Deployment Strategies of Multiple Aerial BSs for User Coverage and Power Efficiency Maximization

Unmanned aerial vehicle (UAV) based aerial base stations (BSs) can provide rapid communication services to ground users and are thus promising for future communication systems. In this paper, we consider a scenario where no functional terrestrial BSs are available and the aim is deploying multiple aerial BSs to cover a maximum number of users within a certain target area. To this end, we first propose a naive successive deployment method, which converts the non-convex constraints in the involved optimization into a combination of linear constraints through geometrical relaxation. Then we investigate a deployment method based on K-means clustering. The method divides the target area into K convex subareas, where within each subarea, a mixed integer non-linear problem (MINLP) is solved. An iterative power efficient technique is further proposed to improve coverage probability with reduced power. Finally, we propose a robust technique for compensating the loss of coverage probability in the existence of inaccurate user location information (ULI). Our simulation results show that, the proposed techniques achieve an up to 30% higher coverage probability when users are not distributed uniformly. In addition, the proposed simultaneous deployment techniques, especially the one using iterative algorithm improve power-efficiency by up to 15% compared to the benchmark circle packing theory

Energy aware network optimization with aerial base stations

To meet the fast-growing and highly diversified traffic demand, it is envisioned that unmanned aerial vehicles (UAVs), also known as drones, will become an indispensable part in the future communication system. Since UAVs are flexible, cost-effective, fast to deploy and have a better communication condition compared to terrestrial communication system, the use of drones is promising in a wide range of wireless networking applications. By moving closer to the targets, UAVs can act as data collectors to prolong the lifetime of wireless sensor networks (WSNs) or be used as energy transmitters to transfer more energy in wireless power transfer (WPT) scenarios. In particular, UAV based aerial base stations (BSs) have the ability to provide rapid and reliable wireless services wherever and whenever there is an excessive data demand and has become increasingly appealing to network service providers. In this thesis, we focus on UAVs serving as BSs to provide wireless services to ground users from the sky. Firstly, we consider the power-efficient deployment of multiple static aerial BSs, with the aim of covering a maximum number of ground users while avoiding inter-cell interference (ICI). The proposed techniques achieve an up to 30% higher coverage probability than the benchmark circle packing theory (CPT) when users are not distributed uniformly. In addition, the proposed iterative algorithm also greatly improves the power-efficiency by up to 15%. Secondly, by fully exploiting the mobility of UAVs, we study the trajectory and UAV-user scheduling and association of moving aerial BSs. The bottom line aim of UAV application, where an aerial BS is dispatched to satisfy the data demand of a maximum number of ground users with a given energy budget is considered. It is found that the moving aerial BS tends to move close to the targeted ground users to reduce path loss and enjoy a good communication condition. Simulation results show both energy and coverage performance gains for the proposed schemes compared to the benchmark technique

Developing aqueous porous carbons for biogas upgrading

Developing novel sorbents is essential for biogas upgrading. In this study, mixed sorbents of aqueous porous carbons were developed to separate CO2 from the biogas, where the porous carbon with the developed micropore structure was identified as the most desirable constituent. Both thermodynamics and kinetics were studied experimentally, and Henry’s constant (KH) and the liquid-side mass-transfer coefficient (kL) of CO2 in the mixed sorbent as well as the selectivity of CO2/CH4 were obtained accordingly. Furthermore, the CO2 separation performance was evaluated with a proposed index, and the cost of biogas upgrading using the mixed sorbent was estimated and compared. The results showed that the porous carbon with the developed micropore structure led to better performance on KH and kL of CO2 in the mixed sorbent, and the mixed sorbent with 3.03 wt% porous carbon exhibited the best CO2 separation performance, reducing 36.2 % in cost compared to the current technologies.Validerad;2023;Nivå 2;2023-10-11 (joosat);CC BY 4.0 LicenseFunder: National Natural Science Foundation of China (No. 22108115)</p

Protocol for efficient and self-healing near-infrared perovskite light-emitting diodes.

Preparation of highly efficient and stable perovskite light-emitting diodes (PeLEDs) with reproducible device performance is challenging. This protocol describes steps for fabrication of high-performance and self-healing PeLEDs. These include instructions for synthesis of charge-transporting zinc oxide (ZnO) nanocrystals, step-by-step device fabrication, and control over self-healing of the degraded devices. For complete details on the use and execution of this protocol, please refer to Teng et al. (2021).Funding agencies: RC Starting Grant (no. 717026), the Swedish Energy AgencyEnergimyndigheten (no. 48758-1), and the Swedish Government Strategic Research Area in Mate-rials Science on Functional Materials Linko ̈ ping University (Faculty Grant SFO-Mat-LiU no. 2009-00971). Y.Z. and B.S. also thank the support from Macau SAR (file no. 0044/2021/A)</p