  Backpressure routing and scheduling, with its throughput-optimal operation
guarantee, is a promising technique to improve throughput in wireless multi-hop
networks. Although backpressure is conceptually viewed as layered, the
decisions of routing and scheduling are made jointly, which imposes several
challenges in practice. In this work, we present Diff-Max, an approach that
separates routing and scheduling and has three strengths: (i) Diff-Max improves
throughput significantly, (ii) the separation of routing and scheduling makes
practical implementation easier by minimizing cross-layer operations; i.e.,
routing is implemented in the network layer and scheduling is implemented in
the link layer, and (iii) the separation of routing and scheduling leads to
modularity; i.e., routing and scheduling are independent modules in Diff-Max,
and one can continue to operate even if the other does not. Our approach is
grounded in a network utility maximization (NUM) formulation and its solution.
Based on the structure of Diff-Max, we propose two practical schemes:
Diff-subMax and wDiff-subMax. We demonstrate the benefits of our schemes
through simulation in ns-2.
