C-band navigation signal design and generation system

Abstract

The invention discloses a C-band navigation signal design and generation system, which comprises a code and message generation module used for generating an I code, an I message, a Q code and a Q message; an I branch modulation part in the baseband modulation module is used for performing XOR on the I code and the I message; the Q branch modulation part is used for carrying out CSK modulation on the Q code and the Q message; the time offset module is used for performing half-chip time offset on the Q branch signal relative to the I branch signal; the waveform mapping module is used for performing waveform mapping on the I-branch signal and the Q-branch offset signal to obtain an I-branch multi-system waveform and a Q-branch multi-system waveform respectively; the quadrature modulation module is used for carrying out band-limited filtering on the I-branch multi-system waveform and the Q-branch multi-system waveform and then carrying out quadrature modulation on the I-branch multi-system waveform and the Q-branch multi-system waveform to obtain radio frequency signals; the digital-to-analog conversion module is used for converting the radio frequency signal into an analog radio frequency signal; and the channel and antenna module is used for filtering, amplifying and transmitting the analog radio frequency signal.

Description

Technical Field

[0001] The invention relates to a C-band navigation signal design and generation system, belonging to the technical field of signal generation. Background Art

[0002] (1) Currently, all major satellite navigation systems based on MEO / GEO / IGSO satellites use L-band signals for navigation. The L-band is already quite crowded, and the use of low-orbit systems involves complex frequency and power coordination. The C-band (5010-5030 MHz) allocated by the ITU for navigation, which is slightly higher than the L-band, has not yet been used and is a relatively clean and easy-to-use band.

[0003] (2) The modulation methods used by L-band navigation signals (BPSK, BOC, AltBOC, etc.) are essentially phase shift keying (PSK) modulation. The corresponding carrier phase is discontinuous, with rich high-frequency components and slow spectrum roll-off. They cannot be directly applied to occasions with strict requirements on out-of-band radiation. For example, for the C-band satellite radio navigation service (RNSS) downlink service band (5010-5030MHz), the low end includes RNSS uplink (5000-5010MHz) and radio astronomy service (RAS, 4990-5000MHz), and the high end includes microwave landing system (MLS, 5030-5150MHz), which have strict requirements on the out-of-band radiation of RNSS downlink signals.

[0004] (3) At the same time, the low-orbit navigation augmentation signal is combined with the GNSS signal to achieve fast and precise positioning services. The low-orbit navigation augmentation signal is required to provide high-precision carrier measurement capabilities. At the same time, it is necessary to broadcast GNSS precision messages / precision correction numbers, and the information rate requirement is not less than 1kbps, which is significantly higher than the traditional GNSS broadcast information rate (50-500bps). It is necessary to study the design of a hybrid transmission signal system that meets measurement and data requirements.

[0005] Currently, no satellite system uses this frequency band for navigation services. The main bottleneck is that on the one hand, it is difficult to meet both measurement and data requirements, and on the other hand, it is difficult for high-power filters to achieve high out-of-band suppression to meet the requirements of the ITU. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the deficiencies of the prior art and to provide a C-band navigation signal design and generation system with continuous phase modulation, which reduces the requirements on the linearity of high-power amplifiers, meets the out-of-band suppression requirements, and meets the requirements for measurement and data transmission.

[0007] The technical solution of the present invention is:

[0008] The present invention discloses a C-band navigation signal design and generation system, comprising: a code and message generation module, a baseband modulation module, a time offset module, a waveform mapping module, an orthogonal modulation module, a digital-to-analog conversion module, and a channel and antenna module; wherein:

[0009] A code and message generation module, used to generate I code, I message, Q code, Q message;

[0010] The baseband modulation module includes an I branch modulation part and a Q branch modulation part; the I branch modulation part is used to perform XOR on the I code and the I telegram to generate an I branch signal; the Q branch modulation part is used to perform CSK modulation on the Q code and the Q telegram to generate a Q branch signal;

[0011] A time offset module, used to time-shift the Q branch signal relative to the I branch signal by half a chip to generate a Q branch offset signal;

[0012] A waveform mapping module, used for waveform mapping the I branch signal and the Q branch offset signal into an I branch multi-base waveform and a Q branch multi-base waveform respectively;

[0013] An orthogonal modulation module is used to perform band-limiting filtering on the I branch multi-level waveform and the Q branch multi-level waveform and then orthogonally modulate them into radio frequency signals;

[0014] A digital-to-analog conversion module, used for converting a radio frequency signal into an analog radio frequency signal;

[0015] Channel and antenna module, used to filter, amplify and transmit analog RF signals.

[0016] Furthermore, in the above system, the multi-binary waveform of the I branch is specifically:

[0017]

[0018] Among them, I T [] is the I branch chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

[0019] Furthermore, in the above system, the Q branch multi-base waveform is specifically:

[0020]

[0021] Among them, Q T [] is the Q branch code chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

[0022] Furthermore, in the above system, the waveform mapping is specifically:

[0023]

[0024] Among them, T c is the duration of one chip; f s is 1 / 2 chip rate; sin() is the sine function.

[0025] Furthermore, in the above system, the CSK modulation is specifically:

[0026] Q[k]=cQ[km xm od L ]

[0027] Where, Q is the code chip sequence after the Q branch modulates the message, cQ is the basic code, m x Indicates Q-way message D Q ; k refers to the kth code piece; L is the code length of the basic code, and mod is the remainder.

[0028] Furthermore, in the above system, the radio frequency signal is specifically:

[0029] s(t)=Res[(I T (t)+jQ T (t))e j2 π ft ]

[0030] Among them, e j2πft is the carrier signal generated by the local oscillator, f is the C-band signal carrier frequency, and Res[] is the real part of the complex number.

[0031] Further, in the above system, the time shifting of the Q branch signal relative to the I branch signal by half a chip is specifically:

[0032] I T [k]=I[k]

[0033] Q T [k] = Q[kT c / 2]

[0034] Among them, T c is the duration of a code chip; k refers to the kth code chip; I is the code chip sequence after the I branch modulates the message; Q is the code chip sequence after the Q branch modulates the message.

[0035] Furthermore, in the above system, the I code, I telegram, Q code and Q telegram are all binary symbol data.

[0036] Furthermore, in the above system, the I code is a binary pseudo-random sequence with a period of MIms, where MI is a positive integer greater than or equal to 1; the code rate is N×1.023Mbps, where N is a positive integer greater than or equal to 1; the I message is the orbit information and clock error information of the satellite, and the bit rate is less than or equal to 500bps.

[0037] Furthermore, in the above system, the Q code is a binary pseudo-random sequence with a period of MQms, where MQ is a positive integer greater than or equal to 1; the code rate is the same as the I code; the Q message is the orbit information and clock correction information of the GNSS, and the bit rate is greater than or equal to 1kbps.

[0038] The beneficial effects of the present invention and the prior art are:

[0039] (1) The present invention designs the half-period sinusoidal waveform mapping of I and Q, and finally meets the measurement and data transmission requirements of the low-orbit navigation enhancement system, achieving higher accuracy (pseudo-code measurement accuracy ≤ 10 cm level) and higher data rate (≥ 1 kbps);

[0040] (2) The present invention finally meets the stringent out-of-band radiation requirements of the C band through phase shift and orthogonal modulation. On the one hand, it meets the protection requirements of aviation radio navigation services: -124.5dBW / (m 2 ) / (150kHz), and on the other hand, it meets the protection requirements for the 4990~5000MHz radio astronomy service: the total interference power within the 10MHz bandwidth of the service is less than -171dBW / (m 2 ).

[0041] (3) The I and Q signals designed in the present invention can be received separately. When a large number of satellites are received, positioning can be achieved by receiving only the I signal, with a positioning accuracy of the meter level. When the Q branch is used to enhance the information, a higher positioning accuracy can be obtained, with a dynamic positioning accuracy of the decimeter level and a static positioning accuracy of the centimeter level. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a system block diagram of the present invention;

[0043] Figure 2 It is a phase relationship diagram of the I and Q branch signal waveforms of the present invention;

[0044] Figure 3 It is a schematic diagram of the signal waveform of the present invention;

[0045] Figure 4 It is a schematic diagram of the binary waveform and the waveform after mapping of the present invention;

[0046] Figure 5 It is the constellation diagram of the QPSK signal after filtering;

[0047] Figure 6 is a constellation diagram of the signal after filtering of the present invention;

[0048] Figure 7 1 is a schematic diagram comparing the spectrum of the signal after filtering of the present invention with that of QPSK;

[0049] Figure 8 Schematic diagram of signal correlation peaks of the present invention. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0051] The present invention discloses a C-band navigation signal design and generation system, comprising: a code and message generation module, a baseband modulation module, a time offset module, a waveform mapping module, an orthogonal modulation module, a digital-to-analog conversion module, and a channel and antenna module; wherein:

[0052] A code and message generation module, used to generate I code, I message, Q code, Q message;

[0053] The baseband modulation module includes an I branch modulation part and a Q branch modulation part; the I branch modulation part is used to perform XOR on the I code and the I telegram to generate an I branch signal; the Q branch modulation part is used to perform CSK modulation on the Q code and the Q telegram to generate a Q branch signal;

[0054] A time offset module, used to time-shift the Q branch signal relative to the I branch signal by half a chip to generate a Q branch offset signal;

[0055] A waveform mapping module, used for waveform mapping the I branch signal and the Q branch offset signal into an I branch multi-base waveform and a Q branch multi-base waveform respectively;

[0056] An orthogonal modulation module is used to perform band-limiting filtering on the I branch multi-level waveform and the Q branch multi-level waveform and then orthogonally modulate them into radio frequency signals;

[0057] A digital-to-analog conversion module, used for converting a radio frequency signal into an analog radio frequency signal;

[0058] Channel and antenna module, used to filter, amplify and transmit analog RF signals.

[0059] Preferably, the multi-binary waveform of the I branch is specifically:

[0060]

[0061] Among them, I T [] is the I branch chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

[0062] Preferably, the Q branch multi-base waveform is specifically:

[0063]

[0064] Among them, Q T [] is the Q branch code chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

[0065] Preferably, the waveform mapping is specifically:

[0066]

[0067] Among them, T c is the duration of one chip; f s is 1 / 2 chip rate; sin() is the sine function.

[0068] Preferably, CSK modulation is specifically:

[0069] Q[k]=cQ[|km x | mod L ]

[0070] Where, Q is the code chip sequence after the Q branch modulates the message, cQ is the basic code, m x Indicates Q-way message D Q ; k refers to the kth code piece; L is the code length of the basic code, and mod is the remainder.

[0071] Preferably, the radio frequency signal is specifically:

[0072] s(t)=Res[(I T (t)+jQ T (t))e j2πft ]

[0073] Among them, e j2πft is the carrier signal generated by the local oscillator, f is the C-band signal carrier frequency, and Res[] is the real part of the complex number.

[0074] Preferably, the Q branch signal is time-shifted by half a chip relative to the I branch signal, specifically:

[0075] I T [k]=I[k]

[0076] Q T [k] = Q[kT c / 2]

[0077] Among them, T cis the duration of a code chip; k refers to the kth code chip; I is the code chip sequence after the I branch modulates the message; Q is the code chip sequence after the Q branch modulates the message.

[0078] Preferably, the I code, I message, Q code and Q message are all binary symbol data.

[0079] Preferably, the I code is a binary pseudo-random sequence with a period of MIms, where MI is a positive integer greater than or equal to 1; the code rate is N×1.023Mbps, where N is a positive integer greater than or equal to 1; the I message is the orbit information and clock error information of the satellite, and the bit rate is less than or equal to 500bps.

[0080] Preferably, the Q code is a binary pseudo-random sequence with a period of MQms, where MQ is a positive integer greater than or equal to 1; the code rate is the same as the I code; the Q message is the orbit information and clock correction information of the GNSS, and the bit rate is greater than or equal to 1 kbps.

[0081] Example

[0082] like Figure 1 As shown, this embodiment provides a C-band navigation signal design and generation system, including:

[0083] Code and telegram generation module, baseband modulation module, time offset module, waveform mapping module, orthogonal modulation module, digital-to-analog conversion module, channel and antenna module.

[0084] a) Code and message generation module

[0085] The code and message generation module includes I code generation, I message generation, Q code generation, and Q message generation parts, all of which are binary symbol data with a value range of {0,1}; Figure 2 shown.

[0086] Among them, the I code is a binary pseudo-random sequence with a period of 1ms and a code rate of N×1.023Mbps; the I message is the orbit, clock error and other information of the satellite, and the bit rate is less than or equal to 500bps.

[0087] The Q code is a binary pseudo-random sequence with a period of 1ms and a code rate that is the same as the I code. The Q message contains information such as the GNSS orbit and clock correction number, and the bit rate is greater than or equal to 1kbps.

[0088] The generated I code sequence is denoted by cI, and the generated Q code sequence is denoted by cQ.

[0089] The generated I message sequence is represented by D I The generated Q message sequence is represented by D Q express.

[0090] b) Baseband modulation module

[0091] The baseband modulation module includes I branch modulation and Q branch modulation. The I branch modulation is realized by performing XOR on the I code and the I message; the Q branch modulation is realized by performing CSK modulation on the Q code and the Q message.

[0092] I branch modulation is performed using the following formula:

[0093] I[k]=D I xOt

[0094] Wherein, k represents the kth symbol.

[0095] The Q branch modulation uses code shift keying, and the cyclic shift version of the basic code cQ is generated using the following formula:

[0096] Q[k]=cQ[|km x|mod L ]

[0097] In the formula, m x Indicates D Q ;

[0098] k is an integer representing the code shift of the xth waveform;

[0099] L is the code length of the basic code.

[0100] c) Time offset module

[0101] The time offset module implements a time offset operation of half a chip on the Q branch relative to the I branch by delaying the Q branch, specifically:

[0102] I T [k]=I[k]

[0103] Q T [k] = Q[kT c / 2]

[0104] Among them, T c is the duration of one chip;

[0105] d) Waveform mapping module

[0106] The waveform mapping adopts the half-sine period mapping form, such as Figure 3 Specifically:

[0107] definition

[0108]

[0109] Among them, T c is the duration of one chip;

[0110] f s is 1 / 2 chip rate;

[0111] Using this formula, the I and Q binary signals are mapped into multi-bit signal waveforms respectively within the duration of one symbol.

[0112] For branch I:

[0113]

[0114] For branch Q:

[0115]

[0116] e) Quadrature modulation module

[0117] The orthogonal modulation module is used to orthogonally modulate the I and Q branch signals to the RF frequency. Before the orthogonal modulation, the I and Q branch signals need to be band-limited filtered, and the band-limited bandwidth should be less than or equal to 20MHz;

[0118] Definition of g I (t) The filtered signal is I f (t), for g I (t) The filtered signal is Q f (t), then the modulated signal is

[0119] s(t)=Res[(I T (t)+jQ T (t))e j2 π ft ]

[0120] Among them, e j2πft is the local oscillator, f is the C-band signal carrier frequency, which is between 5010 and 5030 MHz;

[0121] f) Digital-to-analog conversion module

[0122] A digital-to-analog conversion module is used to convert radio frequency signals from the digital domain to the analog domain;

[0123] g) Channel and antenna module

[0124] The channel and antenna module includes a pre-filtering part, an amplifier, and a post-filtering part, which are used to filter, amplify and transmit the signal.

[0125] Pre-filtering is mainly used to filter out the image produced by digital-to-analog conversion.

[0126] Post-filtering is mainly used to suppress the low noise and other spurious signals raised by the amplifier. This filter is broadband and is not intended to filter out the out-of-band radiation of the signal.

[0127] The MCSK-MSK-F modulation system based on continuous phase modulation also constrains the payload implementation architecture. The core idea is: 1. In the code design and message impact part, the I branch is the measurement branch, using BPSK modulation, and the Q branch is the data branch, using CSK modulation, to ensure both measurement and data transmission; 2. In the waveform and spectrum control part, MSK plus post-filtering is used to ensure the out-of-band attenuation characteristics.

[0128] The baseband part generates pseudo codes and messages for I and Q channels respectively. The I branch realizes the modulation of the basic message and pseudo code of the satellite through direct phase modulation. The data bit rate is low and it mainly realizes the measurement function. The Q branch realizes the modulation of precise message and pseudo code through CSK. The data bit rate is high and it mainly realizes the data transmission function. The two branches are synthesized through modulation, and then pass through circuit equipment such as digital-to-analog conversion and amplification, and finally filtered and output to the antenna.

[0129] In this embodiment, the low-orbit satellite constellation system uses the navigation frequency band 5010-5030 MHz allocated by the International Telecommunication Union as the downlink navigation frequency and uses the MCSK-MSK-F modulation system. The I and Q dual branches broadcast two signals, and the code rate of each branch is 5.115 Mbps.

[0130] The I branch modulates the basic navigation message information of the satellite, with a data rate of ≤100bps; the Q branch modulates the GNSS enhancement information, with a data rate of ≥1kbps and ≤10kbps.

[0131] The I branch signal and the Q branch signal are as follows Figure 4 As shown:

[0132] The final constellation diagram is compared with QPSK as follows Figure 5 , 6 As shown:

[0133] It can be seen that the constant envelope characteristics of the baseband signal remain intact, indicating that it is not affected by the nonlinearity of the amplifier, such as Figure 7 shown.

[0134] From the spectrum, we can see that when the center is near 5020MHz, the roll-off outside 10MHz can reach more than 30dB, and it can be further increased by adding filter suppression. Figure 8 shown.

[0135] It can be seen from the signal correlation peak that the signal still maintains good measurement characteristics and meets the needs of navigation measurement.

[0136] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

[0137] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A C-band navigation signal design and generation system, characterized in that: include: Code and message generation module, baseband modulation module, time offset module, waveform mapping module, orthogonal modulation module, digital-to-analog conversion module and channel and antenna module; wherein, A code and message generation module, used to generate I code, I message, Q code, Q message; The baseband modulation module includes an I branch modulation part and a Q branch modulation part; the I branch modulation part is used to perform XOR on the I code and the I telegram to generate an I branch signal; the Q branch modulation part is used to perform CSK modulation on the Q code and the Q telegram to generate a Q branch signal; A time offset module, used to time-shift the Q branch signal relative to the I branch signal by half a chip to generate a Q branch offset signal; A waveform mapping module, used for waveform mapping the I branch signal and the Q branch offset signal into an I branch multi-base waveform and a Q branch multi-base waveform respectively; An orthogonal modulation module is used to perform band-limiting filtering on the I branch multi-level waveform and the Q branch multi-level waveform and then orthogonally modulate them into a radio frequency signal; A digital-to-analog conversion module, used for converting a radio frequency signal into an analog radio frequency signal; Channel and antenna module, used to filter, amplify and transmit analog RF signals.

2. A C-band navigation signal design and generation system according to claim 1, characterized in that: The multi-level waveform of the I branch is specifically: Among them, I T [] is the I branch chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

3. A C-band navigation signal design and generation system according to claim 1, characterized in that: The multi-level waveform of the Q branch is specifically: Among them, Q T [] is the Q branch code chip sequence; p() is the waveform mapping function; T c is the duration of one chip; k refers to the kth chip.

4. A C-band navigation signal design and generation system according to claim 1, characterized in that: The waveform mapping is specifically: Among them, T c is the duration of one chip; f s is 1 / 2 chip rate; sin() is the sine function.

5. A C-band navigation signal design and generation system according to claim 1, characterized in that: The CSK modulation is specifically: Q[k]=cQ[km xm from L ] Where, Q is the code chip sequence after the Q branch modulates the message, cQ is the basic code, m x Indicates Q-way message D Q ; k refers to the kth code chip; L is the code length of the basic code, and mod is the remainder.

6. A C-band navigation signal design and generation system according to claim 1, characterized in that: The radio frequency signal is specifically: s(t)=Res[(I T (t)+jQ T (t))e j2 π ft ] Among them, e j2πft is the carrier signal generated by the local oscillator, f is the C-band signal carrier frequency, and Res[] is the real part of the complex number.

7. A C-band navigation signal design and generation system according to claim 1, characterized in that: The time shifting of the Q branch signal relative to the I branch signal by half a chip is specifically as follows: I T [k]=I[k] Q T [k]=Q[k-T c / 2] Among them, T c is the duration of a code chip; k refers to the kth code chip; I is the code chip sequence after the I branch modulates the message; Q is the code chip sequence after the Q branch modulates the message.

8. A C-band navigation signal design and generation system according to claim 1, characterized in that: The I code, I message, Q code and Q message are all binary symbol data.

9. A C-band navigation signal design and generation system according to claim 1, characterized in that: The I code is a binary pseudo-random sequence with a period of MIms, where MI is a positive integer greater than or equal to 1; the code rate is N×1.023Mbps, where N is a positive integer greater than or equal to 1; the I message is the orbit information and clock error information of the satellite, and the bit rate is less than or equal to 500bps.

10. A C-band navigation signal design and generation system according to claim 9, characterized in that: The Q code is a binary pseudo-random sequence with a period of MQms, where MQ is a positive integer greater than or equal to 1; the code rate is the same as the I code; the Q message is the orbit information and clock correction information of the GNSS, and the bit rate is greater than or equal to 1kbps.

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