The multiple-access interference (MAI) is one of the major factors threatening the performance of multiuser systems. Transmit beamforming is a powerful strategy to increase the system capacity and mitigate interference. Traditional zeroforcing transmit beamforming (ZFBF) is an effective means to remarkably suppress MAI if the downlink channel is precisely known. However, it is very difficult to get exact information on the actual channel in realistic scenarios. In this paper, we present an approach to achieve orthogonal transmit beamforming (OTBF), only in virtue of statistical information of the downlink channel by using semidefinite programming tools. Different criteria are considered to solve the same problem by satisfying specific constraints between the total transmission power and the quality of service (QoS) requirements of individual users. Furthermore, robust designs for the presented approaches are also analyzed. Simulation results show the effectiveness and the robustness of these strategies