A fast demodulation device suitable for wideband signaling burst spread spectrum

Abstract

The application discloses a kind of fast demodulation devices suitable for wideband signaling burst spread spectrum, it is related to transmission technology of anti-jamming and covert communication in satellite communication.The application realizes the fast demodulation synchronization of burst spread spectrum signal by a variety of technologies such as analog intermediate frequency gain control technology, high dynamic pseudo code fast acquisition and tracking, hierarchical carrier frequency estimation and carrier recovery, frame positioning and frame fusion processing.The anti-jamming capability and real-time performance of the application are particularly suitable for group road burst spread spectrum communication transmission based on time slot ALOHA of wideband satellite communication system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite communication, in particular to a fast demodulation device suitable for wideband signaling burst spread spectrum, which can be used for spread spectrum communication transmission of wideband satellite communication system. BACKGROUND

[0002] Spread spectrum communication has the advantages of strong anti-interference ability, low interception rate, anti-multipath interference and good secrecy, and is widely used in communication systems. Due to the demand for service performance and user efficiency of the system in combat, the link establishment time of the data transmission terminal is required to be as short as possible, and at this time the transmission of information is mostly in short burst mode. Therefore, how to realize fast acquisition and demodulation of signals in low signal-to-noise ratio and large Doppler frequency shift environment, and reduce the communication link establishment time is the key technology for satellite communication implementation.

[0003] For a spread spectrum system, fast acquisition of the spread spectrum code is the premise of fast acquisition of the signal. Most of the existing burst spread spectrum demodulation adopts the PMF-FFT method to realize two-dimensional acquisition of frequency and code phase. For large frequency offset, parallel multi-path acquisition is required to be on duty at the same time, which consumes a lot of resources. The average acquisition time will be greatly increased by using the serial frequency sweeping mode, and the demodulation processing time will be greatly increased under the condition of low signal-to-noise ratio and large Doppler frequency shift. SUMMARY

[0004] Therefore, the present application provides a fast demodulation device suitable for wideband signaling burst spread spectrum, which can realize fast synchronization of burst spread spectrum signals in a low signal-to-noise ratio and high dynamic environment.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0006] A fast demodulation device suitable for wideband signaling burst spread spectrum, comprising an analog intermediate frequency module, an A / D conversion module, a matched filter module, a frequency sweeping and pseudo code acquisition module, a hierarchical frequency estimation and carrier recovery module, a frame positioning and framing module, a timing control module, a code generator, and a code tracking module.

[0007] Further, the analog intermediate frequency module performs down-conversion, filtering and gain control processing on the radio frequency signal received by the antenna, and outputs a baseband signal to the A / D conversion module;

[0008] The A / D conversion module converts the baseband signal into a digital signal through A / D conversion, and outputs a digital baseband signal to the matched filter module; the sampling rate of A / D conversion is not less than 4 times the data rate to be demodulated;

[0009] The matched filter module extracts the digital baseband signal to reduce the sampling rate, and then performs matched filtering to eliminate inter-code crosstalk and filter out out-of-band noise;

[0010] The timing control module performs timing control processing on the timing reference signal output by the access controller, and converts the timing reference signal into a timing indication pulse signal, which is used for demodulation control when the pseudo code is not synchronized;

[0011] The code tracking module generates a code clock according to the local clock, and outputs the code clock to the code generator;

[0012] The code generator generates a spread spectrum code under the drive of the code clock and sends the spread spectrum code to the frequency sweeping and pseudo code acquisition module; when the pseudo code is not synchronized, the code generator generates a period spread spectrum code under the indication of the timing indication pulse signal, and then stops working; after the pseudo code is synchronized, the code generator generates a spread spectrum code under the indication of the pseudo code synchronization indication signal;

[0013] The frequency sweeping and pseudo code acquisition module uses the spread spectrum code generated by the code generator to sweep and quickly acquire the signal output by the matched filter module, completes the frequency offset search, simultaneously realizes two-dimensional coarse synchronization of the local code word and data, outputs the demodulation data to be sent to the hierarchical frequency estimation and carrier recovery module, and outputs the pseudo code synchronization indication signal to the code generator module; when the pseudo code is not synchronized, the frequency sweeping and pseudo code acquisition module works under the control of the timing indication pulse signal;

[0014] The hierarchical frequency estimation and carrier recovery module starts after the pseudo code is synchronized, receives the demodulation data to be sent output by the frequency sweeping and pseudo code acquisition module, and the spread spectrum code output by the code generator; the hierarchical frequency estimation and carrier recovery module uses the spread spectrum code to perform full correlation despreading and carrier recovery on the demodulation data to be sent, and outputs the demodulation data without frequency offset to the frame positioning and framing module, and simultaneously outputs the two-way full correlation despread data in advance and lag to the code tracking module;

[0015] After the pseudo code is synchronized, the code tracking module receives the two-way full correlation despread data output by the hierarchical frequency estimation and carrier recovery module, extracts the data error as the timing error, adjusts the local clock, and realizes the time matching of the local pseudo code and the received data;

[0016] The frame positioning and framing module performs frame positioning processing on the demodulation data after the carrier recovery, locates the decoding data, and then sends the decoding data to the subsequent decoding module after the frame processing.

[0017] Further, the analog intermediate frequency module realizes automatic gain control by using the voltage detection method, compares the input signal voltage with the preset threshold voltage value, amplifies the input signal when the input signal voltage is less than the threshold voltage, and attenuates the input signal when the input signal voltage is greater than the threshold voltage.

[0018] Further, the frequency sweeping and pseudo code acquisition module performs fast pseudo code acquisition in the following manner:

[0019] S301, store the input signal into the memory under the indication of the timing indication pulse signal, and the stored data has a length greater than the product of the sampling rate and the frame length;

[0020] S302, read the stored data by using a high-multiple clock and parallel reading, perform frequency conversion processing with a sweeping frequency f1 and pseudo code capture, if the pseudo code capture is not successful, increase the sweeping frequency by a fixed value, then read the data again and perform frequency conversion processing and pseudo code capture;

[0021] S303, if the pseudo code capture is still not synchronized after all the sweeping frequencies are traversed, switch the reading address of the memory, repeat the process of S302 until the pseudo code capture is synchronized.

[0022] Further, the hierarchical frequency estimation and carrier recovery module comprises a partial correlator, a first frequency estimation module, a first digital down converter, a full correlator, a second frequency estimation module, a second digital down converter, a data storage and carrier recovery module, wherein:

[0023] The partial correlator is configured to perform partial correlation despreading with a length of N / 2 on the spread spectrum code output by the code generator and the matched filtered data after the pseudo code is synchronized, and output partial correlation data;

[0024] The first frequency estimation module performs frequency offset estimation according to the partial correlation data, and outputs a frequency control word to the first digital down converter;

[0025] The first digital down converter performs first frequency offset correction, and sends the first frequency offset corrected data to the full correlator;

[0026] The full correlator performs full correlation despreading with a length of N on the first frequency offset corrected data and the code word, and outputs full correlation data;

[0027] The second frequency estimation module performs frequency estimation according to the full correlation data, and sends the result to the second digital down converter;

[0028] The second digital down converter performs second frequency correction on the full correlation data according to the frequency estimation result of the second frequency estimation module, and sends the second frequency offset corrected data to the data storage and carrier recovery module;

[0029] The data storage and carrier recovery module stores the second frequency offset corrected data, and subsequently performs phase recovery of a carrier loop on the stored second frequency offset corrected data, and outputs demodulated data after carrier recovery.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] 1. The present application is very suitable for carrier frequency capture and pseudo code capture of large frequency offset low speed burst spread spectrum transmission signal, and is very suitable for FPGA implementation.

[0032] 2. The present application can carry out multi-rate demodulation, has the characteristics of variable data rate and intermediate frequency, spread spectrum ratio, and is suitable for group route demodulation based on time slot burst.

[0033] 3. The present application adopts hierarchical frequency estimation method, which can effectively reduce the bandwidth of carrier phase-locked loop, facilitate fast locking, and is suitable for low signal-to-noise ratio demodulation. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a principle block diagram of a fast demodulation device suitable for wideband signaling burst spread spectrum in an embodiment of the present application.

[0035] Figure 2 is a flowchart of frequency sweeping and fast pseudo code capture in an embodiment of the present application.

[0036] Figure 3 is a principle block diagram of hierarchical frequency estimation and carrier recovery module in an embodiment of the present application. DETAILED DESCRIPTION

[0037] As shown in Figure 1 , a fast demodulation device suitable for wideband signaling burst spread spectrum includes analog intermediate frequency module, A / D conversion module, matched filter module, frequency sweeping and pseudo code capture module, hierarchical frequency estimation and carrier recovery module, frame positioning and framing module, timing control module, code generator, code tracking module.

[0038] Among them, the analog intermediate frequency module carries out down-conversion, filtering, gain control processing on the radio frequency signal received by the antenna, and outputs the baseband signal to the A / D conversion module;

[0039] The A / D conversion module carries out A / D conversion on the baseband signal, converts from analog signal to digital signal, and outputs the digital baseband signal to the matched filter module; the sampling rate of A / D conversion is not less than 4 times the data rate to be demodulated;

[0040] The matched filter module carries out decimation on the digital baseband signal to reduce the sampling rate, and then carries out matched filtering to eliminate inter-code crosstalk and filter out out-of-band noise;

[0041] The timing control module carries out timing control processing on the timing reference signal output by the access controller, and becomes a timing indication pulse signal, which is used for demodulation control when the pseudo code is not synchronized;

[0042] The code tracking module generates code clock according to the local clock, and outputs the code clock to the code generator;

[0043] The code generator generates spread spectrum code under the drive of code clock and sends the spread spectrum code to the frequency sweeping and pseudo code capture module; when the pseudo code is not synchronized, the code generator generates a period spread spectrum code under the indication of the timing indication pulse signal and then stops working; when the pseudo code is synchronized, the code generator generates spread spectrum code under the indication of the pseudo code synchronization indication signal;

[0044] The frequency sweeping and pseudo code capture module uses the spread spectrum code generated by the code generator to sweep and quickly capture the signal output by the matching filter module, completes the frequency offset search, simultaneously realizes the two-dimensional coarse synchronization of the local code word and data, outputs the demodulation spread spectrum data to the hierarchical frequency estimation and carrier recovery module, and outputs the pseudo code synchronization indication signal to the code generator module; when the pseudo code synchronization indication signal is at high level, it indicates that the pseudo code is synchronized; when the pseudo code is not synchronized, the frequency sweeping and pseudo code capture module works under the control of the timing indication pulse signal;

[0045] The hierarchical frequency estimation and carrier recovery module starts after the pseudo code is synchronized, receives the demodulation spread spectrum data output by the frequency sweeping and pseudo code capture module and the spread spectrum code output by the code generator; the hierarchical frequency estimation and carrier recovery module uses the spread spectrum code to perform full correlation despreading and carrier recovery on the demodulation spread spectrum data, and outputs the demodulation data without frequency offset to the frame positioning and framing module, and outputs the two-way full correlation despread data in advance and lag to the code tracking module;

[0046] After the pseudo code is synchronized, the code tracking module receives the two-way full correlation despread data output by the hierarchical frequency estimation and carrier recovery module, extracts the data error as the timing error, adjusts the local clock, and realizes the time matching of the local pseudo code and the received data;

[0047] The frame positioning and framing module performs frame positioning processing on the demodulation data after the carrier recovery, locates the decoding data, and then sends the decoding data to the subsequent decoding module after the frame processing.

[0048] Further, the analog intermediate frequency module realizes automatic gain control in the form of voltage detection, compares the input signal voltage with the preset threshold voltage value, amplifies the input signal when the input signal voltage is less than the threshold voltage, and attenuates the input signal when the input signal voltage is greater than the threshold voltage.

[0049] As shown in Figure 2 The frequency sweeping and pseudo code capture module performs fast pseudo code capture in the following way:

[0050] S301, under the indication of the timing indication pulse signal, store the input signal into the memory, and the storage length is greater than the product of the sampling rate and the frame length;

[0051] S302, reading the stored data in a high clock and parallel reading mode, performing frequency conversion processing with a sweeping frequency of f1 and pseudo code capture, if the pseudo code capture is unsuccessful, increasing the sweeping frequency by a fixed value, then re-reading the data and performing frequency conversion processing and pseudo code capture;

[0052] S303, if the pseudo code capture is still not synchronized after all sweeping frequencies are traversed, switching the reading address of the memory, repeating the process of S302 until the pseudo code capture is synchronized.

[0053] As shown in Figure 3 The hierarchical frequency estimation and carrier recovery module includes a partial correlator, a first frequency estimation module, a first digital down converter, a full correlator, a second frequency estimation module, a second digital down converter, a data storage and carrier recovery module, wherein:

[0054] The partial correlator is configured to perform partial correlation despreading with a length of N / 2 on the spread spectrum code output by the code generator and the matched filtered data after the pseudo code is synchronized, and output partial correlation data;

[0055] The first frequency estimation module performs frequency offset estimation according to the partial correlation data, and outputs a frequency control word to the first digital down converter;

[0056] The first digital down converter performs first frequency offset correction, and sends the first frequency offset corrected data to the full correlator;

[0057] The full correlator performs full correlation despreading with a length of N on the first frequency offset corrected data and the code word, and outputs full correlation data;

[0058] The second frequency estimation module performs frequency estimation according to the full correlation data, and sends the result to the second digital down converter;

[0059] The second digital down converter performs second frequency correction on the full correlation data according to the frequency estimation result of the second frequency estimation module, and sends the second frequency offset corrected data to the data storage and carrier recovery module;

[0060] The data storage and carrier recovery module stores the second frequency offset corrected data, and subsequently performs phase recovery of the carrier loop on the stored second frequency offset corrected data, and outputs demodulated data after carrier recovery.

[0061] After the device is turned on, sweeping and fast pseudo code capture are performed first, and then hierarchical frequency correction and carrier recovery are performed. Through the sweeping and fast pseudo code capture process, the synchronization of the received data clock and the local clock is realized, and the coarse frequency offset capture is also realized. The hierarchical frequency correction and carrier recovery module adopts a two-stage frequency estimation and carrier phase-locked loop method to realize the carrier recovery of the demodulated data.

[0062] Specifically, the demodulation steps of the device are as follows:

[0063] (1) The received radio frequency demodulation signal is subjected to down-conversion, filtering, gain control processing after analog intermediate frequency, and outputs a baseband signal;

[0064] The local oscillator frequency of the analog intermediate frequency is determined by the frequency of the received radio frequency signal to be demodulated. The lower sideband converts the radio frequency signal to an approximate baseband signal, and the filter removes the out-of-band signals caused by the conversion.

[0065] The automatic gain control of the received analog intermediate frequency is realized by voltage detection. The input signal voltage is compared with the preset threshold voltage. If it is less than the threshold voltage, the input signal is amplified. If it is greater than the threshold voltage, the input signal is attenuated.

[0066] (2) The base signal is converted into a digital signal by an A / D converter, and a digital baseband signal is output. In order to facilitate the subsequent demodulation processing of the baseband data, the sampling rate is not less than 4 times the data rate to be demodulated;

[0067] (3) The digital baseband signal is subjected to decimation and matched filtering to reduce the sampling rate, eliminate inter-symbol interference, and filter out out-of-band noise;

[0068] The decimation multiple of the input digital baseband signal is determined by its sampling multiple. If it is more than 8 times sampling, it needs to be decimated to 8 times. If it is 8 times sampling or 4 times sampling, the decimation multiple is 1, that is, no decimation is performed.

[0069] (4) The timing reference is processed by the timing control module to become a timing indication signal, which is used for subsequent demodulation control processing;

[0070] (5) The filtered signal enters the frequency sweep and fast pseudo-code capture module to complete frequency offset search and realize two-dimensional coarse synchronization of local code word and data, outputting a pseudo-code synchronization indication signal. The pseudo-code capture module starts working under the timing indication signal and stops working after pseudo-code synchronization. The specific method is as follows:

[0071] (501) First, store the input signal in the memory under the indication of the timing signal. The storage length is greater than the data rate * frame length.

[0072] (502) Use high-multiple clock and parallel reading (reading multiple sample data at a time) to read the stored data for frequency conversion processing with a sweep frequency of f1 and pseudo-code capture. If the pseudo-code capture is unsuccessful, read the data again for frequency conversion processing with a sweep frequency of f1+delta_f and pseudo-code capture until the pseudo-code capture is synchronized.

[0073] (503) If the pseudo-code capture is not synchronized after traversing all the sweep frequencies, the reading address of the memory needs to be switched to repeat the above process until the pseudo-code capture is synchronized.

[0074] (6) After the pseudo code synchronization, the code generator and the hierarchical frequency correction and carrier recovery module are started to realize the carrier recovery and output the frequency offset demodulation data, and meanwhile, the full correlation despread data is output to the pseudo code tracking module to realize the time matching of the local pseudo code and the received data, and the specific method is as follows:

[0075] (601) After the pseudo code synchronization, the code generator outputs the code word to perform the partial correlation despread with the matched filtered data with the length of N / 2 to output the partial correlation data;

[0076] (602) The partial correlation data enters the frequency estimation module to perform the frequency offset estimation, and outputs the frequency control word to the digital down conversion to perform the first stage frequency correction;

[0077] (603) The data after the first stage frequency correction is despread with the code word with the length of N to output the full correlation data;

[0078] (604) The full correlation data enters the frequency estimation module, and the frequency estimation result is sent to the digital down conversion to perform the second frequency correction; the estimation precision is improved, and the bandwidth of the subsequent carrier phase-locked loop is reduced to realize the fast locking.

[0079] (605) The data after the second frequency correction is stored, and the subsequent carrier recovery module performs the phase recovery of the carrier loop on the stored frequency correction data to output the demodulation data after the carrier recovery.

[0080] (7) The frequency offset demodulation data is positioned by the frame positioning and processing module, and is sent to the subsequent decoding module after the frame processing;

[0081] The fast demodulation suitable for the wideband signaling burst spread spectrum is completed.

[0082] In summary, the fast demodulation synchronization of the burst spread spectrum signal is realized through the analog intermediate frequency gain control technology, the high dynamic pseudo code fast acquisition and tracking, the hierarchical carrier frequency estimation and carrier recovery, the frame positioning and frame fusion processing and various technologies. The anti-interference ability and real-time performance of the application are particularly suitable for the group road burst spread spectrum communication transmission based on the time slot ALOHA of the wideband satellite communication system.

Claims

1. A fast demodulation apparatus suitable for wideband signaling burst spread spectrum, characterized in that, The module comprises an analog intermediate frequency module, an A / D conversion module, a matched filter module, a sweep and pseudo code capture module, a hierarchical frequency estimation and carrier recovery module, a frame positioning and framing module, a timing control module, a code generator, and a code tracking module. The analog intermediate frequency module performs down-conversion, filtering, and gain control processing on the radio frequency signal received by the antenna, and outputs a baseband signal to the A / D conversion module. The A / D conversion module converts the baseband signal from an analog signal to a digital signal, and outputs a digital baseband signal to the matched filter module. The matched filter module performs decimation on the digital baseband signal to reduce the sampling rate, and then performs matched filtering to eliminate inter-code interference and filter out out-of-band noise. The timing control module performs timing control processing on the timing reference signal output by the access controller, and converts it into a timing indication pulse signal. The code tracking module generates a code clock based on the local clock, and outputs the code clock to the code generator. The code generator generates a spread spectrum code under the drive of the code clock, and sends the spread spectrum code to the sweep and pseudo code capture module. The sweep and pseudo code capture module performs sweep and fast pseudo code capture on the signal output by the matched filter module using the spread spectrum code generated by the code generator. The hierarchical frequency estimation and carrier recovery module receives the spread spectrum code output by the code generator and the demodulation data to be demodulated output by the sweep and pseudo code capture module, performs full correlation despreading and carrier recovery on the demodulation data to be demodulated using the spread spectrum code, and outputs the demodulation data without frequency offset to the frame positioning and framing module, and outputs the two-way full correlation despread data to the code tracking module. After the pseudo code is synchronized, the code tracking module receives the two-way full correlation despread data output by the hierarchical frequency estimation and carrier recovery module, extracts the data error as the timing error, adjusts the local clock, and realizes the time matching of the local pseudo code and the received data. The frame positioning and framing module performs frame positioning processing on the demodulation data after carrier recovery, locates the decoding data, and then sends the decoding data to the subsequent decoding module after framing processing.

2. A fast demodulator suitable for wideband signaling burst spread spectrum according to claim 1, characterized in that, The analog intermediate frequency module realizes automatic gain control by voltage detection, compares the input signal voltage with the preset threshold voltage value, amplifies the input signal if the input signal voltage is less than the threshold voltage, and attenuates the input signal if the input signal voltage is greater than the threshold voltage.

3. A fast demodulator suitable for wideband signaling burst spread spectrum according to claim 1, characterized in that, The sweep and pseudo code capture module performs fast pseudo code capture in the following manner: S301, store the input signal into the memory under the indication of the timing indication pulse signal, and the storage length is greater than the product of the sampling rate and the frame length; S302, read the stored data by using high-multiple clock and parallel reading, perform frequency conversion processing with the sweeping frequency f1 and pseudo code capture, if the pseudo code capture is unsuccessful, increase the sweeping frequency by a fixed value, then read the data again and perform frequency conversion processing and pseudo code capture; S303, if the pseudo code capture is still not synchronized after all the sweeping frequencies are traversed, switch the reading address of the memory, repeat the process of S302 until the pseudo code capture is synchronized.

4. A fast demodulator suitable for wideband signaling burst spread spectrum according to claim 1, characterized in that, The hierarchical frequency estimation and carrier recovery module comprises a partial correlator, a first frequency estimation module, a first digital down converter, a full correlator, a second frequency estimation module, a second digital down converter, a data storage and carrier recovery module, wherein: The partial correlator is configured to perform partial correlation despreading with a length of N / 2 on the spread spectrum code output by the code generator and the matched filtered data after the pseudo code is synchronized, and output partial correlation data; The first frequency estimation module performs frequency offset estimation according to the partial correlation data, and outputs a frequency control word to the first digital down converter; The first digital down converter performs first frequency offset correction, and sends the first frequency offset corrected data to the full correlator; The full correlator performs full correlation despreading with a length of N on the first frequency offset corrected data and the code word, and outputs full correlation data; The second frequency estimation module performs frequency estimation according to the full correlation data, and sends the result to the second digital down converter; The second digital down converter performs second frequency correction on the full correlation data according to the frequency estimation result of the second frequency estimation module, and sends the second frequency offset corrected data to the data storage and carrier recovery module; The data storage and carrier recovery module stores the second frequency offset corrected data, and performs phase recovery of the carrier loop on the stored second frequency offset corrected data, and outputs demodulated data after carrier recovery.

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