Introduction to LTEaoc-gardenstate.org/lunch_flyers/december/AOC CONDENSED... · 2014-02-12 ·...

1

Introduction to LTE

B d th b kBased on the book

LTE and the Evolution to 4G Wireless

© Agilent Technologies, Inc. 2012

2

LTE = Long Term Evolution = 4Gg1. LTE is now the worldwide standard for cellular systems2. LTE is a scalable and flexible systemy3. LTE accommodates FDD and TDD architectures4. LTE is based on a new “all IP” core network backhaul5. LTE basestations (eNodeB) are nodes on an IP network( )6. LTE is co-located with existing 2G/3G cell systems7. LTE can use Diversity, MIMO, Beamforming8. LTE can deliver ~300 Mbps/cell sector (Release 8)9. LTE has a broadcast variant10.LTE core network uses IP Multimedia Subsystem (IMS)11.LTE supports IPV6 addressing, multiple IP context/UE


3

LTE (4G) in context of new systems• LTE is just one of five major new wireless technology developments

• 3GPP LTE• 3GPP HSPA+• 3GPP Edge Evolution• 3GPP2 UMB* (similar to 802.20)• IEEE WiMAX** (802 16e / WiBRO)• IEEE WiMAX – (802.16e / WiBRO)

• All five systems share very similar goals in terms of spectral efficiency (bits/second/Hz), with the wider systems providing the highest single user data rates

• Spectral efficiency is primarily achieved through use of advanced• Spectral efficiency is primarily achieved through use of advanced modulation schemes and/or multi-antenna technology, ranging from basic Tx/Rx diversity, MIMO, and beamforming

• HSPA+ and Edge Evolution are extensions to existing cellular systems (WCDMA and GSM)(WCDMA and GSM)

• LTE, UMB and WiMAX are new OFDMA systems with no technical precedent other than WiFi and WiBRO

* While UMB is still a documented standard, it is no longer under active development


** WiMAX was deployed in several systems worldwide, but is now in rapid decline

4

3GPP UMTS standards evolution (RAN)Release Functional Main feature of Release

1999Freeze

Rel-99 March 2000 UMTS 3.84 Mcps (W-CDMA FDD & TDD)

Rel-4 March 2001 1.28 Mcps TDD (aka TD-SCDMA)p ( )

Rel-5 June 2002 HSDPA

Rel-6 March 2005 HSUPA (E-DCH)

R l 7 D 2007 HSPA+ (64QAM DL MIMO 16QAM UL)Rel-7 Dec 2007 HSPA+ (64QAM DL, MIMO, 16QAM UL). LTE & SAE Feasibility Study

Rel-8 Dec 2008 LTE Work item – OFDMA air interfaceSAE Work item, New IP core network,Edge Evolution, more HSPA+

Rel-9 TBD UMTS and LTE minor changes, LTE-Advanced feasibility study


2010 Rel-10 TBD LTE-Advanced (4G) work item

5

IS-136 PDCGSMIS-95A

Wireless evolution 1990 - 2012

2G802.11b

TDMA PDCGSMcdma2G

ata

rate

s

2.5G HSCSD iModeGPRSIS-95Bcdma 802.11g

802.11a

andw

idth

and

da

3G E-GPRSEDGE

IS-95Ccdma2000

W-CDMAFDD

W-CDMATDD

TD-SCDMALCR-TDD

802.11n

802.11h

ing

effic

ienc

y, b

3.5G HSUPAFDD & TDD

1xEV-DORelease B

1xEV-DORelease A

1xEV-DORelease 0

HSDPAFDD & TDD

802.16dFixed

WiMAXTM

WiBROLTE Ed 802 16e

Incr

eas

3.9G

4GLTE-

Advanced 802.16m ?

UMB LTERel-8

Edge Evolution HSPA+

802.16eMobile

WiMAXTMUMB


Rel-9/10

6

LTE Major featuresThe motivation behind LTE

• Much untapped potential in HSDPA + HSUPA (HSPA+)• But some LTE requirements can’t be met by HSPA+• LTE goal is to provide further benefits• LTE goal is to provide further benefits

• Spectrum Flexibility (scalable carrier channel bandwidth)• Higher Peak Data Rates with wider 20 MHz channel bandwidth• OFDMA enables less complex implementation of AdvancedOFDMA enables less complex implementation of Advanced

Antennas/MIMO Technology• OFDMA better suited for Broadcast Services

• But UE terminals will have to carry the legacy of GSM/GPRS, y g y ,C2K/EVDO, WCDMA/HSPA+ which increases overall complexity of LTE deployment


7

Nov 2004 LTE/SAE High level

Spectral Efficiency

3-4x HSDPA (downlink)

2-3x HSUPA (uplink)

MHz

1.4

3

LTE at a GlanceNov 2004 LTE/SAE High level

requirements Reduced cost per bit

More lower cost services with better user experience

Latency

Idle active < 100 ms

3

5

10

15

20

SPEED!

experience

Flexible use of new and existing frequency bands

Simplified lower cost network with open interfaces

Reduced terminal complexity and

Small packets < 5 ms

D li k k d t t

20

Reduced terminal complexity and reasonable power consumption

Downlink peak data rates(64QAM)

Antenna config SISO 2x2

MIMO4x4

MIMOPeak data rate Mbps 100 172.8 326.4

Mobility

rate MbpsUplink peak data rates

(Single antenna)

Modulation QPSK 16QAM

64QAM

Peak data 50 57 6 86 4

Optimized: 0–15 km/hHigh performance: 15-120 km/hFunctional: 120–350 km/hU d id ti

MIMO


rate Mbps 50 57.6 86.4 Under consideration: 350–500 km/hMultiple Input Multiple Output

8

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 No2 51.024 2 25.456 No3 102.048 2 51.024 No4 150.752 2 51.024 No5 302.752 4 75.376 Yes5 302.752 4 75.376 Yes

The UE category must be the same for downlink and uplink


9

LTE vs. HSPA+Attribute HSPA+ (Rel-8) LTE targetsAttribute HSPA+ (Rel-8) LTE targets

Peak Data Rate / 5 MHz sector in ideal radio conditions

DL – 42 MbpsUL – 10 Mbps

DL – 43.2 MbpsUL – 21.6 Mbps

Peak Data Rate / 20 MHz sector DL 84 Mbps (10 MHz) DL 172 8 Mbps (20 MHz)Peak Data Rate / 20 MHz sector in ideal radio conditions, 2x2 DL

DL – 84 Mbps (10 MHz)UL – 20 Mbps (10 MHz)

DL – 172.8 Mbps (20 MHz)UL – 86.4 Mbps (20 MHz)

Cell Edge improvement compared to HSPA Release 6

Evolved HSPA & LTE - DL – 3x to 4x; UL – 2x to 3x

All solutions will benefit from ongoing improvements to the radioAll solutions will benefit from ongoing improvements to the radio interface such as UE RX diversity, equalization, interference

cancellation; MIMO, higher order modulation etc.Spectral Efficiency (real world)

Latency: End to End Ping Delay 40 ms

L t Idl t A ti C tl d 600 100Latency: Idle to Active Currently around 600msGoal to reduce to 100 ms

<100 ms

Flexible Bandwidth Utilization? 5 MHz 10 MHz with dual carrier

1.4 MHz to 20 MHz


Suitability for MIMO extensions Challenging with CDMA Much easier with OFDMA

10

LTE vs. WiMAXAttribute

Mobile WiMAX (IEEE 802 16 2005)

3GPP-LTE(E UTRAN)Attribute (IEEE 802.16e-2005) (E-UTRAN)

Core Network WiMAX Forum™ All-IP network

UTRAN moving towards All-IP Evolved UTRA CN with IMS

Access Technology:Access Technology:Downlink (DL)Uplink (UL)

OFDMAOFDMA

OFDMASC-FDMA

Frequency Band 2.3-2.4GHz, 2.496-2.69GHz, 3.3-3.8GHz

Existing and new frequency bands (~2GHz)

Bit-rate/Site:Bit-rate/Site:DLUL

75 Mbps (MIMO 2Tx 2Rx) 25 Mbps

100 Mbps (MIMO 2Tx 2Rx)50 Mbps

Channel bandwidth (BW) 5, 8.75, 10MHz 1.4 - 20 MHzMIMO:DLUL

2 Tx X 2Rx1Tx X NRx -Collaborative SM

2 Tx X 2Rx2 Tx X 2Rx

Cell capacity 100 - 200 users >200 users @ 5MHz>400 users for larger BW

Spectral efficiency Essentially on par comparisons cited often are based on


Spectral efficiency Essentially on par, comparisons cited often are based on dissimilar conditions and can be misleading

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System Architecture Evolution (SAE)

• Today’s core network is a hybrid of elements representing 20+ years evolution of telecommunications

• The evolution and availability of the internet is transformingThe evolution and availability of the internet is transforming the way people look at the core network

• SAE is a project to develop a much flatter, higher performance and cheaper packet-only core network withperformance and cheaper packet-only core network with gateways to legacy networks and non-3GPP technologies

• SAE is separate from but closely coupled to LTE• Some of LTE’s goals like latency targets will not be met• Some of LTE s goals - like latency targets - will not be met

until the evolved packet core network is implemented


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3GPP Release 5 core networkUTRAN – 3G radio Operator ISPGPRS packet routing Application

& ContentISP

Gm (To P-CSFC)

IP Enterprise

& ContentProviders

Other GPRSPLMNRNCNode B

GiGnIub

Iub

Iur

IuPS

GpATM5

ATM2u/5c

ATM2u5c

GGSNBG

GpAMR

SMLC GTP

GTP

SMLCAMR

Uu

Uu

GTPBG

GTP

StandaloneLMU

StandaloneLMU

associatedLMU

associatedLMU

PDN

Gm (To P-CSFC) Gp

IP

AAA DNS RADIUS DHCP

e-mail apps content

IP

IP

RNCNode B

MMSC

SLF

Gr Go

Node B Mw

Mp

Mb

Dx

Gm(from handset)

GfIub

IuCS Gb

I-CSCFcall

server

ATM2u/5c

Mw

MRFPMp

P-CSCFcall

server

SGSN

LgLh

Uu

GGSN

StandaloneLMU

LMU

associatedLMU

PDNGm (To P-CSFC)

SLF

CxCxMr

MRFC

ISC

S-CSCFcall

server

I-CSCFcall

server

Dx

Call Control & operator specific services

Gc

Broadcastservices

EIR

MGWMGCF

MRFC

Si

Mr Mb

MnMg

CxCx S-CSCF

callserver

Si

Sh

ISC

ISC

BGCF

Mj

Mi

FC

D

Gs

CBCCBE

IuBC ?

SIPserver

Sh

server

OSA API

HSSLg

Lc

Lh

Le LCSclient

GMLC

Um

OSASCS

OSA

SCP(gsm SCF)

IP(gsm SRF)

ISC

Sh

OSAapp

server

OSA API

HSSSh

IP

SIPserver

OSASCS

IMS - IP Multimedia ServicesAgprs

Agprs

home network IMS

Enterprise

OLOPSTNG

SMSCSigGW

SiMk

A

Abis

Nb

McMc

ISC

(Ater) PCMMGW

voicemail

Nc ISUP/BICCGMSC

server

BTS

MSC

server

VLRBBTS

BSCPCU

LMU(b)

LMU(b)

LMU(a)

LMU(a)

Um

OSAapp

server

IM-SSFGm (To P-CSFC)from EDGE phones

IP

BGCFOther PSTN

network


GERAN – 2G/3G radio Packet-switched voiceAbis HR, FR, EFR

Roaming partnersMGW(Ater)

HR, FR, EFR

PCMMGWLbSMLC

HR, FR, EFR or AMR or PCM over ATM or QoSIP

The point here is the complexity!

13

Simplified LTE network elements and interfaces

MME = Mobile M

S1 S1

Management entity

S1 S1X2X2

SAE = System Architecture EvolutionX2X2 Evolution


3GPP TS 36.300 Figure 4: Overall Architecture

14

LTE uses an asymetric DL/UL physical layer

• OFDM – Orthogonal Frequency Division Modulation for the downlink.

• SC-FDMA – Single Carrier Frequency Division Multiple Access for the uplink.

• Asymetric physical layer is common in many cellular systems, due to bounds of basestations being stationary and multiuser, while mobiles can be moving and disassociated from other mobiles.


15

Orthogonal Frequency Division Multiplexing

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

• OFDM advantagesOFDM advantages• The use of multiple subcarriers means the channel bandwidth is scalable as

well as supporting frequency selective scheduling within the channel• Wide channels are possible which support higher data rates

Al t l t l i t t t lti th d t l b l• Almost completely resistant to multi-path due to very long symbols• The frequency domain representation of the signal make equalizer design and

MIMO implementation easier then in CDMA systems

• OFDM disadvantages• 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

16

OFDM – Review of Basic Concepts

• Slower symbol rate x multiple carriers = similar bits/sec/Hz

•Less susceptible to:p- single freq. interference- multipath dropouts- impulse noise

. . . . . .

• Carrier spacing creates orthogonality.

• Phase noise, timing and frequency offsets decrease orthogonalityoffsets decrease orthogonality.


17

Orthogonal Basis FunctionsC U C d S b i• Can Use Codes or Subcarriers

• Both are Orthogonal (Separable) Over A Time Interval• Similar In Theoryy• Different in RF Behavior, Design Optimization• Very Different in RF Analysis

CDMA OFDM


CDMA:Dividing Capacity by Code

OFDM:Dividing Capacity by Carrier

18

Orthogonal Frequency Division Multiplexing5 MHz Bandwidth

gemvlu44LG41FFT

.eu4inscTG4wuh1…gafmyh1

Frequency

n Lr

…

25.892 Figure 1: Frequency-Time Representation of an OFDM Signal

OFDM is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation scheme (such as QPSK,


16QAM, 64QAM) at a low symbol rate similar to conventional single-carrier modulation schemes in the same bandwidth.

19

Orthogonal Multiplexing•Multiple carriers may be spaced at multiples of FP and be mutuallyMultiple carriers may be spaced at multiples of FP and be mutually orthogonal, i.e. they do not interfere with one another. The zeros of one pulse occurs exactly on the peaks of the other carriers.

0.8

1

0.2

0.4

0.6

-0.2

0


0 2 4 6 8 10 12-0.4

Freqeuncy (f/Fp)

20

Orthogonal Multiplexing

U i L N b f S h C i Yi ld OFDM Si l•Using a Large Number of Such Carriers Yields an OFDM Signal

2

0P

tK K j nT

n n pK K

x t x t a e t T

0 6

0.8

1

n K n K

0.2

0.4

0.6

-15 -10 -5 0 5 10 15-0.4

-0.2

0


Freqeuncy (f/Fp)

OFDM Operates as a Number of Orthogonal (Non-Interfering) Narrowband Systems

21

OFDMAHow do I add Access (user channels) to this system?

0.8

1

0 2

0.4

0.6

-0.2

0

0.2

-15 -10 -5 0 5 10 15-0.4

Freqeuncy (f/Fp)

Assigned sub-carriers for user 1


Assigned sub-carriers for user 2

22

LTE Downlink Mapping

64QAM16QAM QPSK

P-SS - Primary Synchronization SignalS-SS - Secondary Synchronization SignalPBCH - Physical Broadcast ChannelPDCCH -Physical Downlink Control Channel

64QAM16QAM QPSKPDSCH - Physical Downlink Shared ChannelReference Signal – (Pilot)


23

Pilot Carriers – the Needed Reference forBoth Amplitude and Phase

•A Portion of the Carriers are Not Modulated and Provide Amplitude and Phase References for the Nearby Modulated Channels. These must be spaced close enough for interpolation to provide valid references to the active sub-carriers.

0.4

0.6

0.8

1

-0 4

-0.2

0

0.2


-15 -10 -5 0 5 10 15-0.4

Freqeuncy (f/Fp)

24

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 i diff t f l i i h tuse six different ways of explaining what

SCFDMA is all about

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


provided by OFDMA

25

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

1,1-1,1

I

Q 1, 1 -1,-1 -1, 1 1, -1 1, -1 -1, 1

Sequence of QPSK data symbols to be transmitted

-1,-1 1, 1

p g

1,-1-1,-1QPSK modulating

data symbols

V

CP

V

CP

15 kHzFrequencyfc

OFDMA SC-FDMA

60 kHz Frequency


Data symbols occupy 15 kHz for one OFDMA symbol period

Data symbols occupy M*15 kHz for 1/M SC-FDMA symbol periods

26

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

V

CP

V

CP

15 kHzFrequencyfc

Transmission scheme OFDMA SC-FDMA

60 kHz Frequency

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

27

Multi-antenna Technologies

• Overview of Multi-antenna techniquesq• LTE Terminology• How MIMO works in LTEHow MIMO works in LTE


28

Multi-Antenna Techniques in LTE

• Just because there is more than one antenna, doesn’t mean it’s MIMO

• Diversity can usefully be combined with MIMO Spatial Multiplexing to improve performance

• A focus on the need to provide an increased DL data rate leads to an asymmetric system in LTEy y


29

System & Antenna Configurations, Terms“Input” and “Output” Refer to the Channel

SISO MISO

Tx0 RxTx Rx

Tx1Tx Diversity Beamforming

SIMO

T R 0

MIMO

Tx0 R 0

Tx Diversity, Beamforming

Tx Rx0

Rx1

Tx0

Tx1

Rx0

Rx1Rx Diversity


Rx DiversitySpatial Multiplexing

30

Terminology I

Spatial Multiplexing The process of transmitting data from multiple antennas on the same frequency at the same time

Transmit Diversity Transmission of common data, but modified in some way, on more than one antennay,

ChannelThe entire route, from transmission to reception, including all the analog & RF circuits & antennas, that could introduce unwanted coupling or distortion

(Channel) Rank The number of useable data stream (layers) in a multi-antenna radio system

Correlation A measure of the similarity between different signals Correlation (after the receiver antennas)

Condition Number A short term measure of the increase in SNR needed to recover a spatially multiplexed signal


31

MIMO Spatial Multiplexing and DiversityBoth Important, Different Objectives

Multiple Antennas can be used in a variety of ways:

B f i• Beamforming

• Transmit Diversity

• Receive Diversity• Receive Diversity

Diversity techniques protect against fading, and improve coverage


32

Double Diversity does not make MIMO

Transmit Diversity + Receive Diversity = Spatial MultiplexingTransmit Diversity + Receive Diversity = Spatial Multiplexing

MISO plus MRC

Rx0Tx0Data modified and repeated on

Tx0Tx1

Rx1Tx1MIMO

second symbol (or subcarrier)

Data only transmitted once

Tx0Tx1


33

MIMO Operation in LTE

In the Downlink it’s normally likeIn the Downlink, it’s normally like WLAN, the MIMO transmission is sent to a single mobile.

Known as Single User MIMO

•In the Uplink, two mobiles are used together to create the MIMO signalMIMO signal. •Known as Multi-User MIMO


34

Diversity and Spatial Multiplexing Processes in LTE

The diagram allows for several techniques. To distinguish between SM


and others, ask: “How many receive antennas do I need?”

35

Terminology IICodeword The input data after basic adaptation from the payloadCodeword The input data after basic adaptation from the payload

(Transmission) Layer With spatial multiplexing, it is synonymous with a stream

The process of cross coupling the signals before Precoding

p p g gtransmission (used in closed loop operation) to equalize the demodulated performance of the layers

Codebook The look-up table of cross coupling factors used for precoding; shared by the mobile and base-stationprecoding; shared by the mobile and base station

Closed Loop MIMOA mechanism used to continuously adapt the transmitted signal to suit the channel characteristics, using the precoder

BeamformingThe process of cross coupling the signals at transmitter (or receiver) to adapt to the channel. LTE precoding is one example of doing this

When beamforming with phased array it is the


Beamsteering When beamforming with phased array, it is the process of tracking the movement of the mobile

36

From Codewords to Layers

May/may not be SISOSU-MIMO(4 antennas)

Diversity

or Diversity (with Alamouti)

Single User (or MU) ( )MIMO


37

2 (or 4) Layer Transmit DiversityPaired symbols, frequency based Alamouti techniquePaired symbols, frequency based Alamouti technique Space Frequency Block Coding


38

Combined Spatial Multiplexing & DiversityThe specification allows for this:The specification allows for this:


39

So Tell (or Remind) Me - How does MIMO work?

1: Consider a moment in time at a single frequency and model the1: Consider a moment in time, at a single frequency, and model the channel as a box with fixed components inside:

If we add two completely differentA

If we add two completely different signals at A and B, they’ll get mixed together, but in a precisely defined

way, dependant on the values of Z1- Z4BMIMO is used uncouple signals on twisted pairs

2: Send a training signal first, that’s unique to A and to B. Measure what comes out and therefore how they got coupled. [If you know how they get coupled, you can work out how to uncouple them]

p

y g p y p ]

3: Everything going into the box will be coupled the same way, so you apply what you found to the real data you want to sent


40

… and when does it not work?Noise & interference always limit the modulation we use. With MIMO,

Extreme example: If all the Z’s are the same bothA

y ,there is an ADDITIONAL factor – how well can you uncouple the signals – measured by the Condition Number of the channel matrix

Extreme example: If all the Z s are the same, both outputs are the same. This is a “keyhole” channel, which does not support spatial multiplexing (rank =1)

B

For every dB increase in diti bcondition number, you

may need a dB increase in the SNR


41

The Famous Hand-waving DemoMatrix Condition Number – shows the higher SNR needed for MIMOg

PER vs MIMO Condition Number

0.1

1

10

100

0 5 10 15

PER

%

Condition Number vs Cross Coupling

0

5

10

15

20

25

Con

ditio

n Num

ber (

0dB)

How to get a real feel for it!

Agilent Restricted

Condition Number (dB)-25 -20 -15 -10 -5 0

In Phase Cross Coupling (dB)

As condition number increases, higher SNR is required for the same performance (EVM)

PER vs. Condition Number (example)

Condition Number as a function of symmetric, in-phase coupling

How to get a real feel for it!

eNB

UE

•10 MHz Freq ref.•Time sync

•10 MHz Freq ref.•Time sync•Option phase lock


y

• Frame Trigger

42

Performance Changes with Frequency and TimeCondition number & Frequency response 10 MHz [Pedestrian A]q y p [ ]

0 dB


43

LTE Channel Training Signals• The Reference Signals are what allow the receiver to calculate the

h l ffi i t Th NEVER l b f th t itt dchannel coefficients. They NEVER overlap before they are transmitted

0R 0R

0l0R

0R

0R

6l 0l0R

0R

0R

6l

Resource element (k,l)

Not used for transmission on this antenna port

Reference symbols on this antenna port

0l0R

0R

0R

0R

6l 0l0R

0R

0R

0R

6l 0l

1R

1R

1R

1R

6l 0l

1R

1R

1R

1R

6l

0l0R

0R

0R

0R

6l 0l0R

0R

0R

0R

6l 0l

1R

1R

1R

1R

6l 0l

1R

1R

1R

1R

6l 0l 6l 0l

2R

6l 0l 6l 0l 6l2R

2R

2R

3R

3R

3R

3R


0l 6l 0l 6l 0l 6l 0l 6l 0l 6l 0l 6l 0l 6l 0l 6l

even-numbered slots odd-numbered slots

Antenna port 0


Antenna port 1


Antenna port 2


Antenna port 3

44

What makes a good channel for MIMO?Channel Hh00

• A perfect MIMO channel: 1 0

0 1

00

h11

T0

T1

R0

R1

• By simple observation it follows that R0 = T0 and R1 = T1

• This is a case that creates double the capacity

Channel HBut suppose we create a simple

static channel like this:0.8 0.2

0.3 -0.9How do we know if it will provide capacity gain?


45

The MIMO challenge: Recovering the signal

• If all four paths are the same the original signal cannot• If all four paths are the same the original signal cannotbe recovered since R0 = R1

R0 = T0 + T1 and R1 = T0 + T1 1 1

Channel Hh00T0 R0

0 0 1 1 0 1

• But put in a phase inversion e.g. on ch3 we get:1 1

Channel H

h11T1

R1

R0 = T0 + T1 and R1 = T1 – T0

thus T0 = (R0 - R1)/2 and T1 = (R0 + R1)/2

• The original signal is completely recovered even though the

1 1

-1 1

• The original signal is completely recovered even though the apparently unwanted ch2 and ch3 exist


46

The MIMO challenge: Recovering the signal

S i th li l d b d f MIMO?• So is the earlier example good or bad for MIMO?

0.8 0.2Channel HR0 = 0.8 T0 + 0.3 T1

R = 0 2 T 0 9 T 0.8 0.2

0.3 -0.9R1 = 0.2 T0 - 0.9 T1

T0 = 1.15 R0 + 0.39 R1

Giving:

• We can recover the original signal

T0 1.15 R0 0.39 R1

T1 = 0.26 R0 - 1.03 R1

• We can recover the original signal• In fact any H matrix other than the unity matrix can be

resolved PROVIDED there is no external or internal noise!


47

Why Precode (cross couple) the SM signal?

No precoding – the layer performance is unbalanced

Precoded with 1,1,-1,1 –similar performance for

both layers


48

Precoding Matrix Index definition3GPP TS 36.211 Table 6.3.4.2.3-1

Deals with FDD case

Only 3 choices for spatial multiplexing (16 for the 4 layer case)

For single data stream t i i th ditransmission, the precoding produces beamsteering (with 4 antennas)

Subband PMI reporting canSubband PMI reporting can be configured down to the resource block level


49

Why Apply Cyclic Delay Diversity?

Top: No CDD

Bottom: Large CDD

Test signal with cross coupled static channel

500ns delay, -2dB in one path

Condition Number shows this, and the impact on EVM Spectrum


50

Cyclic Delay Diversity, CDD• Works out to be a very long delay (~33us)Works out to be a very long delay ( 33us)• There are only two choices, Off or “Large”


51

Antenna influence on performance

• The dynamic condition number example did not isolate effects from different components, including the antenna

• In real life the instantaneous channel matrix H is made upIn real life, the instantaneous channel matrix H is made up from the interaction of three components:• The static 3D antenna pattern of the transmitter• The dynamic multipath and Doppler characteristics of the radioThe dynamic multipath and Doppler characteristics of the radio

channel• The static 3D antenna pattern of the receiver

• The overall antenna contribution is the product of the transmit and receive antennas known as the channel correlation matrix


52

Computing the instantaneous channel

The complex instantaneous channel coefficients are obtained by applying each path of the desired fading profile to each channel of the correlation matrix

h00 h01h10 h11

h00

h10

h00T0 R0

h01

h10

h11h11

T1

0

R1

The received signals and condition number are dynamic in both the time and frequency domains according to the h f di fil


chosen fading profile

53

Real life performance

Variation due to instantaneousinstantaneous

correlation

Variation in the ffrequency domain not

shown

Most macrocell activity takes place in this

region


Variation due to fading and variable interference

54

Multi-antenna operation in the Uplink

• Multi-User – two UEs controlled by the eNB to act like a combined transmitter

• Currently more theoretical than practical – of research interest

This demonstration with signal generators allows g gthe introduction of the kinds of timing and power errors that the receiver will have to cope with


have to cope with

55

SummaryMIMO Spatial Multiplexing is a powerful additional transmissionMIMO Spatial Multiplexing is a powerful additional transmission

scheme in the right conditionsThe list of 7 modes for DL transmission highlights how the ENB and UE

will have to work together to choose which multi-antenna technique to use:use:

LTE has seven different downlink transmission modes:

1 Single antenna port; port 0 SISO1.Single-antenna port; port 0 SISO2.Transmit diversity MISO3.Open-loop spatial multiplexing MIMO - no precoding4.Closed-loop spatial multiplexing MIMO - with precoding4.Closed loop spatial multiplexing MIMO with precoding5.Multi-user MIMO MIMO - separate UE (for UL)6.Closed-loop Rank=1 precoding MISO - beamsteering7.Single-antenna port; port 5 MISO - beamsteering


56

The EndThe End


Introduction to LTEaoc-gardenstate.org/lunch_flyers/december/AOC CONDENSED... · 2014-02-12 ·...

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Transcript of Introduction to LTEaoc-gardenstate.org/lunch_flyers/december/AOC CONDENSED... · 2014-02-12 ·...