Long-Term Evolution (LTE) From Fundamental to Advanced

Mobile Broadband Wireless Networking

1

April 22, 2023

Long-Term Evolution (LTE): From Long-Term Evolution (LTE): From Fundamental to AdvancedFundamental to Advanced

Dr Anthony LoDr Anthony Lo

Malaysia University of Technology (UTM), MalaysiaMalaysia University of Technology (UTM), Malaysia

(On sabbatical leave from Delft University of Technology, The (On sabbatical leave from Delft University of Technology, The Netherlands)Netherlands)

Mobile Broadband Wireless Networking2

April 22, 2023

ContentsContents• Background of LTE

• LTE Frequency Bands

• LTE Network Architecture

• OFDM Overview

• Channel Equalization

• OFDMA and SC-FDMA

• MIMO

• LTE-Advanced


April 22, 2023

LTE BackgroundLTE Background• LTE – Long Term Evolution – the next-

generation mobile and wireless broadband network (also known as 3.9G)

• Work on LTE was initiated as a 3GPP Release 7 study item “Evolved UTRA and UTRAN” in December 2004

• Field trials and deployment have started since 2010

• Basic drivers for LTE have been: Reduced latency Higher user data rates Improved system capacity and coverage Cost-reduction


April 22, 2023

LTE RequirementsLTE Requirements• Higher peak data rates:

100 Mb/s (downlink) and 50 Mb/s (uplink)

• Improved spectrum efficiency: 3 – 4 times in downlink and 2 -3 times in uplink higher than UMTS

• Improved latency: Radio access network latency below 10 ms Significantly reduced control plane latency

• Support of scalable bandwidth: 1.4, 3, 5, 10, 15, 20 MHz

• Increased cell edge bit rates• Reduced operation cost

Reduced CAPital and OPerational EXpenditures (CAPEX, OPEX)


April 22, 2023

Cost vs. RevenueCost vs. Revenue

Time

Revenue

LTE CAPEX/OPEX

Existing Cellular Technologies CAPEX/OPEX

Profitability


April 22, 2023

LTE Network ArchitectureLTE Network Architecture

P-GW InterneInternett

S-GW

PCRF

MME

X2

X2 X2

S1

S1 S1

S1

eNode B

eNode B

eNode B

eNode B eNode B Evolved Node B Evolved Node B

EPCEPC Evolved Packet Core, also known as Evolved Packet Core, also known as SAESAE

EPSEPS Evolved Packet SystemEvolved Packet System

E-UTRANE-UTRAN Evolved UTRANEvolved UTRAN

LTELTE also known as E-UTRAN also known as E-UTRAN

MMEMME Mobility Management EntityMobility Management Entity

P-GWP-GW Packet Data Network GatewayPacket Data Network Gateway

PCRFPCRF Policy and Charging Rules FunctionPolicy and Charging Rules Function

SAESAE Service Architecture EvolutionService Architecture Evolution

S-GWS-GW Serving GatewayServing Gateway

LTE

EP C

EP S


April 22, 2023


• Simple architecture

• Flat IP-based architecture

• Reduction in latency and cost

• Split between LTE and EPC

• eNode B’s are interconnected via X2 interface


April 22, 2023


• eNode B All radio interface-related functions

• MME Manages mobility, UE identity and security

parameters

• S-GW Node that terminates the interface towards

E-UTRAN

• P-GW Node that terminates the interface towards

PDN


April 22, 2023

LTE Protocol Architecture – User LTE Protocol Architecture – User PlanePlane

ApplicationApplication

TCPTCP

IPIP

PDCPPDCP

RLCRLC

MACMAC

PHYPHY

PDCPPDCP

RLCRLC

MACMAC

PHYPHY

GTPGTP

UDPUDP

IPIP

L1/L2L1/L2

GTPGTP

UDPUDP

IPIP

L1/L2L1/L2

GTPGTP

UDPUDP

IPIP

L1/L2L1/L2

IPIP

L2L2

L1L1

GTPGTP

UDPUDP

IPIP

L1/L2L1/L2

eNode B S-GW P-GWUE

UDPUDP User Datagram ProtocolUser Datagram Protocol

TCPTCP Transmission Control ProtocolTransmission Control Protocol

PHYPHY Physical LayerPhysical Layer

PDCPPDCP Packet Data Convergence ProtocolPacket Data Convergence Protocol

MAC MAC Medium Access ControlMedium Access Control

IPIP Internet ProtocolInternet Protocol

GTPGTP GPRS Tunneling ProtocolGPRS Tunneling Protocol


April 22, 2023

LTE Protocol Architecture – Control LTE Protocol Architecture – Control PlanePlane

RRCRRC

PDCPPDCP

RLCRLC

MACMAC

PHYPHY

NASNAS

RRCRRC

PDCPPDCP

RLCRLC

MACMAC

PHYPHY

SCTPSCTP

IPIP

L2L2

L1L1

SCTPSCTP

IPIP

L2L2

L1L1

NASNAS

eNode BUE MME

SCTPSCTP Stream Control Transmission Stream Control Transmission ProtocolProtocol

RRCRRC Radio Resource ControlRadio Resource Control

NASNAS Non-Access StratumNon-Access Stratum


April 22, 2023

LTE Key ParametersLTE Key Parameters

Frequency Range UMTS FDD bands and UMTS TDD bands

Channel Bandwidth

1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz

Modulation Schemes

Downlink: QPSK, 16 QAM, 64 QAMUplink: QPSK, 16 QAM, 64 QAM

Multiple Access Schemes

Downlink: OFDMA (Orthogonal Frequency Division Multiple Access)Uplink: SC-FDMA (Single Carrier Frequency Division Multiple Access)

MIMO Downlink: Wide choice of MIMO configuration options for transmit diversity, spatial multiplexing, and cyclic delay (max. of 4 antennas at eNodeB and UE)Uplink: Multi-user collaborative MIMO

Peak Data rate Downlink: 150 Mb/s (UE category 4, 2×2 MIMO, 20 MHz) 300 Mb/s (UE category 5, 4×4 MIMO, 20 MHz)Uplink: 75 Mb/s (20 MHz)


April 22, 2023

Scalable BandwidthScalable Bandwidth

1.4 MHz1.4 MHz

3 MHz3 MHz

5 MHz5 MHz

10 MHz10 MHz

15 MHz15 MHz

20 MHz20 MHz


April 22, 2023

LTE Frequency BandsLTE Frequency BandsBand Uplink (eNodeB receive

and UE transmit)Downlink (eNodeB transmit and UE receive)

Duplex Mode

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD








9 1749.9 MHz – 1784.9 MHz 1844.9 MHz – 1879.9 MHz FDD


11 1427.9 MHz – 1452.9 MHz 1475.9 MHz – 1500.9 MHz FDD




…

17 704 MHz – 716 MHz 734 MHz – 746 MHz FDD…


April 22, 2023

LTE Frequency BandsLTE Frequency Bands

Band Uplink (eNodeB receive and UE transmit)

Downlink (eNodeB transmit and UE receive)

Duplex Mode

33 1900 MHz – 1920 MHz 1900 MHz – 1920 MHz TDD








Multi-pathsMulti-paths

Reflection Diffraction

Scattering


1.25 MHz

200 -300KHz

RECEIVEDPOWERDENSITY

Frequency Selective Fading vs. Flat FadingFrequency Selective Fading vs. Flat Fading


April 22, 2023

Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing (OFDM)(OFDM)

, 0,..., 1s

nn cTf n N Serial-to-parallel Serial-to-parallel converterconverter

Su

bcarr

ier

f 0

Su

bcarr

ier

f 1

Su

bcarr

ier

f 2

Su

bcarr

ier

f 3

Tu

Td

Input Data Input Data bitsbits

OFDM SymbolsOFDM Symbols

• The fundamental transmission technique of the LTE Physical layer

• Divides the transmission bandwidth into Nc orthogonal equally spaced subcarriers

• Individual information symbols are conveyed over the subcarriers

1

1

, 0, ..., 1

, 0, ..., 1u

d

c u

d

kk cT

c

c

u c d

Ru N T

d T

f k N

k f k N

where f is the reference subcarrier frequency

T N T

R f

R

Td = bit duration

Rd = bit rate

Tu = symbol duration

Ru = symbol rate


April 22, 2023

Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing (OFDM)(OFDM)

Frequency

A

Δf = 1/Tu

0 1 2 3 4 5 6 7-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Timef0

f1 = 2f0

f2 = 3f0

f3 = 4f0

f1 f2 f3

Example of 4 subcarriers within one OFDM symbol

Spectra of individual subcarriers


April 22, 2023

OFDM vs. FDMOFDM vs. FDM

Ch.1

Ch.2 Ch.3 Ch.4 Ch.5 Ch.6 Ch.7 Ch.8 Ch.9 Ch.10

Saving of bandwidth

Ch.3 Ch.5 Ch.7 Ch.9Ch.2 Ch.4 Ch.6 Ch.8 Ch.10

Ch.1

Conventional Frequency Division Multiplexing (FDM)

OFDM

50% bandwidth saving

frequency

frequency

Spectra efficient


April 22, 2023

OFDM over Frequency-Selective OFDM over Frequency-Selective ChannelChannel• Since the bandwidth of each subcarrier is

much smaller than the coherence bandwidth of the transmitted channel, each subcarrier sees flat fading

Channel ResponseChannel Response

Frequency


April 22, 2023

OFDM Transceiver StructureOFDM Transceiver Structure

N-p

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OFDM OFDM ModulationModulation

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OFDM OFDM DemodulationDemodulation

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April 22, 2023

OFDM ModulationOFDM Modulation

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X(0), X(1), …, X(NX(0), X(1), …, X(Ncc – – 1)1)

2 0 /j f n Ne

2 1 /j f n Ne

2 ( 1) /cj N f n Ne

……

s(t)s(t)X(1)X(1)

X(NX(Ncc – 1) – 1)

X(0)X(0)

1 12 2 /

0 0

( ) ( ) ( ) ( )c

s

N Nj k f nT j kn N

sk k

s t s nT X k e X k e IDFT

If s(t) is sampled at a rate of fIf s(t) is sampled at a rate of fss = 1/T = 1/Tss = N = N ΔΔf > Nc f > Nc ΔΔf, then f, then

12

0

( ) ( )cN

j k f t

k

s t X k e

IDFIDFTT


April 22, 2023

OFDM DemodulationOFDM Demodulation

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to-P

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s(t)s(t)

2 0j f te

2 1j f te

2 ( 1)cj N f te

……

X(0)X(0)

12 /

0

( ) ( ) , 0,1, ..., 1N

j nk Ns c

n

X k s nT e k N

X(NX(Ncc – 1) – 1)

X(1)X(1)

2

0

( ) ( ) , 0,1, ..., 1uT

j k ftcX k s t e dt k N

0

...uT

0

...uT

0

...uT

DFTDFT

……


April 22, 2023

Cyclic Prefix (CP) InsertionCyclic Prefix (CP) Insertion

• Ts’ = Ts + Tcp, where Tcp is the cyclic prefix extension of the symbol duration Ts

• To maintain orthogonality among subcarriers in the presence of multi-path channel which causes Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI)

OFDM Sym

time

Insertion of cyclic prefix:

T’uTuTcp


April 22, 2023

Channel EqualizationChannel Equalization

• Channel equalization compensates for linear distortion introduced by multi-path propagation channel

• Channel equalization can be carried out in time domain or frequency domain

• For broadband multi-path channels, conventional time domain equalizers are impractical because of complexity: Very long channel impulse response in the time domain Prohibitively large tap size for time domain filter

• Using DFT, equalization can be done in frequency domain

• Because the DFT size does not grow linearly with the length of the channel response, the complexity of Frequency Domain Equalization (FDE) is lower than that of the equivalent time domain equalizer for broadband channel


April 22, 2023

Frequency Domain Equalization (FDE)Frequency Domain Equalization (FDE)

hhx S

ChannelTim

e

Domain

Frequency

Domain

s = h * x

x = h-1 * s

S = H . X

X = H-1 . S

DFT

/IDFT


April 22, 2023

Frequency Domain Equalization (FDE)Frequency Domain Equalization (FDE)

• In DFT, frequency domain multiplication is equivalent to time domain circular convolution

• CP longer than the channel response length is needed to convert linear convolution to circular convolution

• Most of the time domain equalization techniques can be implemented in frequency domain MMSE equalizer, turbo equalizer

CP OFDM Symbol


April 22, 2023

Single Carrier with FDESingle Carrier with FDE

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SC/FDESC/FDE

OFDMOFDM


April 22, 2023

Single Carrier with FDESingle Carrier with FDE

• SC/FDE delivers the same performance similar to OFDM with essentially the same overall complexity, even for long channel delay

• SC/FDE has the advantage over OFDM in terms of Low PAPR Robustness to spectral null Less sensitivity to carrier frequency offset

• Disadvantage to OFDM is that channel-adaptive subcarrier bit and power loading is not possible


April 22, 2023

Orthogonal Frequency Division Multiple Orthogonal Frequency Division Multiple Access (OFDMA)Access (OFDMA)

• OFDMA is a multiple access scheme using OFDM Each mobile terminal occupies a different set of subcarriers

• It has similar transceiver structure to OFDM

• It is one of the downlink multiple access techniques of LTE

subcarriers

Terminal 1Terminal 2Terminal 3


April 22, 2023

Single Carrier FDMA (SC-FDMA)Single Carrier FDMA (SC-FDMA)

• It is a multiple access technique which combines OFDM with single carrier properties

• It has similar transceiver structure to OFDMA• It is one of the uplink multiple access techniques of

LTE


April 22, 2023

SC-FDMA Transceiver StructureSC-FDMA Transceiver Structure

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SC-SC-FDMAFDMA

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SC-FDMASC-FDMA

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April 22, 2023

SC-FDMASC-FDMA

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SC-SC-FDMAFDMA

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Time DomainTime Domain

Sequential transmission of

the modulation symbols

FrequencFrequency Domainy DomainTime DomainTime Domain

FDMA: User multiplexing in frequency

domain


April 22, 2023

SC-FDMA TransmitterSC-FDMA Transmitter

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x(0)x(0)

x(1)x(1)

x(M-x(M-1)1)

…… ……

X(0X(0))X(1X(1))

X(M-1)X(M-1)

……

00

00

S(0)S(0)

S(N-1)S(N-1)

• DFT-based pre-coding is performed on modulated data symbols to transform them into frequency domain

• Each subcarrier carries a portion of superposed DFT spread data symbols, therefore SC-FDMA is also referred to as DFT-spread-OFDM (DFT-S-OFDM)

• N > M, where the N – M unused subcarriers of the IDFT are set to zero amplitude

Single-carrier properties:

• a signal with low power variations

•A bandwidth that depends on M

s(0)s(0)

s(N-1)s(N-1)


April 22, 2023

……

SC-FDMA ReceiverSC-FDMA Receiver

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April 22, 2023

x(3)x(3)

Subcarrier MappingSubcarrier Mapping

• Two subcarrier mapping techniques: Localized DFT-S-OFDM (LFDMA) Distributed DFT-S-OFDM (DFDMA)

NN-p

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x(0)x(0)

x(1)x(1)

x(5)x(5)

……00

S(N-1)S(N-1)

s(0)s(0)

s(N-1)s(N-1)

x(2)x(2)

x(4)x(4)

……

x(3)x(3)

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x(5)x(5)

00

s(0)s(0)

s(N-1)s(N-1)

x(2)x(2)

x(4)x(4)

……

DFT-S-OFDM Localized (LFDMA)DFT-S-OFDM Localized (LFDMA)

00

00

00

00

00

DFT-S-OFDM Distributed DFT-S-OFDM Distributed (DFDMA)(DFDMA)


April 22, 2023

Subcarrier MappingSubcarrier Mapping

subcarriers

Terminal 1Terminal 2Terminal 3

subcarriers

DFT-S-OFDM DistributedDFT-S-OFDM Distributed

DFT-S-OFDM DFT-S-OFDM LocalizedLocalized

• Data block size M = 4, number of subcarriers N = 12, number of terminals Q = 3


April 22, 2023

Subcarrier MappingSubcarrier Mappingx(0)x(0) x(1)x(1) x(2)x(2) x(3)x(3)

X(0)X(0) X(1)X(1) X(2)X(2) X(3)X(3)

12 /

0

( ) ( ) , 0,1, ..., 1M

j nk M

n

X k x n e k M

DFT

X(0)X(0) X(1)X(1) X(2)X(2) X(3)X(3) 00 00 00 00 00 00 00 00

X(0)X(0) 00 X(1)X(1) 00 X(2)X(2) 00 X(3)X(3) 00 00 00 00 00

X(0)X(0) 00 00 X(1)X(1) 00 00 X(2)X(2) 00 00 X(3)X(3) 00 00

subcarriers

S(n)LFDMA

S(n)DFDMA

S(n)IFDMA

• DFT-S-OFDM Interleaved (IFDMA) is a special case of DFDMA with equidistance between occupied subcarriers

Time domain data symbols

Frequency domain data symbols


April 22, 2023

SC-FDMA is similar to OFDMASC-FDMA is similar to OFDMA

• Block-based modulation and use Cyclic Prefix• Divides the transmission bandwidth into smaller

subcarriers• Channel inversion/equalization is carried out in

frequency domain• SC-FDMA is regarded as DFT-precoded or DFT-spread

OFDMA


April 22, 2023

Multiple Input Multiple Output (MIMO)Multiple Input Multiple Output (MIMO)

• Multiple-Input Multiple Output (MIMO) technique improves communication link quality (spatial diversity) and capacity (spatial multiplexing) by using multiple transmit and receive antennas

Tra

nsm

itte

r

Rece

iver

Tra

nsm

itte

r

Rece

iver

Tra

nsm

itte

r

Rece

iver

MIMO MIMO 2×2 SIMO SIMO 1×2 MISO MISO 2×1


April 22, 2023

Spatial DiversitySpatial Diversity

• Improves link quality (SNR) by combining multiple independently faded signal replicas

• With Nt Tx and Nr Rx antennas Nt × Nr diversity gain is achievable

• Two types of spatial diversity: Receive diversity Transmit diversity


April 22, 2023

Receive DiversityReceive Diversity

11

jc e

rCombined SNR N SNRof a signal

22

jc e

SIMO SIMO 1 × Nr

Tra

nsm

itte

rTra

nsm

itte

r

……

• Single-Input Multiple-Output (SIMO)• Coherent combining of signals at receiver to improve

signal strength•

Nr

r

j

Nc e

ss11

ss22

ssNrNr

Receiv

er

Receiv

er

hh1111

hh2121

hhNr1Nr1


April 22, 2023

Receive Diversity – Combining Receive Diversity – Combining techniquestechniques• Selective Diversity Combining (SDC)

Select the strongest signal (or signal with the maximum SNR)

Signals from the other branches are ignored

• Equal Gain Combining (EGC) Combine all the received signals after phase compensation

at each branch with where ci is assumed the same for all branches

The signals are phase aligned when linearly added

• Maximum Ratio Combining (MRC) Add all the received signals after both phase compensation

at each branch with But weight the branches with a factor ci proportional to the

amplitude of the signal of each branch, i.e., ci is set to larger value for received signals of higher SNR

ijic e

ijic e


April 22, 2023

Receive Diversity – CapacityReceive Diversity – Capacity

2log (1 ) / /SISOC SNR b s Hz

2log (1 . ) / /MISO rC N SNR b s Hz

• For an SISO system, the capacity is given by

• For an SIMO (receive diversity) with 1 Tx and Nr Rx antennas, the capacity is given by


April 22, 2023

Spatial Diversity GainSpatial Diversity Gain

SNR (dB)

Sym

bol E

rror

Rate

uncoded

Coding Gain

Log scale

Spatialdiversity Gain


April 22, 2023

Transmit DiversityTransmit Diversity• Multiple-Input Single-Output (MISO)• Two types of transmit diversity techniques:

Closed loop transmit diversity – it relies on feedback Channel State Information (CSI) from receiver

Open loop transmit diversity – it does not rely on feedback CSI from receiver


April 22, 2023

Closed Loop Transmit DiversityClosed Loop Transmit Diversity

11

jc e

22

jc e

MISO MISO Nt × 1

Tra

nsm

itte

rTra

nsm

itte

r

……

Nr

r

j

Nc e

Receiv

er

Receiv

er

hh1111

hh1212

hh1Nt1Nt

Channel State Information (CSI)

• Also known as beamforming• CSI - - is measured at receiver using pilot signals• Two Closed Loop Transmit diversity techniques:

Selective Transmit Diversity (STD) – the transmitter selects the branch based on feedback from the receiver

Transmit Adaptive Array (TxAA) – the receiver is trying to optimize the received power by adjusting the amplitude ci and phase Фi of each branch. This information is fed back to the transmitter

ijic e


April 22, 2023

Open Loop Transmit DiversityOpen Loop Transmit Diversity

MISO MISO Nt × 1

Tra

nsm

itte

rTra

nsm

itte

r

……

Receiv

er

Receiv

er

hh1111

hh1212

hh1Nt1Nt

• No feedback from receiver• Two open loop transmit diversity techniques:

Delay Diversity (DD) Space Time Coding (STC)


April 22, 2023

Open Loop Transmit Diversity - Open Loop Transmit Diversity - DDDD• Signals are transmitted with relative delays for each

branch to create artificial frequency selectivity

MISO MISO Nt × 1

Tra

nsm

itte

rTra

nsm

itte

r

……

Receiv

er

Receiv

er

hh1111

hh1212

hh1Nt1Nt

T1

T2

TNr


April 22, 2023

Open Loop Transmit Diversity - Open Loop Transmit Diversity - STCSTC• Space-Time Block Coding (STBC) operates on pairs of

modulation symbols which form blocks• First antenna transmits x(0) and sign-reversed

complex conjugate of x(1)• Second antenna transmits x(1) and complex conjugate

of x(0)

MISO MISO 2 × 1

STB

CS

TB

C

Receiv

er

Receiv

er

hh1111

hh1212

Tra

nsm

itte

rTra

nsm

itte

r

-x(1)-x(1)**, x(0), x(0)

x(0)x(0)**, x(1), x(1)

x(1), x(0)x(1), x(0)


April 22, 2023

Open Loop Transmit Diversity - Open Loop Transmit Diversity - STCSTC

11 12

* *11 12

11 12* *12 11

(0) (0) (1) (0)

(1) (1) (0) (1)

(0) (0) (0)

(1) (1) (1)

S h x h x n

S h x h x n

h hs x n

h hs x n

s Hx n

• The receiver can recovered the transmitted symbols by applying the matrix HH to the vector s, where

*H 11 12

* *12 11

h h

h h

H


April 22, 2023

Spatial MultiplexingSpatial Multiplexing• Increases data rates by sending multiple data

streams through parallel spatial channels

• With Nt Tx and Nr receive antennas, min(Nt, Nr) multiplexing gain is achievable

……

ss11

ss22

ssNrNr

Receiv

er

Receiv

er

Tra

nsm

itte

rTra

nsm

itte

r

……

hh1111

hh1212

hh1Nt1Nt

hh2222

hh2121

hh2Nt2Nt

hhNrNtNrNt

hhNr1Nr1

hhNr2Nr2

MIMO Channel Matrix


April 22, 2023

Spatial MultiplexingSpatial Multiplexing• Nt × Nr independent paths

• hij is the channel response of each path

• The received signals s can be expressed as

• where H is the Nt × Nr MIMO channel matrix, x is the transmitted signal vector and n is the noise vector

s = Hx + n

11 1

1

...

...

Nt

Nr NrNt

h h

h h

H

… …

. . . 1,...,

T

Ntx xx


April 22, 2023

Spatial MultiplexingSpatial Multiplexing• By the singular value decomposition theorem,

channel matrix H can be decomposed as

• U is an Nr × Nr unitary matrix, V is an Nt × Nt unitary matrix

• D is an Nr × Nt non-negative diagonal matrix

HH = U DV

H

H H H H

s = Hx + n

s UDV x n

U s U UDV Vx U n

s IDIx n

s Dx n


April 22, 2023

Spatial MultiplexingSpatial Multiplexing

……

ss11

ss22

ssNrNr

Receiv

er

Receiv

er

Tra

nsm

itte

rTra

nsm

itte

r

……

hh1111

hh1212

hh1Nt1Nt

hh2222

hh2121

hh2Nt2Nt

hhNrNtNrNt

hhNr1Nr1

hhNr2Nr2

…… Receiv

er

Receiv

er

Tra

nsm

itte

rTra

nsm

itte

r

……

dd1111

dd2222

ddNrNtNrNt

1s

2s

Nrs


April 22, 2023

Unitary PrecodingUnitary Precoding

Unita

ry P

reco

din

g

Tra

nsm

itte

rTra

nsm

itte

r

……

MIMO Channel Matrix

hh1111

hh1212

hh1Nt1Nt

hh2222

hh2121

hh2Nt2Nt

hhNrNtNrNt

hhNr1Nr1

hhNr2Nr2

…… Receiv

er

Receiv

er

xx11

xx22

xxNtNt

1x

2x

Ntx

V

ss11

ss22

ssNrNr

s Hx n


April 22, 2023

Spatial Multiplexing - CapacitySpatial Multiplexing - Capacity

• For an MIMO system, the capacity is given by

2 min( , )min( , ) log (1 . ) / /r

t r

NMIMO t r N NC N N SNR b s Hz


April 22, 2023

Spatial Multiplexing GainSpatial Multiplexing Gain


April 22, 2023

LTE – Radio Frame StructureLTE – Radio Frame Structure


April 22, 2023

Physical Resource Blocks (PRBs)Physical Resource Blocks (PRBs)


April 22, 2023

OFDMA + TDMAOFDMA + TDMA

• LTE downlink multiple access techniques• Channel dependent scheduling assigns PRBs to

different users

SubcarrierSubcarrier

Tim

eT

ime

User 1User 2User 3User 4

PowerPower

Subframe

Subframe


April 22, 2023

Channel-Dependent Scheduling in Channel-Dependent Scheduling in Frequency Domain Frequency Domain

FrequencyFrequency

Ch

ann

el Q

ual

ity

Ch

ann

el Q

ual

ity

PRBPRB

Assign PRBs to users with good channel qualityAssign PRBs to users with good channel quality


April 22, 2023

LTE-AdvancedLTE-Advanced

• LTE-Advanced is evolved from LTE• All relevant requirements of LTE are valid also for LTE-

Advanced• Peak data rates:

• Downlink: 1 Gb/s• Uplink: 500 Mb/s

• Research topics:• Wider bandwidth• Enhancement of uplink multiple access• Enhancement of MIMO techniques• Coordinated Multiple Point transmission and reception (CoMP)• Advanced relaying strategies


April 22, 2023

Wider BandwidthWider Bandwidth

• Achieve wider bandwidth through carrier aggregation• Aggregation of basic frequency blocks called

component carriers (CCs)• Support of both contiguous and non-contiguous CCs


April 22, 2023

Enhancement of Uplink Multiple AccessEnhancement of Uplink Multiple Access

• Within CC• SC-FDMA is used• Non-contiguous data transmission with single DFT (clustered

DFT-s-OFDM) is introduced• Achieve efficient radio resource assignment with relaxed PAPR

requirement• Among CCs

• N-times clustered DFTS-OFDM


April 22, 2023

Enhancement of MIMO TechniquesEnhancement of MIMO Techniques

• Downlink• Extend the number of layers from minimum of 4 to maximum

of 8• Multi-user MIMO

• Uplink• Single-user MIMO up to 4-layer transmission


April 22, 2023

Coordinated Multi-Point Transmission and Coordinated Multi-Point Transmission and Reception (CoMP)Reception (CoMP)

• Downlink• Joint processing among eNBs

• Data is available at each eNB and transmitted at the same time

• Coordinated scheduling/beamforming• Data is available at the serving eNB but user

scheduling/beamforming decisions are made with coordination among eNBs

Joint processing

Coordinated scheduling/beamforming


April 22, 2023

Coordinated Multi-Point Transmission and Coordinated Multi-Point Transmission and Reception (CoMP)Reception (CoMP)

• Uplink• Coordinated multi-point reception

• Uplink signal is received at multiple eNBs• Scheduling decisions can be coordinated among eNBs to

control interference

Coordination on Scheduling

Simultaneous reception


April 22, 2023

Advanced Relaying StrategiesAdvanced Relaying Strategies

• Coverage problem increases for high spectrum• Significant capacity increase can only be achieved by reducing

cell size using relays• Improving cell edge throughput• Types of relays:

• Layer-1 (Amplify-and-Forward) Relay• Layer-2/3 (Decode-and-Forward) Relay

• Relaying strategies• One-way relay• Two-way relay• Cooperative relay• Shared Relay


April 22, 2023

Layer-1 RelayLayer-1 Relay

• Amplify-and-Forward (AF)Amplify-and-Forward (AF)• Used for coverage holes and coverage extensionUsed for coverage holes and coverage extension• Signals and noise are amplified because received signals are Signals and noise are amplified because received signals are

not demodulated and decoded not demodulated and decoded • Minimum delayMinimum delay• Simple Simple


April 22, 2023

Layer-2 RelayLayer-2 Relay

• Decode-and-Forward (DF)Decode-and-Forward (DF)• Used for coverage holes, coverage extension and capacity Used for coverage holes, coverage extension and capacity

enhancementenhancement• Good isolation of signals and noiseGood isolation of signals and noise• Larger delaysLarger delays• Higher complexity as compared with Layer-1 relayHigher complexity as compared with Layer-1 relay


April 22, 2023

One-way RelayOne-way Relay

UEUERelayRelayeNodeBeNodeB

• Work with Layer-1/2/3 relaysWork with Layer-1/2/3 relays• Similar to conventional relaysSimilar to conventional relays• Inefficient for relay operating in half-duplex modeInefficient for relay operating in half-duplex mode


April 22, 2023

Two-way RelayTwo-way Relay

• Work with Layer-1 relaysWork with Layer-1 relays• Avoid the inefficiency of one-way relays operating in half-Avoid the inefficiency of one-way relays operating in half-

duplex modeduplex mode

UEUERelayRelayeNodeBeNodeB

S1S1 S2S2

S1+SS1+S22

S1+SS1+S22


April 22, 2023

Cooperative RelayCooperative Relay

• Allow soft combining of several pathsAllow soft combining of several paths• Work with Layer-1 or Layer-2 relaysWork with Layer-1 or Layer-2 relays• Delay of direct link signals would be required with relative to Delay of direct link signals would be required with relative to

the access link signals the access link signals

UEUE

Relay Relay 11

Relay Relay 22

eNodeBeNodeB

SS

SS

SS

S1S1

S2S2


April 22, 2023

Shared RelayShared Relay

• Work with Layer-2/3 relaysWork with Layer-2/3 relays• Several eNodeBs share a single relaySeveral eNodeBs share a single relay• Shared relay is a multi-antenna relay with k × m antenna, Shared relay is a multi-antenna relay with k × m antenna,

where k = the number of eNodeB, m = the number of antennas where k = the number of eNodeB, m = the number of antennas associated with the eNodeBassociated with the eNodeB


April 22, 2023

Thank You!Thank You!

Documents

Long-Term Evolution (LTE) From Fundamental to Advanced