Polarization division multiple access (PDMA) is a method to simultaneously transmit two independent signals by using vertical and horizontal polarization in the same frequency band. In PDMA systems, the received signal can experience significant interference from cross-polarized signals if the transmit and receive antennas are misaligned in terms of polarization state. In this paper, a precoding technique to solve this problem is discussed and a channel model to disentangle vertical and horizontal components from the received signal and include the rotation of receive antenna is proposed. The precoding technique is designed and analyzed using a channel model assuming a line-of-sight environment. To measure the performance of the precoding technique, a testbed is implemented using a software-defined radio platform. Simulation and measurement show that enhanced channel gain is achieved even when the polarization state between the transmit and receive antennas is mismatched. Comparison between simulation and measurements proves a basic and crucial principle concerning the capability of controlling the polarization state of a transmitted signal.