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37
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 248 (30 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.
Delay analysis for multihop wireless networks
 IEEE INFOCOM
, 2009
"... Abstract—We analyze the delay performance of a multihop wireless network with a fixed route between each sourcedestination pair. There are arbitrary interference constraints on the set of links that can be served simultaneously at any given time. These interference constraints impose a fundamental l ..."
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Cited by 21 (2 self)
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Abstract—We analyze the delay performance of a multihop wireless network with a fixed route between each sourcedestination pair. There are arbitrary interference constraints on the set of links that can be served simultaneously at any given time. These interference constraints impose a fundamental lower bound on the delay performance of any scheduling policy for the system. We present a methodology to derive such lower bounds. For the tandem queue network, where the delay optimal policy is known, the expected delay of the optimal policy numerically coincides with the lower bound. We conduct extensive numerical studies to suggest that the average delay of the backpressure scheduling policy can be made close to the lower bound by using appropriate functions of queue length. I.
Joint Scheduling and Resource Allocation in CDMA Systems
 Proc. of 2nd Workshop on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt ’04
, 2004
"... Abstract. We consider scheduling and resource allocation for the downlink in a CDMA based wireless network. The scheduling and resource allocation problem is to select a subset of the users for transmission and for each of the users selected, to choose the modulation and coding scheme, transmission ..."
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Cited by 20 (4 self)
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Abstract. We consider scheduling and resource allocation for the downlink in a CDMA based wireless network. The scheduling and resource allocation problem is to select a subset of the users for transmission and for each of the users selected, to choose the modulation and coding scheme, transmission power, and number of codes used. We refer to this combination as the physical layer operating point (PLOP). Each PLOP consumes different amounts of code and power resources. The resource allocation task to pick the “optimal ” PLOP taking into account both systemwide and individual user resource constraints that can arise in a practical system. In this paper, we tackle this problem as part of a utility maximization problem framed in earlier papers that includes both scheduling and resource allocation. Using an information theoretic model for the achievable rate per code results in a tractable convex optimization problem. By exploiting the structure of this problem, we give algorithms for finding the optimal solution with geometric convergence. We also use insights obtained from the optimal solution to construct low complexity near optimal algorithms that are easily implementable. Numerical results comparing these algorithms are also given. 1
Scheduling in multichannel wireless networks: Rate function optimality in the smallbuffer regime
, 2009
"... We consider the problem of designing scheduling algorithms for the downlink of cellular wireless networks where bandwidth is partitioned into tens to hundreds of parallel channels, each of which can be allocated to a possibly different user in each time slot. We prove that a class of algorithms call ..."
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Cited by 16 (6 self)
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We consider the problem of designing scheduling algorithms for the downlink of cellular wireless networks where bandwidth is partitioned into tens to hundreds of parallel channels, each of which can be allocated to a possibly different user in each time slot. We prove that a class of algorithms called Iterated Longest Queues First (iLQF) algorithms achieves the smallest buffer overflow probability in an appropriate large deviations sense. The class of iLQF algorithms is quite different from the class of maxweight policies which have been studied extensively in the literature, and it achieves much better performance in the regimes studied in this paper.
Queuing Analysis in Multichannel Cognitive Spectrum Access: A Large Deviation Approach
"... Abstract—The queueing performance of a (secondary) cognitive user is investigated for a hierarchical network where there are N independent and identical primary users. Each primary user employs a slotted transmission protocol, and its channel usage forms a twostate (busy,idle) discretetime Markov ..."
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Cited by 13 (2 self)
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Abstract—The queueing performance of a (secondary) cognitive user is investigated for a hierarchical network where there are N independent and identical primary users. Each primary user employs a slotted transmission protocol, and its channel usage forms a twostate (busy,idle) discretetime Markov chain. The cognitive user employs the optimal policy to select which channel to sense (and use if found idle) at each slot. In the framework of effective bandwidths, the stationary queue tail distribution of the cognitive user is estimated using a large deviation approach for which closedform expressions are obtained when N =2. Upper and lower bounds are obtained for the general N primary user network. For positively correlated primary transmissions, the bounds are shown to be asymptotically tight. Monte Carlo simulations using importance sampling techniques are used to validate the obtained large deviation estimates. Index terms—Effective bandwidth, Queueing analysis, Cognitive radio and Dynamic spectrum access.
On Scheduling for Minimizing EndtoEnd Buffer Usage over Multihop Wireless Networks
"... Abstract—While there has been much progress in designing backpressure based stabilizing algorithms for multihop wireless networks, endtoend performance (e.g., endtoend buffer usage) results have not been as forthcoming. In this paper, we study the endtoend buffer usage (sum of buffer utilizati ..."
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Cited by 11 (0 self)
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Abstract—While there has been much progress in designing backpressure based stabilizing algorithms for multihop wireless networks, endtoend performance (e.g., endtoend buffer usage) results have not been as forthcoming. In this paper, we study the endtoend buffer usage (sum of buffer utilization along a flow path) over a network with general topology and with fixed, loopfree routes using a largedeviations approach. We first derive bounds on the best performance that any scheduling algorithm can achieve. Based on the intuition from the bounds, we propose a class of (backpressurelike) scheduling algorithms called αβalgorithms. We show that the parameters α and β can be chosen such that the system under the αβalgorithm performs arbitrarily closely to the best possible scheduler (formally the decay rate function for endtoend buffer overflow is shown to be arbitrarily close to optimal in the largebuffer regime). We also develop variants which have the same asymptotic optimality property, and also provide good performance in the smallbuffer regime. Our results are substantiated using both analysis and simulation. I.
Scheduling for small delay in multirate multichannel wireless networks
 in INFOCOM
"... Abstract—This paper considers the problem of designing scheduling algorithms for multichannel (e.g., OFDMbased) wireless downlink systems. We show that the ServerSide Greedy (SSG) rule introduced in earlier papers for ONOFF channels performs well even for more general channel models. The key con ..."
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Abstract—This paper considers the problem of designing scheduling algorithms for multichannel (e.g., OFDMbased) wireless downlink systems. We show that the ServerSide Greedy (SSG) rule introduced in earlier papers for ONOFF channels performs well even for more general channel models. The key contribution in this paper is the development of new mathematical techniques for analyzing Markov chains that arise when studying general channel models. These techniques include a way of calculating the distribution of the maximum of a multidimensional Markov chain (note that the maximum does not have the Markov property on its own), and also a Markov chain stochastic dominance result using coupling arguments. Index Terms—Scheduling algorithms, large deviations, small buffer, Markov chain stochastic dominance I.
Lowcomplexity Scheduling Algorithms for Multichannel Downlink Wireless Networks
"... Abstract—This paper considers the problem of designing scheduling algorithms for multichannel (e.g., OFDM) wireless downlink networks with n users/OFDM subchannels. For this system, while the classical MaxWeight algorithm is known to be throughputoptimal, its bufferoverflow performance is very p ..."
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Cited by 9 (1 self)
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Abstract—This paper considers the problem of designing scheduling algorithms for multichannel (e.g., OFDM) wireless downlink networks with n users/OFDM subchannels. For this system, while the classical MaxWeight algorithm is known to be throughputoptimal, its bufferoverflow performance is very poor (formally, we show it has zero rate function in our setting). To address this, we propose a class of algorithms called iHLQF (iterated Heaviest matching with Longest Queues First) that is shown to be throughput optimal for a general class of arrival/channel processes, and also ratefunction optimal (i.e., exponentially small buffer overflow probability) for certain arrival/channel processes. iHLQF however has higher complexity than MaxWeight (n 4 vs. n 2 respectively). To overcome this issue, we propose a new algorithm called SSG (ServerSide Greedy). We show that SSG is throughput optimal, results in a much better peruser buffer overflow performance than the MaxWeight algorithm (positive rate function for certain arrival/channel processes), and has a computational complexity (n 2) that is comparable to the MaxWeight algorithm. Thus, it provides a nice tradeoff between bufferoverflow performance and computational complexity. These results are validated by both analysis and simulations. Index Terms—Scheduling algorithms, large deviations, small buffer, low complexity I.
Large deviations of queues under QoS scheduling algorithms,” Allerton 2006
, 2006
"... Abstract — We consider a model where multiple queues are served by a server whose capacity varies randomly and asynchronously with respect to different queues. The problem is to optimally control large deviations of the queues in the following sense: find a scheduling rule maximizing ..."
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Cited by 7 (0 self)
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Abstract — We consider a model where multiple queues are served by a server whose capacity varies randomly and asynchronously with respect to different queues. The problem is to optimally control large deviations of the queues in the following sense: find a scheduling rule maximizing
Delay and Effective Throughput of Wireless Scheduling in Heavy Traffic Regimes: Vacation Model for Complexity
"... Distributed scheduling algorithms for wireless ad hoc networks have received substantial attention over the last decade. The complexity levels of these algorithms span a wide spectrum, ranging from no message passing to constant/polynomial time complexity, or even exponential complexity. However, by ..."
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Cited by 7 (4 self)
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Distributed scheduling algorithms for wireless ad hoc networks have received substantial attention over the last decade. The complexity levels of these algorithms span a wide spectrum, ranging from no message passing to constant/polynomial time complexity, or even exponential complexity. However, by and large it remains open to quantify the impact of message passing complexity on throughput and delay. In this paper, we study the effective throughput and delay performance in wireless scheduling by explicitly considering complexity through a vacation model, where signaling complexity is treated as “vacations ” and data transmissions as “services,” with a focus on delay analysis in heavy traffic regimes. We analyze delay performance in two regimes of vacation models, depending on the relative lengths of data transmission and vacation periods. State space collapse properties proved here enable a significant dimensionality reduction in the challenging problem of delay characterization. We then explore engineering implications and quantify intuitions based on the heavy traffic analysis.