air interface evolution_the way to lte_(final slides april 2

8/10/2019 Air Interface Evolution_The Way to LTE_(Final Slides April 2

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Air Interface Evolution in Mobile NetworksAir Interface Evolution in Mobile NetworksCapacity & Performance Enhancing TechniquesCapacity & Performance Enhancing Techniques

The Way to LTE & 4The Way to LTE & 4thth Generation NetworksGeneration Networks

Prepared By: Ziad Z. Zorkot

Motorola Lebanon

Date: 14 April 2010


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Air Interface Evolution in Mobile Networks

Wireless EvolutionMobile Networks Evolution Starting from 2G

GSM

HSCSD

GPRS

EDGE

Enhanced EDGE

WCDMA

HSUPA

HSPA+

LTE

|

| HSPA

|

HSDPA

|

|

|

| UTRAN

|

|

|

|

|

|

| GERAN

|

|

|Based on TDMA

Based on CDMA

Based on OFDMA

20091990 1999


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GSM Evolution

CEPT GSM decision

to use TDMA

technology

Phase 1

Phase 2

Phase 2+ (R96)

Service provider display

EFR codec

Multiband operation & roaming

3V SIM SMS Cell Broadcast discontinuous operation

R97

14.4 kb/s data

Data compression

High Speed Circuit Switched Data (HSCSD)

PRM functions (group call, broadcast call, )

Multi-level precedence and pre-emption

Fast moving mobile

SIM application toolkit

Enhanced Advanced Speech Call

Calling Name presentation, CCBS, services

Improved fault management

SIM security

Private Numbering Plan

GPRS (1)

R98

1987

GSM

standardizationtransferred to ETSI

1990 1992 1995 1996 1997 1998

3GPP created


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3G Evolution

2009

R99

1999 2000

Rel-4

Rel-5

New codecs, codec management

Low chip rate TDD UMTS variant Location based services enhancement

UMTS Tx site diversity selection

LCS enhancements

IP multimedia subsystem (IMS)

Adaptive multirate codec

E-to-e QoS concepts

2001 2002 2003 2004 2005 2006 2007 2008

Rel-6

Rel-7

UTRAN Long Term Evolution study

System Architecture study

MIMO studies

UTRAN/GERAN/GAN handover

Rel-8

IMS (2) inc interworking with other IP networks

Packet-switched streaming services

Enhanced network security

Electrically tilting antennas

PS conversational codec characterization GERAN flexible layer 1

Generic access to GERAN services

HSPA+ study

UMTS radio technology (WCDMA)

Charging & billing enhancements

GPRS p-p service

1.5V SIM

Virtual Home Environment

OSA

>>>>>>> Work transferred from ETSI to 3GPP >>>>>>>

Evolved UTRAN [ie LTE]

E-UTRAN interworking with GERAN

eCall data transfer

Services alignment (for FMC) Reduced signalling latency


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Peak Data Rates

2G, 2.5G, 2.75G, 3G, 3.5G, 3.75G & 3.9G

HSPA+

42 Mbps

HSDPA

14.4 Mbps

GSM

9.6 kbps

GPRS in 2000

GSM First callmade in 1991

HSDPA in 2005

3G in 2001

EDGE in 2003

HSPA+ in 2008

LTE

320 Mbps

EDGE

473 kbpsWCDMA384 kbps

GPRS

114 kbps

3G3G

HSPA: 120 million cnt

WCDMA: 238 million cnt

2G2G GSM: 3.8 billion cnt

1990

2000

2003

2004

2006

2009

2010


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The Way to LTE


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Contents

Capacity & Performance Constraints

Enhancing Techniques

OFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels


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Contents



OFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels


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High Data Rates

Fundamental Constraints

Shannon Theorem: The Capacity of a Channel is determined by the Bandwidth

and the signal to noise ratio

C: Capacity, BW: Bandwidth, S: Received Signal power, N: White Noise power

For a given C There is no limit to how small the BW can be provided that the S/N is sufficiently large

There is no limit to how small the S/N can be provided that the BW is large enough

For a given BW

There is no limit to the capacity C provided that the S/N is large enough

There is no limit to how small the S/N can be provided that the capacity C will reduceaccordingly


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Capacity vs. Bandwidth

With Respect to S/N

Rearranging The capacity equation:

When S/N = -30C/B = 0.0014

When S/N = -25C/B = 0.0046

When S/N = -20C/B = 0.014

When S/N = -15C/B = 0.045

When S/N = -10C/B = 0.138

When S/N = -5C/B = 0.396

When S/N is 0C/B = 1

When S/N is largeC/B = 0.322 * S/N

0 5 10 15 20 25 30-30

1

2

4

6

8

10

12

C/B

S/N


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Capacity Limitations

Required Eb/N0as a Function of BW utilization

Re-writing the equation as a function of:

Eb: Energy/bit, R: Information Rate, No: Constant noise power spectral density

= Eb/No (BW Utilization)

High : Any increase in

the data rate requires a

much larger relative

increase in the received

signal power

Low : Any increase of

the data rate requires

approximately the same

relative increase in the

received signal power


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Improving S/N

Increasing Data Rate

Assuming a constant transmit power, the received signal power can always be

increased by reducing the distance between the transmitter and the receiver

In a mobile communication system this would correspond to a reduced cell size andthus the need for more cell sites to cover the same overall area

High data rates are only available for mobile terminals in the center of the cell, i.e. not

over the entire cell area

Another means to increase the overall received signal power for a given transmitpower is the use of additional antennas at the receiver side, also known as

receive-antenna diversity

The signal-to-noise ratio after the antenna combining can be increased in proportion to

the number of receive antennas

Multiple antennas can also be applied at the transmitter side

The use of beam-forming by means of multiple transmit antennas will focus the transmit

power in the direction of the target receiver

Combination of multiple antennas at the transmitter and receiver side can be used to

increase the data rate (MIMO)


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Other Constraints

Nyquists Theorem

Nyquists Theorem: a channel of BW B can carry a maximum capacity of 2Bsymbols per second

C = 2B symbols / second

Example:

C = 9600 bit/s, B = 2000 Hz, Calculate S/N? bits/symbols?

C/B = log2(1 + S/N)

S/N = 14.3 dB

C = 2B symbols / second = 4000 symbols / second (baud)

in order to the required C, each symbol must contain x number of bits

9600 bit/s = x bit * 4000 symbols/s x = 9600/4000 = 2.4

So at least 3 bit/s should be available

use 8PSK modulation


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Higher Order Modulation

High Data Rate Within a Limited BW

The use of higher-order modulation provides the possibility for higher bandwidth

utilization, that is the possibility to provide higher data rates within a given

bandwidth. The higher bandwidth utilization comes at the cost of reduced robustness to noise and

interference

Higher-order modulation schemes, such as 16QAM or 64QAM, require a higher Eb/N0

at the receiver for a given bit-error probability, compared to QPSK

2 bits / symbol 4 bits / symbol 6 bits / symbol


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Spectral Efficiency

Spectral efficiency, spectrum efficiencyor bandwidth efficiencyrefers to the

information rate that can be transmitted over a given bandwidth in a specific

communication system.

It is a measure of how efficiently a limited frequency spectrum is utilized by the physical

layer protocol, and sometimes by the media access control (the channel access

protocol)

The link spectral efficiencyof a digital communication system is measured in bit/s/Hz

or simply (bit/s)/Hz

The spectral efficiency can be improved by radio resource management

techniques such as efficient fixed or dynamic channel allocation, power control,

link adaptation and diversity schemes

frequency reuse, spectrum spreading and forward error correction reduce the spectralefficiency in (bit/s)/Hz but substantially lower the required SNR ratio in comparison to

non-spread spectrum techniques

In Wireless networks, spectral efficiency is better expressed in bit/s/Hz per unit area


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Spectral Efficiency Figures

Comparison Between Different Mobile Technologies


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Contents



OFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels


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Radio Channel Conditions

Instantaneous Variations

Mobile Radio communications are characterized by rapid and significant

variations in the instantaneous channel conditions

Frequency-selective fadingwill result in rapid and random variations in the channel

attenuation related to multipath propagation component having different propagations delays & attenuations;

when summing up in the receiver results in received signal where different frequencies of the

modulated waveform are experiencing different attenuations & phase changes

Shadow fading and distance-dependentpath loss will affect the average received

signal strength significantly (related to mobility of the receiver) The interference at the receiver due to transmissions in other cells and by other MS

Deep Fades


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Link Adaptation

Power Control

Dynamic power control dynamically adjusts the radio-link transmit power to

compensate for variations and differences in the instantaneous channel

conditions

The aim of these adjustments is to maintain a (near) constant Eb/N0at the receiver to

successfully transmit data without a too high error probability

Efficient for circuit switched voice services

transmit-power control

increases the power atthe transmitter when the

radio link experiences

poor radio conditions


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Link Adaptation

Rate Control

Data rate is dynamically adjusted to compensate for the varying channelconditions

Rate control does not aim at keeping the instantaneous radio-link data rate constant

Efficient for packet-switched data traffic Rate control implies that the power amplifier is always transmitting at full power

Radio-link data rate is controlled by adjusting the modulation scheme and/or thechannel coding rate

Rate control maintains the Eb/N0~ P/R at the desired level by changing the rate (not TX PWR)

Changing from 16

QAM 4/3 coding

rate to QPSK, coding rate


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Channel-Dependent Scheduling

Downlink Scheduling

With channel-dependent scheduling, the scheduler takes the instantaneous

radio-link conditions into account.

Scheduling the user with the instantaneously best radio link conditions is often referred

to as max-C/I (or maximum rate) scheduling

Measurements reports & signaling are needed to implement dynamic resource allocation

The channel used for transmission will typically have a high quality and, with rate

control, a correspondingly high data rate can be used

This translates into a high system capacity resulted from Multi-User Diversity


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Different Scheduling Behaviors

Max C/I, RR & PF

Max C/I Scheduling

Beneficial from system

capacity point of view but not

fair in all situation. A mobilewith bad C/I all the time will

never be scheduled

Round Robin Scheduling

the users will take turns in

using the shared resources,

without taking the instant C/Iinto account. Not fair in the

sense of providing same QoS

Proportional-fair Scheduler

it utilizes fast variations in

channel conditions as much

as possible while stillsatisfying some degree of

fairness between users


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Uplink Scheduling

Unlike the downlink, where pure TDMA often can be used, uplink scheduling

typically has to rely on sharing in the frequency and/or code domain in addition to

the time domain

Channel-dependent scheduling is also beneficial in the uplink case

In case of a non-orthogonal multiple-access scheme such as CDMA, power

control is typically essential for proper operation

Power control also serves the purpose of controlling the amount of interferenceaffecting other users

In case of orthogonal multiple-access scheme, intra-cell power control is

fundamentally not necessary and the benefits with channel-dependent

scheduling become more similar to the downlink case A terminal can transmit at full power and the scheduler assigns a suitable part of the

orthogonal resources (suitable part of the overall BW)

In Practice, a certain degree of power control maybe necessary


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Advanced Retransmission Schemes

Hybrid ARQ with Soft Combining

Hybrid ARQ is a combination of:

Forward error-correcting FEC coding

It uses forward error correcting codes to correct a subset of all errors and rely on error detection

to detect uncorrectable errors

Automatic repeat request ARQ

Erroneously received packets are discarded and the receiver requests retransmissions of

corrupted packets

Hybrid ARQ schemes are built around a CRC code for error detection and

convolutional or Turbo codes for error correction

Retransmission in any hybrid ARQ scheme must, by definition, represent the same set

of information bits as the original transmission

The set of coded bits transmitted in each retransmission may be selected differently

Hybrid ARQ with soft combining is categorized into Chase combining and

Incremental Redundancy

The received signal still contains information despite that the packet was not decoded


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Chase Combining

The retransmissions consist of

the same set of coded bits as the

original transmission.

The receiver uses MRC to

combine each received channel bit

with any previous transmissions of

the same bit and the combined

signal is fed to the decoder

Chase combining does not

give any additional coding

gain but only increases the

accumulated received Eb/N0

for each retransmission a lowaverage channel quality. (No

new redundancy is added)


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Multiple Antennas

Multiple antennas at the transmitter and/or the receiver can be used to provide

additional diversity against fading on the radio channel This is called Spatial

Diversity or Transmit / Receive Diversity

Multiple antennas at the transmitter and/or the receiver can be used to shape

the overall antenna beam (transmit beam and receive beam, respectively) in a

certain way This is called Beam Forming or Smart Antenna

For example, to maximize the overall antenna gain in the direction of the targetreceiver/transmitter or to suppress specific dominant interfering signals

The simultaneous availability of multiple antennas at the transmitter and the

receiver can be used to create what can be seen as multiple parallel

communication channels over the radio interface This is called SpatialMultiplexing or MIMO (Multiple Input Multiple Output)

This provides the possibility for very high BW utilization without a corresponding

reduction in power efficiency i.e. the possibility for very high data rates within a limited

bandwidth without an un-proportionally large degradation in terms of coverage


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Receive Diversity

Multiple antennas at the

receiver side. This is often

referred to as receive

diversity or RX diversity.the aim of the multiple

receive antennas is to

achieve additional diversity

against radio channel fading

Phase rotate the signals received

at the different antennas to

compensate for the corresponding

channel phases and ensure that

the signals are phase alignedwhen added together

Weight the signals in proportion totheir corresponding channel gains,

that is apply higher weights for

stronger received signals


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Diversity Benefits

MRC Operation

SNR enhanced

for all users after

MRC


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Spatial Multiplexing

Multiple TX/RX Antennas

Single Antenna Multiple AntennasNL: min {NT, NR)

NT: # of Tx Antennas

# of Rx Antennas

spatial multiplexing: allow for more efficient utilization of high signal-to-noise

/interference ratios and significantly higher data rates over the radio interface


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MIMO Configurations

Single Codeword Transmission

Increases the users Performance

(SNR) by sending the same data

over several channels (multiple TxAntennas for same data)

Multi-Codeword Transmission

Increases the users Throughput

and cell capacity by sending thedifferent data over several

channels (multiple Tx Antennas for

different data)

Space Time Coding



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MIMO Benefits


SU-MIMOIncreases the users

capacity by allowing a

single user to benefit from

multiple data streams

MU MIMO

Increases sector capacity by

selecting users having goodRF channel conditions and

sharing their data streams


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Adaptive MIMO

High SNRLow SNR

Efficiency

STBC Space Time Block Coding SM Spatial Multiplexing

Adaptive Mode

Selection

CoverageEnhancement

Capacity

Enhancement


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Smart Antennas

Beam Forming

Sectorized Configuration Simple Beamforming Full Adaptive Antenna

System

Distribution of radio energy and number of users per radio resource in sector


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Multi-Carriers Transmission

Frequency Selectivity Impact

Multi-carrier transmission is used to increase the overall transmission BW,

without suffering from signal corruption due to radio-channel frequency selectivity

Multi-carrier transmission implies the transmission of multiple narrowband signals

instead of more wideband signal (often referred to as sub-carriers)

Frequency selectivity fading

has more impact on large BW

transmission. All data within

the whole BW will be impacted

and requires retransmission

With Multi-carriers

transmission, the impact of

frequency selective fading

will be on few limited small

BW carriers only


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Concept of Multi-Carriers

Drawbacks: spectrum of each sub-

carrier does not allow for very tight

sub-carrier packing. (negative

impact on overall BW spectrumefficiency) Resulting in limited

number of sub-carriers

The parallel transmission of multiple

carriers will lead to larger variations

in the instantaneous transmit

power. (negative impact on the

transmitter power amplifier -increased power consumption and

power amplifier cost)

Single Carrier Transmission

Multi-carriers

Transmission

Extension to

wider BW


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Dual Carriers Operation

Special Case of Multi-Carriers Transmission

To increase the data rate, it is possible to assign to a mobile station two carriers

in the downlink or uplink

Better resource utilization and spectrum efficiency by means of joint resource allocation

and load balancing across the carriers

Normal Operation in

HSDPA System. 5

MHz CH BW

allocated per user

Dual Carrier Operation

Two carriers can be

allocated to serve one

user, two users or

more


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Contents


Enhancing TechniquesOFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels


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OFDM Concept

Orthogonal Frequency Division Multiplexing (OFDM) is a spread spectrum

technology that distributes the data over a large number of carriers that are

spaced apart at precise frequencies

The carriers for each channel are made orthogonal to one another, allowing them

to be spaced very close together

The number of OFDM subcarriers can range from less than one hundred to

several thousand, with the subcarrier spacing ranging from several hundred kHzdown to a few kHz

This results in the signal having a high tolerance to multipath delay spread, as the delay

spread must be very long to cause significant intersymbol interference

What subcarrier spacing to use depends on what types of environments the

system is to operate in, including the maximum expected radio channel

frequency selectivity and the maximum expected rate of channel variations

For 3GPP LTE the basic subcarrier spacing equals 15 kHz


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OFDM Transmission

Special Case of Multi-Carriers & FDM

Benefits: Use of relatively

large number of sub-carriers.

WCDMA multi-carrier

evolution to a 20MHz

overall transmission

bandwidth could consist of

four (5 MHz BW sub-

carriers). In comparison,

OFDM transmission caninclude several hundred

sub-carriers transmitted

over the same radio link to

the same receiver

Tight frequencydomain packing of

the subcarriers with

a subcarrier spacing

f =1/Tu, where Tu is

the per-subcarrier

modulation-symbol

time

Orthogonal Frequency Division

Multiplexing


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OFDM Processing Steps

Example using BPSK

O


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OFDM Modulation

OFDM transmission is block

based, implying that, during

each OFDM symbol interval,

Nc modulation symbols are

transmitted in parallel.The modulation symbols can

be from any modulation

alphabet, such as QPSK,

16QAM, or 64QAM.

The physical resource in

case of OFDM

transmission is often

illustrated as a time

frequency grid. According

to the Figure, eachcolumn corresponds to

one OFDM symboland

each row corresponds to

one OFDM subcarrier

OFDM S b l & S b i


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OFDM Symbols & Sub-carriers

OFDM D d l ti


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OFDM Demodulation

OFDM demodulator consists

of bank of correlators, one for

each sub-carrier

IFFT & FFT


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IFFT & FFT

OFDM Modulation & Demodulation

IFFT OFDM Modulator

FFT OFDM Demodulator

Important Parameters (Values

related to BW size)

Nc: Number of sub-carriers

N: FFT Size

f: Carrier Spacing

fs: sampling Rate = f x N

ODFM Transmission


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ODFM Transmission

Example

OFDM Operation


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OFDM Operation

Example

IFFT Modulator


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IFFT ModulatorExample

FFT Demodulator


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FFT DemodulatorExample

OFDM


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OFDMOrthogonal Frequencies (Harmonics)

Time Dispersion


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Time Dispersion

In case of a time dispersive

channel, the orthogonality

between the subcarriers will,

at least partly, be lost.

the demodulator

correlation interval for

one path will overlap with

the symbol boundary of adifferent path

This will result in inter-symbol interference

within a subcarrier and

interference between

subcarriers

Cyclic Prefix Insertion CP


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Cyclic Prefix Insertion CP Minimizing the Impact of Time Dispersion

CP: the last part of the

OFDM symbol is copied

and inserted at the

beginning of the OFDM

symbol

subcarrier orthogonality will be preserved in

case of a time-dispersive channel, as long as

the span of the time dispersion is shorter than

the cyclic-prefix length

CP Insertion Example


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CP Insertion Example

OFDM Example


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OFDM ExampleUsing 4 Subcarriers

Channel Estimation


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Channel EstimationOFDM Transmission / Reception

Using a known reference signal

Reference Pilot, the receiver can

estimate the frequency domain

channel and recover properly the

transmitted symbol

Basic OFDM Parameters


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Basic OFDM Parameters

The subcarrier spacing f

The number of subcarriers Nc Together with the subcarrier

spacing, determines the overall

transmission bandwidth of the

OFDM signal

The cyclic-prefix length TCP.

Together with the subcarrier

spacing f =1/TU, the cyclic-prefix

length determines the overall OFDM

symbol time T =TCP+TUor,equivalently, the OFDM symbol rate

Nc

Frequency Diversity


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eque cy e s tyIn coordination with Channel Coding

Each information bit will

experience frequency

diversity in case of

transmission over a radio

channel that is frequency

selective over the

transmission bandwidth.

This is called alsofrequency interleaving

OFDM Multiplexing / Multiple Access


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p g pDownlink / Uplink (Localized)

In the downlink direction, OFDM as a

user multiplexing scheme implies that, in

each OFDM symbol interval, different

subsets of the overall set of available

subcarriers are used for transmission to

different mobile terminals

Similarly, in the uplink direction, OFDM as a

user-multiplexing or multiple-access scheme

implies that, in each OFDM symbol interval,

different subsets of the overall set of subcarriers

are used for data transmission from different

mobile terminals This is often called OFDMA

Distributed Multiplexing


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p gAdditional Frequency Diversity

Distributing the subcarriers to/from a mobile terminal in

the frequency domain is also possible. The benefit of such

distributed user multiplexing or distributed multiple access

is possibility for additional frequency diversity as each

transmission is spread over a wider bandwidth

OFDM vs. OFDMA


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OFDM / OFDMA


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The Choice for 4th Generation Mobile Networks

Contents


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OFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels

SC-FDMA


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Single Carrier Frequency Division Multiple Access

OFDM modulation has a drawback like any kind ,multi-carrier transmission, is the

large variations in the instantaneous power of the transmitted signal

Such power variations imply a reduced power-amplifier efficiency and higher power-

amplifier cost.

This is especially critical for the uplink, due to the high importance of low mobile-

terminal power consumption and cost

SC-FDMA (single carrier frequency division multi access) was chosen because it

combines: The low PAPR techniques of single-carrier transmission systems, such as GSM and

CDMA

With the multi-path resistance and flexible frequency allocation of OFDMA

SC-FDMA is a new multiple access technique that utilizes Single carrier modulation, DFT-spread orthogonal frequency multiplexing, and

frequency domain equalization

DFT Spread OFDM (DFTS-OFDM)F D i G ti


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Frequency Domain Generation

SC-FDMA can be generated in the time domain or in the frequency domain

Frequency-domain-generated SCFDMA is simply a pre-coded OFDMA scheme where

pre-coding is carried out by the DFT matrix

a block of M modulation

symbols from some modulation

alphabet, e.g. QPSK or16QAM, is first applied to a

size-M DFT different mobile

terminals

The output of the DFT is then

applied to consecutive inputs of a

size-N inverse DFT where N >M

and where the unused inputs of

the IDFT are set to zero

Single Carrier

(Time Domain)

Sequential transmission of

the symbols over a single

frequency carrier

FDMA -User multiplexing

in the frequency domain

SC-FDMA Generation


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Despite its name, Single Carrier Frequency Division Multiple Access (SC-FDMA)

also transmits data over the air interface in many sub-carriers but adds an

additional processing step (DFT)

Data symbols in the time domain are converted to the frequency domain using adiscrete Fourier transform (DFT)

Then in the frequency domain they are mapped to the desired location in the overall

channel bandwidth

And after that, converted back to the time domain using an inverse FFT (IFFT)

SC-FDMA ExampleU i 4 S b i


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Using 4 Subcarriers

DFT Converts M symbols in the time domain into M subcarriers in the frequency domain

DFT Length and sampling rate are chosen so that each signal is represented by M bins spaced

15KHz apart

Each Bin will have its own fixed amplitude & phase

OFDMA vs. SC-FDMA


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OFDMA transmits the four

QPSK data symbols in

parallel, one per subcarrier

SC-FDMA transmits the four QPSK

data symbols in series at four times

the rate, with each data symbol

occupying M x 15 kHz bandwidth

Each symbol

represented by awide signal

DFT spreads

symbols over all

subcarriers

Peak To Average Power RatioOFDM vs DFTS OFDM


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OFDM vs. DFTS-OFDM

16 QAM

QPSK

the PAR is significantly lower for DFTS-

OFDM, compared to OFDM. In case of

16QAM modulation, the PAR of DFTS-

OFDM increases somewhat as

expected

For OFDM, the

PAR distribution is

more or less

independent of the

modulationscheme

SC-FDMA Receiver


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The operations are basically the reverse

of those for the DFTS-OFDM signal

generation i.e. size-N DFT (FFT)

processing, removal of the frequency

samples not corresponding to the signal

to be received, and size-M inverse DFT

processing

SC-FDMA & OFDMACommon Elements


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Common Elements

Constellation mapper: Converts incoming bit stream to single carrier symbols (BPSK, QPSK, or 16QAM depending on channel

conditions) Serial/parallel converter: Formats time domain SC symbols into blocks for input to FFT engine

M-point DFT: Converts time domain SC symbol block into M discrete tones

Subcarrier mapping: Maps DFT output tones to specified subcarriers for transmission. SC-FDMA systems either use contiguoustones (localized) or uniformly spaced tones (distributed). LTE uses localized subcarrier mapping

N-point IDFT: Converts mapped subcarriers back into time domain for transmission

SC-FDMA Only Common to OFDMA & SC-FDMA

Uplink Users Multiplexing


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By dynamically adjusting the transmitter DFT size

and, consequently, also the size of the block of

modulation symbols a0, the nominal bandwidth of

the DFTS-OFDM signal can be dynamically

adjusted DFTS-OFDM

By shifting the IDFT inputs to which the DFT outputs

are mapped, the exact frequency-domain position

of the signal to be transmitted can be adjusted. By

these means, DFTS-OFDM allows for uplink FDMA

with flexible bandwidth


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SC-FDMA Distributed


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The PAPR performance

of Distributed SC-FDMA is better

than that of Localized SC-FDMA

PAR Difference (Example)Nc = 256 system subcarriers, M = 64 subcarriers per user


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Nc 256 system subcarriers, M 64 subcarriers per user

Distributed

SC_FDMA

Localized

SC_FDMA

OFDMA

QPSK 16 QAM

In the case of no pulse shaping, thePAPR of Distributed SC-FDMA is 10.5

dB lower than the PAPR of OFDMA

for QPSK modulation. The PAPR of

Localized FDMA is lower than the

PAPR of OFDMA by 3 dB for QPSK

The PAPR of Distributed SC-FDMA is7 dB lower than the PAPR of OFDMA

for 16 QAM modulation. The PAPR of

Localized SC-FDMA is lower than the

PAPR of OFDMA by 2 dB for 16 QAM

Contents


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OFDM OFDMA

SC-FDMA

LTE Overview

LTE InterfacesLTE Physical Layer

LTE Channels

GERAN NetworkGSM, GPRS, EDGE (Releases .., 96, 97, 98 & 99)


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, , ( , , , )

UMTS Release 99 & 4


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UMTS Release 5HSDPA & IP Interfaces


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UMTS Release 6HSUPA


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UMTS Release 7HSPA+ (MIMO)


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UMTS Release 8LTE Introduction


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LTE Overview


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Evolved Packet CoreEvolved Universal Terrestrial

Radio Access Network

LTE Network ElementsEPS (EPC + E-UTRAN + UE)


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LTE Air InterfaceE-UTRA Specifications


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LTE CharacteristicsAdaptive Modulation


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Adaptively select the modulation type and coding ratedepending on the received SINR

LTE Scalable Bandwidth (1.4MHz to 20 MHz)DL Performance Figures


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LTE Soft Frequency Reuse


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SFR

Inner zones of the cell use all sub-bands

with less power

Outer zones uses reserved sub-bands

with high power

LTE CharacteristicsChannel Dependent Scheduling


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Downlink channel-

dependent scheduling

in time and frequency

domains.

in addition to assigning the time

frequency resources to the mobile

terminal, the eNodeB scheduler is also

responsible for controlling the transport

format (payload size, modulation

scheme) the mobile terminal shall use

LTE CharacteristicsHRQ with Soft Combining


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CRC insertion, rate-1/3 Turbo

coding Puncturing to

generate different

redundancy versions match the number of

coded bits to the channel

LTE CharacteristicsHRQ with Soft Combining DL Operation


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LTE CharacteristicsHRQ with Soft Combining UL Operation


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LTE System PerformanceDL/UL FDD & TDD (20 MHz BW)


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E-UTRANEvolved Universal Terrestrial Radio Access Network


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EPCEvolved Packet Core


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UESpectrum, Power & Category


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24

eNodeB Functions


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MME Functions


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PDN GW Functions


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LTE InterfacesEPS Reference Points


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E-UTRAN Protocol StackControl Plane


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Radio Resource Management


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E-UTRAN Protocol StackUser Plane (S1-U)


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E-UTRAN Protocol StackUser Plane (S5-U)


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E-UTRAN Protocol StackControl Plane (S5-C)


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E-UTRAN Protocol StackUser Plane


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E-UTRAN Protocol StackControl Plane (S10)


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E-UTRAN Protocol StackControl Plane (S11)


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E-UTRAN Protocol StackControl Plane (S6a)


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E-UTRAN Protocol StackControl Plane (X2-CP)


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E-UTRAN Protocol StackUser Plane (X2-UP)


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X2 Interface MobilityHandover Initiation


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X2 Interface MobilityHandover Completion


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Contents


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OFDM OFDMA

SC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels

E-UTRA Physical Layer


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Subcarriers TypesData, Reference, Guard & DC

Subcarrier associatedUsed to estimate the RF


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Subcarrier associated

with the channel center

frequency

conditions

Used to carry traffic and

signalingUsed to eliminate inter-

channel interference

OFDM Symbol


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One subcarrier

OFDM Data SubcarriersExample: FFT Size 512


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OFDM Symbol Mapping


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LTE Generic Frame Structure


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LTE Frame Length & Subcarriers


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LTE Time Domain Structure

different time intervals within theLTE radio access specification can

be expressed as multiples of a

basic time unit Ts =1/30720000


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basic time unit Ts 1/30720000

Tframe =307200 *Ts

Tsubframe =30720*Ts.


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Resources per SlotOFDMA Symbols & PRB Within Slot (0.5 msec)


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Resources per Slot3D View(OFDMA Symbols & PRB Within 0.5 msec)


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Downlink resource blockassuming normal cyclic

prefix, i.e. seven OFDM

symbols per slot

Resources AllocationsSub-frame, Slot, PRB, Element


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One slot consist of 7 OFDMsymbols in case of normal CP

and 6 symbols in case of

extended CP

Symbols / SlotCP & eCP Parameters


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2048 Samples160 Samples

144 Samples

Symbols / SlotCP & eCP Parameters (Timing Derivation)

Tu =1/f 66.7s (2048 * Ts).

TCP =160 Ts = 5 2s (first OFDM symbol)


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TCP=160Ts = 5.2s (first OFDM symbol),

TCP =144Ts = 4.7s (remaining OFDM

symbols)

TCP-e = 512Ts = 16.7s

Used for extended

cell range

LTE CP Parameters


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The reduced subcarrier spacing specifically targets MBSFN-

based multicast/broadcast transmissions.

More specifically the possibility to make synchronous multi-

cell multicast/broadcast transmissions appear as a singletransmission over a multi-path channel

Available Resource Blocks


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OFDMA Subcarrier MappingExample: QPSK Symbol Mapping


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SC-FDMA Subcarrier MappingExample: QPSK Symbol Mapping


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OFDM BW Allocation


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OFDMA BW Allocation


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OFDMA Modulation Mapping


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PS Call


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Contents




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OFDM OFDMASC-FDMA

LTE Overview

LTE Interfaces

LTE Physical Layer

LTE Channels

LTE Channel Architecture


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Logical Channels

Common Control Channel (CCCH)

Carries RRC signaling when no RRC

connection currently exists for the UE

Dedicated Control Channel (DCCH)

A bidirectional control channel used

to carry signaling information when an

RRC connection exists for the UE


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Dedicated Traffic Channel (DTCH) A

point-to-point channel dedicated to one

UE for transmission of user data. The

DTCH may be uplink, downlink, or both.

Broadcast Control Channel

Paging Control Channel

Multicast Channel

Transport ChannelsLogical to Transport Channel Mapping


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Downlink Shared Channel

(DL-SCH) Carries DL data

and some control traffic.

Uplink Shared Channel (UL-

SCH) Carries UL data and

some control traffic.

Physical ChannelsTransport to Physical Channel Mapping


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Carries Hybrid ARQ (HARQ) ACKs or

NACKs for the UL transmissions on the

PUSCH. The PHICH uses BPSK encoding.

Transmitted every subframe to inform the UE about

the number of OFDM symbols used for the PDCCH

channel. The PCFICH uses QPSK encoding

Channels MappingLogical to Transport to Physical


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Other Physical Signals


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LTE Specific Signals

Downlink Physical Signals

DL Demodulation Reference Signals (RS)

Synchronization Signals


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Uplink Physical Signals

UL Demodulation Reference Signals

Sounding Reference Signals

Random Access Preamble

Signals and Synchronization Signals.

The eNodeB and UE use Demodulation Reference Signals (DRS) to estimate RF

channel quality (measure SNR)

The eNodeB transmits periodic Synchronization Signals (SS) to synchronize each UE

with the recurring physical slots and frames. The eNodeB uses Sounding Reference Signals (SRS) to control frequency-

dependant scheduling for a UE.


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DL Reference Signal2 Ports & 4 Ports Antennas


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LTE Synchronization ChannelsPrimary & Secondary


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Used for cell search and

identification by the UE.

Carries part of the cell ID

Used for cell search and

identification by the UE.

Carries the remainder of

the cell ID

Uplink DRS & SRSDemodulation and Sounding Reference Signals


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DRS: Used for channel estimation to help

the demodulation of the control and datainformation in the eNB. Located on the 4th

symbol of the SC-FDMA sub-frame and

uses the same BW allocated of the UE in

the UL (0ccupies all Subcarriers)

SRS: provides the eNB uplink

channel quality information to be

used for scheduling when no ULdata transmission is available. The

SRS is transmitted in the last

symbol of the sub-frame

DL LTE FDD Sub-Frame Structure


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FDD LTE DL Frame Structure


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FDD LTE UL Frame StructureShowing PUSCH


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FDD LTE UL Frame StructureMapping of PUCCH in


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air interface evolution_the way to lte_(final slides april 2

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