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Movers and shakers: Kinetic energy harvesting for the internet of things
 IEEE J. Sel. Areas Commun., Special Issue on Wireless Communications
, 2015
"... Abstract—Numerous energy harvesting wireless devices that will serve as building blocks for the Internet of Things (IoT) are currently under development. However, there is still only limited understanding of the properties of various energy sources and their impact on energy harvesting adaptive algo ..."
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Abstract—Numerous energy harvesting wireless devices that will serve as building blocks for the Internet of Things (IoT) are currently under development. However, there is still only limited understanding of the properties of various energy sources and their impact on energy harvesting adaptive algorithms. Hence, we focus on characterizing the kinetic (motion) energy that can be harvested by a wireless node with an IoT form factor and on developing energy allocation algorithms for such nodes. In this paper, we describe methods for estimating harvested energy from acceleration traces. To characterize the energy availability associated with specific human activities (e.g., relaxing, walking, cycling), we analyze a motion dataset with over 40 participants. Based on acceleration measurements that we collected for over 200 hours, we study energy generation processes associated with daylong human routines. We also briefly summarize our experiments with moving objects. We develop energy allocation algorithms that take into account practical IoT node design considerations, and evaluate the algorithms using the collected measurements. Our observations provide insights into the design of motion energy harvesters, IoT nodes, and energy harvesting adaptive algorithms. Index Terms—Energy harvesting, motion energy, measurements, lowpower networking, algorithms, Internet of Things. I.
Shortterm throughput maximization for battery limited energy harvesting nodes
 in IEEE ICC
, 2011
"... Abstract—Deploying energy harvesting nodes can significantly extend the lifetime of a battery powered wireless network. On the other hand, such systems call for specific design principles to efficiently utilize the dynamic levels of instantaneously available energy. In contrast to the conventional ..."
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Abstract—Deploying energy harvesting nodes can significantly extend the lifetime of a battery powered wireless network. On the other hand, such systems call for specific design principles to efficiently utilize the dynamic levels of instantaneously available energy. In contrast to the conventional wireless networks, transmission policies for these systems should take into account the battery recharge process of the node as well as its battery capacity. In this work, we focus on the problem of finding the optimal transmission policy to maximize the shortterm throughput of an energy harvesting transmitter node with power control and a limited energy storage capacity. The transmission policy in this problem is strictly constrained with both the energy recharge process and the energy storage capacity of the node. A discrete model with packets of energy arrivals is considered for energy recharge. Under the assumption of an increasing concave powerrate relationship, the shortterm throughput maximizing transmission policy is identified in this paper. The necessary conditions such a policy should satisfy are identified and an algorithm to yield the unique policy that satisfies these conditions is presented. The performance of this algorithm is then observed through numerical results. I.
Adaptive Transmission Policies for Energy Harvesting Nodes in Fading Channels
 In Conference on Information Sciences and Systems (CISS
"... Abstract—In this paper, we consider a singleuser communication system, where an energy harvesting transmitter communicates with a receiver over a fading wireless channel. We design adaptive transmission policies that adapt to the random energy arrivals at the transmitter and random fluctuations in ..."
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Abstract—In this paper, we consider a singleuser communication system, where an energy harvesting transmitter communicates with a receiver over a fading wireless channel. We design adaptive transmission policies that adapt to the random energy arrivals at the transmitter and random fluctuations in the channel, in order to maximize the average number of bits transmitted by a finite deadline T. We solve for the optimum transmission scheme using stochastic dynamic programming. This optimal solution does not admit a closed form expression and is computationally expensive. We then propose several suboptimal event based adaptive transmission policies that react to the changes in energy arrivals and fading states. We provide extensive simulation results that compare the performances of the optimal and proposed simpler solutions. I.
PowerDelay Tradeoff over Wireless Networks
"... Abstract—When transmitting stochastic traffic flows over wireless networks, there exists an inherent tradeoff between average transmit power and corresponding queuingdelay bound. In this paper, we investigate such a tradeoff and show how average power increases as delaybound requirement for wirel ..."
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Abstract—When transmitting stochastic traffic flows over wireless networks, there exists an inherent tradeoff between average transmit power and corresponding queuingdelay bound. In this paper, we investigate such a tradeoff and show how average power increases as delaybound requirement for wireless network traffics becomes stringent. Specifically, we propose the resource allocation schemes to minimize the power consumption subject to a delay qualityofservice (QoS) constraint, where the delay constraint is in terms of queuelength decay rate when an arrival traffic is transmitted through the wireless networks. We focus on orthogonalfrequencydivisionmultiplexing (OFDM) communications under three different network infrastructures, namely, pointtopoint link, multihop amplifyandforward (AF) network, and multiuser cellular network. We derive the optimal resource allocation policies for each scenario, and compare their performances with other existing resourceallocation policies. The obtained simulation and numerical results show that using our proposed optimal resourceallocation policies, significant power saving can be achieved. Furthermore, our OFDMbased communications systems can significantly reduce the power consumption, especially under stringent delay constraint. Index Terms—Power control, statistical delaybounded qualityofservice (QoS) guarantees, effective capacity, wireless networks, resource allocation and management, scheduling, OFDMbased communications systems, convex optimization, information theory. I.
Optimal offline broadcast scheduling with an energy harvesting transmitter
 EURASIP J. Wireless Commun. Netw
, 2013
"... We consider an energy harvesting transmitter broadcasting data to two receivers. Energy and data arrivals are assumed to occur at arbitrary but known instants. The goal is to minimize the total transmission time of the packets arriving within a certain time window, using the energy that becomes avai ..."
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We consider an energy harvesting transmitter broadcasting data to two receivers. Energy and data arrivals are assumed to occur at arbitrary but known instants. The goal is to minimize the total transmission time of the packets arriving within a certain time window, using the energy that becomes available during this time. An achievable rate region with structural properties satisfied by the twouser AWGN BC capacity region is assumed. Structural properties of power and rate allocation in an optimal policy are established, as well as the uniqueness of the optimal policy under the condition that all the data of the “weaker ” user are available at the beginning. An iterative algorithm, DuOpt, based on block coordinate descent that achieves the same structural properties as the optimal is described. Investigating the ways to have the optimal schedule of two consecutive epochs in terms of energy efficiency and minimum transmission duration, it has been shown that DuOpt achieves best performance under the same special condition of uniqueness. Index Terms Packet scheduling, energy harvesting, AWGN broadcast channel, energyefficient scheduling.
Optimum Policies for an Energy Harvesting Transmitter Under Energy Storage Losses
, 2015
"... We consider an energy harvesting network where the transmitter harvests energy from nature, and the harvested energy can be saved in an imperfect battery which suffers from charging/ discharging inefficiency. In particular, when E units of energy is to be stored in the battery, only ηE units is save ..."
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Cited by 3 (3 self)
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We consider an energy harvesting network where the transmitter harvests energy from nature, and the harvested energy can be saved in an imperfect battery which suffers from charging/ discharging inefficiency. In particular, when E units of energy is to be stored in the battery, only ηE units is saved and (1 − η)E is lost due to charging/discharging inefficiency, where 0 ≤ η ≤ 1 represents the storing efficiency. We determine the optimum offline transmit power schedule for such a system for singleuser and broadcast channel models, for static and fading channels, with and without a finite battery size. We show that the optimum policy is a doublethreshold policy: specifically, we store energy in the battery only when the harvested energy is above an upper threshold, and retrieve energy from the battery only when the harvested energy is below a lower threshold; when the harvested energy is in between these two thresholds, we use it in its entirety in the current slot. We show that the two thresholds remain constant unless the battery is depleted or full. We provide an algorithm to determine the sequence of optimum thresholds. For the case with fading, we develop a directional waterfilling algorithm which has a doublethreshold structure. Finally, we formulate the online problem using dynamic programming, and numerically observe that the online policy exhibits a doublethreshold structure as well.
Optimal Packet Scheduling in a Broadcast Channel with an Energy Harvesting Transmitter
 IEEE International Conference on Communications (ICC
, 2011
"... Abstract—In this paper, we investigate the transmission completion time minimization problem in a twouser additive white Gaussian noise (AWGN) broadcast channel, where the transmitter is able to harvest energy from the nature. The harvested energy is modeled to arrive at the transmitters randomly. ..."
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Abstract—In this paper, we investigate the transmission completion time minimization problem in a twouser additive white Gaussian noise (AWGN) broadcast channel, where the transmitter is able to harvest energy from the nature. The harvested energy is modeled to arrive at the transmitters randomly. In this paper, under a deterministic system setting, we assume that the energy harvesting times and harvested energy amounts are known before the transmission starts. The transmitter has a fixed number of packets to be delivered to each receiver. Our goal is to minimize the time by which all of the packets for both users are delivered to their respective destinations. To this end, we optimize the transmit powers and transmission rates intended for both users. We first analyze the structural properties of the optimal transmission policy. We prove that the optimal total transmit power has the same structure as the optimal singleuser transmit power [1], [2]. We also prove that there exists a cutoff power level for the stronger user. If the optimal total transmit power is lower than this level, all transmit power is allocated to the stronger user, and when the optimal total transmit power is larger than this level, all transmit power above this level is allocated to the weaker user. Based on these structural properties of the optimal policy, we propose an algorithm that yields the globally optimal offline scheduling policy. I.
Joint Transmission and Caching Policy Design for Energy Minimization in the Wireless Backhaul Link
"... Abstract—Caching the most popular contents at Small Base Stations (SBSs) is envisioned as a promising solution to reduce both the load and energy consumption of the backhaul link connecting the SBSs to the core network. This paper considers a set of users whose demands are served by an SBS connected ..."
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Abstract—Caching the most popular contents at Small Base Stations (SBSs) is envisioned as a promising solution to reduce both the load and energy consumption of the backhaul link connecting the SBSs to the core network. This paper considers a set of users whose demands are served by an SBS connected through a wireless backhaul link to a Macro Base Station (MBS). The SBS is capable of caching content in its limited cache memory. The transmission policy at the MBS and the caching policy at the SBS are jointly optimized in order to minimize the energy consumption in the backhaul link. The numerical results show significant improvements with respect to prior works. Index Terms—Proactive caching, wireless backhaul, energyefficiency. I.
Energy Harvesting Communications with Continuous Energy Arrivals
"... Abstract—This work considers an energy harvesting transmitter that gathers a continuous flow of energy from intermittent sources, thus relaxing the modeling assumption of discrete amounts of harvested energy present in all previous work on energy harvesting communications. Tools from convex analysi ..."
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Abstract—This work considers an energy harvesting transmitter that gathers a continuous flow of energy from intermittent sources, thus relaxing the modeling assumption of discrete amounts of harvested energy present in all previous work on energy harvesting communications. Tools from convex analysis are utilized to describe the optimal transmission policy as the boundary of a properly defined region based on the energy profile. The results are extended to include models where the transmitter has a finite capacity battery with various imperfections, as well as those that incorporate a processing cost (circuit power) at the transmitter whenever it is in operation. Index Terms—Energy harvesting wireless transmitter, continuous arrivals, throughput maximization, finite battery, battery imperfections. I.
Wireless content caching for small cell and d2d networks. submitted
, 2015
"... The fifth generation wireless systems must provide fast and reliable connectivity while coping with the ongoing traffic growth. It is of paramount importance that the required resources, such as energy and bandwidth, do not scale with traffic. An important observation to reduce the required resource ..."
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The fifth generation wireless systems must provide fast and reliable connectivity while coping with the ongoing traffic growth. It is of paramount importance that the required resources, such as energy and bandwidth, do not scale with traffic. An important observation to reduce the required resources is that different users tend to request the same content at different time instants. Therefore, caching the most popular content at the network edge is envisioned as a promising solution to reduce the traffic and the energy consumption of the backhaul links. In this paper, two scenarios are considered, where caching is performed either at a small base station, or directly at the user terminals, which communicate using devicetodevice communications. In both scenarios, joint design of the transmission and caching policies is studied when the user demands are known in advance. This joint design offers two different caching gains, namely, the predownloading and local caching gains. It is shown that the finite cache capacity limits the obtainable gains and creates inherent tradeoff between the two. In this context, a continuous time optimization problem is formulated to determine the optimal transmission and caching policies that minimize a generic cost function at the macro base station, such as energy, bandwidth, or throughput. The jointly optimal solution is obtained by demonstrating that caching files at a constant