(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0152471 A1
`(43) Pub. Date:
`Aug. 5, 2004
`MacDonald et al.
`
`US 2004O152471A1
`
`(54) METHODS AND APPARATUS FOR MOBILE
`STATION LOCATION ESTIMATION
`
`(76) Inventors: Alan Denis MacDonald, Bellevue, WA
`(US); Marc W. Sather, Kingston, WA
`(US); John Lawrence Snapp,
`Sammamish, WA (US)
`Correspondence Address:
`KLARQUIST SPARKMAN, LLP
`121 SW SALMON STREET
`SUTE 1600
`PORTLAND, OR 97204 (US)
`(21) Appl. No.:
`10/473,926
`(22) PCT Filed:
`Apr. 3, 2002
`(86) PCT No.:
`PCT/US02/107.91
`Related U.S. Application Data
`(60) Provisional application No. 60/281,147, filed on Apr.
`3, 2001.
`
`Publication Classification
`
`(51) Int. Cl." ....................................................... H04Q 7/00
`(52) U.S. Cl. ..................................... 455/4.56.1; 455/456.5
`
`(57)
`
`ABSTRACT
`
`Methods and apparatus for estimating mobile Station loca
`tion include receiving reported Signal Strengths or other
`attachment indicator values from a mobile Station. The
`reported Signal Strengths are compared with characteristic
`received signal Strength values in a coverage area of a
`mobile network. A mobile Switching center determines if a
`location function is requested and initiates a location esti
`mation process by a mobile location module (MLM). The
`MLM receives the reported Signal Strength contours asso
`ciated with the attachment points. Based on a comparison of
`the reported attachment indicator values with characteristic
`values, the MLM provides a mobile location estimate.
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`Patent Application Publication Aug. 5, 2004 Sheet 3 of 11
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`METHODS AND APPARATUS FOR MOBILE
`STATION LOCATION ESTIMATION
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`0001) This application claims the benefit of U.S. Provi
`sional Patent Application 60/281,147, filed Apr. 3, 2001.
`
`FIELD OF THE INVENTION
`0002 The present invention relates to methods and appa
`ratus for determining the location of a mobile Station in a
`wireleSS network.
`
`BACKGROUND
`0.003 Mobile telephone systems, also called cellular tele
`phone Systems, are becoming increasingly popular. These
`Systems are generally made up of cell Sites that are config
`ured to Serve an associated coverage area that is referred to
`as a cell. The cell Site is a location within a cell at which
`communication hardware Such as antenna(s) and radio base
`Stations are installed. A mobile Station operating within a
`particular cell in the System communicates with the mobile
`telephone System through the associated cell Site. The cell
`Sites are in communication with a mobile Switching center
`that connects the mobile telephone System to a land-line
`telephone network.
`0004 One reason for the popularity of cell phones is that
`they can be used for emergencies. For example, a motorist
`could use the mobile telephone to call for assistance in case
`of a disabled vehicle. Many areas provide a special emer
`gency cellular telephone number. In other areas, users can
`call 911, just as they would from a conventional land-line
`phone.
`0005 One of the problems with using the mobile tele
`phone for emergencies Stems from the mobility of the
`telephone. Public Service providers, Such as police, do not
`know the location of the mobile telephone calling the
`emergency number. In addition, users who call the emer
`gency number often cannot provide enough location infor
`mation to allow the public service provider to find them.
`Thus, it is desirable to provide a mobile telephone system
`that can determine the location of a mobile telephone and
`provide that information to public Service providers.
`0006 Such a mobile telephone location service would be
`desirable in other contexts besides emergency responses.
`For example, a mobile telephone user who is lost may
`request location information from the mobile telephone
`System provider. The location information could be passed
`to the user from the system. Yet another user for such a
`System would be companies which operate fleets of vehicles.
`A home base for company operations could keep track of the
`locations of its vehicles by using a mobile telephone location
`Service. Of course there are many other applications for Such
`a Service.
`0007. In known techniques for mobile telephone location,
`the distance between a mobile telephone and a mobile
`telephone System antenna in a cell Site can be determined by
`analyzing the Signal Strength of a communication signal
`between the cell site antenna and the mobile telephone. If the
`distance between the mobile telephone and a number of cell
`
`Site antennas is calculated, the approximate location of the
`mobile telephone can be determined by a geometric process
`Such as triangulation.
`0008 U.S. Pat. No. 4,891,650, describes a vehicle loca
`tion System which determines an approximate vehicle loca
`tion using a cellular telephone System. The location function
`is initiated when a vehicle transmits an alarm Signal to
`nearby cell Sites. The cell Sites receiving this alarm Signal
`analyze the received alarm Signal to determine its signal
`Strength. The cell Sites then Send Signal Strength information
`through the mobile telephone System to an alarm central
`Station. The alarm central Station then uses the Signal
`Strengths reported from various cells to determine an
`approximate location of the vehicle. A more accurate loca
`tion is achieved by Sending out actual tracking vehicles to
`the approximate location calculated by the central Station. A
`disadvantage of this System is that each of the cell Sites
`requires additional components, which will generate and
`Send an appropriate Signal Strength report message to a
`mobile telecommunications Switching office. The mobile
`telecommunications Switching office also needs Special
`functionality to Send appropriate information to a central
`tracking Station that determines an approximate location of
`the vehicle using the Signal Strengths.
`0009 U.S. Pat. No. 5,218,367 describes a vehicle track
`ing System which uses signal Strengths received from nearby
`cells to calculate an approximate vehicle location. In this
`System, a Special purpose mobile telephone determines
`Signal Strengths being received from a nearby cell and
`generates and Sends an appropriate alarm message, includ
`ing Signal Strength information, to a central Station via the
`mobile telephone System. The central Station then uses this
`information to determine an approximate location of the
`vehicle. The System can improve upon the accuracy of the
`approximate location if the cells are divided into Sectors and
`particular information about the antennas in these SectorS is
`used. Once an approximate location is found, a more accu
`rate location is achieved by Sending out actual tracking
`vehicles to the approximate location calculated by the cen
`tral Station.
`0010) A technique described in U.S. Pat. No. 4,891,650
`requires additional components in each of the cell Sites in
`order to generate and Send appropriate signal Strength report
`messages. Since there are many Such cells in a mobile
`telephone System, Such additional components are undesir
`able. Thus, there is a need for mobile telephone location
`System, which does not require additional components at
`each cell site. Other methods are described in U.S. Pat. No.
`5,724,660 and U.S. Pat. No. 5,732,354.
`0011. Some of the location techniques described in the
`above patents do not calculate an accurate location of the
`mobile telephone. The accuracy of the location is improved
`by Sending out actual tracking vehicles. However, the need
`for Such vehicles makes Such techniques very expensive.
`Improved methods and apparatus for mobile Station location
`estimation are needed.
`
`SUMMARY
`0012 Mobile station location methods include determin
`ing a geographical location based on reported Signal Strength
`(RSS) values reported by a mobile station. The RSS values
`are compared with sets of RSS values obtained by, for
`
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`example, Signal Strength measurements or Signal Strength
`computations, and Stored in a memory. According to repre
`Sentative examples, methods include establishing latitude or
`longitude coordinates with a global positioning System pro
`cessor associated with the mobile station. Reported RSS
`values are compared with predetermined RSS values asso
`ciated with the latitude and longitude coordinates. In addi
`tional examples, the predetermined Sets of RSS values are
`revised based on GPS location coordinates reported by the
`mobile Station.
`0013 Mobile station location processors include an input
`configured to receive attachment indicators associated with
`at least two points of attachment of the mobile Station. A
`memory is configured to Store Sets of predetermined attach
`ment indicators associated with the at least two points of
`attachment, and an estimation unit is configured to provide
`an estimate of the mobile Station location based on a
`comparison of the received attachment indicators and at
`least one set of the at least two predetermined attachment
`indicators. According to additional examples, the received
`attachment indicator values are reported by the mobile
`Station. In other examples, the attachment indicator values
`are reported by one or more points of attachment. In a
`representative example, the attachment indicator values are
`received signal Strength values reported by the mobile
`Station.
`0.014 Mobile location modules include a processor con
`figured to compare at least two reported received signal
`Strength values with at least two predetermined received
`Signal Strength values associated with at least two geo
`graphical locations in a wireleSS network. The mobile loca
`tion modules also include an output configured to deliver a
`mobile location estimate based on the comparison. Accord
`ing to representative examples, the processor is configured
`to determine a Score associated with the comparison of the
`reported received signal Strength values with the predeter
`mined received signal Strength values. In additional
`examples, the reported and received signal Strength values
`relate to mobile-assisted hand-off.
`0.015
`Location units for estimating a geographic location
`of a mobile Station include an input configured to receive
`attachment indicator values associated with a mobile Station,
`and a processor configured to provide a mobile Station
`location estimate based on predetermined attachment indi
`cator contours associated with network attachment points.
`According to representative examples, the attachment indi
`cator values are received signal Strength values reported by
`the mobile Station and the attachment indicator contours are
`received signal Strength contours.
`0016 Methods of locating a mobile station include
`obtaining a set of received signal Strength values associated
`with the mobile Station and determining a mobile Station
`location based on a comparison of the received signal
`Strengths with characteristic Signal Strength values. In rep
`resentative examples, the mobile Station location is deter
`mined by Selecting a location associated with the character
`istic Signal Strength values associated with a Selected error
`Score. In other examples, the methods include Storing the
`characteristic Signal Strength values and retrieving the char
`acteristic values from a memory.
`0017 Methods of locating a mobile station within a
`geographic Service area include obtaining attachment indi
`
`cator values for the mobile station. The mobile station
`attachment indicator values are associated with a Series of
`attachment points and are compared with characteristic
`attachment indicator values associated with the Series of
`attachment points to obtain a mobile Station location esti
`mate. According to additional representative examples, the
`methods include reporting the estimated mobile Station
`location. In other examples, the attachment indicator values
`for the mobile Station are received Signal Strength values
`asSociated with corresponding radio base Stations and
`reported by the mobile Station. In representative examples,
`the mobile Station attachment indicator values and the
`characteristic attachment indicator values are compared by
`determining Scores, and the estimated mobile Station loca
`tion is Selected based on the Scores.
`0018 Methods of locating a mobile station include
`obtaining at least one of a latitude and a longitude location
`estimate based on a global positioning System. An estimate
`of mobile Station location is provided based on a comparison
`of mobile Station attachment indicator values with charac
`teristic attachment indicator values in a region associated
`with the latitude and longitude estimates.
`0019 Methods of estimating a mobile station location
`include receiving Signal Strength values reported by a mobile
`Station and associated with a plurality of antennas. A first
`location area of the mobile Station is calculated as a geo
`graphic coverage area of a Serving cell Site and a Second
`location area of the mobile Station is calculated based on a
`comparison of the reported received signal Strength values
`with predetermined signal Strength values associated with at
`least one location in the geographic coverage area According
`to representative examples, the predetermined signal
`Strength values are represented as Signal Strength contours,
`and the mobile Station location estimate is based on asso
`ciating one or more signal Strength contours with the
`reported received signal Strength values.
`0020 Characteristic attachment indicator values can be
`determined based on a propagation characteristic between a
`geographic location and a point of attachment. In represen
`tative examples, the propagation characteristic can be propa
`gation path Slope, antenna pattern roll-off, or other value.
`0021 Networks configured to provide location estimates
`for a mobile station include a mobile location module that
`receives attachment indicator values associated with points
`of attachment. The network includes a database that includes
`characteristic attachment indicator values for geographic
`locations in a network Service area A mobile location
`estimate is provided based on a comparison of the received
`attachment indicator values and the characteristic attach
`ment indicator values. In Some examples, the received
`attachment indicator values are received signal Strength
`values reported from the mobile station. In additional
`examples, the comparison is based on a calculated Score
`asSociated with the characteristic attachment indicator Val
`ues and the received attachment indicator values. In other
`examples, the characteristic attachment indicator values are
`configured as attachment indicator value contours, and the
`mobile Station location estimate is based on these contours.
`0022 Computer readable media are provided that contain
`computer-executable instructions for determining mobile
`Station location estimates. The media include computer
`executable instructions configured to compare reported
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`attachment indicator values with characteristic attachment
`indicator values associated with corresponding geographic
`locations. In Some examples, instructions for determining
`the characteristic values are provided.
`0023 Methods of providing mobile location information
`include determining a mobile location based on a compari
`Son of reported attachment indicator values with character
`istic attachment indicator values associated with respective
`geographic locations. In Some examples, the mobile location
`is reported to a Service provider, and, in additional examples,
`the mobile location determination is repeated based on
`updated reported attachment indicator values to obtain an
`updated mobile location that is reported to the Service
`provider.
`0024. These and other features are set forth below with
`reference to the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0.025
`FIG. 1 illustrates a geographic service area of a
`wireleSS network.
`0.026
`FIG. 2 is a block diagram illustrating a mobile
`telephone System.
`0.027
`FIG. 3 shows an example mobile-assisted hand-off
`(MAHO) list that includes received signal strengths.
`FIG. 4 illustrates a Hata propagation loss model.
`0028)
`0029 FIG. 5 illustrates a location area as an intersection
`of circles, wherein radii of the circles are overestimates of
`mobile Station distances.
`0030 FIG. 6 illustrates a location area as an intersection
`of circles, wherein radii of the circles are underestimates of
`mobile:Station distances.
`0.031
`FIG. 7 illustrates a location point as an intersection
`of circles, wherein radii of the circles are accurate estimates.
`0.032
`FIG. 8 illustrates a method of reducing error com
`ponents of computed distances.
`0.033
`FIG. 9 is a graph of latitude and longitude coor
`dinates calculated by a GPS receiver/processor over a time
`interval.
`0034 FIG. 10 is a block diagram of a method of calcu
`lating a location of a mobile Station.
`0.035
`FIG. 11 is a schematic block diagram of a wireless
`communication System.
`0.036
`FIG. 12 is a schematic diagram of a division of a
`geographical Service area into Zones.
`0037 FIG. 13 is a schematic diagram of an alternative
`division of a geographical Service area into Zones.
`0.038
`FIG. 14 is a schematic block diagram of a mobile
`Station location module.
`0039 FIG. 15 is a schematic block diagram of a wireless
`network that includes a mobile Station location module.
`0040 FIG. 16 is a schematic diagram illustrating
`received signal Strength contours based on received signal
`Strength values associated with cells of a wireleSS network.
`
`FIG. 17 is a schematic block diagram illustrating a
`0041
`wireleSS network configured to provide mobile Station loca
`tions to a emergency Services provider.
`
`DETAILED DESCRIPTION
`0042 FIG. 1 shows the geographic serving area 100 of a
`mobile telephone system. The serving area 100 is shown
`having 7 hexagonal cells numbered 1-7. Cell 7 is shown in
`the center, Surrounded by adjacent cells 1-6. The Serving
`area 100 of a mobile telephone system would typically
`contain more than 7 cells, however, for ease of reference,
`only 7 cells are shown in FIG. 1. Each cell 1-7 contains an
`antenna 101-107 which is used to transmit signals to and
`receive signals from mobile telephones Such as a mobile
`telephone 120 within the mobile telephone system serving
`area 100.
`0043. A mobile telephone system 200 is shown in FIG.
`2. Cell 7 is shown containing antenna 107 connected to a
`radio base station (RBS) 214. The mobile telephone 120
`shown within cell 7 communicates with the mobile tele
`phone system 200 via an air interface 202. For example, the
`mobile telephone 120 can be a digital mobile telephone that
`operates according to a North American time division mul
`tiple access (TDMA) system according an IS-55 standard,
`and an air interface according to an IS-54 or IS-136 stan
`dard. See, for example, TIA/EIA Interim Standard IS-55-A
`“Recommended Minimum Performance Standards of 800
`MHz Mode Mobile Stations,” September 1993; EIA/TIA
`Interim Standard IS-54-B “Cellular System Dual-Mode
`Mobile Station-Basestation Compatibility Standard.” April
`1992; EIA/TIA Interim Standard IS-136 “Cellular System
`Dual-Mode Mobile Station-Basestation: Digital Control
`Channel Compatibility Standard.” April 1995; which are
`incorporated by reference herein. In addition, a global
`positioning system (GPS) receiver/processor unit 125 can be
`provided in or otherwise associated with the mobile tele
`phone 120 which is to be located. This use of the GPS
`receiver/processor 125 in the mobile telephone 120 will be
`described in further detail below. Cells 1-7 include respec
`tive antennas connected to associated radio base Stations
`(RBS) that are in communication with the mobile switching
`center (MSC) 220.
`0044) The cells 1-7 are assigned a plurality of voice
`channels for transmitting and receiving Voice Signals and
`respective control channels for transmitting and receiving
`control data signals. Referring to FIGS. 1-2, consider mobile
`telephone 120, which is operating in cell 7. The mobile
`telephone 120 is communicating over the air interface 202
`with the mobile telephone system 200 via antenna 107 and
`RBS 214. Voice signals are communicated between the
`mobile telephone 120 and the antenna 107 via one of the
`cell's voice channels, and control data Signals are commu
`nicated between mobile telephone 120 and the antenna 107
`via the cells control channel. In Such a situation, cell 7 is the
`Serving cell Since the Voice data is being communicated
`through that cell. In addition to the communication with the
`serving cell, the mobile telephone 120 also monitors the
`control channels of nearby cells. The mobile telephone 120,
`for mobile-assisted hand-off in accordance with the IS-54
`and IS-136 Standards, measures the Signal Strengths of these
`control channels of nearby cells. These control channel
`signal strength measurements are sent to the MSC 220 as
`described in further detail below. In addition, the mobile
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`telephone 120 measures the Signal Strength of the Voice
`Signal it is receiving from the Serving cell site antenna. This
`Voice channel Signal Strength measurement is periodically
`sent by the mobile telephone 12 to the MSC 220 via the
`Serving cell's reverse Voice channel.
`0045. As the mobile telephone 120 travels within the
`geographic Serving area 100, the Signal Strength of the Voice
`channel signal between the antenna 107 and the mobile
`telephone 120 will vary. As the mobile telephone 120 enters
`another cell Such as, for example, adjacent cell 5, the Signal
`strength of the control channel signal from antenna 105 will
`become Stronger than the Signal Strength of the Voice chan
`nel signal from antenna 107. At this point, it is desirable for
`the mobile telephone 120 to terminate communication over
`the Voice channel with cell 7 and to initiate communication
`via a voice channel of cell 5. This operation is called
`hand-off, and is used to change the Serving cell while the
`mobile telephone 120 is traveling within the geographic
`serving area 100 so that the mobile telephone 120 maintains
`Voice channel communication via the antenna with the
`Strongest Signal.
`0046) In mobile telephones based on the IS-54 and IS 136
`air protocols, this hand-off operation is assisted by the
`mobile telephone itself. Such a function is called mobile
`assisted hand-off (MAHO). The mobile telephone 120 main
`tains a MAHO list, which contains the signal strengths of the
`signals that the mobile telephone 120 is receiving over the
`control channels of nearby cells. Each cell Site has a pre
`defined MAHO list. The MSC 220 stores these MAHO lists
`for each cell Site and Sends the appropriate list to the mobile
`telephone 120, depending on the Serving cell Site. These
`defined MAHO lists generally consist of the cells adjacent to
`the Serving cell. For example, assuming that cell 7 is the
`serving cell, an example MAHO list 300 is shown in FIG.
`3. The list of channels to measure and to include in the
`MAHO list is communicated to the mobile telephone 120 by
`the MSC 220. The list 300 contains an entry for each of the
`adjacent cells 1-6 in this illustration, with a corresponding
`Signal strength (RSSI) which represents the signal strengths
`of the control channels broadcast by cells 1-6 as received by
`mobile telephone 120. Thus, RSSI represents the control
`channel Signal Strength being received by the mobile tele
`phone 120 from the antenna 101 in cell 1; RSSI represents
`the control channel Signal Strength being received by the
`mobile telephone 120 from the antenna 102 in cell 2; etc.
`0047. MAHO measurements are periodically sent from
`the mobile telephone 120 to the MSC 220 via the serving
`cells reverse voice channel. The contents of the MAHO list
`are determined by the IS-54 standard, and thus all digital
`mobile telephones, which comply with this, air protocol will
`maintain a MAHO list.
`0.048. It is often desirable to determine a specific geo
`graphic location of a mobile telephone Such as the mobile
`telephone 120 within the geographic serving area 100. A
`mobile location module (MLM) 230 can be included in the
`mobile telephone system 200 to provide a mobile station
`location. The MLM 230 includes a processor 232 and a
`memory 234. The MLM 230 is connected to the MSC 220,
`and the location function of the MLM 230 can be initiated
`by the MSC 220 as follows.
`0049 Upon initiation of a telephone call by the mobile
`telephone 120, the RBS 214 sends the MSC 220 the tele
`
`phone number of the mobile telephone (the A number) and
`the telephone number of the telephone being called by the
`mobile telephone (the B number). The MSC 220 can be
`configured to perform an A/B number analysis to determine
`whether a location function is to be performed. For example,
`the MSC 220 can initiate the location function each time a
`mobile telephone dials 911. In addition, the mobile tele
`phone System provider can offer this location function as a
`Service to its customers. In this situation, if the user of the
`mobile telephone 120 dials a certain number, the MSC 220
`can initiate the location function and the location of the
`mobile telephone could be communicated to the mobile
`telephone user. Further, the MSC 220 can determine whether
`a location function is requested by referring to a user profile
`stored in the MSC 220. For example, a company, that uses
`a fleet of vehicles may want a location function performed
`each time a call is initiated from one of its mobile tele
`phones. AS Seen by these examples, by performing an A/B
`number analysis, the MSC 220 can initiate a location func
`tion based on various criteria. One skilled in the art would
`recognize that various other A/B number analyses could be
`performed to determine whether initiation of the location
`function is requested. If the MSC 220 determines that a
`location function is requested, a location function in the
`MLM 230 is requested. Whether or not a location function
`is initiated, the Voice portion of the Signal can be sent to the
`appropriate destination. For example, if the mobile tele
`phone 120 called a land line telephone, then the Voice Signal
`can be sent to the public switch telephone network (PSTN).
`Thus, calls that result in the initiation of a location function
`do not need to terminate at the MLM 230. Voice information
`may be transmitted to the appropriate location based upon
`the number dialed.
`0050. In one example, the location of a mobile telephone
`120 within the geographic service area 100 can be deter
`mined by the MLM 230 as follows. The MSC 220 passes the
`following information to the MLM 230. The MAHO list300
`containing the RSSI is sent by the mobile telephone 120.
`The cell site currently serving the mobile telephone 120 is
`identified. The Signal Strength of the Voice channel Signal
`from the Serving cell site, represented as (RSSI), is mea
`sured and sent by the mobile telephone 120.
`0051) The MLM processor 232 then executes computer
`program code 238 stored in memory 234. The computer
`program code 238 describes the location algorithm to be
`performed by the processor 232. This algorithm is shown in
`the flow diagram of FIG. 10. The first step 1002 is to
`calculate two location Zones, Zone 1 and Zone 2. Zone 1 is
`defined by the geographic coverage area of the cell currently
`serving the mobile telephone 120. For example, if the
`serving cell was cell 7 (see FIG. 1) then Zone 1 would be the
`geographic coverage area included in cell 7. Zone 2 is
`calculated by the MLM 230 as described below in conjunc
`tion with FIGS. 4-8.
`0052 The first step in calculating Zone 2 is to evaluate
`RSSI, and RSSIs to determine the three strongest signal
`Strengths. For the present example, assume that cell 7 is the
`Serving cell and the Strongest Signal Strengths are the Voice
`channel signal Strengths (RSSI) being communicated over
`antenna 107, the Signal Strength associated with the control
`channel for cell 2 (RSSI) being communicated over antenna
`102, and the Signal Strength associated with the control
`channel for cell 4 (RSSI) being communicated over antenna
`
`Page 16 of 24
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`

`US 2004/0152471 A1
`
`Aug. 5, 2004
`
`104. Using these signal Strengths, it is possible to estimate
`the distance of the mobile telephone 120 from each of the
`antennas 102, 104,107 using the following equation:
`(1)
`RSSI (dBm)=EIRP(dBm)-Propagation Loss (dB)
`0053. In the above equation, RSSI is the known signal
`Strength being received by a mobile telephone from an
`antenna. EIRP is the effective isotropic radiated power of the
`antenna, and it depends on the power of the transmitter
`(TxPower) and the gain of the antenna (Antenna Gain), Such
`that EIRP (dBm)=TxPower(dBm)+Antenna Gain(dBi). For
`each antenna 102, 104, 107, the TxPower (dBm) and the
`Antenna Gain (dBi) are fixed constants and thus the EIRP
`for each of the antennas is a known value. See, for example,
`C. A. Belanis, Antenna Theory. Analysis and Design, John
`Wiley & Sons, New York, 1982.
`0054) The second term of equation (1), Propagation Loss,
`is modeled based upon the Hata model, which is illustrated
`in FIG. 4. The model is of the form:
`Propagation Loss (dB)=A+B log d,
`0.055 wherein A is the 1 km intercept point which
`depends on the height of the antenna and the frequency
`being transmitted and includes a component which is due to
`the antenna height above the ground. B is the propagation
`path slope, and d is the distance of the mobile telephone
`from the antenna (in kilometers). As shown in FIG. 4,
`EIRP(dBm)-A is the RSSI value of the line 402 at d=1 km,
`and B is the slope of the line at 402. For further information
`on the Hata model see, M. Hata, “Empirical Formula for
`Propagation Loss in Land Mobile Radio Services.” IEEE
`Trans. Vehicular Tech. Vol. VT-29 (August 1980).
`0056