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132
Modeling perflow throughput and capturing starvation in CSMA multihop wireless networks
 In Proc. of IEEE Infocom
, 2006
"... Abstract — Multihop wireless networks employing random access protocols have been shown to incur large discrepancies in the throughputs achieved by the flows sharing the network. Indeed, flow throughputs can span orders of magnitude from near starvation to many times greater than the mean. In this ..."
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Cited by 159 (18 self)
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Abstract — Multihop wireless networks employing random access protocols have been shown to incur large discrepancies in the throughputs achieved by the flows sharing the network. Indeed, flow throughputs can span orders of magnitude from near starvation to many times greater than the mean. In this paper, we address the foundations of this disparity. We show that the fundamental cause is not merely differences in the number of contending neighbors, but a generic coordination problem of CSMAbased random access in a multihop environment. We develop a new analytical model that incorporates this lack of coordination, identifies dominating and starving flows and accurately predicts perflow throughput in a largescale network. We then propose metrics that quantify throughput imbalances due to the MAC protocol operation. Our model and metrics provide a deeper understanding of the behavior of CSMA protocols in arbitrary topologies and can aid the design of effective protocol solutions to the starvation problem. I.
A general model of wireless interference
 ACM INTERNATIONAL CONFERENCE ON MOBILE COMPUTING AND NETWORKING
, 2007
"... We develop a general model to estimate the throughput and goodput between arbitrary pairs of nodes in the presence of interference from other nodes in a wireless network. Our model is based on measurements from the underlying network itself and is thus more accurate than abstract models of RF propag ..."
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Cited by 102 (4 self)
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We develop a general model to estimate the throughput and goodput between arbitrary pairs of nodes in the presence of interference from other nodes in a wireless network. Our model is based on measurements from the underlying network itself and is thus more accurate than abstract models of RF propagation such as those based on distance. The seed measurements are easy to gather, requiring only O(N) measurements in an Nnode networks. Compared to existing measurementbased models, our model advances the state of the art in three important ways. First, it goes beyond pairwise interference and models interference among an arbitrary number of senders. Second, it goes beyond broadcast transmissions and models the more common case of unicast transmissions. Third, it goes beyond homogeneous nodes and models the general case of heterogeneous nodes with different traffic demands and different radio characteristics. Using simulations and measurements from two different wireless testbeds, we show that the predictions of our model are accurate in a wide range of scenarios.
A MeasurementBased Approach to Modeling Link Capacity in 802.11based Wireless Networks
 In To appear in ACM MOBICOM ’07
, 2007
"... We present a practical, measurementbased model that captures the effect of interference in 802.11based wireless LAN or mesh networks. The goal is to model capacity of any given link in the presence of any given number of interferers in a deployed network, carrying any specified amount of offered l ..."
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Cited by 74 (7 self)
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We present a practical, measurementbased model that captures the effect of interference in 802.11based wireless LAN or mesh networks. The goal is to model capacity of any given link in the presence of any given number of interferers in a deployed network, carrying any specified amount of offered load. Central to our modeling approach is a MAClayer model for 802.11 that is fed by PHYlayer models for deferral and packet capture behaviors, which in turn are profiled based on measurements. The target network to be evaluated needs only O(N) measurement steps to gather metrics for individual links that seed the models. We provide two solution approaches – one based on direct simulation (slow, but accurate) and the other based on analytical methods (faster, but approximate). We present elaborate validation results for a 12 node 802.11b mesh network using upto 5 interfering transmissions. We demonstrate, using as comparison points three simpler modeling approaches, that the accuracy of our approach is much better, predicting link capacities with errors within 10 % of the base channel datarate for about 90% of the cases.
Modeling media access in embedded twoflow topologies of multihop wireless networks
 In Proceedings of ACM MobiCom ’05
, 2005
"... In this paper, we decompose a large or smallscale multihop wireless network into embedded subgraphs, each consisting of four nodes and two flow pairs. We systematically study all twelve possible topologies that arise according to whether the different nodes are in radio range of each other. We sh ..."
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Cited by 73 (14 self)
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In this paper, we decompose a large or smallscale multihop wireless network into embedded subgraphs, each consisting of four nodes and two flow pairs. We systematically study all twelve possible topologies that arise according to whether the different nodes are in radio range of each other. We show that under both a random spatial distribution of nodes and random waypoint mobility with shortestpath routing, a critical and highly probable scenario is a class in which the channel state shared by the two flows is not only incomplete (i.e., the graph is not fully connected), but there is also asymmetry in the state between the two flows. We develop an accurate analytical model validated by simulations to characterize the longterm unfairness that naturally arises when CSMA with twoor fourway handshake is employed as a random access protocol. Moreover, we show that another key class of topologies consists of incomplete but symmetric shared state. We show via modeling and simulations that in this case, the system achieves longterm fairness, yet endures significant durations in which one flow dominates channel access with many repeated transmissions before relinquishing the channel. The model predicts the timescales of this unfairness as a function of system parameters such as the maximum retransmission limit.
New insights from a fixedpoint analysis of single cell
 IEEE 802.11 WLANs. In: Proc. IEEE Infocom 2005
, 2005
"... Abstract—We study a fixedpoint formalization of the wellknown analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixedpoint solution and performance measures resulting from it are studied. Uniqueness of the fixed po ..."
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Cited by 69 (4 self)
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Abstract—We study a fixedpoint formalization of the wellknown analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixedpoint solution and performance measures resulting from it are studied. Uniqueness of the fixed point is established. Simple and general throughput formulas are provided. It is shown that the throughput of any flow will be bounded by the one with the smallest transmission rate. The aggregate throughput is bounded by the reciprocal of the harmonic mean of the transmission rates. In an asymptotic regime with a large number of nodes, explicit formulas for the collision probability, the aggregate attempt rate, and the aggregate throughput are provided. The results from the analysis are compared with ns2 simulations and also with an exact Markov model of the backoff process. It is shown how the saturated network analysis can be used to obtain TCP transfer throughputs in some cases. Index Terms—CSMA/CA, performance of MAC protocols, wireless networks. I.
Determining the endtoend throughput capacity in multihop networks: methodology and applications
 In Proc. of ACM SIGMETRICS
, 2006
"... In this paper, we present a methodology to analytically compute the throughput capacity, or the maximum endtoend throughput of a given source and destination pair in a multihop wireless network. The endtoend throughput capacity is computed by considering the interference due to neighboring nodes ..."
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Cited by 56 (2 self)
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In this paper, we present a methodology to analytically compute the throughput capacity, or the maximum endtoend throughput of a given source and destination pair in a multihop wireless network. The endtoend throughput capacity is computed by considering the interference due to neighboring nodes, as well as various modes of hidden node interference. Knowing the throughput capacity is important because it facilitates the design of routing policy, admission control for realtime traffic, as well as load control for wireless networks. We model locationdependent neighboring interference and we use a contention graph to represent these interference relationships. Based on the contention graph, we formulate the individual link capacity as a set of fixed point equations. The endtoend throughput capacity can then be determined once these link capacities are obtained. To illustrate the utility of our proposed methodology, we present two important applications: (a) route optimization to determine the path with the maximum endtoend throughput capacity and, (b) optimal offered load control for a given path so that the maximum endtoend capacity can be achieved. Extensive simulations are carried out to verify and validate the proposed analytical methodology.
The case for noncooperative multihoming of users to access points
 in IEEE 802.11 WLANs,” in Proc. IEEE INFOCOM’06
, 2006
"... Abstract — In many cases, a mobile user has the option of connecting to one of several IEEE 802.11 access points (APs), each using an independent channel. User throughput in each AP is determined by the number of other users as well as the frame size and physical rate being used. We consider the sce ..."
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Cited by 38 (9 self)
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Abstract — In many cases, a mobile user has the option of connecting to one of several IEEE 802.11 access points (APs), each using an independent channel. User throughput in each AP is determined by the number of other users as well as the frame size and physical rate being used. We consider the scenario where users could multihome, i.e., split their traffic amongst all the available APs, based on the throughput they obtain and the price charged. Thus, they are involved in a noncooperative game with each other. We convert the problem into a fluid model and show that under a pricing scheme, which we call the cost price mechanism, the total system throughput is maximized, i.e., the system suffers no loss of efficiency due to selfish dynamics. We also study the case where the Internet Service Provider (ISP) could charge prices greater than that of the cost price mechanism. We show that even in this case multihoming outperforms unihoming, both in terms of throughput as well as profit to the ISP. I.
Starvation mitigation through multichannel coordination in csma multihop wireless networks
 in CSMA Multihop Wireless Networks,” in Proceedings of the International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc
, 2006
"... Existing multichannel protocols have been demonstrated to significantly increase aggregate throughput compared to singlechannel protocols. However, we show that despite such improvements in aggregate throughput, existing protocols can lead to flow starvation in a multihop network, a phenomenon th ..."
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Cited by 38 (0 self)
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Existing multichannel protocols have been demonstrated to significantly increase aggregate throughput compared to singlechannel protocols. However, we show that despite such improvements in aggregate throughput, existing protocols can lead to flow starvation in a multihop network, a phenomenon that also occurs with singlechannel protocols. In this paper, we devise Asynchronous Multichannel Coordination Protocol (AMCP), a distributed medium access protocol that not only increases aggregate throughput, but more importantly, addresses the fundamental coordination problems that lead to starvation. Based on AMCP’s counterstarvation mechanisms, we analytically derive and experimentally validate an approximate lower bound on the throughput of any flow in an arbitrary topology. We also demonstrate that AMCP can deliver significantly higher perflow throughput than both IEEE 802.11 and existing multichannel solutions. In addition to its performance properties, AMCP is both simple in that it operates using the primitives of IEEE 802.11 DCF, and costeffective in that it requires only a single halfduplex transceiver and no infrastructure support.
Measurement and modeling of the origins of starvation in congestioncontrolled mesh networks
 in IEEE INFOCOM
, 2008
"... Abstract—Significant progress has been made in understanding the behavior of TCP and congestioncontrolled traffic over multihop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which onehop flows co ..."
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Cited by 37 (6 self)
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Abstract—Significant progress has been made in understanding the behavior of TCP and congestioncontrolled traffic over multihop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which onehop flows contend with twohop flows for gateway access. In this paper, we demonstrate via real network measurements, testbed experiments, and an analytical model that starvation exists in such a scenario, i.e., the onehop flow receives most of the bandwidth while the twohop flow starves. Our analytical model yields a solution consisting of a simple contention window policy that can be implemented via mechanisms in IEEE 802.11e. Despite its simplicity, we demonstrate through analysis, experiments, and simulations, that the policy has a powerful effect on networkwide behavior, shifting the network’s queuing points, mitigating problematic MAC behavior, and ensuring that TCP flows obtain a fair share of the gateway bandwidth, irrespective of their spatial locations. I.
Performance analysis of contention based medium access control protocols
 Department of Electrical Engineering, Institute of Communications Engineering, National Chiao Tung University of Taiwan. Her
, 2009
"... AbstractThis paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that co ..."
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Cited by 37 (0 self)
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AbstractThis paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that corresponds to the time evolution of the backoff processes at the contending nodes. An extension of the technique is presented to handle the case where service differentiation is provided with the use of heterogeneous protocol parameters, as, for example, in IEEE 802.11e EDCA protocol. Our results provide new insights into the operation of such protocols. The techniques developed in the paper are applicable to a wide variety of contention based MAC protocols. Index TermsCarrier sense multipleaccess protocol with collision avoidance (CSMA/CA), diffusion approximation, fixed point analysis, fluid limit, IEEE 80211, IEEE 80211e, performance evaluation, performance of the medium access control (MAC) protocols, wireless localarea networks (WLANs).