A variable spreading ratio adaptive despreading and demodulation method under high dynamic environment

Abstract

The present invention discloses a variable spreading ratio adaptive despreading and demodulation method under high dynamic environment, including orthogonal down-conversion, matched filtering, large frequency deviation direct spread signal capture, adaptive data despreading, carrier tracking, data positioning, and decoding. The method does not need to receive control instructions, identifies a specific spreading ratio and spreading code through the mode word information carried by the direct spread signal, and performs adaptive despreading and demodulation processing on the data part of the direct spread signal. It has the advantages of flexible and simple processing, less resource occupation, etc., and is particularly suitable for adaptive despreading and demodulation processing of direct spread signals with multiple spreading ratios under high dynamic environment conditions.

Description

Technical Field

[0001] The invention relates to an adaptive despreading and demodulating method with a variable spreading ratio in a high dynamic environment, and belongs to the field of satellite-borne modulation and demodulation in satellite communications. Background Art

[0002] Traditional satellite communication processing payloads often control the working mode and working rate through measurement and control instructions. The supported working mode and rate are relatively single, which can no longer meet the communication needs in various communication terminal scenarios. There are often a large number of miniaturized communication terminals within the coverage of satellite beams, and the supported data communication rate is low. In order to avoid interference with neighboring satellites, data is usually spread spectrum processed. Existing spread spectrum communication processing payloads often only support a single information rate and a single spread spectrum ratio. Even if the processing payload supports multiple information rates and multiple spread spectrum ratios, multiple spread spectrum ratio signal capturers are often configured in the processing payload. It is necessary to control the working rate and working spread spectrum ratio of the processing payload in advance through preset instructions, which occupies a lot of processing resources and is not flexible enough in application. In order to meet the communication needs of small terminals of different types and different rates, the on-board processing payload often needs to support the despreading and demodulation of spread spectrum signals of multiple communication rates. The working rate of the processing payload preset by instructions can no longer meet the growing communication needs. In order to make communication more convenient and processing more flexible, the on-board processing payload needs to have adaptive receiving and processing capabilities in a large dynamic environment. The processing should be simple and easy to implement, and the processing resource occupancy should be reduced as much as possible to adapt to the situation where the weight and power consumption of the satellite communication processing payload are limited.

[0003] In summary, the existing technology generally implements the despreading and demodulating processing of signals with different spreading ratios by means of preset instructions, which can no longer meet the communication needs of terminals of different types and rates. There is an urgent need for a flexible despreading and demodulating processing method that can adapt to signals with multiple spreading ratios. Summary of the invention

[0004] In view of this, the present invention provides a method for adaptive despreading and demodulating with a variable spreading ratio in a high dynamic environment. The method does not need to receive a control instruction, but identifies a specific spreading ratio and a spreading code through the leading header part of a direct spread signal, and adaptively despreads and demodulates the data part of the direct spread signal. The method has the advantages of flexible and simple processing and less resource occupation, and is particularly suitable for adaptive despreading and demodulating direct spread signals with multiple spreading ratios under high dynamic environment conditions.

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

[0006] A variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment comprises the following steps:

[0007] Step 1, select a root raised cosine filter as a matched filter, and perform matched filtering on the data after orthogonal down conversion;

[0008] Step 2, performing large frequency offset direct spread signal capture processing on the matched filtered data, dividing the data into three data branches, and performing direct spread signal capture processing respectively; wherein, the first data branch first performs positive frequency offset pre-correction processing, and then uses the local spread spectrum code to perform spread spectrum code capture processing on the input data, the second data branch directly performs spread spectrum code capture processing, and the third data branch first performs negative frequency offset pre-correction processing, and then performs spread spectrum code capture processing; performing capture decision processing on the captured output data, outputting a capture decision indication, and aligning the capture decision indication with the chip start position of the data;

[0009] Step 3, according to the chip start position determined by the capture decision indication, the data to be despread is subjected to 4-channel code loop tracking processing simultaneously by using the lead-lag gate method, and is despread and code loop tracking processed with 4 local spread spectrum codes with different spread spectrum ratios respectively, wherein the first local spread spectrum code is the same as the leading header spread spectrum code, and after code loop tracking, despread data 1 and data enable signal 1 are output, the second local spread spectrum code outputs despread data 2 and data enable signal 2 after code loop tracking, the third local spread spectrum code outputs despread data 3 and data enable signal 3 after code loop tracking, and the fourth local spread spectrum code outputs despread data 4 and data enable signal 4 after code loop tracking;

[0010] Step 4, performing spreading ratio identification processing on the despread data 1, when the data enable 1 signal is valid, performing correlation operation and matching identification on the despread data 1 and the four local mode word orthogonal sequences respectively, identifying the spreading ratio of the data part of the direct spread signal according to the mode word, and outputting the spreading ratio indication valid signal and the spreading ratio indication signal;

[0011] Step 5, under the main processing clock, according to the 4-way data enable signal, the 4-way despread data are respectively written into the dual-port RAM group for data cache processing, the RAM depth is greater than the data length corresponding to the processing delay of the spreading ratio indication signal, when the spreading ratio indication enable signal is valid, the data in the corresponding RAM is read and output according to the spreading ratio indication signal;

[0012] Step 6, rate conversion is performed on the selected despread data, and the rate conversion is realized by using a dual-port RAM. When the data enable is valid, the data is written into the RAM. When the write address is equivalent to the information length of the spread spectrum signal, the RAM data read operation is started, and the data is continuously read out using the main processing clock until all the despread data are read out, and the data processing rate is converted from the despread symbol rate to the main processing clock rate;

[0013] Step 7, performing carrier tracking processing on the rate-converted data, and obtaining carrier-recovered data after residual frequency offset correction and phase tracking correction;

[0014] Step 8, perform data positioning processing on the data after carrier recovery, perform correlation operation on the sign bit of the data after carrier recovery and the local positioning word sequence, determine the starting position of the valid data according to the correlation peak position combined with the correlation operation delay, and perform phase ambiguity correction on the data according to the phase information of the correlation peak to obtain the data to be decoded, and output the data enable and the data to be decoded at the same time;

[0015] Step 9, decode the data, restore the information bits, and complete the process.

[0016] Compared with the background technology, the present invention has the following advantages:

[0017] 1. The variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment described in the present invention can automatically complete the data spreading ratio recognition according to the mode word information carried by the direct spread signal, and can complete the recognition of various spreading ratio signals without command control, thereby realizing adaptive despreading and demodulation processing of signals with different spreading ratios, having better processing flexibility, and making the use of the demodulator more flexible.

[0018] 2. The variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment described in the present invention realizes a spreading ratio of 512~64 at a frequency deviation of ±9kHz, and despreads and demodulates signals with various information rates corresponding to information rates of 12kbps~96kbps, thus meeting the communication requirements of various information rates.

[0019] 3. The present invention is simple to process and has good scalability. It only needs to cache a portion of the despread data, with low storage resource occupancy. It can adapt to more information rates by tracking the number of expansion code loops, and is particularly suitable for resource-constrained satellite multi-rate communication processing scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The invention is a block diagram of a variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment.

[0021] Figure 2 Schematic diagram of the spread spectrum signal transmission frame format. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0023] like Figure 1As shown in the figure, a variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment includes orthogonal down-conversion, matched filtering, large frequency deviation direct spread signal capture, adaptive data despreading, carrier tracking, data positioning, and decoding, a total of 7 links. Take the information bit using LDPC 1 / 4 coding, QPSK modulation, information rate 12kbps / 24 kbps / 48kbps / 96kbps, spreading ratios of 512 / 256 / 128 / 64, and a chip rate of 12.288Mbps after spreading as an example, the specific processing steps are as follows:

[0024] (1) After orthogonal down-conversion, the data is output at 49.152 Mbps, which is 4 times the chip rate. 49.152 MHz is used as the main processing clock. The data after orthogonal down-conversion is processed by matched filtering. The normalized bandwidth of the filter is 0.25 and the roll-off factor is 0.35. The data rate after matched filtering is still 49.152 Mbps.

[0025] (2) Perform large frequency deviation direct spread signal capture processing on the matched filtered data. The data frame structure is as follows: Figure 2 As shown, the data is divided into three branches for spread spectrum code capture processing respectively. The first branch first performs positive frequency offset pre-correction with a correction value of +6kHz, and then performs spread spectrum code capture processing. The second branch directly performs spread spectrum code capture processing after delaying the data. The third branch first performs negative frequency offset pre-correction with a correction value of -6kHz, and then performs spread spectrum code capture processing. The single-channel frequency offset adaptability is ±3kHz, and the three-channel frequency offset adaptability is ±9kHz. The data output from the three channels is captured and judged, and the channel with a correlation peak value exceeding the threshold value is selected as the data to be despread output. At the same time, a capture indication signal is output, and the capture judgment indication is aligned with the starting position of the data chip. The capture indication signal is high and effective and lasts for 1 clock cycle.

[0026] (3) According to the chip start position determined by the capture decision indication, the data to be despread is simultaneously tracked by 4 code loops using the lead-lag gate method. The main processing clock is 49.152MHz. The first local spread spectrum code is the same as the leading header spread spectrum code. A local spread spectrum code is generated every 4 clock cycles. The despreading ratio is 512. After code loop tracking, the despread data 1 and data enable signal 1 are output. The second local spread spectrum code generates a local spread spectrum code every 8 clock cycles. The despreading ratio is 256. After code loop tracking, the despread data 2 and data enable signal 2 are output. The third local spread spectrum code generates a local spread spectrum code every 16 clock cycles. The despreading ratio is 128. , after code loop tracking, the despread data 3 and data enable signal 3 are output. The 4th local spread spectrum code generates a local spread spectrum code every 32 clock cycles, and the despreading ratio is 64. After code loop tracking, the despread data 4 and data enable signal 4 are output. The clock cycle generated by the 4-channel local spread spectrum code can be dynamically adjusted according to the error value fed back by the lead-lag gate. The data enable signals 1 / 2 / 3 / 4 all last for 1 49.152MHz clock cycle;

[0027] (4) Performing spreading ratio identification processing on the despread data 1. Under the 49.152 MHz clock, when the data enable 1 signal is valid, performing correlation operations on the despread data 1 and the four groups of local mode word orthogonal sequences respectively, comparing the output correlation value with the local threshold value, and when the correlation value exceeds the threshold value, recording the corresponding mode word, identifying the spreading ratio of the data part of the direct spread signal according to the mode word, and outputting the spreading ratio indication valid signal and the spreading ratio indication signal;

[0028] (5) Under the 49.152MHz main processing clock, according to the 4-way data enable signal, when the data enable signal is valid, the 4-way despread data is written into the RAM group respectively. The RAM group consists of 4 dual-port RAMs, and the depth is set to 1024 / 2048 / 4096 / 8192 (greater than 768bit) and the bit width is set to 24bit. When the spreading ratio indication enable signal is valid, the data in the corresponding RAM is read and output according to the spreading ratio indication signal, and the data valid signal (long '1' signal, indicating data validity) and the data enable signal ('1' is valid, indicating data cycle) are output synchronously;

[0029] (6) Perform rate conversion on the selected despread data, and use dual-port RAM to achieve rate conversion. When the data valid signal and the data enable signal are both '1', write the data into the RAM. When the write address is equal to the length of the spread spectrum signal information (taking the data length of 4032 and the data part of 512 times the spread spectrum ratio as an example, plus the leading header pattern word positioning word data length, the value here is 4832), start the RAM data read operation, and use the 49.152MHz main processing clock to continuously read the data until all the despread data are read out, convert the data processing rate from the despread symbol rate to the main processing clock rate, and output the data enable signal and data synchronously;

[0030] (7) Carrier tracking processing is performed on the rate-converted data, and the carrier-recovered data is obtained after data demodulation, frequency offset estimation, residual frequency offset correction, phase error estimation, phase tracking correction, etc.;

[0031] (8) Perform data positioning processing on the data after carrier recovery, perform correlation operation on the sign bit of the data after carrier recovery and the local positioning word sequence, determine the starting position of the valid data according to the correlation peak position combined with the correlation operation delay, and perform phase ambiguity correction on the data according to the phase information of the correlation peak to obtain the data to be decoded, and output data enable and data to be decoded at the same time;

[0032] (9) The data is decoded to restore the information bits and the processing is completed.

[0033] In summary, this method does not need to receive control instructions. It identifies the specific spreading ratio and spreading code through the mode word information carried by the direct-spread signal, and performs adaptive despreading and demodulation on the data part of the direct-spread signal. It has the advantages of flexible and simple processing and low resource occupation. It is particularly suitable for adaptive despreading and demodulation of direct-spread signals with multiple spreading ratios under high dynamic environment conditions.

Claims

1. A variable spreading ratio adaptive despreading and demodulation method in a high dynamic environment, characterized in that: The steps include: Step 1, select a root raised cosine filter as a matched filter, and perform matched filtering on the data after orthogonal down conversion; Step 2, performing large frequency offset direct spread signal capture processing on the matched filtered data, dividing the data into three data branches, and performing direct spread signal capture processing respectively; wherein, the first data branch first performs positive frequency offset pre-correction processing, and then uses the local spread spectrum code to perform spread spectrum code capture processing on the input data, the second data branch directly performs spread spectrum code capture processing, and the third data branch first performs negative frequency offset pre-correction processing, and then performs spread spectrum code capture processing; performing capture decision processing on the captured output data, outputting a capture decision indication, and aligning the capture decision indication with the chip start position of the data; Step 3, according to the chip start position determined by the capture decision indication, the data to be despread is subjected to 4-channel code loop tracking processing simultaneously by using the lead-lag gate method, and is despread and code loop tracking processed with 4 local spread spectrum codes with different spread spectrum ratios respectively, wherein the first local spread spectrum code is the same as the leading header spread spectrum code, and after code loop tracking, despread data 1 and data enable signal 1 are output, the second local spread spectrum code outputs despread data 2 and data enable signal 2 after code loop tracking, the third local spread spectrum code outputs despread data 3 and data enable signal 3 after code loop tracking, and the fourth local spread spectrum code outputs despread data 4 and data enable signal 4 after code loop tracking; Step 4, performing spreading ratio identification processing on the despread data 1, when the data enable 1 signal is valid, performing correlation operation and matching identification on the despread data 1 and the four local mode word orthogonal sequences respectively, identifying the spreading ratio of the data part of the direct spread signal according to the mode word, and outputting the spreading ratio indication valid signal and the spreading ratio indication signal; Step 5, under the main processing clock, according to the 4-way data enable signal, the 4-way despread data are respectively written into the dual-port RAM group for data cache processing, the RAM depth is greater than the data length corresponding to the processing delay of the spreading ratio indication signal, when the spreading ratio indication enable signal is valid, the data in the corresponding RAM is read and output according to the spreading ratio indication signal; Step 6, rate conversion is performed on the selected despread data, and the rate conversion is realized by using a dual-port RAM. When the data enable is valid, the data is written into the RAM. When the write address is equivalent to the information length of the spread spectrum signal, the RAM data read operation is started, and the data is continuously read out using the main processing clock until all the despread data are read out, and the data processing rate is converted from the despread symbol rate to the main processing clock rate; Step 7, performing carrier tracking processing on the rate-converted data, and obtaining carrier-recovered data after residual frequency offset correction and phase tracking correction; Step 8, perform data positioning processing on the data after carrier recovery, perform correlation operation on the sign bit of the data after carrier recovery and the local positioning word sequence, determine the starting position of the valid data according to the correlation peak position combined with the correlation operation delay, and perform phase ambiguity correction on the data according to the phase information of the correlation peak to obtain the data to be decoded, and output the data enable and the data to be decoded at the same time; Step 9, decode the data, restore the information bits, and complete the process.

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