Assisted GPS (A-GPS) is a system that allows the Global Positioning System (GPS) receiver to retrieve information from network resources to assist in satellite positioning. GPS was originally built for military purposes , where it was used to operate aircraft , troops and even bombs. In most cases , the receiver is located in an open area that provides line-of-view access to the satellite. But with the opening of GPS for commercial use , the new application system demands more. This new application requires GPS signals to reach blocked areas, such as trees or roofs, with some types of overhead covers . Thus , the concept of A-GPS or assisted GPS was created.