Telecommunications – Radiotelephone system – Emergency or alarm communication
Reexamination Certificate
1998-03-26
2001-09-11
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Emergency or alarm communication
C455S435100, C455S456500
Reexamination Certificate
active
06289211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods for determining the position of a mobile station in a cellular communication system, and, more particularly, to a method for determining the location of a mobile station in the AMPS system using the mobile station's transmissions on the reverse control channel and reverse voice channel.
BACKGROUND OF THE INVENTION
The Federal Communications Commission (FCC) has recently promulgated regulations requiring cellular phone operators to provide the location of emergency callers within 125 meters by the year 2001. One way to comply with the new regulations would be for the mobile phone to determine its own location and transmit location data upon placing a “911” call. However, most phones do not have the ability to determine their location. Since the FCC regulations apply to all phones which are in use as of the effective date of the regulations, this method for determining location will not likely be sufficient by itself to comply with the FCC regulations. Notwithstanding the FCC requirement, mobile positioning is desirable for numerous other applications. For example, mobile positioning could be used for fleet tracking. Police or other law enforcement authorities could use mobile positioning to track criminals. Also, individual users can use mobile positioning to determine their own location.
Another method for determining the location of a mobile station is to take measurements of signals transmitted from the mobile station at three or more points and to use such measurements to solve for the position. Various types of measurements could be used to solve for the position of the mobile station including time of arrival (TOA), time difference of arrival (TDOA), or angle of arrival (AOA). While TDOA and AOA measurements can be performed on any signal transmitted by the mobile station, TOA measurements can only be performed on known signals. The performance of TOA is often superior to TDOA and hence, it is desirable to make measurements on known signals whenever possible.
In the AMPS system, which is an analog system, the length of known signals transmitted by the mobile station is relatively short. For example, in reverse control channel message transmissions, most of the message bits are unknown except the first 48 bits. Because the length of the known signals is small, it is difficult to perform TOA measurements which are preferred for calculating the location of the mobile station.
Accordingly, there is a need for a new method for determining the position of a mobile station from the mobile station's transmissions in the AMPS system.
SUMMARY OF THE INVENTION
The present invention is a method for determining the location of a mobile station based on transmissions from the mobile station. When the mobile station places an emergency call or any other call requiring positioning is made either by the mobile station or by the network, the nature of the call is identified at the base station serving the mobile station. Several base stations in neighboring cells are alerted and ordered to monitor the frequency to which the mobile station is assigned. The serving base station sends a control message to the mobile station which induces the mobile station to transmit a known bit sequence. The serving base station and neighboring base stations make measurements on the known bit sequence transmitted by the mobile station. The measurements include the time of arrival of the known bit sequence at each of the base stations. The time measurements made by each of the base stations are forwarded to a mobile positioning center which calculates the position of the mobile station using well known algebraic techniques.
In the preferred embodiment of the invention, each base station obtains a quality estimate of the measurements made at that base station. This estimate could be the signal quality of the transmissions from the mobile station. The measurement quality estimates are forwarded to the mobile positioning center along with the time measurements. The mobile positioning center uses the measurement quality estimates to perform a quality check. If the measurement quality is not sufficient to obtain the desired degree of accuracy in the calculation of the mobile station location, the measurement process is repeated. To repeat the measurement process, the mobile positioning center commands the serving base station to repeat the control message. After repeating the control message, the serving base station and neighboring base stations again take measurements on the confirmation from the mobile station and send the new measurements to the mobile positioning center. This process is repeated as many times as necessary until the desired degree of accuracy is obtained. After calculating the position of the mobile station, the mobile positioning center transmits the mobile station's location to the emergency call center, or to any other application requesting the position of the mobile station.
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Hoff Anders Carl Erik
Koorapaty Havish
Lundquist Patrik Nils
Coats & Bennett
Cong Le Thanh
Erksson INC
Nguyen Thuan T.
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