부산대학교 도서관

The idea of moving the workload of channel equalization from the receiver to the transmitter was first presented by Nakagawa and Esmailzadeh in 1993, when they proposed their pre-Rake for spread spectrum radio transmission. Today this idea is also known as preceding or receiver orientation (RO). The low receiver complexity enabled by RO makes it especially attractive for mobile radio downlinks (DL) with their demand of low cost mobile terminals (MT). Mostly, the considered RO transmission schemes considered up to now are linear with the result that their required transmit powers are virtually the same as in systems not resorting to RO. However, low transmit powers are of paramount importance both with respect to the public concern about electromagnetic irradiation, and to checking the disturbance of other radio links. In the present paper we ventilate the possibility of transmit power reduction in RO mobile radio DLs by introducing a non-linear feature. We set out from known linear RO schemes, in the demodulators of which discrete valued target points are aimed at in the complex plane in the sense of "hard" spot landings, and then, instead of this, introduce non-linearity by envisaging "soft" landings somewhere in suitably defined more or less extended continuous valued domains. In this way the constraints on the transmit signals are loosened, which opens the possibility to minimize the transmit powers. We term our approach minimum energy soft precoding (MESP) and demonstrate its efficacy by simulation results for MIMO OFDM multi-user mobile radio downlinks.