Querying Spatio-temporal Patterns in Mobile Phone-Call Databases

Call Detail Record (CDR) databases contain many millions of records with information about mobile phone calls, including the users´ location when the call was made/received. This huge amount of spatio-temporal data opens the door for the study of human trajectories on a large scale without the bias that other sources, like GPS or WLAN networks, introduce in the population studied. Furthermore, it provides a platform for the development of a wide variety of studies ranging from the spread of diseases to planning of public transportation. Nevertheless, previous work on spatio-temporal queries does not provide a framework "flexible" enough for expressing the complexity of human trajectories. In this paper we present Spatio-Temporal Pattern System (STPS) to query spatio-temporal patterns in very large CDR databases. STPS uses a regular-expression query language that is intuitive and that allows for any combination of spatial and temporal predicates with constraints, including the use of variables. The design of the language takes into consideration the layout of the areas being covered by the cellular towers, as well as "areas" that label places of interested (e.g. neighborhoods, parks, etc). A full implementation of the STPS is currently running with real, very large CDR databases at Telefonica Research Labs. An extensive performance evaluation of the STPS shows that it can efficiently find very complex mobility patterns in large CDR databases.