1. “Performance analysis of OFDM over AWGN and
Rayleigh channels”
Presented By: Saroj Dhakal
068/MSI/618
IOE, Pulchowk campus
Date: 2069/6/25

2. 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

3. 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

4. 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

5. 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

6. 
Why OFDM Contd…
-reduces ISI
-minimizes the effect of multipath fading
-results in bandwidth saving

7. Objective
• The study of OFDM performance over AWGN
channel and Rayleigh channel using MATLAB
simulation

8. 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

9. 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 4Bit 3 2X52X104 Bits

10. 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';

11. 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

12. 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)).';

13. Pilot insertion
• Defining pilot carrier
P1 - p2 - - p3 - p4 -
P1 - P2 - - P3 - P4 -

14. Pilot insertion and zero padding
• Defining pilot carrier
and adding zero padding
z1 _ _ z6 p1 - p2 - - p3 - p4 - Z7 - - z12
P1 - p2 - - P3 - p4 -

15. IFFT Implementation

16. Cyclic prefix Insertion
cyclic prefix
cp1
. cp2
.
64 Subcarriers . cp16
. .
. .
. .
80 Subcarriers
Cyclic
Prefix
insertion

17. 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

18. Serial data transmission via
• AWGN channel
• Rayleigh Channel

19. Receiver section of OFDM
The processes are just opposite
to the transmitter part

20. Simulation outcomes for AWGN channel

21. Simulation outcomes for Rayleigh channel

22. 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

23. 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

24. 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

25. Thank You!!!!!!