Corneliu Eugen D. STERIAN Extending Tarokh's Space-Time Codes to 4-D Using Rotationally Invariant Rectangular Constellations for High Data Rate Wireless Communications Abstract. The paper is a new contribution in the field of Multiple Input Multiple Output (MIMO) Antennas, a recent technique that was proven to be very effective in improving the Quality of Service (QoS) of information transmission over radio mobile channels. We start with a rotationally invariant 4-D rectangular constellation whose 2-D constituent constellation has twelve points and is partitioned into four subsets A;B;C; and D. Using a system with two transmit antennas and one or two receive antennas, we then exploit the antenna diversity by devising Space-Time (ST) codes with 16, 32, and 64 states. These codes have both linear and non-linear versions. The codes constructed here demonstrate equal or better performance compared to known 2-D ST codes, having the added value of rotational invariance.