PCS网络基于运动的位置管理的建模及开销分析
首发时间:2012-12-28
摘要:在众多动态位置管理方案中,基于运动的位置管理方案具有高效和易于实施的特点。在该方案中,当穿越的小区数达到预设门限(称为运动门限)时,就执行一次位置更新。在对基于运动的位置管理方案进行建模及信令开销分析时,已有研究采用的数学模型要么过于简单、要么不准确,以致得到的结果不可用。提出嵌入式马尔可夫链模型对基于运动的方案进行建模。利用流体流动模型刻画小区驻留时间和位置区(location area, LA)驻留时间之间的关联性。提出的数学模型考虑了PCS网络用于位置管理的HLR/VLR双层数据库架构,能准确描述由于达到运动门限和穿越LA边界而引起的VLR和HLR位置更新。假定呼叫到达过程为泊松过程、小区驻留时间服从一般分布,推导得到基于运动的位置管理方案的信令开销的闭合解析表达式。对比发现,已有的未考虑HLR/VLR架构的研究得到的结果均是本文结果的特例,已有的考虑了该架构的研究得的结果均有缺陷。数值分析表明,该方案的信令开销是运动门限的向下凸函数,且受到LA中所含小区数的影响。所提数学模型和得到的结果对于在PCS网络中实施基于运动的位置管理方案有指导意义。
关键词: 无线通信技术 基于运动的位置管理方案 建模 开销分析 位置区
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Modeling and Cost Analysis of Movement-Based Location Management in PCS Networks
Abstract:Among dynamic location management schemes, movement-based location management (MBLM) scheme is cost-effective and compatible with the existing personal communication service (PCS) networks. Under the MBLM scheme, a location update (LU) is performed whenever the number of cells crossed reaches a threshold, called movement threshold. The models employed by the existing studies to analyze the signaling cost of the MBLM scheme are either oversimplified or inaccurate so that the results obtained are unavailable. This paper develops an embedded Markov chain model for the MBLM scheme, where the dependency between the cell and location area (LA) residence times is characterized using the fluid flow model. The model takes into account the home location register/visitor location register (HLR/VLR) two-tier database architecture used by existing PCS networks for location management, and can accurately describe VLR and HLR LUs due to the reaching of the movement threshold and the crossing of an LA. Under the assumption that the call arrival process is Poisson and that the cell residence time is generally distributed, closed-form analytical formulas for the LU and paging costs of the MBLM scheme are derived. It follows that the results obtained in the existing studies neglecting the HLR/VLR architecture all are special cases of the results obtained in this paper, and that the results obtained by those considering the HLR/VLR architecture all feature some defects. Numerical study based on the analytical formulas reveals that the overall signaling cost of the MBLM scheme is a downward convex function with respect to the movement threshold, and is affected by the number of the cells making up an LA. The model and results developed in this paper are instrumental to the implementation of the MBLM scheme in PCS networks.
Keywords: wireless communication technology movement-based location management modeling cost analysis location area
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