US 6,801,778 B2
`(10) Patent N0.:
`(12) United States Patent
`
`Koorapaty et al. Oct. 5, 2004 (45) Date of Patent:
`
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`‘U8006801778B2
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`(54) EFFICIENT LOCATION OF MOBILE
`RADIOTELEPHONES USING CELLULAR
`AND GPS INFORMATION
`
`(75)
`
`Inventors: Havish Koorapaty’ Cary, NC (Us); L_
`Scott Bloebaum, Cary, NC (US)
`
`(73) Assignee: Ericsson Inc., Research Triangle Park,
`NC (US)
`
`( 4 ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U S C 154(b) by 699 days
`
`5,365,450 A
`5,418,538 A
`5,774,829 A *
`5,883,594 xx
`
`11/1994 Schuchman et al.
`5/1995 Lau
`6/1998 Cisneros et al.
`3/1999 Lau
`
`............ 701/213
`
`5,983,109 A * 11/1999 Montoya ................. 455/456.2
`5,999,125 A * 12/1999 Kurby ..................... 342/3571
`6,067,045 A *
`5/2000 Castelloe et al.
`...... 342/357.09
`
`6,134,483 A * 10/2000 Vayanos et al.
`.............. 701/13
`
`6,141,558 A * 10/2000 Chen ......
`455/456.1
`6,252,543 B1 *
`6/2001 Camp ........
`.. 342/357.06
`
`
`7/2001 Vannucci ............. 455/12.1
`
`....... 455/4562
`7/2001 Zadeh et al.
`8/2002 Zhao et al.
`............ 342/35709
`
`6,256,475 B1 *
`6,266,533 B1 *
`6,429,811 B1 *
`
`(21) Appl. No.2 09/773,318
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`* Cited by examiner
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`(22)
`
`(65)
`
`Filed:
`
`Jan. 31, 2001
`_
`_
`_
`Pr10r Publlcatlon Data
`US 2002/0102992 A1 Aug. 1, 2002
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`Int. Cl.7 .................................................. H04Q 7/20
`(51)
` (52) US. Cl.
`455/456.1; 455/4042;
`455/4142. 342/357.06' 701/213
`(58) Field of Search .....................i ..... 455/414’2 404.2
`455/440 4561—4566 457. 342/357.01_357.04
`’ 357.06, 357.08, 3,571, 357.12, 357.15:
`701/213
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Primary Examiner—William Trost
`Assistant Examiner—Stephen D’Agosta
`(74) Attorney, Agent, or Firm—Coats & Bennett, P.L.L.C.
`
`(57)
`
`ABSTRACT
`
`The invention specifies various methods for the provision or
`calculation of a reference location for GPS-equipped mobile
`communications devices, specifically, GPS-equipped cellu-
`lar phones. This is accomplished by providing certain GPS-
`related information over the cellular network, and by cal-
`culating reference locations based on various criteria, aided
`by actual position fixes provided by the built-in GPS
`receiver.
`
`4,718,081 A *
`
`1/1988 Brenig ....................... 455/438
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`9 Claims, 1 Drawing Sheet
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`/'
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`'59
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`GPS
`Satellite
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`APPLE 1035
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`g.-—_'4’£341.:4:
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`APPLE 1035
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`1
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`US. Patent
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`Oct. 5, 2004
`
`US 6,801,778 B2
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`gt:,
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`GPS
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`Satellite
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`US 6,801,778 B2
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`1
`EFFICIENT LOCATION OF MOBILE
`RADIOTELEPHONES USING CELLULAR
`AND GPS INFORMATION
`
`FIELD OF THE INVENTION
`
`This invention is related to cellular telephones and, in
`particular, to cellular telephones equipped with the capabil-
`ity of determining their location using the Global Position-
`ing Satellite (GPS) system.
`BACKGROUND OF THE INVENTION
`
`It is required for cellular telephone operation for a cellular
`phone to be aware of what cell it is located within. Cells in
`the cellular telephone system refer to the area covered by
`singular cellular tower, and can overlap. While the area in a
`cell is covered by a single tower, a tower may support
`multiple cells when sectored antennae are used at the tower.
`In general, a cellular phone will monitor the control channel
`of the cellular tower having the strongest signal. Therefore,
`a cellular phone has a rudimentary knowledge of its location,
`but not necessarily in terms of latitude,
`longitude and
`altitude.
`
`However, there are applications, other than the normal
`voice communications capabilities of the cellular phone, that
`may require a more exact knowledge of the phone’s location
`within a cell. These include, for example, an application
`providing location sensitive advertising over the cell phone,
`wherein targeted advertising could be sent to cell phone
`users within a certain proximity of the advertiser’s location.
`Other such applications would be the provision of travel
`directions based on current
`location and enhanced 911
`emergency services from calls made using a cellular phone.
`As a result, it is known to combine a cellular phone with
`GPS receiver in a single unit and to allow applications to
`request that the GPS receiver provide the current position of
`the unit
`to the applications, either periodically or upon
`request of the application.
`To improve certain characteristics of its performance,
`such as time-to-first-fix and sensitivity,
`it
`is possible to
`provide the GPS receiver with various aiding information,
`such as satellite ephemeris, approximate time and reference
`location. The reference location is an approximation or
`estimate of the receiver’s current position, which, when used
`with other information, allows the receiver to determine
`which satellites should be visible and to estimate the signal
`transit times from the respective satellites. Generally, with-
`out this aiding information, acquiring the satellite signals
`and computing the receiver’s exact location could take much
`longer. This delay could have a serious impact on the
`performance of mobile location-based services, which tend
`to be time-sensitive.
`
`Further, it is possible that there are certain locations, such
`as when the receiver is indoors, where the signal strength
`from the GPS satellites is not strong enough to provide a
`location fix. In these circumstances, the reference location
`could provide a rough estimate of location.
`It is therefore desirable to provide a means by which a
`reference location can be provided to a GPS receiver which
`is integrated into a cellular phone.
`SUMMARY OF THE INVENTION
`
`The invention provides a means whereby the reference
`location for the GPS receiver can be computed to a higher
`degree of accuracy using information provided over the
`cellular network, such as the location of the cellular tower,
`the current positions of the GPS satellites, and the GPS time
`reference, and also using positions previously determined
`using actual fixes from the GPS receiver.
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`In particular, at selected times when a GPS equipped cell
`phone is operating in idle (non-call) mode receiving a
`control channel being broadcast on a particular cellular
`system, the cell phone uses the GPS receiver to compute its
`own position. These position computations are associated
`with the control channel to obtain an approximate location
`for the cell. The positions are also associated with the
`neighboring control channels that the cell phone is able to
`receive and with the signal strengths of the received signals.
`This allows the cell phone to increase the accuracy of
`reference locations and differentiate between locations
`within a cell by using “neighbor lists”. The accuracy is
`thereby increased beyond the granularity of the cell but still
`is not as accurate as the instantaneous position that may be
`computed by the GPS receiver when an actual position is
`needed. The accuracy, however, aids the receiver in more
`quickly computing the precise locations when needed.
`The invention also uses the GPS receiver to compute a
`position when a private system not broadcasting a reference
`location is detected by the cell phone. Private systems are
`often located in an indoor environment, where signals from
`the GPS satellites may be undetectable. When the cell phone
`detects that it is in the vicinity of a private system, the the
`cell phone tracks its position until the signals from the GPS
`satellites are no longer detectable. The last recorded position
`is then used as a reference location estimate for applications
`when the cell phone is indoor and in contact with the private
`system.
`The invention also allows the cell phone to form an
`estimate of the size of the cell which helps to determine if
`the reference location of the cell is accurate enough for a
`particular application. Thus, reducing the number of times
`the GPS receiver needs to be used.
`
`The message described in this invention may therefore be
`used to first increase the performance of location estimation
`when a reference location is unavailable and second,
`to
`increase the accuracy of a provided reference location
`without having to use a GPS receiver in real time to obtain
`the location fix. The GPS receiver is used to obtain location
`information for a cell during a prior learning phase. The
`information obtained is stored in the memory of the cell
`phone and may be later used for higher accuracy location
`estimates without having to turn on the GPS receiver to get
`a real time location fix.
`
`DETAILED DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of the system of the current
`invention showing the flow of information and communi-
`cation channels.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`There are some significant advantageous to integrating a
`GPS receiver with a cellular telephone. In particular, the cell
`phone can take advantage of the communication link with
`the network to improve the performance of the integrated
`GPS receiver. The fundamental concept is to capture the
`necessary GPS information from GPS receivers at various
`points within the cellular network and to deliver this infor-
`mation to the cell phone via existing point-to-point or
`broadcast bearers in the network. The integrated GPS
`receiver utilizes the information as assistance to reduce or
`eliminate the uncertainty in the characteristics of the
`received signals from the GPS satellites, thereby improving
`time to first fix and sensitivity. A diagram of the basic
`concept is shown in FIG. 1.
`According to FIG. 1, the GPS-equipped cell phone 20
`receives the assistance from a server 10 connected to a GPS
`receiver 50, from the cellular network 60 via the local radio
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`US 6,801,778 B2
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`3
`base station 40. The assistance may include the provision of
`information such as approximate location (reference
`location) of the cell phone, visible satellites 30 at
`that
`approximate location, and information such as the ephem-
`eris and almanac describing the orbits of satellites 30.
`Preferably, cell phone 20 also receives approximate GPS
`time from server 10.
`
`Almanac and ephemeris data can be provided to GPS-
`equipped cell phone 20 from server 10 in the system without
`knowledge of the reference location of the GPS-equipped
`cell phone 20. Knowledge of a crude reference location
`would enable server 10 to send the data only for the satellites
`30 that are expected to be visible at the time of the position
`fix, but this knowledge is not required. However, provision
`of the reference location and knowledge of the approximate
`time enables cell phone 10 to significantly reduce its time-
`frequency search space for synchronizing to the satellite
`signals and therefore the time to first fix.
`While provision of the reference location via cellular
`network 60 is being standardized for all the major cellular
`radio networks, the availability of the reference location may
`be subject to delays or gaps in deployment. The techniques
`presented in this invention enable GPS-equipped cell phone
`20 to avail of a reference location in such cases and operate
`the GPS receiver with a high degree of efficiency and
`performance. Further, even when the reference location is
`available,
`the invention allows efficient use of the GPS
`receiver by providing techniques for computing a low accu-
`racy position that is an improvement of the reference loca-
`tion without using the GPS receiver. This can be used to
`address applications that have low quality of service require-
`ments in terms of position accuracy. One of these techniques
`involves using an estimate of the cell size among other
`factors to determine if the reference location used meets the
`quality of service requirements. The invention also allows
`independent position estimation when utilizing a private
`system that is indoors.
`When receiving a cellular control channel while operating
`in idle mode, GPS-equipped cell phone 20 captures a
`neighbor list that includes the control channels of surround-
`ing cells that GPS-equipped cell phone 20 must monitor. If
`certain criteria,
`including the differences in the received
`signal strengths between the current and monitored control
`channels, are met for any of the monitored channels, then
`cell phone 20 selects the monitored channel as its current
`channel and operates using a new neighbor list. This process
`of selecting a different control channels based on dynamic
`changes in signal conditions, caused by mobility among
`other things, is called re-selection.
`Computing Reference Locations for Cells with No Avail-
`ability of Reference Locations.
`In one aspect of the invention, a procedure is disclosed for
`computing the reference location corresponding to a par-
`ticular cell. It should be noted that all the position estimates
`referred to are obtained using the GPS receiver in GPS-
`equipped cell phone 20. When no reference location is
`available for a particular cell, GPS-equipped cell phone 20
`determines a suitable reference location using multiple posi-
`tions previously recorded for a particular cell using the GPS
`receiver instead of just storing a single position that was
`measured when camping on the control channel of a par-
`ticular cell. In general, any suitable method of processing the
`previously-stored positions may be used to obtain the ref-
`erence location. For example, the previously-recorded posi-
`tion may be averaged to obtain the reference location, or one
`of the previously recorded positions may be chosen as a
`reference location. The multiple positions do not have to be
`recorded close to each other in time; the positions may have
`been recorded for that particular cell over multiple days.
`GPS-equipped cell phone 20 should only average posi-
`tions that meet certain qualifying criteria. First, when a
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`position is recorded, GPS-equipped cell phone 20 monitors
`the cell identifier of the control channel being received for
`a pre-determined period of time T (e.g., T=5 minutes). Cell
`phone 20 must choose the cell
`identifier for which the
`control channel was received at least some portion of T (e. g.,
`80%). If no channel meets that criterion, then the position is
`not used. Second, if the GPS-equipped cell phone 20 has
`access to the results of a Doppler estimator, this criterion is
`applied. The estimated Doppler frequency is proportional to
`the speed at which the cell phone is moving, and thereby can
`be used to detect fast movements of the cell phone. When a
`position is recorded, the GPS-equipped cell phone 20 also
`records the results from the Doppler estimator. Positions that
`were recorded when the Doppler was below some threshold
`(e.g., 5 Hz) are used, if available.
`Refining Reference Locations Using Received Powers from
`Neighboring Cells
`In a second aspect of the present invention, GPS-equipped
`cell phone 20 may estimate a more accurate initial position
`by correlating positions computed using the GPS receiver in
`the phone within the current cell and received signal strength
`of the current cell and the neighboring cells with the L
`highest received signal strength values that are over a given
`minimum threshold. Timing advance (i.e.,
`transmission
`delay from base station) for the current cell, if known, also
`can be attached to the computed position in the database.
`The novel aspect of this embodiment is the dynamic build-
`ing of such a data base using the GPS receiver in the phone.
`In one embodiment of the invention, a number of positions
`that have the same channel as the current channel and the
`same list of L highest received signal strength neighbors can
`be averaged to obtain a better position.
`In another embodiment, the criteria above can be made
`narrower. For example, positions may be categorized by the
`sequence of the L channels in the list in ascending order of
`received signal strength values. All positions corresponding
`to the same current channel and the same ordered list of L
`channels with highest received signal strength are then
`averaged to obtain a position.
`In other embodiments, the current channel and the set of
`neighbors within a certain received signal strength range are
`used to categorize positions. It is clear that further variations
`of such criteria are possible. For example,
`the current
`channel and the actual received signal strength values for
`neighboring cell channels can be used to categorize posi-
`tions.
`Refining reference locations using received signal
`strength information for neighboring-cell control channels
`would allow GPS-equipped cell phone 20 to determine a
`coarse estimate of its position using the current received
`power of the base station transmissions from the current and
`neighboring cells. This method builds a database of received
`signal powers at various positions using a much higher
`accuracy receiver (GPS) and averaging positions belonging
`to certain power profiles for the current and neighboring
`control channels. This increases the accuracy compared to
`simple power based methods because the database is com-
`piled using a highly accurate GPS receiver. The advantage of
`this technique is that the GPS receiver need not be turned on
`for real-time computation in many applications that do not
`require high accuracy, but require an accuracy greater than
`that enabled by a pure power based method or reference
`location method. The advantage is reduced power consump-
`tion by using previously computed positions to simplify the
`current or future computation of position results.
`In another aspect of the invention, if the base station
`locations are known, a power based location method that
`uses the received signal strength of the neighboring cells
`without utilizing the GPS receiver can be used to compute
`the reference location whenever it is needed. However, as
`stated above, the techniques described earlier that use the
`GPS receiver are expected to achieve better reference loca-
`tion estimates.
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`US 6,801,778 B2
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`5
`Use of Cell Size to Decide if Use of GPS Receiver is
`
`Required for a Particular Application
`An estimate of cell size may be obtained by looking at the
`variance of recorded positions when receiving the control
`channel of a particular cell, especially when the positions are
`recorded before a handoff to another cell. The position
`estimates used should be compiled over a long period of
`time such as many hours or even days. This allows GPS-
`equipped cell phone 20 to estimate whether a GPS estimate
`is required or not for a given application given the cell
`identifier that GPS-equipped cell phone 20 is currently
`seeing on the control channel. It also aids GPS-equipped cell
`phone 20 in estimating if refined reference locations gener-
`ated by it may meet the quality of service criteria of a
`particular position request. In effect, the phone is able to
`learn the movement patterns of the user. Hence, even when
`the actual cell size is large, if the location estimates corre-
`sponding to the cell are concentrated in an area, the phone
`may use these positions to provide the user’s position with
`greater accuracy than the cell size. Hence, the computed cell
`size can be thought of as being personalized to the user’s
`movement patterns.
`Position Estimates for Indoor Private Systems when an
`Estimate is Not Available from the Private System
`This invention provides a technique to provide position
`information when in the vicinity of a private system that is
`indoors when the private system does not broadcast any
`reference location. This is done as follows. When GPS-
`equipped cell phone 20 recognizes that it is close to a private
`system (e.g., via mechanisms existing in standards to detect
`private systems when receiving public-system control
`channels), it uses the GPS receiver to track the position of
`the user from the time it switches to the private system until
`it loses the signal from GPS satellites 30 (GPS satellites 30
`have poor coverage in indoor environments). The last
`recorded position is then used as a position for the private
`system cell or cells on which it camps. If the signals from
`GPS satellites 30 are not lost, then the phone assumes that
`the private system is not an indoor system and the private
`system cells are treated the same way as the public ones.
`This allows GPS-equipped cell phone 20 to learn about the
`positions of private systems even when these private sys-
`tems do not broadcast a reference location.
`The foregoing invention has been described in terms of
`usage with a typical cellular telephone network. The
`invention, however, is not meant to be limited to any single
`implementation of a cellular network. Various standards for
`second-generation cellular radio networks, such as GSM,
`TDMA and cdmaOne,
`incorporate assistance for GPS-
`equipped cellular phones. Furthermore, the invention, need
`not be limited to cellular radio networks. The invention
`could be implemented using any GPS-equipped mobile
`communications device. Therefore, the scope of the inven-
`tion is embodied in the following claims.
`We claim:
`
`1. A method for computing a reference location for a
`mobile communications device having a GPS receiver and
`connected to a communications network comprising the
`steps of:
`identifying a point of connection to said communications
`network; recording, over time, a plurality of actual
`position readings from said GPS receiver qualifying
`said actual position reading by:
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`monitoring said identified point of connection for a
`predetermined period of time after recording each
`position reading;
`determining the percentage of said predetermined time
`period that said mobile communications device was
`connected to said communications network at said
`
`identified point of connection; and
`discarding any position readings recorded from said
`GPS receiver during said predetermined time period
`if said percentage is below a set threshold value;
`correlating said qualified position readings to said iden-
`tified point of connection; and
`processing said plurality of correlated position readings to
`obtain a reference location when connected to said
`
`communications network at said identified point of
`connection.
`
`2. The method of claim 1 wherein processing said plu-
`rality of correlated position readings includes of averaging
`said plurality of position readings.
`3. The method of claim 1 wherein processing said plu-
`rality of correlated position readings includes choosing one
`of said plurality of correlated position readings as said
`reference location.
`4. The method of claim 1 wherein said communications
`network is a cellular telephone network and wherein said
`mobile communications device is a GPS-equipped cellular
`telephone.
`5. The method of claim 1 further comprising the step of
`providing said reference location in response to a position
`request from an application.
`6. The method of claim 1 further comprising the step of
`using said reference location as an aid for computing a final
`position using said GPS receiver in response to a position
`request from an application.
`7. The method of claim 1 wherein qualifying said actual
`position readings comprises:
`accessing a doppler estimator when said position readings
`from said GPS receiver are recorded; and
`discarding position readings obtained when said doppler
`estimator indicates a speed above said threshold.
`8. A method for determining the quality of a computed
`reference location for a mobile communications device
`equipped with a GPS receiver comprising the steps of:
`recording, over a period of time, a plurality of positions
`when connected to a particular identified connection
`point to a communications network;
`estimating, based on the variance of said positions, the
`size of the geographic area associated with said par-
`ticular identified connection point; and
`determining, when a request for position is received, if the
`quality of a computed reference location is sufficient,
`based on the possible deviation of said computed
`reference location from the actual location based on
`
`said estimated size of said geographic area associated
`with said particular identified connection point.
`9. The method of claim 8 further comprising the step of
`obtaining an actual position fiX from said GPS receiver if
`said quality of said computed position is insufficient.
`*
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