1,744 research outputs found
On the stability of flow-aware CSMA
We consider a wireless network where each flow (instead of each link) runs
its own CSMA (Carrier Sense Multiple Access) algorithm. Specifically, each flow
attempts to access the radio channel after some random time and transmits a
packet if the channel is sensed idle. We prove that, unlike the standard CSMA
algorithm, this simple distributed access scheme is optimal in the sense that
the network is stable for all traffic intensities in the capacity region of the
network
Performance of CSMA in Multi-Channel Wireless Networks
We analyze the performance of CSMA in multi-channel wireless networks,
accounting for the random nature of traffic. Specifically, we assess the
ability of CSMA to fully utilize the radio resources and in turn to stabilize
the network in a dynamic setting with flow arrivals and departures. We prove
that CSMA is optimal in ad-hoc mode but not in infrastructure mode, when all
data flows originate from or are destined to some access points, due to the
inherent bias of CSMA against downlink traffic. We propose a slight
modification of CSMA, that we refer to as flow-aware CSMA, which corrects this
bias and makes the algorithm optimal in all cases. The analysis is based on
some time-scale separation assumption which is proved valid in the limit of
large flow sizes
Enabling limited traffic scheduling in asynchronous ad hoc networks
We present work-in-progress developing a communication framework that addresses the communication challenges of the decentralized multihop wireless environment. The main contribution is the combination of a fully distributed, asynchronous power save mechanism with adaptation of the timing patterns defined by the power save mechanism to improve the energy and bandwidth efficiency of communication in multihop wireless networks. The possibility of leveraging this strategy to provide more complex forms of traffic management is explored
CSMA Local Area Networking under Dynamic Altruism
In this paper, we consider medium access control of local area networks
(LANs) under limited-information conditions as befits a distributed system.
Rather than assuming "by rule" conformance to a protocol designed to regulate
packet-flow rates (e.g., CSMA windowing), we begin with a non-cooperative game
framework and build a dynamic altruism term into the net utility. The effects
of altruism are analyzed at Nash equilibrium for both the ALOHA and CSMA
frameworks in the quasistationary (fictitious play) regime. We consider either
power or throughput based costs of networking, and the cases of identical or
heterogeneous (independent) users/players. In a numerical study we consider
diverse players, and we see that the effects of altruism for similar players
can be beneficial in the presence of significant congestion, but excessive
altruism may lead to underuse of the channel when demand is low
MAC Centered Cooperation - Synergistic Design of Network Coding, Multi-Packet Reception, and Improved Fairness to Increase Network Throughput
We design a cross-layer approach to aid in develop- ing a cooperative
solution using multi-packet reception (MPR), network coding (NC), and medium
access (MAC). We construct a model for the behavior of the IEEE 802.11 MAC
protocol and apply it to key small canonical topology components and their
larger counterparts. The results obtained from this model match the available
experimental results with fidelity. Using this model, we show that fairness
allocation by the IEEE 802.11 MAC can significantly impede performance; hence,
we devise a new MAC that not only substantially improves throughput, but
provides fairness to flows of information rather than to nodes. We show that
cooperation between NC, MPR, and our new MAC achieves super-additive gains of
up to 6.3 times that of routing with the standard IEEE 802.11 MAC. Furthermore,
we extend the model to analyze our MAC's asymptotic and throughput behaviors as
the number of nodes increases or the MPR capability is limited to only a single
node. Finally, we show that although network performance is reduced under
substantial asymmetry or limited implementation of MPR to a central node, there
are some important practical cases, even under these conditions, where MPR, NC,
and their combination provide significant gains
An Approximate Inner Bound to the QoS Aware Throughput Region of a Tree Network under IEEE 802.15.4 CSMA/CA and Application to Wireless Sensor Network Design
We consider a tree network spanning a set of source nodes that generate
measurement packets, a set of additional relay nodes that only forward packets
from the sources, and a data sink. We assume that the paths from the sources to
the sink have bounded hop count. We assume that the nodes use the IEEE 802.15.4
CSMA/CA for medium access control, and that there are no hidden terminals. In
this setting, starting with a set of simple fixed point equations, we derive
sufficient conditions for the tree network to approximately satisfy certain
given QoS targets such as end-to-end delivery probability and delay under a
given rate of generation of measurement packets at the sources (arrival rates
vector). The structures of our sufficient conditions provide insight on the
dependence of the network performance on the arrival rate vector, and the
topological properties of the network. Furthermore, for the special case of
equal arrival rates, default backoff parameters, and for a range of values of
target QoS, we show that among all path-length-bounded trees (spanning a given
set of sources and BS) that meet the sufficient conditions, a shortest path
tree achieves the maximum throughput
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