Concepts of 3GPP LTE RF Parametric Tests

Renaud DuverneWireless R&D Market

Initiative Manager

© Copyright 2009 Agilent Technologies, Inc.

Agilent LTE Book

www.agilent.com/find/ltebook

www.amazon.com In print April 16th

The first LTE book dedicated to design and measurement

30 Authors460 pages

Book overview

Chapter 1 LTE Introduction

Chapter 2 Air Interface Concepts

Chapter 3 Physical Layer

Chapter 4 Upper Layer Signaling

Chapter 5 System Architecture Evolution

Chapter 6 Design and Verification Challenges

Chapter 7 Conformance Test

Chapter 8 Looking Towards 4G: LTE-Advanced

3GPP standards evolution (RAN & GERAN)

1999

2010

Release Commercial introduction

Main feature of Release

Rel-99 2003 Basic 3.84 Mcps W-CDMA (FDD & TDD)

Rel-4 Trials 1.28 Mcps TDD (aka TD-SCDMA)

Rel-5 2006 HSDPA

Rel-6 2007 HSUPA (E-DCH)

Rel-7 2008+ HSPA+ (64QAM DL, MIMO, 16QAM UL). Many small features, LTE & SAE Study items

Rel-8 HSPA+ 2009LTE 2010+

LTE Work item – OFDMA air interfaceSAE Work item New IP core networkEdge Evolution, more HSPA+

Rel-9 2011+ UMTS and LTE minor changes

Rel-10 2012+ LTE-Advanced (4G)

2005 2006 2007 2008 2009 2010

First GCF UE certification

Rel-7 Feasibility study

Rel-8 Test development

2011 2012

Rel-8 Specification development

GCF Test validation

First Trial Networks

FirstCommercial

NetworksFurther

Commercial Networks

LSTI Proof of Concept

LSTI IODT

LSTI IOT

LSTI Friendly Customer Trials

LTE timeline

LSTI = LTE/SAE Trial Initiative GCF = Global Certification Forum

UE categories

• In order to scale the development of equipment, UE categories have been defined to limit certain parameters

• The most significant parameter is the supported data rates:

UE Category

Max downlink data rate Mbps

Number of DL transmit data streams

Max uplink data rate Mbps

Support for uplink 64QAM

1 10.296 1 5.18 No

2 51.024 2 25.456 No

3 102.048 2 51.024 No

4 150.752 2 51.024 No

5 302.752 4 75.376 Yes

The UE category must be the same for downlink and uplink

What is OFDM?•Orthogonal Frequency Division Multiplexing•High data rate Tx using lower symbol rate on tens to thousands of closely spaced overlapping narrowband sub-carriers simultaneously•Applications in:

– Broadcasting: Digital TV (DVB-T/H) and Radio (DAB)– Wireless PAN – Certified Wireless USB™ based on WiMedia

Alliance OFDM technology– Wireless LAN – WiFi™ based on IEEE 802.11a/b/g/n – Wireless MAN – Fixed and Mobile WiMAX™ based on IEEE

802.16d and 802.16e – Adopted for 3.9G (LTE) cellular air interface

What is OFDM?- High Data Rate vs. Lower Symbol Rate

Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 64QAM = 12 MSym/sec

1 symbol = one point in time1 point in time = 1 symbol

SCM: OFDM:

Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 48 carriers= 1.5 Mbits/sec @ 64QAM = 250 kSym/sec

1 symbol = 1 point in frequency and time1 point in time = ~meaningless

1 Sym = .083 usec 1 Sym = 4.0 usec

This is a sample;FFT(64 samples) gives

64 freq bins (48 carriers + 4 pilots + 12 zeros)

This is a symbol

= 6 bits

What is OFDM? – Orthogonals Signals?

Signal structure: Many closely spaced individual carriers

Carrier spacing insures orthogonality, i.e. Carrier spectrum = Sin (x)/X shape Carrier placement = Sin (x)/X nulls

BW = #sub-Carriers x Spacing

Advantages of OFDM: Excellent immunity to multi-path distortionExcellent tolerance of single frequency

interferer

Agenda• List of LTE physical layer transmitter tests• LTE modulation quality test requirements

– Downlink– Uplink

• Modulation quality signal analysis and troubleshooting techniques

• Appendix – LTE physical layer RF measurements

FDD and TDD Frame StructuresFrame Structure type 1 (FDD) FDD: Uplink and downlink are transmitted separately

#0 #2 #3 #18#1 ………. #19One subframe = 1ms

One slot = 0.5 msOne radio frame = 10 ms

Subframe 0 Subframe 1 Subframe 9

Frame Structure type 2 (TDD)

DwPTS, T(variable)

One radio frame, Tf = 307200 x Ts = 10 msOne half-frame, 153600 x Ts = 5 ms

#0 #2 #3 #4 #5

One subframe, 30720 x Ts = 1 ms

Guard period, T(variable)

UpPTS, Ｔ (variable)

•5ms switch-point periodicity: Subframe 0, 5 and DwPTS for downlink, Subframe 2, 5 and UpPTS for Uplink•10ms switch-point periodicity: Subframe 0, 5,7-9 and DwPTS for downlink, Subframe 2 and UpPTS for Uplink

One slot, Tslot =15360 x Ts = 0.5 ms

#7 #8 #9

For 5ms switch-point periodicity

For 10ms switch-point periodicity

OFDM symbols (= 7 OFDM symbols @ Normal CP)

The Cyclic Prefix is created by prepending each symbol with a copy of the end of the symbol

160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)

1 frame= 10 sub-frames= 10 ms

1 sub-frame= 2 slots= 1 ms

1 slot= 15360 Ts= 0.5 ms

0 1 2 3 4 5 6etc.

CP CP CP CP CPCPCP

P-SCH - Primary Synchronization Channel S-SCH - Secondary Synchronization Channel

PBCH - Physical Broadcast Channel

PDCCH -Physical Downlink Control Channel

PDSCH - Physical Downlink Shared Channel

Reference Signal – (Pilot)

DLsymbN

#0 #1 #8#2 #3 #4 #5 #6 #7 #9 #10 #11 #12 #19#13 #14 #15 #16 #17 #18

Downlink frame structure type 1

10 2 3 4 5 6 10 2 3 4 5 6

64QAM16QAM QPSK

Downlink mappingP-SCH - Primary Synchronization Channel S-SCH - Secondary Synchronization Channel

PBCH - Physical Broadcast Channel

PDCCH -Physical Downlink Control Channel

PDSCH - Physical Downlink Shared Channel

Reference Signal – (Pilot)

Uplink Frame Structure & PUSCH mapping

10 2 3 4 5 6

#0 #1 #8#2 #3 #4 #5 #6 #7 #9 #10 #11 #12 #19#13 #14 #15 #16 #17 #18

1 frame

10 2 3 4 5 6

1 sub-framePUSCH - Physical Uplink Shared Channel

Demodulation Reference Signal for PUSCH

• • • • •

OFDM symbols (= 7 SC-FDMA symbols @ Normal CP)

The Cyclic Prefix is created by prepending each symbol with a copy of the end of the symbol

160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)

1 slot= 15360 Ts= 0.5 ms

0 1 2 3 4 5 6etc.

CP CP CP CP CPCPCP

ULsymbN

PUSCH

Zadoff-ChuPUSCH ≥ 3RB

QPSKPUSCH < 3RB

or PUCCH

Demodulation Reference Signal (for PUSCH)

PUCCH

Demodulation Reference Signalfor PUCCH format 1a/1b

64QAM QPSK BPSK(1a) QPSK(1b)16QAM

TheUplink

Physical Layer definitionsFS Type 2 Downlink/Uplink assignment

DwPTSGP

UpPTS DwPTSGP

UpPTS

#0 #2 #3 #4 #5 #7 #8 #9

DwPTSGP

UpPTS

5 ms Switch-point periodicity

10 ms Switch-point periodicity

#1 #6

#0 #2 #3 #4 #5 #7 #8 #9#1 #6

ConfigurationSwitch-point periodicity

Subframe number

0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 5 ms D S U U U D S U U D

Downlink

P-SCH

S-SCH

PBCH

PDCCH

PDSCH

Reference Signal DL/UL subframe

Uplink

Reference Signal(Demodulation)

PUSCH

UpPTS

Physical Layer definitionsFrame Structure (TDD 5ms switch periodicity)

10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6

DwPTS(3-12 symbols)

UpPTS(1-2 symbols)

NsymbDL OFDM symbols (=7 OFDM symbols @ Normal CP)

Cyclic Prefix

160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)

1slot = 15360

0 1 2 3 4 5 6

Ts = 1 / (15000x2048)=32.552nsec1 slot

1 subframe

GP(1-10 symbols)

Downlink

P-SCH

S-SCH

PBCH

PDCCH

PDSCH

Reference Signal

Physical Layer definitions Frame Structure (TDD 10ms switch periodicity)

10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6DwPTS

NsymbDL OFDM symbols (=7 OFDM symbols @ Normal CP)

Cyclic Prefix

160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)

1slot = 15360

0 1 2 3 4 5 6

Ts = 1 / (15000x2048)=32.552nsec1 slot

DL/UL subframe

Uplink

Reference Signal(Demodulation)

PUSCH

UpPTS

Orthogonal Frequency Division MultiplexingLTE’s downlink and some uplink transmissions

• OFDM already widely used in non-cellular technologies only recently usable in cellular due to improved processing power

• OFDM advantages– Wide channels are more resistant to fading and OFDM equalizers are much

simpler to implement than CDMA

– Almost completely resistant to multi-path due to very long symbols

– Well suited to MIMO with easy matching of signals to uncorrelated RF channels

– It’s use of lower rate modulated subcarriers makes it scalable in terms of B/W

• OFDM disadvantages– Sensitive to frequency errors and phase noise due to close subcarrier spacing

– Sensitive to Doppler shift which creates interference between subcarriers

– Pure OFDM creates high PAR which is why SC-FDMA is used on UL

– More complex than CDMA for handling inter-cell interference at cell edge

Single Carrier FDMA:The new LTE uplink transmission scheme

• SC-FDMA is a new concept in transmission and it is important to understand how it works

• When a new concept comes along no single explanation will work for everyone

• To help put SC-FDMA in context we will use six different ways of explaining what SCFDMA is all about

• In summary: SC-FDMA is a hybrid transmission scheme combining the low peak to average (PAR) of single carrier schemes with the frequency allocation flexibility and multipath protection provided by OFDMA

Explaining SC-FDMA• The first explanation of SC-FDMA comes from the LTE physical layer “study phase” report

(3GPP TR 25.814) which had the following diagram:

• Colour coding has been added here to show the change from time to frequency and back again. This diagram is not in the final specifications.

• The processing steps explain why SC-FDMA is sometimes described in the specs as Discrete Fourier Transform Spread OFDM (DFT-SOFDM)

TR 25.814 Figure 9.1.1-1 Transmitter structure for SC-FDMA.

DFT Sub-carrier

Mapping

CP insertion

Size-NTX Size-NFFT

Coded symbol rate= R

NTX symbols

IFFT

Frequency domain Time domainTime domain

Explaining SC-FDMA• The three key processing steps shown in 25.814 are formally defined in the physical

layer specification 36.211 v8.1.0 as:

• Although essential for detailed design, formal definitions like these do not provide insight to most people of the underlying concepts

12/

2/

212,

RBsc

ULRB

RBsc

ULRB

s,CP)(

NN

NNk

TNtfkjlkl

leats

1,...,0

1,...,0

)(1

)(

PUSCHscsymb

PUSCHsc

1

0

2

PUSCHsc

PUSCHsc

PUSCHsc

PUSCHsc

PUSCHsc

MMl

Mk

eiMldM

kMlzM

i

M

ikj

PUCCHRBVRBVRB

PUCCHRBsPRBsPRB

s

s

sbsbRB

sbRBVRB

sbRB

sbRBhopVRB

sbsbRB

sbRBhopVRB

sPRB

~)(~)(

hopping subframeintra

hopping subframeinter2

enabled mirroringmodmod~21~disabled mirroringmod~

)(~

Nnn

Nnnnn

n

ni

NNNnNNifn

NNNifnnn

DFT

Subcarrier mapping

IFFT

Comparing OFDMA and SC-FDMAQPSK example using M=4 subcarriers

The following graphs show how a sequence of eight QPSK symbols is represented in frequency and time

15 kHzFrequency

fc

V

Time

OFDMA

sym

bol

OFDMA

sym

bol

CP

OFDMAData symbols occupy 15 kHz for

one OFDMA symbol period

SC-FDMAData symbols occupy M*15 kHz for

1/M SC-FDMA symbol periods

60 kHz Frequency

fc

V

Time

SC-FDM

A

sym

bol

SC-FDM

A

sym

bol

CP

1, 1 -1,-1 -1, 1 1, -1 1,1 1, -1 -1,1 -1,-1

1,1-1,1

1,-1-1,-1

I

Q Time

Page 24

Map data to constellation

Generate time domain

waveformM databits in

Perform M-point DFT (time to freq)

Map symbols to sub-carriers

Perform N-point IFFT

N > M

Upconvert and transmit

De-map constellation

to data

Generate constellation

Perform M-point IDFT(freq to time)

De-map sub-carriers to symbols

Perform N-point DFT

N > M

Receive and downconvert

Time domain Time domainFrequency domain

M databits out

Simplified model of SC-FDMA and OFDMA signal generation and reception

Unique to SC-FDMA Common with OFDMA

SC-FDMA and OFDMA signal generation and reception

Concepts of LTE and LTE-Advanced

Moray Rumney16th March 2009

Comparing OFDMA and SC-FDMAPAR and constellation analysis at different BW

15 kHzFrequency

fc

V

Time

OFDMA

sym

bol

OFDMA

sym

bol

CP

Transmission scheme OFDMA SC-FDMA

Analysis bandwidth 15 kHz Signal BW(M x 15 kHz) 15 kHz Signal BW

(M x 15 kHz)

Peak to average power ratio (PAR)

Same as datasymbol

High PAR (Gaussian)

< data symbol (not meaningful) Same as data symbol

Observable IQ constellation

Same as data symbol at 66.7 μs rate

Not meaningful (Gaussian)

< data symbol (not meaningful)

. Same as data symbol at M X 66.7 µs rate

60 kHz Frequency

V

Time

SC-FDM

A

sym

bol

SC-FDM

A

sym

bol

CP

Comparing OFDMA and SC-FDMAMultipath protection with short data symbols

15 kHzFrequency

fc

V

Time

OFDMA

sym

bol

OFDMA

sym

bol

CP

OFDMAData symbols occupy 15 kHz for

one OFDMA symbol period

SC-FDMAData symbols occupy M*15 kHz for

1/M SC-FDMA symbol periods

fc

The subcarriers of each SC-FDMA symbol are not the same across frequency as shown in earlier graphs but have their own fixed amplitude & phase for the SC-FDMA symbol duration.

The sum of M time-invariant subcarriers represents the M time-varying data symbols.

60 kHz Frequency

V

Time

SC-FDM

A

sym

bol

SC-FDM

A

sym

bol

CP

It is the constant nature of the subcarriers throughout the SC-FDMA symbol that means when the CP is

inserted, multipath protection is achieved despite the modulating data symbols being much shorter.

eNB (DL) Transmitter Characteristics eNB RF conformance test is ready to go !!eNB RF conformance test is ready to go !!

6. Transmitter Characteristics Test Requirement 6.2 Base station output power E-TM1.1 6.3.1 Power Control Dynamic Range E-TM2,3.1,3.2,3.3 6.3.2 Total Power Dynamic Range E-TM2,3.1 6.4 Transmit ON/OFF Power Not defined yet (for TDD) 6.5 Transmitted Signal Quality Not defined yet (apply to the transmitter ON period) 6.5.1 Frequency Error E-TM2,3.1,3.2,3.3 6.5.2 Error Vector Magnitude E-TM2,3.1,3.2,3.3 6.5.3 Time Alignment Between Transmitter Branches E-TM2,3.1,3.2,3.3? (for MIMO case, specified the delay between the

signals from two antennas, less than 65ns)

6.5.4 DL RS power E-TM1.1 (deviation between indicated power on BCH and measured power)

6.6.1 Occupied Bandwidth E-TM1.1 6.6.2 Adjacent Channel Leakage Power Ratio E-TM1.1,1.2 6.6.3.5.1 Operating Band Unwanted Emissions Category A

E-TM1.1,1.2

6.6.3.5.2 Operating Band Unwanted Emissions Category B

E-TM1.1,1.2

6.6.4.5.1 Spurious Emissions Category A E-TM1.1 6.6.4.5.2 Spurious Emissions Category B E-TM1.1 6.6.4.5.3 Protection of the BS receiver of own or different BS

E-TM1.1

6.6.4.5.4 Co-existence with other systems in the same geographical area

E-TM1.1

6.6.4.5.5 Co-existence with co-located base stations E-TM1.1 6.7 Transmitter Intermodulation E-TM1.1 with 5MHz

TS36.141 V8.1.0 (2008-12)

UE Transmitter Characteristics UE RF conformance test is NOT ready yetUE RF conformance test is NOT ready yet 6. Transmitter Characteristics Test Requirement 6.2.2 UE Maximum Output Power Only power class3 6.2.3 UE Maximum Output Power for modulation/bandwidth MPR: less or equal to 1(QPSK), 2(16QAM) at class3 6.2.4 UE Maximum Output Power with additional requirement A-MPR: less or equal to 1 (QPSK,16QAM) 6.3.1 Power Control Power tolerance is defined (-10.5/-13.5dB) 6.3.2 Minimum output power -40dBm 6.3.3 Transmit ON/OFF power -50dBm at “OFF” 6.4.1 Out-of-synchronization handling of output power FFS 6.5.1 Frequency error +- 0.1PPM 6.5.2.1 Error Vector Magnitude QPSK(17.5%), 16QAM(12.5%), 64QAM(tbd) at slot 6.5.2.2 IQ-component Relative carrier leakage power (origin offset) [dBc] 6.5.2.3 In-band emissions Emission (dB) from allocated RB to non-allocated

RB at slot 6.5.2.4 Spectrum flatness Output power of a subcarrier / Average power of

subcarrier 6.6.1 Occupied bandwidth 99% of total integrated mean power 6.6.2.1 Spectrum emissions mask Not exceed UE emission power at f_OOB at each

operation BW ;meas BW (30kHz or 1MHz) 6.6.2.2 Additional spectrum emissions mask Same as the above 6.6.2.3.1 Adjacent Channel Leakage Ratio (EUTRA) 30dBc at operation BW (5,10,15,20MHz) 6.6.2.3.2 Adjacent Channel Leakage Ratio (UTRA) 33dBc, 36dBc at operation BW (5,10,15,20MHz) 6.6.2.4.1 Additional ALLR requirements 43dBc at each operation BW (5,10MHz) at

handover/broadcast message 6.6.3.1 Spurious emissions -36dBm/1k,10k,100kHz at <1GHz, -30dBm/1MHz at

<12.75GHz 6.6.3.2 Spurious emission band UE co-existence -50dBm>at each EUTRA Band 6.6.3.3 Additional spurious emissions -41dBm /300kHz (PHS) 6.7 Transmitter Intermodulation -31,-41dBc at 5MHz, tbd at other,

CW:-40dBc(interferer)TS 36.521-1 V8.0.1 (2008-12) Power class3: 24dBm +1/-3 dB

UE RF conformance test is NOT ready yetper 3GPP TS 36.521-1 V8.0.1 (2008-12)

6.5 Transmit signal quality

Editor’s note: The test cases for Frequency error, EVM, IQ-component and In-band emission are incomplete. The following aspects are either missing or not yet determined:

FDD aspects missing or not yet determined:

• Reference Measurement Channels are undefined• The fixed power allocation for the RB(s) is undefined• The UE call setup details are undefined• The details on how to move from the different measurement points are undefined• The Test system uncertainties and test tolerance applicable to this test are not confirmed• Global In-Channel Tx-Test is not complete• Measurement points (test vectors) are missing • Downlink Cell power levels for the frequency error test procedure are not defined• Test case is not complete for FDD

TDD aspects missing or not yet determined:

Test case is not complete for TDD

• The transmission signal test cases descriptions have been verified to apply for both FDD and TDD exactly as they are

Agenda• List of LTE physical layer transmitter tests• LTE modulation quality test requirements

– Downlink– Uplink

• Modulation quality signal analysis and troubleshooting techniques

• Appendix – LTE physical layer RF measurements

Taking the journey from WiMAX to LTEMar 2009

Key functions between the mobile (UE) and base station (eNB)

o Synchronizing with the base station

o UE/MS Control

o Channel estimation and training

o Transferring Payload data

Taking the journey from WiMAX to LTE

Synchronizing with the Base Station In LTE downlink, time and frequency synchronization is accomplished by P-SS (sub-frame) and S-SS (frame) in the last two symbols of slot #0 and #10. Aligns OFDM symbols to timing reference in eNB using timing advance (TA)

slot #0 slot #10

S-SS S-SS

P-SS

slot #19

P-SS

0 1 2 3 4 5 6 0 1 2 3 4 5 6

UE/MS Control

In LTE downlink – PDCCH, PDBCH, PMCH, PCFICH provide cell identification, control information (RB, power control etc)

slot #1

PDBCH

slot #0

PDCCH (on resources not used by PCFICH/PHICH/RS), PCFICH

PHICH,PMCH – variable resource mapping

Mar 2009

Channel estimation and training In LTE downlink, channel estimation and channel equalization is done by RS

(reference signals)

RS every 6th subcarrier of OFDMA symbols #0 & #4 of every slot, position varies with antenna port, length of CP

slot #0 slot #19

Transferring Payload data In LTE downlink – PDSCH carries payload data.

PDSCH - Physical DL Shared Channel [Available Slots]

slot #0 slot #19

Transmitted Signal Quality – eNB (Downlink)

Currently there are four requirements under the transmitted signal quality category for an eNB:

• Frequency error• EVM • Time alignment between transmitter

branches• DL RS Power

eNB Transmitted Signal Quality: Frequency Error

• A quick test is use the Occupied BW measurement

• An accurate measurement can then be made using the demodulation process

•Minimum Requirement (observed over 1 ms):

±0.05 PPM

If the frequency error is larger than a few sub-carriers, the receiver demod may not operate, and could cause network interference

eNB Transmitted Signal Quality:EVM Measurement Block

TS 36.104 V8.4.0 FigureE.1-1: Reference point for EVM measurement

Pre-/post FFTtime/frequencysynchronization

BS TX Remove CP

FFTPer-subcarrierAmplitude/phasecorrection

Symbol detection/decoding

Reference pointfor EVMmeasurement

Measurement Block: EVM is measured after the FFT and a zero-forcing (ZF) constrained equalizer in the receiver

EVM measurement is defined over one sub-frame (1ms) in the time domain and 12 subcarriers (180kHz) in the frequency domain. However equalizer

is calculated over full frame (10 sub-frames)

Downlink EVM Equalizer Definition

The subsequent 7 subcarriers are averaged over 5, 7 .. 17 subcarriers

From the 10th subcarrier onwards the window size is 19 until the upper edge of the channel is reached and the window size reduces back to 1

The first reference subcarrier is not averaged

The second reference subcarrier is the average of the first three subcarriers

Reference subcarriers TS 36.104 V8.4.0 Figure E.6-1: Reference subcarrier

smoothing in the frequency domain

Rather than use all the RS data to correct the received signal a moving average is performed in the frequency domain across the channel which limits the rate of change of correction

For the downlink, the EVM equalizer has been constrained

Agilent 89600 VSA EVM Setting

Important notes on EVM (DL and UL)No transmit/receive filter will be defined

• In UMTS a transmit/receive filter was defined– Root raised cosine α = 0.22

• This filter was also used to make EVM measurements– Deviations from the ideal filter increased the measured EVM

• In LTE with OFDMA/SC-FDMA no TX/RX filter is defined• The lack of a filter creates opportunities and problems:

– Signal generation can be optimized to meet in-channel and out of channel requirements– Signal reception and measurement have no standard reference

• It is expected that real receivers will use the downlink reference signals (pilots) to correct for frequency and phase

– But no standard for how to do this will be specified

• The lack of a defined transmit filter means that trade-offs can be made between in-channel performance and out of channel performance (ACLR, Spectrum emission mask)

• But applying too aggressive filtering can introduce delays to the signal which appear like multipath and reduce the effective length of the CP

For this reason EVM is defined across a window at two points in time either side of the nominal symbol centre

Important notes on EVMEVM vs. time – impact on CP reduction

Usable ISI free period

CP length

EV

M

Impact of time domain distortion induced by shaping of the transmit signal in the frequency domain

CP Len FFT Size

EVM Window

FFT Size aligned with EVM Window End

EVM is measured at two locations in time and the maximum of the two EVM is reported. i.e.

EVM1 measured at EVM Window StartEVM2 measured at EVM Window EndReported EVM = max(EVM1, EVM2)(Per the Std.)

Important Notes on EVMEVM Window Length

Agilent VSA EVM SettingFFT Size aligned with EVM Window Center

FFT Size aligned with EVM Window Start

eNB Transmitted Signal Quality:Error Vector Magnitude (EVM)

EVM measurement requires the signal to be correctly demodulated

EVM specification differs for each modulation scheme

Minimum Requirement:

Parameter Unit Level

QPSK % 17.5

16QAM % 12.5

64QAM % 8

Signal BW 89650S(typ)

MXA (typ)

5 MHz 0.35 % 0.45 %10 MHz 0.40 % 0.45 %20 MHz 0.45 % 0.50 %

Agilent Signal Analyzer EVM Performance – DL

Basic channel access modesTransmitAntennas

ReceiveAntennas

SISO

The Radio Channel

MISO

Single Input Single Output

Multiple Input Single Output

(Transmit diversity)

ReceiveAntennas

TransmitAntennas

MIMO

The Radio Channel

SIMO

Single Input Multiple Output

(Receive diversity)

Multiple Input Multiple Output(Multiple stream)

MIMO operation

• MIMO gain comes from spatial diversity in the channel• The performance can be optimized using precoding• Depending on noise levels, the rank (number of parallel

streams) can be varied

• The principles of spatial diversity, precoding and rank adaptation can seem complex but can be readily explained by reference to well-known acoustic principles

MIMO in LTETransmitAntennas

ReceiveAntennas

The Radio Channel

SU-MIMO

eNB 1 UE 1

UE 2

UE 1

eNB 1

MU-MIMO

Co-MIMO

eNB 2

eNB 1

UE 1

Σ Σ

Σ

ΣΣ

• Single User: “Conventional” MIMO One user gets the full benefit of the increased capacity

• Example: Downlink in LTE

• Multi-User: The Base Station schedules two mobiles to transmit their own data streams, but as a MIMO signal.

• Example: Uplink in LTE

• Cooperative MIMO: Co-MIMO involves two separate entities at the transmission end. The example here is a downlink case in which two eNB “collaborate” by sharing data streams to precode the spatially separate antennas for optimal communication with at least one UE.

• Example: Part of Advanced LTE

Concept

eNB Transmitted Signal Quality:Time alignment between transmitter branches

• This test is required for eNB supporting TX diversity or spatial multiplexing transmission

• Purpose is to measure time delay between the signals from two transmit antennas

Minimum requirement: < 65 ns

It is RS based measurement. Measures relative timing error between RS on antenna port 0 and RS on antenna port 1. It is one of the many metrics reported under MIMO Info trace.

eNB Transmitted Signal Quality:DL RS Power

Measures RS transmitted power

Test requirement:

DL RS power shall be within [+/- 2.1] dB of the DL RS power indicated on the BCH

RS power, as well as EVM, measured at base station RF output is reported under Frame Summary trace

Agenda• List of LTE physical layer transmitter tests• LTE modulation quality test requirements

– Downlink– Uplink

• Modulation quality signal analysis and troubleshooting techniques

• Appendix – LTE physical layer RF measurements

Transmitted Signal Quality – UE (Uplink)

Frequency error Transmit modulation

Currently there are four requirements under the transmit modulation category for a UE:

1. EVM for allocated resource blocks 2. I/Q Component (also known as carrier leakage power or

I/Q origin offset)3. In-Band Emission for non-allocated resource blocks 4. Spectrum flatness for allocated RB

UE Transmitted Signal Quality: Frequency Error

• A quick test is use the Occupied BW measurement

• An accurate measurement can then be made using the demodulation process

•Minimum Requirement (observed over 1 ms):

UE: ±0.1 PPM

If the frequency error is larger than a few sub-carriers, the receiver demod may not operate

UE Transmit Modulation:Measurement Block

Modulated symbols

DFT

FFT TX Front-end

Channel RF correction FFT

Tx-Rx chainequalizer

In-bandemissions

Meas.

IDFTEVM

meas.

DUT Test equipment

0

0

In-band emissions measurement is made in frequency domain, after FFT, with no equalizer filter. This is “OFDM Freq Meas” trace in 89601A & N9080A LTE application

EVM is made after ZF equalization filter and IDFT. This is “OFDM Meas” trace in 89601A and N9080A LTE application

I/Q origin offset (LO Leakage) must be removed from the evaluated

signal before calculating EVM and In-band emissions.

UE Transmit Modulation:EVM – For allocated resource blocks

Minimum Requirement For signals > -40 dBm,

Parameter Unit Level

QPSK % 17.5

16QAM % 12.5

64QAM % [tbd]

•It is not expected that 64QAM will be allocated at the edge of the signal

TS 36.101 v8.4.0 Table 6.5.2.1.1-1: Minimum requirements for Error Vector Magnitude

Signal BW 89650S(typ)

MXA (typ)

5 MHz 0.35 % 0.56 %10 MHz 0.40 % 0.56 %20 MHz 0.45 % 0.63 %

Agilent Signal Analyzer EVM Performance – UL

EVM for individual channels & signals

Composite EVM plus Data only and RS only EVM

UE Transmit Modulation:I/Q Component

LO Leakage Parameters Relative Limit (dBc)

Output power >0 dBm -25

- 30 dBm ≤ Output power ≤0 dBm -20

-40 dBm Output power < -30 dBm -10

TS 36.101 v8.4.0 Table 6.5.2.2.1-1: Minimum requirements for Relative Carrier Leakage Power

I/Q Component (LO Leakage or IQ Offset) revels the magnitude of the carrier feedthrough present in the signal

I/Q Component is removed from EVM result

Minimum requirements

UE Transmit Modulation:In-band Emission – For non-allocated RBs

The in-band emission is measured as the relative UE output power of any non –allocated RB(s) and the total UE output power of all the allocated RB(s)

It is defined as an average across 12 sub-carriers and as a function of the RB offset from the edge of the allocated UL block.

Measurement is made at the output of the front-end FFT, prior to equalization.

Minimum requirements

In-band emissionRelative emissions (dB)

TS 36.101 v8.4.0 Table 6.5.2.3.1-1: Minimum requirements for in-band emissions

)/)1(103)log20(,25max 10 RBRB NEVM

In-band emission

UE Transmit Modulation:Spectrum flatness

The spectrum flatness is defined as a relative power variation across the subcarrier of all RB of the allocated UL block

Minimum requirements for spectrum flatness (normal conditions)

Spectrum Flatness Relative Limit (dB)

If FUL_measurement - FUL_low ≥ [3MHz]

andIf FUL_high - FUL_measurement ≥ [3 MHz]

[+2/-2]

If FUL_measurement - FUL_low < [3 MHz]

orIf FUL_high - FUL_measurement < [3 MHz]

[+3/-5]

NOTE:1. FUL_low and FUL_high refers to each E-UTRA frequency band specified in Table 5.2-12. FUL_measurement refers to frequency tone being evaluated

Example for LTE UL band 1:

FUL_low – FUL_high

1920 MHz – 1980 MHz

Agenda• List of LTE physical layer transmitter tests• LTE modulation quality test requirements

– Downlink– Uplink

• Modulation quality signal analysis and troubleshooting techniques

• Appendix – LTE physical layer RF measurements

Get basics right,find major problems

Find specificproblems & causes

Signal qualitynumbers, constellation,basic error vector meas.

Frequency,

Frequency & Time

Advanced &

Specific Demod

Basic

Digital Demod

Component design - R&DBase station and receiver

design - R&D

Component design - R&DBase station and receiver

design - R&D

Base station and receiver design - R&D

Measurement & Troubleshooting TrilogyThree Steps to successful Signal Analysis

Step 1 Step 3Step 2

Spectrogram

Tim

e RS transmitted every 6 sub-carrier

P-SS,S-SS occupying center 6 RBs

RS sub-carriers as selected by the spectrogram marker

The Spectrogram shows how the spectrum varies with timeSee entire LTE frame in frequency and time simultaneouslyFind subtle patterns, errors

Spectrogram marker

Frequency

Basic Demodulation

Basic Demodulation – Constellation DiagramConstellation Diagram Demodulates and displays all active channels and signals within the measurement interval. Color coded by channel type

Only control channels and signals are included. (QPSK, 16 QAM and 64QAM data channels are disabled)

All active channels and signals are included

Basic Demodulation: Error Summary

EVM parameters: composite, peak, data and RS EVM

Auto detects CP Length, Cell ID, Cell ID Group/Sector and RS sequence

I/Q impairments

Sync correlation: How well the signal is synchronized to either RS or P-SS (user selected)

EVM of individual active channels and signals

Advanced Demodulation:Measure EVM in Time, Frequency, Slot and RB domain

EVM per Sub-CarrierEVM per Symbol

EVM per RB EVM per Slot

Normal view

Zoomed on 72 Center Sub-Carriers (6 RB) to show P-SS, S-SS & PBCH

EV

M

Sub-Carrier

DC sub-carrier not used for

DL

Error Vector Spectrum: Shows error in %EVM for each of 300 subcarriers (excluding DC) of 5MHz DL BW.

X-Axis is sub-carrier vertical bars show EVM for individual symbols contained In each sub-carrier

Y-Axis is EVM in % Color code relates EVM reading to channel/signal type

Error Vector Spectrum :EVM vs. Time and Frequency

RMS EVM

Error Vector Time:EVM vs. Time and Frequency

Turned off the PDSCH (user data) channel

Error Vector Time: Shows error in %EVM for each of 140 OFDM symbols (Normal CP) of radio frame

• X-Axis is symbol vertical bars show EVM for individual sub-carriers contained

in each symbol

• Y-Axis is EVM in %Color coding makes it easy to visualize which channels/ signals have high EVM. In this example, S-SS and P-SS transmitted on symbols 5 and 6 of slots #1& #10 have the highest EVM (Marker can also be used to identify the channel type as well as EVM values)

EV

M

OFDM Symbol

RB Error Magnitude Spectrum:EVM vs. RB and Slot

BB Filter characteristics

RB Error Magnitude Spectrum Shows error in %EVM for each of 25 RB of 5MHz DL BW.

X-Axis is RB vertical bars show EVM for individual slots contained in each RB

Y-Axis is EVM in %Best EVM trace to view the characteristics of transmit filter or any other impairment that affect the edges of the band.Since data is allocated to each user based on RB, best way to look at performance per each RB.

EVM Window set to “Center”

EVM Window set to “Max of EVM Window Start/End”

EV

M

RB

Agenda• List of LTE physical layer transmitter tests• LTE modulation quality test requirements

– Downlink– Uplink

• LTE signal generation techniques– Testing amplifiers– Testing receivers

• Modulation quality signal analysis and troubleshooting techniques

• Appendix – LTE physical layer RF measurements

Transmit Power – UE“Does the UE transmit too much or too little?”

• MOP (Maximum Output Power)– Method: broadband power

measurement (No change from UMTS)

• MPR (Maximum Power Reduction)– Definition: Power reduction due to higher

order modulation and transmit bandwidth (RB) – this is for UE power class 3

• A-MPR (Additional MPR)– Definition: Power reduction capability to meet

ACLR and SEM requirements

Power measurement for each active channel after demodulation

Channel power measurement using swept spectrum analyzer

Output RF Spectrum Emissions Unwanted emissions consist of:1. Occupied Bandwidth: Emission within the occupied

bandwidth

2. Out-of-Band (OOB) Emissions– Adjacent Channel Leakage Power Ratio (ACLR)– Spectrum Emission Mask (SEM)

3. Spurious Emissions: Far out emissions

Occupied Bandwidth Requirement“Does most UE energy reside within its channel BW?”

Occupied bandwidthMeasure the bandwidth of the LTE signal that contains 99% of the channel power

Occupied channel bandwidthChannel Bandwidth [MHz] 1.4 3.0 5 10 15 20Occupied Bandwidth (MHZ)

1.08(6 RB)

2.7(15 RB)

4.5(25 RB)

9.0 MHz(50 RB)

13.5 MHz(75 RB)

18 MHz(100 RB)

Minimum Requirement: The occupied bandwidth shall be less than the channel bandwidth specified in the table below

ACLR Requirements – eNB case“Does the eNB transmit in adjacent channels?”

ACLR (Adjacent Channel Leakage Ratio) measurement:

Measure the channel power at the carrier frequency

Measure the channel power at the required adjacent channels

Ensure the eNB power at adjacent channels meets specs

ACLR defined for two cases

• E-UTRA (LTE) ACLR 1 and ACLR 2 with square measurement filter

• UTRA (W-CDMA) ACLR 1 and ACLR 2 with 3.84 MHz RRC measurement filter with roll-off factor =0.22.

ACLR limits defined for adjacent LTE carriers

ACLR limits defined for adjacent UTRA carriers

ACLR measurementACLR measurement

• Channel bandwidth E-UTRA (eNB, UE)

• Channel bandwidth UTRA (eNB, UE)

RBW

Frequency offset1 Frequency offset2

RBW RBW RBW RBW

RBW

Frequency offset2

RBW=3.84MHz

Frequency offset1

RBW=3.84MHzRBW=3.84MHzRBW=3.84MHz

Channel bandwidth

BWChannel [MHz] 1.4 3 5 10 15 20

Transmission bandwidth

configuration NRB 6 15 25 50 75 100

Transmission bandwidth

RBW(MHz) 1.08 2.7 4.5 9.0 13.5 18

Spectrum Emission Mask (SEM)“Does the eNB/UE leak RF onto neighbor channels?”

Operating Band (BS transmit)

10 MHz 10 MHz

Operating Band Unwanted emissions limit

CarrierLimits in

spurious domain must be

consistent with SM.329 [4]

OOB domain

Spectrum emissions mask is also known as “Operating Band Unwanted emissions”

These unwanted emissions are resulting from the modulation process and non-linearity in the transmitter but excluding spurious emissions

Measure the Tx power at specific frequency offsets from the carrier frequency and ensure the power at the offsets is within specifications

TR 36.804 v1.2.0 figure 6.6.2.2-1 Defined frequency range for Operating band unwanted emissions with an example RF carrier and related mask shape (actual limits are TBD).

eNB example:Base station SEM limits are defined from 10 MHz below the lowest frequency of the BS transmitter operating band up to 10 MHz above the highest frequency of the BS transmitter operating band.

20MHz MaskRegulatory Masks + Proposed 20MHz LTE Mask

-50

-40

-30

-20

-10

0

10

-24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2

offset (MHz)

lev

el

(dB

m/1

00

kH

z)

WCDMA

FCC band 5

FCC band 2

FCC band 7

Ofcom

Japan PHS

mask 6/7 RBs

mask 15/16 RBs

mask 25 RBs

mask 50 RBs

mask 75 RBs

mask 100 RBs

Spectrum Emission Mask– UE Example

TR 36.803 v1.1.0 Figure 6.6.2.1 -1: Regulatory mask and proposed E-UTRA masks

Spurious Emission Requirements“How much power does UE leak well beyond neighbor?”

Frequency Range Maximum Level Measurement Bandwidth

9 kHz f < 150 kHz -36 dBm 1 kHz

150 kHz f < 30 MHz -36 dBm 10 kHz

30 MHz f < 1000 MHz -36 dBm 100 kHz

1 GHz f < 12.75 GHz -30 dBm 1 MHz

Spurious emissions are emissions caused by unwanted transmitter effects such as harmonics emission & intermodulation products but exclude out of band emissions

Example of spurious emissions limit for a UE

TS 36.101 v8.2.0 table 6.6.3.1-2: Spurious emissions limits

S

SPEED! S

SPEED!

Nov 2004 LTE/SAE High level requirements

Reduced cost per bit

More lower cost services with better user experience

Flexible use of new and existing frequency bands

Simplified lower cost network with open interfaces

Reduced terminal complexity and reasonable power consumption

Nov 2004 LTE/SAE High level requirements

Reduced cost per bit

More lower cost services with better user experience

Flexible use of new and existing frequency bands

Simplified lower cost network with open interfaces

Reduced terminal complexity and reasonable power consumption

Spectral Efficiency3-4x HSDPA (downlink)2-3x HSUPA (uplink)

LatencyIdle active < 100 msSmall packets < 5 ms

Spectral Efficiency3-4x HSDPA (downlink)2-3x HSUPA (uplink)

LatencyIdle active < 100 msSmall packets < 5 ms

Downlink peak data rates(64QAM)

Antenna config

SISO2x2

MIMO4x4

MIMO

Peak data rate Mbps

100 172.8 326.4

Uplink peak data rates(Single antenna)

Modulation QPSK16

QAM64

QAM

Peak data rate Mbps

50 57.6 86.4

MHz

1.4

3

5

10

15

20

Optimized: 0–15 km/hHigh performance: 15-120 km/hFunctional: 120–350 km/hUnder consideration: 350–500 km/h

Optimized: 0–15 km/hHigh performance: 15-120 km/hFunctional: 120–350 km/hUnder consideration: 350–500 km/h

Mobility

Multiple Input Multiple Output

MIMO

LTE at a Glance

RF Module Development

LTE Lifecycle

RF Proto RF Chip/Module

DesignSimulation

BTS and MobileBB Chipset Development

L1/PHY

FPGA and ASIC

Pre-Conformance

Conformance

RF and BB Design

IntegrationL1/PHY

SystemDesign

ValidationSystem Level

RF Testing

BTS orMobile

Protocol DevelopmentL2/L3

Manufacturing

Network Deployment

Systems for RF and Protocol Conformance

ADS and SystemVue

LTE VSA SWSpectrum and signal

Analyzers, Scopes, LA and ADS

Spectrum Analyzers

Signal Studio

Logic Analyzers& Scopes

Signal Generators

Battery DrainCharacterization

Distributed Network AnalyzersDrive Test

PXB MIMO Rx Tester

DigRF v4

N9912A RF Analyzer

RDX for DigRF v4

E6620A Wireless Communications Platform

Agilent/Anite SAT Protocol

Development Toolset

Webcasts on LTE• LTE Concepts• LTE Uplink• LTE Design and Simulation

Application Note coming

Learn more atwww.agilent.com/find/lte

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