CN102625448A - Improved TDOA positioning method for LTE system - Google Patents

Abstract

The invention relates to an improved TDOA (Time Difference of Arrival) for an LTE system, aiming to solve the problem that a mobile platform close to the center of a cell is interfered by a signal from a service base station to be low in positioning precision when receiving a signal from an adjacent cell, the method adopts the scheme that an interference is generated at a receiving end, and is eliminated, so as to improve arriving time estimation accuracy of a down link signal and positioning precision. The method provided by the invention effectively improves the positioning precision of the mobile platform close to the center of the cell under multi-path broadcasting and NLOS environments, the positioning precision of a mobile platform located at the edge of the cell is ensured.

Description

TDOA improves one's methods the location in a kind of LTE system

Technical field

The present invention relates to the Wireless Location in Cellular Network method, relate to particularly that TDOA improves one's methods the location in a kind of LTE system.

Technical background

In Cellular Networks, need measure at least three signal of base station parameters that comprise serving BS and neighbor base station signal simultaneously during positioning mobile station; Because the existence of near-far interference; Travelling carriage is the closer to serving BS; Its difficulty that receives the adjacent cell signal is just big more, and has only when travelling carriage is in cell edge, can receive the adjacent cell signal of better quality.Under the situation of travelling carriage near serving BS, receive the influence of serving BS signal and communication environments, moving table measuring to the characteristic parameter of neighbor base station signal can have very big deviation, and then the site error of the travelling carriage that calculates is also bigger.In many localization methods of Cellular Networks, the TDOA method is so that its positioning accuracy is high, the algorithm computation complexity is low, be easy to plurality of advantages such as realization and receive increasing attention.Yet because wireless propagation environment is abominable, different TDOA location algorithms are applicable to different localizing environments.Two kinds of communication environments that the wireless location precision is had the greatest impact are non line of sight and multipath propagation environment, and therefore to these two kinds of communication environments, numerous experts and scholars constantly are devoted to the improvement technology of TDOA location algorithm.

Adopted the OFDM technology in the LTE cell mobile communication systems; It is a kind of frequency multiplexing technique based on orthogonal multiple carrier; Its main thought is with after the serial/parallel conversion of highspeed serial data stream; Be divided into a large amount of rate data streams, every circuit-switched data adopts Independent Carrier Wave modulation and stack to send, and receiving terminal separates multiple signals according to the quadrature carrier characteristic.We are devoted to seek the TDOA algorithm that can effectively suppress near-far interference, NLOS and multipath error based on this technology.

Summary of the invention

For avoiding the deficiency of above prior art; The present invention proposes that TDOA improves one's methods the location in a kind of LTE system; Can receive the influence of disturbing factors such as serving BS signal, NLOS propagation, multipath transmisstion and noise when receiving the neighbor base station signal, be employed in signal receiving end and rebuild the accuracy of estimation and the positioning accuracy time of advent that disturbs and the method that it is eliminated improved down link signal to travelling carriage.

Technological means of the present invention is following:

TDOA improves one's methods the location in a kind of LTE system, and this method comprises the steps:

1) base station signal that receives is carried out QAM modulation and OFDM modulation, obtain modulation signal x _{T, n}

2) said modulation signal is sent in the time-variant multipath channel,, obtains signal y (t) at receiving terminal through amplitude fading and signal lag:

$y\left(t\right)=\underset{\mathrm{\μ}=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\Σ}}}\underset{p=1}{\overset{P_{\mathrm{\μ}}}{\mathrm{\Σ}}}{a}_{\mathrm{\μ},p}{x}_{\mathrm{\μ}}(t-{\mathrm{\τ}}_{\mathrm{\μ},p})+n\left(t\right)$

3) said signal y (t) is sampled obtain signal Y _n

4) to signal Y _nCarry out OFDM demodulation conversion, extract the pilot tone conversion, QAM demodulation conversion obtains bit data flow;

5) said bit data flow is carried out interference cancellation operation; Promptly the bit data flow pilot tone of carrying out the QAM modulating transformation, insert the pilot tone conversion, obtaining according to said extracted is carried out channel estimating, disturbance reconstruction once more; For some neighbor base station μ; From receive signal, deduct interference signal, promptly obtain signal y through this neighbor base station of interference eliminated _n

6) said pilot signal x ^p _μRespectively with the said signal y that passes through interference eliminated _nThe relevant r that obtains slides _{μ, n}

${\mathrm{\τ}}_{\mathrm{\μ},n}=\underset{k=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\Σ}}}{x}_{\mathrm{\μ},k}^{p,*}{y}_{n+k}$

7), select the propagation delay estimated value of correlation peak, promptly from all τ as base station signal in the frame for said base station μ _{μ, n}The middle maximum of selecting obtains:

${{\widehat{\mathrm{\τ}}}^{\′}}_{\mathrm{\μ},1}=\arg \max \left|{\mathrm{\τ}}_{\mathrm{\μ},n}\right|$

8) to N _FranmesThe estimated value of individual frame Average, obtain the signal propagation delay estimated value of said base station μ:

${\widehat{\mathrm{\τ}}}_{\mathrm{\μ},1}=\frac{1}{N_{\mathrm{Frames}}}\underset{f=1}{\overset{N_{\mathrm{Frames}}}{\mathrm{\Σ}}}{{\widehat{\mathrm{\τ}}}^{\′}}_{\mathrm{\μ},1,f}$

The propagation delay of each base station signal of 9) utilize estimating to obtain, with signal velocity c be that the light velocity multiplies each other, obtain the distance between travelling carriage and each base station.

The advantage that the present invention has:

The present invention has effectively improved under multipath transmisstion and NLOS environment near the positioning accuracy of center of housing estate travelling carriage, has guaranteed to be positioned at the positional accuracy of cell edge travelling carriage simultaneously.

Description of drawings

Fig. 1 is that method of the present invention realizes theory diagram.

Fig. 2 is the Cellular Networks structure chart.

Fig. 3 (a)-3 (b) is the signal propagation delay mean square of error root of method of the present invention under sighting distance (LOS), NLOS and multipath propagation environment and the cumulative distribution function simulation curve figure of position error.

Embodiment

Below TDOA location in this LTE of the present invention system improved one's methods do detailed explanation.The localization method of TDOA is realized as follows in the LTE system:

1, interference eliminated

Bit data flow obtains symbol data S after modulating through QAM _{M, n}(m=0,1,, N _C-1, n=0,1,, N _S-1, N _CAnd N _SRepresent the OFDM number of symbols in an employed OFDM carrier number and the frame respectively).Adopt the Zadoff-chu sequence as pilot tone, carry out the OFDM modulation after the insertion pilot signal, comprise that (transform length is N for serial to parallel conversion, IFFT conversion _FFT), parallel serial conversion and insert Cyclic Prefix (length is N _GI).Wherein the IFFT conversion has realized the parallel transmission of multichannel orthogonal sub-carriers.Signal through after the OFDM modulation can be expressed as:

$x_{t,n}=\frac{1}{\sqrt{N_{\mathrm{FFT}}}}\underset{m=0}{\overset{N_C-1}{\mathrm{\&Sigma;}}}{S}_{m,n}\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000145460120000013.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;m}(t-N_{\mathrm{GI}})}{N_{\mathrm{FFT}}}\right)---\left(1\right)$

T=0 wherein, 1 ..., N _FFT+ N _GI-1, n=0,1 ..., N _S-1.

N _BSThe down link signal of individual base station sends in the time-variant multipath channel through ovennodulation, arrives receiving terminal with different paths and time delay, and each base station signal comprises some paths, and the signal that then receives can be expressed as:

$y\left(t\right)=\underset{\mathrm{\&mu;}=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}\underset{p=1}{\overset{P_{\mathrm{\&mu;}}}{\mathrm{\&Sigma;}}}{a}_{\mathrm{\&mu;},p}{x}_{\mathrm{\&mu;}}(t-{\mathrm{\&tau;}}_{\mathrm{\&mu;},p})+n\left(t\right)---\left(2\right)$

A wherein _{μ, p}And τ _{μ, p}Amplitude and the propagation delay of representing the p paths of base station μ respectively, μ=1,2,, N _BS, p=1,2,, P _μN (t) is that average is zero, and variance is N ₀/ 2 additive white Gaussian noise.The reception signal is N _BSThe multipath signal of individual base station and the stack of noise.

Receive processing to received signal at receiving terminal, carry out a series of opposite conversion, i.e. analog to digital conversion, OFDM demodulation (going protection interval and FFT conversion), extraction pilot tone (being used for channel estimating), QAM demodulation, signal reverts to bit data flow the most at last.

Travelling carriage is when receiving the signal of a certain neighbor base station, and other neighbor base stations especially signal of serving BS can produce this base station signal and disturb, and influence the quality of reception of signal, sometimes even can not receive this signal of base station.In addition, when base station signal is propagated, can cause that multipath effect and NLOS propagate in the mobile communication environment of complicacy, this is very disadvantageous for the estimating signal propagation time, and then can cause bigger location of mobile station evaluated error.In order to reduce above interference and The noise, adopt interference cancellation techniques, in the LTE communication system, add the interference eliminated feedback end.The message bit stream that recovers to obtain is carried out the QAM modulation once more, and insert the pilot frequency sequence that extracts each base station that obtains.Utilize the communication environments of the reconstruction signal as a result of channel estimating, promptly especially the serving BS signal disturbs neighbor base station, multipath disturbs, NLOS disturbs and noise.The reconstruction interference deducts it from receive signal through the OFDM modulation, thereby has obtained the useful signal of this base station.Adopt such method, can be more accurately with each neighbor base station μ (μ=2,3,, N _BS) signal that sends distinguishes each other.

Especially, because the serving BS signal quality that travelling carriage receives is best, need not adopt interference cancellation techniques can obtain the signal of serving BS at receiving terminal.

2, the time is estimated

If adopt interference cancellation techniques, with the pilot signal of each neighbor base station respectively with reception signal through interference eliminated relevant the obtaining of sliding: also be

${\mathrm{\&tau;}}_{\mathrm{\&mu;},n}=\underset{k=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\&Sigma;}}}{x}_{\mathrm{\&mu;},k}^{p,*}{y}_{n+k}---\left(3\right)$

X wherein ^p _μThe pilot signal of expression base station μ, y _nThe sampled signal of the reception signal of expression process interference eliminated, μ=2,, N _BS, n=0,1,, (N _FFT+ N _GI) N _Symbols-1.

Fig. 2 is the Cellular Networks structure chart; For serving BS and the situation that does not adopt interference cancellation techniques; Do not adopt feedback end shown in Figure 1 when the signal propagation delay is estimated, adopt formula (3) directly will receive signal and the pilot signal related operation that slides equally.

For μ base station, select the propagation delay estimated value of correlation peak, promptly from all τ as base station signal in the frame _{μ, n}The middle maximum of selecting obtains:

${{\widehat{\mathrm{\&tau;}}}^{\&prime;}}_{\mathrm{\&mu;},1}=\arg \max \left|{\mathrm{\&tau;}}_{\mathrm{\&mu;},n}\right|---\left(4\right)$

Because each base station signal can not arrive receiving terminal at same sampling time, there is deviation in the propagation delay estimated value of each frame, therefore to N _FranmesThe estimated value of individual frame

Average, finally obtain the signal propagation delay estimated value of base station μ:

${\widehat{\mathrm{\&tau;}}}_{\mathrm{\&mu;},1}=\frac{1}{N_{\mathrm{Frames}}}\underset{f=1}{\overset{N_{\mathrm{Frames}}}{\mathrm{\&Sigma;}}}{{\widehat{\mathrm{\&tau;}}}^{\&prime;}}_{\mathrm{\&mu;},1,f}---\left(5\right)$

3, location of mobile station estimation

The propagation delay of each base station signal that the utilization estimation obtains can calculate the time difference (TDOA) of each base station signal with respect to base station 1 (serving BS) arrival travelling carriage, promptly

μ=2 wherein,, N _BSTime difference and light velocity c are multiplied each other, and it is poor to obtain the signal propagation distance.Article adopts weighted least-squares method estimation user's position coordinates.If (X _i, Y _i) be base station coordinates (i=1,2,, N _BS), (x y) is travelling carriage coordinate to be estimated.Signal propagation distance based on having obtained is poor, sets up the positioning equation group:

R _i，1＝cΔτ _i＝R _i-R ₁ i＝2，…，N (6)

Wherein:

$R_i=\sqrt{{(X_i-x)}^2+{(Y_i-y)}^2}---\left(7\right)$

R _iBe the distance between base station i and the travelling carriage.

Result according to pertinent literature is derived can obtain:

$R_{i,1}^2+{2R}_{i,1}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000145460120000013.png,HDA0000145460120000014.png"\; state="\{\{state\}\}">R</figure-callout>}}_1={-2X}_{i,1}x-{2Y}_{i,1}y+K_i-K_1---\left(8\right)$

Wherein

$K_i=X_i^2+Y_i^2---\left(9\right)$

$\left\{\begin{array}{c}{X}_{i,1}=X_i-X_1\\ Y_{i,1}=Y_i-Y_1\end{array}\right.---\left(10\right)$

Order

$p={[x,y,r]}^T=[{x,y,\sqrt{{(X_1-x)}^2+{(Y_1-y)}^2}]}^T---\left(11\right)$

Can obtain:

h _c＝G _cp+ε _c (12)

Wherein

$h_c=\frac{1}{2}\left[\begin{array}{c}{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000145460120000013.png"\; state="\{\{state\}\}">\; <figure-callout\; id="1"\; label="R"\; filenames="HDA0000145460120000013.png,HDA0000145460120000014.png"\; state="\{\{state\}\}">R</figure-callout>\; </figure-callout>}}_{\mathrm{2,1}}^2-(K_2-K_1)\\ {\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000145460120000013.png,HDA0000145460120000014.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{3,1}}^2-(K_3-K_1)\\ \&CenterDot;\&CenterDot;\&CenterDot;\\ R_{N_{\mathrm{BS}},1}^2-(K_{N_{\mathrm{BS}}}-K_1)\end{array}\right]$ $G_c=\left[\begin{array}{ccc}{\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="HDA0000145460120000013.png"\; state="\{\{state\}\}">X</figure-callout>}}_{\mathrm{2,1}}& {\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="HDA0000145460120000013.png"\; state="\{\{state\}\}">Y</figure-callout>}}_{\mathrm{2,1}}& {\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000145460120000013.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{2,1}}\\ X_{\mathrm{3,1}}& Y_{\mathrm{3,1}}& {\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HDA0000145460120000013.png,HDA0000145460120000014.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{3,1}}\\ & \&CenterDot;\&CenterDot;\&CenterDot;& \\ X_{N_{\mathrm{BS}},1}& Y_{N_{\mathrm{BS}},1}& R_{N_{\mathrm{BS}},1}\end{array}\right]---\left(13\right)$

ε _cFor having the error vector of TDOA noise.

Covariance matrix Q with TDOA measured value error is similar to replacement error ε _cCovariance matrix ψ _s, can obtain the estimation of p:

p＝(G _c ^TQ ^-1G _c) ^-1G _c ^TQ ^-1h _c (14)

Finally obtain the estimated position coordinate

of travelling carriage

$\left\{\begin{array}{c}\hat{x}=p\left(1\right)\\ \hat{y}=p\left(2\right)\end{array}\right.---\left(15\right)$

Fig. 3 (a)-3 (b) is the signal propagation delay mean square of error root of method of the present invention under sighting distance (LOS), NLOS and multipath propagation environment and the cumulative distribution function simulation curve figure of position error.Can find out and adopt this method of the present invention, effectively improve under multipath transmisstion and NLOS environment, guarantee to be positioned at the positional accuracy of cell edge travelling carriage simultaneously near the positioning accuracy of center of housing estate travelling carriage.

Should be appreciated that the above detailed description of technical scheme of the present invention being carried out by preferred embodiment is schematic and nonrestrictive.Those of ordinary skill in the art is reading on the basis of specification of the present invention and can make amendment to the technical scheme that each embodiment put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these are revised or replacement, do not make the spirit and the scope of the essence disengaging various embodiments of the present invention technical scheme of relevant art scheme.

Claims (1)

1. TDOA improves one's methods the location in the LTE system, it is characterized in that this method comprises the steps:

1) base station signal that receives is carried out QAM modulation and OFDM modulation, obtain modulation signal x _{T, n}

2) said modulation signal is sent in the time-variant multipath channel,, obtains signal y (t) at receiving terminal through amplitude fading and signal lag:

$y\left(t\right)=\underset{\mathrm{\&mu;}=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\&Sigma;}}}\underset{p=1}{\overset{P_{\mathrm{\&mu;}}}{\mathrm{\&Sigma;}}}{a}_{\mathrm{\&mu;},p}{x}_{\mathrm{\&mu;}}(t-{\mathrm{\&tau;}}_{\mathrm{\&mu;},p})+n\left(t\right)$

3) said signal y (t) is sampled obtain signal Y _n

4) to signal Y _nCarry out OFDM demodulation conversion, extract the pilot tone conversion, QAM demodulation conversion obtains bit data flow;

5) said bit data flow is carried out interference cancellation operation; Promptly the bit data flow pilot tone of carrying out the QAM modulating transformation, insert the pilot tone conversion, obtaining according to said extracted is carried out channel estimating, disturbance reconstruction once more; For some neighbor base station μ; From receive signal, deduct interference signal, promptly obtain signal y through this neighbor base station of interference eliminated _n

6) said pilot signal x ^p _μRespectively with the said signal y that passes through interference eliminated _nThe relevant r that obtains slides _{μ, n}

${\mathrm{\&tau;}}_{\mathrm{\&mu;},n}=\underset{k=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\&Sigma;}}}{x}_{\mathrm{\&mu;},k}^{p,*}{y}_{n+k}$

7), select the propagation delay estimated value of correlation peak, promptly from all τ as base station signal in the frame for said base station μ _{μ, n}The middle maximum of selecting obtains:

${{\widehat{\mathrm{\&tau;}}}^{\&prime;}}_{\mathrm{\&mu;},1}=\arg \max \left|{\mathrm{\&tau;}}_{\mathrm{\&mu;},n}\right|$

8) to N _FranmesThe estimated value of individual frame

Average, obtain the signal propagation delay estimated value of said base station μ:

${\widehat{\mathrm{\&tau;}}}_{\mathrm{\&mu;},1}=\frac{1}{N_{\mathrm{Frames}}}\underset{f=1}{\overset{N_{\mathrm{Frames}}}{\mathrm{\&Sigma;}}}{{\widehat{\mathrm{\&tau;}}}^{\&prime;}}_{\mathrm{\&mu;},1,f}$

The propagation delay of each base station signal of 9) utilize estimating to obtain, with signal velocity c be that the light velocity multiplies each other, obtain the distance between travelling carriage and each base station.

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