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185
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 142 (14 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.
A framework for opportunistic scheduling in wireless networks
 COMPUTER NETWORKS
, 2003
"... We present a method, called opportunistic scheduling, for exploiting the timevarying nature of the radio environment to increase the overall performance of the system under certain quality of service/fairness requirements of users. We first introduce a general framework for opportunistic scheduling ..."
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Cited by 138 (6 self)
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We present a method, called opportunistic scheduling, for exploiting the timevarying nature of the radio environment to increase the overall performance of the system under certain quality of service/fairness requirements of users. We first introduce a general framework for opportunistic scheduling, and then identify three general categories of scheduling problems under this framework. We provide optimal solutions for each of these scheduling problems. All the proposed scheduling policies are implementable online; we provide parameter estimation algorithms and implementation procedures for them. We also show how previous work by us and others directly fits into or is related to this framework. We demonstrate via simulation that opportunistic scheduling schemes result in significant performance improvement compared with nonopportunistic alternatives.
Fair resource allocation in wireless networks using queuelengthbased scheduling and congestion control
 In Proceedings of IEEE Infocom
, 2005
"... We consider the problem of allocating resources (time slots, frequency, power, etc.) at a base station to many competing flows, where each flow is intended for a different receiver. The channel conditions may be timevarying and different for different receivers. It is wellknown that appropriately ..."
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Cited by 134 (22 self)
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We consider the problem of allocating resources (time slots, frequency, power, etc.) at a base station to many competing flows, where each flow is intended for a different receiver. The channel conditions may be timevarying and different for different receivers. It is wellknown that appropriately chosen queuelength based policies are throughputoptimal while other policies based on the estimation of channel statistics can be used to allocate resources fairly (such as proportional fairness) among competing users. In this paper, we show that a combination of queuelengthbased scheduling at the base station and congestion control implemented either at the base station or at the end users can lead to fair resource allocation and queuelength stability.
Stable scheduling policies for fading wireless channels
 IEEE/ACM TRANSACTIONS ON NETWORKING
, 2005
"... We study the problem of stable scheduling for a class of wireless networks. The goal is to stabilize the queues holding information to be transmitted over a fading channel. Few assumptions are made on the arrival process statistics other than the assumption that their mean values lie within the cap ..."
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Cited by 77 (17 self)
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We study the problem of stable scheduling for a class of wireless networks. The goal is to stabilize the queues holding information to be transmitted over a fading channel. Few assumptions are made on the arrival process statistics other than the assumption that their mean values lie within the capacity region and that they satisfy a version of the law of large numbers. We prove that, for any mean arrival rate that lies in the capacity region, the queues will be stable under our policy. Moreover, we show that it is easy to incorporate imperfect queue length information and other approximations that can simplify the implementation of our policy.
Exploiting multiuser diversity for medium access control in wireless networks
 Proc. of IEEE INFOCOM
, 2003
"... Abstract Multiuser diversity refers to a type of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Using such an approach leads to a system capacity that ..."
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Cited by 69 (4 self)
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Abstract Multiuser diversity refers to a type of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Using such an approach leads to a system capacity that increases with the number of users. However, such scheduling requires centralized control. In this paper, we consider a decentralized medium access control (MAC) protocol, where each user only has knowledge of its own channel gain. We consider a variation of the ALOHA protocol, channelaware ALOHA; using this protocol we show that users can still exploit multiuser diversity gains. First we consider a backlogged model, where each user always has packets to send. In this case we show that the total system throughput increases at the same rate as in a system with a centralized scheduler. Asymptotically, the fraction of throughput lost due to the random access protocol is shown to be 1=e. We also consider a splitting algorithm, where the splitting sequence depends on the users ' channel gains; this algorithm is shown to approach the throughput of an optimal centralized scheme. Next we consider a system with an infinite user population and random arrivals. In this case, it is proved that a variation of channelaware ALOHA is stable for any total arrival rate in a memoryless channel, given that users can estimate the backlog. Extensions for channels with memory are also discussed. I.
On the Asymptotic Optimality of the Gradient Scheduling Algorithm for MultiUser Throughput Allocation
 Operations Research
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Opportunistic Splitting Algorithms For Wireless Networks
, 2004
"... In this paper, we develop medium access control protocols to enable users in a wireless network to opportunistically transmit when they have favorable channel conditions, without requiring a centralized scheduler. We consider approaches that use splitting algorithms to resolve collisions over a sequ ..."
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Cited by 49 (2 self)
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In this paper, we develop medium access control protocols to enable users in a wireless network to opportunistically transmit when they have favorable channel conditions, without requiring a centralized scheduler. We consider approaches that use splitting algorithms to resolve collisions over a sequence of minislots, and determine the user with the best channel. First, we present a basic algorithm for a system with i.i.d. block fading and a fixed number of backlogged users. We give an analysis of the throughput of this system and show that the average number of minislots required to find the user with the best channel is less than 2.5 independent of the number of users or the fading distribution. We then extend this algorithm to a channel with memory and also develop a reservation based scheme that offers improved performance as the channel memory increases. Finally we consider a model with random arrivals and propose a modified algorithm for this case. Simulation results are given to illustrate the performance in each of these settings.
Optimal utility based multiuser throughput allocation subject to throughput constraints
 in Proc. IEEE INFOCOM ’05
, 2005
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Utilizing Multiuser Diversity for Efficient Support of Quality of Service over a Fading Channel
 IEEE Trans. Veh. Technol
, 2005
"... We consider the problem of quality of service (QoS) provisioning for K users sharing a downlink timeslotted fading channel. We develop simple and efficient schemes for admission control, resource allocation, and scheduling, which can yield substantial capacity gain. The efficiency is achieved by vir ..."
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Cited by 34 (6 self)
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We consider the problem of quality of service (QoS) provisioning for K users sharing a downlink timeslotted fading channel. We develop simple and efficient schemes for admission control, resource allocation, and scheduling, which can yield substantial capacity gain. The efficiency is achieved by virtue of recently identified multiuser diversity. A unique feature of our work is explicit provisioning of statistical QoS, which is characterized by a data rate, delay bound, and delaybound violation probability triplet. The results show that compared with a fixedslot assignment scheme, our approach can substantially increase the statistical delayconstrained capacity of a fading channel (i.e., the maximum data rate achievable with the delaybound violation probability satisfied), when delay requirements are not very tight, while yet guaranteeing QoS at any delay requirement. For example, in the case of low signaltonoiseratio (SNR) and ergodic Rayleigh gain for K users with loosedelay requirements, as expected from the classic paper [10] on multiuser diversity. But more importantly, when the delay bound is not loose, so that simpleminded multiuserdiversity scheduling does not directly apply, our scheme can achieve a capacity gain, and yet meet the QoS requirements.
A large deviations analysis of scheduling in wireless networks
 Earlier versions of the paper appeared in the IEEE CDC 2004, IEEE CDC 2005 and IEEE ISIT
, 2006
"... We consider a cellular network consisting of a base station and N receivers. The channel states of the receivers are assumed to be identical and independent of each other. The goal is to compare the throughput of two different scheduling policies (a queuelengthbased policy and a greedy scheduling ..."
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Cited by 33 (5 self)
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We consider a cellular network consisting of a base station and N receivers. The channel states of the receivers are assumed to be identical and independent of each other. The goal is to compare the throughput of two different scheduling policies (a queuelengthbased policy and a greedy scheduling policy) given an upper bound on the queue overflow probability or the delay violation probability. We first consider a simple channel model, where each channel is assumed to be in one of two states (ON or OFF). Given an upper bound on the delay violation probability or an upper bound on the queue overflow probability, we show that the total network throughput of the queuelengthbased policy is strictly larger than the throughput of the greedy policy for all N. Further, the throughput of the queuelengthbased policy is a strictly increasing function of N while the throughput of the greedy policy does not have this property. Finally, for general channel state models, we show that the relative performances of the the greedy and QLB policies have a similar behavior. policy.