Abstract-Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating in high mobility scenarios, channel estimation becomes a challenging issue, due to fast channel variation and severe intercarrier interference (ICI). This paper proposes a novel pilotaided iterative receiver, based on pilot symbols and iterative softestimate of data symbols and parallel interference cancellation (PIC) scheme coupled with decision statistical combining (DSC) is used to cancel the ICI and to improve the data symbols detection. These data symbols are then utilized to refine the channel estimation further, iteratively. The simulation results of both methods are compared and values obtained depict that the PIC-DSC method improve channel estimation and its BER/SNR value remains stable.
Keywords-MIMO; OFDM; DSC;PIC; BER.
I. INTRODUCTIONIn a high mobility environment, the wireless channel is time variant and frequency selective causing the symbol transmission to be impaired by the Doppler spread. The Doppler spread destroys the orthogonality and creates intercarrier interference (ICI) between OFDM sub-carriers. In addition, the channel changes significantly within one OFDM symbol. Standard channel estimation methods that assume the wireless channels to be invariant within one OFDM symbol, or apply a block-type pilot placement, cannot be used in such a high mobility system. In estimation of the time domain channel coefficients is performed by using pilot tones and by linear interpolation of the time domain channel estimates. The authors use a comb-type pilot tones placement. In least-square (LS) and minimum-mean-square-error (MMSE) channel estimation methods, together with various linear interpolation methods such as linear, second order, low pass, spline-cubic and time domain interpolation are investigated. The authors extend the channel estimation method in [1] to take into account ICI and use a comb-type pilot placement instead of a block-type pilot placement. None of these schemes however, utilize data symbols in the channel estimation process.Recently, high mobility transmission has been considered as one of the important key features of LTE standard. This standard needs to provide support for high mobility users that move at speeds up to 350 Km/h. When users are highly mobile, the multipath wireless channel becomes time-variant and frequency-selective within one OFDM Symbol. The Doppler spread, caused by mobility, destroys the orthogonality and creates inter-carrier interference (ICI) between OFDM subcarriers. As a consequence, the existing channel estimation methods that assume an invariant