Towards the Quality of Service for VoIP traffic in IEEE 802.11 Wireless Networks

The usage of voice over IP (VoIP) traffic in IEEE 802.11 wireless networks is expected to increase in the near future due to widely deployed 802.11 wireless networks and VoIP services on fixed lines. However, the quality of service (QoS) of VoIP traffic in wireless networks is still unsatisfactory. In this thesis, I identify several sources for the QoS problems of VoIP traffic in IEEE 802.11 wireless networks and propose solutions for these problems. The QoS problems discussed can be divided into three categories, namely, user mobility, VoIP capacity, and call admission control. User mobility causes network disruptions during handoffs. In order to reduce the handoff time between Access Points (APs), I propose a new handoff algorithm, Selective Scanning and Caching, which finds available APs by scanning a minimum number of channels and furthermore allows clients to perform handoffs without scanning, by caching AP information. I also describe a new architecture for the client and server side for seamless IP layer handoffs, which are caused when mobile clients change the subnet due to layer 2 handoffs. I also present two methods to improve VoIP capacity for 802.11 networks, Adaptive Priority Control (APC) and Dynamic Point Coordination Function (DPCF). APC is a new packet scheduling algorithm at the AP and improves the capacity by balancing the uplink and downlink delay of VoIP traffic, and DPCF uses a polling based protocol and minimizes the bandwidth wasted from unnecessary polling, using a dynamic polling list. Additionally, I estimated the capacity for VoIP traffic in IEEE 802.11 wireless networks via theoretical analysis, simulations, and experiments in a wireless test-bed and show how to avoid mistakes in the measurements and comparisons. Finally, to protect the QoS for existing VoIP calls while maximizing the channel utilization, I propose a novel admission control algorithm called QP-CAT (Queue size Prediction using Computation of Additional Transmission), which accurately predicts the impact of new voice calls by virtually transmitting virtual new VoIP traffic

Passive Duplicate Address Detection for Dynamic Host Configuration Protocol (DHCP)

During a layer-3 handoff, address acquisition via DHCP is often the dominant source of handoff delay, duplicate address detection (DAD) being responsible for most of the delay. We propose a new DAD algorithm, passive DAD (pDAD), which we show to be effective, yet introduce only a few milliseconds of delay. Unlike traditional DAD, pDAD also detects the unauthorized use of an IP address before it is assigned to a DHCP client

IEEE 802.11 in the Large: Observations at an IETF Meeting

We observed wireless network traffic at the 65th IETF Meeting in Dallas, Texas in March of 2006, attended by approximately 1200 engineers. The event was supported by a very large number of 802.11a and 802.11b access points, often seeing hundreds of simultaneous users. We were particularly interested in the stability of wireless connectivity, load balancing and loss behavior, rather than just traffic.We observed distinct differences among client implementations and saw a number of factors that made the overall system less than optimal, pointing to the need for better design tools and automated adaptation mechanisms

Seamless Layer-2 Handoff using Two Radios in IEEE 802.11 Wireless Networks

We reduces the false handoff probability significantly by introducing selective passive scanning

Application Of Data Mining For Reverse Osmosis Process In Seawater Desalination

Reverse osmosis (RO) membrane process has been considered a promising technology for water treatment and desalination. However, it is difficult to predict the performance of pilot- or full-scale RO systems because numerous factors are involved in RO performance, including variations in feed water (quantity, quality, temperature, etc), membrane fouling, and time-dependent changes (deteriorations). Accordingly, this study intended to develop a practical approach for the analysis of operation data in pilot-scale reverse osmosis (RO) processes. Novel techniques such as artificial neural network (ANN) and genetic programming (GP) technique were applied to correlate key operating parameters and RO permeability statistically. The ANN and GP models were trained using a set of experimental data from a RO pilot plant with a capacity of 1,000 m3/day and then used to predict its performance. The comparison of the ANN and GP model calculations with the experiment results revealed that the models were useful for analyzing and classifying the performance of pilot-scale RO systems. The models were also applied for an in-depth analysis of RO system performance under dynamic conditions

Analysis on Response Characteristics of Semiconductor Methane Gas Sensor by Ultrasonic Process

The thin films of Pt and Zn were coated with on the electrode in the board. Thin films of Pt are fabricated by ion plasma and Zn is manufactured by DC sputtering methods. Then the deposited boards were produced by ultrasonic chemical deposition in 0.01M aqueous solution of C6H12N4 and Zn(NO3)2?6H2O. To make the Zinc oxide, prepared-substrates were annealed at 600? for 1h and analysis on response characteristics of ZnO-structured sensors are tested for Methane gas. In the experiments, the concentration of Methane gas was used from 15% to 40% LEL. We measured the change of the voltage before and after the Methane gas injections, it was judged whether it had a suitable performance as the Methane gas sensors. As a result of the sensitivity of the fabricated sensor, it was confirmed that the voltage increases according to the Methane concentration. The sensitivity of the sensor was constantly increase so the graph showed a linear shape. Also, the fabricated sensors showed a very short stabilization time, fast reaction and recovery. As a result, the using possibility of the detector is suggested in the industrial facilities

Wireless Bus Interconnects for Small Satellite Systems

For small satellite engineering systems, successfully managing the hundreds of in-system interconnections caused by a wired interface is a major element in the success of a SmallSat mission. Testing, integration, and mission operation of SmallSat subsystems frequently requires system interfaces to be reconfigured for extended mission capability and system reliability. We propose a Bluetooth Low Energy (BLE) based wireless interface technology to enable post-deployment reconfiguration of in-system interfaces. This wireless inter-face will improve system reliability while enabling ad hoc system level changes and reducing the probability of subsystem failure. While a wireless interconnect brings many benefits, its implementation raises potential technical challenges, including additional power consumption, data latency, interference with ground communications, susceptibility, and emissions. This work presents the concepts of wireless interface technologies, proof-of-concept experimental results of a BLE-based wireless interface system, and analysis of effective solutions for the aforementioned technical challenges. By limiting the RF power of the wireless interfaces, the susceptibility, emissions, and power consumption were be made minimal. Latency and interference were also be minimized through software optimization and error correction techniques. Proof-of-concept prototype lab experiments demonstrate the feasibility and adaptability of the proposed technology with increased ability to reconfigure assets compared to traditional wire-based interconnects

Calculation of Response Characteristics of Various Hydrocarbon Gas Sensors

Technologies for detecting leaks of gases and measuring gaseous concentrations have been widely developed with every sensor type. To manufacture excellent gas leak detector, an excellent gas sensors are necessary parts. In this research, the design of a system to simultaneously measure performances of five gas sensors is introduced. That system need the components of measuring appliances, sensing circuits, control firmware, and PC software to be operated. Also the performances to test gas sensors need response characteristics, accuracy, and repeatability according to output signals for injecting gas amounts into gas sensors. The firmware is implemented to operate sensors and to acquire output data against for input of sensors in real time. Acquired data were stored in the text file according to every sensor during a pre-set measurement interval. Software is coded to draw graphs of the voltage values measured by each sensor in real time. Using proposed a testing system we showed how to test response characteristics and induce better calibration equations of five sensors. This paper compared experimental data of five sensors and verified which gas sensor is the best