International Journal of Scientific & Engineering Research, Volume 5, Issue 12, December-2014 712
ISSN 2229-5518
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http://www.ijser.org
AN EFFICIENT TECHNIQUE FOR ICI
REDUCTION USING WINDOW FUCTIONS
Prateek Nigam, Alok Kumar Dubey
Abstract— In Orthogonal Frequency Division Multiplexing (OFDM) multi carrier modulation technique is used for high data rate stream
transmission. These carriers are orthogonal to each other. The guard bands are not used in Orthogonal Frequency Division Multiplexing
(OFDM) system. With the help of OFDM technique the spectrum of users can overlap and enhance the spectrum efficiency of the system.
In this paper we are used Kaiser, Hamming, Hann, Blackman and Gaussian window functions. With the help of these window functions we
are comparing their ICI and power of desired receive signal. So that we enhance the quality of OFDM modulated transmission system.
Index Terms— Frequency Spectrum, SIR, Power of Desired Signal, Fading and AWGN, OFDM, ICI
—————————— ——————————
1 INTRODUCTION
Orthogonal Frequency Division Multiplexing (OFDM) is
a multi-carrier modulation technique, in which a single high
rate data-stream is first divided into multiple low rate data
streams and is then modulated using sub-carriers which are
orthogonal to each other [3]. Major advantages of OFDM are
its multi-path delay spread tolerance and efficient spectral
usage by allowing overlapping in the frequency domain. Also
another significant advantage is that the modulation and
demodulation can be done in computationally efficient way
using IFFT and FFT operations [4]. In addition to above,
OFDM has several favorable properties like high spectral
efficiency, robustness to channel fading, immunity to impulse
interference, uniform average spectral density, capacity to
handle very strong echoes and non-linear distortion [5, 6].
Hence in multi-carrier modulation, the most commonly used
technique is Orthogonal Frequency Division Multiplexing
(OFDM) which has recently become very popular in wireless
communication. OFDM is a promising modulation technique
which can be used in many new broadband communication
systems.
One of the major limitations of OFDM systems is Inter Carrier
Interference (ICI). OFDM system is exposed to the risk of
being attacked or harmed by frequency-offset errors between
the transmitted & received signals, which may due to
Doppler shift in the channel or by difference between the
Transmitters and receiver local oscillator frequencies. Hence
subcarriers will be no more orthogonal to each other which
results in inter-carrier interference (ICI). If ICI should be
properly compensated otherwise it will results in power
leakage among the subcarriers and orthogonality between
them will be lost which results in degradation of system
performance.
II. WINDOW FUNCTION BASED OFDMA
A. OFDM Signal on Continuous Time Axis
In OFDM each sub-carrier is modulated independently
with complex modulation symbol vector. Let us consider an
OFDM signal consists of N subcarriers spaced by f Hz. The
k
th
subcarriers for symbol duration [0, T] is expressed as,
()=
2∆
1
If there are N different users i.e. N sub-carriers OFDM
system, nth signal block is represented as,
()=
1
√
�
,
−1
=0
( − ) 2
Where Sn,k is the constellation vector of k
th
sub-carrier in nth
block.
Entire continuous time signal,
()=
1
√
��
,
−1
=0
∞
=0
( − ) 3
The constellation vector Sn,k of k
th
sub-carrier is recovered by
using cross correlation of following equation [1-2],
,
=
√
〈
(),
( − )
� � �� � � � � � � � � ��
〉 4
Where 〈
,
〉 = ∫
()
()
� � � � � � �
At receiving end constellation vector is retrieved like,
,
=
√
〈
(),
( − )
� � � � �� � � � � � � � �
〉 5
where rn (t) S n (t ) n(t) is the noisy received signal
and n(t) is AWGN of environment.
B. Window Functions in OFDM
————————————————
• Prateek Nigam PhD Scholar, Dept. of EC, AISECT UNIVERSITY, Bhopal
India, PH-9407216200. E-mail: er.nigam@gmail.com
• Alok kumar dubey M.Tech Scholar, Dept. Of EC, RKDFIST Bhopal,
India, PH-9452794605. E-mail: dubey.alok307@gmail.com
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