  In this work, we derive dynamic output-feedback controllers that render the
closed-loop system externally positive. We begin by expressing the class of
discrete-time, linear, time-invariant systems and the class of dynamic
controllers in the space of input-output behaviors, where a dynamic controller
can be expressed as a static behavioral feedback gain. We leverage the static
form of the controller to derive output-feedback controllers that achieve
monotonic output tracking of a constant non-negative reference output. Further,
we provide a direct data-driven approach to derive monotonic tracking
output-feedback controllers for single-input-single-output (SISO) systems. Our
approaches, model-based and data-based, allow us to obtain output-feedback
controllers that render the closed-loop system externally positive. Finally, we
validate our results numerically in a drone landing control problem.
