ISSN: 2319-5967 ISO 9001:2008 Certified International Journal of Engineering Science and Innovative Technology (IJESIT) Volume 2, Issue 2, March 2013 638 Survey on Intercarrier Interference Self- Cancellation techniques in OFDM Systems Neha 1 , Dr. Charanjit Singh 2 Electronics & Communication Engineering University College of Engineering Punjabi University, Patiala Abstract--Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation technique which divides the available spectrum into many carriers. Efficient spectrum usage makes it most desirable candidate for high data rate transmission. However the major drawback is its sensitivity to CFO which causes Inter carrier Interference (ICI). This ICI causes severe degradation of the Bit error Rate (BER) performance of the OFDM receiver. There are numerous techniques for reducing ICI including time domain windowing, frequency domain equalization and ICI self- cancellation, but the simplest one is self-cancellation. In this paper the two ways for ICI self-cancellation data conversion and data conjugate are described and the comparisons are made. Index Terms: Additive white Gaussian noise (AWGN), Bit error Rate (BER), carrier frequency offset (CFO), inter carrier interference (ICI), orthogonal frequency division multiplexing (OFDM). I. INTRODUCTION OFDM with the high capacity transmission has been applied into many digital transmission systems, such as digital audio broadcasting (DAB) system, digital video broadcasting terrestrial TV (DVB-T) system, asymmetric digital subscriber line (ADSL), IEEE 802.11a/g Wireless Local Area Network (WLAN), IEEE 802.16 Worldwide Interoperability for Microwave Access (WiMax) systems, and ultra-wideband (UWB) systems [1]. There are two major problems in OFDM named as peak average to power ratio (PAPR) and inter carrier interference (ICI). This paper consider Inter Carrier Interference problem. OFDM communication systems require precise frequency synchronization, since otherwise ICI will occur [2]. Themajorcause of ICI is due to synchronization error and Doppler Effect. There are numerous methods to reduce the effect of ICI named: time domain windowing, frequency domain equalization, frequency offset estimation and cancellation and ICI self-cancellation method. Among all these the simplest one is ICI self-cancellation. There are two ways to perform self-cancellation data conversion and data conjugate method. In this paper ICI self-cancellation is discussed based on data conversion and conjugate method. Furthermore, BER performances of data-conversion method and data-conjugate method the original OFDM with or without convolution coding are compared with each other. The rest of the paper is described as: in section II basic OFDM model and the ICI problem is described. In section III ICI self-Cancellation is introduced: data conversion and data conjugate. Next in IV comparison of the two are made. II.OFDM MODEL In OFDM communication system, inverse discrete Fourier transform (IDFT) is performed at transmitter and Discrete Fourier transform (DFT) is performed at receiver. Figure 1 shows the basic OFDM model. At the transmitter side first the high speed data is converted to many low data using serial to parallel conversion, then after modulation the IDFT is performed and finally OFDM symbols are converted to serial. Then the orthogonal symbols are transmitted over wireless channel. Similarly at receiver side the serial data is first converted parallel then FFT is done to get data in frequency domain. Output data is gained after demodulation and serial conversion. In an OFDM communication system, assuming the channel frequency offset normalized by the sub carrier separation is ε and then the received signal on sub carrier k can be written as: N is the total number of the sub carriers, X(k) denotes the transmitted symbol for the kth sub carrier and n k is an additive noise sample. The first term in the right-hand side of eq. (1) represents the desired signal [3]. The second term is the ICI components. The sequence S(l-k) is defined as the ICI coefficient between lth and kth sub carriers, which can be expressed as: