CN106597492A - Satellite navigation receiver and near-far effect resisting method and indoor positioning method thereof - Google Patents
Satellite navigation receiver and near-far effect resisting method and indoor positioning method thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
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Abstract
The invention is applicable to the field of satellite navigation, and especially relates to a satellite navigation receiver and a near-far effect resisting method and an indoor positioning method thereof. The satellite navigation receiver comprises an antenna unit, a radio-frequency unit, a baseband signal processing unit, a control and information processing unit, and a human-computer interaction unit, which are connected in sequence. The baseband signal processing unit is provided with a near-far effect inhibition unit which comprises a signal reconstruction module, a weak satellite signal tracking module, and at least one strong satellite signal tracking module. The strong satellite signal tracking module is composed of a first self-correlation module, a first cross-correlation module, a first subtracter, and a second subtracter. The weak satellite signal tracking module is composed of a second self-correlation module, a second cross-correlation module, a third subtracter, and a fourth subtracter. The ability of the satellite navigation receiver to resist the near-far effect can be enhanced.
Description
Technical Field
The invention belongs to the field of satellite navigation, and particularly relates to a satellite navigation receiver, a near-far effect resisting method thereof and an indoor positioning method.
Background
The current GNSS (Global Navigation Satellite System) mainly includes: the GNSS is a radio Positioning System, and obtains a linear distance from a satellite navigation receiver to a satellite by estimating a propagation delay of radio waves from the satellite to the satellite navigation receiver, which is a distance measurement method using an arrival time.
Due to the limitation of an indoor pseudo satellite system, such as low satellite arrangement height, large elevation angle change, narrow indoor environment, complexity, variability and other factors, a received pseudo satellite signal can be obviously changed when a satellite navigation receiver moves indoors, and the power attenuation can reach 6dB when the distance is doubled. When the satellite navigation receiver is close to one or two pseudo satellites at the same time, the power of the pseudo satellite signal close to the satellite navigation receiver can be obviously improved, so that the ground noise power of the antenna end of the satellite navigation receiver can be improved, namely, the near-far effect occurs, the capturing and tracking of the pseudo satellite signal far away from the satellite navigation receiver are influenced, even the satellite loss situation occurs, and the positioning of the satellite navigation receiver is influenced.
Since the CA codes are not strictly orthogonal, and the isolation is about 24dB, when the power difference between the two pseudolite signals exceeds a threshold, the cross-correlation power of the strong satellite signal and the weak satellite signal is significantly increased, thereby affecting the autocorrelation result of the weak satellite signal, and finally causing the weak satellite signal to be submerged in noise. The key to suppressing cross-correlation interference is to obtain parameters of the strong satellite signal to accurately reproduce the strong satellite signal. The signal parameters include carrier frequency, carrier phase, code phase, amplitude, and textual bits. The effect of cross-correlation suppression depends directly on the accuracy of the locally reproduced strong satellite signal. The satellite navigation receiver can realize accurate tracking on the strong satellite signal through the carrier ring and the code ring of the satellite navigation receiver through stable tracking on the strong satellite signal for a certain time, so that the carrier frequency, the carrier phase and the code phase can be directly extracted and obtained from the loop. The textual bits may be given by a textual predictor. The performance of cross-correlation suppression then depends directly on the accuracy of the estimation of the amplitude.
Disclosure of Invention
The invention aims to provide a satellite navigation receiver capable of resisting a near-far effect, a near-far effect resisting method thereof and an indoor positioning method.
In a first aspect, the present invention provides a satellite navigation receiver, which includes an antenna unit, a radio frequency unit, a baseband signal processing unit, a control and information processing unit, and a human-computer interaction unit, which are connected in sequence, where the baseband signal processing unit has a near-far effect suppression unit, the near-far effect suppression unit includes a signal reconstruction module, a weak satellite signal tracking module, and at least one strong satellite signal tracking module, the strong satellite signal tracking module includes a first autocorrelation module, a first cross-correlation module, a first subtractor, and a second subtractor, the weak satellite signal tracking module includes a second autocorrelation module, a second cross-correlation module, a third subtractor, and a fourth subtractor, where an input end of the first autocorrelation module and an input end of the second autocorrelation module are connected to an output end of the radio frequency unit, an input signal of the first cross-correlation module is 0, the first output end of the first autocorrelation module and the first output end of the first cross-correlation module are respectively connected with two input ends of a first subtracter, the second output end of the first autocorrelation module and the second output end of the first cross-correlation module are respectively connected with two input ends of a second subtracter, the reconstructed signal output end of the first autocorrelation module is connected with the input end of a signal reconstruction module, the amplitude control end of the signal reconstruction module is connected with a control and information processing unit and provided with amplitude control by the control and information processing unit, the output end of the signal reconstruction module is connected with the input end of the second cross-correlation module, the first output end of the second autocorrelation module and the first output end of the second cross-correlation module are respectively connected with two input ends of a third subtracter, the second output end of the second autocorrelation module and the second output end of the second cross-correlation module are respectively connected with two input ends of a fourth subtracter, the enabling end of the first autocorrelation module is connected with the control and information processing unit, the control and information processing unit provides enabling control, the amplitude control end of the second cross-correlation module is connected with the control and information processing unit, the control and information processing unit provides amplitude control, and the output ends of the first subtracter, the second subtracter, the third subtracter and the fourth subtracter are connected with the control and information processing unit and used for the control and information processing unit to perform tracking control.
In a second aspect, the present invention provides a method for resisting a near-far effect of a satellite navigation receiver, where the satellite navigation receiver is the above satellite navigation receiver, and the method includes:
when the carrier-to-noise ratio of a satellite signal in the tracked satellite signals is lower than a low threshold, the satellite navigation receiver searches whether the carrier-to-noise ratio of all the tracked satellite signals is higher than a high threshold;
if the carrier-to-noise ratio of the satellite signal of at least one channel is higher than a high threshold, determining that a near-far effect occurs, enabling a first autocorrelation module of a strong satellite signal tracking module to output a reconstruction signal by a satellite navigation receiver, enabling a signal reconstruction module to output a reconstruction signal, and sending the reconstruction signal into a second cross-correlation module of a weak satellite signal tracking module; in the next tracking interruption, the satellite navigation receiver takes the integration result of the weak satellite signal tracking module after the cross-correlation is reduced as the input of the phase discriminator.
In a third aspect, the present invention provides an indoor positioning method for a satellite navigation receiver, where the satellite navigation receiver is the above satellite navigation receiver, and the method includes:
the satellite navigation receiver is started or reset from a known position, and the signals of all the pseudo satellites are captured in a code phase parallel and frequency serial mode;
after the satellite navigation receiver finishes capturing and pulling each pseudo satellite at a known position, tracking and demodulating a navigation message; after the satellite navigation receiver acquires the coordinates of the satellite from the navigation message of the pseudolite, the carrier whole-cycle ambiguity of the satellite navigation receiver is statically initialized, and after all the pseudolites complete the carrier whole-cycle ambiguity initialization, the satellite navigation receiver completes the static initialization;
after the satellite navigation receiver completes static initialization, the satellite navigation receiver freely moves and extracts a carrier phase measurement value of a pseudo satellite in real time;
according to the carrier phase measurement value of the pseudolite, a CHAN algorithm is adopted as a positioning resolving algorithm to realize indoor positioning of the satellite navigation receiver;
and transmitting the positioning result and the coordinate parameters of each pseudolite to an upper computer for displaying.
In the invention, the near-far effect suppression unit comprises a signal reconstruction module, a weak satellite signal tracking module and at least one strong satellite signal tracking module, the strong satellite signal tracking module comprises a first autocorrelation module, a first cross-correlation module, a first subtracter and a second subtracter, the weak satellite signal tracking module comprises a second autocorrelation module, a second cross-correlation module, a third subtracter and a fourth subtracter, the reconstructed signal output end of the first autocorrelation module is connected with the input end of the signal reconstruction module, the amplitude control end of the signal reconstruction module is connected with the control and information processing unit, amplitude control is provided by the control and information processing unit, and the output end of the signal reconstruction module is connected with the input end of the second cross-correlation module. Therefore, the tracking capability of the satellite navigation receiver for weak satellite signals under the condition of strong interference can be obviously improved, the maximum power value difference value of different pseudo satellites allowed to arrive at the same time is greatly improved, the near-far effect resisting capability of the satellite navigation receiver is obviously enhanced, and the effective positioning area of the satellite navigation receiver in an indoor pseudo satellite system is enlarged.
In addition, according to the carrier phase measurement value of the pseudolite, the CHAN algorithm is adopted as a positioning calculation algorithm to realize the indoor positioning of the satellite navigation receiver, so that the influence of the clock drift of the pseudolite system adopting the constant temperature crystal on the distance measurement result can be effectively eliminated on the premise of realizing time synchronization in the pseudolite system, the high-precision positioning can be realized before the time synchronization of the satellite navigation receiver and the pseudolite system is not finished, and the method is suitable for various indoor pseudolite systems. And the calculation amount of the CHAN is smaller than that of a least square method commonly used by a satellite navigation receiver, so that the satellite navigation receiver can realize real-time positioning.
Drawings
Fig. 1 is a schematic structural diagram of a satellite navigation receiver according to an embodiment of the present invention.
Fig. 2 is a circuit block diagram of a near-far effect suppression unit in a satellite navigation receiver according to an embodiment of the present invention.
Fig. 3 is a circuit block diagram of a first autocorrelation module and a second autocorrelation module in a near-far effect suppression unit of a satellite navigation receiver according to an embodiment of the present invention.
Fig. 4 is a circuit block diagram of a first cross-correlation module in a near-far effect suppression unit of a satellite navigation receiver according to an embodiment of the present invention.
Fig. 5 is a circuit block diagram of a second cross-correlation module in a near-far effect suppression unit of a satellite navigation receiver according to an embodiment of the present invention.
Fig. 6 is a circuit block diagram of a signal reconstruction module in a near-far effect suppression unit of a satellite navigation receiver according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
The first embodiment is as follows:
referring to fig. 1, a satellite navigation receiver according to an embodiment of the present invention may be used for receiving a satellite navigation signal of an indoor pseudo satellite system, and the satellite navigation receiver includes an antenna unit 11, a radio frequency unit 12, a baseband signal processing unit 13, a control and information processing unit 14, and a human-computer interaction unit 15, which are connected in sequence, where the baseband signal processing unit 13 has a near-far effect suppression unit 131.
Referring to fig. 2, the near-far effect suppression unit includes a signal reconstruction module 1311, a weak satellite signal tracking module 1313, and at least one strong satellite signal tracking module 1312, the strong satellite signal tracking module 1312 includes a first autocorrelation module 13121, a first cross-correlation module 13122, a first subtractor 13123, and a second subtractor 13124, the weak satellite signal tracking module 1313 includes a second autocorrelation module 13131, a second cross-correlation module 13132, a third subtractor 13133, and a fourth subtractor 13134, wherein an input terminal of the first autocorrelation module 13121 and an input terminal of the second autocorrelation module 13131 are respectively connected to an output terminal of the radio frequency unit, an input signal of the first cross-correlation module 13122 is 0, a first output terminal of the first autocorrelation module 13121 and a first output terminal of the first cross-correlation module 13122 are respectively connected to two input terminals of the first subtractor 13123, a second output terminal of the first autocorrelation module 13121 and a second output terminal of the first cross-correlation module 13122 are respectively connected to two input terminals of the second subtractor 13124, the reconstructed signal output of the first autocorrelation module 13121 is connected to the input of the signal reconstruction module 1311, the amplitude control of the signal reconstruction module 1311 is connected to the control and information processing unit, the control and information processing unit provides the amplitude control, the output of the signal reconstruction module 1311 is connected to the input of the second cross-correlation module 13132, the first output of the second autocorrelation module 13131 and the first output of the second cross-correlation module 13132 are connected to two inputs of the third subtractor 13133, respectively, the second output of the second autocorrelation module 13131 and the second output of the second cross-correlation module 13132 are connected to two inputs of the fourth subtractor 13134, respectively, the enable of the first autocorrelation module 13121 is connected to the control and information processing unit, the enable control is provided by the control and information processing unit, the amplitude control of the second cross-correlation module 13132 is connected to the control and information processing unit, amplitude control is provided by the control and information processing unit. The outputs of the first 13123, second 13124, third 13133 and fourth 13134 subtractors are connected to the control and information processing unit for tracking control by the control and information processing unit.
Referring to fig. 3, each of the first autocorrelation module and the second autocorrelation module includes a carrier numerically controlled oscillator 21, a pseudo code generator 22, a first integrator 23, and a second integrator 24, where the carrier numerically controlled oscillator 21 generates two orthogonal carriers to multiply the digital intermediate frequency signals output by the radio frequency unit, so as to obtain carrier-stripped digital baseband signals respectively; the pseudo-code generator 22 multiplies the digital baseband signals stripped from the carrier respectively, the multiplied results are respectively used as the input of a first integrator 23 and a second integrator 24, and the output ends of the first integrator 23 and the second integrator 24 are respectively used as the first output end and the second output end of the first autocorrelation module and the second autocorrelation module.
The first autocorrelation module further comprises a text predictor 25, and the in-phase branch of the carrier numerically controlled oscillator 21 is multiplied by the pseudo-code generator 22, the text predictor 25 and the enable signal provided by the control and information processing unit to obtain a reconstructed signal.
Referring to fig. 4, the first cross-correlation module includes a carrier numerically controlled oscillator 31, a pseudo-code generator 32, a third integrator 33 and a fourth integrator 34, where the carrier numerically controlled oscillator 31 generates two orthogonal carriers to multiply the input signal 0, so as to obtain carrier-stripped digital baseband signals respectively; the pseudo-code generator 32 multiplies the digital baseband signals stripped of the carriers by one another, and the multiplication results are input to the third integrator 33 and the fourth integrator 34, respectively, and the output terminals of the third integrator 33 and the fourth integrator 34 are input to the first cross-correlation module as the first output terminal and the second output terminal, respectively. The carrier numerically controlled oscillator and the pseudo-code generator of the first cross-correlation module may be common to the carrier numerically controlled oscillator and the pseudo-code generator of the first autocorrelation module.
Referring to fig. 5, the second cross-correlation module includes a carrier numerically controlled oscillator 41, a pseudo-code generator 42, a fifth integrator 43 and a sixth integrator 44, where the carrier numerically controlled oscillator 41 generates two orthogonal carriers to multiply the reconstructed signals output by the signal reconstruction module, so as to obtain carrier-stripped digital baseband signals respectively; the pseudo-code generator 42 multiplies the digital baseband signals of the stripped carriers respectively, the multiplied results are used as the input of the fifth integrator 43 and the sixth integrator 44 respectively, the output signals of the fifth integrator 43 and the sixth integrator 44 are multiplied with the amplitude control signal provided by the control and information processing unit respectively, and two multiplied output ends are used as the first output end and the second output end of the second cross-correlation module respectively. The carrier numerically controlled oscillator and the pseudo-code generator of the second cross-correlation module may be common to the carrier numerically controlled oscillator and the pseudo-code generator of the second autocorrelation module.
Referring to fig. 6, the signal reconstruction module includes N-way multipliers 51 connected in series to 1-way N-input adders 52, where N is a natural number greater than or equal to 1. The output signal of the first autocorrelation module of each strong satellite signal tracking module is sent to an N input adder 52 after the amplitude of the output signal is controlled by a multiplier 51; the N-input adder 52 is enabled when the satellite navigation receiver determines that there is near-far effect interference, and outputs a reconstructed signal composed of N reconstructed signals to the second cross-correlation module of the weak satellite signal tracking module at each moment.
Example two:
the second embodiment of the present invention provides a method for resisting a near-far effect for a satellite navigation receiver, where the satellite navigation receiver is the first embodiment of the present invention, and the method includes the following steps:
when the carrier-to-noise ratio of a satellite signal in the tracked satellite signals is lower than a low threshold, the satellite navigation receiver searches whether the carrier-to-noise ratio of all the tracked satellite signals is higher than a high threshold;
if the carrier-to-noise ratio of the satellite signal of at least one channel is higher than a high threshold, determining that a near-far effect occurs, enabling a first autocorrelation module of a strong satellite signal tracking module to output a reconstruction signal by a satellite navigation receiver, enabling a signal reconstruction module to output a reconstruction signal, and sending the reconstruction signal into a second cross-correlation module of a weak satellite signal tracking module; in the next tracking interruption, the satellite navigation receiver takes an integral result obtained after cross correlation in the weak satellite signal tracking module is reduced as the input of the phase discriminator;
and if the carrier-to-noise ratio of the satellite signal without the channel is higher than the high threshold, judging that the near-far effect does not occur, and prolonging the coherent integration time of the weak satellite signal tracking module by the satellite navigation receiver.
In the second embodiment of the present invention, the parameters of the strong satellite signal include: navigation message symbol DiCode phase tau of CA codeiCarrier wave doppler fdiCarrier phaseAnd signal amplitude Ai. The normalized amplitude representationIs composed ofThe reconstruction signal output by the signal reconstruction module is as follows:
wherein A is the amplitude used for reference in normalization and is taken from any strong satellite signal channel; t is time; CAiIs a pseudo code variable of strong signal; f. ofIFIs the intermediate frequency.
The parameters of the weak satellite signal include: doppler fdwCarrier phaseSum code phase τw. The cross-correlation operation result of the weak satellite signal and the reconstructed signal is as follows:
wherein, CAwIs a pseudo code variable of a weak signal, and the output of a second cross-correlation module of the weak satellite signal tracking module is IcAnd QcThe output of the second autocorrelation module is I and Q, so that the cross-correlation is reducedw、QwThe road integral result is:
Iw＝I-A·Ic
Qw＝Q-A·Qc
because the algorithm normalizes all the strong signal amplitudes by adopting one reference strong signal amplitude and only uses one estimation channel to estimate the cross-correlation interference of all the strong signals, the hardware overhead is reduced and the hardware implementation is facilitated.
Example three:
the third embodiment of the present invention provides an indoor positioning method for a satellite navigation receiver, where the satellite navigation receiver is the first embodiment of the present invention, and the method includes the following steps:
the satellite navigation receiver is started or reset from a known position, and the signals of all the pseudo satellites are captured in a code phase parallel and frequency serial mode; under the premise that the pseudo satellite system realizes clock synchronization in the network, pseudo satellites captured by the satellite navigation receiver should have the same carrier Doppler value, otherwise, the satellite navigation receiver captures each pseudo satellite signal again;
after the satellite navigation receiver finishes capturing and pulling each pseudo satellite at a known position, tracking and demodulating a navigation message; after the satellite navigation receiver acquires the coordinates of the satellite from the navigation message of the pseudolite, the carrier whole-cycle ambiguity of the satellite navigation receiver is statically initialized, and after all the pseudolites complete the carrier whole-cycle ambiguity initialization, the satellite navigation receiver completes the static initialization;
after the satellite navigation receiver completes static initialization, the satellite navigation receiver freely moves and extracts a carrier phase measurement value of a pseudo satellite in real time;
according to the carrier phase measurement value of the pseudolite, a CHAN algorithm is adopted as a positioning resolving algorithm to realize indoor positioning of the satellite navigation receiver; when the near-far effect occurs in the moving process, the satellite navigation receiver can adopt the method for resisting the near-far effect of the satellite navigation receiver provided by the second embodiment of the invention to inhibit the near-far effect;
and transmitting the positioning result and the coordinate parameters of each pseudolite to an upper computer for displaying.
The Chan algorithm is a positioning algorithm based on a TDOA positioning technology and provided with an analytic expression solution, and the performance is good when TDOA errors follow ideal Gaussian distribution. The TDOA location technique is a method of location using time difference.
In the third embodiment of the present invention, the satellite navigation receiver needs to be initialized from a known position, and the initial coordinates of the satellite navigation receiver are assumed to be (x, y), and the coordinates of the ith pseudolite are assumed to be (xi,yi) The expression of the carrier integer ambiguity at the initial position is as follows:
wherein [ ·]Representing a rounding operation, Ni0Represents the integer ambiguity of the ith pseudolite, or base station, and λ is the carrier wavelength. The carrier phase measurement for the ith pseudolite, i.e., the distance between the satellite navigation receiver and the base station, can be expressed as:
the initial coordinates can be issued by an upper computer through a serial port or acquired by other wireless communication modes. Wherein,is thatThe fractional part of (a) is,the carrier phase change value after the initialization is completed can be obtained by a code ring NCO of a satellite navigation receiver.
The method for realizing indoor positioning of the satellite navigation receiver by using the CHAN algorithm as the positioning calculation algorithm according to the carrier phase measurement value of the pseudolite specifically comprises the following steps:
assuming a two-dimensional planar area, the signal is from the ith base station (x)i,yi) Transmitting to a satellite navigation receiver (x, y), the distance R of the satellite navigation receiver to the base stationiHas a square of
Wherein,let us denote the difference in distance from the ith base station to the first base station as Ri,1Then, then
Where c is the speed of light in vacuum, ti,1Is the measurement time difference of TDOA.
And because of
When the value of i is 1, the value of i,
subtracting formula (2-4) from formula (2-3) to obtain
Wherein x isi,1＝xi-x1，yi,1＝yi-y1. X, y, R1When the unknown number is considered, the equation (2-5) becomes a linear equation system.
Considering the case of only three base stations, the coordinates (x, y) of the satellite navigation receiver in equation (2-5) can be solved as
Substituting formula (2-6) intoIn (b), a compound of formula (I) can be obtained1The positive root of the quadratic equation of (a) is the position estimate of the satellite navigation receiver. When two positive roots appear in the equation, the false root can be eliminated according to the information such as the size of the positioning area, the navigation message and the like.
When four or more base stations participate in the location, the CHAN algorithm optimizes the location result by making use of the redundant TDOA measurements provided by the base stations. Is provided withAs an unknown vector, zp＝[x,y]TFor the position of the object to be determined, the error vector can be obtained from equation (2-5) as
Wherein,
{*}0is a noiseless measurement, {. indicates all expressions, ni,1Representing measurement noise, thenTherefore, the error vector can be expressed as
Wherein, is the Schur product and n is the measurement noise matrix. In the practical application of the method, the air conditioner,the error vector can be viewed as a random vector that is approximately normally distributed with a covariance of
Ψ＝E[ψψT]＝c2BQB (2-9)
Where Q is the covariance matrix of the TDOA measurement noise. The approximate solution of Weighted Least Squares (WLS) of equations (2-9) is
If the undetermined target is far away from the base station, defining a distance R0Andrelatively close, then B ≈ R0I and I are unit arrays. The above formula can be replaced by
If the distance between the object to be determined and the base station is short, an initial solution can be obtained by the formula (2-11)B is calculated and then the satellite navigation receiver position is derived from equation (2-10), which is the first WLS calculation.
Continuing with the WLS calculation, it is necessary to first find the covariance matrix of the estimated position of the satellite navigation receiver. In the case where the noise is considered,
and ish＝h0+ Δ h, due toThe formula (2-7) can be formed into
Order toSubstituted by formula (2-10) to obtain
Retaining only the linear perturbation part of formula (2-14), combining formulas (2-8) and (2-16), to obtain Δ ZaAnd its covariance matrix is
When the TDOA measurement error is small, the deviation is negligible, ZaIs a vector whose mean value is the actual value, ZaCan be expressed as
Wherein e is1,e2,e3The estimation error of each component is respectively. Will ZaThe first two elements are respectively equal to x1,y1Subtracting and then squaring each element
The above formula is abbreviated as
ψ′＝h′-Ga′Za′ (2-19)
The above equation is approximately satisfied only when the error is relatively small. The covariance matrix of psi' is
Psi' obeys a Gaussian distribution as well as psi, the second step WLS is estimated as
The matrix psi 'contains the true coordinates of the satellite navigation receiver, and B' can be represented by ZaThe calculation is carried out by deduction to obtain,can be composed of GaApproximate substitution. Substitution of the result of formula (2-21) into formula (2-9)Matrix B, if the satellite navigation receiver is farther from the base station, ZaCan be expressed as
In this case, the formula (2-21) can be simplified to
Thus, the final estimate of the satellite navigation receiver position is
Wherein Z isa' is the error correction estimated by the second step WLS. And determining the final position of the satellite navigation receiver according to the size of the positioning area, the navigation message and other information.
The CHAN algorithm can also be generalized to the case of three-dimensional positioning, which is not described herein. The CHAN algorithm is a variant of the least square method, but the calculation amount is small, and the hardware cost is small. And the first-order difference result of the carrier phase measurement value between the satellites is used as input, positioning calculation can be realized before the satellite navigation receiver and the pseudolite complete clock synchronization, the influence of clock bias and clock drift of the pseudolite and the satellite navigation receiver is avoided, and the premise is that the pseudolite system completes time synchronization in the network.
In the invention, the near-far effect suppression unit comprises a signal reconstruction module, a weak satellite signal tracking module and at least one strong satellite signal tracking module, the strong satellite signal tracking module comprises a first autocorrelation module, a first cross-correlation module, a first subtracter and a second subtracter, the weak satellite signal tracking module comprises a second autocorrelation module, a second cross-correlation module, a third subtracter and a fourth subtracter, the reconstructed signal output end of the first autocorrelation module is connected with the input end of the signal reconstruction module, the amplitude control end of the signal reconstruction module is connected with the control and information processing unit, amplitude control is provided by the control and information processing unit, and the output end of the signal reconstruction module is connected with the input end of the second cross-correlation module. Therefore, the tracking capability of the satellite navigation receiver for weak satellite signals under the condition of strong interference can be obviously improved, the maximum power value difference value of different pseudo satellites allowed to arrive at the same time is greatly improved, the near-far effect resisting capability of the satellite navigation receiver is obviously enhanced, and the effective positioning area of the satellite navigation receiver in an indoor pseudo satellite system is enlarged.
In addition, according to the carrier phase measurement value of the pseudolite, the CHAN algorithm is adopted as a positioning calculation algorithm to realize the indoor positioning of the satellite navigation receiver, so that the influence of the clock drift of the pseudolite system adopting the constant temperature crystal on the distance measurement result can be effectively eliminated on the premise of realizing time synchronization in the pseudolite system, the high-precision positioning can be realized before the time synchronization of the satellite navigation receiver and the pseudolite system is not finished, and the method is suitable for various indoor pseudolite systems. And the calculation amount of the CHAN is smaller than that of a least square method commonly used by a satellite navigation receiver, so that the satellite navigation receiver can realize real-time positioning.
It will be understood by those skilled in the art that all or part of the steps in the method for implementing the above embodiments may be implemented by relevant hardware instructed by a program, and the program may be stored in a computer-readable storage medium, such as ROM/RAM, magnetic disk, optical disk, etc.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. A satellite navigation receiver comprises an antenna unit, a radio frequency unit, a baseband signal processing unit, a control and information processing unit and a man-machine interaction unit which are connected in sequence, and is characterized in that the baseband signal processing unit is provided with a near-far effect suppression unit, the near-far effect suppression unit comprises a signal reconstruction module, a weak satellite signal tracking module and at least one strong satellite signal tracking module, the strong satellite signal tracking module comprises a first autocorrelation module, a first cross-correlation module, a first subtracter and a second subtracter, the weak satellite signal tracking module comprises a second autocorrelation module, a second cross-correlation module, a third subtracter and a fourth subtracter, wherein the input end of the first autocorrelation module and the input end of the second autocorrelation module are respectively connected with the output end of the radio frequency unit, and the input signal of the first cross-correlation module is 0, the first output end of the first autocorrelation module and the first output end of the first cross-correlation module are respectively connected with two input ends of a first subtracter, the second output end of the first autocorrelation module and the second output end of the first cross-correlation module are respectively connected with two input ends of a second subtracter, the reconstructed signal output end of the first autocorrelation module is connected with the input end of a signal reconstruction module, the amplitude control end of the signal reconstruction module is connected with a control and information processing unit and provided with amplitude control by the control and information processing unit, the output end of the signal reconstruction module is connected with the input end of the second cross-correlation module, the first output end of the second autocorrelation module and the first output end of the second cross-correlation module are respectively connected with two input ends of a third subtracter, the second output end of the second autocorrelation module and the second output end of the second cross-correlation module are respectively connected with two input ends of a fourth subtracter, the enabling end of the first autocorrelation module is connected with the control and information processing unit, the control and information processing unit provides enabling control, the amplitude control end of the second cross-correlation module is connected with the control and information processing unit, the control and information processing unit provides amplitude control, and the output ends of the first subtracter, the second subtracter, the third subtracter and the fourth subtracter are connected with the control and information processing unit and used for the control and information processing unit to perform tracking control.
2. The satellite navigation receiver of claim 1, wherein the first autocorrelation module and the second autocorrelation module each include a carrier numerically controlled oscillator, a pseudo-code generator, a first integrator, and a second integrator, the carrier numerically controlled oscillator generates two orthogonal carriers to multiply the digital intermediate frequency signals output by the radio frequency unit, and the two orthogonal carriers are multiplied by the digital intermediate frequency signals to obtain carrier-stripped digital baseband signals, respectively; the pseudo code generator is respectively multiplied with the digital baseband signals of the stripped carriers, the multiplied results are respectively used as the input of the first integrator and the second integrator, and the output ends of the first integrator and the second integrator are respectively used as the first output end and the second output end of the first autocorrelation module and the second autocorrelation module.
3. The satellite navigation receiver of claim 2, wherein the first autocorrelation module further includes a text predictor, and wherein the in-phase branch of the carrier numerically controlled oscillator is multiplied by the enable signal provided by the pseudo-code generator, the text predictor, and the control and information processing unit to obtain the reconstructed signal.
4. The satellite navigation receiver of claim 1, wherein the first cross-correlation module comprises a carrier numerically controlled oscillator, a pseudo-code generator, a third integrator and a fourth integrator, wherein the carrier numerically controlled oscillator generates two orthogonal carriers to multiply the input signal 0 to obtain carrier-stripped digital baseband signals, respectively; the pseudo code generator is respectively multiplied with the digital baseband signals of the stripped carriers, the multiplied results are respectively used as the input of a third integrator and a fourth integrator, and the output ends of the third integrator and the fourth integrator are respectively used as the first output end and the second output end of the first cross-correlation module.
5. The satellite navigation receiver of claim 1, wherein the second cross-correlation module comprises a carrier numerically controlled oscillator, a pseudo-code generator, a fifth integrator and a sixth integrator, wherein the carrier numerically controlled oscillator generates two orthogonal carriers to be multiplied by the reconstructed signal output by the signal reconstruction module to obtain carrier-stripped digital baseband signals, respectively; the pseudo-code generator is respectively multiplied with the digital baseband signals of the stripped carriers, the multiplied results are respectively used as the input of a fifth integrator and a sixth integrator, the output signals of the fifth integrator and the sixth integrator are respectively multiplied with the amplitude control signal provided by the control and information processing unit, and two multiplied output ends are respectively used as a first output end and a second output end of the second cross-correlation module.
6. The satellite navigation receiver of claim 1, wherein the signal reconstruction module includes N multipliers connected to 1N input adders in sequence, N is a natural number greater than or equal to 1, and an output signal of the first autocorrelation module of each strong satellite signal tracking module is fed to the N input adders after being amplitude-controlled by the multipliers; the N input summers are enabled when the satellite navigation receiver judges that the interference of the near-far effect exists, and a reconstructed signal formed by N paths of reconstructed signals is output to a second cross-correlation module of the weak satellite signal tracking module at each moment.
7. A method for resisting near-far effect of a satellite navigation receiver, wherein the satellite navigation receiver is the satellite navigation receiver of any one of claims 1 to 6, the method comprising:
when the carrier-to-noise ratio of a satellite signal in the tracked satellite signals is lower than a low threshold, the satellite navigation receiver searches whether the carrier-to-noise ratio of all the tracked satellite signals is higher than a high threshold;
if the carrier-to-noise ratio of the satellite signal of at least one channel is higher than a high threshold, determining that a near-far effect occurs, enabling a first autocorrelation module of a strong satellite signal tracking module to output a reconstruction signal by a satellite navigation receiver, enabling a signal reconstruction module to output a reconstruction signal, and sending the reconstruction signal into a second cross-correlation module of a weak satellite signal tracking module; in the next tracking interruption, the satellite navigation receiver takes the integration result of the weak satellite signal tracking module after the cross-correlation is reduced as the input of the phase discriminator.
8. The method of claim 7, wherein after the satellite navigation receiver searches all tracked satellite signals for signals having an on-load-to-noise ratio above a high threshold, the method further comprises: and if the carrier-to-noise ratio of the satellite signal without the channel is higher than the high threshold, judging that the near-far effect does not occur, and prolonging the coherent integration time of the weak satellite signal tracking module by the satellite navigation receiver.
9. An indoor positioning method of a satellite navigation receiver, wherein the satellite navigation receiver is the satellite navigation receiver of any one of claims 1 to 6, the method comprising:
the satellite navigation receiver is started or reset from a known position, and the signals of all the pseudo satellites are captured in a code phase parallel and frequency serial mode;
after the satellite navigation receiver finishes capturing and pulling each pseudo satellite at a known position, tracking and demodulating a navigation message; after the satellite navigation receiver acquires the coordinates of the satellite from the navigation message of the pseudolite, the carrier whole-cycle ambiguity of the satellite navigation receiver is statically initialized, and after all the pseudolites complete the carrier whole-cycle ambiguity initialization, the satellite navigation receiver completes the static initialization;
after the satellite navigation receiver completes static initialization, the satellite navigation receiver freely moves and extracts a carrier phase measurement value of a pseudo satellite in real time;
according to the carrier phase measurement value of the pseudolite, a CHAN algorithm is adopted as a positioning resolving algorithm to realize indoor positioning of the satellite navigation receiver;
and transmitting the positioning result and the coordinate parameters of each pseudolite to an upper computer for displaying.
10. The method of claim 9, wherein the satellite navigation receiver enables a first autocorrelation module of the strong satellite signal tracking module to output the reconstructed signal and enables a signal reconstruction module to output the reconstructed signal and feeds the reconstructed signal into a second cross-correlation module of the weak satellite signal tracking module when a near-far effect occurs during the movement; in the next tracking interruption, the satellite navigation receiver takes the integration result of the weak satellite signal tracking module after the cross-correlation is reduced as the input of the phase discriminator.
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