A control theoretic approach to achieve proportional fairness in 802.11e EDCA WLANs

This paper considers proportional fairness amongst ACs in an EDCA WLAN for provision of distinct QoS requirements and priority parameters. A detailed theoretical analysis is provided to derive the optimal station attempt probability which leads to a proportional fair allocation of station throughputs. The desirable fairness can be achieved using a centralised adaptive control approach. This approach is based on multivariable statespace control theory and uses the Linear Quadratic Integral (LQI) controller to periodically update CWmin till the optimal fair point of operation. Performance evaluation demonstrates that the control approach has high accuracy performance and fast convergence speed for general network scenarios. To our knowledge this might be the first time that a closed-loop control system is designed for EDCA WLANs to achieve proportional fairness

Physical Properties Of Wave Scattering By Chiral Periodic Structure

Attention has been focused on electromagnetic chirality and its potential applications to microwave, millimeter wave and optical wave devices. In this work, wave propagation through a chiral periodic structure with arbitrary shape is investigated. Although perturbation theory and coupled-mode theory have been used to analyze chiral periodic structure, those are approximate methods and can only be used for low frequency applications. In this work, the rigorous mode-matching method is used to solve the problem. Staircase approximation is introduced to change the curved structure to a multilayer structure. The field solutions in the uniform air regions and unbounded air-chiral periodic array have been derived. Finite element method is used to solve the eigenvalues and eigenfunctions in the periodic chiral slabs. Mode-matching method is used at the boundaries to calculate the scattering characteristics. Numerical results are displayed to explain the underlying physical properties of the chiral periodic structure. The Wood\u27s anomalies at high frequencies have been investigated and explained by the excitation of leaky waves guided along the periodic layer. The influence of frequency, chirality parameter, incident angle, curve shape and period are discussed. It has been found that the chiral periodic structure can be used as both a frequency selective device and a mode conversion device. First, the derivation and numeric calculation were done with the principal plane incidence. Then, the discussion was extended to the more general case of oblique incidence by the coordinate transformation

Intelligent Cold Supply Chain Management System with Radio Frequency Identification, Global Positioning System, and Wireless Sensor Network

This thesis establishes an intelligent cold supply chain management system which consists of two parts: one is the intelligent tracking system integrated with Radio Frequency Identification (RFID), Global Positioning System (GPS), and Wireless Sensor Network (WSN); the other is the cold supply chain model. This tracking system is mainly designed to monitor the food products during the transport, including two parts, a data terminal and a data server. The data terminal is installed inside a container, comprised of GPS, Bluetooth, industrial computer, WSN, RFID reader, RFID antenna, and Code Division Multiple Access (CDMA) modem. The data server is a computer which is able to access internet and has one Structured Query Language (SQL) database. Related application programs are developed with JAVA language. The whole system is successfully tested and meets the expectations we desired at the beginning. In this study, a refrigerator is used to simulate the environment of the container. The data terminal collects all information, including temperature inside the container, GPS location, Product's Identification, and current time in five minute intervals (customers will be asked to set this time interval at the beginning). CDMA cellular network provides the communication between the data server and the data terminal. The data server receives all information and saves the information in the SQL database, which can be used to predict the food safety. Advantages of this tracking system include the ability: 1) to trace and track the products starting from the suppliers to retailers; 2) to monitor and store important parameters during the processing and distribution of food products, such as temperature; 3) to communicate in real time for prompt response; and 4) to quantify food safety prediction. The objective of the model developed in this study is to maximize the profit of the cold supply chain. There are one distribution center, multiple retailers and suppliers involved in the cold supply chain. Since the real-time quality situations of products are available even during the transport, retailers can set prices of products based on the real quality situation. The company is able to dynamically plan the quantity of distribution from the distribution or suppliers' site. In addition, retailers are able to manage the inventory based on the real shelf life of products. This thesis also concludes all different inventory results for retailers under different scenarios which can help retailers to predict and manage the inventory. The optimization software, Lindo, is used to demonstrate that this model is capable to dynamically plan the distribution quantity. The sensitivity analysis for prices, transportation costs, and holding costs is discussed to simulate different situations during the transportation and distribution

Spatiotemporal Variations of Precipitation and Climate-Resilient Structure Design in Virginia

How to consider effects of climate change on the design and management of hydrology related infrastructure is crucial but remains a challenge for sustaining resilient society. To address this challenge, existing hydrologic design procedures may need to be revised and/or redeveloped to take into account the precipitation non-stationarity resulting from climate change. Using the state of Virginia as a testbed and advanced statistical techniques such as nonparametric test, spatial autocorrelation, linear regression, distribution fitting, and spatial interpolation, this dissertation developed an innovative framework to detect the historical spatiotemporal variations of various precipitation characteristics, namely maximum precipitation intensity, precipitation amount, simple precipitation intensities, dry and wet spells, precipitation maximums, and precipitation exceedances. The results indicated that the state of Virginia has been experiencing more storms with a larger magnitude, a longer duration, and a greater intensity, making it vital to revisit the existing water management policies and engineering design standards. In this regard, next-generation probability-based IDF curves that consider the precipitation non-stationarity were created using both historical and predicted precipitations for Virginia. Such IDF curves can be a handy and useful tool for practical engineers to size hydraulic structures under nonstationary climates