Abstract:
A Universal Mobile Telecommunications System (“UMTS”) is modified to provide location-determining services similar to Wireless-Assisted-GPS (“WAG”) services to mobiles without requiring the deployment of a GPS receiver inside the UMTS network. The resulting network is known as a UMTS Network Assisted GPS (“UNAG”) network. A UNAG network is created by deploying a UNAG server inside a UMTS network. The UNAG server provides WAG-like services to mobiles. Only one UNAG server is needed in an entire system, allowing the cost of the UNAG server to be amortized over a number of Mobile Switching Centers (“MSCs”) in the UMTS network. The UNAG server provides excellent location-prediction accuracy and reduces the amount of time required to determine the location of a mobile in a UMTS network.

Description:
BACKGROUND OF THE INVENTION 
     Traditionally, in order to estimate the location of a mobile telecommunications unit (“mobile”), such as a cellular phone, a laptop computer, a personal digital assistant or the like, the mobile needs to receive and decode signals from four distinct Global Positioning System (“GPS”) satellites. These signals contain two sources of information from which a mobile&#39;s location can be computed: 1) pseudo-ranging information; and 2) the satellites&#39; ephemeris. Pseudo-ranging information is used to compute the time difference of arrival of the signals from the satellites to a destination (in this case, the mobile). The satellites&#39; ephemeris comprises information about the exact locations of the satellites in space, typically compiled in a tabular format. With these two sources of information, it is possible to determine the location of a mobile using a triangulation technique. 
     There exists IS-95 based WAG systems which provide location predictions with a high level of accuracy (e.g., within about 15 feet). Such WAG systems take advantage of the fact that there are GPS receivers in IS-95 base stations, which have radio connections to mobiles, and in MSCs for synchronization purposes. These same GPS receivers are used by WAG systems to reduce the time required to determine the location of a mobile. The primary goal of WAG is to reduce the processing and computing load on a mobile. This goal is met by removing the need for the mobile to process or compute pseudo-ranging information and ephemeris information contained in a GPS signal. To accomplish this, a WAG server is placed in a MSC accompanied by a full GPS receiver to perform the bulk of the signal processing and computation. Assuming the MSC to which the mobile is connected can receive signals from the same satellites as the mobile because of its proximity to the mobile (e.g., less than 100 km), the MSC can tell the four satellites, from among twenty-four GPS satellites, to which the mobile needs to tune. This information significantly reduces the time required for the mobile to search for visible satellites. Furthermore, since the MSC&#39;s GPS receiver is capable of decoding pseudo-ranging and ephemeris information, it is not necessary for the mobile to process this information, thus reducing the processing load on the mobile. This reduction in processing load on mobiles allows for the use of simplified GPS receivers in WAG-capable mobiles. 
     The present invention concerns the determination of a mobile&#39;s location in a UMTS network. UMTS is a third-generation wireless system which is designed to support high-data-rate multimedia services. However, in a UMTS network, the base stations are not synchronized. This means that GPS receivers are not required for the operation of a UMTS. The lack of GPS receivers complicates the implementation of WAG-like services in a UMTS network. One way of providing WAG-like services in a UMTS would be to add GPS receivers to MSCs in a UMTS landline network. However, this solution would significantly increase the overall cost of the system. 
     Accordingly, it is desirable to provide methods and systems for implementing WAG-like services in UMTS networks that do not require the addition of traditional GPS receivers. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods and systems for determining the location of mobiles in a telecommunications system. More specifically, the present invention comprises methods and systems for locating a mobile within a UMTS network. According to embodiments of the present invention, a UNAG server is deployed within a UMTS landline network and is adapted to provide WAG-like services to mobiles comprising simplified GPS receivers. The UNAG server contacts a GPS Master Control Station (MCS), such as the one located in Colorado Springs, Colorado, to obtain orbital positioning information on all GPS satellites. When a mobile requests information about its location, the UNAG server processes the orbital positioning information to determine which four GPS satellites should be visible to the mobile. The UNAG server then transmits tuning information associated with the four satellites to the mobile, which enables the mobile to receive GPS information from the four satellites. Next, the mobile decodes pseudo-ranging information from within the GPS information and transmits it to the UNAG server. The UNAG server processes the pseudo-ranging information associated with the mobile along with the previously calculated positions of the four satellites to calculate the geographic location of the mobile. Finally, the UNAG server transmits location information back to the mobile. 
    
    
     UNAG networks envisioned by the present invention comprise faster and more cost-effective methods and systems for determining the location of mobiles in a UMTS network. The present invention and its advantages can best be understood with reference to the drawings, detailed description of the invention and claims which follow. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a network according to one embodiment of the present invention. 
     FIG. 2 depicts another schematic representation of a network according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides methods and systems for determining the location of mobiles in a UMTS network. According to one embodiment of the present invention, a novel UMTS network, hereafter referred to as a “UNAG network” is created by deploying a UNAG server within a landline network. The novel network is adapted to locate mobiles using WAG-like, location-determining capabilities without requiring the deployment of traditional GPS receivers in the network. According to the present invention, the geographic location of a mobile can be determined through a series of communications sent back and forth between a mobile and UNAG server. 
     For example, a UNAG server first contacts a GPS MCS at least once a day to obtain information about the position of GPS satellites. When a request for location information arrives from a mobile, the UNAG server is adapted to compute the positions of all of the GPS satellites by processing the information obtained from the GPS MCS and is then adapted to identify four satellites from which the mobile can receive signals. The UNAG server is thereafter adapted to transmit tuning information associated with these four satellites to the mobile. 
     Upon receiving this information from the UNAG server, the mobile is then adapted to tune to these four satellites, to receive information from them, to decode information from within the received information and to subsequently transmit the decoded information to the UNAG server. 
     Upon receiving this decoded information, the UNAG server is adapted to process the information transmitted from the mobile along with the previously calculated positions of the four satellites and is further adapted to calculate the location of the mobile. Finally, the UNAG server is adapted to transmit the calculated location back to the mobile in the form of “location information”. 
     Because the UNAG server processes much of the information transmitted by the satellites and calculates the location of the mobile, this burden is removed from the mobile. This helps reduce the time required to determine the location of the mobile and allows for the use of simpler, less expensive mobiles. The present invention will now be described in detail using additional illustrative examples. 
     FIG. 1 depicts a schematic representation illustrating one embodiment of the present invention. Referring to FIG. 1, UNAG network  1  comprises wireless network  100 , landline network  200 , GPS MCS  300  and GPS satellites  400 . Wireless network  100  comprises a mobile  101 . Mobile  101  is adapted to send and receive information within the wireless network  100  via pathway  110 . Mobile  101  comprises a simplified GPS receiver (“mobile GPS”)  101   a  which is adapted to receive GPS information from GPS satellites  400  and is further adapted to decode only pseudo-ranging information from within GPS information. In an illustrative embodiment of the invention, mobile GPS  101   a  comprises a mobile GPS similar to those used in WAG-capable, IS-95 based mobiles. Continuing, landline network  200  comprises UNAG server  201 . UNAG server  201  is connected to landline network  200  through pathway  210  and is connected to GPS MCS  300  through a dedicated pathway  123 . Landline network  200  and wireless network  100  are adapted to communicate with each other via pathway  120 . In one embodiment of the present invention, UNAG server  201  comprises a general-purpose workstation. 
     Satellites  400  comprise twenty-four satellites which orbit the earth. Satellites  400  are adapted to transmit GPS information to the mobile GPS  101   a  via pathways  140  and to transmit orbital positioning information to the GPS MCS  300  via pathway  143 . The GPS information and orbital information transmitted by satellites  400  is carried within a Course Acquisition (“C/A”) signal. The C/A signal associated with each satellite  400  comprises a unique Pseudo-Random Noise (“PRN”) sequence. This enables GPS-capable devices to tune to particular satellites by matching PRN sequences and further enables such devices to identify which satellite is sending a particular signal. Continuing, GPS MCS  300  is adapted to transmit information to GPS satellites  400  and to adjust/fine-tune their orbital position. UNAG server  201  is adapted to access orbital positioning information in GPS MCS  300  through a dedicated connection or pathway  123 . Thereafter, UNAG server  201  is further adapted to calculate the location of the mobile and to transmit location information to the mobile. A further description of the operation of UNAG network  1  will now be provided. 
     UNAG server  201  is adapted to receive a request for location information from the mobile  101 . In order for the location of mobile  101  to be determined, the mobile GPS  101   a  must receive GPS signals from four satellites. The first step in determining the location of the mobile  101  is to determine the four satellites from which mobile GPS  101   a  can receive signals. Because all of the satellites  400  are constantly moving, the four satellites from which the mobile GPS  101   a  can receive signals are also constantly changing. However, because the movement of satellites  400  is very predictable, their location at a particular time of day can always be calculated. A GPS MCS  300 , such as the one located at Colorado Springs, Colo., is adapted to update and precisely tune the locations of all of the satellites  400  at least once a day to maintain the satellites&#39; proper orbital positions. UNAG server  201  is adapted to contact the GPS MCS  300  at least once a day to obtain orbital positioning information associated with the satellites  400 . This orbital positioning information comprises the satellites&#39; ephemeris and pseudo-ranging information based on the location of GPS MCS  300 . At any time during a day, upon receiving a request from mobile  101  for location information, UNAG server  201  is adapted to compute the exact positions of all twenty-four satellites  400  by processing the orbital positioning information, and is then adapted to identify specific satellites (“visible satellites”), such as satellites  400   a - 400   d , from within satellites  400  which can be seen by the mobile  101 . It should be understood that the present invention is not limited to receiving orbital information from an MCS. To the contrary, the UNAG server  201  may receive the orbital information from an MCS-like source. It so happens, however, that an MCS is presently the only source for such information. 
     Once visible satellites  400   a - 400   d  are identified, UNAG server  201  is adapted to transmit tuning information associated with visible satellites  400   a - 400   d  through landline network  200  and wireless network  100  to mobile  101 . The tuning information comprises the PRN sequences associated with visible satellites  400   a - 400   d . Continuing, mobile GPS  101   a  is adapted to tune to visible satellites  400   a - 400   d by matching the PRN sequences transmitted to it by the UNAG server  201 . Satellites  400   a - 400   d are then adapted to transmit GPS information to mobile GPS  101   a . Mobile GPS  101   a  is thereafter adapted to receive the GPS information and to decode pseudo-ranging information from within the GPS information. Mobile  101  is then adapted to transmit the decoded pseudo-ranging information to UNAG server  201  via the wireless network  100  and landline network  200 . UNAG server  201  is adapted to process the decoded pseudo-ranging information associated with the mobile  101  along with the previously calculated positions of the visible satellites  400   a - 400   d  and is then adapted to calculate the location of the mobile  101 . UNAG server  201  is thereafter adapted to transmit location information back to mobile  101 , thus completing one cycle of an illustrative embodiment of the present invention. 
     FIG. 2 depicts another embodiment of the present invention. In an illustrative embodiment of the present invention, the components of FIG. 2 communicate as indicated by the arrows. Comparing FIG. 2 to FIG. 1, reference numbers which are repeated indicate substantially the same components. 
     Referring to FIG. 2, UNAG network  10  comprises wireless network  100 , landline network  200 , GPS MCS  300  and satellites  400 . Landline network  200  comprises UNAG server  201 , UMTS Mobile Switching Center (“UMSC”)  202 , Serving General Packet Radio Service-Service Node (“SGSN”)  203  and Radio Network Controller (“RNC”)  204 . Mobile connections to landline network  200  are established through RNC  204  in combination with either UMSC  202  or SGSN  203 , depending on the connection type. For voice communications, RNC  204  routes calls to UMSC  202  and then to a Public Switched Telephone Network (not shown). For data communications, the RNC  204  routes data packets to SGSN  203 , through a Gateway GSN (not shown) and then out to a public data network (not shown). Since it is not known, a priori, whether a mobile is set up to transmit voice, data or both, UNAG server  201  is necessarily connected to both UMSC  202  and SGSN  203 . 
     Continuing, wireless network  100  of FIG. 2 comprises mobile  101  and base stations  102   a - 102   c . Mobile  101  comprises mobile GPS  101   a  and is communicatively connected to base station  102   a . The particular configuration of base stations  102   a - 102   c  and mobile  101  is by way of example only. It is to be understood that other embodiments may comprise any number of base stations and/or mobiles. 
     The UNAG network  10  of FIG. 2 operates similarly to the UNAG network  1  in FIG.  1 . Upon receiving a request for location information from mobile  101 , UNAG server  201  is adapted to compute the positions of the satellites  400  by processing orbital positioning information it has received from the satellites  400 , and is then adapted to identify satellites  400   a - 400   d  as those from which the mobile  101  can receive signals. In one embodiment of the invention, UNAG server  201  is adapted to identify visible satellites  400   a - 400   d  based on the location of the base station that is communicatively connected (or “assigned ”) to the mobile  101 . For example, because base station  102   a  is assigned to mobile  101 , the location of base station  102   a  can be used to identify visible satellites  400   a - 400   d . Backtracking somewhat, it is possible to use the location of UMSC  202  to identify visible satellites  400   a - 400   d , as is done in WAG systems which comprise a MSC. However, in a rural environment with very large cells, it is possible that the service area of a MSC could exceed the one hundred-square-mile limit within which a mobile and a MSC are able to receive signals from the same four satellites. The same possibility exists with a UMSC in the UNAG network  10 , since an MSC and UMSC are analogous components. 
     Using the location of UMSC  202  to determine which four satellites are visible to mobile  101 , therefore, could result in the wrong satellites being identified. On the other hand, using the location of base station  102   a  to identify visible satellites  400   a - 400   d  ensures that satellites  400   a - 400   d  will be identified correctly. This is because base stations  102   a - 102   c  will almost always be located so that they can receive signals from the same satellites as the mobiles  101  to which they are assigned. 
     Once visible satellites  400   a - 400   d  are identified, UNAG server  201  is adapted to transmit tuning information associated with satellites  400   a - 400   d  through the landline network  200  and base station  102   a  to mobile  101 . Again, based on this information, mobile GPS  101   a  is adapted to tune to satellites  400   a - 400   d . Once satellites  400   a - 400   d  have transmitted GPS information to mobile  101 , mobile GPS  101   a  is thereafter adapted to decode the pseudo-ranging information within the GPS information. Mobile  101  is then adapted to transmit the decoded, pseudo-ranging information to UNAG server  201  via base station  102   a , RNC  204  and either UMSC  202  or SGSN  203 . UNAG server  201  is adapted to process the decoded pseudo-ranging information associated with the mobile  101  along with the previously calculated positions of visible satellites  400   a - 400   d . Thereafter, UNAG server  201  is adapted calculate the location of the mobile  101  and to transmit location information to mobile  101 , thus completing a cycle of the present invention. 
     In sum, the present invention enables a UNAG network to provide highly accurate, high-speed location information to mobiles in a cost-effective manner. The UNAG server is adapted to perform the functions of a WAG server and a GPS receiver. This allows WAG-like services to be provided to mobiles in existing UMTS networks without requiring the deployment of traditional GPS receivers within UMTS landline networks. Because a UNAG network is created by deploying a single UNAG server in a UMTS network, the cost of the UNAG server can be amortized over the number of MSCs in the network. Since the UNAG server is capable of processing orbital positioning information and transmitting tuning information associated with visible satellites to a mobile, the time required for a mobile to search for visible satellites is reduced. The mobile can quickly tune to visible satellites by matching PRN sequences provided by the UNAG server instead of searching through the PRN sequences associated with all twenty-four GPS satellites. Furthermore, because much of the processing is done by the UNAG server, mobiles need only comprise less expensive, simplified GPS receivers. Such processing also reduces the time required to calculate the location of the mobile. 
     Though much of the discussion above focused on a mobile as an assembled device, such as a cellular phone, the present invention is not so limited. Rather, the present invention envisions embodiments where a “mobile” comprises a component of an assembled device, such as a transceiver. 
     Other advantages of the present invention will be readily apparent to those skilled in the art. It is to be understood that variations can be made by those skilled in the art without exceeding the scope and spirit of the present invention.