CN116248145A - Adaptive despreading demodulation method with variable spreading ratio under high dynamic environment - Google Patents

Abstract

The invention discloses a variable spreading ratio self-adaptive despreading demodulation method in a high dynamic environment, which comprises 7 links including quadrature down-conversion, matched filtering, large frequency offset direct spread signal capturing, self-adaptive data despreading, carrier tracking, data positioning and decoding. The method does not need to receive a control instruction, recognizes a specific spreading ratio and a specific spreading code through the mode word information carried by the direct-spread signal, and performs self-adaptive despreading demodulation processing on the direct-spread signal data part.

Description

Adaptive despreading demodulation method with variable spreading ratio under high dynamic environment

Technical Field

The invention relates to a variable spread spectrum ratio self-adaptive despreading demodulation method in a high dynamic environment, belonging to the field of satellite-borne modulation and demodulation in satellite communication.

Background

The traditional satellite communication processing load often controls the working mode and the working rate through the measurement and control instruction, and the supported working mode and rate are single, so that the communication requirements of various communication terminal scenes can not be met. There are often a large number of miniaturized communication terminals within the satellite beam coverage, supporting low data communication rates. In order to avoid interference to the adjacent satellites, data is typically spread. The existing spread spectrum communication processing load usually only supports a single information rate and a single spread spectrum ratio, even if the processing load supports a plurality of information rates and a plurality of spread spectrum ratios, a plurality of spread spectrum ratio signal capturers are often configured in the processing load, the working rate and the working spread spectrum ratio of the processing load need to be controlled in advance through preset instructions, the processing resource occupation is more, and the application is not flexible enough. In order to meet the communication requirements of small terminals with different types and different rates, satellite processing load often needs to support despreading and demodulation of spread spectrum signals with multiple communication rates, and the working rate of the processing load preset by instructions cannot meet the increasing communication requirements. In order to make communication more convenient and flexible, the on-board processing load is required to have self-adaptive receiving processing capability in a large dynamic environment, the processing is simple and easy to realize, and the occupation of processing resources is reduced as much as possible so as to adapt to the conditions of limited weight and power consumption of the satellite communication processing load.

In summary, in the prior art, despreading and demodulation processing of signals with different spreading ratios is generally realized by a preset instruction mode, so that the communication requirements of terminals with different types and different rates cannot be met, and a flexible despreading and demodulation processing method adaptable to various spreading ratio signals is needed.

Disclosure of Invention

In view of this, the invention provides a variable spread spectrum ratio self-adaptive de-spread demodulation method in a high dynamic environment, which does not need to receive control instructions, recognizes specific spread spectrum ratio and spread spectrum code through the preamble part of a direct spread signal, and performs self-adaptive de-spread demodulation processing on the data part of the direct spread signal.

The technical scheme adopted by the invention is as follows:

a variable spread spectrum ratio self-adaptive despreading demodulation method under a high dynamic environment comprises the following steps:

step 1, selecting a root raised cosine filter as a matched filter, and carrying out matched filtering treatment on data after quadrature down-conversion;

step 2, carrying out large-frequency offset direct-spread signal capturing processing on the data after matched filtering, dividing the data into 3 data branches, and respectively carrying out direct-spread signal capturing processing; the 1 st data branch firstly carries out positive frequency offset pre-correction processing, then carries out spread spectrum code capturing processing on input data by utilizing a local spread spectrum code, the 2 nd data branch directly carries out spread spectrum code capturing processing, the 3 rd data branch firstly carries out negative frequency offset pre-correction processing, and then carries out spread spectrum code capturing processing; performing capture judgment processing on the captured and output data, and outputting a capture judgment instruction which is aligned with the initial position of the chip of the data;

step 3, according to the initial position of the code chip determined by the capture judgment indication, simultaneously carrying out 4 paths of code loop tracking processing on the data to be despread by utilizing a lead-lag gate method, and respectively carrying out despreading and code loop tracking processing on the data to be despread and the local spreading codes with 4 paths of different spreading ratios, wherein the 1 st path of local spreading codes are identical to the preamble spreading codes, the data 1 and the data enabling signal 1 after despreading are output after the code loop tracking, the data 2 and the data enabling signal 2 after despreading are output after the 2 nd path of the data 2 after despreading are output after the code loop tracking, the data 3 and the data enabling signal 3 after despreading are output after the 4 th path of the data 4 and the data enabling signal 4 after despreading are output after the code loop tracking;

step 4, performing spread spectrum ratio identification processing on the despread data 1, respectively performing correlation operation and matching identification on the despread data 1 and 4 local mode word orthogonal sequences when the data enabling 1 signal is effective, identifying the spread spectrum ratio of the direct spread signal data part according to the mode word, and outputting a spread spectrum ratio indication effective signal and a spread spectrum ratio indication signal;

step 5, under the main processing clock, according to 4 paths of data enabling signals, writing the data after 4 paths of despreading into a dual-port RAM group respectively for data caching, wherein the depth of the RAM is larger than the data length corresponding to the delay of the spread spectrum ratio indicating signal processing, and when the spread spectrum ratio indicating enabling signals are effective, reading the data in the corresponding RAM according to the spread spectrum ratio indicating signals and outputting;

step 6, performing rate conversion processing on the gated despread data, realizing rate conversion by using a dual-port RAM, writing the data into the RAM when the data enabling is effective, starting a RAM data reading operation when the writing address is equal to the information length of the spread spectrum signal, continuously reading the data by using a main processing clock until all despread data are read, and converting the data processing rate from the despread symbol rate to the main processing clock rate;

step 7, carrying out carrier tracking processing on the data after rate conversion, and obtaining data after carrier recovery after residual frequency offset correction and phase tracking correction;

step 8, carrying out data positioning processing on the data after carrier recovery, carrying out correlation operation on the sign bit of the data after carrier recovery and a local positioning word sequence, determining the initial position of effective data according to the correlation peak position and the correlation operation time delay, carrying out phase fuzzy correction on the data according to the phase information of the correlation peak value to obtain data to be decoded, and outputting data enabling and the data to be decoded;

and 9, decoding the data, and restoring the information bits to finish the processing.

Compared with the background technology, the invention has the following advantages:

1. the variable spreading ratio self-adaptive despreading demodulation method in the high dynamic environment can automatically finish the recognition of the data spreading ratio according to the mode word information carried by the direct spreading signal, can finish the recognition of various spreading ratio signals without instruction control, realizes the self-adaptive despreading demodulation processing of different spreading ratio signals, has better processing flexibility and ensures that the demodulator is more flexible to use.

2. According to the variable spreading ratio self-adaptive despreading demodulation method in the high dynamic environment, the spreading ratio is 512-64 under the frequency deviation of +/-9 kHz, despreading demodulation of signals with various information rates corresponding to the information rates of 12 kbps-96 kbps is realized, and the communication requirements of various information rates are met.

3. The invention has simple processing and good expandability, only needs to buffer a part of data after despreading, has low storage resource occupancy rate, can adapt to more information rates through the number of the track paths of the spread code ring, and is particularly suitable for being applied to a satellite-borne multi-rate communication processing scene with limited resources.

Drawings

Fig. 1 is a block diagram of a variable spreading ratio adaptive despreading demodulation method in a high dynamic environment.

Fig. 2 is a schematic diagram of a spread spectrum signal transmission frame format.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in FIG. 1, the adaptive despreading demodulation method with variable spreading ratio in the high dynamic environment comprises 7 links of quadrature down-conversion, matched filtering, large frequency offset direct spread signal capturing, adaptive data despreading, carrier tracking, data positioning and decoding. The information bit adopts LDPC 1/4 coding, QPSK modulation mode, the information rate is 12kbps/24 kbps/48kbps/96kbps, the spreading ratio is 512/256/128/64, the chip rate after spreading is 12.288Mbps, the specific processing steps are as follows:

(1) The data after quadrature down-conversion is output at the rate of 49.152Mbps of 4 times of the chip rate, the data after quadrature down-conversion is subjected to matched filtering processing by taking 49.152MHz as a main processing clock, the normalized bandwidth of a filter is 0.25, the roll-off coefficient is 0.35, and the data rate after matched filtering is still 49.152Mbps;

(2) The data after matched filtering is subjected to large frequency offset direct spread signal capturing processing, the data frame structure is shown in figure 2, the data is divided into 3 branches and is subjected to spread spectrum code capturing processing respectively, the first branch is subjected to positive frequency offset pre-correction, the correction value is plus or minus 6kHz, then the spread spectrum code capturing processing is carried out, the second branch is subjected to delay on the data and then is directly subjected to spread spectrum code capturing processing, the third branch is subjected to negative frequency offset pre-correction, the correction value is minus or minus 6kHz, then the spread spectrum code capturing processing is carried out, the single-path frequency offset adaptive capacity is plus or minus 3kHz, and the three-path frequency offset adaptive capacity is plus or minus 9kHz; performing capture judgment on the three paths of data which are captured and output, selecting one path of data with the correlation peak exceeding a threshold value as data to be despread and outputting a capture indication signal, wherein the capture judgment indication is aligned with the initial position of a chip of the data, and the capture indication signal is high in efficiency and lasts for 1 clock period;

(3) According to the initial position of a code chip determined by a capture judgment instruction, carrying out 4 paths of code loop tracking processing on data to be despread by utilizing a lead-lag gate method, and carrying out a main processing clock of 49.152MHz, wherein a 1 st path of local spreading code is identical to a preamble spreading code, 1 local spreading code is generated every 4 clock cycles, the despreading ratio is 512, after code loop tracking, data 1 and a data enabling signal 1 are output after despreading, a 2 nd path of local spreading code generates a local spreading code every 8 clock cycles, the despreading ratio is 256, after code loop tracking, data 2 and a data enabling signal 2 are output, a 3 rd path of local spreading code generates a local spreading code every 16 clock cycles, after code loop tracking, data 3 and a data enabling signal 3 are output, after despreading, every 32 clock cycles, the 4 th path of local spreading code generates a local spreading code, the despreading ratio is 64, after code loop tracking, the data 2 and the 4 th path of local spreading code generates a 4/4 th path of data enabling signal 2, and the 4 th path of local spreading code generates a 1/4 MHz data enabling signal, and the lead-lag value is adjusted according to the clock cycle of 1/2, and the lead-lag value is adjusted;

(4) Performing spread spectrum ratio identification processing on the despread data 1, respectively performing correlation operation on the despread data 1 and 4 groups of local mode word orthogonal sequences when a data enabling 1 signal is effective under a 49.152MHz clock, comparing an output correlation value with a local threshold value, recording a corresponding mode word when the correlation value exceeds the threshold value, identifying the spread spectrum ratio of a direct spread signal data part according to the mode word, and outputting a spread spectrum ratio indication effective signal and a spread spectrum ratio indication signal;

(5) Under a 49.152MHz main processing clock, according to 4 paths of data enabling signals, when the data enabling signals are valid, writing 4 paths of despread data into a RAM group, wherein the RAM group consists of 4 dual-port RAMs, the depth is set to 1024/2048/4096/8192 (greater than 768 bits) respectively, the bit width is set to 24 bits, when the spreading ratio indicates that the enabling signals are valid, reading and outputting the data in the corresponding RAMs according to the spreading ratio indication signals, and synchronously outputting data valid signals (long '1' signals, representing data validity) and data enabling signals ('1' valid, representing data period);

(6) Performing rate conversion processing on the gated despread data, using a dual-port RAM to realize rate conversion, writing the data into the RAM when the data effective signal and the data enabling signal are both '1', when the write address is equal to the information length of the spread spectrum signal (taking the data length 4032 and the data part 512 times of the spread spectrum ratio as an example, adding the preamble pattern word to the data length, and taking the value as 4832), starting the RAM data reading operation, continuously reading the data by using a 49.152MHz main processing clock until all despread data is read, converting the data processing rate from the despread symbol rate to the main processing clock rate, and synchronously outputting the data enabling signal and the data;

(7) Carrying out carrier tracking processing on the data after rate conversion, and obtaining carrier recovered data after data de-modulation processing, frequency offset estimation, residual frequency offset correction, phase error estimation, phase tracking correction and the like;

(8) Carrying out data positioning processing on the data after carrier recovery, carrying out correlation operation on the sign bit of the data after carrier recovery and a local positioning word sequence, determining the initial position of effective data according to the correlation peak position and the correlation operation time delay, carrying out phase fuzzy correction on the data according to the phase information of the correlation peak value to obtain data to be decoded, and outputting data enabling and the data to be decoded;

(9) And decoding the data, restoring the information bits, and finishing the processing.

In a word, the method does not need to receive a control instruction, recognizes a specific spreading ratio and a spreading code through the mode word information carried by the direct-spread signal, and performs self-adaptive despreading demodulation processing on the direct-spread signal data part.

Claims (1)

1. The adaptive despreading demodulation method for the variable spreading ratio in the high dynamic environment is characterized by comprising the following steps:

step 1, selecting a root raised cosine filter as a matched filter, and carrying out matched filtering treatment on data after quadrature down-conversion;

step 2, carrying out large-frequency offset direct-spread signal capturing processing on the data after matched filtering, dividing the data into 3 data branches, and respectively carrying out direct-spread signal capturing processing; the 1 st data branch firstly carries out positive frequency offset pre-correction processing, then carries out spread spectrum code capturing processing on input data by utilizing a local spread spectrum code, the 2 nd data branch directly carries out spread spectrum code capturing processing, the 3 rd data branch firstly carries out negative frequency offset pre-correction processing, and then carries out spread spectrum code capturing processing; performing capture judgment processing on the captured and output data, and outputting a capture judgment instruction which is aligned with the initial position of the chip of the data;

step 3, according to the initial position of the code chip determined by the capture judgment indication, simultaneously carrying out 4 paths of code loop tracking processing on the data to be despread by utilizing a lead-lag gate method, and respectively carrying out despreading and code loop tracking processing on the data to be despread and the local spreading codes with 4 paths of different spreading ratios, wherein the 1 st path of local spreading codes are identical to the preamble spreading codes, the data 1 and the data enabling signal 1 after despreading are output after the code loop tracking, the data 2 and the data enabling signal 2 after despreading are output after the 2 nd path of the data 2 after despreading are output after the code loop tracking, the data 3 and the data enabling signal 3 after despreading are output after the 4 th path of the data 4 and the data enabling signal 4 after despreading are output after the code loop tracking;

step 4, performing spread spectrum ratio identification processing on the despread data 1, respectively performing correlation operation and matching identification on the despread data 1 and 4 local mode word orthogonal sequences when the data enabling 1 signal is effective, identifying the spread spectrum ratio of the direct spread signal data part according to the mode word, and outputting a spread spectrum ratio indication effective signal and a spread spectrum ratio indication signal;

step 5, under the main processing clock, according to 4 paths of data enabling signals, writing the data after 4 paths of despreading into a dual-port RAM group respectively for data caching, wherein the depth of the RAM is larger than the data length corresponding to the delay of the spread spectrum ratio indicating signal processing, and when the spread spectrum ratio indicating enabling signals are effective, reading the data in the corresponding RAM according to the spread spectrum ratio indicating signals and outputting;

step 6, performing rate conversion processing on the gated despread data, realizing rate conversion by using a dual-port RAM, writing the data into the RAM when the data enabling is effective, starting a RAM data reading operation when the writing address is equal to the information length of the spread spectrum signal, continuously reading the data by using a main processing clock until all despread data are read, and converting the data processing rate from the despread symbol rate to the main processing clock rate;

step 7, carrying out carrier tracking processing on the data after rate conversion, and obtaining data after carrier recovery after residual frequency offset correction and phase tracking correction;

step 8, carrying out data positioning processing on the data after carrier recovery, carrying out correlation operation on the sign bit of the data after carrier recovery and a local positioning word sequence, determining the initial position of effective data according to the correlation peak position and the correlation operation time delay, carrying out phase fuzzy correction on the data according to the phase information of the correlation peak value to obtain data to be decoded, and outputting data enabling and the data to be decoded;

and 9, decoding the data, and restoring the information bits to finish the processing.

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