CN111262618B - Solution method for multi-target measurement and control signal parallel access based on same pseudo code - Google Patents

Abstract

The invention provides a solution of multi-target measurement and control signal parallel access based on the same pseudo code, firstly, a reasonable energy accumulation strategy is formulated by combining link parameters and receiver indexes, wherein the energy accumulation strategy comprises coherent accumulation times, non-coherent accumulation times and frequency search stepping; comparing the amplitude of the signal after energy accumulation by combining an empirical judgment threshold, and storing the amplitude, the phase and the frequency offset information which are greater than the threshold in a storage area; after one round of search is completed, different measurement and control signals are distinguished through phase and frequency offset information. The invention uses the same pseudo code as the only spread spectrum code in the measurement and control system facing future commercial spaceflight, can fully utilize the capture module resource, realize the real-time access of multi-target measurement and control signals, finally realize the purpose of single station multi-receiving, greatly improve the measurement and control capability of the measurement and control system and reduce the consumption of hardware resources.

Description

Solution method for multi-target measurement and control signal parallel access based on same pseudo code

Technical Field

The invention relates to signal capture and tracking in a foundation measurement and control system, in particular to a solution of multi-target measurement and control signal parallel access based on the same pseudo code.

Background

The low-earth satellite has a short communication time delay, a high data transmission rate and a high integration level of the mobile terminal, and has a wide application prospect in the 5G/6G communication era. A plurality of enterprises such as one network company (OneWeb), space exploration company (SpaceX), Boeing, Low-orbit satellite company (Leosat) and the like propose and create a satellite constellation consisting of low-orbit satellites and provide Internet access service for the whole world. Meanwhile, the aerospace science and technology group and the aerospace science and technology group in China also respectively put forward low-orbit satellite constellation plans such as 'rainbow cloud', 'swan' and the like, and the autonomous controllable satellite-borne broadband global Internet is constructed by networking. Meanwhile, the number of satellites passing through the same time increases dramatically, and the measurement and control station is under great pressure.

Fig. 1 shows a conventional single-station multi-reception mode, in which multiple sets of servo terminals are provided at a ground station to complete multi-target monitoring by using CDMA technology, which undoubtedly causes great waste of hardware resources. Or combining CDMA and SDMA modes, and simultaneously utilizing space domain information and CDMA technology to jointly improve the measurement and control capability of the measurement and control station, and the method can simultaneously measure and control dozens of satellites. Combining the constellation creation plan of China, simulating the average value in a single beam of the measurement and control station when the number of low-orbit satellites is about 2000 by using STK software, as shown in table 1. The average value of the number of satellites in a single wave beam floats between 7 and 15, and meanwhile, the number of satellites passing through the same antenna is more than 60, so that the existing measurement and control capability of a measurement and control station is difficult to meet the measurement and control requirement.

Table 1 is the average of the number of visible satellites in a single beam simulated by software;

disclosure of Invention

Aiming at the technical problem, the invention provides a solution for multi-target measurement and control signal parallel access based on the same pseudo code, which comprises the following steps:

s1, recording the expression after the carrier frequency of n-path test control signals spread by using the same pseudo code is stripped as follows:

where r (t) is the baseband signal at the receiving end, S_kFor the k-th path in the multi-path parallel signal, A_kIs the k-th signal amplitude, D_kFor the kth drive test control signal data, C (t) is a unique spreading pseudo code, t_kFor the time delay corresponding to the k-th signal, f_kFor the k-th path of residual frequency offset,

the k-th residual carrier phase, n (t), is noise.

S2, determining single coherent accumulation time t by combining link parameters and receiver system indexes_cohNumber of coherent accumulations m₁Number of incoherent times m₂(ii) a While calculating the total coherent accumulation time T_totalAnd frequency offset search step f_bin:

T_total＝t_coh*m₁；

S3, performing FFT with the length of N on a local pseudo code sequence C which is the same as the transmitting pseudo code sequence in advance, and placing data in a memory after taking conjugation;

s4, stepping the received signal according to the search f_binResidual frequency offset compensation is carried out, and then the data stream is processed according to the time length t_cohSegment by segment, m₁Segment data are correspondingly added to finish coherent energy accumulation, the data after coherent accumulation is multiplied by the data in S3 correspondingly after N-point FFT, IFFT is taken to finish energy correlation, and the amplitude value of the IFFT result is taken and accumulated by m according to the period N₂Completing the incoherent energy accumulation;

s5, after the incoherent accumulation is completed, taking the multiple of the mean value of the section of data as a judgment threshold, generally an empirical value, and then comparing the section of data with the threshold one by one;

s6, recording the pseudo code phase phi exceeding the threshold in S5_kAnd each corresponding Doppler residual frequency offset f_kAnd the non-coherent accumulated amplitude a_kAnd bound into a set of data;

s7, multi-target capture judgment strategy: in a multi-frequency point parallel search process, the successfully captured data in S6 are stored in the memory in the order of smaller phase to larger phase. After the search is finished, the difference between every two adjacent groups of data is made, and the difference is phi_ΔkWhen the number of the chips is more than 1, the signals are regarded as two paths of different signals; comparing the residual frequency difference f of two groups of data when the difference is less than or equal to 1 chip_ΔkIf the residual difference is larger than the Doppler spread range f when the signal power is strongest_dopThen, the signals are regarded as two paths of different signals; otherwise, the same signal is captured, one path of data with a smaller peak value is removed, and S7 is repeated until each path of signal is independent;

s8, capturing the signals, sequentially switching to a plurality of tracking modules, completing despreading, demodulating, distinguishing different signals through data information, referring to demodulation of direct sequence signals in the specific process, then releasing the current tracking module, and repeating the steps S4-S8.

The solution of the parallel access of the multi-target measurement and control signals based on the same pseudo code provided by the invention is a parallel access method of the multi-target measurement and control signals using the same pseudo code in a burst mode, and can fully utilize the resources of a capture module and realize the real-time access of the multi-target measurement and control signals using the same pseudo code. Firstly, combining link parameters and receiver indexes to formulate a reasonable energy accumulation strategy, wherein the energy accumulation strategy comprises coherent accumulation times, non-coherent accumulation times and frequency search stepping; comparing the amplitude of the signal after energy accumulation by combining an empirical judgment threshold, and storing the amplitude, the phase and the frequency offset information which are greater than the threshold in a storage area; after one search is completed, different measurement and control signals are distinguished through phase and frequency offset information. The invention uses the same pseudo code as the only spread spectrum code in the measurement and control system facing the future commercial spaceflight, can fully utilize the capture module resource, realize the real-time access of the multi-target measurement and control signal, finally realize the purpose of single station multi-receiving, greatly improve the measurement and control capability of the measurement and control and reduce the consumption of hardware resources.

Drawings

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a single-station multi-receiving of a conventional measurement and control station;

FIG. 2 is a flow chart of multi-target signal access using the same pseudo code of the present invention;

FIG. 3 is a process flow of a detection decision module embodying the present invention;

FIG. 4 shows five signals detected by the capture module according to the present invention;

FIG. 5 is a specific judgment process of the detection judgment module according to the present invention;

fig. 6 is a demodulation constellation diagram of a weak target signal in five signals according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.

FIG. 2 is a flow chart of multi-target signal access using the same pseudo code of the present invention, FIG. 3 is a flow chart of determination based on phase and frequency offset detection, f_dopFor the maximum doppler spread range, as shown in the figure, the solution of the multi-target measurement and control signal parallel access based on the same pseudo code includes the following steps:

s1, recording the expression after the carrier frequency of n-path test control signals spread by using the same pseudo code is stripped as follows:

where r (t) is the baseband signal at the receiving end, S_kFor the k-th path in the multi-path parallel signal, A_kIs the k-th signal amplitude, D_kFor the kth drive test control signal data, C (t) is a unique spreading pseudo code, t_kFor the time delay corresponding to the k-th signal, f_kFor the k-th path of residual frequency offset,

the k-th residual carrier phase, n (t), is noise.

S2, determining single coherent accumulation time t by combining link parameters and receiver system indexes_cohNumber of coherent accumulations m₁Number of incoherent times m₂(ii) a While calculating the total coherent accumulation time T_totalAnd frequency offset search step f_bin:

T_total＝t_coh*m₁；

S3, performing FFT with the length of N on a local pseudo code sequence C which is the same as the transmitting pseudo code sequence in advance, and placing data in a memory after taking conjugation;

s4, stepping the received signal according to the search f_binResidual frequency offset compensation is carried out, and then the data stream is processed according to the time length t_cohSegment by segment, m₁Segment data corresponding addition completes coherent energyAccumulating, namely performing N-point FFT on the coherently accumulated data, then correspondingly multiplying the coherently accumulated data by the data in S3, then taking IFFT to complete energy correlation, and accumulating m by taking the amplitude of the IFFT result according to the period N₂Completing the incoherent energy accumulation;

s5, after the incoherent accumulation is completed, taking the multiple of the mean value of the section of data as a judgment threshold, generally an empirical value, and then comparing the section of data with the threshold one by one;

s6, recording the pseudo code phase phi exceeding the threshold in S5_kAnd each corresponding Doppler residual frequency offset f_kAnd the non-coherent accumulated amplitude a_kAnd bound into a set of data;

s7, multi-target capture judgment strategy: in a multi-frequency point parallel search process, the successfully captured data in S6 are stored in the memory in the order of smaller phase to larger phase. After the search is finished, the difference between every two adjacent groups of data is made, and the difference is phi_ΔkWhen the number of the chips is more than 1, the signals are regarded as two paths of different signals; comparing the residual frequency difference f of two groups of data when the difference is less than or equal to 1 chip_ΔkIf the residual difference is larger than the Doppler spread range f when the signal power is strongest_dopThen, the signals are regarded as two paths of different signals; otherwise, the same signal is captured, one path of data with a smaller peak value is removed, and S7 is repeated until each path of signal is independent;

s8, capturing the signals, sequentially switching to a plurality of tracking modules, completing despreading, demodulating, distinguishing different signals through data information, referring to demodulation of direct sequence signals in the specific process, then releasing the current tracking module, and repeating the steps S4-S8.

The present invention will now be described in detail with reference to the following examples,

fig. 1 is a schematic diagram of a conventional measurement and control algorithm, and the process is as follows: different pseudo code sequences are distributed to the aircrafts by combining a code division multiplexing mode, receiving terminals with the same pseudo codes as the different aircrafts are respectively provided at receiving ends, pseudo code matching is achieved, and then capturing, tracking, decoding and other work are completed.

If five measurement and control signals using the same pseudo code exist in the current environment, the received signals are as follows:

one path of weak signal E_bN₀Is 6.6dB, E of other four signals_bN₀All 18.6dB, the length of the pseudo code sequence C is 1023, the number of FFT points N is 4096, the pseudo code rate is 1.023Mhz, and the data rate is 1000 bps.

Single coherent integration time t_coh1ms, coherent integration time m₁Is 4 times, incoherent times m₂Also 4 times, total coherent integration time T_totalAt 4ms, the frequency offset search step f_binApproximately equal to 160 Hz.

In the signal capturing process, a multi-frequency point code domain parallel capturing mode is adopted, after frequency offset compensation and energy accumulation are completed, data is compared with a detection threshold, capturing is considered to be successful when the data is larger than the threshold, phase and frequency offset information corresponding to the data is stored in a fixed memory, no signal exists in the data when the data is smaller than the detection threshold, and the related peak accumulation effect is as shown in fig. 4. After the current multiple frequency offset search is completed, the stored phase and frequency offset information are compared to perform secondary signal detection and judgment, and finally five paths of signals are obtained, wherein the detection process is shown in fig. 5.

And simultaneously transferring the five captured signals to a plurality of tracking modules, and respectively demodulating data signals. The different signals are distinguished by data information. One of the weak signal demodulation constellations is shown in fig. 6. In the demodulation process, other four signals exist as noise relative to the target signal, and in the complete data accumulation period, the noise can be recorded as:

wherein, the time delay t of the target signal relative to other four-way signals_kGreater than the duration of one chip, where interference of other signals with the target signal may be considered multiple access interference. The total multipath interference power can be expressed as:

in the formula, P_J,kIs the power of the kth interference signal, N_cThe number of spread points.

The power spectral density of the multiple access interference can be equated to the power spectral density of stationary noise, i.e.

N_0,J＝P_J/R_b

In the formula, R_bIs the data rate. The receiver equivalent snr can then be expressed as:

substitution into N₀Interference power P of four strong signals of-174 dB_J,kIs-155.4 dB, the number of spread spectrum points N_cTo 1023, a data rate R_bIs 1000 bps. At the moment, the equivalent signal-to-noise ratio is 6.28dB, the demodulation performance is attenuated by 0.3dB, and the scheme has use value on the premise of meeting the requirement of the bit error rate.

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.

Claims (1)

1. The solution method for multi-target measurement and control signal parallel access based on the same pseudo code is characterized in that: the method comprises the following steps:

s1, recording the expression after the carrier frequency of n-path test control signals spread by using the same pseudo code is stripped as follows:

where r (t) is the baseband signal at the receiving end, S_kFor multiple parallel signalsPath k of (A)_kIs the k-th signal amplitude, D_kFor the kth drive test control signal data, C (t) is a unique spreading pseudo code, t_kFor the time delay corresponding to the k-th signal, f_kFor the k-th path of residual frequency offset,

is the k path residual carrier phase, n (t) is noise;

s2, determining single coherent accumulation time t by combining link parameters and receiver system indexes_cohNumber of coherent accumulations m₁Number of incoherent times m₂(ii) a While calculating the total coherent accumulation time T_totalAnd frequency offset search step f_bin：

T_total＝t_coh*m₁；

S3, performing FFT with the length of N on a local pseudo code sequence C which is the same as the transmitting pseudo code sequence in advance, and placing data in a memory after taking conjugation;

s4, stepping the received signal according to the search f_binResidual frequency offset compensation is carried out, and then the data stream is processed according to the time length t_cohSegment by segment, m₁Segment data are correspondingly added to finish coherent energy accumulation, the data after coherent accumulation is multiplied by the data in S3 correspondingly after N-point FFT, IFFT is taken to finish energy correlation, and the amplitude value of the IFFT result is taken and accumulated by m according to the period N₂Completing the incoherent energy accumulation;

s5, after the incoherent accumulation is completed, taking the multiple of the mean value of the section of data as a judgment threshold, generally an empirical value, and then comparing the section of data with the threshold one by one;

s6, recording the pseudo code phase phi exceeding the threshold in S5_kAnd each corresponding Doppler residual frequency offset f_kAnd the non-coherent accumulated amplitude a_kAnd bound into a set of data;

s7, a multi-target capture judgment strategy is adopted;

s71: in a multi-frequency point parallel search process, the successfully captured data in S6 are stored in a memory from small to large according to the phase;

s72: after the search is finished, making a difference between every two adjacent groups of data;

s73: phase difference phi_ΔkWhen the number of the chips is more than 1, the signals are regarded as two paths of different signals;

s74: phase difference phi_ΔkComparing the residual frequency difference f of two groups of data when the residual frequency difference is less than or equal to 1 chip_Δk；

S75: if the residual frequency difference f_ΔkGreater than the Doppler spread f when the signal power is strongest_dopThen, the signals are regarded as two paths of different signals;

s76: otherwise, the same signal is captured, one path of data with a smaller peak value is removed, and S7 is repeated until each path of signal is independent;

s8, capturing the signals, sequentially switching to a plurality of tracking modules, completing despreading, demodulating, distinguishing different signals through data information, referring to demodulation of direct sequence signals in the specific process, then releasing the current tracking module, and repeating the steps S4-S8.

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