Queueing Networks for Vertical Handover

PhDIt is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access networks. Of particular interest recently is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/ WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This thesis describes the application of queueing-network theory to the modelling of this heterogeneous wireless overlay system. A network of queues (or queueing network) is a powerful mathematical tool in the performance evaluation of many large-scale engineering systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queueing network modelling in the study of cellular/ WLAN interworking systems. In the process of queueing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this thesis, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both homogeneous and non-homogeneous traffic have been considered, circuit switched and packet-switched. Example scenarios have been used to validate the models, the numerical results showing clear agreement with the known validation scenarios

Backward magnetostatic surface spin waves in exchange coupled Co/FeNi bilayers

Propagation of backward magnetostatic surface spin waves (SWs) in exchange coupled Co/FeNi bilayers are studied by using Brillouin light scattering (BLS) technique. Two types of SWs modes were identified in our BLS measurements. They are magnetostatic surface waves (MSSWs) mode and perpendicular standing spin waves (PSSWs) mode. The dispersion relations of MSSWs obtained from the Stokes and Anti-Stokes measurements display respectively positive and negative group velocities. The Anti-Stokes branch with positive phase velocities and negative group velocities, known as backward magnetostatic surface mode originates from the magnetostatic interaction of the bilayer. The experimental data are in good agreement with the theoretical calculations. Our results are useful for understanding the SWs propagation and miniaturizing SWs storage devices

Bulletin (1942-1943)

https://red.mnstate.edu/bulletins/1023/thumbnail.jp

Synergistic treatment of SF6 by dielectric barrier discharge/γ-Al2O3 catalysis

SF6 dielectric barrier discharge (DBD) degradation technology has been a hot spot and difficult problem in environmental protection, because SF6 has very high global warming potential and long atmospheric lifetime. To further improve the destruction and removal efficiency and energy yield of SF6 by DBD, the effects of the synergetic degradation of SF6 by dielectric barrier discharge/γ-Al2O3 were studied under different gases and catalyst masses. Ar was the background gas in the reaction. The initial concentration of SF6 was 2%, and the feed gas was water vapor or oxygen. The experimental results showed the evident synergistic effect of a suitable amount of γ-Al2O3 catalyst and DBD plasma on SF6 removal when the water vapor or oxygen was applied. When the catalyst mass was 5 g, the energy density was 43.5 J/mL, and the feed gas was water vapor, the optimal destruction and removal efficiency of discharge catalytic synergistic system reached 90.13%. This value was 15.5% higher than that of individual DBD degradation. Moreover, the energy yield reached 14 g/kWh, which was approximately 21% higher than that without the catalyst

Erlang's Fixed-Point Approximation for Performance Analysis of HetNets

We consider the analytic modelling of wireless systems with multiple access technologies in the perspective of teletraffic engineering and provide a framework for the performance analysis and evaluation of a wireless HetNet (heterogeneous network) system with both cellular and WLAN access technologies. In particular, an approach with Erlang's fixed-point approximation to calculate the new call blocking and handover call dropping probabilities in such systems is introduced. The model is versatile enough to cover not only cellular/WLAN HetNet systems but other wireless HetNets with difference access technologies in general