MIMO Multicarrier Transmission over Doubly Selective Channels with Virtual Trajectories Receiver

High mobility and multipath propagation induce Doppler and delay dispersion, respectively. When both phenomena affect the transmitted signal, the communication channel is known as a doubly selective channel (DSC). In multicarrier systems under this scenario, intersymbol interference (ISI) and intercarrier interference (ICI) are ineluctably present, severely degrading the systems performance. Therefore, much effort has been invested in researching convenient waveforms that enable the receiver self-interference cancellation, while making use of the available space, time, and frequency diversity. In this paper, a multicarrier multiple-input multiple-output (MIMO) system for communication in DSCs is presented. By using the virtual trajectory (VT) representation of the MIMO channel, direct conversion of Doppler diversity into additional virtual antennas in the receiver is achieved. This concept is developed for a coherent system with one-tap channel estimation (CE) and equalization algorithms of low complexity as well as for incoherent detection using differential space-frequency block codes (DSFBCs), where pilot signals are not used. For both systems, runtime cancellation and/or inversion of complex interference channel matrices is avoided. Diversity of the doubly selective MIMO channel is exploited without sacrificing compatibility with current multicarrier MIMO systems. The presented system offers robustness in DSCs with minimal extra complexity when compared to conventional approaches. The results demonstrate that MIMO orthogonal frequency division modulation (MIMO-OFDM) can be still implemented in extremely high Doppler scenarios if VT reception is incorporated.