Wideband tracking method of low-orbit satellite signals based on square error phase detector

Abstract

The present invention proposes a method for broadband tracking of low-orbit satellite signals based on a square difference phase detector. According to the signal modulation mode of the low-orbit satellite of the StarNet, the method designs a frequency detector and a square difference phase detector, which can accurately identify the frequency and phase of the low-orbit satellite signals of the StarNet, and can maintain a high degree of accuracy even in a complex and rapidly changing signal environment; in addition, the method adopts a second-order frequency locking assisted by a third-order phase locking design, which can more effectively handle the high-dynamic frequency deviation changes caused by the high-speed movement of the low-orbit satellite of the StarNet, and ensure the stability and accuracy of signal tracking. The present invention significantly improves the tracking capability of the low-orbit satellite signals of the StarNet, and can achieve stable frequency and phase locking under high dynamic conditions, ensuring the reliable reception and processing of signals, providing a solid guarantee for the efficient operation of the low-orbit satellite system of the StarNet, and laying an important foundation for the development of the future integrated space-ground network.

Description

Technical Field

[0001] The invention relates to the field of satellite electronic navigation, and in particular to a low-orbit satellite signal broadband tracking method based on a square difference phase detector. Background Art

[0002] With the rapid development of low-orbit satellite technology, StarNet's low-orbit satellite system is in a stage of vigorous development. Due to the progress of low-orbit satellites and modern signal processing technology, higher requirements are placed on the reception and processing of low-orbit satellite signals.

[0003] Compared with traditional GNSS signal tracking, StarNet's tracking of low-orbit satellite signals presents some new features and challenges. First, because low-orbit satellites are close to the ground (500-1200 kilometers) and move at extremely high speeds (7.5-7.8km / s), their Doppler frequency shift change rate is significantly higher than that of traditional GNSS signals, which makes it easy for frequency-locked loops (FLLs) and phase-locked loops (PLLs) to lose lock. High dynamic characteristics make rapid changes in frequency and phase the norm, which places higher demands on the stability and response speed of the frequency-locked phase-locked loop. Secondly, StarNet's low-orbit satellite signals use a modulation method that combines BPSK (binary phase shift keying) and QPSK (quadrature phase shift keying). This complex modulation scheme not only increases the flexibility and anti-interference ability of signal transmission, but also poses new challenges to the design of frequency-locked phase-locked loops. Traditional frequency-locked phase-locked loops optimized for a single modulation method are difficult to meet the needs of such complex modulation signals. It is necessary to develop new frequency-locked phase-locked loop technologies with strong adaptability and high precision to ensure reliable signal tracking. Summary of the invention

[0004] Aiming at the problems that the Doppler frequency change rate of the low-orbit satellites of the Star Network is high and the signals are complex, making it difficult to detect frequency and phase, and the traditional frequency-locked phase-locked loop optimized for a single modulation method is difficult to adapt to complex combined modulation schemes, the present invention proposes a low-orbit satellite signal broadband tracking method based on a square difference phase detector to achieve accurate tracking of the navigation signals of the low-orbit satellites of the Star Network.

[0005] The technical solution of the present invention is:

[0006] A low-orbit satellite signal broadband tracking method based on a square difference phase detector comprises the following steps:

[0007] Step 1: The satellite receiver receives the downlink signal from the StarNet low-orbit satellite, performs frequency and phase discrimination through the designed StarNet low-orbit satellite signal tracking loop, and obtains the carrier phase error and frequency error of the carrier loop, as well as the phase error of the code loop;

[0008] The signal tracking loop of the low-orbit satellite of the star network includes a carrier loop and a code loop; the discriminator in the carrier loop includes a frequency discriminator and a square difference phase discriminator; the discriminator in the code loop is a phase discriminator;

[0009] The square error phase detector in the carrier loop is:

[0010]

[0011] in is the carrier phase error, is the final value obtained in the carrier loop road signal, is the final value obtained in the carrier loop road signal;

[0012] The frequency discriminator in the carrier loop is:

[0013]

[0014] in is the angular velocity error of the signal, according to Get the carrier frequency error ;

[0015] according to

[0016]

[0017] Calculated, is the vector dot product, is the vector cross product, the vector and To set the vector:

[0018]

[0019]

[0020] for The conjugate vector of ; For vector The amplitude of For vector The amplitude of is the time difference between two adjacent epochs; for Frequency Locked Loop road signal, for Frequency Locked Loop road signal, for Frequency Locked Loop road signal, for Frequency Locked Loop road signal;

[0021] The phase detector in the code loop is:

[0022]

[0023] in is the phase error in the code loop, They are respectively the autocorrelation amplitude of the leading branch and the autocorrelation amplitude of the lagging branch in the code loop;

[0024] Step 2: Input the carrier phase error and frequency error of the carrier loop obtained in step 1 into the loop filter of the carrier loop to obtain the carrier NCO adjustment amount of the carrier loop, thereby realizing carrier tracking in the carrier loop; input the code loop phase error obtained in step 1 into the loop filter of the code loop to obtain the adjustment amount of the C / A generator of the code loop, thereby realizing code tracking in the code loop.

[0025] Further, according to the intermediate frequency signal received by the satellite receiver, and The process is:

[0026] Assume that the intermediate frequency signal received by the satellite receiver is:

[0027] S IF (t)= A[c(t)s I (t) cos 2π f d t+ f 0 - c t s Q t sin 2π f d t+ f 0 ]

[0028] In the formula, is the intermediate frequency signal amplitude, is the spread spectrum pseudo code, and They are the I-path component and Q-path component which are in phase and orthogonal respectively. is the Doppler frequency deviation of the intermediate frequency signal; The road signals are:

[0029] i(t) = A [ c ( t ) s I ( t ) cos 2 π f d t + f 0 - c t s Q t sin 2 π f d t + f 0 ]cos(2 π f d t )= 1 2 Ac t s I t [ cos 2 π f d + f d t + f 0 + cos 2 π f d - f d t + f 0 ]- 1 2 Ac t s Q t [ sin 2 π f d + f d t + f 0 + sin 2 π f d - f d t + f 0 ]

[0030] After mixing in the carrier loop The road signals are:

[0031] q(t) = A [ c ( t ) s I ( t ) cos 2 π f d t + f 0 - c t s Q t sin 2 π f d t + f 0 ]sin(2 π f d t )= 1 2 Ac t s I t sin 2 π f d + f d t + f 0 - sin 2 π f d - f d t + f 0 + 1 2 Ac t s Q t [ cos 2 π f d + f d t + f 0 - cos 2 π f d - f d t + f 0 ]

[0032] Assuming the pseudo-random code is aligned, the mixed The mixed signal and After the signals of each channel pass through their corresponding correlators, the Road related results and The road related results are:

[0033]

[0034] q p t = 1 2 As I t sin 2 π f d + f d t + f 0 - sin 2 π f d - f d t + f 0 + 1 2 As Q t [ cos 2 π f d + f d t + f 0 - cos 2 π f d - f d t + f 0 ]

[0035] Again Road related results and The relevant results of each path are integrated, which is equivalent to low-pass filtering, and the final The road signals are:

[0036]

[0037] Get the final The road signals are:

[0038]

[0039] Furthermore, the square error phase detector in the carrier loop is obtained by the following process:

[0040] The final result in the carrier loop is Road signals and The squares of the road signals are:

[0041]

[0042]

[0043] and is the telegram symbol, and its value is ±1, so , so the above formula becomes:

[0044]

[0045]

[0046] Road signal and Subtracting the squares of the signals from each other is:

[0047]

[0048] Road signals and The multiplication of the two-way signal is:

[0049]

[0050] Also because ,so

[0051]

[0052] therefore:

[0053]

[0054] Then the square error phase detector in the carrier loop can be obtained as:

[0055]

[0056] Furthermore, assuming that the pseudo-random code has been aligned, then The signals of I and Q in the frequency-locked loop at time are

[0057]

[0058]

[0059] Furthermore, the discriminator in the carrier loop is obtained by the following process:

[0060] right Duration The coherent integral of Get the time difference between two adjacent epochs

[0061]

[0062] right Duration Coherence integral:

[0063]

[0064] Let vector for

[0065]

[0066] in

[0067]

[0068]

[0069] The frequency discriminator calculates the frequency between two adjacent epochs. The angle at which the vector is rotated is:

[0070]

[0071] Angular velocity error The numerator in the formula The solution is obtained through the following derivation:

[0072] set up:

[0073]

[0074] in for The conjugate vector of and cross product It is expressed as:

[0075]

[0076]

[0077] When the PLL locks on to the signal, The value of is close to 0, that is Approximately equal to , so the discriminator in the carrier loop is expressed as:

[0078]

[0079] Furthermore, the frequency detector and the square difference phase detector in the carrier loop work in time sharing, and the phase detector in the code loop is always in working state.

[0080] Furthermore, the loop filter of the carrier loop adopts a filter solution of a second-order frequency-locked loop assisting a third-order phase-locked loop, and the loop filter of the code loop adopts a second-order filter solution.

[0081] Furthermore, when the loop filter of the carrier loop is working, a pure frequency-locked loop with minimum noise is first used to close the loop, the carrier phase error is set to 0, and the carrier frequency error is input into the phase-locked loop assisted by the frequency-locked loop until the frequency is locked; then the carrier frequency error is set to 0, and the carrier phase error is input into the phase-locked loop assisted by the frequency-locked loop until the phase is locked.

[0082] Beneficial effects:

[0083] Aiming at the tracking difficulties caused by high dynamic frequency deviation and complex modulation signals of low-orbit satellites in StarNet, the present invention proposes an innovative carrier loop frequency discriminator and square difference phase detector design, which can accurately identify the frequency and phase of low-orbit satellite signals in StarNet, maintain high accuracy even in complex and rapidly changing signal environments, and achieve high-precision phase synchronization within a wide frequency deviation range, significantly improving the adaptability to extreme dynamic environments, greatly enhancing the sensitivity and anti-interference ability of signal analysis, and effectively suppressing the mistracking problem caused by multiple correlation peaks; an adaptive second-order frequency locking assisted third-order phase locking design is adopted, which significantly improves the stability under weak signal conditions and the tracking accuracy under multipath interference. The designed frequency discriminator and square difference phase detector are easy to implement in engineering, greatly reducing system resource consumption while ensuring real-time processing performance, and fully realizing the synergistic breakthrough of tracking performance and engineering practicality in high dynamic and complex signal scenarios.

[0084] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0086] Figure 1 This is a low-orbit satellite signal format diagram in the embodiment;

[0087] Figure 2 is a carrier loop diagram in the embodiment;

[0088] Figure 3 is a code loop diagram in the embodiment;

[0089] Figure 4 is a loop filter diagram of a carrier loop in an embodiment;

[0090] Figure 5 A loop filter diagram of a code loop in an embodiment;

[0091] Figure 6 A constellation diagram of a tracking signal in an embodiment;

[0092] Figure 7 Graph showing correlation values ​​of tracking codes in the embodiment. DETAILED DESCRIPTION

[0093] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0094] In view of the problem that the low-orbit satellites of StarNet move at a fast speed and have a large Doppler frequency change rate, and that the frequency-locked phase-locked loop optimized by the traditional single modulation method is difficult to adapt to complex combined modulation schemes, this embodiment proposes a low-orbit satellite signal broadband tracking method based on a square difference phase detector. This method designs a new frequency detector and square difference phase detector that are different from the traditional GNSS system according to the signal modulation method of the low-orbit satellites of StarNet, and can accurately identify the frequency and phase of the low-orbit satellite signals of StarNet, and maintain a high degree of accuracy even in a complex and rapidly changing signal environment. In addition, this method adopts a more advanced frequency-locked phase-locked loop design than the traditional GNSS system: the second-order frequency-locked assisted third-order phase-locked design can more effectively handle the high dynamic frequency deviation changes caused by the high-speed movement of the low-orbit satellites of StarNet, and ensure the stability and accuracy of signal tracking. By using the proposed frequency discriminator and phase discriminator and adopting a high-order frequency-locked phase-locked loop design, this method significantly improves the tracking capability of StarNet low-orbit satellite signals, can achieve stable frequency and phase locking under high dynamic conditions, ensure reliable reception and processing of signals, and provide a solid guarantee for the efficient operation of StarNet low-orbit satellite systems, and lay an important foundation for the development of future integrated space-ground networks.

[0095] This embodiment specifically includes the following steps:

[0096] Step 1: The satellite receiver receives the downlink signal from the StarNet low-orbit satellite, and performs frequency and phase detection through the designed StarNet low-orbit satellite signal tracking loop to obtain the carrier phase error and frequency error of the carrier loop, as well as the phase error of the code loop.

[0097] The modulation signal format of the StarNet low-orbit satellite is as follows: Figure 1 As shown. The modulated signal is described by the power normalized complex envelope. The modulated signal expression is:

[0098]

[0099] in, represents the amplitude of the modulating signal, and They are the I-path component and Q-path component which are in phase and orthogonal respectively. Represents the carrier frequency of the modulating signal.

[0100] The complex envelope of the pilot signal is expressed as:

[0101]

[0102] in, is the pseudo-random code of the pilot segment, Is the imaginary number symbol.

[0103] The signal complex envelope of the data segment can be expressed as:

[0104]

[0105] in, is the pseudo-random code of the data segment, and They are data segment I channel telegram symbols and Q channel telegram symbols respectively.

[0106] Establish a signal tracking loop for the low-orbit satellite of the StarNet. The main structure of the signal tracking loop is similar to that of the GNSS signal tracking loop, including a carrier loop and a code loop. Figure 2 As shown, the code loop is as follows Figure 3 The key to this embodiment is to design the discriminator in the signal tracking loop: Figure 2 As shown, the discriminator in the carrier loop includes a frequency detector and a square difference phase detector, which work in time-sharing mode to achieve the purpose of frequency tracking and phase tracking of the signal. Figure 3 As shown, the discriminator in the code loop is a phase detector, and the phase detector of the code loop is always in a working state to achieve the effect of code tracking of the signal.

[0107] The frequency discriminator and phase discriminator in the star network low-orbit satellite signal tracking loop are obtained through the following process:

[0108] Assume that the intermediate frequency signal received by the satellite receiver is:

[0109] S IF (t)= A[c(t)s I (t) cos 2π f d t+ f 0 - c t s Q t sin 2π f d t+ f 0 ]

[0110] In the formula, is the intermediate frequency signal amplitude, is the spread spectrum pseudo code, is the Doppler frequency deviation of the intermediate frequency signal, is the carrier phase error of the intermediate frequency signal.

[0111] The phase detector in the carrier loop is to obtain the carrier phase error of the intermediate frequency signal. In this embodiment, for the BPSK+QPSK combined modulation mode adopted by the low-orbit satellite of the star network, a square difference phase detector is innovatively proposed to identify the carrier phase error, that is, to identify , the square error phase detector formula used is as follows:

[0112]

[0113] in is the final value obtained in the carrier loop road signal, is the final value obtained in the carrier loop road signal.

[0114] According to the intermediate frequency signal received by the satellite receiver, and The process is:

[0115] Assume that the Doppler frequency deviation captured by the satellite receiver is accurate, that is, the same as the Doppler frequency deviation of the intermediate frequency signal. , then the mixed frequency in the carrier loop The road signals are:

[0116] i(t) = A [ c ( t ) s I ( t ) cos 2 π f d t + f 0 - c t s Q t sin 2 π f d t + f 0 ]cos(2 π f d t )= 1 2 Ac t s I t [ cos 2 π f d + f d t + f 0 + cos 2 π f d - f d t + f 0 ]- 1 2 Ac t s Q t [ sin 2 π f d + f d t + f 0 + sin 2 π f d - f d t + f 0 ]

[0117] After mixing in the carrier loop The road signals are:

[0118] q(t) = A [ c ( t ) s I ( t ) cos 2 π f d t + f 0 - c t s Q t sin 2 π f d t + f 0 ]sin(2 π f d t )= 1 2 Ac t s I t sin 2 π f d + f d t + f 0 - sin 2 π f d - f d t + f 0 + 1 2 Ac t s Q t [ cos 2 π f d + f d t + f 0 - cos 2 π f d - f d t + f 0 ]

[0119] Assuming the pseudo-random code is aligned, the mixed The mixed signal and After the signals of each channel pass through their corresponding correlators, the Road related results and The road related results are:

[0120]

[0121] q p t = 1 2 As I t sin 2 π f d + f d t + f 0 - sin 2 π f d - f d t + f 0 + 1 2 As Q t [ cos 2 π f d + f d t + f 0 - cos 2 π f d - f d t + f 0 ]

[0122] Again Road related results and The relevant results of each path are integrated, which is equivalent to low-pass filtering, and the final The road signals are:

[0123]

[0124] Get the final The road signals are:

[0125]

[0126] The square error phase detector used is derived as follows:

[0127] Road signals and The squares of the road signals are:

[0128]

[0129]

[0130] because and is the telegram symbol, and its value is ±1, so , so the above formula can be transformed into:

[0131]

[0132]

[0133] Road signal and Subtracting the squares of the signals from each other is:

[0134]

[0135] Road signals and The multiplication of the two-way signal is:

[0136]

[0137] Also because ,so

[0138]

[0139] therefore:

[0140]

[0141] Then the square error phase detector in the carrier loop can be obtained as:

[0142]

[0143] The frequency discriminator in the carrier loop is:

[0144]

[0145] in is the angular velocity error of the signal, according to Get the carrier frequency error ;

[0146] according to

[0147]

[0148] Calculated, is the vector dot product, is the vector cross product, the vector and To set the vector:

[0149]

[0150]

[0151] for The conjugate vector of ; For vector The amplitude of For vector The amplitude of is the time difference between two adjacent epochs; for Frequency Locked Loop road signal, for Frequency Locked Loop road signal, for Frequency Locked Loop road signal, for Frequency Locked Loop road signal.

[0152] The specific derivation process of the discriminator in the carrier loop is:

[0153] For the frequency-locked loop, its purpose is to lock the signal frequency, so it only works in the pilot band, and the pilot band has no data information, so After locking the frequency, the operation does not continue, but the phase-locked loop performs phase locking. Assuming that the pseudo-random code has been aligned, then The signals of I and Q in the frequency-locked loop at the time are:

[0154]

[0155]

[0156] in Represents the angular velocity error of the signal.

[0157]

[0158]

[0159] right Duration The coherent integral of Get the time difference between two adjacent epochs

[0160]

[0161] right Duration Coherence integral:

[0162]

[0163] Let vector for

[0164]

[0165] in

[0166]

[0167]

[0168] The frequency discriminator calculates the frequency between two adjacent epochs. The angle at which the vector is rotated is:

[0169]

[0170] The angular velocity error and carrier frequency error The relationship is as follows:

[0171]

[0172] So when the angular velocity error After obtaining, the carrier frequency error can be obtained to achieve frequency discrimination.

[0173] Angular velocity error The numerator in the formula The solution is obtained through the following derivation:

[0174] set up:

[0175]

[0176] in for The conjugate vector of and cross product It is expressed as:

[0177]

[0178]

[0179] When the PLL locks on to the signal, The value of is close to 0, that is Approximately equal to , so the discriminator in the carrier loop is expressed as:

[0180]

[0181] For the frequency detector, since the signals of the I and Q paths in the frequency locked loop are known, the constructed vector and It is known that the corresponding basis

[0182]

[0183] Calculated ,and and For vector and The amplitude of is also a known quantity, so the angular velocity error is calculated by the frequency discriminator , and then get the frequency error , to achieve frequency discrimination.

[0184] The phase detector in the code loop uses the phase detector of the conventional GNSS system:

[0185]

[0186] in is the phase error in the code loop, They are respectively the autocorrelation amplitude of the leading branch and the autocorrelation amplitude of the lagging branch in the code loop.

[0187] At this point, the carrier loop's frequency detector, phase detector and code loop's phase detector have all been derived.

[0188] Step 2: Input the carrier phase error and frequency error of the carrier loop obtained in step 1 into the loop filter of the carrier loop to obtain the carrier NCO adjustment amount of the carrier loop, thereby realizing carrier tracking in the carrier loop; input the code loop phase error obtained in step 1 into the loop filter of the code loop to obtain the adjustment amount of the C / A generator of the code loop, thereby realizing code tracking in the code loop.

[0189] The loop filter of the carrier loop is as follows Figure 4 As shown in FIG. 1 , a filter scheme using a second-order frequency-locked loop (FLL) to assist a third-order phase-locked loop (PLL) is used. The loop filter of the code loop is as follows: Figure 5 As shown, a second-order filter solution is adopted.

[0190] when Figure 4When the error input of the PLL is set to 0, the filter becomes a pure FLL. Similarly, when the error input of the FLL is set to 0, the filter becomes a pure PLL. Therefore, when the loop filter of the carrier loop works, the pure FLL form with minimum noise is first used for loop closure, that is, the carrier phase error is set to 0, and the carrier frequency error is input into the FLL-assisted PLL until the frequency lock is obtained. Then the carrier frequency error is set to 0, and the carrier phase error is input into the FLL-assisted PLL until the phase lock is obtained.

[0191] If the loop noise bandwidth parameter is selected correctly, there is only a very small loss in ideal carrier tracking threshold performance when the carrier loop frequency and phase detectors continue to operate. The natural frequency of the PLL These natural circle frequencies are determined by the desired loop filter noise bandwidth. and To determine, the third-order coefficients in this embodiment and The values ​​of are shown in Table 1.

[0192] Table 1 Loop filter characteristics

[0193]

[0194] Finally, this method is applied to the tracking of low-orbit satellite signals in StarNet. The constellation diagram of the tracking signal is as follows: Figure 6 As shown, the relevant values ​​of the tracking code are as follows Figure 7 As shown, it can be seen that the constellation diagram is a QPSK constellation diagram, which is mixed with the BPSK signal of the pilot segment, and the effect of the code ring is also very good. The correlation value of the instant branch gradually becomes the largest and remains the largest among the three branches, indicating that the tracking method proposed in the present invention can effectively track the low-orbit satellite signal of the StarNet.

[0195] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A broadband tracking method for low-orbit satellite signals based on a square difference phase detector, characterized in that: The following steps are involved: Step 1: The satellite receiver receives the downlink signal from the StarNet low-orbit satellite, performs frequency and phase discrimination through the designed StarNet low-orbit satellite signal tracking loop, and obtains the carrier phase error and frequency error of the carrier loop, as well as the phase error of the code loop; The signal tracking loop of the low-orbit satellite of the star network includes a carrier loop and a code loop; the discriminator in the carrier loop includes a frequency discriminator and a square difference phase discriminator; the discriminator in the code loop is a phase discriminator; The square error phase detector in the carrier loop is: in is the carrier phase error, I p (t) is the final I-channel signal obtained in the carrier loop, Q p (t) is the Q-path signal finally obtained in the carrier loop; The frequency discriminator in the carrier loop is: where ω e (t) is the angular velocity error of the signal, according to ω e (t)=2πf e (t) Get the carrier frequency error f e (t); P cross according to Calculated, P dot is the vector dot product, P cross is the vector cross product, vector r P (t) and r P (t+T coh ) is the setting vector: r P (t)=-(I(t)-Q(t)+j(I(t)+Q(t))) r P (t+T coh )=-(I(t+T coh )-Q(t+T coh )+j(I(t+T coh )+Q(t+T coh ))) For r P The conjugate vector of (t); A P (t+T coh ) is the vector r P (t+T coh ), A P (t) is the vector r P The amplitude of (t), T coh is the time difference between two adjacent epochs; I(t) is the I-way signal of the frequency-locked loop at time t, Q(t) is the Q-way signal of the frequency-locked loop at time t, I(t+T coh ) is t+T coh The frequency-locked loop I signal at time, Q(t+T coh ) is t+T coh The frequency-locked loop Q-channel signal at the moment; The phase detector in the code loop is: where δ cp is the phase error in the code loop, E and L are the autocorrelation amplitude of the leading branch and the autocorrelation amplitude of the lagging branch in the code loop respectively; Step 2: Input the carrier phase error and frequency error of the carrier loop obtained in step 1 into the loop filter of the carrier loop to obtain the carrier NCO adjustment amount of the carrier loop, thereby realizing carrier tracking in the carrier loop; input the code loop phase error obtained in step 1 into the loop filter of the code loop to obtain the adjustment amount of the C / A generator of the code loop, thereby realizing code tracking in the code loop.

2. According to claim 1, a low-orbit satellite signal broadband tracking method based on square difference phase detector is characterized in that: According to the intermediate frequency signal received by the satellite receiver, I p (t) and Q p The process of (t) is: Assume that the intermediate frequency signal received by the satellite receiver is: Where A is the intermediate frequency signal amplitude, c(t) is the spread spectrum pseudo code, s I (t) and s Q (t) are the I-path component and Q-path component in phase and quadrature, respectively. d is the Doppler frequency deviation of the intermediate frequency signal, is the carrier phase error of the intermediate frequency signal; the I-channel signal after mixing in the carrier loop is: The Q-path signal after mixing in the carrier loop is: Assuming that the pseudo-random code is aligned, after the mixed I-channel signal and the mixed Q-channel signal pass through their respective corresponding correlators, the I-channel correlation result and the Q-channel correlation result obtained are: Then the I-channel correlation results and the Q-channel correlation results are integrated respectively, which is equivalent to low-pass filtering, and the final I-channel signal is: The final Q-channel signal is:

3. According to claim 2, a method for broadband tracking of low-orbit satellite signals based on a square difference phase detector, characterized in that: The square error phase detector in the carrier loop is obtained by the following process: The squares of the I-channel signal and the Q-channel signal finally obtained in the carrier loop are: s I (t) and s Q (t) is the message symbol, and its value is ±1, so s I 2 (t) = s Q 2 (t) = 1, so the above formula becomes: The square of the I signal and the Q signal is subtracted to get: The multiplication of the I-channel signal and the Q-channel signal is: Also because of s I 2 (t) = s Q 2 (t) = 1, so therefore: Then the square error phase detector in the carrier loop can be obtained as:

4. The method for broadband tracking of low-orbit satellite signals based on a square difference phase detector according to claim 1, characterized in that: Assuming the pseudo-random code has been aligned, the signals of I and Q in the frequency-locked loop at time t are where ω e (t) is the angular velocity error of the signal.

5. The method for broadband tracking of low-orbit satellite signals based on a square difference phase detector according to claim 4, characterized in that: The discriminator in the carrier loop is obtained by the following process: I(t)+Q(t) is processed for a period of T. coh The coherent integral of coh Get the time difference between two adjacent epochs I(t)-Q(t) is processed for a period of T. coh Coherence integral: Let vector r P (t) is in The frequency discriminator calculates r between two adjacent epochs. P (t) is the angle at which the vector is rotated, that is: Angular velocity error ω e (t) The numerator φ in the formula e (t+T coh )-φ e (t) is solved by the following derivation: set up: in For r P (t); and the dot product P dot and cross product P cross It is expressed as: P dot =A P (t+T coh )A P (t)cos(φ e (t+T coh )-φ e (t)) P cross =A P (t+T coh )A P (t)sin(φ e (t+T coh )-φ e (t)) When the PLL locks the signal, φ e (t+T coh )-φ e The value of (t) is close to 0, that is, sin(φ e (t+T coh )-φ e (t)) is approximately equal to φ e (t+T coh )-φ e (t), so the discriminator in the carrier loop is expressed as:

6. The method for broadband tracking of low-orbit satellite signals based on a square difference phase detector according to claim 1, characterized in that: The frequency detector and square difference phase detector in the carrier loop work in time sharing, and the phase detector in the code loop is always in working state.

7. The method for broadband tracking of low-orbit satellite signals based on a square difference phase detector according to claim 1, characterized in that: The loop filter of the carrier loop adopts a filter solution of a second-order frequency-locked loop assisting a third-order phase-locked loop, and the loop filter of the code loop adopts a second-order filter solution.

8. The method for broadband tracking of low-orbit satellite signals based on a square difference phase detector according to claim 7, characterized in that: When the loop filter of the carrier loop works, the loop is closed in the form of a pure frequency-locked loop with minimum noise, the carrier phase error is set to 0, and the carrier frequency error is input into the phase-locked loop assisted by the frequency-locked loop until the frequency is locked; The carrier frequency error is then set to 0, and the carrier phase error is input into a phase-locked loop assisted by a frequency-locked loop until the phase is locked.

Images