Eun-Seok Ko

A blind OFDM synchronization algorithm based on cyclic correlation

Future wireless systems will need to employ blind estimation to achieve better spectral efficiency. In this letter, we introduce a blind synchronization algorithm for jointly estimating timing and frequency offset in orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator exploits the second-order cyclostationarity of received signals and then uses the symbol-timing and carrier frequency offset information appearing in the cyclic correlation. Because it is a blind estimator, no channel impulse response information is required. Simulations demonstrate that the proposed estimator performs at a sufficiently high level, thus indicating its suitability for use over fading channels.

A Robust STBC-Based Transmit Diversity Scheme for OFDM Systems Over Spatially Transmit Correlated Fading Channels

In this paper, we propose a robust space-time block coded (STBC)-based transmit diversity scheme with low decoding complexity against spatially transmit-correlated fading channels compared with the conventional STBC orthogonal frequency-division multiplexing (STBC-OFDM) schemes. The proposed scheme is comprised of Alamouti code for spatial diversity and a simple mapping process with subcarrier selection for frequency diversity. Proceeding from a detailed analysis of the rank and determinant of the channel correlation matrix, we present a proper subcarrier selection scheme satisfying the conditions for robustness against spatial transmit correlation. Furthermore, when the receiver employs a low-complexity decoder such as a zero-forcing decoder, the proposed scheme shows improved performance compared with the existing space-frequency coded OFDM schemes

Improved space-time block coding with frequency diversity for OFDM systems

Exploiting the effect of frequency diversity based on the frequency-domain channel correlation of OFDM systems, we propose an improved space-time block coding with frequency diversity for OFDM systems in frequency selective fading channels. With only two transmit antennas, the proposed scheme can achieve a fourth-order diversity gain at low complexity. Simulation results for the proposed scheme demonstrate that this joint exploitation of spatial diversity and frequency diversity leads to a remarkable improvement in BER performance.

Effect of imperfect channel information on M-QAM SER performance of orthogonal space-time block codes

The effect of imperfect channel information on the performance of orthogonal space-time block codes is considered in this paper. The symbol error rate of the M-QAM constellation of an orthogonal space-time block code is derived taking into account the effect of imperfect channel information in a Rayleigh fading channel. Derived results show that imperfect channel information destroys the orthogonality of OSTBC, resulting in an error floor that increases with the channel estimation and the normalized Doppler frequency.

Improved transmit diversity using space-time block coding for OFDM systems

We propose an improved transmit diversity using space-time block coding for OFDM systems in frequency selective fading channels. With only two transmit antennas, the proposed scheme can achieve a fourth-order diversity in. gain at low complexity. Simulation results for the proposed scheme show that this joint exploitation of spatial diversity and frequency diversity remarkably improves the BER performance.

A robust transmit diversity for OFDM systems in spatially correlated Rayleigh fading channels

We propose a robust transmit diversity technique for OFDM systems in spatially correlated Rayleigh fading channels. Using the frequency-domain correlation properties of the channel frequency response in OFDM systems and exploiting the effect of frequency diversity, the proposed scheme is more robust against spatial correlation than STBC-OFDM using 𝒢/sub 84/ code. Simulation results confirm that the proposed scheme improves BEP performance more than STBC-OFDM using /spl Gscr//sub 84/ code when spatial correlation increases.