  Ambient backscatter communications (AmBackComs) have been recognized as a
spectrum- and energy-efficient technology for Internet of Things, as it allows
passive backscatter devices (BDs) to modulate their information into the legacy
signals, e.g., cellular signals, and reflect them to their associated receivers
while harvesting energy from the legacy signals to power their circuit
operation. {\color{black} However, the co-channel interference between the
backscatter link and the legacy link and the non-linear behavior of energy
harvesters at the BDs have largely been ignored in the performance analysis of
AmBackComs. Taking these two aspects, this paper provides a comprehensive
outage performance analysis for an AmBackCom system with multiple backscatter
links}, where one of the backscatter links is opportunistically selected to
leverage the legacy signals transmitted in a given resource block. For any
selected backscatter link, we propose an adaptive reflection coefficient (RC),
which is adapted to the non-linear energy harvesting (EH) model and the
location of the selected backscatter link, to minimize the outage probability
of the backscatter link. In order to study the impact of co-channel
interference on both backscatter and legacy links, for a selected backscatter
link, we derive the outage probabilities for the legacy link and the
backscatter link. Furthermore, we study the best and worst outage performances
for the backscatter system where the selected backscatter link maximizes or
minimizes the signal-to-interference-plus noise ratio (SINR) at the backscatter
receiver. We also study the best and worst outage performances for the legacy
link where the selected backscatter link results in the lowest and highest
co-channel interference to the legacy receiver, respectively.
