JP2001159670A - Correlation detecting circuit for gps receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multichannel correlator. SOLUTION: A plurality of URAMs 22-1 to 22-4 are provided. Correlation values obtained by correlators 18-1 to 18-15 are allocated to and written in any of URAMs 22-1 to 22-4 on the basis of the relative relation of their phases. At the time when a CPU 14 reads the correlation values, a part of their read addresses is discriminated by an output data selector 24 to specify the read- origin URAMs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a correlation detection circuit for a GPS (Global Positioning System) receiver having correlators for a plurality of channels. Although the term “GPS” is used in the present application, this is not intended to limit the invention to NAVSTAR / GPS developed and implemented in the United States. The term "GPS" is used to encompass other types of systems based on similar principles.

[0002]

2. Description of the Related Art In a GPS, a GPS in orbit around the earth is used.
A radio signal for positioning is transmitted from the S satellite over spread spectrum, and the radio signal is received by a GPS receiver located on the earth. The GPS receiver is a GPS receiver that is used for positioning calculation from a plurality of GPS satellites that are generally in view.
A predetermined number or more PS satellites are selected, and synchronization establishment (capture) and maintenance (tracking) of a carrier and a spread code with respect to a signal transmitted from the selected GPS satellite are attempted. If the GPS satellites are successfully acquired and tracked for more than the number required for the positioning operation, the GPS receiver obtains the information carried by the received signals from those GPS satellites, and the carrier and code synchronization for the received signals. Based on the information and the like, a positioning operation based on a known logic is performed. The GPS receiver provides the information obtained by the positioning calculation, for example, the current position and the moving speed to the user in a form such as display of characters and images, output by sound, transmission to a communication line, supply to various control circuits, and the like. I do.

Code synchronization, that is, spectrum despreading in a GPS receiver is performed by, for example, a correlator that detects and outputs a correlation value between a received signal and a spread code. In terms of speeding up operation and improving reliability, it is desirable to increase the number of correlators in the GPS receiver as much as possible.

First, a signal transmitted from a GPS satellite and received by a GPS receiver is spectrally spread using a spread code such as a C / A code or a P code. Each of these codes is composed of a number of chips. For example, the C / A code is composed of 1023 chips. Therefore, when trying to acquire a certain GPS satellite, 1023 chips, ie, 1023
It is necessary to detect a correlation value for each of the code phases, and to check at which chip, that is, at which code phase a correlation peak appears. At this time, if the number of correlators is sufficiently large, correlation values at different chips can be obtained simultaneously and in parallel by a plurality of correlators, so that correlation value detection for 1023 chips and correlation peaks from the results are performed. Can be detected in a relatively short time, and tracking of the GPS satellite can be started early, and various advantages can be obtained.

Further, as described above, in order to perform a positioning operation, a predetermined number or more of GPS satellites must be captured and tracked. If the number of correlators, that is, the number of channels is small, it is not possible to track the number of GPS satellites sufficiently larger than the number required for positioning calculation. Therefore, GPS that can be captured
When the number of satellites decreases due to radio wave blocking, the intended positioning calculation may not be performed until another GPS satellite is captured or the blocking is eliminated. Therefore, it can be said that it is better to provide as many correlators as possible from the viewpoint of reliability that the possibility that positioning can be continued for a long time is high.

[0006]

However, even if an attempt is made to improve the speed and reliability by increasing the number of correlator channels, a memory for storing correlation values (hereinafter referred to as "URA").
M) is a bottleneck, and a sufficient effect may not be obtained.

For example, in order to detect a code phase at which a correlation peak appears, it is necessary to obtain a correlation value for a series of code phases and arrange them on the code phase axis to detect a peak position. In order to execute this processing using members such as the above, a URAM which is a memory for storing a correlation value serving as a basis thereof is required. This UR
As access to the AM, firstly, there is an access for writing a correlation value obtained by a correlator, and secondly, for reading a correlation value executed by a CPU or the like in the above-described determination processing. There is access. Normally, reading cannot be performed during writing, and as the number of correlators increases, both writing and reading of correlation values become more frequent. for that reason,
The time required for reading and writing increases, possibly leading to abnormal processing.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to make it possible to normally execute a correlation peak detection process even when the number of correlators is large. Aim.

[0009]

In order to achieve the above object, the present invention provides (1) a method of obtaining a correlation value between a signal received from a GPS satellite and a spreading code corresponding to a spreading code relating to the signal. A correlation detection circuit for a GPS receiver for detecting a code phase at which a peak appears in the correlation value,
(2) Correlators for a plurality of channels for detecting and outputting a correlation value between a received signal and a given spreading code, a plurality of URAMs for storing the correlation values, a URAM to which the correlation values are written, and A selection member for selecting a read source URAM; and a control member for executing setting of a spread code and its code phase for a correlator, reading of a correlation value from the URAM, and detection of a code phase in which a peak appears in the correlation value. Features. In particular, (3) the correlators for the plurality of channels independently or cooperate with each other to calculate the correlation value between the spread code and the received signal set by the instruction from the control member according to the instruction from the control member. For each of the set code phase and the code phase separated from the code phase by a predetermined interval, the detection and the output are performed. (4) When the correlation value is given from the correlator, the selection member writes the correlation value UR
AM is selected according to the relative phase relationship with respect to the set code phase, and the correlation value is written. When a read address is given from the control member, the read source URAM is determined based on the read address. (5) When trying to detect a code phase at which a peak appears in the correlation value with respect to a received signal from an arbitrary GPS satellite, the control member sets the spread code corresponding to the GPS satellite to the above. The code is set for at least one of the correlators for a plurality of channels, and the code phase is changed and set for the correlator from the plurality of URAMs.
The operation of reading the correlation value related to the PS satellite is at least
It is characterized by repeatedly executing until a code phase at which a correlation value exhibits a peak is detected.

As described above, according to the present invention, a plurality of URAMs for storing correlation values are provided, and a selection member for selecting a writing destination URAM and a reading source URAM for correlation values is provided. When detecting a code phase at which a correlation value has a peak with respect to a received signal from an arbitrary GPS satellite,
A correlation value between the spread code set according to an instruction from the control member and the received signal is obtained by appropriately using correlators for a plurality of channels. When the correlation value is given from the correlator, the selecting member selects the writing destination URAM of the correlation value in accordance with the relative phase relation to the code phase set according to the instruction from the control member, and selects the correlation. Write the value. That is, the correlation value (P) at a certain code phase and the correlation value (E, L) at a code phase separated by a predetermined distance from the code phase are written on different URAMs. When reading out the written correlation value, the control member gives a read address to the selected member. The selection member determines the source URAM based on the read address and causes the correlation value to be read.

Therefore, according to the present invention, since a plurality of URAMs are provided, data can be written to each URAM in parallel, and as a result, the probability of abnormal writing occurring decreases, and The time during which read access is possible can be increased, and the probability of abnormal reading occurring decreases. In addition, since the read source URAM is specified from the read address by the selection member, the control member can perform the readout without being particularly aware that a plurality of URAMs are provided. That is, the operation of the control member does not need to be significantly changed from the prior art, and is easily implemented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a GPS according to an embodiment of the present invention.
2 shows a configuration of a correlation detection circuit for a receiver. The circuit according to the present embodiment includes an ASIC (Application Specific Integrated Circuit) including a correlating unit 10, a URAM unit 12, and a CPU 14.
rcuit) 16.

The correlator 10 has a total of 15 channels CH
15 correlators 18-1 to 18-1 related to 0 to CH14
5 is provided. Each correlator 18-i (i = 1, 2,...)
15) receives the setting of the carrier and the spreading code from the CPU 14, respectively. That is, in order to establish and maintain the carrier and code synchronization with respect to the received signal from the GPS satellite, the CPU 14 receives the setting of the carrier frequency, the type of the spread code (GPS satellite number), the code phase of the spread code, and the like. The correlator 18-i obtains a correlation value between the spread code and the spread code in the received signal with respect to the set code phase, and supplies the correlation value to the input data selector 20 in the URAM unit 12.

The URAM section 12 includes an input data selector 2
It has 0 and 4 URAMs 22-1, 22-2, 22-3 and 22-4 and an output data selector 24.
The input data selector 20 allocates and writes the correlation value output from the correlator 18-i to one of the URAMs 22-j (j = 1, 2, 3, 4) according to the relative relationship of the code phase.

The data written in the URAM 22-j, that is, the correlation value, is read out by the CPU 14. At the time of this reading, the CPU 14 specifies a reading address. The predetermined bit of the read address is a bit for specifying one of the four URAMs 22-j, and output data selector 24 determines the read source URAM according to the value of this bit.
And the correlation value on the URAM 22-j is determined by the CPU1.
4 is formed. Each URAM 22-
j outputs a signal indicating that the correlation value is being written to the CPU 14 when the correlation value is being written, and the CPU 14 does not read the signal when the signal is generated.

In this embodiment, the correlation unit 10 sends the URA
The correlator outputs supplied to the M unit 12 include E, P, L
There are three types. Of these, P is the correlation value at the code phase set by the CPU 14, E is the correlation value at the code phase a predetermined chip before,
Indicates a correlation value in a chip after the predetermined chip.

The correlator 10 also performs processing related to carrier synchronization (details thereof are omitted in the present application), and at this time, orthogonal I and Q components are generated. Therefore, E is a set of the EI related to the I component carrier and the EQ related to the Q component carrier. Similarly, P is output as a set of PI and PQ, and L is output as a set of LI and LQ.

When trying to capture a certain GPS satellite,
The CPU 14 sets the spreading code corresponding to the GPS satellite to one or a plurality of correlators 18-i, and sequentially changes and sets the code phase at least until a correlation peak can be detected. To start.
At this time, there are six types of data output from the correlator 18-i as described above, and the input data selector 20 allocates these to any of the URAMs 22-j and stores them.
Specifically, as shown in FIG. 2B, PI is stored in the URAM 22-1, PQ is stored in the URAM 22-2, and (E
-L) / LI is stored in the URAM 22-3, and (EL) / LQ
Are in the URAM 22-4,...
Correlation values are allocated and stored in the RAM 22-j according to the relative relationship between the code phases. Prior art ie U
Compare with the form of storage in a configuration with one RAM (see FIG. 2A). In the figure, PI or the like is assigned a number indicating the acquisition time point.

The CPU 14 accesses the URAM 22-j to detect a correlation peak. In that case CP
For example, as shown in FIG. 3, the read address issued by U14 includes a bit specifying which URAM the read source URAM is (in the figure, the lower 2nd bit and the lower 3rd bit indicate the URAM). Kind of bits). The output data selector 24 connects one of the URAMs 22-j to the CPU 14 by referring to this bit. The CPU 14 detects a correlation peak from the data read from the URAM 22-j.

The appearance of the correlation peak includes, for example, the one shown in FIG. 4A and the one shown in FIG. 4B. In FIG. 4A, the correlation value increases in a certain chip, and decreases in FIG. 4B. The CPU 14 has a correlator 18 in the correlator 10.
By sequentially changing the code phase of the spreading code set for -i, the code phase at which PI becomes a peak and the EI and LI before and after the PI have non-peak values is detected. , It is determined that the GPS satellite has been successfully acquired. Note that EI and L
The fact that both I are not peaks can be determined and detected based on the fact that (EL) read from the URAM 22-j is 0.

As described above, according to the present embodiment, four URAMs are replaced by four URAMs, which were conventionally provided only once.
2-j, and the correlation value is assigned to the URAM 22-j according to the relative relationship of the code phase and written. Therefore, the time required to write the correlation value to the URAM 22-j can be reduced (a plurality of times). Can be written at the same time).
In many cases, the writing of the correlation value to the AM 22-j and the reading of the correlation value from the URAM 22-j can be normally performed. As a result, it is possible to realize multi-channeling, that is, an increase in the number of correlators 18-i, which has been difficult in the past, and to enjoy the effects of this. Further, since the output data selector 24 selects the read source URAM based on a part of the read address,
There is no need for the CPU 14 to be aware that a plurality of URAMs 22-j exist. That is, the operation of the CPU 14 is performed when there is one URAM (see FIG. 2A).
The same operation as described above may be performed.

In the above description, the URAM2
Although the number of 2-j is four, this may be increased as appropriate.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a correlation detection circuit for a GPS receiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a storage form of a correlation value in a URAM. In particular, FIG. 2A shows a conventional technique, that is, a case where there is one URAM, and FIG. FIG.

FIG. 3 is a conceptual diagram showing a configuration of a read address according to the embodiment.

FIG. 4 is a diagram showing how a correlation peak appears when trying to capture a GPS satellite.

[Explanation of symbols]

10 Correlation unit, 12 URAM unit, 14 CPU, 16
ASIC, 18-1, 18-2, ..., 18-15
Correlator, 20 input data selectors, 22-1, 22
2, 22-3, 22-4 URAM, 24 output data selectors, CH0 to CH14 channels, EI, EQ,
PI, PQ, LI, LQ correlation values.

Claims (2)

[Claims] 1. A correlation detection circuit for a GPS receiver for determining a correlation value between a received signal from a GPS satellite and a spreading code corresponding to a spreading code related to the signal and detecting a code phase at which a peak appears in the correlation value. A plurality of correlators for detecting and outputting a correlation value between a received signal and a given spreading code for a plurality of channels; a plurality of RAMs (hereinafter referred to as URAMs) for storing the correlation values; A selection member for selecting a URAM and a source URAM; and a control member for setting a spread code and its code phase for a correlator, reading a correlation value from the URAM, and detecting a code phase at which a peak appears in the correlation value. A correlation detection circuit for a GPS receiver. 2. The correlation detection circuit for a GPS receiver according to claim 1, wherein the correlators for the plurality of channels independently or cooperate with each other with a spreading code set by an instruction from a control member. The correlation value with the received signal is detected and output for the code phase set by the instruction from the control member and the code phase separated by a predetermined interval from the code phase, and the selection member receives the correlation value from the correlator. When the write destination URAM of the correlation value is selected in accordance with the relative phase relationship with respect to the set code phase, the correlation value is written, and when a read address is given from the control member,
Based on the read address, the source URAM is determined and the correlation value is read. When the control member attempts to detect the code phase at which the correlation value has a peak with respect to the received signal from any GPS satellite, A spreading code corresponding to a GPS satellite is set for at least one of the correlators for the plurality of channels, and a code phase is changed for the correlator, and the GPS satellites are read from the plurality of URAMs. A correlation detection circuit for a GPS receiver, wherein the operation of reading a correlation value according to the above is repeatedly executed at least until a code phase at which the correlation value exhibits a peak is detected.