Performance of Partial Response Signaling in Reducing Inter Carrier Interference (ici) Due to Carrier Frequency Offset in Ofdm Systems

As a promising technique for high data-rate transmission, Orthogonal Frequency Division Multiplexing (OFDM) is being considered for many emerging wireless applications. In fact, it has been successfully used in many environments, such as DAB, DVB, and HiperLAN-II. In a classical OFDM system, the entire bandwidth is divided into many orthogonal subcarriers, where information symbols are transmitted in parallel over these subcarriers with long symbol duration in order to deal with frequency-selective fading of wireless environments. The overlapping spectrum of the subcarriers in OFDM system requires an accurate frequency recovering system. However, in time variant mobile radio environment, the relative movement between transmitter and receiver resulted in frequency offset due to Doppler frequency shifts, hence the carriers cannot be perfectly synchronized. This imperfection destroys orthogonality among subcarriers and causes intercarrier interference (ICI) to occur in addition to rotation and attenuation. Furthermore, the degradation of BER performance increases rapidly with increasing frequency offset occurrence in OFDM system [1]. Several methods have been proposed to reduce the effect of the ICI. One of the methods is frequencydomain equalization [2]. Time-domain windowing is another way to reduce the effect of frequency offset [3]. The ICI suppression in multiple-input multiple-output (MIMO) OFDM is studied in [4]. A self-ICIcancellation approach has been proposed, which transmits each symbol over a pair of adjacent or nonadjacent subcarriers with a certain phase shift [5, 6, 7]. This method can suppress the ICI significantly with a reduction in bandwidth efficiency. In single-carrier systems, partial response signaling has been studied to reduce the sensitivity to time offset without sacrificing the bandwidth [8]. In the frequency domain, the partial response with correlation polynomial F(D) = 1– D was used to mitigate the ICI caused by carrier frequency offset [9]. The optimum weights for partial response coding that minimize the ICI power were derived [10]. However, by using polynomial coefficients with integer values reduces the complexity of the receiver. In this paper, we study the effect of partial response OFDM (PR-OFDM) system with integer polynomial coefficients and symbol-bysymbol suboptimum detection technique. Besides than ICI, the effect of this method on the PAPR is also investigated. This paper is organised as follows. In Section 2 we describe a PR-OFDM system. The ICI and PAPR expressions and analysis is included in Section 3. Then, in Section 4, the simulation results are presented to demonstrate the performance of PR-OFDM systems with integer polynomial coefficients.