KR20090030417A - Apparatua for searching using twin-cell in global navigation satellite system and method therefor - Google Patents

Abstract

An apparatus for searching using a twin-cell is provided to reduce the highest value of error of carrier frequency by updating the highest value when the highest value is detected. A fast Fourier transform(20) performs Fourier transform of a spreading code and a positioning signal which is input. A conjugate operation part(30) performs the calculation of the input signal or the spreading code to the complex division. A sign of image number is converted through conjugate complex of the spreading sign. An inverse fast Fourier transform(40) performs an inverse operation of the calculation of performing in the fast Fourier transform. A highest value detection unit(50) detects the first highest value among the input signal, and a second highest value is detected by using the first highest value renewal result.

Description

Apparatua for Searching using Twin-Cell in Global Navigation Satellite System and Method therefor}

The present invention relates to a navigation apparatus and method using dual cells in a global navigation satellite system (hereinafter referred to as 'GNSS'), and more specifically, to obtain a spreading gain in a GNSS. The acquisition process is the first acquisition process. It stores the highest value by the previous search frequency branch, updates the highest value when detecting the highest value by the new search frequency branch, updates the old maximum value and the new value. The present invention relates to a search apparatus and a method using a double cell in a GNSS that detects a peak value having a reduced search error by searching a frequency section between two search frequency branches using a peak value.

GNSS is a system that precisely tracks the position of targets on the ground using satellite networks. In a broad sense, GNSS is a Global Navigation Satellite System (GLONASS), Galileo System, and Global Positioning System (GPS). Etc.).

Since GNSS is a system for transmitting positioning signals from satellites and receiving them from mobile terminals, additional reception gain is required for weak signal reception.

Most GNSSs use a Direct Sequence Spread Spectrum (DS / SS) system as the communication physical layer to secure additional receive gain.

The direct sequence spread band system is a system capable of securing a spreading gain as much as a spreading band by performing a process of spreading and despreading an information signal using a spreading code.

At this time, accurate synchronization is required to secure the spreading gain, and for this purpose, it is common to perform the synchronization process in two steps, an acquisition process and a tracking process.

The acquisition process is a process of determining whether to transmit a signal, an initial code phase, and a carrier frequency based on a correlation value obtained by a correlation operation of a received signal. In the tracking process, a code tracking process and a carrier frequency tracking process are generally performed in parallel. More accurate synchronization is determined by using the initial code phase and carrier frequency obtained as an initial value, and the determined synchronization is maintained.

A general acquisition process is an acquisition process based on a fast Fourier transform (FFT). 1 is a flowchart of an acquisition process based on a fast Fourier transform.

As shown in FIG. 1, first, a GNSS positioning signal is received (S1). Next, a fast Fourier transform is performed on the input signal to reduce the computational complexity of the Discrete Fourier Transform (S2).

In addition to the step S2, a fast Fourier transform process and a conjugate complex operation on a spread code are performed in parallel.

A spreading code is a code for performing spreading and despreading of a direct sequence spreading band system and generally uses a pseudo noise sequence or an extended sequence thereof. The conjugate complex operation is an operation of inverting the sign of the imaginary part through the complex operation of the spreading code when the operation of the input signal and the spread signal is performed by the complex operation.

Next, an inverse process S3 of the fast Fourier transform is performed, and the highest value is detected among the input vectors (S4).

Thereafter, it is determined whether the highest value detected in the step S4 is larger than a preset threshold value (S5).

As a result of the determination in step S5, when the maximum value is larger than the threshold value, the signal is considered to be received, and the procedure is performed in the tracking process by transmitting the code phase and the current search frequency branch index where the highest value is detected.

As a result of the determination in step S5, if the maximum value is not larger than the threshold value, the frequency generator generates the next search frequency by updating the search frequency branch index (S6), and proceeds to step S2.

The acquisition process based on the fast Fourier transform described above can search all code phases through one operation. The carrier frequency search is a serial search that repeats the operation of updating the search frequency branch index when the maximum value is not larger than the threshold.

In the case of GPS, which is widely used among GNSSs, the carrier frequency may be shifted due to the Doppler shift from -5 kHz to +5 kHz based on the center frequency due to the speed difference according to the relative movement of the satellite and the receiver. Therefore, a general GPS receiver performs a two-dimensional search as shown in FIG.

2, N is the number of search branches, and Δ means a frequency search unit. In a typical GPS receiver, Δ = 500 Hz, which is designed for N = 21 because it seeks from -5 kHz to +5 kHz based on the carrier's center frequency.

At this time, the maximum carrier frequency acquisition error is Δ / 2, and the tracking process should be designed to have a dynamic range that can sufficiently compensate for such an error. Therefore, if the maximum carrier frequency acquisition error can be reduced than Δ / 2, the complexity of the tracking process can be reduced.

In addition, when synchronous integration is performed to receive the weak signal, the acquisition complexity increases because the new Δ must be set at an interval obtained by dividing the existing Δ by the number of synchronous integrations.

For example, if 10 synchronous integrations are performed to receive a weak signal, Δ = 50 Hz should be designed, and N = 201 to search the same search range. That is, the complexity increases about 10 times in one fast Fourier transform-based search branch.

The present inventors have completed the present invention by studying a method of adding a multi-cell combining structure such as a double cell to the existing acquisition process to solve such problem (s).

Disclosure of Invention Problems to be Solved by the Invention The present invention is to solve the above problems, and to provide a search apparatus and method using a double cell in GNSS that can reduce the maximum value of the carrier frequency acquisition error.

Another object of the present invention is to solve the above problems, and to provide a search apparatus and method using dual cells in a GNSS with a slight increase in complexity even when performing synchronous integration.

The present invention relates to a search apparatus using dual cells in a GNSS, comprising: a positioning signal input unit configured to receive a GNSS positioning signal; A fast Fourier transform unit for performing Fourier transform on the received positioning signal and spread code; An inverse fast Fourier transform unit performing an inverse operation of an operation performed by the fast Fourier transform unit; A highest value detector for detecting a first highest value among input signals and detecting a second highest value by using the first highest value update result; Storing a first first highest value and updating the first highest value when the highest value detection unit detects a new first highest value, and using the previous first highest value and the new first highest value, two search frequencies; A delay storage unit for searching a frequency section between the branches; A maximum value comparing unit configured to compare the detected second highest value with a preset threshold and transmit a code phase and a current search frequency branch index at which the second highest value is detected when the second highest value is larger than the threshold; A frequency generator for generating a next search frequency by updating a search frequency branch index when the second maximum value is less than or equal to the threshold value; And an output unit for outputting the received code phase and search frequency branch index, thereby allowing the process to move to the tracking process. It includes.

Here, when performing the operation of the spread code by a complex operation, a complex conjugate operation unit for inverting the sign of the imaginary part by performing a complex operation of the spread code; It characterized in that it further comprises.

Specifically, the spread code is characterized by using a pseudo noise sequence.

In more detail, when the delay storage unit updates the new first maximum value, the delay storage unit may output the first first maximum value and then erase the previous maximum value.

On the other hand, the present invention relates to a search method using a double cell in the GNSS, a first process of receiving a GNSS positioning signal; Performing a Fourier transform on the input signal; A third step of performing an inverse operation of the Fourier transform operation; A fourth step of searching for a frequency section between two search frequency branches by detecting and updating a first highest value among input signals from the inverse operation result; The second peak value is detected by comparing the detected second peak value with a preset threshold value using the frequency interval search result. Transmitting a search frequency branch index of the fifth process; And a sixth step of generating a next search frequency by updating a search frequency branch index when the second highest value is equal to or less than a threshold as a result of the comparison of the fifth step, and performing a procedure to the second step. It includes.

Preferably, the second process includes performing a Fourier transform on a spread code; Characterized in that it comprises a.

Here, after performing the Fourier transform, if the operation of the spreading code to perform a complex operation to perform a complex operation of the spreading code to invert the code of the imaginary part; It characterized in that it further comprises.

Specifically, the spread code is characterized by using a pseudo noise sequence.

And after the fourth process, after updating the first highest value, outputting and deleting the previous first highest value; It characterized in that it further comprises.

According to the present invention, compared with the conventional fast Fourier transform based searcher, there is an effect that can significantly reduce the maximum value of the carrier frequency acquisition error.

According to the present invention, the dynamic range of the tracking process can be designed more narrowly than the conventional method, and even if the synchronous integration is performed, the degree of complexity increase is insignificant.

According to the present invention, since it is more robust to additive white normal noise than the conventional method, it is possible to obtain a signal higher than a certain level even in a weak signal environment.

Before describing the details for carrying out the present invention, it should be noted that configurations that are not directly related to the technical gist of the present invention are omitted within the scope of not distracting the technical gist of the present invention.

In addition, the terms or words used in the present specification and claims are consistent with the technical spirit of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term in order to explain the invention in the best way. It should be interpreted as meaning and concept.

Hereinafter, a configuration of a search apparatus using dual cells in a GNSS according to a preferred embodiment of the present invention will be described with reference to FIGS. 3 to 5.

3 is an overall configuration diagram of a search apparatus using dual cells in a GNSS according to a preferred embodiment of the present invention, and FIG. 4 is a diagram illustrating a search structure of a search apparatus using dual cells in a GNSS according to a preferred embodiment of the present invention. It is a schematic diagram and FIG. 5 is a graph which shows the relationship of the position of a search branch, and a correlation value.

As shown in FIG. 3, a search apparatus using dual cells in a GNSS according to a preferred embodiment of the present invention includes a positioning signal input unit 10, a fast Fourier transform unit 20, a complex conjugate operation unit 30, and an inverse. It includes a fast Fourier transform unit 40, the highest value detection unit 50, the delay storage unit 60, the highest value comparison unit 70, the frequency generator 80 and the output unit 90.

The positioning signal input unit 10 receives a GNSS positioning signal.

Since the input of the GNSS positioning signal may be performed in a conventional form, a detailed description thereof will be omitted.

Next, the fast Fourier transform unit 20 converts the input signal into a frequency axis input signal by performing a fast Fourier transform that reduces the computational complexity of the discrete Fourier transform, and performs a fast Fourier transform on a spread code. This converts the frequency axis input signal. This fast Fourier transform enables correlation operations.

In a preferred embodiment of the present invention, the Fourier transform of the fast Fourier transform unit 20 is set to a fast Fourier transform, but the present invention is not limited thereto and may be implemented as a discrete Fourier transform.

A spreading code is a code for performing spreading and despreading of a direct sequence spreading band system, and a pseudo noise sequence or an extended sequence thereof is generally used.

In a preferred embodiment of the invention, the correlation operation can be performed on the time axis and the frequency axis, respectively. In the case of the time axis correlation operation, a convolution operation of the input signal and the spreading code is performed. The correlation operation on the time axis and the frequency axis is based on the cross-intersection characteristic of the Fourier transform operation in which the convolutional integral operation on the time axis is expressed as a simple product on the frequency axis.

Next, when the complex conjugate operation unit 30 performs a complex operation on an input signal or a spread code, the complex complex operation unit 30 inverts the code of the imaginary part by performing a complex conjugate operation on a spread code.

In order to perform a correlation operation on two signals converted by the fast Fourier transform unit 20, a complex conjugate operation is required on any one of two signals. In a preferred embodiment of the present invention, a complex conjugate operation on spreading code is adopted to reduce the computational complexity.

This is because the spreading signal is a predetermined signal, whereas the input positioning signal is a signal that changes according to the environment. Therefore, if the fast Fourier transform is performed on the spread code, the complex conjugate operation on the spread code is performed, and the data is permanently stored in a storage space such as a ROM, the computation complexity may be reduced.

Next, the inverse fast Fourier transform unit 40 performs an inverse process of the operation performed by the fast Fourier transform unit 20.

Next, the highest value detector 50 detects the highest value among the input vectors, and detects the highest value more accurately by using the maximum value update result of the delay storage unit 60 described later.

Next, the delay storage unit 60 stores a correlation value for each search frequency branch. In addition, when the maximum value detector 50 detects the new maximum value while storing the previous maximum value, the new maximum value is updated. When updating to a new high value, a setting can be made to output the old high value and then erase it.

As shown in FIG. 4, a frequency section between two search branches may be searched by adding a value obtained through a fast Fourier transform-based search branch operation to a value obtained through a next search branch operation through simple storage. .

5 shows the relationship between the position of the search branch and the correlation value, (A) indicates a search branch when there is no search error, and (B) indicates a fast Fourier transform-based search branch when there is a search error. It shows the double cell search branch obtained from the background. Here, the cell means a basic unit of search.

In a preferred embodiment of the present invention, the cell is set as a dual cell, but the present invention is not limited thereto.

In FIG. 5A, since the branch indicating the maximum correlation value is determined as an initial carrier frequency and there is no search error, an almost accurate initial carrier frequency can be obtained.

In (b) of FIG. 5, since only a solid line portion is applied, a search error is generated. Therefore, if a fast Fourier transform-based search is performed without applying a double cell search, the initial carrier frequency determined without searching error is transmitted to the tracking process. Done. This means that the dynamic range of the carrier tracker needs to be unnecessarily wide enough to recover the inaccuracy caused by the search error.

However, when the search apparatus using the dual cell according to the preferred embodiment of the present invention is applied, as shown by the dotted line in FIG. 5B, a value close to the actual maximum value can be obtained. This means that the tracking process can be performed based on the initial carrier frequency with the minimum search error.

In addition, the dual cell according to the preferred embodiment of the present invention can significantly reduce the complexity.

For example, when searching for N = 41, the frequency search interval had to be halved in the past. This required an additional multiplication operation by the complexity equivalent to M * log ₂ (M), because the fast Fourier transform and the inverse fast Fourier transform must be performed in sequence. In general, multiplication is at least four times more complex than addition.

However, even in the above-described case, if the dual cell is adopted, the frequency range between the two search branches can be searched by only a few additions while maintaining N = 21, thereby significantly reducing the complexity.

In addition, in an environment in which only additive white normal noise exists, applying a double cell search apparatus according to a preferred embodiment of the present invention is advantageous in detecting weak signals because the signal-to-noise ratio is improved.

That is, in the addition of two signals having normal noise in an additive white normal noise environment, since the noise is uncorrelated, the dispersion of noise is reduced. Reduced noise dispersion means reduced noise power, which improves the overall signal-to-noise ratio.

Next, the maximum value comparator 70 compares the detected maximum value with a preset threshold value. If the maximum value is larger than the threshold value, the signal value is considered to be regarded as a signal received, and the current value of the detected code phase is detected. The frequency branch index is transmitted to the output unit 90.

Next, the frequency generator 80 considers that the signal is not received when the maximum value is less than or equal to the threshold as a result of the comparison of the maximum value comparator 70, and generates the next search frequency by updating the search frequency branch index. Let's do it.

Finally, the output unit 90 outputs the code phase and search frequency branch index of which the highest value is detected, so that the synchronization process can be shifted to the tracking process.

Hereinafter, a search method using dual cells in GNSS according to a preferred embodiment of the present invention will be described with reference to FIG. 6.

6 is an overall flowchart of a search method using dual cells in a GNSS according to a preferred embodiment of the present invention.

First, as shown in FIG. 6, a GNSS positioning signal is received (S10).

Next, a fast Fourier transform is performed on the received positioning signal (S20).

In addition to the step S20, in order to reduce the computational complexity, it is preferable to perform a fast Fourier transform process on a spread code. In addition, in the step S20, when the operation of the spreading code is performed by a complex operation, it is preferable to perform the complex operation of the spreading code to invert the code of the imaginary part in parallel.

Next, an inverse operation of the fast Fourier transform operation is performed (S30).

Next, the highest value is detected among the input vectors (S40).

Next, the highest value stored in advance is updated to a new highest value detected, and a more accurate maximum value is detected by performing a double cell combining search using this (S50).

Next, it is determined whether the detected maximum value is greater than a preset threshold value (S60).

Finally, when the detected maximum value is greater than the preset threshold as a result of the determination in step S60, the signal is received and the procedure is followed by the tracking process by transmitting the index of the detected code phase and the current search frequency branch index. To implement.

As a result of the determination in step S60, when the detected maximum value is less than or equal to a preset threshold, the search frequency branch index is updated to generate the next search frequency (S70), and the procedure proceeds to step S20.

As described above and described with reference to a preferred embodiment for illustrating the technical idea of the present invention, the present invention is not limited to the configuration and operation as shown and described as described above, it is a deviation from the scope of the technical idea It will be understood by those skilled in the art that many modifications and variations can be made to the invention without departing from the scope of the invention. Accordingly, all such suitable changes and modifications and equivalents should be considered to be within the scope of the present invention.

1 is a flowchart of an acquisition process based on a conventional fast Fourier transform.

2 is a schematic diagram of a two-dimensional search structure performed by a general GPS receiver.

3 is an overall configuration diagram of a search apparatus using dual cells in GNSS according to a preferred embodiment of the present invention.

4 is a schematic diagram of a search structure of a search apparatus using dual cells in a GNSS according to a preferred embodiment of the present invention.

5 is a graph showing a relationship between a position of a search branch and a correlation value.

6 is an overall flowchart of a search method using dual cells in a GNSS according to a preferred embodiment of the present invention.

Claims (9)

A positioning signal input unit 10 which receives a global navigation satellite system (GNSS) positioning signal; A fast Fourier transform unit for performing Fourier transform on the received positioning signal and spread code; An inverse fast Fourier transform unit 40 for performing an inverse operation of an operation performed by the fast Fourier transform unit 20; A highest value detector (50) for detecting a first highest value among input signals and detecting a second highest value by using the first highest value update result; The first highest value is stored, and when the highest value detection unit 50 detects the new first highest value, the first highest value is updated, and both values are updated by using the first first highest value and the new first highest value. A delay storage unit 60 for searching a frequency section between the two search frequency branches; The maximum value comparator 70 which compares the detected second highest value with a preset threshold and transmits the code phase and the current search frequency branch index where the second highest value is detected when the second highest value is larger than the threshold. ; A frequency generator (80) for generating a next search frequency by updating a search frequency branch index when the second maximum value is less than or equal to the threshold value; And An output unit 90 for outputting the transmitted code phase and search frequency branch indexes, thereby allowing the process to move to the tracking process; Search device using a double cell in the GNSS comprising a. The method of claim 1, A complex conjugate operation unit 30 for inverting the imaginary part code by performing a complex conjugate operation of a spread code when performing the operation of the spread code by a complex operation; Search device using a double cell in the GNSS, characterized in that it further comprises. The method of claim 1, The spreading code is a search device using a double cell in the GNSS, characterized in that using a pseudo noise sequence. The method of claim 1, The delay storage unit (60) is a search device using a double cell in the GNSS, characterized in that for updating to a new first highest value, after outputting the previous first highest value. A first process of receiving a global navigation satellite system (GNSS) positioning signal; A second process of performing Fourier transform on the input signal; A third step of performing an inverse operation of the Fourier transform operation; A fourth step of searching for a frequency section between two search frequency branches by detecting and updating a first highest value among input signals from the inverse operation result; The second peak value is detected by comparing the detected second peak value with a preset threshold value using the frequency interval search result. Transmitting a search frequency branch index of the fifth process; And A sixth step of generating a next search frequency by updating a search frequency branch index when the second highest value is less than or equal to a threshold as a result of the comparison of the fifth step and performing a procedure to the second step; Search method using dual cells in GNSS comprising a. The method of claim 5, wherein The second process, Performing a Fourier transform on the spread code; Search method using a double cell in the GNSS, comprising a. The method of claim 6, After the Fourier transform process, Inverting the sign of the imaginary part by performing a complex conjugate operation of the spreading code when performing the spreading operation by a complex operation; Search method using a double cell in the GNSS, characterized in that it further comprises. The method of claim 6, The spreading code is a search method using double cells in a GNSS, characterized in that it uses a sequence of pseudo noise. The method of claim 5, wherein After the fourth process, Outputting a first first highest value after updating the first highest value and then erasing the first highest value; Search method using a double cell in the GNSS, characterized in that it further comprises.

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