CN102625448B - 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

In a kind of LTE system, TDOA improves one's methods location

Technical field

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

Technical background

In Cellular Networks, need to measure the signal parameter of at least three base stations that comprise serving BS and neighbor base station signal during positioning mobile station simultaneously, existence due to near-far interference, travelling carriage is the closer to serving BS, its difficulty that receives adjacent cell signal is just larger, and only have when travelling carriage is in cell edge, can receive the adjacent cell signal of better quality.At travelling carriage, near serving BS in the situation that, be subject to the impact of serving BS signal and communication environments, moving table measuring to the characteristic parameter of neighbor base station signal can there is very large deviation, and then the site error of the travelling carriage calculating is also larger.In many localization methods of Cellular Networks, TDOA method is high with its positioning precision, algorithm computational complexity is low, be easy to the plurality of advantages such as realization and be subject to increasing attention.Yet severe due to wireless propagation environment, different TDOA location algorithms are applicable to different localizing environments.Two kinds of communication environments to wireless location Accuracy maximum are non line of sight and multipath propagation environment, and therefore for these two kinds of communication environments, numerous experts and scholars are constantly devoted to the improvement technology of TDOA location algorithm.

In LTE cell mobile communication systems, adopted OFDM technology, it is a kind of frequency multiplexing technique based on orthogonal multiple carrier, its main thought is by after the serial/parallel conversion of highspeed serial data stream, be divided into a large amount of low rate data streams, every circuit-switched data adopts the Independent Carrier Wave transmission of modulate and superpose, and receiving terminal is according to quadrature carrier characteristic separation multiple signals.Based on this technology, we are devoted to find the TDOA algorithm that can effectively suppress near-far interference, NLOS and multipath error.

Summary of the invention

For avoiding above the deficiencies in the prior art, the present invention proposes TDOA in a kind of LTE system improves one's methods location, while receiving neighbor base station signal for travelling carriage, can be subject to the impact of the disturbing factors such as serving BS signal, NLOS propagation, multipath transmisstion and noise, adopt at signal receiving end and rebuild the accuracy of estimation and the positioning precision time of advent that the method for disturbing and it being eliminated has been improved down link signal.

Technological means of the present invention is as follows:

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

1) base station signal receiving is carried out to QAM modulation and OFDM modulation, obtain modulation signal x _{t, n};

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

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

3) described signal y (t) is sampled and obtains signal Y _n;

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

5) described bit data flow is carried out to interference cancellation operation, again to bit data flow carry out QAM modulating transformation, insert pilot tone conversion, the pilot tone that obtains according to said extracted carries out channel estimating, disturbance reconstruction, for some neighbor base station μ, from receive signal, deduct interference signal, obtain through disturbing the signal y of this neighbor base station of eliminating _n;

6) described pilot signal x ^p _μrespectively with the described signal y eliminating through interference _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), for described base station μ, select correlation peak as the propagation delay estimated value of base station signal in a frame, from all τ _{μ, n}middle selection maximum 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 described base station μ:

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

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

The present invention has advantages of:

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

Accompanying drawing explanation

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

Fig. 2 is 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 in this LTE system of the present invention is improved one's methods location and is described in detail.In LTE system, the localization method of TDOA is realized as follows:

1, disturb and eliminate

Bit data flow obtains symbol data S after QAM modulation _{m, n}(m=0,1,, N _c-1, n=0,1,, N _s-1, N _cand N _sthe OFDM carrier number that expression is used respectively and the OFDM number of symbols in a frame).Adopt Zadoff-chu sequence as pilot tone, carry out OFDM modulation after inserting pilot signal, comprise serial to parallel conversion, (transform length is N in IFFT conversion _fFT), parallel serial conversion and insert Cyclic Prefix (length is N _gI).Wherein IFFT conversion has realized the parallel transmission of multichannel orthogonal sub-carriers.Signal after OFDM modulation can be expressed as:

$x_{t,n}=\frac{1}{\sqrt{N_{\mathrm{FFT}}}}\underset{m=0}{\overset{N_C-1}{\mathrm{\Σ}}}{S}_{m,n}\exp \left(j\frac{2\mathrm{\πm}(t-N_{\mathrm{GI}})}{N_{\mathrm{FFT}}}\right)---\left(1\right)$

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 time-variant multipath channel through ovennodulation, with different paths and time delay, arrives receiving terminal, and each base station signal comprises some paths, and the signal receiving can be expressed as:

$y\left(t\right)=\underset{\mathrm{\μ}=1}{\overset{N_{\mathrm{BS}}}{\mathrm{\Σ}}}\underset{p=1}{\overset{P_{\mathrm{\μ}}}{\mathrm{\Σ}}}{a}_{\mathrm{\μ},p}{x}_{\mathrm{\μ}}(t-{\mathrm{\τ}}_{\mathrm{\μ},p})+n\left(t\right)---\left(2\right)$

A wherein _{μ, p}and τ _{μ, p}the amplitude and the propagation delay that represent respectively the p paths of base station μ, μ=1,2,, N _bS, p=1,2,, P _μ.N (t) is that average is zero, and variance is N ₀/ 2 additive white Gaussian noise.Reception signal is N _bSthe multipath signal of individual base station and the stack of noise.

At receiving terminal, carry out to received signal reception & disposal; carry out a series of contrary conversion; be analog to digital conversion, OFDM demodulation (going to protect interval and FFT conversion), extract pilot tone (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 and disturb this base station signal, affect the quality of reception of signal, sometimes even can not receive the signal of this base station.In addition, when base station signal is propagated in complicated mobile communication environment, can cause that multipath effect and NLOS propagate, this is very disadvantageous for the estimating signal propagation time, and then can cause larger location of mobile station evaluated error.In order to reduce the impact of above interference and noise, adopt interference cancellation techniques, in LTE communication system, add to disturb and eliminate feedback end.The message bit stream that recovers to obtain is carried out to QAM modulation again, and insert the pilot frequency sequence that extracts each base station obtaining.Utilize the communication environments of the result reconstruction signal of channel estimating, especially serving BS signal disturbs neighbor base station, multipath disturbs, NLOS disturbs and noise.Reconstruction interference, through OFDM modulation, is deducted from receive signal, thereby has obtained the useful signal of this base station.Adopt such method, can be more accurately by each neighbor base station μ (μ=2,3,, N _bS) signal that sends distinguishes mutually.

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

2, time Estimate

If employing interference cancellation techniques, disturbs relevant the obtaining of reception signal slip of eliminating to process respectively by the pilot signal of each neighbor base station: be also

${\mathrm{\τ}}_{\mathrm{\μ},n}=\underset{k=0}{\overset{N_{\mathrm{FFT}}-1}{\mathrm{\Σ}}}{x}_{\mathrm{\μ},k}^{p,*}{y}_{n+k}---\left(3\right)$

X wherein ^p _μthe pilot signal that represents base station μ, y _nrepresent through disturbing the sampled signal of the reception signal of eliminating, μ=2,, N _bS, n=0,1,, (N _fFT+ N _gI) N _symbols-1.

Fig. 2 is Cellular Networks structure chart, for serving BS and the situation that does not adopt interference cancellation techniques, when signal propagation delay is estimated, do not adopt the feedback end shown in Fig. 1, adopt equally formula (3) related operation that directly reception signal and pilot signal slided.

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

${{\widehat{\mathrm{\τ}}}^{\′}}_{\mathrm{\μ},1}=\arg \max \left|{\mathrm{\τ}}_{\mathrm{\μ},n}\right|---\left(4\right)$

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:

${\widehat{\mathrm{\τ}}}_{\mathrm{\μ},1}=\frac{1}{N_{\mathrm{Frames}}}\underset{f=1}{\overset{N_{\mathrm{Frames}}}{\mathrm{\Σ}}}{{\widehat{\mathrm{\τ}}}^{\′}}_{\mathrm{\μ},1,f}---\left(5\right)$

3, location of mobile station estimation

The propagation delay of each base station signal that utilization estimation obtains, can calculate each base station signal and with respect to base station 1 (serving BS), arrive the time difference (TDOA) of travelling carriage, μ=2 wherein,, N _bS.Time difference and light velocity c are multiplied each other, obtain signal propagation distance poor.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 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 _ifor the distance between base station i and travelling carriage.

The result of deriving according to pertinent literature, can obtain:

$R_{i,1}^2+{2R}_{i,1}{R}_1={-2X}_{i,1}x-{2Y}_{i,1}y+K_i-K_1---\left(8\right)$

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

$h_c=\frac{1}{2}\left[\begin{array}{c}{R}_{\mathrm{2,1}}^2-(K_2-K_1)\\ R_{\mathrm{3,1}}^2-(K_3-K_1)\\ \·\·\·\\ R_{N_{\mathrm{BS}},1}^2-(K_{N_{\mathrm{BS}}}-K_1)\end{array}\right]$ $G_c=\left[\begin{array}{ccc}{X}_{\mathrm{2,1}}& Y_{\mathrm{2,1}}& R_{\mathrm{2,1}}\\ X_{\mathrm{3,1}}& Y_{\mathrm{3,1}}& R_{\mathrm{3,1}}\\ & \·\·\·& \\ X_{N_{\mathrm{BS}},1}& Y_{N_{\mathrm{BS}},1}& R_{N_{\mathrm{BS}},1}\end{array}\right]---\left(13\right)$

ε _cfor thering is the error vector of TDOA noise.

With the covariance matrix Q of TDOA measurement error, be 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 the positioning precision of close center of housing estate travelling carriage under multipath transmisstion and NLOS environment, guarantee to be positioned at the positional accuracy of cell edge travelling carriage simultaneously.

Should be appreciated that the above detailed description of technical scheme of the present invention being carried out by preferred embodiment is illustrative and not restrictive.Those of ordinary skill in the art modifies reading the technical scheme that can record each embodiment on the basis of specification of the present invention, or part technical characterictic is wherein equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution depart from the spirit and scope of various embodiments of the present invention technical scheme.

Claims (1)

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

1) base station signal receiving is carried out to QAM modulation and OFDM modulation, obtain modulation signal x _t,n;

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

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

A wherein _{μ, p}and τ _{μ, p}the signal amplitude and the propagation delay that represent respectively the p paths of base station μ, μ=1,2 ..., N _bS, p=1,2 ..., P _μ, n (t) is that average is zero, variance is N ₀/ 2 additive white Gaussian noise, acknowledge(ment) signal is N _bSthe multipath signal of individual base station and the stack of noise;

3) described signal y (t) is sampled and obtains signal Y _n;

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

5) described bit data flow is carried out to interference cancellation operation, again to bit data flow carry out QAM modulating transformation, insert pilot tone conversion, the pilot tone that obtains according to said extracted carries out channel estimating, disturbance reconstruction, for some neighbor base station μ, from receive signal, deduct interference signal, obtain through disturbing the signal y of this neighbor base station of eliminating _n;

6) pilot signal x ^p _μrespectively with the described signal y eliminating through interference _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), for described base station μ, select correlation peak as the propagation delay estimated value of base station signal in a frame, from all τ _{μ, n}middle selection maximum 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 described base station μ:

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

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