  In this paper, we study the resource allocation algorithm design for
multiuser orthogonal frequency division multiplexing (OFDM) downlink systems
with simultaneous wireless information and power transfer. The algorithm design
is formulated as a non-convex optimization problem for maximizing the energy
efficiency of data transmission (bit/Joule delivered to the users). In
particular, the problem formulation takes into account the minimum required
system data rate, heterogeneous minimum required power transfers to the users,
and the circuit power consumption. Subsequently, by exploiting the method of
time-sharing and the properties of nonlinear fractional programming, the
considered non-convex optimization problem is solved using an efficient
iterative resource allocation algorithm. For each iteration, the optimal power
allocation and user selection solution are derived based on Lagrange dual
decomposition. Simulation results illustrate that the proposed iterative
resource allocation algorithm achieves the maximum energy efficiency of the
system and reveal how energy efficiency, system capacity, and wireless power
transfer benefit from the presence of multiple users in the system.
