“Performance analysis of OFDM over AWGN and

Rayleigh channels”

Presented By: Saroj Dhakal

068/MSI/618

IOE, Pulchowk campus

Date: 2069/6/25

Presentation outlines

• Introduction

• Objective of the project

• OFDM Transmitter block

• Serial data transmission via channel

• Receiver section of OFDM

• Simulation outcomes for AWGN channel

• Simulation outcomes for Rayleigh channel

• Future enhancement

• Conclusion

• References

Introduction

What is OFDM?

• Orthogonal Frequency Division Multiplexing

• uses multiple sub-carriers but the sub-carriers are closely

spaced to each other without causing interference,

removing guard bands between adjacent sub carriers, all

the sub carriers are orthogonal to each other

• Two periodic signals are orthogonal when the integral of

their product, over one period, is equal to zero

Why OFDM?

• In a classical parallel data system, the total signal

frequency band is divided into N non overlapping

frequency sub channels. Each sub channel is modulated

with a separate symbol and then the N sub channels are

frequency-multiplexed

• Results in High Bandwidth occupancy, Inter symbol

interference(ISI) and multipath fading

Why OFDM contd…

• A special case of multicarrier transmission, where a

single data stream is transmitted over a number of lower

rate subcarriers which are orthogonal to each other

Serial To

parallel

converter

Symbol

mapper

Symbol

mapper

Symbol

mapper

g(t)

g(t)

g(t)

R/N bps

R/N bps

R/N bps

So

S1

Sn-1

cos(2πfot)

cos(2πf1t)

cos(2πfN-1t)

R bps

Why OFDM Contd…

-reduces ISI

-minimizes the effect of multipath fading

-results in bandwidth saving

Objective

• The study of OFDM performance over AWGN

channel and Rayleigh channel using MATLAB

simulation

OFDM transmitter block

Digital

serial

data

source

Serial

to

parallel

converter

Cyclic

Prefix

Insertion

Constella

-tion

mapping

Pilot

insertion

and

padding

IFFT Parallel to

serial

converter

Serial data to be

transmitted

104 bits

per frame

2bits

per line QPSK symbol

per line

48 parallel

lines 48 data

symbol+4 pilot

symbol +12

zero padding

64

Subcarriers 80

subcarriers

Digital data source

• Initial parameter needed to be defined for data generation

• Number of bits per frame

• Number of data frames

% Generating and coding data

BPF=2*52; % Number of bits per

frame

NoF=10^4; % Number of Frame

tx_data=randint(1,NoF*BPF);

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

Bit 1 Bit 2 Bit 4 Bit 3 2X52X104 Bits

Serial to parallel conversion

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

1 0

1 0

1 1

0 0

0 1

0 1

1 1

0 0

1 0

1 0

Serial Data

Parallel

Data

% Framing before modulation

creating modulation symbol using

n-bit pattern

fbfm_data=reshape(aint_data,bp

_symbol,(1/Rc)*BPF*NoF*(1/bp_

symbol));

afbfm_data=fbfm_data';

Modulation and constellation mapping

2

2

3

0

1

1

3

0

2

2

% Binary to decimal conversion and 16-QAM

modulation

dec=bi2de(afbfm_data,'left-msb');

mod_data = modulate(M,dec);

1 0

1 0

1 1

0 0

0 1

0 1

1 1

0 0

1 0

1 0

Preparation for pilot insertion and padding

-

-

-

-

-

-

-

-

-

-

Parameter for IFFT

• Number of data

subcarrier= 48

• Pilot subcarrier =4

• Zero padding =12

- - - - - - - - - Input symbol frame 1

Input symbol frame 2

Input symbol frame 3

Input symbol frame 10^4

dfmod_data=reshape(mod_data,1,(1/Rc)*BPF*NoF*(1/bp_symbol));

%%

%16-QAM symbol framing for ODQM symbol formation

par_data=(reshape(dfmod_data,NoDsc,NoF)).';

Pilot insertion

• Defining pilot carrier

P1

- p2

- - p3

- p4

-

P1

- P2 - - P3 - P4 -

Pilot insertion and zero padding

• Defining pilot carrier

and adding zero padding

z1 _ _ z6

p1 - p2 - - p3 - p4 - Z7 - - z12

P1 - p2

- - P3

- p4 -

IFFT Implementation

Cyclic prefix Insertion

cyclic prefix

cp1

. cp2

.

64 Subcarriers . cp16

. . . .

. .

80 Subcarriers

Cyclic

Prefix

insertion

Parallel to serial conversion

1 1

1 0

0 0

1 0

0 1

1 0

1 1

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

Parallel data

streams

Serial data conversion

Conversion can be

done by using matlab

function reshape

Serial data transmission via

• AWGN channel

• Rayleigh Channel

Receiver section of OFDM

The processes are just opposite

to the transmitter part

Simulation outcomes for AWGN channel

Simulation outcomes for Rayleigh channel

Future Enhancements

• To be analyzed for other different channel like Nakagami,

Rice channel etc

• Level of SNR can be maximized and more BER analysis

for larger range can be performed

Conclusion

• Simulation result closely resembles analytical result

• Thus the BER rapidly decreased with increase in SNR in

case of AWGN channel

• Similarly in Rayleigh channel BER slowly decreased with

increased in SNR very quickly

• Hence the BER Versus SNR curve gives the performance

analysis of OFDM over the AWGN and Rayleigh channel

References

• Nick LaSorte, W. Justin Barnes, Hazem H. Refai, Member, IEEE, The History of Orthogonal Frequency Division Multiplexing

• Acosta, Guillermo, OFDM Simulation Using MATLAB, 2000.

• Dr. Jean Armstrong, OFDM – Orthogonal Frequency Division Multiplexing Department of Electronic Engineering La Trobe University

• Marcos Majo, Design and implementation of an OFDM-based communication System for the GNU Radio platform, Master Thesis, University of Stuttgart Germany.

• Edan Bolat, Study of OFDM Performance over AWGN Channel, Eastern Mediterranean University, 2003.

• Erik Dahlman, Stefan Parkvall, 3G Evolution for HSPA and LTE for mobile Broadband

Thank You!!!!!!