2 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
Resource Allocation for Cellular/WLAN Integrated Networks
The next-generation wireless communications have been envisioned to be supported by heterogeneous networks using various wireless access technologies. The popular cellular networks and wireless local area networks (WLANs) present perfectly complementary characteristics in terms of service capacity, mobility support, and quality-of-service (QoS) provisioning. The cellular/WLAN interworking is thus an effective way to promote the evolution of wireless networks. As an essential aspect of the interworking, resource allocation is vital for efficient utilization of the overall resources.
Specially, multi-service provisioning can be enhanced with cellular/WLAN interworking by taking advantage of the complementary network strength and an overlay structure. Call assignment/reassignment strategies and admission control policies are effective resource allocation mechanisms for the cellular/WLAN integrated network. Initially, the incoming calls are distributed to the overlay cell or WLAN according to call assignment strategies, which are enhanced with admission control policies in the target network. Further, call reassignment can be enabled to dynamically transfer the traffic load between the overlay cell and WLAN via vertical handoff. By these means, the multi-service traffic load can be properly shared between the interworked systems.
In this thesis, we investigate the load sharing problem for this heterogeneous wireless overlay network. Three load sharing schemes with different call assignment/reassignment strategies and admission control policies are proposed and analyzed. Effective analytical models are developed to evaluate the QoS performance and determine the call admission and assignment parameters. First, an admission control scheme with service-differentiated call assignment is studied to gain insights on the effects of load sharing on interworking effectiveness. Then, the admission scheme is extended by using randomized call assignment to enable distributed implementation. Also, we analyze the impact of user mobility and data traffic variability. Further, an enhanced call assignment strategy is developed to exploit the heavy-tailedness of data call size. Last, the study is extended to a multi-service scenario. The overall resource utilization and QoS satisfaction are improved substantially by taking into account the multi-service traffic characteristics, such as the delay-sensitivity of voice traffic, elasticity and heavy-tailedness of data traffic, and rate-adaptiveness of video streaming traffic