Method and system of real-time transmission and demodulation of beidou satellite navigation signals

A method, comprising:

• S1:
• constructing small and medium-scale or large-scale or ultra-large-scale parallel signal transmission branches in a navigation satellite transmitter baseband chip FPGA to satisfy quasi-real-time or real-time transmission of subsequently grouped satellite navigation message, wherein the number of small and medium-scale parallel signal transmission branches is smaller than 100, the number of large-scale parallel signal transmission branches is not smaller than 100, and the number of ultra-large-scale parallel signal transmission branches is not smaller than 1000;
• S2:
• generating the satellite navigation messages according to a given structure or constructing the satellite navigation messages with same or different navigation information combinations as a data block with a given length through injection of a ground injection station or in a navigation satellite transmitter DSP chip, and grouping the satellite navigation messages in a set length unit or regrouping fragmented satellite navigation messages or packing the grouped messages based on a group sequence number, time to live and message length and so on, to form the grouped messages into a matrix, wherein performing grouping based on the satellite navigation message structure comprises performing grouping based on a super-frame or a main frame or a sub-frame or a word or a data block, or a bit number with a set length;
• S3:
• sequentially sending the grouped or group-coded satellite navigation messages in rows or columns or based on a given time slot, into the parallel signal transmission branches respectively;
• S4:
• performing a hybrid operation with single state variables or multi-state variables or a function containing different parameters by taking a non-linear strength as a weight, and forming a real part by designing one group of non-linear functions with different diffusion coefficients as weights;
• performing a hybrid operation with another type of single state variable or multi-state variables or a function containing different parameters by taking a non-linear strength as a weight, and forming an imaginary part by designing another group of non-linear functions with different diffusion coefficients as weights;
• driving the interactions of the non-linear functions based on an action value obtained by performing a hybrid operation with tap values of the correlation register, and constructing a non-linear function driven complex shift pseudo-random code generator with an action value obtained by performing the hybrid operation with the non-linear function action values as a feedback end or constructing the linear shift pseudo-code generator with at least two linear shift registers, wherein the real part and the imaginary part of the correlation register state value of the non-linear function driven complex shift pseudo-random code generator form a real part sub-pseudo random code generator and an imaginary part sub-pseudo random code generator respectively;
• S5:
• performing parameter setting for a series and a generated code length of the non-linear function driven complex shift pseudo-random code generator;
• S6:
• initializing the state value of the non-linear function driven complex shift pseudo-random code generator with same or different complex data;
• S7:
• outputting a pseudo-random number through one part of tap combinations of the real part and the imaginary part of the correlation register state value of the non-linear function driven complex shift pseudo-random code generator, obtaining a navigation satellite ranging code by a sorting method, binarization, and modulo-2 sum, and taking the code as the first or non-first parallel signal transmission branch-dedicated sub-ranging code, wherein the branch signal is used to detect existence of the navigation satellite navigation signal in an intercepted baseband satellite navigation signals;
• S8:
• outputting a pseudo-random number through another part of tap combinations of the real part and the imaginary part of the correlation register state value of the non-linear function driven complex shift pseudo-random code generator, and obtaining public sub-ranging codes of all navigation satellite parallel signal transmission branches, which are referred to as navigation satellite public sub-ranging codes, by the sorting method, the binarizaiton and the modulo-2 sum, wherein a sum of the number of all navigation satellite ranging codes and the number of all navigation satellite public sub-ranging codes is not greater than the total number of tap combinations of the real parts and the imaginary parts of all correlation registers state values of the non-linear function driven complex shift pseudo-random code generator, and the navigation satellite public sub-ranging codes are mutually correlated or uncorrelated or orthogonal or non-orthogonal or orthogonal in one part and non-orthogonal in another part;
• S9:
• obtaining remaining parallel signal transmission branch-dedicated sub-ranging codes of the navigation satellite which are referred to as navigation satellite-dedicated sub-ranging codes, by performing modulo-2 sum for the navigation satellite ranging codes and the navigation satellite public sub-ranging codes respectively, wherein these navigation satellite-dedicated sub-ranging codes have good cross correlation, and are stored in a file or a data buffer zone to satisfy a requirement of performing real-time spectrum spreading for the navigation message of each parallel signal transmission branch, and the navigation satellite ranging codes, navigation satellite public sub-ranging codes or the navigation satellite dedicated sub-ranging codes are synchronously driven by a same clock frequency-divided from a high precision and high stability atomic clock;
• S10:
• generating navigation satellite-dedicated sub-ranging codes in real time or obtaining navigation satellite-dedicated sub-ranging codes through the file or the data buffer zone and performing spectrum spreading for the grouped navigation messages in the parallel signal transmission branch respectively, or performing spectrum spreading for the grouped navigation messages with different navigation satellite dedicate sub-ranging codes so as to form single-channel signals after superimposition and allow the signals to be transmitted in the same parallel signal transmission branch, wherein the navigation satellite-dedicated sub-ranging codes are obtained in one of the manners;
• S11:
• modulating spread spectrum signals in the parallel signal transmission branches respectively by using same carriers or complex carriers with different frequency offsets or sub-carriers or complex sub-carriers with different orthogonal phases and different frequency offsets respectively, wherein one of the carriers is taken for modulation;
• S12:
• performing power equalization by adjusting gain factors of navigation satellite-dedicated sub-ranging codes of different branches to reasonably allocate signal powers of different branches, and superimposing or combining carrier-modulated signals of all parallel signal transmission branches or with carrier signals of satellite navigation signals of other branches into single-channel signals, wherein less interference occurs between these carrier signals because the navigation satellite-dedicated sub-ranging codes of different parallel signal transmission branches are uncorrelated with each other;
• S13:
• forming a baseband satellite navigation signal by adding Gaussian white noise or another noise to the superimposed or combined single-channel signal;
• S14:
• transmitting the baseband satellite navigation signal by a single antenna in the form of multi-channel parallel superimposition after radiofrequency modulation and power amplification;
• S15:
• receiving, by a user receiver, the baseband satellite navigation signal obtained by low-noise amplifier and radiofrequency transformation, through single-antenna single-channel or each sub-channel contained in the single-antenna single-channel or single-antenna multi-channel or each sub-channel contained in the single-antenna multi-channel, where a channel implementation manner is mr×nr, wherein mr refers to the number of channels, nr refers to the number of sub-channels contained in each channel respectively, and each sub-channel sequentially performs real-time demodulation for the navigation signal of the parallel signal transmission branch in a sequence number range given by a satellite transmitter respectively, or multi-antenna single-channel or each sub-channel contained in the multi-antenna single-channel or multi-antenna multi-channel or each sub-channel contained in the multi-antenna multi-channel, wherein the single-antenna single-channel or each sub-channel contained in the single-antenna single-channel refers to that each antenna is only connected to one signal processing channel, and the channel or each sub-channel contained in the channel is in charge of receiving all satellite navigation signals;
• the single-antenna multi-channel or each sub-channel contained in the single-antenna multi-channel refers to that each antenna is connected to not less than two signal processing channels, and each channel or each sub-channel contained in the channel is in charge of receiving corresponding satellite navigation signals;
• the multi-antenna single-channel or each sub-channel contained in the multi-antenna single-channel refers to that each antenna is connected to one signal processing channel respectively;
• the multi-antenna multi-channel or each sub-channel contained in the multi-antenna multi-channel refers to that each antenna is connected to not less than two signal processing channels respectively, and each channel or each sub-channel contained in the channel is in charge of receiving the corresponding satellite navigation signals, the channel and the sub-channels contained in the channel are implemented in the user receiver baseband chip;
• the number of the signal processing channels or different sub-channels contained in the channel is sufficient to ensure the real-time demodulation of the received satellite navigation signals;
• since each channel demodulates the navigation signals of not less than one navigation satellite respectively in the same manner, a process of performing real time demodulation for the navigation signals of one navigation satellite with nr sub-channels of one channel will be described below;
• S16:
• selecting a sub-channel number ir as (1≤ir≤nr) and a sequence number it of a parallel signal transmission branch of the satellite transmitter corresponding to the sub-channel being equal to a starting sequence number of the parallel signal transmission branch of the transmitter corresponding to the sub-channel of the channel;
• S17:
• intercepting or intercepting, in a given time slot, a segment of the baseband satellite navigation signal;
• S18:
• generating a local carrier or a complex carrier;
• S19:
• obtaining a carrier-removed signal by performing carrier removal for the navigation signal obtained in S17 by a Doppler frequency shift carrier matching method;
• S20:
• generating a navigation satellite-dedicated sub-ranging code of the parallel signal transmission branch in real time or obtaining the navigation satellite-dedicated sub-ranging code of the parallel signal transmission branch through the file or the data buffer zone, and firstly eliminating cross interface of the dedicated sub-ranging codes by using a multi-user detection technology, and then binarizing the carrier-removed signal by the sorting method to perform relevant processing by an FFT-based cyclic correlation method;
• wherein, when ir=1 and a correlation peak exists, it indicates that the navigation satellite signal exists in the received signals, the navigation message is demodulated with the carrier-removed signal of the baseband satellite navigation signals received from the branch according to the position of correlation peak;
• when ir>1 and the correlation peak exists, the navigation message is demodulated from the carrier-removed signal of the baseband satellite navigation signals received by the branch according to the position of the correlation peak, and S21 is performed;
• otherwise, S17 is performed;
• S21:
• it=it+1, when it is smaller than or equal to a cut-off sequence number of the parallel signal transmission branch of the satellite transmitter corresponding to the sub-channel of the channel, performing S17;
• otherwise, performing S22;
• S22:
• changing the grouped navigation messages or unpacked grouped navigation messages obtained from the parallel signal transmission branches of different sub-channels from parallel transmission to serial transmission and obtaining complete navigation messages of one navigation satellite through the channel;
• S23:
• obtaining visual navigation messages of navigation satellites through different channels respectively according to blocks S15-S22, and performing positioning solution for the navigation messages of four selected navigation satellites by using a microprocessor containing no less than one core to realize rapid navigation positioning;
• and
• S24:
• ending the process.