JP5519223B2 - Satellite signal receiver - Google Patents

Description

  The present invention relates to a satellite signal receiving apparatus having a plurality of tracking channels for tracking a signal from a satellite.

  Conventionally, in a GNSS (Global Navigation Satellite System) such as GPS (Global Positioning System) or Galileo, a satellite signal receiver uses a plurality of tracking channels to track signals (satellite signals) transmitted from a plurality of satellites. Then, the position (receiver position) of the satellite signal receiving device is obtained using information from the satellite obtained by tracking.

  In this case, each tracking channel has a carrier tracking loop that tracks a carrier in a signal by PLL (Phase Locked Loop) control or FLL (Frequency Locked Loop) control, and a code in the signal by DLL (Delay Locked Loop) control. A code tracking loop for tracking is provided, and a carrier wave and a code in a signal are tracked independently for each tracking channel.

  Therefore, in a tracking channel that tracks a strong signal having a relatively strong signal level (a satellite signal having a signal level stronger than noise), tracking performance for the strong signal can be ensured, but on the other hand, a weak signal having a relatively weak signal level. In a tracking channel that tracks (satellite signal of a signal level buried in noise), the tracking performance deteriorates and the tracking becomes unstable, and as a result, there is a possibility that the noise is tracked erroneously instead of the weak signal. There is.

  Therefore, Patent Document 1 supports tracking processing of a tracking channel that tracks a weak signal by using tracking information related to the strong signal that is output from the tracking channel that tracks a strong signal. It has been proposed to improve the tracking performance.

Japanese Patent No. 4109097

  By the way, when the satellite signal receiving device is mounted on the mobile body or when the user has a portable terminal equipped with the satellite signal receiving device, the satellite signal receiving device also moves when the mobile body or the user moves. Therefore, the signal reception frequency changes due to the Doppler shift caused by the change in the relative position of the satellite signal receiving apparatus with respect to the satellite.

  However, since the technique of Patent Literature 1 does not assume any movement of the satellite signal receiving device, it is difficult to improve the tracking performance of the weak signal when the moving satellite signal receiving device receives the weak signal. It is.

  The present invention has been made in consideration of such a problem, and an object of the present invention is to provide a satellite signal receiver capable of improving tracking performance for weak signals in a movable satellite signal receiver. And

A satellite signal receiving device according to the present invention is a satellite signal receiving device having a plurality of tracking channels for tracking a signal from a satellite.
Each tracking channel includes a carrier tracking loop that tracks a carrier wave in the signal and outputs tracking information related to the carrier wave, and a code tracking loop that tracks a code in the signal, respectively.
The satellite signal receiving device is configured to estimate a moving speed of the satellite signal receiving device based on tracking information output from a carrier tracking loop of a tracking channel that tracks a strong signal having a relatively strong signal level; A frequency estimator that estimates a reception frequency of a weak signal having a relatively weak signal level based on a moving speed and outputs the estimated reception frequency to a tracking channel that tracks the weak signal;
The carrier tracking loop of the tracking channel that tracks the weak signal tracks the carrier in the weak signal using the reception frequency estimated by the frequency estimator, while the code tracking loop of the tracking channel It is characterized in that a code in the weak signal is tracked using a reception frequency.

  According to the present invention, the speed estimator uses the tracking information of the strong signal to estimate the moving speed of the satellite signal receiving device, and the frequency estimator uses the moving speed to estimate the reception frequency of the weak signal. The tracking channel for tracking the weak signal can reliably track the weak signal (its carrier and code) using the reception frequency. Therefore, according to the present invention, even when the satellite signal receiving apparatus moves, it is possible to reliably improve the tracking performance for the received weak signal and to stably track even the weak signal.

  That is, since the strong signal is a signal having a signal level stronger than noise, the tracking information obtained based on the strong signal can be regarded as highly reliable information. Therefore, the movement speed is estimated using the tracking information with high reliability, the reception frequency of the weak signal is estimated using the estimated movement speed, and the weak signal is estimated using the estimated reception frequency. By tracking the noise, it is possible to reliably suppress erroneous tracking of the noise, and as a result, it is possible to improve (reduce) the error tracking rate.

It is a block diagram of the satellite signal receiving device used as the premise of this embodiment. It is a block diagram of a satellite signal receiving device according to this embodiment. It is a flowchart for demonstrating operation | movement of the speed estimator of FIG. 2, and a frequency estimator. It is a schematic graph for demonstrating the power distribution of a received signal.

  An embodiment of a satellite signal receiving apparatus according to the present invention will be described. Prior to the description, the configuration of the satellite signal receiving apparatus that is a premise of the present embodiment and its problems will be described with reference to FIG.

  In this item, an embodiment in which the satellite signal receiving device is applied to GPS will be described as an example. However, this embodiment is not limited to GPS, and can be applied to other GNSS such as Galileo. is there.

  The satellite signal receiving apparatus 10 which is the premise of the present embodiment basically has the same configuration as the apparatus according to the related art of Patent Document 1 (FIG. 5 of Patent Document 1), and is shown in FIG. As described above, a plurality of tracking channels 12 i (i = 0 to N) and a positioning calculator 14 are provided.

  In this case, each tracking channel 12 i includes a carrier tracking loop 26 composed of a phase rotator 16, a correlator 18, a discriminator 20, a loop filter 22 and a carrier NCO (Numerically Controlled Oscillator) 24, a correlator 18, a discriminator. Each of the code tracking loop 38 is composed of a notifier 30, a loop filter 32, a code NCO 34, a code generator 36, a multiplier 52, and an adder 54. That is, each tracking channel 12i has the same component.

  Signals (satellite signals) transmitted from a plurality of satellites are, for example, carrier waves (carriers) in the L1 band (1575.42 [MHz]), and C / A codes (1.023 [MHz] of different satellite codes for each satellite. ]) And a high-frequency signal modulated by navigation message data (50 [Hz]). Therefore, the satellite signal receiving apparatus 10 receives satellite signals from each satellite with an antenna (not shown), and a signal (GPS signal) including each received satellite signal is converted to the high-frequency signal (1575.42 [MHz]) by a down converter. A signal having a carrier frequency as a reception frequency is down-converted to an intermediate frequency (IF frequency) signal, and the down-converted GPS signal is A / D converted by an A / D converter and then output to each tracking channel 12i.

  Accordingly, the GPS signal input to the phase rotator 16 in FIG. 1 is a low frequency signal whose reception frequency is converted from a carrier frequency to an IF frequency, and which includes a plurality of satellite signal carriers, C / A codes, and navigation message data. It is a digital signal.

  Each tracking channel 12i tracks the carrier wave and C / A code in the GPS signal for each satellite, and therefore tracks the satellite independently of each other. As described above, since each tracking channel 12i has the same components, here, the configuration of one tracking channel 120 of each tracking channel 12i will be described.

  In the tracking channel 120, the carrier NCO 24 generates a local signal having the same frequency (carrier tracking frequency) as the IF frequency of the GPS signal and outputs the local signal to the phase rotator 16. The phase rotator 16 generates a baseband signal from which the IF frequency component (carrier wave) has been removed from the GPS signal by complex multiplication of the GPS signal and the local signal, and outputs the generated baseband signal to the correlator 18. To do. Here, the signal in the tracking channel 12i is handled as a complex number.

  The code NCO 34 generates a clock signal having a predetermined frequency and outputs it to the code generator 36. Based on the clock signal, the code generator 36 generates the same code (replica code) as the C / A code of the satellite to be tracked by the tracking channel 120, and outputs the generated replica code to the correlator 18. The correlator 18 correlates the baseband signal and the replica code, and outputs the correlation result to the discriminators 20 and 30.

  The carrier tracking loop 26 tracks the carrier in the GPS signal by PLL control or FLL control, while the code tracking loop 38 tracks the C / A code in the GPS signal by DLL control.

  In this case, the carrier tracking loop 26, when acquiring the GPS signal for the first time (initial acquisition), locks the carrier to the frequency of the local signal (carrier tracking frequency) by performing frequency pull-in by FLL control, and then the carrier Is switched to PLL control when the frequency of the local signal can be locked, and phase pull-in is performed by PLL control to lock the phase of the carrier wave to the phase of the local signal. Further, when the phase of the carrier wave is locked by PLL control and the signal level of the satellite signal (GPS signal) becomes a weak signal, the carrier tracking loop 26 has a large phase noise due to the weak signal. Therefore, it is determined that the PLL control cannot be performed, and the PLL control is switched to the FLL control.

  Specifically, when the carrier tracking loop 26 tracks a carrier by FLL control, the discriminator 20 uses the complex number component of the correlation value to determine the amount of frequency deviation between the IF frequency and the local signal frequency (carrier tracking frequency). And the calculated frequency deviation amount is output to the loop filter 22 as tracking information.

  The loop filter 22 functions as a low-pass filter for removing high frequency components in the tracking information and outputting it to the carrier NCO 24 and the multiplier 52. Accordingly, the carrier NCO 24 generates a local signal having the same frequency as the IF frequency so that the carrier wave and the local signal are frequency-synchronized based on the tracking information. As a result, by multiplying the GPS signal and the local signal by complex numbers in the phase rotator 16, the carrier wave in the GPS signal can be drawn into the frequency of the local signal and locked.

  When the carrier tracking loop 26 tracks the carrier by PLL control, the discriminator 20 calculates the phase shift amount between the phase of the carrier and the phase of the local signal based on the complex number component of the correlation value. The amount of phase shift is output to the loop filter 22 as tracking information.

  Also in this case, the loop filter 22 removes the high frequency component in the tracking information and outputs it to the carrier NCO 24 and the multiplier 52, so that the carrier NCO 24 synchronizes the phase of the carrier and the local signal based on the tracking information. Thus, a local signal having the same frequency as that of the carrier wave is generated. As a result, by multiplying the GPS signal and the local signal by complex numbers in the phase rotator 16, the carrier wave can be drawn into the phase of the local signal and locked.

  In the above description, the case where the carrier tracking loop 26 tracks the carrier by either the FLL control or the PLL control has been described. However, the FLL control and the PLL control may be performed simultaneously.

  On the other hand, the discriminator 30 of the code tracking loop 38 has an E (Early) phase code shifted by +1/2 chip with respect to the replica code generated by the code generator 36 and an L (-) shifted by -1/2 chip. (Late) The phase code and the C / A code in the baseband signal are correlated. Next, the discriminator 30 compares the difference between the correlation result between the E-phase code and the C / A code in the baseband signal and the correlation result between the L-phase code and the C / A code in the baseband signal. The code phase shift amount between the C / A code in the baseband signal and the replica code generated by the code generator 36 is calculated based on the above, and the calculated code phase shift amount is output to the loop filter 32 as tracking information.

  The loop filter 32 functions as a low-pass filter for removing high frequency components in the tracking information and outputting it to the adder 54.

  The multiplier 52 of the tracking channel 12i sets the frequency ratio 1/1540 (= 1.031 / 1575.42) between the carrier frequency (1575.42 [MHz]) and the C / A code (1.023 [MHz]). The difference frequency between the carrier tracking frequency and the IF center frequency is multiplied, and the multiplication result is output to the adder 54. In other words, the multiplier 52 multiplies the difference frequency by 1/1540 to convert the tracking information related to the carrier wave to the tracking information related to the C / A code.

  Further, the adder 54 of the tracking channel 12i adds both information of the tracking information input from the discriminator 30 via the loop filter 32 and the tracking information converted by the multiplier 52, and adds the code NCO 34. And output to the code generator 36.

  As a result, the code NCO 34 generates a clock signal based on the tracking information output from the adder 54. Based on the clock signal and the tracking information output from the adder 54, the code generator 36 generates a replica code identical to the C / A code so that the C / A code and the replica code are phase-synchronized. As a result, the C / A code can be tracked by correlating the C / A code in the baseband signal with the replica code in the correlator 18.

  In addition, the code NCO 34 and the code generator 36 of each tracking channel 12i output the set information (tracking information and setting value) to the positioning calculator 14, and the positioning calculator 14 includes information from each tracking channel 12i, Based on the navigation data obtained by demodulating the phase information obtained by the PLL control on the baseband signal and the time information, the pseudo distance between the satellite signal receiving device 10 and the tracking target satellite is obtained and obtained. The position (receiver position) of the satellite signal receiving apparatus 10 is calculated from the pseudo distance, the position of the satellite, and the approximate position of the satellite signal receiving apparatus 10. In addition, since the navigation data used for the satellite position calculation of the positioning calculation by the positioning calculator 14 usually has an effective period of about 4 hours, the positioning calculator 14 calculates using the navigation data acquired in the past. May be.

  Next, the problem of the satellite signal receiving apparatus 10 configured as described above will be described.

  When the satellite signal receiving device 10 is mounted on a mobile body such as an automobile, or when the user carries a portable terminal equipped with the satellite signal receiving device 10, the satellite signal receiving device moves when the mobile body or the user moves. 10, the GPS signal reception frequency (carrier frequency) changes due to the Doppler shift caused by the change in the relative position of the satellite signal reception device 10 with respect to the satellite.

  However, in the satellite signal receiving apparatus 10, each tracking channel 12i independently tracks a GPS signal (its carrier wave and C / A code), and the tracking channel 12i that tracks a weak signal is buried in noise. Since the weak signal is tracked in a state where it is difficult to distinguish between the signal and the noise, tracking becomes unstable due to a high probability of tracking the noise, and there is a risk of mistracking the noise instead of the weak signal. There is.

  The above is the problem of the satellite signal receiving apparatus 10 which is the premise of the present embodiment.

  Next, a satellite signal receiving device 40 according to this embodiment for solving the above-described problem will be described with reference to FIG.

  In the description of the satellite signal receiving device 40, the same components as those of the satellite signal receiving device 10 (see FIG. 1) are denoted by the same reference numerals, and detailed description of the operation is omitted.

  As shown in FIG. 2, the satellite signal receiver 40 further includes a speed estimator 46 and a frequency estimator 48, and each tracking channel 42 i (i = 0 to N) and the tracking channel 440 further include a mixer 50. This is different from the satellite signal receiving apparatus 10 (see FIG. 1) which is a premise of the present embodiment. In FIG. 2, each tracking channel 42 i is a tracking channel that tracks a GPS signal of a strong signal (for example, a signal stronger than a signal level of about −145 [dBm]), and the tracking channel 440 is a weak signal ( For example, it is a tracking channel that tracks a GPS signal of a signal level weaker than a signal level of about −145 [dBm].

  Note that the tracking channel 440 for tracking the weak signal is not limited to one channel as shown in FIG. 2, and may be a plurality of channels. Further, the tracking channel 42i for tracking a strong signal requires four or more channels in order to solve an observation equation described later for obtaining an unknown quantity. That is, when the number of satellites is n and n tracking channels are arranged in the satellite signal receiving apparatus 40 corresponding thereto, the tracking channel for tracking the weak signal becomes the tracking channel 440. Thus, the tracking channel for tracking the strong signal becomes the tracking channel 42i. Therefore, depending on the signal level of the satellite signal transmitted from the satellite, even the same tracking channel may become the tracking channel 42i that tracks the strong signal or the tracking channel 440 that tracks the weak signal. .

  In the satellite signal receiving apparatus 40, in each tracking channel 42 i, 440, the mixer 50 is included in the carrier tracking loop 26, while the multiplier 52 and the adder 54 are included in the code tracking loop 38.

  In the tracking channel 42 i that tracks the strong signal, the discriminator 20 outputs tracking information to the mixer 50 via the loop filter 22 regardless of whether the control is PLL control or FLL control. In this case, the discriminator 20 outputs the frequency shift amount or the phase shift amount to the loop filter 22. The loop filter 22 outputs the current carrier wave tracking frequency to the mixer 50 as carrier wave tracking information corrected by a frequency deviation amount or a phase deviation amount from which a high frequency component has been removed. The mixer 50 outputs the carrier tracking information to the carrier NCO 24 and the multiplier 52.

  The code NCO 34 generates a clock signal based on the tracking information output from the adder 54, and the code generator 36 generates a replica code based on the tracking information output from the adder 54 and the clock signal.

  Further, the carrier NCO 24 of the tracking channel 42 i outputs the set information (tracking information and set value) to the speed estimator 46. Further, the code NCO 34 and the code generator 36 output the set information to the positioning calculator 14 and the speed estimator 46.

On the other hand, in the tracking channel 440 that tracks the weak signal, the discriminator 20 outputs tracking information to the mixer 50 via the loop filter 22 regardless of whether the control is PLL control or FLL control. In this case, the mixer 50 mixes the carrier tracking frequency f ₁ from the loop filter 22 and the carrier tracking frequency f ₂ estimated by the frequency estimator 48 to obtain a new carrier tracking frequency f (1) ) And the tracking information including the generated new carrier tracking frequency f is output to the carrier NCO 24.
f = (w ₁ · f ₁ + w ₂ · f ₂ ) / (w ₁ + w ₂ ) (1)

Here, w ₁ and w ₂ are weights, and the values of these weights w ₁ and w ₂ are dynamically determined by the signal level of the GPS signal. Accordingly, the carrier NCO 24 generates a local signal based on the tracking information including the carrier tracking frequency f. If there is no input of the carrier tracking frequency f ₂ from the frequency estimator 48, the mixer 50 sets w ₂ = 0.

  Further, the multiplier 52 of the tracking channel 440 multiplies the difference frequency between the carrier tracking frequency f and the IF center frequency by 1/1540, thereby converting the tracking information related to the carrier to tracking information related to the C / A code. . The adder 54 adds both the tracking information from the multiplier 52 and the tracking information from the loop filter 32 and outputs the result to the code NCO 34 and the code generator 36. Therefore, the code NCO 34 generates a clock signal based on the tracking information output from the adder 54, and the code generator 36 generates a replica code based on the tracking information output from the adder 54 and the clock signal.

  In addition, the code NCO 34 and the code generator 36 of the tracking channel 440 output the set information only to the positioning calculator 14.

  The positioning calculator 14 obtains a pseudorange based on information from each tracking channel 42i, 440, navigation data and time information, and receives from the obtained pseudorange, the position of the satellite, and the approximate position of the satellite signal receiver 40. The machine position is calculated, and the calculated receiver position is output to the outside and also output to the speed estimator 46.

  Here, the functions of the speed estimator 46 and the frequency estimator 48 will be described with reference to the flowchart of FIG.

The speed estimator 46 is configured by an adaptive filter or by applying a weighted least square method, and is input at each observation time, and the carrier tracking frequency f ₁ (f _d (f _d ) from each tracking channel 42 i is input. ), The receiver position from the positioning calculator 14, the navigation data, and the time information, the moving speed of the satellite signal receiving device 10 is estimated.

  Next, a specific estimation process of the moving speed in the speed estimator 46 will be described.

  In step S1 of FIG. 3, the speed estimator 46 obtains a temporal change amount of the pseudo distance.

That is, the pseudo-range between each satellite S and the satellite signal receiver 40 (hereinafter also referred to as receiver u) at time t is ρ ^S _u (t), the observation interval at receiver u is Δt, and the wavelength of the carrier wave Λ (= 0.19 [m] ≈3 × 10 ⁸ [m / s] / (1.57542 × 10 ⁹ [Hz])), IF center of GPS signal when satellite signal is received from each satellite S a carrier tracking frequency for the frequency f ^S _d, when the weight and alpha ₁ and alpha _2, the time variation of the pseudorange _{^{ρ S u (t) ρ s}} u '(t) is the following (2) formula - It is represented by the formula (4).
ρ ₁ ^S _u ′ (t) = lim {ρ ^S _u (t) −ρ ^S _u (t−Δt)} / Δt
... (2)
ρ ₂ ^S _u ′ (t) = − λ · f ^S _d (t) (3)
ρ ^S _u ′ (t) = {α ₁ · ρ ₁ ^S _u ′ (t) + α ₂ · ρ ₂ ^S _u ′ (t)}
/ (Α ₁ + α ₂ ) (4)

In the expressions (2) to (4), “′” indicates time differentiation, and in the expression (2), the mathematical symbol “lim” indicating the limit is Δt → 0 (Δt approaches 0). ). Further, the expression (2) is an expression showing a time change amount ρ ₁ ^S _u ′ (t) obtained from the pseudo distance ρ ^S _u (t) calculated based on the information from the code tracking loop 38, and (3 ) Is a mathematical expression showing the amount of time change ρ ₂ ^S _u ′ (t) obtained from the carrier tracking frequency f ^S _d from the carrier tracking loop 26. Furthermore, it is desirable that the weights α ₁ and α ₂ are determined based on the frequency ratio (resolution ratio) between the frequency of the C / A code and the carrier frequency and the bands of the loop filters 22 and 32. It may be determined based on the dispersion between the C / A code and the carrier wave.

Accordingly, in step S1, the time variation ρ ^S is calculated from the observed values of the pseudo distance ρ ^S _u (t), the observation interval Δt, the carrier wavelength λ, the carrier tracking frequency f ^S _d , and the weights α ₁ and α _{2. u} ′ (t) is obtained.

In the next step S2, the speed estimator 46 calculates the speed vector (satellite signal receiving apparatus) of the receiver u, which is an unknown quantity, from the time variation ρ ^S _u ′ (t) of the pseudorange obtained by the equation (4). 40) and an observation equation for constructing the clock drift of the satellite signal receiver 40 are constructed.

Here, when the observation vector is y, the design matrix is H, the unknown vector is θ, and the error vector is ε, the observation equation is expressed by the following equation (5).
y = Hθ + ε (5)

Here, the observation vector y, the design matrix H, the unknown vector θ, and the error vector ε are expressed by the following equations (6) to (9).

In equations (6) to (9), S1 to Sn in each symbol represents a satellite number. Further, r ^S1 _u0'~r ^Sn _u0 'is a variation of the geometrical distance between the approximate position (schematically receiver location) u ₀ of the receiver u with each satellite S1 to Sn. Furthermore, c is the speed of light (c≈3 × 10 ⁸ [m]). Furthermore, δt ^S1 ′ to δt ^Sn ′ are clock drifts of the satellites S1 to Sn, and can be calculated from the navigation data in the satellite signals transmitted by the satellites S1 to Sn. U ₀ ′ is a time change amount (rough velocity vector) of the approximate position u ₀ . Further, _u ′ is a velocity vector of the receiver _u , δt _u ′ is a clock drift of the receiver u, and ε ^S1 _{u to} ε ^Sn _u are errors of the respective observation amounts.

Further, in (6) and (7), g ^S1 _u0 ~g ^Sn _u0 is the transpose of the gradient vector obtained from the rough position u ₀ Metropolitan receiver u and position of each satellite S1 to Sn, those The gradient vector transposition g ^S _u0 can be expressed by the following formula (10), where g ^S _u0 is representatively g ^S _u0 and the position of the satellite S is s.

Equation (5) is an observation equation in which the velocity vector _u ′ and the clock drift δt _u ′ (or c · δt _u ′) of the receiver u are unknown quantities. Therefore, in step S3, the speed estimator 46 is From this observation equation, an unknown amount of velocity vector _u ′ and clock drift δt _u ′ are estimated.

Here, if the estimated unknown quantity vector (estimated unknown quantity vector) θ is θa, the estimated unknown quantity vector θa can be expressed by the following equation (11).
θa = (H ^T WH) ⁻¹ H ^T Wy (11)

  Note that W is a weighting matrix whose element is the reciprocal of the error variance of each observation amount.

Therefore, the unknown quantity ( _u ′, δt _u ′) can be estimated by the weighted least square method using the equation (11).

  In addition to the above least square method, the unknown amount may be estimated by modeling the operation of the receiver u (constructing a system equation) and estimating the unknown amount by an extended Kalman filter. In this case, the operation model of the receiver u applies a motion model in which the acceleration or jerk (jerk) of the receiver u is a first-order Markov process, while the operation model of the clock drift of the receiver u is Apply AR model (autoregressive model).

Here, if the speed vector u ′ estimated by the speed estimator 46 is u _a ′, and the estimated clock drift δt _u ′ is δt _ua ′, the speed estimator 46 estimates the unknown quantities (u _a ′, δt _ua ′) is output to the frequency estimator 48.

In step S4 of FIG. 3, the frequency estimator 48 uses the estimated velocity vector u _a ′ and clock drift δt _ua ′ to determine the reception frequency of the weak signal transmitted from the satellite S _j whose tracking is unstable. The estimated value f _dj is estimated by the following equation (12).
f _dj = − {r ^Sj _ua ′ + g ^Sj _ua · u _a ′ + c (δt _ua ′ −δt ^Sj ′)}
/ Λ (12)

Incidentally, r ^Sj _ua 'is the geometric distance between the satellite S _j and the receiver u calculated from u _a (estimate of the receiver position) estimated position of the receiver u obtained by the positioning calculation unit 14 the change amount, g ^Sj _ua is the transpose of the gradient vector obtained from the position of the satellite S _j and the estimated position u _a. Further, δt ^Sj ′ is the clock drift of the satellite S _j calculated from the navigation data.

Accordingly, the frequency estimator 48 outputs the weak signal reception frequency estimate f _dj as the carrier tracking frequency f ₂ to the tracking channel 440 that tracks the weak signal.

In the above description, the case where there is one tracking channel 440 for tracking the weak signal has been described. However, when there are a plurality of tracking channels 440, the frequency estimator 48 estimates the reception frequency for the number of channels. The value f _dj is estimated, and each estimated value f _dj is output to each tracking channel 440.

  Next, the effect of the satellite signal receiver 40 (receiver u) according to this embodiment will be described.

  FIG. 4 is a schematic graph for explaining the power distribution of the satellite signal (received signal) received by the satellite signal receiving device 40.

  Here, the noise power distribution is a chi-square distribution, while the received signal power distribution is a non-central chi-square distribution. In this case, if the signal level of the received signal is stronger than the noise (if the received signal is a strong signal), the average of the power distribution of the noise and the average of the power distribution of the received signal are different, and the noise component and the signal component Are clearly distinguished from each other, so that the received signal can be tracked stably.

  On the other hand, if the average of the noise power distribution is close to the average of the received signal power distribution (when the received signal is a weak signal), the received signal is buried in noise, and the noise component and the signal component are distinguished. Since it is difficult to do so, there is a risk of mistracking noise. In addition, since a large error due to noise is superimposed on the observation information (observation value) necessary for tracking, the tracking of the received signal becomes unstable.

On the other hand, in the satellite signal receiving device 40 according to this embodiment, the speed estimator 46 estimates the moving speed (velocity vector u _a ′) of the satellite signal receiving device 40 using the tracking information of the strong signal, Since the frequency estimator 48 estimates the weak signal reception frequency (estimated value f _dj ) using the velocity vector u _a ′, the tracking channel 440 that tracks the weak signal has an estimated value f _dj (carrier tracking frequency f). ₂ ) can be used to reliably track the weak signal carrier and the C / A code. Therefore, in this embodiment, even when the satellite signal receiving device 40 moves, the tracking performance with respect to the received weak signal (the carrier wave and the C / A code) is reliably improved. Can be tracked stably.

That is, since the strong signal is a signal having a signal level stronger than noise, the tracking information obtained based on the strong signal can be regarded as highly reliable information. Accordingly, the velocity vector u _a ′ is estimated using tracking information with high reliability, the estimated value f _dj of the reception frequency of the weak signal is estimated using the estimated velocity vector u _a ′, and the estimated value f By tracking a weak signal using _dj , erroneous noise tracking can be reliably suppressed, and as a result, the erroneous tracking rate can be improved (reduced).

Conventionally, when tracking a weak signal, the sensitivity of tracking the weak signal is increased by narrowing the band of the loop filter 32 to filter noise. However, as a trade-off for improving the tracking sensitivity, there is a demerit that the tracking performance at the time of acceleration of the satellite signal receiving apparatus 10 is deteriorated. On the other hand, according to the satellite signal receiving apparatus 40 according to this embodiment, the tracking channel 440 uses the estimated value f _dj estimated by the frequency estimator 48 without degrading the tracking performance during acceleration. The tracking sensitivity can be improved by narrowing the band of the loop filter 32.

Further, conventionally, when reception of a satellite signal is interrupted, a point at which the satellite signal is recaptured is predicted using tracking information before the interruption. In this case, even if the reception of the weak signal is interrupted, the error in the tracking information related to the weak signal before the interruption is large, so that the prediction error of the recapture point is also large. On the other hand, according to the satellite signal receiving apparatus 40 according to this embodiment, the tracking channel 440 performs the tracking process on the weak signal using the estimated value f _dj obtained using the tracking information of the strong signal. Therefore, even if reception of the weak signal is interrupted, the recapture point can be estimated with high accuracy. As a result, it is possible to shorten (improve) the time required until the weak signal is received again from the interruption time of reception.

In the satellite signal receiving apparatus 40 according to this embodiment, the speed estimator 46 uses the pseudorange ρ ^S _u (based on the C / A code tracked by the code tracking loop 38 of the tracking channel 42i that tracks the strong signal. t) is calculated. That is, the speed estimator 46 obtains the pseudo-range time change ρ ^S _u ′ (t) using the carrier tracking frequency f ^S _d and the pseudo distance ρ ^S _u (t) from the tracking channel 42 _i, and obtains the obtained time. Based on the change amount ρ ^S _u ′ (t), the clock drift δt _ua ′ and the velocity vector u _a ′ of the satellite signal receiver 40 are estimated. The frequency estimator 48 estimates an estimated value f _dj of the reception frequency of the weak signal based on the clock drift δt _ua ′ and the velocity vector u _a ′.

In this way, the clock drift δt _ua ′ and the velocity vector u _a ′ are estimated using the pseudorange ρ ^S _u (t) and the carrier tracking frequency f ^S _d related to the strong signal, and the estimated clock drift δt _ua ′ and Since the estimated value f _dj of the weak signal reception frequency is estimated using the velocity vector u _a ′, the tracking channel 440 that tracks the weak signal accurately tracks the weak signal using the estimated value f _dj. It becomes possible to do.

  Further, the mixer 50 constituting the carrier tracking loop 26 of the tracking channel 440 obtains the carrier tracking frequency f based on the equation (1), and the carrier tracking loop 26 uses the carrier tracking frequency f obtained by the mixer 50. To track the carrier wave in the weak signal. Further, the multiplier 52 constituting the code tracking loop 38 of the tracking channel 440 is related to the carrier by multiplying the difference frequency between the carrier tracking frequency f output from the mixer 50 and the IF center frequency by 1/1540. The tracking information is converted into tracking information (code tracking frequency) related to the code, and the code tracking loop 38 adds the tracking information converted by the multiplier 52 to track the C / A code.

  Thereby, it becomes possible to further improve the tracking performance of the weak signal carrier and the C / A code.

  Of course, the present invention is not limited to the above-described embodiment, and may employ various configurations.

DESCRIPTION OF SYMBOLS 10, 40 ... Satellite signal receiver 12i, 12N, 42i, 42N, 120, 420, 440 ... Tracking channel 14 ... Positioning calculator 16 ... Phase rotator 18 ... Correlator 20, 30 ... Discriminator 22, 32 ... Loop filter 24 ... Carrier NCO
26 ... Carrier tracking loop 34 ... Code NCO
36 ... Code generator 38 ... Code tracking loop 46 ... Speed estimator 48 ... Frequency estimator 50 ... Mixer 52 ... Multiplier 54 ... Adder

Claims (2)

In a satellite signal receiving apparatus having a plurality of tracking channels for tracking signals from a satellite,
Each tracking channel, obtains the carrier tracking frequency for tracking the signal and track the carriers in the signal, the carrier tracking loop for outputting the carrier tracking frequency was determined as the tracking information related to the carrier, the Each has a code tracking loop that tracks the code in the signal,
The satellite signal receiver is
Using the tracking information output from the carrier tracking loop of the tracking channel that tracks a strong signal having a relatively strong signal level and the pseudo distance obtained based on the code of the tracking channel, the amount of change in the pseudo distance is obtained and obtained. A speed estimator for estimating a clock drift and a moving speed of the satellite signal receiving device based on a change amount of the pseudorange and a clock drift of the satellite;
Based on the clock drift of the satellite signal receiver, the clock drift of the satellite with unstable tracking and the moving speed, the carrier tracking frequency of a weak signal with a relatively weak signal level is estimated as the reception frequency , and the weak signal is tracked A frequency estimator for outputting the estimated reception frequency to the tracking channel
Further comprising
The carrier tracking loop of the tracking channel that tracks the weak signal tracks the carrier in the weak signal using the reception frequency estimated by the frequency estimator, while the code tracking loop of the tracking channel A satellite signal receiving apparatus for tracking a code in the weak signal using a reception frequency. The apparatus of claim 1 .
Carrier tracking loop tracking channels for tracking the pre Kijaku signal, the carrier tracking frequency in which the frequency estimator is estimated, the carrier tracking loop is the weighted average of the carrier tracking frequency determined, carrier tracking frequency of the weighted average And tracking the carrier wave in the weak signal using the carrier tracking frequency obtained,
The code tracking loop of the tracking channel divides the difference frequency between the carrier tracking frequency after the weighted average and the IF center frequency by the frequency ratio between the code frequency of the code and the carrier frequency of the carrier, thereby calculating the code tracking frequency. A satellite signal receiving apparatus characterized in that the code is tracked by adding the obtained code tracking frequency.

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