Adaptive turbo code-multiplexed pilot channel estimation for MIMO MC-CDMA systems in highly time-variant propagation channels

In this work an adaptive channel estimation (CE) scheme is presented for multicarrier CDMA systems with multiple transmit and receive antennas. The scheme is based on orthogonal code-multiplexed pilots that are characterized as virtual users and their number is determined in an adaptive way, on a frame level, according to the propagation channel conditions. The unique underlying pattern of pilots is used for CE before the data despreading operation. In addition, an iterative architecture has been incorporated and operates either in interference cancellation mode, or in virtual user one achieving remarkable results with respect to the residual self-interference elimination produced by the superimposed signal and the deorthogonalization effects caused by the time-variant channel properties. Furthermore, a preamble part has been included in the system design as an option for an initial accurate channel estimation which consequently results in optimization of the resources not only with respect to the spreading codes used for pilots, but also to the number of iterations achieving overall high system robustness. The proposed architecture has been evaluated in realistic highly time-variant propagation channels (802.16e channel model of 3GPP.25.996/SCM definition) for various constellation formats and FEC modes with M_T=2 Tx and M_R=1,hellip,4 Rx antennas operating in spatial diversity mode.