Low interference and privacy are crucial requirements for system reliability and security. Present and further mobile communication systems must support multiple users achieving at same time low interference levels. Several solutions can be adopted to reduce interference between users, such as spreading codes or beam forming. For very high bit rates first solution must be discarded. On the other hand, in environments with a very high number of users beamforming can impose demanding hardware requirements in mobile devices, which is undesirable. Transmitters with directivity introduced at information level where the transmitted constellation is only optimized in the desired direction can also be used to assure low interference. Under this approach, power efficiency on amplification can be also improved, due to the fact that constellations are decomposed into several BPSK (Bi Phase Shift Keying) or QPSK components (Quadri-Phase Shift Keying), being each one separately amplified and transmitted independently by an antenna. Therefore, several users can coexist since each user must know the configuration parameters associated to the constellation configuration, i.e., the direction in which the constellation is optimized, otherwise receives a degenerated constellation with useless data. The simulation results show the effectiveness in user data stream separation of the proposed approach.
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