9,693 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
Smoothed Airtime Linear Tuning and Optimized REACT with Multi-hop Extensions
abstract: Medium access control (MAC) is a fundamental problem in wireless networks.
In ad-hoc wireless networks especially, many of the performance and scaling issues
these networks face can be attributed to their use of the core IEEE 802.11 MAC
protocol: distributed coordination function (DCF). Smoothed Airtime Linear Tuning
(SALT) is a new contention window tuning algorithm proposed to address some of the
deficiencies of DCF in 802.11 ad-hoc networks. SALT works alongside a new user level
and optimized implementation of REACT, a distributed resource allocation protocol,
to ensure that each node secures the amount of airtime allocated to it by REACT.
The algorithm accomplishes that by tuning the contention window size parameter
that is part of the 802.11 backoff process. SALT converges more tightly on airtime
allocations than a contention window tuning algorithm from previous work and this
increases fairness in transmission opportunities and reduces jitter more than either
802.11 DCF or the other tuning algorithm. REACT and SALT were also extended
to the multi-hop flow scenario with the introduction of a new airtime reservation
algorithm. With a reservation in place multi-hop TCP throughput actually increased
when running SALT and REACT as compared to 802.11 DCF, and the combination of
protocols still managed to maintain its fairness and jitter advantages. All experiments
were performed on a wireless testbed, not in simulation.Dissertation/ThesisMasters Thesis Computer Science 201
Fairness index in single and double star Networks
In wireless network, the communication works in half duplex mode and nodes can interfere together. In this context, fairness is not obvious. This paper will focus on fairness in the received packets by each node. Fairness is evaluated for static networks topologies called Single Star Network or Double Star Network. The fairness is quantified by its index. In this work, the evaluation of fairness index for double star network is given. Some value of this index are not possible for double star network topology. For example the index of one can only be possible if the double star network is simular to star network. Then the star networks are studied and some simulations are used to illustrate the way to get fairness in the network by controlling the flow rates
Effects of MAC Approaches on Non-Monotonic Saturation with COPE - A Simple Case Study
We construct a simple network model to provide insight into network design strategies. We show that the model can be used to address various approaches to network coding, MAC, and multi-packet reception so that their effects on network throughput can be evaluated. We consider several topology components which exhibit the same non-monotonic saturation behavior found within the Katti et. al. COPE experiments. We further show that fairness allocation by the MAC can seriously impact performance and cause this non-monotonic saturation. Using our model, we develop a MAC that provides monotonic saturation, higher saturation throughput gains and fairness among flows rather than nodes. The proposed model provides an estimate of the achievable gains for the cross-layer design of network coding, multi-packet reception, and MAC showing that super-additive throughput gains on the order of six times that of routing are possible.United States. Dept. of Defense (Air Force Contract FA8721-05-C-0002)Irwin Mark Jacobs and Joan Klein Jacobs Presidential FellowshipInformation Systems of ASD(R&E
State-of-the-art in Power Line Communications: from the Applications to the Medium
In recent decades, power line communication has attracted considerable
attention from the research community and industry, as well as from regulatory
and standardization bodies. In this article we provide an overview of both
narrowband and broadband systems, covering potential applications, regulatory
and standardization efforts and recent research advancements in channel
characterization, physical layer performance, medium access and higher layer
specifications and evaluations. We also identify areas of current and further
study that will enable the continued success of power line communication
technology.Comment: 19 pages, 12 figures. Accepted for publication, IEEE Journal on
Selected Areas in Communications. Special Issue on Power Line Communications
and its Integration with the Networking Ecosystem. 201
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