JPH03170081A - Satellite navigation receiving device - Google Patents

Abstract

PURPOSE:To extend and expand a time and a space where a position is measurable by generating a correct dummy noise code immediately after the switching point of a dummy noise code when the dummy noise code is switched at a constant period to track signals from plural satellites. CONSTITUTION:Two C/A code generators 1 and 2 are used as a dummy noise code generating means and a switch 7 selects and supplies the outputs of two C/A code generators 1 and 2 to a reception part 3 alternately in order. A switch 6 selects a C/A code generator which generates a C/A code next time between the two C/A code generators 1 and 2. In this case, the C/A code outputted by the C/A code generator 1 is supplied to the reception part 3 in a state shown in a figure and data B is supplied to the C/A code generator 2 which generates a C/A code next. Then the data B is supplied and the C/A code corresponding to the data B can be outputted to the reception part 3 with a specified phase from right after the generator is switched to the side of the C/A code generator 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of industrial application This invention is applicable to receivers in NAVS'r/ltR/GPS (Global Positioning System), etc.
This invention relates to a satellite navigation receiving device that receives radio waves transmitted from the 'ii star and measures the receiving position.

Background of the invention NAVSTAR/GPS is being developed by the U.S. Department of Defense as the next generation satellite navigation system for conventional NNSS, with the Air Force as the main developer.

This system consists of space (multiple navigation satellites placed in fixed satellite orbits), control (ground facilities that transmit each +!It control data to each navigation satellite), and users (multiple navigation satellites transmit control data). It consists of three parts: a receiving device that receives radio waves.

Each satellite has a highly accurate clock and transmits this time signal over radio waves. This signal from the satellite arrives with a delay equal to the distance to the receiver, so the distance can be determined by multiplying this delay time by the propagation speed of the radio wave. If this is done for three satellites, the position of the receiver can be determined in three-dimensional space I2. Since the clock in the receiver is not normally the clock on satellite-L, it receives the radio waves from the other satellite and calculates the four unknowns from the four equations (2).
3D position and time).

The radio waves from each life star use so-called spread spectrum attenuation. That is, the carrier wave is phase-shift keyed modulated using a pseudo-noise coat (noise-like binary code) and then transmitted. Therefore, in order to receive radio waves from satellites, the received signal must be multiplied by a pseudo-noise code that has the same pattern and timing as the transmitted signal.

This means that the signal from the satellite has not been received for the first time, and unless the pseudo-noise code pattern is different or the timing does not match, the signal received will only be perceived as noise.

Although the frequency of the radio waves transmitted by each satellite is the same, each satellite modulates it with its own unique pseudo-noise code pattern.
On the receiver side, a pseudo-noise code is generated corresponding to the satellite to be received, and by matching the timing, it is possible to demodulate the signal of the desired satellite. Also, by matching the tying of this pseudo-noise coat, the distance to the satellite is measured. In addition, two pseudo noise codes, C/A code and P code, are used.
The P code has a higher distance measurement accuracy than the C/A code, but
Only the C/A code is made public, and consumer receivers only use this C/A code.

In addition, each satellite records its own orbit information and various parameters.
It is transmitting at a transfer rate of 0 b/s.

The receiver measures the position of the receiver in terms of latitude, longitude, and height based on this information and the above-mentioned distance.

Furthermore, the moving speed of the receiver can be determined by measuring the Doppler effect of the reception frequency of the carrier signal from the satellite.

(C) Conventional technology The basic configuration of a GPS receiver is to use C/A to maximize the correlation between the C/A code created inside the receiver and the received signal.
/A part that performs spectrum despreading by controlling the phase of the A code, a part that calculates the Doppler shift of the GPS signal by measuring the carrier frequency included in the spectrum despread signal, and a part that performs spectrum despreading and demodulation. It is equipped with a part that collects satellite orbit data, time data, etc. from navigation data at a transmission rate of 5 Q b/s included in the signal.

Each of the functions described in (h) is an essential basic function, but its structure differs depending on the receiver, and each has its own characteristics.

The structures of these receivers can be divided into the following three types.

■1-channel sequential reception method 2 ■1-channel high-speed sequential reception method ■Multi-channel reception method The 1-channel sequential reception method receives almanac data from all satellites from one satellite, and uses multiple channels for positioning based on the almanac data. The satellites are captured and ephemeris data is collected, and then the C/A code from each satellite is measured, for example, for one second each for actual positioning. A disadvantage of this method is that while data from one satellite is being collected, measurements of other satellites cannot be performed, and it takes a long time to complete measurements of all the satellites used for positioning.

The 1-channel high-speed sequential reception method samples one satellite at intervals of, for example, 5 ms, and completes ranging from four satellites in 20 ms. Furthermore, since one bit of a navigation satellite is 20 mS, data from four satellites is collected by high-speed switching during this time.

The multi-channel reception system includes an independent reception section for each satellite, and the hardware is complicated and expensive.

(d) Problems to be Solved by the Invention The one-channel high-speed sequential reception system has simple hardware and eliminates the drawbacks of the one-channel sequential reception system. However, in order to sample and utilize signals from satellites for a short period of time,
It has the disadvantage that the N ratio deteriorates and satellite signals with a poor S/N ratio cannot be captured.

Moreover, with the 1-channel high-speed sequential reception method,
In addition to the fact that the signal was sampled for a short time, it was disadvantageous in terms of S/N ratio for the reasons described below.

Figure 9 is a structural diagram of the main parts of a conventional GPS receiver, Figure 10
The figure is a diagram showing the sampling timing of the signal from the satellite during 20 ms.

In FIG. 9, the C/A code generator 5 receives data A. - Give the C/A code corresponding to D to the receiving section 3. The receiving section 3 receives the C/A code generated by the C/A code generator 5.
In addition to finding the correlation between the A code and the signal from the satellite,
Controls the code phase of C/A code. Therefore, by switching the switch 4 to switch the data A to D given to the C/A code generator 5, it is possible to receive a satellite signal corresponding to the set data.

However, as the C/A code generator 5, for example, a G-series code generator (so-called Gold code generator) as shown in FIG. 8 is used. This is connected to two sets of M-sequence pseudo-noise code generators consisting of shift registers 9 and 10 and selectors 11 and 12 that return bits corresponding to the given data to the first-stage bits, and a pattern corresponding to the given data. generates a pseudo-noise code. Here, shift registers 9 and 10 each have 10 stages and a code length of 1023.
Bit 1, the frequency of the cross signal is 1,023M b
/s, a pseudo-noise code with a one-cycle coat length of 1 ms is generated. However, in such a G-series code generator, since the initial value of the shift register 91O is constant, the code is always generated sequentially from the first bit of the 1023-bit code. Therefore, it is not possible to immediately generate any one of the 023 bits, and the phase of the C/A code must be controlled by changing the timing at which the first bit is generated. Therefore, as shown in FIG. The desired C/A code is not given to the receiving section until a maximum of 1 ms has elapsed since the first bit (indicating the generation timing data) is given. In FIG. 10, the XX portion is the maximum time during which the C/A code is not determined. Therefore, of the sampled 5 ms signal, only a minimum of 4 ms can actually be used. In this way, the available signal time from each satellite was reduced to 4/5, resulting in a further 2 dB drop in the JQS/N ratio.

Since the pattern of the C/A code is constant, it is conceivable to write this pattern in advance to the ROM and generate the C/A code by sequentially specifying the ROM addresses, but there are many ways to do this. ROM of
(gate array), which is not practical.

An object of the present invention is to prevent a decrease in the S/N ratio by effectively utilizing the entire period of a sampled signal from a satellite in the one-channel high-speed sequential reception system described above. ．． An object of the present invention is to provide a satellite navigation receiving device that can sufficiently capture even bad satellite signals of l:l:.

(81 Means for Solving Problems) This invention includes a code generation means for generating a pseudo-noise code, and a code phase that shifts the phase of the code outputted from this code generation means to determine the code phase that maximizes the correlation with the received signal. Depending on the method of determination and the pseudo-noise codes of multiple navigation satellites to be tracked,
A satellite navigation receiver comprising means for switching the code output from the code generation means at regular time intervals, comprising: two code generation means for alternately generating a plurality of types of pseudo-noise codes corresponding to set data; Code data that sets data that determines the phase of the pseudo noise code and the pseudo noise coat for the code generating means that should generate the pseudo noise code in the next concave of the two code generating means, at least one cycle of the pseudo noise code earlier. The present invention is characterized in that a setting means is provided.

(1) Diagrams showing the configuration and sampling timing of the main parts of the satellite navigation receiver of the present invention are shown in FIGS. 1 and 2.

As shown in Fig. 1, as pseudo noise code generation means,
In this example, two C/A code generators l2 are used, and the switch 7 alternately selects the outputs of the two C/A code generators 1.2 and sequentially supplies the C/A codes to the receiving section 3. The switch 6 selects the C/A code generator that should generate the next C/A code from among the two C/A code generators 1.2. Furthermore, the switch 4 is connected to the C/A code generator 1.
Alternatively, the data given to 2 (data representing the type and phase of the C/A code, respectively) is switched between A and D. In the state shown in FIG. 1, the C output from the C/A code generator l is
The /A code is given to the receiving section 3, and the data B is given to the C/A code generator 2 which is to generate a C/A code next time. For example, the switch 7 is switched to the C/A code generator 2 side by giving data B to the C/A code generator 2 at least lms before switching the switch 7 to the C/A code generator 2 side. As is clear from the timing chart shown in FIG.
The maximum interval (marked with XX) in which no code is generated is not used, and only the interval in which the desired C/A code is generated is used. This makes it possible to effectively utilize the entire sampled period of 5 ms.

{O Embodiment FIG. 3 shows an overall block diagram of a GPS receiver which is an embodiment of the present invention.

In Fig. 3, 13 is an antenna, 14 is a circuit that converts the antenna signal to an appropriate intermediate frequency and amplifies it, and 15 is an A-D that samples this signal at about four times the intermediate frequency and converts it into digital data. It is a converter. The gate arrays 16 and 17 each perform spectrum despread demodulation, which will be described later.CP01B reads the correlation value with the C/A code from the gate array 16 and 17, stores it in the data buffer of the RAM 19, and also sends the data to the gate array 1617. and give various setting data. CPU2l is RAM2
Execute the program written in the ROM 23 using 4 as the working area and read the specified tie 4 from cputs.
The phase and carrier frequency of the C/A code are received by the receiver, and positioning calculations are performed. Further, the program executed by the CPU 18 is transferred to the RAM 19 when the power is turned on.

Incidentally, the FPU 2 2 is a subsystem of the CPU 2 1 and performs floating point operations. The CPU 26 uses the RAM 28 as a working area to execute a program written in the ROM 27, and performs navigation calculations to determine, for example, the direction, distance, and required time from the current location to the destination from the positioning calculation results obtained by the CPU 2l. Also CP
The U26 reads the operation contents of the keyboard 33 via the key interface circuit 32, writes display data to the LCD driver 30 to display on the LCD 31, and also communicates with the outside via the serial interface 29. Perform data transmission. Note that the bus arbiters 20 and 25 arbitrate between each bus line.

FIG. 4 shows the configuration of the gate arrays 16, 17 shown in FIG. 3.

In FIG. 4, the IQ separation circuit 40 alternately sends A-D converted data! (in-phase) precept and Q (orthogonal) or part (■
(data at a point delayed by π/2 from the component). The carrier division removal circuit 4l converts the coordinate values expressed by I and Q given from the IQ separation circuit 40 into carrier NGOs.
(Numerically controlled oscillation circuit) 42 performs coordinate rotation by an angle corresponding to the rotational phase data given from the EPL separation circuit 42 and removes carrier components from the I signal and Q signal, respectively.
and output to 45. The carrier NGO circuit 42 generates rotational phase data based on data given from the carrier NGO setting data register 43. As will be described later, the carrier frequency and carrier phase are estimated from each correlation output data, and data is set in the carrier NGO setting data register 43 so as to track the carrier frequency and carrier phase.

EI) L separation circuits 44 and 45 each produce a signal (hereinafter referred to as 0.5 chips (1/2 of the 1-bit length of the C/A code)) that advances the output timing of the I component and Q component from which the carrier components have been removed. It is called the E (EARLY) signal.) and the 0 chip (
Hereinafter, this will be referred to as the P (PUNCTUAI,) signal. )
and ten. 5 chisop (1 of l bit length of C/A code
The signal is separated into signals delayed by /2 (hereinafter referred to as L (LATE) signals) and outputted to the receivers 46 to 51, respectively. These ffL calculators 46 to 51 each receive the C/A code output from the C/A code generator 1 or the C/A code generator 2.
A code will be given. Multipliers 52 to 57 correspond to each multiplier 46
-51 output values are integrated (counted up) for a certain period of time. That is, C/A code generator 1.2 and multipliers 46 to 4.
8 and multipliers 52 to 54, the precept correlator is manipulated, and the C/A code generator 1.2 and multipliers 49 to 5l
The integrator 55 to 57 constitute a correlator for Q.

Figure 7 shows the correlation between the received signal and the E, P, and L signals. As shown in the figure, when the correlation with the P signal is higher than the correlation with the E and L signals, and the correlation with the E signal and the correlation with the L signal are equal, the C/A code phases are considered to match. Can be done.

The results of each integrator 52 to 57 are sent to the CPU 18 shown in FIG.
is read at the required timing. Also, the CPU 18 is the fourth
Various timing controls shown in the figure [for 61-way 5H, C
Various timing control data such as setting timing of C/A code setting data for the /A code generator 1.2 and the timing for generating the C/A code from the C/A code generator 2 to the multipliers 46 to 51. give. Also, CPU1
8 is for the C/A code setting data register 59,
C/A code setting data and C/A code to be generated next time.
How far to shift the free-run clock signal provided inside the A code generator 1.2 to generate the C/A code (set the G sequence code generator shown in Figure 8 to the initial value) Set data representing whether to start from ).

The processing procedure of C P LJ 18 for signal processing shown in FIG. 3 is shown in FIGS. 5 and 6.

Does CP018 have a cross signal generation circuit and an interrupt system? 2
The interrupt processing shown in FIG. 5 is performed based on the interrupt every lms from the No. 11 circuit (not shown). First, the integrated values of the integrators 52 to 57 shown in FIG. Correlation value with the P signal, correlation value with the L signal, and correlation value with the E signal in the Q component of the received signal. Read the correlation value with the P signal and the correlation value with the L signal, and store them in the RAM 19.
The data is stored in a predetermined data buffer area.

The interrupt processing every 1 ms is completed in a very short time, and control is normally performed using the tie control shown in FIG. In the "loop filter calculation" process in FIG. The phase of
As shown in the figure, the carrier frequency and carrier phase are estimated based on the correlation with the E, P, and L signals, and the frequency and phase to be output by the carrier NGO are determined so that the ■ component is maximum and the Q component is 0. (estimate) and store it in a predetermined area in memory.

In addition, in the "setting code, carrier frequency, etc." process, the data obtained by the calculation of the loop filter E is
Settings are made to the carrier NGO setting data register 43 and C/A code setting data register 59 shown in the figure. At that time, the C/A code setting data and the C/A code phase data of the C/A code generators 1 and 2 are changed to 1 from the C/A code switching timing as shown in FIG.
Set rnS at an earlier timing.

In the "data output to the positioning calculation unit" process, each satellite's C/
The A code phase, carrier frequency, etc. are output to the positioning calculation unit (CPU 21 in FIG. 3) once per second. As a result, the positioning calculation unit calculates the current position, moving direction, and speed. In addition, HDOP (horizontal geometric precision decline rate) and the like are also determined.

Furthermore, in the process of "I"Others", assignment of satellites to be used for positioning, history of tracking status of each satellite, and processing at the time of signal interruption are performed.

When sequentially tracking signals from four satellites every 5ms during 2Qms as shown below, track the C/A code phase, carrier frequency, and carrier phase immediately after switching the C/A code. You can start.

(hl Effects of the Invention According to this invention, when tracking signals from a plurality of satellites by switching pseudo-noise codes at regular intervals, it is possible to generate a correct pseudo-noise code immediately from the time of switching the pseudo-noise code. Therefore, the entire sampling period can be used effectively, and there is no drop in the S/N ratio due to a delay in the generation timing of the constant pseudo-noise code.Therefore, satellite signals with a poor S/N ratio can be Also, the time and space in which positioning can be performed is expanded.

[Brief explanation of the drawing]

1 and 2 are diagrams explaining the operation of the present invention, and FIG. 1 is a block diagram of the main part of the satellite navigation receiving device;
FIG. 2 is a diagram showing the control timing. FIG. 3 is an overall block diagram of a GPS receiver according to an embodiment of the present invention, and FIG. 4 is a detailed block diagram of a portion thereof. Fifth
6 and 6 are flowcharts showing the processing procedure of the main parts of the receiver. FIG. 7 is a diagram showing changes in the correlation value between the C/A code and the received signal in the embodiment. 8th
The figure is a circuit diagram showing an example of a C/A code generator. 9th
1 and 10 are block diagrams of the main parts of a conventional GPS receiver and diagrams showing the control timing thereof.

Claims (1)

[Claims] (1) code generation means for generating a pseudo-noise code; means for shifting the phase of the code output by the code generation means to determine the code phase that maximizes the correlation with the received signal; and a plurality of navigation methods to be tracked. Depending on the satellite pseudo-noise code,
A satellite navigation receiver comprising means for switching the code output from the code generation means at regular time intervals, comprising: two code generation means for alternately generating a plurality of types of pseudo-noise codes according to set data; Code data setting for setting data that determines the pseudo-noise code and the phase of the pseudo-noise code for the code generation means that is to generate the pseudo-noise code next time among the two code generation means, at least earlier than one period of the pseudo-noise code. A satellite navigation receiving device characterized by comprising: means.