12 research outputs found
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
CapEst: A Measurement-based Approach to Estimating Link Capacity in Wireless Networks
Estimating link capacity in a wireless network is a complex task because the
available capacity at a link is a function of not only the current arrival rate
at that link, but also of the arrival rate at links which interfere with that
link as well as of the nature of interference between these links. Models which
accurately characterize this dependence are either too computationally complex
to be useful or lack accuracy. Further, they have a high implementation
overhead and make restrictive assumptions, which makes them inapplicable to
real networks.
In this paper, we propose CapEst, a general, simple yet accurate,
measurement-based approach to estimating link capacity in a wireless network.
To be computationally light, CapEst allows inaccuracy in estimation; however,
using measurements, it can correct this inaccuracy in an iterative fashion and
converge to the correct estimate. Our evaluation shows that CapEst always
converged to within 5% of the correct value in less than 18 iterations. CapEst
is model-independent, hence, is applicable to any MAC/PHY layer and works with
auto-rate adaptation. Moreover, it has a low implementation overhead, can be
used with any application which requires an estimate of residual capacity on a
wireless link and can be implemented completely at the network layer without
any support from the underlying chipset
Throughput-Optimal Random Access with Order-Optimal Delay
In this paper, we consider CSMA policies for scheduling of multihop wireless
networks with one-hop traffic. The main contribution of this paper is to
propose Unlocking CSMA (U-CSMA) policy that enables to obtain high throughput
with low (average) packet delay for large wireless networks. In particular, the
delay under U-CSMA policy becomes order-optimal. For one-hop traffic, delay is
defined to be order-optimal if it is O(1), i.e., it stays bounded, as the
network-size increases to infinity. Using mean field theory techniques, we
analytically show that for torus (grid-like) interference topologies with
one-hop traffic, to achieve a network load of , the delay under U-CSMA
policy becomes as the network-size increases, and hence,
delay becomes order optimal. We conduct simulations for general random
geometric interference topologies under U-CSMA policy combined with congestion
control to maximize a network-wide utility. These simulations confirm that
order optimality holds, and that we can use U-CSMA policy jointly with
congestion control to operate close to the optimal utility with a low packet
delay in arbitrarily large random geometric topologies. To the best of our
knowledge, it is for the first time that a simple distributed scheduling policy
is proposed that in addition to throughput/utility-optimality exhibits delay
order-optimality.Comment: 44 page
Clustered wireless sensor networks
The study of topology in randomly deployed wireless sensor networks (WSNs) is important in addressing the fundamental issue of stochastic coverage resulting from randomness in the deployment procedure and power management algorithms. This dissertation defines and studies clustered WSNs, WSNs whose topology due to the deployment procedure and the application requirements results in the phenomenon of clustering or clumping of nodes. The first part of this dissertation analyzes a range of topologies of clustered WSNs and their impact on the primary sensing objectives of coverage and connectivity. By exploiting the inherent advantages of clustered topologies of nodes, this dissertation presents techniques for optimizing the primary performance metrics of power consumption and network capacity. It analyzes clustering in the presence of obstacles, and studies varying levels of redundancy to determine the probability of coverage in the network. The proposed models for clustered WSNs embrace the domain of a wide range of topologies that are prevalent in actual real-world deployment scenarios, and call for clustering-specific protocols to enhance network performance. It has been shown that power management algorithms tailored to various clustering scenarios optimize the level of active coverage and maximize the network lifetime. The second part of this dissertation addresses the problem of edge effects and heavy traffic on queuing in clustered WSNs. In particular, an admission control model called directed ignoring model has been developed that aims to minimize the impact of edge effects in queuing by improving queuing metrics such as packet loss and wait time