Tri-Diagonalizing Approach on Frequency Domain Equalization in a Doubly-Selective Channel

Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a highmobility terminal is assumed in the system, channel transition within an FFT block cannot be ignored. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, we extend the conventional diagonal matrix in FDE to a tri-diagonal matrix. In addition, a simple procedure without strict calculation in tri-diagonalization is proposed. The proposed technique is applied to FDE and frequency-domain turbo equalization (FDTE). The results of numerical analysis show a remarkable improvement by the tri-diagonalization. When the normalized Doppler frequency is 0.0015, the bit error rate (BER) floor is decreased to less than 0.01 in the FDE case; and about 2.8 dB gain at the BER of 0.001 is obtained in the FDTE case.