OFDM Simulation Final.pptx

8/10/2019 OFDM Simulation Final.pptx

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Northern University Bangladesh

The Performance of OFDM Transceiverwith Simulation in MATLAB


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The Performance of OFDM Transceiver

with Simulation in MATLAB

Presented By:

Badar Uddin AhammedID: ECE 070200064

Md. Rezaul KarimID: ECE 070200066

Supervised by:Engr. Md. Badiuzzaman

Head of the dept. of EEE

Northern University Bangladesh


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Objective

The objective of this project is to demonstrate the concept of an OFDM

system, and investigate how its performance is changed by varying some

of its major parameters. This objective is met by developing a MATLAB

program to simulate a basic OFDM system.

4Northern University BangladeshOctober 23, 2014


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Outline

Part I : OFDM Fundamentals

Part II : OFDM Transceiver Design

Part III : OFDM Simulation Result

Part IV : OFDM Simulation Demonstration

Northern University BangladeshOctober 23, 2014


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OFDM Basic Concept

Orthogonal frequency division multiplexing (OFDM) is a multi-carriertransmission technique, which divides the available spectrum into many

subcarriers, each one being modulated by a low data rate stream.

OFDM is a multi-carrier modulation scheme

o First break the data into small portions

o Then use a number of parallel orthogonal sub-carriers to transmit the data

Conventional transmission uses a single carrier, which is modulated with

all the data to be sent

Single Carrier Company

Multi Carrier Company



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OFDM Basic Concept . . .

For FDM

o No special relationship between

the carrier frequencies

o Guard bands have to be inserted

to avoidAdjacent ChannelInterference(ACI)

For OFDM

o Carrier frequencies are

orthogonal to each other.

o Sub-carriers can overlap in the

frequency domain which

increases spectral efficiency

7

OFDM is a special case of Frequency Division Multiplexing(FDM)


Fig: The Spec term of OFDM signal


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Orthogonality

The key to OFDM is maintaining orthogonality of the carriers. If the

integral of the product of two signals is zero over a time period, then

these two signals are said to be orthogonal to each other.

Assume a cosine wave is multiplied by a sinusoid, either sine or

cosine. Then the integral over one period is defined as

where n and m are two unequal integers

is the period in 2/ seconds.



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Orthogonality

Since cos( t) executes a complete cycle every seconds. Therefore,

integrating both cos(n+m) t and cos(n-m) t over an interval

results is zero except in the case where n = m 0. Therefore,

Similar arguments show

and

for all n and m



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Advantages

Makes efficient use of the spectrum by allowing overlap.

By dividing the channel into narrowband sub channels, OFDM is more

resistant to frequency selective fading than single carrier systems.

OFDM is an efficient way to deal with multipath.

Eliminates ISI and ICI through use of a cyclic prefix.

OFDM is computationally efficient by using FFT techniques to implement

the modulation and demodulation functions.



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Disadvantages

OFDM has a relatively large peak-to-average-power ratio, which reducesthe power efficiency of the RF amplifier.

It is more sensitive to carrier frequency offset and drift than single carrier

systems are due to leakage of the FFT.

Adding guard period lowers the symbol rate and lowers the overall

spectral efficiency of the system.

OFDM is Sensitive to high frequency phase noise



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Outline







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OFDM Block Diagram

Fig1 : Block Diagram of OFDM Transceiver13Northern University BangladeshOctober 23, 2014


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OFDM Simulation Flow Chart


Start

Data read

Base Convert

Serial to

Parallel

Is empty

data.tx ?

F.data channel maximum delay

Guard band prevents Inter-Symbol Interference (ISI) due to multipath

The guard time could consist of no signal at all. In that case, the problem

of Inter carrier Interference (ICI ) would arise.

ICI is crosstalk between different subcarriers, which means that they are

no longer orthogonal.

To eliminate ICI , the OFDM symbol is cyclically extended in the guard

time.

This ensures that delayed replicas of OFDM symbol always have an integer

number of cycles within the FFT interval, as long as the delay is smallerthan guard time. As a result, multipath signals with delays smaller than

guard time cannot cause ICI.



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Cyclic Prefix . . .

],[ 00

],[ 11

Diffracted and Scattered Paths

Reflected Path

LOS Path

],[kk


Fig6: Multipath channel


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Cyclic Prefix . . .

Time

[]

Amplitude[]

Example multipath profile

0

1

2

The prefix is made cyclic to avoid inter-carrier-interference(ICI)

(maintain orthogonality)

Multipath introduces inter-symbol-interference(ISI)TU

Prefix is added to avoid ISI

TUTCP


Path Delays

Fig7: Cyclic Prefix


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Cyclic Prefix . . . Now the guard period made up by two sections:

o Half of the guard period time is a zero amplitude transmission called frame guard

o Other half is a cyclic extension of the OFDM symbol to be transmitted.

Now the total length of the symbol is

Ts= Tfg + Tcp + Tu

Where, Ts is the total length of the symbol

Tfg is the length of guard period with zero padding

Tcp is the length of the CP

Tu is the size of the useful data symbol.

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Useful symbol Useful symbolFG CP Useful symbol

TUTfg

TS

Tcp

Tgp

FG CPFG CP

Fig8: Data frame with Cyclic Prefix


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Data Frame 2CP FGData Frame 1CP FGFG

Tcp Tcp TfgTfgTfg Tdf Tdf

Ts Ts

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OFDM Transmitter . . .


Useful symbolCP

CPCP

Tcp Tdf

D =

Dx1 Dy1

Dx2 Dy2

Dx3 Dy3

Dx4 Dy4

.

.

S =

Sx1 Sy1

Sx2 Sy2

Sx3 Sy3

Sx4 Sy4

. . . . . . .

. . . . . . .


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Channel


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Communication Channel

Channel is the electromagnetic media between the transmitter and the

receiver.

The model allows for the signal to noise ratio, multipath, and peak power

clipping to be controlled.

The signal to noise ratio is set by adding a known amount of white noise to the

transmitted signal.


Fig9: Communication Channel

Transmitter Receiver

Channel


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Communication Channel . . .

The most common channel model is the Gaussian channel, which is

generally called the additive white Gaussian noise (AWGN) defined by:

When signal is transmitted through the channel, it is corrupted by the

statistically independent Gaussian noise. This channel model assumes

that the only disturber is the thermal noise at the front end of the

receiver



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OFDM Receiver


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OFDM Receiver


Data Frame 2CP FGData Frame 1CP FGFG

Tcp Tcp TfgTfgTfg Tdf Tdf

Ts Ts

Data Frame 2CPData Frame 1CP

Tcp TcpTdf Tdf

Ts Ts

Data Frame 2Data Frame 1

Ts Ts

Data Frame n

Ts


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FFT The Fast Fourier Transform (FFT) converts the time domain data samples

back into a frequency domain representation of this data.

FFT takes a random signal, multiplies it successively by complex

exponentials over the range of frequencies. It sums each product and

plots the results as a coefficient of that frequency.

The results of the FFT is a frequency domain signal.


Fig10: Conversion in FFT Circuit

Frequency

Am

plitude


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OFDM Receiver


Data Frame 2Data Frame 1

Ts Ts

Data Frame n

Ts

S =

Sx1 Sy1

Sx2 Sy2

Sx3 Sy3

Sx4 Sy4

. . . . . . .

. . . . . . .

Dx1 Dy1

Dx2 Dy2

Dx3 Dy3

Dx4 Dy4

.

.

D =


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Demodulation

October 23, 2014 Northern University Bangladesh

Phase shift keying (PSK):

o The decoding process is reverses process of encoding. The incoming bits are

added together to recreate the input data sequence. A differential decoding

system as shown below.

Where, = Data sequence in

= Differentially Encoded data sequence out

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Fig11: A differential decoder


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OFDM Receiver


[24 135 148 139 142 140 131 . . . . ]

X = [1 0 1 1 0 1 0 0. . . ]

Y1 = [1 0 ]

Y2 = [1 1 ]

Y3 = [0 0]

Y4 = [0 0 ]. . . . . . . . . . .

Yn = [Yx Yy]

OFDM T i O i


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OFDM Transceiver Overview

012

012

Modulator

Demodulator

125 356 356 67 13 98 238 43 23

445 97 125 12 89 65 982 378 43

334 33 454 24 65 234 23 56 8723 43 87 56 65 982 356 334 125

43 378 345 33 454 24 65 234 445

87 56 356 67 546 13 356 356 334

125 65 234 33 123 89 125 125 345

33 454 24 65 234 65 454 454 621

1 1 0 1 1 0 1 0 0

0 0 1 1 0 1 1 1 0

1 1 0 1 1 0 1 0 0

0 0 1 1 0 1 1 1 0

0 1 0 0 1 1 0 0 1

0 0 1 1 0 1 1 1 0

1 0 0 0 1 1 1 0 1

1 0 0 1 1 0 1 1 0 1 0 0

1 1 0 0 0 1 1 0 1 1 1 0

0 0 1 0 1 0 0 1 1 0 0 1

1 1 0 0 0 1 1 0 1 1 1 0

1 0 1 1 0 0 0 1 1 1 0 1

1 1 0 1 1 0 1 0 0

0 0 1 1 0 1 1 1 0

1 1 0 1 1 0 1 0 0

0 0 1 1 0 1 1 1 0

1 1 0 1 1 0 1 0 0

0 0 1 1 0 1 1 1 0

125 356 356 67 13 98 238 43 23

445 97 125 12 89 65 982 378 43

334 33 454 24 65 234 23 56 87

23 43 87 56 65 982 356 334 125

43 378 345 33 454 24 65 234 445

87 56 356 67 546 13 356 356 334

125 65 234 33 123 89 125 125 345

33 454 24 65 234 65 454 454 621

1 0 0 1 1 0 1 1 0 1 0 0

1 1 0 0 0 1 1 0 1 1 1 0

0 0 1 0 1 0 0 1 1 0 0 1

1 1 0 0 0 1 1 0 1 1 1 0

1 0 1 1 0 0 0 1 1 1 0 1


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Outline







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Simulation Parameters

Table 1: OFDM system parameters used for this simulations

Parameter Value

Source Image Size 345 x 216 (Bitmap Image)

Carrier Modulation used QPSK

FFT size 1024

Number of carrier used 500

Guard Time FFT_Size/4 (25%)

Guard Period Type Half zero signal, half a cyclic

extension of the symbol

Channel Model AWGN

Signal-to-Noise Ratio 10 db

T itt Pl t


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Transmitter Plots

Fig13: OFDM Transmitter input data Fig14: OFDM Modulated data

Fig16: OFDM Transmitted Signal with AWGN NoiseFig15: OFDM Transmitted Signal


Fig13: OFDM Transmitter input dataFig14: OFDM Modulated DataFig15: OFDM Transmitted SignalFig16: OFDM Transmitted Signal with AWGN Noise

R i Pl t


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Receiver Plots

Fig17:: OFDM Receved data Phase Fig18: OFDM Demodulated data

Fig19: SNR vs Error rate


Fig17: OFDM Receved data PhaseFig18: OFDM Demodulated dataFig19: SNR vs Error rate


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BER/SNR AnalysisSNR(db) BPSK_BER QPSK_BER 16-PSK_BER 256-PSK_BER

1 5.212024 23.256844 73.984836 98.377617

2 3.416868 18.671162 71.225845 98.213902

3 2.028818 14.022746 67.938808 98.016640

4 1.093666 10.117754 64.443773 97.788513

5 0.509595 6.668009 60.731347 97.576490

6 0.196088 3.951288 56.298980 97.274557

7 0.061057 2.111849 51.635802 96.814278

8 0.015264 0.968532 46.270129 96.388889

9 0.001510 0.369028 41.286232 95.958132

10 0.000335 0.125470 35.609903 95.526033

11 0.000000 0.021471 30.244230 95.03354812 0.000000 0.005703 24.618894 94.480676

13 0.000000 0.000335 19.346484 93.855341

14 0.000000 0.000000 14.547772 93.059581

15 0.000000 0.000000 10.267713 92.340311

46Table 2: BER vs SNR due to M-PSK Modulation


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October 23, 2014 Northern University Bangladesh 47

BER/SNR Analysis

Fig20: BER for M-PSK modulation over AWGN Noise


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October 23, 2014 Northern University Bangladesh 48

Pixel Error Rate(PER)

Fig21: PER for M-PSK modulation


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Transmitted Image

TransmittedImage



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Received Images using QPSK


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Received Images using QPSK

QPSK; SNR = 10 dB

QPSK; SNR = 0 dB

QPSK; SNR = 15dB

QPSK; SNR = 5 dB


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Received Images using 256 PSK


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Received Images using 256-PSK

256-PSK; SNR = 10 dB

256-PSK; SNR = 0 dB

256-PSK; SNR = 15dB

256-PSK; SNR = 5 dB

Matlab Code


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Matlab Code


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Referance

Schulze, Henrik and Christian Luders. Theory and Applications of OFDM and CDMAJohn Wiley & Sons, Ltd. 2005

Theory of Frequency Division Multiplexing:

http://zone.ni.com/devzone/cda/ph/p/id/269

Acosta, Guillermo. OFDM Simulation Using MATLAB 2000\

A Brief History of OFDM

http://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-

of-ofdm

Lui, Hui and Li, Guoqing. OFDM-Based Broadband Wireless Networks Design and

Optimization Wiley-Interscience 2005

Litwin, Louis and Pugel, Michael. The Principles of OFDM 2001

http://zone.ni.com/devzone/cda/ph/p/id/269http://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://www.wimax.com/commentary/wimax_weekly/sidebar-1-1-a-brief-history-of-ofdmhttp://zone.ni.com/devzone/cda/ph/p/id/269


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Outline







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OFDM Simulation Final.pptx

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