  In the fifth generation era, the pervasive applications of Internet of Things
and massive machine-type communications have initiated increasing research
interests on the backscatter wireless powered communication (B-WPC) technique
due to its ultra high energy efficiency and low cost. The ubiquitous B-WPC
network is characterized by nodes with dynamic spatial positions and sporadic
short packets, of which the performance has not been fully investigated. In
this paper, we give a comprehensive analysis of a multi-antenna B-WPC network
with sporadic short packets under a stochastic geometry framework. By
exploiting a time-space Poisson point process model, the behavior of the
network is well captured in a decentralized and asynchronous transmission way.
We then analyze the energy and information outage performance in the energy
harvest and backscatter modulation phases of the backscatter network,
respectively. The optimal transmission slot length and division are obtained by
maximizing the network-wide spatial throughput. Moreover, we find an
interesting result that there exists the optimal tradeoff between the durations
of the energy harvest and backscatter modulation phases for spatial throughput
maximization. Numerical results are demonstrated to verify our analytical
findings and show that this tradeoff region gets shrunk when the outage
constraints become more stringent.
