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32
Optimality of Myopic Sensing in Multichannel Opportunistic Access
, 2008
"... We consider opportunistic communication over multiple channels where the state (“good ” or “bad”) of each channel evolves as independent and identically distributed Markov processes. A user, with limited channel sensing and access capability, chooses one channel to sense and subsequently access (bas ..."
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Cited by 112 (38 self)
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We consider opportunistic communication over multiple channels where the state (“good ” or “bad”) of each channel evolves as independent and identically distributed Markov processes. A user, with limited channel sensing and access capability, chooses one channel to sense and subsequently access (based on the sensed channel state) in each time slot. A reward is obtained whenever the user senses and accesses a “good ” channel. The objective is to design an optimal channel selection policy that maximizes the expected total (discounted or average) reward accrued over a finite or infinite horizon. This problem can be cast as a Partially Observable Markov Decision Process (POMDP) or a restless multiarmed bandit process, to which optimal solutions are often intractable. We show in this paper that a myopic policy that maximizes the immediate onestep reward is always optimal when the state transitions are positively correlated over time. When the state transitions are negatively correlated, we show that the same policy is optimal when the number of channels is limited to 2 or 3, while presenting a counterexample for the case of 4 channels. This result finds applications in opportunistic transmission scheduling in a fading environment, cognitive radio networks for spectrum overlay, and resourceconstrained jamming and antijamming.
Order optimal delay for opportunistic scheduling in multiuser wireless uplinks and downlinks
 Proc. of Allerton Conf. on Communication, Control, and Computing (invited paper
, 2006
"... Abstract — We consider a onehop wireless network with independent time varying channels and N users, such as a multiuser uplink or downlink. We first show that general classes of scheduling algorithms that do not consider queue backlog necessarily incur average delay that grows at least linearly wi ..."
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Cited by 45 (6 self)
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Abstract — We consider a onehop wireless network with independent time varying channels and N users, such as a multiuser uplink or downlink. We first show that general classes of scheduling algorithms that do not consider queue backlog necessarily incur average delay that grows at least linearly with N. We then construct a dynamic queuelength aware algorithm that stabilizes the system and achieves an average delay that is independent of N. This is the first analytical demonstration that O(1) delay is achievable in such a multiuser wireless setting. The delay bounds are achieved via a technique of queue grouping together with basic Lyapunov stability and statistical multiplexing concepts.
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 37 (7 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.
Delay analysis for max weight opportunistic scheduling in wireless systems. arXiv:0806.2345v1
, 2008
"... Abstract—We consider the delay properties of maxweight opportunistic scheduling in a multiuser ON/OFF wireless system, such as a multiuser downlink or uplink. It is well known that maxweight scheduling stabilizes the network (and hence yields maximum throughput) whenever input rates are inside t ..."
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Cited by 23 (3 self)
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Abstract—We consider the delay properties of maxweight opportunistic scheduling in a multiuser ON/OFF wireless system, such as a multiuser downlink or uplink. It is well known that maxweight scheduling stabilizes the network (and hence yields maximum throughput) whenever input rates are inside the network capacity region. We show that when arrival and channel processes are independent, average delay of the maxweight policy is orderoptimal, in the sense that it does not grow with the number of network links. While recent queuegrouping algorithms are known to also yield orderoptimal delay, this is the first such result for the simpler class of maxweight policies. I.
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 18 (7 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.
Delay considerations for opportunistic scheduling in broadcast fading channels
 IEEE Trans. Wireless Commun
, 2007
"... We consider a singleantenna broadcast block fading channel with users where the transmission is packetbased. We define the (packet) delay as the minimum number of channel uses that guarantees all users successfully receive packets. This is a more stringent notion of delay than average delay and is ..."
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Cited by 13 (1 self)
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We consider a singleantenna broadcast block fading channel with users where the transmission is packetbased. We define the (packet) delay as the minimum number of channel uses that guarantees all users successfully receive packets. This is a more stringent notion of delay than average delay and is the worst case (access) delay among the users. A delay optimal scheduling scheme, such as roundrobin, achieves the delay of. For the opportunistic scheduling (which is throughput optimal) where the transmitter sends the packet to the user with the best channel conditions at each channel use, we derive the mean and variance of the delay for any and. For large and in a homogeneous network, it is proved that the expected delay in receiving one packet by all the receivers scales as, as opposed to for the roundrobin scheduling. We also show that when grows faster than, for some, then the delay scales as. This roughly determines the timescale required for the system to behave fairly in a homogeneous network. We then propose a scheme to significantly reduce the delay at the expense of a small throughput hit. We further look into the advantage of multiple transmit antennas on the delay. For a system with antennas in the transmitter where at each channel use packets are sent to different users, we obtain the expected delay in receiving one packet by all the users. Index terms: broadcast channel, fading, opportunistic scheduling, packet delay, longest queue. 1
Stochastic Optimization for Markov Modulated Networks with Application to Delay Constrained Wireless Scheduling
, 2009
"... We consider a wireless system with a small number of delay constrained users and a larger number of users without delay constraints. We develop a scheduling algorithm that reacts to time varying channels and maximizes throughput utility (to within a desired proximity), stabilizes all queues, and sa ..."
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Cited by 13 (8 self)
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We consider a wireless system with a small number of delay constrained users and a larger number of users without delay constraints. We develop a scheduling algorithm that reacts to time varying channels and maximizes throughput utility (to within a desired proximity), stabilizes all queues, and satisfies the delay constraints. The problem is solved by reducing the constrained optimization to a set of weighted stochastic shortest path problems, which act as natural generalizations of maxweight policies to Markov modulated networks. We also present approximation results that do not require apriori statistical knowledge, and discuss the additional complexity and delay incurred as compared to systems without delay constraints. The solution technique is general and applies to other constrained stochastic network optimization problems.
On powerofchoice in downlink transmission scheduling
 Inform. Theory and Applicat. Workshop
, 2008
"... Abstract — A lowcomplexity guiding principle is considered for transmission scheduling from n homogeneous queues whose channel states fluctuate independently. The scheduler transmits from a longest queue within d randomly chosen queues with eligible channel states. A Markovian model is studied wher ..."
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Cited by 5 (0 self)
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Abstract — A lowcomplexity guiding principle is considered for transmission scheduling from n homogeneous queues whose channel states fluctuate independently. The scheduler transmits from a longest queue within d randomly chosen queues with eligible channel states. A Markovian model is studied where mean packet transmission time is n −1 and packet arrival rate is λ < 1 per queue. Equilibrium distribution of queue occupancy is obtained in the limit as n → ∞ and it is shown to have tails that decay as Θ((λ/d) k). If transmissions are scheduled from a longest eligible queue in the entire system then almost all queues are empty in equilibrium; the number of queues with one packet is Θ(1) and the number of queues with more than one packet is o(1) as n → ∞. Equilibrium distribution of the total number of packets in the system is also characterized in this latter case. I.
When HeavyTailed and LightTailed Flows Compete: The Response Time Tail Under Generalized MaxWeight Scheduling
"... This paper focuses on the design and analysis of scheduling policies for multiclass queues, such as those found in wireless networks and highspeed switches. In this context, we study the response time tail under generalized maxweight policies in settings where the traffic flows are highly asymmet ..."
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Cited by 4 (1 self)
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This paper focuses on the design and analysis of scheduling policies for multiclass queues, such as those found in wireless networks and highspeed switches. In this context, we study the response time tail under generalized maxweight policies in settings where the traffic flows are highly asymmetric. Specifically, we study an extreme setting with two traffic flows, one heavytailed, and one lighttailed. In this setting, we prove that classical maxweight scheduling, which is known to be throughput optimal, results in the lighttailed flow having heavytailed response times. However, we show that via a careful design of interqueue scheduling policy (from the class of generalized maxweight policies) and intraqueue scheduling policies, it is possible to maintain throughput optimality, and guarantee lighttailed delays for the lighttailed flow, without affecting the response time tail for the heavytailed flow.
Dynamic packet scheduler optimization in wireless relay networks
 Selected Areas in Communications, IEEE Journal on
, 2012
"... In this work, we investigate the optimal dynamic packet scheduling policy in a wireless relay network (WRN). We model this network by two sets of parallel queues, that represent the subscriber stations (SS) and the relay stations (RS), with random link connectivity. An optimal policy minimizes, in s ..."
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Cited by 1 (0 self)
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In this work, we investigate the optimal dynamic packet scheduling policy in a wireless relay network (WRN). We model this network by two sets of parallel queues, that represent the subscriber stations (SS) and the relay stations (RS), with random link connectivity. An optimal policy minimizes, in stochastic ordering sense, the process of cost function of the SS and RS queue sizes. We prove that, in a system with symmetrical connectivity and arrival distributions, a policy that tries to balance the lengths of all the system queues, at every time slot, is optimal. We use stochastic dominance and coupling arguments in our proof. We also provide a lowoverhead algorithm for optimal policy implementation.