HK1139462B - Method and apparatus for improving radio location accuracy with measurements - Google Patents

Description

Method and apparatus for improving radio positioning accuracy using measurements

The present application is a divisional application of the invention patent application having application number 200380101586.0, international application date 10/17/2003, entitled "method and apparatus for improving radio positioning accuracy by measurement".

This application claims priority from the following prior applications: U.S. patent provisional application No. 60,419,680, filed on 17/10/2002, and U.S. patent provisional application No. 60/433,055, filed on 13/12/2002.

Technical Field

The present invention relates generally to location determination. More particularly, the present invention relates to a method and apparatus for providing a more accurate position estimate for a wireless terminal using a set of measurements.

Technical Field

It is often desirable, and sometimes necessary, to know the location of a wireless user. For example, the Federal Communications Commission (FCC) has adopted reports and orders for enhanced 911(E9-1-1) wireless services that require the location of a wireless terminal (e.g., a cellular telephone, a modem, a computer with wireless capability, a Personal Digital Assistant (PDA), or any other such mobile or handheld device with wireless communication capability) to be provided to a Public Safety Answering Point (PSAP) each time a 911 call is made from the terminal. FCC mandate that positioning for terminals based on handset technology such as assisted GPS (a-GPS) is accurate to within 50 meters for 67% of calls and to within 150 meters for 95% of calls. In addition to the FCC mandate, service providers may use location services (i.e., services that identify the location of a wireless terminal) in various applications to provide value-added features that may generate additional revenue.

Various different systems may be used to determine the location of a wireless terminal. One such system is the well-known Global Positioning System (GPS), which is a reasonably distributed "constellation" of 24 satellites that orbit the earth. Each GPS satellite transmits a signal encoded with information that allows the receivers to measure the time of arrival of the received signal relative to an arbitrary point in time. This relative time-of-arrival measurement may then be converted into a "pseudorange" (which is the sum of the actual distance between the satellite and the terminal plus all errors associated with the measurement. The three-dimensional position of a GPS receiver can be accurately estimated (to within 10 to 100 meters for most GPS receivers) based on pseudorange measurements to a sufficient number of satellites (typically four) and their positions.

A wireless communication system, such as a cellular communication system, may also be used to determine the location of the wireless terminal. Similar to GPS signals, a terminal may receive a "terrestrial" signal from an earth-bound base station and determine the time of arrival of the received signal. Furthermore, time of arrival measurements may be converted to pseudoranges. Then pseudorange measurements for a sufficient number of base stations (typically three or more) may be used to estimate the two-dimensional position of the terminal.

In a hybrid position determination system, signals from terrestrial base stations may be used in place of or in addition to signals from GPS to determine the position of a wireless terminal. A "hybrid" terminal may include a GPS receiver for receiving GPS signals from satellites and a "terrestrial" receiver for receiving terrestrial signals from base stations. Signals received from the base stations may be used for timing by the terminals or converted to pseudoranges. The three-dimensional position of the terminal can be estimated based on a sufficient number of measurements for the satellites and base stations (typically four for CDMA networks).

The three different position determination systems described above (i.e., GPS, wireless, and hybrid) may provide position estimates (or "fixes") with different degrees of accuracy. The position estimate derived based on signals from the GPS is the most accurate. However, because of the large distance between the satellite and the receiver, the GPS signals are received at a very low power level. Moreover, most conventional GPS receivers have great difficulty receiving GPS signals inside buildings, under dense foliage, in urban settings where tall buildings block much of the sky, and so on. The position estimate of the hybrid system has a lower accuracy, while the position estimate based on signals from the wireless communication system has a lower accuracy. This is because the pseudo range calculated based on the signals from the base station tends to exhibit larger errors than the pseudo range calculated from the GPS signals because of timing and hardware errors inside the base station, timing and hardware errors inside the terminal, errors caused by terrestrial propagation paths, and the like.

The position of the terminal can be estimated based on any of the three systems described above. It is desirable to obtain a position estimate that is as accurate as possible. Therefore, if a sufficient number of GPS signals are available, a GPS solution will be used. If this is not the case, a hybrid solution will be used if one or more GPS signals plus a sufficient number of terrestrial signals are available. A cellular solution may be obtained if there are no GPS signals available but a sufficient number of terrestrial signals are available.

The number of signals required for any of the three solutions described above may not be reached. In this case, the location of the terminal may be estimated using some additional location determination technique. One of these additional techniques is the cell-ID technique, which provides a reference (or serving) base station with which a terminal communicates with a designated location as a location estimate for the terminal. This designated location may be the center of the base station coverage, the location of the base station antenna, or some other location within the base station coverage. An enhanced cell identification scheme may combine cell identification information from a reference base station with cell identification information from another base station and/or including loop-back delay measurements and/or signal strength measurements from at least one base station in communication with a terminal. When a more accurate solution cannot be obtained independently because there are not a sufficient number of signals available, a cell identity or enhanced cell identity solution may be provided as a "fall-back" or "safety-net" solution. Unfortunately, the quality of the position estimate provided by the above-mentioned further techniques may be very poor, since it depends on the size of the base station coverage.

Therefore, there is a need in the art for a method and apparatus that provides a more accurate position estimate for a terminal using available measurements.

Disclosure of Invention

The methods and apparatus described herein utilize position location measurements to improve the accuracy of an initial position estimate for a wireless terminal. These measurements may be a partial set of measurements or a "complete set" of measurements. The partial set of measurements includes measurements available but not enough to produce an independent position fix for the terminal at a predetermined quality of service (i.e., a predetermined accuracy). However, rather than discarding these measurements as is typically done, they are used to derive a revised position estimate for the terminal that has improved accuracy over the initial position estimate. In another method and apparatus, an initial position estimate is refined by using an entire set of measurements. A complete set of measurements is a set of measurements from which a position location solution with a sufficiently high quality of service can be derived, but which solution can still be improved by the method and arrangement of the invention. Such methods and apparatus are essentially the same whether a partial set of measurements or a complete set of measurements is used. Thus, for ease of discussion, the disclosed methods and apparatus are described in the context of only one partial set of measurements.

In a method for determining a position estimate for a wireless terminal, an initial position estimate for the terminal is first obtained based on a cell identity or enhanced cell identity solution or other position location estimation scheme. A partial set of measurements is also obtained for the terminal from one or more position determination systems. The partial set of measurements may include measurements from satellites, wireless base stations, and/or access points or a combination of satellite and terrestrial measurements. The initial position estimate is then updated with a partial set of measurements to obtain a revised position estimate for the terminal.

The updating may be performed by first deriving a measurement vector based on the initial position estimate and a partial set of measurements. The measurement vector typically includes the residual amount of pseudoranges of the transmitter whose measurements are within the partial set. The residual amount of each pseudorange is the difference between (1) the "measured" pseudorange from the terminal position to the transmitter (derived based on the measurements) and (2) the "computed" pseudorange from the initial position estimate to the transmitter. An observation matrix may also be formed for the partial set of measurements. A weighting matrix for combining the initial position estimate and a partial set of the set of measurements may also be determined. Then, a correction vector can be derived based on the measurement vector, the observation matrix, and the weighting matrix. The initial position estimate is then updated with a correction vector that includes a modification to the initial position estimate.

Various aspects and examples of the method and apparatus are described in further detail below.

Brief Description of Drawings

The features, nature, 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 corresponding elements and wherein:

FIG. 1 illustrates a system including a plurality of position determination systems;

FIG. 2 illustrates a process for using a partial set of measurements for providing a more accurate position estimate for a wireless terminal;

FIGS. 3A through 3C illustrate three example operational scenarios in which the disclosed method and apparatus can provide a more accurate position estimate;

FIGS. 4A-4E are diagrams illustrating a process for combining initial position estimation with satellite and/or cellular measurements;

FIG. 5 shows a particular embodiment of the process shown in FIG. 2;

FIG. 6 illustrates a process for combining state domain information and measurement domain information to provide a more accurate position estimate; and is

Fig. 7 is a block diagram of an embodiment of a receiver unit, which may be a component of a wireless terminal.

Detailed Description

FIG. 1 is a block diagram illustrating a system 100 that includes a number of position determination systems. One such position determination system is the Satellite Positioning System (SPS), which may be the well-known Global Positioning System (GPS). Another such position determination system is a cellular communication system, which may be a Code Division Multiple Access (CDMA) communication system, a Global System for Mobile (GSM) communication system, or some other wireless system. In general, system 100 includes any number of position determination systems, which may be of any type (e.g., Bluetooth, Wireless Fidelity (WiFi), Ultra Wideband (UWB), or any other system capable of providing location-related information). If the system is designed to provide localized signal coverage, then this system may be referred to as a Local Area Positioning System (LAPS).

As shown in fig. 1, the terminal 110 may receive transmitted signals from a number of transmitters (or transceivers), each of which may be a base station 120 of a cellular communication system or a satellite 130 of an SPS. The terminal 110 may be a cellular telephone, a modem, a computer with wireless capability, a Personal Digital Assistant (PDA), or any other such mobile or handheld device with wireless communication capability. In general, any type of transmitter that may be placed at a known location or that may be ascertained may be used to determine the location of the terminal. For example, the terminal 110 may receive a signal from an access point in a bluetooth system. As used herein, a base station may be any terrestrial transmitter or transceiver that can transmit and/or receive signals that can be used for position determination.

Terminal l10 may be any terminal capable of receiving and processing signals from a position determination system to obtain timing, ranging, and/or positioning information. It should be noted that timing and ranging need not be combined. For example, simply receiving a signal from a short-range system, such as a bluetooth system, may provide sufficient information for wirelessly locating a terminal. Terminal 110 may be a cellular telephone, a fixed terminal, an electronic unit with a wireless modem (e.g., a computer system, Personal Digital Assistant (PDA), etc.), a receiver unit that can receive signals from a satellite and/or a base station, and so on. In another example, terminal 110 may be any device capable of sending signals to position determination systems, which may therefore acquire timing, ranging, and/or positioning information. The location of the wireless terminal may be determined based on signals from one or more location determination systems. For example, if system 100 includes an SPS and a cellular communication system, the position of the terminal may be estimated based on signals from (1) the SPS alone, (2) the cellular communication system alone, or (3) both the SPS and the cellular communication system. Techniques for determining the location of a terminal based solely on measurements of base stations in a cellular communication system are known as advanced forward link positioning (a-FLT), uplink time of arrival (U-TOA) or uplink time difference of arrival (U-TDOA), enhanced observed time difference (E-OTD) and observed time difference of arrival (OTDOA).

Each position determination system may provide a position estimate (or fix) with a degree of accuracy and may be available to certain operating environments. If the system 100 includes SPS and cellular communication systems, the accuracy and availability of these systems may be briefly summarized (in decreasing order of general accuracy) as shown in table 1.

TABLE 1

Type of measurement	Type of scenario	Description of the invention
			SPS	Mobile phone base	SPS-only based schemes. The highest accuracy. May not be available in certain environments (e.g., deep indoors).
SPS+A-FLT	Hybrid type	Hybrid schemes based on combining SPS and cellular communication systems. Moderate accuracy. Improved indoor usability.
			LAPS	WLAN base	A solution based only on local area network communication systems. The accuracy depends on the maximum distance characteristic of the system. Very good indoor usability.
A-FLT	Network base	Based solely on cellular communication system solutions. The accuracy is low. Typically in urban areas and available in locations where GPS is not available (e.g., deep indoors).
			Enhanced cell-ID	Cell base	Based solely on cellular communication system solutions. The accuracy is low. Typically depending on the size of the cell sector and the accuracy of the loopback delay or similar measurement. Other cellular measurements, such as observations and signal strengths of more than one transmitter, may also be included.
Cell ID	Cell base	Based solely on cellular communication system solutions. The accuracy is the lowest. Only the cell identity in which the terminal is located is provided. Therefore, the accuracy depends on the size of the cell.

The "SPS-based" solution in table 1 has the highest accuracy. However, in certain operating environments (such as indoors) where such a solution is computed, a sufficient number of SPS satellites (typically four) may not be available. The "hybrid" solution has the next highest accuracy but requires signals from one or more SPS satellites plus a sufficient number of base stations. Furthermore, for some operating environments, a required number of signals (typically four) may not be available. A "cell-based" solution, such as a-FLT, may be obtained based on measurements of a sufficient number of base stations (three or more). If no required number of base stations are available, a "network-based" cell identity or enhanced cell identity solution may be obtained based on measurements on a single base station. This base station is typically the one with which the terminal communicates and is often referred to as the "reference" base station. In another example, an enhanced cell identification solution may include information from multiple base stations or cells, such as cell coverage descriptions, observations from multiple transmitters, and signal characteristics, such as signal strength, signal interference, and so forth.

Techniques for acquiring hybrid solutions are described in detail in U.S. patent No. 5,999,124, entitled "satellite positioning system augmentation with wireless communication signals," published at 12/7/1999, which is incorporated herein by reference in its entirety.

Conventionally, one of the solutions shown in table 1 is provided whenever a terminal requires a position estimate. The most accurate solution is obtained if the required number of measurements (i.e. one complete set of measurements) is available for the solution. If the number of measurements available is less than the required number, a less demanding or safety net solution such as cell identity or enhanced cell identity solution may be provided.

Methods and apparatus for improving the accuracy of coarse initial position estimates using a partial set of measurements acquired from one or more position determination systems are described herein. The initial position estimate may be provided by, for example, a cell identity, an enhanced cell identity, or a LAPS solution. It will be appreciated by those skilled in the art that some other method for determining an initial position estimate is known, such as by using dead reckoning (dead reckoning), an estimate directly input by the user, and so forth.

The partial set of the set of measurements may include SPS and/or cellular measurements. The partial set of the set of measurements is defined by the fact that. I.e. it cannot include a sufficient number of measurements needed to obtain an independent position estimate for the terminal at a predetermined quality of service. Those skilled in the art will appreciate that the predetermined quality of service should be determined based on the particular application for which the position location determination is to be used. For example, the quality of service required to provide information about what points of interest are nearby (e.g., an Automated Teller Machine (ATM), a restaurant, a particular type of store, etc.) may be relatively low (inaccurate). Conversely, for applications such as navigating through a maze of narrow streets separated by relatively small distances, a relatively high (accurate) predetermined quality of service may be required. Even higher service may be required to provide information about the particular store or restaurant you happen to be in. For example, in one application, an end user may want to download a menu of restaurants on the street that he wants to enter, with many competing restaurants in close proximity to each other (i.e., adjacent to each other). In order to distinguish them from each other, a relatively high quality of service is required.

However, rather than discarding these measurements which are insufficient to obtain the predetermined quality of service, as is commonly done, the method and apparatus of the present invention uses these measurements to obtain a revised position estimate which has improved accuracy over the initial position estimate. One exception is the LAPS solution. If the LAPS maximum signal range or range from the LAPS transmitter is less than the initial position estimate, then the initial position estimate is updated (or replaced) by a LAPS solution, which may have been obtained from a single LAPS measurement. Such a LAPS measurement may be a distance measurement, a signal characteristic, a simple indication of signal reception, or may be based on a description of the LAPS coverage.

In another method and apparatus, an initial position estimate is refined by using a complete set of measurements. A complete set of measurements is a set of measurements from which it is possible to derive a position location solution with a sufficiently high quality of service, which can nevertheless be improved by the method and arrangement. Whether a complete combined measurement or a partial set of measurements is used, the method and apparatus of the present invention are essentially the same. Thus, for ease of discussion, the disclosed methods and apparatus are described in the context of only a partial set of measurements.

Fig. 2 is a block diagram of an embodiment of a process 200 for providing a more accurate position estimate for a wireless terminal using a partial set of measurements. The process begins by obtaining an initial position estimate for the terminal (step 212). Such initial position estimates may be obtained from one or more position determination systems. Moreover, the initial position estimate can represent the most accurate solution that can be obtained using any available position determination technique. For example, the initial position estimate may be provided by a cell identification solution, an enhanced cell identification solution, or some other solution.

A partial set of measurements may also be obtained from one or more position determination systems (step 214). The partial set of measurements does not include a sufficient number of measurements to obtain an independent position estimate for the terminal at the predetermined quality of service. However, if a required number of measurements are available, a separate position estimate may be obtained for the terminal, and this position estimate is generally more accurate than the initial position estimate. The partial set of measurements may include measurements from only the SPS, measurements from only the cellular communication system, or measurements from both the SPS and the wireless communication system or any number of other position determination systems.

The initial position estimate is then updated with the partial set of measurements to obtain a revised position estimate for the terminal (step 216). The revised position estimate has a higher accuracy than the initial position estimate. The amount of improvement in accuracy depends on different factors such as (1) the accuracy (or inaccuracy) of the initial position estimate, (2) the number and types of measurements available for updating, the geometry (i.e., the relative position of the transmitter from which the signal may be received), and so on. The updating is described below.

To more clearly describe the method and apparatus, the derivation of a terminal-computed position estimate based on a complete set of measurements is first described. In the following description, a measurement coordinate system is used and a three-dimensional (3-D) position is defined by latitude (north), longitude (east), and altitude (up).

For a terminal located at a given 3-D coordinate, its exact location can be determined based on the actual (or "true") distances to the three transmitters of known locations. However, the true distance to each transmitter often cannot be determined because of clock or other measurement errors. Instead, a "pseudorange" may be determined, which includes the true range plus an offset due to clock and other measurement errors. Then a fourth measurement is needed to remove the common offset in all measurements.

Position of the terminal, position of the ith transmitter and pseudo range PR from the position of the terminal to the position of the ith transmitter_iIs expressed as:

equation (1)

Wherein Lat, Long and Alt represent the 3-D plane space coordinates of the real position of the terminal;

Lat_i、Long_iand Alt_iCoordinates representing the ith transmitter position; and is

T represents a time coordinate.

As shown in equation (1), a set of four equations, i ═ 1, 2, 3, 4, can be obtained for four different transmitters.

By using an incremental relationship, the basic equation can be linearized as follows:

Long＝Long_init+Δe，

Lat＝Lat_init+Δn，

Alt＝Alt_init+Δu，

T＝T_init+ΔT，and

PR_i＝PR_init，i+ΔPR_ifor i ═ {1, 2, 3, 4} equation (2)

Wherein Lat_init、Long_init、Alt_initAnd T_initInitial values for Lat, Long, Alt, and T, respectively (a best estimate in advance);

Δ e, Δ n, Δ u, and Δ T represent initial values Lat, respectively_nint、Long_initAlt_init、T_initThe correction amount of (a);

PR_initrepresents pseudorange measurements (i.e., a "computed" pseudorange) from the initial position estimate to the i-th transmitter;

PR_irepresents a pseudorange measurement (i.e., a "measured" pseudorange) from the terminal position to the i-th transmitter; and

ΔPR_irepresenting the difference between the computed and measured pseudoranges (which is also referred to as the "pseudorange residual").

In equation set (2), Lat_init、Long_initAnd Alt_initRepresenting the initial 3-D position estimate of the terminal, while Lat, Long and Alt represent the true 3-D position of the terminal (or a later best estimate). The initial position estimate is the best estimate of the current availability to the terminal.

Pseudorange measurement PR_init，iIs an initial position estimate (Lat)_init、Long_initAnd Alt_init) And known position of the ith transmitter (Lat)_i、Long_iAnd Alt_i) A calculated value of the pseudo-range therebetween. The pseudorange measurement may be represented as:

equation (3)

The pseudorange measurement PR_iIs considered a "measured" value because it is obtained based on the signal received by the terminal from the i-th transmitter. In particular, if the time at which a signal is transmitted from the ith transmitter is known (e.g., the signal is time stamped or timing information is encoded in the signal), the time it takes for the signal to travel to the terminal can be determined by observing the time at which the signal is received at the terminal (based on the terminal's internal clock). However, the amount of time between transmission and reception is often not accurately determined because of the offset between the clock of the transmitter and the clock of the terminal and other measurement errors. Therefore, the pseudorange is derived based on the difference between the reference time and the received signal time. In another example, a signal characteristic or combination of signal characteristics, such as signal strength, may be used to obtain pseudorange measurements. Pseudoranges obtained from signals received from SPS satellites are known in the art and will not be described in detail herein.

Pseudorange residual Δ PR for ith transmitter_iCan be expressed as:

ΔPR_i＝PR_i-PR_init，iequation (4)

Substituting the incremental expression in equation set (2) into the basic equation (1) and ignoring the second level of error terms, the following can be obtained:

equation (5)

The four linearized equations shown by equation (5) may be more conveniently represented in matrix form as follows:

equation (6)

WhereinIs the direction cosine of the angle between the pseudorange to the ith transmitter and the x-direction vector, where x may be eastward, northward, or up. Equation (6) may be used to determine or update the terminal position as long as there is a complete and independent set of pseudorange measurements for four transmitters.

FIG. 3A is a diagram illustrating an example operating scenario in which the disclosed method and apparatus may be used to provide a more accurate position estimate. In FIG. 3A, terminal 110 receives signals from base station 120x and two SPS satellites 130x130 y. These three signals are not sufficient to derive a 3-D mixing position fix. Then, using basic knowledge of the base station 120x communicating with the terminal 110, a cell identification solution may be obtained. If base station 120x is designed to approximate the geographic area covered by circle 310, then the location of terminal 110 may be estimated to be the location of the base station or some other designated location within the coverage area.

To increase system capacity, the coverage area of each base station may be divided into a number of sectors (e.g., three sectors). Each sector may be served by a corresponding Base Transceiver Subsystem (BTS). For a coverage area that has been sectorized (usually referred to as a sectorized cell), the base station serving that coverage area includes all BTSs serving the sectors of the coverage area. Then an enhanced cell identification solution can be obtained with additional information identifying the particular BTS sector with which the terminal is communicating. In this case, the uncertainty of the terminal position can be reduced to a pie-shaped area, which is labeled as sector a in fig. 3A. Then the location of the terminal may be estimated as being at the center of the BTS (point 312) coverage sector or some other location specified.

Additional information is also available, such as the received signal strength from the BTS, the loop back delay (RTD) between the terminal and the BTS, the Time Advance (TA) of the received signal (GSM), the loop back time (RTT) between the terminal and the BTS (W-CDMA), etc. If such additional information is available, the position estimate of the terminal may be adjusted accordingly.

As explained above, cell identification or enhanced cell identification techniques may provide a coarse position estimate for a terminal. This then represents the best prior estimate of 2-D for the terminal (i.e., the initial position estimate). The initial position estimate for the terminal may be given as (Lat)_initAnd Long_init). Then a revised position estimate with improved accuracy may be obtained for the terminal using the two pseudorange measurements to the two SPS satellites 130x and 130 y.

The linearized equation for a terminal with two pseudorange measurements to two satellites may be expressed as:

equation (7)

Where Δ H is an altitude residual amount representing a difference between a current estimate of the altitude of the terminal and an actual altitude; and is

Δ CB represents the difference between the current reference time estimate and the "true" reference time.

In equation (7), the pseudorange PR may be based on a computed for that satellite_init，IAnd measured pseudo range PR_iDetermining a pseudorange residual Δ PR for each of two satellites of an SPS_iAs shown in equation (4).Pseudo range PR_{init， I}Initial position estimate (Lat) for a terminal_init、Long_initAnd Alt_init) And the location of the ith satellite (Lat)_i、Long_iAnd Alt_i) Is calculated by the distance between the terminal and the altitude at terminal Alt_initMay be estimated to be equal to the altitude of the serving BTS or some other altitude. Given some additional information about the reference time, Δ CB may be used to account for the difference between the current reference time estimate and the "true" reference time. In one example, the propagation time between the serving BTS and the terminal may be measured and used to provide information about the reference time delay. Pseudo range PR_iIs acquired based on signals received from the ith satellite and is a measure of the distance from the ith satellite to the actual ("true") position of the terminal.

Equation (7) can also be expressed in a more compact form as follows:

r＝Hxequation (8)

WhereinrIs a vector with four elements being the pseudorange residuals (i.e., the "measurement" vector);

xis a vector with four elements corrected for user location and time (i.e., the "correction" vector); while

HIs a 4 x 4 "observation" matrix.

Then, the vector is correctedxCan be determined as:

x＝H ^-1 requation (9)

Equation (9) is a correction vectorxAn unweighted solution is provided. The equation gives the information related to the initial position estimate (e.g., obtained from cell identification some other technique) and the distance information for the SPS satellites with the same weight. To better combine the two information, the initial position estimate and pseudorange measurements may be assigned appropriate weights.

A covariance matrix may be determined for the linearized equation shown in equation set (7)VIt is also known as the measurement noise matrix and can be expressed as:

equation (10)

Wherein, V₁₁Is to measure PR the pseudorange to the first satellite₁A change in error;

V₂₂is as a pairPseudo-range measurements PR for two satellites₂A change in error;

V_his a change to a height measurement error;

V_his a change to a measurement error related to a reference time;

element V₁₁And V₂₂Can be expressed asWhileWherein sigma_pr1And σ_pr2Is a pseudo-range measurement PR₁And PR₂Standard deviation of the respective errors. Weighting matrixWCan be defined as an offset matrixVIs reversed (i.e.:W＝V ^-1)。Wdetermines a weight for information related to the initial position estimate in the pseudorange measurements and the offset of the revised position estimate.WThe element of (c) is inversely related to the cross product of the expected value of the square and the error in the measurement. This would then result in the quantities being given higher weights when combining the initial position estimate and the pseudorange measurements.

Pseudorange PR to the ith satellite_iCan be defined as:

PR_i＝R_i+CB+SV_i+Tr_i+I_i+M_i+η_iequation (11)

Wherein R is_iIs the true or actual distance from the terminal location to the ith satellite;

CB represents an error due to the reference time;

SV_irepresents all errors associated with the ith satellite;

Tr_irepresents the error due to passage of the SPS signal through the troposphere;

I_irepresenting the error due to SPS signal crossing the ionosphere;

M_irepresenting errors associated with the signal propagation environment, including multipath; and is

η_iRepresenting errors (or thermal noise) associated with the receiver measurement noise.

Then, the error estimate V_iiAll errors in the pseudorange measurement for the ith satellite will be included. Equation (10) assumes that the pseudorange measurements are independent of each other, and this noise matrixVAre known in the art and will not be described in detail here.

Then one is used to correct the vectorxThe weighted solution of (a) can be expressed as:

x＝(H ^T WH)^-1 H ^T Wrequation (12)

Wherein the content of the first and second substances,H ^τrepresentsHThe transposed matrix of (2).

Equation (9) or (12) may be used to obtain the correction vectorx. The vector will include two non-zero terms, Δ e and Δ n. Then, the revised 2D position estimate for the terminal may be calculated as:

Long_rev＝Long_init+Δe

and Lat_rev＝Lat_init+ Δ n. equation (13)

This process of combining the initial position estimate with SPS and/or other measurements is described in further detail below with reference to fig. 4A through 4D.

FIG. 3B is a diagram illustrating another example operating scenario in which the disclosed method and apparatus may be used to provide a more accurate position estimate. In fig. 3B, terminal 110 has received two signals from base stations 120x and 120 y. These two signals are not sufficient to derive a network-based (e.g., a-FLT) position fix. Similar to fig. 3A discussed above, a cell identity or enhanced cell identity solution may be derived based on the positioning of the base station designated to the terminal's serving base station. The initial position estimate for the terminal may be given as Lat_initAnd Long_init。

Similar to SPS satellites, pseudoranges to each base station may be estimated based on signals received from the base stations. For CDMA systems, each base station is assigned a pseudo-random noise (PN) sequence with a particular offset (or start time). The PN sequence is used to spread data across the spectrum (spectrum) prior to transmission from the base station. Each base station also transmits a pilot, which is a simple sequence of all 1's (or all 0's) with an assigned PN sequence spread. The signal transmitted by the base station is received at the terminal and the time of arrival of the signal is determined based on the phase used for propagation of the PN sequence. Because the pilot is typically processed to obtain this PN phase information, the measurements at the terminal are also considered pilot phase measurements. The pilot phase measurements are used to estimate the amount of time it takes for a signal to propagate from the base station to the terminal. The travel time may be converted to pseudoranges similar to those performed for SPS satellites. Pseudorange measurements obtained from terrestrial signals (such as pilot phase measurements) are denoted PP to distinguish them from pseudorange measurements obtained from SPS signals.

The linearized equation for a system with two pseudorange measurements for two base stations may be expressed as:

equation (14)

As shown in equation (14), assume that the terminal and base station are on the same elevation plane and there is no observation matrixAn item. However, depending on the relative geometry (e.g., the BTS may be at a peak and the terminal may be at a valley), there is observability of the PP measurement in the vertical direction. In this case, the first two rows of the observation matrix include the "up" (i.e., the first two rows of the observation matrix) referenceItem) is suitable. Equation (14) shows that the pseudorange residuals Δ PP calculation for terrestrial signals is similar to the pseudorange residuals Δ PR calculation for SPS signals, which is shown in equation (7). Another method for computing a position estimate is an algebraic solution without linearization.

Then, the correction vectorxCan be solved by using equation (9) or (12) and it includes two non-zero terms, Δ e and Δ n. Revised position estimate (Lat) for a terminal_revAnd Long_rev) It can be calculated as shown in equation (13).

FIG. 3C is a diagram illustrating yet another example operating scenario in which the disclosed method and apparatus may be used to provide a more accurate position estimate. In FIG. 3C, terminal 110 is slave baseStation 120x receives signals and receives signals from SPS satellites 130 x. These two signals are not sufficient to obtain a hybrid position fix. Based on the positioning of base station 120x, as described above in fig. 3A, a cell identity or enhanced cell identity solution may be obtained to provide an initial position estimate (Lat) for the terminal_initAnd Long_init)。

Pseudorange PR may be obtained based on signals from SPS satellites 130x₁And pseudorange PP may be obtained based on signals from base station 120x₁. The linearized equation for each terminal, with two pseudorange measurements for one satellite and one base station, may be expressed as:

equation (15)

Then, the correction vectorxCan be solved by using equation (9) or (12) and it includes two non-zero terms, Δ e and Δ n. Revised position estimate (Lat) for a terminal_revAnd Long_rev) It can be calculated as shown in equation (13).

A particular coordinate (dimension) may be fixed or constrained in the derivation of the revised position estimate. For example, if signals from base stations are used to update the initial position estimate, then the vertical direction is not observable. In this case, the height coordinate in the revised position estimate may be (1) fixed, and thus the same as the initial position estimate (i.e., Δ H is 0) or (2) a predetermined criterion is set by calculating a predetermined height remaining amount Δ H. The height can be constrained by appropriately setting the observation matrix as follows:

equation (16)

As shown in equation (16), one element of the measurement vector and one row of the observation matrix may be defined, and thus, when Δ H is applied, the height estimate is driven to a predetermined value (where Δ u may be driven to 0 or some other value). The altitude limit may be automatically applied if base station measurements are used for updating. The altitude limit may or may not be applied (i.e., it is optional) if the satellite and base station measurements or if only the satellite measurements are used for updating. The height constraint effectively provides one of the measurements to account for one of the unknowns in the three-dimensional positioning height (fig. 3A, which i consider to be included). Fig. 4A-4D are diagrams that graphically illustrate a process of combining an initial position estimate with SPS and/or other measurements. In FIG. 4A, the initial 2-D position estimate for the terminal is X_init＝[Lat_init，Long_init]With an uncertainty defined by the error ellipse shown by the shaded area in figure 4A. The error ellipse may also be represented by a covariance measurement noise matrix, which may be expressed as:

equation (17)

Wherein V_eIs the change in the east direction of the initial position estimation error;

V_nis the change in the initial position estimation error in the north direction;

V_enis the cross-correction of the error in the initial position estimate between the east and north faces.

For simplicity, the error term V is cross-corrected_enAnd V_neIn fig. 4A, 0 is assumed.

In the example depicted in FIG. 4A, where the uncertainty of the initial position is represented by a covariance matrix, the initial position estimate may be directly converted to an observation equation.

Equation (18)

Here, the measurement equations obtained from the satellite and terrestrial positioning systems are shown in equation (15) as an SPS and a base station measurement. These equations can be easily extended by those skilled in the art to any number of SPS and base station measurements (such as in equations (14) and (7)). In this example, the values of Δ E and Δ N are selected to represent an initial position estimate with respect to the estimated terminal position, around which the estimation equation is linearized. In the case where the initial position estimate is the position of the terminal in the estimated two-dimensional space, these values may be set to 0 and 0, respectively.

In this case, the covariance and weighting matrix may be set to represent the uncertainty in the initial position. For example, the covariance matrix may be set as:

equation (19)

Wherein, V_pnIs a pseudorange measurement PR for the first satellite₁A variation in error of (a);

V_ppis a pseudorange measurement PP measured for a first base station₁A variation in error of (a);

V_e、V_en、V_neand V_nSet in equation (17) above;

and V_hThe above equation (10) is set. The weighting matrix can then be calculated as an inverse covariance matrix and the position solution can be calculated in equation (12).

In another embodiment, the location update may be calculated using a maximum likelihood approach. For example, observations from a satellite positioning system and/or terrestrial base station transmitters may be used to determine a solution space: () The likelihood of different points. Furthermore, an initial position comprising information about the east and north positions may be used to improve the likelihood in the solution space on a given imaginary point representing the most likely position (location) of the terminal. A covariance matrix or more generally a probability density function may be used to determine the likelihood of different locations in the solution space. The height value (Δ u) may be fixed or limited for determining the position of maximum likelihood. A solution space of relative likelihoods may also be searched to determine the selected most likely position determination error estimate.

A location Line (LOP) may be acquired 414 for the terminal based on a distance measurement, such as an SPS measurement or a base station measurement (or some other measurement). Initial position estimate X_initThe revised (or final) position estimate may be obtained for the terminal in conjunction with the SPS position line, as described aboveX_rev. The uncertainty (or error) with this revised position estimate is represented by the band along line 414. For simplicity, the tape is not shown in fig. 4A. The width of the band depends on the potential uncertainty of the distance measurement used to acquire the LOP. The strip line is bounded by an initial uncertainty, which is the shaded area 412 of the error ellipse of the initial position estimate.

In fig. 4B, an initial position estimate for the terminal is obtained from the cell identification solution, which is based on the sector of the BTS serving the terminal. Then, this uncertainty of the initial position estimate may have a shape that is close to the coverage 422 of the pie-shaped (also referred to as a cell sector) of the BTS. Furthermore, the initial position estimate X_initSPS position line 424 may be combined to obtain a revised position estimate X for the terminal_rev. The revised position estimate will have an uncertainty represented by the band along line 424 bounded by the initial uncertainty, which is shaded area 422.

In fig. 4C, an enhanced cell identity based solution may obtain an initial position estimate X for the terminal_initThis is done based on sector 422 of the serving BTS and the loop-back delay (BTD) to that BTS. The RTD may be obtained based on pilot phase measurements to the BTS. Then, the initial position estimate X_initThere will be an uncertainty represented by band 432. The width of this band of uncertainty depends on the uncertainty (or error) in the RTD measurement. Initial position estimate X_initMay be combined with the location line 434 of the SPS to obtain a revised position estimate X for the terminal_rev。

In fig. 4D, an accurate RTD for the terminal to acquire to the BTS. This results in an initial position estimate X_initA narrower uncertainty band 442. Thus, X is estimated based on the initial position_initAnd a location line 444 of the SPS may obtain a more accurate revised position estimate X for the terminal_revAnd reduces uncertainty. Note that an accurate RTD may also provide a good Δ CB measurement for an accurate reference time estimate.

In fig. 4E, the initial position estimate X of the terminal is obtained based on the enhanced cell identity solution_init. In this example, an initial position estimate X_initCombined with the two SPS position lines 452 and 454 to obtain a revised position estimate X for the terminal_rev. The uncertainty in the revised position estimate is then dependent on the uncertainty in the two SPS position lines 452 and 454 and the initial position estimate.

For clarity, fig. 3A through 3C and fig. 4B through 4D use cell identification or enhanced cell identification techniques to provide an initial position estimate for a terminal. In general, the initial position estimate may be computed by any available position determination technique. As an example, an initial position estimate may be obtained by combining cell identities obtained by a number of base stations received by the terminal or an enhanced cell identity solution. This may provide a more accurate initial position estimate for the terminal, since information received by the terminal about further base stations may also be used. As another example, the initial position estimate may also be derived from a combination of typical coverage areas for many base stations received by the terminal. This coverage-Based location Determination technique is further described in detail in U.S. patent application serial No.10/280,639 entitled "Area Based location Determination for Wireless Network terminals in a Wireless Network," filed on 2002, month 10, and day 22, which is assigned U.S. patent No.6.865,395. Which is assigned to the assignee of the present invention and incorporated herein by reference. The initial position estimate may also be a network-based solution obtained by using the a-FLT.

Different types of measurements may be used to obtain a location line and a subsequent revised position estimate for the terminal based on the initial position estimate. Generally, the measurements used to update the initial position estimate should be of high accuracy. That is, if a sufficient number of measurements are available to obtain an independent position estimate for the terminal, the independent position estimate should be more accurate than the initial position estimate. Thus, if the initial position estimate is provided by a cell identity, an enhanced cell identity, or some other comparable technique, measurements of base stations and/or satellites may be used for updating. This is because network-based (a-FLT) solutions obtained from base station measurements only, hybrid solutions obtained from satellite and base station measurements, and SPS solutions obtained from satellite measurements only are generally more accurate than cell identification and enhanced cell identification solutions. If the initial position estimate is a cell-based solution, then satellite measurements can be used for updating. In a signal-limiting environment, a local positioning system may be used to generate an initial position estimate or to update an initial position estimate obtained from another source.

The number of measurements required for updating depends on the initial position estimation and updating method. Fig. 4A through 4D illustrate how a single LOP measurement can be used to revise a 2-D initial position estimate. More than the minimum number of measurements required may also be used to update the initial position estimate. For some updated methods, one or more coordinates (time-space dimensions) (e.g., altitude, reference time) may also be fixed or constrained by appropriately setting the observation matrix as described above. In this case, fewer measurements are needed for the update. For a lap based update method, a single measurement may be used.

Fig. 5 is a flow diagram of a process 200a for providing a more accurate position estimate for a terminal using a partial set of measurements. Process 200a is a particular embodiment of process 200 shown in FIG. 2 and is represented by FIG. 4E. The process 200a begins by obtaining an initial position estimate (e.g., based on a cell identity, an enhanced cell identity solution, or some other solution) for a terminal (step 212 a). Two measurements are also obtained for two transmitters, each of which may be a satellite or a base station (step 214a)

The initial position estimate is updated with a partial set of measurements to obtain revised bits for the terminalPosition estimation (step 216 a). To perform this update, measurement vectors are first acquired based on initial position estimates and measurementsr(step 222). Depending on the type of measurement used for the update (e.g., SPS or cellular), the measurement vector may be displayed at the left hand end of equations (7), (14), (15), or (18). An observation matrix is then formed for the measurement (e.g., as shown in equations (7), (14), (15), or (18))H(step 224). Next, a weighting matrix is determinedWAs described above (step 226). Then, as shown in equation (12), a correction vector is obtainedx(step 228). The initial position estimate is then updated with the correction vector to obtain a revised position estimate, as shown in equation (13) (step 230). The process then terminates.

Some of the above positioning techniques may be viewed as expanding the position (or state) domain information with measurement domain information of a partial set of measurements. Specifically, the expansion (augmentation) of the present invention can be used in cell identification based schemes. In general, expanding state domain information with measurement domain information requires a complete set of measurements, which greatly limits the situations where expansion can be used.

Fig. 6 is a flow diagram of one embodiment of a process 600 for combining state domain information and measurement domain information to provide a more accurate position estimate for a wireless terminal. Initially, state domain information is obtained for the terminal (step 612). The state domain information may be an initial position estimate obtained by using a different technique, such as cell identification or enhanced cell identification techniques. Measurement domain information is also obtained for the terminal (step 614). The measurement domain information contains a partial set of measurements that are not sufficient to obtain an independent position fix for a predetermined quality of service, but may be combined with the state domain information.

The state domain information is then combined with the measurement domain information to obtain a location estimate for the terminal that has at least as good an accuracy as the state domain (step 616).

Fig. 7 is a block diagram of one embodiment of a receiver unit 700, which may be a component of a wireless terminal. Receiver unit 700 is designed with the capability to process signals from multiple position determination systems, such as SPS and wireless communication systems. In the embodiment shown in FIG. 7, receiver unit 700 includes an antenna 710, a terrestrial receiver 712a, an SPS receiver 712b, a processing unit 716, a memory unit 718, and a controller 720.

Antenna 710 receives signals from a number of transmitters (which may be any combination of SPS satellites and/or base stations) and provides received signals to terrestrial and SPS receivers 712a and 712 b. Terrestrial receiver 712a includes front-end circuitry (e.g., Radio Frequency (RF) circuitry and/or other processing circuitry) that processes signals transmitted from base stations to obtain information for position determination. For example, terrestrial receiver 712a may measure the phase of pilots in the forward link signal received from each base station to obtain timing information (e.g., time of arrival). This timing information may then be used to obtain pseudoranges to the base stations.

Terrestrial receiver 712a may implement a "rake" receiver that is capable of processing multiple signal instances (or multipath components) in a received signal simultaneously. The "rake" receiver includes a number of demodulation elements (often called "fingers"), each of which may be assigned to process and track a particular component. Even if multiple fingers are assigned to handle multiple multipath components for a given base station, only one pseudorange acquired for one multipath component (e.g., the earliest arriving multipath component, or the most robust multipath component) is typically used for position determination. Alternatively, a timing (or ranging) relationship between different fingers may be established and maintained. In this way, it is possible to use different multipath components for a given base station to locate based on fading and multipath effects.

SPS receiver unit 712b includes front end circuitry that processes signals transmitted from SPS satellites to obtain information for positioning. Such processing of the information extracted from the SPS and terrestrial signals by receivers 712a and 712b is well known in the art and will not be described in detail herein. In one embodiment, terrestrial receiver unit 712a performs SPS signal processing. The receivers 712a and 712b provide various types of information to the processing unit 716 such as timing information, signal characteristics, the identity and location of the transmitter whose signal was received, etc.

The processing unit 716 may obtain an initial position estimate for the receiver unit 700 whenever required. The processing unit 716 may also determine a pseudorange residual for each base station and satellite to update the initial position estimate, as described above. Thereafter, the processing unit 716 may update the initial position estimate based on the pseudorange residuals to obtain a revised position estimate for the receiver unit.

The memory unit 718 stores various data for determining a position. For example, memory unit 718 may store information for SPS satellite positions (which may be derived from almanac and/or ephemeris transmitted by satellites or provided by terrestrial sources (such as a wireless network)), positions of base stations (which may be provided via signaling), and pseudorange residuals. A memory unit 718 may also store program codes and data for the processing unit 716.

The controller 720 may direct the operation of the processing unit 716. For instance, controller 720 may select a particular type of solution to be computed (e.g., SPS-based, network-based, hybrid, cell-based, LAPS, security mesh, and other combinatorial schemes), a particular algorithm to be used (if more than one is available), and so on.

Although not shown in fig. 7, receiver unit 700 may communicate with a location server 140 (see fig. 1), which may help determine a location estimate for the terminal. The positioning server may perform calculations to derive a position estimate, or may provide certain information for: (1) obtain satellite and/or base station measurements (e.g., acquisition assistance, timing assistance, information related to the position of SPS satellites and/or base stations, etc.), and/or (2) determine revised position estimates. For embodiments in which the location server performs location determination, the basic measurements and initial position estimates from the various location systems are communicated to the location server (e.g., over a wireless and/or wired link). An example of such a location server is described in U.S. patent No.6,208,290, which is incorporated herein by reference.

The methods and apparatus described herein may be used in a variety of different wireless communication systems and networks. For example, the disclosed methods and apparatus may be used for CDMA, Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and other wireless communication systems. These systems may implement one or more of the available criteria. For example, a CDMA system may perform IS-95, CDMA2000, IS-856, W-CDMA, and so on. A TDMA system may implement GSM, GPRS, etc. These various standards are well known in the art and are incorporated herein by reference. Other wireless communication systems include non-cellular wireless systems such as IEEE802.11 systems, bluetooth systems, and Wireless Local Area Networks (WLANs).

The methods and apparatus described herein may be used in a variety of Satellite Positioning Systems (SPS), such as the united states Global Positioning System (GPS), the russian glonass satellite system, and the european galileo system. Furthermore, the disclosed methods and apparatus may be used in positioning systems that use pseudolites (pseudolites) or a combination of satellites and pseudolites. Pseudolites are ground-based transmitters that broadcast a PN code or other ranging code (similar to a GPS or CDMA cellular signal) modulated on an L-band (or other frequency) carrier signal, which may be synchronized with GPS time. Each such transmitter may be assigned a unique PN code to allow identification by a remote receiver. Pseudolites are useful in situations where GPS signals from an orbiting satellite are unavailable, such as in tunnels, mines, buildings, urban canyons or other enclosed areas. Another implementation of pseudolites is wireless lighthouses. The term "satellite" as used herein is intended to include pseudolites, equivalents of pseudolites, and possibly other types. The term "SPS signals" as used herein is intended to include SPS-like signals from pseudolites or equivalents thereof. The term "base station" as used herein is intended to include cellular, wireless, LAN, WAN, LAPS, Bluetooth, 802.11 access points, and other terrestrial signal sources.

The methods and apparatus described herein may be implemented by various means, such as hardware, software, or a combination of both. For a hardware implementation, the methods and apparatus of the present invention may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

For a software implementation, the disclosed methods may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory 718 in fig. 7) and executed by a processor (e.g., processing unit 716 or controller 720). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (31)

1. A method of determining a position estimate for a wireless terminal in a position determination system, comprising the steps of:

obtaining an initial position estimate for the terminal;

obtaining a set of measurements from one or more location determination systems;

deriving a measurement vector based on the initial position estimate and the set of measurements;

deriving a correction vector based on at least the measurement vector; and

updating the initial position estimate with the correction vector to obtain a revised position estimate for the terminal.

2. The method of claim 1, wherein the set of measurements is a partial set of measurements.

3. The method of claim 1, wherein the set of measurements is a complete set of measurements.

4. The method of claim 1, wherein the initial position estimate is obtained based on a cell ID scheme.

5. The method of claim 1, wherein the initial position estimate is obtained based on at least one scheme selected from an enhanced cell ID scheme, a local area positioning system, and an advanced forward link trilateration scheme.

6. The method of claim 1, wherein the step for deriving a correction vector comprises:

forming an observation matrix for the set of measurements; and

deriving the correction vector based on the measurement vector and the observation matrix.

7. The method of claim 1, wherein the step for deriving a measurement vector comprises:

determining a pseudorange to each transmitter based on a respective measurement of the set of measurements,

calculating pseudoranges from said initial position estimate to each transmitter, an

The pseudorange residuals are determined for each transmitter,

and, said measurement vector comprises a pseudorange residual of a transmitter, while measurements of said transmitter are within said set of measurements.

8. The method of claim 1, wherein the updating step comprises using a maximum likelihood method.

9. The method of claim 1, further comprising: determining weights for the initial position estimate and the set of measurements, wherein the updating step is performed using the weights.

10. The method of claim 1, wherein one or more dimensions are constrained for the revised position estimate.

11. The method of claim 10 wherein a vertical dimension is constrained for the revised position estimate.

12. The method of claim 1, wherein the set of measurements is obtained based on signals received from a Satellite Positioning System (SPS).

13. The method of claim 1, wherein the set of measurements is obtained based on a signal received from a wireless communication system.

14. The method of claim 1, wherein the set of measurements is obtained based on signals received from at least one of a Satellite Positioning System (SPS) and a wireless communication system.

15. The method of claim 1, wherein the set of measurements includes at least one line of position (LOP).

16. The method of claim 1, wherein the step for obtaining a set of measurements comprises:

a set of measurements is obtained for a plurality of transmitters, where each transmitter is a satellite or a base station.

17. The method of claim 6, wherein the observation matrix comprises the initial position estimate.

18. The method of claim 2, further comprising: determining weights for the partial set of measurements, wherein the updating step is performed using the weights.

19. The method of claim 17, wherein the initial position estimate is used to create an equation for the observation matrix.

20. The method of claim 19, wherein the uncertainty of the initial position estimate is used to create weights for the observation matrix.

21. A receiver unit in a wireless communication system, comprising:

a first receiver for receiving and processing the received signal to provide data to a first position determination system;

a second receiver for receiving and processing said received signal to provide data to a second position determination system; and

a processing unit coupled to the first and second receivers for:

for the receiver unit, obtaining an initial position estimate,

obtaining a set of measurements from the first or second position determination system, or from both systems,

deriving a measurement vector based on the initial position estimate and the set of measurements;

deriving a correction vector based on at least the measurement vector; and

updating the initial position estimate with the correction vector to obtain a revised position estimate for the receiver unit.

22. The receiver unit of claim 21, wherein the first receiver is operative to process signals from SPS satellites.

23. The receiver unit of claim 21, wherein the second receiver is configured to process signals from a base station in a wireless communication system.

24. The receiver unit of claim 21, wherein the processing unit is further to:

forming an observation matrix for the set of measurements;

deriving the correction vector based on the measurement vector and the observation matrix.

25. The receiver unit of claim 21, wherein the processing unit obtains the initial position estimate for the receiver unit based on at least one scheme selected from a cell ID scheme, an enhanced cell ID scheme, a local area positioning system, and an advanced forward link trilateration scheme.

26. The receiver unit of claim 21, wherein weights are determined for the initial position estimate and the set of measurements, and wherein updating the initial position estimate with the set of measurements is performed using the weights.

27. The receiver unit of claim 21, wherein the processing unit derives the measurement vector by:

determining a pseudorange to each transmitter based on a respective measurement of the set of measurements,

calculating pseudoranges from said initial position estimate to each transmitter, an

The pseudorange residuals are determined for each transmitter,

and, said measurement vector comprises a pseudorange residual of a transmitter, while measurements of said transmitter are within said set of measurements.

28. The receiver unit of claim 21, wherein a vertical dimension is constrained for the revised position estimate.

29. The receiver unit of claim 21, wherein the set of measurements is obtained based on signals received from a Satellite Positioning System (SPS).

30. The receiver unit of claim 21, wherein the set of measurements is obtained based on a signal received from a wireless communication system.

31. The receiver unit of claim 21, wherein the set of measurements includes at least one line of position (LOP).