Time-varying FIR decision feedback equalization for MIMO transmission over doubly selective channels

In this paper we propose time-varying decision feedback FIR equalization techniques for multiple-input multiple-output (MIMO) transmission over doubly selective channels. The doubly selective channel is approximated using the basis expansion model (BEM), and equalized by means of time-varying FIR filters. The time-varying FIR filters are modeled using the BEM. By doing so, the time-varying deconvolution problem is converted into a two-dimensional time-invariant deconvolution problem in the time-invariant coefficients of the channel BEM and the time-invariant coefficients of the equalizer BEM. The DFE can be designed according to two different scenarios. In one scenario, the DFE is based on feeding back previously estimated symbols on one particular antenna to cancel/reduce inter-symbol interference (ISI) on that antenna, while in the other scenario, the previously estimated symbols on all transmit antennas are made available, and hence allows to cancel/reduce ISI in a joint fashion. The performance of the proposed equalizers in the context of MIMO transmission is demonstrated by numerical simulations.