WO2016122860A1

WO2016122860A1 - Method and apparatus for obtaining arrival time difference in mobile positioning

Info

Publication number: WO2016122860A1
Application number: PCT/US2016/012871
Authority: WO
Inventors: Wenfeng Zhang
Original assignee: Zte Corporation
Priority date: 2015-01-29
Filing date: 2016-01-11
Publication date: 2016-08-04

Abstract

New method for obtaining arrival time differences for TDOA-based mobile positioning, with the reference node to be determined on either user equipment side or network side. According to some embodiments, one eNB is selected, among a second number of eNBs or a sub-group of the second number of eNBs, when the selected eNB corresponds to the earliest arrival time of positioning signal among the positioning signals transmitted by the second number of eNBs or the sub-group of the second number of eNBs. According to some embodiments, a common offset value is subtracted from the second number of detected arrival times to obtain the second number of adjusted arrival times and the second number of adjusted arrival times are then transmitted to the network side for determining the current position of the user equipment.

Description

METHOD AND APPARATUS FOR OBTAINING ARRIVAL TIME DIFFERENCE IN MOBILE POSITIONING

TECHNICAL FIELD

[0001] The present application relates to mobile positioning and, in particular to, method apparatus to obtain the time difference of arrival (TDOA) measurement used in mobile positioning. The present application has a specific application but not limited to the mobile positioning in 3GPP Long Term Evolution (LTE) system that is one of the candidates for the 4-th generation wireless system.

BACKGROUND

[0002] It is expected that location based services (LCS) will bring great convenience and new exciting services to subscribers of future mobile communication networks and therefore generate significant revenues to the operators. LCS requires the integration of wireless network infrastructure, mobile terminals, and a range of location-specific applications and content. The fundamental technology supporting LCS, however, is mobile terminal positioning.

[0003] There are mainly five mobile positioning techniques discussed in 3GPP standard body. They are methods based on cell-ID, assisted-GPS signal, angle-of-arrive (AO A) measurement, time-of-arrival (TOA) measurement and time-difference-of-arrival (TDOA) measurement (also called observed-time-difference-of-arrival (OTDOA)). Among them, TDOA based positioning technique has been chosen by 3 GPP standard body as the solution in E-UTRAN LTE release 9. In TDOA positioning solution as shown in Figure 1, the network, or the network node responsible for mobile positioning, configures the mobile terminal, or so-called "user equipment" (UE), to measure the positioning signals transmitted by one reference base station, or so-called "reference eNB", and a number of neighboring base stations (i.e. neighboring eNB), where the reference eNB and the neighboring eNBs are synchronized with each other regarding the transmission of positioning signals. Such configuration is conveyed to the UE via UE's serving eNB. The UE measures those positioning signals transmitted by configured eNBs and detects the arrival time (^⁰ ) of the positioning signal transmitted by the reference eNB and the arrival times (^ ,l≤i≤N) of positioning signals transmitted by N neighboring eNBs. In the example shown in Figure 1, the arrival time (^¹ ) for the neighboring eNB 1 is the earliest, followed by the arrival times for the reference eNB (^⁰ ) and other neighboring eNBs. The UE further calculates the N arrival time differences between each arrival time ,l≤i≤N) of positioning signal coming from each of N neighboring eNBs and the arrival time (^⁰ ) of positioning signal coming from the reference eNB. These N arrival time differences, (l≤i≤N), along with their correspondence to the N neighboring eNBs are reported to the network via serving eNB of the UE. Given reported arrival time difference ^{tj t(i} , the network can assume the UE' s position is close to the joint locations of N hyperbolic curves (for two-dimensional positioning) or N hyperbolic surfaces (for three-dimensional positioning), each of which is determined by the location of i-th neighboring eNB, the location of reference eNB and the propagation distance difference ^~ ^ assuming line-of-sight (LOS) propagation condition, where c is the speed of light. Therefore, the best estimated UE position is the one that has the least square of error distances to all N hyperbolic curves or surfaces.

[0004] Mathematically, assume the following two-by-one (for 2D positioning) or three-by-one (for 3D positioning) vectors:

• P = (x, yf or (x, y, z)^T to represent the location of UE.

• P₀ = (x₀ , y₀ Y or (x₀ , y₀ , z₀ )^T to represent the location of reference eNB.

• P_t = (x, , y_t Y or (x_; , y_j , z_j )^T (1 < / < N ) to represent the locations of N neighboring eNBs.

[0005] The TDOA measurements can lead to N equations by definition:

P - P \ for \≤i≤N (1) where P - P (0 < i < N ) is the distance between location P of UE and location P_t of i-th eNB (i=0 refers to the reference eNB, i>0 refers to the neighboring eNB), and equals to

case). In order to remove the square-root operation and to reach a simple linear formulation in terms of P , both sides of equation (1) are squared, i.e. P - P₀1 + Δ_Ί . ) = |R - ^. | , which further gives (?, - ? ^■? + A, P - P_n P P. A, for 1 < i < N (2)

[0006] The equation (2) is a typical linear optimization problem based on N linear equations, in terms of three unknown variables (x,y, P - P_n ) (for 2D positioning) or four unknown variables (x, y, z, P - P_n ) (for 3D positioning). The mathematic solution for such optimization problem could be straight-forward, depending on whether the additional constraint between (x,y) or (x,y,z) and P -P. is taken into account.

[0007] However, when the above equation (1) is converted into the above equation

(2) with the "square" operation applied on both side of equation (1), the equation (2) includes two cases for each index i:

• Case-1 : P - P, p - p, This is the true condition align with equation (1).

• Case-2: P - P_n P - P . This is the false condition not align with equation (1).

[0008] Due to the inaccurate measurements of · (l≤i≤ th_e optimal solution of

P could come from the case-2 condition rather than the case-1 condition. In other words, some optimization solutions derived from the linear equation (2) may not work for the original equation (1), and therefore could contain large positioning errors.

SUMMARY

[0009] The present application provides a new method for obtaining arrival time differences for TDOA-based mobile positioning, with the reference node to be determined on either user equipment side or network side.

[0010] According to a first aspect of the present invention, a method for obtaining arrival time differences for TDOA based mobile positioning is performed by a network and a user equipment. The method comprises the following steps: sending, by a network, configuration information to a user equipment (UE) to configure the UE with a first number of eNBs; upon receipt of the configuration information from the network, measuring and detecting, by the UE, arrival times of positioning signals transmitted from a second number of eNBs among the first number of eNBs; selecting, by the UE, one eNB among the second number of eNBs, wherein one of the selected eNBs corresponds to an earliest arrival time of positioning signal among the positioning signals transmitted by the second number of eNBs; and taking, by the UE, the selected eNB as a reference eNB and the others of the second number of eNBs as neighbouring eNBs, and calculating, by the UE, a third number of arrival time differences by subtracting the arrival time of the reference eNB from the arrival times of the neighbouring eNBs.

[0011] According to a second aspect of the present invention, a method for obtaining arrival time differences for TDOA based mobile positioning is performed by a network and a user equipment. The method comprises the following steps: sending, by a network, configuration information to a user equipment (UE) to configure the UE with a first number of eNBs; upon receipt of the configuration information from the network, measuring and detecting, by the UE, arrival times of positioning signals transmitted from a second number of eNBs among a first number of configured eNBs; subtracting, by the UE, a common offset value from detected arrival times of the second number of eNBs to obtain a second number of adjusted arrival times; reporting, by the UE, to the network the second number of adjusted arrival times and their correspondences to the second number of eNBs for which the positioning signal arrival times are detected; upon receipt of the report from the UE, selecting, by the network, one eNB from the reported second number of eNBs, wherein the selected eNBs corresponds to an earliest adjusted arrival time among the reported second number of adjusted arrival times; and taking, by the network, the selected eNB as a reference eNB and the rest of the reported second number of eNBs as neighbouring eNBs, and calculating a third number of arrival time differences by subtracting the reported adjusted arrival time of the reference eNB from the reported adjusted arrival times of the neighbouring eNBs.

[0012] According to a third aspect of the present invention, an apparatus for obtaining arrival time differences for TDOA based mobile positioning is configured to: send configuration information to a user equipment (UE) to configure the UE with a first number of eNBs; upon receipt of from the UE a report containing a second number of adjusted arrival times and a corresponding second number of eNBs, select one eNB from the second number of the reported eNBs, where the selected eNB corresponds to an earliest adjusted arrival time among the second number of reported adjusted arrival times; take the selected eNB as a reference eNB and the others of the second number of reported eNBs as neighbouring eNBs, and calculate a third number of arrival time differences by subtracting a reported adjusted arrival time of reference eNB from reported adjusted arrival times of the neighbouring eNBs. [0013] According to a fourth aspect of the present invention, a method for obtaining arrival time differences for TDOA based mobile positioning is performed by a user equipment. The method comprises the following steps: measuring and detecting, by a user equipment (UE), arrival times of positioning signals transmitted from a second number of eNBs among a first number of configured eNBs; subtracting, by the UE, a common offset value from the detected arrival times of the second number of eNBs to obtain a second number of adjusted arrival times; and reporting, by the UE, to a network the second number of adjusted arrival times and their correspondence to the second number of eNBs for which the positioning signal arrival times are detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 depicts an example of TDOA system involving eNBs and UE, as well as the arrival time schematic.

[0015] Figure 2 depicts the TDOA positioning performances on the horizontal 2D surface and elevation with and without the method of the present application.

[0016] Figure 3 depicts the TDOA procedure with reference eNB determined on the

UE side according to some embodiments of the present application.

[0017] Figure 4 depicts the TDOA procedure with reference eNB determined on the network side according to some embodiments of the present application.

DETAILED DESCRIPTION

[0018] The present application is directed to a method to minimize the impact of the above case-2 false condition by making at least one of the TDOA measurements ^to ) to be non-negative. Although the method is designed for mobile positioning in 3GPP LTE system, the same principle can be used in other positioning system based on the TDOA technique.

[0019] These and other implementations and examples of the present application in software and hardware are described in greater details below. [0020] It can be seen that the above case-2 condition can possibly occur when ^ is negative; therefore one method to minimize the impact of the case-2 false condition for the i- th TDOA formulation in equation (2) is to make the TDOA arrival time difference ^ or equivalently (1 < ^/' < N ) non-negative, i.e., the reference eNB should have earlier arrival time at the UE than i-th neighboring eNB. This not only means that the determination of the reference eNB is performed on a per-UE basis, but also means that such determination depends on the detected arrival times and therefore should be done after the UE successfully measures the arrival times.

[0021] Figure 2 shows positioning accuracy on both horizontal surface and elevation between the following two methods:

• The reference eNB is selected to have the earliest arrival time so that the arrival time difference (TDOA) is always non-negative.

• The reference eNB is randomly selected so that the arrival timing difference (TDOA) can be either positive or negative.

[0022] The positioning accuracy shown in Figure 2 is indicated by cumulative density function (CDF) curve, which represents the probability for the positioning error to be less than a specific distance value. For example, for a probability of 60%, the positioning error on horizontal surface is no larger than 35m if the reference eNB is selected to have earliest arrival time, and is above 55m if the reference eNB is randomly selected. Note that the method of reference eNB selection disclosed in the present application is more effective to improve the positioning performance. In the simulation to obtain the CDF curves shown in Figure 2, the UE is assumed to measure and detect positioning signals transmitted from 10 eNBs, and the propagation paths between eNB and UE do not necessarily meet the line-of- sight condition.

[0023] In some embodiments, the reference eNB can be determined by the UE after the UE detects the arrival times and before the UE position is estimated by applying equation (1) or (2). The following steps focus on the application where the reference eNB is determined by the UE. Note that the current LTE standard also allows the UE to change the reference eNB differently from the one configured by the network. However, the current LTE standard does not specify the criteria for such change on the UE side. The steps performed in both network side and UE side to derive the arrival time differences and to use the derived arrival time differences for mobile positioning are shown in Figure 3 and given with details as following.

[0024] The network configures (310) the UE with a number (>N+1) of eNBs that are synchronized with each other in terms of transmission of positioning signals. According to this configuration, even though the network does not need to assign one specific eNB as reference eNB, it can inform the UE of certain restrictions on the selection of reference eNB. Such restriction information can be the information indicating which of the configured eNBs can be or cannot be used by the UE as reference eNB. Such indication information can be in the form of an indication flag attached to each configured eNB, where the indication flag can indicate, by either its existence or its value, whether the corresponding eNB can be used as a candidate in reference eNB selection. For example, different eNBs may have different capabilities to synchronize to a common time clock such as GPS time clock. This network node synchronization error, if existing in the reference eNB, would propagate to all calculations of arrival time difference. Therefore, the network can attach a flag or assign a specific flag value to each of a sub-group of configured eNBs, whose network node synchronization is not highly accurate, to prevent UE from selecting the reference eNB from those eNBs. In some embodiments, the network may also attach a flag or assign a specific flag value to each of a sub-group of eNBs, whose network node synchronization is highly accurate, to direct the UE to select reference eNB from these eNBs. Network node synchronization accuracy is one exemplary criterion for the restriction signaling. Other criteria for the network to take into account are also possible and may be used in combination with the criterion above.

[0025] Upon receipt of the configuration information from the network, the UE measures (320) the arrival times of positioning signals transmitted by the configured eNBs and detects the (N+l) arrival times, ^ (0 < ^/' < N^ ₀f th_e positioning signals transmitted by (N+l) configured eNBs.

[0026] The UE selects (330) one eNB among these (N+l) eNBs or a sub-group of these (N+l) eNBs, where the UE-selected eNB corresponds to the earliest (i.e. smallest) arrival time of positioning signal among those transmitted by these (N+l) eNBs or the subgroup of these N+l eNBs. The sub-group of these (N+l) eNBs, if applicable, is determined locally on the UE side by taking into account various information such as the quality of timing detection (signal-to-noise ratio, timing variance, etc.) and the restriction information configured by the network indicating which eNBs can be or cannot be used as reference eNB.

[0027] The UE takes (340) the selected eNB, whose index is assumed to be ^z° (

0≤ ^zo ^≤ _{as re}f_erence gjs^ _ancj _rest ]sj _e fBs as neighboring eNBs, and calculates N TDOA arrival time differences by ^t,a for 0 < z < N _ancj ¹≠ ^zo

[0028] The UE reports (350) to the network, via higher-layer signaling, the selection of reference eNB, the N TDOA arrival time differences and their correspondences to N neighboring eNBs. In the report, the TDOA arrival time differences can be in quantization form; each of reference eNB and neighboring eNB is identified by the corresponding cell identification number of the eNB.

[0029] Upon receipt of the report from the UE, the network determines (360) the location of the UE based on the location of reported reference eNB, the locations of N reported neighboring eNBs and the N reported arrival time differences. The algorithm used in the location determination can follow equation (1), equation (2) or other optimization principles.

[0030] In some embodiments, the reference eNB can be determined by the network.

The following steps focus on the application where the reference eNB is determined by the network. The steps performed in both the network side and the UE side to derive the arrival time differences and to use the derived arrival time differences for mobile positioning are shown in Figure 4 and given with details as following.

[0031] The network configures (410) the UE with a number (>N+1) of eNBs that are synchronized with each other in terms of transmission of positioning signals. According to this configuration, the network does not need to assign one specific eNB as reference eNB.

[0032] Upon receipt of the configuration information from the network, the UE measures (420) the arrival times of positioning signals transmitted by the configured eNBs and detects the (N+l) arrival times, ^ ( 0 < ^/' < N ^ ₀f fa_e positioning signals transmitted by N+l configured eNBs. [0033] The UE may subtract (430) a common offset value, ^toffset , from the (N+1) detected arrival times to obtain (N+1) adjusted arrival times, ^toffset (0 < ^/' < N^ that are to be reported to the network. One purpose of this step is to reduce the number of digitized bits required to report the arrival time so as to save certain reporting overhead. One example to achieve this benefit is ^{toffset m n} ^ . The subtracted common offset value ( ^tqffset ) does not need to be known to the network and does not need to be the same for different UEs.

[0034] The UE reports (440) to the network, via higher-layer signaling, the (N+1) adjusted arrival times and their correspondences to the (N+1) eNBs for which the positioning signal arrival times are detected. In the report, the adjusted arrival times can be in

quantization form; each of the (N+1) eNB is identified by the corresponding cell

identification number. The UE can also include in the report other information that can be used by the network to assist the determination of reference eNB, such as the quality of timing detection (signal-to-noise ratio, timing variance, etc.). It should be noted that, in cases where the common offset value used to subtract the detected arrival times is the detected arrival time for a specific eNB, and such setting of common offset value is known to the network, the corresponding adjusted arrival time is deemed to be zero, such that UE may omit the adjusted arrival time for that specific eNB from the report, but still needs to inform in the report the identification of that specific eNB, if that information is not known by network. In such a case, the UE's report only contains N adjusted arrival times, but the network would know there is a (N+l)-th adjusted arrival time, though not reported, whose value is zero.

[0035] Upon receipt of the UE's report, which contains (N+1) adjusted arrival times and the corresponding (N+1) eNBs, the network selects (450) one eNB from these (N+1) eNBs or a sub-group of these (N+1) eNBs, where the selected eNB corresponds to the earliest (i.e., smallest) adjusted arrival time among those (N+1) adjusted arrival times or the subgroup of those (N+1) adjusted arrival times. The sub-group, if applicable, is determined on the network side, by taking into account various information such as the reported quality of timing detection (signal-to-noise ratio, timing variance, etc.) and the information such as which eNB can be or cannot be used as reference eNB. If the network knows that the common offset value used by UE to subtract the detected arrival times to obtain adjusted arrival times is equal to the detected arrival value for a specific eNB, and the report received by the network contains only N adjusted arrival times, the network adds the (N+l)-th adjusted arrival time whose value is zero and uses all of the (N+1) adjusted arrival times to select reference eNB as mentioned above.

[0036] The network takes (460) the selected eNB, whose index is assumed to be ^z° (

0≤ ^zo^≤ _{as re}f_erence gjs^ _ancj _{me rest} ]sj reported eNBs as neighboring eNBs, and calculates N arrival time differences by subtracting the adjusted arrival time corresponding to the determined reference eNB from the adjusted arrival times corresponding to the N determined neighboring eNBs, i.e. ^{~ toffset} ^^~ ^° ^{~ toffset} ) ^{= t}- ^~ for ^{0≤ i≤ N} and ^1≠1° .

[0037] The network determines (470) the location of the UE based on the location of the determined reference eNB, the locations of N determined neighboring eNBs and the N TDOA arrival time differences. The algorithm used in location determination can follow equation (1), equation (2) or other optimization principles.

[0038] As mentioned above, TDOA-based mobile positioning requires that the reference eNB and neighboring eNBs are synchronized with each other in terms of transmission of positioning signals. In some embodiments, the condition of "synchronized" refers to both of following cases:

• All the eNBs transmit the positioning signals at the same time instance;

• The eNBs transmit the positioning signals at either the same or different time

instances, i.e., the synchronization differences are either zero or non-zero. However, these synchronization differences, if non-zero, are known to the network. The known synchronization difference between the i-th neighboring eNB and reference eNB can be compensated in the TDOA algorithm by subtracting the synchronization difference from the measured arrival time difference ( t, - 1₀ ) associated with i-th neighboring eNB and reference eNB. Therefore, the two eNBs, whose positioning signal transmission timings are not aligned with each other, are still considered satisfying the "synchronized" condition if the time difference between the positioning signal transmission timings is known to the network.

[0039] Throughout this application, the positioning nodes on the network side are called "reference eNB" and "neighboring eNB". Note that the positioning nodes may also be named as "reference cell" and "neighboring cell" in some other embodiments. [0040] The operations depicted in Figure 3 and Figure 4 on the network side can be implemented in one or multiple apparatuses or modules in one or multiple network nodes. The operations shown in Figure 3 and Figure 4 on the UE side can be implemented in one or multiple apparatuses or modules in one UE.

[0041] In some embodiments, the above described methods and their variations may be implemented as computer software or firmware instructions. Such instructions may be stored in an article with one or more machine-readable storage devices connected to one or more computers or integrated circuits or digital processors such as digital signal processors and microprocessors. In a communication system of 3GPP LTE, the claimed method and related operation process may be implemented in form of software instructions or firmware instructions for execution by a processor in the transmitter and receiver or the transmission and reception controller. In operation, the instructions are executed by one or more processors to cause the transmitter and receiver or the transmission and reception controller to perform the described functions and operations.

Claims

CLAIMS What is claimed is:

1. A method for obtaining arrival time differences for TDOA based mobile positioning, comprising:

sending, by a network, configuration information to a user equipment (UE) to

configure the UE with a first number of e Bs;

upon receipt of the configuration information from the network, measuring and detecting, by the UE, arrival times of positioning signals transmitted from a second number of eNBs among the first number of eNBs;

selecting, by the UE, one eNB among the second number of eNBs, wherein the selected eNB corresponds to an earliest arrival time of positioning signal among the positioning signals transmitted by the second number of eNBs; and taking, by the UE, the selected eNB as a reference eNB and the others of the second number of eNBs as neighboring eNBs, and calculating, by the UE, a third number of arrival time differences by subtracting the arrival time of the reference eNB from the arrival times of the neighboring eNBs.

2. The method according to claim 1, wherein the configuration information sent by the network does not differentiate the reference eNB from the neighboring eNBs.

3. The method according to claim 1, wherein the configuration information sent by the network contains restriction information for the reference eNB selection.

4. The method according to claim 3, wherein the restriction information indicates which of the second number of eNBs can be used as the reference eNB.

5. The method according to claim 3, wherein the restriction information indicates which of the second number of eNBs cannot be used as the reference eNB.

6. The method according to claim 1, wherein the selected eNB is determined by the user equipment.

7. The method according to claim 6, wherein the determination of the selected eNB is based on restriction information provided by the network.

8. A method for obtaining arrival time differences for TDOA based mobile positioning, comprising:

sending, by a network, configuration information to a user equipment (UE) to

configure the UE with a first number of eNBs;

upon receipt of the configuration information from the network, measuring and

detecting, by the UE, arrival times of positioning signals transmitted from a second number of eNBs among a first number of configured eNBs;

subtracting, by the UE, a common offset value from detected arrival times of the second number of eNBs to obtain a second number of adjusted arrival times; reporting, by the UE, to the network the second number of adjusted arrival times and their correspondences to the second number of eNBs for which the positioning signal arrival times are detected;

upon receipt of the report from the UE, selecting, by the network, one eNB from the reported second number of eNBs, wherein the selected eNBs corresponds to an earliest adjusted arrival time among the reported second number of adjusted arrival times; and

taking, by the network, the selected eNB as a reference eNB and the rest of the

reported second number of eNBs as neighboring eNBs, and calculating a third number of arrival time differences by subtracting the reported adjusted arrival time of the reference eNB from the reported adjusted arrival times of the neighboring eNBs.

9. The method according to claim 8, wherein the configuration information sent by the network does not differentiate the reference e B from the neighboring eNBs.

10. The method according to claim 8, wherein the common offset value is determined by the user equipment.

11. The method according to claim 10, wherein the common offset value is set to be a

minimum of the detected arrival times.

12. An apparatus for obtaining arrival time differences for TDOA based mobile positioning, wherein the apparatus is configured to:

send configuration information to a user equipment (UE) to configure the UE with a first number of eNBs;

upon receipt of from the UE a report containing a second number of adjusted arrival times and a corresponding second number of eNBs, select one eNB from the second number of the reported eNBs, where the selected eNB corresponds to an earliest adjusted arrival time among the second number of reported adjusted arrival times;

take the selected eNB as a reference eNB and the others of the second number of reported eNBs as neighboring eNBs, and calculate a third number of arrival time differences by subtracting a reported adjusted arrival time of reference eNB from reported adjusted arrival times of the neighboring eNBs.

13. The apparatus according to claim 12, wherein the configuration information does not differentiate the reference eNB from the neighboring eNBs.

14. The apparatus according to claim 12, where the apparatus is a network node.

15. A method for obtaining arrival time differences for TDOA based mobile positioning, comprising: measuring and detecting, by a user equipment (UE), arrival times of positioning signals transmitted from a second number of e Bs among a first number of configured eNBs;

subtracting, by the UE, a common offset value from the detected arrival times of the second number of eNBs to obtain a second number of adjusted arrival times; and reporting, by the UE, to a network the second number of adjusted arrival times and their correspondence to the second number of eNBs for which the positioning signal arrival times are detected.

16. The method according to claim 15, wherein the common offset value is set to be a

minimum of the detected arrival times.