The present invention is directed, in general, to wireless networks and, more specifically, to a system for locating a mobile station in wireless network.
Reliable predictions indicate that there will be over 300 million cellular telephone customers worldwide by the year 2000. Within the United States, cellular service is offered by cellular service providers, by the regional Bell companies, and by the national long distance operators. The enhanced competition has driven the price of cellular service down to the point where it is affordable to a large segment of the population.
The current generation of cellular phones is used primarily for voice conversations between a party using a subscriber handset (i.e., a wireless mobile station) and another party through the wireless network. A smaller number of wireless mobile stations are data devices, such as personal computers (PCs) equipped with cellular/wireless modems. Because the bandwidth for a current generation wireless mobile station is typically limited to a few tens of kilobits per second (Kbps), the applications for the current generation of wireless mobile stations are relatively limited.
However, this is expected to change in the next (or third) generation of cellular/wireless technology, sometimes referred to as xe2x80x9c3Gxe2x80x9d cellular/wireless, where a much greater bandwidth will be available to each wireless mobile station (e.g., 125 Kbps or greater). The higher data rates will make Internet applications for wireless mobile stations much more common, including web browser applications, streaming audio and/or video applications, and the like.
The 3G wireless systems will also provide a number of new services and features that either are not available or are rarely available in conventional wireless networks. These new features of 3G wireless systems include position location capabilities that may be used to determine the location of a wireless mobile station. In some instances, position location capabilities will be mandated by law. For example, the Federal Communications Commission (FCC) has mandated that 3G wireless networks must be able to determine the location of a mobile station making an emergency call (e.g., E-911 call).
A number of conventional techniques have been used to determine the location of wireless mobile stations. These prior art techniques include: Time of Arrival (TOA), Angle of Arrival (AOA), and Time Difference of Arrival. Some conventional position location systems combine two or more of these techniques, such as TOA/AOA and TDOA/AOA. Also, a mobile station may include a global positioning system (GPS) device that determines the location of the mobile station and transmits this position information to the wireless network.
However, each of the prior art systems has numerous drawbacks. In a TOA position locating system, all mobile stations serviced by the network must be able to calculate highly accurate mobile station processing times. Also, TOA position locating systems are susceptible to timing errors caused by multiple signal reflections and require a minimum of three base station receivers to perform triangulation. AOA position locating systems require a minimum of three base station receivers equipped with multi-array antennas to perform triangulation. These multi-array antennas are expensive and replace conventional antenna arrays. TDOA position locating systems also require a minimum of three base station receivers. However, if the mobile station is too close to one base station receiver, it is usually out of the listening range of the other two base stations. GPS-based systems increase the cost of the wireless handset and are dependent on a line-of-sight to the GPS satellites.
Therefore, there is a need in the art for improved systems and methods for locating a mobile station. In particular, there is a need in the art for improved systems and methods for accurately locating a mobile station that has placed an emergency (or 911) call. More particularly, there is a need in the art for improved systems and methods for accurately locating a mobile station that do not require costly multi-array antennas.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a wireless network comprising a plurality of base stations capable of communicating with a plurality of mobile stations, a mobile station locating system associated with a first one of the plurality of base stations for determining the location of a first one of the plurality of mobile stations. In an advantageous embodiment of the present invention, the mobile station position locating system comprises: 1) a timer capable of measuring a first round trip delay time associated with a position locator message transmitted from the first base station to the first mobile station and a position locator acknowledgment message transmitted from the first mobile station back to the first base station; 2) a power monitor capable of measuring a power level of the position locator acknowledgment message received by the first base station and determining that the received power level has saturated a receiver associated with the first base station; and 3) a data processor coupled to the timer and to the power monitor capable of causing the first base station to transmit at least one power control message to the first mobile station capable of causing the first mobile station to increase a transmission power level of the position locator acknowledgment message, the increased transmission power level causing the receiver to saturate, wherein the data processor, in response to a determination that the first base station receiver has saturated, calculates from the first round trip delay time a first distance between the first mobile station and the first base station.
According to one embodiment of the present invention, the data processor, in response to the determination that the receiver has saturated, transmits a first position location command to a selected second one of the plurality of base stations, wherein the first position location command is capable of causing a second mobile station locating system associated with the selected second base station to calculate a second distance between the first mobile station and the selected second base station.
According to another embodiment of the present invention, the selected second base station transmits the second distance to the data processor in the first base station and wherein the data processor determines from the first distance and the second distance the location of the first mobile station.
According to still another embodiment of the present invention, the data processor, in response to the determination that the receiver has saturated, transmits a second position location command to a selected third one of the plurality of base stations, wherein the second position location command is capable of causing a third mobile station locating system associated with the selected third base station to calculate a third distance between the first mobile station and the selected third base station.
According to yet another embodiment of the present invention, the selected third base station transmits the third distance to the data processor in the first base station and wherein the data processor determines from the first distance, the second distance, and the third distance, the location of the first mobile station.
According to a further embodiment of the present invention, the first base station comprises a sectored antenna capable of receiving the position locator acknowledgment message in a plurality of antenna sectors, and wherein the data processor is capable of determining a first of the plurality of antenna sectors that is most strongly receiving the position locator acknowledgment message.
According to still further embodiment of the present invention, the data processor is capable of determining from the first antenna sector a general direction of the first mobile station with respect to the first base station.
According to a yet further embodiment of the present invention, the data processor selects the selected second base station and selects the selected third base station based on the general direction of the first mobile station.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.