Simultaneous wireless information and power transfer with finite-alphabet input signals

Simultaneous wireless information and power transfer (SWIPT) has emerged as a promising technology, enabling the transmission of both data and energy to a receiver equipped with an RF energy-harvesting circuitry. In this paper, we consider a point-to-point communication system in which a source transmits finite-alphabet signals. The receiver has information-decoding (ID) and energy-harvesting (EH) components, and power-splitting scheme is applied to carry out these operations concurrently. In order to improve the rate-energy tradeoff characteristics, we have introduced a novel approach that assigns probabilities non-uniformly to different signals in the constellation. According to the relationship between signal probabilities and energy consumption, these signal probabilities can be dynamically adjusted using two techniques, namely static slope characteristics and dynamic slope characteristics, given the minimum harvested energy constraint. Intuitively, advantage of one approach over the other depends on the improvement of the power-splitting factor when high energy input signals become more likely to be transmitted. In order to determine the optimal solution, we formulate an optimization problem and develop an algorithm taking into account the key parameters, e.g., splitting factor and signal probabilities. Numerical results are provided to justify the theoretical characterizations, considering 16-QAM.