  We consider a two-phase Wireless-Powered Communication Network under
Nakagami-m fading, where a wireless energy transfer process first powers a
sensor node that then uses such energy to transmit its data in the wireless
information transmission phase. We explore a fixed transmit rate scheme
designed to cope with the reliability and delay constraints of the system while
attaining closed-form approximations for the optimum wireless energy transfer
and wireless information transmission blocklength. Then, a more-elaborate rate
control strategy exploiting the readily available battery charge information is
proposed and the results evidence its outstanding performance when compared
with the fixed transmit rate, for which no battery charge information is
available. It even reaches an average rate performance close to that of an
ideal scheme requiring full Channel State Information at transmitter side.
Numerical results show the positive impact of a greater number of antennas at
the destination, and evidence that the greater the reliability constraints, the
smaller the message sizes on average, and the smaller the optimum information
blocklengths. Finally, we corroborate the appropriateness of using the
asymptotic blocklength formulation as an approximation of the non-asymptotic
finite blocklength results.
