Abstract
Early simulation experience with wireless ad hoc networks suggests
that their capacity can be surprisingly low, due to the requirement
that nodes forward each others’ packets. The achievable capacity
depends on network size, traffic patterns, and detailed local
radio interactions. This paper examines these factors alone and
in combination, using simulation and analysis from first principles.
Our results include both specific constants and general scaling relationships
helpful in understanding the limitations of wireless ad hoc
networks.
We examine interactions of the 802.11 MAC and ad hoc forwarding
and the effect on capacity for several simple configurations and
traffic patterns. While 802.11 discovers reasonably good schedules,
we nonetheless observe capacities markedly less than optimal
for very simple chain and lattice networks with very regular traffic
patterns. We validate some simulation results with experiments.
We also show that the traffic pattern determines whether an ad hoc
network’s per node capacity will scale to large networks. In particular,
we show that for total capacity to scale up with network size
the average distance between source and destination nodes must
remain small as the network grows. Non-local traffic patterns in
which this average distance grows with the network size result in
a
rapid decrease of per node capacity. Thus the question “Are large
ad hoc networks feasible?” reduces to a question about the likely
locality of communication in such networks.
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