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This paper proposes a two-dimensional switching diversity (2DSD) technique to enhance the collaborative spatial multiplexing (CSM) scheme for uplink wireless access. By the 2DSD, a single data stream is transmitted over multiple antennas and the mobile station (MS) alternates the transmit antennas from one time-frequency resource unit (RU) to another or from one group of RUs to another. That is, the RU-to-Antenna mapping pattern can change in both time and frequency domains. The new scheme has several advantages. First, by sharing one pilot pattern among multiple transmit antennas belonging to one MS, it is backward compatible with the legacy CSM specified in the WiMAX Forum mobile system profile Release 1.0 where two users each with one transmit antenna are scheduled in the same RUs to communicate with a common base station. Second, it saves the pilot overhead and allows as many MSs as possible to be involved in the CSM. Third, it can work in an open-loop manner and does not require additional signaling overhead. Finally, it achieves the power gain and diversity gain to improve the performance, as verified by computer simulations.