Noncoherent space-frequency coding in MIMO-OFDM is an important method to obtain space and frequency diversity in the absence of channel state information. In this paper

we address a new view of the transmission of space-frequency codes which transform the transmission in frequency selective channels into flat fading channels. Then

a sub-block noncoherent space-frequency coding is proposed which divides the space-frequency plane into small sub-blocks and each one constitutes a space-frequency codeword. By a modified signal model

an asymptotic analysis of the pairwise error probability (PEP) is derived and thus the design criteria for full diversity-achieving code is explicitly defined. We also propose a code construct that achieves the promised order of diversity and demonstrate our conclusion by computer simulation.