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LTE e-NodeBFieldtesting
Franz-Josef DahmenAnritsu GmbH22. April 2010
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Agenda
� LTE Technology Overview� LTE Specifications� LTE Terms� LTE vs. 3G Comparison� LTE RF Measurements� LTE Modulation Measurements� LTE Over-the-Air (OTA) Measurements
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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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Duplex modes� FDD: Simultaneous downlink/uplink transmission in separate frequency
bands� Paired spectrum required� Used in all commercial cellular systems
� TDD: Non-overlapping downlink/uplink transmission in the same frequency band� Possibility for deployment in single (unpaired) spectrum� Need for tight inter-cell synchronization/coordination� Reduced coverage due to non-continuous transmission (duty cycle < 1)
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E-UTRA Frequency Bands
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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
SubframeFrame10 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
DLsymbN ����������
�� ������������ slotT
0=l 1DLsymb −= Nl
RB
scD
LR
BN
N×
RB
scN
RBsc
DLsymb NN � ���� ����
� ���� � � � ���
� ���� � � � �� ),( lk
0=k
1RBsc
DLRB −= NNk
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Compatible Bandwidths������������������� ������� �������
20 MHz BW
5 MHz BW
1.4 MHz BW
10 MHz BW
15 MHz BW
3 MHz BW
���
����� �
10075502515 6Transmission bandwidth configuration NRB
20151053 1.4Channel bandwidth BWChannel [MHz]
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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
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3GPP LTE SpecificationsThe specifications for the LTE E-UTRA and E-UTRAN are containedin the 36 series of Release 8, divided into the following sections:
� 36.100 series covering radio specifications and evolved Node B (eNB) � 3GPP TS 36.141 CT Specification e-NodeB� 3GPP TS 36.521 CT Specification UE
� 36.200 series covering layer 1 (physical layer) specifications� 36.300 series covering layer 2 and 3 air interface signaling specifications� 36.400 series covering network signaling specifications� 36.500 series covering user equipment conformance testing� 36.800 and 36.900 series, which are technical reports containing background
http://www.3gpp.org
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Test Model for Transmitter Characteristics3GPP TS 36.141 CT Specification e-NodeB
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LTE terms similarity to 3G termsLTE W-CDMA
� RS (Reference Signal) CPICH
� P-SS (Primary Synchronizing Signals) P-SCH
� S-SS (Secondary Synchronizing Signals) S-SCH
� PCFICH (Physical Control Format Indicator Channel) NA
� PBCH (Physical Broadcast Channel) BCCH
� PHICH (Physical Hybrid ARQ Indicator Channel) NA
� PDCCH (Physical Downlink Control Channel ) P/S-CCPCH & PICH
� PDSCH (Physical Downlink Shared Channel) Traffic DCHs
� EVM (Signal Quality) EVM
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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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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
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Tx1 / Rx1
Tx2 / Rx2
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Key Performance Indicators vs. LTE Field Measurement
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LTE Field Measurement vs. eNodeB Field Replaceable Units
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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
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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,������ �������� 7������
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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
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� 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,������ �������� 7������
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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
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Troubleshooting Guide and Coverage Mapping App Note
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� Thank you for your participation
� More information available at
www.anritsu.com
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