Carrier Frequency Offset Estimation for OFDM System using Extended Kalman Filter Sankassa B. Senevirathna ∗ , Chandimal Jayawardena † , Sumudu S. Perera ‡ , Chandima L. Perera ‡ , Dhanushka Ranasignhe ‡ , Sureni R. Wijerathna ‡ and Thisara N. Bandara ‡ ∗ Lanka Bell (PVT) LTD, Colombo 03, Sri Lanka Email: sankassab@gmail.com † Sri Lanka Institute of Information Technology, Malabe, Sri Lanka Email: chandimal.j@sliit.lk ‡ Sri Lanka Institute of Information Technology, Malabe, Sri Lanka Email: csnofdm@gmail.com Abstract—The ability of Orthogonal Frequency Division Multiplexing (OFDM) systems to achieve higher data rates and facilitate bandwidth friendly communication [1]-[3] is impaired by the presence of Carrier Frequency Offset (CFO) in the OFDM communication system. CFO can be caused by Doppler frequency shift, or by the differences of the transmitter and the receiver local oscillator frequencies. We propose a new method for CFO estimation for (OFDM) communication systems, with experimental proof which was gathered in the process of real world data transmission using the OFDM communication system in a simulation environment (MATLAB). Keywords—Carrier Frequency Offset (CFO), Orthogonal Fre- quency Division Multiplexing (OFDM), Extended Kalman Filter (EKF) I. I NTRODUCTION The CFO estimation bears a major importance in OFDM communication systems as OFDM is highly sensitive to CFO [4] and it would agitate the orthogonal nature of the OFDM sub carriers, violating the basics of OFDM communication systems. The above fact would leave the OFDM communication system vulnerable to the Inter carrier Interference (ICI), resulting in an increase in the Bit Error Rate (BER). OFDM has been chosen for the European digital audio and video broadcasting standards, as well as for the wireless local-area networking standards IEEE 802.11a, HIPERLAN2 and WiMAX standards IEEE 802.16. Thus, CFO estimation and removal of the received data is highly critical in OFDM systems and has drawn significant attention in the recent past. There are quite a number of EKF based estimation systems in OFDM related areas. Some of these methods could be summarized as follows. An EKF based method has been used for channel estimation for MIMO-OFDM system. This has the capability to exploit the pilot symbols and provide the channel estimation using EKF without any prior knowledge of channel statistics [5]. The EKF has also been used to estimate the Common Phase Error (CPE) in OFDM communication system [6]. Once again a Kalman filter based method has been used for the estimation of time-frequency-selective fading channels in OFDM systems. And it was proposed to use a low-dimensional Kalman filter for the estimation of each subchannel. Then, a minimum mean square-error (MMSE) combiner was used to refine the Kalman estimates [7]. Along with all these EKF applications on OFDM communication system, this research is focused on the CFO estimation of OFDM communication system using the EKF. II. OFDM COMMUNICATION SYSTEM An OFDM system with N subcarriers and 1/N T s fre- quency spacing is considered here, where T s is the symbol period. Let x(n) represent the OFDM symbol and X m ’s represent the baseband symbols on each subcarrier. x(n)=1/N N-1  m=0 X m e (j2πnm/N) (1) The digital to analog (D/A) converter then creates an analog time domain signal which is transmitted through an Additive White Gaussian Noise (AWGN) channel. Figure 1, depicts the baseband OFDM communication system which is thoroughly studied in this research. As illustrated in Fig. 1, the signal is converted back to a discrete N point sequence y(n), corresponding to the each subcarrier at the receiver. The demodulated symbol stream can be described as Y (m)= N-1  n=0 y(n)e (-j2πnm/N) + W (m) (2) 978-1-4244-2900-4/08/$25.00 c 2008 IEEE ICIAFS08 351