  This paper considers a multi-user simultaneous wireless information and power
transfer (SWIPT) system with a non-linear energy harvesting model, in which a
multi-antenna base station (BS) estimates the downlink channel state
information (CSI) via uplink pilots. Each single-antenna user is equipped with
a power splitter. Three crucial issues on resource management for this system
include: (i) power-efficient improvement, (ii) user-fairness guarantee, and
(iii) non-ideal channel reciprocity effect mitigation. Potentially, a resource
allocation scheme to address jointly such issues can be devised by using the
framework of multi-objective optimization. However, the resulting problem might
be complex to solve since the three issues hold different characteristics.
Therefore, we propose a novel method to design the resource allocation scheme.
In particular, the principle of our method relies on structuralizing
mathematically the issues into a cross-layer multi-level optimization problem.
On this basis, we then devise solving algorithms and closed-form solutions.
Moreover, to instantly adapt the CSI changes in practice while reducing
computational burdens, we propose a closed-form suboptimal solution to tackle
the problem. Finally, we provide numerical results to show the achievable
performance gains using the optimal and suboptimal solutions, and then validate
the proposed resource allocation scheme.
