Non-data-aided low-speed spread spectrum high-dynamic self-adaptive carrier synchronization device

Abstract

The invention discloses a non-data-aided low-speed spread-spectrum high-dynamic self-adaptive carrier synchronization device, and relates to the field of high-maneuverability communication systems of airborne, missile-borne and other special platforms in satellite communication. According to the method, the frequency offset is reduced to a certain range by mainly adopting a mode of combining frequency sweeping and frequency estimation, and then the frequency offset change of the receiver is tracked by utilizing a frequency offset change rate estimation method, so that the problems of difficult carrier tracking synchronization and frequent lock losing caused by large frequency offset change are solved; high-dynamic tracking synchronization under a low signal-to-noise ratio can be realized by using a non-data-assisted frequency offset change rate estimation mode and a real-time compensation, real-time monitoring and estimation method. The method is easy to implement, few in occupied resources, operable and high in transportability. The method is very suitable for FPGA implementation, facilitates low-signal-to-noise-ratio demodulation, and can be used for high-maneuvering satellite communication such as broadband and low orbit.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication, and in particular to a non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device, which can improve the concealment and anti-interference communication capabilities in broadband satellite communication. Background Art

[0002] Low-orbit satellites have extremely high relative motion speeds to ground stationary targets. When the target carrier connected to the other end of the satellite link is a high-speed aircraft or other highly maneuverable platform or other spacecraft, the relative motion speed of the two communicating parties is even higher. This is reflected in the signal level as a large carrier frequency offset in the received signal. On the other hand, since the communication satellite moves in a circle around the center of the earth, the radial velocity between it and the communication target carrier is time-varying, and the resulting carrier Doppler frequency deviation also has a time-varying characteristic, that is, the carrier frequency deviation has a certain high-order rate of change. In particular, when the target carrier is a high-speed, highly maneuverable platform such as an aircraft or a missile, the above-mentioned Doppler effect is more significant.

[0003] The ability of carrier synchronization algorithms to counteract strong Doppler effects is gradually increasing. The design of carrier frequency acquisition algorithms and carrier phase tracking algorithms needs to fully consider the large frequency deviation and high-order frequency change rate factors caused by strong Doppler effects. Most typical high-dynamic carrier synchronization algorithms are implemented based on data-assisted methods, that is, the carrier synchronization of the received signal is based on the estimation of parallel pilots or serial pilots as the key to auxiliary synchronization, while the application of non-data-assisted direct synchronization methods is relatively limited. Summary of the invention

[0004] The purpose of the present invention is to provide a non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device. The present invention can ensure normal communication of a highly mobile platform while experiencing large frequency deviation changes, and solve the problem of difficulty in carrier synchronization tracking when experiencing large frequency deviation changes.

[0005] The technical solution adopted by the present invention is:

[0006] A non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device, comprising:

[0007] The preprocessing module is used to preprocess the baseband signal to be demodulated and then output it to the digital down-conversion module; the preprocessing includes DC removal, filtering and power adjustment;

[0008] The digital down-conversion module is used to perform frequency shifting on the pre-processed signal under the control of the frequency control word, and output the frequency-shifted signal to the code capture module;

[0009] The code capture module is used to perform pseudo code capture on the frequency-shifted signal, achieve coarse synchronization between the frequency-shifted signal and the local spread spectrum code, and output the coarsely synchronized spread spectrum signal and the local spread spectrum code to the code tracking module;

[0010] The code tracking module is used to extract and correct the code phase error of the spread spectrum signal and the local spread spectrum code after the coarse synchronization based on the delay locked loop, and output the corrected local spread spectrum code and spread spectrum signal to the partial despreading module;

[0011] The partial despreading module is used to perform partial despreading of the corrected spread spectrum signal by half a symbol period length using the corrected local spread spectrum code, and output the partial despreading result to the frequency deviation estimation module, the change rate estimation module and the full despreading module;

[0012] The full despreading module is used to perform addition of one symbol period using the partial despreading results, recover the symbol data, and output it to the carrier phase recovery module and the residual frequency offset estimation module;

[0013] The frequency offset estimation module is used to perform carrier frequency offset estimation using the partial despreading result under the instruction of the control module, and output the frequency offset estimation result to the frequency control module;

[0014] The change rate estimation module is used to estimate the frequency deviation change rate using the partial despreading result under the instruction of the control module, and output the frequency deviation change rate estimation result to the frequency control module;

[0015] The frequency control module is used to collect the frequency deviation estimation results and the frequency deviation change rate estimation results, and convert them into the frequency control word corresponding to the digital down-conversion clock, and output them to the digital down-conversion module;

[0016] The residual frequency offset estimation module is used to estimate the residual frequency offset of the symbol data output by the full despreading module, and output the frequency offset estimation result to the control module;

[0017] The control module is used to periodically compare the frequency deviation estimation results, start the frequency deviation estimation module once when the set threshold is exceeded, and stop the frequency deviation change rate estimation of the change rate estimation module when the frequency deviation estimation module is started; and start the change rate estimation module again after the frequency deviation estimation is completed;

[0018] The carrier phase recovery module is used to estimate the phase of the symbol data output by the full despreading module and recover the local carrier to complete the high dynamic carrier synchronization of the low-speed spread spectrum signal.

[0019] Furthermore, the specific process of the frequency offset estimation module using the partial despreading result to estimate the carrier frequency offset is as follows:

[0020] The adjacent partial despread symbols of the same symbol are used to perform differential operation, and the operation results are accumulated for a set length L, and the phase angle angle is calculated for the accumulated results. The estimated value of the carrier frequency offset is angle / 2 / π.

[0021] Furthermore, the specific process of the change rate estimation module using the partial despreading result to estimate the frequency offset change rate is as follows:

[0022] 1) Performing adjacent symbol differences on some of the despreading results;

[0023] 2) Accumulate the difference results;

[0024] 3) Perform autocorrelation operation on the accumulated result with a delay of k, where k ranges from 1 to 10;

[0025] 4) Subtracting the phase angles of adjacent autocorrelation values ​​to obtain a phase difference value;

[0026] 5) The phase difference is windowed and accumulated, and converted to frequency, which is the frequency deviation change rate estimation result.

[0027] Furthermore, the processing of the control module is specifically as follows:

[0028] 1) After power-on initialization, the frequency deviation estimation module is started once after acquisition synchronization;

[0029] 2) After the frequency offset estimation module completes the carrier frequency offset estimation, the change rate estimation module is started;

[0030] 3) When the rate of change estimation module is estimating the frequency offset change rate, the control module detects the frequency offset estimation result output by the remaining frequency offset estimation module. If the frequency offset estimation result exceeds one percent of the symbol rate, the frequency offset estimation module is stopped.

[0031] Compared with the background technology, the present invention has the following advantages:

[0032] 1. The present invention does not require data assistance, the communication signal format is simple, and the spectrum utilization and transmission efficiency are improved.

[0033] 2. The present invention is suitable for carrier tracking of low-speed spread spectrum transmission signals, is very suitable for FPGA implementation, and has the characteristics of fast synchronization and low power consumption.

[0034] 3. The non-data-assisted rate of change estimation algorithm adopted by the present invention is independent of the spreading ratio, is universal for spread spectrum or non-spread spectrum systems, has excellent performance, and is suitable for low signal-to-noise ratio demodulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the principle of non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0037] like Figure 1 As shown, a non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device comprises:

[0038] The preprocessing module is used to preprocess the baseband signal to be demodulated and then output it to the digital down-conversion module; the preprocessing includes DC removal, filtering and power adjustment.

[0039] The digital down-conversion module is used to perform frequency shifting on the pre-processed signal under the control of the frequency control word, and output the frequency-shifted signal to the code capture module.

[0040] The code capture module is used to perform pseudo code capture on the frequency-shifted signal, achieve coarse synchronization between the frequency-shifted signal and the local spread spectrum code, and output the coarsely synchronized spread spectrum signal and the local spread spectrum code to the code tracking module.

[0041] The code tracking module is used to extract and correct the code phase error of the coarsely synchronized spread spectrum signal and the local spread spectrum code based on the delay locked loop, and output the corrected local spread spectrum code and spread spectrum signal to the partial despreading module.

[0042] The partial despreading module is used to perform partial despreading of the corrected spread spectrum signal by half a symbol period length using the corrected local spread spectrum code, and output the partial despreading result to the frequency deviation estimation module, the change rate estimation module and the full despreading module;

[0043] The full despreading module is used to perform addition of one symbol period using the partial despreading results, recover the symbol data, and output it to the carrier phase recovery module and the residual frequency offset estimation module;

[0044] The frequency offset estimation module is used to perform carrier frequency offset estimation using the partial despreading result under the instruction of the control module, and output the frequency offset estimation result to the frequency control module;

[0045] The specific process of using the partial despreading result to estimate the carrier frequency offset is as follows:

[0046] The adjacent parts of the same symbol are used to perform differential operations on the despread symbols, and the operation results are accumulated with a set length L, and the phase angle angle is calculated for the accumulated results. The estimated value of the carrier frequency offset is angle / 2 / π. L is generally set to 1024 to meet the low signal-to-noise ratio demodulation requirements.

[0047] The change rate estimation module is used to estimate the frequency deviation change rate using the partial despreading result under the instruction of the control module, and output the frequency deviation change rate estimation result to the frequency control module;

[0048] The specific process of estimating the frequency deviation change rate using the partial despreading result is as follows:

[0049] 1) Performing adjacent symbol differences on some of the despreading results;

[0050] 2) Accumulate the difference results;

[0051] 3) Perform autocorrelation operation on the accumulated result with a delay of k, where k ranges from 1 to 10;

[0052] 4) Subtracting the phase angles of adjacent autocorrelation values ​​to obtain a phase difference value;

[0053] 5) The phase difference is windowed and accumulated, and converted to frequency, which is the frequency deviation change rate estimation result.

[0054] The frequency control module is used to collect the frequency deviation estimation results and the frequency deviation change rate estimation results, and convert them into a frequency control word corresponding to the digital down-conversion clock, and output it to the digital down-conversion module.

[0055] The residual frequency offset estimation module is used to estimate the residual frequency offset of the symbol data output by the full despreading module, and output the frequency offset estimation result to the control module.

[0056] The control module is used to periodically compare the frequency offset estimation results, start the frequency offset estimation module once when the set threshold is exceeded, and stop the frequency offset change rate estimation of the change rate estimation module when the frequency offset estimation module is started; the change rate estimation module is started again after the frequency offset estimation is completed; the processing process is specifically as follows:

[0057] 1) After power-on initialization, the frequency deviation estimation module is started once after acquisition synchronization;

[0058] 2) After the frequency offset estimation module completes the carrier frequency offset estimation, the change rate estimation module is started;

[0059] 3) When the rate of change estimation module is estimating the frequency offset change rate, the control module detects the frequency offset estimation result output by the remaining frequency offset estimation module. If the frequency offset estimation result exceeds one percent of the symbol rate, the frequency offset estimation module is stopped.

[0060] The carrier phase recovery module is used to estimate the phase of the symbol data output by the full despreading module and recover the local carrier to complete the high dynamic carrier synchronization of the low-speed spread spectrum signal.

[0061] The present invention mainly adopts a combination of frequency scanning and frequency estimation to reduce the frequency deviation to a certain range, and then uses the frequency deviation change rate estimation method to track the frequency deviation change of the receiver, which solves the problems of carrier tracking synchronization difficulties and frequent loss of lock caused by large frequency deviation changes. The non-data-assisted frequency deviation change rate estimation method and real-time compensation, real-time monitoring and estimation methods can achieve high-dynamic tracking and synchronization under low signal-to-noise ratio. It is simple to implement, occupies few resources, and is highly operational and portable. It is very suitable for FPGA implementation, is conducive to low signal-to-noise ratio demodulation, and can be used for high-mobility satellite communications such as broadband and low-orbit.

[0062] The contents not described in detail in this specification are known contents in the art.

[0063] The above is a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent replacement or change made by a person skilled in the art based on the technical solution and inventive concept of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device, characterized in that: include: The pre-processing module is used to pre-process the baseband signal to be demodulated and then output it to the digital down-conversion module; The pre-processing includes DC removal, filtering and power adjustment; The digital down-conversion module is used to perform frequency shifting on the pre-processed signal under the control of the frequency control word, and output the frequency-shifted signal to the code capture module; The code capture module is used to perform pseudo code capture on the frequency-shifted signal, achieve coarse synchronization between the frequency-shifted signal and the local spread spectrum code, and output the coarsely synchronized spread spectrum signal and the local spread spectrum code to the code tracking module; The code tracking module is used to extract and correct the code phase error of the spread spectrum signal and the local spread spectrum code after the coarse synchronization based on the delay locked loop, and output the corrected local spread spectrum code and spread spectrum signal to the partial despreading module; The partial despreading module is used to perform partial despreading of the corrected spread spectrum signal by half a symbol period length using the corrected local spread spectrum code, and output the partial despreading result to the frequency deviation estimation module, the change rate estimation module and the full despreading module; The full despreading module is used to perform addition of one symbol period using the partial despreading results, recover the symbol data, and output it to the carrier phase recovery module and the residual frequency offset estimation module; The frequency offset estimation module is used to perform carrier frequency offset estimation using the partial despreading result under the instruction of the control module, and output the frequency offset estimation result to the frequency control module; The change rate estimation module is used to estimate the frequency deviation change rate using the partial despreading result under the instruction of the control module, and output the frequency deviation change rate estimation result to the frequency control module; The frequency control module is used to collect the frequency deviation estimation results and the frequency deviation change rate estimation results, and convert them into the frequency control word corresponding to the digital down-conversion clock, and output them to the digital down-conversion module; The residual frequency offset estimation module is used to estimate the residual frequency offset of the symbol data output by the full despreading module, and output the frequency offset estimation result to the control module; The control module is used to periodically compare the frequency deviation estimation results, start the frequency deviation estimation module once when the set threshold is exceeded, and stop the frequency deviation change rate estimation of the change rate estimation module when the frequency deviation estimation module is started; and start the change rate estimation module again after the frequency deviation estimation is completed; The carrier phase recovery module is used to estimate the phase of the symbol data output by the full despreading module and recover the local carrier to complete the high dynamic carrier synchronization of the low-speed spread spectrum signal.

2. A non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device according to claim 1, characterized in that: The specific process of the frequency offset estimation module using the partial despreading result to estimate the carrier frequency offset is as follows: The differential operation is performed using adjacent partial despread symbols of the same symbol, and the operation results are accumulated for a set length L, and the phase angle angle is calculated for the accumulated results. The estimated value of the carrier frequency offset is angle / 2 / π.

3. A non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization device according to claim 1, characterized in that: The specific process of the change rate estimation module using the partial despreading result to estimate the frequency deviation change rate is as follows: 1) Performing adjacent symbol differences on some of the despreading results; 2) Accumulate the difference results; 3) Perform autocorrelation operation on the accumulated result with a delay of k, where k ranges from 1 to 10; 4) Subtracting the phase angles of adjacent autocorrelation values ​​to obtain a phase difference value; 5) The phase difference is windowed and accumulated, and converted to frequency, which is the frequency deviation change rate estimation result.

4. A non-data-assisted low-speed spread spectrum high-dynamic adaptive carrier synchronization method according to claim 1, characterized in that: The processing of the control module is as follows: 1) After power-on initialization, the frequency deviation estimation module is started once after acquisition synchronization; 2) After the frequency offset estimation module completes the carrier frequency offset estimation, the change rate estimation module is started; 3) When the rate of change estimation module is estimating the frequency offset change rate, the control module detects the frequency offset estimation result output by the remaining frequency offset estimation module. If the frequency offset estimation result exceeds one percent of the symbol rate, the frequency offset estimation module is stopped.

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