Improvemence And Modeling Analysis Of Movement-Based Location Update Scheme For PCS Networks

As an important component of wireless mobile communication network, location management (LM) is to track the location of the mobile terminals (MTs) and deliver paging signals to MTs to provide nice and reliable services.LM contains two main operations:location update and paging. Referring to the two operations, most studies are to find a trade-off scheme. LM schemes are partitioned into two main parts:static scheme and dynamic scheme. The static scheme is not applied to all MTs, and neglected now. Most studies pay more attention to the dynamic scheme. The dynamic scheme is divided into three respects:the distance-based, the time-based and the movement-based schemes. The distance-based scheme is efficient but is the most difficult to implement to the networks. The time-based scheme is the easiest to implement one but is not efficient.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.In this paper, an improved movement-based location update (iMBLU) scheme is proposed to reduce the location update (LU) cost of the conventional movement-based location update (CMBLU) scheme. The main idea is that instead of simply keeping counts of the number of cell boundary crossings, the counter of a mobile station (MS) stores the distance information between the currently residing cell and the last registered cell and an LU is performed whenever the counter value reaches a predefined threshold, called movement threshold. Unnecessary LUs are avoided when the MS moves around the recently visited cells. Simulation results demonstrate that the iMBLU scheme has achieved a considerable reduction in LU cost compared to other schemes under irregular cell configuration in real personal communication service (PCS) networks.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 a fluid flow model. The model takes into account the home location register/visitor location register (HLR/VLR) two-tier database architecture used by the 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 or is Hyper-Erlang distribution, closed-form analytical formulas for the LU and paging costs of the MBLM scheme are derived. Simulation results prove our results. 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 developed and results derived in this paper are instrumental to the implementation of the MBLM scheme in PCS networks.