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Next-generation cellular networks, i.e., beyond fifth generation (B5G) and sixth generation (6G) networks, aim at significantly increasing capacity by deploying a massive number of small cells (SCs) and leveraging millimeter wave (mmWave) links that have large bandwidth availability. However, as optical connections to a large number of base stations (BSs) are not cost effective, wireless backhaul (BH) links may be used to connect SCs to the core network using mmWave frequencies and forming multihop mesh BH paths. While very flexible in deployment, the uncertainty in user demand, which varies over time and place, makes network planning and management challenging. In this work, we propose novel algorithms to solve the joint problem of energy-efficient user association, BH traffic routing and BS/BH link on/off switching. We first formulate an exact model assuming user traffic demand uncertainty leveraging -robustness theory. As the model is intractable for large-scale instances, we develop a novel greedy robust heuristic (P-HEUR), which includes a robustifying step to effectively cope with demand uncertainty. Our evaluation demonstrates that P-HEUR provides robust and energy-efficient solutions quickly for different scenarios and traffic demand uncertainty levels, and it significantly outperforms state-of-the-art approaches while achieving up to 83% of the optimal capacity, even in the most demanding scenarios in terms of traffic load and demand uncertainty, with up to 200k times lower complexity. This research was supported by MCIN/AEI/10.13039/501100011033 and ERDF “A way of making Europe” under grant PGC2018-099945-BI00 (also responsible for the Article Processing Charges) and H2020-5G PPP 5G-COMPLETE (grant agreement 871900). All authors approved the version of the manuscript to be published.

With the expected increase in data traffic (e.g., video) and in the user devices generating new traffic (e.g., device-to-device communication, Internet of Things, etc.), the evolution of next-generation mobile networks (e.g., 5G networks) has gone towards heterogeneous deployments where multiple small cells coexist in the same area covered by a macro base station. To reduce the capital expenses in the network, a wireless mesh can be used, which is made of millimeter-wave links that route the data traffic of the mobile users inside the backhaul network. Such an increase in the number of deployed base stations inevitably increases the power consumption; hence, the operating expenses and the CO2 consumption also increase. To achieve greener mobile communications, sleep-mode strategies have been considered in order to switch off the unused network components. However, the switching on/off should be made according to the traffic demanded by the users and with the aim of guaranteeing the demanded service at any time. Given that the traffic demand and networking traffic fluctuate over time at each location, we propose a robust mixed integer linear problem that jointly solves the user association, the backhaul routing paths in the wireless mesh and the switching off of the unused links with the aim of minimizing the power consumption. The robust strategy is based on the $\Gamma $ -robust approach and is able to guarantee the user demand while taking into account its intrinsic variability. A thorough evaluation has been performed in order to analyze the impact of the robust strategy on the network performance.

Next generation, i.e., fifth generation (5G), cellular networks will provide a significant higher capacity per area to support the ever-increasing traffic demands. In order to achieve that, many small cells need to be deployed that are connected using a combination of optical fiber links and millimeter-wave (mmWave) backhaul architecture to forward heterogeneous traffic over mesh topologies. In this paper, we present a general optimization framework for the design of policies that optimally solve the problem of where to associate a user, over which links to route its traffic towards which mesh gateway, and which base stations and backhaul links to switch off in order to minimize the energy cost for the network operator and still satisfy the user demands. We develop an optimal policy based on mixed integer linear programming (MILP) which considers different user distribution and traffic demands over multiple time periods. We develop also a fast iterative two-phase solution heuristic, which associates users and calculates backhaul routes to maximize energy savings. Our strategies optimize the backhaul network configuration at each timeslot based on the current demands and user locations. We discuss the application of our policies to backhaul management of mmWave cellular networks in light of current trend of network softwarization (Software-Defined Networking, SDN). Finally, we present extensive numerical simulations of our proposed policies, which show how the algorithms can efficiently trade-off energy consumption with required capacity, while satisfying flow demand requirements.

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The introduction of fourth-generation wireless technologies has fueled the rapid development of cellular networks, significantly increasing the energy consumption and the expenditures of mobile network operators (MNOs). In addition, network underutilization during low-traffic periods (e.g., night zone) has motivated a new business model, namely, infrastructure sharing, which allows the MNOs to have their traffic served by other MNOs in the same geographic area, thus enabling them to switch off part of their network. In this paper, we propose a novel infrastructure-sharing algorithm for multioperator environments, which enables the deactivation of underutilized base stations during low-traffic periods. Motivated by the conflicting interests of the MNOs and the necessity for effective solutions, we introduce a game-theoretic framework that enables the MNOs to individually estimate the switching-off probabilities that reduce their expected financial cost. Our approach reaches dominant strategy equilibrium, which is the strategy that minimizes the cost of each player. Finally, we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved in multioperator environments, incentivizing the MNOs to apply the proposed scheme.

©2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The anticipated explosion in the total data traffic load will impose to mobile network operators (MNOs) the necessity to densify their networks to provide coverage. At the same time, since MNOs plan their networks according to their high-peak traffic load, base station (BS) underutilization during the low traffic hours raises the issue of unnecessary power consumption and excessive cost. In this paper, we plan to study the energy and cost efficiency of a heterogeneous network (HetNet) that is a cooperation result of many MNOs. Each MNO is owner of a HetNet, composed of eNodeBs and small cells and they cooperate by sharing their infrastructure and by switching off a part of it. BS type and traffic load constitute switching off criteria and a roaming-cost-based user association scheme is used to roam traffic to neighboring BSs. We assess the cost alterations created by the possible MNO coalitions and we propose a bankruptcy game to allocate the obtained cost to the cooperative MNOs and to motivate them thus to maintain their sharing agreement instead of following a non-cooperative tactic. The bankruptcy game uses Shapley Value to portray each MNO's contribution to cost savings. The MNOs’ satisfaction from their payoffs (i.e., the allocated cost) and the overall fairness of the method are evaluated. According to the extracted results, the proposed switching off scheme achieves significant improvement of energy efficiency for the studied network, while the proposed bankruptcy game achieves a balanced and satisfactory cost allocation for different MNO traffic loads.

Статья посвящена исследованию проблемы коммутационных потерь в IGBT-модулях. Показано, что основными препятствиями на пути дальнейшего увеличения частоты переключений IGBT являются значительная величина «хвостового тока» и динамических потерь включения и выключения. Обоснована возможность снижения величины «хвостового тока» и динамических потерь выключения за счет профилирования структуры полупроводникового прибора путем протонного облучения. Протонное облучение IGBT позволяет создать большую концентрацию дырок вблизи коллектора, оставляя остальную структуру кристалла без изменений. При этом потери выключения снижаются в 2 раза. Дальнейшее снижение динамических потерь становится возможным благодаря введению в силовую схему четырехквадрантного IGBT-ключа коммутирующего (снабберного) транзистора. Представленная структура позволяет разгрузить основные силовые транзисторы и уменьшить тем самым динамические потери выключения. Предварительная оценка показывает, что тепловая нагрузка на такой модуль снижается на 25% по сравнению со стандартными IGBT. Такие приборы могут быть использованы на дизель- и электропоездах нового поколения., Стаття присвячена дослідженню проблеми комутаційних втрат в модулях IGBT Показано, що основними перепонами на шляху подальшого збільшення частот переключень IGBT є значні величини «хвостового струму» та динамічних втрат вмикання та вимикання. Обґрунтовано можливість зниження величин «хвостового струму» та динамічних втрат при вимиканні за рахунок профілювання структури напівпровідникового приладу шляхом протонного опромінення. Протонне опромінення дозволяє створити більшу концентрацію дірок поблизу колектора, залишаючи інші частини структури кристалу без змін. При цьому динамічні втрати при вимкненні зменшуються у 2 рази. Подальше зниження рівня динамічних втрат є можливим за рахунок введення до силової схеми чотириквадрантного IGBT-ключа комутаційного (снаберного) транзистора. Представлена структура дозволить розвантажити основні силові транзистори і тим самим знизити динамічні втрати вимикання. Попередня оцінка показує, що теплове навантаження на такий модуль є на 25% нижчим, ніж на стандартний IGBT. У подальшому такі прибори можуть бути використані на дизель- та електропоїздах нового покоління., Article is devoted researching of a problem of switching losses in IGBT modules. It is shown that the main obstacles in a way of further increasing in frequency of switchings of IGBT are the considerable size of "tail current" and dynamic losses of inclusion and switching off. The possibility of decrease in size of "tail current" and dynamic losses of switching off due to profiling of structure of the semiconductor device by proton radiation is proved. Proton radiation of IGBT allows to create big concentration of holes near a collector, leaving other structure of a crystal without changes. At the same time losses of switching off decrease twice. Further decrease in dynamic losses becomes possible thanks to introduction to the power scheme of a four-quadrant IGBT key of the switching (snubber) transistor. The presented structure allows to unload the main power transistors and to reduce thereby dynamic losses of switching off. The preliminary estimate shows that thermal load of such module decreases by 25% in comparison with standard IGBT. Such devices can be used on the diesel- and electric trains of new generation.

The emerging traffic demand has triggered an impressive deployment of network infrastructure, including macro Base Stations (BSs) and Small Cells (SCs), leading to increased energy consumption and expenditures. However, the network underutilization during low traffic periods (e.g., night zone) enables the Mobile Network Operators (MNOs) to save energy by having their traffic served by third-party SCs, thus being able to switch off their BSs. In this paper, we propose a novel market approach to foster the opportunistic utilization of unexploited SCs capacity, where the MNOs lease the resources of third-party SCs and deactivate their BSs. Motivated by the conflicting interests of the MNOs and the restricted capacity of the SCs that is not adequate to carry the whole traffic in multioperator scenarios, we introduce a combinatorial auction framework, which includes: i) a bidding strategy, ii) a resource allocation scheme, and iii) a pricing rule. We propose a multiobjective framework to provide an energy efficient solution for the resource allocation problem and we provide extensive analytical and experimental results to estimate the potential energy savings.

The introduction of fourth-generation wireless technologies has fueled the rapid development of cellular networks, significantly increasing the energy consumption and the expenditures of mobile network operators (MNOs). In addition, network underutilization during low-traffic periods (e.g., night zone) has motivated a new business model, namely, infrastructure sharing, which allows the MNOs to have their traffic served by other MNOs in the same geographic area, thus enabling them to switch off part of their network. In this paper, we propose a novel infrastructure-sharing algorithm for multioperator environments, which enables the deactivation of underutilized base stations during low-traffic periods. Motivated by the conflicting interests of the MNOs and the necessity for effective solutions, we introduce a game-theoretic framework that enables the MNOs to individually estimate the switching-off probabilities that reduce their expected financial cost. Our approach reaches dominant strategy equilibrium, which is the strategy that minimizes the cost of each player. Finally, we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved in multioperator environments, incentivizing the MNOs to apply the proposed scheme.

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. The emerging data traffic demand has caused a massive deployment of network infrastructure, including Base Stations (BSs) and Small Cells (SCs), leading to increased energy consumption and expenditures. However, the network underutilization during low traffic periods enables the Mobile Network Operators (MNOs) to save energy by having their traffic served by third party SCs, thus being able to switch off their BSs. In this paper, we propose a novel market approach to foster the opportunistic utilization of the unexploited SCs capacity, where the MNOs, instead of requesting the maximum capacity to meet their highest traffic expectations, offer a set of bids requesting different resources from the third party SCs at lower costs. Motivated by the conflicting financial interests of the MNOs and the third party, the restricted capacity of the SCs that is not adequate to carry the whole traffic in multi-operator scenarios, and the necessity for energy efficient solutions, we introduce a combinatorial auction framework, which includes i) a bidding strategy, ii) a resource allocation scheme, and iii) a pricing rule. We propose a multiobjective framework as an energy and cost efficient solution for the resource allocation problem, and we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved. In addition, we investigate the conditions under which the MNOs and the third party companies should take part in the proposed auction.

The emerging data traffic demand has caused a massive deployment of network infrastructure, including Base Stations (BSs) and Small Cells (SCs), leading to increased energy consumption and expenditures. However, the network underutilization during low traffic periods enables the Mobile Network Operators (MNOs) to save energy by having their traffic served by third party SCs, thus being able to switch off their BSs. In this paper, we propose a novel market approach to foster the opportunistic utilization of the unexploited SCs capacity, where the MNOs, instead of requesting the maximum capacity to meet their highest traffic expectations, offer a set of bids requesting different resources from the third party SCs at lower costs. Motivated by the conflicting financial interests of the MNOs and the third party, the restricted capacity of the SCs that is not adequate to carry the whole traffic in multi-operator scenarios, and the necessity for energy efficient solutions, we introduce a combinatorial auction framework, which includes i) a bidding strategy, ii) a resource allocation scheme, and iii) a pricing rule. We propose a multiobjective framework as an energy and cost efficient solution for the resource allocation problem, and we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved. In addition, we investigate the conditions under which the MNOs and the third party companies should take part in the proposed auction.

Network infrastructure sharing and base station switching off mechanisms have been recently introduced as promising solutions toward energy and cost reduction in cellular networks. Although these techniques are usually studied independently, their combination offers new alternatives to MNOs for serving their users and could potentially provide them with additional benefits. In this article we introduce the concept of intra-cell roaming-based infrastructure sharing, where the MNOs may switch off their BSs and roam their traffic to active BSs operated by other MNOs in the same cell. Motivated by the coexistence of multiple operators in the same area, we present possible network deployments and architectures in current and future cellular scenarios, discussing their particular characteristics. In addition, we propose an innovative distributed game theoretic BS switching off scheme, employing an integrated cost function that takes into account all the different cases for a given operator to serve its own traffic (i.e. through active BSs of neighboring cells or exploiting intra-cell roaming-based infrastructure sharing). Finally, we demonstrate some indicative simulation results in realistic scenarios to quantify the potential energy and financial benefits that our proposed scheme offers to the MNOs in multi-operator environments, providing them with the necessary incentives to participate in the infrastructure sharing.