While localization is essential to many applications, there are quantities of wireless nodes whose accurate locations remain unknown or hard to tell. As a remedy, this paper is leveraging a GPS-capable Android handset that features portability and computing capability to collect data and display localization results thereof. Our objective is to locate the unknown nodes in consideration of radio-signal irregularity. To this end, we devise a hybrid means to incorporate received signal strengths used in range-based schemes with the notion of estimative regions adopted in range-free methods to refine the area of interest for localization. Our scheme operates without involved computations such as to accommodate many usable reference coordinates. Our treatment mitigates the errors of estimation resulting from different radio signal propagation scenarios, by taking an additional parameter to narrow region size for ameliorating localization accuracy. Experiments are conducted to demonstrate our performance results overlying Google Maps on the handset and through quantitative comparisons with trilateration under different settings. Performance results show the effectiveness of our development.

This paper is concerned with caching support of access points (APs) for fast handoff within IEEE 802.11 networks. A common flavor of current schemes is to let a mobile station preauthenticate or distribute the security context of the station proactively to neighboring APs. Each target AP caches the received context beforehand and can save itself backend-network authentication if the station reassociates. We present an approach to ameliorating cache effectiveness under the least recently used (LRU) replacement policy, additionally allowing for distinct cache miss penalty indicative of authentication delay. We leverage the widely used LRU caching techniques to effect a new model where high-penalty cache entries are prevented from being prematurely evicted under the conven-tional replacement policy so as to save frequent, expensive authentications with remote sites. This is accomplished by introducing software-generated reference requests that trigger cache hardware machinery in APs to refresh certain entries in an automated manner. Performance evaluations are conducted using simulation and analytical modeling. Performance results show that our approach, when compared with the base LRU scheme, reduces authentication delay by more than 51 percent and cache miss ratio by over 28 percent on average. Quantitative and qualitative discussions indicate that our approach is applicable in pragmatic settings.

Recently, Yang and Lee13 proposed a powerful data structure, the 2D B-string, to express the spatial knowledge embedded in iconic images. The data structure can be used to describe images with partly- or completely- overlapping objects without the need for partitioning the objects. We propose a signature file method for similarity retrieval of symbolic images described in 2D B-strings. The signatures of images are extracted by the disjoint coding and the superimposed coding techniques. A linear hashing function is adopted to organize the signature file. The experimental results show that the method has better performance than the one proposed by Lee, Yang and Chen.11