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1 of 30 LTE e-NodeB Fieldtesting Franz-Josef Dahmen Anritsu GmbH 22. April 2010

Anritsu LTE E-Node B Field Testing

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Page 1: Anritsu LTE E-Node B Field Testing

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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

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

���

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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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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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