Gestion du Handover dans les réseaux hétérogènes mobiles et sans fil

Since 1990, networking and mobile technologies have made a phenomenal unprecedented progress. This progress has been experienced on multiple fronts in parallel; especially on the application level and the user's needs one. This rapid evolution of the technology imposed a need for the existence of heterogeneous environments where the coverage is ensured throughout the different available networks. The challenge with such architecture would be to provide the user with the ability to navigate through the different available networks in a transparent and seamless fashion. However, the navigation among different types of networks is commonly referred to as vertical Handover. The IEEE 802.21 standard offers a component that is called Media Independent Handover (MIH) which has a function that provides the capability of transmitting the state of the connection of the mobile nodes from the lower to upper layers. This layer would exist between layer 2 and layer 3 within the protocol architecture. The main role of MIH is to help the mobile node transfer without interrupt among different types of networks, but the logic of selection is left without implementation. In this context, we worked on the improvement of the Handover management by proposing a new architecture, called VHMC and based on MIH by offering new methods for selecting the destination network. The first solution is a new algorithm called Multiple Criteria Selection Algorithm (MCSA) based on multiple parameters of the quality of service. We used Network Simulator (NS2) for testing our approach and study the number of lost packets and lost time during Handover. The second solution is a new model for selecting the destination network based on fuzzy logic techniques. The distinctive characteristic of this model lies in the study of genuine Handover records taken from a Lebanese mobile operator called "Alfa". A third proposed solution for network selection is based on multiple linear regression theory.Depuis les années 90, la technologie réseau et radio mobile a fait l'objet de progrès phénoménaux. Cette avancée technologique s'est faite en parallèle du côté réseau, du côté application et du coté besoin de l’utilisateur. L’évolution rapide de la technologie a eu pour conséquence l’existence d’un environnement hétérogène où la couverture est assurée par la coexistence de plusieurs types de réseaux. Le défi soulevé par cette architecture est de pouvoir naviguer entre plusieurs réseaux d’une façon transparente. La navigation entre réseaux de types différents est connue sous le nom du Handover vertical. Le standard IEEE 802.21 offre une composante appelée Media Independent Handover (MIH) qui contient une fonction capable de transmettre l’état des liens du nœud mobile depuis les couches inférieures vers les couches supérieures. MIH s’intercale entre le niveau 2 et le niveau 3 dans la pile protocolaire. Le rôle principal de MIH est d’aider le nœud mobile à faire un transfert sans coupure entre des réseaux de types différents, mais la logique de sélection est laissée sans implémentation.Dans ce contexte nous avons travaillé sur l’amélioration de la gestion du Handover en proposant une nouvelle architecture appelée VHMC et basée sur MIH offrant des nouvelles méthodes de sélection du réseau destination. La première proposition est un nouvel algorithme nommé Multiple Criteria Selection Algorithm (MCSA) basé sur plusieurs paramètres de qualité du service. Nous avons utilisé le simulateur Network Simulator (NS2) pour évaluer nos propositions en étudiant le nombre de paquets perdus et le temps de latence du Handover durant la période du transfert. La deuxième contribution est un nouveau modèle de sélection du réseau destination basé sur la technique de la logique floue. La base d’inférence, qui est l’élément central de la décision de ce modèle, est déduit grâce à une étude basée sur un nombre élevé de cas de Handover réels collectés des serveurs de la compagnie de télécommunication libanaise "Alfa". Une troisième solution est proposée à travers un nouveau modèle de sélection du réseau destination basé sur la théorie de la régression linéaire multiple

IP-Based Mobility Management and Handover Latency Measurement in heterogeneous environments

One serious concern in the ubiquitous networks is the seamless vertical handover management between different wireless technologies. To meet this challenge, many standardization organizations proposed different protocols at different layers of the protocol stack. The Internet Engineering Task Force (IETF) has different groups working on mobility at IP level in order to enhance mobile IPv4 and mobile IPv6 with different variants: HMIPv6 (Hierarchical Mobile IPv6), FMIPv6 (Fast Mobile IPv6) and PMIPv6 (Proxy Mobile IPv6) for seamless handover. Moreover, the IEEE 802.21 standard provides another framework for seamless handover. The 3GPP standard provides the Access Network and Selection Function (ANDSF) to support seamless handover between 3GPP – non 3GPP networks like Wi-Fi, considered as untrusted, and WIMAX considered as trusted networks. In this paper, we present an in-depth analysis of seamless vertical handover protocols and a handover latency comparison of the main mobility management approaches in the literature. The comparison shows the advantages and drawbacks of every mechanism in order to facilitate the adoption of the convenient one for vertical handover within Next Generation Network (NGN) environments. Keywords: Seamless vertical handover, mobility management protocols, IEEE 802.21 MIH, handover latenc

Penggunaan Teknologi Kampus Astro dalam kalangan guru sekolah luar bandar

Program jangkau luar (outreach programme) Kampus Astro merupakan satu usaha kerjasama di antara pihak korporat dan Kementerian Pendidikan Malaysia dalam memberikan pendidikan bentuk bergambar sebagai sumber rujukan pendidikan bagi mengimbangi jurang maklumat kawasan Bandar dan luar Bandar. Projek tersebut memberikan peluang kepada guru khususnya di sekolah luar Bandar untuk menggunakan teknologi terkini dalam menyampaikan maklumat pembelajaran secara menarik dan menghiburkan kepada pelajar mereka. Justeru kajian ini dijalankan untuk mengenalpasti persepsi guru terhadap penggunaan Teknologi Kampus Astro (TKA) ini dalam kalangan guru sekolah luar Bandar. Kajian ini memfokuskan kepada empat aspek yang mempengaruhi guru terhadap penggunaan Kampus Astro iaitu faktor kekerapan penggunaan, faktor dorongan guru terhadap penggunaan, faktor kekangan guru terhadap penggunaan, dan faktor sikap guru terhadap penggunaan. Kajian ini berbentuk tinjauan deskriptif dengan melibatkan dua buah sekolah luar Bandar di Negeri Kedah. Instrumen kajian adalah menggunakan borang soal selidik berstruktur yang mengandungi 31 item dengan menggunakan maklumbalas Skala Likert. Nilai kebolehpercayaan Alpha Cronbach bagi instrumen soal selidik ialah 0.85. Data-data yang diperolehi dianalisis menggunakan perisian Statistical Package for Social Sciences (SPSS) Versi 16 bagi mendapatkan nilai peratusan dan frekuensi. Hasil dapatan kajian telah menunjukkan bahawa guru mempunyai pandangan yang positif terhadap penggunaan Teknologi Kampus Astro di mana guru kerap menggunakannya dalam proses pengajaran dan pembelajaran

Relationships between university students’ achievement motivation, attitude and academic performance in Malaysia

Student achievement problems are often highlighted in academic literature and the mass media and therefore, it is pertinent for educators to be aware and to study the factors related to student achievements such as achievement motivation and attitude. The purpose of this study was to identify the relationships between the achievement motivation, attitude and student academic performance. The research design employed was a descriptive correlational. Data were collected by self-reported questionnaire on a sample using cluster sampling technique based on the different faculty of studies in the university. The respondents were 1484 students from a local university (1102 females and 382 males). They were following the education, science, humanities, agriculture/technical/engineering programmes. Results indicated a positive significant correlation between students’ attitude towards learning and achievement motivation (r= 0.53, p .05) was observed between students’ achievement motivation (nAch) and their academic achievement. The implications of the findings were also discussed in the paper

Ruddlesden Popper 2D perovskites as Li-ion battery electrodes

The electrochemical performance of 2-dimensional hybrid perovskite electrodes for Li-ion batteries are investigated using a high-molarity electrolyte. The effect of changing the halide content and layering structure is systematically explored.</p

Relationship between personality, misbehavior and academic achievement among freshmen in a university

The national educational philosophy stated that the aim of education is to produce individuals not only knowledgeable but also possessing healthy personality. It is therefore the aim of this paper to determine the relationship between personality, misbehavior and academic achievement among freshmen at a local higher educational institution. The methodology employed in this study is descriptive correlation. The sample size is 372 first year students (180 boys and 192 girls) from 12 residential colleges of the university. The Eysenck Junior Personality Inventory was utilized to measure the personality aspect. By using the pearson correlation analysis, the results showed that there were a significant negative correlation (r=-0.191, p<0.01) between the extrovert scores and academic achievement and a significant positive correlations between neurotic scores and academic achievement. Findings also show that there was no relationship between misbehavior and academic achievement. In conclusion, the findings showed that individuals with good academic performance do not necessarily have good personality

The relationship between mathematics self-efficacy and mathematics achievement

The purposes of this study was to examine the relationship between mathematics self-efficacy and mathematics achievement for 339 high school students aged between 15 and 17 years. Pearson product-moment correlation showed that mathematics self-efficacy was significantly correlated with mathematics achievement (r=0.30, p< .01). Results showed taht students with higher mathematics self-efficacy were more likely to achieve better mathematics achievement. The finding was generally consistent with the basic assumptions of Bandura's (1986) self-efficacy

Effects Of Three-Step Magnesium Doping In p-GaN Layer On The Properties Of InGaN Based Light Emitting Diode

In this works, indium gallium nitride (InGaN) based light emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition. Three-step magnesium (Mg) doping profile was proposed to enhance the efficiency of the LED and the attention was paid to the effects of the Mg doping concentration of the second p-GaN layer. The Mg doping levels were varied by changing the flow rates of bis-cyclopentadienyl magnesium (Cp2Mg), i.e., 150, 250, and 300 sccm. To assess the electrical, crystallographic, and optical properties of the InGaN-based LEDs, various characterization tools were used. The results showed that, the hole concentration was affected by Cp2Mg flow rate. For the light output power, it was found that LEDs with low and high hole concentration exhibit lower output power due to low conductivity and low mobility. Apart from that, it was also found that the light emission of the LED wavelength, redshifted as the hole concentration increases. Through this study, it can be deduced that the hole concentration of the second p-GaN layer has a signifcant effect on the performance of the LED

Effects Of Three-Step Magnesium Doping In p-GaN Layer On The Properties Of InGaN Based Light Emitting Diode

In this works, indium gallium nitride (InGaN) based light emitting diode (LED) was grown on a 4-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition. Three-step magnesium (Mg) doping profile was proposed to enhance the efficiency of the LED and the attention was paid to the effects of the Mg doping concentration of the second p-GaN layer. The Mg doping levels were varied by changing the flow rates of bis-cyclopentadienyl magnesium (Cp2Mg), i.e., 150, 250, and 300 sccm. To assess the electrical, crystallographic, and optical properties of the InGaN-based LEDs, various characterization tools were used. The results showed that, the hole concentration was affected by Cp2Mg flow rate. For the light output power, it was found that LEDs with low and high hole concentration exhibit lower output power due to low conductivity and low mobility. Apart from that, it was also found that the light emission of the LED wavelength, redshifted as the hole concentration increases. Through this study, it can be deduced that the hole concentration of the second p-GaN layer has a signifcant effect on the performance of the LED

Inhomogeneity Of An InGaN Based Blue Led Studied By Secondary Ion Mass Spectrometry (SIMS) And Atom Probe Tomography (APT)

InGaN/GaN multiquantum wells (MQWs) grown on 2-inch c-plane patterned sapphire substrate using metal-organic chemical vapor deposition was characterized by secondary ion mass spectrometry and atom probe tomography. The average In mole fraction by APT was found to be around 16% in the InGaN well which is consistent with SIMS analysis. SIMS analysis was also performed to analyze the In distribution in the InGaN well layer, where the results were found to be nonuniform in the InGaN active layer, as opposed to the results obtained from APT measurement. Further from SIMS measurement, the upper interfaces of the QWs were slightly more diffused than the lower interfaces. Meanwhile, APT measurement showed In clustering or In rich regions based on different color distributions, indicating different In concentration. The results of APT and SIMS for average In mole fracrtion were validated by XRD measurement