CA2343237C - Call maintenance during position location - Google Patents
Call maintenance during position location Download PDFInfo
- Publication number
- CA2343237C CA2343237C CA002343237A CA2343237A CA2343237C CA 2343237 C CA2343237 C CA 2343237C CA 002343237 A CA002343237 A CA 002343237A CA 2343237 A CA2343237 A CA 2343237A CA 2343237 C CA2343237 C CA 2343237C
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- CA
- Canada
- Prior art keywords
- position location
- information
- subscriber unit
- base station
- location procedure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/23—Testing, monitoring, correcting or calibrating of receiver elements
- G01S19/235—Calibration of receiver components
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/246—Acquisition or tracking or demodulation of signals transmitted by the system involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
- G01S19/254—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to Doppler shift of satellite signals
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
- G01S19/256—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to timing, e.g. time of week, code phase, timing offset
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
-
- 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
- G01S5/0009—Transmission of position information to remote stations
- G01S5/0018—Transmission from mobile station to base station
- G01S5/0036—Transmission from mobile station to base station of measured values, i.e. measurement on mobile and position calculation on base station
-
- 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
- G01S2205/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S2205/001—Transmission of position information to remote stations
- G01S2205/008—Transmission of position information to remote stations using a mobile telephone network
-
- 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
- G01S5/0009—Transmission of position information to remote stations
- G01S5/0045—Transmission from base station to mobile station
- G01S5/0063—Transmission from base station to mobile station of measured values, i.e. measurement on base station and position calculation on mobile
Abstract
The present invention is a novel and improved method and apparatus for performing position location in wireless communications system. In one embodiment the invention comprises a method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station including the step of receiving a position location request during a communication, entering a position location mode, transmitting frames to the base station while performing a position location procedure, and returning to communications mode when said position location procedure has been completed.
Description
NOV-2 1 -00 1 A : 1 0 FROM = CA 02343237 2001-03-08 1 p , PAGE 9/ 19 PCTIUS 9~~?0343 II~41US ~ s N O~I 2000 CALL MAINTENANCE DURING POSTTION LOCATION
EACKGROUND OF THE INVENTION
I_ Field of the Invention The present invention relates to position location. More particularly, the present invention relates to a novel and improved method and apparatus for performing position location in wireless communications systezn TI. Description of the Related Art --- Both government regulation and consumer demand have driven the demand for position location functionality in cellular telephones. The global positioning systezlz (GT'S) is currently available for performing position location using a Gl-'S receiver in conjunction with a set of earth orbiting satellites. Zt is therefore desirable to introduce GPS functionality into a cellular telephone.
Cellular telephones, however, are extremely sensitive to cost, weight and power consumption considerations_ Thus, sixnply adding additional circuitry~ for performing GPS location is an unsatisfactory solution for pro~-iding position location functionality in a cellular telephone. Thus, the y_ present invention is directed to providing GPS functionality in a cellular telephone systezx~ with a minimum of additional hardware, cost and power consumption.
SUMMARY OF THE IN'V'ENTION
JO
The present invention is a novel and improved method and apparatus for performing position location in wireless comzxiunications system. In one embodiznent the invention comprises a method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station, including the step of receiving a position location request during a communication, entering a position location mode, transmitting frames to the base station while performing a position location procedure, and returning to AMEfi!~!~Q EHrET
EACKGROUND OF THE INVENTION
I_ Field of the Invention The present invention relates to position location. More particularly, the present invention relates to a novel and improved method and apparatus for performing position location in wireless communications systezn TI. Description of the Related Art --- Both government regulation and consumer demand have driven the demand for position location functionality in cellular telephones. The global positioning systezlz (GT'S) is currently available for performing position location using a Gl-'S receiver in conjunction with a set of earth orbiting satellites. Zt is therefore desirable to introduce GPS functionality into a cellular telephone.
Cellular telephones, however, are extremely sensitive to cost, weight and power consumption considerations_ Thus, sixnply adding additional circuitry~ for performing GPS location is an unsatisfactory solution for pro~-iding position location functionality in a cellular telephone. Thus, the y_ present invention is directed to providing GPS functionality in a cellular telephone systezx~ with a minimum of additional hardware, cost and power consumption.
SUMMARY OF THE IN'V'ENTION
JO
The present invention is a novel and improved method and apparatus for performing position location in wireless comzxiunications system. In one embodiznent the invention comprises a method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station, including the step of receiving a position location request during a communication, entering a position location mode, transmitting frames to the base station while performing a position location procedure, and returning to AMEfi!~!~Q EHrET
communications mode when said position location procedure has been completed.
More particularly, the invention provides a method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station, comprising the steps of: receiving a position location request from the base station; in response to the position location request, tuning a receiver of the subscriber unit away from the current frequency to a position location frequency in order to receive position location information;
and receiving information over the position location frequency and using the received information to perform a position location procedure, while transmitting information to the base station; retuning the receiver to once again receive from, as well as transmit to the base station when said position location procedure has been completed.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:
Fig. 1 is a block diagram of the Global Positioning System (GPS) waveform generator;
Fig. 2 is a highly simplified block diagram of a cellular telephone system configured in accordance with the use of present invention;
Fig. 3 is a block diagram of a receiver configured in accordance with one embodiment of the invention;
2a Fig. 4 is another block diagram of the receiver depicted in Fig. 3;
Fig. 5 is a receiver configured in accordance with an alternative embodiment of the invention;
Fig. 6 is a flow chart of the steps performed during a position location operation;
Fig. 7 is a block diagram of a DSP configured in accordance with one embodiment of the invention;
Fig. $ is a flow chart illustrating the steps performed during a search performed in accordance with one embodiment of the invention;
Fig. 9 is a time line illustrating the phases over which fine and coarse searches are performed in one embodiment of the invention;
Fig. 10 is a time line of the search process when performed in accordance with one embodiment of the invention;
Fig. 11 is a diagram of search space;
Fig. 12 is a block diagram of a receiver in accordance with another embodiment of the invention.
DETAI7~ED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A novel and improved method and apparatus for performing position location in wireless communications system is described. The Id0 V-2 1 -00 18 = 1 1 FROM : CA 02343237 2001-03-08 I p : PAGE 1 1 / 19 PG~II~~ ~~'?a3~+3 exemplary embodiment is desczibed in the context of the digital cellular telephone system_ While use within this context is advantageous, diffezent ennbodiments of the invention may be incorporated in different environments or configurations. In general, the various systems described herezn may be formed using software controlled processors, integrated circuits, or discreet logic, however, implementation in an integrated circuit is preferred. The data, instructions, commands, information, signals, symbols and chips that lazay be referenced throughout the application are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or a combination thereof. Additionally, the blocks shown in each block diagram may represent haxdware or method steps.
Fig. 1 is a block diagram of the Global Positioning System (GPS) waveforzn generator. The circle with a plus sign designates modulo-2 addition. in general, the GPS constellation consists of 24 satellites: 21 space vehicles (SVs) used for navigation and 3 spares. Each SV contains a clock that is synchronized to GPS time by monitoring ground stations. To determine a position and time, a GPS receiver processes the signals received from several satellites. At least 4 satellites must be used to solve for the 4 unknowns (x, y, z, time).
Each SV transmits 2 microwave carriers: the 1575.42 MHz Ll carrier, which carries the signals used for Standard Positioning Service (SPS}, and the 1227.60 MHz L2 carrier, ~.vhich carries signals needed for Precise -- Positioning Service {PPS). PPS is used by governmental agencies and allows --- 25 a higher degree of accuracy in positioning.
The L1 carrier is modulated by the Coarse Acquisition (C/A) code, a X023--chip pseudorandom code transmitted at 1.023 hlcps that is used for civil position location services. (The Coarse Acquisition code should not be contused with the coarse and fine acquisitions described herein, which both in~~olve the use of the C/A codes.) Each satellite has its own C/A code that repeats every lms. The P code, which is used for PPS, is a 10.23 MHz code that is 267 days in length. The P code appears on both carriers but is 90 degrees out of phase with the C/A code on the L1 carrier. The 54Hz navigation message, which is exclusive-0Red with both the C/A code and P
code before carrier modulation, provides system information such as satellite orbits and clock corrections.
~,: a _,,.,:..._ . _. _, Each satellite has a different C/A code that belongs to a family of codes called Gold codes. Gold codes are used because the cross-correlation between them is small. The C/A code is generated using two 10-stage shift registers. A G1 generator uses the polynomial 1+X3+Xlo, while a G2 generator uses the polynomial 1+X2+X3+X6+X8+X9+Xlo.
The C/A code is generated by exclusive ORing the output of the G1 shift register with 2 bits of the G2 shift register.
Fig. 2 is a highly simplified block diagram of a cellular telephone system configured in accordance with the use of the disclosed method and apparatus. Mobile telephones 10 are located among base stations 12, which are coupled to base station controller (BSC) 14. Mobile switching center MSC 16 connects BSC 14 to the public switch telephone network (PSTN). During operation, some mobile telephones are conducting telephone calls by interfacing with base stations 12 while others are in standby mode.
As described in copending US Patent Serial No.
6,081,229 entitled "SYSTEM AND METHOD FOR DETERMINING THE
POSITION OF A WIRELESS CDMA TRANSCEIVER" assigned to the assignee of the present invention, position location is facilitated by the transmission of a position request message containing "aiding information" that allows the mobile telephone to quickly acquire the GPS signal. This information includes the ID number of the SV (SV ID), the estimated code phase, the search window size around the estimate code phase, and the estimated frequency Doppler.
Using this NOV-2 1 -00 1 A : 1 2 FROM : CA 02343237 2001-03-08 1 p _ PAGE 1 3/ 19 PCTIUS ~ ~ ~ 2 0 3 4 3 1~~~~~~~ ~ ~OV 2000 information, the mobile unit can acquire the GPS signals and determine its location more quickly.
In response to the aiding message, the mobile unit tunes to the GPS
frequency and begins correlating the received signal with its locally generated C/A sequences for the SVs indicated by the base station. It uses the aiding information to narrow the search space and compensate for Doppler effects, and obtains pseudo-ranges for each satellite using time correlation. Note that these pseudo-ranges are based on mobile unit time (referenced from the CDMA receiver's combiner system time counter), which is a delayed version of Gr'S time.
Once this information is calculated, the mobile unit sends the pseudo-ranges fox each satellite (preferably to 1/8 chip resolution) and the tune the nneasurements were taken to the base station. The mobile unit '- then retunes to CDMA to continue the call.
Upon, receipt of the information, the BSC uses the one-way delay estimate to converts the pseudo-ranges from mobile unit time to base station time and computes the estimated position of the mobile unit by solving for the intersection of several spheres.
Another parameter provided by the aiding message is the frequency Doppler or Doppler offset. The Doppler effect manifests as an apparent change in the frequency of a received sisal due to a relative velocity between the transmitter and receiver. The effect of the Doppler on the carrier is referred to as frequency Doppler, while the effect on the baseband signal is referred to as code Doppler.
Tn the GPS case, frequency Doppler changes the received carrier frequency so the effect is the same as demodulating with a carrier offset.
Since the base station's GPS receiver is actively tracking the desired satellite, it knows the frequency Doppler due to satellite movement. Moreover, the satellite is so far away from the base station and the mobile unit that the Doppler seen by the mobile unit is effectively the same as the Doppler seen by the base station. Tn one embodiment of the invention, to correct for the frequency Dopplez~ value, the mobile unit uses a rotator in the receiver. The frequency Doppler ranges from -~5QOHz to +4500Hz, and the rate of change is on the order of 1 Hz/s.
The effect of the code Doppler is to change the 1.023Mhz chip rate, which effectively compresses oz expands the width of the received C/A code chips. In one embodiment of the invention, the mobile unit coz~rect for code Doppler by multiplying the frequency Doppler by the ratio 1.023/1575.42.
The mobile unit can then correct for code Doppler over time by dewing ~YIi~'.ii~
NOV-2 1 -00 1 A = 1 2 FROM : CA 02343237 2001-03-08 1 p _ PAGE 14/ 19 ~~,~-, ,, _ ~~3~3 6 IP~~.~~~ ~, ~ NOV 2000 (introducing delay into) the phase of the received IQ samples in 1/16 chip increments as necessary_ Fig. 3 is a block diagram of the receiver portion of a cellular telephone (wireless subscriber unit) configured in accordance with one embodiment of the invention_ The received waveform 100 is modeled as the C/A signal c(n) modulated with a carrier at frequency w~ + wd, where w~ is the nominal carrier frequency 1.575.42 MHz, and wd is the Doppler frequency created by satellite movement. The Doppler frequency ranges from 0 when the satellite is directly overhead, to about 4.5kHz in the worst case. The receiver analog section can be nnodeled as demodulation with a carrier at frequency wr and random phase 8, followed by low pass filtering.
The resulting basebazld signal is passed through an A/D converter (not sho~~n) to produce digital I and Q samples, which are stored so that they may be repeatedly searched. The sa~atples are generated at two times the C/A code chip rate (chzpx2) which is a lower resolution than necessary to perform the fine search algorithm, but which allows 18 zns of sanclple data to be stored in a reasonable amount of nnemory. In general, it is desirable to perform the searching over something greater than l0ms in order to allow acquisition in most environmental conditions, with l8ms being a preferred integration period. These environmental conditions include being inside or not having a direct view to the satellite.
During operation, the samples are first rotated by rotator 102 to correct for the Doppler frequency offset. The rotated I and Q samples are correlated with various offsets of the satellite's C/A sequence and the resulting products are coherently integrated over Nc chips by integrators 104.
The coherent integration sums are squared and added together to remove the effect of the unknown phase offset 8. To augment the hypothesis test for a particular offset, several coherent intervals are non-coherently combined.
This despreading is performed repeatedly at various time offsets to find the tune offset of the satellite signal. Rotator 102 removes the frequency Doppler created by satellite movement. It uses the Doppler frequency specified by the base station (preferably quantized to lOHz intezw'als) and rotates the Z and Q
samples to rezxlove the frequency offset.
In one embodiment of the invention, the rotation is continuous only over the coherent integration window. That is, the rotator stops in between coherent integration periods of, for example, 1 ms. Any resulting phase difference is eliminated by the square and sum.
More particularly, the invention provides a method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station, comprising the steps of: receiving a position location request from the base station; in response to the position location request, tuning a receiver of the subscriber unit away from the current frequency to a position location frequency in order to receive position location information;
and receiving information over the position location frequency and using the received information to perform a position location procedure, while transmitting information to the base station; retuning the receiver to once again receive from, as well as transmit to the base station when said position location procedure has been completed.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:
Fig. 1 is a block diagram of the Global Positioning System (GPS) waveform generator;
Fig. 2 is a highly simplified block diagram of a cellular telephone system configured in accordance with the use of present invention;
Fig. 3 is a block diagram of a receiver configured in accordance with one embodiment of the invention;
2a Fig. 4 is another block diagram of the receiver depicted in Fig. 3;
Fig. 5 is a receiver configured in accordance with an alternative embodiment of the invention;
Fig. 6 is a flow chart of the steps performed during a position location operation;
Fig. 7 is a block diagram of a DSP configured in accordance with one embodiment of the invention;
Fig. $ is a flow chart illustrating the steps performed during a search performed in accordance with one embodiment of the invention;
Fig. 9 is a time line illustrating the phases over which fine and coarse searches are performed in one embodiment of the invention;
Fig. 10 is a time line of the search process when performed in accordance with one embodiment of the invention;
Fig. 11 is a diagram of search space;
Fig. 12 is a block diagram of a receiver in accordance with another embodiment of the invention.
DETAI7~ED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A novel and improved method and apparatus for performing position location in wireless communications system is described. The Id0 V-2 1 -00 18 = 1 1 FROM : CA 02343237 2001-03-08 I p : PAGE 1 1 / 19 PG~II~~ ~~'?a3~+3 exemplary embodiment is desczibed in the context of the digital cellular telephone system_ While use within this context is advantageous, diffezent ennbodiments of the invention may be incorporated in different environments or configurations. In general, the various systems described herezn may be formed using software controlled processors, integrated circuits, or discreet logic, however, implementation in an integrated circuit is preferred. The data, instructions, commands, information, signals, symbols and chips that lazay be referenced throughout the application are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or a combination thereof. Additionally, the blocks shown in each block diagram may represent haxdware or method steps.
Fig. 1 is a block diagram of the Global Positioning System (GPS) waveforzn generator. The circle with a plus sign designates modulo-2 addition. in general, the GPS constellation consists of 24 satellites: 21 space vehicles (SVs) used for navigation and 3 spares. Each SV contains a clock that is synchronized to GPS time by monitoring ground stations. To determine a position and time, a GPS receiver processes the signals received from several satellites. At least 4 satellites must be used to solve for the 4 unknowns (x, y, z, time).
Each SV transmits 2 microwave carriers: the 1575.42 MHz Ll carrier, which carries the signals used for Standard Positioning Service (SPS}, and the 1227.60 MHz L2 carrier, ~.vhich carries signals needed for Precise -- Positioning Service {PPS). PPS is used by governmental agencies and allows --- 25 a higher degree of accuracy in positioning.
The L1 carrier is modulated by the Coarse Acquisition (C/A) code, a X023--chip pseudorandom code transmitted at 1.023 hlcps that is used for civil position location services. (The Coarse Acquisition code should not be contused with the coarse and fine acquisitions described herein, which both in~~olve the use of the C/A codes.) Each satellite has its own C/A code that repeats every lms. The P code, which is used for PPS, is a 10.23 MHz code that is 267 days in length. The P code appears on both carriers but is 90 degrees out of phase with the C/A code on the L1 carrier. The 54Hz navigation message, which is exclusive-0Red with both the C/A code and P
code before carrier modulation, provides system information such as satellite orbits and clock corrections.
~,: a _,,.,:..._ . _. _, Each satellite has a different C/A code that belongs to a family of codes called Gold codes. Gold codes are used because the cross-correlation between them is small. The C/A code is generated using two 10-stage shift registers. A G1 generator uses the polynomial 1+X3+Xlo, while a G2 generator uses the polynomial 1+X2+X3+X6+X8+X9+Xlo.
The C/A code is generated by exclusive ORing the output of the G1 shift register with 2 bits of the G2 shift register.
Fig. 2 is a highly simplified block diagram of a cellular telephone system configured in accordance with the use of the disclosed method and apparatus. Mobile telephones 10 are located among base stations 12, which are coupled to base station controller (BSC) 14. Mobile switching center MSC 16 connects BSC 14 to the public switch telephone network (PSTN). During operation, some mobile telephones are conducting telephone calls by interfacing with base stations 12 while others are in standby mode.
As described in copending US Patent Serial No.
6,081,229 entitled "SYSTEM AND METHOD FOR DETERMINING THE
POSITION OF A WIRELESS CDMA TRANSCEIVER" assigned to the assignee of the present invention, position location is facilitated by the transmission of a position request message containing "aiding information" that allows the mobile telephone to quickly acquire the GPS signal. This information includes the ID number of the SV (SV ID), the estimated code phase, the search window size around the estimate code phase, and the estimated frequency Doppler.
Using this NOV-2 1 -00 1 A : 1 2 FROM : CA 02343237 2001-03-08 1 p _ PAGE 1 3/ 19 PCTIUS ~ ~ ~ 2 0 3 4 3 1~~~~~~~ ~ ~OV 2000 information, the mobile unit can acquire the GPS signals and determine its location more quickly.
In response to the aiding message, the mobile unit tunes to the GPS
frequency and begins correlating the received signal with its locally generated C/A sequences for the SVs indicated by the base station. It uses the aiding information to narrow the search space and compensate for Doppler effects, and obtains pseudo-ranges for each satellite using time correlation. Note that these pseudo-ranges are based on mobile unit time (referenced from the CDMA receiver's combiner system time counter), which is a delayed version of Gr'S time.
Once this information is calculated, the mobile unit sends the pseudo-ranges fox each satellite (preferably to 1/8 chip resolution) and the tune the nneasurements were taken to the base station. The mobile unit '- then retunes to CDMA to continue the call.
Upon, receipt of the information, the BSC uses the one-way delay estimate to converts the pseudo-ranges from mobile unit time to base station time and computes the estimated position of the mobile unit by solving for the intersection of several spheres.
Another parameter provided by the aiding message is the frequency Doppler or Doppler offset. The Doppler effect manifests as an apparent change in the frequency of a received sisal due to a relative velocity between the transmitter and receiver. The effect of the Doppler on the carrier is referred to as frequency Doppler, while the effect on the baseband signal is referred to as code Doppler.
Tn the GPS case, frequency Doppler changes the received carrier frequency so the effect is the same as demodulating with a carrier offset.
Since the base station's GPS receiver is actively tracking the desired satellite, it knows the frequency Doppler due to satellite movement. Moreover, the satellite is so far away from the base station and the mobile unit that the Doppler seen by the mobile unit is effectively the same as the Doppler seen by the base station. Tn one embodiment of the invention, to correct for the frequency Dopplez~ value, the mobile unit uses a rotator in the receiver. The frequency Doppler ranges from -~5QOHz to +4500Hz, and the rate of change is on the order of 1 Hz/s.
The effect of the code Doppler is to change the 1.023Mhz chip rate, which effectively compresses oz expands the width of the received C/A code chips. In one embodiment of the invention, the mobile unit coz~rect for code Doppler by multiplying the frequency Doppler by the ratio 1.023/1575.42.
The mobile unit can then correct for code Doppler over time by dewing ~YIi~'.ii~
NOV-2 1 -00 1 A = 1 2 FROM : CA 02343237 2001-03-08 1 p _ PAGE 14/ 19 ~~,~-, ,, _ ~~3~3 6 IP~~.~~~ ~, ~ NOV 2000 (introducing delay into) the phase of the received IQ samples in 1/16 chip increments as necessary_ Fig. 3 is a block diagram of the receiver portion of a cellular telephone (wireless subscriber unit) configured in accordance with one embodiment of the invention_ The received waveform 100 is modeled as the C/A signal c(n) modulated with a carrier at frequency w~ + wd, where w~ is the nominal carrier frequency 1.575.42 MHz, and wd is the Doppler frequency created by satellite movement. The Doppler frequency ranges from 0 when the satellite is directly overhead, to about 4.5kHz in the worst case. The receiver analog section can be nnodeled as demodulation with a carrier at frequency wr and random phase 8, followed by low pass filtering.
The resulting basebazld signal is passed through an A/D converter (not sho~~n) to produce digital I and Q samples, which are stored so that they may be repeatedly searched. The sa~atples are generated at two times the C/A code chip rate (chzpx2) which is a lower resolution than necessary to perform the fine search algorithm, but which allows 18 zns of sanclple data to be stored in a reasonable amount of nnemory. In general, it is desirable to perform the searching over something greater than l0ms in order to allow acquisition in most environmental conditions, with l8ms being a preferred integration period. These environmental conditions include being inside or not having a direct view to the satellite.
During operation, the samples are first rotated by rotator 102 to correct for the Doppler frequency offset. The rotated I and Q samples are correlated with various offsets of the satellite's C/A sequence and the resulting products are coherently integrated over Nc chips by integrators 104.
The coherent integration sums are squared and added together to remove the effect of the unknown phase offset 8. To augment the hypothesis test for a particular offset, several coherent intervals are non-coherently combined.
This despreading is performed repeatedly at various time offsets to find the tune offset of the satellite signal. Rotator 102 removes the frequency Doppler created by satellite movement. It uses the Doppler frequency specified by the base station (preferably quantized to lOHz intezw'als) and rotates the Z and Q
samples to rezxlove the frequency offset.
In one embodiment of the invention, the rotation is continuous only over the coherent integration window. That is, the rotator stops in between coherent integration periods of, for example, 1 ms. Any resulting phase difference is eliminated by the square and sum.
Claims (8)
1. A method for performing position location in a subscriber unit in a CDMA wireless communications system having a base station, comprising the steps of:
receiving a position location request from the base station;
in response to the position location request, tuning a receiver of the subscriber unit away from the current frequency to a position location frequency in order to receive position location information; and receiving information over the position location frequency and using the received information to perform a position location procedure, while transmitting information to the base station;
retuning the receiver to once again receive from, as well as transmit to the base station when said position location procedure has been completed.
receiving a position location request from the base station;
in response to the position location request, tuning a receiver of the subscriber unit away from the current frequency to a position location frequency in order to receive position location information; and receiving information over the position location frequency and using the received information to perform a position location procedure, while transmitting information to the base station;
retuning the receiver to once again receive from, as well as transmit to the base station when said position location procedure has been completed.
2. The method of claim 1, wherein the information received from the subscriber unit during the position location procedure contains power control information.
3. The method of claim 1, wherein the information received from the subscriber unit during the position location procedure notifies the base station that the subscriber unit is position location made.
4. The method of claim 1, wherein the information received from the subscriber unit during the position location procedure notifies the base station of a status of the position location procedure.
5. The method of claim 1, wherein the information received from the subscriber unit during the position location procedure includes a request for additional aiding information for performing the position location procedure, and the position location procedure is completed using the additional aiding information.
6. The method of claim 1 wherein information received from the subscriber unit during the position location procedure contains timing information.
7. The method as set forth in claim 1, wherein the information received from the subscriber unit during the position location procedure is used for conducting communications.
8. The method as set forth in claim 1, wherein the information received from the subscriber unit during the position location procedure is transmitted after signal samples from a set of satellites are collected, but before the position location procedure in completed.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/150,075 US6211820B1 (en) | 1998-09-09 | 1998-09-09 | Call maintainance during position location |
| US09/150,075 | 1998-09-09 | ||
| PCT/US1999/020343 WO2000014570A1 (en) | 1998-09-09 | 1999-09-02 | Call maintenance during position location |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2343237A1 CA2343237A1 (en) | 2000-03-16 |
| CA2343237C true CA2343237C (en) | 2006-07-04 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002343237A Expired - Fee Related CA2343237C (en) | 1998-09-09 | 1999-09-02 | Call maintenance during position location |
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| US (1) | US6211820B1 (en) |
| EP (2) | EP1847847A3 (en) |
| JP (1) | JP4522584B2 (en) |
| KR (1) | KR100646142B1 (en) |
| CN (1) | CN1228645C (en) |
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| BR (1) | BR9913551A (en) |
| CA (1) | CA2343237C (en) |
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| ID (1) | ID29146A (en) |
| IL (2) | IL141706A0 (en) |
| WO (1) | WO2000014570A1 (en) |
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-
1998
- 1998-09-09 US US09/150,075 patent/US6211820B1/en not_active Expired - Lifetime
-
1999
- 1999-09-02 CN CNB998107255A patent/CN1228645C/en not_active Expired - Lifetime
- 1999-09-02 KR KR1020017003064A patent/KR100646142B1/en not_active IP Right Cessation
- 1999-09-02 BR BR9913551-5A patent/BR9913551A/en not_active IP Right Cessation
- 1999-09-02 ID IDW20010801A patent/ID29146A/en unknown
- 1999-09-02 WO PCT/US1999/020343 patent/WO2000014570A1/en active IP Right Grant
- 1999-09-02 EP EP07014430A patent/EP1847847A3/en not_active Withdrawn
- 1999-09-02 AU AU59087/99A patent/AU761917B2/en not_active Ceased
- 1999-09-02 CA CA002343237A patent/CA2343237C/en not_active Expired - Fee Related
- 1999-09-02 AT AT99946749T patent/ATE557290T1/en active
- 1999-09-02 EP EP99946749A patent/EP1112511B1/en not_active Expired - Lifetime
- 1999-09-02 IL IL14170699A patent/IL141706A0/en active IP Right Grant
- 1999-09-02 JP JP2000569260A patent/JP4522584B2/en not_active Expired - Lifetime
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2001
- 2001-02-28 IL IL141706A patent/IL141706A/en not_active IP Right Cessation
- 2001-03-02 FI FI20010420A patent/FI114579B/en not_active IP Right Cessation
- 2001-12-24 HK HK01109039A patent/HK1038260A1/en not_active IP Right Cessation
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| CN1228645C (en) | 2005-11-23 |
| IL141706A0 (en) | 2002-03-10 |
| FI114579B (en) | 2004-11-15 |
| HK1038260A1 (en) | 2002-03-08 |
| CA2343237A1 (en) | 2000-03-16 |
| AU5908799A (en) | 2000-03-27 |
| ID29146A (en) | 2001-08-02 |
| EP1112511B1 (en) | 2012-05-09 |
| EP1112511A1 (en) | 2001-07-04 |
| BR9913551A (en) | 2002-04-23 |
| FI20010420A (en) | 2001-03-02 |
| ATE557290T1 (en) | 2012-05-15 |
| KR100646142B1 (en) | 2006-11-14 |
| AU761917B2 (en) | 2003-06-12 |
| KR20010082197A (en) | 2001-08-29 |
| JP2002524948A (en) | 2002-08-06 |
| JP4522584B2 (en) | 2010-08-11 |
| EP1847847A3 (en) | 2008-01-23 |
| IL141706A (en) | 2006-04-10 |
| US6211820B1 (en) | 2001-04-03 |
| EP1847847A2 (en) | 2007-10-24 |
| CN1317092A (en) | 2001-10-10 |
| WO2000014570A1 (en) | 2000-03-16 |
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