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11
Optimal Packet Scheduling in an Energy Harvesting Communication System
"... We consider the optimal packet scheduling problem in a singleuser energy harvesting wireless communication system. In this system, both the data packets and the harvested energy are modeled to arrive at the source node randomly. Our goal is to adaptively change the transmission rate according to th ..."
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Cited by 126 (26 self)
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We consider the optimal packet scheduling problem in a singleuser energy harvesting wireless communication system. In this system, both the data packets and the harvested energy are modeled to arrive at the source node randomly. Our goal is to adaptively change the transmission rate according to the traffic load and available energy, such that the time by which all packets are delivered is minimized. Under a deterministic system setting, we assume that the energy harvesting times and harvested energy amounts are known before the transmission starts. For the data traffic arrivals, we consider two different scenarios. In the first scenario, we assume that all bits have arrived and are ready at the transmitter before the transmission starts. In the second scenario, we consider the case where packets arrive during the transmissions, with known arrival times and sizes. We develop optimal offline scheduling policies which minimize the time by which all packets are delivered to the destination, under causality constraints on both data and energy arrivals.
Optimal broadcast scheduling for an energy harvesting rechargeable transmitter with a finite capacity battery
 IEEE Trans. Wireless Commun
"... Abstract—We consider the minimization of the transmission completion time with a battery limited energy harvesting transmitter in an Muser AWGN broadcast channel where the transmitter is able to harvest energy from the nature, using a finite storage capacity rechargeable battery. The harvested ener ..."
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Cited by 40 (19 self)
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Abstract—We consider the minimization of the transmission completion time with a battery limited energy harvesting transmitter in an Muser AWGN broadcast channel where the transmitter is able to harvest energy from the nature, using a finite storage capacity rechargeable battery. The harvested energy is modeled to arrive (be harvested) at the transmitter during the course of transmissions at arbitrary time instants. The transmitter has fixed number of packets for each receiver. Due to the finite battery capacity, energy may overflow without being utilized for data transmission. We derive the optimal offline transmission policy that minimizes the time by which all of the data packets are delivered to their respective destinations. We analyze the structural properties of the optimal transmission policy using a dual problem. We find the optimal total transmit power sequence by a directional waterfilling algorithm. We prove that there exist M − 1 cutoff power levels such that user i is allocated the power between the i−1st and the ith cutoff power levels subject to the availability of the allocated total power level. Based on these properties, we propose an algorithm that gives the globally optimal offline policy. The proposed algorithm uses directional waterfilling repetitively. Finally, we illustrate the optimal policy and compare its performance with several suboptimal policies under different settings. Index Terms—Energy harvesting, rechargeable wireless networks, broadcast channels, finitecapacity battery, transmission completion time minimization, throughput maximization. I.
Delay Minimization in Multiple Access Channels
"... Abstract—We investigate a delay minimization problem in a multiple access wireless communication system. We consider a discretetime nonfading additive white Gaussian noise (AWGN) multiple access channel. In each slot, bits arrive at the transmitters randomly according to some distribution, which i ..."
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Cited by 2 (2 self)
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Abstract—We investigate a delay minimization problem in a multiple access wireless communication system. We consider a discretetime nonfading additive white Gaussian noise (AWGN) multiple access channel. In each slot, bits arrive at the transmitters randomly according to some distribution, which is i.i.d. from user to user and from slot to slot. Each transmitter has an average power constraint of P. Our goal is to allocate rates to users, from the multiple access capacity region, based on their current queue lengths, in order to minimize the average delay of the system. We formulate the problem as a Markov decision problem (MDP) with an average cost criterion. We first show that the value function is increasing, symmetric and convex in the queue length vector. Taking advantage of these properties, we show that the optimal rate allocation policy is one which tries to equalize the queue lengths as much as possible in each slot, while working on the dominant face of the capacity region. I.
Trading Rate for Balanced Queue Lengths for Network Delay Minimization
"... Abstract—We consider a communication channel with two transmitters and one receiver, with an underlying rate region which is approximated as a general pentagon. Different from the Gaussian multiple access channel (MAC) capacity region, the sumrate on the dominant face of this pentagon is not a cons ..."
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Cited by 2 (0 self)
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Abstract—We consider a communication channel with two transmitters and one receiver, with an underlying rate region which is approximated as a general pentagon. Different from the Gaussian multiple access channel (MAC) capacity region, the sumrate on the dominant face of this pentagon is not a constant. We allocate rates from this rate region to users according to their current queue lengths in order to minimize the average delay in the system. We formulate the problem as a Markov decision problem (MDP), and derive the structural properties of the corresponding discountedcost MDP. We show that the delayoptimal policy has a switch curve structure. For the discountedcost problem, we prove that the switch curve has a limit along one of the dimensions. The delayoptimal policy divides the entire queue state space into two via a switch curve. If the queue state is on one side of the switch curve, the system operates at one of the corner points of the rate pentagon which favors maximum sumrate. When the queue state switches to the other side of the switch curve, the system operates at the other corner point of the rate pentagon which favors balancing the queue lengths. As a result, the system does not always operate at the sumrate maximizing rate pair, but trades rate for balanced queue lengths for the goal of minimizing the overall delay. The existence of a limit in the switch curve along one of dimensions implies that, once the queue state is beyond the limit, the system always operates at one of the corner points, implying that the queues can be operated partially distributedly. Index Terms—Delay minimization, ratedelay tradeoff, queuelength based rate allocation, multiple access channel, Markov decision processes. I.
EnergyDelay tradeoff in Multiple Access Channels
, 2009
"... In this paper we study the tradeoff between energy and delay in a multiple access channel (MAC). Messages arrive at the queues of the individual users and users decide whether to service them. Transmission of a message consumes energy and is successful only if one user transmits at a time. Users do ..."
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Cited by 1 (0 self)
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In this paper we study the tradeoff between energy and delay in a multiple access channel (MAC). Messages arrive at the queues of the individual users and users decide whether to service them. Transmission of a message consumes energy and is successful only if one user transmits at a time. Users do not communicate but can observe a broadcasted feedback message from the base station indicating the success or not of the previous transmission. Delays are captured by considering the queue lengths of each user. We formulate this problem as a decentralized stochastic control problem, the two controllers being the two users who, in the presence of limited information about each other, decide whether to transmit at each time slot. The decentralized aspect of this control problem makes it fundamentally different from the corresponding singleuser counterparts and multiuser counterparts assuming a centralized controller. As a result, the tools from Markov decision processes (MDPs) and partially observed MDPs (POMDPs) cannot be directly applied. Our contribution is twofold. First, we identify structural properties of the optimal transmission strategies for the two users so that the domain of the optimal strategies is not increasing with time. Second, based on the above structural properties, we identify the optimal strategies as the solution of a fixed point equation.
Delay Minimization with a General Pentagon Rate Region
"... Abstract—We consider a communication channel with two transmitters and one receiver, with an underlying rate region which is approximated as a general pentagon. Different from the Gaussian multiple access channel (MAC) capacity region, the sumrate on the dominant face of this pentagon is not a cons ..."
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Cited by 1 (1 self)
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Abstract—We consider a communication channel with two transmitters and one receiver, with an underlying rate region which is approximated as a general pentagon. Different from the Gaussian multiple access channel (MAC) capacity region, the sumrate on the dominant face of this pentagon is not a constant. We allocate rates from this rate region to users according to their current queue lengths in order to minimize the average delay in the system. We formulate the problem as a Markov decision problem (MDP), and derive the structural properties of the corresponding discountedcost MDP. We show that the delayoptimal policy has a switch curve structure. For the discountedcost problem, we prove that the switch curve has a limit along one of the dimensions. I.
WIRELESS COMMUNICATIONS UNDER QOS CONSTRAINTS: ENERGY . . .
, 2012
"... This dissertation deals with various issues in wireless communications under statistical quality of service (QoS) constraints. Effective capacity, which provides the maximum constant arrival rate that a wireless channel can sustain while satisfying statistical QoS constraints, is adopted as the perf ..."
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This dissertation deals with various issues in wireless communications under statistical quality of service (QoS) constraints. Effective capacity, which provides the maximum constant arrival rate that a wireless channel can sustain while satisfying statistical QoS constraints, is adopted as the performance metric. Energy efficiency of pointtopoint links is first studied by characterizing the spectral efficiencybit energy tradeoff in the lowpower and wideband regimes. Different transmission strategies (with variable or fixed rate) and power policies are studied. Then, the effective capacity region for fading multipleaccess channels (MAC) is investigated for different transmission strategies: Superposition coding with successive decoding and time division multiple access (TDMA). With fixed power, it is shown that varying the decoding order
ABSTRACT Title of dissertation: DELAY MINIMIZATION IN ENERGY CONSTRAINED WIRELESS COMMUNICATIONS
"... In wireless communications and networks, especially for many realtime applications, the average delay packets experience is an important quality of service criterion. Therefore, it is imperative to design advanced transmission schemes to jointly address the goals of reliability, high rates and low ..."
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In wireless communications and networks, especially for many realtime applications, the average delay packets experience is an important quality of service criterion. Therefore, it is imperative to design advanced transmission schemes to jointly address the goals of reliability, high rates and low delay. Achieving these objectives often requires careful allocation of given resources, such as energy, power, rate, among users. It also requires a close collaboration between physical layer, medium access control layer, and upper layers, and yields crosslayer solutions. We first investigate the problem of minimizing the overall transmission delay of packets in a multiple access wireless communication system, where the transmitters have average power constraints. We formulate the problem as a constrained optimization problem, and then transform it into a linear programming problem. We show that the optimal policy has a threshold structure: when the sum of the queue lengths is larger than a threshold, both users should transmit a packet during the current slot; when the sum of the queue lengths is smaller than a threshold, only
1DelayOptimal Server Allocation in MultiQueue MultiServer Systems With TimeVarying
"... Abstract—This paper considers the problem of optimal server allocation in a timeslotted system with N statistically symmetric queues and K servers when the arrivals and channels are stochastic and timevarying. In this setting, we identify two classes of “desirable ” policies with potentially compe ..."
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Abstract—This paper considers the problem of optimal server allocation in a timeslotted system with N statistically symmetric queues and K servers when the arrivals and channels are stochastic and timevarying. In this setting, we identify two classes of “desirable ” policies with potentially competing goals of maximizing instantaneous throughput versus balancing the load. Via an example, we show that these goals, in general, can be incompatible, implying an empty intersection between the two classes of policies. On the other hand, we establish the existence of a policy achieving both goals when the connectivities between each queue and each server are random and either “on” or “off”. We use dynamic programming and properties of the value function to establish the delayoptimality of a policy which, at each timeslot, simultaneously maximizes the instantaneous throughput and balances the queues. Index Terms—Communication models, intermittent connectivity, multiqueue multiserver, orthogonal frequency division multiple access, optimal transmission scheduling, queuing analysis. I.