Iterative (Turbo) Estimation and Detection Techniques for Frequency Selective Channels with Multiple Frequency Offsets in MIMO System

We propose an iterative channel estimation and data detection technique for multiple-input multiple-output (MIMO) frequency selective channels with distinct frequency offsets (FOs) for each multipaths. The pilot symbols are generally inadequate to obtain an accurate estimate of the frequency offsets due to the limitation on the frequency resolution of the estimator. Therefore we initially use the pilot sequence for the estimation and equalization of the channel without consideration to frequency offsets, however we then use the soft estimates of the transmitted signal as a long pilot sequence to determine multiple frequency offsets and to refine the channel estimates iteratively. In the iterative channel estimator, the MIMO frequency selective channel is decoupled into multiple single-input single-output (SISO) flat fading sub-channels through appropriately cancelling both intersymbol-interference (ISI) and the inter-user-interference (IUI) from the received signal. The refined channel estimates and the corresponding frequency offset estimates are then obtained for each resolved MIMO multipath taps. We verify the detection performance using the BER curves and the estimation performance through comparison of the variance of the estimates with the corresponding Cramer-Rao lower bounds (CRLB).