A context‐aware handover decision based on user perceived quality of service trigger

Growing demands for pervasive and ubiquitous services over wireless mobile networks and evolution of such networks towards heterogeneous solutions have emphasized the necessity of more intelligent handoff decisions. The existing handoff management methods in the literature are mostly using signal strength measurements and other link quality evaluations not addressing the knowledge about context of mobile devices, users and networks. Recently, context‐aware handoff management has been considered as a novel candidate for fourth generation (4G) wireless technology. In this paper, user perceived quality of service has been considered in addition to traditional contexts such as user preferences, application requirements, network parameters and link quality for decision making. User perceived quality (UPQ) has been employed as a trigger source, in addition to link layer triggers which are emerged using media independent handover (MIH) event service. This paper presents a policy based mechanism for handoff decision making where fuzzy petri nets (FPNs) have been utilized as its evaluation algorithm. A case study has been provided by simulations to show the usability and user level satisfaction. Simulation results show superior performance in terms of UPQ, jitter and packet delivery measures. Copyright © 2009 John Wiley & Sons, Ltd.     

New efficient cross‐layer and multihoming mechanisms at layer 2 for inter‐radio access technology handover between UMTS and WiMAX

Next generation mobile networks will provide seamless mobility between existing cellular systems and other wireless access technologies. To realize a seamless vertical handover (inter‐radio access technology handover) among these different access technologies, a multi‐interfaced mobile station (i.e., multihomed) is a good approach to provide better handover performance in terms of packet loss rate and handover latency. In this article, we propose a novel layer 2 multihoming approach for inter‐radio access technology handover between Universal Mobile Telecommunications System (UMTS) and Worldwide Interoperability for Microwave Access (WiMAX) in both integrated and tight coupling architectures. This layer 2 multihoming approach has the ability of enabling either soft handover or make‐before‐break handover to adapt to mobility scenarios for the sake of a lossless and short latency handover procedure. Our simulation results show that, in case of handover from UMTS to WiMAX for transmission control protocol (TCP) traffics, the layer 2 multihoming approach can achieve a lossless and zero latency handover procedure by enabling soft handover. In case of handover from WiMAX to UMTS, because of the fact that the performance gain of soft handover is more affected by the differences of bandwidth and transmission delay between these wireless links, the make‐before‐break handover is preferred to achieve lossless and short latency handover procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Microcontroller‐based simple maximum power point tracking controller for single‐stage solar stand‐alone water pumping system

A simple microcontroller‐based maximum power point tracking controller is proposed for a single‐stage solar stand‐alone water pumping system for remote, isolated, and nonelectrified population, where less maintenance, low cost, and an efficient system is of prime interest. It consists of a photovoltaic (PV) module, a DC–AC converter utilizing space‐vector pulse‐width modulation, an induction motor coupled with a water pump, a voltage sensor, and a current sensor. A space‐vector pulse‐width modulation‐controlled DC–AC converter aided by a fast‐acting on–off supervisory controller with a modified perturb‐and‐observe algorithm performs both the functions of converting PV output voltage to a variable voltage, variable frequency output, as well as extracting the maximum power. A limited variable step size is preferred during transient state, and a steady frequency, which is calculated on the basis of steady‐state oscillation, is set during steady state. A fast‐acting on–off supervisory controller regulates DC link voltage during steady state and enables maximum power point tracking algorithm only during transient state to draw a new voltage reference. In the event of low voltage, the controller switches off the motor but continuously scans for an available PV voltage. The system is not protected against an overcurrent because the maximum current is equal to its short circuit current. The 16‐bit microcontroller dsPIC6010A (Microchip Technology, Inc., Chandler, AZ, USA) is used to implement the control functions. The proposed controller is verified through simulation as well as tested in the laboratory prototype model. The simulation and experimental results show good correlation. Copyright © 2011 John Wiley & Sons, Ltd.