United States Patent (19)
`Rudrapatna et al.
`
`54 METHOD FOR PREDICTING THE
`LOCATION OF A MOBILE STATION INA
`MOBILE COMMUNICATIONS NETWORK
`
`75 Inventors: Ashok N. Rudrapatna, Basking Ridge,
`N.J.; Dharma P. Agrawal, Raleigh,
`N.C.; Prathima Agrawal, New
`Providence, N.J.
`73 Assignee: AT&T Corp, New York, N.Y.
`
`21 Appl. No.: 08/941,231
`22 Filed:
`Sep. 30, 1997
`(51) Int. Cl. ................................................. H04Q 7/20
`52 U.S. Cl. ........................... 455/456; 455/441; 455/436
`58 Field of Search ..................................... 455/429, 432,
`455/436,438, 437, 439, 440, 441, 442,
`443, 422, 456, 525, 38.3, 524, 435, FOR 101,
`FOR 102, FOR 103; 379/FOR 105
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,214,789 5/1993 George.
`5,222,249 6/1993 Carney.
`5,230,082 7/1993 Ghisler et al..
`5,390,234 2/1995 Bar-Noy et al..
`5,408,466 4/1995 Albay ...................................... 455/426
`5,432,842 7/1995 Kinoshita et al.
`... 455/441
`5,465,389 11/1995 Agrawal et al. ..
`... 455/441
`5,471,497 11/1995 Zehavi .................................... 375/200
`5,524,136 6/1996 Bar-Noy et al..
`5,572,221 11/1996 Marlevi et al. ......................... 455/440
`5,642,398 6/1997 Tiedemann, Jr. ....................... 455/435
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`9/1992 European Pat. Off. ...... 379/FOR 105
`3/1989 Japan ............................ 379/FOR 105
`OTHER PUBLICATIONS
`
`OOO5892.79
`401073925
`
`“Automatic Vehicle Location-An Overview', authors: S.
`Riter, J. McCoy; IEEE Transactions on Vehicular Technol
`ogy, Vo. VT-26, No. 1, pp. 7-11, Feb. 1977.
`
`US006052598A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,052,598
`Apr. 18, 2000
`
`“Estimating Position and Velocity of Mobiles in a Cellular
`Radio Network', authors: M. Hellebrandt, R. Mathar, M.
`Scheibenbogen; IEEE Transactions on Vehicular Technol
`ogy, vol. 46 No. 1, Feb. 1997, pp. 65-71.
`“Location Management Strategies for Mobile Cellular Net
`works of 3rd Generation', author: D. Plassmann, 1994 IEEE
`44th Vehicular Technology Conference, vol. 1, pp. 649-643,
`Jun. 8–10, 1994.
`“A Alternative Strategy for Location Tracking”, author: S.
`Tabbane, IEEE Journal of Selected Areas in Communica
`tions, vol. 13, No. 5, pp. 880–892, Jun. 1995.
`“Efficient and Flexible Location Management Techniques
`for Wireless Communication Systems”, authors: J. Jannink,
`D. Lam, N. Shivakumar, J. Widom, D.C. Cox; Mobicom '96,
`pp. 38–49, Nov. 10-12, 1996.
`“Location Uncertainity in Mobile Networks: A Theoretical
`Framework’, authors: C. Rose, R. Yales; IEEE communi
`cations Magazine, pp. 94-101, Feb. 1997.
`(List continued on next page.)
`Primary Examiner Dwayne D. Bost
`ASSistant Examiner Jean Gelin
`57
`ABSTRACT
`The approximate position of a mobile Station in a cell can be
`predicted by measuring the Signal Strength between the
`mobile station and the base station of the cell in which it is
`located and the base Stations of the neighboring cells. After
`a Series of instantaneous Signal Strength measurements have
`been collected, the Velocity and direction of the mobile unit
`can be determined. Based on the velocity and direction of
`the mobile unit, future locations of the mobile unit can be
`predicted including the projected Signal Strength between the
`mobile station and the base stations of the cell in which it is
`located and neighboring cells. Analyzing the projected Sig
`nal strength values, the time when the mobile unit will
`require handover to a neighboring cell can be determined
`and if desired, resources in a neighboring cell can be
`allocated in anticipation of the mobile unit being handed
`over to that cell. New Signal Strength measurements are
`periodically collected and new projections are made to
`increase the accuracy of the estimate of when handover will
`occur and to what neighboring cell.
`
`15 Claims, 3 Drawing Sheets
`
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`SET VALUES OF HANDOVER THRESHOLDS Th; AND The
`
`MEASURE AND COMPUTE SIGNAL STRENGTH WALUES
`FORCURRENT ANNEIGHBORING CELLS
`
`EXTRAPOLATEESTIMATES OF SIGNAL STRENGTH
`OWER TIME FORCELS
`
`IS PROJECTED SIGNAL STRENGTH Sm(Tim) x Tho
`IS PROJECTED SIGNAL STRENGTH OF ANY
`NEIGHBORING CELL S(T) > Thi?
`
`DETERMINE MOST SUITABLE CEL FOR ANDOWER
`
`DETERMINE TIME t = Ti,
`WHERE
`S (t{T,) > The AND Si (t > Ti) > Thi
`PREDICT LOCATION OF MOBILE
`AT TIME t < T, AND t > Ti,
`
`
`
`
`
`Page 1 of 9
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`SAMSUNG EX-1029
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`

`6,052,598
`Page 2
`
`U.S. PATENT DOCUMENTS
`5,687,217 11/1997 Bliss et al. .............................. 455/423
`5,787,348 7/1998 Willey et al. ........................... 455/441
`5,825,759 10/1998 Liu ....................
`... 455/433
`5,884,178 3/1999 Ericsson et al. ........................ 455/441
`
`
`
`OTHER PUBLICATIONS
`“A Knowledge-Based Resource Allocation Algorithm for
`Cellular Networks”, authors: A. Rudrapatna, P. Agrawal,
`D.P. Agrawal, C. Giardina; ICPWC97, pp. 1-5, Aug. 20,
`1997.
`
`Page 2 of 9
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`

`

`U.S. Patent
`
`Apr. 18, 2000
`
`Sheet 1 of 3
`
`6,052,598
`
`FIG. 1
`
`MSC
`
`
`
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`
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`
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`
`
`
`FIG. 2
`
`SET VALUES OF HANDOVER THRESHOLDS Thi AND Th
`
`MEASURE AND COMPUTE SIGNAL STRENGTH WALUES
`FOR CURRENT AND NEIGHBORING CELS
`
`EXTRAPOLATE ESTIMATES OF SIGNAL STRENGTH
`OWER TIME FOR CELS
`
`
`
`
`
`
`
`IS PROJECTED SIGNAL STRENGTH Sm(Tm) < Tho?
`
`IS PROJECTED SIGNAL STRENGTH OF ANY
`NEIGHBORING CELL S(T) > Thi?
`YES
`DETERMINE MOST SUITABLE CELL FOR HANDOWER
`
`DETERMINE TIME t = Ti WHERE
`
`PREDICT LOCATION OF MOBILE
`AT TIME t < T AND t > Ti,
`
`Page 3 of 9
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`

`

`U.S. Patent
`
`Apr. 18, 2000
`
`Sheet 2 of 3
`
`6,052,598
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`0?I - OUTOHSENHI
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`
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`§ "?) I „H
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`Page 4 of 9
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`

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`U.S. Patent
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`Apr. 18, 2000
`
`Sheet 3 of 3
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`6,052,598
`
`FIG. 4
`
`R6
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`
`TRANSMISSION
`LINKS
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`

`

`1
`METHOD FOR PREDICTING THE
`LOCATION OF A MOBILE STATION INA
`MOBILE COMMUNICATIONS NETWORK
`
`TECHNICAL FIELD
`This invention relates to predicting the location of a
`mobile Station in a mobile communications network and,
`more particularly, to a Scheme for approximating the loca
`tion of a mobile station at cell level in a mobile network,
`which can be used to estimate a time for handover.
`
`BACKGROUND OF THE INVENTION
`Most existing mobile communication Systems incorporate
`a cellular architecture in which geographical areas are
`divided into roughly equal sized cells. Each cell contains a
`base Station for interfacing mobile units in the cell to a
`mobile switching center (MSC) and a backbone wired
`network. The MSC connects the base stations together for
`communication therebetween. A base Station is equipped
`with radio transceivers that enable rf communications over
`available frequency channels with mobile units in the cell.
`Techniques for determining the location of mobile Sta
`tions exist in the prior art. One known method involves
`using a global positioning System (GPS). To determine the
`location of a mobile station, GPS requires that the mobile
`station be in the field of view of a satellite. Mobile stations
`travel through tunnels and into buildings and many other
`areas where Satellite Signals cannot penetrate. Thus, when a
`mobile station is in one of these areas, GPS cannot deter
`mine the location of the mobile station. Furthermore, mobile
`Stations need to communicate GPS location information to
`the network requiring use of rf channels.
`Another method directly measures radio Signals traveling
`between a set of base Stations and a mobile Station and then
`back to the base Stations. Time or phase measurements
`obtained by Such a trilateration method are used to deter
`mine the length or direction of the radio path. This requires
`expensive Systems at the base Station and precise Synchro
`nization acroSS base Stations to obtain reliable location data.
`Recently, a highly accurate method for estimating the
`position and Velocity of mobile Stations has been developed
`which is described in the article entitled “Estimating Posi
`tion and Velocity of Mobiles in Cellular Radio Networks” by
`Hellebrandt et al. in IEEE Transactions on Vehicular
`Technology, Vol. VT-26, No. 1, pp. 7-11, February 1997.
`According to this technique, the actual downlink Strength of
`Six adjacent base Stations is measured by mobile Stations at
`predefined locations. Profiles are developed for the pre
`defined locations and Stored in a database. Then, the average
`Signal Strength of the Six base Stations is measured by the
`mobile Station at its current location. The best Squares are
`estimated and compared with the profiles Stored in the
`database. The point in the cell providing the minimum
`least-Square error and Satisfying the transformed Signal data
`is considered as the location of the mobile station. Here
`again, the location information which is known to the mobile
`Station needs to be conveyed to the network via wireleSS
`channels.
`
`SUMMARY OF THE INVENTION
`The present invention overcomes the shortcomings of the
`prior art by providing a Scheme which determines the
`approximate location of a mobile Station in a cell. In contrast
`to the prior art Schemes which attempt to locate the precise
`position of the mobile Station in a cell, the present invention
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`is directed to determining the location of the mobile Station
`directly from the network and anticipating the next cell to
`which the mobile station is likely to enter. The present
`invention can be adapted to project the anticipated crossing
`of a cell boundary So that resources in a neighboring cell to
`which the mobile Station is projected to enter can be
`reserved.
`Knowing the cell where a mobile unit is located, a
`measurement of the velocity of the mobile unit, and the
`direction in which the mobile unit is traveling, the probabil
`ity of crossing the current cell boundary and the anticipated
`time for cell crossing can be determined. The received
`power of the mobile unit can be measured by adjacent base
`Stations or the received power of base Stations can be
`measured by the mobile unit. Such uplink/downlink power
`can be measured for either analog or digital cellular/PCS
`Systems.
`Power averaged over a certain duration can be estimated
`to Smooth temporary localized fading and other types of
`multipath fading caused by obstructions, Such as buildings
`and mountains. According to an illustrative embodiment of
`the present invention, power averaging can be achieved by
`using a “rolling window of Signal Strength values to deter
`mine the averaged signal Strength values. That is, as the
`mobile unit moves, new signal Strength values are obtained
`and used in power averaging. The network can use the
`averaged signal Strength values to estimate the Velocity of
`the mobile unit and the direction in which the mobile unit is
`traveling.
`The measured velocity and direction of the mobile unit
`can be used to project anticipated Velocity and direction of
`mobiles for times in the immediate future, and can be used
`to anticipate cell handover needs. That is, it can be projected
`when the signal strength of the mobile unit will fall below
`a threshold in which handover must occur, and an appro
`priate cell can be identified to which a call can be handed
`over. Accordingly, the network can utilize this information
`to anticipate resource allocation needs of a mobile unit.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The present invention will now be described in more
`detail with reference to preferred embodiments of the
`invention, given only by way of example, and illustrated in
`the accompanying drawings in which:
`FIG. 1 is a portion of a wireleSS communications network
`according to an illustrative embodiment of the present
`invention.
`FIG. 2 is a flow chart illustrating the steps involved in an
`exemplary embodiment of the method of the present inven
`tion.
`FIG. 3 is an illustrative graph of received Signal Strength
`over time in accordance with an exemplary embodiment of
`the method of FIG. 2.
`FIG. 4 shows an exemplary physical realization of the
`invention.
`
`DETAILED DESCRIPTION
`An illustrative methodology for predicting the location of
`a mobile Station in a mobile communications System will be
`described according to the present invention. While the
`mobile system described below relates to a traditional cel
`lular phone System, it is to be understood that the present
`invention can be applied to all types of mobile communi
`cations Systems including, but not limited, to Satellite
`Systems, micro cellular Systems, Systems utilizing FDMA,
`
`Page 6 of 9
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`3
`TDMA, or a hybrid thereof, and other wireless communi
`cation Systems. Also, other types of personal communication
`devices can be implemented in these Systems including, but
`not restricted to, a portable television, a wireleSS audio Video
`phone, and a pager.
`The present invention may be used in connection the
`invention described in the commonly assigned, co-filed
`application entitled "Intelligent Dynamic Channel Alloca
`tion Scheme for a Mobile Communications Network” by the
`Same inventors of the instant application, which is incorpo
`rated by reference herein.
`An illustrative mobile network is shown in FIG. 1 includ
`ing three cells, M, i, and i, and a mobile Switching center
`MSC. The cells, M, i, and i, contain a corresponding base
`15
`Station bSM, bsi, and bsi, respectively. Located in cell M
`is mobile unit MU. It is to be understood that the mobile
`network depicted in FIG. 1 is illustrative, and that other
`wireleSS network Structures are considered within the Scope
`of the invention.
`An illustrative method for cell-level location predicting
`according to the present invention is Set forth in FIG. 2 and
`described with reference to FIGS. 1-3. FIG. 3 is a graph
`showing the received signal Strength over time for an
`illustrative embodiment of the present invention described in
`connection with FIGS. 1 and 2. Referring to FIG. 1, the cell
`M represents the cell in which the mobile unit MU is
`currently traveling. The cells i and i represent cells neigh
`boring cell M. For purposes of this illustration, it is assumed
`that the mobile unit MU is moving toward neighboring cells
`i and i, Such that the signal strength between MU and bSM
`(i.e., S(t)) is declining and the Signal strengths between
`MU and bsi and bsi (i.e., Si(t) and Si(t), respectively) is
`increasing. This can be seen by inspection of FIG. 3.
`At step S1, threshold values for incoming handoff Th,
`and outgoing handoff The are defined. The threshold values
`Th and The are typically predefined or preset in the mobile
`network. Threshold Th represents the mobile link minimum
`Signal strength in the forward link (base to mobile) or
`reverse link (mobile to base) at which a call can be accepted
`for handoff by a neighboring cell. For example, if the
`projected Signal Strength is less than Th, for the mobile link
`between the base station bsi and the mobile unit MU at a
`given time then celli is not a candidate for handover at that
`time. Threshold The represents the mobile link Signal
`strength in the forward link (base to mobile) or reverse link
`(mobile to base) at which the mobile network actively seeks
`to handover a call from the current cell (e.g., M) to a
`neighboring cell (e.g., ii). Although, the thresholds Th and
`The could theoretically be the Same, This Somewhat larger
`than Th.
`At Step S2, the network computes the instantaneous
`average Signal Strength between the mobile unit MU and the
`base Station bSM and the Signal Strengths between the
`mobile station MU and the base stations in neighboring cells
`including bsi and bsi and other base stations in neighbor
`ing cells which are not shown. The mobile link Signal
`Strength can be measured in either the forward or reverse
`direction. Either forward or reverse link measurements can
`be used in AMPS or TDMA, but it is easier to implement
`measurements in the reverse direction in AMPS. Measure
`ments in the forward direction are better used in TDMA. For
`simplicity, either the forward or reverse direction will be
`used on a consistent basis for measuring the Signal Strength
`in the mobile network. The Signal Strength measurements
`can be made by each of the base Stations bSM, bsi, and bSi.
`These values are preferably transferred to the MSC or a
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`centralized part of the mobile network. Alternatively, the
`Signal Strength measurements could be transferred to the
`base station in the cell in which the mobile is located bSM.
`In step S3, the MSC extrapolates the estimates of signal
`strength over time for the mobile unit MU and the base
`Stations of the current cell M and the neighboring cells i,
`i, ... etc. That is, the MSC projects what the Signal Strength
`between the mobile unit MU and the base stations of the
`current cell and neighboring cells will be at times in the
`future based on the actual measurements up to the current
`time. Extrapolation uses Standard curve fitting techniques. In
`each cellular area, an appropriate propagation model will be
`used based on the known propagation environment in the
`cell. Propagation behavior can vary from cell to cell based
`on multipath fading resulting from factorS Such as topogra
`phy and buildings.
`In FIG. 3, the actual measurements for the Signal Strengths
`of the cells M, i1 and is are represented by the Solid lined
`portion of the curves (cell M, cell i, and cell i) left of the
`dashed vertical line identified as current time t. The
`extrapolated or projected Signal Strengths are shown by the
`portion of those same lines to the right of the current time t,
`in FIG. 3.
`It should be understood that at least two instantaneous
`measurements must be made in Step S2, prior to the first time
`Signals Strength estimates are extrapolated in Step S3, to
`obtain the velocity and direction of the mobile unit MU.
`Generally, the more Signal Strength measurements taken, the
`more accurate the projections. Signal Strength measurements
`can be made on a periodic basis which may be a function of
`the cell size or an expected maximum speed or average
`Speed of a mobile in the current cell. For example, in a
`mobile network with cells having approximately a five-mile
`radius, it would be appropriate to measure Signal Strength on
`the order of every 15 seconds. Similarly, based on the
`expected Velocity of a mobile unit at a particular time of day,
`for example rush hour, a less frequent measurement may be
`Sufficient. Also, the periodic interval may be determined in
`real time and based on factors including, but not restricted
`to, maximum estimated or average Velocity of the mobile
`unit and network traffic.
`In Step S4, it is determined whether the projected Signal
`strength between the mobile station MU and its current base
`station bsM will drop below the threshold for call handover
`Th. For accuracy purposes, projections are best made for a
`limited time into the future. For example, projections may
`only be made for one minute into the future. The appropriate
`time period in which to project signal Strength measurement
`can be preset in accordance with factors including, but not
`limited to, cell size, maximum estimated Velocity of a
`mobile unit in the particular cell, time-of-day, day-of-week,
`and neighboring cell channel traffic Volume. Alternatively,
`the time period for projections may be determined on a real
`time basis in accordance with factorS Such as the Velocity of
`the mobile unit and the current radio channel traffic condi
`tions of neighboring cells.
`If the projected signal strength between the mobile MU
`and its current base station bsM does not fall below Th, (i.e.,
`S(T)2Th, where T is the estimated time at which
`S(t)=Th) then control returns to S2 and additional signals
`Strength data is collected and average Signal Strengths are
`computed and at Step S3 the extrapolated estimates are
`updated and the proceSS continues. Updating does not
`require recomputing the entire curve. It can be used to refine
`existing data.
`If the projected signal strength between the mobile MU
`and its current base station bs.M falls below Tho (i.e.,
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`Sr)<The) then the process shifts to step S5. At step S5,
`it is determined whether the projected Signal Strength of any
`neighboring cell is greater than the incoming handover
`threshold Th, (e.g., is Si(T)>Th or Si(T)>Th?). In
`other words, is there a neighboring cell which is appropriate
`for handover at the projected time that the Signal Strength
`between the mobile unit MU and its current base stations
`bSM falls below the threshold for outgoing handover. If not,
`then control returns to S2 and the aforedescribed StepS are
`repeated.
`If a neighboring cell is appropriate for handover, then
`control shifts to step S6. In step S7, the projected signal
`Strength for each of the neighboring cells appropriate for
`handover (i.e., Sij(T)>Th) are compared with each other
`and the most Suitable cell is selected. Determination of the
`most Suitable cell is a matter of design choice and may be,
`but is not limited to, the cell having the highest projected
`Signal strength over a Selected (e.g., longest) duration or the
`cell having the highest projected Signal Strength at the
`estimated time of handover T.
`Next, control passes to step S7 where the time (e.g., t=Ti)
`is determined when the neighboring cell (e.g., ii) Selected
`for handover has a Signal Strength appropriate for incoming
`handover (Si(tdTi)>Th) and when the signal strength
`between the mobile unit and the current base station is
`greater than the outgoing handover threshold (S(t-Ti)
`>Th), which is typically below Th.
`Control of the process passes to step S8, where the
`determined time (t=Ti) provides the time at which handover
`can be set to occur in accordance with the Signal Strength
`projections, and the predicted location of the mobile unit.
`Thus, following this example, for t<Ti, the predicted loca
`tion of the mobile unit will be in cell M, at time t=Til it is
`predicted that handover will occur, and at time tdTi the
`predicted location of the mobile unit will be in celli. Thus,
`wireleSS resources can be allocated for the mobile unit in cell
`i in anticipation of handover occurring at time t=Ti.
`After step S8, handover into a neighboring cell (e.g., i.)
`has occurred. Thus, the neighboring cell can be viewed as
`the current cell. Control returns to step S2 to predict the
`mobile location in the new current cell (e.g., ii) and the
`former cell M now is a neighboring cell to the current cell
`(e.g., i2).
`Typically, the signal strength between the mobile unit MU
`45
`and the neighboring cell base Station bSM decreases, while
`the signal strength between the mobile unit MU and at least
`one other adjacent base Station increases. There may be
`instances where after Some time in the new cell, the Signal
`strength between the mobile unit and the former base station
`increases at which time a new projection algorithm will have
`to be used. A new projection algorithm may also have to be
`used when a change from a decrease to an increase in Signal
`Strength between the mobile unit and the base Station of a
`neighboring cell occurs or Vice versa. A new projection
`algorithm may be implemented when an instantaneous Sig
`nal Strength directional change is detected, although it is
`preferable to implement the new projection algorithm after
`a Series of instantaneous signal Strength values continues to
`increase or decrease following a directional change.
`FIG. 4 shows an exemplary physical realization of the
`invention. The power levels of the mobile station R5 at
`Suitable intervals are measured at the base station R3-1
`Serving mobile Station R5 and neighboring base Stations
`Such as base station R3-N with the assistance of the MSC
`65
`R1-1. The MSC knows which base stations are the neigh
`boring base Stations for each mobile Station actively engaged
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`in a call. The measurements are collected and processed by
`a location database R2. This information may be relayed via
`the base station R3-1 serving the mobile station R5, the
`MSC R1-1, and the transmission and signaling links to the
`location database R2. The location database R2 processes
`the power level data of the mobile station R5 and projects
`the probable location of the mobile station R5 into the
`future. The method described above can be implemented in
`the location database R2, which can be used to project
`wireleSS resources needs in the future, as well as for other
`applications. Physically, the location database R2 may reside
`at an MSC as an adjunct processor to the Switch, or at a
`Service control point, which is an element of the advanced
`intelligent network (AIN) architecture. The local database
`R2 can be accessed by MSCs or other databases and call
`control/application processors (if not locally implemented)
`via a signaling network Such as the Signaling System number
`7. Also, a local database R2 can be configured to Serve a
`large cellular geographic Serving area, Such as a metropoli
`tan area including Several MSC Serving areas.
`While particular embodiments of the present invention
`have been described and illustrated, it should be understood
`that the invention is not limited thereto Since modifications
`may be made by perSons skilled in the art. The present
`application contemplates any and all modifications that fall
`within the Spirit and Scope of the underlying invention
`disclosed and claimed herein.
`What is claimed is:
`1. A method for predicting a location of a mobile unit in
`a mobile communications network including a plurality of
`cells, each of the cells having a base Station, Said method
`comprising the Steps of:
`measuring a first Series of instantaneous signal Strength
`values over time between a mobile unit and a base
`Station in a current cell where the mobile unit is located;
`measuring a Second Series of instantaneous Signal Strength
`values over time between the mobile unit and base
`Stations in neighboring cells,
`projecting Signal Strength values between the mobile
`Station and the base Station of the current cell and the
`mobile Station and the base Stations of the neighboring
`cells for a future time based on the first and second
`Series of instantaneous Signal values,
`determining a handover time when the projected Signal
`Strength value between the mobile Station and the base
`Station of the current cell is not less than an outgoing
`handover threshold; and
`Selecting a neighboring cell in which the projected Signal
`Strength value between the mobile Station and the base
`Station in the neighboring cell is greater than an incom
`ing handover threshold at the handover time, wherein a
`predicted location of the mobile station after the han
`dover time is in the Selected neighboring cell and the
`predicted location of the mobile station before the
`handover time is in the current cell.
`2. The method according to claim 1, wherein the Step of
`Selecting includes the Steps of
`identifying the neighboring cells in which the projected
`Signal Strength value between the mobile Station and
`the base Station of the neighboring cell is greater than
`an incoming handover threshold at the handover time;
`and
`comparing the projected Signal Strength values between
`the mobile station and the base stations of the identified
`neighboring cells.
`3. The method according to claim 2, wherein Said Step of
`comparing includes finding the neighboring cell having the
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`6,052,598
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`highest projected Signal Strength value over the longest
`projected duration.
`4. The method according to claim 1, wherein Said Step of
`measuring the first Series of instantaneous signal Strength
`values includes measuring the first Series of instaneous
`Signal Strength values in the forward direction and wherein
`Said Step of measuring the Second Series of instantaneous
`Signal Strength values includes measuring the Second Series
`of instantaneous signal Strength values in the forward direc
`tion.
`5. The method according to claim 1, wherein said step of
`measuring the first Series of instantaneous signal Strength
`values includes measuring the first Series of instantaneous
`Signal Strength values in the reverse direction and wherein
`Said Step of measuring the Second Series of instantaneous
`Signal Strength values includes measuring the Second Series
`of instantaneous signal Strength values in the reverse direc
`tion.
`6. The method according to claim 1, wherein Said Step of
`projecting includes extrapolating the Signal Strength values
`between the mobile station and the base station of the current
`cell and the mobile station and the base stations of the
`neighboring cells for the future time using Velocity and
`direction of the mobile unit determined from the first series
`and Second Series of instantaneous signal Strength values.
`7. The method according to claim 1, wherein said step of
`projecting includes extrapolating the Signal Strength values
`between the mobile station and the base station of the current
`cell and the mobile station and the base stations of the
`neighboring cells for the future time using a propagation
`model.
`8. The method according to claim 1, wherein instanta
`neous Signal Strength Values are measured at periodic inter
`vals.
`9. The method according to claim 8, wherein the periodic
`intervals are preset based on size of the current cell.
`
`15
`
`25
`
`35
`
`8
`10. The method according to claim 8, wherein the periodic
`intervals are set based on estimated velocity of the mobile
`unit in the current cell.
`11. The method according to claim 8, wherein the periodic
`intervals are set based on a time-of-day.
`12. The method according to claim 1, wherein wireleSS
`resource needs of the mobile unit are anticipated based on
`the predicted location of the mobile unit.
`13. The method according to claim 1, wherein wireless
`resources for the mobile unit are allocated in the Selected
`neighboring cell based on the predicted location of the
`mobile unit.
`14. The method of claim 1, wherein Said outgoing han
`dover threshold is less than Said incoming handover thresh
`old.
`15. A mobile communication System method, comprising
`the Steps of:
`Setting values of an incoming threshold and an outgoing
`threshold;
`measuring a plurality of instantaneous signal Strength
`values of Signals between a mobile unit and a plurality
`of base Stations,
`extrapolating signal strengths (i) between said mobile unit
`and a current base station, and (ii) between said mobile
`unit and a neighboring base Station, for a future period
`of time; and
`determining a handover time wherein, at Said handover
`time, an extrapolated Signal Strength between Said
`mobile unit and Said current base Station is not leSS than
`Said outgoing threshold, and an extrapolated Signal
`Strength between said mobile unit and said neighboring
`base Station is greater than Said incoming threshold.
`
`k
`
`k
`
`k
`
`k
`
`k
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