A satellite-borne adaptive low-spreading-factor ratio tracking despreading receiver

Abstract

This invention discloses a spaceborne adaptive low spread ratio tracking and despreading receiver, relating to the field of satellite communication. The device includes an AD data processing module, an orthogonal downconversion module, a burst acquisition module, a timing module, a tracking and despreading module, and a demodulation and decoding module. The AD data processing module obtains local clock domain data from an externally input intermediate frequency signal; the orthogonal downconversion module obtains overall baseband data; the burst acquisition module adaptively acquires useful signal data; the timing module performs timing processing on the acquired data; the tracking and despreading module performs tracking and despreading processing on the timed data; and the demodulation and decoding module demodulates and decodes the despread data to recover the transmitted data. This invention supports low spread ratio signal reception and can adaptively complete the acquisition, tracking, and despreading processing of signals with different spread ratios. It has advantages such as simple implementation, low resource consumption, good scalability, low processing latency, and stable performance.

Description

Technical Field

[0001] This invention relates to the field of satellite communications, and more particularly to a spaceborne adaptive low spreading ratio tracking and despreading receiver. In low spreading ratio communication scenarios, this invention adaptively completes the acquisition, tracking, and despreading of signals with different spreading ratios. It solves the problem of despreading failure caused by chip offset due to timing with less resource overhead, and exhibits low latency in tracking and despreading processing. It is particularly suitable for scenarios with limited spaceborne resources. Background Technology

[0002] In satellite communication systems employing direct sequence spread spectrum, the onboard receiver needs to perform despreading and recover the original information through pseudocode synchronization. The synchronization process typically consists of two phases: acquisition (coarse synchronization) and tracking (fine synchronization). The performance of the tracking phase, especially the accuracy and stability of the delay-locked loop, directly determines the final demodulation signal-to-noise ratio and the system bit error rate.

[0003] A low spreading ratio means a shorter spreading code length, which poses some challenges to precise synchronization: First, the autocorrelation function of a short spreading code has a large main peak width and relatively high side lobes, resulting in a flat slope of the phase detection curve of the timing error detector near the zero point; Second, the system's anti-interference margin is reduced, and noise and multiple access will severely distort the shape of the correlation peak.

[0004] Currently, precise synchronization is widely achieved using delay-locked loops (DLLs). In traditional DLLs, an error signal is generated by comparing the capability difference between the "leading" and "lagging" correlated branches. In high spread ratio systems, the sharp correlation peaks make this approach work well. However, in low spread ratio systems, its shortcomings become more pronounced.

[0005] 1. Tracking accuracy is severely reduced: The flat phase detection curve makes it insensitive to small timing offsets, resulting in large loop steady-state errors and making it impossible to achieve high-precision tracking at the "chip level" or even the "sub-chip level".

[0006] 2. Poor stability and easy to lose lock: When the signal-to-noise ratio is low or there is interference, the distorted correlation peak can easily cause the error signal to become disordered, causing loop jitter or even loss of lock;

[0007] 3. Performance degradation in multipath environments: The inability to effectively distinguish closely spaced multipath signals leads to tracking point drift and exacerbates performance loss.

[0008] To overcome these problems, synchronization algorithms based on maximum likelihood estimation or adaptive filtering have been developed. However, these solutions often have high computational complexity, require a large amount of hardware resources and cannot be applied in environments with limited onboard resources; or they require known pilot sequences to assist, which reduces the transmission efficiency of the system. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and to design a spaceborne adaptive low spread ratio tracking and despreading receiver. This invention has advantages such as simple implementation, good scalability, low processing delay, low resource consumption, and stable and reliable performance.

[0010] The technical solution adopted in this invention is as follows:

[0011] A spaceborne adaptive low spread ratio tracking and despreading receiver, characterized in that it includes an AD data processing module 1, an orthogonal downconversion module 2, a burst acquisition module 3, a timing module 4, a tracking and despreading module 5, and a demodulation and decoding module 6;

[0012] The AD data processing module 1 is used to receive external input intermediate frequency digital signals, perform cross-clock domain processing to obtain local clock domain data, and send the data to the quadrature downconverter module 2;

[0013] The quadrature downconversion module 2 is used to receive data from the AD data processing module 1, perform quadrature downconversion processing on the carrier group, obtain the overall baseband signal, and send it to the burst acquisition module 3.

[0014] The burst acquisition module 3 performs sliding correlation operation on the obtained baseband signal and the unique word sequence corresponding to different local spreading ratios. It compares the correlation peaks obtained under different spreading ratios, selects the maximum peak to determine the spreading ratio, and then compares the maximum peak of the spreading ratio with the acquisition threshold. If it is greater than the acquisition threshold, it outputs the data of the corresponding length according to the frame format of the spreading ratio and sends it to the timing module 4; otherwise, it continues to perform acquisition calculation.

[0015] The timing module 4 receives the captured signal, performs real-time calculation and interpolation based on four consecutive input samples, and records the result as the timed data. The timed data is then output to the tracking and despreading module 5 based on four consecutive input samples.

[0016] The tracking and despreading module 5 constructs a parallel data path with the maximum spreading ratio plus one sample point by sequentially removing half of the sample data with the maximum spreading ratio from the beginning and adding half of the sample data with the maximum spreading ratio from the beginning, according to the maximum spreading ratio in the system protocol. When it is necessary to remove some sample data, zeros are added to the end of the data. When it is necessary to add sample data, zeros are added to the beginning of the data and then the corresponding number of data points are removed from the end of the data. This ensures that the constructed data path has the same frame length as the corresponding spreading ratio. Then, each data path is first descrambled and then despread. The despread data is stored in RAM on one hand, and the signal energy value is calculated by squaring and summing the squares of the data on the other hand. Due to the descrambling, the signal energy value calculated by the multiple data paths constructed according to the maximum spreading ratio will have a significant maximum value under the lower multiple spreading condition. Therefore, the energy values ​​of each signal are compared and the signal with the largest output signal energy is the correctly tracked and despread signal. That is, the signal with the largest signal energy is read from RAM and sent to the demodulation and decoding module 6.

[0017] The demodulation and decoding module 6 demodulates and decodes the despread data according to the modulation and encoding methods to recover the transmitted data.

[0018] The advantages of this invention compared to the prior art are:

[0019] 1. The spaceborne receiver of the present invention can adaptively acquire, track, and despread various low spread ratio signals in low spread ratio scenarios. It can be expanded according to the spreading multiple and the number of carriers. The implementation method is simple and has good scalability.

[0020] 2. The spaceborne receiving device of the present invention does not require additional data assistance communication overhead, and can achieve accurate despreading by shifting back and forth and calculating signal energy.

[0021] 3. The spaceborne receiving device of the present invention adopts a pipeline processing flow, stores the data after multi-channel tracking and despreading, selects the optimal despreading signal for output, and has the characteristics of small buffer usage and low processing latency.

[0022] 4. The spaceborne receiver of the present invention is implemented on a programmable logic device, which has the advantages of small hardware resource consumption, stable layout and routing timing, and reliable and stable performance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the implementation principle of the adaptive low spread ratio tracking and despreading spaceborne receiver of the present invention.

[0024] Figure 2 This is an example diagram of the burst transmission frame structure used in this invention.

[0025] Figure 3This is an example diagram of the data construction method of the data shifting module used in this invention.

[0026] Figure 4 This is a schematic diagram illustrating the implementation principle of the tracking and despreading module of this invention. Detailed Implementation

[0027] Reference Figure 1 The present invention provides a spaceborne adaptive low spread ratio tracking and despreading receiver, comprising an AD data processing module 1, an orthogonal downconversion module 2, a burst acquisition module 3, a timing module 4, a tracking and despreading module 5, and a demodulation and decoding module 6. Figure 1 This is a schematic diagram of an embodiment of a spaceborne adaptive low spread ratio tracking and despreading receiver according to the present invention. The embodiment is based on... Figure 1 Connect the lines.

[0028] The entire process of the device is as follows Figure 1 As shown, the AD data processing module 1 receives externally input intermediate frequency digital signals, performs cross-clock domain processing to obtain local clock domain data, and sends the data to the quadrature downconversion module 2. The quadrature downconversion module 2 receives data from the AD data processing module 1, performs quadrature downconversion processing on the carrier group to obtain the overall baseband signal, and sends it to the burst acquisition module 3. The burst acquisition module 3 performs sliding correlation operation on the obtained baseband signal and the unique word sequences corresponding to different local spreading ratios, compares the correlation peaks obtained under different spreading ratios, selects the maximum peak to determine the spreading ratio, and then compares the maximum peak of the spreading ratio with the acquisition threshold. If it is greater than the acquisition threshold, the acquired signal is output as data of the corresponding length according to the frame format of the spreading ratio. The data is sent to timing module 4; otherwise, the acquisition calculation continues. Timing module 4 receives the acquired signal, performs real-time calculation and interpolation based on four consecutive input samples, and records the result as the timed data. The timed data is then sequentially output to tracking and despreading module 5 based on four consecutive input samples. Tracking and despreading module 5, according to the maximum spreading ratio in the protocol, increments by one sample point, sequentially removing half the sample data of the maximum spreading ratio from the beginning and adding half the sample data of the maximum spreading ratio to the beginning to construct the maximum spreading ratio plus one parallel data path. When removing several sample data points, zeros are added to the end of the data; when adding sample data points, zeros are added to the beginning of the data, and then the corresponding number of data points are removed from the end of the data. Figure 3As shown, this ensures that the constructed data path has the same frame length as the corresponding spreading ratio. Then, each data path is first descrambled and then despread. The despread data is stored in RAM, and the signal energy value is calculated by squaring and summing the squares of the data. Due to the descrambling, the signal energy value calculated by the multiple data paths constructed according to the maximum spreading ratio at a lower multiple of spreading will have a significant maximum value. Therefore, the energy values ​​of each signal are compared, and the signal with the largest output signal energy is the correctly tracked and despread signal. That is, the signal with the largest signal energy is read from RAM and sent to demodulation and decoding module 6. Demodulation and decoding module 6 demodulates and decodes the despread data according to the modulation and encoding methods to recover the transmitted data.

[0029] The tracking and despreading module 5, as described above Figure 4 As shown, the tracking and despreading module 5 includes a data shifting module 5-1 and multiple data processing channels. Each channel includes a descrambling and despreading module 5-2 and an integration and summing module 5-3. It also includes a comparator 5-4 and a data storage module 5-5. The data shifting module 5-1 is used for signals from the timing module 4. The maximum spreading ratio in the system protocol is represented by N. Based on the maximum spreading ratio in the system protocol, the data from the timing module is sequentially processed in steps of 1 sample point, from samples with half the maximum spreading ratio removed to samples with half the maximum spreading ratio added, constructing N+1 parallel data channels. Figure 3 As shown, in this embodiment, the maximum spreading ratio N=4, and the data from the timing module is denoted as {x1,x2,x3,……,xn-2,xn-1,xn}; the constructed N+1 parallel data channels are sent to the descrambling and despreading modules 5-2 of each channel; the descrambling and despreading module 5-2 of each channel first performs descrambling operation on the data from the data shifting module 5-1, and then performs despreading operation according to the spreading ratio determined by the burst capture module (3). On the one hand, the data of this channel is sent to the integration and summation module 5-3 of this channel, and on the other hand, the data of this channel is sent to the data storage module 5-5. When programming, block 5-5 allocates the maximum RAM resources, and stores data according to the actual situation to ensure no data overflow. The integration and summation module 5-3 of each channel first performs a summation of squares on each sample point of the I and Q channels of the despread data, and then adds the sums of squares of each sample point to obtain the sum of the whole frame. Then, the total sum of squares of the data of this channel is sent to comparator 5-4. Comparator module 5-4 compares the total sum of squares of each channel from integration and summation module 5-3, outputs the sequence number of the maximum total sum of squares and sends it to data storage module 5-5 to select the corresponding data and output it to demodulation and decoding module 6.

[0030] The specific frame format of the burst data frames mentioned in the above process is as follows: Figure 2 As shown.

[0031] Each functional module in the embodiments can be implemented on Xilinx's original FPGA series products.

[0032] The basic working principle of this invention is as follows:

[0033] A burst acquisition module 3 of a spaceborne adaptive low spread ratio tracking and despreading receiver performs sliding correlation operation on the baseband signal obtained after AD sampling and downconversion with unique word sequences corresponding to different local spread ratios. It compares the correlation peaks obtained under different spread ratios, selects the maximum peak to determine the spread ratio, and then compares the maximum peak of this spread ratio with a capture threshold. If the maximum peak is greater than the capture threshold, the captured signal is output as data of the corresponding length according to the frame format of the spread ratio and sent to the timing module 4. The timing module 4 uses the captured signal and four consecutive input samples to perform real-time calculations without data assistance and interpolation to obtain the timed data, which is then output to the tracking and despreading module 5. The tracking and despreading module 5, according to the maximum spread ratio in the system protocol, increments the data from the timing module by one sample point. The system constructs a parallel data stream with the maximum spreading ratio plus one channel by removing half of the sample data from the previous data and adding half of the sample data from the previous data. Each data stream is first descrambled and then despread. The despread data is stored in RAM, and the signal energy value is calculated by summing the squares of the data. Due to the descrambling, the signal energy value calculated by the multiple data streams constructed according to the maximum spreading ratio will have a significant maximum value under a lower spreading ratio. Therefore, the energy values ​​of each signal are compared, and the signal with the largest output signal energy is the correctly tracked and despread signal. That is, the signal with the largest signal energy is read from RAM and sent to demodulation and decoding module 6. Demodulation and decoding module 6 demodulates and decodes the despread data according to the modulation and encoding methods to recover the transmitted data.

Claims

1. A spaceborne adaptive low spreading ratio tracking and despreading receiver, characterized in that, It includes an AD data processing module (1), an orthogonal downconversion module (2), a burst acquisition module (3), a timing module (4), a tracking despreading module (5), and a demodulation decoding module (6). The AD data processing module (1) is used to receive external input intermediate frequency digital signals, perform cross-clock domain processing, obtain local clock domain data, and send the data to the quadrature downconverter module (2). The quadrature downconversion module (2) is used to receive data from the AD data processing module (1), perform quadrature downconversion on the carrier group, obtain the overall baseband signal, and send it to the burst acquisition module (3). The burst acquisition module (3) performs sliding correlation operation on the obtained baseband signal and the unique word sequence corresponding to different local spreading ratios. It compares the correlation peaks obtained under different spreading ratios, selects the maximum peak to determine the spreading ratio, and then compares the maximum peak of the spreading ratio with the acquisition threshold. If it is greater than the acquisition threshold, it outputs the data of the corresponding length according to the frame format of the spreading ratio and sends it to the timing module (4); otherwise, it continues to perform acquisition calculation. The timing module (4) receives the captured signal, calculates and interpolates in real time based on four consecutive input samples, and records the result as the timed data. The timed data is then output to the tracking and despreading module (5) based on four consecutive input samples. The tracking despreading module (5) constructs a parallel data path with the maximum spreading ratio plus one path by taking one sample point as a step from the data from the timing module (4) by removing half of the sample data with the maximum spreading ratio and adding half of the sample data with the maximum spreading ratio. When it is necessary to remove several sample data points, zeros are added to the end of the data. When it is necessary to add sample data points, zeros are added to the beginning of the data and then the corresponding number of data points are removed from the end of the data. This ensures that the constructed data path has the same frame length as the corresponding spreading ratio. Then, each data path is first descrambled and then despread. The despread data is stored in RAM on one hand and the signal energy value is calculated by squaring and summing the squares on the other hand. The signal energy values ​​of each data path are compared, and the data path with the largest signal energy value is read from RAM and sent to the demodulation and decoding module (6). The demodulation and decoding module (6) demodulates and decodes the despread data according to the modulation and encoding methods to recover the transmitted data.

2. The apparatus according to claim 1, wherein the apparatus is a satellite-borne adaptive low-spreading-factor tracking despreading receiver, characterized in that, The tracking despreading module (5) includes a data shifting module (5-1) and multiple data processing channels. Each channel includes a descrambling and despreading module (5-2) and an integration and summation module (5-3). It also includes a comparator (5-4) and a data storage module (5-5). The data shifting module (5-1) is used to receive the signal from the timing module (4). According to the maximum spreading ratio in the system protocol, the data from the timing module is sequentially processed by removing half of the sample data with the maximum spreading ratio from the front and supplementing half of the sample data with the maximum spreading ratio from the front to construct the maximum spreading ratio plus 1 parallel data. Each data is sent to the descrambling and despreading module (5-2) of each channel. The descrambling and despreading module (5-2) of each channel first performs descrambling operation on the data from the data shifting module (5-1), and then performs despreading operation according to the spreading ratio determined by the burst capture module (3). On the one hand, the data of this channel is sent to the integration and summation module (5-3) of this channel, and on the other hand, the data of this channel is sent to the data storage module (5-5). The integration and summation module (5-3) of each channel first performs a square summation operation on each sample point of the I and Q channels of the despread data, then adds the sum of squares of each sample point to obtain the sum of the whole frame, and then sends the total sum of squares of the data of this channel to the comparator (5-4). The comparator (5-4) compares the total sum of squares from each channel from the integration and summation module (5-3), outputs the index of the maximum total sum of squares and sends it to the data storage module (5-5) to select the corresponding data and output it to the demodulation and decoding module (6).

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