CN101400047A - Apparatus and method for eliminating blind region of arrival time difference positioning algorithm in cellular communication system - Google Patents

Abstract

A method for eliminating blind zone for location algorithm of time difference of arrival in cellular communication system comprises steps: sequentially ranking and three in one group according to characteristic parameter of transmitted signal between mobile station and multiple base station; selecting characteristic parameter combination S<i>; measuring time difference of arrival between adjacent base station and main service base station in combination S<i>; judging the type of blind zone; judging if traversing all combination, if it is true then entering into step f, if it is false, then repeating step c; mobile station is located at blind zone of all base station combination, the positioning fails; selecting base station combination not in blind zone as base station combination for participating in triplet algorithm of time difference of arrival for positioning. The inventive method can effectively eliminate blind zone resulting from positioning algorithm of time difference of arrival, thereby reducing positioning error and promoting positioning precision.

Description

Apparatus and method for eliminating blind zone of arrival time difference positioning algorithm in cellular communication system

Technical Field

The invention relates to a device and a method for eliminating blind areas of a cellular wireless network time difference of arrival (TDOA) positioning algorithm.

Background

The positioning of a mobile station in a wireless positioning system is carried out by detecting characteristic parameters (such as electromagnetic field strength, propagation time or time difference, incident angle, etc.) of signals propagating between the mobile station and a plurality of fixed-position transceivers to estimate the geometric position of the target mobile station. In cellular networks, wireless location schemes for mobile stations can be classified into three categories according to the location at which location estimation is performed, the location subject, and the equipment employed: mobile station based positioning schemes, network based positioning schemes and GPS assisted positioning schemes. According to different positioning methods, the method mainly comprises the following steps: time of arrival (TOA) location methods, time difference of arrival (TDOA) location methods, angle of arrival (AOA) location methods, Cell-ID based location and time lift-off (TA) based location methods.

Currently, time difference of arrival (TDOA) positioning, also called hyperbolic positioning algorithm, is a technology mainly studied and adopted in the current cellular communication network positioning technology. As shown in the figure, when the distance difference R between the BS1 and BS2 and the mobile station is known₂₁＝R₂-R₁When the mobile station is located at the focus of two base stations, the distance difference between the mobile station and the two base stations is always R₂₁On the hyperbolic solid line. When the distance differences R between the base stations BS1 and BS3 and the mobile station are known at the same time₃₁＝R₃-R₁Then another set of two base stations BS can be obtained₁And BS₃Is a focal point, and has a constant distance difference R from the two focal points₃₁On the dashed hyperbolic pair. As a result of this, the number of the,the intersection of the two sets of hyperbolas represents an estimate of the mobile station.

Let the coordinates of the mobile station be (x)₀，y₀) And the coordinates of the base station are (x)_i，y_i) (i 1, 2, 3.) has the following relationship

$\left\{\begin{array}{c}{(\sqrt{{(x_o-x_2)}^2+{(y_0-y_2)}^2}-\sqrt{{(x_o-x_1)}^2+{(y_0-y_1)}^2})}^2=R_{21}^2\\ {(\sqrt{{(x_o-x_3)}^2+{(y_0-y_3)}^2}-\sqrt{{(x_o-x_1)}^2+{(y_0-y_1)}^2})}^2=R_{31}^2\end{array}\right.---\left(1\right)$

Wherein R is₂₁And R₃₁By measuring the time difference between the arrival of the signals from the two base stations at the target mobile terminal or the time difference t between the arrival of the signals from the mobile station at the two base stations₂₁And t₃₁To be determined. Is obviously provided with R₂₁＝c×t₂₁And R₃₁＝c×t₃₁Wherein c is the propagation speed of the electromagnetic wave in the air.

In order to solve the nonlinear hyperbolic equation, linearization process can be performed first, and the distance between the mobile station and the ith base station is set as R_iThen, then

Wherein, $K_i=x_i^2+y_i^2---\left(3\right)$

because of this, it is possible to reduce the number of the, $R_i^2={({\mathrm{<figure-callout\; id="1"\; label="R\; i"\; filenames="A200710151538E00141.png,A200710151538E00171.png"\; state="\{\{state\}\}">R</figure-callout>}}_i+R_1)}^2---\left(4\right)$

is unfolded $R_{i1}^2+2R_{i1}{R}_1+R_1^2=K_i-2x_i{x}_0-2y_i{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="A200710151538E00171.png"\; state="\{\{state\}\}">y</figure-callout>}}_0+x_0^2+y_0^2---\left(5\right)$

According to (2) obtaining ${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A200710151538E00141.png,A200710151538E00171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^2==K_1-2x_1{x}_0-2y_1{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="A200710151538E00171.png"\; state="\{\{state\}\}">y</figure-callout>}}_0+x_0^2+{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="A200710151538E00171.png"\; state="\{\{state\}\}">y</figure-callout>}}_0^2---\left(6\right)$

(5) - (6) to obtain $R_{i1}^2+2R_{i1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A200710151538E00141.png,A200710151538E00171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1=K_i-2(x_i-x_1)x_0-2(y_i-y_1)y_0-K_1---\left(7\right)$

When the number of available base stations is 3, (7) can be expressed as

<math> <mrow> <mrow> <mfenced open='[' close=']' separators=' '> <mtable> <mtr> <mtd> <msub> <mi>x</mi> <mn>0</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>y</mi> <mn>0</mn> </msub> </mtd> </mtr> </mtable> </mfenced> </mrow> <mo>=</mo> <mo>-</mo> <msup> <mrow> <mfenced open='[' close=']'> <mtable> <mtr> <mtd> <msub> <mi>x</mi> <mn>2</mn> </msub> <mo>-</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> </mtd> <mtd> <msub> <mi>y</mi> <mn>2</mn> </msub> <mo>-</mo> <msub> <mi>y</mi> <mn>1</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>x</mi> <mn>3</mn> </msub> <mo>-</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> </mtd> <mtd> <msub> <mi>y</mi> <mn>3</mn> </msub> <mo>-</mo> <msub> <mi>y</mi> <mn>1</mn> </msub> </mtd> </mtr> </mtable> </mfenced> </mrow> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mo>&times;</mo> <mrow> <mo>{</mo> <mrow> <mfenced open='[' close=']' separators=' '> <mtable> <mtr> <mtd> <msub> <mi>R</mi> <mn>21</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msub> <mi>R</mi> <mn>31</mn> </msub> </mtd> </mtr> </mtable> </mfenced> </mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <mrow> <mfenced open='[' close=']' separators=' '> <mtable> <mtr> <mtd> <msubsup> <mi>R</mi> <mn>21</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <mo>+</mo> <msub> <mi>K</mi> <mn>1</mn> </msub> </mtd> </mtr> <mtr> <mtd> <msubsup> <mi>R</mi> <mn>31</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msub> <mi>K</mi> <mn>3</mn> </msub> <mo>+</mo> <msub> <mi>K</mi> <mn>1</mn> </msub> </mtd> </mtr> </mtable> </mfenced> </mrow> <mo>}</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>8</mn> <mo>)</mo> </mrow> </mrow></math>

Substituting (8) for formula (6) to obtain a compound related to R₁Is calculated back to (8) to obtain the estimated position (x) of the mobile station₀，y₀)。

By the above derivation, the solution is about R₁The quadratic equation of (a) can obtain two solutions, and the two solutions can be classified into the following types according to different conditions:

1.R₁there are two positive roots in the real number domain, which correspond to two intersections of two pairs of hyperbolas respectively. Therefore, in the hyperbolic positioning algorithm, a deblurring area exists, and the position of the mobile station cannot be positioned on the premise of no prior information, which is called as a position ambiguity area.

2.R₁There is a positive root in the real number domain, there is a unique intersection point corresponding to two pairs of hyperbolas, the estimated position of the mobile station is unique, and the position of the mobile station can be estimated.

3.R₁Without positive root or R in the real number domain₁Without a real number, there is no intersection point for the two pairs of hyperbolas, and the location of the mobile station is not estimable.

Therefore, when the hyperbolic positioning algorithm is applied to the cellular communication network, a fuzzy and non-estimable area of the mobile station exists, which is called as a blind area of the time difference of arrival positioning algorithm, and positioning errors are introduced due to the existence of the blind area, so that the positioning accuracy is reduced.

Disclosure of Invention

The invention aims to provide a device and a method for eliminating blind areas of an arrival time difference positioning algorithm in a cellular communication system.

To achieve the above object, a method for eliminating blind areas in an arrival time difference positioning algorithm in a cellular communication system comprises the steps of:

a) arranging every three groups according to the characteristic parameter sequence of the signals transmitted between the mobile station and the base stations;

b) selecting a characteristic parameter combination S_i；

c) Measurement combination S_iThe arrival time difference between the adjacent base station and the main service base station;

d) judging the type of the blind area;

e) judging whether all the combinations are traversed, if true, entering the step f, and if false, repeating the step c;

f) the mobile station is positioned in the blind area of all the base station combinations, and the positioning fails;

g) and selecting the base station combination which is not in the blind area as the base station combination participating in the arrival time difference triangulation algorithm to perform positioning operation.

The invention provides a method for eliminating blind areas of a time difference of arrival (TDOA) positioning algorithm in a cellular communication system, which mainly comprises the following steps: by analyzing the cause of the blind zone brought by the time difference of arrival algorithm in the cellular communication system, different conditions of the blind zone generation are further provided. According to different conditions of blind areas, a method for eliminating the blind area of an arrival time difference algorithm in a cellular communication system by introducing prior information of cell radius is provided. And the contribution of the method on reducing the positioning error and improving the positioning precision is proved through simulation data.

Drawings

FIG. 1 is a diagram of a time difference of arrival location method;

FIG. 2 is a reference coordinate system diagram;

FIG. 3 is a cellular network diagram;

FIG. 4 is a blind spot elimination flow chart;

FIG. 5 is a Wimax LBS network reference model;

FIG. 6 is a functional block diagram of a mobile terminal;

FIG. 7 is a plot of the blind spot elimination algorithm positioning error CDF.

Detailed Description

To further discuss the multi-solution problem of the hyperbolic positioning algorithm, the following analysis method is introduced, and the coordinate relationship of the base stations participating in positioning is set as shown in fig. 2

Let R₂₁And R₃₁The distances between the mobile station BS2, BS3 and the primary serving BS1, respectively, are (x)₀-x₂)²+y²＝(R₁-R₂₁)² (9a)

(x₀-x₃)²+(y-y₃)²＝(R₁-R₃₁)² (9b)

Wherein $R_1^2=x_0^2+{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="A200710151538E00171.png"\; state="\{\{state\}\}">y</figure-callout>}}_0^2---\left(10\right)$

Can be solved from (10) and (9a)

x＝AR₁+B (11)

Wherein, $A=\frac{R_{21}}{x_2},$ $B=\frac{x_2^2-R_{21}^2}{2x_2}---\left(12\right)$

similarly, according to (10) and (9b), the following results are obtained

y₀＝CR₁+D (13)

Wherein, $C=\frac{R_{31}-x_{3}A}{y_3},$ $D=\frac{x_3^2+y_3^2-R_{31}^2-2x_{3}B}{2y_3}---\left(14\right)$

to obtain a compound of formula R₁The equation of (c):

(A²+C²-1)R₁+2(AB+CD)R₁+(B²+D²)＝0 (15)

in addition, α ═ AB + CD, β ═ a²+C²-1 (16)

R if β ≠ 0 and α ≠ 0₁Is solved as

<math> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>-</mo> <mfrac> <mrow> <msup> <mi>B</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <mi>D</mi> <mn>2</mn> </msup> </mrow> <mrow> <mn>2</mn> <mi>&alpha;</mi> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>17</mn> <mo>)</mo> </mrow> </mrow></math>

R if β ≠ 0₁Is solved as

<math> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <mi>&alpha;</mi> <mo>&PlusMinus;</mo> <msqrt> <msup> <mi>&alpha;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>&beta;</mi> <mrow> <mo>(</mo> <msup> <mi>B</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <mi>D</mi> <mn>2</mn> </msup> <mo>)</mo> </mrow> </msqrt> </mrow> <mi>&beta;</mi> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>18</mn> <mo>)</mo> </mrow> </mrow></math>

The multi-solution case of the hyperbolic positioning equation can be classified into the following cases:

1.β<0

then R1 has two real solutions with opposite signs and takes the positive solution as R₁Is determined.

2.β＝0

If and only if α<At 0, R₁There is a unique positive real solution.

3.β>0

When alpha is<At 0, R₁Has two positive roots, when alpha>At 0, R₁There are two negative roots.

In summary, the ambiguity resolution region of the time difference of arrival (TDOA) location algorithm exists when β is>0 and alpha<0 (k). Meanwhile, according to (18), when β ≠ 0 and α²-β(B²+D²)<At 0, the equation is unsolved and the position of the mobile station is not estimated. The invention provides a positioning algorithm of time difference of arrival in actual cellular network positioning, and the invention provides a method for adopting cell halfThe path is used as prior information to further analyze three different conditions generated by the dead zone of the arrival time difference positioning algorithm.

a.R₁There are two positive roots and both are smaller than the cell radius. The mobile station is located in the blind spot.

b.R₁There is no root. The mobile station is located in the blind spot.

c.R₁There is one and only one positive root that is smaller than the radius of the cell. The mobile station location can be estimated.

According to the above analysis of the dead zone of the arrival time difference algorithm, the present invention provides an algorithm for eliminating the dead zone by applying the arrival time difference positioning algorithm in the cellular network as shown in fig. 3, and the flow chart is shown in fig. 4, and the steps are as follows:

401. each triplet is ordered according to the characteristic parameters (electromagnetic field strength, signal-to-noise ratio, signal-to-interference ratio, etc.) of the signals transmitted between the mobile station and the base stations. Taking the signal-to-noise ratio as an example, let

SNR_BS1>SNR_BS2>SNR_BS3>SNR_BS4>....SNR_BSi-1>SNR_BSiThe selected combination is

S_i(i ═ 1, 2.. N), where S is₁＝[BS1，BS2，BS3]，S₂＝[BS1，BS2，BS4]，...

S_N＝[BS1，BSi-1，BSi]。

402. Selection of combinations S_iLet the initial value of i be 1.

403. The time difference of arrival of the neighbor base station and the primary serving base station in the combination is measured.

404. And judging the type of the blind area according to the criterion of judging the blind area of the arrival time difference positioning algorithm. According to the analysis of the three different cases of the blind area, for the case c, the only reasonable positive solution of R1 is found by using the prior information of the cell radius. Step 407 is entered. For cases a and b, i ═ i +1, step 405 is entered.

405. Judging whether all combinations are traversed, if so, entering step 406; if false, step 403 is repeated.

406. The mobile station is located in the blind area of all the base station combinations, and the positioning fails.

407. And selecting the base station combination with the mobile station position not in the blind area as the base station combination participating in the time difference of arrival triangulation algorithm to perform positioning operation.

Examples

Fig. 4 shows a specific embodiment for implementing the method for providing location services in a Wimax network and providing location accuracy according to the present invention. It should be emphasized here that although the method of the present patent provides a method for eliminating the dead zone of the time difference of arrival positioning algorithm for implementing the method of providing the positioning service in the Wimax network, the method of the present patent is not strictly limited to the Wimax network, but should be suitable for any cellular network, and the Wimax network is taken as an example here.

In the Wimax forum (hereinafter abbreviated as "Wimax forum") network group (hereinafter abbreviated as "NGW") conference held in san francisco, usa, between No. 4 and No. 5 and No. 4 in 2007, a proposal provided by samsung and Intel corporation is accepted by this conference, and becomes a reference (hereinafter referred to as "baseline") manuscript for the second Stage (hereinafter referred to as "Stage-2"). Fig. 5 shows a Wimax Location Service (LBS) network reference model in a non-roaming state defined in the baseline document. The network architecture of Wimax, from the large functional distinction, includes three parts: mobile station (hereinafter referred to as MS), access service network ASN, connection service network CSN. The ASN includes a base station (hereinafter abbreviated BS) and an access service network gateway (hereinafter abbreviated ASN GW). The interface between the MS and the BS is generally referred to as an air interface, and in the Wimax network reference model, is an R1 interface; the interface between the BS and the ASN GW is an R6 interface; the interface between the CSN and the ASN GW is an R3 interface. In the Wimax LBS network reference model in the non-roaming state, the LBS-related modules include:

(1) location Server (Location Server, LS for short below)

The LS is a functional entity located on the CSN, and the relationship with the external location client is the relationship of "client < - > server", and provides the function of authorization check for the external client and the mobile station requesting the location information. In addition, the LS may also have a function of positioning calculation.

(2) Positioning Controller (Location Controller, LC for short)

The LC is responsible for determining and reporting location information and location parameters of the mobile station, which the LC may provide to entities within the LS, MS or other ASN, such as a Radio Resource Management (RRM) module and a Mobility Management (MM) module. Upon request from internal modules within the MS, LS or ASN, the LC triggers location related measurements, collects parameters needed for location calculation and performs location calculation. The LC is typically located within the ASN network, if for a decomposed ASN, on the ASN GW.

(3) Positioning Agent (Location Agent, LA for short below)

The main function of the LA is to perform location related measurements and optionally also to collect and report location related parameters to the LC. The functions of the LA may be located at the BS, the MS, or both. If the MS has LA functionality, the corresponding BS also has LA functionality.

The position of the method for eliminating the blind zone of the time difference of arrival positioning algorithm in the network is shown in the figure, wherein bc (blind cancel) is a blind zone elimination module. The BC may be located in the LA or LC, depending primarily on whether the positioning algorithm is network-based or terminal-based. If the positioning algorithm is based on the terminal, the dead zone eliminating algorithm of the arrival time difference positioning algorithm is positioned in the LA module, and if the positioning algorithm is based on the network, the dead zone eliminating algorithm of the arrival time difference positioning algorithm is positioned in the LC module.

The following specifically describes the functional blocks of the dead zone elimination algorithm in the terminal and their relationship with other functional blocks based on the terminal positioning method. A block diagram of a terminal according to an embodiment of the present invention is shown in fig. 6. The hardware parts and the basic functions that each part should accomplish are described as follows:

antenna 601

For receiving and transmitting radio signals, the antenna should be able to search for the frequencies used by the network.

Radio frequency module 602

The radio frequency module is connected with the modem.

Modem 603

The function of the physical layer is realized, and comprises channel interleaving/de-interleaving of a transmission channel, multiplexing of the transmission channel, de-multiplexing of a code combination channel, rate matching, mapping of the code combination channel to the physical channel, and power weighting and combination of modulation and demodulation of the physical channel;

protocol processing module 604

The module is responsible for completing the functions of the air interface layer 2 and the protocol stacks above the air interface layer, and comprises a media access control layer (MAC for short), a data link layer (RLC for short), a radio resource control layer (RRC for short) and a non-access layer (NAS for short).

Control module 605

The module is responsible for centralized control of each control of the terminal, provides an operation platform for application layer software in the terminal, bears the application software module, and completes sending, receiving and processing of air interface signaling, control of a calling process, distribution and scheduling of air interface messages and internal instructions and the like.

Loudspeaker 606

Used for amplifying and outputting various prompt tones, such as incoming call prompt tones and the like.

Keyboard 607

The interface function is used for inputting information, transmitting the information input by the user to the control module, and finishing the interaction between the user and the terminal together with the display unit, the loudspeaker, the microphone and the like.

Display unit 608

The display unit generally includes a display screen and the like, and can display various characters, icons and the like to a user under the control of the control module.

Memory 609

And the data storage module in the terminal stores data necessary for normal operation of the terminal.

Power supply module 610

And providing power supply for each module.

SIM card 611

The SIM card mainly performs two functions: storing data (controlling access to various data) and completing the whole process of customer identity authentication and customer information encryption algorithm under the safety condition (personal identification number PIN, authentication key Ki are correct). This function is mainly performed by a microprocessor with an operating system in the SIM card.

Dead zone elimination algorithm 612 of arrival time difference positioning algorithm

The main function is to carry out the blind zone elimination algorithm of the arrival time difference positioning algorithm from the TDOA information measured from the modem, and send the blind zone elimination algorithm to the positioning algorithm for positioning.

Positioning module 613

The main function is to select the base station combination selected by the blind area elimination algorithm to carry out positioning operation.

The above embodiment is explained based on a general terminal function module, and is not explained for a specific system, but this does not hinder the function position of the dead zone elimination algorithm of the arrival time difference positioning algorithm.

The invention provides a method for eliminating blind areas caused by applying a time difference of arrival positioning algorithm in a cellular network, provides specific execution steps and functional modules of the method, explains the position of the method in the network, and describes the positions of the functional modules and the functional modules at a terminal. The method provided by the invention can effectively eliminate the blind zone caused by the arrival time difference positioning algorithm, thereby reducing the positioning error and improving the positioning precision. The specific simulation results are shown in fig. 7.

The simulation result shows the influence of the implementation of the method and the steps proposed by the invention on the positioning accuracy under the same channel simulation model. Because the positioning error caused by the dead zone of the arrival time difference positioning algorithm is eliminated, the positioning precision of the method is obviously improved compared with the method without the dead zone elimination algorithm. It should be noted that the illustrated simulation accuracy is intended to represent the relative contribution of the present invention in positioning accuracy, the adopted channel model is a line-of-sight model under shadow fading, and the positioning accuracy may have a gap under different channel models.

Claims (13)

1. A method for eliminating blind areas in a time difference of arrival positioning algorithm in a cellular communication system, comprising the steps of:

a) arranging every three groups according to the characteristic parameter sequence of the signals transmitted between the mobile station and the base stations;

b) selecting a characteristic parameter combination S_i；

c) Measurement combination S_iThe arrival time difference between the adjacent base station and the main service base station;

d) judging the type of the blind area;

e) judging whether all the combinations are traversed, if true, entering the step f, and if false, repeating the step c;

f) the mobile station is positioned in the blind area of all the base station combinations, and the positioning fails;

g) and selecting the base station combination which is not in the blind area as the base station combination participating in the arrival time difference triangulation algorithm to perform positioning operation.

2. The method of claim 1, wherein said characteristic parameters include electromagnetic field strength, signal-to-noise ratio, and signal-to-interference ratio.

3. The method of claim 1, wherein the distance between the mobile station and the base station is calculated as follows:

<math> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mo>-</mo> <mi>&alpha;</mi> <mo>&PlusMinus;</mo> <msqrt> <msup> <mi>&alpha;</mi> <mn>2</mn> </msup> <mo>-</mo> <mi>&beta;</mi> <mrow> <mo>(</mo> <msup> <mi>B</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <mi>D</mi> <mn>2</mn> </msup> <mo>)</mo> </mrow> </msqrt> </mrow> <mi>&beta;</mi> </mfrac> <mo>.</mo> </mrow></math>

4. the method of claim 3, wherein the equation has two positive roots and both are smaller than the cell radius.

5. The method of claim 3, wherein the equation has no root.

6. A method according to claim 3, characterized in that the equation has only one positive root smaller than the radius of the cell.

7. The method of claim 1, wherein the base stations comprise at least 3.

8. The method of claim 1, characterized in that the radius of the cell is used as a priori condition for eliminating blind areas.

9. An apparatus for time difference of arrival location algorithm blind spot cancellation in a cellular communication system, comprising:

antenna, radio frequency module, modem, agreement processing module, control module, speaker, keyboard, display element, memory, power module, SIM card, still include:

the blind area elimination module is used for carrying out a dead area elimination algorithm of arrival time difference from TDOA information obtained by measurement in the modem;

and the positioning algorithm module is used for sending the base station combination selected by the blind area elimination algorithm to the positioning algorithm module for positioning operation.

10. The apparatus of claim 9, wherein the number of base stations is at least 3.

11. The apparatus of claim 9, wherein said blind spot eliminating means is located on the network side.

12. The apparatus of claim 11, wherein the network is a WiMAX network, and the shadow elimination apparatus is located in the LC on the WiMAX network side.

13. The apparatus according to claim 9, wherein said blind spot eliminating means is located at a terminal side.

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