  This paper investigates the average throughput of a wireless powered
communications system, where an energy constrained source, powered by a
dedicated power beacon (PB), communicates with a destination. It is assumed
that the PB is capable of performing channel estimation, digital beamforming,
and spectrum sensing as a communication device. Considering a time splitting
approach, the source first harvests energy from the PB equipped with multiple
antennas, and then transmits information to the destination. Assuming
Nakagami-m fading channels, analytical expressions for the average throughput
are derived for two different transmission modes, namely, delay tolerant and
delay intolerant. In addition, closed-form solutions for the optimal time
split, which maximize the average throughput are obtained in some special
cases, i.e., high transmit power regime and large number of antennas. Finally,
the impact of co-channel interference is studied. Numerical and simulation
results have shown that increasing the number of transmit antennas at the PB is
an effective tool to improve the average throughput and the interference can be
potentially exploited to enhance the average throughput, since it can be
utilized as an extra source of energy. Also, the impact of fading severity
level of the energy transfer link on the average throughput is not significant,
especially if the number of PB antennas is large. Finally, it is observed that
the source position has a great impact on the average throughput.
