CA2367572C - Method and system for locating a mobile subscriber in a cdma communication system - Google Patents
Method and system for locating a mobile subscriber in a cdma communication system Download PDFInfo
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- CA2367572C CA2367572C CA002367572A CA2367572A CA2367572C CA 2367572 C CA2367572 C CA 2367572C CA 002367572 A CA002367572 A CA 002367572A CA 2367572 A CA2367572 A CA 2367572A CA 2367572 C CA2367572 C CA 2367572C
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- received
- base station
- subscriber unit
- time difference
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/0205—Details
- G01S5/0218—Multipath in signal reception
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/12—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
Abstract
The invention determines the geographic location of a subscriber unit within a CDMA communication system. At least one base station transmits a spread spectrum signal with a chip code sequence unique to that base station. A subscriber unit receives the base station signal and transmits a spread spectrum signal wiht a unique chip code sequence time synchronized with the chip code sequence of the received base station signal. The base station receives the subscriber unit signal and compares the chip code sequence of the received subscriber unit singal with the chip code sequence signal transmitted by the base station to determine the location of the subscriber unit.
Description
METHOD AND SYSTEM FOR LOCATING A MOBILE SUBSCRIBER IN A CDMA COMMUNICATION
SYSTEM
Field of the Invention This invention generally relates to spread spectrum code division multiple access (CDMA) communication systems. More particularly, the present invention relates to a system and method that determines the geographic location of a subscriber unit within a CDMA communication system.
Description of the Prior Art Wireless systems capable of locating a subscriber are presently known in the art. One wireless technique uses the global positioning system (GPS). In GPS, the communication handset receives data transmitted continuously from the 24 NAVSTAR satellites. Each satellite transmits data indicating the satellite's identity, the location of the satellite and the time the message was sent. The handset compares the time each signal was received with the time it was sent to determine the distance to each satellite. Using the determined distances between the satellites and the handset along with the location of each satellite, the handset can triangulate its location and provide the information to a communication base station.
However, the incorporation of a GPS within a subscriber unit increases its cost.
--- --- -- ~~Lra euyL nvrtvit;.r.c. US 009920257 1 J-E~4-200 j Another subscriber location technique is disclosed in TJ.S. Patent hlo.
5,732,354. A mobile telephone using time division multiple access (TDMA) as the aiz interface is located within a plurality of base stations. The mobile telephone measures the received signal strength from each of the base stations and transmits each strength to each respective base station. At a mobile switching center, the zeceived signal strengths from the base stations are compared and processed. 'The result yields the distance between the mobile telephone and each base station. From these distances, the location of the nrxobile telephone is calculated.
Wireless communication systems using spread spectrum modulation techniques are increasing in popularity. ~n code division multiple access (CDMA) systems, data is transmitted using a wide bandwidth (spread spectrum) by modulating the data with a pseudo random chip code sequence. The advantage gained xs rhat CbMA systems arc more resistant to signal distortion and interfering frequencies in the transmission path than communication systems usiing the more connmo~a time division multiple access (TDM.A) or frequency division multiple access (F77MA) techniques.
EP 0 865 223 AZ is a position estimation scheme for a cellular mobile system. A Burst and a second signal sequence are exchanged between the mobile station and the base station. These signals may be CDMA signals. A phase difference between the first and second sequence is used to determine a distance _2_ Emvfan8steit l9.Aar. 15:48 AMENDED SHEET
~....s, im ~iv .»v t7~otr YULY~ A1V~ ltU~N1(a,Y.G.
:19-04-2001 , US 009920257 CA 02367572 2001-09-21 , between the mobile and base station. Using multiple base stations, the position is estimated usi~ag triangulation.
U.S. Patent No. 5,600,705 is a position systenausing a range determination in a CDMA system. The system uses pilot signals and time difference of arrival ('l'DOA) and absolute tithe of arrival (TOA) in the position determination.
WO 9$118018 discloses locating a ~onobile te~ninal using two antennas of an array in a time division multiple access communication system. A plisse difference in the signals received by the two antennas is used to determine an angle fxom the ce~aterline of the antennas to the mobile terminal. Received signal strength is used to estimate the tern~nal's distance. The terminal's location is determined using the determined angle and distance.
'VfO 97147148 discloses deternnining aposit<on of amobile tcrnrinalwithin a cellular system A signal is transmitted at a low power level, The power level is temporarily increased. The signal transmitted at the increased power level is . used to make a position measurement of the terminal.
U.S. Patent Na. 5,'736,964 discloses a CDMA, system for locating a communication unit. A base station transmits a location request to the unit.
The unit transmits a receive time Qf~the message to the.base station. A group of base stations also determine a receive time of a symbol sequence iu the unit's ~0 transmissions. Using the time measurements, the location of the unit is determined.
-2a-Emafangsteit l9.Apr. 15;48 AMENDED SHEET
us : 4s FAX 215 588 B499 yOF.PE AND KOENIG, P. C. US 009920257 .19-04-2001 -'CJ.S. Patent No, 5,SQ6,864 discloses a system,for detex~minina a distance between a base station and a remote unit in a CDMA system. The base station transmits a base CDMA. signal to the remote unit. The remote unit transmits a remote CDMA. signal to the base station. The remote CDMA signal has its timing synchronized to 'the received base CDMA signal. The base station determines the distance to the remote unit by comparing the chip code sequences of the transmitted base CD1VIA signal and the received remote CDMA signal.
There exists a need for an accurate mobile subscriber unit location system that uses data already available in an existing CDMA communication system -2b-Emvfangszeit l9:Avr. 15:4g AMENDED SHEET
_ 19-04-2001 _Q9v 48 FI~ 215 588, 6499 . VOLPE ~3ND KOENIG,P. C. US 009920257 SUMMARY OF T'~ 1NV'ENTIOI~
A subscriber unit is geographically located using a plurality of base stations in a wireless CDMA communication system Each base station transmits a first spread spectrum signal having a first code. For.each received first signal, the subscriber unit transmits a second spread spectrum signal having a~second code. The second spread spectrum signal is time synchronized with its received first signal. An impulse response of each received ft~rst signal is analyzed to determine a first received component, At each base station, an impulse response of that base station's received second signal is analyzed to determine a first .. . ~ 10 received component. A distance between each base station and the subscriber unit is. determined. The distance determination is based on in part a timing difference between the received signal and the transmitted signal and the determined first received component for the second signals. The location of the subscriber unit is based on in part the deternaiued distances, a fixed location of each base station and a maximum likelihood estimation.
B~iIEF DESCRIPTION OF 1'HE ~.7lt.A.VVINGS
Figuure 1 is an illustration of a simplified, prior art CDMA system.
Figure 2 is an illustration of a prior art CDMA system.
Figure 3 is a block diagram of major components witba~n a prior art CD1VIA system.
EmofangsZeit l9.Avr. 15;48 AMENDED SHEET
.19-04-2001 -_ -- _ _ ___ _- -____._ _-__._. US 009920257 vamai~i 08:49 FAX 215 56B 6488 VOLPE AND KOENIG.P.C. r~uua Figure 4 is a block diagram of components within a prior art CDM~A
system.
k'igure 5 is an illustration of a global~pilot signal and an assigned pilot signal being communicated between a base stafiion and a subscriber unit.
-3a-EmpfangsZeit 19.A~r, 15:48 AMENDED SHEET
Figure 6 is a block diagram of a first embodiment of the present invention using at least three base stations.
Figure 7 is an illustration of locating a subscriber unit using the first embodiment of the present invention with at least three base stations.
Figure 8 is a block diagram of a second embodiment of the present invention showing components used in a subscriber unit.
Figure 9 is an illustration of locating a subscriber . unit using the second embodiment of the present invention with two base stations.
Figure 10 is an illustration of locating a subscriber unit using the second embodiment of the present invention with more than two base stations.
Figure 11 is a detailed illustration of the third embodiment of the present invention having a base station with multiple antennas.
Figure 12 is an illustration of the third embodiment having a base station with multiple antennas.
Figure 13 is a block diagram of components used in the third embodiment.
Figure 14 is an illustration of multipath.
Figure 15 is a graph of a typical impulse response of multipath components.
Figure 16 is a block diagram of components within a fourth embodiment correcting for multipath.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments will be described with reference to the drawing figures where like numerals represent like elements throughout.
Shown in Figure 1 is a simplified CDMA communication system. A data signal with a given bandwidth is mixed with a spreading code generated by a pseudo random chip code sequence generator producing a digital spread spectrum signal.
Upon reception, the data is reproduced after correlation with the same pseudo random chip code sequence used to transmit the data. Every other signal within the transmission bandwidth appears as noise to the signal being despread.
For timing synchronization with a receiver, an unmodulated pilot signal is required for every transmitter. The pilot signal allows respective receivers to synchronize with a given transmitter, allowing despreading of a traffic signal at the receiver.
In a typical CDMA system, base stations send global pilot signals to all subscriber units within their communicating range to synchronize transmissions in a forward direction. Additionally, in some CDMA systems, for example a B-CDMATM system, each subscriber unit sends a unique assigned pilot signal to synchronize transmissions in a reverse direction.
Figure 2 illustrates a CDMA communication system 30. The communication system 30 comprises a plurality of base stations 36,, 362 ... 36n. Each base station 361, 362 ... 36" is in wireless communication with a plurality of subscriber units 401, 402 ... 40", which may be fixed or mobile. Each subscriber unit 401, 402 ...
40"
communicates with either the closest base station 361 or the base station 361 which provides the strongest communication signal. Each base station 361, 362 ...
36~ is in communication with other components within the communication system 30 as shown in Figure 3.
A local exchange 32 is at the center of the communications system 30 and communicates with a plurality of network interface units (N>ZJs) 341, 342 ...
34".
Each N1U is in communication with a plurality of radio carrier stations (RCS) 381, 382 ... 38" or base stations 361, 362 ... 36~. Each (RCS) 381, 382 ... 38" or base station 361, 362 ... 36n communicates with a plurality of subscriber units 401, 402 .:. 40~
within its communicating range.
Figure 4 depicts a block diagram of the pertinent parts of an existing spread spectrum CDMA communication system. Each independent base station 361, 362 ...
36" generates a unique global pilot signal using a global pilot chip code generating means 421 and spread spectrum processing means 441. The global pilot chip code generating means 421 generates a unique pseudo random chip code sequence. The unique pseudo random chip code sequence is used to spread the resultant signals bandwidth such as to 15 MHZ as used in the B-CDMATM air interface. The spread spectrum processing means modulates the global pilot chip code sequence up to a desired center frequency. The global pilot signal is transmitted to all subscriber units 401 by the base station's transmitter 461.
A receiver 481 at a subscriber unit 401 receives available signals from a plurality of base stations 361, 362 ... 36". As shown in Figure 5, the global pilot 501 travels from the base station 361 to the subscriber unit 401 and can be represented as:
~1- al.
c Equation (1) The time the signal travels from the base station 361 to the subscriber unit 401, in equals the distance between the base station 361 and subscriber unit 401, dl, divided by the speed of light, c.
Refernng back to Figure 4, a global pilot chip code recovery means 541 within the subscriber unit 401 can receive global pilot chip code sequences from a plurality of base stations 361, 362 ... 36". The subscriber unit 401 generates a replica of a global pilot chip code sequence and synchronizes the generated replica's timing with the received global pilot 501. The subscriber unit 401 also has a processor 821 to perform the many analysis functions of the subscriber unit 401.
The subscriber unit 401 generates an assigned pilot signal 521 using assigned pilot chip code generating means 561 and spread spectrum processing means 581.
The assigned pilot chip code generating means 561 generates a pseudo random chip code sequence with its timing synchronized with the recovered global pilot chip code sequence. As a result, the assigned pilot chip code sequence is delayed by il with respect to the base station 361, 362 ... 36". The spread spectrum processing means 581 generates the assigned pilot signal 521 by modulating the assigned pilot chip code sequence up to a desired center frequency. The assigned pilot signal 521 is transmitted to all base stations 361, 362 ... 36" within range to receive the assigned pilot signal 521.
The base station 361 receives the assigned pilot signal 521 with the base station's receiver 621. The received assigned pilot 521 travels the same distance dl as the global pilot signal 501 as shown in Figure 5. Accordingly, the received ' assigned pilot signal will be delayed by ~l with respect to the mobile unit 401 and by 2i1 with respect to the global pilot 501 generated at the base station 361.
Since the chip code sequence of the assigned pilot 521 received at the base station 361 will be delayed by 2i1 with respect to the chip code sequence of the global pilot signal 501 generated at the base station 361, the round trip propagation delay, 2~1, can be determined by comparing the timing of the two chip code sequences. Using the round trip propagation delay, 2i1, the distance dl between the base station 361 and subscriber unit 401 can be determined by:
dl - c ~ 2i1.
Equation (2) _g_ If a spreading sequence having a chipping rate of at least 80ns is used and the communication system has the ability to track 1/16''' of a chip, the distance d1 can be measured to within 2 meters.
Figure 6 is a block diagram of a first embodiment of the present invention.
No additional hardware is required in the subscriber unit 401. The only changes are implemented by software within the subscriber unit's processor 821 and the processors 661, 662 ... 66", 68, 701, 702 ... 70" located within the base station 361, NIU
341 or Local Exchange 321, Precincts 741, 742 ... 74" and Ambulance Dispatcher 76.
The subscriber unit 401 is sent a signal by a base station 361 indicating that a 911 call was initiated and to begin the subscriber location protocol. Upon receipt, the subscriber unit 401 will sequentially synchronize its transmission chip code sequence to at least three base stations' chip code sequences. To allow reception by the base stations 362, 363 ... 36~ outside of the subscriber unit's normal communicating range, these transmissions will be sent at a higher than normal power level temporarily over-riding any adaptive power control algorithms.
A processor 661 within each base station 361, 362 ... 36n is coupled to the assigned pilot chip code recovery means 641 and the global pilot chip code generator 421. The processor 661 compares the two chip code sequences to determine the round trip propagation delay il, i2 ... i" and the respective distance dl, d2 ... do between the subscriber unit 401 and the respective base station 361, 362 ...
36n.
Within either a NIIJ 341 or the local exchange 32, a processor 68 receives the distances dl, d2 ... do from the processors 661, 662 ... 66" within all the base stations 361, 362 ... 36". The processor 68 uses the distances dl, dz ... do to determine the location of the subscriber unit 401 as follows.
By using the known longitude and latitude from three base stations 361, 362, 363 and distances d,, d2, d3, the location of the subscriber unit 401 is determined. As shown in Figure 7 by using the three distances dl, d2, d3, three circles 781, 782, 783 with radiae 801, 802, 803 are constructed. Each circle 781, 782, 783 is centered around a respective base station 361, 362, 363. The intersection of the three circles 781, 782, 783 is at the location of the subscriber unit 401.
Using the Cartesian coordinates, the longitude and latitude corresponding with each base station 361, 362 ... 36" is represented as X", Y", where X" is the longitude and Y" is the latitude. If X, Y represents the location of the subscriber unit 401, using the distance formula the following equations result:
(Xl-X)2 +(Yl-Y)2 = d12 Equation (3) (XZ_~2 +(y2_y)2 = d22 Equation (4) (X3_2 +(y3_y)2 - d32 Equation (5) In practice due to small errors in calculating the distances dl, d2 , d3, Equations 3, 4 and 5 cannot be solved using conventional algebra. To compensate for the errors, a maximum likelihood estimation is used to determine the location and are well known to those skilled in the art. For increased accuracy, additional base stations 364, 365 ... 36" can be used to calculate additional distances for inclusion in the estimation analysis.
The subscriber unit's location is sent through the communication system 30 to at least one precinct 741, 742 ... 74" and an ambulance dispatcher 76. A
processor 701 within each precinct 741, 742 ... 74" and the ambulance dispatcher 76 receives the location of all 911 calls originating in the system and displays the location on a conventional computer monitor 721. The display comprises a listing of all 911 calls and addresses on a geographic map.
~ 0 An alternate approach reduces the number of processors by transmitting raw data through the communication system 30 and processing the raw data at a single site.
Figure 8 is a second embodiment of a location system. At least two base stations 361, 362 ... 36" have their internal timing synchronized with each other and transmit their respective global pilot signals 521, 522 ... 52" with time synchronized chip code sequences. The subscriber unit 401 receives the global pilots 521, 522 ...
52". However, the received global pilots 521, 522 ... 52" are not synchronized. The global pilot 521 from a first base station 361 will travel distance dl and is delayed by il. The global pilot 522 from a second base station 362 travels distance d2 and is delayed by ~2. The subscriber unit 401 recovers each base station's global pilot chip code sequence with its global pilot chip code recovery means 541. A processor within the subscriber unit 401 is coupled to each global pilot chip code recovery means 541, 522 ... 54". The processor 821 compares the chip code sequences of each pair of pilot chip code sequences and calculates the time differences ~tl, Otz ... 0t"
between the sequences as follows.
Within the subscriber unit 401, the chip code sequences used by each base station 361, 362 ... 36" are stored. After synchronizing with.the first base station's pilot 361, the processor 821 will store where within the sequence synchronization was obtained. This process is repeated for the other base stations 362, 363 ...
36". The synchronization process can be done sequentially (synchronizing to the first base station's chip code sequence then the second, etc.) or in parallel (synchronizing to all base stations at the same time).
By using the relative time difference between il, i2, ... i" each base station's chip code sequence and knowing that each base station's pilot was sent at the same time, with two base stations the time differences are calculated as follows:
W ='~2 -il Equation (6) ~t2 = '~3-i2 Equation (7) The time differences Otl, ~tz ... Ot" are transmitted to at least one of the base stations 361.
At least one base station 361 recovers the time difference data from the received signals using time difference recovery means 841. The time difference data is sent with the distance data dl through the communications system to a processor 68. The processor 68 determines the location of the subscriber unit 401 using the time difference data Otl, Otz ... fit" and the distance data dl, d2 .., d" as follows.
Using information from only two base stations 361, 362 as shown in Figure 9, the processor uses distances dl, dz to create two circles 781, 782. Using the time difference, Otl, a hyperbola 861 can be constructed as follows.
All the points along the hyperbola 861 receive the global pilot signals 521, from the synchronized base stations 361, 362 with the same time difference, ~tl. The time difference ~tl can be converted to a distance difference Odl by substituting ~tl for tl and ~dl for dl in Equation 1. Using the distance formula and X, Y as the location of the subscriber unit 401, the following equation results:
Qdl = ~~,1 _~2 +lYl _ ~2 _ ~XZ _~2 +~Y2 _ ~2 Equation (8) By using Equation 8 with Equations 3 and 4 in a maximum likelihood estimation, the location of the subscriber unit 401 can be determined. The subscriber unit's location is subsequently sent to the nearest police precinct 741, 742 ... 74n and ambulance dispatcher 76 in the cellular area.
For improved accuracy, additional base stations 361, 362 ... 36" are used.
Figure 10 shows the invention used with three base stations 361, 362, 363. The distances dl, d2, d3 are used to create three circles 781, 782, 783. Using time differences Otl, Otz, two intersecting hyperbolas 861, 862 are constructed.
With maximum likelihood estimation, the subscriber units' location calculated with two hyperbolas 861, 862, and three circles 781, 782, 783 yields greater accuracy.
As shown in Figure 8, the subscriber unit 401 is required to process each global pilot chip code sequence to determine the time differences Otl, ~tz ...
Ot".
An alternate approach removes the processing from the subscriber unit 401.
With reference to Figure 6, the mobile unit 401 will synchronize the assigned pilot to one of the base station's global pilot chip code sequences, such as the nearest base station 361 with a delay of ~1. The assigned pilot 501 is transmitted to all base stations 361, 362 ... 36". The assigned pilot 501 will be received at each base station with a respective delay, il + i1, il + i2, il + i3. Each base station 361, 362 ... 36" will send the delayed chip code sequence along with the calculated distance to a processor 68 located in a N1U 341 or local exchange 32. The processor 68 will calculate the time differences Otl, Otz ... Ot" by comparing the received assigned pilot chip code sequences. Since all received assigned pilot chip code sequences are delayed by ~1, the il delay will cancel out of the resultant time differences Otl, Otz ... Otn. Accordingly, the subscriber unit 401 can be located using hyperbolas 861, 862 as previously described.
Another embodiment shown in Figures 11,12 and 13 uses a base station 361 with multiple antennas 881, 882 ... 88". Two of the antennas 881, 882 lie along a centerline 92 at a known distance, l, apart as shown in Figure 11. Both antennas 881, 88z receive the assigned pilot signal 901, 902 from the subscriber unit 401.
However, the antenna 882 further away from the subscriber unit 401 receives the signal over a slightly longer distance d1' and with a slight delay with respect to the nearer antenna 881. This delay results in a carrier phase difference, ~, between the signals received at each antenna as shown on Figure 13. A processor 66 using the received carrier phase difference and the chip code sequence recovered by each assigned pilot chip code recovery means 961, 962 ... 96" can determine the location of the subscriber unit 401 as follows.
As shown in Figure 12, the subscriber unit 401 is located at distance dl at angle a from the centerline 92 of the antennas 881, 882. As seen at the scale of Figure 12 both received assigned pilot signals 901, 902 appear to be coincident.
However, as shown in Figure 11, the received assigned pilot signals 901, 902 are slightly separated. The received assigned pilot signal 901 returning to the first antenna 881 travels a distance dl. The received assigned pilot signal 902 returning to the second antenna 882 travels a slightly longer distance dl'. As shown in Figure 11, the difference between the two distances d1, dl' is a distance m.
Since the distances dl, dl' between the antennas 881, 882 and the subscriber unit 401 are much larger than the distance Z between the antennae 881, 882 both received assigned pilot signals 901, 902 follow approximately parallel paths.
By constructing a right triangle using a point 94 which is distance dl from the subscriber unit 401 as shown in Figure 11, the angle « can be determined by the following geometric relationship:
« = COS'1 (m/~. Equation (9) The distance m can be determined by using the carrier phase difference, ~, between the two received signals 901, 902 as follows:
Equation (10)
SYSTEM
Field of the Invention This invention generally relates to spread spectrum code division multiple access (CDMA) communication systems. More particularly, the present invention relates to a system and method that determines the geographic location of a subscriber unit within a CDMA communication system.
Description of the Prior Art Wireless systems capable of locating a subscriber are presently known in the art. One wireless technique uses the global positioning system (GPS). In GPS, the communication handset receives data transmitted continuously from the 24 NAVSTAR satellites. Each satellite transmits data indicating the satellite's identity, the location of the satellite and the time the message was sent. The handset compares the time each signal was received with the time it was sent to determine the distance to each satellite. Using the determined distances between the satellites and the handset along with the location of each satellite, the handset can triangulate its location and provide the information to a communication base station.
However, the incorporation of a GPS within a subscriber unit increases its cost.
--- --- -- ~~Lra euyL nvrtvit;.r.c. US 009920257 1 J-E~4-200 j Another subscriber location technique is disclosed in TJ.S. Patent hlo.
5,732,354. A mobile telephone using time division multiple access (TDMA) as the aiz interface is located within a plurality of base stations. The mobile telephone measures the received signal strength from each of the base stations and transmits each strength to each respective base station. At a mobile switching center, the zeceived signal strengths from the base stations are compared and processed. 'The result yields the distance between the mobile telephone and each base station. From these distances, the location of the nrxobile telephone is calculated.
Wireless communication systems using spread spectrum modulation techniques are increasing in popularity. ~n code division multiple access (CDMA) systems, data is transmitted using a wide bandwidth (spread spectrum) by modulating the data with a pseudo random chip code sequence. The advantage gained xs rhat CbMA systems arc more resistant to signal distortion and interfering frequencies in the transmission path than communication systems usiing the more connmo~a time division multiple access (TDM.A) or frequency division multiple access (F77MA) techniques.
EP 0 865 223 AZ is a position estimation scheme for a cellular mobile system. A Burst and a second signal sequence are exchanged between the mobile station and the base station. These signals may be CDMA signals. A phase difference between the first and second sequence is used to determine a distance _2_ Emvfan8steit l9.Aar. 15:48 AMENDED SHEET
~....s, im ~iv .»v t7~otr YULY~ A1V~ ltU~N1(a,Y.G.
:19-04-2001 , US 009920257 CA 02367572 2001-09-21 , between the mobile and base station. Using multiple base stations, the position is estimated usi~ag triangulation.
U.S. Patent No. 5,600,705 is a position systenausing a range determination in a CDMA system. The system uses pilot signals and time difference of arrival ('l'DOA) and absolute tithe of arrival (TOA) in the position determination.
WO 9$118018 discloses locating a ~onobile te~ninal using two antennas of an array in a time division multiple access communication system. A plisse difference in the signals received by the two antennas is used to determine an angle fxom the ce~aterline of the antennas to the mobile terminal. Received signal strength is used to estimate the tern~nal's distance. The terminal's location is determined using the determined angle and distance.
'VfO 97147148 discloses deternnining aposit<on of amobile tcrnrinalwithin a cellular system A signal is transmitted at a low power level, The power level is temporarily increased. The signal transmitted at the increased power level is . used to make a position measurement of the terminal.
U.S. Patent Na. 5,'736,964 discloses a CDMA, system for locating a communication unit. A base station transmits a location request to the unit.
The unit transmits a receive time Qf~the message to the.base station. A group of base stations also determine a receive time of a symbol sequence iu the unit's ~0 transmissions. Using the time measurements, the location of the unit is determined.
-2a-Emafangsteit l9.Apr. 15;48 AMENDED SHEET
us : 4s FAX 215 588 B499 yOF.PE AND KOENIG, P. C. US 009920257 .19-04-2001 -'CJ.S. Patent No, 5,SQ6,864 discloses a system,for detex~minina a distance between a base station and a remote unit in a CDMA system. The base station transmits a base CDMA. signal to the remote unit. The remote unit transmits a remote CDMA. signal to the base station. The remote CDMA signal has its timing synchronized to 'the received base CDMA signal. The base station determines the distance to the remote unit by comparing the chip code sequences of the transmitted base CD1VIA signal and the received remote CDMA signal.
There exists a need for an accurate mobile subscriber unit location system that uses data already available in an existing CDMA communication system -2b-Emvfangszeit l9:Avr. 15:4g AMENDED SHEET
_ 19-04-2001 _Q9v 48 FI~ 215 588, 6499 . VOLPE ~3ND KOENIG,P. C. US 009920257 SUMMARY OF T'~ 1NV'ENTIOI~
A subscriber unit is geographically located using a plurality of base stations in a wireless CDMA communication system Each base station transmits a first spread spectrum signal having a first code. For.each received first signal, the subscriber unit transmits a second spread spectrum signal having a~second code. The second spread spectrum signal is time synchronized with its received first signal. An impulse response of each received ft~rst signal is analyzed to determine a first received component, At each base station, an impulse response of that base station's received second signal is analyzed to determine a first .. . ~ 10 received component. A distance between each base station and the subscriber unit is. determined. The distance determination is based on in part a timing difference between the received signal and the transmitted signal and the determined first received component for the second signals. The location of the subscriber unit is based on in part the deternaiued distances, a fixed location of each base station and a maximum likelihood estimation.
B~iIEF DESCRIPTION OF 1'HE ~.7lt.A.VVINGS
Figuure 1 is an illustration of a simplified, prior art CDMA system.
Figure 2 is an illustration of a prior art CDMA system.
Figure 3 is a block diagram of major components witba~n a prior art CD1VIA system.
EmofangsZeit l9.Avr. 15;48 AMENDED SHEET
.19-04-2001 -_ -- _ _ ___ _- -____._ _-__._. US 009920257 vamai~i 08:49 FAX 215 56B 6488 VOLPE AND KOENIG.P.C. r~uua Figure 4 is a block diagram of components within a prior art CDM~A
system.
k'igure 5 is an illustration of a global~pilot signal and an assigned pilot signal being communicated between a base stafiion and a subscriber unit.
-3a-EmpfangsZeit 19.A~r, 15:48 AMENDED SHEET
Figure 6 is a block diagram of a first embodiment of the present invention using at least three base stations.
Figure 7 is an illustration of locating a subscriber unit using the first embodiment of the present invention with at least three base stations.
Figure 8 is a block diagram of a second embodiment of the present invention showing components used in a subscriber unit.
Figure 9 is an illustration of locating a subscriber . unit using the second embodiment of the present invention with two base stations.
Figure 10 is an illustration of locating a subscriber unit using the second embodiment of the present invention with more than two base stations.
Figure 11 is a detailed illustration of the third embodiment of the present invention having a base station with multiple antennas.
Figure 12 is an illustration of the third embodiment having a base station with multiple antennas.
Figure 13 is a block diagram of components used in the third embodiment.
Figure 14 is an illustration of multipath.
Figure 15 is a graph of a typical impulse response of multipath components.
Figure 16 is a block diagram of components within a fourth embodiment correcting for multipath.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments will be described with reference to the drawing figures where like numerals represent like elements throughout.
Shown in Figure 1 is a simplified CDMA communication system. A data signal with a given bandwidth is mixed with a spreading code generated by a pseudo random chip code sequence generator producing a digital spread spectrum signal.
Upon reception, the data is reproduced after correlation with the same pseudo random chip code sequence used to transmit the data. Every other signal within the transmission bandwidth appears as noise to the signal being despread.
For timing synchronization with a receiver, an unmodulated pilot signal is required for every transmitter. The pilot signal allows respective receivers to synchronize with a given transmitter, allowing despreading of a traffic signal at the receiver.
In a typical CDMA system, base stations send global pilot signals to all subscriber units within their communicating range to synchronize transmissions in a forward direction. Additionally, in some CDMA systems, for example a B-CDMATM system, each subscriber unit sends a unique assigned pilot signal to synchronize transmissions in a reverse direction.
Figure 2 illustrates a CDMA communication system 30. The communication system 30 comprises a plurality of base stations 36,, 362 ... 36n. Each base station 361, 362 ... 36" is in wireless communication with a plurality of subscriber units 401, 402 ... 40", which may be fixed or mobile. Each subscriber unit 401, 402 ...
40"
communicates with either the closest base station 361 or the base station 361 which provides the strongest communication signal. Each base station 361, 362 ...
36~ is in communication with other components within the communication system 30 as shown in Figure 3.
A local exchange 32 is at the center of the communications system 30 and communicates with a plurality of network interface units (N>ZJs) 341, 342 ...
34".
Each N1U is in communication with a plurality of radio carrier stations (RCS) 381, 382 ... 38" or base stations 361, 362 ... 36~. Each (RCS) 381, 382 ... 38" or base station 361, 362 ... 36n communicates with a plurality of subscriber units 401, 402 .:. 40~
within its communicating range.
Figure 4 depicts a block diagram of the pertinent parts of an existing spread spectrum CDMA communication system. Each independent base station 361, 362 ...
36" generates a unique global pilot signal using a global pilot chip code generating means 421 and spread spectrum processing means 441. The global pilot chip code generating means 421 generates a unique pseudo random chip code sequence. The unique pseudo random chip code sequence is used to spread the resultant signals bandwidth such as to 15 MHZ as used in the B-CDMATM air interface. The spread spectrum processing means modulates the global pilot chip code sequence up to a desired center frequency. The global pilot signal is transmitted to all subscriber units 401 by the base station's transmitter 461.
A receiver 481 at a subscriber unit 401 receives available signals from a plurality of base stations 361, 362 ... 36". As shown in Figure 5, the global pilot 501 travels from the base station 361 to the subscriber unit 401 and can be represented as:
~1- al.
c Equation (1) The time the signal travels from the base station 361 to the subscriber unit 401, in equals the distance between the base station 361 and subscriber unit 401, dl, divided by the speed of light, c.
Refernng back to Figure 4, a global pilot chip code recovery means 541 within the subscriber unit 401 can receive global pilot chip code sequences from a plurality of base stations 361, 362 ... 36". The subscriber unit 401 generates a replica of a global pilot chip code sequence and synchronizes the generated replica's timing with the received global pilot 501. The subscriber unit 401 also has a processor 821 to perform the many analysis functions of the subscriber unit 401.
The subscriber unit 401 generates an assigned pilot signal 521 using assigned pilot chip code generating means 561 and spread spectrum processing means 581.
The assigned pilot chip code generating means 561 generates a pseudo random chip code sequence with its timing synchronized with the recovered global pilot chip code sequence. As a result, the assigned pilot chip code sequence is delayed by il with respect to the base station 361, 362 ... 36". The spread spectrum processing means 581 generates the assigned pilot signal 521 by modulating the assigned pilot chip code sequence up to a desired center frequency. The assigned pilot signal 521 is transmitted to all base stations 361, 362 ... 36" within range to receive the assigned pilot signal 521.
The base station 361 receives the assigned pilot signal 521 with the base station's receiver 621. The received assigned pilot 521 travels the same distance dl as the global pilot signal 501 as shown in Figure 5. Accordingly, the received ' assigned pilot signal will be delayed by ~l with respect to the mobile unit 401 and by 2i1 with respect to the global pilot 501 generated at the base station 361.
Since the chip code sequence of the assigned pilot 521 received at the base station 361 will be delayed by 2i1 with respect to the chip code sequence of the global pilot signal 501 generated at the base station 361, the round trip propagation delay, 2~1, can be determined by comparing the timing of the two chip code sequences. Using the round trip propagation delay, 2i1, the distance dl between the base station 361 and subscriber unit 401 can be determined by:
dl - c ~ 2i1.
Equation (2) _g_ If a spreading sequence having a chipping rate of at least 80ns is used and the communication system has the ability to track 1/16''' of a chip, the distance d1 can be measured to within 2 meters.
Figure 6 is a block diagram of a first embodiment of the present invention.
No additional hardware is required in the subscriber unit 401. The only changes are implemented by software within the subscriber unit's processor 821 and the processors 661, 662 ... 66", 68, 701, 702 ... 70" located within the base station 361, NIU
341 or Local Exchange 321, Precincts 741, 742 ... 74" and Ambulance Dispatcher 76.
The subscriber unit 401 is sent a signal by a base station 361 indicating that a 911 call was initiated and to begin the subscriber location protocol. Upon receipt, the subscriber unit 401 will sequentially synchronize its transmission chip code sequence to at least three base stations' chip code sequences. To allow reception by the base stations 362, 363 ... 36~ outside of the subscriber unit's normal communicating range, these transmissions will be sent at a higher than normal power level temporarily over-riding any adaptive power control algorithms.
A processor 661 within each base station 361, 362 ... 36n is coupled to the assigned pilot chip code recovery means 641 and the global pilot chip code generator 421. The processor 661 compares the two chip code sequences to determine the round trip propagation delay il, i2 ... i" and the respective distance dl, d2 ... do between the subscriber unit 401 and the respective base station 361, 362 ...
36n.
Within either a NIIJ 341 or the local exchange 32, a processor 68 receives the distances dl, d2 ... do from the processors 661, 662 ... 66" within all the base stations 361, 362 ... 36". The processor 68 uses the distances dl, dz ... do to determine the location of the subscriber unit 401 as follows.
By using the known longitude and latitude from three base stations 361, 362, 363 and distances d,, d2, d3, the location of the subscriber unit 401 is determined. As shown in Figure 7 by using the three distances dl, d2, d3, three circles 781, 782, 783 with radiae 801, 802, 803 are constructed. Each circle 781, 782, 783 is centered around a respective base station 361, 362, 363. The intersection of the three circles 781, 782, 783 is at the location of the subscriber unit 401.
Using the Cartesian coordinates, the longitude and latitude corresponding with each base station 361, 362 ... 36" is represented as X", Y", where X" is the longitude and Y" is the latitude. If X, Y represents the location of the subscriber unit 401, using the distance formula the following equations result:
(Xl-X)2 +(Yl-Y)2 = d12 Equation (3) (XZ_~2 +(y2_y)2 = d22 Equation (4) (X3_2 +(y3_y)2 - d32 Equation (5) In practice due to small errors in calculating the distances dl, d2 , d3, Equations 3, 4 and 5 cannot be solved using conventional algebra. To compensate for the errors, a maximum likelihood estimation is used to determine the location and are well known to those skilled in the art. For increased accuracy, additional base stations 364, 365 ... 36" can be used to calculate additional distances for inclusion in the estimation analysis.
The subscriber unit's location is sent through the communication system 30 to at least one precinct 741, 742 ... 74" and an ambulance dispatcher 76. A
processor 701 within each precinct 741, 742 ... 74" and the ambulance dispatcher 76 receives the location of all 911 calls originating in the system and displays the location on a conventional computer monitor 721. The display comprises a listing of all 911 calls and addresses on a geographic map.
~ 0 An alternate approach reduces the number of processors by transmitting raw data through the communication system 30 and processing the raw data at a single site.
Figure 8 is a second embodiment of a location system. At least two base stations 361, 362 ... 36" have their internal timing synchronized with each other and transmit their respective global pilot signals 521, 522 ... 52" with time synchronized chip code sequences. The subscriber unit 401 receives the global pilots 521, 522 ...
52". However, the received global pilots 521, 522 ... 52" are not synchronized. The global pilot 521 from a first base station 361 will travel distance dl and is delayed by il. The global pilot 522 from a second base station 362 travels distance d2 and is delayed by ~2. The subscriber unit 401 recovers each base station's global pilot chip code sequence with its global pilot chip code recovery means 541. A processor within the subscriber unit 401 is coupled to each global pilot chip code recovery means 541, 522 ... 54". The processor 821 compares the chip code sequences of each pair of pilot chip code sequences and calculates the time differences ~tl, Otz ... 0t"
between the sequences as follows.
Within the subscriber unit 401, the chip code sequences used by each base station 361, 362 ... 36" are stored. After synchronizing with.the first base station's pilot 361, the processor 821 will store where within the sequence synchronization was obtained. This process is repeated for the other base stations 362, 363 ...
36". The synchronization process can be done sequentially (synchronizing to the first base station's chip code sequence then the second, etc.) or in parallel (synchronizing to all base stations at the same time).
By using the relative time difference between il, i2, ... i" each base station's chip code sequence and knowing that each base station's pilot was sent at the same time, with two base stations the time differences are calculated as follows:
W ='~2 -il Equation (6) ~t2 = '~3-i2 Equation (7) The time differences Otl, ~tz ... Ot" are transmitted to at least one of the base stations 361.
At least one base station 361 recovers the time difference data from the received signals using time difference recovery means 841. The time difference data is sent with the distance data dl through the communications system to a processor 68. The processor 68 determines the location of the subscriber unit 401 using the time difference data Otl, Otz ... fit" and the distance data dl, d2 .., d" as follows.
Using information from only two base stations 361, 362 as shown in Figure 9, the processor uses distances dl, dz to create two circles 781, 782. Using the time difference, Otl, a hyperbola 861 can be constructed as follows.
All the points along the hyperbola 861 receive the global pilot signals 521, from the synchronized base stations 361, 362 with the same time difference, ~tl. The time difference ~tl can be converted to a distance difference Odl by substituting ~tl for tl and ~dl for dl in Equation 1. Using the distance formula and X, Y as the location of the subscriber unit 401, the following equation results:
Qdl = ~~,1 _~2 +lYl _ ~2 _ ~XZ _~2 +~Y2 _ ~2 Equation (8) By using Equation 8 with Equations 3 and 4 in a maximum likelihood estimation, the location of the subscriber unit 401 can be determined. The subscriber unit's location is subsequently sent to the nearest police precinct 741, 742 ... 74n and ambulance dispatcher 76 in the cellular area.
For improved accuracy, additional base stations 361, 362 ... 36" are used.
Figure 10 shows the invention used with three base stations 361, 362, 363. The distances dl, d2, d3 are used to create three circles 781, 782, 783. Using time differences Otl, Otz, two intersecting hyperbolas 861, 862 are constructed.
With maximum likelihood estimation, the subscriber units' location calculated with two hyperbolas 861, 862, and three circles 781, 782, 783 yields greater accuracy.
As shown in Figure 8, the subscriber unit 401 is required to process each global pilot chip code sequence to determine the time differences Otl, ~tz ...
Ot".
An alternate approach removes the processing from the subscriber unit 401.
With reference to Figure 6, the mobile unit 401 will synchronize the assigned pilot to one of the base station's global pilot chip code sequences, such as the nearest base station 361 with a delay of ~1. The assigned pilot 501 is transmitted to all base stations 361, 362 ... 36". The assigned pilot 501 will be received at each base station with a respective delay, il + i1, il + i2, il + i3. Each base station 361, 362 ... 36" will send the delayed chip code sequence along with the calculated distance to a processor 68 located in a N1U 341 or local exchange 32. The processor 68 will calculate the time differences Otl, Otz ... Ot" by comparing the received assigned pilot chip code sequences. Since all received assigned pilot chip code sequences are delayed by ~1, the il delay will cancel out of the resultant time differences Otl, Otz ... Otn. Accordingly, the subscriber unit 401 can be located using hyperbolas 861, 862 as previously described.
Another embodiment shown in Figures 11,12 and 13 uses a base station 361 with multiple antennas 881, 882 ... 88". Two of the antennas 881, 882 lie along a centerline 92 at a known distance, l, apart as shown in Figure 11. Both antennas 881, 88z receive the assigned pilot signal 901, 902 from the subscriber unit 401.
However, the antenna 882 further away from the subscriber unit 401 receives the signal over a slightly longer distance d1' and with a slight delay with respect to the nearer antenna 881. This delay results in a carrier phase difference, ~, between the signals received at each antenna as shown on Figure 13. A processor 66 using the received carrier phase difference and the chip code sequence recovered by each assigned pilot chip code recovery means 961, 962 ... 96" can determine the location of the subscriber unit 401 as follows.
As shown in Figure 12, the subscriber unit 401 is located at distance dl at angle a from the centerline 92 of the antennas 881, 882. As seen at the scale of Figure 12 both received assigned pilot signals 901, 902 appear to be coincident.
However, as shown in Figure 11, the received assigned pilot signals 901, 902 are slightly separated. The received assigned pilot signal 901 returning to the first antenna 881 travels a distance dl. The received assigned pilot signal 902 returning to the second antenna 882 travels a slightly longer distance dl'. As shown in Figure 11, the difference between the two distances d1, dl' is a distance m.
Since the distances dl, dl' between the antennas 881, 882 and the subscriber unit 401 are much larger than the distance Z between the antennae 881, 882 both received assigned pilot signals 901, 902 follow approximately parallel paths.
By constructing a right triangle using a point 94 which is distance dl from the subscriber unit 401 as shown in Figure 11, the angle « can be determined by the following geometric relationship:
« = COS'1 (m/~. Equation (9) The distance m can be determined by using the carrier phase difference, ~, between the two received signals 901, 902 as follows:
Equation (10)
2 ~c The distance m equals the phase difference between the two signals, ~, in radians multiplied by the wavelength of the signal, ~,, divided by 2~. The wavelength, ~,, can be derived from the known frequency f of the assigned pilot signal as follows:
~, = clf.
Equation (11) The processor 68 also compares the chip code sequences of the global pilot generating means 421 with the recovered assigned pilot chip code sequence to determine the distance dl as shown in Figure 6. Using both the angle « and distance dl, the processor 661 locates the subscriber unit 401 using simple geometry.
There are many techniques well known to those skilled in the art to eliminate the ambiguity between locations above and below the antennas 881, 882. One such technique is using antennas employing sectorization. Subsequently, the subscriber unit's location is sent to the precincts 741, 742 ... 74n and ambulance dispatcher 76.
Additional antennas may be used to improve on the accuracy of the system.
An alternate embodiment uses more than one base station 361, 362 ... 36". A
processor 68 located within either a NIL1 341 or the local exchange 32 collects distance and angle information from more than one base station 361, 362 ...
36" as well as the time differences ~tl, Otz ... Otn, between the base stations 361, 362... 36".
Using the maximum likelihood estimation technique, the processor 68 determines a more accurate location of the subscriber unit 401.
A fourth embodiment corrects for multipath. Figure 14 illustrates multipath.
A signal such as a global pilot signal is transmitted from a base station 361.
The signal follows a multitude of paths 981, 982 ... 98" between the base station 361 and subscriber unit 401.
Figure 13 is a graph showing the impulse response 136 of the received multi-path components. Since each received multipath component travels a unique path, it arrives at a receiver with a propagation delay determined by the length of the path 98,,982...98". The impulse response 106 shows the collective signal magnitude of all the multipath components received at each propagation delay.
The previously described subscriber unit location techniques assumed the sub-scriber unit 401 synchronizes with the line of sight multipath component 981 traveling distance dl. However, if the subscriber unit synchronizes with a non-line of sight multipath component 981,982...98", the distance calculation will be in error due to the delay MD1 as shown in Figure 15.
Figure 16 is a system correcting for errors resulting from multipath. The global pilot 501 is sent from the base station 361 to subscriber unit 401. The subscrit~er unit 401 collects all of the multipath components using a multipath receiver 1021 such as disclosed in U.S. Patent No. 5,796,776, Lomp et al. A processor 821 within the subscriber unit 401 analyzes the impulse response 100 of the received global pilot signal 501.
Since the line of sight multipath component 981 travels the shortest distance dl, the first received component 981 is the line of sight component. If the line of sight component is not received, the first received component 981 will be the closest and, accordingly, the best available estimate for the line of sight component. The processor 821 compares the chip code sequence of the first received component with the chip code sequence used to synchronize the assigned pilot chip code sequence. This comparison determines the delay due to multipath, MDl. The multipath delay, MDI, is transmitted to the base station 361.
A processor 661 and multipath receiver 1041 within the base station 361 perform the same analysis on the received assigned pilot signal. As a result, the multipath delay, MD2, of the assigned pilot signal is determined.
Additionally, multipath delay recovery means 1061 recovers the transmitted global pilot signal's multipath delay MDl for use by the processor 661. The processor 661 compares the generated global pilot chip code sequence to the recovered assigned pilot chip code sequence to determine the round trip propagation delay 2i1. To correct for multipath, the processor 661 subtracts both the global pilot signal's multipath delay MDl and the assigned pilot signals multipath delay MD2 from the calculated round trip propagation delay, 2i1. The corrected round trip propagation delay is used to determine the subscriber unit's location in one of the techniques as previously described.
Although the invention has been described in part by making detailed reference to certain specific embodiments, such detail is intended to be instructive rather than restrictive. It will be appreciated by those skilled in the art that many variations may be made in the structure and mode of operation without departing from the scope of the invention as disclosed in the teachings herein.
~, = clf.
Equation (11) The processor 68 also compares the chip code sequences of the global pilot generating means 421 with the recovered assigned pilot chip code sequence to determine the distance dl as shown in Figure 6. Using both the angle « and distance dl, the processor 661 locates the subscriber unit 401 using simple geometry.
There are many techniques well known to those skilled in the art to eliminate the ambiguity between locations above and below the antennas 881, 882. One such technique is using antennas employing sectorization. Subsequently, the subscriber unit's location is sent to the precincts 741, 742 ... 74n and ambulance dispatcher 76.
Additional antennas may be used to improve on the accuracy of the system.
An alternate embodiment uses more than one base station 361, 362 ... 36". A
processor 68 located within either a NIL1 341 or the local exchange 32 collects distance and angle information from more than one base station 361, 362 ...
36" as well as the time differences ~tl, Otz ... Otn, between the base stations 361, 362... 36".
Using the maximum likelihood estimation technique, the processor 68 determines a more accurate location of the subscriber unit 401.
A fourth embodiment corrects for multipath. Figure 14 illustrates multipath.
A signal such as a global pilot signal is transmitted from a base station 361.
The signal follows a multitude of paths 981, 982 ... 98" between the base station 361 and subscriber unit 401.
Figure 13 is a graph showing the impulse response 136 of the received multi-path components. Since each received multipath component travels a unique path, it arrives at a receiver with a propagation delay determined by the length of the path 98,,982...98". The impulse response 106 shows the collective signal magnitude of all the multipath components received at each propagation delay.
The previously described subscriber unit location techniques assumed the sub-scriber unit 401 synchronizes with the line of sight multipath component 981 traveling distance dl. However, if the subscriber unit synchronizes with a non-line of sight multipath component 981,982...98", the distance calculation will be in error due to the delay MD1 as shown in Figure 15.
Figure 16 is a system correcting for errors resulting from multipath. The global pilot 501 is sent from the base station 361 to subscriber unit 401. The subscrit~er unit 401 collects all of the multipath components using a multipath receiver 1021 such as disclosed in U.S. Patent No. 5,796,776, Lomp et al. A processor 821 within the subscriber unit 401 analyzes the impulse response 100 of the received global pilot signal 501.
Since the line of sight multipath component 981 travels the shortest distance dl, the first received component 981 is the line of sight component. If the line of sight component is not received, the first received component 981 will be the closest and, accordingly, the best available estimate for the line of sight component. The processor 821 compares the chip code sequence of the first received component with the chip code sequence used to synchronize the assigned pilot chip code sequence. This comparison determines the delay due to multipath, MDl. The multipath delay, MDI, is transmitted to the base station 361.
A processor 661 and multipath receiver 1041 within the base station 361 perform the same analysis on the received assigned pilot signal. As a result, the multipath delay, MD2, of the assigned pilot signal is determined.
Additionally, multipath delay recovery means 1061 recovers the transmitted global pilot signal's multipath delay MDl for use by the processor 661. The processor 661 compares the generated global pilot chip code sequence to the recovered assigned pilot chip code sequence to determine the round trip propagation delay 2i1. To correct for multipath, the processor 661 subtracts both the global pilot signal's multipath delay MDl and the assigned pilot signals multipath delay MD2 from the calculated round trip propagation delay, 2i1. The corrected round trip propagation delay is used to determine the subscriber unit's location in one of the techniques as previously described.
Although the invention has been described in part by making detailed reference to certain specific embodiments, such detail is intended to be instructive rather than restrictive. It will be appreciated by those skilled in the art that many variations may be made in the structure and mode of operation without departing from the scope of the invention as disclosed in the teachings herein.
Claims (12)
1. A method for geographically locating a subscriber unit (40 1) using a plurality of base stations (36) in a wireless CDMA communication system, each base station (36) transmitting a first spread spectrum signal having a first code, for each received first signal, the subscriber unit (401) transmits a second spread spectrum signal having a second code to that received first signal's base station (36) time synchronized with that received first signal, the method characterized by:
for each received first signal at the subscriber unit (40 1), analyzing an impulse response of multipath components of that received first signal to determine a first received component of that received first signal;
at each base station (36), analyzing an impulse response of multipath compon-ents of that base station's received second signal to determine a first received component of that base station's received second signal;
for each base station (36), determining a distance between that base station (36) and the subscriber unit (40 1) based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal; and determining the location of the subscriber unit (40 1) based on in part the deter-mined distances, a fixed location of each base station (36) and a maximum likelihood estimation.
for each received first signal at the subscriber unit (40 1), analyzing an impulse response of multipath components of that received first signal to determine a first received component of that received first signal;
at each base station (36), analyzing an impulse response of multipath compon-ents of that base station's received second signal to determine a first received component of that base station's received second signal;
for each base station (36), determining a distance between that base station (36) and the subscriber unit (40 1) based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal; and determining the location of the subscriber unit (40 1) based on in part the deter-mined distances, a fixed location of each base station (36) and a maximum likelihood estimation.
2. The method of claim 1 further characterized by the base stations (36) are time synchronized to each other; the subscriber unit (40 1) determines a time difference of reception between the received first signals and transmits a representation of the time difference; and the maximum likelihood estimation uses the determined time difference to determine the subscriber unit location.
3. The method of claim 1 further characterized by the base stations (36) are tune synchronized to each other; a time difference of reception between each base station's received second signal is determined; and the maximum likelihood estimation uses the determined time difference to determine the subscriber unit location.
4. The method of claim 2 or 3 further characterized by using a formula for a hyperbola associated with each time difference and a formula for a circle associated with each determined distance in the maximum likelihood estimation.
5. The method of claim 1, 2, 3 or 4 further characterized by the transmission of each second signal is time synchronized to the determined first received component of its received first signal.
6. The method of claim 1, 2, 3 or 4 further characterized by the subscriber unit (40,) transmitting, for each base station (36), a representation of a time difference between the first received component of that base station's received second signal and a synchronization time of the transmitted second signal of that base station (36).
7. A wireless CDMA communication system for locating a subscriber unit (40,) using a plurality of base stations (36), each base station (36) transmitting a first spread spectrum signal having a first code, for each received first signal, the sub-scriber unit (40 1) transmits a second spread spectrum signal having a second code to that received first signal's base station (36) time synchronized with that received first signal, the system characterized by:
the subscriber unit (40 1) comprising means (82 1), for each received first signal, for analyzing an impulse response of multipath components of that received first sig-nal to determine a first received component of that received first signal;
each base station (36) comprising means (66) for analyzing an impulse re-sponse of multipath components of that base station's received second signal to determine a first received component of that base station's received second signal, means for determining a distance between that base station (36) and the subscriber unit (40) based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal;
and means (66, 68, 70) for determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station (36) and a maximum likelihood estimation.
the subscriber unit (40 1) comprising means (82 1), for each received first signal, for analyzing an impulse response of multipath components of that received first sig-nal to determine a first received component of that received first signal;
each base station (36) comprising means (66) for analyzing an impulse re-sponse of multipath components of that base station's received second signal to determine a first received component of that base station's received second signal, means for determining a distance between that base station (36) and the subscriber unit (40) based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal;
and means (66, 68, 70) for determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station (36) and a maximum likelihood estimation.
8. The system of claim 7 further characterized by the base stations(36) are time synchronized to each other; the subscriber unit (40 1) having means (82 1) for determining a time difference of reception between the received first signals;
and means (60 1) for transmitting a representation of the time difference; and the maximum likelihood estimation using the determined time difference to determine the subscriber unit location.
and means (60 1) for transmitting a representation of the time difference; and the maximum likelihood estimation using the determined time difference to determine the subscriber unit location.
9. The system of claim 7 further characterized by the base stations (36) are time synchronized to each other; the system further comprising means (66, 68, 70) for determining a time difference of reception between each base station's received second signal; and the maximum likelihood estimation using the determined time difference to determine the subscriber unit location.
10. The system of claim 8 or 9 further characterized by using a formula for a hyperbola associated with each time difference and a formula for a circle associated with each determined distance in the maximum likelihood estimation.
11. The system of claim 7, 8, 9 or 10 further characterized by the transmission of each second signal is time synchronized to the determined first received component of its received first signal.
12. The system of claim 7, 8, 9 or 10 further characterized by the subscriber unit (40 1) comprising means (60 1) for transmitting for each base station, a representation of a time difference between the closest line of sight component and a synchronization time of the transmitted second signal of that base station (36).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2489816A CA2489816C (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/274,081 US6603800B1 (en) | 1999-03-22 | 1999-03-22 | CDMA location |
| US09/274,081 | 1999-03-22 | ||
| PCT/US1999/020257 WO2000057661A1 (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2489816A Division CA2489816C (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
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| Publication Number | Publication Date |
|---|---|
| CA2367572A1 CA2367572A1 (en) | 2000-09-28 |
| CA2367572C true CA2367572C (en) | 2005-03-22 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2767090A Abandoned CA2767090A1 (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
| CA2489816A Expired - Fee Related CA2489816C (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
| CA002367572A Expired - Fee Related CA2367572C (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
Family Applications Before (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2767090A Abandoned CA2767090A1 (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
| CA2489816A Expired - Fee Related CA2489816C (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
Country Status (20)
| Country | Link |
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1999
- 1999-03-22 US US09/274,081 patent/US6603800B1/en not_active Expired - Lifetime
- 1999-09-03 CA CA2767090A patent/CA2767090A1/en not_active Abandoned
- 1999-09-03 ES ES04027093T patent/ES2316914T3/en not_active Expired - Lifetime
- 1999-09-03 EP EP08014870A patent/EP1988736A3/en not_active Withdrawn
- 1999-09-03 CN CNB998164747A patent/CN1189056C/en not_active Expired - Fee Related
- 1999-09-03 IL IL14528399A patent/IL145283A0/en active IP Right Grant
- 1999-09-03 CA CA2489816A patent/CA2489816C/en not_active Expired - Fee Related
- 1999-09-03 AU AU58069/99A patent/AU756930B2/en not_active Ceased
- 1999-09-03 ES ES99945478T patent/ES2232173T3/en not_active Expired - Lifetime
- 1999-09-03 BR BRPI9917225-9A patent/BR9917225B1/en not_active IP Right Cessation
- 1999-09-03 SG SG200201895A patent/SG127676A1/en unknown
- 1999-09-03 JP JP2000607432A patent/JP3765984B2/en not_active Expired - Fee Related
- 1999-09-03 AT AT99945478T patent/ATE282935T1/en not_active IP Right Cessation
- 1999-09-03 SG SG200201894A patent/SG126694A1/en unknown
- 1999-09-03 DE DE69922054T patent/DE69922054T2/en not_active Expired - Lifetime
- 1999-09-03 EP EP04027093A patent/EP1513366B1/en not_active Expired - Lifetime
- 1999-09-03 AT AT04027093T patent/ATE413782T1/en not_active IP Right Cessation
- 1999-09-03 CA CA002367572A patent/CA2367572C/en not_active Expired - Fee Related
- 1999-09-03 EP EP99945478A patent/EP1163819B1/en not_active Expired - Lifetime
- 1999-09-03 KR KR10-2001-7011877A patent/KR100454309B1/en not_active IP Right Cessation
- 1999-09-03 WO PCT/US1999/020257 patent/WO2000057661A1/en active IP Right Grant
- 1999-09-03 MX MXPA01009520A patent/MXPA01009520A/en active IP Right Grant
- 1999-09-03 DE DE69939884T patent/DE69939884D1/en not_active Expired - Lifetime
- 1999-09-03 DK DK04027093T patent/DK1513366T3/en active
- 1999-09-03 ID IDW00200102042A patent/ID30242A/en unknown
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2000
- 2000-03-15 TW TW089104718A patent/TW478285B/en not_active IP Right Cessation
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2001
- 2001-09-04 IL IL145283A patent/IL145283A/en not_active IP Right Cessation
- 2001-09-18 NO NO20014539A patent/NO326457B1/en not_active IP Right Cessation
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2002
- 2002-02-12 US US10/074,399 patent/US6798824B2/en not_active Expired - Lifetime
- 2002-02-12 US US10/074,398 patent/US6748008B2/en not_active Expired - Lifetime
- 2002-05-02 HK HK02103322.1A patent/HK1041757B/en not_active IP Right Cessation
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2004
- 2004-05-04 US US10/838,599 patent/US7116701B2/en not_active Expired - Fee Related
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- 2005-09-01 HK HK05107689.6A patent/HK1076343A1/en not_active IP Right Cessation
- 2005-09-30 JP JP2005287696A patent/JP2006094538A/en active Pending
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2008
- 2008-08-14 NO NO20083541A patent/NO20083541L/en not_active Application Discontinuation
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