Why Doesn't GPS Work Inside a Building?by Hans Fredrick
GPS signals are carried through waves at a frequency that does not move easily through solid objects. A GPS device relies on a series of satellites in order to determine where it is physically located. The signals sent from these satellites do not penetrate all kinds of barriers with ease. When you use a GPS inside a building, a wide variety of physical barriers and potential interference sources make it difficult for the device to pinpoint your location accurately.
Line of Sight
A GPS works better when the device has a clear line of sight to the sky. The more GPS satellites that your personal device can access, the more accurate it is. When inside, there is often no direct line from the satellite signals to your device. The signal weakens or distorts as it travels through the building to your GPS, and the result is inaccurate operation.
The construction materials in a building affect how well a consumer GPS device will work inside. If you're in a house and stand near enough to the windows, or if you're in an office tower with large windows, your GPS could still work. GPS signals pass through glass much more easily than they do through thick, solid materials such as brick, metal, stone or wood.
At 1575.42 MHz, GPS signals are a high-frequency signal. They are classified as part of the UHF (ultra-high frequency) band of signals. Another problem that occurs indoors is that there are more potential sources of UHF interference that could conflict with the GPS signal and cause it to not work properly. TV antennas are a particularly bad source of interference for GPS signals.
The next generation of positioning technology is being designed to overcome the limitations of GPS. While GPS devices don't work particularly well indoors, IPS (Indoor Positioning System) technologies are being developed by companies like Google, Microsoft and Nokia to offer pinpoint location accuracy even while users are inside. These technologies utilize different types of signals to triangulate the position of the user while indoors. Wi-Fi hot spots, Bluetooth signals and cellphone signals have all been experimented with by the various companies refining this technology. A 2011 Forbes article looked at the future of IPS based partly on the work of technology analyst Bruce Krulwich's firm, Grizzly Analytics. According to that article, Krulwich feels that IPS is going to be one of the hottest growing parts of the mobile technology sector as these industry leaders continue to develop in the area.