阅读说明：本技术 使用双天线的多径检测和抑制方法及系统 (Multipath detection and suppression method and system using dual antennas ) 是由 陈佳佳 何智力 袁洪 刘杨斌 于 2020-05-06 设计创作，主要内容包括：本发明涉及一种使用双天线的多径检测和抑制方法及系统,包括获取GNSS信号的载波相位和广播星历；根据所述载波相位、已知的天线基线长度和广播星历计算误差平方和；将所述误差平方和与门限值作比较,判断所述误差平方和的数值是否大于所述门限值,若大于,则认为当前接收的卫星信号中存在至少一个多径信号,否则,认为当前不存在多径信号；计算多径信号引起的载波相位误差估计值,并根据所述载波相位以及所述载波相位误差估计值计算所述载波相位估计值；对天线进行定位。本发明可以实现多径抑制的目的,并降低成本,实现实时检测和解算。(The invention relates to a multipath detection and inhibition method and a system using double antennas, which comprises the steps of obtaining carrier phase and broadcast ephemeris of GNSS signals; calculating the error square sum according to the carrier phase, the known length of the antenna base line and the broadcast ephemeris; comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, determining that at least one multipath signal exists in the currently received satellite signal, otherwise, determining that the multipath signal does not exist currently; calculating a carrier phase error estimation value caused by a multipath signal, and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value; the antenna is positioned. The invention can realize the purpose of multi-path inhibition, reduce the cost and realize real-time detection and calculation.)

1. A method for multipath detection and mitigation using dual antennas, comprising the steps of:

step S1: acquiring a carrier phase and a broadcast ephemeris of a GNSS signal;

step S2: calculating the error square sum according to the carrier phase, the known length of the antenna base line and the broadcast ephemeris;

step S3: comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, determining that at least one multipath signal exists in the currently received satellite signal, and entering a step S4, otherwise, determining that the multipath signal does not exist currently, and entering a step S5;

step S4: calculating a carrier phase error estimation value caused by a multipath signal, and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value;

step S5: the antenna is positioned.

2. The multipath detection and mitigation method using dual antennas of claim 1, wherein: the method for calculating the error square sum according to the carrier phase, the known antenna base length and the broadcast ephemeris comprises the following steps: and calculating a baseline vector observation value according to the carrier phase and the broadcast ephemeris, calculating a baseline vector estimation value according to the baseline vector observation value and the antenna baseline length, and calculating a sum of squares of errors according to the baseline vector estimation value.

3. The multipath detection and mitigation method using dual antennas of claim 2, wherein: the method for calculating the baseline vector observed value comprises the following steps: assuming that the number of the current observable satellites is N, selecting the satellite signal with the highest elevation angle as a reference satellite; carrier phase double-difference observation matrixWhereinIs a (N × 1) matrix representing a carrier phase double difference observation matrix, H is a (N × 3) matrix representing the direction cosine difference between the satellite and the reference satellite and calculated from the broadcast ephemeris, N_rBAIs (N × 1) matrix, is zero mean Gaussian white noise and is recorded asThe observed value DeltaX of the baseline vector can be obtained by calculation by using a least square method_BA，Wherein A ═ H^TH)^-1H。

4. The method of multipath detection and mitigation using dual antennas of claim 3The method is characterized in that: the method for calculating the baseline vector estimation value according to the baseline vector observation value and the antenna baseline length comprises the following steps: singular Value Decomposition (SVD) of the matrix H:wherein in the Chinese formulaIs the positive singular value, λ, of the matrix H_iIs a characteristic value of H, D ═ diag (σ)₁,σ₂,σ₃) Is a diagonal matrix, and σ₁≥σ₂≥σ₃>0，μ_i、v_iColumn vectors of orthogonal matrices U and V, respectively; Δ X_BAThe variances of (d) are respectively noted as:ΔX_BAis marked asb_BA＝[b_x,b_y,b_z]^TIs the true value of the baseline vector, σ_X＝[σ_x,σ_y,σ_z]^T(ii) a Using observed values Δ X_BAAnd estimating a truth value with a known base line length d to construct an iterative equation b'_n+1＝b′_n+_XnWherein b'_nAnd b'_n+1B for the n-th and n + 1-th iteration, respectively_BAThe value of the estimated value is,_Xnis the residual of the nth estimate, the base length d can be expressed asLinear expansion of base length d using first order Taylor's formulaCalculating by using a least square method again to obtain residual error of each iteration_XnInitial value of iteration is observed value delta X of baseline vector_BAAnd iteratively calculated convergence value is recorded as b'_BAViewed as the true value b of the baseline vector_BAAn estimate of (d).

5. The multipath detection and mitigation method using dual antennas of claim 4, wherein: the method for calculating the sum of the squares of errors from the baseline vector estimates is: from b'_BAFor Δ X_BAThe result of normalization was designated as Δ X'_BA：ΔX'_BA＝(ΔX_BA-b'_BA)/σ_XWherein Δ X'_BA＝[Δx'_BA,Δy'_BA,Δz'_BA]^T,b'_BA＝[b′_x,b'_y,b′_z]^T(ii) a Using the sum of squared errors statistic to determine the quality of the baseline vector estimate, defining a sum of squared errors value Q as:

6. the multipath detection and mitigation method using dual antennas of claim 5, wherein: the threshold value is determined based on a false alarm rate.

7. The multipath detection and mitigation method using dual antennas of claim 6, wherein: the method for determining the threshold value according to the false alarm rate comprises the following steps: at a certain false alarm rate P_faLower setting of a suitable threshold value Q_th，WhereinIs x²(3) Δ X 'if there is at least one multipath signal in the currently received satellite signal'_BAN (0,1), then the Q statistic should obey a chi-square distribution with a degree of freedom of 3, noted as χ²(3) If there is a multipath signal, the Q index should beWhen the non-central chi-square distribution with the compliance degree of freedom of 3 and the parameter of gamma is recorded as chi²(3,γ)，

8. The multipath detection and mitigation method using dual antennas of claim 1, wherein: the method for calculating the carrier phase error estimated value caused by the multipath signal comprises the following steps: if the carrier phase error estimateBaseline vector observations containing multipath signalsThenWherein the carrier phase double difference observation matrixIs marked as Is a matrix of (N × 1) and is a baseline vector observation of carrier phase multipath error containing multipath signals

9. The multipath detection and mitigation method using dual antennas of claim 1, wherein: when at least one multipath signal exists in the currently received satellite signal, outputting prompt information of 'having multipath'; otherwise, outputting the prompt information of 'no multipath'.

10. A multipath detection and mitigation system using dual antennas, comprising:

the acquisition module is used for acquiring a carrier phase and a broadcast ephemeris of the GNSS signal;

the first calculation module is used for calculating the error square sum according to the carrier phase, the known antenna base length and the broadcast ephemeris;

the judging module is used for comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, considering that at least one multipath signal exists in the currently received satellite signal, and entering the second calculating module, otherwise, considering that the multipath signal does not exist currently, and directly entering the positioning module;

the second calculation module is used for calculating a carrier phase error estimation value caused by a multipath signal and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value;

and the positioning module is used for positioning the antenna.

Technical Field

The invention relates to the technical field of satellite measurement and control, in particular to a multipath detection and suppression method and system using double antennas.

Background

Navigation plays a very critical role throughout the development of human civilization, and its fundamental task is to clarify the location information of a carrier and guide the carrier from the current location to a destination according to a specified time and route. With the rapid improvement of the positioning precision of a global navigation satellite system (GNSS for short), the subjects of aviation, transportation, mapping, disaster monitoring and the like put higher requirements on high-precision positioning. The carrier phase ranging accuracy is higher than the code phase ranging accuracy, so the carrier phase ranging is usually adopted in the high-precision positioning and navigation scenarios. However, errors caused by satellite clock errors, satellite ephemeris errors, ionospheric delays, tropospheric delays and multipath effects can have a serious impact on the positioning accuracy. Multipath effects generally refer to the fact that the receiver not only receives the direct navigation signal, but also is interfered by various indirect signals, which are referred to as multipath signals. Since systematic errors can be eliminated based on the principle of difference or modeling, while multipath errors are usually time-varying and vary with the user's environment, they are usually difficult to suppress based on the difference technique, and have become the most important errors affecting high-precision positioning.

Current multipath detection and mitigation techniques are generally classified into three types: the design of navigation signals, antenna technology and data post-processing technology. The navigation signal design needs to change the existing navigation signal structure, and the implementation difficulty is quite huge. Antenna technologies are generally classified into two types, one is a right-hand circularly polarized antenna, a chocking antenna, and the like, which essentially prevent multipath signals from entering the antenna, thereby suppressing the multipath signals. However, this technique requires redesigning the receiving antenna and cannot fully utilize the existing low-cost antenna; another antenna technology is to use an antenna array, which can extract more information about satellite signals and reduce the influence of multipath signals well in subsequent processing, but the antenna array usually needs more than four antennas, which is relatively large in size and cost.

Data post-processing techniques typically do not require adjustments to the architecture of the receiver. The technology utilizes the frequency and the period characteristics of multipath, and processed information mainly comprises pseudo range, carrier phase and the like received by a receiver. The current research on the data post-processing technology is very sufficient and is widely used in engineering, but the technology has obvious defects, the technology needs to carry out long-time data observation, cannot carry out real-time processing, and has very limited application conditions.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to overcome the problems of the prior art that real-time processing cannot be performed and the application conditions are limited, thereby providing a method and a system for multi-path detection and suppression using dual antennas, which can perform real-time processing and have small limitation on the application conditions.

In order to solve the above technical problem, a multipath detection and suppression method using dual antennas of the present invention includes: step S1: acquiring a carrier phase and a broadcast ephemeris of a GNSS signal; step S2: calculating the error square sum according to the carrier phase, the known length of the antenna base line and the broadcast ephemeris; step S3: comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, determining that at least one multipath signal exists in the currently received satellite signal, and entering a step S4, otherwise, determining that the multipath signal does not exist currently, and entering a step S5; step S4: calculating a carrier phase error estimation value caused by a multipath signal, and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value; step S5: the antenna is positioned.

In one embodiment of the present invention, the method for calculating the sum of the squares of the errors according to the carrier phase, the known base length, and the broadcast ephemeris is: and calculating a baseline vector estimation value according to the carrier phase and the broadcast ephemeris, calculating a baseline vector observation value and an antenna baseline length, and calculating a sum of squares of errors according to the baseline vector estimation value.

In one embodiment of the present invention, the method of calculating the baseline vector observations is: assuming that the number of the current observable satellites is N, selecting the satellite signal with the highest elevation angle as a reference satellite; carrier phase double-difference observation matrixWhereinIs (N)× 1) matrix representing a carrier phase double difference observation matrix, H is an (N × 3) matrix representing the direction cosine difference between the satellite and the reference satellite and calculated from the broadcast ephemeris, N_rBAIs (N × 1) matrix, is zero mean Gaussian white noise and is recorded asThe observed value DeltaX of the baseline vector can be obtained by calculation by using a least square method_BA，Wherein A ═ H^TH)^-1H。

In an embodiment of the present invention, a method for calculating a baseline vector estimation value according to the baseline vector observation value and the antenna baseline length comprises: singular Value Decomposition (SVD) of the matrix H:wherein in the Chinese formulaIs the positive singular value, λ, of the matrix H_iIs a characteristic value of H, D ═ diag (σ)₁,σ₂,σ₃) Is a diagonal matrix, and σ₁≥σ₂≥σ₃>0，μ_i、v_iColumn vectors of orthogonal matrices U and V, respectively; Δ X_BAThe variances of (d) are respectively noted as: ΔX_BAis marked asb_BA＝[b_x,b_y,b_z]^TIs the true value of the baseline vector, σ_X＝[σ_x,σ_y,σ_z]^T(ii) a Using observed values Δ X_BAAnd are knownEstimating the truth value by the length d of the base line to construct an iterative equation b_n'₊₁＝b_n'+_XnWherein b'_nAnd b'_n+1B for the n-th and n + 1-th iteration, respectively_BAThe value of the estimated value is,_Xnis the residual of the nth estimate, the base length d can be expressed asLinear expansion of base length d using first order Taylor's formulaCalculating by using a least square method again to obtain residual error of each iteration_XnInitial value of iteration is observed value delta X of baseline vector_BAAnd iteratively calculated convergence value is recorded as b'_BAViewed as the true value b of the baseline vector_BAAn estimate of (d).

In one embodiment of the invention, the method of calculating the sum of the squares of errors from the baseline vector estimates is: from b'_BAFor Δ X_BAThe result of normalization was designated as Δ X'_BA：ΔX'_BA＝(ΔX_BA-b'_BA)/σ_XWherein Δ X'_BA＝[Δx'_BA,Δy'_BA,Δz'_BA]^T,b'_BA＝[b _{^' x},b'_y,b _{^' z}]^T(ii) a Using the sum of squared errors statistic to determine the quality of the baseline vector estimate, defining a sum of squared errors value Q as:

in one embodiment of the invention, the threshold value is determined based on a false alarm rate.

In an embodiment of the present invention, the method for determining the threshold value according to the false alarm rate includes: at a certain false alarm rate P_faLower setting of a suitable threshold valueWhereinIs x²(3) Δ X 'if there is at least one multipath signal in the currently received satellite signal'_BAN (0,1), then the Q statistic should obey a chi-square distribution with a degree of freedom of 3, noted as χ²(3) If there are multipath signals, the Q index should obey a non-central chi-squared distribution with a degree of freedom of 3 and a parameter of γ, denoted as χ²(3,γ)，

In one embodiment of the present invention, a method for calculating an estimated value of a carrier phase error caused by a multipath signal comprises: if the carrier phase error estimateBaseline vector observations containing multipath signalsThenWherein the carrier phase double difference observation matrixIs marked as Is a matrix of (N × 1) and is a baseline vector observation of carrier phase multipath error containing multipath signals

In one embodiment of the invention, when at least one multipath signal exists in the currently received satellite signal, the prompt message of 'multipath exists' is output; otherwise, outputting the prompt information of 'no multipath'.

The present invention also provides a multipath detection and mitigation system using dual antennas, comprising: the acquisition module is used for acquiring a carrier phase and a broadcast ephemeris of a mixed signal in the GNSS system; the first calculation module is used for calculating the error square sum according to the carrier phase, the known antenna base length and the broadcast ephemeris; the judging module is used for comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, considering that at least one multipath signal exists in the currently received satellite signal, and entering the second calculating module, otherwise, considering that the multipath signal does not exist currently, and directly entering the positioning module; the second calculation module is used for calculating a carrier phase error estimation value caused by a multipath signal and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value; and the positioning module is used for positioning the antenna.

Compared with the prior art, the technical scheme of the invention has the following advantages:

the multipath detection and suppression method and system using the double antennas acquire the carrier phase and the broadcast ephemeris of the GNSS signal, thereby being beneficial to calculating the error square sum; calculating the sum of squares of errors according to the carrier phase, the known length of the antenna base line and the broadcast ephemeris, and being beneficial to judging whether the test is satisfied; comparing the error square sum with a threshold value, judging whether the numerical value of the error square sum is larger than the threshold value, if so, considering that at least one multipath signal exists in the currently received satellite signal, and needing to suppress the multipath signal, otherwise, considering that the multipath signal does not exist currently; calculating a carrier phase error estimation value caused by a multipath signal, and calculating the carrier phase estimation value according to the carrier phase and the carrier phase error estimation value, thereby achieving the purpose of multipath signal suppression; the antenna is positioned, so that the positioning precision is effectively improved, in addition, the detection system and the size can be effectively reduced, the cost is reduced, and the real-time detection and the calculation are realized.

Drawings

In order that the present disclosure may be more readily and clearly understood, reference is now made to the following detailed description of the embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which

Fig. 1 is a flow chart of a multipath detection and mitigation method using dual antennas of the present invention.

Detailed Description