KR101547598B1 - Apparatusand method for receiving signal in global navigation satellite system - Google Patents

Abstract

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

The present invention provides an apparatus and method for acquiring signals for rapid signal tracking without requiring additional hardware in existing signal acquisition devices.

An apparatus for acquiring a satellite signal in a receiver of a satellite navigation system according to an embodiment of the present invention, the apparatus for detecting an identifier of the satellite in a signal received from a satellite, calculating a code phase and a Doppler, And a second calculation unit for correcting the code phase and the Doppler using the values calculated by the first calculation unit and the carrier frequency and the code frequency of the satellite, Signal acquisition device.

Doppler, code phase, navigation system, signal acquisition

Description

[0001] APPARATUS AND METHOD FOR RECEIVING SIGNAL IN GLOBAL NAVIGATION SATELLITE SYSTEM [0002]

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

"The present invention was derived from research carried out by the Ministry of Knowledge Economy and the National Institute of Information and Communications Technology as part of the propagation broadcasting industry promotion project [Task No. 2007-S-301-03, Project Name: Satellite Navigation Ground Station System and Navigation Structure terminal technology development].

A satellite navigation system is a system for estimating a position using signals received from a plurality of satellites in geostationary orbit. These satellite navigation systems include the widely used Global Positioning System (GPS), Galileo positioning system in Europe, and GLONASS in Russia.

The satellite navigation system consists of a number of satellites and receivers. Many satellites transmit signals to the signalers, and the types of signals include L1 C / A and GPS L5. At least three satellites are required to estimate the position using signals received from multiple satellites in geostationary orbits. However, it is assumed that a receiver receives a signal from one satellite in order to describe a problem occurring during a process of receiving a transmission signal from a satellite and calculating a code phase, a Doppler, and the like necessary for the signal tracking process.

The receiver receives the signal from the satellite and calculates the code phase, Doppler, etc. based on the received signal for signal tracking. The calculated code phase, Doppler, etc. are used for signal tracking. 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 the satellites and calculates the signal acquisition result to be used for signal tracking. The signal gain result values include a satellite number, a code phase and a 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 stage to operate properly, the Doppler signal must be accurate. The code phase should be accurate to within one chip error.

In the signal acquisition phase, the code period of the GPS L5 signal received from the satellite is 1 ms, which is the same as L1 C / A, but the code frequency is 10.23 MHz. The ship is bigger. Since the code frequency of the GPS L5 signal is high, the positioning accuracy is improved compared to the L1 C / A signal. However, since the code length of the GPS L5 signal is 10 times larger, it takes a longer time to process the signal acquisition result value to be used in the signal tracking step. In addition, since the code phase and Doppler changes with time, the signal tracking result from the signal acquisition result up to the time it takes to acquire the signal acquisition result value from the time of receiving the initial navigation signal, It fails.

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

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

Referring to FIG. 1, a 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 from the time t0 to the time t3, and the signal tracking step 14 shows from the time t3 to the time t6.

First, the receiver receives the navigation data from the satellite in one code cycle. The code 1 cycle is from the time t0 to the time t2. Therefore, the receiver receives the navigation data 11 of one cycle of code from the time t0 to the time t2 in the signal acquisition step 10. At this time, the initial code phase 12a exists at the time t1. Since the receiver receives the code 1 period from the time t0 to the time t2, the position of the initial code phase 12a exists between the time t0 and the time t2. Then, the receiver computes the initial code phase based on the navigation data of one cycle of code received from the time t0 to the time t2 for the time from t2 to t3. By calculating the initial code phase, satellite number, code phase, Doppler, etc. can be obtained. At this time, the time from the time t2 to the time t3 is referred to as a signal acquisition processing time 13, and the signal acquisition processing time 13 takes longer than the time for receiving one code cycle.

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

That is, when the signal acquisition step 10 receives the navigation data and performs the signal acquisition step 10, the initial code phase 12b can be obtained when the signal acquisition processing time 13 elapses. At this time, it is assumed that the navigation data is re-received when the signal acquisition processing time 13 elapses, and the code phase calculated based on the navigation data is the initial code phase 12b located at the time t4. However, when the code 1 cycle navigation data 14 from the time t3 to the time t6 when the signal acquisition processing time 13 has elapsed is received and the code phase is retrieved, the position of the actual code phase is not at the time t4, . At this time, for the successful signal tracing process, the time point of t4, which is the position of the initial code phase 12b, and the time point of t5, which is the changed code phase position, must be equal or within one chip. However, since the signal acquisition processing time 13 takes longer than the time for receiving the code 1 cycle navigation data, an error of one chip or more occurs.

If an error of more than one chip occurs, the signal can not be tracked or the signal may be lost. In general, the code phase and Doppler change naturally with time. Therefore, it is necessary to newly compensate the code phase so that an error within one chip occurs in the code phase.

In order to solve such a problem, in the prior art, a method of minimizing the signal acquisition processing time is used so that an error of one chip or more does not occur in the code phase. However, in order to reduce the signal acquisition time, it is necessary to implement hardware based on a matched filer method or a multi-correlator method having a number of taps as long as the code length, so that the hardware implementation becomes complicated and the cost increases.

In addition, the Doppler does not change significantly depending on the signal acquisition processing time. However, if the Doppler is not calculated correctly, there may be a lot of attenuation of the signal power and the signal tracking may fail. Therefore, in order to obtain accurate Doppler, the code search is performed by increasing the frequency search resolution. In other words, using a high frequency search resolution to improve the accuracy of the Doppler can perform code search as precisely as possible. However, because the computation amount increases proportionally with the frequency search resolution, the signal acquisition processing time becomes longer or the implementation complexity increases.

That is, in order to obtain an accurate Doppler, a high frequency search resolution can be used to search a large number of frequencies. Hereinafter, the search cell structure according to the frequency search resolution will be described with reference to FIG. 2 and FIG.

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

 FIGS. 2 and 3 show the case where the receiver receives the GPS L5 signal for one cycle of code from the satellite. The GPS L5 signal received during one code cycle consists of 20460 chips. The x and y axes respectively indicate the Doppler frequency search resolution and code. Doppler Frequency Search Code is searched cell by cell in the range of -7 KHz ~ 7 KHz according to resolution. Since the receiver receives the GPS L5 signal in one cycle of code from the satellite, the code is in the 20450 chip range. In addition, since an error within one chip in the code phase does not cause a failure in signal tracking, the cell is constituted by a half chip.

FIG. 2 is a case of searching for a frequency when the frequency search resolution is 500 Hz. In FIG. 2, the code search starts from 0 KHz without fixing the Doppler, and codes existing in the 20450 chip are searched. First, a code search starts from 0 KHz, and codes existing in the 20450 chip are searched from the beginning to the end (210). Thereafter, the Doppler incremented by the frequency search resolution is again returned to +500 Hz (220) to retrieve the code. Since the frequency search resolution is 500 Hz, the frequency search starts from +500 Hz, and the codes existing in the 20450 chip are searched from the beginning to the end (230). If the above procedure is repeatedly performed in the range of -7 KHz to 7 KHz in units of 500 Hz in the order of + and -, a total of 29 (17) code searches are executed.

3 is a case of searching for a frequency when the wave number search resolution is 250 Hz. In FIG. 3, code search is started from 0 KHz without fixing the Doppler, and code existing in the 20450 chip is searched. First, a code search starts from 0 KHz, and code existing in the 20450 chip is searched from the beginning to the end (310). Thereafter, the Doppler incremented by the frequency search resolution is again returned to +250 Hz (320) to retrieve the frequency. Since the frequency search resolution is 250 Hz, the frequency search starts from +250 Hz, and the code existing in the 20450 chip is searched from the beginning to the end (330). If the above procedure is repeatedly performed in the range of -7 KHz to 7 KHz in units of 250 Hz while searching for + and - alternately, a total of 57 (18) code searches are executed which are twice the number of code searches performed in FIG.

In other words, using a high frequency search resolution to improve the accuracy of the Doppler can perform code search as precisely as possible. However, because the computation amount increases proportionally with the frequency search resolution, there arises a problem that the signal acquisition processing time becomes longer or the implementation complexity increases.

Therefore, the present invention provides an apparatus and method for acquiring a signal that does not require additional hardware in a conventional signal acquisition apparatus.

The present invention also provides an apparatus and method for acquiring signals for rapid signal tracking.

An apparatus for acquiring a satellite signal in a receiver of a satellite navigation system, in accordance with an embodiment of the present invention, detects an identifier of the satellite in a signal received from a satellite, calculates a code phase and a Doppler, And a second calculation unit for correcting the code phase and the Doppler using the values calculated by the first calculation unit and the carrier frequency and the code frequency of the satellite.

A method for acquiring a satellite signal in a receiver of a satellite navigation system according to an embodiment of the present invention includes detecting an identifier of the satellite in a signal received from a satellite, calculating a code phase and a Doppler, And a second calculation process of correcting the code phase and the Doppler using the calculated values and the carrier frequency and the code frequency of the satellite in the first calculation process.

The use of the satellite signal acquisition device of the present invention does not require additional hardware in the existing signal acquisition device, and can acquire signals for rapid signal tracking.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, preferred 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 calculation unit 420, a second calculation unit 430, and a tracking unit 440. Here, the RF unit 410, the first calculation unit 420, and the second calculation unit 430 are used to perform the signal acquisition step. In addition, the tracing unit 440 is used to perform the signal tracing step. The first calculation unit 420 includes a buffer 421 and a signal acquisition result calculation unit 422. The second calculation unit 430 includes a precision code phase re-searching unit 431 and a precision Doppler recalculator 432 .

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

Next, the precise 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 signal acquisition processing time

Here, the carrier frequency and the code frequency depend 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. 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 the time required to calculate the signal acquisition result value based on the initially received navigation data. That is, the signal acquisition processing time starts to search the frequency from 0 KHz without fixing the Doppler as shown in FIG. 2 and FIG. 3, and it is necessary to search the code phase while alternating between + and - within the range of -7 KHz to 7 KHz Lt; / RTI > time.

Doppler refers to the frequency resolution at which the initial code phase is retrieved. That is, the signal acquisition result calculation unit 422 searches for codes existing in the 20450 chip of one cycle of code from the beginning to the end. In this case, the phase of the cell in which the signal power is the largest is the initial code phase, and the frequency resolution at the time when the initial code phase is searched corresponds to Doppler.

The changed code phase calculated using Equation (1) is the code phase changed by the Doppler during the signal acquisition processing time. Therefore, the precision code phase recomputer 431 uses Equation (2) to calculate the recalculated initial code phase from the initial point of time when the navigation data is received to the point at which the signal acquisition processing time has elapsed.

The recalculated initial code phase = the initial code phase calculated in the first calculation unit + the changed code phase

As shown in Equation (2), the precision code phase recomputer 431 compares the initial code phase calculated based on the navigation data at the initial time point with the changed code phase during the signal acquisition processing time, And calculates a recalculated initial code phase up to the point at which the acquisition processing time has elapsed.

Here, the Doppler used in Equation (1) is a value at a time when a code phase is searched while a code phase is searched for every frequency search resolution without fixing the Doppler, as shown in FIG. 2 and FIG. Also, since Doppler is a computation result based on the initial navigation data, Doppler and code phase include errors.

If more than one chip error in the code phase or Doppler is inaccurate, then the correct code phase should be rediscovered around the re-computed code phase, since it may fail to track or lose the signal.

For this, the RF unit 410 re-receives the navigation data and temporarily stores it in the buffer 421 when the signal acquisition processing time is synchronized with 1 ms in order to redetect the correct code phase around the re-calculated code phase. Thereafter, the signal acquisition result calculator 422 removes the carrier using the Doppler frequency detected at the time of acquiring the initial signal, and re-computes the code phases around the re-calculated code phase in Equation (2). At this time, the process of re-calculating the code phases around the re-calculated code phase requires the signal acquisition result calculation unit 422 to be used as it is, so that no additional hardware is required. In addition, since the code phase is searched for only a few chips around the code phase in the fixed Doppler, the calculation amount does not increase greatly. Therefore, the signal acquisition result value can be newly obtained in a short time.

The signal acquisition result calculation unit 422 searches for a chip in several places around the code phase recalculated in the fixed Doppler. At this time, the signal acquisition result calculator 422 compares the signal power around the re-calculated code phase to determine the code phase in which the largest value is found as the precise code phase.

Thereafter, the precision code phase recalculator 431 calculates the changed precision code phase that does not include the error using Equation (3).

Modified Precision Code Phase = Precision Code Phase - Initial Code Phase

Meanwhile, the changed code phase calculated using Equation (1) is an incorrect value because it includes a code phase error due to the Doppler error by the frequency search resolution. However, since the changed precise code phase calculated using Equation (3) uses the precise code phase obtained by re-executing the signal acquisition around the re-calculated code phase calculated using Equation (2) It is a precise value removed. Therefore, the accurate Doppler recalculator 432 calculates the accurate Doppler using the changed precision code phase from which the code phase error is removed. That is, the accurate Doppler recalculator 432 calculates the accurate 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 a value calculated using Equation (3). In addition, the carrier frequency and the code frequency are different according to the input signal as described above. The signal acquisition processing time is the time required to calculate the signal acquisition result value based on the initially received navigation data.

The precise Doppler calculated by the precise Doppler recalculator 432 and the precise code phase searched by the precise code phase re-searching unit 431 may be used for tracking the signal, (440).

Since there is no error in the changed precision code phase calculated through the above process and the Doppler is accurate, the signal tracking step can be executed accurately and quickly. Hereinafter, the procedure of the signal acquisition process will be described with reference to FIG.

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

Referring to FIG. 5, in step 510, the RF unit 410 receives the navigation data of one cycle of code from the satellite and temporarily stores the navigation data in the 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 result of the signal acquisition includes a satellite number, a code phase, a Doppler, and the like. The time from when the RF unit 410 receives the navigation data from the satellite to when the signal acquisition result calculation unit calculates the signal acquisition result value is called signal acquisition processing time. At this time, the signal acquisition processing time should be corrected to the time synchronized with 1 ms. For example, it is assumed that a GPS L5 signal with a code period of 1 ms is received from a satellite, and the signal acquisition processing time is 495.3 ms. In step 530, the signal acquisition result calculation unit 422 corrects the signal acquisition processing time to 496 ms, which is the synchronization time of 1 ms.

Next, the precise code phase re-search unit 431 calculates the code phase changed during the signal acquisition processing time using 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 precise code phase re-search unit 431 determines in step 550 that the signal acquisition processing time has elapsed from the initial point by using Equation (2) Lt; / RTI > Here, since the Doppler used in calculating the changed code phase is a calculated value based on the initial-time navigation data, the Doppler and the changed code phase include an error.

If more than one chip error in the code phase or Doppler is inaccurate, then the correct code phase should be rediscovered around the re-computed code phase, since it may fail to track or lose the signal.

To do this, the RF unit 410 re-receives the navigation data and temporarily stores it in the buffer 421 when the signal acquisition processing time is synchronized with 1 ms in order to re-search the correct code phase around the re-calculated code phase in step 560. Thereafter, the signal acquisition result calculator 422 removes the carrier using the Doppler frequency detected at the acquisition of the initial signal in step 570, and re-computes the code phases around the re-calculated code phase. The signal acquisition result calculator 422 compares the signal power around the recalculated code phase in step 580 and determines the largest value as the precise code phase of the retrieved code phase. Thereafter, the precision code phase recomputer 431 calculates the corrected code phase that does not include an error using Equation (3).

On the other hand, the changed code phase calculated using Equation (1) is an incorrect value because it includes a code phase error due to the Doppler error by the frequency search resolution. However, since the modified precision code phase calculated using Equation (3) uses the precise code phase obtained by re-executing the signal acquisition around the re-calculated code phase calculated using Equation (2) It is precise value with error removed. Therefore, the accurate Doppler recalculator 432 calculates the accurate Doppler using the changed precision code phase from which the code phase error is removed. That is, the fine Doppler recalculator 432 calculates the fine Doppler using Equation (4) in step 590.

1 is a diagram 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 a frequency search resolution is 500 Hz,

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

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

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

Claims (10)

An apparatus for acquiring a satellite signal at a receiver of a satellite navigation system, A first calculator for detecting an identifier of the satellite in 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 for correcting 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 apparatus according to claim 1, 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 spent in the calculation. 3. The apparatus according to claim 1 or 2, Calculating a change amount of the code phase using the Doppler calculated by the first calculation unit and the measurement time required for the calculation and the carrier frequency and the code frequency of the satellite, A code phase re-search unit, And a Doppler recalculation unit for recalculating the Doppler using the code phase re-searched by the code phase re-search unit, the Doppler calculated by the first calculation unit, the measurement time required for the calculation, and the carrier frequency and the code frequency of the satellite Wherein the signal acquisition device comprises: The apparatus according to claim 3, wherein the code phase re- The modified code phase is calculated using Equation (5) below, the initial code phase is recalculated using Equation (6), and the re-calculated code phase is retrieved from the value obtained by fixing the Doppler, And calculates a corrected precision code phase using Equation (7): " (7) " &Quot; (5) " Modified Code Phase = Doppler / Carrier Frequency

Code frequency

Signal acquisition processing time &Quot; (6) &quot; The recalculated initial code phase = the initial code phase calculated in the first calculation unit + the changed code phase &Quot; (7) &quot; Corrected Precision Code Phase = Precision Code Phase - Initial Code Phase. 5. The Doppler flowmeter according to claim 4, And a Doppler recalculator for recalculating the Doppler using Equation (8): < EMI ID = 8.0 > &Quot; (8) &quot; Recalculated Doppler = (corrected precision code phase

Carrier frequency) / (code frequency

Signal acquisition processing time). A method for acquiring a satellite signal at a receiver of a satellite navigation system, A first calculation step of detecting an identifier of the satellite in a signal received from a satellite, calculating a code phase and a Doppler, and measuring a time required 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. 7. The method of claim 6, A buffering step of temporarily storing a signal received from the satellite, A signal acquisition result calculation step of detecting an identifier of the satellite in the buffered signal, calculating a code phase and a Doppler, and measuring a time spent in the calculation. 8. The method according to claim 6 or 7, Calculating a change amount of the code phase using the Doppler calculated in the first calculation process and the measurement time spent in the calculation and the carrier frequency and the code frequency of the satellite, A code phase re-searching step, A Doppler recalculation step of recalculating the Doppler using the code phase re-searched in the code phase re-searching step, the Doppler calculated in the first calculation process, the measurement time spent in the calculation, and the carrier frequency and code frequency of the satellite Wherein the signal acquisition method comprises the steps of: 9. The method of claim 8, Calculating a modified code phase using Equation (9) below, Recalculating an initial code phase using Equation (10), searching for a recalculated code phase at a value obtained by fixing a Doppler, and searching for a precise code phase; Calculating a corrected precision code phase using Equation (11): < EMI ID = 11.0 > &Quot; (9) &quot; Modified Code Phase = Doppler / Carrier Frequency

Code frequency

Signal acquisition processing time &Quot; (10) &quot; The recalculated initial code phase = the initial code phase calculated in the first calculation unit + the 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 comprises: And a Doppler recalculation step of recalculating the Doppler using Equation (12): < EMI ID = 12.0 > &Quot; (12) &quot; Recalculated Doppler = (corrected precision code phase

Carrier frequency) / (code frequency

Signal acquisition processing time).

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