630 research outputs found
Max-min Fairness in 802.11 Mesh Networks
In this paper we build upon the recent observation that the 802.11 rate
region is log-convex and, for the first time, characterise max-min fair rate
allocations for a large class of 802.11 wireless mesh networks. By exploiting
features of the 802.11e/n MAC, in particular TXOP packet bursting, we are able
to use this characterisation to establish a straightforward, practically
implementable approach for achieving max-min throughput fairness. We
demonstrate that this approach can be readily extended to encompass time-based
fairness in multi-rate 802.11 mesh networks
Approaching Throughput-optimality in Distributed CSMA Scheduling Algorithms with Collisions
It was shown recently that CSMA (Carrier Sense Multiple Access)-like
distributed algorithms can achieve the maximal throughput in wireless networks
(and task processing networks) under certain assumptions. One important, but
idealized assumption is that the sensing time is negligible, so that there is
no collision. In this paper, we study more practical CSMA-based scheduling
algorithms with collisions. First, we provide a Markov chain model and give an
explicit throughput formula which takes into account the cost of collisions and
overhead. The formula has a simple form since the Markov chain is "almost"
time-reversible. Second, we propose transmission-length control algorithms to
approach throughput optimality in this case. Sufficient conditions are given to
ensure the convergence and stability of the proposed algorithms. Finally, we
characterize the relationship between the CSMA parameters (such as the maximum
packet lengths) and the achievable capacity region.Comment: To appear in IEEE/ACM Transactions on Networking. This is the longer
versio
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
Life-Add: Lifetime Adjustable Design for WiFi Networks with Heterogeneous Energy Supplies
WiFi usage significantly reduces the battery lifetime of handheld devices
such as smartphones and tablets, due to its high energy consumption. In this
paper, we propose "Life-Add": a Lifetime Adjustable design for WiFi networks,
where the devices are powered by battery, electric power, and/or renewable
energy. In Life-Add, a device turns off its radio to save energy when the
channel is sensed to be busy, and sleeps for a random time period before
sensing the channel again. Life-Add carefully controls the devices' average
sleep periods to improve their throughput while satisfying their operation time
requirement. It is proven that Life-Add achieves near-optimal proportional-fair
utility performance for single access point (AP) scenarios. Moreover, Life-Add
alleviates the near-far effect and hidden terminal problem in general multiple
AP scenarios. Our ns-3 simulations show that Life-Add simultaneously improves
the lifetime, throughput, and fairness performance of WiFi networks, and
coexists harmoniously with IEEE 802.11.Comment: This is the technical report of our WiOpt paper. The paper received
the best student paper award at IEEE WiOpt 2013. The first three authors are
co-primary author
Distributed Energy-Saving Algorithms for Wireless Networks
The rapid growth of wireless networks has led to increasing interest in designing
new algorithms that can efficiently reduce the energy consumption of routers
and other devices. We present a new formulation of the Network Flow problem
that takes into account the energy consumption of the data flows, and reduces
the overall network energy expenditure.
We introduce an energy model for wireless connections and analyse its validity
with real measurements. Then we propose a convex optimization problem
that establishes energy constraints on the links, and encourages energy savings
that induce sparsity (shut-off of links). We propose several algorithms that can
be computed in a distributed fashion for different types of capacity constraints.
Finally we justify the sparsity of the solution by using the theory of proximal
methods and present simulations for different scenarios. Our algorithms have
application both in wired networks as well as in TDMA and 802.11 wireless
networks
Resource Allocation for Next Generation Radio Access Networks
Driven by data hungry applications, the architecture of mobile networks is
moving towards that of densely deployed cells where each cell may use a different
access technology as well as a different frequency band. Next generation
networks (NGNs) are essentially identified by their dramatically increased data
rates and their sustainable deployment. Motivated by these requirements, in
this thesis we focus on (i) capacity maximisation, (ii) energy efficient configuration
of different classes of radio access networks (RANs). To fairly allocate
the available resources, we consider proportional fair rate allocations. We
first consider capacity maximisation in co-channel 4G (LTE) networks, then
we proceed to capacity maximisation in mixed LTE (including licensed LTE
small cells) and 802.11 (WiFi) networks. And finally we study energy efficient
capacity maximisation of dense 3G/4G co-channel small cell networks.
In each chapter we provide a network model and a scalable resource allocation
approach which may be implemented in a centralised or distributed manner
depending on the objective and network constraints
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