SUMMARYIn this paper, a new SDMA (Space Division Multiple Access) configuration is proposed in which the number of multitudes of SDMA can be increased by using dual polarization antennas at both the smart antenna base stations and the mobile terminals. In the proposed configuration, the smart antennas at the base stations constantly monitor the mutual correlations between the mobile terminals at the time of reception. Then, the polarization (vertical or horizontal) to be transmitted by each mobile terminal is determined in such a way that the mutual correlation between the mobile terminals connected at the same time is minimized. The mobile terminal used in the proposed system has a configuration in which the antennas with vertical and horizontal polarizations can be switched for transmission. Transmission is carried out with the polarization specified by the base station. The proposed configuration is expected not only to improve spatial division capability of SDMA by the smart antenna base station with vertical and horizontal polarizations but also to compensate the deterioration of the transmission quality along with the increase of multiplicity of SDMA by means of the switching configuration of the transmission polarization of the mobile terminal while the interference between the mobile terminals is taken into account. The proposed configuration can be applied to the uplinks in the TDD or FDD channels. By means of the numerical simulation, the basic characteristics of the proposed configuration are clarified in the case where the cross polarization discrimination (XPD) and the number of mobile terminals vary. In this way, it is demonstrated that the mobile terminal discrimination capability is improved over the conventional SDMA with the vertical polarization and the system is useful for increased multiplicity of SDMA. Further, the propagation characteristics (amplitude and phase) of the vertical and horizontal polarizations are obtained when the base station antenna and the mobile terminal antenna are placed on a steel tower and on a vehicle, respectively. The characteristics of the proposed configuration are presented where several mobile terminals exist. Usefulness of the proposed configuration in an actual environment for increased multiplicity of SDMA is presented.
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