Low complexity energy efficient joint transmission for OFDM multiuser downlinks

A specially favorable concept for interference reduction in future mobile radio systems consists in the application of joint detection in the uplink and joint transmission in the downlink. Concerning joint detection both optimum nonlinear and low complexity suboptimum linear signal processing algorithms are well known. This is not the case for joint transmission, where up to now most research work focuses on linear signal processing algorithms, which are dual to the ones applied for joint detection. In the present paper a novel signal processing algorithm for joint transmission, termed transmit nonlinear zero forcing, is presented. The main characteristic is the application of an unconventional multiply connected quantization scheme, which allows to improve the energy efficiency, i.e., for data symbols to be transmitted over channels with high attenuations without introducing excessive interferences. Especially in scenarios with large gain differences of the channels between the access point and individual mobile terminals said improved energy efficiencies allow a significant reduction of the required transmitted powers, a feature mitigating intercell interference in cellular systems and thereby enhancing system capacity. In practical systems such gain differences, due to shadowing and largely different distances between the access point and the mobile terminals, prevail.