Abstract: Time-varying channel estimation for MIMO OFDM systems is challenging.Based on piecewise linear model, this paper proposes an estimation method that first estimates the slope of linear variant and the channel impulse response at the middle time of the current OFDM symbol using pilot sequences, and then estimates the whole channel impulse response through the estimated parameters.Along with the estimation scheme, pilot tone placement is studied.It is better to group pilot tones together into clumps that are equispaced in the frequency domain.Simulation results show effectiveness of the proposed scheme and demonstrate superiority of using the equispaced-grouped pilot sequences.

Key words: pilot sequences, time-varying channel estimation, piecewise linear model, MIMO OFDM