KR100510533B1 - Method for compensating clock frequency and for navigation using kalman filter algorithm and apparatus for practicing thereof - Google Patents

Abstract

Disclosed are a clock frequency compensation method, a satellite navigation method, and a device implementing the clock oscillator in a GPS receiver using a Kalman filter. The present invention provides a clock generator for generating a clock signal for controlling the operation of a GPS receiver for navigation, comprising a reference clock oscillator for generating a predetermined reference clock signal using a TCXO, and operation of the GPS receiver from a reference clock signal. And a clock compensator for generating a clock signal for synchronizing the clock signal, and a clock compensator for removing clock noise components included in the clock signal. The clock compensator uses a Kalman filter that estimates and suppresses clock noise components. Therefore, according to the present invention, when a low-cost TCXO is used as the reference clock oscillator, the noise component of the bias component and the drift component included in the TCXO output is modeled and removed through the Kalman filter. The operation of the GPS receiver is synchronized by the clock signal with the noise component removed, thus providing a stable navigation solution.

Description

Method for compensating clock frequency and for navigation using kalman filter algorithm and apparatus for practicing algorithm for clock oscillator in GPS receiver using Kalman filter

The present invention relates to a satellite navigation system (GPS), and more particularly, to a clock frequency compensation method and a satellite navigation method of a clock oscillator of a GPS receiver using a Kalman filter, and apparatuses implementing the same.

Global Positioning System (GPS) is a system developed by the United States for defense purposes and uses a number of satellites orbiting around the earth to calculate the position of a user on the earth. GPS can measure the position of a stationary or moving object by receiving information from satellites anywhere in the world, whether on the ground, at sea or in the air, without time constraints.

The space portion of GPS consists of 24 satellites, which orbit over 20,200 km in altitude and are designed to receive radio waves from five to six GPS satellites anywhere in the world. The GPS receiver, the user part of the GPS, consists of a radio frequency (RF) reception section, an intermediate frequency (IF) processing section, and a digital signal processing section. Estimate GPS receivers come in a variety of sizes, and recently, they are small enough to fit into a cell phone. The GPS control center receives signals from each satellite and transmits control signals as needed.

1 is a diagram illustrating a typical GPS receiver. Referring to this, the GPS receiver 100 receives signals from the first to twenty fourth GPS satellites 11, 12,..., 13 through the antenna 102. The signals received from the GPS satellites 11, 12, ..., 13 are ultra-high frequency signals of the 1.5 GHz band. The preamp unit is composed of a low noise amplifier (LNA) that amplifies a signal received through the antenna 102. The ultra-high frequency signal amplified by the preamplifier 104 is converted to an intermediate frequency of 4 MHz band through the down converter 106.

The signal processor 108 estimates the location of the GPS receiver 100 by estimating a message and a pseudo distance from a carrier and a code included in a signal received from the GPS satellites 11, 12,..., 13. Perform the operation to find the speed. The down converter 106 and the signal processor 108 are operated in response to the local timing signals LO. The local timing signals LO are clock synthesizers for synthesizing the clock generated by the reference clock oscillator 112. generated by the clock synthesizer 114 to synchronize the operation of the down converter 106 and the signal processor 108.

Here, the reference clock oscillator 112 may include an Oven Compensated Crystal Oscillator (OCXO), a Temperature Compensated Crystal Oscillator (TCXO), or the like. Expensive OCXO takes advantage of the characteristic that the crystal changes temperature sensitively, and uses an oven to keep the temperature around the crystal constant so that an error does not occur. OCXO is the most accurate of the modified applications, but it is bulky and uses various power sources of 12V, 24V and 30V, so it is mainly used for defense such as repeater, missile or satellite rather than personal mobile communication.

Inexpensive TCXOs are commonly used in commercial GPS receivers. TCXOs employ temperature compensation circuits, thermistors, and voltage controlled oscillators (VCOs) to improve crystal operating performance. The temperature compensation circuit limits the TCXO output frequency change as the operating temperature changes. Thermistors reduce oscillation frequency errors of oscillators that vary with temperature. VCOs are widely used as reference frequency sources because they have high frequency stability against temperature changes from a few MHz to tens of MHz.

However, the GPS receiver 100 using TCXO as the reference clock oscillator 112 includes noise of a bias component and a drift component at the oscillator output. The bias component and the drift component are factors that increase the error of the oscillator oscillation frequency.

Therefore, there is a need for an inexpensive GPS receiver with high precision performance as a GPS receiver using an expensive OCXO by removing bias and drift components in a GPS receiver using a low-cost TCXO.

An object of the present invention is to provide a clock generator for removing noise components included in the TCXO output.

Another object of the present invention is to provide a GPS receiver using a TCXO.

It is another object of the present invention to provide a clock generation method for removing noise components included in a TCXO output.

A still further object of the present invention is to provide a satellite navigation method for solving the navigation solution of a GPS receiver using a TCXO.

In order to achieve the above object, the present invention provides a clock generator for generating a clock signal for controlling the operation of the GPS receiver for navigation solution, comprising: a reference clock oscillator for generating a predetermined reference clock signal; A clock synthesizer for generating a clock signal for synchronizing the operation of the GPS receiver from the reference clock signal; And a clock compensator for removing clock noise components included in the clock signal.

Preferably, the reference clock oscillator is a TCXO (Temperature Compensated Crystal Oscillator), and the clock compensator uses a Kalman filter that estimates and suppresses a clock noise component. Clock noise component Is modeled as ; And Using the state equation of the Kalman filter consisting of Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F , And the observation transition matrix H is represented by [1 0 0 0].

In order to achieve the above object, the present invention provides a GPS receiver for solving the navigation solution, comprising: a reference clock oscillator for generating a predetermined reference clock signal; A clock synthesizer for generating a clock signal from the reference clock to synchronize the operation of the GPS receiver; A clock compensator which removes a clock noise component included in the clock signal; An antenna for receiving an ultra-high frequency GPS satellite signal; A preamplifier for amplifying a GPS satellite signal; A down converter for converting GPS satellite signals into an intermediate frequency band; And a signal processor for estimating a message and a pseudo distance from a carrier and a code included in a satellite signal to obtain a position and a speed of a GPS receiver in response to the clock signal from which the clock noise component is removed.

A clock signal generation method for controlling an operation for obtaining a navigation solution of a GPS receiver in order to achieve the above object, the method comprising: generating a reference clock signal by a clock oscillator; Generating a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; And modeling a clock noise component included in the clock signal and removing the same through a Kalman filter.

Clock noise component Is modeled as ; And Using the state equation of the Kalman filter consisting of Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F , And the observation transition matrix H is represented by [1 0 0 0].

In order to achieve the above still further object, the present invention provides a satellite navigation method for obtaining a navigation solution of the GPS receiver, comprising: receiving a satellite signal of a very high frequency with a GPS receiver; Amplifying the satellite signal; Converting the ultra-high frequency satellite signal into an intermediate band frequency; Generating a reference clock signal by a clock oscillator; Generating a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; Modeling and removing a clock noise component included in the clock signal through a Kalman filter; And calculating a position and a speed of the GPS receiver by estimating a message and a pseudo distance from a carrier and a code included in the satellite signal in response to the clock signal from which the noise component has been removed.

Therefore, according to the present invention, when using a low-cost TCXO as a reference clock oscillator, the noise component of the bias component and the drift component included in the TCXO output is modeled and removed through the Kalman filter. As a result, the GPS receiver operation is synchronized by the clock signal from which the noise component is removed, thereby providing a stable navigation solution.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that describe exemplary embodiments of the present invention and the contents described in the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

2 is a diagram illustrating a GPS receiver 200 according to an embodiment of the present invention. Referring to this, the GPS receiver 200 includes a preamplifier 104, a down converter 106, a reference clock oscillator 112, a clock synthesizer 114, a signal synthesizer 210, and a Kalman filter 220. It includes. The preamplifier 104, the down converter 106, the reference clock oscillator 112, and the clock synthesizer 114 are almost identical to the operation in the conventional GPS receiver 100. The detailed description is omitted to avoid duplication of explanation.

The GPS receiver 200 calculates a distance between the GPS receiver 200 and the satellite by measuring a time of arrival (TOA) of radio waves received from several GPS satellites, and uses a geometric trigonometry to obtain the GPS receiver. Calculate the position of 200. Knowing the distance from one satellite, the current position is somewhere on the surface of the sphere where the radius of the circle is about the satellite and the distance from that satellite. In addition, knowing the distance from one satellite, the current position is somewhere on the circumference where the two spheres overlap each other. The intersection between the circle and the two spheres by one distance from another satellite becomes one.

The distance between the GPS satellites and the GPS receiver 200 is obtained by the difference between the time when the signal is transmitted from the GPS satellites and the time when the signal is received by the GPS receiver. It is obtained by measuring a pseudo range including a certain error, that is, a clock error, at every moment. The pseudo distance PRi is expressed as follows.

Here, PRi is a pseudo distance measurement between the i-th GPS satellite and the GPS receiver 200, Ri is the actual distance between the i-th GPS satellite and the GPS receiver 200, and Δtu is a signal from the GPS receiver 200. △ tsvi is the time when the signal is transmitted from the GPS satellite, c is the speed constant of light (approximately 300,000 km / sec), △ tai is the error in the troposphere, ionosphere, etc. Means Gaussian white noise.

The clock signal Sclk generated from the reference clock oscillator 112 of the GPS receiver 200 of this embodiment includes a noise component. In particular, the clock Sclk generated in the TCXO used as the reference clock oscillator 112 includes a bias component and a drift component. Modeling the bias component and the drift component included in the clock signal Sclk may be defined as follows.

Here, C1 and C2 are linearization parameters, and τ is a parameter estimated using the Least-Square Estimation Technique, which is repeatedly calculated until the change of the solution converges within the threshold.

Since the C1, C2, τ parameter values vary with temperature, Kalman filter 220 is used to estimate these parameter values. The error model of Equation 2 may be represented by the difference equation as follows.

Here, Ts is a sampling time and means a calculation period of the Kalman filter. Then, from equation (1), e (0) = C2 is obtained.

When Equation 3 is input to the Kalman filter 220, an output clock signal obtained by removing the bias component and the drift component of the clock by the operation characteristics of the Kalman filter 220 is obtained.

The prediction algorithm of the Kalman filter 220 is expressed as follows.

Where x (k) is Represents the state equation at the kth discrete time interval represented by It represents the noise state equation represented by. F means the state transition matrix and is represented by the following matrix equation.

H is represented by an observation transition matrix represented by [1 0 0 0].

Using Equations 4 and 5, the Kalman filter 220 estimates the noise component e (k + 1) including the bias component and the drift component of the input clock signal to suppress the noise component.

 After that, the clock signal Sclk from which the noise component e (k + 1) is removed is provided to the signal processor 210, and the code and the carrier in the IF signal converted to an intermediate frequency of 4MH band through the down converter 106 are provided. Used as a synchronization signal for stripping carriers. The band-filtered signal through the down converter 106 is generated with in-phase component I (t) and quadrature component Q (t). The in-phase component (I (t)) and the quarter-phase component (Q (t)) are 90 ° in phase.

The signal processor 210 includes a base band unit 212, a software unit 214, an FFT tachometer 216, and a memory 218. The base band unit 212 is a code generator for generating a code of the same frequency as the code sent from the satellite, that is, a replica code, a correlator for comparing the satellite clock with the GPS receiver 200 clock, and the code. And a Numerically Controlled Oscillator (NCO) that strips the carrier.

The base band unit 212 is operated to separate noise and interference included in the in-phase signal I (t) and the quadrature signal Q (t). Noise and interference are significantly reduced by spread spectrum transmission techniques that are modulated by known pseudo-random code. Digitized samples are modulated with the pseudorandom code for the sine / cosine signal of the IF signal, and the pseudorandom code is a satellite from a noise level that is significantly higher than the signal level. Used to extract the signal.

The code generated by the code generator correlates the replica code generated by the baseband 212 with code tracking by changing the estimated delay time through the NCO to maintain correlation at or near its peak value. Thus, noise and interference are eliminated. As a result, a significantly improved signal-to-noise ratio can be obtained.

The software 214 includes a recognition unit for identifying the ID of the satellite, a data demodulation unit for decoding the satellite navigation message, a tracking unit for obtaining a position from the decoding result, an interface unit, a navigation filter, and a location solution unit. The software unit 214 obtains a navigation solution (location, speed) using all the information related to the location of the satellite stored in the memory 218, the gold code, and the information that can be sensed by the GPS receiver 200. The FFT accelerometer is an additional navigation sensor that is used to increase the performance of the GPS receiver 200. The FFT accelerometer is an "optimal" or a component of a particular navigational state vector, given an initial evaluation value of the state vector and a past history of the measured value. It is used auxiliary to calculate the "best".

Therefore, in this embodiment, a low-cost TCXO is used as the reference clock oscillator to generate a clock signal for operating the GPS receiver 200. Noise components of the bias and drift components included in the TCXO clock are modeled and removed by the Kalman filter 220. Accordingly, the operation of the GPS receiver 200 is synchronized by the clock signal Sclk from which the noise component is removed, thereby stably obtaining a navigation solution.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the present invention described above, in using a low-cost TCXO as a reference clock oscillator, the noise component of the bias component and the drift component included in the TCXO output is modeled and removed through the Kalman filter. As a result, the GPS receiver operation is synchronized by the clock signal from which the noise component is removed, thereby providing a stable navigation solution.

1 is a diagram illustrating a typical GPS receiver.

2 is a diagram illustrating a GPS receiver according to an embodiment of the present invention.

Claims (16)

In the clock generator for generating a clock signal for controlling the operation of the GPS receiver for navigation solution, A reference clock oscillator for generating a predetermined reference clock signal; A clock synthesizer configured to generate a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; And And a clock compensator for removing clock noise components included in the clock signal. The method of claim 1, wherein the reference clock oscillator Clock generation unit characterized in that the TCXO (Temperature Compensated Crystal Oscillator). The method of claim 1, wherein the clock signal compensator And a Kalman filter for estimating and suppressing the clock noise component. The method of claim 3, wherein the clock noise component is Clock generation unit characterized in that the model. The method of claim 3, wherein the prediction algorithm of the Kalman filter ; And The clock noise component is removed using a state equation consisting of Where x (k) is Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F And the observation transition matrix H is represented by [1 0 0 0]. In the GPS receiver for navigation solution, A reference clock oscillator for generating a predetermined reference clock signal; A clock synthesizer configured to generate a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; A clock compensator which removes a clock noise component included in the clock signal; An antenna for receiving an ultra-high frequency GPS satellite signal; A preamplifier configured to amplify the GPS satellite signal; A down converter converting the GPS satellite signal into an intermediate frequency band; And And a signal processor configured to calculate a position and a speed of the GPS receiver by estimating a message and a pseudo distance from a carrier and a code included in the satellite signal in response to the clock signal from which the clock noise component has been removed. GPS receiver. The method of claim 6, wherein the reference clock oscillator GPS receiver, characterized in that the TCXO (Temperature Compensated Crystal Oscillator). The method of claim 6, wherein the clock signal compensation unit And a Kalman filter for estimating and suppressing the clock noise component. The method of claim 8, wherein the clock noise component is GPS receiver, characterized in that modeled as. The method of claim 8, wherein the prediction algorithm of the Kalman filter ; And The clock noise component is removed using a state equation consisting of Where x (k) is Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F And the observation transition matrix H is represented by [1 0 0 0]. A clock signal generation method for controlling an operation for obtaining a navigation solution of a GPS receiver, Generating a reference clock signal by a clock oscillator; Generating a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; And Modeling a clock noise component included in the clock signal and removing the clock noise component by using a Kalman filter. The method of claim 11, wherein the clock noise component is Clock signal generation method, characterized in that the model. 12. The method of claim 11, wherein the prediction algorithm of the Kalman filter is ; And The clock noise component is removed using a state equation consisting of Where x (k) is Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F And the observation transition matrix H is represented by [1 0 0 0]. A satellite navigation method for obtaining a navigation solution of a GPS receiver, Receiving an ultra-high frequency satellite signal with the GPS receiver; Amplifying the satellite signal; Converting the ultra-high frequency satellite signal into an intermediate band frequency; Generating a reference clock signal by a clock oscillator; Generating a clock signal from the reference clock signal to synchronize the operation of the GPS receiver; Modeling and removing a clock noise component included in the clock signal through a Kalman filter; And And calculating a position and a velocity of the GPS receiver by estimating a message and a pseudo distance from a carrier and a code included in the satellite signal in response to the clock signal from which the noise has been removed. Way. 15. The method of claim 14, wherein the clock noise component is Satellite navigation method, characterized in that the model. 15. The method according to claim 14, wherein the prediction algorithm of the Kalman filter is ; And The clock noise component is removed using a state equation consisting of Where x (k) is Where the state equation at the kth discrete time interval, denoted by u (k) The noise state equation, denoted by the state transition matrix F And the observation transition matrix H is represented by [1 0 0 0].