Collision-aware design of rate adaptation for multi-rate 802.11 WLANs

Choi, Jaehyuk; Na, Jongkeun; Lim, Yong Beom; Park, Kihong; Kim, Chong-kwon

doi:10.1109/jsac.2008.081003

Cited by 31 publications

(23 citation statements)

References 20 publications

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“…There has been some work [5,38] on estimating the number of competing nodes in a single collision domain with no hidden nodes and no channel errors, which can allow for estimation of the probability of direct collision, but only in these limited scenarios. In [7], Choi et. al.…”

Section: List Of Figuresmentioning

confidence: 99%

Exploiting Spatial Channel Occupancy Information in WLANs

Krishnan¹

2014

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Professor Avideh Zakhor, Chair Current 802.11 networks do not typically achieve the maximum potential throughput despite link adaptation and cross-layer optimization techniques designed to alleviate many causes of packet loss. A primary contributing factor is the difficulty in distinguishing between various causes of packet loss, including collisions caused by high network use, co-channel interference from neighboring networks, and errors due to poor channel conditions. In current 802.11 networks, there are two adaptations occurring simultaneously but independently each using packet loss as an indication of a different problem. The first is contention window adaptation, which implicitly assumes all losses are due to collision, and the second is rate adaptation, which implicitly assumes all losses are due to channel errors. Thus, in all high-loss scenarios, at least one of these two adaptations behaves incorrectly, unnecessarily increasing the impact of packet loss.In this thesis, we propose a novel method for estimating various collision type probabilities locally at a given node of an 802.11 network. The key to our approach is a signal we call the busy-idle (BI) signal, which is a binary-valued record of the channel occupancy over time as observed locally by a given node. We show that if the access point(AP) periodically broadcasts its BI signal to associated nodes at an overhead of less than 2%, the nodes can use this information in conjunction with locally observable quantities to obtain partial spatial information about the network traffic. With this spatial information, nodes can estimate their probabilities of various types of loss and make adaptations to improve throughput and/or network utility.We provide a systematic assessment and definition of the different types of collision, and show how to approximate each of them using local information and the AP's BI signal. We verify our methods using NS-2 simulations, as well as using the Ath5k open source wireless card driver in an experimental testbed. We show that our proposed methodology accurately estimates overall collision probability to within 5%. This experimental verification 1 demonstrates the feasibility of our collision probability estimation approach and the resulting throughput gains in practice.In addition, we describe a suite of methods which exploit these loss probability estimates and the BI signal to improve network throughput and utility. We show via NS-2 simulations that we can achieve gains of up to 400% via modulation rate adaptation, 350% via contention window adaptation, 25% via packet length adaptation, and 50% via carrier sense threshold adaptation. 2This thesis is dedicated to my parents, whose hard work provided me with both the opportunities and the inspiration to pursue my PhD.i

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Section: List Of Figuresmentioning

confidence: 99%

Exploiting Spatial Channel Occupancy Information in WLANs

Krishnan¹

2014

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“…The information on the number of idle slots is not available, however, in general commodity cards. Therefore, in [23] the authors overcome this difficulty by using retry information in 802.11 MAC headers as an indicator of the channel condition, as each station can monitor the medium and get access to the MAC header of every packet transmitted in the medium. If a large number of retransmitted packets are observed, it is inferred that the network is handling a high traffic load.…”

Section: B Packet-loss Based Estimatesmentioning

confidence: 99%

H-RCA: 802.11 Collision-Aware Rate Control

Huang

Duffy

Malone

2013

IEEE/ACM Trans. Networking

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Abstract-Rate control methodologies that are currently available in 802.11 network cards seriously under-utilize network resources and, in addition, per-second throughputs suffer from high variability. In this article we introduce an algorithm, H-RCA, that overcomes these shortcomings, giving substantially higher, and less variable, throughput. The approach solely uses information already available at the driver-level to function and can be implemented on 802.11e commodity hardware.H-RCA's design objective is to minimize the average time each packet spends on the medium (including retries) in order to maximize total network throughput. It uses a development of a recently proposed estimation scheme to distinguish transmission failures due to collisions from those caused by channel noise. It employs an estimate of the packet loss ratio due to noise in assessing whether it is appropriate to change rate. We demonstrate experimentally that packet loss ratio is not necessarily a monotonic increasing function of rate; this is accounted for in H-RCA's design.As H-RCA statistically separates noise losses from those caused by collisions, ns-2 simulations show that it is robust to changing environments. H-RCA does not require specific hardware support nor any change to the IEEE 802.11 protocol. This point is substantiated with results from an experimental implementation.

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“…To minimize the collisions among opportunistic APs, each AP estimates the number of neighbor APs [35] and takes a mini-slot back-off [36] at the end of MAC header part of the ongoing frame (line 11). The back-off value is set in proportion to the number of contending APs.…”

Section: Imapmentioning

confidence: 99%

A distributed message in message aware concurrent transmission protocol in IEEE 802.11 WLANs

Kang

Yoo

Lee

et al. 2012

J Wireless Com Network

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The IEEE 802.11 distributed coordination function (DCF) employs the carrier sense technology to avoid frame collisions. However, recent measurement studies demonstrate that the physical layer (PHY) capture effect frequently occurs; even when frames collide, one of them can be decoded successfully if its relative signal strength is high enough. Furthermore, a new wireless PHY technology, called Message In Message (MIM), adopts an advanced preamble detection function to enhance the PHY capture effect. To fully exploit MIM in multi-collision environments, frame transmission orders have to be carefully scheduled. It also requires tight time synchronization at multiple access points (APs), thus induces large overheads. In this article, we propose an opportunistic concurrent transmission protocol called Distributed Opportunistic MIM-aware Concurrent Transmission (DOMCT) which exploits the MIM functionality in a distributed manner obliterating the centralized control. In DOMCT, APs first prepare interference MAPs to discover the possible simultaneous MIM transmission opportunities. Detecting the inadvertent frame transmission from a neighboring AP, an AP transmits another frame intentionally if both frames can successfully be decoded at destination nodes by the MIM capture effect. Through both analysis and extensive ns-2 simulations, we show that DOMCT outperforms the legacy DCF by up to 61% and observe comparable performance to that of the centralized approach.

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Collision-aware design of rate adaptation for multi-rate 802.11 WLANs

Cited by 31 publications

References 20 publications

Exploiting Spatial Channel Occupancy Information in WLANs

Exploiting Spatial Channel Occupancy Information in WLANs

H-RCA: 802.11 Collision-Aware Rate Control

A distributed message in message aware concurrent transmission protocol in IEEE 802.11 WLANs

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