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Network Adiabatic Theorem: An Efficient Randomized Protocol for Contention Resolution
"... The popularity of Aloha(like) algorithms for resolution of contention between multiple entities accessing common resources is due to their extreme simplicity and distributed nature. Example applications of such algorithms include Ethernet and recently emerging wireless multiaccess networks. Despit ..."
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Cited by 88 (10 self)
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The popularity of Aloha(like) algorithms for resolution of contention between multiple entities accessing common resources is due to their extreme simplicity and distributed nature. Example applications of such algorithms include Ethernet and recently emerging wireless multiaccess networks. Despite a long and exciting history of more than four decades, the question of designing an algorithm that is essentially as simple and distributed as Aloha while being efficient has remained unresolved. In this paper, we resolve this question successfully for a network of queues where contention is modeled through independentset constraints over the network graph. The work by Tassiulas and Ephremides (1992) suggests that an algorithm that schedules queues so that the summation of “weight ” of scheduled queues is maximized, subject to constraints, is efficient. However, implementing such an algorithm using Alohalike mechanism has remained a mystery. We design such an algorithm building upon a MetropolisHastings sampling mechanism along with selection of“weight” as an appropriate function of the queuesize. The key ingredient in establishing the efficiency of the algorithm is a novel adiabaticlike theorem for the underlying queueing network, which may be of general interest in the context of dynamical systems.
On Combining ShortestPath and BackPressure Routing Over Multihop Wireless Networks
, 2008
"... Abstract—Backpressure based algorithms based on the algorithm by Tassiulas and Ephremides have recently received much attention for jointly routing and scheduling over multihop wireless networks. However a significant weakness of this approach has been in routing, because the traditional backpress ..."
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Cited by 65 (5 self)
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Abstract—Backpressure based algorithms based on the algorithm by Tassiulas and Ephremides have recently received much attention for jointly routing and scheduling over multihop wireless networks. However a significant weakness of this approach has been in routing, because the traditional backpressure algorithm explores and exploits all feasible paths between each source and destination. While this extensive exploration is essential in order to maintain stability when the network is heavily loaded, under light or moderate loads, packets may be sent over unnecessarily long routes and the algorithm could be very inefficient in terms of endtoend delay and routing convergence times. This paper proposes new routing/scheduling backpressure algorithms that not only guarantees network stability (throughput optimality), but also adaptively selects a set of optimal routes based on shortestpath information in order to minimize average pathlengths between each source and destination pair. Our results indicate that under the traditional backpressure algorithm, the endtoend packet delay first decreases and then increases as a function of the network load (arrival rate). This surprising lowload behavior is explained due to the fact that the traditional backpressure algorithm exploits all paths (including very long ones) even when the traffic load is light. On the otherhand, the proposed algorithm adaptively selects a set of routes according to the traffic load so that long paths are used only when necessary, thus resulting in much smaller endtoend packet delays as compared to the traditional backpressure algorithm. I.
QCSMA: Queuelength based CSMA/CA algorithms for achieving maximum throughput and low delay in wireless networks
 IN IEEE INFOCOM
, 2010
"... Recently, it has been shown that CSMAtype random access algorithms can achieve the maximum possible throughput in wireless ad hoc networks. However, the delay performance of these algorithms can be quite bad. On the other hand, although some simple heuristics (such as distributed approximations of ..."
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Cited by 64 (6 self)
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Recently, it has been shown that CSMAtype random access algorithms can achieve the maximum possible throughput in wireless ad hoc networks. However, the delay performance of these algorithms can be quite bad. On the other hand, although some simple heuristics (such as distributed approximations of greedy maximal scheduling) can yield much better delay performance for a large set of arrival rates, they may only achieve a fraction of the capacity region in general. In this paper, we propose a discretetime version of the CSMAtype random access algorithm that allows us to incorporate simple heuristics which lead to very good delay performance while retaining the throughputoptimality property. Central to our results is a discretetime distributed randomized algorithm that generates data transmission schedules according to a productform distribution, a counterpart of similar results obtained earlier for continuoustime models under the perfect CSMA assumption where collisions can never occur. An appealing feature of this algorithm is that it explicitly takes collisions into account during the exchange of control packets.
Routing Without Routes: The Backpressure Collection Protocol
"... Current data collection protocols for wireless sensor networks are mostly based on quasistatic minimumcost routing trees. We consider an alternative, highlyagile approach called backpressure routing, in which routing and forwarding decisions are made on a perpacket basis. Although there is a con ..."
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Cited by 58 (6 self)
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Current data collection protocols for wireless sensor networks are mostly based on quasistatic minimumcost routing trees. We consider an alternative, highlyagile approach called backpressure routing, in which routing and forwarding decisions are made on a perpacket basis. Although there is a considerable theoretical literature on backpressure routing, it has not been implemented on practical systems to date due to concerns about packet looping, the effect of link losses, large packet delays, and scalability. Addressing these concerns, we present the Backpressure Collection Protocol (BCP) for sensor networks, the first ever implementation of dynamic backpressure routing in wireless networks. In particular, we demonstrate for the first time that replacing the traditional FIFO queue service in backpressure routing with LIFO queues reduces the average endtoend packet delays for delivered packets drastically (75 % under high load, 98 % under low load). Further, we improve backpressure scalability by introducing a new concept of floating queues into the backpressure framework. Under static network settings, BCP shows a more than 60 % improvement in maxmin rate over the state of the art Collection Tree Protocol (CTP). We also empirically demonstrate the superior delivery performance of BCP in highly dynamic network settings, including conditions of extreme external interference and highly mobile sinks. 1.
BackoftheEnvelope Computation of Throughput
 Distributions in CSMA Wireless Networks,” Technical Report available at http://arxiv.org/pdf/0712.1854.pdf
, 2007
"... Abstract — This paper presents a simple method for computing throughputs of links in a CSMA network. We call our method backoftheenvelop (BoE) computation, because for many network configurations, very accurate results can be obtained by simple hand computation. BoE beats prior methods in terms o ..."
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Cited by 45 (8 self)
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Abstract — This paper presents a simple method for computing throughputs of links in a CSMA network. We call our method backoftheenvelop (BoE) computation, because for many network configurations, very accurate results can be obtained by simple hand computation. BoE beats prior methods in terms of both speed and accuracy. To explain BoE, we construct a theory based on the model of an “ideal CSMA network ” (ICN). We find that link throughputs are insensitive to the distributions of the backoff countdown time and transmission time in ICN given the ratio of their mean c. The BoE computation method emerges from ICN in the limit 0→c. The insensitivity result explains why BoE works so well for IEEE 802.11 networks, in which the backoff countdown process is one that has memory and the transmission time can be arbitrarily distributed. Furthermore, c does not have to be very small for BoE to be highly accurate. BoE allows us to make shortcuts in performance evaluation, bypassing complicated stochastic analysis. An immediate application of BoE is for quick identification of starved links in the network so that remedies can be devised to solve the problem. Index Terms—CSMA, 802.11, WiFi, multiple access. I.
Distributed random access algorithm: Scheduling and congestion control
 IEEE TRANS. INFORM. THEORY
, 2009
"... This paper provides proofs of the rate stability, Harris recurrence, and εoptimality of CSMA algorithms where the backoff parameter of each node is based on its backlog. These algorithms require only local information and are easy to implement. The setup is a network of wireless nodes with a fixed ..."
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Cited by 43 (13 self)
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This paper provides proofs of the rate stability, Harris recurrence, and εoptimality of CSMA algorithms where the backoff parameter of each node is based on its backlog. These algorithms require only local information and are easy to implement. The setup is a network of wireless nodes with a fixed conflict graph that identifies pairs of nodes whose simultaneous transmissions conflict. The paper studies two algorithms. The first algorithm schedules transmissions to keep up with given arrival rates of packets. The second algorithm controls the arrivals in addition to the scheduling and attempts to maximize the sum of the utilities of the flows of packets at the different nodes. For the first algorithm, the paper proves rate stability for strictly feasible arrival rates and also Harris recurrence of the queues. For the second algorithm, the paper proves the ǫoptimality. Both algorithms operate with strictly local information in the case of decreasing step sizes, and operate with the additional information of the number of nodes in the network in the case of constant step size.
On the design of efficient CSMA algorithms for wireless networks
 In Proceedings of CDC 2010
, 2010
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DiffQ: Practical Differential Backlog Congestion Control for Wireless Networks
 In Proc. of INFOCOM, Rio de Janeiro
, 2009
"... Abstract—Congestion control in wireless multihop networks is challenging and complicated because of two reasons. First, interference is ubiquitous and causes loss in the shared medium. Second, wireless multihop networks are characterized by the use of diverse and dynamically changing routing paths. ..."
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Cited by 35 (0 self)
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Abstract—Congestion control in wireless multihop networks is challenging and complicated because of two reasons. First, interference is ubiquitous and causes loss in the shared medium. Second, wireless multihop networks are characterized by the use of diverse and dynamically changing routing paths. Traditional end point based congestion control protocols are ineffective in such a setting resulting in unfairness and starvation. This paper adapts the optimal theoretical work of Tassiulas and Ephremedes [33] on crosslayer optimization of wireless networks involving congestion control, routing and scheduling, for practical solutions to congestion control in multihop wireless networks. This work is the first that implements in real offshelf radios, a differential backlog based MAC scheduling and routerassisted backpressure congestion control for multihop wireless networks. Our adaptation, called DiffQ, is implemented between transport and IP and supports legacy TCP and UDP applications. In a network of 46 IEEE 802.11 wireless nodes, we demonstrate that DiffQ far outperforms many previously proposed “practical” solutions for congestion control. I.
Distributed CSMA/CA algorithms for achieving maximum throughput in wireless networks
 in Proc. Inf. Theory Appl. Workshop
, 2009
"... Recently, it has been shown that CSMAtype random access algorithms can achieve the maximum throughput in wireless ad hoc networks. Central to these results is a distributed randomized algorithm which selects schedules according a productform distribution. The productform distribution is achieved ..."
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Cited by 35 (1 self)
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Recently, it has been shown that CSMAtype random access algorithms can achieve the maximum throughput in wireless ad hoc networks. Central to these results is a distributed randomized algorithm which selects schedules according a productform distribution. The productform distribution is achieved by considering a continuoustime Markov model of an idealized CSMA protocol under which collisions cannot occur. In this paper, we present an algorithm which achieves the same productform distribution in a discretetime setting where collision of data packets is avoided through the exchange of control messages (however, the control messages are allowed to collide as in the 802.11 suite of protocols). In our discretetime model, each time slot consists of a few control minislots followed by a data slot. We show that two control minislots are sufficient for our distributed scheduling algorithm to realize the same steadystate distribution as in the continuoustime case. Thus, the overhead can be as low as twice the ratio of a control minislot to a data slot. 1
Markov Approximation for Combinatorial Network Optimization
"... Many important network design problems can be formulated as a combinatorial optimization problem. A large number of such problems, however, cannot readily be tackled by distributed algorithms. The Markov approximation framework studied in this paper is a general technique for synthesizing distribut ..."
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Cited by 31 (14 self)
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Many important network design problems can be formulated as a combinatorial optimization problem. A large number of such problems, however, cannot readily be tackled by distributed algorithms. The Markov approximation framework studied in this paper is a general technique for synthesizing distributed algorithms. We show that when using the logsumexp function to approximate the optimal value of any combinatorial problem, we end up with a solution that can be interpreted as the stationary probability distribution of a class of timereversible Markov chains. Certain carefully designed Markov chains among this class yield distributed algorithms that solve the logsumexp approximated combinatorial network optimization problem. By three case studies, we illustrate that Markov approximation technique not only can provide fresh perspective to existing distributed solutions, but also can help us generate new distributed algorithms in various domains with provable performance. We believe the Markov approximation techniques will find application in many network optimization problems, and this paper serves as a call for participation of it.