Date Added: Jun 2010
In this paper, the authors propose a general beam-forming criterion for pre-FFT processing in Orthogonal Frequency Division Multiplexing (OFDM) systems with multiple transmit and receive antennas. The proposed criterion depends on a single parameter ?, which establishes a tradeoff between the energy of the equivalent SISO channel (after Tx-Rx beam-forming) and its spectral flatness. The proposed cost function embraces most reasonable criteria for designing Tx-Rx pre-FFT beam-formers. In general, the proposed criterion results in a non-convex optimization problem. However, they show that the problem can be approximately solved by Semi-Definite Relaxation (SDR) techniques.