LTE TDD What to Test andLTE TDD What to Test and · PDF fileLTE TDD What to Test andLTE TDD What to Test and Why ... Instantaneous downlink peak data rate: ... • SC-FDMA operates

LTE TDD What to Test and WhyLTE TDD What to Test and Why

© 2012 LitePoint Corp.© 2 0 1 2 L i t e P o i n t , A T e r a d yn e C o m p a n y. Al l r i g h t s r e s e r ve d .

Agenda

• LTE Overview• LTE Measurements• Testing LTE TDD – Where to Begin?• Building a LTE TDD Verification Plan• Optimizing a LTE TDD Verification PlanOptimizing a LTE TDD Verification Plan

© 2012 LitePoint Corp. •32

Why LTE? – Something for Everyone

For the user..Higher Performance (Data Rate)

Instantaneous downlink peak data rate:150 Mbit/s in a 20MHz downlink spectrum (5 bit/s/Hz)

Instantaneous uplink peak data rate:75 Mbit/ i 20MH li k t (2 5 bit/ /H )75 Mbit/s in a 20MHz uplink spectrum (2.5 bit/s/Hz)

For the service provider…Cell capacity – more users per cell

up to 200 active users per cell (5 MHz) (i.e., 200 active data clients)

1st all-data network: packet-switchedSimplifies network architecture – no difference between voice & data


Key Features of LTE

Multiple access scheme• Downlink (DL): OFDMA enables maximum spectrum utilization by the base station • Uplink (UL): SC-FDMA relaxes the linearity requirements for the handsetUplink (UL): SC FDMA relaxes the linearity requirements for the handset

Multiple Uplink Transmission Modes• FDD: balanced DL / UL data traffic by using different channels• TDD: enables asymmetric DL / UL capacity, sharing a single channely p y, g g

Adaptive Modulation and CodingLTE dynamically changes modulation based on channel conditions to optimize its capacity• DL modulations: QPSK, 16QAM, and 64QAM• UL modulations: QPSK and 16QAM

Channel Bandwidth Scalability Scalable channel bandwidth allows efficient operation in differently-sized allocated spectrum bands

Multiple Antenna Technology – MiMoMultiple Antenna techniques enables higher data rate, improve network reliability and data capacity


OFDM meets Cellular…

• LTE is the first cellular standard to use OFDMA modulation- Combining time and frequency multiplexing, enabling multiple users to

operate in a single time slotoperate in a single time slot

OFDMA

•OFDM Modulation


OFDMA Highlights• LTE uses OFDMA for the downlink

- Uses a large number of narrow sub-carriers for multi-carrier transmission

- “Resource blocks” and “elements”•Each resource block and element is defined in “frequency” and “time” (1 block = 180 kHz; 0.5 ms)

Dynamically assigns these resource blocks to- Dynamically assigns these resource blocks to LTE users, thus improving spectrum utilization

- Subcarrier spacing – 15 kHz compared to 312 .5 kHz for WLAN

•The basic LTE downlink physical resource can be seen as a time-frequency grid:


SC-FDMA

• The LTE uplink transmission scheme based on a pre-coded version of OFDMA known as SC-FDMA (Single Carrier Frequency Division Multiple Access).

• SC-FDMA operates with a lower Peak to Average Power Ratio (PAPR) than OFDM- High PAPR requires expensive and inefficient power amplifiers

• SC-FDMA reduces the linearityrequirement for power amplifier

• Two LTE UL transmission modes: - FDD - TDD


LTE-FDD & LTE-TDD

FDD• downlink and uplink traffic is transmitted simultaneously at separate carrier frequencies• is the preferred mode by most cellular systems wherever paired spectrum is available –• is the preferred mode by most cellular systems, wherever paired spectrum is available –

easy transition from existing 3G networks

TDD • transmission in uplink and downlink is at the same carrier frequency• is a good option where spectrum (carriers) availability is lower• is necessary when pair spectrum is not available

FDD

TDD fDL

fUL fDL/UL

© 2012 LitePoint Corp.

time time

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LTE-FDD vs. LTE-TDD

• The two versions of LTE are actually quite similar• The only differences are in the physical layer, enabling support of both

TDD and FDD with a single chipset- All major LTE chipset vendors have released chipsets that support both FDD

and TDD

Parameter LTE-FDD LTE-TDDPaired spectrum Requires spectrum pairs – TX

and RX on different frequenciesNo spectrum pair required – TX and RX on the same frequency

UL / DL asymmetry Data capacity determined by spectrum allocations

Possible to dynamically changeUL / DL to meet capacity demandspectrum allocations UL / DL to meet capacity demand

Guard interval impact on data capacity

Increasing guard interval (due to distance from base station) does not impact data capacity

Increasing guard interval (due to distance from base station) reduces data capacity


•LTE Growth – China and LTE-TDD will play a key rolerole

It i t d th t b 2016 Chi M bil ill t 15 t f th t t l LTE

•2011 •2016

•It is expected that by 2016, China Mobile will represent over 15 percent of the total LTE market, with its TDD LTE deployment.

© 2012 LitePoint Corp. •40•Source: Signals and Systems Telecom 4/2012

New Challenges in LTE – More Bands

Band Frequency Range

ChannelBandwidths

Mode

33 to 41 <2.69 GHz 1.4, 3, 5, 10, 15 20 MH TDD33 to 69 G 15, 20 MHz

© 2012 LitePoint Corp.•More bands means more test time

•41

New Challenges in LTE – More Configurations• LTE has many configurations to test – more test time

- Per channel…

Modulation RB Config PWR LevelsQPSK 50,0 4QPSK 12,0 4QPSK 12,38 2QPSK 1,0 1QPSK 1,24 1QPSK 1 49 1QPSK 1,49 1

16 QAM 50,0 216 QAM 12,38 216 QAM 12 0 216 QAM 12,0 216 QAM 50,0 164 QAM 50,0 1


•LTE threatens to reduce test throughput… Higher cost test? •42

New Challenges in LTE – More Bandwidth• Spectrum Emission Mask (SEM): 6.6.2.1• Adjacent Channel Leakage Ratio (ACLR): 6.6.2.3

SE M k•SE Mask

•20 MHz Channel•Limit: -25 dB

•25 MHz•25 MHz

•SEM = 70 MHz Total Bandwidth


Testing LTE: Key Requirements

RF Frequency Range• The test equipment must support the frequency bands 698 MHz - 2690 MHz

The test equipment must support handsets with an increasing number of antennas• The test equipment must support handsets with an increasing number of antennas

VSA / VSG Bandwidth• The test equipment must have at least 20 MHz VSA/VSG bandwidthq p

- LTE requires support for six channel bandwidths (from 1.4 to 20 MHz)- With LTE-Advanced, this requirement will become 100 MHz- >70 MHz required for single-shot LTE ACLR & Spectrum Emission Mask testing

MiMo Technology• Support for accurate MiMo testing is necessary in both R&D and MFG

I ti l it i ti l t h lti l VSA / VSG t f DL / UL MIMO i l• In particular, it is essential to have multiple VSA / VSG ports for DL / UL MIMO signal

Transmission SchemesS t t t i i h f d li k d li k (OFDMA SC FDMA)


• Support two transmission schemes for downlink and uplink (OFDMA, SC-FDMA)• Support two transmission modes (FDD and TDD)

•44

Testing LTE TDD: Where to Begin?

• LTE complexity introduces more than 10x configurations to test- Testing every scenario is not practical

• In production, we are looking to validate manufacturing quality

• Goal is to exercise the mobile as much as possible while minimizing test time


Testing LTE TDD: Where to Begin?

• What to test in mobile manufacturing verification:- Physical layer RF measurements- TX power- TX modulation quality- TX frequency- TX / RX timing- RX sensitivity (min / max)

• What NOT to test in mobile manufacturing verification- Software- Digital Design- Redundant (overlapping) tests or configurations


LTE UE Transmitter TestsMeasurement Why is this Important?

TX Power LTE network performance is highly dependent on accurate power controlp

Error Vector Magnitude Primary TX quality measurement – detects distortions that will ultimately degrade accurate transmission of data

Frequency Error Critically important to avoid communication interference

ACLR Ensures that transmission does not interfere with neighboring channels

Occupied Bandwidth Confirms that signal is contained within channel allocation

Spectrum Emissions Mask Ensures that signal in adjacent channels rolls off to minimize interference

Carrier Leakage An indication of mismatch in the I/Q modulator

Transmit Time Mask Verifies UE timing accuracy – particularly important for LTE TDD since the UL/DL are on the same frequency

In-Band Emissions for non-allocated RBs

Ensures that a UE’s assigned RBs (within a channel) do not interfere with the unassigned RBs in the channel


non-allocated RBs interfere with the unassigned RBs in the channel

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•3GPP Measurements

LTE UE Receiver Tests

• TX measurements give direct access to the signal via the UE antenna• Unlike TX measurements RX signal quality issues remain buried until the

Measurement Notes

• Unlike TX measurements, RX signal quality issues remain buried until the signal is fully decoded

RX Bit Error Rate (BER) Fundamental test of a receiver’s ability to decode the inbound signal. Typically performed at both min & max RX input powerReceive signal strength is a parameter often measured as part of calibration Since the initial TX power level is calculated perRX Sensitivity (RSSI) of calibration. Since the initial TX power level is calculated per the measured RSSI, accuracy of this measurement directly impacts UE power transmission

•3GPP Measurements


LTE Test Plan Development

• Several different approaches to develop a test plan:

- Use the 3GPP standard’s recommendations

U th IC f t ’ d ti- Use the IC manufacturer’s recommendations

- Use historical data from similar devices

- Apply some reasonable logic to look for likely failure modes and apply 3GPP spec conditions


Building a LTE TDD TX Verification Test PlanPer-Band / Per-ChannelPer Band / Per ChannelA “reasonable” LTE test plan covered in 21 configurationsShowing config 1-11

Parameters 1 2 3 4 5 6 7 8 9 10 11Test Configuration

•Varies in RB Offset for RB = 1, QPSK channel

•Varies TX Power for RB = 12 QPSK channel

TX Power +23 +23 +23 +23 +3.2 -30 -40 +23 +3.2 -30 -40Modulation QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSKRB 1 1 1 12 12 12 12 12 12 12 12RB Offset 0 24 49 0 0 0 0 38 38 38 38DL Power -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57Measurements 1 2 3 4 5 6 7 8 9 10 11Measurements 1 2 3 4 5 6 7 8 9 10 11PowerEVMEVM FlatnessFrequency AccuracyCarrier FeedthroughTX Time Mask

•RB Offset Extremes

TX Time MaskOccupied BandwidthACLRSEMIn-Band Emissions forNon-Allocated RBs


Building a LTE TDD TX Verification Test PlanPer-Band / Per-ChannelPer Band / Per ChannelA “reasonable” LTE test plan covered in 21 configurationsShowing config 12-21

•Min / Max •Min / Max •Min / Max

Parameters 12 13 14 15 16 17 18 19 20 21Test Configuration

Power•for QPSK RB = 50

•Tests Absolute Power Setting

Power for 16 QAM•RB = 12

Power for 16 QAM•RB = 50

TX Power +23 -40 +6.4 -5.6 +23 -40 +23 -40 +23 -40Modulation QPSK QPSK QPSK QPSK 16QAM 16QAM 16QAM 16QAM 16QAM 16QAMRB 50 50 50 50 12 12 12 12 50 50RB Offset 0 0 0 0 0 0 38 38 0 0DL Power -57 -57 -57 -57 -57 -57 -57 -57 -57 -57Measurements 12 13 14 15 16 17 18 19 20 21Measurements 12 13 14 15 16 17 18 19 20 21PowerEVMEVM FlatnessFrequency AccuracyCarrier Feedthrough

•RB Offset Extremes

TX Time MaskOccupied BandwidthACLRSEMIn-Band Emissions for Non Allocated RBs


Non-Allocated RBs

Optimizing the TX Test Plan

•Configurations 1, 3, 12, & 20 test the extremes of modulation and RB allocations / offsets•Configuration 4 is a “typical” use case

Parameters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21TX Power +23 +23 +23 +23 +3.2 -30 -40 +23 +3.2 -30 -40 +23 -40 +6.4 -5.6 +23 -40 +23 -40 +23 -40Modulation QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK QPSK 16QAM 16QAM 16QAM 16QAM 16QAM 16QAMRB 1 1 1 12 12 12 12 12 12 12 12 50 50 50 50 12 12 12 12 50 50RB Offset 0 24 49 0 0 0 0 38 38 38 38 0 0 0 0 0 0 38 38 0 0

Test Configuration

DL Power -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57Measurements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21PowerEVMEVM FlatnessFrequency AccuracyCarrier FeedthroughTX Time MaskOccupied BandwidthOccupied BandwidthACLRSEMIn-Band Emissions for Non-Allocated RBs

No Need for Mid- Covered by Already Tested Band Covered by Can be covered by any absolute Covered by Config 20 &

Channel Offset Config 21 Edges in Configs 1 & 3 Config 21 by any absolute power setting 21, do not need mid-RB

•Configurations we


definitely want to keep

Condensed Test Plan• Reduced to 7 TX configurations• Added RX tests• Increases number of measurements while reducing test time• Increases number of measurements while reducing test time

Parameters T1 T2 T3 T4 T5 T6 T7TX Power +23 +23 +23 +23 +3.2 +23 -40Modulation QPSK QPSK QPSK QPSK QPSK 16QAM 16QAM

Test Configuration

RB (UL / DL) 1 1 12 50 12 12 50RB Offset 0 49 24 0 24 0 0DL Power -57 -57 -57 -94 -57 -25 -60Measurements TX1 TX2 TX3 TX4 TX5 TX6 TX7Power MPR MPR MPRPower MPR MPR MPREVMEVM FlatnessFrequency AccuracyCarrier FeedthroughTX Time MaskTX Time MaskOccupied BandwidthACLRSEMIn-Band Emissions forN All t d RB


Non-Allocated RBsMeasurements RX1 RX2 RX3RX BERRX Level

LTE TDD Manufacturing Test

• LTE increases test complexity 5 to 10X- More measurements, more antennas, wider bandwidth, higher performanceg p- IQxstream’s unique architecture makes LTE test simple and fast

• Test plan development for LTE needs to focus on exercising the mobileTest plan development for LTE needs to focus on exercising the mobile device with the minimum test time

A test plan can be created to maximize• A test plan can be created to maximizethe coverage of the device by using the test equipment in an efficient manner- Number of configurations take more test time than number of tests- Number of configurations take more test time than number of tests- Scale test plan to multi-DUT through turnkey non-signaling solutions - No sacrifice in product quality with shorter per-DUT test times


Documents

LTE TDD What to Test andLTE TDD What to Test and · PDF fileLTE TDD What to Test andLTE TDD What to Test and Why ... Instantaneous downlink peak data rate: ... • SC-FDMA operates