Multiple Input Multiple Output System with Multi User Support Based on Directive Information Transmission

Low interference and privacy are crucial requirements for system reliability and se- curity. 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 be- tween 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. Transmit- ters 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 ap- proach, 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 asso- ciated 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.