LTE Course for Technical Personnel

Summer School ATHENA 2011

LTE

Air Interface

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History - Details 1G FDMA (NMT, AMPS, TACS) 80’s

- Voice (analog traffic, digital signaling)

2G TDMA (GSM, D-AMPS, PDC) and CDMA (IS-95) 90’s- Voice, SMS, CS data transfer ~ 9.6 kbit/s (50 kbit/s HSCSD)

2.5G TDMA (GPRS) 00’s- PS data transfer ~ 50 kbit/s

2.75G TDMA (GPRS+EDGE) 00’s- PS data ~ 150kbit/s

3-3.5G WCDMA (UMTS) and CDMA 2000 00’s- PS & CS data transfer ~ 14-42 Mbit/s (HSPA/HSPA+), Voice, SMS

3.9G OFDMA (LTE/SAE) 10’s- PS Data and Voice (VoIP) ~ 100Mbit/s

4G IMT Advanced source

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3G Evolution

HSPA Evolution

– gradually improved performance at a low additional cost prior to

the introduction of LTE

LTE

– improved performance in a wide range of spectrum allocations

HSUPA

MBMS

Rel 6

MIMO

HOM

CPC

Rel 7Rel 4R99

HSDPA

Rel 5

4G

Further

enhancements

WCDMA/HSPAWCDMA HSPA Evolution

Rel 8

LTELTE

Advanced

source

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R99

LTE

HSPA

evolved

HSPA

Enhanced UplinkHSDPA

3GPP Rel 99/4 Rel 5 Rel 6

WCDMA EvolvedWCDMA

Rel 7 Rel 8

LTE

HSPA Evolved

LTE

HSPA+

3GPP standard evolution

Initial packet data in Rel 99/Rel 4

High Speed Downlink Packet Access in Rel 5

Enhanced Uplink in Rel 6

”High Speed Packet Access+” in Rel 7 e.g.:– Multiple Input Multiple Output (MIMO)

– Higher order modulation DL/UL

Long Term Evolution in Rel 8

384

kbps

14.4 /

5.8

Mbps

28 /

12

Mbps

>100

Mbps

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Telephony

WWW

@

Office

TV

MobileHome

Why LTE/SAE ? - Mobile Triple Play- Telephony, Data and Video/TV

all service delivered by one network

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LTE – Targets High data rates

– Downlink: >100 Mbps– Uplink: >50 Mbps– Cell-edge data rates 2-3 x HSPA Rel. 6 (@ 2006)

Low delay/latency – User plane RTT: < 10 ms RAN RTT (fewer nodes, shorter TTI)– Channel set-up: < 100 ms idle-to-active

(fewer nodes, shorter messages, quicker node resp.)

High spectral efficiency – Targeting 3 X HSPA Rel. 6 (@ 2006 )

Spectrum flexibility– Operation in a wide-range of spectrum allocations, new and existing– Wide range of Bandwidth: 1.4, 1.6, 3.0/3.2, 5, 10, 15 and 20 MHz, FDD and TDD

Simplicity – Less signaling, Auto Configuration e-NodeB– ”PnP”, ”Simple as an Apple”

Cost-effective migration from current/future 3G systems

State-of-the-art towards 4G

Focus on services from the packet-switched domain

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EPS Architecture

eNB eNB

eNB

MME/S-GW MME/S-GW

S1

X2

X2

X2

SAE

(System Architecture

Evolution)

LTE

(Long Term Evolution)

EPC

(Evolved

Packet Core)

E-UTRAN

EPS

(Evolved

Packet

System)

UE

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PCRF

Overall Architecture

X2-UP

S1-UP (User Plane)

EPC

S1-CP (Control Plane)

E-UTRAN

eNodeBeNodeB

S11

MME

S-GW

P-GW

S5/S8

X2-CP

P-CSCF

S7/Gx

Network & Service

management

OSS-RC EMA

MM DNS/ENUM

HSS

S-CSCF

I-CSCFIMS Control

layer

Platforms / Concepts

TSP/NSP or

TSP/IS

DNS/

ENUMMGC

MGW

SUN

IS

A-SBG

CPP /

RBS6000

Juniper/

Redback

WPP

GERAN UTRAN

Broadband

Wired Access

GPRS

Packet

Core

SGSN

GGSN

CDMA2000

HRPD

(EV-DO)

WLAN

N-SBG

Internet

S6a

CS Core

MSC

GWMSC

PSTN

PDSN

S1-AP, X2-AP

H.248

ISUP

Diameter

S3

S4

GTP-C

Gxa

S103

S2a

RNCOther

SIP/UDP or SIP/TCP

Rx+

User data

RTP/UDP GTP/UDP

S101

IMS Connectivity

layer

Service LayerASAS AS

Application ServersMTAS

S6d

Uu

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Typical Implementation of SAE/LTE- combined SGSN/MME

Iub

3G (HSPA & DCH)

S1-UP

UTRAN

Node B

InternetEvolved

Packet

Core

S1-CP

Iu-CP

LTE

Gi

S4/S11

SAE

BTS

Gb

Abis

2G

GERAN

BSC

SGSN/

MME

P/S-GW

RNC

X2-UPE-UTRAN

eNodeBeNodeB X2-CP

Gn

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Multiple Access Approaches

Frequency

Division

Multiple

Access

Each User has a unique

frequency

(1 voice channel per user)

All users transmit at the

same time

AMPS, NMT, TACS

Each Transmitter has a

unique

Scrambling Code

Each Data Channel has a

unique Channelization

code

Many users share the

same frequency and time

IS-95, cdma2000,

WCDMA

Code

Division

Multiple

Access

Spread

Spectrum

Multiple

Access

Each User has a unique

time slot

Each Data Channel has a

unique

position within the time slot

Several users share the

same frequency

IS-136, GSM, PDC

Time

Division

Multiple

Access

Orthogonal

Frequency

Division

Multiple

Access

Each User and each channel

has a unique

Time and Frequency

Resource

Many users are separated in

frequency and/or time

LTE, Wimax

(WLAN 802.11a,g, DAB radio)

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LTE Physical Layer

Flexible bandwidth– Possible to deploy in 6 different bandwidths

up to 20 MHz

Uplink: SC-FDMA with dynamic bandwidth (Pre-coded OFDM)

– Low PAPR Higher power efficiency

– Reduced uplink interference (enables intra-cell

orthogonality )

Downlink: Adaptive OFDM

– Channel-dependent scheduling and link adaptation

in time and frequency domain

Multi-Antennas, both RBS and terminal

– MIMO, antenna beams, TX- and RX diversity, interference rejection

– High bit rates and high capacity TX RX

frequency

frequency

Harmonized FDD and TDD concept– Maximum commonality between FDD and TDD

Minimum UE capability: BW = 20 MHz

10 15 20 MHz3

fDL

fUL

FDD-onlyfDL

fUL

Half-duplex FDDfDL/UL

TDD-only

Δf=15kHz

180 kHz

User #2 scheduledUser #1 scheduled

User #3

scheduled

1.4 5

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Time-domain

Structure FDD

Normal CP, 7 OFDM

symbols per slot

TCP Tu 66.7 s

#0 #1 #9

One OFDM symbol

One slot (0.5 ms) = 7 OFDM symbols

One subframe (1 ms) = two slots

One radio frame (10 ms) = 10 subframes = 20 slots

#2 #3 #4 #5 #6 #7 #8

•PBCH sent in subframe #0, slot 1, symbol 0-3 over 4 consequtive radio frames (40 ms)

•SCH sent in subframe #0 and #5, slot 0 and 10, symbol 5-6 (4-5 in case of extended CP)

PBCH

S-SCH P-SCH S-SCH P-SCH

frequency

Δf=15kHz

180 kHz

User #2 scheduledUser #1 scheduled

User #3

scheduled

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20 ptSegmentation, ARQ

Ciphering

Header Compr.

Hybrid ARQHybrid ARQ

MAC multiplexing

Antenna and

resrouce mapping

Coding + RM

Data modulation

Antenna and

resource mapping

Coding

Modulation

Antenna and

resource

assignment

Modulation

scheme

MA

C s

ch

ed

ule

r Retransmission

control

Priority handling,

payload selection

Payload selection

RLC#i

PHY

PDCP#i

User #i User #j

MAC

Concatenation, ARQ

Deciphering

Header Compr.

Hybrid ARQHybrid ARQ

MAC demultiplexing

Antenna and

resrouce mapping

Coding + RM

Data modulation

Antenna and

resource demapping

Decoding

Demodulation

RLC

PHY

PDCP

MAC

eNodeB UE

Redundancy

vers

ion

IP packet IP packet

EPS bearers

E-UTRA Radio

Bearers

Logical Channels

Transport Channels

Physical Channels

Radio

interface

structure

source

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MAC Layer

Segmentation, ARQ

Ciphering

Header Compr.

Hybrid ARQHybrid ARQ

MAC multiplexing

Antenna and

resrouce mapping

Coding + RM

Data modulation

Antenna and

resource mapping

Coding

Modulation

Antenna and

resource

assignment

Modulation

scheme

MA

C s

ch

ed

ule

r Retransmission

control

Priority handling,

payload selection

Payload selection

RLC#i

PHY

PDCP#i

User #i

MAC

IP packet

MAC layer for the LTE access can

be compared to the Rel-6 MAC-

hs/MAC-e and covers mainly

similar functionality:

• HARQ,

• priority handling (scheduling),

• transport format selection

• DRX control

source

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Channel mapping

UL-SCHPCH DL-SCH

PCCHLogical Channels “type of information”

(traffic/control)

Transport Channels“how and with what

characteristics”

(common/shared/mc/bc)

Downlink Uplink

PDSCH

Physical Channels“bits, symbols,

modulation, radio

frames etc”

MTCH MCCH BCCH DTCH DCCH DTCH DCCH CCCH

PRACH

RACH

CCCH

MCH BCH

PUSCHPBCH PCFICH PUCCH

-CQI

-ACK/NACK

-Sched req.

-Sched TF DL

-Sched grant UL

-Pwr Ctrl cmd

-HARQ info

MIB SIB

PMCH PHICHPDCCH

ACK/NACKPDCCH

info

Physical Signals“only L1 info”

RS SRSP-SCH S-SCH RS

-meas for DL sched

-meas for mobility

-coherent demod

-half frame sync

-cell id -frame sync

-cell id group -coherent demod-measurements

for UL scheduling

source

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Tx & Rx physical layer processing

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

Not shown:

Rate Matching

HARQ

MIMO mapping...

OFDM(IFFT) OFDM(FFT)

Tx Rx

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Tx Coding

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

OFDM(IFFT) OFDM(FFT)

Tx Rx

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CRC Coding – error detection

Cyclic-Redundancy Check (CRC) Coding– Identifies any corrupted data left

after error correction function in receiver

– CRC is used for checking BLER(Block Error Ratio) in the outer loop power control

Checksum 24 bits

110010110011

Original Data

244 bits

CRC

GeneratorOriginal Data

1001011010..

CRC

GeneratorRe-Generated Checksum

110010110001

Transmitter

Receiver

If Checksums do not match,

there is an error

Received Data

1001010010..

Received Checksum

110010110011

RF

Transmission Path

The longer the checksum, the greater is

the accuracy of the process. Why???

Answer:Various combinations of errors in the data and the

checksum would produce the same checksum. The

longer the checksum the less likely it is for this to

happen.

Example: 24 bits of binary information

represents 16 777 216 (224) different

combinations

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FEC Coding

Error Correction

Help the receiver correct bit errors caused by the air interface.

– How do you correct errors at the receiver?

Sendmessage

many times?

010010110,010010110,010010110,010010110,010010110,

ForwardError

Correction!

Up to 6x data expansion...

But the most powerful results

Advantage:

The more times the data is

transmitted the better is the error

protection.

Disadvantage:

However the bandwidth is also

increased proportionally

Need to find a FEC technique with minimum

BW requirements!!

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FEC Coding Approaches

– Block Codes (Hamming Codes, BCH Codes, Reed-Solomon Codes)

– Continuous Codes (Convolutional Codes, Turbo Codes) Data is processed continuously through FEC generator Resulting data stream has built-in redundancy that can

be extracted to correct bit errors.

– LTE uses Turbo codes with rate 1/3 for DL-SCH transmissions.

– Convolutional coding used for BCH

source

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FEC Coding

Original Data

00011011...FEC

Generator

FEC Encoded data

1010011100110110...

Original Data

00011011Viterbi/

Turbo

Decoder

Transmitter

Receiver

RF

Transmission Path

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Tail Biting Convolutional Encoder

D D D DD D

G0 = 133 (octal)

G1 = 171 (octal)

G2 = 165 (octal)

kc

)0(kd

)1(kd

)2(kd

Constraint length 7

Coding rate 1/3

source

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Radio Channel problems -

Multipath Propagation

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

OFDM(IFFT) OFDM(FFT)

Tx Rx

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Multipath Propagation• Up to date cellular systems have used single carrier modulation

schemes almost exclusively.

• LTE uses OFDM rather than single carrier modulation

• single carrier systems face extreme problems with multipath

induced channel distortion

• A measure of multipath distortion is

provided by delay spread describes

the amount of time delay at the receiver

from a signal traveling from the

transmitter along different paths.

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Multipath Propagation

One user’s signal reflects off many objects

The received signal contains many time-delayed

replicas

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Multipath Propagation- and the resulting impulse response

Multipath Propagation gives rise to:

1. InterSymbol Interference (ISI)

2. Fast fading (Rayleigh fading)

source

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Multipath Propagation- and the resulting impulse response

Fast fading (Rayleigh fading)

τ0 τ1 τ2 t(μs)

P0

P1

P2

Power

(dB)

Impulse response

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Multipath Propagation- and the resulting impulse response

InterSymbol Interference (ISI)

τ0 τ1 τ2 t(μs)

P0

P1

P2

Power

(dB)

P2,τ1

P0,τ0 P1,τ2

Impulse response

Direct signal

Reflected signal

Path delay

difference

ISI

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Multipath FadingDirect Signal

Reflected Signal

Combined Signal

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Path loss and Fast fading

Power

distance

Time between fades is related to

• RF frequency

• Geometry of multipath vectors

• Vehicle speed:

Up to 4 fades/sec per kilometer/hour

path loss

Rayleigh

Deep fade caused by destructive summation

of two or more multipath reflections

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Block Interleaving

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

OFDM(IFFT) OFDM(FFT)

Tx Rx

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Block Interleaving

Time

Am

plit

ude

To

decoder

Original Data Samples

1 2 3 4 5 6 7 8 9

Interleaving

Matrix

1 2 3

4 5 6

7 8 9

Transmitter

Interleaved Data Samples

1 4 7 2 5 8 3 6 9

RF

Transmission Path

Interleaved Data Samples

1 4 7 2 5 8 3 6 9

Errors Clustered

De-

Interleaving

Matrix

1 2 3

4 5 6

7 8 9

De-Interleaved Data Samples

1 2 3 4 5 6 7 8 9

Receiver

Errors Distributed

Solution:

use a block-interleaving technique as shown:

source

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Scrambling in LTE

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

OFDM(IFFT) OFDM(FFT)

Tx Rx

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Interference in LTE

PROBLEM STATEMENT

In LTE, a frequency reuse of 1 will typically be used. This means that

all cells use the same frequency band(s). For UEs close to the cell

border, this will lead to massive interference in both UL and DL.

Solutions

1. In order to reduce this inter cell interference, a cell specific bit-

level scrambling is applied for all transmissions in both UL and

DL.

2. Inter Cell Interference Co-ordination (ICIC). ICIC co-ordinates

the radio resource allocations (scheduling) between neighboring

cells that experience problems

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Scrambling in LTE

Cell specific bit-level scrambling used in LTE for all

datastreams in UL and DL– used in order to achieve interference randomization

between cells

No frequency planning (freq reuse 1)– massive inter-cell interference mitigated by scrambling and

interference co-ordination techniques (e.g. ICIC)

Common scrambling used for cells in

broadcast/multicast service transmissions (MBMS)

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Modulation

Coding

Scrambling

Modulation

CRC

Decoding

Descrambling

Demodulation

CRC check

Radio Channel

OFDM(IFFT) OFDM(FFT)

Tx Rx

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ModulationNext step after channel coding and scrambling is modulation.

Modulation: A process that maps blocks of scrambled bits (bit rate) onto

symbols (symbol rate or baud rate) Over the air interface we apply

digital modulation techniques; a digital signal modulates an analog carrier

different symbols correspond to a specific amplitude and/or phase shift

of the carrier wave.

Three different modulation schemes are supported in E-UTRAN;

• QPSK (Quadrature Phase shift keying)

• 16-QAM (16 Quadrature Amplitude Modulation)

• 64-QAM (64 Quadrature Amplitude Modulation)

QPSK is a pure phase modulation it has constant amplitude,

16-QAM and 64-QAM both uses a combination of phase and amplitude.

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Modulation

The sub-carriers are modulated with a certain modulation scheme

– maps the data bits into a carrier phase and amplitude (symbols)

E-UTRAN user data channels supports QPSK, 16QAM and 64QAM

16QAM allows for twice the peak data rate compared to QPSK

64QAM allows for three times the data rate compared to QPSK

Higher order modulation more sensitive to interference

– Useful mainly in good radio channel conditions

(high C/I, Little or no dispersion, Low speed)

e.g. Close to cell site & Micro/Indoor cells

BPSK is used for some signaling (PHICH)

2 bits/symbol 4 bits/symbol 6 bits/symbol64-QAM16-QAMQPSK

1 bit/symbolBPSK

0

1

00

11

10

01 1111 111111

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OFDM Principle Parallel transmission using a large number of narrowband “sub-carriers”

“Multi-carrier” transmission

Implemented with IFFT (Inverse Fast Fourier Transform) at transmitter and FFT at receiver side

Uplink uses similar approach, but with precoder to achieve single carrier properties

f = 15 kHz

20 MHz (example)

S/P

f1

f2

fM

IFFT

Coded and

modulated

data split

f1

f2

fM

filter

FFT

Tx Rx

P/S

source

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Background

OFDM – Orthogonal Frequency Division Multiplex

– a modulation scheme, not a multiple-access scheme

Basic principle known since the 50’s

– Kineplex system by Collins, …

Popular/feasible with the ‘discovery’ of FFT in 1965 and

its efficient implementation in HW

– Bell Labs, 1971, implementation through FFT

– Used by LTE, DAB, DVB, WiMax, xDSL, …

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Orthogonal Frequency Division MultiplexingPrinciples

Benefits

+ Frequency diversity

+ Robust against ISI

+ Easy to implement

+ Flexible BW

+ Suitable for MIMO

+ Classic technology

(WLAN, ADSL etc)

Drawbacks

- Sensitive to Doppler

and freq. errors

- High PAPR (not

suitable for uplink)

- Overhead

• Orthogonal: all other subcarriers zero at sampling point

• Delay spread << Symbol time < Coherence time

• Tu – symbol time per subcarrier -> Subcarrier spacing f = 1/Tu

f

source

See next slides

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Orthogonal Frequency Division MultiplexingPrinciples

Coherence time - Physics

coherence time in electromagneti wave theory is the time

over which a propagating wave may be considered coherent.

it is the time interval within which its phase is, on average,

predictable.

Coherence time is related to the classical uncertainty principle

and it relates the bandwidth (spread in frequency)

of signal or wave to its temporal extent df = 1/dt Thus

phenomena with long coherence times will be sharply peaking

with respect to their spectrum, i.e., they will be composed of

less frequencies.

The limit of this is an infinite coherence time, which would

mean the signal is composed of a singular frequency

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Orthogonal Frequency Division MultiplexingPrinciples

Coherence time - Physics

Waves of different frequencies interfere

to form a pulse if they are coherent Spectrally incoherent waves

interferes to form continuous wave

with a randomly varying phase and

amplitude

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Orthogonal Frequency Division MultiplexingPrinciples

Coherence time - Telecom

In communications systems, a communication channel may

change with time Coherence time is the time duration over

which the channel impulse response is considered to be not

varying.

Important: Such channel variation is much more significant in

wireless communications systems, due to doppler effects.

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Orthogonal Frequency Division MultiplexingPrinciples

1 11( ) ( ) ( )t ty t x t t h t

1( )th t

2 22( ) ( ) ( )t ty t x t t h t

Coherence time - EXAMPLE

simple model

a signal x(t) transmitted at time t1 will be received as:

Where is the channel impulse response (CIR) at time t1

A signal transmitted at time t2 will be received as

Now, if is relatively small, the channel may be

considered constant within the interval t1 to t2.

Coherence time (Tc) will therefore be given by

And from Clark’s model

2 1( ) ( )t th t h t

2 1cT t t 0,423

c

d

Tf

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OFDM multicarrier transmission

Single carrier transmission– each user transmits and receives data stream with only one carrier at

any time

Multicarrier transmission– a user can employ a number of carriers to transmit data

simultaneously

– FFT to replace the banks of sinusoidal generators

IFFT

1cos(2 )f t

2cos(2 )f t

cos(2 )Nf t

( )s t

( )s tS/P

bk

N

k

tfjk

kebtx1

2

N

k

ftkjkebtx

1

2

x(t) x(t)

x1(t)

x2(t)

xN(t)

tfje 12

tfje 22

tfj Ne2

source

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Fourier transform

)]([)()( 2 txFdtetxfX ftj

fxFdfefXtx ftj 12)()(

ff

f

eefj

dtetdtettF

fjfj

ftjftj

sinc)sin(

2

1

)()()]([ 2

1

2

122

Periodic and non-periodic signals, continuous spectrum

Example for rectangular pulse shape:

source

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OFDM Transmission

freq=

freq*

freq

t

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OFDM Transmission

freq

freqtime

freqtime

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-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

OFDM Transmission

1subcarrier f

2subcarrier f

3subcarrier f

4subcarrier f

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1.5

-1

-0.5

0

0.5

1

1.5

2

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-2

-1

0

1

2

3

4

-10 -5 0 5 10-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Time domain Frequency domain

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Discrete Fourier Transform (DFT)

N-point DFT:

N-point IDFT:

Discrete sequence of sampled signal, discrete spectrum

Four-point DFT: multiplying with {1, -1, j, -j}

21

0

nkN jN

n

X k x n e

21

0

nkN jN

k

x n X k e

0x

1x

2x

3x

0X

1X

2X

3X

j

j

1

j

1

1

j

1

0X

1X

2X

3X

0x

1x

2x

3x

Fast Fourier Transform: FFT

Derived to “radix-4 algorithm”

N-point DFT

– N2 multiplications or phase

rotation

– N2 complex additions

FFTmultiplications

additions

2

3log 2

8N N

2logN N

source

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Orthogonality

Time domain Frequency domain

Example of four subcarriers within one OFDM symbol Spectra of individual subcarriers

*

1 2( ) ( ) 0x t x t dt

*

1 2( ) ( ) 0X f X f df

source

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Orthogonal Frequency Division Multiplexing

Receiver integrates for symbol integral

Orthogonality criteria:

fTjT

tffj

Ttfjtfj

T

efT

fTdte

dteedttxtx k

2

0

2

0

*22

0

*2112

sin21

1

1

0

1

0

2N

k

k

N

k

tfjk txebtx k

if , n is a non-zero integer, i.e. , thenfT n n

fT

12 0

source

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OFDM and Multicarrier Transmission

(A)

(E)

(D)

(C)

(B)

1cf f 2cf f 3cf f 4cf f 5cf f

1

T

1

T

Orthogonal

Non-orthogonal

Orthogonal, n=3

Orthogonal, n=2

Orthogonal, n=1

(OFDM)

source

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Guard time and Cyclic Prefix

Direct path:

Reflected path:

Integration interval

We rely on that the subcarriers are orthogonal

Short subcarrier spacing (f=15 kHz) long symbol duration

Intersymbol interference is eliminated almost completely by introducing a guard interval with zero padding in every OFDM symbol.

Direct path:

Reflected path:

Integration interval

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FFT-based OFDM System

Serial-to-

Parallel

Converter

Signal

MapperIFFT

Parallel-

to-Serial

Converter

Guard

Interval

Insertion

Serial

Data

Input

x bits0d

1d

1nd

0s

1s

1ns

D/A &

Low pass

Filter

Up-

Converter

Down-

ConverterA/D

Guard

Interval

Removal

Serial-to-

Parallel

Converter

FFTOne-tap

Equalizer

Signal

Demapper

Parallel-

to-Serial

Converter

Serial

Data

Output

0dx bits

1d

1ˆ

nd

0s

1s

1ˆns

Channel

)(ts

Time

Frequency

Subchannels

Fast Fourier

Transform

Guard

Intervals

Symbols

source

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Links and references

www.3gpp.org

Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2, 36.300

Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation, 36.211

Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding , 36.212

Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures, 36.213

Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements , 36.214

LTE Physical Layer – General Description, 36.201

A good book: 3G Evolution – HSPA and LTE for Mobile Broadband, Academic Press 2007

Erik Dahlman; Stefan Parkvall; Johan Sköld; Per Beming

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36.201 – Physical layer general description

36.211 – Physical channels and modulation

36.212 – Multiplexing and channel coding

36.213 – Physical layer procedures

36.214 – Physical layer measurements

36.300 – E-UTRA overall description

36.302 – Services provided by the physical layer

36.304 – UE Functions related to idle mode

36.306 – UE radio access capabilities

36.321 – Medium Access Control (MAC)

Protocol Specification

36.322 – Radio Link Control (RLC)

Protocol Specification

36.323 – Packet Data convergence Protocol (PDCP)

Protocol Specification

36.331 – Radio Resource Control (RRC)

Protocol Specification

36.101 – UE radio transmission and reception (FDD)

36.104 – BTS radio transmission and reception (FDD)

36.113 – Base station EMC

36.133 – Requirements for support of Radio Resource

Management (FDD)

36.141 – Base station conformance testing (FDD)

36.401 – E-UTRA Architecture Description

36.410 – S1 interface general aspects & principle

36.411 – S1 interface Layer 1

36.412 – S1 interface signalling transport

36.413 – S1 application protocol S1AP

36.414 – S1 interface data transport

36.420 – X2 interface general aspects and principles

36.421 – X2 interface layer1

36.422 – X2 interface signalling transport

36.423 – X2 interface application part X2AP

36.442 – UTRAN Implementation Specific O&M Transport

All specifications can be found on the

web site www.3gpp.org

LTE Specifications

23.002 – Network Architecture

23.003 – Numbering, addressing and identification

23.009 – Handover Procedures

23.048 – Security mechanisms for USIM application

23.401 – GPRS enhancements for eUTRA

23.907 – QoS Concept

24.301 – NAS Protocol for Evolved Packet System (EPS)

24.302 – Access to the EPC via non 3GPP networks

33.401 – System Architecture Evolution (SAE);

Security Architecture

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Links and references

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