LTE resource PCI learning

1 © Nokia Siemens Networks

OFDMALTE Air Interface Course


OFDMA

FDD and TDD ModesBasics of OFDM OFDM Transmitter OFDM Receiver OFDM Key Parameters for FDD and TDD ModesData Rate Calculation OFDMA OFDM Transmitter Simulation


Air Interface Main Issues

UL

DL

UE 1

UE 2

UE 3

Air Interface

UE

eNodeB

1. Duplex Transmission

2. Multiple Access

eNodeB

eNodeB


LTE FDD and TDD Modes

Uplink Downlink

Bandwidthup to 20MHz

Duplex Frequencyf

t Bandwidthup to 20MHz

GuardPeriod

f

t

Uplink

Downlink

Bandwidthup to 20MHz


In FDD, DL & UL use different bands with the same bandwidth• => DL throughput = UL throughput• What happens if throughput requirements are different for DL and UL?

• Potential solution: Use different bandwidth for DL & UL?

• Hard to manage frequency bands in this case

• Simpler solution• DL & UL are duplexed in time rather than in frequency => TDD (Time Division

Duplexing)• DL & UL share the same bandwidth• DL and UL are active in different subframes

TDD vs. FDD (1/2)


TDD vs. FDD (2/2)

Downlink Downlink

Uplink

Uplink

FDD TDD

Time

Frequency

Throughput

DL DLUL UL

Only this is needed

Wasted

We get what we need

Downlink throughput is also affected


RF FDD architecture

Duplex filters for each Tx and Rx pathCirculator has the role of separating DL & UL waves• It must exhibit great isolation properties, so that Tx signal does not leak

into Rx path

Power amplifier

Low-Noise amplifier

TX

RX

TX Duplex Filter

RX Duplex Filter


RF TDD architecture

Duplexer must switch between Tx and Rx paths• Switching driving signal must be accurate• Good timing control of the signal

Power amplifier

Low-Noise amplifier

TX

RX

Channel Filter

Channel Filter

TX

RX

Duplexer


FDD and TDD Modes Comparison

FDD and TDD mode included together in the same specification

Same radio interface schemes for both uplink and downlink(OFDM and SC-FDMA)

Same subframe formats

Same network architecture

Same air interface protocols

Same physical channels procedures

FDD and TDD modes Harmonisation(commonalities)

In LTE there is a high degree of harmonisation between

FDD and TDD modes

1. Spectrum Allocation: TDD is using the same frequency bands for

both UL and DL→ FDD requires a paired spectrum with

duplex separation in frequency →TDD requires an unpaired spectrum with

some guard bands in time to separate UL and DL

2. UE complexity:In FDD the UE is requiring an duplex filter

(for UL – DL separation)In TDD the filter is not needed → Lower complexity for TDD terminals

FDD and TDD modes differences regarding the air interface


Multiple Access

Time

1 2 3 4 5

2

12345

4 2

1

23

45

31

15

53

3

24

1

Pow

er

Frequency

TDMATime Division

Multiple Access,2G e.g. GSM,

PDC

FDMAFrequency Division

Multiple Access1G e.g. AMPS,

NMT, TACS

CDMACode Division

Multiple Access3G e.g. UMTS,

CDMA2000

1 2 3UE 1 UE 2 UE 3 4 UE 4 UE 55

OFDMAOrthogonal

Frequency DivisionMultiple Access

e.g. LTE


Multiple Access

• In LTE OFDMA = Orthogonal Frequency Division Multiple Access it is used in the Downlink

• In the UL SC-FDMA = Single Carrier Frequency Division Multiple Access Access it is used

• OFDMA and SC-FDMA will be used for both FDD and TDD Modes!

• Approach for the explanation:• First OFDM as technology will be explained (for single user case)• Second it is shown how OFDM could be used to separate users

• UL SC-FDMA will be explained in the next chapter


OFDMA



Challenges for the Air Interface Design

For the LTE Air Interface design it should be considered a trade-off between the following factors (based on the LTE requirements):

1. What should be the required radio spectrum ?

2. Speed of data transmission (bit rate as high as possible)

3. Complexity of implementation (as small as possible)

→ How could it be realised ?

Solution: use the rectangular pulse shape (see next slide)


The Rectangular Pulse

Advantages:+ Simple to implement: there is no complex filter system required to detect such pulses and to generate them.+ The pulse has a clearly defined duration. This is a major advantage in case of multi-path propagation environments as it simplifies handling of inter-symbol interference.

Disadvantage: - it allocates a quite huge spectrum. However the spectral power density has null points exactly at multiples of the frequency fs = 1/Ts. This will be important in OFDM.

time

ampl

itude

Ts

f s 1Ts

Time Domain

frequency f/fs

spec

tral

pow

er d

ensi

ty Frequency Domain

fs

FourierTransform

Inverse FourierTransform


Fourier Transform

InverseFourier Transform

Time Domain

Frequency Domain

W 1Tc

Tc

Fc

1.3 * W

Pulse Form and Spectrum in WCDMA

As a counter example look at the root raised cosine roll off pulse that is used in WCDMA. As one can see this pulse is not clearly located in the time domain. So if we put two such pulses one after another, there will be always some interference from the first to the second. On the other hand the spectrum of these pulses is concentrated in a clearly defined frequency band.


OFDM Basics• Transmits hundreds or even thousands of separately modulated radio signals using orthogonal subcarriers spread across a wideband channel

Orthogonality:

The peak ( centre frequency) of one subcarrier …

…intercepts the ‘nulls’ of the neighbouring subcarriers

15 kHz in LTE: fixed

Total transmission bandwidth


OFDM Basics

• Data is sent in parallel across the set of subcarriers, each subcarrier only transports a part of the whole transmission

• The throughput is the sum of the data rates of each individual (or used) subcarriers while the power is distributed to all used subcarriers

• FFT ( Fast Fourier Transform) is used to create the orthogonal subcarriers. The number of subcarriers is determined by the FFT size ( by the bandwidth)

Power

frequency

bandwidth


The OFDM Signal



The usage of the pulse leads to other challenges to be solved:

1. ISI = Intersymbol InterferenceDue to multipath propagation

2. ACI = Adjacent Carrier Interference Due to the fact that FDM = frequency division multiplexing will be used

3. ICI = Intercarrier Interference Losing orthogonality between subcarriers because of effects like e.g. Doppler

→ What should be the solutions to these challenges?(see next slides)


1. Multi-Path Propagation and Inter-Symbol Interference

1. Inter Symbol Interference

BTSTime 0 Ts

+

d1(Direct path)

d3

d2

d1< d2 < d3

Time 0 Tt Ts+Tt

Tt


Multi-Path Propagation and the Guard Period2

time

TSYMBOL

Time Domain

1

3

time

TSYMBOL

time

TSYMBOL

Tg

1

2

3

Guard Period (GP)

Guard Period (GP)

Guard Period (GP)

(Direct path)


Obviously when the delay spread of the multi-path environment is greater than the guard period duration (Tg), then we encounter inter-symbol interference (ISI)

Propagation Delay Exceeding the Guard Period

12

34

time

TSYMBOLTime Domain

time

time

Tg

1

2

3

time

4


Cyclic Prefix

symbolCP

time

Tsymb

12

3

1

2

3

Tcp

symbolCP symbolCP

symbolCP symbolCP symbolCP

symbolCP symbolCP symbolCP


Cyclic Prefix

T [TS] 160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048

T [µs] 5,2 66,7 4,7 66,7 4,7 66,7 4,7 66,7 4,7 66,7 4,7 66,7 4,7 66,7

max. delay [km] 1,6 1,4 1,4 1,4 1,4 1,4 1,4

T [TS] 512 2048 512 2048 512 2048 512 2048 512 2048 512 2048

T [µs] 16,7 66,7 16,7 66,7 16,7 66,7 16,7 66,7 16,7 66,7 16,7 66,7

max. delay [km] 5,0 5,0 5,0 5,0 5,0 5,0

In LTE the slot of 500 µs is subdivided in the (useful part of the) symbol (grey) and CPs as follows:

For the extended CP slot structure the overall 500 µs is kept but the number of symbols is reduced in order to extent the cyclic prefix durations:


Challenges for the Air Interface Design The usage of the pulse leads to other challenges to be solved:

1. ISI = Intersymbol InterferenceDue to multipath propagation → solution: use cyclic prefix


3. ICI = Intercarrier Interference Losing orthogonality between subcarriers because of effects like e.g. Doppler



Multi-Carrier Modulation

The center frequencies must be spaced so that interference between different carriers, known as Adjacent Carrier Interference ACI, is minimized; but not too much spaced as the total bandwidth will be wasted.

Each carrier uses an upper and lower guard band to protect itself from its adjacent carriers. Nevertheless, there will always be some interference between the adjacent carriers.

frequency

∆fsubcarrier

f0 f1 f2 fN-1fN-2

∆fsub-used

2. ACI = Adjacent Carrier Interference


OFDM: Orthogonal Frequency Division Multi-Carrier

OFDM allows a tight packing of small carrier - called the subcarriers - into a given frequency band.

No ACI (Adjacent Carrier Interference) in OFDM due to the orthogonal subcarriers !

Pow

er D

ensi

ty

Pow

er D

ensi

ty

Frequency (f/fs) Frequency (f/fs)

Saved Bandwidth



The usage of the pulse leads to other challenges to be solved:



→ solution: orthogonal subcarriers 3. ICI = Intercarrier Interference

Losing orthogonality between subcarriers because of effects like e.g. Doppler



Inter-Carrier Interference (ICI) in OFDM

•The price for the optimum subcarrier spacing is the sensitivity of OFDM to frequency errors.•If the receiver’s frequency slips some fractions from the subcarriers center frequencies, then we encounter not only interference between adjacent carriers, but in principle between all carriers. •This is known as Inter-Carrier Interference (ICI) and sometimes also referred to as Leakage Effect in the theory of discrete Fourier transform.• One possible cause that introduces frequency errors is a fast moving Transmitter or Receiver (Doppler effect).


f0 f1 f2 f3 f4

∆P

I3

I1I4I0

3. IC

I = In

ter-

Car

rier I

nter

fere

nce

Leakage Effect due to Frequency Drift: ICI

Two effects begin to work:1.-Subcarrier 2 has no longer its power density maximum here - so we loose some signal energy.

2.-The rest of subcarriers (0, 1, 3 and 4) have no longer a null point here. So we get some noise from the other subcarrier.


Challenges for the Air Interface Design The usage of the pulse leads to other challenges to be solved:



→ solution: orthogonal subcarriers

3. ICI = Intercarrier Interference Losing orthogonality between subcarriers because of effects like e.g. Doppler→ solution: use reference signals – will be explained in chapter 7


OFDMA



LowPass

cos(2πfct)

-sin(2πfct)

I

Q

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

BinaryCodedData

.

.

.

D

Ax0, x1, …, xN-1 IQSplit

LowPass

D

A

RF

freq.f1 f2f0 fN-1

…

s0

s1 sN-1

s2

Freq

uenc

y D

omai

n

timet1 t2t0 tN-1

…x0 x1

xN-1

x2

TimeDomain

CP/

Gua

rdG

ener

atio

n I

Q

OFDM Transmitter

Time Domain Signal

Frequency Domain Signal:(Collection of Sinusoids)

•Each entry to the IFFT module corresponds to a different sub-carrier•Each sub-carrier is modulated independently•Modulation Schemes:•BPSK,QPSK, 16QAM, 64QAM


OFDMA



reference(pilot)

Cha

nnel

Cor

rect

ion

Dem

odul

ator

Bit Mapping

j

I

Q

A

D

ChannelEstimation

RF

Low

Noi

se A

mp.

+ B

andp

ass

A

D

AGCAutomatic

Gain Control

De-rotator

sign

al s

tren

gth

LNA gain

Frequency And Timing Sync

sign

al a

utoc

orre

atio

n

phas

e co

rrec

tion

timee

adju

st

.

.

.

s’0

s’1

s’N-1

chan

nel

resp

onse

s0

Bit Mappings1

Bit MappingsN-1

.

.

.

.

.

.

.

.

.

B10 ,B11,…

B20 ,B21,…

BN-1 0 …

Bit

Dis

trib

utio

n

Soft BitCodedData

freq.f1 f2f0 fN-1

…

s0

s1 sN-1

s2

Frequency Domain

Time Domain

timet1 t2t0 tN-1

…y0 y1

yN-1

x2

QPSK

Im

Re

10

11

00

01

sk

d11

d10

OFDM Receiver

Win

dow

ing

+FF

T

Freq

uenc

y D

omai

n


OFDMA



OFDM Key Parameters

2. Subcarrier Spacing (Δf = 15 KHz) → The Symbol time isTsymbol = 1/ Δf = 66,7μs

Δf

A compromise needed between: → Δf as small as possibile so that the symbol time Tsymbol is as large as possibile. This is beneficial to solve Intersymbol Interference in time domain → A too small subcarrier spacing it is increasing the ICI = Intercarrier Interference due to Doppler effect

TSYMBOL

TCP SYMBOL

TCP

TS

Frequency

Time

Powerdensity

Amplitude

1. Variable Bandwidth (BW) Bandwidth options: 1.4, 3, 5, 10, 15 and 20 MHz

Frequency

A higher Bandwidth is better because a higher peak data rate could be achived and also bigger capacity. Also the physical layer overhead is lower for higher bandwidth


OFDM Key Parameters

3. The number of Subcarriers Nc→ Nc x Δf = BW

In LTE not all the available channel bandwidth (e.g. 20 MHz) will be used. For the transmission bandwidth typically 10% guard band is considered (to avoid the out band emissions).If BW = 20MHz → Transmission BW = 20MHz – 2MHz = 18 MHz→ the number of subcarriers Nc = 18MHz/15KHz = 1200 subcarriers

TransmissionBandwidth [RB]

Transmission Bandwidth Configuration [RB]

Channel Bandwidth [MHz]

Resource block

Channel edge

Channel edge

DC carrier (downlink only)Active Resource Blocks


OFDM Key Parameters

4. FFT (Fast Fourier Transform) size Nfft

Nfft should be chosen so that:1.Nfft > Nc number of subcarriers (sampling theorem) 2.Should be a power of 2 (to speed-up the FFT operation) Therefore for a bandwidth BW = 20 MHz → Nc = 1200 subcarriers not a power of 2→ The next power of 2 is 2048 → the rest 2048 -1200 = 848 padded with zeros

5. Sampling rate fs

This parameter indicates what is the sampling frequency:→ fs = Nfft x ΔfExample: for a bandwidth BW = 5 MHz (with 10% guard band)The number of subcarriers Nc = 4.5 MHz/ 15 KHz = 300 300 is not a power of 2 → next power of 2 is 512 → Nfft = 512Fs = 512 x 15 KHz = 7,68 MHz → fs = 2 x 3,84 MHz which is the chip rate in UMTS!!

The sampling rate is a multiple of the chip rate from UMTS/ HSPA. This was acomplished because the

subcarriers spacing is 15 KHz. This means UMTS and LTEhave the same clock timing!


Resource Block and Resource Element

– 12 subcarriers in frequency domain x 1 slot period in time domain.

0 1 2 3 4 5 6 0 1 2 3 4 5 6Subcarrier 1

Subcarrier 12

180

KH

z

1 slot 1 slot

1 ms subframe

RB

• Capacity allocation is based on Resource Blocks

• Resource Element ( RE): – 1 subcarrier x 1 symbol period– Theoretical minimum capacity

allocation unit.– 1 RE is the equivalent of 1

modulation symbol on a subcarrier, i.e. 2 bits for QPSK, 4 bits for 16QAM and 6 bits for 64QAM.

Resource Element

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 6

6. Physical Resource Block or Resource Block (PRB or RB)


OFDM Key Parameters for FDD and TDD Modes


OFDMA



Data Rate Calculation

1. Maximum channel data rate

The maximum channel data rate is calculated taking into account the total number of the available resource blocks in 1 TTI = 1msMax Data Rate = Number of Resource Blocks x 12 subcarriers x (14 symbols/ 1ms)

= Number of Resouce Blocks x (168 symbols/1ms)

2. Impact of the Channel Bandwith: 5, 10, 20 MHz

For BW = 5MHz -> there are 25 Resource Blocks-> Max Data Rate = 25 x (168 symbols/1ms) = 4,2 * Msymbols/sBW = 10MHz -> 50 Resource Blocks -> Max Data Rate = 8,4 Msymbols/s BW = 20MHz -> 100 Resource Blocks -> Max Data Rate =16,8 Msymbols/s

3. Impact of the Modulation: QPSK, 16QAM, 64QAM

For QPSK – 2bits/symbol; 16QAM – 4bits/symbol; 64QAM – 6 bits/symbol QPSK: Max Data Rate = 16,4 Msymbols/s * 2bits/symbol = 32,8 Mbits/s (bandwith of 20 MHz)16QAM: Max Data Rate = 16,4 Msymbols/s * 4 bits/symbols = 65,6 Mbits/s64QAM: Max Data Rate = 16,4 Msymbols/s * 6 bits/symbols = 98,4 Mbits/s


Data Rate Calculation

4. Impact of the Channel Coding

Channel Coding will be discussed in chapter 6. In LTE Turbo coding of rate 1/3 will be used. The effective coding rate is dependent on the Modulation and Coding Scheme selected by the scheduler in the eNodeB. In practice several coding rates can be obtained. Here it is considered 1/2 and 3/41/2 coding rate: Max Data rate = 98,4 Mbits/s * 0,5 = 49,2 Mbits/s 3/4 coding rate: Max Data rate = 98,4 Mbits/s * 0,75 = 73,8 Mbits/s

5. Impact of MIMO = Multiple Input Multiple Output

MIMO is discussed in chapter 9. If spatial diversity it is used (2x2 MIMO) then the data rate will be doubled since the data is sent in parallel in 2 different streams using 2 different antennas2x2 MIMO: Max Data Rate = 73,8 Mbit/s * 2 = 147,6 Mbits/s

6. Impact of physical layer overhead and higher layers overhead

The real data rate of the user will be further reduced if the physical layer overhead is considered. Also the higher layers may introduce overhead as shown in chapter number 2. For example IP , PDCP , RLC and MAC are introducing their own headers. This type of overheads are not discussed here


OFDMA



OFDM Multiple Access

Up to here we have only discussed simple point-to-point or broadcast OFDM.

Now we have to analyze how to handle access of multiple users simultaneously to the system, each one using OFDM.

OFDM can be combined with several different methods to handle multi-user systems:

1.-Plain OFDM

3.-Orthogonal Frequency Division Multiple Access OFDMA®

2.-Time Division Multiple Access via OFDM


OFDM

•OFDM stands for Orthogonal Frequency Division Multicarrier•OFDM: Plain or Normal OFDM has no built-in multiple-access mechanism.• This is suitable for broadcast systems like DVB-T/H which transmit only broadcast and multicast signals and do not really need an uplink feedback channel (although such systems exist too).

•Now we have to analyze how to handle access of multiple users simultaneously to the system, each one using OFDM.

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Plain OFDM

time

subc

arrie

r

...

...

...

...

...

...

...

...

...

1 2 3 common info(may be addressed via Higher Layers)

UE 1 UE 2 UE 3


OFDMA®

•OFDMA® stands for Orthogonal Frequency Division Multiple Access •It is a registered trademark by Runcom Ltd. •The basic idea is to assign subcarriers to users based on their bit rate services. With this approach it is quite easy to handle high and low bit rate users simultaneously in a single system.•But still it is difficult to run highly variable traffic efficiently.•The solution to this problem is to assign to a single users so called resource blocks or scheduling blocks.•Such block is simply a set of some subcarriers over some time. •A single user can then use one or more Resource blocks.

11

1

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2

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3

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Orthogonal FrequencyMultiple Access

OFDMA®time

...

...

...

...

...

...

...

...

...

11

1 1

222

2 2

3 33 3 3

1

subc

arrie

r

11 1 1

111

3 3 333 3 3 33

Resource Block (RB)1 2 3 common info

(may be addressed via Higher Layers)

UE 1 UE 2 UE 3


OFDMA



OFDM Transmitter Simulation – Assumptions

• All 1200 subcarriers subcarriers are transmitted (assuming that the system bandwidth is 20 MHz)

• Transmit only one OFDM symbol (66.7 us)

• No difference between the subcarriers used for physical layer overhead and the subcarriers used for transmission of user data – No difference between different physical channels like e.g. PBCH (Physical Broadcast

Channel). The difference could be seen in parameters like e.g. modulation

• The serial to parallel convertor is not considered (because it assumed to transmit only one OFDM symbol)

• Cyclic prefix insertion neglected (less relevant for simulation – impact on symbol duration only)


Serial toParallel

Converter(Bit

Distrib.)

BinaryCodedData

b10

b20

bN-1

A random string is generated with N=1200 integers numbers from 0 to 3 that needs to be transmitted; For simplicity only first 40 integers are plotted (the same is true for the rest of the simulation) One can look at this sequence vertically, as being the output of the serial to parallel block (only one OFDM symbol is transmitted )

Data Generation


OFDM Transmitter

LowPass

cos(2πfct)

-sin(2πfct)

I

Q

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

.

.

.

D


LowPass

D

A

RF

Freq

uenc

y Do

mai

nTime

Domain

CP/

Gua

rdG

ener

atio

n I

Q

BinaryCodedData

• QPSK modulation assumed(16QAM or 64QAM also possibile)


QPSK ModulationOur Tx Bit 1 Bit 0 I Q

0 0 0 +1 +1

1 0 1 -1 +1

2 1 0 -1 -1

3 1 1 +1 -1

Step 1 of QPSK modulation: map the input bits to the symbols using the constelation diagram I + jQ (complex = inphase + quadrature)

Step 2 of the QPSK modulation : in LTE the complex symbols are input for the IFFT !


ModulationMapper

ModulationMapper

ModulationMapper

s0

s1

sN-1

.

.

.

Note that the sequence … is a complex sequence = I + jQ (Inphase and Quadrature)s0 sN-1


OFDM Transmitter

LowPass

cos(2πfct)

-sin(2πfct)

I

Q

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

.

.

.

D


LowPass

D

A

RF

Freq

uenc

y Do

mai

nTime

Domain

CP/

Gua

rdG

ener

atio

n I

Q

BinaryCodedData

• IFFT = Inverse Fast Fourier Transformation


IFFTTime

Domain

x0, x1, …, xN-1

IFFT Result –> Time Domain

Result interpretation:1. The signal is complex =

I+jQ2. The signal is almost

white noise (1200 subcarriers each with equal

magnitude)


Zero padded subcarriers2048-1200 = 848

First 600 subcarriersBW=600*15kHz=9MHz

Last 600 subcarriersBW=600*15kHz=9MHzTotal BW=18MHz

IFFT Result -> Frequency Domain

The spectrum is splitted in 2 parts because of the zero padding in

the middle of the sequence

Low pass filtering requiredto achieve a compact spectrum


OFDM Transmitter

cos(2πfct)

-sin(2πfct)

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

.

.

.

x0, x1, …, xN-1 IQSplit

LowPass

I

Q

D

A

LowPass

D

A

RF

Freq

uenc

y Do

mai

nTime

Domain

CP/

Gua

rdG

ener

atio

n I

Q

BinaryCodedData

•Digital to Analog Conversion and Low Pass Filtering


LowPass

I

Q

D

A

LowPass

D

A

Note the delay produced by the filtering process (low pass filtering)


OFDM Transmitter

LowPass

cos(2πfct)

-sin(2πfct)

I

Q

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

.

.

.

D


LowPass

D

A

RF

Freq

uenc

y Do

mai

nTime

Domain

CP/

Gua

rdG

ener

atio

n I

Q

BinaryCodedData

•Up - Conversion


This is the signal transmitted over the air interface It can be observed the large value of the PAR (peak to average ratio) in the time response

Up-conversion -> Time Domain Result


Up-conversion -> Frequency Domain Result


OFDM Transmitter Overview

LowPass

cos(2πfct)

-sin(2πfct)

I

Q

ModulationMapper

IFFT

s0

ModulationMapper

s1

ModulationMapper

sN-1

b10 ,b11,…

Serial toParallel

Converter(Bit

Distrib.)

b20 ,b21,…

bN-1 0 …

.

.

.

D


LowPass

D

A

RF

Freq

uenc

y Do

mai

nTime

Domain

CP/

Gua

rdG

ener

atio

n I

Q

BinaryCodedData

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