Abstract : In this paper, we propose a tridimensional tensor coding for multiple-input multiple-output (MIMO) communication systems. This coding allows spreading and multiplexing the transmitted symbols in both space and time domains, owing the use of two allocation matrices. Assuming flat Rayleigh fading channels, the signals received by K receive antennas during P time blocks, composed of N symbol periods each, with J chips per symbol, form a fourth-order tensor that satisfies a new constrained tensor model. A two-step alternating least squares (ALS) algorithm is proposed for blindly and jointly estimating the channel and the transmitted symbols. The performance of the proposed blind receiver is evaluated by means of computer simulations.