Channel Matrix Pre-Computation For Mimo Ofdm Systems In High Mobility Fading Channels

--A novel technique to enhance the robustness of space–frequency block coded (SFBC) orthogonal frequency-division multiplexing (OFDM) systems. The proposed system shapes the channel matrix of a frequency-selective fading channel into a piecewise flat--fading over each block of two adjacent subcarriers. Analytical and simulation results show that the proposed scheme substantially outperforms the conventional SFBC in frequency-selective fading channels, which assumes that the channel parameters are equal over the duration of the codeword. Moreover, we demonstrate that the proposed system offers a superior performance in fast time-varying channels where the interference that results from the channel variations acts only as an additive noise. In addition to its superior performance, the proposed system has low computational complexity, because it is based on the short-block-length Walsh–Hadamard transform `Walsh–Hadamard transforms (WHTs) has required A modified SFBC decoder to resolve the frequency selectivity problem has been implemented in existing system. The main drawback of this technique is that it requires accurate knowledge of the channel response difference across adjacent subcarriers. In an embedded Alamouti (EA) SFBC-OFDM system is designed to reduce the impact of the inter carrier interference (ICI) caused by the channel variations by separating the Alamouti code words by B subcarriers and using a three-tap frequency-domain equalizer (FDE) reduce the BER degradation. Keywords—Frequency selective channels, orthogonal frequency division multiplexing (OFDM), precoding, space frequency block coded (SFBC), space time block codes (STBCs).