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
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';
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)).';
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
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