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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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LTE Base Station Testing BasicsEmilio Franchy Senior Product Manager March 31st, 2010

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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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LTE Basic Technologies OFDMA

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

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What is OFDMA?Different users

Orthogonal Frequency Division Multiple AccessAssigns 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


Allows many users to be supported

At variable bit rate Scheduling many users With different quality of service Complex

Time System Overhead4 of 30

LTE Physical Channel Names (Downlink)


Reference Signal Similar to Pilots in 802.11 Subcarrier varies with MIMO transmitter & Cell ID Primary & Secondary Synchronizing Signals Contains cell ID Physical Control Format Indicator Channel How many symbols are used for PDCCH







Physical Broadcast Channel

PHICH (not shown)

Physical Hybrid ARQ Indicator Channel Sends Acknowledgements or Not Acknowledgements Part of Error Protection system for the uplink Physical Downlink Control Channel Whos assigned to what resources? Physical Downlink Shared Channel Where all the user data goesShared




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LTE Frame Structure (FDD)



10 ms 1 ms 10 per frame


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 ms6 of 30

Resource Blocks

Resource Block (RB)

12 subcarriers * 1 slot

1 slot = 0.5 ms 2 slots/subframe 10 subframes/frame 1 frame = 10 ms



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Compatible BandwidthsTime1.4 MHz BW 3 MHz BW

Control Channels in center of channel BW

5 MHz BW

10 MHz BW

15 MHz BW

20 MHz BW


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MIMO (2X2 examples)

MIMO = Multiple Input, Multiple Output MIMO (Transmit Diversity)

Multi-beam antennas

Dual 2X2 (eNodeB Tx) 4X2 (UE Rx) Quad 4X4 All signal paths

MIMO Tx Diversity

Data stream repeated

Increase coverage

MIMO (Spatial Multiplexing)

Different data streams Higher data rate Relies on Multi-path

MIMO Spatial Multiplexing

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LTE terms similarity to 3G termsLTE

CDMAPilot Sync NA NA Paging NA Paging Traffic Rho Freq Accy


RS (Reference Signal) P-SS (Primary Synchronizing Signals) S-SS (Secondary Synchronizing Signals) PCFICH (Physical Control Format Indicator Channel) PBCH (Physical Broadcast Channel) PHICH (Physical Hybrid ARQ Indicator Channel) PDCCH (Physical Downlink Control Channel ) PDSCH (Physical Downlink Shared Channel) EVM (Signal Quality) Frequency Accuracy

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LTE Measurements


W-CDMA Measurements



Channel Spectrum Power vs. Time Spectral Emission Mask ACLR

Channel Spectrum Power vs. Time Spurious Emission ACLR

Modulation Quality


Resource Element Power Control & Traffic Channel Power Spectral Flatness Constellation

CDP (Code Domain Power)

Control & Traffic Channel Power




Sync Signal Scan Channel Power Monitor

Pilot Scan Multipath

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LTE Measurements


CDMA MeasurementsRF


Channel Spectrum Power vs. Time Operating Band Unwanted Emissions (Spectrum Emission Mask) ACLR

Channel Spectrum Power vs. Time Spurious Emission ACPR

Modulation Quality


Resource Element Power Control & Traffic Channel Power Spectral Flatness Constellation

CDP (CDP MAC/Data, Graph/Table) Control Channels



Sync Signal Scan Channel Power Monitor

Pilot Scan Multipath

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eNodeB : Traditional installAir Interface Interference GPS Antenna Antennas

Traditional configuration

2x2 MIMO

2 Radios per sector

Extreme weather Key HW in shelter Traditional Testing Transmitter Antenna & jumper cables LTE signal quality

Coaxial/Waveguide RF Cable Jumper if close to antenna

Test Needs

Traditional TMAs Coaxial Feedline to TMA

Direct Connect

Fiber Optic Baseband Cable with DC Power short run Backhaul GigE

Tx1 / Rx1

Use Test Port Interference Coverage Backhaul Fiber

Directional Coupler / Test PortChannel Cards Power Supply

Radio Server

Tx2 / Rx2

Remote Radio Heads located close to Base Band Radio

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Key Performance Indicators vs. LTE Field MeasurementKey Performance Indicators vs. TestSync Power RS Power Occupied BW, ACLR, & SEM EVM (pk) EVM Freq Error Rx Noise Floor OTA EVM

Call/Session Blocking Power shortage Resource Block shortage UL Interference Call/Session Drop Radio Link Timeout UL Interference DL Interference x x x x x x x x x x x x x x x x x x x x xx xx xx

x = probable, xx = most probable

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LTE Field Measurement vs. eNodeB Field Replaceable UnitsTest vs. BTS Field Replaceable UnitsSync Power RS Power Occupied BW Adjacent Channel Leakage Ratio (ACLR) Spectral Emission Mask (SEM) Error Vector Magnitude Peak (EVM pk) Error Vector Magnitude (EVM) Frequency Error OTA EVM xx x x x x x Freq Ref Signal Generation x x x x x x x MCPA xx xx xx x x xx x x x xx xx xx x x Filters Antenna x x Antenna Down Tilt

x = probable, xx = most probable

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LTE (RF) Occupied Bandwidth

Guideline Direct Connect

Per defined LTE bandwidth

1.4, 3.0, 5.0, 10, 15, 20 MHz


Leads to interference with neighboring carriers Dropped calls/data sessions Low capacity

Common Faults

Tx filter MCPA Channel cards Antennas

Occupied Bandwidth

A measurement of the spectrum used by the carrier The occupied bandwidth contains 99% of the signals RF power

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LTE Adjacent Channel Leakage Ratio (ACLR)

Guideline Direct Connect

-45 dBc for the adjacent channels -45 dBc for the alternate channels


Leads to interference with neighboring carriers Low capacity Blocked calls/data sessions

Common Faults

Tx filter MCPA Channel cards Cable connectors

ACLR (single-carrier displayed)

Measures how much of the carrier gets into neighboring RF channels Checks the closest (adjacent) and the next closest (alternate)

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LTE Spectral Emission Mask (SEM)

Guideline Direct Connect

Must be below mask Received power levels matter so be sure to use the right external attenuation value


Interference with neighboring carriers Legal liability Low signal quality

Common Faults

Spectral Emission Mask

Check amplifier output filtering Look for intermodulation distortion Look for spectral re-growth

SEM checks closer to the signal than ACLR does Regulators may require regular measurements of spectral emissions

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LTE Error Vector Magnitude (EVM)

Guidelines Direct Connect

QPSK - 17.5% 16 QAM 12.5% 64 QAM 8% dropped calls/data sessions low data rate low sector capacity blocked calls/data sessions distortion in the channel cards Power amplifier filter antenna system


Common Faults


The ratio of errors, or distortions, in the actual signal, compared to a perfect signal EVM applies to the entire signal

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LTE Control Channels


Per RF Engineering 0.5 dB 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

Control Channels

Improper settings in the eNodeB

Verifies Control Channel power is set correctly

Signal processing Control section

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LTE Frequency Error

Guideline OTA with GPS

0.05 ppm (wide area BS) 0.1 (local area BS) 0.25 (home BS) Calls will drop when mobiles travel at higher speed In some cases, cell phones cannot hand off into, or out of the cell Reference frequency Frequency distribution system GPS, if used Backhaul


Common Faults

Frequency Error

Checks to see that the carrier frequency is precisely correct Regulatory requirement in many countries

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eNode-B ; Remote Radio UnitAir Interface Interference GPS Antenna Antennas

Single Sector

2x2 MIMO

RF Cable Jumper if close to antenna

2 Radios per sector Tx1 has Sync Signal Tx2 may have Sync Signal Test Needs

Remote Radio Heads Ideally located close to antenna Fiber Optic Baseband Cable with DC Power

Transmitter Antenna & jumper cables LTE signal quality

Directional Coupler / Test Port

OTA if No Access to RRU

Backhaul GigE .

Tx1 / Rx1Channel Cards Power Supply

Interference Coverage Backhaul Fiber

Tx2 / Rx2

Radio Server

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LTE Synchronization Signal Scanner

Guideline Direct Connect

3 or fewer codes Within 10 dB of dominant code Over 95% of the coverage area


Low data rate Low capacity Excessive soft handoffs

Common faults

Antenna down tilt Scrambling code power Illegal repeaters

Downlink Coverage Quality

Synchronization Signal Power

Indicates which sectors are present at the current location Too many strong sectors creates pilot pollution

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LTE OTA Modulation Quality Testing

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 OTA Scanner validates location

Valid OTA Location

Dominance >10 dB

If Pass becomes sweet spot

OTA Modulation Quality

Note GPS location Becomes location for future OTA Modulation Quality Testing Record and create OTA Pass/Fail limits

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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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 siteStart

Found Valid OTA spot? Y Run OTA or Direct Connect Pass/Fail Test Start Direct Connect Transmitter Test

Find valid Over-the-Air (OTA) location

If not, direct connect Checks Feed Line Quality, if OTA Checks RF Quality Checks Modulation Quality Use PC data card DONE Feed lines and antenna system Base station field replaceable units Downlink Coverage issues Interference problems Backhaul bit-error-rates


Run one-step Pass/Fail Test

Troubleshoot Feed Lines Base Station Coverage Interference

Test data throughput

Pass? N Y Run PC-based Throughput Test

If everything passes

If not troubleshoot

Good Throughput? Y Done


Troubleshoot Backhaul

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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 BenefitSpectrum 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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