HK1036108B - Method and apparatus for operating a satellite positioning system receiver - Google Patents

Description

Method and apparatus for operating a satellite positioning system receiver

Background

The present invention relates to a method of operating a Satellite Positioning System (SPS) receiver, and more particularly to a system in which the receiver provides information about its position over a wireless communication link.

Conventional Satellite Positioning Systems (SPS), such as the Global Positioning System (GPS), use signals from satellites to determine their position. GPS receivers typically determine their position by calculating the relative times of arrival of signals transmitted simultaneously from multiple GPS satellites. These satellites transmit as part of a message satellite positioning data as well as data relating to the time of day plus clock timing (collectively referred to herein as ephemeris data). The process of searching for and acquiring GPS signals, reading ephemeris data for a plurality of satellites and calculating the position of the receiver from these data is time consuming, typically requiring several minutes. In many cases, this long-term treatment is unacceptable, and this results in a shortened battery life when portable operation and application.

Another limitation with current GPS receivers is that their operation is limited to a situation where multiple satellites must be clearly visible in view without ambiguity and where good quality antennas must be employed to receive these signals. Thus, such receivers are generally not useful in body-mounted portable device applications, nor in areas or buildings where foliage or building obstructions are significant.

The GPS receiving system has two main functions: (1) calculating pseudo-ranges relative to each GPS satellite; and (2) a calculation of the position of the receiving platform using the pseudoranges and satellite timing and ephemeris data. The pseudorange is simply the time delay measured between the signal received from each satellite and the local clock in the GPS receiver. The satellite ephemeris and timing data is extracted from the GPS signals after being acquired and tracked. As mentioned above, collecting this information typically takes a considerable amount of time (e.g., 30 seconds to several minutes) and must be done with good received signal levels, resulting in a low error rate.

In recent years, GPS receivers have been used with radio transmitters, such as cellular or mobile phones in vehicles, to transmit the position of the receiver while the vehicle is moving. Conventional combined GPS/communication systems typically transmit a location from a radio transmitter to a base station located at a remote location. Typically, the GPS receiver will determine its position and then provide this information to the transmitter, which then transmits the determined position before the GPS receiver has determined the next position. This enables an operator at a remotely located base station passing through the radio signal receiving location to track the path of the GPS receiver as it moves over time. In another embodiment, as described in U.S. patent No. 5,663,734, a mobile GPS receiver including a communications transmitter transmits time-stamped pseudoranges instead of a complete position calculation (e.g., latitude, longitude and altitude of the GPS receiver). At this point, a mobile unit including a GPS receiver will collect GPS signals and process those signals to determine the location of the mobile unit by transmitting pseudoranges to satellites in view at specific times, and then a transmitter will transmit those pseudoranges to remotely located base stations which process those pseudoranges with time stamps of ephemeris added to the pseudoranges collected at the base stations or provided to the base stations. At the same time, a set of pseudoranges will be transmitted before the GPS receiver determines the next set of pseudoranges.

While these prior art methods provide a way to track the path of a mobile GPS receiver, there are several concerns with using these techniques. In the case of a mobile GPS receiver determining its position and transmitting the position to a remotely located base station, the mobile unit must be able to see the sky and receive multiple satellites clearly in order to be able to calculate pseudoranges and read ephemeris data before the GPS receiver can determine its position. In addition, when the mobile GPS receiver attempts to compute several positions and then transmits them in one transmission, the receiver is typically unable to benefit from differential GPS corrections unless a large set of differential corrections are buffered at the base station. A mobile GPS receiver that collects a series of digitized samples of GPS signals and transmits the series of digitized samples in one transmission will consume a significant amount of battery power and congestion in the wireless link can occur due to the large amount of data being collected, stored and transmitted. See european patent 0508405.

When the mobile GPS receiver transmits one pseudorange at a time, the communication transmitter must be constantly powered on to transmit each set of pseudoranges after the pseudoranges have been determined. This can shorten the life of the battery in the mobile unit and also cause congestion in the wireless communication link between the mobile unit and the base station. In addition, the air time cost of such operations is also high.

It would therefore be desirable to have an improved method and system for providing multiple sets of location information over a period of time by a mobile GPS unit.

Summary of The Invention

The present invention provides a method and apparatus for operating a satellite positioning system receiver so that the position of the receiver can be tracked at any time.

In one example of a method according to the present invention, a first plurality of pseudoranges is determined at a first time and a second plurality of pseudoranges is determined at a second (and possibly further) time after the first time. The first plurality of pseudoranges and the second plurality of pseudoranges are stored within a satellite positioning system receiver. After a second time, the first plurality of pseudoranges and the second plurality of pseudoranges are transmitted from the mobile SPS receiver.

In one particular example of the method of the present invention, a set of pseudoranges taken in a column is stored in a queue and transmitted upon the occurrence of a predetermined type of event or alarm condition from a mobile GPS unit. And sending according to the judgment that the event of the preset type or the alarm condition occurs. Typically, the GPS receiver will receive a first GPS signal determined as a first plurality of pseudoranges and also receive a second GPS signal determined as a second plurality of pseudoranges. The mobile unit will also determine a first receive time at which the first GPS signal was received at the mobile unit and determine a second receive time at which the second GPS signal was received at the mobile unit. These receive times will be sent along with the pseudorange sets. The base station will receive a group queue of pseudoranges in a single signal transmission or similar in a packet-like manner and will use these pseudoranges and the time of receipt of the pseudoranges and the ephemeris to determine the respective times specified by the mobile GPS unit time of receipt. If a predetermined type of event (or alarm condition) does not occur, then in some embodiments, pseudorange information is not transmitted at any time. Various other aspects and embodiments of the invention are described below.

Brief Description of Drawings

The invention is described below with reference to non-limiting examples in the accompanying drawings. In the drawings, like numbering represents like elements.

FIG. 1A depicts a system for tracking the path of a mobile GPS unit in accordance with an example of the present invention.

Fig. 1B illustrates an example of a method performed by a mobile GPS unit by which a remotely located location server can determine a location at various times throughout the mobile unit.

Fig. 1C illustrates an example method by which a location server determines respective positions from a pseudorange set queue obtained from a mobile unit over time.

Figure 2 illustrates another example system that employs a cellular communication system to track the location of a mobile unit over time.

Fig. 3 illustrates an example of a location server that may be used with the cellular communication system of an example of the invention.

Figure 4 illustrates an example of a mobile GPS receiver combined with a communication system according to an example of the present invention.

FIG. 5 illustrates an example of a GPS reference station for use with an example of the present invention.

Detailed Description

The present invention relates to the use of Satellite Positioning System (SPS) receivers to provide position information indicative of the movement of the receiver at any time. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. However, some well-known conventional details are not described in detail to avoid obscuring the understanding of the present invention.

FIG. 1 is an example system for tracking the position of a mobile GPS receiver as it moves. On the map of the figure, a mobile GPS receiver 12 is shown, the current location of which is located on a road 11. Their previous positions 14, 16, 18, 20, 22 and 24 are also shown on the road 11. In the particular example shown in FIG. 1A, we assume that the user of the rover GPS receiver 12 is traveling on a roadway 11 and that the starting point is position 14, passes through positions 16, 18, 20, 22 and 24, and is now at the position in FIG. 1A. The mobile GPS receiver 12 comprises a GPS receiver, which may be a conventional GPS receiver, which may provide pseudorange outputs to a transmitter that is part of a communication system, such as the communication system transceiver 78 shown in fig. 4, which is an example of the mobile GPS receiver 12. Additionally, the mobile GPS receiver may be similar to the GPS receiver and communication system described in U.S. patent 5,663,734. In either embodiment, the mobile GPS receiver 12 will include a memory that stores the pseudoranges and a time stamp indicating when the GPS signals were received at the time the pseudoranges were determined.

The system shown in FIG. 1A also includes a positioning server 25, the positioning server 25 being coupled via a wireless communication system to a communication system coupled to the mobile GPS unit 12 or being part of the mobile GPS unit 12. The base station 25 typically includes a memory 26 that stores time series of differential GPS and satellite ephemeris information. The base station 25 also typically includes a GPS reference receiver 27, which reference receiver 27 can read satellite ephemeris data from satellites that are in view and can also provide GPS time and differential GPS information. Therefore, the GPS reference receiver 27 can determine the differential GPS and satellite ephemeris information and time stamp the GPS, which the base station can then store in the memory 26. This is done so that over time each satellite in the field of view has ephemeris and a series of differential GPS information.

In other embodiments, the GPS reference receiver 27 may be replaced by the same type of information source at the remote end that it provides to the base station server 25. For example, a small network of GPS receivers may be used to provide such information to a large number of geographically dispersed base stations, thereby reducing the total number of GPS reference receivers required.

Fig. 1B shows an example of a method according to the invention. The method begins at step 31 with receiving a GPS signal by a mobile GPS unit and determining a plurality of pseudoranges to a plurality of GPS satellites. As explained above, the GPS receiver may be a conventional receiver that employs hardware correlation to determine pseudoranges. In addition, pseudoranges may also be determined in the manner described in U.S. Pat. No. 5,663,734. Alternatively, the received, digitized and stored GPS signals are time stamped to indicate the time at which the signal was received. At this time, these digitized signals are transmitted, not the pseudoranges. This alternative approach requires larger memory and larger transmission bandwidth in order to store and transmit this larger amount of data. At step 33, a plurality of pseudoranges are time stamped and a plurality of these pseudoranges are stored with corresponding time stamps. The time stamp may be derived by reading the time from a GPS signal received by the mobile unit or, in some cases, by using a CDMA cellular communication system as the communication system used for messaging between the mobile unit 12 and the base station 25. The CDMA signal includes time as part of the signal that the communication system and mobile unit 12 can use to time-stamp the time of receipt of the GPS signal to determine pseudorange. Another method for determining GPS collection time for determining pseudoranges is described in U.S. patent application 08/794,649 to Norman f.krasner, 1997, 3/2, which is incorporated herein by reference.

In a method according to an example of the invention, it is determined in step 35 that a predetermined event (or alarm) has occurred. The reader will appreciate that this step is optional and is typically used when determining whether to transmit a pseudorange stored with a corresponding time stamp. If a predetermined type of event (or alarm condition) has not occurred, then the process returns to step 31 where additional GPS signals are received and additional pseudoranges are determined. Until a predetermined type of event (or alarm condition) has not occurred, the process continues to loop through steps 31, 33 and 35, collecting a plurality of pseudoranges obtained at different times, each pseudorange having its own time stamp thereon, and storing them in the memory of the mobile unit 12. An example of such a memory is shown as memory 81 in fig. 4. When the predetermined type of event does occur, step 35 proceeds to step 37 where the stored pseudoranges and corresponding time stamps are communicated over the wireless communication system, e.g., a CDMA cell communication signal is communicated to a location server. Also, the memory storing the pseudoranges and time stamps is cleared for this portion of memory as shown in step 37. This allows another set of pseudoranges and their corresponding time stamps to be collected at the same time and stored for later transmission.

This approach has several advantages over the prior art where the position is determined at each point and then transmitted. It is also advantageous to determine several positions at any time, but not to transmit them, and to transmit them after collecting the positions. Attempting to determine the location of the mobile unit will require a proper view of the sky and proper ability to read signals from enough satellites so that satellite ephemeris data can be obtained. In addition, such an approach does not allow for the use of Differential Gps (DGPS) information that can improve the accuracy of the position calculation (unless the communication link is used to transmit DGPS data, which in turn requires the use of more energy). With the method of the present invention, only pseudoranges need to be determined by the mobile unit at any time. Therefore, it is not required to be able to read the satellite ephemeris data. With the improved processing technique described in U.S. patent 5,663,734, in most cases pseudoranges are obtained to enough satellites even when the sky is dark or the signal is weak. The pseudorange queues and transmissions that rely solely on the occurrence of events minimize the transmission "air time" and allow determinations to be made as historically required by the mobile location.

In the example shown in FIG. 1A, the mobile GPS receiver 12 will receive GPS signals at the locations 14, 16, 18, 20, 22, 24 and at the current location, and will also determine pseudoranges from these signals, which are stored in memory along with corresponding time stamps. If the predetermined type of event is a seventh set of signals collected for which pseudoranges are determined, then the mobile unit 12 will transmit all seven pseudoranges and corresponding time stamps for the mobile unit 12 at the position shown in FIG. 1A. There are a myriad of other possible predetermined events that may cause the transmission of a time-stamped pseudorange sequence. As already mentioned, one event is that some number of stored pseudoranges have been reached. Another predetermined type of event may be a sensor or detecting an alarm condition or some other condition and causing an alarm to be transmitted with stored pseudoranges. One such example is the detection of an accident vehicle, or the detection of an inflated airbag, or the detection of a vehicle warning. Another predetermined event may be a request by the base station to transmit a stored pseudorange in order to determine the current position of the mobile GPS receiver, as well as a previous position indicated in the time-stamped pseudorange. Another predetermined event may be that a memory limit has been reached for the stored pseudoranges. Another predetermined event may be that a predetermined time has elapsed since the last pseudorange transmission. If this time is variable, the stored number of pseudoranges may also be varied accordingly by changing the interval between signals collected and processed to determine pseudoranges. In another example of a predetermined event, it may also be that the user simply presses a button on the mobile GPS receiver.

Fig. 1C illustrates an example of operations performed on a location server, such as location server 25, in accordance with the method of the present invention. The method shown in fig. 1C begins at step 41 with the location server determining and storing a plurality of differential GPS corrections at each time in a series of time points and storing a time stamp for each respective plurality of differential GPS corrections. As described above with respect to the system shown in FIG. 1A, the positioning server 25 may receive or determine differential GPS corrections from GPS reference receivers having known locations. In the case of base stations and mobile units employing ad-hoc radio communication (and not widely distributed cellular systems), the GPS reference receiver is typically co-located with the positioning server and also typically has the same satellites in view as the mobile unit being tracked by the positioning server 25. The GPS reference receiver 27 may determine the differential GPS corrections in a conventional manner and also provides an indication of the times at which the GPS signals from which the differential GPS corrections were determined were received and provides this set of information for each time to the location server which causes the information to be stored in the memory 26. It should be appreciated that step 41 is generally continuous in the process shown in FIG. 1C. That is, the operations described in step 41 will be repeated and will occur sequentially to arrive at a queue of differential GPS corrections and a corresponding time stamp for each correction. This would enable differential GPS collection to be performed over extended travel times of mobile units such as mobile unit 12. For example, if it takes an hour for the mobile unit 24 to travel on the road 11 from the location 14 to the current location past the location 24, then at least one hour of differential GPS correction is required. However, if there is a limit on the duration in determining each mobile unit location history, then these corrected queue sizes may be made smaller (e.g., the queues may correspond to the last minute period).

The reader will appreciate that when a base station (location server) serves a large geographic area, the reference network of GPS reference servers may be required to provide differential corrections throughout the network. This will be described further below. Returning now to fig. 1C, at step 43, the location server receives a transmission containing sets of pseudoranges and corresponding time stamps for each set of pseudoranges. The reader will also understand that although the pseudoranges and time stamps are transmitted in one transmission, the transmission may be over several packets or may be interrupted, although for the purposes of the present invention this may be viewed as one transmission of a pseudorange queue already having a time stamp. The location server may select the most appropriate differential GPS corrections to use with each set of pseudoranges by comparing the time stamp of the differential GPS corrections with the time stamp of each set of pseudoranges at step 45. In effect, the location server determines a differential GPS correction, which may apply a time stamp whose time is closest in time to the pseudorange. After the appropriate differential GPS corrections are selected, the set of pseudoranges is corrected with these differential GPS corrections. It should be understood that while the preferred embodiment employs this differential GPS correction queue, it is not necessary to practice certain embodiments of the invention. At step 47, the location server determines the location of the transmitting mobile GPS unit from each set of corrected pseudoranges and corresponding time stamps. In this manner, the location server may determine the location of the mobile unit 12 at a time represented by a time stamp associated with a pseudorange derived from the mobile unit at the location 14, and the location server may also determine the locations 16, 18, 20, 22, 24 and their current locations and determine the times at which the mobile unit is at those locations. In this manner, the location server can track the movement of the mobile unit both spatially and temporally. This information can be used in several different ways in step 49. For example, the base station may provide the concierge service or routing information to the operator of mobile unit 12 by transmitting assistance information back to mobile unit 12 via the wireless communication system.

A pseudorange time history with a time history of the computed position is available so that the server can track the position and velocity of the vehicle. This is important to identify vehicles in emergency situations such as car accidents where the vehicle antenna is not operational.

Although the foregoing description generally assumes a point-to-point communication system between the communication system of mobile unit 12 and the communication system of base station 25, it should be understood that the communication systems may also be cellular communication systems, as described below.

Fig. 2 shows an example of a system 101 according to the present invention. The system includes a cellular communication system that includes a plurality of cell sites, each serving a particular geographic area or location. Examples of such cellular or cell communication systems are well known in the art, such as cell phone systems. It should be understood that the overlap of cells has been illustrated in fig. 2. However, the signal coverage areas of the cells may in fact overlap. The cell communication system shown in fig. 1 comprises three cells 102, 103 and 104. The reader will appreciate that multiple cells with corresponding cell sites and/or cellular service areas may also be included within system 101 and coupled to one or more cell switching centers, such as mobile switching center 105 and mobile switching center 106. Within each cell, such as cell 102, there is a wireless cell site (sometimes referred to as a base station), such as cell site 102a, that communicates with a communication system, typically including a receiver and transmitter that communicate using cell communication signals and a mobile GPS receiver, via a wireless communication medium. Such a combined communication system and mobile GPS receiver provides a combined system such as the receiver 102b shown in fig. 2. An example of such a combined system having a GPS receiver and a communication system is shown in fig. 4, and may also include a GPS antenna 77 and a communication system antenna system 79. Each cell site is typically coupled to a mobile switching center. In fig. 2, cell sites 102a and 103a are coupled to switching center 105 by connections 102c and 103c, respectively, while cell site 104a is coupled to a different mobile switching center 106 by connection 104 c. These connections are typically wired connections between the respective cell sites and mobile switching centers 105 and 106. Each cell site includes an antenna for communicating with the communication system serviced by the particular cell site/base station. In one example, a cell site may be a cellular telephone cell site that communicates with a mobile cellular telephone (integrated with a GPS receiver) in an area served by the cell site.

In an exemplary embodiment of the present invention, a mobile GPS receiver, such as receiver 102b, comprises a cellular communication system integrally mounted with a GPS receiver such that the GPS receiver and the communication system are enclosed within the same housing. One example is a cellular telephone with an integrally mounted GPS receiver that shares a circuit with the cellular telephone transceiver. When the combined system is used for cellular telephone communications, communications occur between the receiver 102b and the base station 102 a. The transmission from the receiver 102b to the base station 102a is then transmitted on a connection 102c to the mobile switching center 105, then to another cellular telephone within the cell served by the mobile switching center 105, or to another telephone via a connection (typically wired) through the land-based telephone system/network 112. The reader will appreciate that the term wired includes optical fibers and other non-wireless connections such as copper cables and the like. Transmissions from other telephones in communication with the receiver 102b are transmitted back to the receiver 102b from the mobile switching center 105 via the connection 102c and the base station 102a in a conventional manner.

In the example shown in fig. 2, each Mobile Switching Center (MSC) is coupled to at least one regional Short Message Service Center (SMSC) through a communications network 115, referred to as a signaling system 7 (SS7) network. The network enables short messages, such as control information and data, to be transmitted between elements of the telephone network. The reader will understand that the illustration in figure 2 is an example and that in practice there may be several MSCs coupled to a regional SMSC. The network 115 couples the MSCs 105 and 106 with the regional SMSCs 107 and 108. The example in FIG. 2 also shows two GPS location servers 109 and 110 coupled to the area SMSC107 and the area SMSC108 through a network 115. In the distributed system of one embodiment shown in fig. 2, the network 115 may be a permanent packet-switched data network that interconnects the various regional SMSCs and MSCs with the various GPS location service areas. This enables each regional SMSC to act as a router to select a route requesting location services to any GPS location server in the event that the location server is congested or fails. Therefore, if the location server 109 becomes congested, or has a fault, or is unable to service a location service request, the regional SMSC107 can select a route for the location service request from the mobile GPS receiver 102b (e.g., a user of the mobile GPS receiver 102b dials an integrally installed cell phone) to the GPS location server 110.

Each GPS location server is typically coupled to GPS reference stations of the wide area network, which provide differential GPS corrections and satellite ephemeris data to the GPS location server. The GPS reference stations of the wide area network, such as GPS reference network 111 in the figure, are typically coupled to each GPS location server through a dedicated packet switched data network. Therefore, location server 109 receives data from network 111 over connection 109a, and server 110 receives data from network 111 over connection 110 a. The reference network 111 may be coupled to a communication network 112. Alternatively, the GPS reference receiver is used at each location server to provide the GPS location server with the satellite ephemeris and GPS time. As shown in fig. 2, each GPS location server is also coupled to a communication network such as the Public Switched Telephone Network (PSTN) to which two application servers 114 and 116 are coupled.

Two GPS location servers are used in one embodiment to determine the location of a mobile GPS receiver (e.g., receiver 102b) using GPS signals received by the mobile GPS receiver.

Each GPS location server will receive pseudoranges from the mobile GPS receiver, satellite ephemeris data from the GPS reference network and compute a path for the location of the mobile GPS receiver which will then be transmitted over a network 112, such as the public switched telephone network PSTN, to one (or both) application servers which will display the location (e.g. on a map) to the user at the application server. Typically, the GPS location server calculates the location at the GPS location server but does not display (e.g., via a display). The application server may send a request for the location of a particular GPS receiver in the cell to the GPS location server, which then talks to the particular mobile GPS receiver through the mobile switching center to determine the location path of the GPS receiver and report these locations back to the particular application party. In another embodiment, the position determination of the GPS receiver may be made by a user of the mobile GPS receiver, for example, the user of the mobile GPS receiver may press 911 on a cellular telephone indicating an emergency situation is occurring at the mobile GPS receiver and may also initiate a positioning process in the methods described herein.

It should be noted that a serving or cell communication system is a communication system having more than one transmitter, each of which preferably serves a different geographical area at any predetermined time. Typically, each transmitter is a wireless transmitter that serves a cell having a geographic radius of less than 20 miles, although the area covered depends on the particular cellular system. There are various cellular communication systems such as cellular phones, PCS (personal communication system), SMR (dedicated mobile radio), one-way and two-way pager systems, RAM, ARDIS and wireless packet data systems. Generally, a predetermined geographic area refers to a cell and a plurality of cells divided into cellular service areas and coupled with one or more cellular switching centers that provide connectivity to land-based telephone systems and/or networks. The service area is typically used for charging. There may be cases where more than one service area is connected to a switching centre. In addition, it is sometimes the case that cells within a service area are connected to different switching centres, especially where the access is dense. In general, a service area is defined as a set of cells that are geographically close to each other. Another cellular system suitable for the above description is a satellite-based cellular system, where the cellular base stations or cell sites are satellites that are generally orbiting the earth. In these systems, the cell sectors and service areas may be large and their movement as a function of time. Examples of such systems include Iridium, Globalstar, Orbcomm, and Odyssey.

Fig. 3 shows an example of a GPS location server 50 that may be used as the GPS location server 109 or the GPS location server 110 of fig. 2. The GPS positioning server 50 shown in fig. 3 comprises a data processing unit 51, which may be a fault tolerant digital computer system. The GPS location server 50 also includes a modem or other communication interface 52, and modem or other communication interface 53, and modem or other communication interface 54. These communication interfaces provide a connection between the three different networks (shown as networks 60, 62, and 64) for the exchange of information to and from the location servers shown in figure 3. Network 60 includes one or more mobile switching centers and/or land-based telephone system switches or cell sites. An example of such a network is shown in fig. 2, where GPS location server 109 represents server 50 shown in fig. 3. Therefore, the network 60 can be seen as including mobile switching centers 105 and 106 and cells 102, 103, and 104. The network 64 may be viewed as including application servers 114 and 116, each of which is a computer system with a communication interface, and may also include one or more "PSAPs" (public safety answering points), which are typically control centers that answer 911 emergency telephone calls. The network 62 represents the GPS reference network 111 shown in fig. 2, which is a network of GPS receivers, which are GPS reference receivers, for providing differential GPS correction information and GPS signal data including satellite ephemeris to the data processing unit. When the server 50 serves a large geographic area, a local optional GPS receiver, such as optional GPS receiver 56, can view all GPS satellites that are within the field of view of the mobile SPS receiver throughout the area. Thus, the network 62 collects and provides satellite ephemeris data and differential GPS correction data over a wide area in accordance with the present invention.

As shown in fig. 3, a mass storage device 55 is coupled with the data processing unit 51. Typically, the mass memory 55 will include memory for data and software for performing GPS position calculations after receiving pseudoranges from a mobile GPS receiver, such as the receiver 102b shown in FIG. 2. These pseudoranges are typically received through the cell site and mobile switching center and modem or other interface 53. The mass storage device 55 also includes software that, at least in one embodiment, is used to receive and use satellite ephemeris data provided by the GPS reference network 111 through a modem or other interface 54. The mass memory device 55 also typically includes a database or memory 55a, the memory 55a specifying a time-stamped satellite ephemeris queue and differential GPS corrections, as described above.

In an exemplary embodiment of the present invention, the optional GPS receiver 56 is not necessary because the GPS reference network 111 shown in FIG. 2 (network 62 in FIG. 3) provides differential GPS information and corresponding time stamps within the field of view of the various reference receivers in the GPS reference network, as well as source satellite data messages from the satellites. The reader will appreciate that satellite ephemeris data obtained from the network via the modem or other interface 54 may be used in a conventional manner with pseudoranges obtained from a mobile GPS receiver to calculate position information for the mobile GPS receiver. Each of the interfaces 52, 53 and 54 may be a modem or other suitable communication interface for coupling the data processing unit to, in this example, a network 64 and to, in this example, a cellular communication system in the network 60 and to a transmitting device such as a computer system in the network 62. In one embodiment, the reader will appreciate that the network 62 includes a decentralized set of GPS reference receivers distributed over a geographic area. In some embodiments, differentially corrected GPS information obtained from a cell site or cellular service area in close proximity to communicate with the mobile GPS receiver over the cellular communication system will provide differentially corrected GPS information suitable for proper positioning of the mobile GPS receiver.

Fig. 4 shows a generalized combined system including a GPS receiver and a communication system transceiver. In one example, the communication system transceiver is a cellular telephone. The system 75 includes a GPS receiver 76 having a GPS antenna 77, and a communication system transceiver 78 having a communication antenna 79. The GPS receiver 76 is coupled to the communication system transceiver 78 by a connection 80 shown in fig. 4. The memory 81 stores the determined sequence of pseudoranges and the corresponding time stamps as described above. The memory 81 is coupled to the GPS receiver 76 and to the communication system transceiver (e.g., the memory is a dual port memory). In one mode of operation, the communications system transceiver 78 receives the approximated Doppler information via the antenna 79 and provides the approximated Doppler information on the link 80 to the GPS receiver 76, and the GPS receiver 76 performs pseudorange determinations by receiving GPS signals from GPS satellites via the GPS antenna 77. The determined pseudoranges are then transmitted to the GPS location server via the communication system transceiver 78. Typically, the communication system transceiver 78 transmits a signal through antenna 79 to the cell site, which in turn forwards the information back to the GPS location server. Various embodiments for system 75 are well known in the art. For example, U.S. patent No. 5,663,734 describes an example of a combined GPS receiver and communication system employing an improved GPS receiver system. Another example of a combined GPS communication system is shown in co-pending patent application 08/652,833, filed on 1996, month 5, 23. Most conventional GPS receivers may be modified to the receiver 76 shown in fig. 4, although receivers such as described in U.S. patent 5,663,734 may provide improved performance. The system 75 shown in fig. 4, as well as a myriad of other communication systems having SPS receivers, typically time-stamp the time of receipt of GPS signals for which pseudoranges are determined. In particular, the system 75 may time-stamp the time of reception at the mobile unit of the SPS signal with GPS time (received or estimated from GPS satellites), or with time transmitted from CDMA (in a preferred embodiment).

FIG. 5 illustrates one embodiment of a GPS reference station. The reader will appreciate that each reference station may be constructed in this manner and coupled to a communication network or communication medium. Typically, each GPS reference station, such as the GPS reference station 90 shown in fig. 5, will include a dual frequency GPS reference receiver 92 coupled to a GPS antenna 91, the antenna 91 receiving GPS signals from GPS satellites within its field of view. GPS reference receivers are well known in the art. The GPS reference receiver 92 according to one embodiment of the invention provides at least two types of information as outputs of the receiver 92. Pseudorange outputs 93 are provided to the processor and network interface 95 and these pseudorange outputs (and the time at which SPS signals are received which are used to determine reference pseudoranges) are used to compute pseudorange differential corrections in a conventional manner for those satellites within view of the GPS antenna 91. The processor and network interface 95 may be a conventional digital computer system having an interface for receiving data from a GPS reference receiver, as is well known in the art. The processor 95 typically includes software designed to process the pseudorange data to determine the appropriate pseudorange corrections for each satellite within the field of view of the GPS antenna 91. These pseudorange corrections (and their corresponding time stamps) are then communicated over the network interface to a communication network or medium that is also coupled to other GPS reference stations. The GPS reference receiver 92 also provides a satellite ephemeris data output 94. The data is provided to the processor and network interface 95, and the processor and network interface 95 then transmits the data to the communications network 96 included in the GPS reference network 111 shown in fig. 2.

The satellite ephemeris data output 94 typically provides at least a portion of the entire source 50 baud navigation binary data encoded with the actual GPS signal received from each GPS satellite. The satellite ephemeris data is part of a navigation message that is broadcast as a data stream of 50 bits per second in GPS signals from GPS satellites, as described in detail in the GPS ICD-200 document. The processor and network interface 95 receives the satellite ephemeris data output 94 and transmits it in real time or near real time to a communications network 96. As will be described below, the satellite ephemeris data transmitted into the communications network is later received over a network at various GPS location servers in accordance with aspects of the invention.

In some embodiments of the invention, only certain segments of navigation messages, such as satellite ephemeris data messages, may be transmitted to the positioning server in order to reduce bandwidth requirements for the network interface and the communications network. Also, typically the data is not necessarily provided continuously. For example, only the first three frames containing ephemeris information, rather than the 5 frames, may be periodically transmitted to the communication network 96 in real time or near real time. The reader will appreciate that in one embodiment of the present invention, the positioning server may receive the entire navigation message transmitted from one or more GPS reference receivers in order to perform the method of measuring satellite data messages related thereto, such as the method described in co-pending U.S. patent application 08/794,649, filed 3/2/1997, the inventor being Norman f.krasner. The term "satellite ephemeris data" as used herein includes only a portion of the satellite navigation messages (e.g., 50 baud messages) transmitted for the GPS satellites, or at least a mathematical representation of the satellite ephemeris data. For example, the term satellite ephemeris data refers to a portion of a 50 baud data message encoded into GPS signals transmitted from GPS satellites. The reader will also appreciate that the GPS reference receiver 92 decodes the different GPS signals from the different GPS satellites in view of the reference receiver 92 to provide a binary data output 94 containing satellite ephemeris data.

When the method of the present invention is used to track the path of a mobile unit over time in the cell system of figure 2, a location server tracks the movement of a particular mobile unit from one cell to several other cells. Due to the interconnectivity of such systems, signals received from mobile units beginning in cell 102 may be tracked by the same location server even after the mobile unit has moved to cell 104. Additionally, as a location server moves from one cell site or cellular service center to another, one location server may forward path data representing the location and time that has been determined for a particular mobile unit to another location server that in turn tracks the mobile unit.

Although the method and apparatus of the present invention have been described above in relation to GPS satellites, it will be appreciated that the principles are equally applicable to positioning systems employing quasi-satellites or a combination of satellites and quasi-satellites. Pseudolites are terrestrial transmitters that broadcast a PN code (similar to a GPS signal) modulated on an L-band carrier signal that is typically synchronized with GPS time. Each transmitter may be assigned a unique PN code so that it can be identified by a remote receiver. Quasi-satellites are used in situations where there may be no GPS signals from orbiting satellites, such as tunnels, mines, buildings or other enclosed areas. The term "satellite" as used herein includes quasi-satellites or equivalents of quasi-satellites, while the term GPS signals as used includes equivalent GPS-like signals from quasi-satellites or quasi-satellites.

In the foregoing discussion, the invention has been described with reference to the united states Global Positioning Satellite (GPS) system. It is clear, however, that these methods are equally applicable to similar satellite positioning systems, in particular the russian Glonass system. The Glonass system differs from the GPS system primarily in that the different satellite radiations are due to the slightly different carrier frequencies, rather than due to the different pseudo-random codes. In this case, substantially all of the previously described circuits and rules may be employed, except that different power multipliers corresponding to different carrier frequencies are employed to preprocess the data as new satellite radiation is processed. The term "GPS" as used herein includes such additional satellite positioning systems, including the Russian Glonass system.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims (17)

1. A method of operating a satellite positioning system, SPS, receiver, the method comprising:

determining a first plurality of pseudoranges at a first time;

determining a second plurality of pseudoranges at a second time subsequent to said first time;

storing said first plurality of pseudoranges and storing said second plurality of pseudoranges;

after the second time, transmitting the first plurality of pseudoranges and the second plurality of pseudoranges.

2. The method of claim 1, further comprising determining whether a predetermined type of event has occurred, and transmitting said first plurality of pseudoranges and said second plurality of pseudoranges based on determining that said predetermined type of event has occurred.

3. The method of claim 2, wherein the predetermined type of event is one of the following: (a) a sensor detects a condition; or (b) the memory limit has been reached; or (c) a predetermined number of pseudoranges have been stored; or (d) a predetermined time has elapsed since the last set of pseudoranges was transmitted; or (e) there is a command from an external source over the communication link.

4. The method of claim 1, further comprising:

receiving, in said SPS receiver, a first SPS signal from which said first plurality of pseudoranges is determined;

determining a first receive time when the first SPS signal is received at the SPS receiver;

receiving, in said SPS receiver, a second SPS signal from which said second plurality of pseudoranges is determined;

determining a second receive time when the second SPS signal is received at the SPS receiver;

transmitting the first receive time and the second receive time.

5. The method of claim 4, further comprising:

determining whether a predetermined type of event has occurred, and in accordance with the determination that the predetermined type of event has occurred, transmitting the first and second pluralities of pseudoranges and the first and second times of receipt.

6. The method of claim 5, wherein the predetermined type of event comprises a predetermined period of time having elapsed since a last set of pseudoranges has been transmitted.

7. The method of claim 6, wherein the predetermined period of time may be variable.

8. The method of claim 7, wherein a change in said predetermined period of time causes a time interval between said first plurality of pseudoranges and said second plurality of pseudoranges to also change.

9. A method as recited in claim 4, wherein said first plurality of pseudoranges and said second plurality of pseudoranges are part of a series of pseudoranges that are determined and stored sequentially over time and subsequently transmitted as a set of data.

10. A satellite positioning system, SPS, receiver, comprising:

an SPS RF receiver to receive SPS signals;

a processor coupled to said SPS RF receiver, said processor determining a plurality of pseudoranges from said SPS signals, said processor determining a first plurality of pseudoranges from SPS signals received at a first time and determining a second plurality of pseudoranges from SPS signals received at a second time subsequent to said first time;

a memory coupled with the processor, the memory storing the first plurality of pseudoranges and the second plurality of pseudoranges;

a transmitter coupled with the memory, the transmitter transmitting the first plurality of pseudoranges and the second plurality of pseudoranges after the second time.

11. An SPS receiver as in claim 10 wherein said transmitter transmits said first plurality of pseudoranges and said second plurality of pseudoranges based on a predetermined type of event.

12. An SPS receiver as in claim 11 wherein said SPS RF receiver receives a first SPS signal and said first plurality of pseudoranges is determined from said first SPS signal and said SPS RF receiver receives a second SPS signal and said second plurality of pseudoranges is determined from said second SPS signal, and wherein a first time of reception is determined when said first SPS signal is received and stored in said memory and said second time of reception is determined when said second SPS signal is received and stored in said memory, and wherein said transmitter transmits said first time of reception and said second time of reception.

13. An SPS receiver as in claim 12 wherein said first receive time and said second receive time are determined from SPS signals.

14. An SPS receiver as in claim 12 wherein said first receive time and said second receive time are determined from a time signal received from a cell communication signal received by a communication receiver coupled to said processor.

15. A method for determining position from Satellite Positioning System (SPS) information, the method comprising:

receiving a first plurality of pseudoranges determined from a first SPS signal received at a first time;

receiving a second plurality of pseudoranges determined from a second SPS signal received at a second time subsequent to the first time;

determining a first position from said first plurality of pseudoranges and a second position from said second plurality of pseudoranges, wherein said first plurality of pseudoranges and said second plurality of pseudoranges are received in one transmission after said second time.

16. The method of claim 15, wherein the one transmission occurs after a predetermined type of event.

17. The method of claim 15, further comprising:

storing a first plurality of pseudorange corrections for a respective first time of correction and storing a second plurality of pseudorange corrections for a respective second time of correction;

the first position is also determined from the first plurality of pseudorange corrections, and the second position is also determined from the second plurality of pseudorange corrections.