On the Performance of Carrier Interferometry OFDM by Wavelet Transform

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 11 | Nov -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 480
On the Performance of Carrier Interferometry OFDM by Wavelet
Transform
Cebrail CIFLIKLI1, Bilgin YAZLIK2
1Professor, Department of Electronics and Automation, Erciyes University Kayseri Vocational College,
Melikgazi, Kayseri, Turkey
2Specialist, Erciyes University Technology Development Zone, Melikgazi, Kayseri, Turkey
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - Nowadays, orthogonal frequency division
multiplexing (OFDM) is attracting a great deal of attention.
However, the many advantages responsible for the
widespread application of OFDM systems are limited by
multipath fading. To enhance the performance of OFDM,
many models utilize channel coding. Recent studies have
focused on carrier interferometry coding for OFDM. In this
paper, we present a novel design of carrier interferometry
(CI) spreading codes by using a wavelet transform instead of
a fast Fourier transform (FFT) which is widely used for
realizing carrier interferometry in OFDM systems. The
performance of the proposed technique is simulated over
Rayleigh fading and Rician fading channels. In the
simulations, the performances of OFDM, FFT-based
CI/OFDM, and wavelet transform-based CI/OFDM over
multipath channels are compared. The simulation results
show that the wavelet-based CI codes are more robust at
SNR larger than approximately 10 dB over the Rician fading
and 7 dB over the Rayleigh fading channels.
Key Words: Carrier interferometry, Multipath fading,
OFDM, Wavelet transform, FFT.
1.INTRODUCTION
In the recent years, OFDM has great attention, OFDM gives
opportunities to system designers especially when they
need high data rates. Today, there is a huge demand for
mobile devices which connect to internet and this
situation leads high data usage on wireless
communications systems. To be able to get high data rates
on wireless communication systems, multicarrier schemes
can be employed and OFDM is one of the best multicarrier
scheme [1].
In OFDM, high-speed data stream is converted into low-
speed parallel data streams with the help of serial-parallel
convertors. Then, these low-speed data streams are sent
to channel by using of orthogonal carriers. We know that
OFDM can reduce inter-symbol interference, because it
has flat fade carriers [2]. This situation leads to unique
carrier signals with different amplitudes.
PAPR reduction and BER performance increase are
possible by the use of carrier interferometry (CI) codes as
spreading codes in OFDM systems. In the literature, many
techniques have been proposed for using CI in OFDM
systems. CI/OFDM improves the performances of OFDM-
based WLANs as presented in [3]. It is possible to
implement CI codes in CDMA and TDMA wireless systems
[4, 5] and 64-QAM OFDM systems [6]. Moreover, in [7, 8,
9] pseudo-orthogonal CI coding has been used in OFDM
systems. CI codes are spreading codes and are of different
types, such as coded CI [10] and turbo coded CI [11]. In
[12], CI OFDM is realized by using FFT and the effect of the
proposed technique in terms of average bit error rate
(BER) is analyzed. Narrowband interference rejection in
OFDM via CI is carried out by Nassar in [13].
In the literature, many articles show that a wavelet
transform has many advantages over a fast Fourier
transform (FFT) [14, 15]. While a FFT gives only frequency
components of the signal, a wavelet transform can supply
both time and frequency information simultaneously.
In this paper, we present a novel design of CI spreading
codes by using a wavelet transform instead of a FFT,
because of the advantages of wavelet transform. The
performance of the proposed technique is simulated over
Rayleigh fading and Rician fading channels for an OFDM
system. In the simulations, the performances of OFDM,
FFT based CI/OFDM and wavelet transform based
CI/OFDM over multipath channels are compared. The
simulation results show that the wavelet transform-based
CI codes are more robust to narrowband interference than
are FFT-based CI codes.
2. CI /OFDM SYSTEM DESCRIPTION
In Figure 1, a block diagram of the conceptual CI/OFDM
transmitter is given. As shown in this figure, system
modulates every symbols onto all carriers and system uses
carrier interferometry codes to spread the symbols to
same carrier, carrier interferometry can be considered as
phase offset. We can define CI spreading code for kth
symbol as: 𝛽 = (𝑒 , 𝑒 , … , , 𝑒 , … , , 𝑒 (
,

where 𝜃 = (2𝜋/𝑁 𝑘 which helps to secure
orthogonality among transmitted symbols [4].
Fig – 1: Conceptual block diagram of the CI/OFDM
transmitter
The symbol which is transmitted in a CI/OFDM for kth
symbol is:
𝑠 (𝑡 = 𝐴. 𝑅𝑒 {∑ 𝛼 𝑒 ( . .
} (1)
where 𝛼 is the nth symbol in the kth symbol stream,
2𝜋/𝑁. 𝑘. 𝑖 is the phase offset value and it is used to get the
spreading code of the kth symbol and it helps to secure
orthogonality among the N symbols and A defines energy.
Fig – 2: Conceptual block diagram of the CI/OFDM
receiver
The received signal for CI/OFDM system is mathematically
described as:
𝑠(𝑡 = 𝐴. ∑ ∑ 𝛼 cos (2𝜋𝑓 𝑡 + 2𝜋𝑓 𝑡 + 𝑖.
2𝜋
𝑁
. 𝑘) (2)
3.DESCRIPTION OF THE PROPOSED CI/OFDM
SYSTEM
In this paper, we obtained the CI codes by using a wavelet
transform. In Figure 3, the block diagram of the proposed
system is given. As shown in this figure, the wavelet
transform is applied to a baseband modulated signal for
realizing CI. The background of the proposed system is
based on the block. In the transmitter, data are modulated
with a QAM modulator, and after QAM modulation the
signal is spread by the wavelet as in a CI/FFT system. CI
code length is equal to number of carrier. Then the spread
signal is modulated by using an inverse fast Fourier
transform (IFFT). After IFFT step we used wavelet to
realize CI spread. The resulting symbols after the IFFT
block are extended by using a cyclic prefix and transmitted
over the fading channel. At the receiver end, operations
inverse to those realized at the transmitter end are carried
out.
Fig – 3: Block diagram of the proposed CI/OFDM system
Fig – 4: Block diagram of the proposed CI/OFDM system’s
wavelet spreading phase
Fig – 5: Block diagram of the proposed CI/OFDM system’s
wavelet despreading phase
4.WAVELET TRANSFORM
Wavelet transform contributes to analyze of the signals
not only by their frequency domain but also by the time
domain. FFT gives us only frequency information, but
wavelet transform supplies both frequency and time
information of the signal. To be able to analyze the signal
both in time and frequency domains, it is necessary to
SerialtoParallel
IFFT
ak sk
FFT
DECISIONBLOCK
W1
WN-1
C*k,0
C*k,1
C*k,N-1
Equalizer Despreading
TOTAL
Data
Gen.
QAM
Mod.
IFFT Wavelet
Spreading
Cyclic
Prefix
Channel
QAM
Demod
FF
T Wavelet
Despread
ing
Remove
Cyclic
Prefix
Output
Real Part
Imaginer
Part
Wavelet
Wavelet
Recombi-
nation of
Signals
IFFT
Wavelet
Wavelet
Real
Part
Imaginer
Part
Decombi-
nation of
Signals
FFT
W0
s(t)
CI0
CI1
CIN-1

divide the signal into small parts. At this work, we use
Haar filter for wavelet transform. The Haar filter is:
(𝑡
=
√𝑁
{
2 /
( /2 𝑡 ( . /2
2 /
( . /2 𝑡 /2
𝑡 𝑒 𝑖𝑠𝑒
(3)
While a, determines the amplitude of the function; l,
determines location of the function. Haar transform filter
is orthogonal as well as the CI codes.
In this paper we have realized carrier interferometry
OFDM with the wavelet transform instead of FFT. The
results show that the system has better performance than
the original CI-FFT OFDM system, but this system
demands more energy and computational power.
5.SIMULATIONS AND RESULTS
In this section, we test the performance of the wavelet-
based CI/OFDM system and compare with the
performance of the OFDM system and FFT-based
CI/OFDM system in the presence of narrowband
interference. Simulations are performed over AWGN,
Rayleigh and Rician fading channels in the MATLAB
environment. The results show that proposed system
performs same under AWGN but better under Rayleigh
and Rician fading channels.
Table – 1: Simulation Parameters
Number of Subcarrier 256
Baseband Modulation QPSK
Wavelet Function Haar
Level of Wavelet 8
FFT Size 256
Cyclic Prefix 64
CI Code Length 256
Totally 10 coefficients are used in algorithm such as level
of wavelet, fft size, number of sub carrier etc.
Because of its symmetric, orthogonal, biorthogonal
structure, Haar is selected. The subject of the paper is in
mainframe to send an orthogonal signal to the receiver so
that it is important to use orthogonal system to improve
the performance.
In Figure 6, the performance of the proposed system is
given for the AWGN fading channel. It can be seen in the
figure that the OFDM system based on CI using both a
wavelet transform and FFT is more robust than the OFDM
system without CI.
given for the Rayleigh fading channel. It can be seen in the
system without CI. Moreover, the proposed system
performs better over the Rayleigh fading channel. In
particular, the wavelet-based technique is more robust at
SNR larger than approximately 7 dB.
Fig – 6:. Performance of the proposed system over a
AWGN channel
Fig – 7:. Performance of the proposed system over a
Rayleigh fading channel
given for the Rician fading channel. It can be seen in the
system without CI. Moreover, the proposed system
performs better over the Rician fading channel. The
wavelet-based technique is more robust at SNR larger
than approximately 10 dB.

Fig – 8:. Performance of the proposed system over a Rician
fading channel
6.CONCLUSIONS
A novel wavelet-based CI/OFDM system is proposed in
this paper as an alternative to FFT-based CI/OFDM
systems in the presence of narrowband interference. The
performance of the proposed system is simulated in the
MATLAB environment over AWGN, Rayleigh and Rician
fading channels and compared to OFDM and FFT-based
CI/OFDM systems. The simulation results show that the
wavelet-based system is absolutely robust to narrowband
interference. Furthermore, the proposed system performs
better than the OFDM system without CI and FFT-based
CI/OFDM proposed in the literature. The wavelet-based
technique is more robust at SNR larger than
approximately 10 dB over the Rician fading channel and 7
dB over the Rayleigh fading channel. Wavelet transform of
course makes the system a bit more complex, for example
simulation takes 130,19 seconds for proposed system in
Rician channel but 88,84 seconds takes for traditional CI
system, further works will be focused on that point. We
know that CI codes improve PAPR performance of OFDM
systems. PAPR performance of the proposed system will
be investigated for future work.
REFERENCES
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BIOGRAPHIES
Cebrail Ciflikli was born in K.
Maras, Turkey, in 1961. He received
the Ph.D. degree in electronics
engineering from Erciyes University
in 1990. In 2004, he joined Erciyes
University Kayseri Vocational
College as Professor where he is
now Principal. Dr. Ciftlikli's current
research interests include spread-
spectrum communications, wireless
ATM/LAN, signal processing, DS-
CDMA system engineering, RF
power amplifier linearization for
wireless communication systems.
Bilgin Yazlik was born in Van,
Turkey, in 1983. He is PhD student
in Erciyes University. Since 2005 he
has been working as a Specialist at
Erciyes University, Kayseri and he is
general manager at Erciyes Science
Park. His current research interests
are in the areas of carrier
interferometry, computer grids,
multi-carrier communications.

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On the Performance of Carrier Interferometry OFDM by Wavelet Transform