An orthogonal multi-beam based MIMO scheme for multi-user wireless systems

In this paper, we propose a multiple-access transmission scheme that can simultaneously achieve both diversity and multiplexing gain in the multi-user multi-input multi-output (MIMO) domain, by using orthogonal multiple random beams. Orthogonal multiple beams are generated so that the users encounter multiple channels at the same time, enabling the use of multi-user diversity through each channel. Although the signal-to-noise power ratio (SNR) of each channel is reduced in proportion to the number of beams, multiple beams are utilized so that the multiplexing gain is larger than the decrease of SNR, increasing the overall system capacity. The proposed scheme can generate spatial channels as many as the number of transmit antennas regardless of the number of receiver antennas, while requiring partial channel information at the transmitter. Thus, the proposed scheme is applicable to multi-input single-output (MISO) schemes as well as MIMO schemes, enabling the use of flexible antenna structures in the receiver.