This paper studies the problem of safe placement of multi-antenna wireless chargers(SPINNER),that is,given a set of wireless rechargeable devices and a set of wireless chargers,each equipped with multiple directional antennas,scheduling both the power level and the strategy(the position and the orientations of antennas)of each charger,so that the overall charging utility can be maximized and any position in the field satisfies electromagnetic radiation(EMR)safety constraints.In this paper,we consider two different scenarios,that is,safe placement of multi-antenna wireless chargers with a given position set(SPINNER-G)and safe placement of multi-antenna wireless chargers with arbitrary points(SPINNER-A).First,we adopt a piecewise constant function to approximate the nonlinear charging power function and partition the 2D field into a limited number of subareas.Thus,the num-ber of EMR constraints is limited.Then,for SPINNER-G,we propose a maximal coverage set extraction method to further limit the number of orientations of chargers.For SPINNER-A,we construct maximal intersection condition set to limit the searching space for the positions and orientations of chargers.Then,for SPINNER-G and SPINNER-A,we propose two linear programming based greedy schemes,both of which achieve an approximation ratio of 1/2-e.Simulations show that the charging utility of our algorithm improves by at least 54.2％comparte to the three comparison algorithms.
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