JPH07280914A - Gps receiving apparatus - Google Patents

Abstract

PURPOSE:To shorten the phase and frequency tuning time of a PRN code until a navigation message is demodulated from received radio waves. CONSTITUTION:The GPS receiving apparatus is provided with a PRN-code-sum generation means 17 which creates the sum or the logical sum of several PRN codes out of a plurality of satellites as receiving objects, a satellite-combination designation means 16 which designates by which satellite combination the sum of the PRN codes is tube taken in the PRN-code-sum generation means 17, and a multiplication means 11 which takes the product of received radio waves containing navigation message from the plurality of PRN-diffused artificial satellites multiplied by the sum of the PRN codes generated by the PRN- code-sum generation means 17. The sum or the logical sum of several patterns whose phase has been shifted by the identical PRN code of the satellites as the receiving objects may be created.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to GPS (Global Position
ioning system) The present invention relates to a GPS receiver that obtains its own position and velocity vector by receiving a navigation message from an artificial satellite and decoding it. For example, it is widely used to obtain the current position of a car or ship as an absolute position on the earth. It can be used.

[0002]

2. Description of the Related Art A conventional GP will now be described with reference to the drawings.
An example of the S receiver will be described. Figure 3 shows the conventional GP
1 shows a schematic configuration of an S receiver. In FIG. 3, 31 is multiplication means, 32 is navigation message decoding means,
33 is PRN code generation means, 34 is a voltage controlled oscillator, 3
Reference numeral 5 is an upper processing means.

The operation of the conventional GPS receiver having the above structure will be described below. The GPS receiver is a device that calculates the position and speed of the user on the earth and provides the calculated result to the user. For that purpose, it is necessary to receive the radio waves of at least three GPS satellites, decode the navigation message, and obtain the propagation time from each satellite to the receiving device and the Doppler shift frequency.

The radio waves of each GPS satellite are, for example, L1.
It is sent on a transmission wave of (1575.42MHz), but it is phase-modulated by a pseudo noise code called C / A or P code unique to the satellite, and the carrier wave is Doppler-shifted by the movement of the satellite and the user. It is characterized by including frequency error. Therefore, the GPS receiver is 3
The navigation message is extracted from the PRN code spread radio waves of more than one satellite by despreading processing and frequency / phase matching processing.

First, the upper processing means 35 determines satellites that can be received now from the present time and backup data, and activates the receiving processing task for each satellite in parallel so as to simultaneously receive those satellite radio waves. In general, the accuracy of the calculated position changes depending on the satellite placement, so that as many satellites as possible are received and a good combination is selected, or position calculation with less error from the least squares method is performed using all satellites. Do. Therefore, it is necessary to activate four or more, for example, eight reception processing tasks that are activated simultaneously.

The PRN code generation means 33 calculates the PRN code of the satellite designated by the upper processing means 35 and synchronizes with the clock generated by the voltage controlled oscillator 34 (the frequency obtained by adding the Doppler shift amount to 1.023 MHz). And outputs a PRN code. The output PRN code pattern is multiplied by the received radio wave by the multiplication means 31.
Since the product sum of a certain satellite code contained in the received radio wave and the same code produced by the GPS receiver for a certain period of time is calculated, the autocorrelation is obtained in digital signal processing. Since the autocorrelation of the PRN code has a steep peak only when the frequency and the phase match, the upper processing means 35 cancels the influence of the phase difference between the two codes and the Doppler shift so as to obtain the above autocorrelation value. Go. Specifically, by changing the frequency of the voltage-controlled oscillator 34, the frequency of the synchronous clock of the PRN code is changed, and the PR
The N code generating means 33 adjusts the phase of the PRN code. Regarding the phase, the PRN code is 1.023Mbps, so 0.977
It is necessary to match with an analysis capability of [sec] (1 / 1.023MHz) or less.

The upper processing means 35 calculates the current position from the navigation messages of a plurality of satellites obtained from each reception processing task as described above and the current time information internally held,
A velocity vector (velocity value and direction) is calculated from the canceled Doppler shift amount (Doppler shift frequency).

By the above method, it is possible to construct a GPS receiving device which can receive the navigation message of the required satellite from the spread spectrum radio waves and calculate the position and velocity vector of the user.

[0009]

However, in the above-mentioned configuration, since it is necessary to have a reception processing task for each satellite to be received, for example, eight satellites are required to receive eight satellites. The minute reception processing task had to be realized by concrete hardware and software processing. Therefore, there are problems that the processing load of hardware and software is heavy, the cost is high, and the circuit scale is large.

Even when receiving one satellite, if the best phase of S / N is searched while shifting the difference in PRN code (1.023 Mbps) bit by bit, one autocorrelation is obtained. S / N
The maximum time Tmax required to find the best phase of
Becomes Tmax = Ts * 1023 (1). If Ts is 1 [msec], it will be approximately 1 [se
c] It takes a long time. Further, when the frequency of the carrier wave is also shifted due to the influence of Doppler shift, the phase adjustment is performed while changing the frequency, so that it takes more time, and in some cases takes 1 minute or more. That is, conventionally, there has been a problem that it takes a very long time to match the phase of the PRN code.

An object of the present invention is to solve such a conventional problem, and an object thereof is to provide a GPS receiver which is small in size and low in cost and capable of performing high-speed processing.

[0012]

In order to achieve the above object, the GPS receiver of the present invention takes the sum or logical sum of a plurality of PRN codes as a PRN code pattern on the receiver side used for autocorrelation and outputs the result. The PRN code sum generating means is provided.

[0013]

According to the present invention, with the above-mentioned configuration, the amount of hardware and software constituting the reception processing task can be reduced to achieve downsizing and cost reduction, and the processing until the navigation message can be retrieved with good S / N is speeded up. Can be done.

[0014]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a GPS receiving apparatus according to the first embodiment of the present invention. Figure 1
In the figure, 11 is a multiplication means, 12 is a navigation message decoding means, 13 is a PRN code generation means, 14 is a voltage controlled oscillator, 15 is an upper processing means, 16 is a satellite combination designation means, and 17 is a PRN code sum generation means.

Since the basic principle of receiving the navigation message of the GPS satellite has been described in the conventional example, it will be omitted. The upper processing means 15 determines the satellite which can be received now from the current time and the backup data, as in the conventional example. The satellite combination designating means 16 further divides the plurality of satellites into some small groups by using judgments such as those having similar expected Doppler shift frequencies or various assumed signal levels. Multiple receive processing tasks are launched in parallel to receive these small groups simultaneously.

Each reception processing task has PRN code generating means 13 for the number of constituents of a small group (on the contrary, the number of constituents of a small group is limited by the number of PRN code generating means 13), but for each PRN code. The generating means 13 calculates the PRN code of the satellite designated by the satellite combination designating means 16. Next, by the PRN code sum generation means 17, the PR
The sum or logical sum of the PRN code obtained by the N code generating means 13 is obtained. The PRN code sum is output in synchronization with the clock generated by the voltage-controlled oscillator 14 (the frequency obtained by adding the Doppler shift amount to 1.023 MHz), and is further multiplied by the reception radio wave by the multiplication means 11.

Here, the received radio wave a and the PRN of the GPS receiver
The autocorrelation value X1 with the code b can be expressed as in equation (2) using a and b. X1 = a # b (2) Similarly, the autocorrelation value X2 between the received radio wave a and the PRN code c of the GPS receiver can be expressed as in equation (3) using a and c. X2 = a # c (3)

Next, if the autocorrelation between the sum of the codes of two satellites b and c and the received radio wave a is taken inside the GPS receiver, the distribution law holds for the autocorrelation (convolution). It becomes like Formula (4). a # = (b + c) = (a # b) + (a # c) = X1 + X2 (4)

Since the autocorrelation of the PRN code has a steep peak only when the frequency and the phase match, the high-order processing means 15 sets the frequency and the phase of the synchronous clock of the PRN code output from the voltage controlled oscillator 14 to a small unit. A point where the autocorrelation value takes the maximum value is searched for while shifting each by one. However, if the PRN code sum is used as the signal taking the correlation value, either peak of X1 or X2 is found as shown in equation (4). The navigation message of the satellite that can be found earlier is decided to be received, and at that time, the other satellite does not receive or is assigned to another reception processing task. Specifically, instead of summing the PRN code, the PRN code of only the discovery satellite and the received radio waves are integrated.

By performing the above processing, even if there are 32 satellites orbiting the earth, for example, within limited hardware and software, that is, within limited reception processing tasks, it is possible to improve It is possible to search for navigation messages of many satellites.

(Embodiment 2) Next, a second embodiment of the present invention will be described. FIG. 2 shows a schematic configuration of a GPS receiver in the second embodiment of the present invention. In FIG. 2, 21 is a multiplication means, 22 is a navigation message decoding means, 23 is a PRN code generation means, 24 is a voltage controlled oscillator, 25 is a high-order processing means, 26 is a phase shift means, and 27.
Is a PRN code sum generation means.

Also in this embodiment, first, the upper processing means 25 determines the satellites that can be currently received from the current time and backup data, and activates the receiving processing tasks for each satellite in parallel so as to simultaneously receive the satellite radio waves. . Further, the upper processing means 25 sets the autocorrelation value to the maximum value,
By changing the frequency of the voltage controlled oscillator 24, the frequency of the synchronous clock of the PRN code is changed, and the PRN code generating means 2
In 3, the phase of the PRN code is adjusted. At this time, in order to speed up the phase adjustment, the same PRN is used by the phase shift means 26.
Several types of patterns in which the phases of the codes are changed are created, and the PRN code sum generation means 27 takes the sum or logical sum of the PRN codes. For example, if the PRN code sum is a pattern obtained by summing the total of four types of patterns that are phase-shifted by π / 2, π, 3π / 2 and the original pattern (phase 0), the phase is moved to maximize the autocorrelation value. The time to obtain the value is four times faster, simply thinking. Of course, the larger the number of patterns for which the sum is added, the worse the S / N of the autocorrelation value becomes, and therefore the number of patterns to be added (type of phase) depends on the required S / N. Therefore, in the concrete design, there is a trade-off between the speedup and the S / N, but according to the desktop calculation, up to 2 to 3 patterns can be used without any problem.

As described above, according to the second embodiment,
The phase of the PRN code can be adjusted so that the autocorrelation value takes the maximum value faster than before, and as a result, it becomes possible to calculate the position of the PRN code faster.

[0024]

As described above, according to the present invention, by using the sum of PRN codes of a plurality of satellites as a pattern for taking an autocorrelation with a received radio wave, a navigation message of a larger number of satellites with limited hardware and software. Can be searched for, and as a result, the speed of position calculation can be increased.

The present invention also uses a sum of a plurality of patterns whose phases are changed by the PRN code of a certain satellite as a pattern for taking an autocorrelation with a received radio wave, so that the target satellite is far better than before. The phase of the PRN code can be adjusted so that the autocorrelation value takes the maximum value very quickly, and as a result, the position calculation can be performed at higher speed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a GPS receiver according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a GPS receiving device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of a conventional GPS receiver.

[Explanation of symbols]

 11 Multiplying Means 12 Navigation Message Decoding Means 13 PRN Code Generating Means 14 Voltage Controlled Oscillators 15 Upper Processing Means 16 Satellite Combination Designating Means 17 PRN Code Sum Generating Means 21 Multiplying Means 22 Navigation Message Decoding Means 23 PRN Code Generating Means 24 Voltage Controlled Oscillators 25 Upper processing means 26 Phase shift means 27 PRN code sum generating means 31 Multiplying means 32 Navigation message decoding means 33 PRN code generating means 34 Voltage controlled oscillator 35 Upper processing means

Claims (2)

[Claims] 1. A GPS receiver for determining its own position and velocity vector by receiving and decoding navigation messages from a plurality of GPS satellites, wherein some PRNs among a plurality of satellites to be received. A PRN code sum generating means for creating a sum or a logical sum of codes;
Satellite combination designation means for designating which satellite combination the RN code sum generation means takes to obtain the PRN code sum, and PR
GP having a multiplication means for taking the product of the received radio waves containing navigation messages from a plurality of N-spread artificial satellites and the PRN code sum generated by the PRN code sum generation means
S receiver. 2. A GPS receiving apparatus that obtains its own position and velocity vector by receiving and decoding navigation messages from a plurality of GPS satellites, the phase being determined by the same PRN code of a plurality of satellites to be received. Phase shift means for creating some shifted patterns, PRN code sum generating means for creating the sum or logical sum of the several phase shifted patterns, and navigation messages from a plurality of PRN spread artificial satellites GP comprising: a multiplication means for taking a product of the received radio wave included therein and the PRN code sum generated by the PRN code sum generation means.
S receiver.