HK1081034A - Area based position determination for terminals in a wireless network - Google Patents

Description

Area-based positioning of terminals in a wireless network

Background

RELATED APPLICATIONS

This application claims priority from U.S. provisional application No. 60/402,339 filed on 8/2002.

Technical Field

The present invention relates generally to positioning, and more particularly to a method and apparatus for performing area-based positioning for a terminal in a wireless network.

Background

Knowing the location of the wireless user is often desirable and sometimes necessary. For example, the Federal Communications Commission (FCC) has adopted a report and order for enhanced 911(E-911) wireless services that requires the location of a wireless terminal to be provided to a Public Safety Answering Point (PSAP) each time a 911 call is made from the terminal. In addition to FCC mandates, service providers may provide various applications using location services (i.e., services that identify the location of a wireless terminal). Such applications may include, for example: location sensitive accounting, asset tracking, asset monitoring and recovery, fleet and resource management, personal location services, gatekeeper services, and the like.

The location of a wireless terminal may be estimated using a variety of techniques, including "range domain" and "location domain" techniques. The range domain technique uses a plurality of range-related measurements to calculate the location of the terminal. Range-related measurements include measurements that can be used to determine the actual distance between the transmitter and the terminal. Alternatively, the range measurement may be the relative distance from the terminal to the plurality of transmitters. In the case of relative distance measurements, the distance between the terminal and each transmitter is unknown, but a common offset is added to each distance value. It should be understood that the value may be negative. Some examples of range-related measurements include, but are not limited to: pseudo-range, real range, temporal estimation, and spatial bearing estimation. The position-related measurements may be obtained from one or more positioning systems. In particular, a 6PS position fix may be obtained from range-related measurements (i.e., pseudoranges) from multiple satellites in GPS. Alternatively, AFLT (advanced Forward Link trilateration) position fixes may be calculated from range-related measurements of multiple base stations in a cellular (e.g., CDMA) communication system. Further, a hybrid position fix may be calculated from range-related measurements of multiple satellites and base stations.

Location domain techniques estimate the location of a terminal using the location of a Base Transceiver Subsystem (BTS) that is "serving" (i.e., communicating with) the terminal. That is, because the two are communicating, the terminal must be within a known finite radius of the serving BTS. Generally, each BTS serves a predefined area, commonly referred to as a "cell". A cell may be divided into "sectors. This is typically done by coupling different antennas to the BTS to cover different sectors of the cell. In this way, terminals in each sector can be distinguished from terminals in each other sector based on the antenna through which the terminal establishes communication.

The approximate location of the terminal may then be estimated as any of the following: (1) the center of the BTS sector, (2) the BTS antenna location, (3) an internally provided location, (4) a default location, (5) some other location somewhat associated with the BTS location. The position fixes computed using position domain techniques are less accurate than the range domain position fixes. However, location domain fixes may be valuable as initial fixes. This initial fix is used to help compute the position fix for a range domain. The location-domain fix may also be helpful as the final fix if the range-domain location fix is either unavailable or of poor quality.

Regardless of how the position fix is calculated, it is highly desirable to provide an approximate position estimate for the terminal that is as accurate as possible. Since location-domain fixes are not always available or accurate, it may be helpful to be able to more accurately calculate the location of a wireless terminal using location-domain techniques.

Disclosure of Invention

This document describes methods and apparatus for more accurately estimating the approximate location of a terminal in a wireless network. In one embodiment of the method and apparatus, the approximate location of the terminal is estimated based on an "expected area" associated with a "reference Base Transceiver Subsystem (BTS)". The reference BTS may be any BTS with which the terminal is communicating. The expected area associated with a BTS is the area in which it is likely that the terminal will be located given the ability to receive signals from that BTS. The expected areas are: (1) a location provided as an estimated location of the terminal, and (2) an area in which the terminal may be located, wherein the likelihood is given by a particular percentage. The expected area associated with each BTS may be modeled based on various parameters, such as the location and direction of the BTS antennas, the Maximum Antenna Range (MAR), and so forth.

In another embodiment of the disclosed method and apparatus, an accurate position field position fix for a terminal is estimated by combining the expected areas of multiple BTSs. A terminal may receive signals from multiple BTSs in a wireless network. However, it is not necessary to use information associated with all BTSs from which signals are received to determine the location fix for the terminal. If information about a BTS is used to approximate the location of a terminal, the BTS is referred to as the "BTS under test". The expected areas of the BTSs under test may be combined to determine a combined expected area, which may then be provided as a location-domain position fix for the terminal.

In yet another embodiment of the disclosed method and apparatus, the center and size of the desired area associated with each BTS under test may be adjusted based on various factors before combining. These factors include: (1) received signal strength (generally given as E) of a signal received at a terminal from a BTS_c/I_o) (2) the received power of the BTS (generally given as E)_c) Or some other factor. The adjusted expected areas for all of the BTSs under test may then be combined to determine a combined expected area.

In yet another embodiment of the disclosed method and apparatus, a location-domain location fix for a terminal may be determined by any of the above-described embodiments, the fix being combined with some other location estimate for the terminal to determine a more accurate location estimate for the terminal. Other position estimates may be derived based on GPS, AFLT, or both.

Various aspects and embodiments of the disclosed methods and apparatus are described in further detail below. In particular, methods, program code, digital signal processors, terminals, systems, and other apparatuses and elements that implement various aspects, embodiments, and features of the disclosed methods and apparatuses are described in further detail below.

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 elements have like numerals wherein:

FIG. 1 is a schematic diagram of a wireless communication network;

FIG. 2 is a schematic diagram illustrating sectorized coverage areas of the four BTSs shown in FIG. 1;

FIG. 3 is a schematic diagram illustrating modeling of an expected area associated with each BTS in the network;

FIG. 4 is a diagram illustrating the use of multiple expected areas of multiple BTSs under test to compute a more accurate position estimate for a terminal;

FIGS. 5A and 5B are schematic diagrams illustrating modeling of the expected area of two different BTSs;

FIGS. 6A and 6B are diagrams illustrating adjusting an expected area associated with a BTS based on received signal strength;

FIG. 7A is a schematic diagram illustrating combining two overlapping expected regions M and N based on a weighted average to derive a combined expected region;

FIG. 7B is a schematic diagram illustrating combining two non-overlapping intended regions M and N based on a weighted average to derive a combined intended region;

FIG. 8 is a flow chart of a process for deriving a more accurate approximate position fix based on position determination; and

fig. 9 is a simplified block diagram of various elements of the network shown in fig. 1.

Detailed Description

Fig. 1 is a schematic diagram of a wireless communication network 100, which network 100 may be a Code Division Multiple Access (CDMA) network, a Time Division Multiple Access (TDMA) network, a Frequency Division Multiple Access (FDMA) network, or other type of wireless communication network. The CDMA network may be designed according to one or more CDMA standard systems such as an IS-95 system, an IS-2000 system, or a W-CDMA system. The TDMA network may be designed according to one or more TDMA standard systems, such as the GSM system. The details of these standard systems are well known in the art.

The network 100 includes a plurality of Base Transceiver Subsystems (BTSs) 104, each BTS 104 serving a particular geographic area. Only four BTSs 104 a-104 d are shown in fig. 1 for simplicity. The coverage area of a BTS is commonly referred to as a "cell". The coverage area is the area in which the terminal receives signals from the BTS 104. The size and shape of a cell generally depends on various factors such as terrain, obstacles, etc., and may also change over time. Although a BTS is often referred to as a "cell," this document distinguishes between devices referred to herein as "BTSs" and coverage areas referred to herein as cells.

A plurality of terminals 106 are typically distributed throughout the network. Only one is shown in fig. 1 for simplicity. The BTS transmits to the terminal 106 on the forward link and the terminal transmits to the BTS on the reverse link. Each terminal 106 may actively communicate with one or more BTSs. Each active communication between a terminal and more than one BTS is referred to as a "soft handoff. Active communication means that the terminal has registered with the network and can be identified by the BTS. It may receive pilot, paging, and/or other signaling messages from the BTS, as well as the terminal not in active communication with the BTS. In the example shown in fig. 1, the terminal 106 receives pilots from all four BTSs 104a through 104 d. It should be understood that merely receiving a pilot signal from a BTS is not indicative of active communication between the terminal and the BTS.

The BTS 104 typically communicates with a Base Station Controller (BSC)120 that coordinates communication between the BTS and terminals in active communication with the BTS. For position location, the base station controller 120 may communicate with a Position Determination Entity (PDE) 130. The PDE 130 receives information from/provides information to the base station controller 120, as described in further detail below.

In a typical network deployment, each cell may be divided into multiple sectors (e.g., three sectors) to increase system capacity (i.e., the number of users that the system can support at one time). Each sector is then served by a corresponding BTS. For a sectorized cell, the BTS serving the cell includes multiple BTSs (e.g., three). Each BTS is associated with a respective one of the sectors in the cell. Fig. 2 is a schematic diagram of a system in which there are four "sectorized" cells and there are four BTSs for the respective cells.

In the example shown in fig. 2, the cell covered by each BTS is represented by an ideal circle. Each sector of the cell is defined by an ideal 120 sector of a circle. In actual network deployment, the shape of the cell covered by each BTS is typically different from an ideal circumference, depending on the various factors described above. In addition, the sectors of a sector cell may overlap at the edges. For simplicity, five sectors a through E are shown in fig. 2 for only the four cells served by BTSs 105a through 105 d.

As mentioned above, it is often desirable, and sometimes necessary, to know the location of a wireless terminal. The terminal location may be estimated using a range domain or location domain technique. For range domain techniques, a plurality of range-related measurements (e.g., ranges, pseudoranges, etc.) are used to compute a position fix for a terminal. Each range-related measurement is made with reference to a transmitter (e.g., a satellite or BTS). The position fix of the location field is generally of higher accuracy. In some cases, however, there may not be a sufficient number of range-related measurements available to compute the position fix for the range domain.

Various embodiments of the disclosed method and apparatus are described herein to provide more accurate location fix of a location domain for a terminal. In one embodiment, the approximate location of the terminal is estimated based on the "expected area" associated with the "reference BTS". The reference BTS may be any BTS with which the terminal is communicating. As used herein, the intended region associated with a transmitter (such as a BTS) is the region in which the terminal may be located assuming it can receive signals from the transmitter. Modeling of the expected area associated with each BTS is described below.

In another embodiment, a more accurate location-domain position fix is determined for the terminal by combining the expected areas associated with several BTSs. In yet another embodiment, the center and size of the expected area associated with each BTS under test may be adjusted based on various factors before combining. If information about a BTS is used to approximate the location of a terminal, the BTS is referred to as the "measured" BTS. Factors for adjusting the expected area of the BTS under test include: (1) received signal strength, (2) received power, etc. Other factors and the manner in which they are used are detailed further below. The adjusted expected areas of the BTSs under test are then combined to determine a combined expected area.

In yet another embodiment, the location field position fix for a terminal may be combined with some other position estimate for the terminal to estimate a more accurate position for the terminal. Other position estimates may be derived based on GPS, AFLT, or a combination of both. These various embodiments of the disclosed methods and apparatus are described in further detail below.

Fig. 3 is a schematic diagram illustrating the anticipated areas associated with each BTS in the network shown in fig. 2. The expected area associated with each BTS of fig. 3 is modeled as a circle 314, the circle 314 representing a particular probability (e.g., a 1-sum Σ or 67% probability) that a terminal that is receiving a signal from a BTS is located within the expected area. Thus, if a terminal receives a signal from a given BTS, the terminal has a 67% probability of being located in the expected area associated with that BTS.

Each expected area is associated with a location that can be provided as an estimated location of the terminal, assuming the terminal receives signals from the BTS. This location is typically the center of the intended area. However, some other location within the expected area may also be provided as a location estimate. As shown in fig. 3, the center of each expected area is marked with an "x" 312. The center, size and shape of the desired area may be provided as part of the position fix of the terminal location field. The center of the expected area will represent the estimated location of the terminal, and the size and shape of the expected area will represent the certainty of using the center of the expected area as the estimated location of the terminal.

The size, shape, and center of the expected area associated with each BTS may be determined based on one or more parameters. Some parameters may be associated with the BTS, such as: (1) the location and direction of the BTS antennas, (2) the maximum antenna range, and so on. Other parameters may be related to physical attributes of the BTS coverage area such as: (1) terrain, (2) obstacles, and so forth. In addition, some parameters may be related to other characteristics of the BTS coverage area, such as the statistical distribution of the end users within the coverage area.

In the example shown in fig. 3, the terminal 106 is located in/near the overlapping area of the intended areas a and D. The terminal position can then be estimated as either: (1) the center of intended zone a if BTS105a is the reference BTS for the terminal, or (2) the center of intended zone D if BTS 105D is the reference BTS.

As shown in the above example, the position fix of the location field is generally of coarser accuracy. However, the position fix of the position domain may be valuable as an initial fix, which is then used to compute the position fix of a range domain. Alternatively, if the location fix for the range domain is poor or unavailable, the fix for the location domain may be used as the final fix. In either case, it is highly desirable to provide as accurate a location-domain position fix as possible.

Fig. 4 is a diagram illustrating the use of several expected areas, each associated with a respective one of several BTSs under test, to estimate a more accurate location of terminal 106. The terminal 106 may receive signals from the BTSs 105a through 105 e. Of the five received BTSs, only three BTSs 105a, 105d, and 105e are used to approximate the location of the terminal. Thus, as described above, these three BTSs 105a, 105d, and 105e are referred to as the measured BTSs for the terminal. The expected areas of the BTSs 105a, 105d, and 105e under test are then determined (e.g., retrieved from a memory location) and adjusted (e.g., based on received signal strength).

The adjusted and/or unadjusted prospective regions of the BTS under test are then combined to provide a combined prospective region centered at location 412, the size and shape of which is represented in fig. 4 by a circle 414. The center, size and shape of the combined expected area are then provided as a position estimate for the terminal.

As shown in the illustration in fig. 4, the combined expected area represents a more accurate approximation of the terminal 106 than any of the five individual expected areas a through E shown in fig. 4. In particular, the center of the combined expected area is a more accurate estimate of the location of the terminal than the center of any one of the individual expected areas. Further, the uncertainty of using the center of the combined expected area as the estimated location of the terminal may be less than the uncertainty of using the center of any of the three separate expected areas A, D and E used to determine the combined expected area. That is, the circumference 414 is smaller than the circumference defining the individual prospective regions, which indicates that a greater number of terminals considered to be within the combined prospective regions will be closer to the center (i.e., within the smaller circumference).

Fig. 5A and 5B are schematic diagrams illustrating modeling of the expected area of two different BTSs. In fig. 5A, BTS105x is designed to provide coverage for a sector 510a of approximately 120 °, the outer perimeter of which is determined by the Maximum Antenna Range (MAR) of the BTS. The expected area associated with the BTS may be modeled as a sector 510a, a circle 514a, or some other combination of shapes and sizes. Likewise, the prospective region center 512b can be provided as an estimated location of the terminal.

For both fig. 5A and 5B, the expected region is modeled based on a 2-dimensional gaussian normal distribution. In this model, the terminal is more likely to be located at or near the center of the coverage area of the BTS than far from the center of the coverage area. A circle or some other shape may then be defined to represent the area in which the terminal may be located, with a certain certainty, given that it is able to receive signals from the BTS. For a circumferential expected region of 1-sigma, if the terminal receives a signal from a BTS, it will be in the expected region with 37% certainty. The expected area may be defined for any given certainty, typically using 1-sigma. The expected area is thus defined according to some statistical parameters, not just the circle with hard handover.

The 1-sigma expected region may be determined based on various formulas. In one embodiment, the 1-sigma desired region is defined by a 1-sigma axis γ_aBy definition, the axis is represented as:

formula (1)

As shown in equation (1), the 1-sigma axis γ_a(corresponding to the radii of the circumferences 514a and 514B in fig. 5A and 5B) is derived based on the estimated Maximum Antenna Range (MAR) of the BTS. In another embodiment, the 1-sigma expected area estimates position error (HEPE) gamma from a 1-sigma level_hTo define, γ_hCan be expressed as:

formula (2)

1-Sigma HEPE gamma as shown in equation (2)_hIt can also be derived based on the maximum antenna range of the BTS. Other expressions for the 1-sigma expected region may also be used.

In fig. 5A and 5B, if the 1-sigma axis γ is used_aOr 1-sigma HEPE gamma_hNeither circle 514a nor 514b is drawn to scale as the radius of the 1-sigma expected region represented by circles 514a and 514 b.

In general, various shapes, sizes, and center positions may be used for the intended area associated with each BTS, depending on the parameters used to model the intended area. In one implementation, a circumferential model is used for the expected area associated with each BTS. The circumferential model of the expected area is particularly good if the distribution of terminals within the coverage area of the BTS approximates a circumferential pattern. The circumferential statistical model also allows for a convenient mathematical formulation, as will be seen from the discussion below.

In another embodiment of the disclosed method and apparatus, the center and size of the expected area associated with each BTS under test may be adjusted based on one or more factors. If the only information available is that the terminal receives a signal from a BTS, the expected area associated with that BTS, without any adjustments, can be provided as an approximate location fix for the terminal. However, if other information is available for the terminal, the expected area associated with the BTS may be adjusted based on the other information to determine a more accurate expected area associated with the terminal.

Various factors may be used to adjust the desired area associated with a BTS for a terminal. One such factor is the received signal strength, which is generally expressed as the energy per chip to total noise ratio (E)_c/I_o). The received signal strength may be determined based on a pilot or some other measurement from the BTS transmission. Alternatively, the received signal strength may be determined based on the reverse link signal received at the BTS from the terminal.

The received signal strength at the terminal for a given BTS may be mapped to a scaling factor. The scaling factor may be used to adjust the desired area associated with the BTS. In one implementation, E of 0dB_c/I_oIs mapped to a scaling factor of 0.9 (i.e., S ═ 0.9), E of-40 dB_c/I_oIs mapped to a scaling factor of 1.1, i.e. (S ═ 1.1). Linear interpolation may then be used to determine scaling factors for other received signal strength values. For this implementation, the scaling factor S may be expressed as:

formula (3)

The scaling factor may also be limited to a particular range of values (e.g., 0.9 ≦ S ≦ 1.1). A scale factor of less than 1 reduces or shrinks the desired area and a scale factor of greater than 1 enlarges the desired area.

In another implementation, E of 0dB_c/I_oIs mapped to a scaling factor of 0.6 (i.e., S ═ 0.6), E of-40 dB_c/I_oIs mapped intoThe scaling factor is 1.4 i.e. (S ═ 1.4). Linear interpolation may also be used to determine scaling factors for other received signal strength values. For this implementation, the scaling factor S may be expressed as:

formula (4)

The slope of this implementation is steeper than the implementation described above. Other mappings between received signal strength and scaling factor may also be used, as should be connected.

Another factor that may be used to adjust the expected area associated with a BTS for a given terminal is the received power of the signal from the BTS, as measured at the terminal. The received power may be expressed as energy per chip (E)_c) Considering only the signal of interest while ignoring noise and interference (I)_o). The received power may also be calculated from the pilot or some other signal component transmitted by the BTS. The received power is then mapped to a scaling factor, expressed as:

s＝f(E_c) Equation (5)

Where f (Ec) is some predefined function of Ec.

Another factor to consider when adjusting the desired area is the transmit power level. Each BTS typically transmits its signal at a particular power level determined by the network operator. The network operator may set the transmit power level of all BTSs to be the same. Alternatively, different power levels may be used for different BTSs. In this way, the BTS transmit power level can be used to adjust the desired area. The received power (Ec) and the transmit power level (P) may then be mapped to a scaling factor, expressed as:

s＝f(E_c，P)， formula (6)

Where f (Ec, P) is some predefined function of Ec and P. In one particular example, the received power from the BTSs may be normalized to compensate for the different transmit power levels used by the different BTSs. The normalized received power can then be used to adjust the expected area of the BTS.

Yet another factor that may be used to adjust the expected area associated with a BTS is Round Trip Delay (RTD). The terminal can identify the earliest arriving multipath component (with sufficient strength) in the forward link signal from the BTS. The time of arrival of the multipath component at the terminal antenna can be determined. This time is then used as a reference time for the terminal. The terminal may then transmit a reverse link signal back to the BTS with a 2 τ delay from the time the forward link signal was transmitted when the reverse link signal was received by the BTS. This 2 τ delay is called RTD. The RTD can be measured at the BTS and used to adjust the expected area associated with the BTS. Other factors may also be used to adjust the desired area associated with the BTS.

As described above, the size of the desired area associated with a BTS may be adjusted based on the scaling factor assigned to that BTS. The scaling factor may also be used to move the center of the desired area toward or away from a nominal center. By adjusting the size and center of the desired area, the distribution of the relevant BTSs can be adjusted accordingly when deriving the position estimate for the terminal.

Fig. 6A and 6B are diagrams illustrating adjusting an expected area associated with a BTS based on received signal strength. Due to path loss in the propagation environment, the power level of the received signal at the terminal is inversely related to the square of the distance from the transmitting BTS. This general form assumes that the transmitted signal is not degraded by other transmission phenomena, such as multipath signals. The received signal strength can be used as an estimate of the distance between the BTS (or BTS antenna) and the terminal. The center and size of the expected area associated with the BTS for that terminal may then be adjusted based on the received signal strength.

In fig. 6A, the received signal strength is strong, indicating that the terminal may be closer to the transmitting BTS. The center of the desired area is then moved from the nominal center 612x to a new center 612a closer to the BTS. The new center 612a is located on a straight line between the nominal center 612x and the BTS antenna. In addition, the new center 612a is moved to a particular point on the line, which is determined by the scaling factor. If the scale factor is equal to 1.0, then the new hub 612a is located at the nominal hub 612x, and if the scale factor is less than 1.0, then the new hub 612a is moved towards the BTS.

As also shown in fig. 6A, the size of the intended area is also reduced from the nominal size to a smaller size represented by circumference 614 a. The smaller size more closely matches the smaller area where this strong signal strength is likely to be received.

In fig. 6B, the received signal strength is weak, indicating that the terminal may be far from the transmitting BTS. The center of the desired area can then be moved from the nominal center 612x to a new center 612b, the new center 612b being further (radially) from the BTS. Further, the size of the intended area may be enlarged from the nominal size to a larger size represented by the circumference 614 b. The larger size represents a larger area where such weak signal strength may be received.

The adjustment of the desired zone may be selectively performed for some BTSs and not for some other BTSs. For example, the received signal strength of each BTS may be observed over a particular time interval. The expected area associated with each BTS is adjusted if the fluctuation in received signal strength is below a certain threshold and not adjusted if the fluctuation is above the certain threshold.

Further, the scaling factor for modifying the size of the desired area and the scaling factor for moving the center of the desired area may be independently selected. For example, the scale factor for the desired region size may be selected based on Ec, and the scale factor for the center of the desired region may be selected based on Ec/Io.

In yet another embodiment of the disclosed method and apparatus, a more accurate position fix for a terminal is determined by combining the expected areas of multiple BTSs under test. As described above, the desired area associated with each BTS may or may not be adjusted. The multiple prospective regions of the BTS under test may be combined in various ways to determine a combined prospective region, which is then provided as an approximate location fix for the terminal.

In one implementation, the combined expected area is determined based on a weighted average of the expected areas of the measured BTSs. In a simple case, the two expected areas M and N of the two BTSs under test are combined to determine a combined expected area. The expected area M of the first BTS under test may be defined as a rectangular coordinate with a center of (x)_m，y_m) Size/shape is represented by the second circumference. The center of the combined expected area may then be defined as the rectangular coordinate of (x)_p，y_p) It can be calculated as:

x_p＝W_mx_m+W_nx_nformula (7)

y_p＝W_my_m+W_ny_n，

Wherein W_mAnd W_nAre the weights used for the expected regions M and N, respectively, and W_m+W_n1. The weights may be derived as follows. As shown in equation (7), the rectangular coordinates (x) of the center of the expected area are combined_p，y_p) Is a weighted average of the dimensions of the centers of the two expected regions combined.

If more than two desired regions are to be combined, equation (7) can be summarized as follows:

and formula (8)

Wherein N is_BTSIs the number of expected regions that are combined,

weight W used by each expected area_iAre determined based on various parameters. In one implementation, the weight for each expected region is determined based on the size of the expected region. For this implementation, the weight W of the ith expected area_iCan be expressed as:

formula (9)

Wherein HEPE_iIs the position error of the horizontal estimate, which can be expressed as:

formula (10)

σ_EastAnd σ_NorthIs eastward sum associated with the ith expected areaVariance towards north. In particular, σ_EastIs the distance from the center of the intended region to the east (i.e., right) edge of the 1-sigma circumference, sigma_NorthIs the distance from the center of the desired region to the north (i.e., upper) edge of the 1-sigma circumference. The weight W of the i-th expected area, as shown in equation (9)_iHEPE with the intended area_iThe square of (a) is inversely related. The weighting in equation (9) is similar to a normally weighted least squares average, e.g., in terms of weight and 1/σ²In the proportional one-dimensional case. By using equation (9), smaller expected regions (i.e., regions with less uncertainty) are assigned more weight than larger expected regions.

It should be noted that the weights may also be derived based on some other parameter or any combination of parameters.

The size of the combined expected area indicates the uncertainty in using the combined expected area as an estimate of the location of the terminal. The size (or uncertainty) of the combined expected area is determined based on the following factors: the size (or uncertainty) of all the combined expected areas, the weights used to combine the expected areas, or a combination thereof.

One factor used to determine the combined expected area size is related to the number of BTSs tested that are combined. If it is assumed that the measurements from the BTSs are independent, the size of the combined expected area is reduced by a number equal to the number of BTSs being combined (e.g., the root-mean-square thereof). A limit may be placed on the amount of reduction in the combined expected zone size based on the number of BTSs tested. As a specific example, even if more than 10 BTSs under test are used, the size of the combined desired area is prevented from being reduced.

Another factor in determining the combined expected area size relates to the minimum size of all the combined expected areas. There is a reasonable "fit" between the individual expected areas that are combined if the measurements from the BTSs help to derive a more accurate combined expected area. In this case, the size of the combined expected area should no longer be larger than the smallest size of all the combined individual expected areas. Each prospective region further reduces the size of the combined prospective region.

Yet another factor used to determine the size of the combined expected area relates to the "unit error" which indicates how the individual expected areas overlap the combined expected area. If there is a "poor" fit between the various measurements (as described below with reference to FIG. 7B), the size of the combined expected area may actually be greater than (or worse than) the size of the smallest individual expected area. In this case, the unit error may be larger than 1.0, and the combined expected area size may be enlarged by the unit error (and then the HEPE of the combined expected area may be increased accordingly).

The unit error may be calculated based on the combined expected region and the normalized average "spacing-sigma" between the individual expected regions used to determine the combined expected region. In one implementation, the spacing of the ith desired region is sigma_iIs defined as:

formula (11)

Wherein D_iIs the distance between the center of the combined expected area and the center of the ith expected area, and RSS is the square root of the sum of the ith expected area HEPE and the combined expected area HEPE.

The unit error F can then be defined as:

formula (12)

As shown in equation (12), the unit error F represents the least mean square value.

If the unit error calculated for the combined expected area is greater than one (i.e., F > 1.0), the size of the combined expected area may be enlarged by the unit error. Otherwise, if the unit error is less than one (i.e., F < 1.0), then combining the sizes of the expected areas reduces the unit error. If the unit error is less than one (i.e., F < 1.0), this may be due to the correlation of the expected area, rather than an overestimated expected area size. As a result, it is generally better to ignore F values less than 1, rather than to shrink the combined expected area size as described above.

Fig. 7A is a diagram illustrating the combining of two overlapping expected areas M and N of two BTSs under test based on a weighted average to determine a combined expected area 714 p. Each of the two prospective regions is either an unadjusted prospective region (i.e., a scaling factor of 1.0) or an adjusted prospective region determined based on the scaling factor Si of the BTS assigned to the prospective region. The expected area M of the first BTS under test is centered at position 712M and is sized/shaped as indicated by the circumference 714M. Similarly, the expected area N of the second BTS under test is centered at position 712N, and the size/shape is represented by a circle 714N. The centers of the expected regions M and N are respectively defined by rectangular coordinates (x)_m，y_m) And (x)_n，y_n) And (4) defining. The rectangular coordinate of the center of the combined expected area is (x)_p，y_p) The coordinates may be determined in equation (7). As shown, a straight line can be drawn between the two prospective region centers 712m and 712 n. The center of the combined expected area is located on the straight line according to the weighted average, and the exact position is assigned to the weights W of the expected areas M and N by the distribution_mAnd W_nTo be determined. More specifically, if the distance between the two prospective region centers 712m and 712n is D, the distance D between the two prospective region centers 712m and 712n and the combined prospective region center 712p is_mAnd D_nCan be expressed as:

D_m＝W_nd, Hehe formula (13)

D_n＝W_mD，

Wherein D_m+D_n＝D。

For the example shown in fig. 7A, there is a reasonable fit between the two expected regions that are combined. In this way, the size (and uncertainty) of the combined expected area is reduced: (1) the number of BTSs under test that are combined, in this example 2, and (2) the smaller of the two expected areas that are combined, i.e., the size of expected area M.

Fig. 7B is a schematic diagram illustrating the combination of two non-overlapping intended regions M and N based on a weighted average to derive a combined intended region 714 q. The two prospective regions are centered at positions 712m and 712n, which are represented by rectangular coordinates (x), respectively_m，y_m) And (x)_n，y_n) And (4) defining. The size and shape of these two desired regions are represented by circles 714m and 714 n.

The combined expected area is centered at position 712q and has a rectangular coordinate of (x)_p，y_p) The coordinates may be determined in equation (7). For the example shown in FIG. 7B, the two combined expected regions M and N are non-overlapping, and the unit error is determined to be greater than one (i.e., F > 1.0). In this case, the size of the combination expectation area is enlarged by the unit error. The size of the combined expected area would then be larger than the smaller of the two expected areas being combined, as illustrated in FIG. 7B.

Fig. 8 is a flow diagram of a process 800 for estimating a more accurate approximate location for a terminal using area-based positioning. First, an expected area that can be used for location domain positioning is determined for each BTS (step 812). As described above, the expected area may be determined based on the maximum antenna range of the BTS and/or some other parameter. The expected area of the BTS is then saved in a memory unit such as a base station almanac. The expected area is typically determined once, for example at the time of network deployment. Thereafter, the desired region may be obtained from the memory cell as needed, as represented by the dashed box of step 812.

For each location fix for the location domain, an indication is first received indicating that signals from multiple BTSs are received at the terminal (step 814). A set of BTSs under test is then identified from among all the received BTSs (step 816). The measured BTS is the BTS that will be used to estimate the approximate location of the terminal. The expected area associated with each BTS under test may then be determined (e.g., retrieved from memory) and may then be adjusted to determine an adjusted expected area associated with that BTS (step 818). The adjustment of the expected area associated with each BTS under test may be performed based on the scaling factor assigned to that BTS. Which in turn is determined based on the received signal strength and/or some other factor, as described above. By setting the scaling factor of any BTS to one (S)_i1.0), adjustments to the BTS may also be omitted.

Next, the adjusted and/or unadjusted prospective areas of all of the BTSs under test are combined to determine a combined prospective area, which may be provided as an approximate location fix for the terminal (step 820). The center of the expected area represents the estimated position of the terminal and the size of the expected area represents the certainty of the estimated position. For example, if a combined expected area of 1-sigma circumference is provided, the terminal has a 39% probability of being within the combined expected area. The combination of the expected areas may be performed as described above.

The location field fix based on combining the expected areas may also be combined with some other location estimate available to the terminal (step 822). This other position may be estimated based on some other measurement type, such as GPS, AFLT, or (3) hybrid GPS and AFLT. GPS position is generally estimated based on GPS satellites, generally with the highest possible accuracy, but it is generally not available for a particular environment (e.g., some indoor locations). The AFLT position is estimated based on measurements from the wireless communication system and has reduced accuracy. However, AFLT position estimates are typically available in urban areas as well as other areas where GPS is not available. The hybrid location may be estimated based on measurements from both the GPS and the wireless communication system. Step 822 is optional and is shown by the dashed box.

Steps 816 through 822 are performed at the terminal, BTS, PDE, or some other network entity.

It should be understood that variations and modifications of the above-described embodiments may be made based on the principles described herein. In addition, other embodiments of the methods and apparatus described herein may be derived. Some such other embodiments are described below.

In one other embodiment, the expected area associated with the BTS is adjusted based on: (1) received power P_rxWhich is the power received at the terminal of the BTS, and (2) the predicted power P_preWhich is the power predicted to be received by the terminal of the BTS.

Predicted power P_preMay be calculated based on a path loss prediction model and a set of parameters. Various path loss prediction models may be used to calculate the predicted power, one example being the Okumura-Hata model. Predicted power P at the terminal of a given BTS_preCan be expressed as a function of these parameters, as follows:

P_preg (G, P, D, T, L, and m), and formula (14)

Where P is the power at the antenna port of the BTS (before the antenna amplifier),

g is the antenna gain of the BTS,

d represents a propagation model (e.g. Okumura-Hata),

t denotes a terrain database, which contains terrain relief information for path loss prediction,

l denotes a ground coverage/ground usage database, which contains information such as dense cities, suburbs, waters, etc. for propagation paths,

m is the possible location of the terminal (assuming the terminal is located at location m to calculate the predicted power), an

g is a function of all parameters as edges.

The parameters P and G may be combined to provide the input power to the path loss prediction model.

The predicted power P is expressed by equation (14)_preIs a function of the possible location m of the terminal. If the center of the expected area is used as the possible location m, the expected area center may be adjusted to minimize the difference between the predicted power and the received power. This criterion can be expressed as:

formula (15)

Where { M, M ∈ M } represents the set of all possible positions allowed by the center of the expected region.

The adjusted expected area associated with the BTS may then be provided as a location domain estimate for the terminal. Alternatively, this adjusted expected area may be combined with the adjusted and/or unadjusted expected areas of other BTSs under test to determine a combined expected area, which is then provided as the location domain estimate for the terminal.

In another alternative embodiment, the expected areas of multiple BTSs under test may be adjusted and combined based on the received power and predicted power of each of these BTSs. If the center of the combined expected area is used as a possible location of the terminal, the center of the combined expected area may be adjusted to minimize the root mean square difference between the predicted power and the received power of the BTS under test. The criterion can be expressed as:

formula (16)

Where { M, M ∈ M } represents the set of all possible positions allowed to combine the center of the expected area, and { K, K ∈ K } represents the set of all BTSs under test. The specific position m to be used as the center of the combined expected area is a position having the minimum value in formula (16), and thus is an estimated position of the terminal. This embodiment is an alternative way of adjusting and combining the expected areas of the BTSs under test.

Fig. 9 is a simplified block diagram of various elements of network 100. Terminal 106x may be a cellular telephone, a computer with a wireless modem, a stand-alone location unit, or some other unit. BTS105x is shown operatively coupled to PDE 130x (e.g., via BSC 120, which is not shown in fig. 9 for simplicity).

On the forward link, a modulator/transmitter (Mod/TMTR)920 processes (e.g., encodes, modulates, filters, amplifies, quadrature modulates, and frequency upconverts) the data, pilot, and signaling to be transmitted by BTS105x to provide a forward link modulated signal, which is transmitted via an antenna 922 to the terminals in the BTS coverage area. Terminal 106x receives forward link modulated signals from a plurality of BTSs (including BTS105 x) at antenna 952, with the received signals being routed to a receiver/demodulator (RCVR/Demod) 954. RCVR/Demod 954 then processes the received signal in the reverse manner to provide the various types of information that may be used for positioning. In particular, RCVR/Demod 954 may provide the identity and received signal strength (or received power) of each received BTS to processor 960. RCVR/Demod 954 may implement a rake receiver that is capable of processing multiple received signal instances (or multipath components) in a received signal in parallel for multiple received BTSs. The rake receiver includes a plurality of finger processors (or fingers), each assigned to process and track a particular point of multipath components.

On the reverse link, a modulator/transmitter (Mod/TMTR)964 processes data, pilot, and/or signaling to be transmitted by BTS 106x to provide a reverse link modulated signal. The reverse link modulated signal is then transmitted via an antenna 952 to a plurality of BTSs. BTS105x receives the reverse link modulated signal from terminal 106x at antenna 922. The received signal is then routed to a receiver/demodulator (RCVR/Demod) 924. RCVR/Demod924 processes the received signal in a reverse manner to provide various types of information that may be provided to processor 910.

In the embodiment shown in fig. 9, a communication (Comm) port 914 within BTS105x is operatively coupled to a communication port 944 within PDE 130 x. Communication ports 914 and 944 enable BTS105x and PDE 130x to exchange relevant information for position location (which may be received from terminal 106 x).

The calculation of the terminal approximate position fix using area-based positioning may be performed at terminal 106x, BTS105x, PDE 130x, or some other network entity. The entity performing area-based positioning carries the relevant information needed to derive an approximate position fix. Such information may include, for example, the identity of the BTS under test (e.g., base ID) used to determine the combined expected area, the expected area (e.g., center, size, and shape) of each BTS under test, the received signal strength or received power of each BTS under test, and so on. A portion of this information may be obtained from the base station almanac. The almanac may include various types of information, such as: (1) identification of each BTS, (2) BTS sector center location, (3) maximum antenna range, (4) antenna direction, etc. The designated network entity then derives a combined expected area. The combined expected area may then be provided as an approximate location fix for the terminal.

The process of estimating the terminal position fix may be performed by: a processor 960 in terminal 106x, a processor 910 in BTS105x, or a processor 940 in PDE 130 x. Memory units 962, 912, and 942 may be used to maintain various types of information used to determine a location, such as base station almanac, received signal strength or received power, etc. Memory units 962, 912, and 942 may also store program codes and data for processors 960, 910, and 940, respectively.

The methods and apparatus described herein may be used to determine a more accurate position fix for a terminal that is communicating with and/or capable of receiving signals from multiple BTSs without requiring a full time of arrival (TOA) or time difference of arrival (TDOA) based solution. By combining the expected areas of multiple BTSs under test, the terminal position can be estimated two to three times more accurately than conventional position estimates based on the coverage area of a single (e.g., reference) BTS. In one specific test performed in an urban environment, the general error found for the prospective regional solution was 1 to 2 kilometers, while the general error found for the combined prospective region was 250 to 500 meters, which is a considerable improvement in accuracy.

An approximate position fix derived with the region-based positioning may be used as an initial position estimate for the terminal. This initial position estimate may be needed, for example, to provide assistance information used to perform range-domain position fixes. Initial position estimates may also be used to shorten the time required to derive range domain position fixes, which is desirable. The approximate position fix may also be used as a final position estimate for the terminal. This final position estimate may be provided, for example, if the range domain position solution fails, or is less accurate than the position domain solution. As a final position fix, it is highly desirable to provide a position field position fix that is as accurate as possible.

The methods and apparatus described herein may be implemented by various means, such as hardware, software, or combinations thereof. For a hardware implementation, the methods and apparatus described herein may be implemented within the following elements: in 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 methods described herein 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 962, 912, or 942 of fig. 9) and executed by a processor (e.g., processor 960, 910, or 940). 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. The invention is thus not limited to the embodiments shown here. But is only limited by the language of the following claims.

Claims (42)

1. A method of estimating a location of a wireless terminal, comprising:

determining an expected area associated with a transmitter, the expected area for determining an approximate location estimate for the terminal;

adjusting the intended region based on at least one scaling factor to determine an adjusted intended region; and

providing the adjusted expected area as an estimated location of the terminal.

2. The method of claim 1, wherein at least one scaling factor is determined based on a received signal strength of a transmitter measured at a terminal.

3. The method of claim 1, wherein at least one scaling factor is determined based on a received power of a transmitter measured at a terminal.

4. The method of claim 1, further comprising:

the position estimate is combined with the second estimate of position to estimate a final position of the terminal.

5. A method of estimating a location of a wireless terminal, comprising:

receiving identities of a plurality of transmitters, the identities being used to estimate a location of a terminal;

determining a plurality of expected regions for the plurality of transmitters; and

combining the multiple expected areas of the multiple transmitters to estimate the location of the terminal.

6. The method of claim 5, wherein approximating the position estimate further comprises estimating an uncertainty in position.

7. The method of claim 6, wherein the uncertainty is provided by an area in which the terminal may be located.

8. The method of claim 5, further comprising:

the approximate position estimate is combined with the second position estimate to estimate a final position of the terminal.

9. A method as claimed in claim 5, characterised in that, assuming that only signals from the transmitters are received by the terminal, the expected area associated with each transmitter comprises the estimated position of the terminal and an area in which the terminal is likely to be located.

10. The method of claim 5, further comprising:

the expected area associated with each transmitter is adjusted based on at least one assigned scaling factor to determine an adjusted expected area associated with the transmitter.

11. The method of claim 10, wherein adjusting the expected area associated with each transmitter comprises:

the center of the desired area is moved based on the first assigned scaling factor.

12. The method of claim 11, wherein adjusting the expected area associated with each transmitter further comprises:

scaling the size of the intended region based on the scaling factor of the first allocation.

13. The method of claim 10, wherein adjusting the expected area associated with each transmitter further comprises:

scaling the size of the desired area based on the first assigned scaling factor, an

The center of the desired area is moved based on the second assigned scaling factor.

14. The method of claim 10, wherein adjusting the expected area associated with each transmitter comprises:

the center of the expected area is moved based on the predicted power and the received power of the transmitter.

15. The method of claim 14, wherein the predicted power is determined based on a path loss prediction model.

16. The method of claim 10, wherein the at least one scaling factor for each transmitter is determined based on a received signal strength of the transmitter measured at the terminal.

17. The method of claim 10, wherein the at least one scaling factor for each transmitter is determined based on received power of the transmitter measured at the terminal.

18. The method of claim 10, wherein the at least one scaling factor for each transmitter is determined based on a transmit power of the transmitter.

19. The method of claim 10, wherein at least one scaling factor for each transmitter is determined based on a Round Trip Delay (RTD) made by the transmitter.

20. The method of claim 5, wherein the plurality of prospective regions are combined to determine a combined prospective region, which is provided as an estimate of the location of the terminal.

21. The method of claim 20, wherein combining the plurality of expected regions comprises:

the centers of the plurality of prospective regions are combined to determine a center of the combined prospective region.

22. The method of claim 20, wherein combining the plurality of expected regions comprises:

the centers of the plurality of expected areas are combined based on the predicted power and the received power of each transmitter to determine a center of the combined expected area.

23. The method of claim 22, wherein the center of the combined expected area is determined to minimize a root mean square difference between predicted and received powers for the plurality of transmitters.

24. The method of claim 20, wherein combining the plurality of expected regions comprises:

determining a unit error of combining the expected areas, an

Scaling the combined expected area based on the unit error.

25. The method of claim 24, wherein the single-bit error is determined based on a normalized mean-spacing-sigma between the combined expected region and each of the plurality of expected regions.

26. The method of claim 5, wherein combining the plurality of expected regions comprises:

determining a plurality of weights for a plurality of expected regions, wherein the plurality of expected regions are combined based on the plurality of weights.

27. The method of claim 26, wherein the weight for each expected region is determined based on an uncertainty associated with the expected region.

28. The method of claim 27, wherein the uncertainty associated with each expected area is represented as a level estimated position error (HEPE).

29. The method of claim 5, wherein combining the plurality of expected regions comprises:

determining a plurality of weights for the plurality of expected regions,

scaling the plurality of expected regions based on the associated weights,

combining the scaled prospective regions to determine a combined prospective region,

the centers of the plurality of expected regions are scaled based on the associated weights,

combining the scaled centers of the plurality of expected areas to determine a center of a combined expected area, wherein the combined expected area and the combined expected area center are provided as an estimate of the location of the terminal.

30. The method of claim 5, wherein the expected area associated with each transmitter is determined based on a maximum antenna range associated with the transmitter.

31. The method of claim 5, wherein the expected area associated with each transmitter is determined based on the antenna position and orientation of the transmitter.

32. The method of claim 5, wherein the expected area associated with each transmitter comprises a location to be used as the estimated location of the terminal and an area in which the terminal may be located.

33. A method of estimating a location of a terminal in a wireless communication network, comprising:

receiving identities of a plurality of transmitters, the identities to be used to estimate a location of a terminal;

determining a desired region and a scaling factor for each of the plurality of transmitters;

adjusting each prospective region based on the associated scaling factor to provide an adjusted prospective region;

determining a plurality of weights for the plurality of transmitters;

combining the plurality of adjusted expected areas based on the plurality of weights to determine a combined expected area to be provided as the estimated location of the terminal.

34. The method of claim 33, wherein the scaling factor for each transmitter is determined based on a received signal strength or a received power of the transmitter measured at the terminal.

35. The method of claim 33, wherein the weight for each expected region is determined based on an uncertainty associated with the expected region.

36. The method of claim 33, wherein combining a plurality of expected regions comprises:

weighting the centers of the plurality of expected regions based on the associated weights,

combining the weighted centers of the prospective regions to determine a center of the combined prospective region,

scaling the plurality of expected regions based on the associated weights, an

The scaled prospective regions are combined to determine a combined prospective region.

37. The method of claim 33, wherein the wireless communication network is a CDMA network.

38. A memory communicatively coupled to a Digital Signal Processing Device (DSPD) capable of interpreting digital signals to:

receiving identities of a plurality of transmitters, the identities being used to estimate a location of a terminal;

determining a plurality of expected regions for the plurality of transmitters; and

combining the plurality of expected areas of the plurality of transmitters to estimate the location of the terminal.

39. An apparatus in a wireless communication network, comprising:

means for receiving identities of a plurality of transmitters, the identities being used to estimate a location of a terminal;

means for determining a plurality of expected regions for the plurality of transmitters; and

means for combining a plurality of expected areas of the plurality of transmitters to estimate a location of a terminal.

40. The apparatus of claim 39, further comprising:

means for weighting the centers of the plurality of prospective regions based on the associated weights,

means for combining the weighted centers of the prospective regions to determine a center of the combined prospective regions,

means for scaling the plurality of expected regions based on the associated weights, and

means for combining the scaled expected regions to determine a combined expected region.

41. A terminal comprising the apparatus of claim 39.

42. A Position Determining Entity (PDE) comprising the apparatus of claim 39.