In this invention, the formulas of optimizing radiation pattern of the smart antenna have been deduced and a set of weights, including amplitude and phase shift weight or only phase shift weights, for optimal channel assignment is generated using optimization techniques (e.g., advance algorithms) for smart antennas. These algorithms can deal with the Spatial Division Multiple Access (SDMA) to enlarge the capacity of communication systems and maximize the main lobes toward the users as well as minimize the pattern nulling toward the interfering sources by iterating both the amplitude weights and phase shift weights or the phase shift weight only of a cost function. Thus, an optimal radiation pattern could be derived based on the output power of the cost function with iterated amplitude and phase shift weights or only phase shift weights. At the same time, SDMA of smart antennas can be come true.