A bandwidth-efﬁcient method for cancellation of ICI in OFDM systems Arvind Kumar∗ , Rajoo Pandey
Department of Electronics and Communication Engineering, National Institute of Technology (Deemed University), Kurukshetra 136119, India Received 18 September 2007; accepted 14 April 2008
Abstract Orthogonal frequency division multiplexing (OFDM) is a very important modulation technique in wideband wireless communication and multimedia communication systems. While, it can effectively deal with multipath delay spread produced by frequency fading channels, its main drawback is the effect of frequency offset (FO) produced by the receiver local oscillator or by motion-induced Doppler. The FO breaks the orthogonality among the subcarriers and hence causes intercarrier interference (ICI). In this paper, ICI caused by frequency drift is eliminated by equalizing the complex weighting coefﬁcients of interference. In most of the commonly used ICI cancellation schemes, bandwidth efﬁciency suffers because of the requirement of redundancy in the transmission. In the proposed scheme, repetition of data symbols or transmission of training sequence is not required. Thus, the bandwidth efﬁciency of normal OFDM system is maintained. The improved performance of the present scheme is conﬁrmed through extensive simulations. 2008 Elsevier GmbH. All rights reserved. Keywords: OFDM; Intercarrier interference; Self-ICI cancellation; Interference coefﬁcients equalization
Orthogonal frequency division multiplexing (OFDM) is becoming the chosen multi-carrier modulation technique for wireless and multimedia communication systems. Multimedia wireless services require high-bit-rate transmission over mobile radio channels [1,2]. OFDM can provide large data rates with sufﬁcient robustness to radio channel impairments. OFDM is a method that allows to transmit high data rates over extremely hostile channels at a comparable low complexity . The OFDM has been used in wireless LAN standards such as American IEEE802.11a and European equivalent HYPERLAN/2 and in multimedia wireless services such as Japanese Multimedia Mobile Access Communications. ∗ Corresponding author. Tel.: +91 1744233429.
E-mail addresses: email@example.com (A. Kumar), firstname.lastname@example.org (R. Pandey). 1434-8411/$ - see front matter doi:10.1016/j.aeue.2008.04.007 2008 Elsevier GmbH. All rights reserved.
In OFDM, the entire bandwidth is divided into N small parts, and a block of N data symbols is modulated on N corresponding subcarriers, which are orthogonal to each other. These sub-channels are transmitted in parallel, thereby increasing the symbol duration and reducing the intersymbol interference (ISI). In OFDM systems the effect of ISI can be signiﬁcantly reduced by cyclically extending the OFDM symbol. Therefore, OFDM is a very attractive technique for the transmission of the high-bit-rate data. The major limitation of the OFDM is that it is very sensitive to frequency errors caused by frequency differences between the local oscillators in the transmitter and receiver. The FO may also arise due to motion-induced Doppler. Since in an OFDM system a block of N data symbols is modulated into N corresponding subcarriers, which are orthogonal to each other, the FO will destroy the orthogonality of the subcarriers and in turn induce the intercarrier interference and degrade the system performance signiﬁcantly [4–7].
A. Kumar, R. Pandey / Int. J. Electron. Commun. (AEÜ) 63 (2009) 569 – 575
A number of methods, namely self-ICI cancellation schemes [8–11], discrete Fourier transform (DFT)-based ICI cancellation scheme , and channel estimation and frequency domain equalization [13,14], have been developed to reduce this sensitivity to FO. The self-ICI cancellation scheme requires repetition of input data which reduces the bandwidth efﬁciency of the normal OFDM...