2,559 research outputs found
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
Approaching Optimal Centralized Scheduling with CSMA-based Random Access over Fading Channels
Carrier Sense Multiple Access (CSMA) based distributed algorithms can attain
the largest capacity region as the centralized Max-Weight policy does. Despite
their capability of achieving throughput-optimality, these algorithms can
either incur large delay and have large complexity or only operate over
non-fading channels. In this letter, by assuming arbitrary back-off time we
first propose a fully distributed randomized algorithm whose performance can be
pushed to the performance of the centralized Max-Weight policy not only in
terms of throughput but also in terms of delay for completely-connected
interference networks with fading channels. Then, inspired by the proposed
algorithm we introduce an implementable distributed algorithm for practical
networks with a reservation scheme. We show that the proposed practical
algorithm can still achieve the performance of the centralized Max-Weight
policy.Comment: accepted to IEEE Communications Letter
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
Decentralised Learning MACs for Collision-free Access in WLANs
By combining the features of CSMA and TDMA, fully decentralised WLAN MAC
schemes have recently been proposed that converge to collision-free schedules.
In this paper we describe a MAC with optimal long-run throughput that is almost
decentralised. We then design two \changed{schemes} that are practically
realisable, decentralised approximations of this optimal scheme and operate
with different amounts of sensing information. We achieve this by (1)
introducing learning algorithms that can substantially speed up convergence to
collision free operation; (2) developing a decentralised schedule length
adaptation scheme that provides long-run fair (uniform) access to the medium
while maintaining collision-free access for arbitrary numbers of stations
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