CN116418639A

CN116418639A - Method, system and storage medium for resisting frequency offset based on wireless data chain

Info

Publication number: CN116418639A
Application number: CN202310312396.2A
Authority: CN
Inventors: 曹占生; 王继胜; 严称灵; 段连喜
Original assignee: Beijing Zhongtian Xingkong Science & Technology Development Co ltd
Current assignee: Beijing Zhongtian Xingkong Science & Technology Development Co ltd
Priority date: 2023-03-28
Filing date: 2023-03-28
Publication date: 2023-07-11

Abstract

The invention discloses a method, a system and a storage medium for resisting frequency offset in a wireless data chain. A method for resisting frequency offset based on wireless data chain is applied to a coherent demodulation process of demodulation equipment, and comprises the following steps: for a modulated signal, carrier frequency offset is corrected through a Costas loop of 4 times phase discrimination to recover the carrier signal, the Doppler frequency offset deviation range can be corrected to be about plus or minus 20Khz through a Coatas loop frequency discrimination of 4 times, channel estimation is given before a frequency offset tracking and carrier recovery module of the system works, and the frequency offset correction generated by Doppler frequency offset of high-speed equipment movement can be adapted through a cross product channel estimation method, so that the method has the characteristic of effective carrier capability of recovering signals, and solves the problem of huge frequency offset generated by high-speed communication between two equipment, so that effective communication is ensured.

Description

Method, system and storage medium for resisting frequency offset based on wireless data chain

Technical Field

The present invention relates to the field of wireless data link communication devices in the field of wireless communication, and in particular, to a method, a system, and a storage medium for resisting frequency offset in a wireless data link.

Background

In wireless data link communications, the operation speed of many devices is faster and faster, the carrier speed has gradually increased from Mach 1 to Mach 10, and such high speed generates a huge frequency offset for communications between two devices, where a frequency offset value is briefly calculated, and assuming that the frequency offset is caused by Doppler shift completely, the frequency offset [1] caused by crystals of the two devices is ignored:

the method comprises the following steps:

when v=10 mach, the carrier frequency f=8ghz, c is the speed of light, Δf=91.67 Khz

Under such large frequency offset, normal communication cannot meet normal communication working requirements, and some additional technical methods are needed to be adopted to realize frequency offset calibration, carrier signals are needed to be recovered for coherent demodulation, demodulation performance is needed to be obtained, carrier signals are recovered, and carrier frequency offset is needed to be corrected for carrier recovery for a large dynamic Doppler frequency shift system.

Disclosure of Invention

The invention provides a method, a system and a storage medium for resisting frequency offset based on a wireless data chain, which are used for solving the problem that high speed is difficult to ensure effective communication because of huge frequency offset generated for communication between two devices.

In a first aspect, an embodiment of the present invention provides a method for resisting frequency offset in a wireless data link, which is applied to a coherent demodulation process of a demodulation device, including: for the modulated signal, the carrier frequency offset is corrected by the Costas loop of the 4 th order phase discrimination to recover the carrier signal.

Preferably, the phase detector of the Costas loop adopts a frequency discrimination mode of

I (t) Q (t) (I (t) -Q (t)) (I (t) +q (t)) frequency calibration is performed using 4Δθ as the bias, wherein I (t) and Q (t) are quadrature down-converted data of the modulated signal of QPSK type.

Preferably, the demodulation device obtains the Doppler frequency offset value of the signal through channel estimation;

the Doppler frequency offset value is sent to a frequency offset tracking and carrier recovery module of the demodulation equipment to be used as a frequency preset quantity;

the correcting carrier frequency offset by the Costas loop of the 4 th-order phase discrimination to recover the carrier signal specifically comprises: and starting a frequency offset tracking and carrier recovery module of the demodulation equipment, and correcting the carrier frequency offset through a Costas loop of the 4 th-order phase demodulation to recover the carrier signal.

Preferably, the demodulation device obtains the doppler frequency offset value of the signal through channel estimation, and specifically includes: before transmitting data information, a transmitting end gives a pilot frequency sequence, wherein the pilot frequency sequence is used for transmitting information which is larger than a preset time threshold value according to a preset data code pattern;

the receiving end detects the pilot sequence, obtaining Doppler frequency offset value of the pilot frequency sequence;

preferably, the pilot sequence is information that is transmitted in 00110011 pattern of greater than 30 us.

Preferably, the obtaining the doppler frequency offset value of the pilot sequence specifically includes:

for the modulated signal, continuous sampling is performed to obtain IQ values of (I1, Q1), (I2, Q2) of two continuous points of α1, α2, and:

tan(α2-α1)＝(tanα2-tanα1)/(1+tanα2*tanα1)

＝(Q2/I2-Q1/I1)/(1+Q2/I2*Q1/I1)

＝(Q2I1-Q1I2)/(I1*I2+Q1*Q2)

when the sampled signals are dense, there is i1×i2+q2×q2 approximately equal to 1, tan (α2—α1) =q2i1—q1i2, and after the amplitude normalization, there are: α2- α1 is approximately equal to tan (α2- α1) =q2i1-Q1I 2;

defining I (t) =sin (pi/4×n+2pi fxΔt+θ0), Q (t) =cos (pi/4×n+2pi fxΔt+θ0), wherein I (t) and Q (t) are data after quadrature down-conversion of the modulation signal of BPSK or QPSK type;

2 pi fxΔt=α2- α1=q2i1-q1i2, from which the cross product calculation frequency formula is derived:

fx= (Q2I 1-Q1I 2) c, where the constant c=1/2pi Δt, Δt is the sampling period;

a frequency formula is calculated from the cross product, and obtaining the Doppler frequency offset value of the pilot frequency sequence.

In a second aspect, the present invention provides a system for resisting frequency offset in a wireless data link, applied to a coherent demodulation process of a demodulation device, including: and the demodulation module is used for correcting the carrier frequency offset through the Costas loop of the 4 th-order phase discrimination for the modulated signal so as to recover the carrier signal.

Preferably, the phase detector of the Costas loop adopts a frequency discrimination mode of I (t) Q (t) (I (t) -Q (t)) (I (t) +q (t)), and performs frequency calibration by using 4Δθ as a deviation, where I (t) and Q (t) are data after quadrature down-conversion of the modulated signal of the=qpsk type.

Preferably, the method further comprises: the channel estimation module is used for obtaining Doppler frequency offset values of the signals through channel estimation;

the frequency presetting module is used for sending the Doppler frequency offset value to a frequency offset tracking and carrier recovery module of the demodulation equipment to be used as a frequency presetting quantity; the method comprises the steps of carrying out a first treatment on the surface of the

The demodulation module is specifically configured to: and starting a frequency offset tracking and carrier recovery module of the demodulation equipment, and correcting the carrier frequency offset through a Costas loop of the 4 th-order phase demodulation to recover the carrier signal.

In a third aspect, the present invention further provides a computer storage medium, where instructions are stored, and when the instructions are executed, the method for resisting frequency offset in a wireless data link is executed.

The invention can correct the Doppler frequency shift deviation range about plus or minus 20Khz by 4 th power Coatas loop frequency discrimination based on the anti-frequency deviation method, the system and the storage medium in the wireless data chain, and can not effectively solve the problem when reaching 90Khz and above frequency shift for large dynamic Doppler frequency shift by only relying on Costas and 4 th power frequency discrimination, and the channel estimation is needed to be given before the frequency deviation tracking and carrier recovery module of the system works, and the invention can adapt to the frequency deviation calibration generated by Doppler frequency shift of high-speed equipment movement by a cross product channel estimation method, thereby having the characteristic of effectively recovering the carrier capability of signals.

Drawings

Fig. 1 is a flowchart of a method for resisting frequency offset in a wireless data link according to a first embodiment of the present invention;

FIG. 2 is a schematic block diagram of a Costas loop in accordance with a first embodiment of the present invention;

FIG. 3 is a waveform diagram of a transmitted pilot signal and a signal subjected to a Doppler shift of 60Khz according to an example embodiment of the present invention;

FIG. 4 is a waveform diagram of a demodulation result after a cross product algorithm and a fourth-order correction are evaluated according to an embodiment of the present invention;

fig. 5 is a block diagram of a system based on anti-frequency offset in a wireless data chain according to an embodiment of the present invention.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.

Example 1

Fig. 1-4 are flowcharts of a method for resisting frequency offset in a wireless data link according to a first embodiment of the present invention, which is applied to a coherent demodulation process of a demodulation device, and includes: and S11, for the modulated signal, correcting carrier frequency offset through a Costas loop of 4 times phase discrimination to recover the carrier signal.

In this embodiment, the phase detector of the Costas loop adopts the frequency discrimination mode:

i (t) Q (t) (I (t) -Q (t)) (I (t) +q (t)) frequency calibration is performed using 4Δθ as the offset, wherein I (t) and Q (t) are data after quadrature down-conversion of a QPSK (Quadrature Phase Shift Keying ) type modulated signal.

As shown in fig. 2, the Costas loop mainly consists of a phase detector, loop filter and VCO (voltage controlled oscillator), low pass filter, etc. The phase discriminator is used for acquiring the phase difference of the IQ signals; loop filtering is used for calculating the extracted phase difference; the VCO generates a corresponding local oscillator signal according to the phase difference, and adjusts the down-conversion signal. Through continuous feedback iteration of the Costas loop, the locking of the whole loop can be finally realized, and carrier recovery of the corresponding signal is completed.

Phase detector principle: the phase discriminator is used to obtain a phase difference function, and the phase discrimination mode and the phase discrimination performance directly determine the locking performance of the Costas loop. The commonly used Costas phase detector comprises a multiplication phase detector, a tangent phase detector, an arc tangent phase detector and the like, and the effects of different phase discrimination modes are different. Taking BPSK (Binary Phase Shift Keying ) and QPSK system as examples, the invention also refers to the adopted modulation mode when selecting the actual phase discrimination method, and adopts different phase discrimination methods for different modulation modes.

It is assumed that the QPSK modulated signal is expressed after down-conversion as:

I(t)＝sin(π/4*n+2πfxΔt+θ0)...②

Q(t)＝cos(π/4*n+2πfxΔt+θ0)

then: i (t) Q (t) -Q (t)) (I (t) +q (t))=1/2 sin (2×pi/4×n+2×2pi fxΔt+2×θ0) cos (2×pi/4×n+2×2pi fxΔt+2×θ0) =1/4 sin (4×pi/4×n+4×2pi fxΔt+4×θ0=1/4 sin.

Wherein: the pi modulation symbol becomes integer multiple of pi after 4 times frequency multiplication, positive and negative symbols are regulated by phase direction, 8 pi fx delta t is phase change caused by frequency offset, when 8 pi fx delta t+4 x theta 0 is 0, demodulator can normally track phase change caused by demodulation frequency offset, simplifying the term, let 8 pi fx delta t+4 x theta 0=4delta theta, delta theta=2pi fx delta t+theta 0, where fx is relative frequency offset between devices, delta t is sampling period, theta 0 is initial phase, and in fourth-order frequency discrimination method, 4 delta theta is used as deviation to perform frequency calibration, thus not affected by signal characteristic data content, and has rapid frequency discrimination tracking capability.

I(t)Q(t)*(I(t)-Q(t))(I(t)+Q(t))＝1/4sin(π*n+4Δθ)...③

As shown in fig. 1, in some embodiments, how quickly to achieve an estimate of doppler shift over a limited signal length range is a key consideration for high dynamic, large range doppler shifts.

For the carrier tracking and correction, the Doppler frequency shift deviation range can be corrected to be about plus or minus 20Khz, and for the large dynamic Doppler frequency shift, when the frequency shift reaches 90Khz and above, the problem can not be effectively solved by relying on Costas and frequency discrimination to the power of 4, and the channel estimation needs to be given before the system works.

Before S11, S12-S13 are also included:

and S12, the demodulation equipment obtains Doppler frequency offset value of the signal through channel estimation.

Wherein S12 comprises S121-S122.

And S121, giving a pilot sequence before the transmitting end transmits data information, wherein the pilot sequence is information which is transmitted according to a preset data code pattern and is larger than a preset time threshold.

In this embodiment, in order to accurately evaluate the frequency offset of the signal, a pilot sequence is given before the transmitting end transmits the data information. The pilot sequence is information that is transmitted greater than 30us according to the 00110011 pattern.

S122, the receiving end detects the pilot frequency sequence to obtain the Doppler frequency offset value of the pilot frequency sequence.

In this embodiment, obtaining the doppler frequency offset value of the pilot sequence specifically includes:

for the modulated signal continuous sampling, IQ values of two points of α1, α2 are obtained as (I1, Q1), (I2, Q2), and there are:

tan(α2-α1)＝(tanα2-tanα1)/(1+tanα2*tana1)

＝(Q2/I2-Q1/I1)/(1+Q2/I2*Q1/I1)

＝(Q2I1-Q1I2)/(I1*I2+Q1*Q2)

defining I (t) =sin (pi/4×n+2pi fxΔt+θ0), Q (t) =cos (pi/4×n+2pi fxΔt+θ0), where I (t) and Q (t) are quadrature down-converted data of a modulation signal of BPSK or QPSK type;

fx＝(Q2I1-Q1I2)*c...④

wherein, the constant c=1/2pi Δt, Δt is the sampling period;

and obtaining the Doppler frequency offset value of the pilot frequency sequence according to the cross product calculation frequency formula.

S13, the Doppler frequency offset value is sent to a frequency offset tracking and carrier recovery module of demodulation equipment to serve as a frequency preset quantity.

S11 specifically comprises: and starting a frequency offset tracking and carrier recovery module of the demodulation equipment, and correcting the carrier frequency offset through a Costas loop of the 4 th-order phase demodulation to recover the carrier signal.

The channel estimation algorithm determines the performance of the wireless communication system to a great extent due to the fact that the channel has a plurality of factors such as frequency offset multipath and the like. The wireless channel has the characteristics of unfixed, strong randomness, complex propagation path and the like. In order to ensure good performance of a receiving end in a wireless communication system, coherent demodulation is generally required, and a channel estimator with better performance is adopted to dynamically track channel state changes. And correcting and recovering the data of the receiving end according to the pre-judged channel characteristics so as to realize data transmission with high reliability and low error rate. Channel estimation is one of key technologies for ensuring performance of a wireless communication system, and is mainly used for obtaining accurate and detailed channel information so as to accurately demodulate a transmitted signal at a receiving end, wherein the performance is an important index for measuring the performance of the wireless communication system. The method for acquiring the channel estimation response information of the pilot frequency position is simpler and simpler, but how to acquire the subcarrier channel response of the data position through the subcarrier channel response of the pilot frequency position is different, and the influence of different methods on the performance is different. In this embodiment, a channel estimation algorithm with good performance is explored from the point of view, and the method has important significance for improving the performance of the whole wireless mobile communication system.

The following examples illustrate the application and technical effects of the anti-frequency offset method: fig. 3-4, wherein fig. 3 shows the transmitted pilot signal and the signal subjected to doppler shift at 60Khz, and fig. 4 shows the result of demodulation after the QPSK signal is subjected to doppler shift at 60Khz (this is an example describing the processing procedure of doppler shift), and cross product evaluation and fourth-order correction at the demodulation end: daI _in and daQ _in are Doppler frequency shifted input signals, cos and sin are VCO output signals for tracking external frequency offset, da_firI and da_firQ are IQ demodulation signals recovered after correction, and as can be seen from the figure, the Doppler frequency shift of the original signal is no longer existed, the cross product evaluation and fourth-order correction are relieved, syn_01 is a demodulated frame synchronization signal, databefoser is a demodulated correction signal, and the generated pulse indicates that the demodulator output is correct.

Example two

As shown in fig. 5, the present invention further provides a system for resisting frequency offset in a wireless data link, which includes: a coherent demodulation process for use in a demodulation apparatus, comprising: the demodulation module 21 is configured to correct the carrier frequency offset for the modulated signal through the Costas loop of the 4 th order phase demodulation to recover the carrier signal.

i (t) Q (t) (I (t) -Q (t)) (I (t) +q (t)) frequency calibration is performed using 4Δθ as the offset, where I (t) and Q (t) are quadrature down-converted data of a QPSK type modulated signal.

In some embodiments, a channel estimation module 22 is further included for obtaining a doppler frequency offset value of the signal through channel estimation.

tan(α2-α1)＝(tanα2-tanα1)/(1+tanα2*tana1)

＝(Q2/I2-Q1/I1)/(1+Q2/I2*Q1/I1)

＝(Q2I1-Q1I2)/(I1*I2+Q1*Q2)

when the sampled signals are dense, there is i1×i2+q2×q2 approximately equal to 1, tan (a 2-a 1) =q2i1-Q1I 2, and after the amplitude normalization, there are: α2- α1 is approximately equal to tan (α2- α1) =q2i1-Q1I 2;

fx= (Q2I 1-Q1I 2) c wherein the constant c=1/2 pi Δt, Δt is the sampling period;

The frequency presetting module 23 sends the Doppler frequency offset value to the frequency offset tracking and carrier recovering module of the demodulation equipment to be used as the frequency presetting quantity.

The demodulation module 21 is specifically configured to: and starting a frequency offset tracking and carrier recovery module of the demodulation equipment, and correcting the carrier frequency offset through a Costas loop of the 4 th-order phase demodulation to recover the carrier signal.

The system of this embodiment may execute any of the methods based on anti-frequency offset in the wireless data chain provided in the foregoing embodiments, so that corresponding technical effects can also be achieved, and the foregoing details have been described in detail, which is not repeated here.

The embodiment of the invention also provides computer equipment, which comprises a processor and a memory; the memory is used for storing computer instructions, and the processor is used for executing the computer instructions stored in the memory to execute any of the remote control methods for sewage treatment processes provided in the foregoing embodiments, so that corresponding technical effects can be achieved, and the foregoing details are not repeated here.

Accordingly, the embodiment of the present invention further provides a computer readable storage medium, in which instructions are stored, and when the instructions are executed, any one of the remote control methods for sewage treatment processes provided in the foregoing embodiments is executed, so that corresponding technical effects can be achieved, and the foregoing details are described in detail and are not repeated herein.

It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

From the above description of the embodiments, it will be clear to those skilled in the art that the above-described embodiment method may be implemented by means of software plus a necessary general hardware platform, but of course may also be implemented by means of hardware, but in many cases the former is a preferred embodiment. Based on such understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art in the form of a software product stored in a storage medium (e.g. ROM/RAM, magnetic disk, optical disk) comprising several instructions for causing a terminal device (which may be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) to perform the method of the embodiments of the present invention.

The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather is intended to cover any equivalents of the structures or equivalent processes disclosed herein or in the alternative, which may be employed directly or indirectly in other related arts.

Claims

1. The method is characterized by being applied to a coherent demodulation process of demodulation equipment and comprising the following steps of: for the modulated signal, the carrier frequency offset is corrected by the Costas loop of the 4 th order phase discrimination to recover the carrier signal.

2. The method of claim 1, wherein the phase detector of the Costas loop performs frequency calibration using 4Δθ as bias with a frequency discrimination of I (t) Q (t) x (I (t) -Q (t)) (I (t) +q (t)), wherein I (t) and Q (t) are quadrature down-converted data of the modulated signal of QPSK type.

3. The method for resisting frequency offset in a wireless data link according to claim 1 or 2,

the demodulation equipment obtains Doppler frequency offset value of the signal through channel estimation;

4. The method for resisting frequency offset in a wireless data link according to claim 3, wherein the demodulation device obtains the doppler frequency offset value of the signal through channel estimation, and specifically comprises: before transmitting data information, a transmitting end gives a pilot frequency sequence, wherein the pilot frequency sequence is used for transmitting information which is larger than a preset time threshold value according to a preset data code pattern;

and the receiving end detects the pilot frequency sequence to obtain the Doppler frequency offset value of the pilot frequency sequence.

5. The method of resisting frequency offset in a wireless data chain as recited in claim 4 wherein the pilot sequence is information transmitted in accordance with 00110011 pattern of greater than 30 us.

6. The method for resisting frequency offset in a wireless data link as recited in claim 4, wherein,

the obtaining the Doppler frequency offset value of the pilot frequency sequence specifically comprises the following steps:

tan(α2-α1)＝(tanα2-tanα1)/(1+tanα2*tanα1)

＝(Q2/I2-Q1/I1)/(1+Q2/I2*Q1/I1)

＝(Q2I1-Q1I2)/(I1*I2+Q1*Q2)

7. A system for resisting frequency offset in a wireless data link, comprising: and the demodulation module is used for correcting the carrier frequency offset through the Costas loop of the 4 th-order phase discrimination for the modulated signal so as to recover the carrier signal.

8. The system of claim 7 wherein the phase detector of the Costas loop performs frequency calibration using 4Δθ as bias with I (t) Q (t) I (t) -Q (t)) (I (t) +q (t)), wherein I (t) and Q (t) are quadrature down-converted data of the QPSK type modulated signal.

9. The wireless data link based anti-frequency offset system of claim 7 or 8, further comprising: the channel estimation module is used for obtaining Doppler frequency offset values of the signals through channel estimation;

10. A computer storage medium having stored therein instructions which, when executed, perform a method of combating frequency offset in a wireless data link according to any of claims 1 to 7.