Precoding for Multiuser Load-Modulated Arrays on the Downlink

Load-modulated arrays (LMA) use a single central power amplifier (CPA) and tune (modulate) the antenna loads according to the information signal, eliminating the need for traditional RF chains (consisting of DACs, mixers, and filters) at the transmitter. We consider LMAs in multiuser communication on the downlink. A base station is equipped with an LMA to transmit data to multiple users. Toward designing a precoder for this system, the single CPA at the transmitter necessitates the consideration of an instantaneous sum power constraint on the transmitted signal. We propose a precoding scheme which addresses this constraint. The proposed scheme, based on block diagonalization, is such that all the precoded signal vectors lie on the surface of a multidimensional hypersphere. This scheme not only satisfies the power constraint, but also aids power-efficient operation of the CPA due to its constant envelope nature