This document describes the simulation of an OFDM system using MATLAB. It discusses how OFDM works and its advantages for wireless communications. The simulator allows analyzing the performance of BPSK, QPSK, and QAM modulation under Rayleigh fading and multipath channels. It measures bit error rate as a function of signal to noise ratio. The GUI interface facilitates changing parameters and visualizing the transmitted and received OFDM frames, spectra, and constellations. Simulation results demonstrate the variation in performance between modulation techniques in different channel conditions.

1. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 9, September 2013)
493
OFDM Simulator Using MATLAB
Deepak Sharma1
, Praveen Srivastava2
1
Research Scholar, 2
Assistant Professor, EC Department, KIT Kanpur
Abstract— Orthogonal frequency division multiplexing
(OFDM) is a special case of multicarrier transmission and
frequency division multiplexing, where a single data stream is
transmitted over several lower rate subcarriers, placed
orthogonal to each other. Today it is becoming the chosen
modulation technique for wireless communications. It can
provide large data rates with optimum bit error rate and
enough robustness to radio channel impairments. In this
paper, a user interface is designed using GUI tool of MATAB
which facilitates us to analyze the performance of OFDM
system in terms of SNR vs. BER variation. BPSK, QPSK and
QAM techniques are analyzed in reference to OFDM
processing. Rayleigh Fading channel and Multipath fading
channels are used as a communication channel.
Keywords— AWGN, Bit Error Rate, GUI, ISI, Multi Path
fading channel, OFDM, Signal to Noise ratio
I. INTRODUCTION
Wireless communications is an emerging field, which
has seen enormous growth in the last several years. The
huge uptake rate of mobile phone technology, Wireless
Local Area Networks (WLAN) and the exponential growth
of the Internet have resulted in an increased demand for
new methods of obtaining high capacity wireless networks.
Most WLAN systems currently use the IEEE802.11b
standard, which provides a maximum data rate of 11 Mbps.
Newer WLAN standards such as IEEE802.11a and
HiperLAN2, are based on OFDM technology and provide a
much higher data rate of 54 Mbps. [1]
However systems of
the near future will require WLANs with data rates of
greater than 100 Mbps, and so there is a need of technology
which supports these higher data rates and maximum
spectral efficiency. OFDM is most suitable techniques for
these high data rate applications. OFDM is presently used
in a number of wired and wireless communication systems.
It is a special case of data transmission, where a single data
stream is transmitted over a number of sub carriers (SCs) to
increase robustness against frequency-selective fading or
narrowband interference. OFDM is leading the engineers
into a new era of digital transmission and is becoming the
chosen modulation technique worldwide. This thesis
investigates the performance of various modulation
schemes by analyzing the transmitted and received OFDM
frame, frequency spectrum and their constellation diagram
for the removal of noise and inters signal interference.
II. DIGITAL MODULATION TECHNIQUES
The move to digital modulation provides more
information capacity, compatibility with digital data
services, higher data security, better quality
communications, and quicker system availability. Digital
Modulation Techniques can be classified into following
categories as [5]
 Binary Amplitude Shift Keying (BASK)
 Binary Frequency shift Keying (BFSK)[5]
 Binary Phase Shift Keying (BPSK)
 Differential Phase Shift Keying (DPSK)
 Quadrature Phase Shift Keying (QPSK)
 M- Array Quadrature Amplitude Modulation
(QAM) (M=4, 8, 6, 64, 128, 256,etc)
This Simulator is designed only for BPSK. QPSK, 4-
QAM and 16-QAM Techniques.
III. ORTHOGONAL FREQUENCY DIVISION MULTIPLE
ACCESS
OFDM is referred as Multi-Carrier, Multi-Tone and
Fourier Transform. The OFDM concept is based on
spreading the data to be transmitted over a large number of
carriers, each being modulated at a low rate the carriers are
made orthogonal to each other by appropriately choosing
the frequency spacing between them. A multicarrier
system, such as FDM divides the total available bandwidth
in the spectrum into sub-bands for multiple carriers to
transmit in parallel. It combines a large number of low data
rate carriers to construct a composite high data rate
communication system. [5]
Orthogonality gives the carriers a
valid reason to be closely spaced with overlapping without
ICI. Let ( ) is a function and its orthogonal function will
be ( ) so the condition of Orthogonality is given by „(1)‟
and represented in Fig 1. Here different colors are for sine
and cosine component. [3]
    0*
 dttxtx (1)
Here all the subcarriers are sine waves. The area under
one period of a sine or cosine wave, or any other sinusoidal
with some phase angle, is zero. This can be shown
diagrammatically by Fig 1.

2. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 9, September 2013)
494
Figure 1 Orthogonality of two subcarriers
IV. PERFORMANCE MEASUREMENT IN O.F.D.M.
A. Bit Error Rate
Mathematically BER can be defined by „(2)‟s.
(2) [1]
( ) ( ) (3)
There are some more factors that affect on BER. If the
transmission speed and transmission medium are good in a
particular time but Signal-to-Noise (SNR) is high then BER
will be very low. [6]
B. Signal to Noise Ratio(SNR)
The SNR mathematically can be defined by „(4)’
(4)
SNR is an indicator commonly used to evaluate the
quality of a communication link. Higher value of SNR
means better quality of the communication link. [7]
V. OFDM MODELLING IN MATLAB
The basic concept behind multi-tone modulation is to
replace one wideband signal with many simultaneously
transmitted narrowband signals with the same overall
bandwidth as the original signal. [1]
To implement OFDM
in Simulink, transmitters and receivers in discrete time,
Inverse fast Fourier transform (IFFT) and Fast Fourier
transform (FFT) methods are used respectively. OFDM
transmit symbols that have a longer time duration, which is
less or equal to the maximum delay spread. To combat ISI,
guard intervals are used between OFDM symbols. Fig. 2
which is showing the basic processing involved in OFDM
system OFDM processing can be implemented through the
communication block-set of Simulink. [6]
Figure 2 OFDM System in Simulink
VI. SIMULATION RESULTS
The main objective of this paper is to implement a user
interface for the study of OFDM processing which is
shown in fig. 3. A Simulink model for BPSK technique is
shown in fig. 4. [7]
On the basis of model of BPSK
techniques, Simulink models can be designed for other
techniques also. This GUI enables us to examine the
variation of Bit error rate against the different values of
Signal to Noise ratio. Table 1 shows the simulation
parameter for proposed simulator. [8]
TABLE I
SIMULATION PARAMETER
Parameter Values
Simulation Time 0.10 ms
Cyclic Prefix Length 26
FFT Points 1024
Total Bits 7.5e+004
Doppler Spread 20 Hz
Gain -8dB
Excess delay vector: 3e-6s

3. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 9, September 2013)
495
Figure 3 GUI interface for parameter variation
Figure 4 Simulink Model of BPSK Scheme
The transmitted and received Magnitude spectrum,
OFDM frame and constellation diagram are represented
through fig 5, fig 6, Fig 8 etc under different channel
conditions. BER variation is represented by fig 9.
Figure 3 Transmitted and Received Signal Pattern for BPSK
Technique
Figure 4 Transmitted and Received Signal spectrum for QPSK
Technique

4. International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 9, September 2013)
496
Figure 5 Transmitted and Received Signal spectrum for 4 QAM
Technique
Figure 6 Transmitted and Received Signal spectrum for 16 QAM
Technique
Figure 7 BER vs. SNR variation
VII. CONCLUSION
Thus the purpose of this simulator has achieved. It
makes the study of OFDM processing very easy. By simply
taking the values of SNR, we can easily observe the BER
variation on a graph. If we can move in details of Simulink
models, then just by changing the values of FFT points, we
can easily observe the effect on OFDM received frame.
This simulator also enables us to monitor the change in
OFDM processing by radio button „with OFDM‟ and „no
OFDM‟. This simulator has been tested and verified for
standard results as discussed in previous articles.
REFERENCES
[1] Jigisha N. Patel & Prof.(Mrs.) Upena D Dalal, “A Comparative
Performance Analysis of OFDM using MATLAB Simulation with
M-PSK and M-QAM Mapping”, International Conference on
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W. and Marchionini, G. 1997 A Study on Video Browsing
Strategies. Technical Report. University of Maryland at College
Park.
[2] D.K Sharma., A. Mishra & Rajiv Saxena, “Analog & Digital
Modulation, Techniques: An Overview”, International Journal of
Computing Science and Communication Technologies, Vol.3, No.1,
July 2010Tavel, P. 2007 Modeling and Simulation Design. AK
Peters Ltd.
[3] An initiative Guide of OFDM, 2004.
[4] Vandana B Malode & Bhagwat P Patil, “BER Performance of LBC
Coded OFDM in different channels”, IEEE Control and System
Graduate Research Colloquium 2012.
[5] R Bhagya, Dr. A G Ananth, “Performance of OFDM Multiplexing
Transmission using different Digital Modulation Schemes”,
IJAET/Vol .II/ Issue I/January-March 2011.Brown, L. D., Hua, H.,
and Gao, C. 2003. A widget framework for augmented interaction in
SCAPE.
[6] Ashok Kamboj Geeta Kaushik, “Study & Simulation of O.F.D.M
System”, IJMER, Vol.2, Issue.1, Jan-Feb 2012.
[7] Jun Zhang, Zhongpei Zhang, “Simulation and Analysis of OFDM
System based on Simulink”, IEEE, 2010.
[8] Mohammed Safiqul Islam, Gouri Rani Barai , Atiq Mahmood, “
Performance Analysis of different modulation schemes using OFDM
Techniques in Rayleigh Fading Channel”, IJFPS, Vol.1, No.1, pp.
22-27, March, 2011