标题: 应用于WCDMA/WLAN异质网路之乏晰逻辑允诺控制
Call Admission Control for WCDMA/WLAN Heterogeneous Networks Using Fuzzy Logic Theorem
作者: 陈咏翰
张仲儒
电信工程研究所
关键字: 呼叫允诺控制;异质网路;乏晰逻辑;宽频分码多重接取;无线区域网路;多用户检测;快速换手;垂直换手;call admission control;heterogeneous network;fuzzy logic;WCDMA;WLAN;multiuser detection;fast handoff;vertical handoff
公开日期: 2006
摘要: 藉由整合不同无线通讯网路所构成的异质网路(heterogeneous network)是有效提升整体服务容量与品质的方法之一。本篇论文所研究之宽频分码多重进接(WCDMA)系统与无线区域网路(WLAN)共存之异质网路,除两者皆为现今使用最广泛的通讯标准外,其个别之通讯特性更具有高度的互补性。WCDMA通讯覆盖范围大,支援高速移动通讯服务,并且具备完整之信令架构与核心网路,提供无线资源管理极佳的平台,唯其网路建置成本高,而且面对日益精致之多媒体服务,但各通道之最高资料传输速率仍不足;虽有如多用户侦测(multiuser detection)等进阶机制可提升系统容量,但所需的高运算量仍是实际必须考量之处。而WLAN则具备高传输速率以及网路建置成本低之优势,但一般覆盖范围较小且多为区域性,再加上行动服务支援度低,因此无法有效提供行动用户无缝式之宽频服务。由此可知,在设计WCDMA/WLAN异质网路资源管理机制时,可针对彼此之特性截长补短,提供更优良的宽频行动网路服务。

允诺控制(admission control)是WCDMA/WLAN异质网路资源管理中极为重要的管理机制之一。面对使用者所提出的连线与服务品质(QoS)要求,允诺控制必须能有效掌握各个网路之通讯品质状态以及资源利用之程度,对于行动用户经由换手(handoff)而产生的连线要求,更必须考虑该原有服务之连续性。因此本篇论文首先提出在WCDMA系统中应用多用户侦测方法时的呼叫允诺控制器设计。利用序列式干扰消除(successive interference cancellation;SIC)而达成多用户侦测的目的可大幅提升系统容量,也由于接收讯号经过SIC再处理后特性已有改变,主要干扰源将变成来自于邻近细胞。因此在我们所提出之呼叫允诺控制将邻近细胞干扰的影响比例提高,并且引进乏晰逻辑技术,针对多变之系统状态作出最佳之允诺决策。

其次,本篇论文也针对WLAN系统提出一结合允诺控制与排程之机制设计,其中针对讯号品质与服务要求,为使用者上下链路传输安排适当之传输机会(transmission opportunity)。另外鉴于WLAN中缺乏迅速有效之换手方式,因此我们也提出一套相容于IEEE 802.11e标准之快速换手协定(fast handoff protocol;FHP),以消除换手要求封包在竞争传输通道时的延迟不确定性,以利于换手预先动作(pro-active)启动时机的选择。

最后,本篇论文整合考虑WCDMA与WLAN共存异质网路中的允诺控制器设计。其中考虑两系统个别之系统状态、使用者QoS要求、以及使用者移动状态估测等关键量测值,并利用具适应能力之类神经-乏晰推论系统(neural-fuzzy inference system)与Q-learning自我学习机制,决定新进使用者或换手使用者连线要求的允诺与否,以及允诺之最适合网路。故此一设计不但具备允诺控制功能,同时也能作为WCDMA/WLAN异质网路中的网路选择(network selection)控制器。
The heterogeneous network is a type of the most direct and efficient infrastructure to extend the system capacity and service quality for the demanding multimedia environment. In this dissertation, two of the most popular systems, wideband code division multiple access (WCDMA) system and wireless local area network (WLAN) system, are considered to form the heterogeneous network. As the global cellular system, the WCDMA system has almost universal coverage in the world with high-mobility support and comprehensive core networks. But the cost of deployment and insufficient bandwidth for the growing multimedia services are its major disadvantages. WLAN system provides higher data rate to support multimedia services with lower cost, but the smaller service area and lack of complete handoff procedures restrict the mobility services. Hence, WCDMA and WLAN systems are highly complementary to each other. Basing on these features, we develop call admission control (CAC) schemes with fuzzy logic theorem for WCDMA and WLAN systems to achieve quality-of-service (QoS) guarantee and higher system utilization in the heterogeneous networks.

Multiuser detection (MUD) has been discussed and studied for a couple of years. Its impressive increase in capacity has attracted WCDMA systems to consider to adopt this technology. The capacity limit, however, still exists due to other cells’ multiple access interference (MAI) in a cellular system. As a result, a CAC scheme is essential to control the number of mobile users from the view of point of MUD. This dissertation proposes an outage-based fuzzy call admission controller with multiuser detection (OFCAC-MUD) for WCDMA systems. The successive interference cancellation (SIC) is used as MUD because it has lower complexity and more suitable for the fading channel with imperfect power control. The OFCAC-MUD determines the new call admission based on the uplink signal-to-interference ratios from home and adjacent cells and system outage probabilities. The OFCAC-MUD possesses both the effective reasoning capability of fuzzy logic system and the aggressive processing ability of MUD. Simulation results reveal that OFCAC-MUD without power control (PC) improves the system capacity by 70.5% as compared to an SIR-based CAC-RAKE with perfect PC. It also enhances the system capacity by 53.9% as compared to an OFCAC-RAKE with perfect PC, by 6.7% as compared to an SIR-based CAC-MUD without PC, and by 12.9% as compared to an OFCAC-MUD with perfect PC, given the same outage probability requirements. Moreover, OFCAC-MUD can prevent the violation of outage probability requirements in the hotspot environment, which is hardly achieved by SIR-based CAC.

For the WLAN systems, we propose an intuitive scheduling and admission control (ISAC) scheme based on hybrid coordination function (HCF) mode in IEEE 802.11e cellular WLAN systems. The ISAC scheme considers admission control, based on not only the quality of service (QoS) required by each application but also the link quality of air interface influenced by the co-channel interference from adjacent cells. Furthermore, we also propose a fast handoff protocol (FHP) for cellular IEEE 802.11e WLAN systems. The FHP, which is standard compatible, provides a controlled contention period (CCP) designated for handoff requests (HO-REQs), arranges these HO-REQs to contend sequentially in CCP, and proposes a fuzzy adjustment method (FAM) to determine a proper length for CCP. Simulation results reveal that the FHP can significantly decrease the forced termination rate of HO-REQ and enhance the system throughput of contention period for cellular IEEE 802.11e WLAN systems.

Finally, a fuzzy Q-learning admission control (FQAC) mechanism is proposed for WCDMA/WLAN heterogeneous networks in this dissertation. The FQAC consists of dwelling estimation and admissibility estimation to consider the mobility pattern and essential system measures. The dwelling estimation can assess the dwell time length for a mobile user in the reachable subnetworks and output dwelling costs. The admissibility estimation can judge which reachable subnetwork(s) can support the required QoS and output admissibility costs. With Q-learning method, the FQAC can adaptively adjust the actions to output the costs without the knowledge of system state transition probability. In order to minimize the expected maximal impact (cost) of the user’s admission request, the decision maker applies the Minimax criterion for these costs and decides the most suitable subnetwork or reject the user request. Simulation results show that FQAC can almost maintain the system QoS because it can appropriately admit or reject the users’ admission requests. The dwelling estimation can significantly reduce the number of handoffs, which makes FQAC to have lower handoff blocking probability in those real-time services.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT008913807
http://hdl.handle.net/11536/77191
显示于类别:Thesis


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