Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
1998-12-11
2001-02-20
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C455S456500
Reexamination Certificate
active
06191737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates, in general, to determining the position of a mobile station within a mobile cellular telecommunications network, and specifically to a system and method for more accurately determining mobile station position along border regions within the mobile cellular telecommunications network.
2. Background and Objects of the Invention
Mobile radio position determination is an emerging field that has gained a great deal of interest lately, and it is now desirable to include a position determination capability in future cellular mobile radio systems. The Time Difference of Arrival (TDOA) position determination method, which is known from military applications, has been used successfully for determining the position of mobile radio terminals. A typical TDOA position determination system can be either terminal based, whereby Time Of Arrival (TOA) measurements are made on the “downlink” in the mobile station (MS), or network based, whereby the network performs the TOA measurements on the “uplink” in the radio base transceiver stations (BTSs). These TOA measurements are then used to calculate TDOA parameters and estimate the position of the mobile station (MS).
A network-based method for determining the position of cellular mobile stations is disclosed in commonly-assigned Swedish Patent Application No. 9303561-3 to R. Bodin. In order to determine the position of a mobile station, a handover procedure is initiated between a serving base transceiver station and the new base transceiver station. The mobile station transmits access request signals to a new base transceiver station. The base transceiver station measures the time delay for the access request signal to travel between the mobile station and the base transceiver station. This procedure is repeated between the mobile station and one or more additional base transceiver stations. A service node in the cellular network calculates the position of the mobile station by utilizing information about the known positions of the base transceiver stations and the measured access time delays.
This network-based method of determining the position of cellular mobile stations relies on so-called asynchronous handovers, where the target base transceiver stations measure the access delays to the mobile station. Each access delay is used as a measure of the distance between the mobile station and the respective base transceiver station. In specific situations, i.e., MS positioning, a number of BSs may concurrently tune to the same transmitting MS in order to make time delay of arrival measurements between the MS and the BSs. The time delay of the signal transmitted by the mobile station during a handover procedure may be measured by the BSs for use by a processing unit to determine the position of the mobile station.
Although the above-described system illustrates considerable progress in the cellular position determination field, there are still a number of deficiencies to be improved upon. There are circumstances in existing systems having TOA-based mobile station positioning capabilities in which the determination of a mobile station position may not be highly accurate. Specifically, the location of a mobile station may be most accurately determined by measuring time delays from locations which surround the mobile station to be located and performing a triangulation calculation based upon the measured time delays. Existing systems may potentially measure time delays from locations which fail to surround the mobile station to be located, especially when the mobile station is located near the border between two areas served by separate mobile switching centers (MSCs) or other entities within the network. Consequently, location determinations in such a scenario will not be highly accurate. There exists a need for a system for more accurately determining the position of a mobile station within a mobile cellular telecommunications network.
SUMMARY OF THE INVENTION
The present invention is directed to a system and method for accurately determining the location of a mobile station in a mobile cellular telecommunications network. The mobile telecommunications network includes a plurality of mobile switching centers (MSCs) to which a number of base station systems are communicatively associated to provide wireless telecommunication services as is known in the art. In addition, a plurality of mobile location centers (MLCs) are associated with the MSCs in the telecommunications network to control network resources in executing a mobile station positioning determination. A single MLC may be associated with a number of MSCs within the telecommunications network. Further, a database is maintained by each MSC which includes a listing of the neighboring MSCs possessing mobile station positioning capabilities.
The present system further includes a plurality of location measurement units (LMUs) which perform radio measurements for supporting the MLCs in determining TOA-based mobile station positioning. Specifically, an LMU is capable of measuring a time of arrival of access burst signals transmitted by the mobile station to be located. An LMU communicates with its respective MLC via its assigned base station and MSC.
According to the present invention, an application may request the location of a particular mobile station. The MLC corresponding to the visiting MSC (VMSC) serving the mobile station may be forwarded the location determination request. Based upon the general location of the mobile station within the area served by the VMSC, the corresponding MLC identifies the appropriate LMUs for most accurately measuring the TOA of signals transmitted by the mobile station. In the event the mobile station is roaming near the border of two areas served by neighboring MSCs controlled by the same MLC, such as the areas served by the VMSC and one of its neighboring MSCs, at least one of the LMUs identified by the MLC for performing the TOA measurements may be located in the area served by the neighboring MSC. The MLC transmits a signal to the VMSC including information pertaining to the identified LMUs and their corresponding MSCs (the VMSC and the neighboring MSC, in this case).
Upon reception of the information, the VMSC accesses its database to verify that information pertaining to another MSC transmitted by the MLC is a neighboring MSC and possesses location determination capabilities. The VMSC then forwards the signal to its own identified LMUs as a DTAP message. Upon verifying that the identified MSC is a neighboring MSC having positioning capabilities, the VMSC encapsulates a DTAP message within a signal and transmits the encapsulated DTAP message to the identified, neighboring MSC. The neighboring MSC unpacks the DTAP message and forwards the DTAP message on to its LMU identified by the MLC. Following each LMU identified by the MLC receiving the DTAP message, the TOA measurements are undertaken.
Upon completion of the TOA measurements, each LMU returns the measurement information to the VMSC. The timing measurements taken by the LMU(s) associated with the neighboring MSC are transmitted as a DTAP message to the neighboring MSC, after which the neighboring MSC encapsulates the DTAP message and forwards the encapsulated message to the VMSC. The VMSC unpacks the encapsulated DTAP message and sends the received DTAP messages to the MLC. Based upon the timing measurements, the MLC calculates the position of the mobile station. By employing one or more LMUs of a neighboring MSC in the TOA analysis so as to suitably surround the mobile station to be located, the position of the mobile station is very accurately determined.
REFERENCES:
patent: 6064885 (2000-05-01), Rouhollahzadeh et al.
Havinis Theodore
Papadimitriou Dimitris
Ericsson Inc.
Jenkens & Gilchrist P.C.
Mull Fred H.
Tarcza Thomas H.
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