01 LTE Physical Layer_p1

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LTE Physical Layer part 1


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Physical layer overview

OFDM: Downlink Modulation

SC-FDMA: Uplink Modulation

MIMO (Multiple Input Multiple Output)

Agenda

for Conf. Call 2009-12-04 2


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Physical layer overview


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Channel Mapping

PBCH PDSCH PCFICH PDCCH PHICH PUCCH PUSCH PRACH

ACK/NACK

- Sched TF DL

- Sched grant UL

- Pwr Ctrl cmd

- HARQ infoPDCCH info

PCCH BCCH DTCH DCCH CCCH DTCH DCCH CCCH

- CQI

- ACK/NACK

- Sched req

PCH BCH DL-SCH UL-SCH RACH

MIB SIB

Physical Channel

bit, symbol, modulation,radio frame etc.

Transport Channel

how and with whatcharacteristics data are

transferred

Logical Channel

what type of informationis transferred

UplinkDownlink


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Downlink (OFDM)


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Solutions for high-speed wireless telecommunication

Issues Solutions

InterSymbol interference(ISI)

Fading

Spacing more

between symbols

Dividing into sub-carrier

Frequency scheduling

/Adaptive modulation

RAKE receiver

to combine multipath

(for CDMA)


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Fading

Multipath Fading

Frequency selective fading

reflective

wave (B)

direct

wave (A)

The composite wave attenuates in order to combine the direct wave

with the reflective wave which has different phase shift.

composite w ave

(A)+(B)

Quality of the particular bandwidth drops due to mult ipath.

It may vary with time and geographical position.

Ampl itude

Frequency


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Downlink - OFDM

Parallel transmission using multiple narrowband sub-

carrier.

s(t)is given by:

whereN is the number of sub-carriers.

0*f0

S/P

Frequency

f0 = 15kHz

=

=

==1

0

2

00

1

0

0)2sin2cos()(N

n

tnfj

nn

N

n

n edtnfbtnfats

20MH (example)d0, d1,, dN-1

1*f0

(N-1)*f0Time (t)

s(t)

T= 1 /f0

s(t)

(di_= ai+ jbi)


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Downlink - OFDM

In order to implement this function,Ndigital modulators andNcarrier wave generators are needed. (In case of LTE, maximum

number ofNis 2400)

Consider that s(t)( )is sampled during symbol period T at1/N

intervals.

=

=

=

===

1

0

21

0

21

0

20

00N

n

N

nkj

n

N

n

Nf

knfj

n

N

n

TN

knfj

n edededT

N

ks

Unrealistic!!

This means that s(t) can be computed

by Inverse FFT from dn(n=0,..., N-1).

Tt


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Uplink (SC-FDMA)


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Disadvantage of OFDM (1)

sub-carrier 1

sub-carrier 2

sub-carrier 3

High Peak

Consisting of a large number of sub-carriers results in

a high PAPR (Peak to Average Power Ratio).


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Disadvantage of OFDM (2)

Performance of Power Amplifier

Linear zone Non-linear zone

Input

Output

Distortion!!

Saturation

Point

FrequencyActual bandwidth

Ampl ification on non-linear zone

causes harmonic component.

Interference with adjacent bandwidth


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MIMO


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Type of Multi-antenna technology

Beam Forming Tx Diversity Space Multiplexing

OmnidirectionalDirectional Reducing the effect of fading Multiplexing data streamsAntenna / Beam forming gain

(e.g.) (e.g.) (e.g.)

Delay

S/P

Transmit ting the same

signal in all directions

Transmitting signal

in best direction

Transmitting

multiple signals

in different directions

MIMO

(Multiple Input Multiple Output)

MISO

(Multiple Input Single Output)

MISO

(Multiple Input Single Output)


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Precoding

UE estimates the channel, selects the best precoding matrixand feeds back the selected index in the codebook to

eNodeB.

Pre-

coding

Feedback Precoding Matrix Index

W: Selected from pre-defined codebook known at eNodeB and UE

=

1

0

s

sS

=

1110

0100

hh

hhH

W

nSWHy

yY +=

=

1

0

.


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Usage of multi antenna technology for LTE

Throughput

Coverage

Space

Multiplexing

Combined wi th

Space Multiplexing &

Beamforming

TX Diversi ty

Beamforming

Different antenna technology can be used

in accordance with the objective.


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Overview of physical channel processing

Downlink

Uplink

Scrambling Modulationmapper

Transformprecoder

Resource

element mapperSC-FDMAsignal gen.

ScramblingModulation

mapper

Layer

mapperPrecoding

Resource element

mapper

OFDM signal

generation

Resource elementmapper OFDM signalgenerationScrambling Modulationmapper

layers antenna portscode words

from

channel

coding

fromchannel

coding

To

Antenna

ToAntenna


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backup


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Reference Signal

There are three ways to transmit reference signal. Cell Specific

Common in the cell (similar to CPICH on UMTS)

Consist of the sequence identifying cell (similar to SC on UMTS)

When a reference signal is transmitted from one antenna port,it is not transmitted from any other antenna ports in order toidentify antenna port.

UE SpecificIt is used for a particular UE. (e.g. beamforming)

MBSFN SpecificExtended CP is taken into consideration.


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Reference Signal

There are three ways to transmit reference signal. Cell Specific

Common in the cell (similar to CPICH on UMTS)

Consist of the sequence identifying cell (similar to SC on UMTS)

When a reference signal is transmitted from one antenna port,it is not transmitted from any other antenna ports in order toidentify antenna port.

UE SpecificIt is used for a particular UE. (e.g. beamforming)

MBSFN SpecificExtended CP is taken into consideration.


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01 LTE Physical Layer_p1