Abstract-In this paper, we consider the design of Matrix Rotation Based (MRB) space-time signals based on the design criterion of minimizing the union bound on pairwise block error probability (P BEP ). We further propose to design the signal parameters via non-integer searching to get better signals. Superiority of our improved design over the previous design are demonstrated through numerical calculations and performance simulations. With our proposed design for two transmit antennas and one or two receive antennas, we achieve the coding gain of about 1 dB over that of the previous design.