  Power splitting (PS) based simultaneous wireless information and power
transfer (SWIPT) is considered in a multi-user multiple-input-single-output
broadcast scenario. Specifically, we focus on jointly configuring the transmit
beamforming vectors and receive PS ratios to minimize the total transmit energy
of the base station under the user-specific latency and energy harvesting (EH)
requirements. The battery depletion phenomenon is avoided by preemptively
incorporating information regarding the receivers' battery state and EH
fluctuations into the resource allocation design. The resulting time-average
sum-power minimization problem is temporally correlated, non-convex (including
mutually coupled latency-battery queue dynamics), and in general intractable.
We use the Lyapunov optimization framework and derive a dynamic control
algorithm to transform the original problem into a sequence of deterministic
and independent subproblems, which are then solved via two alternative
approaches: i) semidefinite relaxation combined with fractional programming,
and ii) successive convex approximation. Furthermore, we design a
low-complexity closed-form iterative algorithm exploiting the
Karush-Kuhn-Tucker optimality conditions for a specific scenario with delay
bounded batteryless receivers. Numerical results provide insights on the
robustness of the proposed design to realize an energy-efficient SWIPT system
while ensuring latency and EH requirements in a time dynamic mobile access
network.
