channel Power Monitor
RF Channel Spectrum Power vs. Time Spurious Emission ACPR
Demodulator CDP (CDP MAC/Data, Graph/Table) Control Channels
OTA Pilot Scan Multipath
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eNodeB : Traditional install Traditional configuration
2x2 MIMO 2 Radios per sector
Extreme weather Key HW in shelter Traditional Testing
Test Needs Transmitter Antenna & jumper cables LTE signal quality
Direct Connect Use Test Port
Interference Coverage Backhaul Fiber
Directional Coupler / Test Port
Channel Cards
Power Supply Remote Radio Heads
located close to Base Band Radio
Radio Server
Coaxial/Waveguide RF Cable Jumper if close to antenna
Backhaul GigE
GPS Antenna
Fiber Optic Baseband Cable with DC Power – short run
Antennas
Air Interface
Interference
Traditional TMA’s
Coaxial Feedline to TMA
Tx1 / Rx1
Tx2 / Rx2
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Key Performance Indicators vs. LTE Field Measurement
x = probable, xx = most probable
Key Performance Indicators vs. Test Sync
Power RS Power
Occupied BW,
ACLR, & SEM
EVM (pk) EVM Freq Error Rx Noise Floor OTA EVM
Call/Session Blocking
Power shortage x x x
Resource Block shortage x xx xx
UL Interference x xx
Call/Session Drop
Radio Link Timeout x x x x x x x
UL Interference x x
DL Interference x x x x x x
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LTE Field Measurement vs. eNodeB Field Replaceable Units
x = probable, xx = most probable
Test vs. BTS Field Replaceable Units Freq Ref Signal
Generation MCPA Filters Antenna Antenna Down Tilt
Sync Power x xx x
RS Power x xx x
Occupied BW x xx xx
Adjacent Channel Leakage Ratio (ACLR) x x xx x
Spectral Emission Mask (SEM) x x xx x
Error Vector Magnitude Peak (EVM pk) x xx
Error Vector Magnitude (EVM) x x x x
Frequency Error xx
OTA EVM x x x x x
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LTE (RF) Occupied Bandwidth
Occupied Bandwidth A measurement of the spectrum used
by the carrier The occupied bandwidth contains 99%
of the signal’s RF power
Guideline – Direct Connect Per defined LTE bandwidth
1.4, 3.0, 5.0, 10, 15, 20 MHz
Consequences Leads to interference with neighboring
carriers
Dropped calls/data sessions
Low capacity
Common Faults Tx filter
MCPA
Channel cards
Antennas
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LTE Adjacent Channel Leakage Ratio (ACLR)
ACLR (single-carrier displayed) Measures how much of the carrier gets into
neighboring RF channels Checks the closest (adjacent) and the next
closest (alternate)
Guideline – Direct Connect -45 dBc for the adjacent channels
-45 dBc for the alternate channels
Consequences Leads to interference with neighboring
carriers
Low capacity
Blocked calls/data sessions
Common Faults Tx filter
MCPA
Channel cards
Cable connectors
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LTE Spectral Emission Mask (SEM)
Spectral Emission Mask SEM checks closer to the signal than
ACLR does Regulators may require regular
measurements of spectral emissions
Guideline – Direct Connect Must be below mask
Received power levels matter so be sure to use the right external attenuation value
Consequences Interference with neighboring carriers
Legal liability
Low signal quality
Common Faults Check amplifier output filtering
Look for intermodulation distortion
Look for spectral re-growth
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LTE Error Vector Magnitude (EVM)
EVM The ratio of errors, or distortions, in the
actual signal, compared to a perfect signal
EVM applies to the entire signal
Guidelines – Direct Connect QPSK - 17.5% 16 QAM – 12.5% 64 QAM – 8%
Consequences dropped calls/data sessions low data rate low sector capacity blocked calls/data sessions
Common Faults distortion in the channel cards Power amplifier filter antenna system
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LTE Control Channels
Control Channels Verifies Control Channel power is set
correctly
Guideline Per RF Engineering ± 0.5 dB
Consequences If power set too low
Blocked calls/data sessions Initiating calls/data sessions
Dropped calls/data sessions During handoffs
If power set too high Possible interference Lower Throughput
Common Faults Improper settings in the eNodeB
Signal processing Control section
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LTE Frequency Error
Frequency Error Checks to see that the carrier frequency
is precisely correct Regulatory requirement in many
countries
Guideline – OTA with GPS ± 0.05 ppm (wide area BS) ± 0.1 (local area BS) ± 0.25 (home BS)
Consequences Calls will drop when mobiles travel at
higher speed In some cases, cell phones cannot hand
off into, or out of the cell Common Faults
Reference frequency Frequency distribution system GPS, if used Backhaul
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eNode-B ; Remote Radio Unit Single Sector
2x2 MIMO 2 Radios per sector Tx1 has Sync Signal Tx2 may have Sync Signal
Test Needs Transmitter Antenna & jumper cables LTE signal quality
OTA if No Access to RRU Interference Coverage Backhaul Fiber
Company Confidential
Tx1 / Rx1
Tx2 / Rx2 D
irec
tiona
l Co
uple
r /
Test
Po
rt
Channel Cards
Power Supply
Remote Radio Heads Ideally located close
to antenna
Radio Server
RF Cable Jumper if close to antenna
Backhaul GigE ….
GPS Antenna
Fiber Optic Baseband Cable with DC Power
Antennas
Air Interface
Interference
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LTE Synchronization Signal Scanner
Synchronization Signal Power Indicates which sectors are present at
the current location Too many strong sectors creates pilot
pollution
Guideline – Direct Connect 3 or fewer codes
Within 10 dB of dominant code
Over 95% of the coverage area
Consequences Low data rate
Low capacity
Excessive soft handoffs
Common faults Antenna down tilt
Scrambling code power
Illegal repeaters Downlink Coverage Quality
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LTE OTA Modulation Quality Testing
MIMO presents a challenge to measure EVM Need to measure PBCH which has Transmit Diversity
Measures both Tx1 & Tx2 Valid EVM OTA measurement
OTA Modulation Quality
OTA Modulation Quality Testing Valid signal quality measurements can be
made OTA Guidelines are established from a known good
base station Must be taken in valid location
Valid OTA Location OTA Scanner validates location
Dominance >10 dB
If Pass – becomes sweet spot Note GPS location Becomes location for future
OTA Modulation Quality Testing Record and create
OTA Pass/Fail limits
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Downlink Coverage Mapping OTA Scanner has Auto-Save
Need GPS Receiver and Antenna
Collects data ≈ every 5-10 s
Time depends on number of Sync
codes and whether Modulation is turned
on
Master Software Tools can export data
to a KML file
Import into Google Maps/Earth
Mouse over point to see Scanner results Downlink Coverage Quality
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One quick test – OTA Pass/Fail – checks health of cell site
Find valid Over-the-Air (OTA) location If not, direct connect
Run one-step Pass/Fail Test Checks Feed Line Quality, if OTA Checks RF Quality Checks Modulation Quality
Test data throughput Use PC data card
If everything passes DONE
If not troubleshoot Feed lines and antenna system Base station field replaceable units Downlink Coverage issues Interference problems Backhaul bit-error-rates
Found Valid OTA spot?
Run OTA or Direct Connect Pass/Fail Test
Start
Start Direct Connect
Transmitter Test N
Done
Run PC-based Throughput Test
Pass?
Troubleshoot Feed Lines
Base Station Coverage
Interference N
Good Through-
put?
Troubleshoot Backhaul
N
Y
Y
Y
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Troubleshooting Guide and Coverage Mapping App Note
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LTE Measurements Training Course LTE Theory and Measurements Using the BTS & Spectrum Masters
An intense two-day instructor led training course that focuses on LTE Base Station measurements, helping you reduce operating expenses by enhancing the skill set of your employees. Available at your site or at a nearby Anritsu facility.
Who Should Attend Cell Technicians System Performance Engineers/Field Engineers Base Station OEMs Site Managers BTS Installers
How You Will Benefit Spectrum Analysis Basics - how to use a spectrum analyzer, identifying signal types, common
measurements such as Occupied Bandwidth, ACLR and Channel Power. Includes extensive labs. Digital Modulation Theory – PSK and QAM, EVM, Bit error rate vs. CINR, Orthogonal FDM theory RF Propagation & LTE Air Interface theory– time and frequency structure, air interface, MIMO, diversity,
physical channels description, 3GPP Transmitter performance specs, frequency reuse, C/I vs. co-channel reuse. Includes extensive labs.
LTE Downlink Quality Measurement – Channel Power, Occupied Bandwidth, Spectral Emission mask, EVM, Constellation, Frequency error, OTA measurements such as Multiple-signal inventory, dominance, and modulation quality. Includes extensive labs.
LTE Pass/Fail Measurements - Learn what is critical and what is acceptable.
See http://www.us.anritsu.com/training/ for more info.
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Question & Answers
Thank you for your participation
More information available at
www.us.anritsu.com
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