  This paper investigates the many-to-one throughput capacity (and by symmetry,
one-to-many throughput capacity) of IEEE 802.11 multi-hop networks. It has
generally been assumed in prior studies that the many-to-one throughput
capacity is upper-bounded by the link capacity L. Throughput capacity L is not
achievable under 802.11. This paper introduces the notion of "canonical
networks", which is a class of regularly-structured networks whose capacities
can be analyzed more easily than unstructured networks. We show that the
throughput capacity of canonical networks under 802.11 has an analytical upper
bound of 3L/4 when the source nodes are two or more hops away from the sink;
and simulated throughputs of 0.690L (0.740L) when the source nodes are many
hops away. We conjecture that 3L/4 is also the upper bound for general
networks. When all links have equal length, 2L/3 can be shown to be the upper
bound for general networks. Our simulations show that 802.11 networks with
random topologies operated with AODV routing can only achieve throughputs far
below the upper bounds. Fortunately, by properly selecting routes near the
gateway (or by properly positioning the relay nodes leading to the gateway) to
fashion after the structure of canonical networks, the throughput can be
improved significantly by more than 150%. Indeed, in a dense network, it is
worthwhile to deactivate some of the relay nodes near the sink judiciously.
