A method for generating preamble structures to be used in multi-mode wireless communication systems. The method includes generating a basic element sequence in a predefined length, wherein the basic element sequence has a circularly orthogonal property; generating a type-A preamble by repeating the basic element sequence a number of predefined times; and generating a type-B preamble by adding respective values of real parts to values of imaginary parts of elements in the type-A preamble. The type-A preamble and type-B preamble are cross-correlated.