Improving relay based cellular networks performance in highly user congested and emergency situations

PhDRelay based cellular networks (RBCNs) are the technologies that incorporate multi-hop communication into traditional cellular networks. A RBCN can potentially support higher data rates, more stable radio coverage and more dynamic services. In reality, RBCNs still suffer from performance degradation in terms of high user congestion, base station failure and overloading in emergency situations. The focus of this thesis is to explore the potential to improve IEEE802.16j supported RBCN performance in user congestion and emergency situations using adjustments to the RF layer (by antenna adjustments or extensions using multi-hop) and cooperative adjustment algorithms, e.g. based on controlling frequency allocation centrally and using distributed approaches. The first part of this thesis designs and validates network reconfiguration algorithms for RBCN, including a cooperative antenna power control algorithm and a heuristic antenna tilting algorithm. The second part of this thesis investigates centralized and distributed dynamic frequency allocation for higher RBCN frequency efficiency, network resilience, and computation simplicity. It is demonstrated that these benefits mitigate user congestion and base station failure problems significantly. Additionally, interweaving coordinated dynamic frequency allocation and antenna tilting is investigated in order to obtain the benefits of both actions. The third part of this thesis incorporates Delay Tolerate Networking (DTN) technology into RBCN to let users self-organize to connect to functional base station through multi-hops supported by other users. Through the use of DTN, RBCN coverage and performance are improved. This thesis explores the augmentation of DTN routing protocols to let more un-covered users connect to base stations and improve network load balancin

Joint Trajectory-Task-Cache Optimization in UAV-Enabled Mobile Edge Networks for Cyber-Physical System

This paper studies an unmanned aerial vehicle (UAV)-enabled mobile edge network for Cyber-Physical System (CPS), where UAV with fixed-wing or rotary-wing is dispatched to provide communication and mobile edge computing (MEC) services to ground terminals (GTs). To minimize the energy consumption so as to extend the endurance of the UAV, we intend to jointly optimize its 3D trajectory and the task-cache strategies among GTs to save the energies spent on flight propulsion and GT tasks. Such joint trajectory-task-cache problem is difficult to be optimally solved, as it is non-convex and involves multiple constraints. To tackle this problem, we reformulate the optimizing of task offloading and cache into two tractable linear program (LP) problems, and the optimizing of UAV trajectory into three convex Quadratically Constrained Quadratically Program (QCQP) problems on horizontal trajectory, vertical trajectory and flight time of the UAV respectively. Then a block coordinate descent algorithm is proposed to iteratively solve the formed sub-problems through a successive convex optimization (SCO) process. A high-quality sub-optimal solution to the joint problem then will be obtained, after the algorithm converging to a prescribed accuracy. The numerical results show the proposed solution significantly outperforms the baseline solution

Characterization of a sol-gel derived CuO/CuAl2O4 oxygen carrier for chemical looping combustion (CLC) of gaseous fuels: relevance of gas-solid and oxygen uncoupling reactions

A new sol–gel CuO/CuAl2O4 material was characterized in a thermogravimetric analyzer (TGA) for chemical looping combustion (CLC) with gaseous fuels, including the relevance of the oxygen uncoupling mechanism in oxygen transference was considered. This material possesses high reactivity and oxygen transport capacity, which combines the best features of the previously reported impregnated and spray-dried materials. During the cycles with N2 and air, CuO was fully decomposed into Cu2O in N2 and then regenerated to CuO in air, similarly to chemical looping with oxygen uncoupling (CLOU) for solid fuels. Decomposition of CuAl2O4 to CuAlO2 was quite slow, and the followed regeneration cannot be accomplished. Subsequently, the adequate and stable reaction rates of this material were examined in high numbers of cycles (>50 cycles) with gaseous fuels. The material undergone such cycles with gaseous fuels was then subjected to cycles with N2 and air. Segregation of CuO from Al2O3 in the CuAl2O4 was observed during gaseous fuels combustion, which produced more available oxygen for CLOU than the initial material. Finally, the relative importance of gas–solid reactions in CLC against oxygen uncoupling in CLOU was examined with the appearance of gaseous fuel.This work was supported by “National Natural Science Foundation of China (51390494)”, and “National Basic Research and Development Program (2011CB707300)”. Daofeng Mei is grateful for the support provided by the China Scholarship Council (CSC201306160054).National Natural Science Foundation of ChinaChinese Scholar CouncilPeer reviewe

Topological quantum transition driven by charge-phonon coupling in higher-order topological insulators

We investigate a second-order topological quantum transition of a modified Kane-Mele model driven by electron-phonon interaction. The results show that the system parameters of the bare modified Kane-Mele model are renormalized by the electron-phonon interaction. Starting from the second-order topological phase for the bare model, the increasing electron-phonon coupling strength can drive the second-order topological insulator into a semimetal phase. Such a secondorder topological phase transition is characterized by the band-gap closing, discontinuity of averaged ferminoic number and topological invariant.Comment: 8 pages,6 figure

Characteristics of multiple‐year nitrous oxide emissions from conventional vegetable fields in southeastern China

The annual and interannual characteristics of nitrous oxide (N2O) emissions from conventional vegetable fields are poorly understood. We carried out 4 year measurements of N2O fluxes from a conventional vegetable cultivation area in the Yangtze River delta. Under fertilized conditions subject to farming practices, approximately 86% of the annual total N2O release occurred following fertilization events. The direct emission factors (EFd) of the 12 individual vegetable seasons investigated ranged from 0.06 to 14.20%, with a mean of 3.09% and a coefficient of variation (CV) of 142%. The annual EFd varied from 0.59 to 4.98%, with a mean of 2.88% and an interannual CV of 74%. The mean value is much larger than the latest default value (1.00%) of the Intergovernmental Panel on Climate Change. Occasional application of lagoon‐stored manure slurry coupled with other nitrogen fertilizers, or basal nitrogen addition immediately followed by heavy rainfall, accounted for a substantial portion of the large EFds observed in warm seasons. The large CVs suggest that the emission factors obtained from short‐term observations that poorly represent seasonality and/or interannual variability will inevitably yield large uncertainties in inventory estimation. The results of this study indicate that conventional vegetable fields associated with intensive nitrogen addition, as well as occasional applications of manure slurry, may substantially account for regional N2O emissions. However, this conclusion needs to be further confirmed through studies at multiple field sites. Moreover, further experimental studies are needed to test the mitigation options suggested by this study for N2O emissions from open vegetable fields

On a highly reactive Fe2O3/Al2O3 oxygen carrier for in situ gasification chemical looping combustion

Interest in the direct use of solid fuel in chemical looping combustion (CLC) technology makes the in-situ Gasification Chemical Looping Combustion (iG-CLC) an attractive approach for the low-cost capture of CO2. Highly reactive material is required in iG-CLC in order to achievea fast reaction between the fuel and oxygen carrier. In this work, a material,Fe2O3/Al2O3 synthesized by sol-gel,was evaluated in a fluidized-bed reactor by reaction with lignite. This is the first time sol-gel-derived Fe2O3/Al2O3 material has been used in an iG-CLC process. Operation conditions, including steam content in the fluidization gas, temperature and potential oxygen ratio were investigated to explore their influence on combustion and char conversion. The results show that a higher steam concentration can greatly enhance the rate of char gasification and hence the reaction between the lignite and the oxygen carrier, where as a negligible effect of the steam content was noticed on volatile combustion. In addition, the use of the highly reactive Fe-based material prepared by the sol-gel method significantly increased the char gasification rate as compared to other previously evaluated materials. Moreover, the combustion efficiencies of volatiles and char from the lignite,respectively,were studied. Using the Fe2O3/Al2O3 material enabled a low oxygen carrier inventory of 600 kg/MWth to be reached in order to achieve 99% char combustion, which is much lower than that reported in other works. These findings suggest that Fe2O3/Al2O3 prepared by sol-gel is a highly reactive oxygen carrier for iG-CLC.This work was supported by “National Natural Science Foundation of China (51390494)”, and “National Basic Research and Development Program (2011CB707300)”. Daofeng Mei is grateful for the support provided by the Chinese Scholar Council (CSC201306160054). Appreciation is also shown to the staff of the Analytical and Testing Center, Huazhong University of Science and Technology for the related experimental analysis.National Natural Science Foundation of ChinaChinese Scholar CouncilPeer reviewe

Multi-Layer Cloud-RAN With Cooperative Resource Allocations for Low-Latency Computing and Communication Services

To improve low-latency computing and communication services, a new type of mobile edge computing architecture named multi-layer cloud radio access network (Multi-layer CRAN) is designed in this paper. In Multi-layer CRAN, a high-level edge cloud is deployed next to base band unit pool to handle the computing tasks of user equipment (UE) in centralized way. Meanwhile, a low-level edge cloud is deployed in each remote radio head (RRH) to locally handle UEs' computing tasks in a distributed way. Based upon Multi-layer CRAN, a cooperative communication and computation resource allocation (3C-RA) algorithm is further designed for lower service latency and energy cost, and higher network throughput in this paper. 3C-RA utilizes a distributed RRH cell coloring algorithm to enable each RRH to work out the resource allocation in an efficient and distributed way. 3C-RA employs a proportional fairness-based approach to allocate communication and computation resource in each RRH cell. A series of simulations on Multi-layer CRAN with 3C-RA were carried out. The simulation results validate that Multi-layer CRAN is more capable of providing low-latency computing and communication services, and 3C-RA enables Multi-layer CRAN to have lower service latency and energy cost and higher network throughput

Joint Resource Allocation Algorithm for Energy Harvest-based D2D Communication Underlaying Cellular Networks Considering Fairness

In this paper, we aim to maximize the minimum data volume for the energy harvest (EH)-based D2D communication underlaying cellular network. The formulated problem is a mixed integer nonlinear programming (MINLP), which we split into two sub-problems to solve separately. We first employ the Successive Convex Approximation (SCA) method to solve the time and power allocation, while putting the spectrum multiplexed pairs as fixed. Then, we develop a fair allocation mechanism to allocate spectrum resources. Numerical results show that our developed algorithm outperforms other benchmark schemes in terms of the minimum and overall data volumes

Joint Cache Content Placement and Task Offloading in C-RAN Enabled by Multi-Layer MEC

In this paper, we work on a Cache and Multi-layer MEC enabled C-RAN (CMM-CRAN) to handle various user tasks with minimized latency and energy cost. We intend to solve two particular problems of CMM-CRAN. First, because CMM-CRAN has to maximally cache the most frequently requested data from Service Provide Server (SPS) to Remote Radio Head (RRH) and later offered to proximity mobile users, the cache content placement from SPSs to RRHs becomes a many-to-many matching problem with peer effects. Second, because of multi-layer MEC, a user task has to be dynamically controlled to be offloaded to the best fit cloud, i.e., either local MEC or remote MEC, to get served. This dynamic task offloading is a Multi-Dimension Multiple-Choice Knapsack (MMCK) problem. To solve these two problems, we provide a Joint Cache content placement and task Offloading Solution (JCOS) to CMM-CRAN that utilizes Proportional Fairness (PF) as the user scheduling policy. JCOS applies a Gale-Shaply (GS) method to work out the cache content placement, and a Population Evolution (PE) game theory coupled with a use of Analytic Hierarchy Process(AHP) to work out the dynamic user task offloading. According to the simulation results, CMM-CRAN with JCOS is proved to be able to provide highly desired low-latency communication and computation services with decreased energy cost to mobile users

Synthesis of Aminoalkyl Sclareolide Derivatives and Antifungal Activity Studies

Sclareolide was developed as an efficient C-nucleophilic reagent for an asymmetric Mannich addition reaction with a series of N-tert-butylsulfinyl aldimines. The Mannich reaction was carried out under mild conditions, affording the corresponding aminoalkyl sclareolide derivatives with up to 98% yield and 98:2:0:0 diastereoselectivity. Furthermore, the reaction could be performed on a gram scale without any reduction in yield and diastereoselectivity. Additionally, deprotection of the obtained Mannich addition products to give the target sclareolide derivatives bearing a free N-H group was demonstrated. In addition, target compounds 4–6 were subjected to an antifungal assay in vitro, which showed considerable antifungal activity against forest pathogenic fungi.Financial support from the National Natural Science Foundation of China (Nos. 21761132021 and 21606133) and IKERBASQUE, Basque Foundation for Science