| Summary: | 博士 === 國立交通大學 === 資訊工程系 === 91 === Location tracking is one of the most important issues of mobility management in Personal Communication System (PCS) networks. Current mobility management standards, such as EIA/TIA IS-41 and ETSI GSM MAP, employ a two-level architecture of location databases with a single home location register (HLR) and visit location registers (VLRs) architecture for tracking the locations of mobile subscribers. In the two-level HLR/VLRs architecture, the single HLR may become the bottleneck in location tracking or call setup procedures as the number of mobile subscriber increases. In order to resolve the bottleneck problem of the single HLR architecture, several researchers have proposed multiple HLR schemes to reduce both signal traffics and/or call setup time. However, multiple HLR schemes incur extra signaling in updating multiple HLR databases. In the first part of this thesis, we propose a batch-update strategy, instead of the immediate update method, to reduce the signaling overhead for the location tracking schemes with replicated location information. The numerical results show that the distributed HLRs architecture, compared with the IS-41 standard, can effectively decrease the signaling cost of location registration and call delivery, and our batch-update approach can further reduce the multiple HLR update overhead incurred by the immediate update method.
On the other hand, it is well known that there is a trade-off between location update and paging. Many researchers have proposed different location update strategies in order to optimize the signaling cost of location update and/or paging procedure. Most of the previous research efforts focus on the per-user-based schemes that dynamically adjust the location update and paging operations according to the moving pattern of mobile subscribers. However, according to some recent research results, the majority of users normally move toward a specific target with a particular purpose, instead of “walking” in a random way, which has not been exploited in the previous investigations. In the second part of this thesis, we propose a novel location tracking approach that performs a location update when the mobile changes its direction of movement. Since the direction-based approach can utilize effectively the forward-prone moving characteristic of the mobile subscribers, it can reduce the signal cost of both location update and paging procedure. Our numerical result shows that the direction-based approach outperforms the most recognized distance-based scheme for the mobile subscribers with normal-walking behavior.
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