能源互联网下基于储能调度及多源供能的数据中心能效优化

近年来,数据中心能效优化问题得到业界的普遍关注.同时,能源互联网的发展为数据中心能效优化问题提供了新的研究思路.能源互联网中的用户,尤其是大型的工业用户,通常具备一定的储能能力和一定的智能化能源管理能力.随着清洁能源的大规模部署以及售电公司的快速发展,数据中心等大型能耗用户也随之获得购电的选择权,可以根据电价、清洁程度等因素,从不同的能源供应商购买能源,从而降低能源成本,提高能效.研究表明在污染指数及实时电价的调节下,用户更趋向于在用电低谷期买入更多廉价且清洁的能源.因此,一方面综合考虑污染指数函数与实时电价,构建多源购电成本模型;另一方面综合考虑储能的操作成本及潜在收益成本,构建储能充放电成本模型,简称储能成本模型.以此为基础,建立了有储能系统下的数据中心多源能源选择模型,并与无储能时序调度策略时的系统性能做了对比.仿真结果表明:提出的模型可以通过对储能时序及多源能源选择的综合优化,一定程度上降低数据中心的日能源成本,同时提高清洁能源利用率.

痛风急性关节炎期双源CT的应用价值

目的:探讨双源CT(DSCT)在痛风急性关节炎期的影像表现和诊断价值。方法:回顾性分析88例以关节红肿热痛为首发症状入院的患者的DSCT影像表现。结果:88例患者中,80例临床确诊为痛风急性关节炎,其中有58例痛风患者CT图像中发现尿酸盐结晶,诊断灵敏度72.5%,尿酸盐结晶在痛风急性关节炎期以单发关节内为主。结论:DSCT对痛风急性关节炎诊断具有较高的价值,为临床诊断提供了可靠的依据。

SWN: An SDN Based Framework for Carrier Grade WiFi Networks

With the rapid growth of mobile data traffic and vast traffic offloaded from cellular network, Wi-Fi has been considered as an essential component to cope with the tremendous growth of mobile data traffic. Although operators have deployed a lot of carrier grade Wi-Fi networks, but there are still a multitude of arrears for nowadays Wi-Fi networks, such as supporting seamless handover between APs, automatic network access and unified authentication, etc. In this paper, we propose an SDN based carrier grade Wi-Fi network framework, namely SWN. The key conceptual contribution of SWN is a principled refactoring of Wi-Fi networks into control and data planes. The control plane has a centralized global view of the whole network, can perceive the underlying network state by network situation awareness(NAS) technique, and bundles the perceived information and network management operations into northbound Application Programming Interface(API) for upper applications. In the data plane, we construct software access point(SAP) to abstract the connection between user equipment(UE) and access point(AP). Network operators can design network applications by utilizing these APIs and the SAP abstraction to configure and manage the whole network, which makes carrier grade Wi-Fi networks more flexible, user-friendly, and scalable.

Cross-layer resource allocation based on potential game theory in multi-cell OFDMA networks

A cross-layer resource allocation scheme based on potential game(CLRA_ PG) is proposed for the downlink multi-cell orthogonal frequency-division multiple-access(OFDMA) system with universal frequency reuse.As a method to mitigate inter-cell interference(ICI),base station coordination has been considered.In the process of the objective function modeling,this paper adopts a pricing mechanism which not only maximizes the individual utility but also considers the interference to other users.Based on the potential game theory,the objective problem is converted to a potential function which can be easily solved.The Karush-Kuhn-Tucker(KKT) conditions and the iterative water-filling algorithm are employed to solve the constraint objective optimization problem.Moreover,extensive simulations are conducted to evaluate how the pricing factors affect the algorithm.At the same time,comparing with the traditional policy,our simulation results show that the proposed scheme can significantly improve the performance of the system.

蜂窝移动网络低成本高精度授时

传统的网络授时和卫星授时方法受制于授时精度和部署环境,难以满足移动网络业务对高精度同步的需求。针对这一问题,提出了一种移动终端低成本基带授时模组设计,并基于软件定义了无线电的移动通信基站和展锐模组,实现了原型授时系统。定义了移动网络授时端到端的误差源模型和基于空中接口物理层信号的网络授时技术的原理,并重点阐述了如何基于授时信令精确下发绝对时间及如何基于多种空口物理层信号的时延估计补偿、误差感知、鲁棒的机制和统计补偿等方法在移动网络中实现亚微秒的同步精度。实验结果表明,单次空口授时精度优于10^(-7)s。

面向多样化需求的网络切片业务链部署

网络切片通过业务链部署来实现切片的创建和编排。针对网络切片中的业务链部署,考虑了业务链的多样化需求,并引入了虚拟网络功能共享和准入控制,以降低部署成本并提高业务链的接受率。将上述问题建模成一个最大化网络净收益的优化模型,提出了部署算法。仿真结果表明,所提的部署算法优于已有的基准算法,能达到接近最优的性能。

Performance analysis of LTE-U coexistence network with WiFi using queueing model

The unforeseen mobile data explosion as well as the scarce of spectrum resource pose a major challenge to the performance of today＇s cellular networks which are in urgent need of novel solutions to handle such voluminous mobile data. Long term evolution-unlicensed （LTE-U）, which extends the LTE standard operating on the unlicensed band, has been proposed to improve system throughput. In LTE-U system, arriving users will contend the unlicensed spectrum resource with wireless fidelity （WiFi） users to transmit data information. Nevertheless, there is no clear consensus as to the benefits of transmission using unlicensed bands for LTE users. To this end, in this paper an analytical model is presented based on a queue system to understand the performance achieved by unlicensed based LTE system taking quality of services （QoS） and LTE-U users＇ behaviors into account. To obtain the stead-state solutions of the queue system, a matrix geometric method is used to solve it. Then, the average delay and utilization of unlicensed band for the LTE-U users is derived by using the queuing model. The performance of LTE-U coexistence is evaluated with WiFi using the proposed model and provide some initial insights as to the advantage of LTE-U in practice.

Joint hybrid beamforming and power splitting design in millimeter-wave simultaneous wireless information and power transfer system

A joint hybrid beamforming and power splitting(JHBPS) design problem for simultaneous wireless information and power transfer(SWIPT) in millimeter-wave(mmWave) system is studied.The considered scenario is a multi-antenna base station(BS) transfers information and energy simultaneously to multiple single-antenna receivers.BS adopts hybrid digital and analog beamforming architecture to reduce hardware costs.Receivers separate acquired signals with power splitters either for information decoding(ID) or energy harvesting(EH).The aim is minimizing total transmission power by joint design of hybrid beamforming and PS under ID and EH requirements.It is difficult to obtain the optimal hybrid beamformer directly since the analog beamformer and digital beamformer are multiplied.Therefore,a two-stage algorithm is proposed to solve the problem.In the first stage,the optimal beamformer and PS ratios are obtained by solving the joint transmission beamforming and PS design problem.In the second stage,the optimal beamformer is approximated with the product of analog beamformer and digital beamformer.The superiority of proposed algorithm over the existing algorithms is demonstrated through simulations.Moreover,the effectiveness of approximation algorithm is testified.

Improving throughput through dynamically tuning contention window size in dense wireless network

With the boom of wireless devices, the number of wireless users under wireless local area networks （WLANs） has increased dramatically. However, the standard baekoff mechanism in IEEE 802.11 adopts fixed initial contention window （CW） size without considering changes of network load, which leads to a high collision probability and low channel utilization in bursty arrivals. In this paper, a novel CW dynamic adjustment scheme is proposed to achieve high throughput performance in dense user environment. In the proposed scheme, the initial CW size is dynamically adjusted to optimum according to the measured packet collision probability. Simulation results show that the proposed scheme can significantly improve the throughput performance.

Adaptive WiFi-offloading algorithm based on attractor selection in heterogeneous wireless networks

The unforeseen mobile data explosion poses a major challenge to the performance of today＇s cellular networks, and cellular networks are in urgent need of novel solutions to handle such voluminous mobile data. Obviously, data offioading through third-party WiFi access points （APs） can effectively alleviate the data load in the cellular networks with a low operational and capital expenditure. In this paper, we propose and analyze an adaptive WiFi-offioading algorithm based on attractor selection in heterogeneous wireless networks. In the proposed WiFi-offloading algorithm, the WiFi system throughput and cellular throughput in the coverage area of WiFi, are mapped into the activity of the attractor, which is the reflector of the current network environment. When the current attractor activity is low, the network is dominated by the noise. Then, the noise triggers the controller to select adaptive attractor, an optimal WiFi-offloading ratio 4, to adapt to the dynamic network environment. And users offload the specific portion of traffic to the WiFi networks with the ratio of φ, which improves the throughput of heterogeneous wireless networks and alleviates the load of cellular networks. Through simulation, we show that the proposed WiFi-offioading algorithm outperforms the existing ones with 21% higher heterogeneous network throughput in a dense traffic environment.

On-line learning algorithm for dynamic sensitivity control in IEEE 802. 11ax network

The popularity of IEEE 802. 11 based wireless local area network（ WLAN） increased significantly in recent years and resulted in the dense deployment of WLANs. While densification can contribute to increasing coverage,it could also lead to increasing interference and cannot insure high spatial reuse due to the current physical carrier sensing of IEEE 802. 11. To tackle these challenges,the dynamic sensitivity control（ DSC） is considered in IEEE802. 11 ax,which dynamically selects the appropriate carrier sensing threshold（ CST） to improve spectrum efficiency and enhance spatial reuse in densely deployed network. A dynamic Q-learning based CST selection method is proposed to enable a network to select the optimal CST according to the channel condition. Simulation results show that the proposed scheme provides 40% aggregate throughput gain of a dense network when compared with legacy IEEE 802. 11.

Performance analysis and enhancement of random access process in cellular-IoT

Narrowband Internet of things(NB-IoT) and enhanced machine-type communications(eMTC) are two new IoT-oriented solutions introduced by the 3 rd generation partnership project(3 GPP) in Rel-13. In order to meet the new requirements(such as long battery life, low device cost, low deployment cost, extended coverage and support for a massive number of devices) of machine-to-machine(M2 M) communication, these two technologies had some improvements on the random access(RA) mechanism compared to traditional long term evolution(LTE). For example, repetition of preamble transmission and coverage enhancement(CE) levels have been proposed to offer communication services in a wider area. In addition, NB-IoT has adopted a new spectrum allocation method and proposed a new type of preamble structure to meet the requirement of big amount of connections. We summarize details and differences of the RA process in LTE, eMTC and NB-IoT. Afterwards, as an improvement, we propose an enhanced access protocol for NB-IoT. Finally, performance analysis and comparison are presented in terms of access success probability, average access delay, access spectrum efficiency and average number of RA attempts.

Joint system consumption minimization and workload allocation in edge-core network

The explosive increase of smart devices and mobile traffic results intolerable network latency and degraded service to the end-users. in heavy burden on backhaul and core network, As a complement to core network, edge network contributes to relieving network burden and improving user experience. To investigate the problem of optimizing the total consumption in an edge-core network, the system consumption minimization problem is fromulated, considering the energy consumption and delay. Given that the formulated problem is a mixed nonlinear integer programming （MNIP） , a low-complexity workload allocation algorithm is proposed based on interior-point method. The proposed algorithm has an extremely short running time in practice. Finally, simulation results show that edge network can significantly complement core network with much reduced backhaul energy consumption and delay.

Spectrum efficiency maximization with trajectory design in UAV-enabled mobile relaying

With the advantages of low cost and high mobility,unmanned aerial vehicles(UAVs)have played an important role in wireless communication.We investigate a UAV-enabled mobile relaying system,where a UAV is used as a mobile relay to assist in the communication from a ground source to a ground destination since their direct link is blocked.Unlike the conventional mobile relay in which the UAV adopts straight line or circular trajectory,we consider a more general elliptical trajectory and use realistic channel models.By assuming that the UAV employs time-division duplexing(TDD)based decode-and-forward(DF)relaying,we jointly optimize the time allocations and the UAV trajectory to formulate the maximization of spectrum efficiency(SE).The simulation results show that the trajectory we designed achieves a higher SE than the optimal circular trajectory and static relaying.

Service-oriented network performance evaluation framework based on LA-FAHP

Since the different characteristics of various network services determine that their requirements for network are also disparate, the performance of one network varies according to the services running on it. However, most of previous network performance evaluation （NPE） researches conduct evaluations based on the network parameters, but without considering from the perspective of specific service running on the network. In view of this issue, a novel service-oriented NPE framework is proposed. First, the characteristics discrepancy among different types of services are investigated. Next, in order to conduct comprehensive evaluation of multiple services, an enhanced low-complexity adaptive （LA）-fuzzy analytical hierarchy process （FAHP） is introduced; meanwhile by applying the experts-construct-directly （ECD） algorithm proposed later, the consistency check required in previous studies can be omitted, thereby significantly reducing the computation complexity and assessment workload for experts. Then, in accordance with the features of each service, corrections are made to their respective membership functions, thus making the proposed LA-FAHP adaptive to various service evaluation scenarios. The subsequent comparison with other NPE methods well proves the effectiveness and high sensitivity of proposed framework, and the analysis verifies the low computation complexity of the proposed algorithms as well.

Robustness analysis of interdependent PV grids and communication network based on complex network

Currently,the photovoltaic（ PV） cloud network is an important research point in energy Internet. From the perspective of the robustness analysis of PV cloud network,traditional robustness index,the relative size of the giant connected component before and after the cascading,which is focused on the giant component,is not appropriate for the distributed PV network because of the big difference between PV generators and large power grid. In this paper,a new index is proposed,the minimum removed nodes number（ MRNN）,which can make the entire system collapse,to evaluate the robustness of PV cloud network system. Simulation results show that MRNN can clearly indicate the system robustness under different parameters.

Pre-scan based fast handoff scheme for enterprise IEEE 802.11 networks

In IEEE 802.11 networks, many access points（APs） are required to cover a large area due to the limited coverage range of APs, and frequent handoffs may occur while a station（STA） is moving in an area covered by several APs. However, traditional handoff mechanisms employed at STAs introduce a few hundred milliseconds delay, which is far longer than what can be tolerated by some multimedia streams such as voice over Internet protocol（Vo IP）, it is a challenging issue for supporting seamless handoff service in IEEE 802.11 networks. In this paper, we propose a pre-scan based fast handoff scheme within an IEEE 802.11 enterprise wireless local area network（EWLAN） environment. The proposed scheme can help STA obtain the best alternative AP in advance after the pre-scan process, and when the handoff is actually triggered, STA can perform the authentication and reassociation process toward the alternative AP directly. Furthermore, we adopt Kalman filter to minimize the fluctuation of received signal strength（RSS）, thus reducing the unnecessary pre-scan process and handoffs. We performed simulations to evaluate performance, and the simulation results show that the proposed scheme can effectively reduce the handoff delay.

Reduced frame set on wireless distorted video for quality assessment

Objective video quality assessment methods often evaluate all the frames regardless of their importance. For wireless distorted videos, not every frame has the same contribution to the final overall quality due to the channel fading and interference, which may lead to the capacity variation in temporal. Besides, with the content similarity and error propagation pattern in temporal domain, it is possible to evaluate the overall quality with only part of the frames. In this paper, a demonstration is performed to show that the video quality can be evaluated with reduced frames set（RFS）, and a state transition model is proposed to extract the RFS. At last, a video quality assessment（VQA） method is carried out based on RFS. Compared with several state-of-the-art methods, our method can achieve a suitable accuracy with less frames to be processed.

QoE based power control scheme for interference mitigation in high-density WLANs

Mobile data traffic is going through an explosive growth recently as mobile smart devices become more and more ubiquitous, causing huge pressure on cellular network. Taking advantage of its low cost and easy-to-deploy feature, wireless local-area networks（WLAN） becomes increasingly popular to offload data streams from cellular network, followed by higher and higher density of its deployment. However, the high density of WLAN will cause more interference, which results in degradation of its performance. Therefore, in order to enhance the performance of the network, we aim to minimize the interference caused by high density of WLAN. In this paper, we propose a novel power control scheme to achieve the above aim. We use the quality of experience（QoE） evaluation to coordinate the power of each access point（AP） and finally realize the optimization of the entire network. According to the simulation results, our scheme improves the performance of the network significantly in many aspects, including throughput and QoE.

Best-effort service QoE assessment using visual information based Weber-Fechner law

Quality of experience（QoE） has been one of the most important factors for service providers and operators to develop and deploy services. Previous works have shown that Weber-Fechner law（WFL） can be used to promote the accuracy of best-effort（BE） services＇ QoE assessment. In this paper, based on WFL, we take a deep insight into the visual information of BE services and its role in WFL, especially in web browsing services, and propose an enhanced QoE assessment model for BE services by taking the visual information into account. Both images and texts visual information are extracted and combined to get the visual information for web pages. Finally, a subjective experiment is performed to validate performance of proposed QoE assessment model, which shows that it performs better than traditional WFL based model.