A maximin approach for robust MIMO design: combining OSTBC and beamforming with minimum transmission power requirements

We address the problem of the design of a transmitter in a multi-input-multi-output (MIMO) space diversity system. We consider a design which is robust to errors in the channel estimate available at the transmitter. The design is based on the minimization of the necessary transmit power while guaranteeing a minimum and specified quality of service (QoS) in terms of signal to noise ratio (SNR) with a certain probability. According to this objective, the transmitter exploits all the eigenmodes of the MIMO channel estimate, distributing the transmit power in a robust way among the channel modes by using orthonormal temporal signatures. In order to guarantee a full rate transmission, the orthonormal temporal signatures designed for real constellations in orthogonal space-time block codes (OSTBC) are used, leading to a system structure based on a combination of OSTBC and orthogonal weighted beamforming.