• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1721-1735
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• 2016

Power-efficient base station (BS) operation is one of the important issues in future green cellular networks. Previously well-known BS operation schemes, the cell zooming scheme and the cell wilting and blossoming scheme, require tight cooperation between cells in cellular networks. With the previous schemes, the non-cooperative BSs of a serving cell and neighboring cells could cause coverage holes between the cells, thereby seriously degrading the quality of service as well as the power saving efficiency of the cellular networks. In this paper, we propose a novel power-efficient BS operation scheme for green downlink heterogeneous cellular networks, in which the networks virtually adjust the coverage of a serving macrocell (SM) and neighboring macrocells (NMs) without adjusting the transmission power of the BSs when the SM is lightly loaded, and the networks turn off the BS of the SM when none of active users are associated with the SM. Simulation results show that our proposed scheme significantly improves the power saving efficiency without degrading the quality of service (e.g., system throughput) of a downlink heterogeneous LTE network and outperforms the previous schemes in terms of system throughput and power saving efficiency. In particular, with the proposed scheme, macrocells are able to operate independently without the cooperation of a SM and NMs for green heterogeneous cellular networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4145-4164
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• 2016

Energy harvesting is an increasingly attractive source of power for cellular networks, and can be a promising solution for green networks. In this paper, we consider a cellular network with power beacons powering multiple mobile terminals with microwave power transfer in energy beamforming. In this network, the power beacons are powered by grid and renewable energy jointly. We adopt a dual-level control architecture, in which controllers collect information for a core controller, and the core controller has a real-time global view of the network. By implementing the water filling optimized power allocation strategy, the core controller optimizes the energy allocation among mobile terminals within the same cluster. In the proposed green energy cooperation paradigm, power beacons dynamically share their renewable energy by locally injecting/drawing renewable energy into/from other power beacons via the core controller. Then, we propose a new water filling optimized green energy cooperation management strategy, which jointly exploits water filling optimized power allocation strategy and green energy cooperation in cellular networks. Finally, we validate our works by simulations and show that the proposed water filling optimized green energy cooperation management strategy can achieve about 10% gains of MT's average rate and about 20% reduction of on-grid energy consumption.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.114-121
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• 2010

In this paper, an auctioning strategy is proposed for cellular networks that ensures net energy savings. The pricing scheme, in conjunction with a two dimensional bid structure, incentivizes cooperation at the terminal nodes for better interference management at receivers and for cooperative relaying. It is shown that, for the proposed auctioning strategy, network operators are guaranteed revenue gains, mobile nodes' dominant strategy is to bid their true valuation of their energy resources, and overall effective energy gains occur under the assumption of a reserve price for bidding. Simulation results show that significant energy savings can be achieved by employing this auctioning mechanism for a 3G cellular set-up.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.600-609
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• 2016

In this paper, we propose a two-stage base station (BS) sleeping scheme to save energy consumption in cellular networks. The BS sleeping mode is divided into a light sleeping stage and a deep sleeping stage according to whether there is a user in the BS's coverage. In the light sleeping stage, a BS will retain its coverage and frequently switch between the on state and the doze state according to the service characteristics. While in the deep sleeping stage analysis, the BS will shut down its coverage, and neighbor BSs will patch the coverage hole. Several closed-form formulas are derived to demonstrate the power consumption in each sleeping stage and the stage switching conditions are discussed to minimize the average power consumption. The average traffic delay caused by BS sleeping and the average deep sleeping rate under a given traffic load have also been studied. In addition, it is shown that BS sleeping is not always possible because of the limited quality of service (QoS) requirements. Simulation results show that the proposed scheme can effectively reduce the average BS power consumption, at the cost of some extra traffic delay. In summary, our proposed framework provides an essential understanding of the design of future green networks that aim to take full advantage of different stages of BS sleeping to obtain the best energy efficiency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.91-96
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• 2015

Heterogeneous cellular networks support various wireless environments for mobile service. Recently, data services as well as voice services are exponentially increased in cellular networks and the technical transition of LTE-A and IEEE 802.16m so that more base stations are requested to provide suitable service. Base stations consume most of energy in cellular networks, and the energy saving is needed for the base station. In this paper, we propose a saving power scheme by the dynamic energy management. In this paper we consider the simulation evaluations of handover for the low powered base station.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4848-4863
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• 2016

The explosive wireless data service requirement accompanied with carbon dioxide emission and consumption of traditional energy has put pressure on both industria and academia. Wireless networks powered with the uneven and intermittent generated renewable energy have been widely researched and lead to a new research paradigm called green communication. In this paper, we comprehensively consider the total generated renewable energy, QoS requirement and channel quality, then propose a utility based renewable energy allocation policy. The utility here means the satisfaction degree of users with a certain amount allocated renewable energy. The energy allocation problem is formulated as a constraint optimization problem and a heuristic algorithm with low complexity is derived to solve the raised problem. Numerical results show that the renewable energy allocation policy is applicable not only to soft QoS, but also to hard QoS and best effort QoS. When the renewable energy is very scarce, only users with good channel quality can achieve allocated energy.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.567-579
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• 2016

Several energy saving techniques in cellular wireless networks such as active base station (BS) selection, transmit power budget adaptation and user association have been studied independently or only part of these aspects have been considered together in literature. In this paper, we jointly tackle these three problems and propose an integrated framework, called dynamic cell reconfiguration (DCR). It manages three techniques operating on different time scales for ultimate energy conservation while guaranteeing the quality of service (QoS) level of users. Extensive simulations under various configurations, including the real dataset of BS topology and utilization, demonstrate that the proposed DCR can achieve the performance close to an optimal exhaustive search. Compared to the conventional static scheme where all BSs are always turned on with their maximum transmit powers, DCR can significantly reduce energy consumption, e.g., more than 30% and 50% savings in uniform and non-uniform traffic distribution, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8B
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• pp.904-909
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• 2011

Cell zooming adjusts the cell range of base stations depending on traffic condition. The cell zooming can be implemented by the adjustment of antenna angles, the clustering of the base stations, and the cell relay. The base stations can adjust the cell range in term of energy efficiency, which can then reduce the overall energy consumption of cellular networks. There is, however, a trade-off between the energy savings and the blocking probability of user calls. A periodic scheme that manages the cell zooming of the base stations was proposed but it was inadequate for dealing with the dynamic nature of traffic patterns. This paper proposes a semi-periodic cell zooming scheme along with the algorithms that select such base stations and define the operation procedure. Simulation results show that the proposed method outperforms the existing scheme in terms of the energy savings without the degradation of the blocking probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.3
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• pp.1057-1073
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• 2015

In this paper, we consider cooperative D2D communications in cellular networks. More precisely, a cellular user leases part of its spectrum to facilitate the D2D communication with a goal of improving the energy efficiency of a D2D pair. However the D2D pair is untrusted to the cellular user, such resource sharing may result in the information of this cellular user unsecured. In order to motivate the cellular user's generosity, this D2D pair needs to help the cellular user maintain a target secrecy rate. To address this issue, we formulate a joint spectrum and power allocation problem to maximize the energy efficiency of the D2D communication while guaranteeing the physical layer security of the cellular user. Then, a theorem is proved to indicate the best resource allocation strategy, and accordingly, an algorithm is proposed to find the best solution to this resource allocation problem. Numerical results are finally presented to verify the validity and effectiveness of the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.2
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• pp.53-60
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• 2014

The recent electric power shortage has led to the vigorous study for energy conservation in the many different fields. In this paper, cell zooming technology, which can reduce the energy loss at the base stations controlling the transmission power of the stations depending on the changing trffic density for reduce energy consumption that occurs when there is little or no trffic in the service area, is proposed and energy conservation is confirmed by comparing base stations' service scenario depending on traffic change.