KR20110044099A - Method of controlling loop bandwidth for optimal signal tracking of dgps reference receivers - Google Patents

Abstract

PURPOSE: A method of controlling loop bandwidth for optimal signal tracking of DGPS reference receivers is provided to reduce signal acquirement consumption time. CONSTITUTION: An interrelating unit(10) generates correlation value by multiplying and integrating an early code signal and late code signal generated from a code generating unit(50). A phase discriminator(20) calculates phase error using the correlation value of the interrelating unit. A loop filter(40) eliminates a noise component of the phase error according to a control signal of a band width adjustment part(30). The code generating unit generates the early code signal and late code signal. The band width adjustment part controls the band width of the loop filter.

Description

Method of controlling loop bandwidth for optimal signal tracking of DGPS reference receivers

The present invention relates to a loop bandwidth adjustment method for signal tracking of a receiver for a DGPS reference station.

Satellite radio navigation systems that provide location and visual information anywhere in the world are rapidly expanding their range of applications, including maritime navigation, in that they provide more accurate positioning services than terrestrial navigation systems such as Loran-C. However, standalone positioning using only the satellite propagation system alone does not satisfy the positioning accuracy required in areas with high traffic volume and high risk of collision between ships. A representative method to solve this problem is DGPS (Differential Global Positioning System) positioning method, which is a kind of GNSS augmentation system. DGPS positioning method improves the positioning accuracy by extracting the error component of the satellite signal by using the receiver of the reference station installed in the reinforcement system and transmitting the extracted error component to the neighboring satellite radio navigation users. . In particular, the pseudorange-based DGPS positioning method used in the offshore maritime navigation field has a small amount of correction information, so there is no burden on information transmission, and a user simply uses arithmetic processing using the received pseudo distance error correction information. This has the advantage of increasing the positioning accuracy. In May 1995, Korea completed the construction of the MDGPS (Maritime Differential GPS) reference station network including the East Sea and the South Sea in 2001. Real-time DGPS correction information is transmitted to domestic coast and island area for accuracy.

The accuracy of DGPS positioning is affected by the accuracy of pseudorange error correction information generated by the reference station receiver installed in the satellite radiocommunication reinforcement system.The accuracy of the pseudorange error correction information is based on the measured noise level of the raw information measured by the reference station receiver. get affected. The reason is that the pseudorange error correction information generated by the reference station receiver cannot be removed by DGPS positioning as a non-common error as well as ion layer / tropospheric delay error, satellite clock error, and satellite orbit error, which are common errors with the user's GPS receiver. This is because it contains the original information measurement noise. For this reason, international organizations have specified limits on the measurement noise of raw information provided by reference station receivers for satellite navigation system.The performance of measurement noise on reference station receivers used in the maritime navigation field is RTCM Maritime Services) is defined as shown in Table 1.

Performance Measurement of Raw Noise of Reference Station Receivers Item Performance regulations Remarks Pseudorange measurement accuracy 30 centimeters or less (rms) Reference station receiver clock error time offset exclusion Doppler measurement accuracy 4 centimeters per second or less (rms) Reference station receiver clock error
Frequency Offset Exclusion

Receivers for DGPS reference stations shall have the capability to efficiently reduce the noise of the source information measurement. For this purpose, the reference station receiver generally uses a fixed narrowband signal tracking loop technique to optimize measurement noise sensitive to thermal noise and input signal strength. Here, the fixed narrowband signal tracking loop technique reduces the bandwidth of the signal tracking loop to the minimum possible value based on the lower limit of the input signal strength allowed to reduce the measurement noise of the raw information. have.

However, the fixed narrowband signal tracking loop technique not only increases the time required for signal acquisition in the initial synchronization stage, but also makes it impossible to achieve optimal signal tracking for all input signals.

In other words, if the noise bandwidth of the signal tracking loop is reduced, it requires a narrow pull-in range of the tracking loop, which narrows the size of the search grid in the initial synchronization process to reduce the number of cells to be searched. Causes increasing problems.

Figure 1 shows the relationship between the pseudo-range measurement noise and the signal tracking loop bandwidth according to the input signal strength, and shows that the optimum measurement noise cannot be obtained only by reducing the bandwidth of the signal tracking loop. It also confirms that the loop bandwidths for optimizing measurement noise vary according to the signal strength (signal-to-noise ratio). That is, since the input signal of the DGPS reference station receiver has different signal strengths and has time varying characteristics for each satellite, the conventional fixed narrowband tracking loop technique cannot minimize the original information measurement noise.

The present invention was devised to improve the above problems, and it is possible to reduce the signal acquisition time in the initial synchronization stage and to increase the signal tracking capability of the input signal, and thus the loop bandwidth for signal tracking of the receiver for the DGPS reference station. The purpose is to provide a coordination method.

)을

에 의해 결정하고, 반송파 추적루프의 대역폭(

)을

에 의해 결정하며, 여기서, k1=0.0161³, h1=(0.0817×10^-3)²이고,In order to achieve the above object, a loop bandwidth adjustment method for signal tracking according to the present invention is a loop bandwidth adjustment method of a receiver for a DGPS reference station, and the bandwidth of the pseudo distance tracking loop (

)of

The bandwidth of the carrier tracking loop (

)of

, Where k1 = 0.0161 ³ , h1 = (0.0817 × 10 ^-3 ) ² ,

이며,

Is,

Tc is the chip period of the pseudo-noise code, Rc = 1 / Tc, C / No is the signal-to-noise strength, B _RF is the RF bandwidth of the receiver for the DGPS reference station, T is the pre-detection integral time, D is the fast code signal of the correlator and slow The chip spacing between the code signals, F, is an input signal state coefficient, which is 2 for strength near a threshold value and 1 for no value.

According to the loop bandwidth adjustment method for signal tracking of the DGPS reference station receiver according to the present invention, it is possible to reduce the raw information measurement noise of the reference station receiver and to reduce the signal acquisition time in the initial synchronization stage.

Hereinafter, a loop bandwidth adjustment method for signal tracking of a receiver for a DGPS reference station according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a signal tracking device of the receiver for the DGPS reference station according to the present invention.

Referring to FIG. 2, the signal tracking device includes a correlator 10, a phase discriminator 20, a bandwidth adjuster 30, a loop filter 40, and a code generator 50.

The correlator 10 multiplies and integrates the input signal of the receiver and the fast code signal (early code signal) and the slow code signal (late code signal) generated by the code generator 50 for signal tracking to generate respective correlation values. Let's do it.

The phase discriminator 20 calculates a phase error using the correlation value generated by the correlator 10.

The loop filter 40 removes noise components of the phase error for the indicated bandwidth according to the control signal of the bandwidth adjuster 35.

The code generator 50 generates an early code signal and a late code signal to compensate for the phase error by using the phase error from which the noise generated by the loop filter 40 is removed.

The bandwidth adjusting unit 30 controls the bandwidth of the loop filter 40 by using the output time of the correlator 10 and the output signal of the phase discriminator 20.

The bandwidth adjuster 30 includes an input signal strength estimator 31, a GPS signal dynamic estimator 33, and a bandwidth adjuster 35.

The input signal strength estimator 31 calculates and outputs the signal-to-noise strength C / No from the output signal of the correlator 30.

The GPS signal dynamics estimator 33 calculates the pseudo distance change amount.

The bandwidth adjusting unit 35 adjusts the bandwidth of the loop filter 40 by using the signal-to-noise strength provided by the input signal strength estimator 31 and the pseudo distance change amount data provided by the GPS dynamic estimator.

The bandwidth adjustment process of the bandwidth adjustment unit 30 will be described in detail below.

Expressing the pseudo-range and carrier measurement noise of the reference station receiver raw information by reflecting the line-of-ight dynamic characteristics between the DGPS reference station receiver and the GPS satellites, Equations 1 and 2 below.

Where σ _DLL is the pseudorange measurement noise (chip), Tc is the chip cycle of the pseudonoise code (second), B _n-DLL is the bandwidth of the pseudorange tracking loop, and B _RF is the RF bandwidth (Hz) of the receiver for the DGPS reference station. Where C / No is the signal-to-noise strength (Hz), Ss (f) is the power density of the signal, T is the pre-detection integration time (seconds), and D is the chip spacing between Early and Late chip), σ _FLL is the carrier measurement noise (Hz), B _n-FLL is the bandwidth of the carrier tracking loop, F is the input signal state coefficient, which is 2 for strength near threshold, 1 otherwise.

 From Equations 1 and 2 above, the optimal bandwidth of the signal tracking loop that minimizes measurement noise is calculated as Equations 3 and 4 below.

Where k1 = 0.0161 ³ , h1 = (0.0817 × 10 ⁻³ ) ² , Rc = 1 / Tc,

이다.

to be.

This loop bandwidth adjustment method obtains a signal tracking loop bandwidth satisfying the maximum measured noise value (η _B ) required for a reference station receiver from Equations 1 and 2, and calculates a loop bandwidth that minimizes measured noise at the corresponding input signal strength. You can do this using 3 and 4.

Figure 3 shows the relationship between the pseudorange measurement noise and the optimum bandwidth according to the input signal strength.

Meanwhile, the results of comparing the loop bandwidth adjustment method according to the present invention with the conventional fixed narrowband signal tracking loop method are shown in FIGS. 4 and 5 and Tables 2 and 3.

As can be seen from the comparison results, when the conventional fixed narrowband signal tracking loop scheme is designed for an input signal strength of 30 dB-Hz, the proposed method of the present invention shows how many cells should be searched in terms of initial synchronization than the prior art. Confirm that there are less and how much more the measurement noise is reduced.

Comparison of the Adjustment Method of the Invention and the Initial Synchronous Search Cell Count of the Prior Art Tracking loop bandwidth (Hz) GPS input signal strength 30
dB-Hz 35
dB-Hz 40
dB-Hz 50
dB-Hz Fixed Narrowband Signal Tracking Loop Technique 0.0317 0.0317 0.0317 0.0317 Of the present invention
Loop Bandwidth Adjustment Method Stage 1 0.05 (①) 0.27 (②) 1.05 (③) > 2 (④) Step 2 0.0317 0.0407 0.0502 0.0705 Ratio of initial synchronous search cells (prior to the present invention) 1.6: 1 8.5: 1 33.1: 1 > 63.1: 1

Comparison of measurement noise magnitudes between the adjustment method of the present invention and the prior art Pseudo-range measurement noise (cm) GPS input signal strength 30
dB-Hz 35
dB-Hz 40
dB-Hz 50
dB-Hz Fixed-Narrow Signal Tracking Loop Technique (A) 77.61 42.54 (⑤) 29.60 (⑥) 18.15 (⑦) Loop Bandwidth of the Invention
How to adjust (B) 77.61 38.08 21.93 7.85 Improvement degree of the adjusting method of the present invention
((AB) / A) [%] - 8.1 25.9 56.7

In particular, the loop bandwidth adjustment method of the present invention reduces the measurement noise by up to two times or more in terms of pseudorange measurement noise size as the strength of the GPS input signal increases, and performs the initial synchronization process by up to 63 times or more in terms of initial synchronization. It has the effect of finishing.

1 is a graph illustrating a relationship between a typical pseudorange measurement noise and a signal tracking loop bandwidth.

2 is a block diagram of a signal tracking device of a receiver for a DGPS reference station according to the present invention;

3 is a graph illustrating an application example of a loop bandwidth adjustment method for optimal signal tracking;

4 is a graph showing a result of comparing the loop bandwidth and the measured noise amplitude by the fixed narrowband signal tracking method and the loop bandwidth adjustment method according to the present invention;

5 is an enlarged view of a portion of FIG. 4.

Claims (1)

In the loop bandwidth adjustment method for signal tracking of a receiver for a DGPS reference station, Bandwidth of the pseudorange tracking loop

)of

Determined by Bandwidth of the carrier tracking loop (

)of

Determined by Where k1 = 0.0161 ³ , h1 = (0.0817 × 10 ^-3 ) ² ,

Is,

Tc is the chip period of the pseudo-noise code, Rc = 1 / Tc, C / No is the signal-to-noise strength, B _RF is the RF bandwidth of the receiver for the DGPS reference station, T is the pre-detection integral time, D is the fast code signal of the correlator and slow The chip spacing between the code signals, F is an input signal state coefficient, which is 2 for strength near a threshold value, and 1 for otherwise, 1 for a signal tracking of a receiver for a DGPS reference station.

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