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1 of 30 LTE Base Station Testing Basics Emilio Franchy Senior Product Manager March 31 st , 2010

LTE Base Station Testing Basics

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Page 1: LTE Base Station Testing Basics

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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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