54 research outputs found
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
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