異質無線網路中根據偏好值之網路選擇機制

Abstract

在未來4G的時代，不同特性的無線網路逐漸整合，業者賦予行動用戶多模(multi-mode)的能力，使得行動用戶能無縫(seamless)的網路接取，使用者根據各自通道狀況及自身的服務品質需求(QoS requirement)選擇最適宜自己的無線網路。為了支援高傳輸速率的多媒體服務以及高速的行動用戶，一個WCDMA/WMAN/WLAN的異質無線網路被提出。 在WCDMA/WMAN/WLAN的異質無線網路系統中，在本篇論文中我們提出了一個根據偏好值的網路選擇機制，希望在保證使用者的服務品質需求下，增加可容納的使用者個數、降低換手(handoff)的發生頻率。此機制包含了三階段，分別是候選網路選擇(candidate cells selection)、偏好值計算(preference value calculation)、目標網路選定(target cell determination)。在得到候選網路後，我們計算每個候選網路的偏好值，每個偏好值考慮了三個因素：服務品質(QoS)、負載狀況(loading)、以及移動速度(mobility)來達到我們的目標，最後選擇偏好值最大的網路當成目標網路。模擬結果顯示我們提出的方法可以增加系統傳輸速率(throughput)以及滿足服務品質需求，並且增加可容納的使用者個數以及降低換手的發生頻率。

The thesis proposes a preference value-based cell selection (PVCS) scheme to satisfy quality of service (QoS) requirements, maximize accommodated number of calls and minimize handoff occurrence frequency in heterogeneous wireless networks. The PVCS scheme contains three stages, candidate cells selection, preference value calculation, and target cell determination. The candidate cells selection is used to sift out the candidate cells for the call request. All suitable cells form candidate cell set. The preference value calculation will calculate the preference value of each cell in the candidate cell set, which is optimized by considering QoS factor, loading factor, and mobility factor, for the purpose of maintaining call request’s QoS requirements, maximizing overall system utilization, and minimizing handoff occurrence frequency. Eventually, the target cell, which has the maximum preference value, could be selected for the call request. Simulation results show that PVCS scheme achieves higher total throughput than UGT while satisfying the QoS requirements. It also has lower new call blocking rate and handoff call dropping rate than UGT, which means more accommodated calls than UGT. Besides, PVCS reduces the total handoff occurrence frequency by about 20% as compared to UGT.