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Energy Cooperation in Energy Harvesting Communications
, 2013
"... In energy harvesting communications, users transmit messages using energy harvested from nature during the course of communication. With an optimum transmit policy, the performance of the system depends only on the energy arrival profiles. In this paper, we introduce the concept of energy cooperatio ..."
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Cited by 23 (8 self)
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In energy harvesting communications, users transmit messages using energy harvested from nature during the course of communication. With an optimum transmit policy, the performance of the system depends only on the energy arrival profiles. In this paper, we introduce the concept of energy cooperation, where a user wirelessly transmits a portion of its energy to another energy harvesting user. This enables shaping and optimization of the energy arrivals at the energyreceiving node, and improves the overall system performance, despite the loss incurred in energy transfer. We consider several basic multiuser network structures with energy harvesting and wireless energy transfer capabilities: relay channel, twoway channel and multiple access channel. We determine energy management policies that maximize the system throughput within a given duration using a Lagrangian formulation and the resulting KKT optimality conditions. We develop a twodimensional directional waterfilling algorithm which optimally controls the flow of harvested energy in two dimensions: in time (from past to future) and among users (from energytransferring to energyreceiving) and show that a generalized version of this algorithm achieves the boundary of the capacity region of the twoway channel.
Throughput maximization for an energy harvesting communication system with processing cost
 Proc. IEEE Information Theory Workshop (ITW
, 2012
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Cooperative Energy Harvesting Communications with Relaying and Energy Sharing
"... Abstract—This paper considers twohop communication networks where the transmitters harvest their energy in an intermittent fashion. In this network, communication is carried out by signal cooperation, i.e., relaying. Additionally, the transmitters have the option of transferring energy to one anoth ..."
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Cited by 9 (4 self)
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Abstract—This paper considers twohop communication networks where the transmitters harvest their energy in an intermittent fashion. In this network, communication is carried out by signal cooperation, i.e., relaying. Additionally, the transmitters have the option of transferring energy to one another, i.e., energy cooperation. Energy is partially lost during transfer, exposing a tradeoff between energy cooperation and use of harvested energy for transmission. A multiaccess relay model is considered and transmit power allocation and energy transfer policies that jointly maximize the sumrate are found. It is shown that a class of power policies achieves the optimal sumrate, allowing a separation of optimal energy transfer and optimal power allocation problems. The optimal energy transfer policy is shown to be an ordered node selection, where nodes with better energy transfer efficiency and worse channels transfer all their energy to the relay or other source nodes via the relay. For the special case of single source, the optimal policy requires the direction of energy transfer to remain unchanged unless either node depletes all of its energy. Overall, the findings provide the insight that cooperation of the source nodes by sharing energy with the relay node leads to them indirectly cooperating with each other, and that such cooperation can be carried out in a lastminute fashion. I.
Optimum policies for an energy harvesting transmitter under energy storage losses
 IEEE J. Sel. Areas Commun
, 2015
"... AbstractWe 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 unit ..."
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Cited by 4 (3 self)
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AbstractWe 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. Index TermsEnergy harvesting communications, optimal packet scheduling, nodes with rechargeable batteries, inefficient energy storage. I. INTRODUCTION We consider an energy harvesting network where the transmitter harvests energy from nature to sustain its operation. In particular, the transmitter uses the energy harvested from nature to transmit its data packets. Such energy harvesting capabilities bring new constraints into the communication problem in the physical layer in the form of energy causality and noenergyoverflow conditions. The first constraint imposes that the energy that has not yet been harvested cannot be used for communication, and the second constraint imposes that no harvested energy should be allowed to overflow due to a finite battery size. Therefore, in such energy harvesting systems, packet scheduling and the corresponding energy management
Energy Harvesting Diamond Channel with Energy Cooperation
"... Abstract—We consider the energy harvesting diamond channel, where the source and two relays harvest energy from nature, the relays help deliver the source’s messages via signal cooperation, and the source has the option of wirelessly transferring some of its energy to the relays via energy cooperati ..."
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Cited by 4 (3 self)
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Abstract—We consider the energy harvesting diamond channel, where the source and two relays harvest energy from nature, the relays help deliver the source’s messages via signal cooperation, and the source has the option of wirelessly transferring some of its energy to the relays via energy cooperation. We find the optimal offline transmit power allocations and energy transfer policies that maximize the endtoend throughput. For the case of no energy cooperation, we decompose the problem into inner and outer maximization problems, and solve the overall problem iterating between the two. We show that the class of procrastinating policies, where energy is transferred only when it will be immediately used, is optimal. We then show that the problem with energy cooperation is equivalent to a problem without energy cooperation with suitably modified rate expressions. We show that, in this system, if the source sends more energy to a relay, then it sends less data, showing us how data and energy should flow together optimally in this network. I.
Twohop networks with energy harvesting: The (non)impact of buffer size
 in Proceedings of the GlobalSIP 2013 Symposium on Energy Harvesting and Green Wireless Communications
, 2013
"... Abstract—In this paper, a twohop channel is considered with energy harvesting transmitter nodes. In particular, the offline throughput maximization problem is solved for a constant power relay, and a relay with one energy arrival, in both cases assuming a finite buffer is available at the relay fo ..."
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Abstract—In this paper, a twohop channel is considered with energy harvesting transmitter nodes. In particular, the offline throughput maximization problem is solved for a constant power relay, and a relay with one energy arrival, in both cases assuming a finite buffer is available at the relay for temporarily storing data received from the source. The focus is on assessing the impact of this data buffer at the relay on optimal transmission policies. The solution is found indirectly, by first assuming that the relay has an infinite size buffer, and then proving that an optimal policy exists that does not require any data buffer at the relay, thus solving the problem regardless of the data buffer size at the relay. Numerical results demonstrate that the proposed solution performs significantly better than naı̈ve policies, and a constant relay rate limits the average throughput as the peak energy harvest rate for the source increases. Index Terms—Energy harvesting nodes, twohop channel, relay channel, throughput maximization, finite buffer. I.
Energy Harvesting Wireless Communications: A Review of Recent Advances
"... Abstract—This paper summarizes recent contributions in the broad area of energy harvesting wireless communications. In particular, we provide the current state of the art for wireless networks composed of energy harvesting nodes, starting from the informationtheoretic performance limits to transmis ..."
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Cited by 3 (0 self)
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Abstract—This paper summarizes recent contributions in the broad area of energy harvesting wireless communications. In particular, we provide the current state of the art for wireless networks composed of energy harvesting nodes, starting from the informationtheoretic performance limits to transmission scheduling policies and resource allocation, medium access, and networking issues. The emerging related area of energy transfer for selfsustaining energy harvesting wireless networks is considered in detail covering both energy cooperation aspects and simultaneous energy and information transfer. Various potential models with energy harvesting nodes at different network scales are reviewed, as well as models for energy consumption at the nodes. Index Terms—Energy harvesting communications, energy cooperation, simultaneous wireless information and energy transfer. I.
Energy Harvesting Cooperative Diamond Channel
"... Abstract—We consider the energy harvesting diamond channel, where the source and two relays harvest energy from nature. The physical layer is modeled as a concatenation of a broadcast and a multiple access channel. We find the optimal offline transmit power and rate allocations that maximize the end ..."
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Cited by 1 (1 self)
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Abstract—We consider the energy harvesting diamond channel, where the source and two relays harvest energy from nature. The physical layer is modeled as a concatenation of a broadcast and a multiple access channel. We find the optimal offline transmit power and rate allocations that maximize the endtoend throughput. First, we show that there exists an optimal source power allocation which is equal to the singleuser optimal power allocation for the source energy arrivals and does not depend on the relay energy arrivals. Second, we show that the fraction of the power spent on each broadcast link depends on the energy arrivals for the relays. Specifically, we show that the optimal source rate allocation can be found by solving an optimal broadcasting problem with slotdependent user priorities and these priorities can change only at instants where one of the relay data buffers is empty. Finally, we decompose the problem into inner and outer optimization problems and solve the overall problem by iterating between the two. I.
Optimal Power and Rate Allocation in the Degraded Gaussian Relay Channel with Energy Harvesting Nodes
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Relay Selection for Energy Harvesting Cooperative Communication Systems
"... Abstract—Energy harvesting (EH) has recently emerged as a promising technique for green communications, as it can power communication systems with renewable energy. In this paper, we investigate how to adopt cooperative relay selection to improve the shortterm performance of EH communication system ..."
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Abstract—Energy harvesting (EH) has recently emerged as a promising technique for green communications, as it can power communication systems with renewable energy. In this paper, we investigate how to adopt cooperative relay selection to improve the shortterm performance of EH communication systems. The main focus is on how to efficiently utilize the available side information (SI), including channel side information (CSI) and energy side information (ESI). We formulate relay selection problems with either noncausal or causal SI, with an emphasis on the more practical causal case. For this causal SI case, we propose a lowcomplexity relay selection strategy based on the relative throughput, that is, in each block, the relay with enough energy and with the highest instantaneous throughput compared with the average throughput is selected. This relay selection rule captures the key characteristic of EH systems, namely, each relay should have some chance to be selected so that the harvested energy can be efficiently utilized, and it should be selected only if its throughput is near its own peak. Simulation results will show that the proposed relay selection method provides significant throughput gain over the conventional one which is only based on the current side information. Index Terms—Energy harvesting, cooperative communication, relay selection, noncausal/causal side information. I.