  Backpressure (BP) routing is a well-established framework for distributed
routing and scheduling in wireless multi-hop networks. However, the basic BP
scheme suffers from poor end-to-end delay due to the drawbacks of slow startup,
random walk, and the last packet problem. Biased BP with shortest path
awareness can address the first two drawbacks, and sojourn time-based backlog
metrics were proposed for the last packet problem. Furthermore, these BP
variations require no additional signaling overhead in each time step compared
to the basic BP. In this work, we further address three long-standing
challenges associated with the aforementioned low-cost BP variations, including
optimal scaling of the biases, bias maintenance under mobility, and
incorporating sojourn time awareness into biased BP. Our analysis and
experimental results show that proper scaling of biases can be achieved with
the help of common link features, which can effectively reduce end-to-end delay
of BP by mitigating the random walk of packets under low-to-medium traffic,
including the last packet scenario. In addition, our low-overhead bias
maintenance scheme is shown to be effective under mobility, and our
bio-inspired sojourn time-aware backlog metric is demonstrated to be more
efficient and effective for the last packet problem than existing approaches
when incorporated into biased BP.
