CN115685268A

CN115685268A - Data demodulation judgment method based on low-orbit MCSK modulation

Info

Publication number: CN115685268A
Application number: CN202310000525.4A
Authority: CN
Inventors: 陈永刚; 曹海涛
Original assignee: Chengdu Qixin Microelectronics Co ltd
Current assignee: Chengdu Qixin Microelectronics Co ltd
Priority date: 2023-01-03
Filing date: 2023-01-03
Publication date: 2023-02-03
Anticipated expiration: 2043-01-03
Also published as: CN115685268B

Abstract

The invention discloses a data demodulation decision method based on low-orbit MCSK modulation, which comprises the following steps: s1: an FFT operation unit is arranged in the multi-channel MCSK integral circuit for operation; s2: the FFT arithmetic unit supports 4096-point FFT, a single arithmetic unit is compatible with FFT and IFFT calculation, and single channel scheduling can carry out 3 rounds of FFT arithmetic; s3: while the operation is carried out, the MCSK multi-path integrating circuit finishes the carrier removal and down sampling d (i) of data and sends out the down sampling d (i) of 24 channels; s4: arbitrating the sent 24-channel downsampling data, and applying an FFT (fast Fourier transform) operation unit to calculate a cycle integral; s5: the FFT of the PRN is computed by the pre-fetch mechanism at the channel time immediately preceding the current channel, denoted as y0.

Description

Data demodulation judgment method based on low-orbit MCSK modulation

Technical Field

The invention relates to the field of GNSS, in particular to a high dynamic GNSS tracking method.

Background

In a binary spread spectrum modulation mode used by a traditional GNSS signal, only 1bit of information is transmitted by a waveform of a plurality of spread spectrum periods, and the frequency band utilization rate is not high. The information rate can be effectively improved under the condition of not changing the parameters of the spread spectrum codes by the commonly adopted multilevel modulation of the low-orbit LEO satellite, and the CSK modulation is a novel multilevel modulation mode and has the advantages of high information rate and high flexibility.

However, compared with the traditional navigation bit information demodulation, the navigation bit information decision computation amount of each code period is increased by tens of times, which brings challenges to hardware implementation.

Disclosure of Invention

The invention aims to: when receiving multipath satellite, the channel number is the number of satellite channels multiplied by the number of channels, the result is very huge, and a large amount of hardware resources are occupied for calculation.

The technical scheme adopted by the invention is as follows: a data demodulation decision method based on low-orbit MCSK modulation comprises the following steps: s1: setting an FFT operation unit in the multi-channel MCSK integral circuit for operation; s2: the FFT arithmetic unit supports 4096-point FFT, a single arithmetic unit is compatible with FFT and IFFT calculation, and single channel scheduling can carry out 3 rounds of FFT arithmetic; s3: while the operation is carried out, the MCSK multi-path integrating circuit finishes the carrier removal and down sampling d (i) of data and sends out the down sampling d (i) of 24 channels; s4: arbitrating the sent down-sampled data of each channel of the 24 channels, and applying for an FFT (fast Fourier transform) operation unit to calculate a cycle integral; s5: calculating FFT of PRN at the time of a channel before the current channel by a pre-fetching mechanism, and marking as y0, calculating a down-sampled data FFT result of the arbitrated channel by an FFT operation unit, and marking as y1; s5: taking the first 64 values of the IFFT result after calculation through an operation formula, and comparing the moduli of the 64 values, wherein the maximum value is the required integral phase; s6: and determining 6 bit demodulation results of the MCSK for obtaining the current channel according to the position (0-63) of the maximum value.

The traditional satellite channel modulation is usually modulated by CSK, the CSK modulation is a multi-system orthogonal signal essentially, the principle is that a basic spread spectrum sequence is circularly shifted to represent different symbols, each bit is circularly shifted backwards by n positions on the basis of a basic spread spectrum code, a section of new spread spectrum code can be obtained, and the section of code can be used for representing a symbol n. The CSK modulation is determined by 2 parameters, the number of bits U per symbol and the number of repetitions N of the spreading code in each symbol period, denoted CSK (U, N)

Wherein:

is a basic spreading code, C is

The number of chips that are crossed per cycle,

for a series of modulation codes generated by cyclic shifting, tc is the chip spacing,

is the number of shifts of the code of the x-th symbol compared to the basic spreading code.

In the receiving aspect, in each symbol period, a fixed code sequence is used for despreading in conventional GNSS tracking demodulation, and the operation formula is as follows:

cm is a spread spectrum sequence and dm is a data sequence after tracking down-sampling

For receiving the MCSK signal, it is necessary to calculate the results of multiple code phases at the same time, and compare the respective accumulated results of multiple code phases to determine the current demodulation symbol. The formula is as follows:

such as MCSK-R (6, 1) modulation, M is 64, and the despreading results of 64 paths are calculated in parallel.

Further, the multi-channel MCSK integrating circuit in step S1 obtains the modulation data by receiving the MCSK signal.

Further, after reception through the MCSK signal, the result is obtained by simultaneously calculating several code phases.

Further, the current demodulation symbol is judged by comparing the respective accumulation results of a plurality of code phases.

Furthermore, the operation formula in step S5 is to take y1 as a conjugate and multiply it by y0, the result is denoted as y2, and y2 is used to calculate IFFT.

Further, when the arbitration in step S4 is that the integral value of a single channel is valid, FFT operation is applied, and the operation adopts a first-come first-calculated mechanism, and if the integral values arrive at the same time, the channel numbers are sorted according to the channel numbers, and the sorting position with the lower channel number is earlier.

Further, the FFT operation in step S1 adopts a long-point FFT operation.

Further, in step S5, when performing the 64-channel parallel operation, the first 64 values of the IFFT result are taken, and after the IFFT result is upgraded to the 128-channel parallel operation, the corresponding first 128 values of the IFFT result are taken.

Further, in step S5, when performing the 64-channel parallel operation, the first 64 values of the IFFT result are taken, and after the IFFT result is upgraded to the 256-channel parallel operation, the corresponding first 256 values of the IFFT result are taken.

Further, the multichannel MCSK integrating circuit adopts 64-path phase parallel operation.

Further, the arbitration in step S4 arbitrates channel down-sampled data every millisecond.

The invention has the following beneficial effects:

according to the data demodulation judgment method based on low-orbit MCSK modulation, the FFT method is adopted for calculating 64-path phase results in parallel, the result is selected to be large to judge the demodulation result, however, only one path of FFT operation unit is adopted, hardware resources are greatly reduced, meanwhile, related operation of FFT is high in efficiency, and area consumption is even smaller than that of single-path 64-path parallel operation. The FFT computation correlation is only one of the methods, not the only one. The FFT operation with long points adopted by the method is very convenient for multi-path (at present 64 paths) phase calculation, and the subsequent upgrade is carried out to 128 paths or 256 paths, the hardware circuit can be upgraded only by carrying out very little parameter modification, while the traditional parallel multi-path related method needs to copy correspondingly increased paths, and the upgrade is very inconvenient.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a block diagram of an operation algorithm of a multi-channel MCSK integration circuit in the method of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

Example 1

As shown in fig. 1, a data demodulation decision method based on low-track MCSK modulation includes the following steps: s1: setting an FFT operation unit in the multi-channel MCSK integral circuit for operation; s2: the FFT arithmetic unit supports 4096-point FFT, a single arithmetic unit is compatible with FFT and IFFT calculation, and single channel scheduling can carry out 3 rounds of FFT arithmetic; s3: while carrying out operation, the MCSK multi-path integrating circuit finishes carrier removal and down sampling d (i) of data and sends out down sampling d (i) of 24 channels; s4: arbitrating the sent 24-channel downsampling data, and applying an FFT (fast Fourier transform) operation unit to calculate a cycle integral; s5: calculating FFT of PRN at the time of a channel before the current channel by a pre-fetching mechanism, and marking as y0, calculating a down-sampled data FFT result of the arbitrated channel by an FFT operation unit, and marking as y1; s5: calculating by an operation formula, then taking the first 64 values of the IFFT result, comparing the moduli of the 64 values, and taking the maximum value as the required integral phase; s6: and determining 6 bit demodulation results of the MCSK for obtaining the current channel according to the positions (0 to 63) of the maximum value.

The specific operation steps of the algorithm are as follows: because the parallel computation of 64 paths of integrals consumes huge resources, the design designs 64 paths of computation and maximum judgment into an independent computation module, and each channel shares the computation resources.

The calculation of 64-way shift correlation uses FFT to calculate the correlation function, thus eliminating the time required for the code phase sliding process. The capturing method based on the FFT has the advantages that the fast FFT calculation can further reduce the resource consumption, and in order to further shorten the calculation time, the channel can be pre-calculated, so that the time for calculating the FFT in one round is saved. The algorithm block diagram is shown in fig. 1.

In the traditional implementation method, 64 paths of correlation operation are independently designed in each channel, and after parallel computation, the maximum power of one path is judged according to the result to be used as the demodulation judgment result, so that when multiple paths of satellites are received, the number of the channels is the number of the satellite paths multiplied by 64, the result is very large, and a large amount of hardware resources are occupied. The method adopts the FFT method to calculate 64 paths of phase results in parallel, also adopts the result selection to judge the demodulation result, but the FFT arithmetic unit only has one path, thus greatly reducing the hardware resource, simultaneously, the FFT is used for the related arithmetic to realize the high efficiency, and the area consumption is even less than the 64 paths of parallel arithmetic of a single channel. The FFT computation correlation is only one of the methods, not the only one. The long-point FFT operation adopted by the method is very convenient for multi-path (at present, 64 paths) phase calculation, and the subsequent upgrade is carried out to 128 paths or 256 paths, and the hardware circuit can be upgraded only by carrying out very little parameter modification, while the traditional parallel multi-path related method needs to copy the correspondingly increased paths, and the upgrade is very inconvenient.

In the step S1, the multi-channel MCSK integrating circuit obtains the modulation data by receiving the MCSK signal. After receiving through the MCSK signal, the result of several code phases is calculated simultaneously. The current demodulated symbol is decided by comparing the respective accumulated results of several code phases. The operation formula in step S5 is to take y1 as conjugate and then multiply it with y0, the result is denoted as y2, and y2 is used to calculate IFFT. If the arbitration in step S4 is that the integral value of a single channel is valid, FFT operation is applied, and the operation adopts a first-come first-calculated mechanism, and if the integral values arrive at the same time, the channel numbers are sorted according to the channel numbers, and the sorting position with the lower channel number is in the front. The FFT operation in step S1 adopts a long-point FFT operation.

In step S5, when performing the parallel operation of 64 channels, the first 64 values of the IFFT result are taken, and after the parallel operation of 128 channels is upgraded, the corresponding first 128 values of the IFFT result are taken. In step S5, when performing the parallel operation of 64 channels, the first 64 values of the IFFT result are taken, and after the parallel operation of 256 channels is upgraded, the corresponding first 256 values of the IFFT result are taken. The multi-channel MCSK integrating circuit adopts 64-path phase parallel operation. The arbitration in step S4 is to arbitrate the channel down-sampled data every millisecond.

The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

1. A data demodulation decision method based on low-orbit MCSK modulation is characterized by comprising the following steps:

s1: setting an FFT operation unit in the multi-channel MCSK integral circuit for operation;

s2: the FFT arithmetic unit supports 4096-point FFT, a single arithmetic unit is compatible with FFT and IFFT calculation, and single channel scheduling can carry out 3 rounds of FFT arithmetic;

s3: while the operation is carried out, the MCSK multi-path integrating circuit finishes the carrier removal and down sampling d (i) of data and sends out the down sampling d (i) of 24 channels;

s4: arbitrating the sent 24-channel downsampling data, and applying an FFT (fast Fourier transform) operation unit to calculate a cycle integral;

s5: calculating FFT of PRN at the time of a channel before the current channel comes by a pre-fetching mechanism, and marking as y0, calculating a down-sampled data FFT result of the arbitrated channel by an FFT arithmetic unit, and marking as y1;

s5: calculating by an operation formula, then taking the first 64 values of the IFFT result, comparing the moduli of the 64 values, and taking the maximum value as the required integral phase;

s6: and determining 6 bit demodulation results of the MCSK for obtaining the current channel according to the position (0-63) of the maximum value.

2. The data demodulation decision method based on low-track MCSK modulation according to claim 1, wherein in step S1, the multi-channel MCSK integrating circuit obtains the modulation data through receiving MCSK signals.

3. The method for data demodulation decision based on low-orbit MCSK modulation according to claim 2, characterized in that after MCSK signal reception, the result of several code phases is calculated simultaneously.

4. The method as claimed in claim 3, wherein the current demodulation symbol is determined by comparing the accumulated result of several code phases.

5. The method for demodulating and deciding data based on low-orbit MCSK modulation as claimed in claim 1, wherein the operation formula in step S5 is to take conjugate of y1 and then multiply y0, the result is recorded as y2, and y2 is used to calculate IFFT.

6. The method as claimed in claim 1, wherein when the arbitration in step S4 is that the integral value of a single channel is valid, FFT operation is applied, and the operation adopts a first-come-first-serve mechanism, and if the integral values arrive at the same time, the data are sorted according to the channel number, and the sorting position of the channel number is earlier.

7. The method for demodulating and deciding data based on low-track MCSK modulation according to claim 1, wherein the FFT operation in step S1 is a long-point FFT operation.

8. The method for determining data demodulation based on low-track MCSK modulation according to claim 1, wherein the first 64 IFFT results are taken when 64 channels are operated in parallel in step S5,

after the parallel operation is upgraded to 128 paths, the corresponding first 128 values of the IFFT result are taken;

or after upgrading to 256 paths of parallel operation, taking the corresponding first 256 values of the IFFT result.

9. The low-orbit MCSK modulation-based data demodulation decision method as claimed in claim 1, wherein the multichannel MCSK integrating circuit adopts 64-way phase parallel operation.

10. The low-orbit MCSK modulation-based data demodulation decision method as claimed in claim 1, wherein the arbitration in step S4 is to arbitrate channel downsampled data every millisecond.