KR20110092930A - Geolocation in wibro network using down-link preamble signal and a method of enhancing its hearability - Google Patents

Abstract

PURPOSE: A Wibro based positioning system using a downlink preamble signal is provided to simultaneously apply an interference signal removing method and a synchronization device overlapping method. CONSTITUTION: A frequency estimating unit estimates and compensates a residual frequency error about a signal which is received from a receiver. A device overlapping part performs a synchronization device overlapping about preamble signals which are repeatedly generated. An interference canceling unit eliminates signals from a received downlink preamble signals by turns. A location recognition part estimates the location of a terminal using a delay time estimation unit and the location information of base stations.

Description

Geolocation in WiBro network using down-link preamble signal and a method of enhancing its hearability}

The present invention relates to a WiBro-based positioning system using a downlink preamble signal, and more particularly, to a positioning method in which a WiBro terminal device can provide high-precision position information using a downlink preamble symbol of the WiBro system.

With the advent of the one-person wireless terminal and the increasing demand for location-based services, it is expected that provision of location-based services in wireless terminals will become essential. Moreover, WiBro networks will be able to provide powerful location-based services based on low data rates. Therefore, the provision of location information based on the WiBro network is expected to be an essential technology to be developed.

Terrestrial positioning technology using a mobile communication network is a key technology for constructing LBS along with GPS. The WiBro system is attracting attention as a fourth generation mobile communication technology, and TDOA wireless positioning is possible by using the characteristics of a preamble symbol broadcast every frame in the WiBro network.

However, since the WiBro system has a cellular structure, it suffers from shared channel interference, and due to the cell plan, it is difficult for the terminal to obtain distance information from a plurality of base station signals. Therefore, it is necessary to increase audibility in the wireless positioning using trilateral surveying in the WiBro network. Audibleness can be improved by using long-term superposition and interfering signal cancellation.

Location-Based Service (LBS) is a content service that provides specific information based on a user's location, and includes public safety services, location-based information services, and tracking services. Base technologies for LBS include positioning technology, location processing platform technology, location information application technology, and LBS-related standardization is underway in the Open Mobile Alliance (OMA) and Open Geospatial Consortium (OGC).

Global Positioning System (GPS) is a satellite navigation system that is widely used around the world. Current GPS uses L1 C / A codes to provide position information having a root mean square (RMS) error of about 12 m. According to the GPS modernization plan, if additional L2C codes are provided in the future, the position error is expected to be reduced to about 4-5m.

However, when using GPS, the signal reaching the receiver is about -130dBm or less, so it may not be able to receive the signal. In particular, there is a shadow area where the location cannot be obtained. As a technique to compensate for this problem, technologies such as GPS and other positioning systems, and AGPS (Assisted GPS) technology, which increases sensitivity using a mobile communication network, have been developed.

Typical positioning systems used with GPS include dead-reckoning using inertial sensors and terrestrial geolocation using mobile networks. In particular, a terrestrial positioning using a mobile communication network uses a cell ID technique using a cell radius of a base station and a trilateration technique using a plurality of base station signals.

Trilateration can provide uniform positioning accuracy even with large cell radius, but this requires acquisition of signals from three or more base stations for two-dimensional positioning. In a cellular network, it is difficult to receive a plurality of base station signals in most callable areas except cell boundary areas, and thus, it is necessary to improve audibility.

WiBro system has a cellular network structure similar to the existing mobile communication system. Therefore, for terrestrial positioning using a WiBro network, it is necessary to improve audibility as in a conventional cellular network. The factors that lower the audibility in cellular networks are co-channel interference and path loss. Audibleness can be increased by reducing channel sharing interference and compensating for path loss.

Therefore, in order to improve audibility in terrestrial positioning using a WiBro network, it is required to develop a technique for wireless positioning using an interference cancellation technique and synchronous long-term superposition.

The present invention has been made to improve the prior art as described above, and relates to a terrestrial positioning system in a WiBro network to which an interference cancellation technique and a synchronous superposition technique are applied, and utilizes an existing signal without changing a system specification for a wireless positioning. Therefore, it is easy to introduce the technology, and to provide a method of dramatically increasing audibility in the WiBro network by simultaneously applying a technique for removing interference signals and a synchronous long-term superposition technique.

In order to achieve the above object and solve the problems of the prior art, the WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention, the frequency for estimating and correcting the residual frequency error for the signal received at the receiver Estimator; A long-term overlap unit for synchronizing long-term overlapping the preamble signal having a repetitive characteristic; An interference canceling unit which sequentially removes signals detected from the received downlink preamble signal as interference signals; And a location recognizing unit for estimating the location information of the terminal by using the delay time estimate delivered from the interference removing unit and the location information of the base stations.

In addition, a WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention estimates a delay time of a signal from a received downlink preamble signal and uses the correlator for measuring the delay time of the position recognizing unit. Characterized in that the front end is configured.

In addition, in the WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention, the interference cancellation unit includes a signal reconstruction unit for estimating the magnitude, initial phase, and delay time of the signal and restoring the interference signal through the interference cancellation unit. In addition, the signal reconstruction unit uses a mixture of a combination of linear and nonlinear processing techniques and MUSIC (multiple signal) using an optimal condition technique using a maximum likelihood (ML), a linear processing technique using zero forcing (ZF) or a minimum mean square error (MMSE). The magnitude, initial phase, and delay time of the signal are estimated based on a subspace technique such as classification.

In addition, in the WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention, the location recognizing unit applies a TDOA (Time Difference Of Arrival) technique using a relative delay time between the base stations. Characterized in that recognize.

According to the WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention, since the downlink preamble symbol is used, wireless positioning is possible without changing the configuration of the base station. Should not be weighted.

In addition, by applying interference cancellation and synchronous long-term overlap at the same time, it is possible to dramatically increase audibility and provide high-precision location information by using the TDOA technique, which is a type of trilateration technique.

In addition, it can be applied to most cellular networks using pseudo noise codes, can provide positioning information for LBS with high accuracy, and can provide location information to terminals without interruption indoors or outdoors by using a technique of increasing audibility. .

1 is a diagram illustrating a configuration of a WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention.
Figure 2 is a diagram showing the configuration of the organ overlapping portion according to an embodiment of the present invention.
3 is a diagram illustrating a configuration of an interference canceling unit according to an exemplary embodiment of the present invention.
4 is a diagram illustrating a configuration of a position recognizing unit according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In a WiBro terrestrial system, downlink preamble symbols are allocated according to a base station and a sector, and the correlation between each preamble symbol is very low. In addition, the transmission time of the preamble signal is the same in all base stations synchronized with GPS, and the same preamble symbol is transmitted every 5 milliseconds.

WiBro terrestrial systems are cellular systems that share a single physical channel. Therefore, shared channel interference may occur. In particular, when a base station signal of an outer cell is received inside a cell, the base station signal of the inner cell acts as an interference, causing a problem. And when constructing a cellular system, a cell plan is performed to optimize base station installation. Therefore, signals of neighboring base stations are not weakly received or detected in one base station cell.

In addition, since WiBro's main service area is a dense urban area, the signal strength decreases rapidly as the distance between the base station and the terminal increases. Therefore, the terminal may not be able to obtain the minimum measurement for recognizing the location.

The configuration of the WiBro-based positioning system using a downlink preamble signal according to an embodiment of the present invention includes a frequency estimator, a long-term overlap unit, an interference canceller, and a position recognizer.

The frequency estimating unit according to an embodiment of the present invention performs a function of estimating and correcting a frequency error of a received signal, which is necessary to maximize the effect of long-term overlap. The organ overlap unit according to an embodiment of the present invention serves to improve sensitivity using a synchronous organ overlap technique as shown in FIG. 2.

As shown in FIG. 3, the interference canceling unit performs a function of sequentially removing signals detected from the received downlink preamble symbols as interference signals. In this case, the estimation and interference signal recovery unit estimates the magnitude, initial phase, delay time, and the like, and restores the interference signal.

For the estimation of parameters such as signal size, initial phase, delay time, etc., ML method shows the best performance, but MMSE method, sub-space method, and nonlinear method can be used. The correlator according to an embodiment of the present invention estimates the delay time of the signal from the received downlink preamble signal and uses it as a measurement value of the position recognizer. The correlator may use a parameter of the interference canceller without installing the correlator separately. .

According to an embodiment of the present invention, the location recognizing unit estimates the location information of the terminal as shown in FIG. 4 using the delay time estimate delivered in the previous step and the location information of the base stations. At this time, the location-aware algorithm uses the TDOA technique.

Hereinafter will be described in more detail to aid in understanding the present invention.

In a WiBro signal of a physical profile having a bandwidth of 8.75 MHz, a frame is fixed at 5 msec, and one frame includes 42 Orthogonal Frequency Division Multiple Access (OFDMA) symbols. Since WiBro uses a time division duplex (TDD) scheme, one WiBro frame is composed of uplink and downlink, and includes TTG / RTG (Transmit / Receive Transition Gaps) time required for switching of each link.

In addition, the subcarriers are arranged at intervals of 9.756 525 KHz in the frequency domain and consist of 1024 subcarriers. Each symbol is 1024 length Inverse Fast Fourier Transform (IFFT) procedure is added after the addition of 12.8usec Cyclic Prefix (CP), the result is that the total length of the symbol is 115.2usec.

The preamble is located in the first symbol of each frame, and the UE can check the presence of the base station by searching for the preamble. In addition to the cell search, the preamble may be used for time synchronization acquisition, frequency offset compensation, and channel estimation between the base station and the terminal. One preamble symbol uses one set of three sets of segments in the frequency domain, and one segment includes 284 subcarriers. At this time, to distinguish the preamble of each base station and sector, a segment is assigned a PN pseudo-random noise sequence having a length of 284.

Like other symbols, the preamble symbol is transmitted after a 1024-IFFT procedure is added to the CP. The autocorrelation function of the transmitted preamble symbol has one main peak and three subpeaks each of left and right. The WiBro system can distinguish each other by using preambles having different PN series while the base stations share the same physical channel.

Therefore, by using preamble signals having orthogonality to each other, signals received from a plurality of base stations can be distinguished from each other by using one physical channel, and when the arrival times are used, the position of the terminal can be obtained by trilateration. . On the other hand, as described above, the base stations of the WiBro network can apply one-way ranging because timing synchronization is performed using GPS and every frame is transmitted simultaneously from all base stations.

Since the WiBro system does not transmit time information from the base station to the terminal, the TDOA method using a relative delay time between each base station is suitable rather than the TOA method. Since each base station broadcasts the same preamble every frame, there is an advantage in that the use of the preamble symbol facilitates continuous positioning and applies a long-term superposition technique for improving audibility.

In a cellular network, interference signals from other users sharing a channel exist. The influence of such interference signal is called shared channel interference and has been steadily studied with the development of wireless communication. Interference problems occur in both uplink and downlink, and power control in uplink is a representative interference avoidance technique. In addition, FFR (Fractional Frequency Reuse), interference cancellation receiver, and intelligent Scheduling, multi-user multiple-input multiple-output (MU-MIMO) has been proposed.

MIMO, interference cancellation receivers, beamforming techniques, etc. have been proposed for downlink interference avoidance techniques. MIMO and beamforming techniques use thermal antennas to avoid interference. In general, the WiBro receiver uses a single antenna structure, which is not suitable as an interference avoidance technique in hardware.

The downlink interference canceling receiver can be applied to the WiBro receiver.

Assuming a transmission signal having a normalized average power is s (t), an acquisition signal at the receiver may be implemented through Equation 1.

Where α is the magnitude of the received signal, τ is the delay time, θ is the phase, and L is the index according to the base station. n (t) is a complex white Gaussian noise with a variance of σ ² .

If the signal discretized using a sampling frequency of 1 / T _S is r [n], the correlator output signal for the first base station signal may be implemented through Equation 2.

은 복제 신호의 시간 지연으로

가 정수라는 조건을 만족한다.In this case, N _sym is a symbol length, s' [n] is a duplicate signal generated by a receiver,

Is the time delay of the replica signal

Satisfies the condition that is an integer.

이며,

이다.

은 복소 백색 가우시안 잡음으로

의 분산을 가진다. T_h를 검출 임계값이라 하고,

이라 하면, 기지국 1과 2가 검출이 되어야 한다. 이때,

이고,

이다. here,

,

to be.

Is a complex white Gaussian noise

Has a variance of. T _h is called the detection threshold,

In this case, base stations 1 and 2 should be detected. At this time,

ego,

to be.

However, the detection of the signal in the receiver is detected based on the Signal to Noise plus Interference Ratio (SNIR), and the SNIR may be expressed as Equation 3 below.

이지만,

이고,

의 값에 따라 SNIR₂는 검출 임계값보다 작은 값이 될 수 있다. SNIR이 최대인 신호(SNIR₁)는 다른 신호(SNIR₂)에 대하여 간섭으로 크게 작용하게 되므로 이 신호부터 차례대로 상쇄를 한다면 SNIR₂와 SNR₂의 값을 비슷하게 만들어 검출할 수 있다. here,

as,

ego,

SNIR ₂ may be smaller than the detection threshold depending on the value of. Since the signal SNIR ₁ having the maximum SNIR acts as an interference with respect to the other signal SNIR ₂ , if the signal is canceled sequentially from this signal, the values of SNIR ₂ and SNR ₂ can be similarly detected.

This process is as follows, which has a structure as shown in FIG.

Step 1. Estimate α, τ, and θ satisfying Equation 4 for the signal having the maximum SNIR.

Step 2. Use the estimated value to cancel the signal.

에 대하여 적용한다면 기지국 1 신호를 제거한 후의 식은 수학식 5와 같다.This

For Equation 5, Equation 5 after removing the base station 1 signal is given by Equation 5.

And SNIR ₂ may be implemented through Equation 6.

는 k₁의 전력이다. 따라서

이므로 검출이 가능하다.At this time,

Is the power of k ₁ . therefore

Can be detected.

For the estimation of the interference signal, the optimal condition method using the maximum likelihood (ML), the linear processing method using the zero forcing (ZF) or the minimum mean square error (MMSE), and the mixed method using the linear and nonlinear processing methods and the MUSIC ( Estimators based on subspace techniques such as Multiple Signal Classification. An estimator based on the ML and Subspace methods provides good performance, but has a disadvantage in that it has a large amount of computation. In addition, the mixing technique has the advantage of not estimating the channel response of the interference signal, but has the disadvantage of being optimized for a specific condition.

Long-term superposition is a method of increasing the audible by overlapping the periodic signal, in the case of the WiBro signal can use the periodicity of the preamble signal. Long-term nesting techniques are divided into synchronous long-term nesting and asynchronous long-term nesting according to the cumulative technique. The asynchronous long-term superposition takes the absolute value of the signal to remove the influence of the frequency residual error and the phase difference, and then superimposes the magnitudes of the signals.

In the case of asynchronous long-term superposition, the phase ambiguity is removed by the absolute value calculation, and nonlinearity occurs between the interference signal and the signal to be detected, so it is difficult to apply the interference cancellation technique after the asynchronous long-term superposition. In the case of synchronous long-term superposition, the phase characteristic of the signal is not removed and a non-linear relationship does not occur between the interference signal and the signal to be detected, and thus the interference cancellation technique can be applied both before and after synchronous superposition.

In theory, the gain of synchronous overlap is improved in proportion to the number of overlaps. However, if there is a carrier frequency residual error when demodulating the received signal, a synchronous long-term overlap loss occurs, and the magnitude thereof may be implemented through Equation 7.

Where M _c Is the number of synchronous long-term overlap symbols, Δf is the frequency residual error, and T _s is the overlap period. The overlap period in the wibro signal is fixed at 5 ms, which is the broadcast period of the preamble.

Depending on the characteristics of the OFDM and the UE, the frequency residual error is generally known as 0.2-0.5% of the subcarrier spacing. Therefore, in the case of the WiBro signal, a frequency residual error of 20 to 50 Hz may occur. However, if the residual frequency is estimated and compensated using frequency domain analysis, Kalman filter, or maximum likelihood method, the frequency residual error can be made several Hz or less.

In particular, when estimating the residual frequency in the frequency domain using Fast Fourier Transform (FFT), it is known to have Mean Square Frequency Error (MSFE) of -40dB for sinusoidal signals with SNR (Signal to Noise Ratio) of -5dB or more. have. Therefore, if the above technique is applied to the WiBro signal, the frequency residual error can be made within 1Hz, which is -40dB of the subcarrier spacing, and the gain by synchronous long-term overlap can be maximized.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above-described embodiments, which can be variously modified and modified by those skilled in the art to which the present invention pertains. Modifications are possible. Accordingly, the spirit of the present invention should be understood only by the claims set forth below, and all equivalent or equivalent modifications thereof will belong to the scope of the present invention.

Claims (4)

A frequency estimator for estimating and correcting the residual frequency error with respect to the signal received by the receiver;
A long-term overlap unit for synchronizing long-term overlapping the preamble signal having a repetitive characteristic;
An interference canceling unit which sequentially removes signals detected from the received downlink preamble signal as interference signals; And
Location recognizing unit for estimating the location information of the terminal by using the delay time estimation value delivered from the interference cancellation unit and the location information of the base stations
WiBro (WiBro) using a downlink preamble signal, characterized in that it comprises a; Wireless Broadband based positioning system. The method of claim 1,
The downlink-based positioning system using the downlink preamble signal may include a correlator configured to estimate a signal delay time from the received downlink preamble signal and use it as a measurement value of the position recognition unit. Wibro based positioning system using link preamble signal. The method of claim 1,
The interference canceling unit includes an estimation and interference signal restoring unit estimating a magnitude, an initial phase, and a delay time of the signal, and restoring the interference signal through the interference elimination unit, and the estimation and interference signal restoring unit includes an optimal condition technique using a maximum likelihood (ML). Signal size, initial size based on subspace techniques such as linear processing technique using ZF and Zero Forcing (ZF) or Minimum Mean Square Error (MMSE), mixed techniques using linear and nonlinear processing techniques, and multiple signal classification (MUSIC). A WiBro-based positioning system using a downlink preamble signal, characterized in that it estimates phase and delay time. The method of claim 1,
And the location recognizing unit recognizes the location of the terminal by applying a time difference of arrival (TDOA) technique using a relative delay time between the base stations.

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