JP4578261B2 - Satellite positioning method and system - Google Patents

Description

The present invention relates to a satellite positioning method and its system.

In a positioning satellite (for example, GPS) receiver or the like, the code is demodulated by synchronizing the same code generated inside the receiver with the radio wave code from the received satellite.
However, since the positioning satellite is moving, the Doppler effect occurs, and therefore the frequency of the received radio wave is different from that transmitted from the satellite. Therefore, Doppler correction is performed by a GPS receiver or the like to make this frequency the same as when it was transmitted from the satellite.

Further, if there is a frequency error of the local oscillator (internal oscillator) in the receiver, the error after the frequency conversion is superimposed on the error of the local oscillator in addition to the frequency error due to the Doppler effect of the satellite itself.
At this time, if the Doppler correction is to be performed only by the receiver itself, it is necessary to try the frequency range that can be considered by estimating the frequency error by itself, and it is necessary to repeat until the code demodulation is possible. There was a drawback that a long processing time was required. That is, it has a fatal defect that it takes a considerable time to demodulate the code.

In addition, even if an accurate satellite frequency error is obtained from outside, if the error of the local oscillator is unknown, Doppler correction needs to try the frequency range that can be considered by estimating the frequency error by itself as in the above case. There is a drawback that it is necessary to repeat the calculation until the code can be demodulated.
In order to completely eliminate the error of the local oscillator, an ultra-stable oscillator is required. For example, an expensive rubidium oscillator or the like is required, and the system is expensive.

In order to solve this drawback, it has been widely practiced to incorporate a signal having an accurate frequency from the outside and detect an error in the oscillation frequency inside the receiver by this phase detection circuit. That is, means (radio timepiece, JJY, etc.) that locks the oscillation frequency inside the receiver to a signal having an accurate frequency from the outside by a phase-locked loop circuit and uses the same frequency is generally widely used. This means is generally known as a PLL (Phase Lock Loop) circuit (see, for example, Patent Document 1).
JP-A-7-321644

In the conventional method, when the received signal received from the outside is subjected to the Doppler effect from the outside or is a signal that is devoted to noise, the error of the oscillation frequency inside the receiver with reference to the received signal received from the outside It is extremely difficult to accurately detect.

In the satellite positioning method of the present invention, a receiver terminal having a local oscillation unit receives a signal from a satellite,
A satellite positioning method in which the receiver terminal obtains a pseudo-range between the satellite and the received signal based on a received signal, and a frequency more accurate than a local frequency at which the receiver terminal oscillates at the local oscillator is transmitted from an external oscillator. Measure the local frequency oscillated in the local oscillating unit with reference to the external frequency obtained from the external oscillating unit, detect the error of the local oscillating frequency given in advance from the measured local frequency, The frequency range is specified using the frequency calculated by adding and subtracting the maximum error of the external frequency given in advance as the upper and lower limits, and multiple local frequency error candidate values that are accurate within the specified frequency range are specified. And correlating the signals received from the satellites by performing Doppler correction using the frequency error due to the Doppler effect of the satellites and the candidate values of the local frequency errors. Results By detecting the correct local frequency error, and detects a delay value from the exact local frequency error the correlation calculation results shown, obtaining the pseudorange from the delay value.

The satellite positioning system of the present invention is a satellite positioning system in which a receiver terminal receives a satellite signal from a satellite, and the receiver terminal obtains a pseudorange between the satellite and the received signal.
The receiver terminal uses a local oscillator that oscillates a frequency, a receiver that receives an accurate frequency from the external oscillator as a local frequency oscillated by the local oscillator, and an external frequency obtained from the external oscillator as a reference A first stage detecting unit for measuring the local frequency of the local oscillating unit and detecting an error of the local oscillating frequency given in advance from the measured local frequency, and within a predetermined frequency region including the error of the local oscillating frequency A Doppler correction unit that receives a plurality of set local frequency error candidate values and receives a signal received from the satellite using the Doppler effect of the satellite and the respective local frequency error candidate values. A correlation calculation unit that performs correlation calculation on the signal processed by the Doppler correction unit, a second stage detection unit that detects an accurate local frequency error based on the correlation calculation result, A pseudo-range detection unit that detects a delay value from the correlation calculation result indicating the frequency error and obtains the pseudo-range from the delay value, and further, an error of the local oscillation frequency detected by the first-stage detection unit A frequency region is specified with the frequency calculated by adding and subtracting the maximum error of the external frequency given in advance as upper and lower limits, and a plurality of candidate values for accurate local frequency error within the specified frequency region Is set.

The present invention makes it possible to make the signal-to-noise ratio remarkably improved, and to detect the frequency error of the local oscillating unit, even if it is a very weak signal with noise. Processing time can be shortened. That is, high sensitivity and high processing speed can be achieved. Further, the arithmetic processing circuit for detecting the frequency error of the local oscillating unit becomes a small scale, and the apparatus (receiver terminal) can be simplified.

Therefore, in the past, an ultra-sensitive and expensive oscillator was required to make the Doppler correction respond accurately and quickly. However, in the present invention, the Doppler correction is performed even for an inexpensive oscillator that is generally used. It can be done accurately and quickly.

Hereinafter, the present invention will be described in detail with reference to the drawings shown in the embodiments.
In the embodiment of the present invention shown in FIGS. 1 to 8, FIG. 1 is an overall block diagram showing an outline of an embodiment of a satellite positioning method and a satellite positioning system of the present invention.
In FIG. 1, A ₁ , A ₂ , A ₃ and A ₄ indicate satellites (positioning satellites), and 1 is a base station. The base station 1 is provided to send the Doppler information of each positioning satellite A (frequency error due to the Doppler effect of each positioning satellite A) to the receiver terminal 11.
The base station 1 includes a receiving antenna 2 installed in an environment with a good view, receives a GPS reference signal by the server receiver 3, and a frequency error due to the Doppler effect of the satellite A from the GPS signal by the arithmetic unit 4 ( Doppler information) is extracted.

And the information in the calculating part 4 is transmitted to the receiver terminal 11 side by the transmission part (transmitter) 5.
L ₁ is a communication line, and information of the calculation unit 4 is transmitted to the receiving unit 12 of the receiver terminal 11 through the communication line L ₁ .

Reference numeral 17 denotes an external oscillation unit that oscillates a frequency that is more accurate than the local frequency that oscillates in the receiver terminal 11. External frequency oscillated by the external oscillation portion 17 receiving portion 12 of the receiver terminal 11 in the communication line L ₂
Sent to.
Note that the communication lines L ₁ and L ₂ are all possible communication lines, and may be electromagnetic communication means, for example, terrestrial broadcasting, mobile phone communication, communication for broadcasting information via a communication satellite Internet connection is also acceptable. Also, the communication lines L ₁ and L ₂ can be freely set as the same communication line.

In addition, the receiver terminal 11 is used for information such as broadcasting (cell phone, Internet, etc.)
It is assumed that many terminals 11 can receive simultaneously. FIG. 1 shows a case where there is one receiver terminal 11 for ease of explanation.

Reference numeral 14 denotes an antenna unit of the receiver terminal 11. The location of the receiver terminal 11 (antenna unit 14) is not only where the satellite A can be seen directly, but also in the shade of trees, in buildings, etc.
It also assumes places where PS radio wave strength is quite weak.
13 is a PN signal obtained by down-converting the GPS signal from satellite A (removing the carrier wave) (C
/ A code) is a GPS receiver that A / D converts, and the GPS receiver 13 has a local oscillator 34 (see FIG. 2). Reference numeral 15 denotes a portion (memory: RAM) for storing the signal. Reference numeral 6 denotes a first stage detection unit that detects (calculates) a frequency error (local oscillation frequency error) generated by the local oscillation unit 34. A Doppler correction unit 16 corrects a frequency error from the PN signal. Then, the Doppler correction unit 16 uses the accurate local oscillation frequency error candidate value of the local oscillation unit 34 and the carrier Doppler information from the base station 1 for the accumulated PN signal (I component, Q component) of the GPS signal. ,
Perform carrier Doppler correction.

The receiver terminal 11 also includes a correlation calculation unit 9 that performs correlation calculation on the signal processed by the Doppler correction unit 16.
And a second stage detection unit 7 for detecting an accurate local frequency error from the correlation calculation result. Reference numeral 19 is a pseudorange detection unit that obtains a pseudorange from the correlation calculation result indicating an accurate local frequency error, and 20 detects the self-position of the receiver terminal 11 based on the pseudorange information obtained here. It is a position calculation part to do.

FIG. 3 is a flowchart until the receiver terminal 11 receives the received signal of the satellite A and the external frequency of the external oscillation unit 17 and obtains the pseudorange.
1 and 3, the satellite positioning method of the present invention will be described.
First, the first stage detection unit 6 measures the local frequency oscillated by the local oscillation unit 34 (shown in FIG. 2) based on an external frequency that is more accurate than the local frequency, and is given in advance from the measured local frequency. Detect local oscillation frequency error. Next, set a plurality of candidate values for accurate local frequency error (local oscillation frequency error) within a predetermined frequency range including this local oscillation frequency error,
Each candidate value is input to the Doppler correction unit 16. Then, in the Doppler correction unit 16, the antenna unit 14
The Doppler correction is performed on the satellite signal received in step 1 by using the frequency error due to the Doppler effect of the satellite A and each candidate value of the local frequency error. The correlation calculation unit 9 performs correlation calculation on the satellite signal from which the frequency error has been canceled, and the second stage detection unit 7 detects an accurate local frequency error from the correlation calculation result.
Then, the pseudo distance detection unit 19 detects the delay value τ from the correlation calculation result indicating the accurate local frequency error, and obtains the pseudo distance from the delay value τ. The position calculator 20 based on the pseudo distance obtained here, the base station position from the receiver 12, each satellite position, and the pseudo distance between the base station 1 and each satellite A.
Thus, the self-position of the receiver terminal 11 can be known.

Hereinafter, the operation in each processing block will be described in detail. 2 and 4 are block diagrams showing the configuration of the receiver terminal 11. As shown in FIG. In FIG. 4, the first stage detection unit 6 is, for example, shown in FIG.
) Or an embodiment as shown in FIG. 4B. First, the case of the embodiment of FIG. 4A will be described.
The first stage detection unit 6 includes a counter 23. The counter 23 counts the local frequency. The external frequency is more accurate than the local frequency.
The local oscillator 34 is a local oscillator (frequency synthesizer), and an inexpensive crystal oscillator that is generally used can be used. The local oscillator 34 has a frequency error.

The local frequency oscillated by the local oscillator 34 and the external frequency received by the receiver 12 are input to the first stage detector 6. Then, the counter 23 starts counting the local frequency with the external reference clock as a reference. The predetermined time that the external reference clock counts is, for example, 1 sec.
A local frequency error (local oscillation frequency error) is calculated from the local frequency measured by the counter 23. Error = (measured value of local oscillation frequency) − (design frequency). This local frequency error includes a slight error of the external frequency.

When the local oscillator 34 is a PLL (Phase Lock Loop) circuit (not shown), the frequency is reduced to 1 / N (N is a predetermined number) by a frequency divider constituting the circuit. The local frequency error detected by the first stage detection unit 6 is multiplied by N. Note that the number of frequency dividers, the value of the degree of reduction N, etc. at this time can be freely changed in design.

As shown in FIG. 4B, the first stage detection unit 6 includes a frequency conversion unit 18 that down-converts the local frequency and the external frequency, and a Fourier transform unit 25 as a frequency counter. May be.

The local frequency error calculated by the first stage detection unit 6 is transmitted to the candidate value setting unit 51 in the receiver terminal 11 (see FIG. 2), and the maximum error of the external frequency given in advance to this local frequency error. The frequency region is specified with the frequency calculated by adding and subtracting as the upper limit value and the lower limit value. Further, the candidate value setting unit 51 sets a plurality of accurate local frequency error candidate values within the specified frequency region.

The method of setting the candidate value will be described in detail. For example, when the local frequency error is calculated as 2000 Hz by the first stage detection unit 6 and the maximum error of the external frequency given in advance is 100 Hz, it is accurate. The local frequency error is from the local frequency error 2000 Hz to the maximum external frequency error 100
It exists in the frequency range (1900Hz-2100Hz) between 2100Hz and 1900Hz which added and subtracted Hz. Then, within the specified frequency region (1900 Hz to 2100 Hz), a frequency having a maximum error of 100 Hz (for example) centered on 2000 Hz every 10 Hz is set as a plurality of accurate local frequency error candidate values. In this case, the candidate values are 1900Hz, 1910Hz, 1920H
z, 2080 Hz, 2090 Hz, and 2100 Hz.
In addition, the candidate value is set for every 10 Hz with a maximum error of 100 Hz centered on 2000 Hz, but the method of setting the candidate value may be set according to the performance of the receiver terminal 11, for example, a Doppler correction unit described later It may be set corresponding to 16 pieces.

The plurality of set candidate values are input to the Doppler correction unit 16. The Doppler correction unit 16
Are provided, and in the above example, 21 are provided (see FIG. 5).
The Doppler correction unit 16 also receives signals obtained by the I signal conversion unit 35 and the Q signal conversion unit 36 (see FIG. 6).

Next, the satellite signal is received and processed by the I signal conversion unit 35 and the Q signal conversion unit 36, and the Doppler correction unit
The process up to input in 16 will be described.
In FIG. 2, a GPS receiving unit 13 includes a high frequency amplifying unit 32 that receives a PN signal from the receiving antenna unit 14, a frequency converting unit 33 that down-converts the frequency, and an I signal converting unit 35 (I signal converting carrier removal). Part), a Q signal conversion part 36 (Q signal conversion carrier wave removal part), a 90-degree phase shifter 37,
A / D converter units 38 and 39 and a memory unit 15 (RAM) for temporarily storing signals are provided.

FIG. 6 shows an outline of operations in an I signal conversion (carrier wave removal) unit 35 and a Q signal conversion (carrier wave removal) unit 36 for obtaining an I signal and a Q signal from the signal processed by the frequency conversion unit 33. FIG. 47 and 48 are multipliers, and 49 and 50 are low-pass filters.

The operation will be described with reference to FIG. 2 and FIG. 6. A 1.5 GHz band GPS signal subjected to spread spectrum modulation using a PN signal is received by the high frequency amplifier 32 from the receiving antenna unit 14. The PN signal is down-converted by the local oscillating unit (frequency synthesizer) 34 and the frequency converting unit 33, and converted into a frequency region of, for example, a 70 MHz band.
The local oscillator 34 and the 90-degree phase shifter 37 multiply each other by a 70 MHz carrier wave having a phase difference of 90 degrees, that is, the parts of the I signal conversion unit 35 and the Q signal conversion unit 36. The carrier wave of 70 MHz is removed, and the PN code (C / A code code) of I component and Q component orthogonal to each other is taken out.

The operation for removing the carrier wave will be described with reference to FIG.
The PS signal is represented by PN.cos ((W + ΔW) t + Φ). ΔW is a Doppler frequency, and ΔW is a combination of the Doppler frequency fluctuation of the satellite signal captured by the antenna unit 14 and the frequency fluctuation of the local oscillation unit 34 (frequency synthesizer). Here, if the Doppler frequency variation of the satellite signal (Doppler frequency error of satellite A) is Δ W _C and the frequency variation (local frequency error) of the local oscillator 34 is Δ W _L , then ΔW = Δ W _C + Δ W _L.

Then, the signal from the local oscillating unit 34 and the 90-degree phase shifter 37 shown in FIG. 2 are represented as carriers cos (Wt) and sin (Wt) orthogonal to each other. When these orthogonal signals and the signal PN.cos ((W + ΔW) t + Φ) from the frequency converter 33 are multiplied by multipliers 47 and 48 and passed through the low-pass filters 49 and 50, PN.cos (ΔWt + Φ), −PN.sin (Δwt + Φ). These conversions are generally used as I and Q converters.
In FIG. 6, the input signal PN.cos ((W + ΔW) t + Φ) in each of the I and Q signal conversion units 35 and 36.
Is multiplied by carrier waves cos (Wt) and sin (Wt) orthogonal to each other,
Since both are the same, the carrier wave component is removed from both.

Next, the signals (analog signals) orthogonal to each other from which the carrier wave components are removed are converted from analog signals into digitized discretized signals by the A / D converter units 38 and 39, respectively. These two signals are accumulated in a memory unit (RAM) 15 for a predetermined time, and data of I signal and Q signal are transmitted from the memory unit 15 to the Doppler correction unit 16.

The high frequency amplification unit 32, frequency conversion unit 33, local oscillation unit 34, I signal conversion unit 35, Q signal conversion unit 36, 90 degree phase shifter 37, and A / D converter units 38 and 39 described above are generally used. This is a part and is generally used, and a description of the specific configuration is omitted.
In the embodiments of the present invention, the PN signal is described as the PN signal from which the carrier component is removed. However, the PN signal may be configured as a PN signal including the carrier component.
That is, in FIG. 2, the I signal conversion unit 35 and the Q signal conversion unit 36 may be configured as a circuit that does not remove the carrier wave.
Further, in this case, the low-pass filter 49 and the Q signal converter 36 in the I signal converter 35 in FIG.
The low-pass filter 50 may be a band pass filter (BPF).

In FIG. 5, a plurality of accurate local frequency error candidate values Δ W _L ′ and carrier wave Doppler information (frequency error due to the Doppler effect of satellite A) Δ W _C are combined and input. The signal F _x is input to the Doppler correction unit 16. In FIG. 7, the input signal F _x is cos (
ΔWt ′) or sin (ΔWt ′), and ΔWt ′ = ΔW _C + ΔW _L ′.
Further, the same number of input signals F _x as the number of candidate values exist, and it is desirable to input one input signal F _x for each Doppler correction unit 16 in order to perform a quick calculation process.

In FIG. 7, the local oscillation unit for the PN signal (I component, Q component) of the accumulated GPS signal
An operation of performing carrier Doppler correction from 34 accurate frequency error candidate values and carrier Doppler information from the base station 1 is shown.
26, 27, 28, and 29 are multipliers, 30 is an adder, and 31 is a subtractor. The input signals here are discretized data stored in the memory unit 15, respectively. Further, t represents a discretized value.
The input signal I signal and Q signal data input to the Doppler correction unit 16 are respectively PN.cos (Δ
Wt + Φ), -PN.sin (ΔWt + Φ).

For these signals, input signals cos (ΔWt ′) and sin (ΔWt ′) are multiplied by multipliers 26, 27, 28.
, 29 and passing through the adder 30 and the subtractor 31, −PN.sin (ΔWxt + Φ) and PN.cos (Δ
Wxt + Φ) is obtained. These signals are discretized digital signals. Where ΔWx
t is the error (shift) of the candidate value ΔW _L ′ with respect to the exact local frequency error ΔW _L , which results from the candidate value containing a slight frequency error of the external frequency. Therefore, if a candidate value such that ΔWxt is close to 0 is detected, an accurate local frequency error is detected. This detection process will be described below.

Each signal processed by the Doppler correction unit 16 is transmitted to the correlation calculation unit 9 (see FIG. 4).
. The correlation calculation unit 9 calculates a peak value by calculating a correlation between each received signal and a replica PN code (C / A code signal) that the receiver terminal 11 has in advance (described later) (see FIG. 5). ).
The correlation calculation is a well-known content, but will be briefly described below.

In general, a plurality of GPS satellites A travel around the earth, and each satellite A transmits a 1575.42 MHz carrier wave to the earth after being subjected to spread spectrum modulation with a PN signal signal corresponding to each individual satellite A. . For example, 1575.42 MHz, satellite A ₁ is PN signal a, satellite A ₂ is P
It is assumed that the N signal b is transmitted by performing spread spectrum modulation. In order to extract (demodulate) the signal of the satellite A ₁ at the receiver terminal 11, the same PN as the PN signal “a” is previously set at the receiver terminal 11
The signal a ′ is stored, and the satellite A ₁ sends the PN signal a to the receiver terminal by the PN signal a ′.
11 is demodulated.

In order to receive the satellite A ₂ , the same PN signal b ′ as the PN signal b must be stored in advance on the receiver terminal 11 side. Therefore, each satellite A is previously placed on the receiver terminal 11 side.
If all the PN signals corresponding to the satellites A are not emitted, the signals of the satellites A cannot be received. In the present invention, the PN signal prepared in advance is used as a replica PN code.
Each replica PN code corresponding to each GPS satellite A (demodulating the satellite reception signal) is stored in advance in the ROM 46 of the signal processing unit 21 provided in the GPS receiver terminal 11.

In general, data X is x (n) (where n = 0: N), and data Y is h (n) (where n = 0: N).
, K is an integer, and 0 ≦ k ≦ N, it is expressed as the following equation (1).

Then, y (1), y (2), y (3)... Y (N) is calculated. Here, in the calculation of y (k), the number of data additions is N. Accordingly, it is known that the noise component is reduced to 1 / √N by adding N times if the noise superimposed on the signal at this time is Gaussian with a statistical property. Therefore, the noise reduction by this calculation is 1 / √N. This calculation is called correlation calculation. (Equivalent correlation calculation is a well-known method that uses FFT as a high-speed operation. Here, a general calculation method is shown for explaining the principle.)

As a frequency error detection method, for example, the correlation calculation result indicating the maximum peak value is selected by the second stage detection unit 7 from the results of correlation calculation performed by the correlation calculation unit 9, and the result indicating the maximum peak value is obtained. The candidate value is detected as an accurate local frequency error. Alternatively, as shown in FIG. 8, these peak values (P _{1 to} P _n ) are used to estimate an approximate curve (curve Z) (from the extreme value Y of the curve Z).
An accurate local oscillation frequency error can be detected.

From the correlation calculation result showing the error of this accurate local oscillation frequency, the pseudo-range detection unit
The delay value τ is detected at 19, and the pseudo distance detection unit 19 obtains the pseudo distance between the receiver terminal 11 and the satellite A from the delay value τ.
The pseudo distance detection unit 19 obtains the pseudo distance from the signal from which the frequency error of the frequency has been canceled, and can be used by usual means and will not be described.
Thereafter, in the block of the position calculation unit 20 in FIG. 1, information on the base station position from the base station 1, each satellite position, and the pseudorange between each satellite and the base station is acquired by the receiving unit 12 of the receiver terminal 11. Self-position is determined. Note that the position calculation unit 20 is generally well known and can be easily realized from the pseudo distance obtained here, the base station position, each satellite position, and the method for determining the self position from the pseudo distance between each satellite and the base station. .

In FIG. 2, the digital signal processing unit 21 includes a CPU unit 42 connected to the receiving unit 12 and a RAM (memory) connected to the CPU unit 42 in order to process data obtained via the receiving unit 12. )
45, ROM (memory) 46, DSP section 41 connected to memory section (RAM) 15, DSP section
A ROM (memory) 44 connected to 41 and a pattern calculation unit 22 are included.
The pattern calculation unit 22 is a calculation storage part that generates an internal PN code pattern and stores it in advance. The CPU unit 42 and the DSP unit 41 are connected to each other, and the CPU unit 42, RAM 45, ROM
It works as a microprocessor with 46.
Further, the pattern calculation unit 22 may be configured by a portion in which an internal PN code pattern created in advance is stored in a memory.

The internal PN code pattern (replica PN signal) will be briefly described.
In general, positioning satellites (for example, GPS) orbit around the earth, and from each satellite, carrier waves (1575.42 MHz in the case of GPS) are transmitted to PN signals (C / A) corresponding to the individual satellites.
(Also called code) is spread spectrum modulated and transmitted to the earth.
For example, it is assumed that 1575.42 MHz is transmitted by performing spread spectrum modulation with the satellite A _{1 using} the PN signal a and the satellite A _{2 using} the PN signal b. In order to extract (demodulate) the signal of the satellite A ₁ at the receiver terminal 11, the receiver terminal 11 stores in advance the PN signal a ′ that is the same as the PN signal a and uses the PN signal a ′ as a satellite. A ₁ demodulates the PN signal a at the receiver terminal 11.
In order to receive the PN signal b from the satellite A ₂ , the same PN signal b ′ as the PN signal b must be stored in the receiver terminal 11 in advance.
Therefore, if the receiver terminal 11 does not have all the PN signals corresponding to each satellite A transmitted from each satellite A in advance, the signal of each satellite A cannot be received.
In the present invention, this PN signal prepared in advance is used as an internal PN code pattern (replica PN signal).

The ROM 46 is a part that mainly stores a digital signal processing execution program. The hardware part of the digital signal processing unit 21 includes a DSP unit 41, a CPU unit 42, a RAM 45, a ROM 46,
The configuration of the ROM 44, and these configurations have conventionally been CPU, DSP and memory (RA
M and ROM) are widely used as general-purpose digital signal processing configurations, and the description thereof is omitted.

In the reference example shown in FIG. 9, FIG. 9 is a block diagram showing the configuration of the receiver terminal 11. The receiver terminal 11 has a local oscillating unit 34, and information on the center frequency and its error range is input to the CPU unit 42 in the digital signal processing unit 21. The local oscillating unit 34 can know the center frequency and the error range in advance. Further, the external oscillation unit 17 and the first stage detection unit 6 that obtains an external frequency from the external oscillation unit 17 and detects an error in the local frequency are not provided.

The operation in each processing block will be described.
First, an error in the local oscillation frequency is detected from the local oscillation frequency oscillated by the local oscillation unit 34 and the center frequency. Next, the candidate value setting unit 51 includes the detected local oscillation frequency error (CPU
A plurality of accurate local frequency error candidate values are set within an error range (obtained from the unit 42). Then, the Doppler correction unit 16 performs Doppler correction on the signal received from the satellite A using the frequency error due to the Doppler effect of the satellite A and each candidate value of the local frequency error. The correlation calculation unit 9 performs correlation calculation on the signal processed by the Doppler correction unit 16, and an accurate local frequency error is detected from the correlation calculation result. Then, the pseudorange detector 19 detects the delay value τ from the correlation calculation result indicating the error of the accurate local oscillation frequency, and the pseudorange detector 19 detects the receiver terminal 11 and the satellite A from the delay value τ.
And the pseudo distance.
In FIG. 9, the same reference numerals as those in FIG. 2 have the same configurations as those in FIG.

As described above, according to the satellite positioning method of the present invention, the receiver terminal 11 having the local oscillator 34 receives the signal from the satellite A, and the receiver terminal 11 communicates with the satellite A by the received signal. A satellite positioning method for obtaining a pseudorange, in which the receiver terminal 11 receives a frequency that is more accurate than the local frequency oscillated by the local oscillator 34 from the external oscillator 17, and uses the external frequency obtained from the external oscillator 17 as a reference Measure the local frequency oscillated by the local oscillation unit 34, detect the error of the local oscillation frequency given in advance from the measured local frequency, the maximum error of the external frequency given in advance to this local oscillation frequency error The frequency region is specified using the frequency calculated by adding and subtracting as the upper limit value and the lower limit value, a plurality of accurate local frequency error candidate values are set within the specified frequency region, and the signal received from the satellite A is transmitted to the satellite. A's Dop The correlation error is calculated by Doppler correction using the frequency error due to the La effect and each candidate value of the local frequency error, the accurate local frequency error is detected from the correlation calculation result, and the accurate local frequency error is delayed from the correlation calculation result indicated. The value τ is detected and the delay value τ
Therefore, even if the signal from the satellite A is received in a building or the like, that is, the signal from the very weak satellite A that has been subjected to Doppler fluctuations that are stagnant by noise. However, the oscillation frequency error of the local oscillation unit 34 included in the receiver terminal 11 can be self-detected with ultrahigh sensitivity and good response.
In other words, in the past, an ultra-sensitive and expensive oscillator was required in order to make Doppler correction respond quickly and accurately, but in the present invention, Doppler correction can be performed even for an inexpensive oscillator that is commonly used. It can be done accurately and quickly.
Furthermore, since the receiver terminal 11 receives a frequency that is more accurate than the local frequency oscillated by the local oscillating unit 34 from the external oscillating unit 17, the processing time for detecting the frequency error of the local oscillating unit 34 can be shortened. Further, the arithmetic processing circuit for detecting the frequency error of the local oscillating unit 34 becomes small, and the device (receiver terminal 11) can be simplified.
Further, the error of the external frequency included in the frequency error of the local oscillation unit 34 can be removed, and the accurate frequency error of the local oscillation unit 34 can be detected. As a result, the pseudo distance can be detected with higher sensitivity.
In addition, since the frequency region is specified with the frequency calculated by adding and subtracting the maximum error of the external frequency given in advance to the approximate value of the local frequency error as the upper limit value and the lower limit value, it is an accurate candidate value for the local frequency error Can be set from a limited range, and an accurate local frequency error can be detected efficiently.

In the satellite positioning system of the present invention, the receiver terminal 11 receives the satellite signal from the satellite A,
In a satellite positioning system in which the receiver terminal 11 obtains a pseudorange between the satellite A and the received reception signal, the receiver terminal 11 oscillates a local oscillation unit 34 that oscillates a frequency, and a local oscillation unit 34 oscillates. The receiving unit 12 that receives a frequency more accurate than the local frequency from the external oscillating unit 17, and the local frequency of the local oscillating unit 34 is measured based on the external frequency obtained from the external oscillating unit 17 and is given in advance from the measured local frequency. A first stage detection unit 6 for detecting a local oscillation frequency error, and a plurality of accurate local frequency error candidate values set within a predetermined frequency region including the local oscillation frequency error; and The Doppler correction unit 16 that performs Doppler correction on the signal received from the satellite A based on the frequency error due to the Doppler effect of the satellite A and each candidate value of the local frequency error, and the correlation processing of the signal processed by the Doppler correction unit 16 are performed. The function calculation unit 9, the second stage detection unit 7 for detecting an accurate local frequency error based on the correlation calculation result, and the delay value τ is detected from the correlation calculation result indicating the accurate local frequency error, and the delay value τ is detected. Since it includes a pseudo distance detection unit 19 for obtaining a pseudo distance,
Even when a signal from the satellite A is received in a building or the like, that is, even a signal from the very weak satellite A subjected to Doppler fluctuations that are affected by noise, it is extremely sensitive and The oscillation frequency error of the local oscillation unit 34 included in the receiver terminal 11 can be self-detected with good responsiveness.
In other words, in the past, an ultra-sensitive and expensive oscillator was required in order to make Doppler correction respond quickly and accurately, but in the present invention, Doppler correction can be performed even for an inexpensive oscillator that is commonly used. It can be done accurately and quickly.
Furthermore, since the receiver terminal 11 receives a frequency that is more accurate than the local frequency oscillated by the local oscillating unit 34 from the external oscillating unit 17, the processing time for detecting the frequency error of the local oscillating unit 34 can be shortened. Further, the arithmetic processing circuit for detecting the frequency error of the local oscillating unit 34 becomes small, and the device (receiver terminal 11) can be simplified.
Further, the error of the external frequency included in the frequency error of the local oscillation unit 34 can be removed, and the accurate frequency error of the local oscillation unit 34 can be detected. As a result, the pseudo distance can be detected with higher sensitivity.

In addition, the frequency range is specified by using the frequency calculated by adding and subtracting the maximum error of the external frequency given in advance to the error of the local oscillation frequency detected by the first stage detection unit 6 as the upper limit value and the lower limit value. Since multiple candidate values for accurate local frequency error are set within the specified frequency domain, accurate local frequency error candidate values can be set from a limited range, and accurate local frequency error can be detected efficiently. Can do.

Is an overall block diagram showing an outline of implementation of the present invention. It is a block diagram which shows the structure of a receiver terminal. It is a flowchart figure after receiving a satellite signal until it acquires a pseudorange. It is operation | movement explanatory drawing of a receiver terminal. It is operation | movement explanatory drawing which detects an exact local frequency error. It is operation | movement explanatory drawing explaining an I signal conversion part and a Q signal conversion part. It is operation | movement explanatory drawing explaining the Doppler correction part which performs Doppler correction of a carrier wave from IQ signal. It is a graph figure for description. It is a block diagram which shows the structure of the receiver terminal of a reference example .

6 1st stage detection part 7 2nd stage detection part 9 Correlation calculation part
11 Receiver terminal
12 Receiver
16 Doppler correction section
17 External oscillator
19 Pseudo distance detector
34 Local oscillator A Satellite τ Delay value

Claims (2)

A receiver terminal (11) having a local oscillating unit (34) receives a signal from the satellite (A), and the receiver terminal (11) determines a pseudo distance between the satellite (A) and the received signal. A satellite positioning method
The receiver terminal (11) receives a frequency that is more accurate than the local frequency oscillated by the local oscillator (34) from the external oscillator (17) and is based on the external frequency obtained from the external oscillator (17). Measure the local frequency oscillated by the local oscillator (34), detect the error of the local oscillation frequency given in advance from the measured local frequency, and the maximum of the external frequency given in advance to the error of the local oscillation frequency The frequency range is specified by using the frequency calculated by adding and subtracting the error as the upper limit value and the lower limit value, and a plurality of accurate local frequency error candidate values are set within the specified frequency range, and received from the satellite (A). The signal is subjected to Doppler correction using the frequency error due to the Doppler effect of the satellite (A) and each candidate value of the local frequency error to calculate the correlation, and an accurate local frequency error is detected based on the correlation calculation result. A satellite positioning method, wherein a delay value (τ) is detected from a correlation calculation result indicating a partial frequency error, and the pseudorange is obtained from the delay value (τ). In a satellite positioning system, a receiver terminal (11) receives a satellite signal from a satellite (A), and the receiver terminal (11) obtains a pseudorange with the satellite (A) by the received signal. And
The receiver terminal (11) has a local oscillator (34) that oscillates a frequency, and a receiver that receives an accurate frequency from the external oscillator (17) than the local frequency that the local oscillator (34) oscillates ( 12) and the local frequency of the local oscillation unit (34) is measured based on the external frequency obtained from the external oscillation unit (17), and an error in the local oscillation frequency given in advance is detected from the measured local frequency. The first stage detection unit (6) and a plurality of candidate values of an accurate local frequency error set within a predetermined frequency region including an error of the local oscillation frequency are input and received from the satellite (A). A Doppler correction unit (16) for performing Doppler correction on the signal based on the frequency error due to the Doppler effect of the satellite (A) and each candidate value of the local frequency error, and a correlation calculation of the signal processed by the Doppler correction unit (16) A correlation calculator (9); A second stage detection unit (7) for detecting an accurate local frequency error based on the function calculation result, and a delay value (τ) detected from the correlation calculation result indicating the accurate local frequency error; A pseudo-range detector (19) for obtaining the pseudo-range from the above, and further adding a maximum error of the external frequency given in advance to the error of the local oscillation frequency detected by the first-stage detector (6) A satellite positioning system characterized in that a frequency region is specified using the frequency calculated by subtraction as an upper limit value and a lower limit value, and a plurality of candidate values for an accurate local frequency error are set within the specified frequency region.

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