Title of Thesis
MOBILITY MANAGEMENT TECHNIQUES IN WIRELESS NETWORKS

Summary:

With wireless networks advancing so fast, mobility is no longer an exception but a basic criterion to be complied for 3rd generation mobile communications. Among other challenges, the importance of location management should not be underestimated. An efficient operation is an absolute necessity to ensure a satisfactory realization to the vision of an anywhere, anytime data communications.

This thesis was devoted to enhance the existing operations in tackling the challenge of location tracking. The research work was divided into two parts; while the first part emphasized for applications mainly in cellular network (i.e. an example of homogeneous mobility), the second part focused on the task of managing mobility between heterogeneous networks.

On the applications of cellular networks, to better utilize the distinct characteristics of individual users on the traveling directions, two tracking schemes, the directivity-aware location updating scheme and the Kalman-filter based update scheme, and a corresponding sectional paging scheme were developed in this thesis. Other achievement included the development of a new mobility model that simplifies the existing presentation of Markovian movement model. More specifically, for an update threshold of D, the number of states necessary to model the movements has reduced from an initial quantity of 3D^2+3D-5 to 2(D-1). Even when comparing to more recent developments of similar purpose, this simplification still outperforms.

As an extension to the conventional distance-based update scheme, in the directivity-aware location updating scheme, the selection of the optimal threshold was made adaptive not only to the mobility rate, but also to the traveling patterns. For example, for mobiles demonstrating frequent movements in a more restrictive area, an optimal tracking strategy should be able to reduce the size of the corresponding location area in order to minimize the unnecessary paging load that could otherwise incur upon call arrivals.

The Kalman-filter based update scheme improved the prediction accuracy with the incorporation of a Kalman filter. Gauss Markov distribution was used to model the level of correlation between traveling directions. Accordingly, based on the Kalman filter theory, a shape of the update area that best reflects the distinct features of the mobile in concern was able to be determined. Acknowledging the fundamental operation of location tracking is to optimize the time the mobile resides in the assigned location area, with the selection of such an optimal location area, greater improvement was achievable through cost reductions. Simulation results showed that as long as some sort of directivity consistency is evident whether due to individual movement profiles or geographical characteristics, the proposed scheme achieved superior performance with minimal requirement of the additional intelligence. In the worse case where the movement pattern was random, the performance approximates to that obtainable with the existing schemes.

A corresponding sectional paging scheme was developed aiming to further reduce the operational cost. By identifying the section of most likely residence, paging areas were assigned accordingly in the location area. As an additional merit, it was noted that the designed technique could be used for all basic update schemes.
In managing mobility between heterogeneous networks, the biggest deficiency evident with the existing solution was the complex signaling involved in accommodating frequent registrations at the home network.  An obvious solution is to localize the management of mobility when the mobile appears to roam in a domain away from its subscribed network.  Three schemes, the pointer forwarding scheme (PFS), the user profile replications (UPR), and the local anchoring scheme (LAS) were originally proposed for applications in cellular networks to minimize the cost and reliance at HA.  With the cellular technology coming to a mature stage, it was anticipated that valuable lessons could be learned to provide essential guidance in the development of mobility management in IP.

With simulations performed to identify the characteristics of individual schemes, possible incorporation of the cellular techniques PFS and UPR onto the operations of IP was the most promising. In this thesis, a set of potential solutions was proposed with such purposes. Preliminary analysis on the designed solutions showed enlightening performance. Subsequently, to enable more precise quantification of the improvement, a set of design criteria were proposed in addition to a matching set of quantifying characteristics. It is most appealing to extend the work on the developments of such IP-based mobility managing technique as a continuation from this thesis. Apart from the challenge of location tracking, other research areas that fulfill the operations of mobility management were also identified in this thesis for the interest of other researchers in the community.