1.
Design and Implementation of a Simulator for the
Analysis of Bit Error rates by using Orthogonal
Frequency Division Multiplexing
Abhishek Datta1
, Rupam Chowdhury1
, Sudip Dogra1
,
Electronics & Communication Dept.
Meghnad Saha Inst. Of Technology
Kolkata,India
e-mail: abhi06548@yahoo.com
rupam_ece@rediffmail.com dogra_sudip@rediffmail.com
Subir Kumar Sarkar2
Electronics & Telecommunication Dept.
Jadavpur University
Kolkata,India
Abstract---Orthogonal Frequency Division Multiplexing
(OFDM) has become very popular for its advantages. The
researches are till going on for the development of OFDM. In
this paper we have described a new simulator that can per-
form the BER analysis using OFDM technology and generate
respective plots for bit errors vs signal energy (Eb/No) for
several modulation schemes & different noise effects in three
types of channels (namely AWGN, Rayleigh and Rician).
Index Terms---- BER, Fading, Multipath, Noise.
I. INTRODUCTION TO OFDM
OFDM has become very popular since its inception. This
is used in many communication systems . The performance
analysis of this system for various modulation schemes un-
der different noise channels is an important issue while
choosing this for communication . We have implemented a
simulator using MATLAB 7.3 that can calculate & plot the
graphs showing bit errors vs signal energy (Eb/No) . This
helps us in performance analysis of the system. This GUI
based simulator can take inputs ( channel type, modulation
scheme, guard interval ength etc) & plots the graphs show-
ing BER vs Eb/No . This simulator can be very useful for
practiceng engineers and researchers for simulating their
designed systems with OFDM. The designed simulateor is
very user friendly. Our paper is organized as follows: In
section II we have described OFDM in brief. In section III
we have described various channel effects. In section IV we
have described our designed simulator. We concluded with
section IV.
II. OFDM IN BRIEF
OFDM is one of the dominant techniques of present day
wireless communication and also for future usage in mo-
bile industries. The key requirements for future mobile
communications include much higher peak data rate,
spectrum efficiency, and user capacity in high mobility en-
vironments.It is necessary to notice that the spectrum effi-
ciency advantages of OFDM are mainly achieved at an op-
eration point of relative high SNR. This is a quite different
from CDMA, which is mostly interference limited. Thus
severe problem arises with the high frequency reuse factor
of CDMA which may not be available for OFDM tech-
niques. OFDM is a kind of Multi Carrier Transmission sys-
tem where a single data stream is transmitted over a number
of subcarriers.
A. Properties of OFDM spectrum—
1. Each sub carrier in an OFDM spectrum has exactly an
integer number of cycles in the interval and the numbers of
cycles between adjacent subcarriers differ by exactly one.
2. Flexible bandwidth allocations are easily supported by
OFDM, at least from a baseband perspective, by varying
the number of OFDM subcarriers used for transmission.
B. OFDM Signal Representation---
C. OFDM—Advantage---
It increases the robustness against narrow band interfe-
rence, combat impulsive noise & multipath distortion. ICI
and ISI removed by orthogonal property and guard interval.
Efficient usage of channel bandwidth. Almost 50% band-
width is saved in case of OFDM.
Figure 1: Bandwidth saved using OFDM
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2.
III. DIFFERENT CHANNEL EFFECTS
A. Additive White Gaussian Noise (AWGN) channel—
This channel model is one in which the information is given
a single impairment: a linear addition of wideband or white
noise with a constant spectral density (expressed as watts
per hertz of bandwidth) and a Gaussian distribution of noise
samples. The model does not account for the phenomena of
fading, frequency selectivity, interference, nonlinearity or
dispersion. Wideband Gaussian noise comes from many
natural sources, such as the thermal vibrations of atoms in
antennas (referred to as thermal noise or Johnson-Nyquist
noise), shot noise, black body radiation from the earth and
This channel model is one in which the information is given
a single impairment: a linear addition of wideband or white
noise with a constant spectral density (expressed as watts
per other warm objects, and from celestial sources such as
the Sun.
B. Multipath Rayleigh Fading channel---
In electromagnetic wave propagation, phase-interference
fading is caused by multipath, which may be approximated
by the Rayleigh distribution.
C. Multipath—
The propagation phenomenon resulting in radio signals
reaching the receiving antenna by two or more paths. Caus-
es of multipath include atmospheric ducting, ionospheric
reflection and refraction, and reflection from terrestrial ob-
jects, such as mountains and buildings. The effects of mul-
tipath include constructive and destructive interference, and
phase shifting of the signal.
The Rayleigh probability density function is
, For
D. Rician channel—
The Ricean distribution is given by
The parameter A denotes the peak amplitude of the domi-
nant signal and I0 (•) is a modified form of Bessel function
of the first kind and zero-order. The Ricean distribution is
often described in terms of a parameter K which is defined
as the ratio between the deterministic signal power and the
variance of the multipath. It is given by K= A2/ (2σ2) or, in
terms of dB
Figure 2: PDF of Ricean distributions:
K = – ∞ dB (Rayleigh) and K=6 dB. For K >> 1, the Ricean
pdf is approximately Gaussian about the mean.The parame-
ter K is known as the Ricean factor and completely speci-
fies the Ricean distribution.
As A → 0, K → –∞ dB, and also as the dominant path de-
creases in amplitude, the Ricean distribution degenerates to
a Rayleigh distribution.
IV. DESCRIPTION OF OUR SIMULATOR
We have designed a simulator to simulate the signal trans-
mission using OFDM technique and to obtain the variation
of BER with respect to SNR(Eb/N0). How much SNR is
required to achieve a particular BER, , can be obtained from
those curves. To make our simulator more user friendly we
have designed it in GUI (Graphical User Interface). Here
the input file is a random data. The user has the flexibility
to choose the modulation technique like BPSK, QPSK,
16PSK, 64PSK, QAM etc. Under the different modulation
technique and under the different environment like AWGN
environment, Rayleigh fading environment, the user can
simulate it and can get the desired output i.e. BER Vs SNR
curve and can obtain the relationship between the two pa-
rameters. The steps required to simulate the OFDM signals
in the simulator, a few screen shots are given below.

3.
Figure 3: A screen shot of our simulator for user input for channel selec-
tion (The help window is displayed also)
In the simulator, for proper simulation, the user has to set
the input parameters first like symbol rate, FFT length,
guard interval length etc. Based on the set parameters, the
simulator simulate the OFDM signals under the selected
modulation technique and provide the modulation curves
that are shown in figures of BER analysis for AWGN, Ray-
leigh and Ricean channel.
The simulator is totally designed upon MATLAB platform
and works on auto-generated codes that makes up the GUI,
it is necessary to run the whole project from MATLAB
command window itself.
All the screens apperar with help windows. When the
mouse pointer is placed on any input box , relevant help
file is displayed automatically. Even if some mistake hap-
pens during input of data, warning message comes.
Figure 4 : A screen of our simulator for modulation type,symbol rate,
guard interval input.
The default parameters those have been used in our simu-
lator are shown in table 1.
Table 1: Default parameters used in simulation
Simulation Results ---
Since we have made use of the AWGN, Rayleigh and
Ricean fading channels, examples are provided for every
modulation scheme used for each channel.
All the figures give us the relation of Bit-Error rate
against the Signal to Noise power (Eb/No). A feature that
has been added to the plots in order to make things more
versatile and user-friendly is the provision of display of the
parameter values on the graph itself. In this way, we can
change values and compare the minute changes that occur
in the corresponding plots. The user interface for the simu-
lator keeps provision for such changes which a user can
make within specified ranges, from among the different
options for parameters mentioned in the interface.
Fig 5 : BER analysis for AWGN channel
Subcarriers 52
FFT/IFFT 64 point
Symbol time 4 µs
Guard time 800 ns
Modulation BPSK, QPSK,16- QAM,64-QAM
Coding rates 1/2, 3/4, 2/3
Bit rates 6,12,18,24,36,48,54 Mbps
Channel spacing 20 MHz

4.
Fig 6 : BER analysis for Rayleigh Fading channel
Fig 7 : BER analysis for Rician Fading channel
Since our topic of OFDM simulation is a vast one, we have
concentrated on the findings of BER against Signal-Noise
ration only. There are many other data error rates through
transmission channels, like Symbol Error rate (SER), Mu-
tual information loss against SNR, Mean Square error
(MSE) of channel estimator etc which also prove to be
much helpful in gathering data transmission information.
V. CONCLUSION
In this paper we have described OFDM simulator with
changeable inputs. The design of such simulators for
OFDM-CDMA, COFDM , Mc-CDMA etc will also be
beneficial for the students and researchers. We are trying to
improvise upon this simulator, which will be much more
functional in obtaining any characteristic curves of several
other digital modulation techniques and will also be more
user friendly. Simulation therefore would be more unified.
ACKNOWLEDGEMENT
The design of such simulators for OFDM-CDMA,
COFDM, Mc-CDMA etc will be beneficial for the students
and researchers. The project , in itself, an introduction to
the recent technological development in mobile communi-
cations which has lately come to use. In order to gather as
much information as we could, we needed to consult lots of
texts on OFDM technology along with several articles on
3G-4G concepts. Last but not the least, Internet had been a
great guide for us; a bulk of web pages which were huge
sources to our knowledge. We have been under the guide of
our departmental H.O.D. who has also assisted us whole-
heartedly. We devoted most of the time in order to make it a
grand success.
REFERENCES
A few references have been enlisted herein, at the end of the
4-page manuscript. These are some of the books, articles,
web pages and videos that we have taken the help of , for
the successful completion of the project by Matlab pro-
gramming and simulation. Internet has been the greatest
guide to us and thereby bulks of web pages and links have
been stated below. The whole concept of recent wireless
developments and OFDM technology had been clarified
from those web links. Moreover, learning MATLAB was
also a mammoth task and we had actually consulted refer-
ence books to get ourselves accustomed with MATLAB
new versions and have found out that the software itself was
a big guide to us, all through the project.
[1] “OFDM for wireless multimedia communications” Richard Van Nee,
Ramjee Prasad
[2] “Simulation and software radio for mobile communications “-Hiroshi
Harada, Ramjee Prasad
[3] “The suitability of OFDM as a modulation technique for wireless
telecommunications, with a CDMA comparison” by Eric Lawrey
[4] Mastering MATLAB 7 - Duane C Hanselman, Bruce L Littlefield
[5] MATLAB link: http://blinkdagger.com/matlab/matlab-gui-querying-
the-user-for-input
[6] Link: dsp.ucsd.edu/students/present.../mik/matlabgui/outline.html
[7] The performance of OFDM in Mobile Radio Channel by Teddy
Purnamirza
[8] Link: www.intelligent-systems.info / classes / ee509/ gui.html
[9] Link: video.filestube.com/m/matlab+gui
[10] Link: en.wikipedia.org/Orthogonal_frequency-division_multiplexing
[11] Link: rfdesign.com/next_generation_wireless/ofdm
[12] Robertson, P. Kaiser, S. "The effects of Doppler spreads in
OFDM (A) mobile radio systems", Vehicular Technology
Conference, 1999 .VTC 1999 - Fall. IEEE VTS