US 20110115670 A1
Method and apparatus for a GPS device that uses at least one cellular acquisition signal is described. More particularly, a GPS device is configured to receive at least one cellular acquisition signal for obtaining benefits associated with AGPS with only a small subset of AGPS circuitry to interact with a cell phone network. This facilitates use of GPS devices without subscription to a cell phone service provider, thus avoiding cellular subscription fees.
1. A method for determining position of a Global Positioning System (GPS) handheld device in proximity to a base station of a wireless network, the method comprising:
obtaining from the base station without having to have fee-based access to the wireless network at least one of location information and identification information; and
determining, responsive to the at least one of location information and identification information, a position estimate of the GPS handheld device.
2. The method of
3. The method of
computing, responsive to the position estimate, a pseudorange; and
determining, responsive to the pseudorange, a window of delay search for receiving GPS signals.
4. The method of
5. The method of
computing, responsive to the position estimate, a pseudorange rate; and
determining, responsive to a pseudorange rate, a window of frequency search for receiving a GPS signal.
6. The method of
7. The method of
8. The method of
9. A Global Positioning System (GPS) mobile device, comprising:
at least one antenna;
a first front end communicatively coupled to the at least one antenna, the first front end being adapted to receive an acquisition signal from a wireless network;
a second front end communicatively coupled to the at least one antenna, the second front end being adapted to receive a satellite signal from at least one satellite of a GPS network;
a baseband processor adapted to (i) receive from the first front end a first signal that is associated with the acquisition signal, and (ii) receive from the second front end a second signal that is associated with the satellite signal;
a reference oscillator communicatively coupled to the baseband processor;
a general-purpose processor communicatively coupled to the baseband processor; and
memory communicatively coupled to the general-purpose processor.
10. The device of
11. The device of
12. The device of
13. The device of
14. The device of
This application is a divisional of co-pending U.S. patent application Ser. No. 09/993,335, filed Nov. 6, 2001, which is a continuation-in-part of U.S. patent application Ser. No. 09/884,874, filed Jun. 19, 2001, now U.S. Pat. No. 6,560,534, which is a continuation-in-part of U.S. patent application Ser. No. 09/875,809, filed Jun. 6, 2001, now U.S. Pat. No. 6,542,820. Each of the aforementioned related patent applications is herein incorporated by reference. This application contains subject matter that is related to co-pending U.S. patent application Ser. No. 09/715,860, filed Nov. 17, 2000, now U.S. Pat. No. 6,417,801, which is herein incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to mobile wireless devices for mobile location systems, and more particularly to Global Positioning Satellite (GPS) receivers with improved indoor penetration for personal location systems.
2. Description of the Related Art
With the advent of GPS, there has been a growing demand for mobile devices that may be used to provide a person's or an object's location. Devices built using conventional GPS receivers have been developed by a number of companies. However, these devices have significant limitations, one of which is indoor penetration.
To address the above limitation of conventional GPS receivers, a combination of mobile GPS receivers and cellular infrastructure communicating via wireless links has evolved. This combination of technologies, known as Assisted GPS (AGPS), combines a GPS receiver with a cellular handset. The cellular handset provides a two-way link for communicating positioning data (“aiding data”).
In particular, performance of a conventional GPS mobile device in indoor environments may be limited by ability of the GPS mobile device to decode a navigation data stream broadcast by each of a plurality of satellites. Among other components, each navigation data stream contains a satellite trajectory model having parameters describing a respective satellite's orbit and dock variation as a function of time. The satellite trajectory model in the navigation data stream is sometimes referred to as “broadcast ephemeris.” GPS mobile devices traditionally receive and decode the navigation data stream to extract the broadcast ephemeris, which is needed to compute position. However, a signal-to-noise ratio in indoor environments is often insufficient for navigation data bit decoding of the broadcast ephemeris. Thus, another means of ascertaining satellite orbit and clocks variations was needed.
In AGPS systems, the satellite orbit and dock variation, or information derived from these components, is provided to the GPS mobile device via a two-way cellular link. A two-way cellular link is used to request and receive information on such satellites, and the AGPS service is conventionally available only to authorized subscribers to a cellular network.
While AGPS offers improvements in indoor penetration, addition of a cellular handset and a subscription to a wireless provider adds to the cost and power consumption of a GPS receiver. Cellular handsets contain complex and costly components. For example, the cost of adding a cell phone alone to a GPS receiver may be prohibitive for GPS applications where a phone would otherwise be an unnecessary addition, let alone the addition of a subscription fee of a cellular provider. Moreover, cellular transmission consumes power.
Therefore, it would be desirable to provide a GPS mobile device that is comparable in cost to conventional GPS handheld devices but with the indoor penetration benefits associated with AGPS handsets.
The present invention provides apparatus and method for obtaining benefits associated with AGPS without requiring complete integration of a GPS device with a cellular handset. Furthermore, the present invention facilitates a GPS handheld or mobile device configured to operate without subscription to a cell phone service provider, and thus eliminates fees for such subscription. An aspect of the present invention is a GPS handheld device that comprises a cellular acquisition signal receiver or front end. It will be appreciated that circuitry required to receive an acquisition signal comprises only a portion of a complete cellular handset. Particularly, a transmitter portion for communicating with a base station of a cellular network is not included in the GPS handheld device. Furthermore, digital signal processor and application processor(s) configured for modulating, demodulating, voice processing, call protocols, subscriber identification and the like are absent in the GPS handheld device. The cellular acquisition signal receiver allows the GPS handheld device to have an accurate time of day and/or frequency reference, thus assisting in GPS signal acquisition and GPS position computation.
An aspect of the present invention is a method for receiving a GPS signal. More particularly, a frequency correction burst is obtained from a cellular network. A frequency offset responsive to the frequency correction burst is determined, and a window of frequency search responsive to the frequency offset is determined for receiving the GPS signal. This may be done without having to transmit a cellular signal to the cellular network, and this may be done without having to have a subscription to the cellular network.
Another aspect of the present invention is a method for receiving a GPS signal to a GPS handheld device. More particularly, a time synchronization burst is obtained from a cellular network. A timing offset responsive to the time synchronization burst is determined, and a time of day responsive to the timing offset is determined for receiving the GPS signal. This may be done without having to transmit a cellular signal to the cellular network, and this may be done without having to have a subscription to the cellular network.
Another aspect of the present invention is a method for determining position of a GPS handheld device in proximity to a cellular base station of a cellular network. More particularly, at least one of location information and identification information is obtained from the cellular base station, and a position estimate of the GPS handheld device responsive to the at least one of location information and identification information is determined. This may be done without having to transmit a cellular signal to the cellular network, and this may be done without having to have fee-based access to the cellular network.
Another aspect of the present invention is GPS mobile device. More particularly, the GPS mobile device comprises at least one antenna. The at least one antenna is coupled to a cellular acquisition signal front end couple to receive a cellular acquisition signal. A GPS signal front end is coupled to the at least one antenna to receive a GPS signal. A GPS/cellular processor is coupled to the GPS front end and to the cellular acquisition front end. The GPS/cellular processor is configured with a GPS baseband processor in communication with the GPS front end and a cellular acquisition signal baseband processor in communication with the cellular acquisition signal front end. A reference oscillator is coupled to the GPS/cellular processor. A general purpose processor is coupled to the cellular acquisition signal baseband processor and to the GPS baseband processor, and memory is coupled to the general purpose processor.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The present invention relates to implementing a GPS system using a GPS handheld configured for receiving acquisition signals from a cellular provider without requiring integration of the GPS receiver with a two-way capable cellular handset. The present invention provides one or more benefits conventionally associated AGPS while eliminating the requirement for obtaining aiding data from a cellular network.
An aspect of the present invention is a method for configuring the GPS device to store satellite trajectory data that replaces assistance data provided in AGPS systems. In AGPS systems, receiving assistance data from a cellular network requires a two-way capable cellular handset to request and receive such assistance data. Moreover, such services are commonly available only to paying subscribers to the cellular network. In particular, in one aspect of the present invention, satellite trajectory models are stored in memory in a GPS mobile device. The source of the satellite trajectory models stored in memory may be broadcast ephemeris, received and decoded when a GPS mobile device is outside in at least a medium signal strength signal environment in which navigation data decoding is feasible. Alternatively, satellite trajectory models may be supplied to the GPS mobile device through a computer network connection. If the satellite trajectory models comprise broadcast ephemeris, the satellite trajectory models may be valid for between approximately two and six hours. In another aspect of the invention, long-term satellite trajectory models are used, which may be valid for days. Once the satellite trajectory models are obtained and are in memory, the GPS mobile device may function indoors for the period of validity of the long-term satellite trajectory models. This eliminates the need to more frequently obtained assistance data as with conventional AGPS.
Another aspect of the present invention is a method for determining time offset of a GPS mobile device. More particularly, a cellular acquisition signal may comprise a time synchronization signal that is received by the GPS mobile device, enabling the GPS mobile device to establish a time of day for applying satellite trajectory data. In addition, the time synchronization signal, if sufficiently precise, may be used to establish a delay search window, decreasing the search time required for GPS signal acquisition. In addition, the time synchronization signal may be used to align coherent averaging intervals with GPS signal data bits to improve signal to noise ratio.
Another aspect of the present invention is a method for determining time offset of a GPS mobile device. More particularly, a cellular acquisition signal can comprise a time synchronization signal that is received at the GPS mobile device, enabling the GPS mobile device's receiver to establish a time of day for applying satellite trajectory data. In addition, the time synchronization signal, if sufficiently precise, may be used to establish a delay search window, decreasing search time required for GPS signal acquisition. In addition, the time synchronization signal may be used to align coherent averaging intervals with GPS signal data bits to improve signal-to-noise ratio.
Another aspect of the present invention is a GPS mobile device comprising: one or more antennas configured to receive cellular acquisition signals and GPS satellite signals; radio frequency (RF) front end circuitry for the GPS signals; RF front end circuitry for the cellular acquisition signals; a cellular acquisition signal baseband processor; a GPS signal baseband processor; a time keeping counter common to the baseband processors; a reference oscillator coupled to the time keeping counter, baseband processors and front end circuitry; a processor coupled to the baseband processors; and memory coupled to the processor. In some embodiments, the GPS mobile device may additionally comprise a computer network-docking interface or a data modem or both.
In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention.
Alternatively, server 23 may be put in communication with publicly switched telephone network (PSTN) 25 via network 21. PSTN 25 may be put in communication with telephone 26, which may be put in communication with GPS mobile device 10. In this embodiment, a phone number, such as a toll free number, may be dialed in order to download one or more trajectory models to GPS mobile device 10.
Connection between mobile device 10 and server 23 may be established to refresh satellite trajectory models 39. At other times, this connection may be absent. For example, in field conditions lacking computer network 21 connectivity, GPS handheld 10 may obtain satellite information from one or more satellite signals 12 shown in
In another embodiment, satellite tracking data from GPS reference stations 27-1, 27-2, and 27-3 is used in server 23 to create long-term satellite trajectory models 39, which may be valid for periods of up to approximately one week. Orbit models and associated long-term orbit trajectory data are described in more detail in co-pending and related applications entitled “LONG TERM EPHEMERIS” to James W. LaMance, Charles Abraham and Frank van Diggelen, application Ser. No. 09/884,874, filed Jun. 19, 2001, and “METHOD AND APPARATUS FOR GENERATING AND DISTRIBUTING SATELLITE TRACKING” to James W. LaMance, Charles Abraham and Frank van Diggelen, application Ser. No. 09/875,809, filed Jun. 6, 2001. In one aspect of the present invention, long-term orbit trajectory models are used in GPS mobile device 10 to extend the period of validity of satellite trajectory models 39 provided by server 23. This increases the interval over which GPS mobile device 10 may be used in conditions wherein computer network 21 is not readily accessible.
Conventionally, cellular acquisition signals are provided to enable, at least in part, a cellular handset to synchronize to a cellular base station, as a first step in establishing communication with a cellular network. In particular, in the first phase of establishing communication, the cellular handset monitors specific frequencies for the acquisition signals. In accordance with one or more aspects of the present invention one or more cellular acquisition signal is received, but a GPS mobile device does not continue with the subsequent steps needed to establish two-way communication with the cellular network. In particular, in accordance with one or more aspects of the present invention, a GPS mobile device does not transmit any data or message or both to the cellular network. Furthermore, a GPS mobile device may receive one or more acquisition signals without a cellular network subscription.
The nature of a frequency correction signal 31 varies depending on the cellular network. In CDMA systems, frequency correction signal 31 may comprise a pilot channel. The pilot channel is a common channel that is broadcast over a cell coverage area. Conventionally, the pilot channel uses a repeating pseudonoise (PN) sequence of 215 chips. Multiple base stations transmit the same PN code but at different timing offsets to avoid mutual interference. To detect the pilot channel, GPS mobile device 10 may scan a range of PN code offsets until energy is detected, indicating a cellular base station transmitter, using a cellular acquisition front end 131 of
In GSM systems, frequency correction signal 31 is a frequency correction burst transmitted periodically by a base station on one of several frequency channels assigned to the base station. The frequency correction burst signal 31 is an unmodulated tone transmitted at a specific offset from a carrier frequency of the channel. GPS mobile device 10 may make an open loop measurement of frequency error from the frequency correction burst to determine frequency offset 35A.
As one or more of broadcast signals 31, 32, 33, 34A and 34B are well-known, for example in General System Mobile (GSM) systems and Code Domain Multiple Access (CDMA) systems, among other known cellular systems, unnecessary details regarding such signals are not repeated here for purposes of clarity.
In an alternative embodiment, optional reference oscillator steering circuit 142 of
An example of a frequency and delay search window 45 for a particular GPS satellite signal 11 is shown in
With continuing reference to
With renewed reference to
With renewed reference to
In GSM systems, time synchronization signal 32 is a synchronization burst transmitted periodically by base station 13 on one of several frequency slots assigned to cellular base station 13. Time synchronization signal 32 contains a unique header, such as a known sequence of bits, that identifies a starting point of a burst. In addition, time synchronization signal 32 carries a timing message 33 that comprises, among other elements, a GSM time stamp associated with such synchronization burst. In a GSM compatible embodiment, GPS device 10 receives time synchronization signal 32, and uses header information therefrom to identify a starting point of a synchronization burst therein relative to local timekeeping counter 139. GPS device 10 uses this information, combined with timing message 33, to compute time offset 36. In this manner time offset 36 provides an offset between local timekeeping counter 139 and GSM timing of base station 13. In some GSM networks, GSM timing is not synchronized with GPS time. Therefore, time offset 36 does not provide an absolute time offset to GPS time. Time offset 36 may however be used beneficially as an indicator of relative time, as discussed below.
Time accuracy of time offset 36 will be dependent on the cellular network implementation. In systems such as CDMA that incorporate GPS timing within the cellular network, there is a high degree of timing accuracy. In other networks, for example GSM, relative timing of a time synchronization burst may be good, but an unknown offset may exist to GPS time. Finally in some systems, a time indicator may be an absolute indicator, but with limited accuracy, for example time coming from a computer server 23 (shown in
Depending on accuracy, available time offset 36 may be employed for several purposes within GPS device 10. If timing offset 36 has precision substantially better than one millisecond, precise time component 41 of timing offset 36 may be incorporated into frequency and delay search window 45. Specifically, with additional reference to
With continuing reference to
Optionally, time offset 36 is provided to coherent averaging 50. Coherent averaging 50 improves signal-to-noise ratio in each search bin by averaging correlation results from several consecutive cycles of C/A code. When coherent averaging, impact of 50 bps navigation data bits on a GPS signal is to be considered. Specifically, due to navigation data bits, a GPS signal undergoes a potential 180 degree phase transition every 20 cycles of C/A code. For signal-to-noise ratio enhancement, coherent averaging is performed over twenty consecutive cycles of C/A code comprising a single navigation data bit. Furthermore, to enhance performance this averaging process should be synchronous with navigation data bit timing, otherwise changing data bits may partially defeat such an averaging process. For this reason, it is desirable to achieve synchronization of coherent averaging 50 with navigation data bit timing. Navigation data bit timing is uniform for all satellites 11 (shown in
Timing of a data bit arriving at GPS device 10 is a function of local timekeeping counter 139 as well as pseudorange delay between GPS device 10 and a satellite 11 (shown in
Time of day 42 is the absolute component of time offset 36, converted to units of GPS time units. This conversion can take several forms, for example, a conversion from a Julian data system, or some other timekeeping standard employed by the cellular network. Time of day 42 may be utilized within GPS receiver 10 even in an application where precision of time offset 36 is not better than one millisecond, namely, when precise time component 41 cannot be generated. In particular, time of day 42 provides a reference time for ascertaining satellite positions 43. Specifically, time of day 42 provides a reference time for satellite trajectory model 39. As satellites 11 move rapidly through the sky, it is preferable that time of day 42 be accurate, within approximately at least ten milliseconds, so that errors in prediction of satellite positions will be on the order of meters or less. If, however, time of day 42 does not provide this level of accuracy, error in time of day 42 may be solved for as part of a navigation solution. In the latter situation, accuracy of time of day 42 is unimportant, and a rough estimate of time is sufficient, such as the time provided by a server or a real time clock. An example of such a method is Time Free GPS, as described in more detail in co-pending application entitled “METHOD AND APPARATUS FOR TIME-FREE PROCESSING OF GPS SIGNALS” to Frank van Diggelen, application Ser. No. 09/715,860, filed Nov. 17, 2000, now U.S. Pat. No. 6,417,801.
If time offset 36 has an arbitrary relationship to GPS time, time of day 42 will not be directly available. However, time offset 36 may be beneficial as an indicator of relative time. For example, GPS mobile device 10 may determine an initial time of day by the conventional method of decoding the time of week (TOW) portion of a navigation data stream. TOW can be used to determine a relationship between cellular network time and GPS time. For example, time offset 36 may represent offset between GSM system time and GPS time of day. Once this relationship is established, it may remain constant for extended time periods as cellular base stations use precise oscillators to generate their timing signals. Thus, GPS mobile device 10 may use time offset 36 to determine time of day 42 based on a previously determined relationship between a cellular network and GPS time. In this manner, GPS mobile device 10 may be able to obtain positions in indoor operating environments, utilizing a time synchronization burst from time synchronization signal 32 to ascertain time of day. Furthermore, GPS mobile device 10 can function without a battery powered real-time clock to maintain time.
Cellular base station 13 may provide a cell identification number 34A. The details of this message vary with cellular network. Cell identification number 34A may be used to look up location of cellular base station 13 in a lookup table 37 stored in memory of GPS mobile device 10. This will give an approximate or estimated position 38 of GPS mobile device 10, namely, GPS mobile device 10 will be within the sector associated with longitude and latitude of communication tower 13 location. As sector sizes vary from rural, suburban and metropolitan area networks, this position estimate 38 will vary accordingly depending on location of cellular base station 13 within one of the above-mentioned area networks. In those instances where cellular base station 13 is configured to provide its cell location 35B, cell location lookup table 37 may be avoided and an estimate of position 38 provided based on cell location signal 34B.
Estimate of position 38 is provided for line of sight calculation 40. Specifically, estimate of position 38 is combined with satellite positions, velocities and clock estimates 43 to determine expected pseudoranges and pseudorange rates 44, and unit vectors 49 between GPS device 10 and each GPS satellite 11 (shown in
Pseudo range and pseudorange rates 44 are provided to frequency and delay search window 45. In particular, pseudorange rate provides an estimate of Doppler shift between GPS mobile device 10 and each GPS satellite (shown in
Integrated circuit 135 may comprise a time keeping counter 139 for providing clock signals to baseband processors 136 and 137. A reference oscillator 138 may be used to provide a determined frequency within a tolerance to timekeeping counter 139. A general purpose processor, such as a microprocessor, 141 is coupled to receive information from acquisition signal baseband 136 to provide an output to GPS baseband 137, as described with reference to
It should be appreciated that the incremental circuitry in the GPS device to receive and utilize cellular acquisition signals is minimal. In particular, the scope and cost of this circuitry is far less than that of a complete cell phone, which would include transmission circuitry, digital signal processing circuitry, voice processing circuitry, a protocol stack processor, and many other components. Thus, it is anticipated that a GPS system in accordance with one or more aspects of the present invention may be manufactured with less cost than that to produce conventional AGPS system.
While the embodiments described herein have provided details for GSM and CDMA systems, it should be apparent that the invention can be employed in all types of cellular networks including iDEN, TDMA, AMPS, GPRS, CDMA-2000 and other 2.5 networks, and W-CDMA and other 3G networks. Furthermore, the invention can accept multiple types of cellular acquisition signals in a single device. In particular cellular acquisition front end 131 and cellular acquisition baseband 136 may be configured to incorporate simultaneous or sequential processing of signals from multiple networks. This would further facilitate use of a GPS device 10 anywhere in the world, not just within a prescribed coverage region, and accordingly it would be desirable to provide an ability to receive and use a set of cellular network signals.
Though GPS satellites were described, it should be appreciated that one or more aspects of the present invention may be used with pseudolites, ground based transmitters that broadcast a PN code similar to a GPS signal. Accordingly, the term “satellites”, as used herein, is intended to include pseudolites and equivalents thereof. Moreover, the term “satellite signals” or “GPS signals” is intended to include satellite-like and GPS-like signals from pseudolites and equivalents thereof. Furthermore, though a GPS system was described, it should be appreciated that one or more aspects of the present invention are equally applicable to similar satellite positioning systems, including without limitation the Russian Glonass system.
While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.