CDMA2000 Location Based Services


 Frequently Asked Questions:


Q: What is MEID?

A: MEID or Mobile Equipment Identifier is a globally unique serial number for a cell phone.


Q: What is MS?

A: The MS is Mobile Station or more commonly called a Cell Phone.


Q: What is GPS?

A: The Global Positioning System is a term used for satellite navigation systems. More than two dozen GPS satellites orbit the Earth, transmitting radio signals which allow GPS receivers to determine their location, speed and direction.


Q: What are Location based services (LBS)?

A: Location Based services are the ability for your device to get its current position from the Location Server on the Sprint network and provide you the ability to find nearby locations such as Gas stations, Hotels, Restaurants, Banks, etc. LBS is used for emergency locate requests as well.


Q: What is a Location Server?

A: Location Servers contain a variety of additional data such as geographic altitude data, GPS ephemeris and Base Station Almanac (information about cell sectors within the cellular network) used to assist a cell phone location attempt.


Q: Does a Sprint subscribed cell phone actually use GPS satellites to calculate its locations?

A: It depends. If you are indoors, then the answer is no – instead, AFLT is used. AFLT uses base station triangulation to calculate your location. If you are outside, then it will use MS-Based GPS and actual satellites are used to determine your location.


Q: What is A-GPS?

A: Assisted-GPS means that a “Location Server” assists a wireless device client to produce location fixes. The Location Server uses either (1) MS-Based: The cell phone performs the actual location calculations using assistance data such as ephemeris and Base Station Almanac supplied by the Location Server or (2) MS-Assisted: The Location Server performs the calculations based on location data supplied by the cell phone and the cellular network equipment.


Q: How accurate is A-GPS?

A: Accuracy is typically 5 meters up to 30 meters.


Q: What is MS-Based?

A: The cell phone performs the actual location calculations using assistance data such as ephemeris and Base Station Almanac supplied by the Location Server.


Q: What is MS-Assisted?

A: The Location Server performs the calculations based on location data supplied by the cell phone and the cellular network equipment


Q: What is Hybrid GPS?

A: In Sprint’s network implementation, gpsOne® Hybrid uses both GPS pseudoranges and CDMA Pilot measurements in the same trilateration calculation. Hybrid combines GPS pseudoranges with cellular Pilot measurements to maximize accuracy. Hybrid is typically more accurate than AFLT only, but less accurate than GPS. Hybrid allows the maximum in accuracy when a GPS-only solution is not possible (e.g., two or fewer GPS pseudoranges are available).


Q: How accurate is Hybrid GPS?

A: Accuracy is typically 5 meters to 50 meters.


Q: What is AFLT?

A: Advanced Forward Link Trilateration. AFLT is a type of device-based position location technology. Trilateration is a method for determining the intersections of three sphere surfaces given the centers and radii of the three spheres. Unlike A-GPS, AFLT does not use GPS satellites to determine location. To determine location, the cell phone takes measurements of signals from nearby cellular base stations (towers) and reports the time/distance readings back to the network, which are then used to triangulate an approximate location of the cell phone. In general, at least three surrounding base stations are required to get an optimal position fix. For successful results, AFLT requires an accurate Base Station Almanac consisting of cell sector identity information, cell sector GPS coordinates, a proper AFLT calibration, and values for uncertainties in measurements.


Q: How accurate is AFLT if you are not using real satellites.

A: AFLT accuracy is limited to the geometry of the Cell towers surrounding the cell phone requesting location information. The better the triangulation the more accurate the fix. AFLT is capable of 15.26 meter resolution. AFLT accuracy is typically 50 meters to 200 meters.


Q: What is Cell Sector location technique?

A: Cell Sector location methodology is the least accurate of Sprint’s location techniques and simply determines the Cell Tower Site and Antenna Sector on which the cell phone is communicating.


Q: How accurate is Cell Sector location technique?

A: The Cell Sector location technique determines to which antenna on a cell tower site the cell phone is communicating. Accuracy depends on the height of the antenna on the tower and the cell site communications radio power level and can range from 100 meters to multiple kilometers.


Q: Will Cell Phone location services work indoors?

A: Yes, but AFLT is used to determine the cell phone location.


Q: What are GPS pseudoranges?

A: The pseudorange is a first-approximation measurement for the distance between a satellite and a navigation satellite receiver.


Q: What are CDMA Pilot measurements?

A: A cell phone measures the travel time of CDMA Pilot signals that it sees. A location server associates each Pilot measurement to a nearby tower. Cell tower positions are maintained in a database known as the “Base Station Almanac”. Trilateration is used to turn the tower positions and Pilot measurements in to a position solution, much like GPS.


Q: What is a Base Station Almanac?

A: Base Station Almanacs consist of cell sector identity information and cell sector GPS coordinates.




Note that much of this material was derived from the Sprint Location Services User Guide and the CDMA University CDMA2000 End-to-End Location Based Services textbook.

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