Chris,
Your wording "trades signals with 24 GPS satellites" could be understood to mean that the satellites receive information from any handset. It is my understanding that the GPS satellites are transmitters, while any GPS device is a receiver. Just like a radio station transmits, and a radio receives. There is no two way communication.
I have heard people say the the GPS satellite system knows where you are. It is the cellphone system that has two way communication, not GPS.
What do you think?
The Global Positioning System (GPS) has come a long way since it was developed in 1973. Today, anybody with an equipped wireless handset automatically receives signals from 24 GPS satellites in orbit while smartphone providers, carriers, and “check in” services like Foursquare continuously take note. Elsewhere, GPS is integral in traffic management, navigation, military operations and medical emergency services. Today’s GPS receivers are able to locate themselves with an error of 5 meters outdoors.
When it comes to indoors, however, GPS signals are typically marginal or unavailable because of signal lose caused by obstructions. A report from consulting firm Indoor LBS points out that the majority of the world’s commerce and social interaction takes place indoors, yet can’t take advantage of conventional outdoor GPS receivers. You can’t use it to find your wife or kids at the mall.
An indoor equivalent of GPS, known as indoor positioning system (IPS), would open a world of new applications ranging from mobile advertising and product shopping to indoor maps and navigation. IPS would also provide for increased public safety, emergence response, and assist the elderly and the blind by complementing technology in smart homes. Furthermore, it could potentially be used to guide unmanned aircraft and ground vehicles safely through small openings as they enter buildings.
The quest to develop IPS has been underway for quite sometime, but a standard has yet to emerge. While the technology exists and commercial systems are on the market, there is no perfect solution for getting a fix on a user’s position regardless if the system uses radio (e.g., Nokia), ultrasound (e.g., Sonitor), infrared (e.g., Nikon Metrology NV), or any other signals.
The latest approach comes from a team of Stanford students who launched WiFiSLAM, which uses existing wireless networks and everyday smartphones. 
The goal of the start-up is to develop mobile applications that allow your smartphone to pinpoint its location (and the location of your friends) in real-time to within 2.5 meters using WiFi signals already present in buildings. The phone’s internal compass and accelerometer also play a role in determining its location. The team envisions the technology enabling step-by-step indoor navigation, product-level retail customer engagement, and social networking based on proximity.
Further along the path is an Australian firm called Locata which claims to have launched the first “GPS-style” indoor positioning solution for warehousing and industrial applications. Locata uses a proprietary technology called “TimeTenna” that delivers positioning accuracy within a few centimeters. It consists of transmitters that are chronologically “locked” together to create a synchronous network.
Locata’s solution (LocataTech) relies on a network of small, ground-based transmitters that blanket a chosen area with strong radio-positioning signals (see technology brief- PDF). Locata will partner with a company called Hexagon to develop receivers that provide high-accuracy positioning, machine automation and robotics applications indoors without the use of satellites.
The intersection of IPS and LBS is a busy place and the two examples above barely scratch the surface. According to Indoor LBS, there are 100 companies that are working on indoor location, tracking, mapping, and navigation, including Apple, Google, Microsoft, Cisco, AT&T, Skyhook Wireless, and Point Inside. As solutions emerge, old school navigation aides like shopping mall directories and paper museum maps could become a thing of the past.
Related:
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