WO2010121453A1

WO2010121453A1 - Apparatus and method for correcting frequency shift

Info

Publication number: WO2010121453A1
Application number: PCT/CN2009/073285
Authority: WO
Inventors: 王曼; 朱昀
Original assignee: 中兴通讯股份有限公司
Priority date: 2009-04-24
Filing date: 2009-08-18
Publication date: 2010-10-28
Also published as: CN101873285A; CN101873285B

Abstract

An apparatus and method for correcting the frequency shift. The apparatus includes an Automatic Frequency Control (AFC) circuit and a frequency shift elimination module. The frequency shift elimination module which is located at the front-end of the AFC circuit is used to correct the frequency of an input signal of the apparatus and eliminate the Doppler frequency shift in the input signal of the apparatus when an UE is confirmed in a high speed motion. The AFC circuit is used to receive the output signal of the frequency shift elimination module, and perform automatic frequency control according to the output signal.

Description

Device and method for correcting frequency offset

TECHNICAL FIELD The present invention relates to frequency control techniques in the field of wireless communications, and in particular to an apparatus and method for correcting frequency offsets. BACKGROUND OF THE INVENTION Automatic Frequency Control (AFC) is a frequency control method that maintains a determined relationship between the frequency of an output signal and a given frequency. An AFC circuit that realizes automatic frequency control, also called an AFC ring, is mainly composed of a frequency comparator 10, a low-pass filter 20, and a controllable frequency device 30, as shown in FIG. Wherein the effect of frequency comparator 10 ^ ¹ is the input signal frequency f _c and a controllable frequency generating device 30 is controlled by the local oscillation frequency f. Comparing, detecting the frequency offset, and outputting the error voltage; the low-pass filter 20 is configured to perform interference and noise filtering on the error voltage outputted by the frequency comparator 10, and retain low-frequency information; the controllable frequency device 30 mostly adopts voltage-controlled oscillation The device is configured to generate a local controlled oscillation frequency f according to the low frequency information. . When the AFC loop is closed, the error voltage output by the frequency comparator 10 causes the locally controlled oscillation frequency f of the controllable frequency device 30. The deviation is reduced to pull the output signal frequency of the AFC circuit to the nominal value.

The working principle of the AFC circuit is: f. Compare with f _c in frequency comparator 10, when f. When =f _c , the frequency comparator 10 has no error voltage output, the control voltage is 0, and the local controlled oscillation frequency f of the controllable frequency device 30. Stay the same; when f. When ≠f _c , the frequency comparator 10 has an error voltage output which is proportional to the frequency error f _c -f. The error voltage overpass filter 20 filters out the dry 4 and especially the noise to obtain a control voltage that controls the local controlled oscillation frequency f output by the controllable frequency device 30. A change occurs, resulting in a frequency error of f _c -f. When the value is reduced to a certain value f, the automatic frequency control process is stopped and the controllable frequency device 30 is stabilized at f. =f _c ± f , the loop enters the locked state, and the locked state f is called the steady-state frequency error. This kind of negative frequency feedback through the frequency, through the repeated cycle adjustment of the AFC circuit, can make the relationship between the frequency of the output signal and the given frequency eventually reach equilibrium, so that the operating frequency of the system remains stable and the deviation is small. However, the traditional AFC circuit is usually for the input signal with constant frequency and phase. If the frequency and phase of the input signal are constantly changing, the frequency and phase of the controllable frequency device must be constantly changed. The frequency and phase of the ground 3 input signal are changed. As described above, the frequency variation range of the input signal in the prior art is very small, and in a high-speed motion scenario, such as when a user equipment (User Equipment, called UE) in a high-speed train communicates with a base station on the ground, The frequency variation range of the input signal is increased due to the presence of Doppler shift. For example: The starting frequency of the input signal is f _c . Due to the influence of the Doppler shift, the frequency is changed in the channel as: f _c '=f _c +Af, where Af represents Doppler shift, frequency f _c 'The frequency of the input signal in the AFC circuit. If the original AFC circuit has reached equilibrium, then the frequency of the input signal suddenly changes greatly, which will cause the frequency of the input signal and the locally controlled oscillation frequency f. The frequency difference suddenly becomes large, and it is difficult for the system to reach an equilibrium state in a short time, thereby affecting the performance of the AFC circuit. On the one hand, it is necessary to increase the range of the frequency difference, so that the system can correct the frequency difference of the larger range of changes, which can be achieved by adjusting the parameters of the components of the AFC circuit; on the other hand, it needs to be able to adjust in real time. Frequency information (Doppler shift) that produces a deviation in the channel. In view of how to find the frequency deviation information (Doppler shift) generated in high-speed motion in the related art and correct the frequency information of the deviation in real time, an effective solution has not been proposed yet. SUMMARY OF THE INVENTION The present invention has been made in view of the problem of how to find frequency deviation information generated in high-speed motion and correct the frequency information of the deviation in real time, and the main object of the present invention is to provide a A device for correcting frequency offset to solve the above problem. In order to achieve the above object, in accordance with an aspect of the present invention, an apparatus for correcting frequency offset is provided. The apparatus for correcting frequency offset according to the present invention includes: a frequency offset canceling module and an automatic frequency control AFC circuit. Wherein, the frequency offset elimination module is located at the front end of the AFC circuit, and is used for correcting the frequency of the input signal of the device when determining that the UE is in high-speed motion, and eliminating the Doppler frequency shift in the input signal of the device; the AFC circuit, The signal outputted by the frequency offset elimination module is received, and automatic frequency control is performed according to the signal. Preferably, the frequency offset elimination module includes: a determining submodule, configured to determine whether the UE is located in a high speed motion, and obtain a judgment result; a correction submodule, configured to correct a frequency of the input signal to cancel a Doppler shift in the input signal when the UE is in a high speed motion according to the judgment result of the judging submodule; and the frequency shift acquisition submodule, It is used to obtain the Doppler shift in the above input signal and provide it to the judgment sub-module. Preferably, the frequency shift acquisition sub-module obtains a Doppler shift by subtracting the initial frequency of the signal sent by the base station from the frequency of the actual received signal obtained by the UE. Preferably, the determining sub-module determines whether the UE is in high-speed motion by comparing the obtained Doppler shift with the set frequency threshold. Preferably, the frequency offset cancellation module further includes: a speed measurement submodule, configured to measure the real-time speed of the UE according to the azimuth difference between the UE and the base station in a fixed time period, and obtain the measurement result by frequency shifting The sub-module is provided to the judging sub-module; correspondingly, the judging sub-module is configured to compare the measurement result with the set speed threshold to determine whether the UE is in high-speed motion. Preferably, the frequency shift acquisition submodule calculates a Doppler shift according to the measured real-time speed of the UE by using a formula f _d =^cos0/c; wherein f _d represents a Doppler shift; f represents a UE operation Frequency; V represents the real-time speed of the UE; Θ represents the angle between the direction of motion of the UE and the line formed by the UE and the base station; c represents the speed of light. In order to achieve the above object, according to an aspect of the present invention, a method of correcting frequency offset is provided. The method for correcting the frequency offset according to the present invention includes: correcting the frequency of the input signal of the device for correcting the frequency offset when determining that the UE is in the high speed motion, eliminating the Doppler frequency shift in the input signal; correcting the frequency according to the frequency The input signal is used for automatic frequency control. Preferably, the method further comprises: measuring a real-time speed of the UE according to an azimuth difference between the UE and the base station in a fixed period of time, and comparing the measured real-time speed of the UE with the set speed threshold If the real-time speed is greater than the speed threshold, it is determined that the UE is in high-speed motion; otherwise, it is determined that the UE is not in high-speed motion. Wherein, the Doppler shift is calculated according to the formula f _d =^cose/c; wherein f _d represents the Doppler shift; f represents the operating frequency of the UE; V represents the real-time speed of the UE Degree; Θ indicates the angle between the direction of motion of the UE and the line formed by the UE and the base station; c indicates the speed of light. Preferably, the method further comprises: subtracting an initial frequency of the signal sent by the base station from a frequency of the actual received signal obtained by the UE to obtain a Doppler frequency shift; and obtaining the obtained Doppler frequency shift and the set frequency The threshold values are compared. If the Doppler shift is greater than the frequency threshold, it is determined that the UE is in high speed motion; otherwise, it is determined that the UE is not in high speed motion. The apparatus and method for correcting frequency offset according to the present invention, the frequency offset canceling module corrects the frequency of the UE input signal when determining that the UE is in high speed motion, eliminates the Doppler frequency shift in the UE input signal, and is used by the AFC circuit. Automatic frequency control is performed based on the frequency-corrected input signal. In this way, the Doppler frequency shift caused by the high-speed motion of the UE can be detected and eliminated in time, so that the frequency of the UE received signal can be ensured as close as possible to the initial frequency of the signal sent by the base station during the high-speed motion of the UE, and the UE is reduced. The amplitude of the received signal frequency is increased, which improves the communication quality. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram showing the structure of an AFC circuit in the related art; FIG. 2 is a flow chart of a method for correcting frequency offset according to an embodiment of the present invention; FIG. 3 is a diagram of a device for correcting frequency offset according to an embodiment of the present invention. FIG. 4 is a first structural block diagram of a frequency offset canceling module according to an embodiment of the present invention; FIG. 5 is a second structural block diagram of a frequency offset canceling module according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to the problem of how to find frequency deviation information generated in high-speed motion and to correct the frequency information of the deviation in real time in the related art, and the frequency offset elimination module determines the UE. When located in high-speed motion, the frequency of the UE input signal is corrected to eliminate the Doppler shift in the UE input signal, and the AFC circuit performs automatic frequency control based on the frequency-corrected input signal. In this way, the Doppler frequency shift caused by the high-speed motion of the UE can be detected and eliminated in time, so that the frequency of the UE received signal can be ensured as close as possible to the initial frequency of the signal sent by the base station during the high-speed motion of the UE, and the UE is reduced. The amplitude of the received signal frequency is increased, which improves the communication quality. In accordance with an embodiment of the present invention, a method of correcting frequency offsets is provided. 2 is a flow chart of a method for correcting frequency offset according to an embodiment of the present invention. As shown in FIG. 2, the method includes the following steps S201 to S202: The implementation process of the embodiment of the present invention will be described in detail below with reference to examples. . Step S201: When determining that the UE is in high speed motion, correct the frequency of the input signal to eliminate Doppler shift in the input signal. The input signal refers to the frequency offset elimination module and the AFC circuit as a whole, corresponding to the overall input signal. Before the input signal enters the AFC circuit, in order to detect and eliminate the Doppler shift generated in the high-speed motion in time, the signal subjected to the AFC processing is not affected by the Doppler shift, and the present invention adds a new one at the front end of the AFC circuit. The frequency offset elimination module corrects the frequency of the input signal when determining that the UE is in high speed motion, eliminates the Doppler frequency shift in the input signal, and then supplies the frequency corrected input signal to the AFC circuit. . Step S202, performing automatic frequency control according to the frequency-corrected input signal. The frequency offset elimination module supplies the frequency corrected input signal to the AFC circuit, and the AFC circuit performs AFC processing on the input signal, that is, performs automatic frequency control. The specific operation of the AFC treatment in the present invention will be described in detail in the following examples. In accordance with an embodiment of the present invention, an apparatus for correcting frequency offset is provided that is applied to a UE. 3 is a structural block diagram of an apparatus for correcting frequency offset according to an embodiment of the present invention. As shown in FIG. 3, the apparatus includes a frequency comparator 10, a low pass filter 20, a controllable frequency device 30, and a frequency offset canceling module. 40. The structure will be described in detail below. The frequency comparator 10, the pass-through filter 20, and the controllable frequency device 30 constitute an AFC circuit in the prior art. In the present invention, the connection relationship between the three functions and the respective functions are compared with those in the prior art. The AFC circuit is similar and will not be described here. The frequency offset cancellation module 40 is located at the front end of the AFC circuit for correcting the frequency of the input signal of the device when determining that the UE is in high speed motion, and eliminating the Doppler shift in the input signal. The AFC circuit composed of the frequency comparator 10, the pass filter 20 and the controllable frequency device 30 is configured to receive the signal output from the frequency offset canceling module 40 and perform AFC processing based on the signal. In the present invention, the specific process of the AFC process is: The frequency comparator 10 compares the frequency f _{c of the} output signal of the frequency offset cancellation module 40 with the locally controlled oscillation frequency f generated by the controllable frequency device 30. Compare, when f. When =f _c , the frequency comparator 10 has no error voltage output, the control voltage generated by the pass filter 20 is 0, and the oscillation frequency of the controllable frequency device 30 remains unchanged; When ≠f _c , the frequency comparator 10 has an error voltage output which is proportional to the frequency error f _c -f. After the error voltage is passed through the filter 20 to filter out interference and noise, a control voltage is obtained, and the control voltage controls the local controlled oscillation frequency f outputted by the controllable frequency device 30. A change occurs, resulting in a frequency error of f _c -f. When the value is reduced to a certain value f, the automatic frequency control process is stopped and the controllable frequency device 30 is stabilized at f. At =f _c ± f, the AFC circuit enters the locked state. 4 is a first structural block diagram of a frequency offset canceling module according to an embodiment of the present invention. As shown in FIG. 4, the frequency offset canceling module 40 of the present invention specifically includes: a determining submodule 41, a frequency correcting submodule 42 and a frequency shift. The sub-module 43 is acquired, and the structure will be described in detail below. The determining sub-module 41 is configured to determine whether the UE is located in high-speed motion, and notify the frequency correction sub-module 42 when determining that the UE is in high-speed motion; and the frequency correction sub-module 42 is configured to: when the UE is in high-speed motion, The frequency of the input signal is corrected to eliminate the Doppler shift in the input signal; the frequency shift acquisition sub-module 43 is configured to acquire the Doppler shift in the input signal, and provide the judgment sub-module 41 to determine the UE. Whether it is located in high speed motion, if it is determined that the UE is in high speed motion, the frequency correction sub-module 42 is entered to perform the Doppler shift cancellation. The specific operation of Doppler shift cancellation is: Subtract the Doppler shift of the frequency of the UE input signal. The frequency after the Doppler shift cancellation is output to the frequency comparator 10. For the operation of the frequency shift acquisition sub-module 43 to obtain the Doppler frequency shift in the input signal, it is pointed out that the signal normally sent by the base station to the UE carries the frequency of the transmitted signal, and the frequency is sent by the base station. The initial frequency of the signal. When the UE is in high-speed motion, due to the influence of the Doppler shift, the frequency of the signal sent by the base station received by the UE may be deviated from the initial frequency, that is, the Doppler frequency shift. Because the UE can not only receive the initial frequency of the signal sent by the base station, but also obtain the frequency of the actual received signal, the frequency shift acquisition sub-module 43 can use the initial frequency of the signal sent by the base station and the actual received signal obtained by the UE through measurement. The frequency is subtracted to obtain a Doppler shift. Correspondingly, the judging sub-module 41 can compare whether the UE is located in the high-speed motion by comparing the Doppler shift obtained by the frequency shift obtaining sub-module 43 with the set frequency threshold, specifically: If Doppler If the frequency shift is greater than the frequency threshold, it is determined that the UE is in high speed motion; otherwise, it is determined that the UE is not in high speed motion. The frequency threshold can be set as needed, for example: If a speed above 120 km/h is defined as a high-speed motion scene, the frequency threshold can be obtained by the following formula: f _d =^cose/c, where f _d represents the Doppler shift, the unit is Hz; f represents The operating frequency of the UE; V represents the real-time speed of the UE; Θ represents the angle between the direction of motion of the UE and the line formed by the UE and the base station; c represents the speed of light; when the direction of motion of the UE is at an angle of 0 with the line formed by the UE and the base station When cos9=l, f _d takes the maximum value, that is, f _dmax =:^/c (V is a fixed value, such as when v=120km/h), then f _{dmax is taken} as the frequency threshold, if the frequency shift The acquisition Doppler 43 acquires a Doppler shift greater than f _dmax , and then determines that the UE is in high speed motion. The frequency offset elimination module 40 shown in FIG. 4 is more suitable for a UE that does not have a Global Positioning System (GPS) function, and is of course also applicable to a GPS-enabled UE. For a UE with GPS function, since the location information of the base station is stored therein, and the information is automatically updated after the UE performs cell handover, the location information of the UE can be updated in real time through the GPS, so the UE is saved at any time. The azimuth information of the UE and the base station, so that the frequency offset cancellation module 40 can perform the real-time measurement of the UE according to the azimuth difference between the UE and the base station in a fixed time period, and more directly according to the real-time speed of the measured UE. It is judged whether the UE is in high speed motion. Of course, for a UE that does not have a GPS function, other methods in the prior art can also be used to measure the real-time speed of the UE. FIG. 5 is a second structural block diagram of a frequency offset canceling module according to an embodiment of the present invention. As shown in FIG. 5, the frequency offset canceling module 40 of the present invention specifically includes: a determining submodule 41, a frequency correcting submodule 42 and a frequency shift. The submodule 43 and the velocity measuring submodule 44 are acquired, and the structure will be described in detail below. The measurement of the UE real-time speed may be implemented by the speed measurement sub-module 44 in the frequency offset cancellation module 40. The judging sub-module 41 compares the real-time speed measured by the speed measuring sub-module 44 with the set speed threshold to determine whether the UE is in high-speed motion, specifically: if the measured real-time speed is greater than the speed threshold, It is determined that the UE is in high speed motion; otherwise, it is determined that the UE is not in high speed motion. The speed threshold can be set as needed. For example, the speed threshold is set to 120km/h according to requirements. When the measured real-time speed is greater than 120km/h, it is determined that the UE is in high-speed motion. According to the UE real-time speed obtained by the speed measurement sub-module 44, the frequency shift acquisition sub-module 43 can calculate the Doppler shift by the formula f _d =^cos9/c. It should be noted that the frequency offset elimination module 40 shown in FIGS. 4 and 5 only describes the case where it is determined that the UE is in high-speed motion, and does not describe the case where it is determined that the UE is not in high-speed motion. When it is determined that the UE is not in high speed motion, the frequency offset canceling module 40 does not perform the related operation of Doppler shift cancellation, and directly supplies the signal input by the device to the AFC circuit to perform normal AFC processing. The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, and modifications made within the principles and principles of the present invention. It should be included in the scope of protection of the present invention.

Claims

Claim

A device for correcting frequency offset, characterized in that the device comprises an automatic frequency control AFC circuit and a frequency offset elimination module, wherein

The frequency offset cancellation module is located at a front end of the AFC circuit, and is configured to correct a frequency of an input signal of the device when determining that the UE is in a high speed motion, and eliminate Doppler frequency in an input signal of the device. Move

The AFC circuit is configured to receive a signal output by the frequency offset cancellation module and perform automatic frequency control according to the signal.

2. The apparatus for correcting frequency offset according to claim 1, wherein the frequency offset canceling module comprises:

a determining sub-module, configured to determine whether the UE is located in a high-speed motion, and obtain a judgment result;

a frequency correction submodule, configured to correct a frequency of the input signal when the UE is in a high speed motion according to a judgment result of the determining submodule, and cancel a Doppler frequency shift in the input signal;

And a frequency shift acquisition submodule, configured to acquire a Doppler shift in the input signal, and provide the judgment submodule.

3. The apparatus for correcting frequency offset according to claim 2, wherein the frequency shift acquisition submodule is configured to compare an initial frequency of a signal sent by a base station with a frequency of an actual received signal obtained by the UE by measurement. In a subtractive manner, the Doppler shift is obtained.

4. The apparatus for correcting frequency offset according to claim 2 or 3, wherein the determining sub-module determines the said by comparing the obtained Doppler shift with a set frequency threshold Whether the UE is in high speed motion.

The device for correcting frequency offset according to claim 2, wherein the frequency offset cancellation module further comprises: a speed measurement submodule, configured to: according to an azimuth difference between the UE and a base station in a fixed time period And measuring the real-time speed of the UE, and providing the measurement result to the determining sub-module through a frequency shift obtaining sub-module; Correspondingly, the determining submodule is configured to compare the measurement result with a set speed threshold to determine whether the UE is in high speed motion.

6. The apparatus for correcting a frequency offset according to claim 5, wherein the frequency shift acquisition sub-module calculates the real-time speed of the UE obtained by the formula f _d =fvcos9/c Doppler shift;

Where f _d represents the Doppler shift; f represents the operating frequency of the UE; V represents the real-time speed of the UE; Θ represents the angle between the direction of motion of the UE and the line formed by the UE and the base station; c represents the speed of light.

7. A method of correcting frequency offset, the method comprising:

Correcting the frequency of the input signal of the device for correcting the frequency offset when determining that the UE is in high speed motion, eliminating the Doppler frequency shift in the input signal;

Automatic frequency control is performed based on the frequency-corrected input signal.

8. The method for correcting frequency offset according to claim 7, wherein the method further comprises: performing real-time speed of the UE according to an azimuth difference between the UE and a base station in a fixed time period. Measuring, and comparing the measured real-time speed of the UE with a set speed threshold, if the real-time speed is greater than the speed threshold, determining that the UE is in high-speed motion; otherwise, determining that The UE is not in high speed motion.

9. The method of correcting frequency offset according to claim 8, wherein the Doppler shift is calculated according to a formula _fd = cos9/c;

Wherein f _d represents a Doppler shift; f represents an operating frequency of the UE; V represents a real-time speed of the UE; Θ represents an angle between a moving direction of the UE and a line formed by the UE and the base station; Speed of light.

The method for correcting frequency offset according to claim 7, wherein the method further comprises: subtracting an initial frequency of the signal sent by the base station from a frequency of the actual received signal obtained by the UE by the measurement. a Pöpple shift; and comparing the obtained Doppler shift to a set frequency threshold, and if the Doppler shift is greater than the frequency threshold, determining that the UE is in high speed motion Otherwise, it is determined that the UE is not in high speed motion.