ofdm performance analysis
TRANSCRIPT
“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!!!!!!