JP2008224683A - Satellite positioning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a satellite positioning system that has a high precision and is very fast in processing speed even in the case of a very weak static-laden signal from a satellite. <P>SOLUTION: A satellite positioning system in which a receiving terminal having an internal oscillation section receives a signal from a satellite and calculates a pseudo-distance from the satellite according to the signal thus received. The receiving terminal obtains a large number of pieces of data incrementally lagging a slight amount of time i behind data corresponding in a predetermined amount of time T to a signal obtained by eliminating, from the received signal, the value of a frequency error due to the Doppler effect of the satellite. Next, the large number of pieces of data are divided into a plurality of blocks B, and each of the blocks B is subjected to correlated calculation and FFT computation in sequence. Then, the value of a frequency error in the internal oscillation section is detected by synchronously adding data acquired through computation for each block B. The receiving terminal includes a quasi-distance detection section for calculating the pseudo-distance according to the received signal from which the value of the frequency error due to the Doppler effect of the satellite and the value of the frequency error in the internal oscillation section have been eliminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a satellite positioning 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.

Also, if there is a frequency error of the local oscillator (internal oscillation unit) in the receiver, the error after the frequency conversion is superimposed on the frequency 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

The problem to be solved is that the signal taken from the outside has a restriction that the frequency stability is sufficiently accurate than the frequency stability inside the receiver and the signal electric field strength is more than the corresponding strength. . Also, with this means, the received signal received from the outside is subjected to the Doppler effect from the outside, or the signal is devoted to noise. Accurate detection has the disadvantage that it is extremely difficult.

  The satellite positioning system according to 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 with the satellite based on the received signal received. The machine terminal oscillates a frequency signal, a Doppler correction unit that corrects a frequency error from the received signal, and a frequency error value due to the Doppler effect of the satellite is removed from the received signal by the Doppler correction unit. A large amount of data is acquired by delaying from a predetermined time of the data of the received signal, and the large number of data is divided into a plurality of blocks, and correlation calculation, FFT, and synchronous addition are sequentially performed for each block. A frequency error detection unit that detects a frequency error value of the internal oscillation unit, a frequency error value due to the Doppler effect of the satellite, and a frequency error value of the internal oscillation unit are removed. In which and a pseudo-range detection unit for obtaining the pseudorange from the signal.

In a satellite positioning system in which a receiver terminal receives a satellite signal from a satellite, and the receiver terminal obtains a pseudorange with the satellite based on the received signal, the receiver terminal An internal oscillation unit that oscillates a signal, a Doppler correction unit that corrects a frequency error from the received signal, and a signal obtained by removing the frequency error value due to the Doppler effect of the satellite from the received signal by the Doppler correction unit for a predetermined time. A large amount of data is acquired from the data of each time delayed by a small amount of time, the large number of data is divided into a plurality of blocks, and correlation calculation and FFT are performed for each block.
And a first stage detection unit for detecting the frequency error value of the internal oscillation unit by sequentially performing synchronization and addition, and the frequency error value of the internal oscillation unit with higher accuracy than the frequency error value detected by the first stage detection unit. A plurality of candidate values are set so as to include the internal oscillation from each received signal obtained by removing the frequency error value due to the Doppler effect of the satellite and the frequency error candidate values of the internal oscillation unit in the Doppler correction unit. A second stage detection unit that detects a high-accuracy frequency error value of the unit, a frequency error value due to the Doppler effect of the satellite and a high-accuracy frequency error value detected by the second stage detection unit from the received signal And a pseudo distance detection unit for obtaining the pseudo distance.

In addition, the second stage detection unit identifies a frequency region where the true value of the frequency error of the internal oscillation unit exists, and within the frequency region, the minimum frequency unit that can be indicated by the first stage detection unit. The frequency divided for each small frequency unit is set as a plurality of candidate values of the frequency error of the internal oscillation unit, and the Doppler correction unit calculates the frequency error value due to the Doppler effect of the satellite and each candidate value of the frequency error of the internal oscillation unit. Correlation calculation is performed on each of the removed received signals, and a highly accurate frequency error value of the internal oscillation unit is detected from the correlation calculation result indicating the maximum peak value among the correlation calculation results.

The present invention makes it possible to make the signal-to-noise ratio remarkably improved and to detect the frequency error of the internal oscillating unit even if the signal is very weak due to noise. Processing time can be shortened. That is, high accuracy and high processing speed can be achieved.

Therefore, in the satellite positioning system of the present invention, even when a signal from a satellite is received in a building or the like, that is, a signal from a very weak satellite that has been subjected to Doppler fluctuation due to noise. However, it is possible to detect an oscillation frequency error of the internal oscillator included in the receiver terminal with ultra-high sensitivity and good responsiveness.
In other words, in the past, an ultra-high precision and expensive oscillator was required in order to make Doppler correction respond quickly and accurately. However, 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.

In addition, the invention described in Japanese Patent Application No. 2003-297572 has been proposed for self-detection of the frequency error of the internal oscillation unit from a very weak signal that is noisy to noise, but the satellite positioning of the present invention is also proposed. The system is excellent in that the calculation processing time for detecting the frequency error of the internal oscillation unit can be remarkably shortened and that the calculation processing can be performed with a small circuit (memory).

FIG. 1 is an overall block diagram showing an outline of an embodiment of a satellite positioning system of the present invention, and FIG. 3 is a flowchart of the present invention from when a satellite signal is received until a pseudorange is obtained.
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 Doppler information 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 value due to the Doppler effect of the satellite A from the GPS signal by the calculation 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 is a communication line, and information of the calculation unit 4 is transmitted to the receiver terminal 11 via the communication line L. The communication line L is a communication path for sending the information of the calculation unit 4 to the receiver terminal 11 side. The communication line L covers all possible communication lines, and may be an electromagnetic communication means, for example, terrestrial broadcasting It may be a mobile phone communication, a communication that broadcasts information via a communication satellite, or an Internet line.

The receiver terminal 11 receives information of the calculation unit 4 from the base station 1 by broadcasting or the like. Information of the calculation unit 4 is received by the reception unit 12 included in the GPS receiver terminal 11.
The GPS 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 (C / A code) obtained by down-converting the GPS signal (removing the carrier wave)
Is a GPS receiver for A / D conversion, and 15 is a part for storing the signal (memory: RAM)
It is. Reference numeral 16 denotes a Doppler correction unit that corrects a frequency error from the PN signal (reception signal). Then, the Doppler correction unit 16 performs carrier Doppler correction on the accumulated PN signal (I component, Q component) of the GPS signal from the carrier Doppler information from the base station 1. That is, the Doppler correction unit 16 removes the frequency error value due to the Doppler effect of the satellite A from the received signal. Note that a plurality of Doppler correction units 16 are provided, and for example, a number corresponding to the number of satellites A that travel around the earth may be provided.

The reception signal corrected by the Doppler correction unit 16 is a PN signal (I component, Q component) including a Doppler component due to a frequency error of the internal oscillation unit (local oscillator) 34 (shown in FIG. 2).
For the PN signal including the Doppler component, that is, the PN signal (I component and Q component) including the Doppler component generated by the frequency error of the internal oscillation unit 34, the frequency error detection unit 6 uses the frequency of the internal oscillation unit 34. Perform error detection.

If the local frequency error value is obtained, Doppler correction of the PN signal can be easily performed from the detected frequency error. That is, the local frequency error value detected by the frequency error detection unit 6 is input to the Doppler correction unit 16, and the Doppler correction unit 16 removes the local frequency error value from the received signal.
And frequency error (frequency error value due to Doppler effect of satellite A and local frequency error value)
The pseudo-range detecting unit 19 obtains a pseudo-range between the receiver terminal 11 and the satellite A based on the canceled signal. The position calculation unit 20 knows the self-position of the receiver terminal 11 based on the pseudo distance obtained here, the base station position from the receiving unit 12, the position of each satellite, and the pseudo distance between the base station 1 and each satellite A. be able to.

The receiver terminal 11 has a second stage detection unit 7 in order to obtain a frequency error value with higher accuracy than the local frequency error value detected by the frequency error detection unit 6. After the local frequency error value is detected by the frequency error detection unit 6, a high-accuracy frequency error value is detected by the second stage detection unit 7, and the local frequency error value detected by the second stage detection unit 7 is detected. Input to Doppler correction unit 16 and Doppler correction unit
In step 16, the local frequency error value is removed from the received signal. Then, a pseudo distance between the receiver terminal 11 and the satellite A is obtained by the pseudo distance detecting unit 19 based on the signal from which the frequency error (frequency error value and local frequency error value due to the Doppler effect of the satellite A) is canceled.
That is, the frequency error detection unit 6 is used as the first stage detection unit 66, and after the coarse local frequency error value is obtained by the first stage detection unit 66 (first stage detection step), the second stage detection unit 7 A highly accurate local frequency error value is detected (second stage detection step).

Hereinafter, the operation in each processing block will be described in detail. FIG. 2 is a block diagram showing the configuration of the receiver terminal 11.
14 is a reception antenna unit, 32 is a high frequency amplification unit that receives a PN signal from the reception antenna unit 14, and 33 is a frequency conversion unit that down-converts the frequency.
The internal oscillating unit 34 is a local oscillating unit (frequency synthesizer) or the like, and 35 is an I signal converting unit (I
Signal conversion carrier removal unit), 36 is a Q signal conversion unit (Q signal conversion carrier removal unit), 37 is a 90 degree phase shifter, 38 and 39 are A / D converter units, and 15 is a memory for temporarily storing signals. Part (RAM),
41 is a DSP unit, 42 is a CPU unit, 22 is a pattern calculation unit, 44 is a ROM for the DSP unit 41, 45 is R
AM and 46 are ROMs connected to the CPU unit 42.
Reference numeral 12 denotes a receiving unit for obtaining information from the base station 1 shown in FIG.
The Doppler correction unit 16, the frequency error detection unit 6 (first stage detection unit 66), the second stage detection unit 7, the pseudo distance detection unit 19, and the position calculation unit 20 in FIG. Corresponds to 21.

FIG. 4 is a diagram showing 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 a signal processed by the frequency conversion unit 33. is there. FIG.
Here, 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. 4. A 1.5 GHz band GPS signal that has been subjected to spread spectrum modulation with a PN signal is received by the high frequency amplifying unit 32 from the receiving antenna unit 14. The PN signal is down-converted by the internal oscillating unit (frequency synthesizer) 34 and the frequency converting unit 33, and converted into, for example, a frequency region of 70 MHz band.
The parts that are multiplied by the 70 MHz carrier wave whose phases are different from each other by 90 degrees in the internal oscillation part 34 and the 90 degree phase shifter 37, that is, the parts of the I signal converting part 35 and the Q signal converting part 36 are mutually connected. 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 internal oscillator 34 is a local oscillator (frequency synthesizer), and a generally used inexpensive crystal oscillator can be used. The internal oscillator 34 has a frequency error.

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 the 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 internal oscillation unit 34 (frequency synthesizer). Here, assuming that the Doppler frequency variation of the satellite signal (Doppler frequency error of satellite A) is Δ W _C and the frequency variation of the internal oscillation unit 34 (local frequency error value) is Δ W _L , ΔW = Δ W _C + Δ W _L.

Then, the signal from the internal oscillating unit 34 in FIG. 2 and the 90-degree phase shifter 37 represent signals having a phase difference of 90 degrees as carrier waves 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. 4, the input signal PN.cos ((W + ΔW) t + Φ) is input to 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. Then, these two signals are stored in the memory unit (RAM) 15 for a predetermined time.
The high frequency amplification unit 32, frequency conversion unit 33, internal 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.
Furthermore, 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. 2, a digital signal processing unit 21 includes a CPU unit 42 connected to the receiving unit 12 and a RAM (memory) 45 connected to the CPU unit 42 in order to process data obtained via the receiving unit 12. And R
It comprises an OM (memory) 46, a DSP unit 41 connected to the memory unit (RAM) 15, a ROM (memory) 44 connected to the DSP unit 41, and a pattern calculation unit 22.
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 take out (demodulate) the signal of the satellite A ₁ at the receiver terminal 11, the receiver terminal 11 stores the PN signal a ′ that is the same as the PN signal a in advance and uses the PN signal a ′ to store the 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 receiver terminal 11 is previously connected to P
The same PN signal b 'as the N signal b must be stored.
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, the 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 been conventionally made up of a CPU, DSP and memory (RAM).
And a general-purpose digital signal processing configuration using a ROM), the description is omitted.

Then, the hardware unit of the digital signal processing unit 21 executes the functional blocks of the Doppler correction unit 16 and the frequency error detection unit 6 of FIG. The case where this functional block is executed by digital signal processing by software will be described.
The signals obtained by the I signal conversion unit 35 and the Q signal conversion unit 36 include a Doppler component. The Doppler frequency ΔW is information from the base station (server) 1 and is obtained from the receiving unit 12 of the receiver terminal 11.

The correction performed by the Doppler correction unit 16 can be performed by external Doppler information or by internal processing. That is, the receiver terminal 11 may receive the external Doppler information from the base station 1, or the receiver PN 11 receives the received PN at the arithmetic unit (not shown) of the receiver terminal 11.
You may perform a Doppler correction by calculating from a signal.

FIG. 5 shows an operation for performing Doppler correction based on external Doppler correction information.
In FIG. 5, reference numerals 26, 27, 28, and 29 denote multipliers, 30 denotes an adder, and 31 denotes a subtracter. The input signals here are discretized data stored in the memory unit 15, respectively. Further, t represents a discretized value.
The data of the input signal I signal and Q signal in FIG. 5 are PN.cos (ΔWt + Φ) and −PN.sin (Δ
Wt + Φ)

For these signals, the Doppler frequency fluctuation component ΔWc of the received signal obtained from the receiving unit 12
Signals cos (ΔWct) and sin (ΔWct) obtained from the signals are multiplied by multipliers 26, 27, 28, 29 as shown in FIG.
, And pass through the adder 30 and the subtractor 31, then −PN.sin (Δ W _L t + Φ) and PN.cos (Δ W _L
t + Φ) is obtained. These signals are discretized digital signals. The output PN code is subjected to Doppler due to the frequency error of the internal oscillation unit 34.
This PN code is used as an input signal to the frequency error detector 6 shown in FIG.

Next, referring to FIG. 6, the operation of detecting the local frequency error value by the frequency error detector 6 (first stage detector 66) will be described.
A signal from which the Doppler frequency error value of the satellite A is removed by the Doppler correction unit 16 is sent to the frequency error detection unit 6 (first stage detection unit 66). The frequency error detection unit 6 acquires a large number of data by delaying by a minute time i from the data for a predetermined time T of the transmitted signal, and divides the large number of data into a plurality of blocks B.
For example, the case where the predetermined time T is 1 sec, the minute time i is 1 msec, and the block B is divided every 20 msec will be described.
The data for a predetermined time T is 1 sec data and the minute time i is 1 msec for a total of 10
Sampling 00 pieces of data. This data is divided into blocks B every 20 msec, and 1 sec worth of data is divided into 50 blocks B.

Next, the frequency error detection unit 6 sequentially performs correlation calculation and FFT calculation processing for each block B.
The correlation calculation unit 9 included in the signal processing unit 21 performs correlation calculation with the replica PN code (C / A code signal) that the receiver terminal 11 has in advance for each block B (every 20 msec). 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 take out (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 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, if the receiver terminal 11 does not have all the PN signals corresponding to each satellite A emitted from each satellite A in advance,
The signal of each satellite 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 shown in FIG. 7A, the correlation calculation result for one block B is detected for peak values P _{0 to} P ₁₉ every x ₀ to ₁₉ which is 1 msec data. FIG. 7B shows the peak values of P _{0 to} P ₁₉ arranged on the time (t) axis. In FIG. 7B, Z is a beat line passing through each vertex of the peak values of P _{0 to} P ₁₉ , and this beat line Z represents a local frequency error value. That is, the peak values P _{0 to} P ₁₉ indicate the amplitude of the waveform representing the local frequency error value.

The discretized data in FIG. 7B is 1 block B data (peak values P _{0 to} P ₁₉ ), but 1 sec data has 1000 data of 1 msec. Next, the peak values P _{0 to} P ₉₉₉ of 1000 pieces of data are inputted into the formula 2 and the Fourier transform unit 8 included in the signal processing unit 21 performs F
FT. That is, the value of Pn (n = 0 to 999) is input to the formula 2 as x (n).

When the peak values P _{0 to} P ₉₉₉ are input to x (n) and FFT is performed, the local frequency error value Xm can be calculated. In the equation (2), n and m are integers of 0, 1,..., N−1, and N = 1000 in this embodiment.

Then, the frequency components obtained by performing the FFT for each block B are synchronously added by the synchronous adder 10 included in the signal processing unit 21, and even if the signal is noisy, the local frequency error value ΔW _L
Can be detected.
In general, synchronous addition is widely known as a method for reducing noise in a periodic signal in a digital signal processing circuit. To describe this calculation, in general, when one cycle of a periodic signal is sampled with s sampling pulses and data for m cycles is obtained, data of D (1: m, 1: s) can be obtained ( s is the number of samples, m is the number of additions). At this time, the synchronous addition average result of the Mth row is expressed by the equation (3).

Assuming that the noise superimposed on the signal is Gaussian with a statistical property, the noise component is known to be reduced to 1 / √m by m additions. In the embodiment of the present invention, m = 1000. Therefore, noise reduction by the synchronous addition of the present invention is 1 / √1000.

When the local frequency error value delta W _L by the frequency error detector 6 is detected, it sends the data of the local frequency error value delta W _L Doppler correction unit 16, the Doppler satellite A from the received signal by the Doppler correction unit 16 The frequency error value Δ W _C and the local frequency error value Δ W _L are removed.
Specifically, the input signal I signal PN.cos (ΔWt + Φ) shown in FIG. 5 and the Q signal−PN.sin (ΔWt
+ Φ), the signal cos (ΔWct) obtained from the Doppler frequency error value ΔW _{C of} satellite A and si
n other than (ΔWct), the local frequency error value delta W _L from the obtained signal cos (Δ W _L t) and sin (Δ W _L
t) is multiplied by multipliers 26, 27, 28, and 29, and then passed through adder 30 and subtractor 31 (not shown). Then, -PN.sinΦ and PN.cosΦ, which are signals obtained by removing the Doppler frequency error value and the local frequency error value of satellite A from the received signal, are obtained. Each signal of PN.sinΦ and PN.cosΦ is stored in the RAM 45 (see FIG. 2).

The signals (-PN.sinΦ and PN.cosΦ) stored in the RAM 45 are synchronously added by the synchronous adder 10, and the correlation added signal is correlated with the replica PN code by the correlation calculator 9. Then, the I signal and the Q signal are synthesized and stored in the RAM 45.

Next, the operation of the pseudo distance detection unit 19 will be described. The pseudo-range detection unit 19 includes a correlation calculation unit 9
The data having the maximum absolute value is retrieved from the data calculated by the correlation and stored in the RAM 45. The absolute value of the correlation peak value having the maximum absolute value and the delay value τ are detection results.

If this delay value τ is obtained, a pseudo distance (a distance between the satellite S and the GPS receiver terminal 11) can be obtained from the delay value τ. It should be noted that the correlation calculation performed by the correlation calculation unit 9, I signal · Q
The signal synthesis and means for obtaining the pseudo distance from the delay value τ are generally well known 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. .

Further, in order to obtain a frequency error value with higher accuracy than the local frequency error value detected by the frequency error detection unit 6, after the local frequency error value is detected by the frequency error detection unit 6 (first stage detection unit 66) ( After the first stage detection step), the second stage detection unit 7 detects a highly accurate frequency error value (performs the second stage detection step).
Specifically, first, the frequency region where the true value of the frequency error of the internal oscillation unit 34 exists is specified. In the embodiment described above, since the block B is divided every 20 msec, a frequency unit smaller than 50 Hz cannot be measured. In this case, for example, if the first stage detection unit 66 detects a local frequency error value of 150 Hz, it can only be measured every 50 Hz, so the true value of the frequency error can be measured one step above and one step below 150 Hz. The value is between 100Hz and 200Hz. The region greater than 100 Hz and less than 200 Hz is the frequency region to be specified.

Next, the frequency divided into frequency units smaller than the minimum frequency unit (50 Hz) that can be indicated by the first stage detection unit 66 within the specified frequency region (greater than 100 Hz and less than 200 Hz) is set in the internal oscillation unit 34. A plurality of candidate values for high-accuracy frequency errors are used. For example, when dividing into 10 Hz smaller than 50 Hz, the candidate values are set to 110 Hz, 120 Hz,..., 180 Hz, 190 Hz.
Then, the signals cos (ΔWct) and sin (ΔWc) obtained from the Doppler frequency error value ΔW _{C of} the satellite A
t) and signals cos (ΔW _L t) ′ and sin (Δ W _L t) ′ obtained from the respective candidate values Δ W _L ′
And the input signals F1, F2,..., Fx. As shown in FIG. 8, the input signals (F1, F2,..., Fx) are input to a plurality of Doppler correction units 16 (see FIG. 5), and the Doppler frequency error value of satellite A and each candidate value are received from the received signal. And remove. Each Doppler correction unit
The correlation calculation unit 9 performs correlation calculation on the received signal processed in 16 and selects the correlation calculation result indicating the maximum peak value from the correlation calculation result to detect the highly accurate frequency error value of the internal oscillation unit 34 To do.

The received signal data from which the frequency error value due to the Doppler effect of the satellite A and the high-accuracy frequency error value detected by the second stage detection unit 7 are removed is input to the pseudorange detection unit 19 and delayed by the pseudorange detection unit 19. The value τ is detected, and the pseudorange is obtained from the delay value τ.
The block B that divides the data received in the first detection step may be divided, for example, every 40 msec in addition to every 20 msec, and may be divided according to the performance of the receiver terminal 11 or the like. . Furthermore, a practical local frequency error value can be detected even if only the first stage detection step is performed without performing the second stage detection step.

In addition, the satellite positioning system of the present invention can be freely changed in design, and the frequency error value of the internal oscillator 34 detected by the frequency error detector 6 (first stage detector 66) and the second stage detector 7 and high accuracy. The frequency error value or the candidate value is input to the Doppler correction unit 16 shown in FIG. 5 together with the Doppler frequency error value of the satellite A for processing, and from the signal from which only the Doppler frequency error value of the satellite A is removed, The Doppler correction unit 16 may remove the frequency error value or the like of the internal oscillation unit 34. That is, the Doppler correction unit 16 may independently correct the Doppler frequency error of the satellite A and the frequency error of the internal oscillation unit 34.
Further, the correlation calculation and the FFT calculation processing for each block B shown in FIG. 6 may be performed in parallel using a plurality of processing devices, respectively, or the calculation processing is performed for each block B by a single processing device. You may make it repeat.

As described above, in the satellite positioning system according to the present invention, the receiver terminal 11 receives the satellite signal from the satellite A, and the receiver terminal 11 obtains the pseudorange between the satellite A and the received reception signal. In the positioning system, the receiver terminal 11 includes an internal oscillation unit 34 that oscillates a frequency signal, a Doppler correction unit 16 that corrects a frequency error from the received signal, and a Doppler of the satellite A from the received signal by the Doppler correction unit 16. A large number of data is acquired by delaying by a minute time i from the data for a predetermined time T of the signal from which the frequency error value due to the effect is removed, and the large number of data is divided into a plurality of blocks B and correlated for each block B. A frequency error detection unit 6 that detects the frequency error value of the internal oscillation unit 34 by sequentially performing calculation, FFT, and synchronous addition, a frequency error value due to the Doppler effect of the satellite A, and a frequency error value of the internal oscillation unit 34 And a pseudo-range detecting unit 19 that obtains a pseudo-range from the received signal that has been removed. Therefore, even when the signal from the satellite A is received in a building or the like, that is, the Doppler fluctuation caused by noise is detected. Even for the received signal from the very weak satellite A, the oscillation frequency error of the internal oscillation unit 34 of the receiver terminal 11 can be self-detected with high sensitivity and good response.
In other words, in the past, an ultra-high precision and expensive oscillator was required in order to make Doppler correction respond quickly and accurately. However, 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.
Further, since the correlation calculation and the FFT calculation are performed for each block B, the calculation processing time for detecting the frequency error of the internal oscillator 34 can be remarkably shortened, and the calculation processing can be performed with a small circuit (memory). It can be carried out.

In the satellite positioning system in which the receiver terminal 11 receives a satellite signal from the satellite A, and the receiver terminal 11 obtains a pseudo distance from the satellite A based on the received signal, the receiver terminal 11 An internal oscillation unit 34 that oscillates a frequency signal, a Doppler correction unit 16 that corrects a frequency error from the received signal, and a predetermined signal obtained by removing the frequency error value due to the Doppler effect of the satellite A from the received signal by the Doppler correction unit 16 A large amount of data is acquired by delaying the minute time i from the data of time T, and the large number of data is divided into a plurality of blocks B, and correlation calculation and FF are performed for each block B.
A first stage detection unit 66 for detecting the frequency error value of the internal oscillation unit 34 by sequentially performing T and synchronous addition;
A plurality of candidate values are set so as to include the frequency error value of the internal oscillation unit 34 with higher accuracy than the frequency error value detected by the first stage detection unit 66, and the frequency error due to the Doppler effect of the satellite A by the Doppler correction unit 16. The second stage detection unit 7 for detecting a high-accuracy frequency error value of the internal oscillation unit 34 from each received signal from which the value and each candidate value of the frequency error of the internal oscillation unit 34 are removed, and the Doppler effect of the satellite A And a pseudo-range detecting unit 19 for obtaining a pseudo-range from the received signal from which the frequency error value and the high-accuracy frequency error value detected by the second stage detecting unit 7 are removed. Even if the signal is received from a very weak satellite A that has been subjected to Doppler fluctuations that are steeped in noise, the receiver terminal 11 is highly sensitive and responsive. Oscillation frequency error of internal oscillator 34 Can be detected.
In other words, in the past, an ultra-high precision and expensive oscillator was required in order to make Doppler correction respond quickly and accurately. However, 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.
Further, since the correlation calculation and the FFT calculation are performed for each block B, the calculation processing time for detecting the frequency error of the internal oscillator 34 can be remarkably shortened, and the calculation processing can be performed with a small circuit (memory). It can be carried out.
In addition, since the second stage detection unit 7 can detect the frequency error value of the internal oscillation unit 34 with high accuracy, an accurate pseudo distance can be measured.

Further, the second stage detection unit 7 specifies a frequency region where the true value of the frequency error of the internal oscillation unit 34 exists, and is smaller than the minimum frequency unit that can be indicated by the first stage detection unit 66 in the frequency domain. The frequency divided for each small frequency unit is set as a plurality of candidate values of the frequency error of the internal oscillation unit 34, and the frequency error value due to the Doppler effect of the satellite A and the candidate value of the frequency error of the internal oscillation unit 34 in the Doppler correction unit 16 Is calculated from the correlation calculation result indicating the maximum peak value in the correlation calculation result, and the highly accurate frequency error value of the internal oscillation unit 34 is detected. The accuracy of frequency error value detection can be further improved, and an accurate pseudorange can be measured.

It is a whole block diagram which shows the outline of one Embodiment of this 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 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 operation | movement explanatory drawing until a local frequency error value is detected in a frequency error detection part. It is a graph which shows the correlation calculation result in a frequency error detection part. It is operation | movement explanatory drawing until a Doppler correction part and a 2nd step | paragraph detection part detect a highly accurate local frequency error value.

Explanation of symbols

6 Frequency error detector 7 Second stage detector
11 Receiver terminal
16 Doppler correction section
19 Pseudo distance detector
34 Internal oscillator
66 First stage detector A Satellite B Block i Minute time T Predetermined time τ Delay value

Claims (3)

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) includes an internal oscillating unit (34) that oscillates a frequency signal, a Doppler correction unit (16) that corrects a frequency error from the received signal, and the Doppler correction unit (16). A large number of data is acquired by delaying a minute time (i) from the data for a predetermined time (T) of the signal from which the frequency error value due to the Doppler effect of the satellite (A) is removed from the signal, and the multiple data is obtained. A frequency error detector (6) that divides into a plurality of blocks (B) and sequentially performs correlation calculation, FFT, and synchronous addition for each block (B) to detect the frequency error value of the internal oscillator (34). And the frequency error value due to the Doppler effect of the satellite (A) and the internal oscillator (34).
And a pseudorange detector (19) for obtaining the pseudorange from the received signal from which the frequency error value is removed. 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) includes an internal oscillating unit (34) that oscillates a frequency signal, a Doppler correction unit (16) that corrects a frequency error from the received signal, and the Doppler correction unit (16). A large number of data is acquired by delaying a minute time (i) from the data for a predetermined time (T) of the signal from which the frequency error value due to the Doppler effect of the satellite (A) is removed from the signal, and the multiple data is obtained. A first stage detection unit (divided into a plurality of blocks (B) and sequentially performing correlation calculation, FFT, and synchronous addition for each block (B) to detect the frequency error value of the internal oscillation unit (34) (
66) and the internal oscillation unit (34) with higher accuracy than the frequency error value detected by the first stage detection unit (66).
A plurality of candidate values are set so as to include the frequency error value of the satellite, and each of the frequency error value due to the Doppler effect of the satellite (A) and the frequency error of the internal oscillation unit (34) in the Doppler correction unit (16). A second stage detection unit (7) for detecting a highly accurate frequency error value of the internal oscillation unit (34) from each received signal from which the candidate value has been removed, and a frequency error value due to the Doppler effect of the satellite (A) And a pseudorange detector (19) for obtaining the pseudorange from the received signal from which the high-accuracy frequency error value detected by the second stage detector (7) is removed. . The second stage detection unit (7) specifies a frequency region where the true value of the frequency error of the internal oscillation unit (34) exists, and is indicated by the first stage detection unit (66) within the frequency region. The frequency divided into frequency units smaller than the smallest possible frequency unit is set as a plurality of candidate values of the frequency error of the internal oscillation unit (34), and the frequency due to the Doppler effect of the satellite (A) in the Doppler correction unit (16) Each received signal from which the error value and each frequency error candidate value of the internal oscillator (34) are removed is subjected to correlation calculation, and the internal oscillation is calculated from the correlation calculation result indicating the maximum peak value in the correlation calculation result. The satellite positioning system according to claim 2, wherein a highly accurate frequency error value of the section (34) is detected.

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