Low-complexity Iterative Equalization for Time-Variant Channels in OFDM Systems

Abstract：In order to tackle the inter-carrier interference (ICI) problem caused by time-variant channels in orthogonal frequency division multiplexing (OFDM) systems, a low-complexity iterative equalization technique was proposed in this paper. The impulse response of a time-variant channel was represented by the first-order polynomial basis expansion model to reduce channel parameters. Since the frequency-domain channel matrix was nearly banded, it was divided by the positions of pilot clusters into blocks along the diagonal for equalization. Then the linear zero-forcing equalization was applied to each block. In order to simplify the computational complexity, the Gaussian belief propagation (GaBP) algorithm was used to solve the linear equations in the equalization. Thus the proposed algorithm avoided the matrix inverse operation, and canceled the effects of inter-carrier interference efficiently. Computational complexity analysis and simulation results showed that the proposed equalization technique reduced the bit error rate significantly with low computational cost. In summary, the proposed block-GaBP equalizer has the superiority of low computational complexity and distributed approach for equalization, and therefore, is suitable for hardware implementation such as application-specific integrated circuit.