HK1036106B - Satellite positioning reference system and method - Google Patents

Description

Satellite positioning reference system and method

RELATED APPLICATIONS

This application is a partial renewal application of U.S. patent application No.08/842,559 by Norman f.krasner, 1997, 4/15.

Background of the invention

The present invention relates to satellite positioning systems employing reference receivers, and more particularly to a reference receiver network for a satellite positioning system.

Conventional Satellite Positioning Systems (SPS), such as the Global Positioning System (GPS) in the united states, use signals from satellites to determine their position. Conventional GPS receivers generally determine their position by calculating the relative times of arrival of signals transmitted simultaneously from a number of GPS satellites orbiting the earth. Each satellite transmits satellite positioning data and clock timing data as part of its navigation information, and the clock timing data defines its position and clock state at a certain moment; this data appearing in sub-frames 1-3 of the GPS navigation information is often referred to as satellite clock and ephemeris data, also referred to as satellite ephemeris data. Conventional GPS receivers typically search for acquired GPS signals, read navigation information from each signal to obtain satellite ephemeris data for their respective satellites, determine pseudoranges to the satellites, and calculate a position of the GPS receiver based on the pseudoranges and the satellite ephemeris data from the satellites.

The positioning accuracy can be improved by applying some conventional technique known as differential GPS. With conventional differential GPS, a single differential reference station broadcasts different GPS corrections to users in a local area, and thus there are generally three main components of a conventional differential GPS system. The first component is a reference station at a known location where a GPS receiver is located, typically with all satellites in view, and the reference station is optionally software that can be inserted into the GPS receiver for calculating pseudorange corrections and encoding them for a particular broadcast format. Another component is the radio link that sends the different correction values to the mobile GPS receiver in real time. The third component is a mobile GPS receiver which also includes a receiver for receiving the differential correction broadcast from the reference station.

The rover GPS receiver corrects the pseudorange data obtained by calculating the relative times of arrival of the GPS signals transmitted by the GPS satellites with the differential GPS correction values in a conventional manner. Conventional differential GPS does not necessarily have to do work in real time or provide correction values to the mobile GPS receiver, although it is often done so. In the patent and non-patent literature, many improved methods for differential GPS have been described, focusing primarily on differential correction calculations, application algorithms, and methods of providing differential correction values. In the field of measurement (pseudorange, accumulated delta distance, and closing velocity error estimation). Most likely a differential correction.

Conventional differential GPS can greatly improve positioning accuracy if the reference receiver and the participating mobile GPS receivers are very close to each other. However, as the separation distance of the two receivers increases, the accuracy of the differential GPS increases and deteriorates. One remedy is to provide a network of GPS reference receivers distributed over an area covering a region consistent with the area in which a mobile GPS receiver may operate, so that the same set of satellites is seen. Thus, the rover GPS receiver may pick up differential corrections for more than one differential reference station, and the rover GPS receiver may select the differential corrections for the satellites in view based on its relative proximity to two or more reference stations. The use of multiple reference stations for a differential GPS system is sometimes referred to as wide area differential GPS (wadgps).

Another form of the WADGPS reference system includes a GPS reference receiver and network of host stations which communicate with the reference stations to receive their measurements and calculate a set of combined ephemeris and clock correction estimates for each GPS satellite viewed by the reference stations. The console can then provide a differential GPS message via the transmitter, the correction value of which is adapted to a certain propagation range. Examples of such wide area differential GPS reference systems include those described in U.S. patent nos. 5,323,322 and 5,621,646.

Regardless of the coverage of a particular differential reference system, the primary purpose of a differential GPS system is to provide a differential service that helps a mobile GPS receiver eliminate errors in GPS measurements or measurement-derived solutions. The GPS system errors that the network attempts to eliminate are related to the multiple reference stations, their spatial displacement and the complexity of the algorithms executed at the central processing unit. The second role of the differencing network is to provide integrity and reliability for the differencing service through various checks of the measurement and state space domains.

The above systems, while improving the accuracy of mobile GPS receivers, are not compatible with client/server GPS architectures. In a client/server GPS configuration, a mobile GPS receiver acts as a client system to provide pseudorange measurements to a remote server, which calculates a position solution using the pseudoranges obtained from the mobile GPS receiver and ephemeris data. The present invention provides an improved method and apparatus for providing flexibility in positioning of a positioning server, and for improving efficiency and reducing costs of a client/service system.

Disclosure of Invention

The method and the device provided by the invention are suitable for a satellite positioning system reference system.

One aspect of the present invention is an exemplary method for processing satellite positioning information using at least two SPS reference receivers. According to the method, a first digital processing system receives first satellite ephemeris data from a first SPS reference receiver having a first known position, receives second satellite ephemeris data from a second SPS reference receiver having a second known position, receives a plurality of pseudorange data from a mobile SPS receiver, and calculates position information (e.g., latitude, longitude, and altitude) of the mobile SPS receiver using the plurality of pseudorange data and at least one of the first and second satellite ephemeris data. In a particular embodiment of the present invention, the first and second satellite ephemeris data are each a subset of "raw" 50bps satellite navigation information received by the satellites from view of the two reference receivers by the first and second SPS reference receivers, respectively. In one example, such satellite navigation information may be 50 bits/second data information encoded into GPS signals that have been received and decoded by the reference receiver and transmitted to the first digital processing system in a manner that is implemented or nearly implemented.

In accordance with another aspect of the invention, a satellite position information processing system includes a plurality of Satellite Positioning System (SPS) reference receivers having known locations and a plurality of digital processing systems. A plurality of SPS reference receivers are dispersed throughout an area, and each receiver receives satellite ephemeris data transmitted from satellites in view of the receiver and transmits the received satellite ephemeris data to a communications network. The system also includes a plurality of digital processing systems, each coupled to the communication network to receive at least some of the satellite ephemeris data transmitted via the communication network. In one embodiment, there are at least two such digital processing systems. The first digital processing system receives a first plurality of pseudoranges from the first mobile SPS receiver and calculates first position information (e.g., latitude and longitude) for the first mobile SPS based on the pseudorange data and satellite ephemeris data received from the communication network. Typically, the first digital processing system selectively receives the appropriate satellite ephemeris data from the network for at least those satellites in view of the first mobile SPS receiver. The second digital processing system receives a second plurality of pseudorange data from the second mobile SPS receiver and calculates second position information for the second mobile SPS receiver based on these data and satellite ephemeris data received from the communication network. In one example of the present invention, the second digital processing system selectively receives from the network the appropriate satellite ephemeris for those satellites in view of the second mobile SPS receiver. In another example of the present invention, the first and second digital processing systems each receive from the net the most recent satellite ephemeris data in view of the net.

In yet another embodiment of the present invention, another digital processing system may be coupled to the communication network in order to receive measurements (e.g., differential corrections) from the reference receivers and generate a set of network differential corrections. Various other aspects and embodiments of the invention are described further below.

Brief description of the drawingsThe above-mentioned

The following is an illustration of the present disclosure, not to be taken in a limiting sense, the contents of the accompanying drawings in which like reference numerals refer to similar elements.

Fig. 1 illustrates a cellular communication system having a plurality of cells, each cell being served by a cell site, each cell site being connected to a cell switching center (sometimes referred to as a mobile switching center).

Fig. 2 shows an implementation of a location server system according to an embodiment of the invention.

FIG. 3A illustrates an example of a combined SPS receiver and communication system in accordance with an embodiment of the invention.

FIG. 3B illustrates an example of a GPS reference station in accordance with one embodiment of the present invention.

FIG. 4 illustrates an SPS reference receiver network in accordance with an embodiment of the invention.

FIGS. 5A and 5B are flow diagrams illustrating a method according to an embodiment of the invention.

Fig. 6 shows a data flow of a network correction processor, which may be used in an embodiment of the present invention with reference to a receiver network.

Fig. 7 illustrates an example of data flow associated with a location server in accordance with an embodiment of the present invention.

Detailed description of the invention

The SPS reference receiver network of the present invention provides at least a portion of satellite navigation information, such as satellite ephemeris data, for use by a digital processing system in the following manner. Before describing the reference system in various details, a general use of such a reference receiver is described. Thus. Before discussing SPS reference receiver networks in the system of the present invention, a preliminary discussion will be made with reference to fig. 1, 2, and 3A.

Fig. 1 illustrates an example cellular communication system 10 that includes a plurality of cell sites, each serving a particular geographic area or location. Examples of such cellular or cellular communication systems are well known in the art, such as cellular telephone systems. The cellular communication system 10 includes two cells 12 and 14, both of which are confined within a cellular service area 11. System 10 also includes cells 18 and 20. It should be apparent that in a system 10 coupled to one or more cellular switching centers (e.g., cellular switching centers 24 and 24b), a plurality of other cells having corresponding cell sites and/or cellular service areas may also be included.

Within each cell, such as cell 12, there is a wireless cell site or cell site (e.g., cell site 13) that includes an antenna 13a for communicating over a wireless communication medium with a communications receiver, which may be combined with a mobile GPS receiver, such as receiver 16 shown in fig. 1. An example of such a combined system equipped with a GPS receiver and a communication system is shown in fig. 3A and may include a GPS antenna 77 and a communication system antenna 79.

Each cell site is coupled to a cellular switching center. In fig. 1, cell sites 13, 15 and 19 are coupled to switching center 24 by connections 13, 15b and 19b, respectively, and cell site 21 is coupled to a different switching center 24b by connection 21 b. These connections are typically wire connections between the cell sites and the cellular switching centers 24 and 24 b. Each cell site includes an antenna for communicating with the communication system serviced by the cell site. In one embodiment, the cell site may be a cellular telephone cell site that communicates with mobile cellular telephones within the cell site service area. It will be appreciated that a communication system within a cell, such as receiver 22 in cell 4, may actually be communicating with cell site 19 in cell 18 due to congestion (or other reasons station 21 may not be able to communicate with receiver 22).

In an exemplary embodiment of the invention, the mobile GPS receiver 16 comprises a cellular communication system integrated with the GPS receiver such that the GPS receiver and the communication system are housed in the same housing. An example of this is a cellular telephone with an integrated GPS receiver that shares common circuitry with the cellular telephone transceiver. When the combined system is applied to cellular telephone communications, transmission is effected between receiver 16 and cell site 13. The transmission from receiver 16 to cell site 13 then travels through connection 13b to cellular switching center 24 and then to another cellular telephone in the cell served by center 24 or via land-based telephone system/network 28 to another telephone through connection 30 (typically a wire). Obviously, the conductors include optical fibers and other non-wireless connections (e.g., copper cables, etc.). Transmissions from another telephone with which the receiver 16 is communicating may be transmitted back to the receiver 16 by the cellular switching center 24 via the connection 13b and the cell site 13 in a conventional manner.

The remote data processing system 26 (which may be referred to as a GPS server or a positioning server in some embodiments) included in the system 10 may use GPS signals received by a GPS receiver to determine the status (e.g., position and/or velocity and/or time) of a mobile GPS receiver (e.g., receiver 16). The GPS server 26 may be coupled to a land-based telephone system/network 28 by a connection 27, may be selectively coupled to the cellular switching center 24 by a connection 25, and may be selectively connected to the center 24b by a connection 25 b. Obviously, the connections 25 and 27 are typically wire connections, but may of course also be wireless connections. As shown, an optional component of the system 10 is an interrogation terminal 29, which may comprise another computer system coupled to the GPS server 26 through a network 28. The interrogation terminal 29 may issue a request to the GPS server 26 to interrogate a particular GPS receiver in a cell for location and/or velocity, whereupon the server 26 talks to the particular GPS receiver through the cellular switching center to determine the location and/or velocity of the GPS receiver and report the information to be interrogated to the interrogation terminal 29. In another embodiment, a position determination may be made by a mobile GPS receiver user to a GPS receiver; for example, a mobile GPS receiver user may press 911 on a cell phone indicating some emergency condition at the location of the mobile GPS receiver, which initiates the positioning process performed in the manner described herein.

It should be noted that a cellular or cell communication system is a communication system having more than one transmitter, each serving a different geographical area which is scheduled in real time. Generally, each transmitter is a radio transmitter serving a cell having a geographic radius of less than 20 miles, although the area of coverage depends on the particular cellular system. There are various categories of cellular communication systems such as cellular phones, PCS (personal communication system), SMR (specialized mobile phone), one-way and two-way paging systems, RAM, ARDIS and wireless packet data systems. Generally, a predetermined geographic area is referred to as a cell, and a plurality of cells are collectively referred to as a cellular service area, such as cellular service area 11 shown in fig. 1, and such plurality of cells are coupled to one or more cellular switching centers, which are in turn connected to a land-based telephone system and/or network. Service areas are often used for billing. Thus, more than one cell of the serving area may be connected to one switching center. As in fig. 1, cells 1 and 2 are located in service area 11 and cell 3 is located in service area 13, but these three cells are all connected to switching center 24. Or in some cases, cells within a service area may be connected to different switching centers. This is particularly true in densely populated areas. Typically, a service area is defined as a set of cells within a neighborhood. Another type of cellular system that meets the above-described situation is based on satellites, with cellular base stations or cell sites being the satellites that typically orbit the earth. In such systems, the movement of cell sectors and service areas is a function of time. Such systems include Ividium, Globalstar, Orbcomm, Odyssey, and the like.

Fig. 2 shows an example of a GPS server 50, which may be used as the GPS server 26 of fig. 1, that includes a data processing unit 51, which may be a fault tolerant digital computer system, and that includes a modem or other communication interface 52, and modem or other communication interfaces 53 and 54. These communication interfaces provide a continuation to the exchange of information by the location server shown in fig. 2 between the three different networks 60, 62 and 64. Network 60 includes a cellular switching center and/or a land-based telephone system or cell site. In the network example of fig. 1, the GPS server 26 represents the server 50 of fig. 6. Thus, the network 60 can be considered to include the cellular switching centers 24 and 24b, the land-based telephone system/network 28, the network service area 11, and the cells 18 and 20. The network 64 may be considered to include the interrogation terminal 29 or "PSAP" of fig. 1, which is a public safety answering point, typically a control center, that answers 911 telephone emergency calls. In the case of the interrogation terminal 29. The terminal may be used to query the server 26 to obtain status (e.g., location) information from a designated mobile SPS receiver located within each cell in the cellular communication system. At this time, the positioning operation is initiated by a person other than the mobile GPS receiver user. In the case of a 911 telephone call made by a mobile GPS receiver, including a cellular telephone, the location process is initiated by the user of the cellular telephone. The network 62, which is representative of the GPS reference network 32 of fig. 1, is a GPS receiver network that is a GPS reference receiver for providing differential GPS correction information to the data processing unit and also providing GPS signal data including at least a portion of satellite navigation information such as satellite ephemeris data. When the server 50 is servicing a very large area, a locally selected GPS receiver, such as the optional GPS receiver 56, may not be able to observe all of the GPS satellites that are in view of the mobile SPS receivers throughout the area. Thus, it is within the broad scope of an embodiment according to the present invention that the network 62 collects and provides at least a portion of the satellite navigation information, such as satellite ephemeris data and differential GPS correction data.

As shown in fig. 6, the mass memory 55 is coupled to the data processing unit 51. Typically, the mass memory 55 will include memory for storing software and data for performing GPS position calculations upon receiving pseudoranges from a mobile GPS receiver (e.g., the receiver 16 of FIG. 1). These pseudoranges are typically received through a cell site, a cellular switching center and a modem or other interface 53. In at least one embodiment, the mass memory 55 also includes software for receiving and utilizing satellite ephemeris data provided by the GPS reference network 32 via a modem or another interface 54.

In an exemplary embodiment of the present invention, the optional GPS receiver does not have to provide differential GPS information as with the GPS reference network 32 of FIG. 1 (network 62 of FIG. 2), but rather provides raw satellite navigation information from the satellites in view of the various reference receivers in the GPS reference network. It will be appreciated that satellite ephemeris data obtained from the network via the modem or another interface 54, together with pseudoranges obtained from a mobile GPS receiver, may be used in a conventional manner to calculate position information for the mobile GPS receiver. The interfaces 52, 53 and 54 may be modems or other suitable communication interfaces for coupling the data processing unit to other computer systems (in the case of network 64), to a cellular communication system (in the case of network 60), and to a transmitting device, such as a computer system in network 62. In one embodiment, the network 62 apparently includes a decentralized and centralized GPS reference receiver dispersed throughout a certain geographic area.

Figure 3A illustrates a general combination 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 with a GPS antenna 77 and a communications transceiver 78 with a communications antenna 79. The GPS receiver 76 is coupled to the communications transceiver 78 via connection 80 of fig. 3A. In one mode of operation, the communications system transceiver 78 receives approximate Doppler information via antenna 79 and provides this information via link 80 to the GPS receiver 76, which receives GPS signals from GPS satellites via GPS antenna 77 for pseudorange determination. The pseudoranges are then transmitted through the communication system transceiver 78 to a location server (location server) such as the GPS server shown in fig. 1. Typically, the communication system transmitter 78 transmits a signal via antenna 79 to the cell site, which in turn transmits this information back to a GPS server, such as GPS server 26 of fig. 1. Various embodiments of system 75 are known in the art, and an example of a combined GPS receiver and communication system is described in U.S. patent No.5,663, 734, which employs an improved GPS receiver system. Another example of a combined GPS and communication system is described in co-pending patent application No.08/652,833, filed 5/23 1996. The system 75 of fig. 3A, as well as other communication systems having SPS receivers, may employ the method of the present invention to operate with the GPS reference network of the present invention.

FIG. 3B illustrates one embodiment of a GPS reference station. It will be apparent that each reference station can be configured and coupled to a communication network or medium in this manner. Generally, each GPS reference station (e.g., GPS reference station 90 of FIG. 3B) will include a single or dual frequency GPS reference receiver 92 coupled to a GPS antenna 91, with antenna 91 receiving GPS signals from GPS satellites in view of antenna 91. GPS reference receivers are well known in the art. According to one embodiment of the invention, the GPS reference receiver provides at least two types of information as its output. The pseudorange output 93 is provided to a processor and network interface 95 for calculating pseudorange corrections for those satellites in view of the GPS antenna 91 in a conventional manner. The processor and network interface 95 may be a conventional digital computing 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 as range data to determine appropriate pseudorange corrections for each satellite in view of the GPS antenna 91. These pseudorange correction values (and/or pseudorange data outputs) are then sent through the network interface to a communication network or medium 96, which communication network or medium 96 is also coupled to other GPS reference stations. In one embodiment, the GPS reference receiver 92 also includes a representation of at least a portion of the satellite navigation information (e.g., satellite ephemeris data output 94) and provides this data to a processor and network interface 95, which in turn transmits the data to a communication network 96.

In one embodiment, each reference receiver transmits the entire navigation message into the network at a higher than normal rate. Some conventional GPS receivers may output raw (digital) navigation information data every 6 seconds (which may be considered a normal rate); such as some NovAtel GPS receivers. Such receivers collect the navigation information digital data (300 bits in a standard GPS signal) for one sub-frame into a buffer and then shift out the data of the buffer every 6 seconds (after buffering the full sub-frame 300 bits) to provide this data at the receiver output. However, in one embodiment of the present invention, at least a portion of the representation of the digital navigation information is transmitted into the network at a rate of every 600 milliseconds. Such high data rates may perform a method of measuring time. Such as the method described in co-pending U.S. patent application No.08/794,649, filed 3/2/1997. In this embodiment of the invention, a portion of the navigation information may be transmitted into the network every 600 milliseconds by only pooling a portion of the sub-frames (e.g., 30 bits) in the buffer and moving out after the portion is pooled. Thus, the processor 95 transmits the navigation information portion of the inbound packet to be less than the information portion provided by a packet created by a full sub-frame (300 bit) buffer. It is apparent that once the buffer aggregates the portion of the sub-frame (e.g., 30 bits), the data can be shifted out into packets transmitted at very high data rates (e.g., 512Kbps) over the inventive network. The packets are then reassembled (less than the full sub-frame) by extracting data from the packets and concatenating the data to reconstruct the complete sub-frame in the receiving digital processing system.

In one embodiment of the invention, each GPS reference station transmits at least a portion of the satellite navigation information along with a representation of pseudorange data (not pseudorange correction data). Pseudorange correction data may be derived from pseudorange and ephemeris information for a particular satellite. Thus, the GPS reference station may transmit pseudorange correction data or ephemeris (or both) into the network. However, in a preferred embodiment, pseudorange data (instead of pseudorange correction data) is transmitted into the network by each GPS reference station, since corrections from different receivers can be derived from different sets of ephemeris data, resulting in differences in corrections from different receivers. According to the preferred embodiment, a central correction processor (such as the network correction processor 110 of FIG. 4) uses a consistent set of up-to-date ephemeris data received from either GPS reference receiver, thus avoiding these discrepancies. The set of data is consistent for a particular instant in time, as it includes a collection of ephemeris, range measurements (e.g., pseudoranges) and/or corrections from multiple satellites. Each group can be merged with the data of the other groups as long as the applicable time of the group overlaps.

Referring back to FIG. 3B, the satellite ephemeris data output 94 typically provides at least a portion of the entire original 50 baud navigation binary data that has been encoded in the actual GPS signal received from each GPS satellite. The satellite ephemeris data is part of navigation information broadcast as a data stream of 50 bits per second in the GPS signals from the GPS satellites, and is described in detail in the GPS cmd-200 file. The processor and network interface 95 receives this satellite ephemeris data output 94 and transmits it in real time or near real time to the communications network 96. As will be described below, according to aspects of the invention, this satellite ephemeris data transmitted into the communication network is later received by the positioning servers via the network.

In some embodiments of the present invention, only certain segments of satellite navigation information are sent to the positioning server in order to reduce bandwidth requirements for the network interface and communication network. Moreover, continuous provision of such data is not required. For example, only the first three subframes containing ephemeris information may be transmitted into the communications network 96 instead of all 5 subframes if the three subframes contain update information. It should be apparent that in one embodiment of the present invention, the positioning server may perform a method of measuring time related satellite data information using navigation information data transmitted by one or more GPS reference receivers, such as the method described in co-pending U.S. patent application No.08/794,649 filed on 3/2/1997 by Norman f. It will also be appreciated that the GPS reference receiver 92 decodes the different GPS signals from the different GPS satellites in view of the receiver 92 to provide a binary data output 94 containing the satellite ephemeris data.

Typically the data packet is not provided to a particular location server and includes part of the navigation information and an identifier of the data received from a certain satellite; in some embodiments, the packet may also specify an identifier of the transmitting reference station. In some embodiments, the optional GPS receiver 56 may be the primary navigation information data source used by the local positioning server, and the network of the present invention may provide information as desired.

Fig. 4 shows an example of a GPS reference receiver network, and the overall system 101 includes two location servers 115 and 117 coupled to a communications network or medium 103, corresponding to the communications network 96 of fig. 3B. Network correction processors 110 and 112 are also coupled to the communication network 103. FIG. 4 shows five GPS reference stations 104, 105, 106, 107 and 108, all coupled to the communications network 103. Each GPS reference station, such as station 104, corresponds to the exemplary GPS reference station 90 of FIG. 3B, while the communication network 103 corresponds to the communication network 96 of FIG. 3B. It will be appreciated that the GPS reference stations (e.g., 104-108) are dispersed throughout a geographic region to provide receiver coverage for GPS signals that may also be received by the mobile GPS receiver. This coverage between adjacent reference stations generally overlaps to completely cover the entire territory. The area of the entire grid of reference stations may extend throughout the world or any subset thereof, such as a city, state, map home, or continent. Each GPS reference station (e.g., station 104) provides pseudorange correction data to the communications network 103 and also provides raw navigation data information for use by a location server (e.g., server 115). As will be described below, the number of location servers may be less than the number of reference stations, so pseudorange data from widely distributed mobile GPS receivers will be processed. For example, one location server may be processing pseudorange data from a mobile GPS receiver in california and a reference station in california, while the same location server may be processing pseudorange data from a mobile GPS receiver in new york and a reference station in new york, and thus a single location server may be receiving navigation information from two or more reference stations in a wide distribution. As shown in fig. 4, the communication network may be a data network such as frame relay or an ATM network, or other high speed digital communication network.

FIG. 4 also shows two network correction processors 110 and 112; in one embodiment, the processors provide grid-tie corrections to a plurality of reference stations and may also provide ionospheric data to a location server. The operation of one embodiment of the network correction processor is described below. The processors typically determine appropriate pseudorange corrections based on pseudoranges and ephemeris data having the same time of applicability, combine the associated sets of corrections with ephemeris data into a set having the same or overlapping time of applicability, and then retransmit the combined value on the network for receipt by location servers coupled to the network.

Fig. 5A and 5B illustrate, in flow chart form, a method in accordance with an embodiment of the present invention. In the method 200, each GPS reference receiver receives satellite ephemeris data from satellites in view of the particular reference receiver and transmits the data (navigation information) into a communication network, such as the packet data network 103 shown in fig. 4. In an exemplary embodiment of this step 201, each GPS signal from a GPS satellite in view of the particular reference receiver is decoded to provide a 50 bit-per-second binary data stream present in the GPS signal and transmitted into the communication network in real-time or near real-time. In another embodiment, only a portion of such data streams are transmitted into the network, as described above. In step 203, each GPS reference receiver determines corrections for pseudoranges to the GPS satellites in view of the reference receiver; performing this operation may be performed in a conventional manner using a controller computer, such as the processor and network interface 95 of FIG. 3B. These pseudorange corrections from each GPS reference receiver are then transmitted into a communications network, such as communications network 96 or 103 of fig. 4. In step 205, a processor (e.g., the network correction processor 110) coupled to the communications network (e.g., figure 103) receives satellite ephemeris data and pseudorange correction values. The network correction processor may generate a set of combined pseudorange corrections and perform other operations as described below. These combined pseudorange corrections are then transmitted into a communications network (e.g., network 103) for receipt by various location servers also coupled to the communications network.

The method continues to step 207 where the first location server receives at least a portion of the navigation information (e.g., satellite ephemeris data) and the combined pseudorange corrections from the network. Thus, for example, the positioning server 115 may receive navigation information data that has been transmitted into the network by each GPS reference station. Such data is typically provided in near real-time, and each positioning server will typically receive at least satellite ephemeris data from two and often more reference stations. The positioning server decodes the received satellite navigation information data to provide satellite clock and ephemeris data, which is stored in the server, allowing the positioning server to calculate the satellite position and clock state as required. This ephemeris data is used to calculate the position of a mobile GPS receiver, which then provides pseudoranges to the satellites in view of the mobile GPS receiver. Thus, at step 209, the first positioning server receives pseudoranges from the first mobile GPS receiver and determines the position of the first mobile GPS receiver based on the satellite ephemeris data received from the grid and the pseudoranges from the first mobile GPS receiver. The use of a network of reference stations enables the location server to calculate the position of mobile GPS receivers scattered over an area corresponding to the coverage area of the network of GPS reference receivers. Thus, rather than having a single GPS receiver located at a location server and providing ephemeris data to a location server, the decentralized network of GPS reference stations shown in fig. 4 allows the location server to provide location calculations for a wide distribution of mobile GPS receivers. As shown in fig. 4, a second location server may also be coupled to the communication network 103 to provide location resolution operations for the mobile GPS receivers. It should be apparent that in one embodiment, upon failure of the location server 115, the server 117 may be a redundant/backup server for that server 115. Generally, each location server should be a fault tolerant computer system. In the case where a high data processing requirement is provided for a particular location server due to dense population within the location server coverage area, several location servers may be deployed in addition to the redundant location servers in the area. Steps 211 and 213 show a second positioning server applied in the method of the invention. In step 211, the second positioning server receives satellite ephemeris data and corrected pseudorange corrections from the communications network. It is clear that the satellite ephemeris data received from the network may be satellite specific to those satellites of the reference stations in the respective area served by the in-view positioning server 117. This is accomplished by submitting header packets (header packets) or other addressing data to a particular location server by placing the data along with the satellite ephemeris data and corrected pseudorange corrections transmitted by a reference station. The second positioning server receives pseudoranges from the second mobile GPS receiver and determines the state (e.g., position) of the second mobile GPS receiver based on the satellite navigation information data received from the network and the pseudoranges originated by the second mobile GPS receiver at step 213.

Fig. 6 illustrates an example data flow associated with a network correction processor, such as processor 110 of fig. 4. Each network correction processor combines the correction values from the plurality of reference stations into a set of correction values (and adjustment values) having substantially the same time of applicability to the positioning server application. In one embodiment, if a particular location server fails to receive correction data from a particular network correction processor, it may request the same information from a backup network processor at a different location. Upon reaching a network correction processor, each correction set is cached in memory for lookup. Can be used when needed. After atmospheric error cancellation, the correction values are combined to best estimate the range error caused by satellite clock and position errors (including SA jitter). These combined network corrections are then transmitted to the concerned satellites for observation, along with the critical ionospheric data and up-to-date navigation information. In a particular embodiment, this information is sent to all designated location servers (which have been designated as addresses for correction values from the network correction processor). Since each satellite carrier is tracked by more than one reference receiver in one embodiment, each set of network corrections can be checked to ensure internal consistency. In this way, the pseudorange correction values from a first reference station may be compared to pseudorange correction values from neighboring reference stations for the same satellite to ensure internal consistency. As shown in fig. 6, the reference station 301 represents a geographically dispersed reference station, such as the stations 104 and 108 of fig. 4. In one embodiment, pseudorange correction data 303 and a 50-bit data stream including at least a portion thereof contained in a GPS signal are sent to a network corrector, which extracts ionization parameters 310 and establishes a correction set for a single signal epoch (single epoch) 309. The atmospheric delay is eliminated and a combined correction 316 is established. The data flow for the various operations described herein is also illustrated in FIG. 6.

Fig. 7 shows a data flow on one side with respect to a location server, which shows at least three different parts of a system located remotely with respect to the location server. The reference receiver network 401 corresponds to the reference station 104 and 108 of fig. 4. The reference stations are coupled to the location server via a communication network, such as network 103 of fig. 4. The reference receiver network 401 provides the correction values and/or pseudorange data via a data network 403 and also provides at least a portion of the navigation information 405 via the data network. The navigation information typically includes so-called satellite ephemeris data, in one embodiment a 50 baud data stream in the GPS signal from each GPS satellite. The correction values are combined and internally checked for consistency in the correction processor and passed to the location server via the communications network as the correction values 408 or, optionally, as regional correction values. The navigation information data 407 is used to extract ephemeris data for state (e.g., position) calculations for the mobile GPS receiver. The state (e.g., location) calculation 410 may be aided by altitude estimates from the regional altitude database 411. The location server typically receives correction data and navigation information data on a continuous basis via a communication network, such as network 103. Thus, the source of satellite ephemeris data is neither from a local GPS receiver co-located with the positioning server nor from the GPS reference receiver network of reference stations 104-108 of FIG. 4. In this approach, the location server serves a large area that is not accessible to a reference GPS receiver located with the location server.

The positioning server also accepts requests for the position of a mobile GPS receiver (shown as client 424) while continuously receiving at least a portion of the satellite navigation information data and correction data from the GPS reference receiver network. Contact with a mobile GPS receiver typically begins with a data exchange. Generally, doppler data 423 is provided to mobile GPS receiver 424 (based on approximate position data from the mobile receiver or cellular element), which then provides pseudorange data 425 to client interface 420 on the location server. As described above, such location processing may be initiated by the mobile GPS receiver by pressing 911 (in the case of a cellular telephone) or may be initiated by a remote operator 422, which is considered to correspond to the access terminal 29 of fig. 1. As shown in fig. 7, the doppler estimate 414 is provided from the location server to the mobile GPS receiver 424 through the client interface 420. Which typically responds with pseudorange data 425 and determines its position along with ephemeris data. The position calculation can be made using any conventional position algorithm in a conventional GPS receiver and this position, shown as the navigation solution 414, is then provided to the client interface 420, which can in turn communicate this information to the remote operator 422 via the execution module 421 (typically a software module). In one embodiment, remote operator 422 is a PSAP (public safety answering Point), which is a control center that answers 911 telephone calls.

The client interface 420 manages the communication link between the location server and the client (e.g., mobile GPS receiver). In one embodiment, the executive interface assigns a client interface target to each mobile GPS receiver. The client interface may generally be implemented by software operations on a local service. The execution module 421, which is also typically software operated on the location server, allocates interfaces to handle remote operation requests, also controls interfaces to external databases, performs network management and other necessary external interactions. A particular location server typically provides multiple remote operator interfaces, such as standard frame relay, x.25 and TCP/IP network connectivity, to meet the requirements of the remote operator.

While the foregoing has contemplated a particular configuration in which the mobile SPS receiver receives SPS signals from SPS satellites, determines pseudoranges for those satellites, and transmits the pseudoranges along with a time stamp to a location server, which determines the position of the mobile receiver, the present invention expressly contemplates other configurations. For example, a mobile SPS receiver may determine its own position by receiving SPS signals and determining pseudoranges, and receiving and applying satellite ephemeris data (e.g., data from a position location server that transmits the relevant satellite ephemeris data based on the approximate position of the receiver as determined by the cell site with which the mobile SPS receiver is in communication). In this example, the positioning server receives satellite ephemeris data from receivers of the reference network and transmits the relevant satellite ephemeris data to the mobile receiver via a cellular communication system (e.g., a cellular telephone system) in response to a request for positioning of the mobile receiver. The satellite ephemeris data concerned is typically determined from the approximate position of the mobile receiver; the approximate location may be determined by the location of the cell site with which the mobile receiver established the cell wireless communication link. The location server may determine an approximate location using an identifier provided by the cell site; various techniques for determining and applying this approximate location are described in co-pending U.S. patent application No.08/842,559, filed on 15/4/1997 by Norman f.krasner, which is incorporated herein by reference. Approximate positioning will determine the satellites that are within view and the positioning server then transmits satellite ephemeris data for these satellites to the mobile receiver through the mobile switching center and the cell site. In this example, the location server may also transmit doppler estimation data and/or satellite almanac and/or pseudorange correction values to the mobile SPS receiver.

Although the method and apparatus of the present invention have been described with reference to GPS satellites, it is clear that they are equally applicable to positioning systems using quasi-satellites or a combination of satellites and quasi-satellites (pseudolites). Quasi-satellites are terrestrial transmitters that broadcast a PN code (similar to a GPS signal) modulated with an L-band carrier signal, typically synchronized with GPS time, each transmitter being assigned a unique PN code to be identified by a remote receiver. Pseudolites are useful in situations where GPS signals are not available from satellites orbiting the earth, such as tunnels, mines, counties or other enclosed areas. The term "satellite" herein is intended to include quasi-satellites or equivalents thereof, while GPS signals are intended to include GPS-like signals from quasi-satellites or equivalents thereof.

In the above discussion, the present invention has been described with reference to the patent application "U.S. 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 main difference between the Glonass system and the GPS system is that the transmissions of different satellites are distinguished from each other by applying slightly different carrier frequencies rather than different pseudo-random codes. In this case, essentially all of the circuits and algorithms described above are applicable, except that the data is preprocessed using different exponential multipliers corresponding to different carrier frequencies when processing the transmissions of a new satellite. The term "GPS" herein includes such satellite positioning systems, including the Russian Glonass system.

In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof, and it will 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 (46)

1. A method of processing satellite position information in a satellite positioning system, SPS, the method comprising:

receiving, at a first digital processing system, first satellite ephemeris data from a first SPS receiver having a first known position;

receiving, at the first digital processing system, second satellite ephemeris data from a second SPS receiver having a second known position;

receiving, at the first digital processing system, a plurality of pseudorange data from a mobile SPS receiver;

calculating position information for the mobile SPS receiver using the plurality of pseudorange data and at least one of the first and second satellite ephemeris data.

2. The method of claim 1, wherein the first digital processing system calculates the location information.

3. The method of claim 1, wherein said first digital processing system is remotely located relative to said first known location, and wherein said first SPS receiver is a first reference receiver.

4. A method as in claim 3 wherein said first digital processing system is remotely located with respect to said second known location and wherein said second SPS receiver is a second reference receiver.

5. A method as in claim 1 wherein said first satellite ephemeris data is received from a first set of SPS satellites in view of said first SPS receiver and wherein said second satellite ephemeris data is received from a second set of SPS satellites in view of said second SPS receiver.

6. The method of claim 1, wherein the method further comprises:

receiving, at the first digital processing system, first pseudorange correction data from the first SPS receiver;

second pseudorange correction data is received at the first digital processing system from the second SPS receiver.

7. A method as in claim 6 wherein at least one of said first and second pseudorange correction data is used to correct said plurality of pseudorange data from said mobile SPS receiver to provide a corrected plurality of pseudorange data.

8. The method of claim 7, wherein said position information is calculated based on said corrected plurality of pseudorange data and at least one of said first and second satellite ephemeris data.

9. The method as recited in claim 5, wherein said first satellite ephemeris data comprises navigation information from said first set of SPS satellites and said second satellite ephemeris data comprises navigation information from said second set of SPS satellites.

10. The method of claim 1, wherein the method further comprises:

receiving, at a second digital processing system, first pseudorange data from the first SPS receiver;

receiving, at the second digital processing system, second pseudorange data from the second SPS receiver;

correcting with the first pseudorange data to provide combined first pseudorange correction data and correcting with the second pseudorange data to provide combined second pseudorange correction data;

at least one of the merged first and second pseudorange correction data is transmitted to the first digital processing system.

11. A method as in claim 10 wherein at least one of said combined first and second pseudorange data is used to correct said plurality of pseudorange data from said mobile SPS receiver to provide a plurality of corrected pseudorange data.

12. A method according to claim 11, wherein said position information is calculated from said corrected plurality of pseudorange data and at least one of said first and second satellite ephemeris data.

13. A method as in claim 12 wherein said first satellite ephemeris data is derived from navigation information from a first set of SPS satellites in view of said first SPS receiver and said second satellite ephemeris data is derived from navigation information from a second set of SPS satellites in view of said second SPS receiver.

14. A method as in claim 13 wherein said first satellite ephemeris data is received from said first SPS receiver via said second digital processing system and said second satellite ephemeris data is received from said second SPS receiver via said second digital processing system.

15. A method as in claim 12 wherein said first digital processing system comprises a first fault tolerant computer system and said second digital processing system comprises a second fault tolerant computer system, wherein said first pseudorange data comprises at least one of a first pseudorange relative to a satellite from which said first SPS receiver is seen and a first pseudorange correction value relative to a satellite from which said first SPS receiver is seen.

16. The method as in claim 12 wherein said first digital processing system is coupled to said mobile SPS receiver through a cellular wireless communication system.

17. The method of claim 16, wherein the cellular wireless communication system comprises a mobile switching center.

18. A method as in claim 17 wherein said first and second SPS receivers and said first and second digital processing systems are coupled together via a packet data network.

19. The method of claim 10, wherein the method further comprises:

receiving, at a third digital processing system, the first pseudorange data from the first SPS receiver;

receiving, at the third digital processing system, the second pseudorange data from the second SPS receiver;

correcting at said third digital processing system with said first pseudorange data to provide said combined first pseudorange correction data and correcting with said second pseudorange correction data to provide said combined second pseudorange correction data, wherein said first digital processing system is capable of receiving said combined first and second pseudorange correction data from said third digital processing system.

20. A system for processing satellite position information, the system comprising:

a plurality of Satellite Positioning System (SPS) reference receivers each having a known location, the plurality of SPS reference receivers being dispersed throughout a region, each of the plurality of SPS reference receivers transmitting satellite ephemeris data received from satellites in view of the plurality of SPS reference receivers into a communications network;

a plurality of digital processing systems each coupled to said communications network to receive satellite ephemeris data transmitted through said communications network, said plurality of digital processing systems including first and second digital processing systems, said first digital processing system receiving a first plurality of pseudorange data from a first mobile SPS receiver and computing first position information for said first mobile SPS receiver based on said first plurality of pseudorange data and satellite ephemeris data received from said communications network, said second digital processing system receiving a second plurality of pseudorange data from a second mobile SPS receiver and computing second position information for said second mobile SPS receiver based on said second plurality of pseudorange data and satellite ephemeris data received from said communications network.

21. A system as in claim 20 wherein said first digital processing system is communicatively coupled to said first mobile SPS receiver through a cellular wireless communication system and said second digital processing system is communicatively coupled to said second mobile SPS receiver through said cellular wireless communication system.

22. The system of claim 21, wherein said communication network is a packet data network.

23. A system as in claim 21 wherein said first digital processing system is remotely located with respect to at least some of said plurality of SPS reference receivers.

24. A system as in claim 21 wherein said plurality of SPS reference receivers comprises first and second SPS reference receivers, wherein said first and second SPS reference receivers transmit first and second satellite ephemeris data, respectively, into said communication network, said first satellite ephemeris data being derived from navigation messages received from a first set of SPS satellites in view of said first SPS reference receiver, and said second satellite ephemeris data being derived from navigation messages transmitted from a second set of SPS satellites in view of said second SPS reference receiver.

25. A system as in claim 24 wherein said first digital processing system is capable of calculating said first position information of said first mobile SPS receiver using said first and second satellite ephemeris data and said second digital processing system is capable of calculating said second position information of said second mobile SPS receiver using said first and second satellite ephemeris data.

26. A system as in claim 24 wherein said first and second digital processing systems receive first pseudorange correction data derived from data from said first SPS reference receiver and second pseudorange correction data derived from data from said second SPS reference receiver.

27. A system as in claim 26 wherein said first SPS reference receiver transmits said first pseudorange correction data into said communication network and said second SPS reference receiver transmits said second pseudorange correction data into said communication network.

28. A system according to claim 27, wherein at least one of said first and second pseudorange correction data is used to correct said first plurality of pseudorange data to provide a combined first plurality of pseudorange data, and wherein said first position is determined from at least one of said combined first plurality of pseudorange data and said first and second satellite ephemeris data.

29. The system of claim 24, further comprising:

a further digital processing system coupled to said communications network, said further digital processing system receiving first pseudorange data from said first SPS reference receiver and second pseudorange data from said second SPS reference receiver and correcting said first pseudorange data to provide combined first pseudorange correction data and correcting said second pseudorange data to provide combined second pseudorange correction data, said further digital processing system transmitting said first combined pseudorange correction data and second combined pseudorange correction data to said first digital processing system.

30. A system for processing satellite position information, the system comprising:

a communication medium;

a first Satellite Positioning System (SPS) reference receiver having a first known location and a first communication interface coupled to the communication medium, the first SPS reference receiver transmitting first satellite ephemeris data into the communication medium;

a second SPS reference receiver having a second known location and a second communication interface coupled to the communication medium, the second SPS reference receiver transmitting second satellite ephemeris data into the communication medium; and

a first digital processing system coupled to the communication medium for receiving at least one of the first and second satellite ephemeris data and providing satellite information to a mobile SPS receiver to determine a navigation solution for position information for the mobile SPS receiver, wherein the mobile SPS receiver is coupled to a wireless cellular receiver that receives the satellite information and provides the satellite information to the mobile SPS receiver.

31. A system as in claim 30 wherein said first satellite ephemeris data is received from a first set of SPS satellites in view of said first SPS reference receiver and wherein said second satellite ephemeris data is received from a second set of SPS satellites in view of said second SPS reference receiver.

32. A system according to claim 31, wherein the communication medium comprises a packet data network, and wherein the first communication interface and the second communication interface provide the first and second satellite ephemeris data, respectively, in the form of packet data.

33. A system as in claim 31 wherein said first and second SPS receivers transmit first and second pseudorange data, respectively, into said communication medium, wherein said first pseudorange data comprises at least one first pseudorange relative to satellites in view of said first SPS reference receiver and a first pseudorange correction value relative to satellites in view of said first SPS reference receiver.

34. The system of claim 33, wherein the system further comprises:

a second digital processing system coupled to said communication medium, said first digital processing system receiving said first and second pseudorange data and correcting said first pseudorange data to provide first corrected pseudorange correction data transmitted into said communication medium and correcting said second pseudorange data to provide second corrected pseudorange correction data transmitted into said communication medium.

35. A system as in claim 30 wherein said satellite information comprises at least one of satellite ephemeris data for satellites in view of said mobile SPS receiver or doppler data or satellite almanac data for said satellites in view, wherein said satellite information is transmitted from said first digital processing system to said mobile SPS receiver, and wherein said satellite ephemeris data for satellites in view of said mobile SPS receiver is derived from at least one of said first and second satellite ephemeris data.

36. A system as in claim 35 wherein said mobile SPS receiver determines said navigation solution.

37. A system for transmitting satellite ephemeris information, the system comprising:

a communication medium;

a first Satellite Positioning System (SPS) reference receiver having a first known location and a first communication interface coupled to said communication medium, said first SPS reference receiver transmitting first packets of first satellite ephemeris data into said communication medium, each said first packet being less than one subframe of satellite ephemeris data;

a second SPS reference receiver having a second known location and a second communication interface coupled to the communication medium, the second SPS reference receiver transmitting second packets of second satellite ephemeris data into the communication medium, each of the second packets being less than one subframe of satellite ephemeris data.

38. A system as in claim 37 wherein said first satellite ephemeris data is received from a first set of SPS satellites in view of said first SPS reference receiver and wherein said second satellite ephemeris data is received from a second set of SPS satellites in view of said second SPS reference receiver.

39. A system according to claim 38, wherein said communication medium comprises a packet data network, and wherein said first communication interface provides said first satellite ephemeris data in the form of packet data.

40. A system according to claim 39, wherein the second communication interface provides the second satellite ephemeris data in the form of packetized data.

41. A system as in claim 38 wherein said first SPS receiver transmits first pseudorange data into said communication medium and wherein said first pseudorange data comprises at least one first pseudorange relative to satellites in view of said first SPS reference receiver and a first pseudorange correction value relative to satellites in view of said first SPS reference receiver.

42. A system as in claim 41 wherein said second SPS receiver transmits second pseudorange data into said communication medium.

43. The system of claim 42, wherein the system further comprises:

a first digital processing system coupled to the communication medium, the first digital processing system receiving the first pseudorange data and correcting the first pseudorange data to provide first corrected pseudorange correction data transmitted into the communication medium.

44. A system as in claim 43 wherein said first digital processing system receives said second pseudorange data and corrects said second pseudorange data to provide second corrected pseudorange correction data which is transmitted into said communication medium.

45. A system as in claim 37 wherein said first satellite ephemeris data is received from a first set of SPS satellites in view of said first SPS reference receiver.

46. A system for processing satellite position information, the system comprising:

a communication medium;

a first Satellite Positioning System (SPS) reference receiver having a first known location and a first communication interface coupled to said communication medium, said first SPS reference receiver transmitting first packets of first satellite ephemeris data into said communication medium, each said first packet being less than one subframe of satellite ephemeris data, whereby said first packets are transmitted into said communication medium at a packet per second rate greater than one packet every 6 seconds.