A method is provided for determining reference signal positions in a frequency-time domain in an Orthogonal Frequency Division Multiple Access (OFDMA) system. A plurality of sub-carriers are selected in one resource block according to a predetermined mother pattern for reference signal allocation. When a single resource block is assigned for transmission to a user, the reference signal positions are determined corresponding to the plurality of selected sub-carriers in the single resource block. When multiple resource blocks are assigned for transmission to a user, the reference signal positions are determined in the multiple resource blocks by reducing a number of the plurality of selected sub-carriers in the mother pattern for at least one of the multiple resource blocks.