SINR maximization approach for partial equalization in OFDM systems

Abstract

In orthogonal frequency division multiplexing (OFDM) system, a cyclic prefix (CP) as redundant information is appended to each OFDM symbol in order to mitigate the impact of intersymbol interference (ISI) on data transmission over multipath channels. On the one hand, the CP interval should not be shorter than the channel impulse response (CIR) length in order to eliminate the ISI completely and on the other hand, appending the CP decreases the bandwidth efficiency of the OFDM systems. In this paper a new TEQ design method based on maximizing signal-to-interference plus noise ratio (SINR) is proposed in order to equalize the received signal partially and eliminate a potion of the ISI when the appended CP interval is shorter than the CIR length. The true SINR for the OFDM system is formulated based on a relative delay, D, between the starting point and the effective point of overall impulse response (OIR) (convolution of the CIR and the equalizer impulse response). The proposed method called maximum SINR time-domain equalization (MSINR-TEQ) estimates the tap coefficients of the equalizer by maximizing the SINR at the output of the equalizer based on the value of the relative delay, D. The MSINR performance is evaluated for data transmission over multipath fading channels with additive white Gaussian noise. Computer simulations show that when the CIR interval is longer than the CP interval, the TEQ designed based on the MSINR method improves the performance of the OFDM system significantly in comparison with the system without an equalizer.