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200
The impact of imperfect scheduling on crosslayer congestion control in wireless networks
, 2005
"... In this paper, we study crosslayer design for congestion control in multihop wireless networks. In previous work, we have developed an optimal crosslayer congestion control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the under ..."
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Cited by 321 (29 self)
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In this paper, we study crosslayer design for congestion control in multihop wireless networks. In previous work, we have developed an optimal crosslayer congestion control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the underlying layers. However, the scheduling component in this optimal crosslayer congestion control scheme has to solve a complex global optimization problem at each time, and is hence too computationally expensive for online implementation. In this paper, we study how the performance of crosslayer congestion control will be impacted if the network can only use an imperfect (and potentially distributed) scheduling component that is easier to implement. We study both the case when the number of users in the system is fixed and the case with dynamic arrivals and departures of the users, and we establish performance bounds of crosslayer congestion control with imperfect scheduling. Compared with a layered approach that does not design congestion control and scheduling together, our crosslayer approach has provably better performance bounds, and substantially outperforms the layered approach. The insights drawn from our analyses also enable us to design a fully distributed crosslayer congestion control and scheduling algorithm for a restrictive interference model.
A tutorial on crosslayer optimization in wireless networks
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS
, 2006
"... This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable my ..."
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Cited by 204 (22 self)
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This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable myopic policies are shown to optimize system performance. We then describe key lessons learned and the main obstacles in extending the work to general resource allocation problems for multihop wireless networks. Towards this end, we show that a cleanslate optimization based approach to the multihop resource allocation problem naturally results in a “loosely coupled” crosslayer solution. That is, the algorithms obtained map to different layers (transport, network, and MAC/PHY) of the protocol stack are coupled through a limited amount of information being passed back and forth. It turns out that the optimal scheduling component at the MAC layer is very complex and thus needs simpler (potentially imperfect) distributed solutions. We demonstrate how to use imperfect scheduling in the crosslayer framework and describe recently developed distributed algorithms along these lines. We conclude by describing a set of open research problems.
Maxweight scheduling in a generalized switch: State space collapse and workload minimization in heavy traffic
 The Annals of Applied Probability
, 2004
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Throughput guarantees through maximal scheduling in multihop wireless networks
, 2005
"... We address the question of providing throughput guarantees through distributed scheduling, which has remained an open problem for some time. We consider a simple distributed scheduling strategy, maximal scheduling, and prove that it attains a guaranteed fraction of the maximum throughput region in a ..."
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Cited by 101 (13 self)
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We address the question of providing throughput guarantees through distributed scheduling, which has remained an open problem for some time. We consider a simple distributed scheduling strategy, maximal scheduling, and prove that it attains a guaranteed fraction of the maximum throughput region in arbitrary wireless networks. The guaranteed fraction depends on “interference degree ” of the network which is the maximum number of sessions that interfere with any given session in the network and do not interfere with each other. Depending on the nature of communication, the transmission powers and the propagation models, the guaranteed fraction can be lower bounded by the maximum link degrees in the underlying topology, or even by constants that are independent of the topology. The guarantees also hold in networks with arbitrary number of frequencies. We prove that the guarantees are tight in that they can not be improved any further with maximal scheduling. I.
Distributed link scheduling with constant overhead
 In Proceedings of ACM Sigmetrics
, 2007
"... This paper proposes a new class of simple, distributed algorithms for scheduling in wireless networks. The algorithms generate new schedules in a distributed manner via simple local changes to existing schedules. The class is parameterized by integers k ≥ 1. We show that algorithm k of our class ach ..."
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Cited by 90 (2 self)
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This paper proposes a new class of simple, distributed algorithms for scheduling in wireless networks. The algorithms generate new schedules in a distributed manner via simple local changes to existing schedules. The class is parameterized by integers k ≥ 1. We show that algorithm k of our class achieves k/(k +2) of the capacity region, for every k ≥ 1. The algorithms have small and constant worstcase overheads: in particular, algorithm k generates a new schedule using (a) time less than 4k + 2 roundtrip times between neighboring nodes in the network, and (b) at most three control transmissions by any given node, for any k. The control signals are explicitly specified, and face the same interference effects as normal data transmissions. Our class of distributed wireless scheduling algorithms are the first ones guaranteed to achieve any fixed fraction of the capacity region while using small and constant overheads that do not scale with network size. The parameter k explicitly captures the tradeoff between control overhead and scheduler throughput performance and provides a tuning knob protocol designers can use to harness this tradeoff in practice. 1.
Scheduling in a Queueing System with Asynchronously Varying Service Rates
 Probability in the Engineering and Informational Sciences
"... We consider the following queueing system which arises as a model of a wireless link shared by multiple users. There is a nite number N of input
ows served by a server. The system operates in discrete time t = 0; 1; 2; : : :. Each input
ow can be described as an irreducible countable Markov chain; ..."
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Cited by 86 (9 self)
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We consider the following queueing system which arises as a model of a wireless link shared by multiple users. There is a nite number N of input
ows served by a server. The system operates in discrete time t = 0; 1; 2; : : :. Each input
ow can be described as an irreducible countable Markov chain; waiting customers of each
ow are placed in a queue. The sequence of server states m(t); t = 0; 1; 2; : : : , is a Markov chain with nite number of states M. When server is in state m it can serve m i customers of ow i (in one time slot). The scheduling discipline is a rule that in each time slot chooses the
ow to serve based on the server state and the state of the queues. Our main result is that a simple online scheduling discipline, Modied Largest Weighted Delay First, along with its generalizations, is throughput optimal, namely it ensures that the queues are stable as long as the vector of average arrival rates is within the system maximum stability region. 1
A.L.: Scheduling flexible servers with convex delay costs: Heavytraffic optimality of the generalized cμrule
 Oper. Res
, 2004
"... doi 10.1287/opre.1040.0152 ..."
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Distributed Throughput Maximization in Wireless Mesh Networks via PrePartitioning
, 2006
"... This paper considers the interaction between channel assignment and distributed scheduling in multichannel multiradio Wireless Mesh Networks (WMNs). Recently, a number of distributed scheduling algorithms for wireless networks have emerged. Due to their distributed operation, these algorithms can a ..."
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Cited by 74 (4 self)
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This paper considers the interaction between channel assignment and distributed scheduling in multichannel multiradio Wireless Mesh Networks (WMNs). Recently, a number of distributed scheduling algorithms for wireless networks have emerged. Due to their distributed operation, these algorithms can achieve only a fraction of the maximum possible throughput. As an alternative to increasing the throughput fraction by designing new algorithms, we present a novel approach that takes advantage of the inherent multiradio capability of WMNs. We show that this capability can enable partitioning of the network into subnetworks in which simple distributed scheduling algorithms can achieve 100 % throughput. The partitioning is based on the notion of Local Pooling. Using this notion, we characterize topologies in which 100 % throughput can be achieved distributedly. These topologies are used in order to develop a number of centralized channel assignment algorithms that are based on a matroid intersection algorithm. These algorithms prepartition a network in a manner that not only expands the capacity regions of the subnetworks but also allows distributed algorithms to achieve these capacity regions. We evaluate the performance of the algorithms via simulation and show that they significantly increase the distributedly achievable capacity region. We note that while the identified topologies are of general interference graphs, the partitioning algorithms are designed for networks with primary interference constraints.
Scaling Internet Routers Using Optics
 ACM SIGCOMM
, 2003
"... Routers built around a singlestage crossbar and a centralized scheduler do not scale, and (in practice) do not provide the throughput guarantees that network operators need to make e#cient use of their expensive longhaul links. In this paper we consider how optics can be used to scale capacity and ..."
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Cited by 73 (16 self)
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Routers built around a singlestage crossbar and a centralized scheduler do not scale, and (in practice) do not provide the throughput guarantees that network operators need to make e#cient use of their expensive longhaul links. In this paper we consider how optics can be used to scale capacity and reduce power in a router. We start with the promising loadbalanced switch architecture proposed by CS. Chang. This approach eliminates the scheduler, is scalable, and guarantees 100% throughput for a broad class of tra#c. But several problems need to be solved to make this architecture practical: (1) Packets can be missequenced, (2) Pathological periodic tra#c patterns can make throughput arbitrarily small, (3) The architecture requires a rapidly configuring switch fabric, and (4) It does not work when linecards are missing or have failed. In this paper we solve each problem in turn, and describe new architectures that include our solutions. We motivate our work by designing a 100Tb/s packetswitched router arranged as 640 linecards, each operating at 160Gb/s. We describe two di#erent implementations based on technology available within the next three years.
Constanttime distributed scheduling policies for ad hoc wireless networks
 in Proceedings of IEEE Conference on Decision and Control
, 2006
"... Abstract — We propose two new distributed scheduling policies for ad hoc wireless networks that can achieve provable capacity regions. Known scheduling policies that guarantee comparable capacity regions are either centralized or need computation time that increases with the size of the network. In ..."
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Cited by 71 (7 self)
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Abstract — We propose two new distributed scheduling policies for ad hoc wireless networks that can achieve provable capacity regions. Known scheduling policies that guarantee comparable capacity regions are either centralized or need computation time that increases with the size of the network. In contrast, the unique feature of the proposed distributed scheduling policies is that they are constanttime policies, i.e., the time needed for computing a schedule is independent of the network size. Hence, they can be easily deployed in large networks. I.