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International Journal of Advanced Research in Computer Engineering & Technology
Volume 1, Issue 4, June 2012

BER AND SIMULATION OF OFDM
MODULATOR AND DEMODULATOR FOR
WIRELESS BROADBAND APPLICATIONS
V.SRIDHAR 1 M.V BRAMHANANDA REDDY 2 M.NAGALAXMI3 G.NAGENDRA4
M.RENUKA5
1
Assistant Professor, ECE, Vidya Jyothi Institute of Technology, Hyderabad
2
Associate professor ,CSE ,Sri vishveshwaraiah institute of science and technology,Chitoor
3
4
Associate professor, ECE ,VBIT,KADAPA
5
1
varadalasri@gmail.com,2bramhareddy999@gmail.com,
3
nalaxmi_sep07@yahoo.com , 4nag20209@gmail.com,5renu_404@yahoo.com

ABSTRACT: With the rapid growth of digital wireless communication in recent years, the need for high speed mobile data
transmission has increased. New modulation techniques are being implemented to keep up with the desired more communication
capacity. Processing power has increased to a point where OFDM has become feasible and economical. Some examples of current
applications using OFDM include DVB (Digital video broadcasting), DAB (Digital audio broadcasting), and HDTV (high - definition
television).OFDM as a transmission technique has been known having a lot of strengths compared to any other transmission
technique, such as its high spectral efficiency, its robustness to the channel fading. Orthogonal. frequency division multiplexing
(OFDM) has become very popular, allowing high speed wireless communications. Orthogonal frequency division multiplexing
(OFDM) has become very popular, allowing high speed wireless communications. A basic OFDM system consists of a QAM or QPSK
modulator, a serial to parallel data, and an IFFT and FFT module, Guard interval inserter, in phase and quadrature phase signal
generator, and parallel to serial data. In this thesis I have implemented the OFDM modulator and demodulator by using different
types of digital modulation techniques such as BPSK, QPSK, 8-QAM. BER for OFDM by using 8-QAM,16-QAM, 64-QAM .
MATLAB environment was used for simulation of proposed algorithm.

Keywords: OFDM, Multipath delay, FADING, ISI, BER.

I . INTRODUCTION
One of the proposed 3rd generation telecom systems is together than standard FDM. This leads to OFDM providing
Universal Mobile Telecommunication System (UMTS), which high spectral efficiency.It is robust against ISI and FADING.
aims to provide a more flexible data rate, a higher capacity
and more tightly integrated services than the second II OFDM- FOR MOBILE COMMUNICATION
generation mobile. Most 3rd generation mobile phone system
are using CDMA or extended TDMA by improving flexibility
OFDM represents a different system-design
of service available but CDMA was found to perform poorly
approach. It can be thought of as a combination of modulation
in single cellular system and high Inter-user interference.
and multiple-access schemes that segments a communications
Several techniques, with aim of improving cell capacity,
channel in such a way that many users can share it. Whereas
providing multipath immunity, flexibility, high tolerance to
TDMA segments are according to time and CDMA segments
peak power clipping and channel noise and also providing a
are according to spreading codes, OFDM segments are
high spectral efficiency includes Orthogonal Frequency
according to frequency. It is a technique that divides the
Division Multiplexing. OFDM allows many users to transmit
spectrum into a number of equally spaced tones and carries a
in an allocated band by subdividing the available B.W into
portion of a user's information on each tone. A tone can be
many carriers called tones.They arepacked much closer

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thought of as a frequency, much in the same way that each
key on a piano represents a unique frequency. OFDM can be
viewed as a form of frequency division multiplexing (FDM), By adding guard time, called a cyclic prefix. The
however, OFDM has an important special property that each channel can be made to behave as if the transmitted
tone is orthogonal with every other tone. FDM typically waveforms ensure orthogonality, which essentially prevents
requires there to be frequency guard bands between the
one subcarrier from interfering with another. The cyclic prefix
frequencies so that they do not interfere with each other.
OFDM allows the spectrum of each tone to overlap, and is actually a copy of the last portion of data symbol appended
because they are orthogonal, they do not interfere with each to the front of the symbol during the guard interval as in
other. By allowing the tones to overlap, the overall amount of Fig.3.
spectrum required is reduced.
OFDM is a modulation technique in that it enables
user data to be modulated onto the tones by adjusting the
tone’s phase, amplitude or both. In the most basic form, a
tone may be present or disable to indicate a 1or0 bit of
information; however either PSK &QAM is typically
employed. An OFDM system takes a data stream & splits it
into N parallel data streams, each at rate 1/N of the original
rate. Each stream is then mapped to a tone at a unique
frequency combined together using the IFFT (Inverse Fast
Fourier Transform) to yield the time-domain waveforms to be
transmitted. Note that the peak of each tone corresponds to a Figure 3 Cyclic Extension of Sinusoid
zero level or null for every other tone.
Multipath causes tones and delayed replicas of tones
to arrive at the receiver with some delay spread. This leads to
misalignment between sinusoidal which need to be aligned be
orthogonal. The cyclic prefix allows the tones to be realigned
at the receiver, thus regaining orthogonality.

III OFDM TRANSMITTER AND RECEIVER
BLOCK DIAGRAM

Figure 1 Tones for OFDM

Thus each user can be assigned a predetermined
number of tones when they information to send, or
alternatively a user can be assigned a variable number of
tones based on the amount of information that they have to
send. The assignments are controlled by the media access
control [MAC] layer, which schedules the resource
assignments based on user demand.

Figure 4: OFDM Tx and Rx block diagram

Figure 2 OFDM transmitter chain

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transmitter, mixing the RF signal to base band for processing,
then using a Fast Fourier Transform (FFT) to analyze the
signal in the frequency domain. The amplitude and phase of
the sub carriers is then picked out and converted back to
digital data. The IFFT and the FFT are complementary
function and the most appropriate term depends on whether
the signal is being received or generated. In cases where the
signal is independent of this distinction then the term FFT and
IFFT is used interchangeably respectively.

IV OFDM Transmitter and Receiver:

4(a) Serial to Parallel Conversion Data: The input serial data
stream is formatted into the word size required for
transmission, e.g. 2bit/word for QPSK and 4bit/word for 16-
QAM shifted into a parallel format. The data is then
transmitted in parallel by assigning each data word to one
carrier in the transmission as shown in above figure3.7 (a).
Figure: 5(a) OFDM Transmitter
4(b) Modulation of Data: The data to be transmitted on each
carrier is then differential encoded with previous symbols,
then mapped into a phase shift-keying format. Since
differential encoding requires an initial phase reference an
extra symbol is added at the start for this purpose. The data on
each symbol is then mapped to a phase angle based on the
modulation method. For example QPSK the phase angles used
are 0, 90, 180, and 270 degrees. The use of phase shift keying
produces a constant amplitude signal and was chosen for its
simplicity and to reduce problems with amplitude fluctuations
due to fading.

4(c) Inverse Fourier Transform : After the required spectrum
is worked out, an inverse Fourier transform is used to find the
corresponding time waveform. The guard period is then added
Figure: 4(b) OFDM Receiver to the start of each symbol

4(d) Guard Period : The guard period used was made up of
two sections. Half of the guard period time is a zero amplitude
transmission. The other half of the guard period is a cyclic
extension of the symbol to be transmitted. This was to allow
Figure: 5(b) OFDM Receiver for symbol timing to be easily recovered by envelope
detection. However it was found that it was not required in
any of the simulations as the timing could be accurately
Figure 4 shows the block diagram of a typical OFDM determined position of the samples. After the guard has been
transceiver. The transmitter section converts digital data to be added, the symbols are then converted back to a serial time
transmitted, into a mapping of sub carrier amplitude and waveform. This is then the base band signal for the OFDM
phase. It then transforms this spectral representation of the transmission.
data into the time domain using an Inverse Discrete Fourier
Transform (IDFT). The Inverse Fast Fourier Transform 4(e) Channel :A channel model is then applied to the
(IFFT) performs the same operations as an IDFT, except that transmitted signal. The model allows for the signal to noise
it is much more computationally efficiency, and so is used in ratio, multipath, and peak power clipping to be controlled. The
all practical systems. signal to noise ratio is set by adding a known amount of white
noise to the transmitted signal. Multipath delay spread then
In order to transmit the OFDM [4] signal the added by simulating the delay spread using an FIR filter. The
calculated time domain signal is then mixed up to the required length of the FIR filter represents the maximum delay spread,
frequency. The receiver performs the reverse operation of the

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while the coefficient amplitude represents the reflected signal
magnitude.
VI : OFDM SIMULATION RESULTS
4(f) Receiver :The receiver basically does the reverse
operation to the transmitter. The guard period is removed. The
FFT of each symbol is then taken to find the original QPSK Modulation: (tx data = 64)
transmitted spectrum. The phase angle of each transmission
carrier is then evaluated and converted back to the data word
by demodulating the received phase. The data words are then
combined back to the same word size as the original data.

V .PERFORMANCE OF OFDM

The performance of OFDM technique can be compared using
OFDM simulated results given below.

VALUE
PARAMETER

SUB CARRIERS 16

FFT SIZE 64 FFT
Figure 6.1(a): Transmitted signals

GUARD PERIOD 800 ns

BPSK, QPSK, 8-QAM,
16-QAM,
MULTIPLE ACCESS
64-QAM

BIT RATES 6,12,18,24,36,48,54
Mbs

CHANNEL SPACING 20MHZ

Table1.1 OFDM system parameters used for the simulation
Figure 6.1(c): OFDM signal

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Figure 6.1(b): Signal constellation diagram

Figure 6.2(a): Transmitted signals

Figure 6.1(d): Received signals

BPSK Modulation: (tx data = 32)

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8-QAM Modulation: (tx data = 128)

Figure 6.2(c): OFDM signal Figure 6.3(a): Transmitted signals


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VII: COMPARISION OF BER

Figure 6.3(c): OFDM signal

Figure 8: BER vs SNR for 8-QAM,16-QAM,64QAM

VII: CONCLUSION

This paper highlights the unique design challenges
faced by mobile data systems that result from the vagaries of
the harsh wireless channel. OFDM has been shown to address
these challenges and to be a key enabler of a system design
that can provide high performance mobile data
communication. Also OFDM is well positioned to meet the
unique demands of mobile packet data traffic. OFDM is
supports 3g technology and also 4g.such as MIMO-
OFDM,WIMAX technology.


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References :
[1] T. Rappaport, “Wireless Communications, Principle & Practice”, IEEE
Press, Prentice Hall, pp. 3, 1996.

[2] Wayne tomasi, “advanced electronic communications systems”,
5thEdition.
M.V.Bramhananda Reddy, Assoc. Professor, in CSE
[3] Chang, R.w and Gibbey, R.A (1968). A theoretical study of performance DepartmentTECHNOLOGY(SVIST),SRIVISHVESWARAIAHINSTITUTE
of an orthogonal multiplexing data transmission scheme, IEEE OFSCIENCEANDTECHNOLOGY,ANGALLU,MADANAPALLE ,M.Tech
transactions on communications technology 16(4), 529-540. in Computer Science Engineering at JNTU, Kakinada, B.Tech in CSE at
JNTU, Hyderabad. He is having seven years teaching experience His areas of
[4] Simon Haykin, Digital Communications, Wiley Publications Ltd, interest for doing theresearchinDATAMINGING, DIGITAL IMAGE
Singapore, 1988. PROCESSING, EMBADDED SYSTEMS, COMPUTERNETWORKS AND
ARTIFICIAL INTELLIGENCE.
[5] S. Swales, M. Beach, “Third Generation Wireless Networks”, University
of Bristol, Future Communication Systems course, April 1994

[6] A. Bahai and B.K saltzberg multicarrier digital communication: theory
and applications of OFDM, Springer 2004.

[7] P. Banelli and S. Cacopardi. Theoretical analysis and performance of
OFDM signals in nonlinear channels. IEEE Trans. on Communications
Mar. 2000.

[8] “Air interface for fixed and mobile broadband wireless access systems”,
IEEE802.16e/d, 2005.

T.NAGALAXMI working as an Assistant
professor in ECE department at Vidya Jyothi institute of technology,
hyderabaad from 2008 to till date. And also pursuing M.TECH(Embedded
systems) ,affiliated college by JNTUH. She is having
Authors Biography sixyearsofteachingexperience.Her areasof research interest are
embeddedsystems,VLSI,embeddedandrealtimesystems,digitalsignalprocessin
gandarchitechtures,Microprocessor&Micro controller.

V.SRIDHAR working as Assistant professor in ECE department at Vidya
Jyothi Institute of Technology,Hyderabad from 2009. completed M.Tech
withSpecialization Wireless and mobile communication systems from
vardhaman college of engineering (AUTONOMOUS)JNTU,Hyderabad in
2011.he has completed M.Sc (IT)from Nagarjuna University, guntur, Andhra
Pradesh.completed Electronics and telecommunication engineering from
vidya jyothi institute of technology,JNTU Hyderabad in 2007.His areas of G.NAGENDRA is working as Associate
research interests include Wireless and Mobile communications, Digital professor in Electronics and communication Engineering for
signal processing, image processing, Telecommunications, communication VBIT,Proddatur,kadapa.. He completed M.Tech(Communications and signal
systems, signal processing.He is Lifetime Member of ISTE and processing) from S.K University,Ananthapur.. He completed B.tech Degree
IETE,IAENG AND SDIWC. in E.C.E from J.N.T.U Hyderabad.His areas of research include
sDigitalSignalprocessing,Digitalimageprocessing,Embeddded
systems,Mobilecommunications and Artificial neural networks.

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M.RENUKA working as Assistant professor in ECE
department vidyajyothi institute of technology hyderabad .she is pursuing
M.Tech(VLSI)fromMahaveerinstituteofscienceandtechnologyJNTU,HYDER
ABAD.She worked as “hardware design engineer” in ECIL from 2007 to
2008.and also she worked as assistant trainee officer in the year 2008 to
2009.her areas of research intrests include VLSI,Embedded systems, EDC
and Digital signal processing.

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