An Efficient Location Management Technique for Diurnal Mobility in Wireless Cellular Networks

Abstract

Location management in cellular communication refers to location update (LU) and location search (LS) (or, commonly known as paging). LU requires occasional update of the entries corresponding to an MT in its location registers (LRs), namely home LR (HLR) and visiting LR (VLR). LS consists of two sub-processes: (i) pre-paging-probe (PPP) -- to identify the paging area, in which the MT currently resides, using the HLR/VLR entries created by LUs, and (ii) paging -- to page the identified area. Since decrease in LU frequency increases LS effort, and vice versa, good location management techniques attempt to optimize the total signalling cost due to LU plus LS in the network. A recent paper [1] has reduced the LU cost by a novel pointer forwarding mechanism, wherein the previous VLR keeps a forward pointer to the current VLR instead of updating the HLR when an MT changes the VLR. This process creates a chain of forwarding pointers through VLRs, if the MT changes multiple VLRs. Though this technique reduces costly HLR updates, a relatively lengthy VLR traversal takes place, using the forward pointer chain, to locate the current VLR during the LS for the MT. Thus, due to successive probing through the chain of pointers, the PPP cost increases. To avoid this problem, our proposed LU technique restricts the chain length to unity so that PPP cost remains constant. We do so by introducing the concept of a home VLR in line with the home agent concept of mobile IP. The home VLR acts like a pseudo-HLR for the MT, thereby reducing costly HLR updates too. Our LU scheme can adopt various HLR update strategy (e.g., movement based update, or cell-sojourn time based update). Using simulation, we find that the reduction in PPP cost, with respect to [1], becomes more significant as the call-to-mobility ratio (CMR) increases. Further simulation study reveals that our proposed technique is best suited for diurnal mobility [7] of an MT, and there it reduces both LU and LS costs considerably.