Geometrical Characterization of Offloading through Wireless LANs
Abstract: The offloading of cellular traffic through WLAN APs (wireless local area network access points) distributed in a homogeneous Poisson process (HPP) is theoretically evaluated. The probability Pw that a user can use WLAN and the expected number of vertical handovers andovers Nh are evaluated as the basic performance metrics of WLAN AP coverage. Explicit formulas are derived for the metrics, and the fundamental relationships between the metrics and many parameters such as the shape of each WLAN coverage region D1, D2,. D2,... .. are described. These metrics depend on the size and perimeter length of Di but do not depend on their other shape parameters for a convex Di. In addition, it is proven that a disk-shaped disk Di minimizes Nh for a fixed WLAN coverage size and that Pw is ofte often n insensitive to the perimeter length of Di. It is also proven that the Pw of a user at a random location is equal to that moving along a random straight line or a random bounded curve. One hundred empirical location data sets of WLAN APs in Japan, Korea, and the US were used to confirm the theoretical results. Although these locations do not follow an HPP, many theoretical results are shown to be valid. For example, Nh is minimized by a disk disk-shaped shaped Di. Simultaneously, we find that Pw slightly increases when n a slender Di is used for highly clustered AP locations.