Safe and independent mobility by persons with severe visual impairments remains a challenge. To relieve such persons of their dependence on guide dogs or a sighted human guide, various portable navigational aids using a Global Positioning System (GPS) receiver have been marketed. a) Conduct an Internet investigation of GPS as the basis for a portable navigational aid for the blind. Address the following issues: How does GPS work? Can GPS signals be reliably received at every location? How accurate are GPS signals in terms of resolution? Is this level of resolution sufficient for finding the entrance to a building? Can dead reckoning and inertial guidance help when GPS signals are lost?