阅读说明：本技术 一种基于星载vde的qpsk-cpm扩频多用户检测方法 (QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE ) 是由 向前 李惠媛 殷惠惠 荣师洁 张喆 于 2021-09-17 设计创作，主要内容包括：本发明公开了一种基于星载VDE的QPSK-CPM扩频多用户检测方法,包括步骤1：对接收的VDE信号进行GPS的UTC时隙校正对齐和数据截取,在截取的数据中取前4096个采样点和补零后的本地帧头序列进行FFT相关运算；步骤2：取64个点为底噪滑动窗口大小,滑动找到任一频率的4096点相关峰值功率最小窗口计算底噪平均幅度值,并以底噪平均幅度值的固定倍数作为底噪门限；步骤3：依次找到幅度大于底噪门限,且幅度较大的64个相关峰值,记为最大相关峰组,用频偏和延时组成的二维区域扫描算法剔除同区域内的次大相关峰值和其它相关峰值,选出最大值；步骤4：对CPM相关固有的频率域旁瓣毛刺进行了干扰剔除。(The invention discloses a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE, which comprises the following steps of 1: carrying out UTC time slot correction alignment and data interception of a GPS (global positioning system) on a received VDE (vertical data acquisition) signal, and carrying out FFT (fast Fourier transform) correlation operation on front 4096 sampling points and a zero-filled local frame header sequence in the intercepted data; step 2: taking 64 points as the size of a bottom noise sliding window, sliding to find a 4096-point correlation peak power minimum window of any frequency, calculating a bottom noise average amplitude value, and taking a fixed multiple of the bottom noise average amplitude value as a bottom noise threshold; and step 3: sequentially finding 64 correlation peak values with amplitude larger than the background noise threshold and larger than the amplitude, recording the correlation peak values as a maximum correlation peak group, eliminating a secondary large correlation peak value and other correlation peak values in the same region by using a two-dimensional region scanning algorithm consisting of frequency deviation and time delay, and selecting a maximum value; and 4, step 4: and carrying out interference elimination on side lobe burrs of a CPM related inherent frequency domain.)

1. A QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE is characterized by comprising the following steps:

step 1: carrying out down-conversion and filtering on satellite-borne received VDE signals, carrying out UTC time slot correction alignment and data interception of a GPS, and carrying out FFT (fast Fourier transform) correlation operation on front 4096 sampling points and a zero-filled local frame header sequence in the intercepted whole frame data;

step 2: taking 64 points as the size of a bottom noise sliding window, sliding to find a minimum power window of 4096-point correlation peak values of any frequency, calculating a bottom noise average amplitude value, and taking a fixed multiple of the bottom noise average amplitude value as a bottom noise threshold;

and step 3: sequentially finding 64 correlation peak values with amplitude larger than the background noise threshold and larger than the amplitude, recording the 64 correlation peak values as a maximum correlation peak group, eliminating a secondary large correlation peak value and other correlation peak values in the same region by using a two-dimensional region scanning algorithm consisting of frequency deviation and time delay, and selecting a maximum value to avoid false detection in the same region;

and 4, step 4: and carrying out interference elimination on side lobe burrs of a CPM related inherent frequency domain.

2. The QPSK-CPM spread spectrum multiuser detecting method according to claim 1, wherein in step 3, the two-dimensional region scanning algorithm scans other peak values of the maximum correlation peak group starting with the maximum correlation peak value, and if the maximum correlation peak is found to be in the same region as the maximum correlation peak, the maximum correlation peak group is removed; similarly, finding a second maximum value in the maximum correlation peak group after being removed, scanning other peak values of the maximum correlation peak group, and removing the maximum correlation peak group if the second maximum correlation peak is found to be in the same region; scanning in turn according to the method to find out a single maximum correlation peak value in each different area.

3. The QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE according to claim 2, wherein in step 4, the CPM related intrinsic frequency domain sidelobe elimination is required to be performed on the single maximum correlation peak in the different regions found in step 3, the intrinsic sidelobe is related to the CPM spread spectrum and the oversampling multiple, the two-dimensional region scanning elimination is performed on the sidelobe frequency region according to the relation between the spread spectrum and the oversampling multiple, and the finally eliminated maximum correlation peak group is the required multi-user detection frequency and the delay position.

Technical Field

The invention relates to the technical field of satellite-borne communication, in particular to a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE.

Background

The satellite-borne VDE system receives and transmits VDE signals by using a near-earth orbit satellite, and can realize satellite-ground communication of ships in all sea areas within the coverage area of an antenna. The G1139 VDES standard defines that a Link ID 20 physical layer frame format must be used for a data acknowledgement signaling channel and a random access channel in an uplink of a satellite, and the Link ID 20 physical layer frame format adopts a QPSK-CPM spread spectrum modulation mode, wherein CPM spread spectrum uses a CPM waveform to perform 16-fold spread spectrum on QPSK modulation signals. Due to the fact that multi-user competition exists during random access, the QPSK-CPM spread spectrum multi-user detection capability is improved, namely the random access capability of the user can be effectively improved, the overall performance of VDE communication is improved, and a foundation is laid for the future complex and multifunctional marine VDE communication application.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE, which solves the problem of multi-user signal aliasing collision existing in a data confirmation signaling channel and a random access channel in satellite-borne VDE communication.

In order to achieve the above purpose, the technical solution for solving the technical problem is as follows:

a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE comprises the following steps:

step 1: carrying out down-conversion and filtering on satellite-borne received VDE signals, carrying out UTC time slot correction alignment and data interception of a GPS, and carrying out FFT (fast Fourier transform) correlation operation on front 4096 sampling points and a zero-filled local frame header sequence in the intercepted whole frame data;

step 2: taking 64 points as the size of a bottom noise sliding window, sliding to find a minimum power window of 4096-point correlation peak values of any frequency, calculating a bottom noise average amplitude value, and taking a fixed multiple of the bottom noise average amplitude value as a bottom noise threshold;

and step 3: sequentially finding 64 correlation peak values with amplitude larger than the background noise threshold and larger than the amplitude, recording the 64 correlation peak values as a maximum correlation peak group, eliminating a secondary large correlation peak value and other correlation peak values in the same region by using a two-dimensional region scanning algorithm consisting of frequency deviation and time delay, and selecting a maximum value to avoid false detection in the same region;

and 4, step 4: and carrying out interference elimination on side lobe burrs of a CPM related inherent frequency domain.

Further, in step 3, the two-dimensional region scanning algorithm starts with the maximum correlation peak value, scans other peak values of the maximum correlation peak group, and rejects the maximum correlation peak group if the maximum correlation peak is found in the same region as the maximum correlation peak; similarly, finding a second maximum value in the maximum correlation peak group after being removed, scanning other peak values of the maximum correlation peak group, and removing the maximum correlation peak group if the second maximum correlation peak is found to be in the same region; scanning in turn according to the method to find out a single maximum correlation peak value in each different area.

Further, in step 4, the single maximum correlation peak values in different areas found in step 3 need to be subjected to CPM correlation inherent frequency domain side lobe elimination, the inherent side lobes are related to the spreading and oversampling multiples of CPM, according to the relation of the spreading and oversampling multiples, two-dimensional area scanning elimination is performed on the side lobe frequency area, and finally the eliminated maximum correlation peak group is the required multi-user detection frequency and delay position.

Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:

the invention provides a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE, which is designed by combining the maximum demodulation capacity of satellite-borne VDE uplink QPSK-CPM spread spectrum and facing to a multi-user complex time slot conflict environment, and the invention eliminates the interference of CPM frequency domain sidelobes, enhances the multi-user accurate detection capacity of aliasing of strong signals and weak signals, reduces the complexity of frame header synchronous scanning search and hardware realization difficulty, prevents the false detection of the same region of related peaks and the influence of strong signal related peak sidelobes on weak signal detection, and improves the comprehensive processing capacity of a plurality of aliased user signals.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:

FIG. 1 is a flowchart illustrating an implementation of a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE according to the present invention;

FIG. 2 is a VDE satellite communication timeslot assignment scheme;

FIG. 3 is a three-dimensional graph of correlation peaks of a QPSK-CPM spread spectrum signal for a single user;

FIG. 4 is a diagram of a delay direction correlation peak at a frequency offset of a signal peak;

FIG. 5 is a plot of the direction of the frequency offset correlation peak at the peak delay of the signal;

FIG. 6 is a diagram of a side lobe correlation peak in the frequency offset direction at the time delay of the peak of the signal;

FIG. 7 is a three-dimensional graph of correlation peaks after QPSK-CPM spread spectrum signal aliasing for 8 users;

FIG. 8 is a diagram of delay direction correlation peaks after mixing and overlapping QPSK-CPM spread spectrum signals for 8 users;

FIG. 9 is a diagram of frequency offset direction correlation peaks after mixing and overlapping 8 users QPSK-CPM spread spectrum signals;

fig. 10 is a diagram of the peak values of the frequency offset direction correlation after the two user signals with 12dB power difference are mixed.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the present embodiment discloses a QPSK-CPM spread spectrum multi-user detection method based on satellite-borne VDE, which includes the following steps:

step 1: carrying out down-conversion and filtering on satellite-borne received VDE signals, carrying out UTC time slot correction alignment and data interception of a GPS, and carrying out FFT (fast Fourier transform) correlation operation on front 4096 sampling points and a zero-filled local frame header sequence in the intercepted whole frame data;

step 2: taking 64 points as the size of a bottom noise sliding window, sliding to find a minimum power window of 4096-point correlation peak values of any frequency, calculating a bottom noise average amplitude value, and taking a fixed multiple of the bottom noise average amplitude value as a bottom noise threshold;

and step 3: sequentially finding 64 correlation peak values with amplitude larger than the background noise threshold and larger than the amplitude, recording the 64 correlation peak values as a maximum correlation peak group, eliminating a secondary large correlation peak value and other correlation peak values in the same region by using a two-dimensional region scanning algorithm consisting of frequency deviation and time delay, and selecting a maximum value to avoid false detection in the same region;

and 4, step 4: and carrying out interference elimination on side lobe burrs of a CPM related inherent frequency domain. The efficient regional scanning algorithm can effectively reduce the hardware resource occupation of multi-user detection, improves the accuracy and effectiveness of QPSK-CPM spread spectrum multi-user detection of satellite-borne VDE, and enhances the processing capability of multi-user detection.

Further, in step 3, the two-dimensional region scanning algorithm starts with the maximum correlation peak value, scans other peak values of the maximum correlation peak group, and rejects the maximum correlation peak group if the maximum correlation peak is found in the same region as the maximum correlation peak; similarly, finding a second maximum value in the maximum correlation peak group after being removed, scanning other peak values of the maximum correlation peak group, and removing the maximum correlation peak group if the second maximum correlation peak is found to be in the same region; scanning in turn according to the method to find out a single maximum correlation peak value in each different area.

Further, in step 4, the single maximum correlation peak values in different areas found in step 3 need to be subjected to CPM correlation inherent frequency domain side lobe elimination, the inherent side lobes are related to the spreading and oversampling multiples of CPM, according to the relation of the spreading and oversampling multiples, two-dimensional area scanning elimination is performed on the side lobe frequency area, and finally the eliminated maximum correlation peak group is the required multi-user detection frequency and delay position.

Specifically, the G1139 VDES standard defines that a Link ID 20 physical layer frame format, such as a DSCH (data acknowledgment signaling) timeslot channel and an RAC (random access) timeslot channel in fig. 2, must be used for a data acknowledgment signaling channel and a random access channel in a satellite uplink, and the Link ID 20 physical layer frame format is a QPSK-CPM spread spectrum modulation method, where CPM spreading uses a CPM waveform to perform 16-fold spreading on QPSK modulated signals. Due to the fact that multi-user competition exists during random access, the QPSK-CPM spread spectrum multi-user detection capability is improved, and the random access capability of the user can be effectively improved. In order to improve the multi-user communication and access efficiency of a satellite-borne VDE communication system and effectively receive user information, the embodiment provides a QPSK-CPM spread spectrum multi-user detection method based on the satellite-borne VDE, a two-dimensional region scanning rejection algorithm consisting of frequency deviation and time delay is adopted to select a maximum value, other values in the same region are rejected, false detection is avoided, frequency domain burrs inherent to the CPM are rejected in an interference mode, the accuracy and effectiveness of CPM spread spectrum multi-user detection are improved, and a foundation is laid for the future complex and multifunctional marine VDE signal communication application.

The main physical layer indexes of the satellite uplink Link ID 20 defined by the G1139 VDES standard are as follows:

Link ID	20
		channel bandwidth	50KHz
Bandwidth of signal	42KHz
		CPM spreading chip rate	33.6kcps
Multiple of spread spectrum	16 times of
		Symbol rate	2.1Ksps
Burst signal occupancy	5 time slots
		Burst signal duration	125.3ms
Length of sync word	48 symbols
		Synchronous word and data modulation scheme	QPSK-CPM spread spectrum
Number of symbols of burst signal	263 are provided with

Firstly, a satellite receives QPSK-CPM spread spectrum signals in a Link ID 20 physical layer frame format according to a received data confirmation signaling determined by a protocol layer and a corresponding time slot of a random access channel, after down-conversion is carried out on the received VDE signals, sampling processing is carried out at 4 times of symbol rate (the chip rate of CPM spread spectrum is 33.6Kcps, the 4 times of sampling rate is 134.4KHz), according to a satellite-to-ground signal transmission delay range calculated in a G1139 VDES standard, time correction of a corresponding time slot UTC of the received GPS signals and interception of the whole frame data starting at the 2ms (corresponding to 269 sampling points) time are carried out, and in the intercepted whole frame data, front 4096 sampling points and a local frame header sequence after zero padding are taken to carry out FFT correlation operation, wherein the sequence composition of the local 4096 sampling points is as follows: the frame header is 48 symbols x 16 times spread x 4 times samples +1024 0 complements.

The scanning correlation method is to perform two-dimensional scanning correlation on frequency and time delay, wherein, because 4 times of sampling is selected, the sampling rate is 134.4KHz, 4096-point cyclic shift FFT is performed on a local sequence, 1 bit is shifted in each cycle, the frequency stepping is 32.8Hz (namely 134.4KHz is divided by 4096 points), according to the satellite orbit Doppler frequency shift and the antenna coverage angle range proposed in the VDES standard of G1139, the satellite receiving maximum frequency offset range is +/-4.5 KHz, namely 275-point frequency scanning (namely 9KHz is divided by 32.8Hz) is required, and the maximum frequency offset range of +/-4.5 KHz can be covered.

The correlation of local and external input data is equivalent to circular correlation in the time domain, and the time domain convolution is equivalent to frequency domain multiplication, i.e. the circular correlation in the time domain and the FFT in the frequency domain have the following relationship:

where x (k), y (k) are the fourier transforms of x (k), y (k), respectively, "+" indicates the conjugate.

For the above correlated signal r_xyAnd (m) taking an absolute value, and then carrying out maximum value detection on the correlation peak value after the absolute value is taken.

Based on the frequency and delay two-dimensional scanning correlation results, 275 groups of 4096-point correlation peak values are generated in total, for example, the three-dimensional result of the correlation peak of the QPSK-CPM spread spectrum signal in the case of a single user is shown in FIG. 3; the delay direction correlation peak value is as shown in fig. 4, because the spread spectrum chip is oversampled by 4 times, the width area of the delay direction correlation peak value is within +/-5 sampling points; the peak value of the frequency deviation direction correlation is shown in fig. 5, the frequency step is 32.8Hz, and the width area of the frequency direction correlation peak is within ± 2 frequency deviation points (i.e., ± 65.6 Hz).

In addition, after the observation range of the frequency deviation direction is expanded, as shown in fig. 6, 2 related peak side-lobe signals with smaller amplitude are also arranged on two sides of the main peak of the frequency deviation direction at the same delay position.

According to the related peak characteristics of the QPSK-CPM spread spectrum signal, the size of the rejection region is selected as +/-5 sampling points for recording the maximum peak delay position, and +/-65.6 Hz of the maximum peak frequency offset position is the rejection region.

And taking any 4096 point correlation peak values in 275 groups and calculating a bottom noise threshold value. The method for calculating the background noise threshold value is to set the size of a background noise sliding window to be 64 points, for example, slide and find a 64-point window with 4096-point correlation peak value minimum power to calculate a background noise average value, and use 8 times of the minimum background noise window average amplitude value as the background noise threshold for eliminating subsequent background noise signals.

And (4) carrying out pipeline comparison on the generated 275 groups of 4096-point correlation peak values and a background noise threshold, directly rejecting the correlation peak values if the correlation peak values are smaller than the threshold, recording and comparing the correlation peak values with the previous maximum values if the correlation peak values are larger than the threshold, and recording a plurality of maximum values and positions (64 maximum records) corresponding to frequency and delay time in a descending order.

The general processing method is that the sampling is firstly carried out by the maximum peak value time delay grouping and then the frequency offset removing method, the processing is complex, the calculated amount is large, and the innovative region scanning removing method is adopted to remove the signals in the same region.

In order to enhance the multi-user detection capability, particularly for the detection of a correlation peak of a signal with a smaller amplitude in multi-user aliasing, interference elimination needs to be performed on the frequency domain burrs inherent to the CPM autocorrelation so as to avoid false detection and improve the accuracy and effectiveness of CPM spread spectrum multi-user detection.

Firstly, rejecting 1 st area signal, using +/-5 sampling points of the recorded maximum peak position, using +/-65.6 Hz of the maximum peak frequency as a rejection area, and rejecting 2-64 recorded peak values for the rejection area according to +/-5 sampling points of the side lobe burr signal of the inherent frequency domain of the 1 st area, wherein +/-65.6 Hz of the side lobe frequency of the inherent frequency domain is the rejection area, and the unreleased peak values are sequentially numbered as 2, 3, 4; rejecting a 2 nd area signal, and rejecting 2 nd to 64 th recording peak values and rejecting 3 rd to 64 th recording peak values by using +/-5 sampling points of the newly recorded 2 nd signal peak value position and +/-65.6 Hz of the peak frequency as a rejection area, and for +/-5 sampling points of the burr signal of the side lobe of the natural frequency domain of the 2 nd area, and +/-65.6 Hz of the burr frequency of the side lobe of the natural frequency domain as the rejection area, wherein the unreleased peak values are sequentially marked as 3, 4, 5,; the 8 th area is removed in sequence according to the method, and the peak value of the 8 areas can be found. And performing frequency compensation according to the frequency offset positions of the 8 regional peaks, intercepting by taking the maximum peak delay position of each region as the position of data delay interception, intercepting the current frame data, and sending the current frame data to a subsequent despreading and demodulation program for despreading and demodulation.

The following uses 8 user aliasing and two user signal aliasing with larger power difference as an example to further explain the usage of this method.

Fig. 7 is a three-dimensional graph of correlation peaks after QPSK-CPM spread spectrum signal mixing and superposition for 8 users, fig. 8 is a graph of delay direction correlation peaks at signal peak frequency offset, and fig. 9 is a graph of frequency offset direction correlation peaks at signal peak delay. The single maximum peak value in the 8 maximum peak value areas can be found by the specific method, the relevant peak frequency offset and the time delay position of 8 users can be accurately and effectively distinguished, and the relevant peak frequency offset and the time delay position are sent to the subsequent de-spread demodulation.

Generally, the power difference of VDE signals received by a satellite is not large, if two user signals with large power difference are aliased, for example, the difference is 12dB, the correlation result is as shown in fig. 10, and the sidelobe peak value of the correlation peak of a large signal is larger than the main correlation peak value of a weak signal, so that the sidelobe frequency offset signal of the large signal needs to be removed in an area. According to the specific method, after the relevant main peak of the strong signal is judged, the fixed frequency deviation positions at the two sides of the strong signal are subjected to region elimination, the peak value region of the side lobe of the strong signal can be eliminated, the 2 nd maximum peak value region search is carried out on the rest region, the relevant main peak value of the weak signal can be found, and the interception and the subsequent despreading and demodulation of the weak signal are not influenced.

The above parameters are the best ones, and the reason is: 4096-point correlation is selected because the FFT correlation butterfly length should be selected to be the N power of 2, and 4096-point FFT can cover the length of 48 synchronization head spread spectrum symbols of VDE, and 1024-point margin outside the synchronization head length can satisfy the satellite-to-ground signal transmission delay difference range of 8 ms; through simulation and FPGA realization analysis, the hardware resource occupation of the area scanning rejection algorithm is far smaller than that of the conventional two-dimensional sequential comparison rejection algorithm.

According to the QPSK-CPM spread spectrum multi-user detection method based on the satellite-borne VDE, a novel two-dimensional region scanning rejection algorithm formed by frequency deviation and time delay is adopted, the maximum value is selected, all other values in the same region are rejected, false detection is avoided, region interference rejection is performed on side lobe burrs of a CPM inherent frequency domain, accuracy, effectiveness and access efficiency of CPM spread spectrum multi-user detection are improved, and a foundation is laid for future complex and multifunctional marine VDE signal communication application.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.