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Throughput Analysis of CSMA Wireless Networks with Finite Offered-load
This paper proposes an approximate method, equivalent access intensity (EAI),
for the throughput analysis of CSMA wireless networks in which links have
finite offered-load and their MAC-layer transmit buffers may be empty from time
to time. Different from prior works that mainly considered the saturated
network, we take into account in our analysis the impacts of empty transmit
buffers on the interactions and dependencies among links in the network that is
more common in practice. It is known that the empty transmit buffer incurs
extra waiting time for a link to compete for the channel airtime usage, since
when it has no packet waiting for transmission, the link will not perform
channel competition. The basic idea behind EAI is that this extra waiting time
can be mapped to an equivalent "longer" backoff countdown time for the
unsaturated link, yielding a lower link access intensity that is defined as the
mean packet transmission time divided by the mean backoff countdown time. That
is, we can compute the "equivalent access intensity" of an unsaturated link to
incorporate the effects of the empty transmit buffer on its behavior of channel
competition. Then, prior saturated ideal CSMA network (ICN) model can be
adopted for link throughput computation. Specifically, we propose an iterative
algorithm, "Compute-and-Compare", to identify which links are unsaturated under
current offered-load and protocol settings, compute their "equivalent access
intensities" and calculate link throughputs. Simulation shows that our
algorithm has high accuracy under various offered-load and protocol settings.
We believe the ability to identify unsaturated links and compute links
throughputs as established in this paper will serve an important first step
toward the design and optimization of general CSMA wireless networks with
offered-load control.Comment: 6 pages. arXiv admin note: text overlap with arXiv:1007.5255 by other
author
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