KR20110018216A - Apparatus and method for receiving signal in global navigation satellite system - Google Patents

Abstract

PURPOSE: Signal acquiring apparatus and method in a global positioning system are provided to obtain satellite signals without an additional hardware by detecting the identifier of a satellite and calculating a code phase and Doppler. CONSTITUTION: A signal acquiring apparatus in a global positioning system includes a first calculating part(420) and a second calculating part(430). The first calculating part detects the identifier of a satellite from a signal from the satellite. A code phase and Doppler are calculated, and a time required for calculation is measured. A second calculating part corrects the code phase and the Doppler using the carrier frequency and the code frequency of the satellite and the calculated values of the first calculating part.

Description

Apparatus and method for acquiring signal in satellite navigation system {APPARATUS®AND METHOD FOR RECEIVING SIGNAL IN GLOBAL NAVIGATION SATELLITE SYSTEM}

The present invention relates to an apparatus and method for obtaining signals in a satellite navigation system, and more particularly, to an apparatus and method for obtaining navigation signals in a satellite navigation system.

"The present invention is derived from the research conducted as part of the radio broadcasting industry promotion development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunication Research and Development. [Task No. 2007-S-301-03, Title: Satellite navigation ground station system and search Rescue terminal technology development]. "

Satellite navigation systems are systems for estimating position using signals received from multiple satellites in geostationary orbit on Earth. Such satellite navigation systems include widely used global positioning systems (GPS), Galileo positioning systems in Europe, and GLONASS in Russia.

The satellite navigation system consists of a number of satellites and a receiver. Many satellites transmit signals with signal signals, and signal types include L1 C / A and GPS L5. At least three satellites are needed to estimate position using signals received from multiple satellites in geostationary orbit on Earth. However, it is assumed that the receiver receives a signal from one satellite in order to explain in detail a problem that occurs during the receiver receiving a transmission signal from the satellite and calculating a code phase, a Doppler, etc. required for the signal tracking process.

The receiver receives signals from satellites and calculates code phase, Doppler, etc. based on the received signals for signal tracking. The calculated code phase, Doppler, etc. are used for signal tracking. As such, the processing steps of the signals transmitted from the satellites are divided into a signal acquisition step and a signal tracking step.

In the signal acquisition step, the receiver receives signals from satellites and calculates a signal acquisition result value to be used for signal tracking. The signal acquisition result includes satellite number, code phase and Doppler, and these values are provided to the signal tracking step. Here, the satellite number can be detected using a satellite identifier for distinguishing each satellite. The receiver executes the signal acquisition step based on the signal acquisition result value calculated in the signal acquisition step. In order for the signal tracking step to work properly, the signal tracking Doppler must be accurate. The code phase must be accurate to within 1 chip error.

The code period of the GPS L5 signal received from the satellite in the signal acquisition phase is 1ms, which is the same as L1 C / A, but the code frequency is 10.23 MHz, and the code length is 10,230 received in one cycle from the satellite, which is 10 compared to the L1 C / A signal. The belly is bigger. The high code frequency of the GPS L5 signal improves positioning accuracy compared to the L1 C / A signal. However, since the code length of the GPS L5 signal is 10 times larger, the processing time of the signal acquisition result value to be used in the signal tracking step is longer. Also, since the code phase and the Doppler, which are the signal tracking results, change with time, if the signal tracking is performed using the signal acquisition result value from the time of receiving the initial navigation signal to the time required to obtain the signal acquisition result value, Will fail.

Hereinafter, a signal acquisition step and a signal tracking step will be described with reference to FIG. 1.

1 is a view for explaining the change of the code phase information according to the signal acquisition processing time.

Referring to FIG. 1, the receiver is divided into a signal acquisition step 10 and a signal tracking step 16 according to a signal processing function. The signal acquisition step 10 shows the time from t0 to t3, and the signal tracking step 14 shows the time from t3 to t6.

First, the receiver receives navigation data in one cycle of code from the satellite. One cycle of code is from time t0 to time t2. Therefore, the receiver receives the navigation data 11 of one code period from the time t0 to the time t2 in the signal acquisition step 10. At this time, the initial code phase 12a exists at time t1. Since the receiver has received one cycle of code from time t0 to time t2, the position of the initial code phase 12a exists between time t0 and time t2. Thereafter, the receiver calculates an initial code phase based on the navigation data of one cycle of code received from the time point t0 to the time point t2 for the period from time t2 to time t3. By calculating the initial code phase, the satellite number, code phase and Doppler can be obtained. At this time, the time from the time t2 to the time t3 is called the signal acquisition processing time 13, and the signal acquisition processing time 13 takes longer than the time for receiving one code cycle.

When the initial code phase 12a is at the time t1, the initial code phase 12b calculated based on the navigation data received from the time t0 to the time t2 is located at the time t4.

That is, when the navigation signal is received in the signal acquisition step 10 and the signal acquisition step 10 is performed, the initial code phase 12b can be obtained at the time when the signal acquisition processing time 13 has elapsed. At this time, it is assumed that the navigation data is re-received when the signal acquisition processing time 13 has elapsed, and the code phase calculated based on the navigation data is the initial code phase 12b located at time t4. By the way, when the code phase is retrieved by receiving the code one-period navigation data 14 from the time point t3 to the time point t6 when the signal acquisition processing time 13 has elapsed, the actual code phase is located at time t5 instead of time t4. Is searched. At this time, for the successful signal tracking process, an error of less than one chip or the same time as t4 as the position of the initial code phase 12b and t5 as the changed code phase position should occur. However, since the signal acquisition processing time 13 takes longer than the time for receiving the code one cycle navigation data, an error of one chip or more occurs.

If more than one chip error occurs, signal tracking may fail or the signal may be lost. In general, code phase and Doppler are natural because they change over time. Therefore, the code phase must be compensated newly so that the error of one chip wife occurs in the code phase.

In order to solve this problem, the prior art has used a method of reducing the signal acquisition processing time as much as possible so as not to cause an error of more than one chip in the code phase. However, in order to reduce the signal acquisition time, the hardware must be implemented based on the Matched Filer method or the multi-correlator method having the number of taps as long as the code length. Therefore, the hardware implementation is complicated and the cost increases.

In addition, Doppler does not change significantly depending on the signal acquisition processing time. However, if Doppler is not calculated correctly, a lot of signal power attenuation may occur and signal tracking may fail. Therefore, to get accurate Doppler, the frequency search resolution is increased to search the code. In other words, if you use high frequency search resolution to increase the accuracy of Doppler, you can search the code precisely. However, since the computational amount increases in proportion to the frequency search resolution, the signal acquisition processing time becomes long or the implementation complexity increases.

In other words, a high frequency search resolution can be used to retrieve many frequencies to obtain accurate Doppler. Hereinafter, a search cell structure according to frequency search resolution will be described with reference to FIGS. 2 and 3.

FIG. 2 is a diagram illustrating a search cell structure when the frequency search resolution is 500 Hz, and FIG. 3 is a diagram illustrating a search cell structure when the frequency search resolution is 250 Hz.

 2 and 3 illustrate a case where a receiver receives a GPS L5 signal for one period of code from a satellite. The GPS L5 signal received during one cycle of code consists of 20460 chips. The x and y axes represent Doppler frequency search resolution and code, respectively. Doppler frequency search Searches for codes in cells, ranging from -7 KHz to 7 KHz, depending on the resolution. Since the receiver receives the GPS L5 signal from the satellite in one cycle of code, the code is in the 20450 chip range. In addition, the cell is composed of 1/2 chip because an error within 1 chip in the code phase does not fail the signal tracking.

2 shows a case where a frequency is searched when the frequency search resolution is 500 Hz. In FIG. 2, the code search is started from 0 KHz without the Doppler fixed, and the code existing in the 20450 chip is searched. First, the code is searched from 0 KHz and the code existing in the 20450 chip is searched from beginning to end (210). Thereafter, it returns to +500 Hz again to retrieve the code in Doppler increased by the frequency search resolution (220). Since the frequency search resolution is 500 Hz, the frequency search starts from +500 Hz and searches for codes existing in the 20450 chip from beginning to end (230). If the above process is searched alternately between + and-within the range of -7 KHz to 7 KHz in 500 Hz units, a total of 29 (17) code searches are performed.

3 shows a case where a frequency is searched when the wave search resolution is 250 Hz. In FIG. 3, the code search is started from 0 KHz without the Doppler fixed, and the code existing in the 20450 chip is searched. First, a code search is started from 0 KHz and a code existing in the 20450 chip is searched from beginning to end (310). Thereafter, it returns to +250 Hz again to search for frequencies in Doppler increased by the frequency search resolution (320). Since the frequency search resolution is 250 Hz, the frequency search starts from +250 Hz and searches for codes existing in the 20450 chip from beginning to end (330). When the above process is searched alternately in the range of -7 KHz to 7 KHz in 250 Hz units, + and-are searched for a total of 57 times (18) code searches, which are twice the number of code searches performed in FIG.

In other words, if you use high frequency search resolution to increase the accuracy of Doppler, you can search the code precisely. However, since the computational amount increases in proportion to the frequency search resolution, the signal acquisition processing time becomes long or the implementation complexity increases.

Accordingly, the present invention provides a signal acquisition device and method that does not require additional hardware in the existing signal acquisition device.

The present invention also provides a signal acquisition device and method for rapid signal tracking.

An apparatus for obtaining a satellite signal in a receiver of a satellite navigation system according to an embodiment of the present invention, detects the identifier of the satellite in the signal received from the satellite, calculates code phase and Doppler, A first calculation unit for measuring time, and a second calculation unit for correcting the code phase and Doppler using the values calculated by the first calculation unit and the carrier frequency and the code frequency of the satellite.

A method for obtaining a satellite signal in a receiver of a satellite navigation system according to an embodiment of the present invention, detects the identifier of the satellite in the signal received from the satellite, calculates code phase and Doppler, A first calculation process for measuring time, and a second calculation process for correcting the code phase and Doppler using the values calculated in the first calculation process and the carrier frequency and the code frequency of the satellite.

By using the satellite signal acquisition device of the present invention, additional hardware is not required for the existing signal acquisition device, and signals can be acquired for fast signal tracking.

In describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a block diagram of a receiver according to the present invention.

Referring to FIG. 4, the receiver includes an RF unit 410, a first calculator 420, a second calculator 430, and a tracker 440. The RF unit 410, the first calculator 420, and the second calculator 430 are used to perform a signal acquisition step. In addition, the tracking unit 440 is used to perform a signal tracking step. The first calculator 420 includes a buffer 421 and a signal acquisition result calculator 422, and the second calculator 430 uses the precision code phase redetector 431 and the precision Doppler recalculator 432. Include.

The RF unit 410 receives the navigation data of one code period from the satellite. The buffer 421 of the first calculator 420 temporarily stores the navigation data received from the RF unit 410. The signal acquisition result calculator 422 of the first calculator 420 calculates a signal acquisition result value based on navigation data of one cycle of code temporarily stored in the buffer 421. The signal acquisition result values include satellite number, code phase, and Doppler. The time from the time when the RF unit 410 receives the navigation data of one code period from the satellite to the time when the signal acquisition result calculation unit 422 calculates the signal acquisition result value is called a signal acquisition processing time. At this time, the signal acquisition processing time should be modified to the point synchronized with 1ms. For example, assume that a GPS L5 signal having a code period of 1 ms is received from a satellite, and a signal acquisition processing time is 495.3 ms. Then, up to 496ms, which is 1ms synchronized, is modified to the signal acquisition processing time.

Next, the precision code phase re-search unit 431 calculates the code phase changed during the signal acquisition processing time using Equation (1).

변경된 코드 위상 = 도플러 / 캐리어주파수 코드 주파수 신호획득 처리시간

Modified Code Phase = Doppler / Carrier Frequency Code Frequency Acquisition Processing Time

Here, the carrier frequency and the code frequency vary depending on the input signal. For example, if the received signal is GPS L5, the carrier frequency is 1176.45 MHz, the code frequency is 10.23 MHz, and the code period is 1 ms. In addition, when the received signal is GPS L1, the carrier frequency is 1574.42 MHz, the code frequency is 1.032 MHz, and the code period is 1 ms. The signal acquisition processing time is a time taken to calculate a signal acquisition result value based on initially received navigation data. That is, the signal acquisition processing time is required to search the code phase alternately between + and-within the range of -7 KHz to 7 KHz by starting the frequency search from 0 KHz without fixing the Doppler as shown in FIGS. 2 and 3. Includes time to be.

Doppler refers to the frequency resolution at which the initial code phase is found. That is, the signal acquisition result calculator 422 searches for codes existing in the 20450 chip of one code cycle from beginning to end. At this time, the phase of the cell in which the value of the largest signal power is found becomes the initial code phase, and the frequency resolution at the time when the initial code phase is found corresponds to Doppler.

The changed code phase calculated using Equation 1 is the code phase changed by Doppler during the signal acquisition processing time. Therefore, the precision code phase recalculation unit 431 uses Equation 2 below to calculate the recalculated initial code phase from the initial time of receiving the navigation data to the time when the signal acquisition processing time has elapsed.

Recalculated initial code phase = initial code phase calculated by the first calculation unit + changed code phase

As shown in Equation 2, the precision code phase recalculation unit 431 signals from an initial time point at which the navigation data is received by adding the initial code phase calculated based on the navigation data at the initial time point and the code phase changed during the signal acquisition processing time. The recalculated initial code phase until the acquisition processing time has elapsed is calculated.

Here, the Doppler used in Equation 1 is a value at the point in time when the code phase is searched while searching for the code phase by the frequency search resolution unit without fixing the Doppler as shown in FIGS. 2 and 3. In addition, since Doppler is a result calculated based on navigation data of an initial time, Doppler and code phase contain errors.

If more than one chip of error occurs in the code phase or the Doppler is inaccurate, signal tracking may fail or the signal may be lost. Therefore, the correct code phase should be searched around the recalculated code phase.

To this end, the RF unit 410 re-receives the navigation data at a time point when the signal acquisition processing time is synchronized for 1 ms to re-search the correct code phase around the recalculated code phase and temporarily stores it in the buffer 421. Thereafter, the signal acquisition result calculator 422 removes the carrier by using the Doppler frequency found at the time of initial signal acquisition, and re-searches code phases around the code phase recalculated by Equation (2). In this case, the re-calculation of the code phases around the code phases may be performed by using the signal acquisition result calculation unit 422 as it is, so that no additional hardware is required. In addition, since the code phase needs to be searched for only a few chips around the code phase in the fixed Doppler, the amount of computation does not increase significantly. Therefore, a new signal acquisition result can be obtained in a short time.

The signal acquisition result calculator 422 searches for chips in several of the code phases that are recalculated by the fixed Doppler. At this time, the signal acquisition result calculation unit 422 compares the signal power around the recalculated code phase and determines the code phase in which the largest value is found as the fine code phase.

After that, the precision code phase recalculation unit 431 calculates the changed precision code phase that does not include an error by using Equation (3).

Precision code phase changed = Precision code phase-Initial code phase

On the other hand, the changed code phase calculated using Equation 1 is incorrect because it includes a code phase error due to the Doppler error equal to the frequency search resolution. However, since the modified precision code phase calculated using Equation (3) uses the precision code phase obtained by re-acquiring the signal around the recalculated code phase calculated using Equation (2), The exact value removed. Therefore, the precision Doppler recalculation unit 432 calculates the precision Doppler using the changed precision code phase from which the code phase error is removed. That is, the precision Doppler recalculation unit 432 calculates the precision Doppler using Equation 4 below.

정밀 도플러 = (변경된 정밀코드위상 캐리어주파수) / (코드주파수 신호획득 처리시간)

Precision Doppler = (Modified Precision Code Phase Carrier Frequency) / (Code Frequency Signal Acquisition Processing Time)

The precision code phase changed in Equation 4 is calculated using Equation 3. In addition, the carrier frequency and the code frequency depend on the input signal as described above. The signal acquisition processing time is a time taken to calculate a signal acquisition result value based on initially received navigation data.

In conclusion, the code phase calculated by the signal acquisition result calculation unit 422 and the precision code phase and the precision Doppler calculated by the precision Doppler recalculation unit 432 retrieved by the fine code phase redetection unit 431 are trackers for signal tracking. 440 is sent.

Since the error does not exist in the modified precision code phase calculated through the above process and the Doppler is accurate, the signal tracking step can be executed accurately and quickly. Hereinafter, a procedure of a signal acquisition process will be described with reference to FIG. 5.

5 is a view for explaining the procedure of the signal acquisition process according to the present invention.

Referring to FIG. 5, in step 510, the RF unit 410 receives navigation data of one code period from a satellite and temporarily stores the navigation data in a buffer 421. The signal acquisition result calculation unit 422 calculates an initial signal acquisition result value based on the navigation data temporarily stored in the buffer 421 in step 520. The signal acquisition result values include satellite number, code phase, and Doppler. The time from the time when the RF unit 410 receives the navigation data from the satellite to the time when the signal acquisition result calculation unit calculates the signal acquisition result value is called a signal acquisition processing time. At this time, the signal acquisition processing time should be modified to the point synchronized with 1ms. For example, assume that a GPS L5 signal having a code period of 1 ms is received from a satellite, and a signal acquisition processing time is 495.3 ms. In operation 530, the signal acquisition result calculator 422 modifies the signal acquisition processing time to 496 ms, which is a 1 ms synchronization point.

Next, the precision code phase re-search unit 431 calculates the code phase changed during the signal acquisition processing time using the equation (1) in step 540. Since the changed code phase is the code phase changed by the Doppler during the signal acquisition processing time, the precision code phase redetection unit 431 uses the Equation 2 at step 550 to time the signal acquisition processing time elapses from the initial point. Compute the code phase up to Here, the Doppler and the changed code phase include an error because the Doppler used to calculate the changed code phase is a result value calculated based on the navigation data of the initial time point.

If more than one chip of error occurs in the code phase or the Doppler is inaccurate, signal tracking may fail or the signal may be lost. Therefore, the correct code phase should be searched around the recalculated code phase.

To this end, the RF unit 410 re-receives the navigation data at a time point when the signal acquisition processing time is synchronized by 1 ms in order to re-search the correct code phase around the code phase recalculated in step 560 and temporarily stores it in the buffer 421. In operation 570, the signal acquisition result calculator 422 removes the carrier using the Doppler frequency found at the time of initial signal acquisition, and re-searches code phases around the recalculated code phase. The signal acquisition result calculator 422 compares the signal power around the code phase recalculated in step 580 and determines the largest value as the precise code phase of the retrieved code phase. Thereafter, the precision code phase recalculation unit 431 calculates the changed precision code phase that does not include an error by using Equation 3 above.

On the other hand, the changed code phase calculated using Equation 1 is incorrect because it includes a code phase error due to Doppler error equal to the frequency search resolution. However, since the changed precision code phase calculated using Equation 3 is used as the precision code phase obtained by re-acquiring a signal around the recalculated code phase calculated using Equation 2, This is a precise value with the error removed. Therefore, the precision Doppler recalculation unit 432 calculates the precision Doppler using the changed precision code phase from which the code phase error is removed. That is, the precision Doppler recalculation unit 432 calculates the precision Doppler using Equation 4 at step 590.

1 is a view for explaining a change in code phase information according to a signal acquisition processing time;

2 is a diagram for explaining a search cell structure when the frequency search resolution is 500 Hz;

3 is a diagram for explaining a search cell structure when the frequency search resolution is 250 Hz;

4 is a block diagram of a receiver according to the present invention;

5 is a view for explaining the procedure of the signal acquisition process according to the present invention.

Claims (10)

An apparatus for obtaining a satellite signal at a receiver of a satellite navigation system, A first calculation unit for detecting an identifier of the satellite from a signal received from the satellite, calculating a code phase and a Doppler, and measuring a time required for the calculation; And a second calculator configured to correct the code phase and the Doppler using the values calculated by the first calculator and the carrier frequency and the code frequency of the satellite. The method of claim 1, wherein the first calculation unit, A buffer for temporarily storing a signal received from the satellite, And a signal acquisition result calculation unit for detecting an identifier of the satellite from the signal stored in the buffer, calculating a code phase and a Doppler, and measuring a time required for the calculation. The method of claim 1 or 2, wherein the second calculation unit, The amount of change in the code phase is calculated by using the Doppler calculated by the first calculator, the measurement time required for the calculation, and the carrier frequency and the code frequency of the satellite, and the calculated amount of code phase is changed to the initial phase calculated by the first calculator. Code phase re-search part to correct, A Doppler recalculator that recalculates Doppler using the code phase re-searched by the code phase redetector, the Doppler calculated by the first calculator, the measurement time required for the calculation, and the carrier frequency and the code frequency of the satellite. Signal acquisition device characterized in that. The method of claim 3, wherein the code phase re-search unit, Calculate the changed code phase by using Equation 5 below, recalculate the initial code phase by using Equation 6, and then search for the code phase recalculated from the fixed Doppler value. A signal acquisition device, characterized in that for calculating the corrected code phase corrected using Equation (7), <Equation 5> Modified code phase = Doppler / carrier frequency

Code frequency

Signal acquisition processing time <Equation 6> Recalculated initial code phase = initial code phase calculated by the first calculation unit + changed code phase <Equation 7> Corrected precision code phase = Precision code phase-Initial code phase. The method of claim 4, wherein the Doppler recalculation unit, Signal acquisition apparatus comprising a Doppler recalculation unit for recalculating the Doppler using Equation 8, <Equation 8> Recalculated Doppler = (corrected precision code phase

Carrier frequency) / (code frequency

Signal acquisition processing time). A method for obtaining a satellite signal at a receiver of a satellite navigation system, A first calculation process of detecting an identifier of the satellite in a signal received from the satellite, calculating a code phase and a Doppler, and measuring a time taken for the calculation; And a second calculation step of correcting the code phase and the Doppler using the values calculated in the first calculation step and the carrier frequency and the code frequency of the satellite. The method of claim 6, wherein the first calculation process, A buffering step of temporarily storing a signal received from the satellite; And a signal acquisition result calculating step of detecting an identifier of the satellite from the buffered signal, calculating a code phase and a Doppler, and measuring a time required for the calculation. The method of claim 6 or 7, wherein the second calculation process is The amount of change in the code phase is calculated by using the Doppler calculated in the first calculation process, the measurement time required for the calculation, the carrier frequency and the code frequency of the satellite, and corrected for the initial phase calculated in the first calculation process. Code phase rescan step, A Doppler recalculation step of recalculating Doppler using the code phase rescanned in the code phase rescanning step, the Doppler calculated in the first calculation process, the measurement time required for the calculation, and the carrier frequency and code frequency of the satellite; Signal acquisition method comprising the. The method of claim 8, wherein the code phase rescanning step comprises: Calculating a changed code phase by using Equation 9 below; Recalculating the initial code phase using Equation 10, and then retrieving the code phase recalculated from the Doppler fixed value to search for the fine code phase; A signal acquisition method comprising the step of calculating the corrected code phase corrected using Equation 11, &Quot; (9) &quot; Modified code phase = Doppler / carrier frequency

Code frequency

Signal acquisition processing time <Equation 10> Recalculated initial code phase = initial code phase calculated by the first calculation unit + changed code phase <Equation 11> Corrected precision code phase = Precision code phase-Initial code phase. 10. The method of claim 9, wherein the Doppler recalculation step is Signal acquisition method, characterized in that it comprises a Doppler recalculation step of recalculating the Doppler using Equation 12 <Equation 12> Recalculated Doppler = (corrected precision code phase

Carrier frequency) / (code frequency

Signal acquisition processing time).

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