KR100581080B1 - Apparatus and method for closed-loop frequency synchronization by estimation and compensation of doppler shift in a mobile terminal - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a synchronization device and method using Doppler transition estimation and compensation in a mobile terminal.

2. The technical problem to be solved by the invention

According to the present invention, the mobile station estimates the Doppler transition according to its movement and compensates it in advance to transmit a signal, thereby reducing the initial frequency error range at the central station and thereby improving the complexity and performance gain of the central station system. It is an object of the present invention to provide a synchronization device through Doppler transition estimation and compensation in a mobile terminal, and a method thereof.

3. Summary of Solution to Invention

The present invention provides a synchronization apparatus through Doppler transition estimation and compensation in a mobile terminal, comprising: position estimation means for estimating a position of the mobile terminal itself; Doppler transition estimating means for estimating a Doppler transition value due to the movement of the mobile terminal based on position information periodically input from the position estimating means; Parameter input means for providing a transmission (Tx) reference frequency as a parameter; Combining means for combining a transmission (Tx) reference frequency, the Doppler transition estimate, and a frequency offset received from a central station to generate a TX Frequency signal; And mixing means for mixing the transmission frequency signal and the transmission data.

4. Important uses of the invention

The present invention is used for maintaining synchronization between a mobile terminal and a central station.

Mobile terminal, central station, Doppler transition, closed loop frequency synchronization, frequency error estimation

Description

Apparatus and Method for Closed-Loop Frequency Synchronization by estimation and compensation of Doppler Shift in a mobile terminal             

1 is a configuration diagram of a central station and a mobile terminal for conventional frequency synchronization;

2 is a flowchart illustrating a frequency synchronization method between a conventional central station and a mobile terminal;

3 is a block diagram of an embodiment of a closed loop frequency synchronization device using Doppler transition estimation and compensation in a mobile terminal according to the present invention;

4 is a flowchart illustrating a closed loop frequency synchronization method through Doppler transition estimation and compensation in a mobile terminal according to the present invention;

5 is a timing diagram for frequency synchronization acquisition in a mobile station and a central station according to the present invention;

6 is a configuration diagram of an embodiment of the loop filter of FIG. 3 according to the present invention.

* Explanation of symbols for the main parts of the drawings

301: position estimator 302: Doppler transition estimator

303: parameter input unit 304: loop filter 1

305: loop filter 2 306: synthesis section

307 mixer

The present invention relates to a synchronization device through Doppler transition estimation and compensation in a mobile terminal, and more particularly, to a mobile terminal by estimating the Doppler transition according to its movement and compensating it in advance to transmit a signal. The present invention relates to a synchronization device through Doppler transition estimation and compensation in a mobile terminal, and to a method for reducing an initial frequency error range at a central station and thereby improving the complexity and performance gain of the central station system.

Recently, the wireless communication system has been changed into a broadband communication system with a high data rate, and has been developed to maximize resource efficiency. At this time, the initial frequency error range of the central station and the terminal is an important parameter for the complexity of the central station and the efficiency of resource use.

That is, in a wireless communication system, it is essential to acquire and maintain frequency synchronization between a transmitting unit (for example, a mobile terminal) and a receiving unit (for example, a central station). In general, in order to obtain frequency synchronization between a transmitter and a receiver, the complexity of the receiver's frequency synchronization algorithm and receiver demodulation performance are greatly influenced by the initial frequency error range and the estimated frequency error accuracy. Transmitters and receivers use different oscillators, and Doppler frequency transitions occur as the transmitter or receiver moves. The sum of the frequency errors caused by these two causes becomes the frequency difference value of the transmitter and receiver.

In general, in a fixed satellite communication, frequency synchronization demodulates a signal transmitted by a mobile station at a central station, estimates a frequency error of the signal, and passes it to the terminal. Subsequently, when the mobile station transmits the next signal, the mobile station can compensate for the estimated frequency error, thereby reducing the frequency error between the terminal and the central station. However, in the mobile satellite communication, even if the above process is performed, it is difficult for the central station to compensate for the frequency shift caused by the movement of the mobile terminal.

Hereinafter, the prior art will be described in detail.

1 is a diagram illustrating a configuration of a central station and a mobile terminal for conventional frequency synchronization, and performs a method for maintaining closed loop frequency synchronization.

The frequency error estimator 111 of the central station 110 estimates a difference between the frequency transmitted by the mobile terminal 100 and the frequency of the central station and transmits the difference to the terminal.

Then, the loop filter 102 performs the following function. When the mobile station 100 compensates for the frequency offset estimated by the frequency error estimator 111 of the central station 110, the mobile station 100 compensates the estimated frequency difference as it is. If there is an error, the error may be made more severe. The loop filter 102 serves to smooth this error value.

On the other hand, the parameter input unit 101 is an input unit of a transmission (Tx) reference frequency.

Next, the mixer 104 will be described. The output of the loop filter 102 is an amount of change in frequency to be transmitted by the mobile terminal 110. The mixer 104 performs mixing by using the transmission frequency Tx Frequency, which is the sum of the frequency change amount and the reference frequency input as a parameter 103.

2 is a flowchart illustrating a frequency synchronization method between a conventional center station and a mobile terminal.

The central station 110 demodulates the signal transmitted to the return link (mobile terminal → central station) to estimate the frequency error. By transmitting the estimated frequency error to the mobile terminal 100, the mobile terminal 100 performs frequency error compensation when transmitting the next signal to retransmit.

The prior art is a technique implemented to acquire and maintain frequency synchronization by repeatedly performing the above process.

However, in the prior art, the frequency error is compensated by the frequency error estimate of the central station. That is, there is a problem that the change of the channel is not considered.

The present invention has been proposed to solve the above problems, and the mobile station estimates the Doppler transition according to its movement and compensates it in advance to transmit a signal, thereby reducing the initial frequency error range in the central station and thereby the central station system. It is an object of the present invention to provide a synchronization device through Doppler transition estimation and compensation in a mobile terminal, and a method thereof, which can improve the complexity and the performance gain of the mobile terminal.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. In addition, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a synchronization device through Doppler transition estimation and compensation in a mobile terminal, comprising: position estimation means for estimating a position of the mobile terminal itself; Doppler transition estimating means for estimating a Doppler transition value due to the movement of the mobile terminal based on position information periodically input from the position estimating means; Parameter input means for providing a transmission (Tx) reference frequency as a parameter; Combining means for combining a transmission (Tx) reference frequency, the Doppler transition estimate, and a frequency offset received from a central station to generate a TX Frequency signal; And mixing means for mixing the transmission frequency signal and the transmission data. The apparatus of the present invention further comprises: first loop filtering means for removing an error of the Doppler transition estimation value estimated by the Doppler transition estimation means; And second loop filtering means for canceling an error of the frequency error estimate received from the central station.

Meanwhile, the present invention provides a synchronization method through estimation and compensation of Doppler transition in a mobile terminal, wherein the Doppler transition value is estimated based on the position information of the mobile terminal, and the Doppler transition value is compensated for a transmission signal. Doppler transition compensation and primary transmission step to transmit to; And a transmission signal that compensates for the Doppler transition value estimated based on the frequency error estimate received from the central station and the position information of the mobile terminal, until the frequency error estimate received from the central station is within a predetermined range. The frequency error / Doppler transition to be transmitted includes the step of compensating and transmitting. The method may also include a first loop filtering step of eliminating an error of the Doppler transition estimate; And a second loop filtering step of eliminating an error of the frequency error estimate received from the central station.

The present invention is to improve the system complexity and the performance gain by reducing the initial frequency error in the central station by estimating the Doppler transition due to the movement of the terminal (mobile station) in the satellite mobile communication system and transmitting it in advance.

 The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, 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 gist 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.

3 is a diagram illustrating an embodiment of a closed loop frequency synchronization device using Doppler transition estimation and compensation in a mobile terminal according to the present invention.

The position estimator 301 estimates the position of the mobile terminal itself, and the Doppler shift estimator 302 moves the mobile terminal based on the position information periodically input from the position estimator 302. Estimate the Doppler transition due to

Next, the loop filter 1 304 and the loop filter 2 will be described.

When the mobile terminal compensates for the Doppler shift value estimated by the mobile terminal, the error is made more severe when the estimated value has an error. Therefore, Loop Filter_1 304 serves to reduce this error value.

Meanwhile, when the mobile station compensates for the frequency error estimated by the frequency error estimator 311 of the central station, if the mobile station compensates the estimated frequency difference as it is, an error of the estimated value is obtained. If there is a case that makes the error more severe. Loop Filter_2 serves to reduce this error value.

On the other hand, the outputs of the two loop filters 304 and 305 are variations in frequency to be transmitted by the mobile terminal. The combining unit 306 generates the TX frequency signal by adding the frequency variations and the reference frequency input as a parameter through the parameter input unit 303. Here, the parameter input unit 303 provides a transmission (Tx) reference frequency.

A mixer 307 mixes the TX frequency signal and the transmission data.

The frequency error estimator 311 of the central station estimates a difference between the frequency transmitted by the mobile station and the frequency of the central station and transmits the difference to the mobile station.

3 illustrates a technique implemented to perform frequency error compensation as the method of FIG. 1 after the mobile terminal estimates and corrects a Doppler transition due to the movement of the mobile terminal before transmitting data to the central station. That is, the scheme of FIG. 3 is a technique implemented by the mobile terminal to estimate the Doppler frequency according to its movement and maintain the frequency synchronization by reflecting this value.

4 is a flowchart illustrating a closed loop frequency synchronization method using Doppler transition estimation and compensation in a mobile terminal according to the present invention. Structure implemented to reduce scope

When the mobile station first estimates the Doppler transition and compensates for it, and then transmits the primary to the central station (401), the central station receives the estimated frequency error and transmits the estimated frequency error to the mobile station (402).

Then, the mobile station estimates the Doppler transition again, compensates for it, and transmits the secondary to the central station (403). The central station estimates the frequency error and transmits the estimated frequency error to the mobile station (404).

Then, if necessary, the mobile station estimates the Doppler transition and compensates it and transmits it to the central station (405). The central station estimates the frequency error and transmits the frequency error estimate to the mobile terminal (406). Is repeated until the error estimate of the central station is nearly zero.

As described above, FIGS. 3 and 4 are related to a technique for reducing the frequency error estimation and the compensation range of the central station through the Doppler transition estimation of the mobile terminal.

The maximum Doppler frequency (Fdm) under the following conditions is

Fdm = v / c / λ = 27,778 Hz (v = 1000 km / h, c = 3 × 10 ⁸ m / s, λ = 1/30 GHz)

However, the Doppler transition value Fd does not change by Fdm instantaneously in the steady state of the mobile terminal, but it means that the Doppler transition value changes within Fdm according to the change of the speed of the mobile station. The instantaneous variation of the Doppler transition is very small at steady state. Therefore, the mobile station estimates the current Doppler transition, compensates for the transmission frequency, and transmits a signal, thereby reducing the frequency error due to the Doppler transition.

First, when the Doppler transition does not exist (fixed communication), the frequency synchronization method is briefly described as follows.

The initial frequency difference between the central station and the mobile station is Fo = Ft-Fr.

(1) Foe = Ft-Fr: Estimated frequency error in the central station during 1st transmission of the terminal

(2) F't = Ft-Foe: Frequency value during 2nd transmission of the terminal

(3) F'oe = F't-Fr ≒ 0: Compensates the estimated frequency error for 1st transmission

                    Estimated Frequency Error Measured by Central Station in 2nd Transmission

Through the above process, F'oe converges to zero.

On the other hand, when the Doppler transition exists (mobile communication), the frequency synchronization method will be briefly described as follows.

Initial frequency difference between central station and mobile station: Fo + Fd = Ft-Fr

(1) Foe = (Ft-Fde)-Fr: Frequency at the central station in 1st transmission of mobile terminal

                              Error estimate

      (2) F't = (Ft-Fde)-Foe: Transmission frequency value for 2nd transmission of mobile terminal

(3) F'oe = F't-Fr ≒ 0: Estimated frequency error at 1st transmission, estimated frequency error measured at central station at 2nd transmission

Through the above process, F'oe converges to zero.

Above, Fo is the frequency error due to the oscillator difference between the center station and the terminal, Ft is the oscillator frequency of the mobile terminal, Fr is the oscillator frequency of the central station, Fd is Doppler transition (frequency transition value due to terminal movement), Fde is the mobile terminal position Doppler transition estimated by receiving information from the estimation device, Foe is the frequency error between the center station and the terminal estimated by the central station, F't is the transmission frequency value during 2nd transmission of the mobile terminal, F'oe is the center station for 2nd transmission It represents the frequency error of one central station and the terminal.

5 is a timing diagram for frequency synchronization acquisition in the central station and mobile terminal according to the present invention.

First, suppose that: (1) The terminal and the central station recognize that the transmission and reception frequency is 30 GHz (central station: Fr GHz, mobile terminal: Ft GHz). (2) However, the actual frequency difference Fo of the oscillator of the central station and the terminal is 25 kHz. (3) The Doppler shift Fd due to the movement of the mobile terminal is 20 kHz.

A. The mobile station compensates and transmits the Doppler transition estimate Fde to the terminal oscillator clock Ft toward the central station. The transmission frequency Ftx is Ft-Fde, as shown in FIG.

B. The central station receives the signal transmitted from the terminal. The reception frequency Frx is Fr-Fde + Fd. Since Fr = Ft-Fo, the reception frequency (Frx) is Ft-Fde + Fd-Fo (Ft-21kHz + 20kHz-25kHz). In FIG. 5, an actual frequency offset estimation value should be -26 kHz, but an example of a frequency offset estimation (Foe_B) value -25 kHz is shown.

C. Compensate for the frequency offset estimation (Foe_B) value in B so that the second Ftx becomes Ft-Fde-Foe_B (Ft-21kHz-(-25kHz)). The terminal transmits to the central station using this frequency.

D. The second reception frequency (Frx) of the central station is Ft-Foe_B-Fde + Fd-Fo (Ft + 25kHz -21kHz + 20kHz-25kHz) as shown in FIG. In D, the frequency offset was accurately estimated, and the frequency offset estimation (Foe_D) value was 1 kHz.

E. Compensating for the frequency offset estimation (Foe_D) value in D, the third Ftx is Ft-Fde-Foe_B-Foe_D (Ft-21kHz-(-25kHz)-(-1kHz)). The terminal transmits to the central station using this frequency.

F. The third reception frequency (Frx) of the central station is Ft-Foe_B-Foe_D-Fde + Fd-Fo (Ft + 25kHz + 1kHz-21kHz + 20kHz-25kHz) as shown in the figure. In F, as in D, frequency offset was accurately estimated, and an example of frequency offset estimation (Foe_F) was estimated to be 0 kHz.

Through this process, frequency synchronization is estimated and maintained, and when Ftx is determined by applying Fde and Foe as shown in FIG. 5, a loop filter is shown to smooth the estimation error as shown in FIG. 3. ). For example, the first-order IIR filter as shown in FIG. 6 is designed.

FIG. 6 is a block diagram illustrating an exemplary embodiment of the loop filter of FIG. 3 according to the present invention, and illustrates a first order IIR filter 601.

If the column of estimated values is a (0), a (1), a (2), ...,, a (N), ..., the output Z (N) of the loop filter is Z ( n) = Kv * (a (n) + k * Z (n-1)). The output of this filter is used to adjust Ftx as shown in FIG. 5 to maintain frequency synchronization with the central station.

Meanwhile, the IIR filter 601 may be used for the loop filters 1 and 2 304 and 305.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention as described above, by reducing the frequency error estimation and compensation range of the central station by estimating the Doppler transition of the mobile terminal, there is an effect of reducing the complexity of the central station frequency estimation and compensation unit, and also increases the efficiency of the resource.

That is, the terminal (mobile station) having the Doppler transition estimation (self position estimation) apparatus according to the present invention predicts the Doppler transition according to the movement of the terminal in advance, compensates for the Doppler transition to the transmission frequency, and transmits the initial frequency at the central station. By reducing the error, there is an effect of reducing the complexity of the center station frequency estimation and compensation unit, and also increasing the demodulation performance and resource efficiency of the center station.

In addition, the present invention has an effect that it is possible to efficiently maintain the acquisition and maintenance of frequency synchronization with the central station by estimating the doppler transition of the mobile terminal in the satellite communication system in which the mobile terminal exists.

Claims (6)

A synchronization device using Doppler transition estimation and compensation in a mobile terminal, Position estimation means for estimating the position of the mobile terminal itself; Doppler transition estimating means for estimating a Doppler transition value due to the movement of the mobile terminal based on position information periodically input from the position estimating means; Parameter input means for providing a transmission (Tx) reference frequency as a parameter; Combining means for combining a transmission (Tx) reference frequency, the Doppler transition estimate, and a frequency offset received from a central station to generate a TX Frequency signal; And Mixing means for mixing the TX frequency signal and transmission data A synchronization device through the Doppler transition estimation and compensation comprising a. The method of claim 1, First loop filtering means for removing an error of the Doppler transition estimation value estimated by the Doppler transition estimation means; And Second loop filtering means for canceling an error of the frequency error estimate received from the central station A synchronization device through Doppler transition estimation and compensation further comprising. The method of claim 2, The frequency error estimate value in the second loop filtering means is And a center station estimates a difference between a frequency of a signal transmitted from a mobile terminal and its own frequency and transmits the difference to the mobile terminal. A synchronization method using Doppler transition estimation and compensation in a mobile terminal, A Doppler transition compensation and primary transmission step of estimating a Doppler transition value based on the position information of the mobile terminal, and transmitting the Doppler transition value to a central station by compensating the Doppler transition value for a transmission signal; And Until the frequency error estimation value received from the central station is within a predetermined range, the transmission signal compensated for the Doppler transition value estimated based on the frequency error estimation value received from the central station and the position information of the mobile station to the central station. Transmitting Frequency Error / Doppler Compensation and Transmitting Phase A synchronization method through Doppler transition estimation and compensation comprising a. The method of claim 4, wherein First loop filtering to remove an error of the Doppler transition estimate; And A second loop filtering step of removing an error of the frequency error estimate received from the central station; A synchronization method through Doppler transition estimation and compensation further comprising. The method according to claim 4 or 5, The Doppler transition value estimation process in the Doppler transition compensation and the first transmission step, And a Doppler transition estimation and compensation method comprising estimating a Doppler transition value due to movement of the mobile terminal based on position information periodically input from a position estimation means of a mobile terminal.

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