HK1054988B - Methods for determining an ordered set of sps satellites in view of a mobile sps receiver - Google Patents

Description

Method for determining ordered set of SPS satellites in field of view of mobile SPS receiver

Technical Field

The present invention relates to receivers capable of determining position information of satellites, and more particularly to receivers that find application in Satellite Positioning Systems (SPS), such as the united states Global Positioning System (GPS).

RELATED APPLICATIONS

The present invention relates to and therefore claims the benefit of the filing date of two provisional applications by the same inventor, Leonid Sheynblat. The 1 st provisional application is serial No. 60/190,600 of the 2000-3-20-month application entitled "Methods and Apparatus for using assistance data Relating to Satellite Position Systems". The 2 nd application is serial No. 60/228,258 of 25/8.2000, entitled "Methods and apparatus for Using Satellite state information in Satellite positioning systems".

Background

GPS receivers typically determine their position by calculating the time of arrival of signals transmitted simultaneously by multiple GPS satellites. As part of their messages, these satellites transmit satellite positioning data as well as clock timing data called "ephemeris" data. The process of searching for and acquiring GPS signals, reading ephemeris data for multiple satellites, and calculating the position of the receiver from that data is time consuming, often requiring several minutes. In many cases, this lengthy processing time is unacceptable and greatly limits the life of the battery in miniaturized portable applications.

The GPS receiving system has two main functions. The 1 st is the calculation of pseudoranges to various GPS satellites and the 2 nd is the calculation of the position of the receiver using these pseudoranges and satellite timing and ephemeris data. The pseudoranges are simply the times of arrival of the satellite signals measured by the local clock. This definition of pseudorange is also sometimes referred to as code phase. Once the GPS signal is acquired and tracked, satellite ephemeris and timing data is extracted from the signal. As mentioned above, collecting this information typically takes a relatively long time (30 seconds to several minutes) and must be done with a better received signal level in order to achieve a lower error rate.

Most GPS receivers use correlation methods to compute pseudoranges. These correlation methods are typically performed in real time with a hardware correlator. The GPS signal comprises a high-rate repetitive signal called a pseudo-random (PN) sequence. Codes available for civilian use are referred to as C/a (coarse/acquisition) codes and have a binary phase inversion rate or "chip slicing" rate of 1.023MHz and a repetition rate of 1023 chips for a1 millisecond code period. The code sequence belongs to a series known as gold codes, and each GPS satellite broadcasts a signal with a unique gold code.

For a received signal from a given GPS satellite, after down-conversion processing to baseband, the relevant receiver multiplies the received signal by a stored copy of the appropriate gold code contained in its local memory, and then integrates or low-pass filters the product to obtain an indication of the presence of the signal. This process is referred to as a "correlation" operation. By sequentially adjusting the relative timing of the stored copies with respect to the received signal, and observing the correlation output, the receiver is able to determine the time delay between the received signal and the local clock. The initial determination of the occurrence of such an output is referred to as "capture". Once acquisition occurs, the process enters a "tracking" phase in which the timing of the local reference is adjusted by a small amount in order to maintain a high correlation output. The correlation output during the tracking phase can be viewed as a GPS signal with the pseudorandom code removed, or as "despreading" in general terms. The signal is narrow-band, having a bandwidth comparable to Binary Phase Shift Keying (BPSK) data superimposed on a GPS waveform of 50 bits per second.

The correlation acquisition process is very time consuming, especially if the received signal is weak. To improve acquisition time, most GPS receivers utilize multiple correlators (typically up to 36) which allow parallel searches for correlation peaks.

Conventional GPS receiving devices are typically designed to receive GPS signals in open space, since the satellite signals are line-of-sight and therefore can be obstructed by metal or other substances. The improved GPS receiver provides signal sensitivity that allows for tracking of GPS satellite signals indoors, or in the case of weak multipath signals or purely reflected signals. However, the ability to acquire such weak GPS signals generally causes other problems. For example, simultaneous tracking of strong and weak signals may cause the receiver to lock onto a cross-correlated signal that is not a true signal. The peaks of the stronger cross-correlation can be captured instead of finding the weaker real peaks. Tracking a weak satellite signal does not guarantee that it is a direct signal. The weak signal may be a reflected signal or a combination of direct and indirect signals. The combined signal is referred to as a multipath signal. The path of the reflected signal is typically longer than the path of the direct signal. Such differences in path lengths cause the arrival time measurements of the reflected signals to be typically delayed or cause the corresponding code phase measurements to contain a positive offset. The magnitude of the deviation is generally proportional to the relative delay between the reflected signal and the direct signal. The potential lack of direct signal components makes existing multipath mitigation techniques (such as narrow or gated correlators) obsolete.

A GPS navigation message is information sent from a GPS satellite to a GPS receiver. Which is in the form of a data stream of 50 bits per second modulated on top of the GPS signal.

The data message is contained in a data frame that is 1500 bits long. It has 5 subframes, each containing GPS system time. Each subframe consists of 10 words, each word being 30 bits. Subframes 1 through 3 are repeated every 30 seconds. There are 25 data pages in the 4 th and 5 th sub-frames in turn; one every 30 seconds. Thus, each of these 25 pages repeats every 750 seconds.

Subframes 4 and 5 contain two types of GPS satellite health or status data: (a) each of the 32 pages containing almanac data related to clock/ephemeris provides 8-bit satellite health status work for the satellites that carry the almanac data for that satellite, and (b) page 25 of subframes 4 and 5 collectively contains up to 32-bit health status data for the satellites. Additional satellite health data is given in subframe 1.

A GPS receiver will typically receive information about the state of a satellite (e.g., "health") and then process the GPS signals by not acquiring and tracking unhealthy satellites as it acquires and tracks GPS signals from healthy satellites. On the other hand, standalone GPS receivers can be designed to acquire and track unhealthy satellites, but avoid Using their signals in Position location calculations after reading health Status data from ephemeris messages of signals from unhealthy satellites (see related provisional patent application "Method and Apparatus for Using Satellite state Information in Satellite Position Systems," serial No. 60/228,258, filed 25.8.2000, incorporated herein by reference).

Satellite positioning systems have used various types of assistance data to improve the performance of SPS receivers. For example, the SPS receiver may receive doppler estimates from an external source (e.g., a radio transmission to the SPS receiver). Another type of assistance data may be the identification of satellites at locations in view of an estimated or known SPS receiver. In the past, the identification of these satellites did not contain any indication as to whether the satellites are likely to be in a poor geometry relative to the estimated position of the SPS receiver or to each other. Also, in the past, the identification of satellites in view of an SPS receiver did not include an indication of poor geometry with the health data of the satellites.

Summary of The Invention

The present invention relates to a method and apparatus for determining an ordered set of SPS satellites in view of a mobile SPS receiver. A method includes determining an ordered set of SPS satellites in view of a location (e.g., a typical location) in a cell of a cellular communication system, and then transmitting the ordered set of SPS satellites from a cellular transmission site located within or near the cell so that an SPS receiver located in the cell of the cellular communication system can receive the ordered set of SPS satellites.

The ordering of SPS satellites in the ordered set may be performed according to different methods, such as by minimizing a geometric dilution of precision (GDOP); by minimizing a position dilution of precision (PDOP), by minimizing a horizontal dilution of precision (HDOP), by providing a position solution that uses SPS satellites having a desired geometry relative to each other, by providing a position solution that uses SPS satellites having a desired geometry relative to the mobile SPS receiver; ranking based on probability of SPS signal acquisition; ranking based on estimates of measurement quality from an ordered set of SPS satellites; ranking is performed by providing an optimal geometric trilateration solution, and ranking is based on user-defined selection criteria. Further, the ranking may include satellite health information.

In one embodiment, an apparatus for establishing an ordered set of SPS satellites comprises: the system includes a server that determines an ordered set of SPS satellites in view of a cell of a cellular communication system at a given time, and a transmitter coupled to the server that transmits the ordered set of SPS satellites from a cellular transmission site located within or near the cell. Thus, a mobile SPS receiver located in a cell may receive the ordered set of SPS satellites.

In one embodiment, the server further comprises a processor; and an information source coupled to the processor. The information source includes a plurality of sets of SPS satellites in view of a cell of a cellular service area, and the processor determines an ordered set of SPS satellites for the cell of the cellular service area. The server may be a GPS reference server, a cellular switching center, a positioning server, a cellular transmission site, a base station controller, or a mobile SPS receiver.

In one embodiment, a method for obtaining an ordered set of SPS satellites in view of a mobile SPS receiver includes receiving, with the mobile SPS receiver configured to receive both SPS signals and signals transmitted from a cellular transmission site, the ordered set of SPS satellites via transmissions from the cellular transmission site. Thus, the mobile SPS receiver is allowed to search for SPS satellites according to the order of the ordered set of SPS satellites obtained from the transmission. The mobile SPS receiver may modify the search for SPS satellites based on SPS satellite health data before or after acquiring SPS satellites.

In one embodiment, an apparatus for receiving an ordered set of SPS satellites comprises: a mobile SPS receiver that receives SPS signals; and a receiver configured to receive a signal transmitted from a cellular transmission site; such that the ordered set of SPS satellites may be transmitted to the receiver via the cellular transmission site and the mobile SPS receiver may search for SPS satellites according to the order of the ordered set of SPS satellites.

Another embodiment of the present invention provides a method and apparatus for allowing two-way communication with a mobile SPS receiver. In accordance with the method of this embodiment of the present invention, a transmission is received from a mobile SPS receiver within a cell of a cellular service area, the mobile SPS receiver being configured to transmit and receive cellular signals; determining, at a given time, an ordered set of SPS satellites in view of a mobile SPS receiver based in part on the received transmissions; and transmitting the ordered set of SPS satellites from a cellular transmission site; such that the mobile SPS receiver may receive the ordered set of SPS satellites.

In one embodiment, an apparatus for facilitating two-way communication with a mobile SPS receiver includes a receiver to receive a transmission from the mobile SPS receiver sent from a cell of a cellular service area, the mobile SPS receiver configured to transmit and receive cellular signals; a transmitter for transmitting cellular network signals from a cellular network transmission site; and a server that determines an ordered set of SPS satellites in view of the SPS receiver; such that the ordered set of SPS satellites is transmitted by the transmitter and received by the mobile SPS receiver.

In one embodiment, the server further comprises a processor; and an information source coupled to the processor. The information source includes a plurality of sets of SPS satellites in view of a cell of a cellular service area, and the processor determines an ordered set of SPS satellites for the cell of the cellular service area. The server may be a GPS reference server, a cellular switching center, a positioning server, a cellular transmission site, a base station controller, or a mobile SPS receiver.

In one embodiment, a method of facilitating acquisition of an ordered set of SPS satellites in view of a mobile SPS receiver by two-way communication by the mobile SPS receiver includes transmitting, with the mobile SPS receiver configured to receive SPS signals and to transmit and receive cellular signals, from a cell of a cellular service area to a cellular transmission site that receives transmissions from the cell. The mobile SPS receiver receives an ordered set of SPS satellites from a cellular transmission site. The ordered set of SPS satellites are those in view of the mobile SPS receiver at a given time; such that the mobile SPS receiver may search for SPS satellites according to the order of the ordered set of SPS satellites obtained from the received transmissions from the cellular transmission site. Satellite health data may be included in the transmission, and the mobile SPS may modify the search for SPS satellites based in part on SPS satellite health data before or after acquisition of SPS satellites. Further, the mobile SPS receiver may modify the ordered set after reception.

In one embodiment, an apparatus for facilitating acquisition of an ordered set of SPS satellites in view of a mobile SPS receiver via two-way communication by the mobile SPS receiver includes an SPS receiver that receives SPS signals; a receiver configured to receive a signal transmitted from a cellular transmission site; and a transmitter for transmitting the cellular network signal to a cellular network transmission site; such that when a transmitter located within a cell of a cellular service area establishes communication with the cellular transmission site, an ordered set of SPS satellites may be transmitted to the receiver by the cellular transmission site, and the mobile SPS receiver may search for SPS satellites according to the order of the ordered set of SPS satellites.

Another embodiment of the present invention provides a method of receiving an ordered set of SPS satellites as determined by a mobile SPS receiver.

Another embodiment of the present invention uses a history of stored GPS satellite signal quality information for a location to determine an ordered set of SPS satellites.

Another embodiment of the present invention uses mobile SPS receiver information to determine an ordered set of SPS satellites.

Another embodiment of the invention comprises: determining an ordered set of SPS satellites in view of the mobile SPS receiver at a given time; and transmitting the ordered set of SPS satellites to a cellular transmission site; such that a server may receive the ordered set of SPS satellites in view of the mobile SPS receiver.

Brief Description of Drawings

FIG. 1A illustrates a set of satellites in view of a Satellite Positioning System (SPS) receiver.

FIG. 1B illustrates a top-down view of the satellites shown in FIG. 1A relative to the SPS receiver.

Figure 1C illustrates a cellular communication system having a plurality of cells, each of which is served by a cell site and each of which is connected to a cellular switching center.

FIG. 1D illustrates an example of a combined SPS receiver and communication system in accordance with an embodiment of the invention.

Figure 2 illustrates one embodiment of a cellular network based information source that provides associations between priority order groups for cellular service areas and/or cellular cell stations at a given time in accordance with the teachings of the present invention.

Fig. 3 is a flow chart illustrating a method for prioritizing in-view satellites in accordance with the teachings of the present invention.

Detailed Description

The present invention, in one embodiment, relates to the determination of an ordered set of SPS satellites in view of an SPS receiver. The order of the ordered set of satellites is based on an approximate location of the SPS receiver, which is determined from a cellular transmission site that identifies or knows cellular communication with the SPS receiver communication system. The knowledge of the cellular transmission site may be implicit in the case where the data identifying the SPS satellites in view of the SPS receiver is provided by being located in the vicinity of the cellular transmission site that is in geographic communication with the SPS receiver. In one embodiment of the invention, the order of the ordered set of satellites is further based on the position of the satellites relative to the adjacent position of the SPS receiver.

FIG. 1A shows a set of SPS satellites in view of SPS receiver 100. The SPS receiver also includes a communication system such as a two-way cellular telephone or a two-way (or one-way) pager. An example of such a communication system coupled to an SPS receiver is described in co-pending U.S. patent application No. 08/842,559, filed on 15/4/1997. See also PCT publication WO 98/25157. FIG. 1B illustrates a top-down view of the satellites shown in FIG. 1A relative to SPS receiver 100. The positions of satellites 102, 104, 106, 108, 110, and 112 at a time of day are shown. It should be noted that some of the SPS satellites shown in fig. 1A are not visible to SPS receiver 100 at different times due to the changing positions of the satellites over time. Moreover, the SPS receiver 100 is typically mobile. Thus, as SPS receiver 100 moves to different locations, the satellites in view of SPS receiver 100 may change. Also in other embodiments, the source of the SPS signal may become blocked (e.g., hidden behind a building) or severely attenuated. This blockage or attenuation may be considered when selecting an ordered list of satellites, as described below.

Figure 1C illustrates a cellular network-based communication system 10 having a plurality of cell stations, each of which is designed to serve a particular geographic area or location. Examples of such cellular network based communication systems are well known in the art. See, for example, U.S. patent 5,519,760 describing a cellular network system. The cellular based communication system 10 includes two cells 12 and 14 defined to be located within a cellular service area 11. In addition, system 10 includes cells 18 and 20. It will be appreciated that a plurality of other cells and their corresponding cell sites and/or cellular service areas may also be included in the system 10. And couples them to one or more cellular switching centers such as cellular switching center 24 and cellular switching center 24 b.

In each cell, such as cell 12, there is a wireless cell site, such as cell site 13, or cellular web site, which includes an antenna 13a designed to communicate over a wireless communication medium with a communication receiver, which may be a combined mobile GPS receiver and communication system, such as receiver 16 shown in fig. 1 c. An example of such a combined system is shown in fig. 1D, and may include both a GPS antenna 377 and a communication system antenna 379. It will be understood that alternative embodiments may use a single antenna or more than two antennas.

Each cell station is coupled to a cellular network switching center. In fig. 1C, cell stations 13, 15, and 19 are coupled to switching center 24 by connections 13b, 15b, and 19b, respectively, and cell station 21 is coupled to a different switching center 24b by connection 21 b. These connections are typically wire connections between the respective cell sites and the cellular switching centers 24 and 24 b. Each cell station includes an antenna and a transmitter and receiver for communicating with a communication system serviced by the cell station. It will be appreciated that a communication system in one cell, such as receiver 22 shown in cell 4, may actually be communicating with cell station 19 in cell 18 due to congestion (or other reasons cell station 21 is unable to communicate with receiver 22).

In an exemplary embodiment of the invention, the mobile GPS receiver includes a cellular network based communication system that is integrated into the GPS receiver such that both the GPS receiver and the communication system are enclosed in the same housing. When the combined system is used for cellular telephone communications, transmissions occur between receiver 16 and cell station 13. The transmission from receiver 16 to cell site 13 is then propagated on connection 13b to cellular switching center 24 and then to another cellular telephone in a cell served by cellular switching center 24 or through a connection 30 (typically wired) to another telephone through land-based telephone system/network 28. It will be understood 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 16 are transmitted from the cellular switching center back to the receiver 16 via the connection 13b and the cell station 13 in a conventional manner.

A remote data processing system 26 (which may be referred to as a GPS server or a positioning server in some embodiments) is included in the system 10 and, in some embodiments, the system 26 is used when a mobile GPS receiver in a particular cell is used to determine the location of a receiver using GPS signals received by the GPS receiver. The GPS server may be coupled to a land-based telephone system/network 28 via connection 27 and may optionally also be connected to cellular switching center 24 via connection 25 and may optionally also be connected to center 24b via connection 25 b. It will be appreciated that while the connections 25 and 27 may be wireless, they are typically wired. Also shown as an optional component of system 10 is a query terminal 29, which may constitute another computer system coupled to the GPS server via network 28. The inquiring terminal 29 may send a request to the GPS server 26 for the location of a particular GPS receiver in one of the cells, which then initiates a dialog with a particular GPS receiver through the cellular switching center to determine the location of the GPS receiver and report the location back to the inquiring terminal 29.

It should be noted that a cellular network based communication system is a communication system having more than one transmitter, each of which serves a different geographical area, which is predefined at any instant in time. Cell sites may also be mobile rather than fixed terrestrial locations; for example, cell sites in the Iridium (Iridium) and Globalstar (Globalstar) systems are satellites that orbit the Earth's low orbits. Each transmitter is typically a wireless transmitter of a serving cell, which has a geographic radius of less than 20 miles, although the area covered depends on a particular cellular network system. There are many types of cellular communication systems such as cellular telephones, PCS (personal communication system), SMR (dedicated mobile radio), one-way and two-way paging systems, RAM, ARDIS, and wireless packet data systems. The predetermined distinct geographic areas are typically referred to as cells, a plurality of which are grouped together to form a cellular service area, such as cellular service area 11 shown in fig. 1C, and these plurality of cells are connected to one or more cellular switching centers that provide connectivity to land-based telephone systems and/or networks. Service areas are commonly used for billing purposes. It may thus be the case that cells within more than one service area are connected to one switching centre. For example, in fig. 1C, cells 1 and 2 are in service area 11 and cell 3 is in service area 18, but all 3 cells are connected to switching center 24. On the other hand, it is sometimes the case that cells in one service area are connected to different switching centres, especially in densely populated areas. A service area is generally defined as a set of cells that are in a region that is geographically close to each other. Another type of cellular system suitable for the above description is satellite-based, where the cellular base stations are typically satellites that orbit the earth. In these systems, the cell sectors and service areas move as a function of time. Examples of such systems include Iridium, Globalstar, Orbcomm, and Odyssey.

FIG. 1D illustrates a general combined GPS and communication transceiver system. The system 375 includes a GPS receiver 376 with a GPS antenna 377 and a communication transceiver 378 with a communication antenna 379. The GPS receiver 376 is coupled to a communications transceiver 378 by a connection 380 shown in fig. 1D. In normal operation, the communication system transceiver 378 receives the approximated doppler information via antenna 379 and provides the approximated doppler information on link 390 to the GPS receiver 376, which receives signals from GPS via GPS antenna 377 for pseudorange determination. Various embodiments of the combination system 375 are known in the art and are described in the above-referenced co-pending applications.

The order of preferential acquisition of the satellites 102 and 112 is determined for the positions of the satellites 102 and 112 and the SPS receiver 100 shown in FIG. 1A. The sequence represents an optimal sequence for obtaining SPS signals from SPS satellites based on, for example, the geometry of the satellites relative to the position of the SPS receiver. In one embodiment of the invention, the satellites 102 and 112 are arranged in an order that provides the desired geometry between the satellites 102 and 112 and the SPS receiver 100. For example, the altitude and angle of the satellites 102 and 112 relative to the SPS receiver 100 may be factors in determining the order of priority. In yet another embodiment, the best prioritization/selection results in the smallest GDOP (geometric dilution of precision) and/or PDOP (position dilution of precision) and/or HDOP (horizontal dilution of precision). The positioning server responsible for message generation typically selects the satellites according to the "best n (best-n)" method. In one example of such a method, the selected satellites are those that optimize the geometry between their location and the location of the SPS receiver 100. For example, in the best 4 configuration, the SPS satellites in fig. 1A would be selected to populate an ordered list of satellites, and they would be ordered as follows (from highest priority to lowest priority): 108. 104, 112 and 102. The best n satellite selection method provides information about the satellite acquisition strategy that SPS receiver 100 should follow. In one embodiment of the present invention, SPS receiver 100 may choose to stop the satellite acquisition process once the best n satellites have been acquired. Thus, not all satellites in view need to be prioritized. In fact, less desirable satellites may not be used at all in analyzing the position of SPS receiver 100. In another embodiment, the positioning server may provide assistance to a subset of satellites in view of the SPS receiver, such as the best n-set. The order is typically chosen to attempt to first acquire those SPS satellites that are less close to the horizon and those that provide the optimal geometric trilateration solution. The former requirement generally means that SPS signals can be more easily received from satellites that are not close to the horizon, while the latter requirement means that the position solution (from pseudoranges to the highest ranked satellites in the sequence) will be more accurate (less error) than the position solution that would use the lowest ranked satellites in the sequence. The sequence may reflect a desired quality of the measurement (e.g., satellite 1 in the desired sequence provides a higher quality measurement than the remaining satellites in the sequence).

It should be appreciated that satellite acquisition is a step in the position determination process. It is also understood that if the azimuth and elevation data is provided to the SPS receiver, it may use such data to further optimize its satellite acquisition strategy. It is further understood that criteria other than geometry or relative position, such as satellite health, may be used to prioritize the order in which satellites are acquired.

Satellite health assists in protecting against spoofed satellite measurements. In a fairly often severe signal blocking environment, GPS satellite signals are received with a very large dynamic range. Receiving GPS signals with signal strengths that differ by more than about 17dB may cause the GPS receiver to acquire cross-correlated signals rather than relatively weak real signals. A process that may be used to detect and possibly correct or remove cross-correlation measurements is described in co-pending U.S. patent application serial No. 09/241,334, filed on 2/1/1999, which is incorporated herein by reference. However, for a GPS receiver to detect the presence of cross-correlation signals, all signals from healthy and unhealthy satellites should be acquired. A problem arises if a strong "bad" satellite signal is cross-correlated with a weak "healthy" satellite signal. Without being aware of the presence of a "bad" signal, the GPS receiver may not be able to detect the cross-correlation condition.

In one embodiment of the present invention, a GPS reference receiver (also referred to as a Position Determination Entity (PDE) in a CDMA cellular telephone system and a Serving Mobile Location Center (SMLC) in a GSM cellular telephone system) that provides reference data to a location service area acquires and tracks all healthy and unhealthy satellites in view. Furthermore, all GPS technologies (e.g., GPS receivers) integrated with or connected to wireless devices (e.g., cellular telephones or two-way pagers) also acquire and track all healthy and unhealthy satellites in view. In a wireless assisted gps (wag) mode (see, for example, co-pending U.S. patent No. 08/842,559, filed on 4/15/1997, which is incorporated herein by reference), a location server may provide "health" status information to mobile devices communicating with a wireless network served by the location server. This health status information may be accompanied by any other assistance information provided by the location server. The aiding information generally allows for rapid acquisition of GPS signals in highly constrained signal environments. To achieve such performance improvements, the aiding information may specify the satellites to search for, the estimated times of arrival of these signals, and the expected frequencies of the signals (doppler effect). Such aiding information may be provided to improve a 3-dimensional search for satellite signals. When acquiring signals of satellites, pseudorange, doppler, and other satellite signal measurements are analyzed for cross-correlation conditions. To perform this analysis, measurements should be made on all healthy and unhealthy satellites in the field of view. In this embodiment, satellite health information is used to detect cross-correlation conditions and then cross-correlated and/or "unhealthy" satellites are analyzed to determine whether they should be included in or corrected for the positioning calculation process. When the aiding information is provided only to healthy satellites (the health of the satellites is implicit in the satellite list) and currently valid satellite health information is not available to the mobile GPS receiver, the mobile device will attempt to acquire only the healthy satellites. In this case, the mobile device will not be aware of the possible presence of a "strong" unhealthy satellite potentially correlated with a relatively weak healthy satellite, and will therefore not make a determination of it. The use of undetected cross-correlation signals may result in large position errors, affecting the quality of location services.

The priority may be modified based on health information of the satellites.

Alternatively, the health information may be received directly from the satellite and used in the same manner as the health information received from the transmitter at the cell site as described herein.

This information may be transmitted from a cellular telephone base station ("cell site") by broadcasting health information to all satellites in view of the cell site. Alternatively, this information may be provided to the cellular telephone upon request (upon request) of the location of the telephone; the health information may be transmitted from a cellular telephone base station to a cellular telephone, which may then provide the health information to a GPS receiver coupled to the cellular telephone. In the case of transmitting information upon request, the GPS server may determine appropriate (e.g., updated health) information based on a cell site in cellular radio/wireless communication with the telephone, the cell site determining an appropriate location for determining satellites in view of the location and then causing the updated health information for those satellites to be transmitted (in one case) to the cellular telephone, which then provides the information to the mobile GPS receiver for processing SPS signals in the GPS receiver. In another case, the GPS server may retain the updated health information and use it to process received pseudoranges (e.g., correlation measurements) from the mobile GPS receiver to determine the position of the mobile GPS receiver. In both cases, pseudoranges (e.g., correlation measurements specifying code phases) and estimated doppler are determined even for known unhealthy GPS satellites, enabling cross-correlation to be detected as described herein. For example, the GPS receiver may receive updated health information from the cell site, but still obtain GPS signals from GPS satellites indicated as unhealthy from the transmitted updated health information. Co-pending U.S. application serial No. 08/842,559, filed on 4/15/1997, describes a method for identifying a cell site that is in wireless communication with a cellular telephone and then determining satellite assistance data for satellites in view based on an approximate position derived from identifying the cell site. The method may be used in connection with the present invention, wherein in this case the satellite assistance data is either a satellite health condition (e.g. based on satellite ephemeris) or an updated satellite health condition (e.g. more current than existing information of satellite ephemeris messages regarding satellite health).

In another embodiment, based on the stored or obtained information, the SPS receiver may autonomously determine an optimal order of satellites and provide an ordered list to a location server that undertakes message generation (and can then provide the ordered list to other SPS receivers and/or provide assistance data in the order provided by the SPS receivers).

In yet another embodiment, based on information provided from the mobile SPS receiver or stored information (e.g., a history of GPS signal quality), the location server may determine an ordered list of satellites that will reflect the likelihood of successful signal acquisition (e.g., satellites near the horizon will have a lower likelihood of successful signal acquisition).

Figure 2 illustrates an example of a cellular network based information source that, in one embodiment, is maintained on an SPS server, such as a Global Positioning System (GPS) server. Alternatively, the information source may be maintained at a cellular switching center, base station controller, or other cell site. This information source is typically maintained and routinely updated on an SPS server coupled to the cellular switching center. The information source may store data in a variety of formats, and it is understood that the format 200 shown in FIG. 2 is merely illustrative of one example of such a format.

Typically, each set of prioritization information at a particular time, such as prioritization group a1 at time t1, will include a corresponding location or identification for a cell site or service area. For example, for the priority orders a1 and a2, there is a corresponding identification of cellular service area a and a latitude and longitude to represent the location in that service area. It is understood that the longitude and latitude are typically "average" locations, which are generally centrally located within the geographic area of the cellular service area. However, other possible approximations may be used, particularly where the cellular network service area includes unused terrain.

As shown in the exemplary cellular network-based information source of fig. 2, the cellular network-based information source includes a column 202 that specifies the service area of the cellular network, and a column 204 that specifies the cell site identification or number. Note that for cellular service area a, no cell site identification or location is specified, and thus the approximate location is based on a representative location in the cellular service area, such that the priority order a1 and a2 for obtaining SPS satellites is based on that location according to a certain time, such as time t1 and t 2. Column 206 includes a description of the longitude and latitude of a representative location in the service area. Column 208 includes a description of the longitude and latitude of the location of a cell site in the cellular service area, which may be used as a representative location for a mobile SPS receiver in receive priority order. Column 210 includes a priority order for satellites in view at times t1 and t2 for the appropriate representative location. In another embodiment, the ordered list (and corresponding cellular network-based information) may be determined in real time, near real time, continuously, or on demand.

FIG. 3 is a flow chart illustrating one embodiment of a method for prioritizing SPS satellites in view according to the teachings of the present invention. In operation 302, an approximate position of the SPS receiver is determined from a cell-based information source. The SPS receiver is in wireless radio/cellular communication with at least one wireless cell site. The approximate location is based on at least one of a representative location in a cellular service area that includes the cell or a representative location of a wireless cell site in the cellular service area, and also represents an approximate location of an SPS receiver served by the wireless cell site. The approximate location may be located or determined using a cellular based information source (see, e.g., fig. 2) based on an identification of a wireless cell site in communication with a cellular communication system coupled to the SPS receiver. Alternatively, the cellular network-based information source may be used to look up or determine the appropriate prioritization directly from the identity of the wireless cell station in communication with the SPS receiver. In operation 304, a prioritization based on the approximate position of the SPS receiver (or the identity of a wireless cell site communicating with the SPS receiver through a cellular communication system connected to the SPS receiver) is determined for satellites in view of the approximate position. In one embodiment of the invention, satellites are prioritized based on their location relative to the approximate location of the SPS receiver. In another embodiment of the invention, the satellites are prioritized according to their position relative to each other and relative to the approximate position. It is understood that other criteria besides geometry may be used to prioritize. In operation 306, the priority order is transmitted from the wireless cell site to the SPS receiver, which then searches for and acquires SPS signals from SPS satellites in the order specified in the priority order transmitted to the SPS receiver.

A more detailed discussion of cellular Communication systems and their use with SPS receivers is disclosed in U.S. patent application No. 08/842,559, now U.S. patent No. 6208290 entitled "An Improved GPS receivetransmit a Communication Link," filed by Norman f.krasner on 1997, 4/15.

The prioritization of SPS satellites provided by or derived from the location service area may be used to increase the time to acquire satellites, the time required to determine position information, and may reduce bandwidth requirements for providing data from the location server to the SPS receiver.

In the present discussion, embodiments of the present invention have been described with reference to the United states Global Positioning System (GPS) system, which is one example of an SPS system. However, it should be apparent that these embodiments are equally applicable to other satellite positioning systems such as the Russian Glonass system. Thus, the term "GPS" as used herein includes such alternative satellite positioning systems, including the Russian Glonass system. Likewise, the term "GPS signals" includes signals from alternative satellite positioning systems.

Furthermore, although embodiments of the invention are described in terms of GPS satellites, it will be appreciated that the teachings are equally applicable to positioning systems utilizing pseudolites or a combination of satellites and pseudolites. pseudolites are terrestrial transmitters that broadcast a PN code (similar to a GPS signal) modulated on an L-band (or other frequency) carrier signal that is generally synchronized with GPS time. Each transmitter may be assigned a unique PN code to allow identification by a remote receiver. Pseudolites are useful in situations where GPS signals from an orbiting satellite might be unavailable, such as tunnels, buildings, urban canyons or other enclosed areas. The term "satellite" as used herein is intended to include pseudolites or equivalents of pseudolites, and the term "GPS signals" as used herein is intended to include GPS-like signals from pseudolites or equivalents of pseudolites.

In the foregoing detailed description, the apparatus and methods of the present invention have 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 scope and spirit of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims (5)

1. A method for providing information to a Satellite Positioning System (SPS) receiver, the method comprising:

an ordered set of SPS satellites in view of a mobile SPS receiver having an approximate position is determined, the ordered set of SPS satellites based on the approximate position, the approximate position being determined from at least one of a location in a cellular service area including a cellular transmission site in cellular communication with a communication system coupled to the mobile SPS receiver or a representative location associated with the cellular transmission site, wherein the order of SPS satellites in the ordered set of SPS satellites is based on locations of at least some of the SPS satellites.

2. The method of claim 1, wherein the order of SPS satellites in the ordered set of SPS satellites provides a position solution that uses SPS satellites having a desired geometry relative to each other.

3. The method of claim 1, wherein the sequence of SPS satellites in the ordered set of SPS satellites provides a position solution that uses SPS satellites having a desired geometry relative to the mobile SPS receiver.

4. The method of claim 1, wherein the order of SPS satellites in the ordered set of SPS satellites is based on a probability of SPS satellite signal acquisition.

5. The method of claim 1, wherein the order of SPS satellites in the ordered set of SPS satellites is based on an estimate of measured quality from the SPS satellites.