JP2003222667A - GPS receiver - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable a frequency search to be executed successfully even when the accuracy of a reference clock is low. When an RSSI value output from a transmission / reception unit of a PDC-P module is high, a high-speed frequency search is realized by narrowing a search frequency range in the GPS module. If the RSSI value is low, the frequency search failure is eliminated (reduced) by widening the search frequency range. Since the RSSI value indicates the received signal strength and indirectly indicates the accuracy of the reference clock REFCLK, the frequency search failure is eliminated (reduced) by setting the search frequency range according to the RSSI value, and the required search time is shortened as a whole. it can.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a GPS (Global P
ositioning System) receiver, in particular a communication module for connecting to a wireless communication system, eg PDC
-P (Personal Digital Cellular-Packet) relates to a GPS receiver equipped with a PDC-P module for connecting to a network.

[0002]

2. Description of the Related Art As a GPS receiver, in addition to an autonomous GPS receiver capable of completing positioning processing by itself, a GPS receiver of a server-assisted type which executes positioning processing or a part thereof by receiving support from an external server. GPS receivers have been conventionally developed. Typical of the latter, the PDC for connecting to the server
There is a snap-track GPS receiver that utilizes -P. "SnapTrack" is a trademark of SnapTrack Inc. and SnapTrack Japan.

FIG. 1 shows a GPS receiver configured as a snap track type mobile terminal. This GPS receiver includes a GPS module 10 and a PDC-P module 2
Has 0. Since both are circuits that handle high-frequency signals, the GPS module 10 and the PDC-P module 20 are electromagnetically shielded. In addition, to ensure portability, the GPS module 10 and PD
The CP module 20 is housed in a common housing.
A GPS antenna 11 for receiving signals from GPS satellites, a PDC antenna 21 for wireless transmission / reception with a PDC-P base station, and the like are provided on the surface or inside of this housing. Although not shown, switches and keys operated by the wearer, a light emitting element for providing information to the wearer, a display unit, a sound output unit, and the like are appropriately provided. It also has a battery that supplies power to each member in the terminal.

Among these modules, the GPS module 10 is a module that accommodates a circuit for receiving and capturing signals from GPS satellites and deriving a pseudorange, and
The DC-P module 20 is a PDC-P base station (PDC
A module containing a circuit for connecting to a server (location server) on the network using the P network. The GPS module 10 includes a down converter 12 for down converting received signals from GPS satellites, a snapshot RAM 13 for storing received signals in a snapshot period, a DSP 14 for executing data processing including FFT, a clock GPS for the GPS module 10.
The TCXO15 etc. which generate CLK are stored.
Although not shown, the GPS module 10 also includes an A / D converter for A / D converting the signal output from the down converter 12. PDC-P module 20
Includes a transmission / reception unit 22 that executes transmission / reception using the PDC antenna 21, and a control unit 2 that controls the operation of the transmission / reception unit 22.
3. CPU 24 that executes signal transmission mediation between both modules and local control; RA that provides a working storage area
An M25, a ROM 26 for storing software and the like are stored.

In the snap track system, when detecting the position of a GPS receiver as a terminal, the server selects a GPS satellite to be received by the terminal and issues a positioning instruction to the terminal. Commands issued by the server related to system operation and positioning, including this positioning instruction,
It is called a server command. On the other hand, a command related to an operation in the terminal that does not need to be supported by the server, such as an operation condition setting of the DSP 14, is called a local command, and is issued by the CPU 24 in the illustrated example.
In the illustrated example, according to the disclosure of Japanese Patent Application No. 2001-387420, the members such as the CPU 24 related to the local control are provided in the PDC-P module 20, but the members related to the local control are different modules (control module). Can also be

The operation procedure of the terminal is as follows.
When the power switch of this terminal is turned on, the CPU 24 issues a local command to the DSP 14 to execute various settings. For example, the REFCLK frequency is set. After that, the DSP 14 stops the power supply to the down converter 12, the clock supply to the A / D converter (not shown), etc. and stands by to prevent the battery power consumption. In that state, when the server issues a positioning instruction to this terminal and the positioning instruction is received by the PDC antenna 21 and the transmission / reception unit 22 via the network, the CPU
24 cooperates with the control unit 23 that controls the operation of the transmission / reception unit 22 and transfers the positioning instruction to the DSP 14. When the DSP 14 receives the positioning instruction, the DSP 14 issues a response indicating that the positioning instruction has been received, while starting the operation for deriving the pseudo distance. DSP14
Since the response issued at this time is a response to the positioning instruction which is a server command, it is transmitted to the server through a route reverse to the transmission of the positioning instruction. Further, the GPS module 10 is in the low power consumption state at the time of receiving the positioning instruction due to the stop of the power supply, the stop of the clock supply, and the like. Therefore, when starting the operation for deriving the pseudo distance, the DSP 14 restarts the supply of power and clock to these members. Next, the DSP 14
The pseudo distance deriving procedure is sequentially executed according to the positioning instruction. When the pseudo distance is derived, the DSP 14 causes the down conversion unit 1
While stopping the power supply to No. 2 and stopping the clock supply to the A / D converter, the CPU 24 is notified of the transmission of the pseudo distance and the end of the processing. The CPU 24 controls the pseudo distance by the control unit 23 and the transmission / reception unit 2 of the PDC-P module 20.
2. Send to the server via the PDC antenna 21.

A series of operations performed by the DSP 14 from the response to the positioning instruction to the processing end notification, that is, the pseudo distance derivation is executed as follows. First, the positioning instruction includes the number of the GPS satellite to be received. The DSP 14 receives the GPS antenna 11 via the down converter 12 and the A / D converter during the snapshot period.
Capture the signal received by. The DSP 14 stores this received signal in the snapshot RAM 13 (snapshot). After that, the DSP 14 executes FFT processing for pseudo distance detection on the snapped received signal while applying frequency correction, and cumulatively adds the results. Since this frequency correction compensates for the Doppler shift generated according to the relative moving speed of the satellite to the terminal, it is necessary to perform the frequency correction for each satellite and while gradually changing the frequency correction amount (frequency search). Since it takes time to perform the frequency search over a wide frequency range, the Doppler shift amount (approximate estimated value) is given to each satellite in the positioning command in the snap track method.
Therefore, in the snap track method, the satellite signal can be captured from the received signal on the snapshot RAM 13 in a short time only by performing a frequency search within a very narrow search frequency range as described later, and thus the pseudo range to the satellite is obtained. Can be detected in a short time. When the DSP 14 can derive the pseudo distance through the FFT processing of the received signal on the snapshot RAM 13, the CPU 24 causes the PDC-P module 20 to send a message indicating the result to the server. The server receives this and calculates the position of the GPS receiver.

Further, the frequency correction in the above frequency search is executed within the search frequency range. DSP1
If the GPSCLK from the TCXO (temperature-compensated crystal oscillator) 15 which is the operation reference clock of 4 is sufficient and always highly accurate, the search frequency range is set to 0.3 ppm, for example.
By narrowing down to a very narrow range (about 473 Hz for the L1 carrier wave of GPS), the pseudo distance can be derived in a short time. However, the oscillation accuracy of the TCXO15 is usually not sufficient, and a frequency error of about 3 ppm, which is larger than the search frequency range, appears in GPSCLK. In such a state, the satellite signal may not be captured from the received signal on the snapshot RAM 13 even if the frequency search is performed. As a method of capturing a signal and deriving a pseudorange regardless of the accuracy of GPSCLK, there is a method of supplying an accurate reference clock REFCLK from the transmission / reception unit 22 to the DSP 14. That is,
A circuit connected to a wireless communication system such as a PDC-P usually has an automatic frequency control (AF) for establishing frequency synchronization with a carrier of a received signal from a PDC-P base station.
C) Provide a circuit. Generally, in the state where the frequency synchronization is preferably established by the operation of the AFC circuit, the frequency of the clock regenerated from the received signal or the oscillation clock by the oscillator controlled to be frequency synchronized with the received signal is
If the signal strength is strong, the accuracy is as high as 0.1 ppm. Therefore, even in the terminal for the snap track system, for example, the AF described above is provided in the transmission / reception unit 22.
It is conceivable that a C circuit and a clock generating means are provided and the resulting clock is supplied to the DSP 14 as REFCLK. By doing so, even if the oscillation accuracy of the TCXO 15 is somewhat poor, it can be compensated for.

As described above, in the snap track method, the mobile terminal operates on the premise of the support from the server, so that the wireless assist type GPS (WAG: Wireless Assist
d GPS). Since much of the arithmetic processing is carried out by the server, the load on the terminal is lightened. Also,
As shown in FIG. 1, the terminal for the snap track system can have a configuration in which two modules (or three modules including the control module) are housed in a single housing.
A portable terminal can be obtained, and its assembly and manufacturing are relatively easy. Applicant filed Japanese Patent Application No. 2001-3874
By incorporating the CPU 24 and its peripheral circuits in the PDC-P module 20 as disclosed in No. 20,
It is possible to reduce the number of constituent modules, achieve further size reduction and weight reduction, and manufacturing cost / component cost reduction. Furthermore,
As a characteristic effect of the snap track method, the conventional G
It can be pointed out that a positioning signal at a low level can be received / captured (that is, high-sensitivity reception / capture can be realized) and the operation speed thereof is higher than that of a PS receiver. This is achieved by introducing the above-described cumulative addition of received signals, introducing high-speed arithmetic processing such as FFT, and frequency search with a very narrow range.

[0010]

[Problems to be Solved by the Invention] However, PDC
-The frequency synchronization of REFCLK with respect to the P base station is not always ensured appropriately. GPS module 1
The search frequency range at 0 is, for example, 0.3 as described above.
Since it is fixedly set to about ppm, if the frequency accuracy of REFCLK becomes worse than 0.3 ppm, it may not be possible to capture the satellite signal from the received signal on the snapshot RAM 13. That is, the clock generated by the transmitter / receiver 22 is used as it is as REFCLK and the DSP 14
, The pseudo-range may fail to be derived.

The present invention has been made to solve the above problems, and a clock generated in a PDC-P module (more generally expressed as a communication module) has low accuracy. One of the purposes is to be able to execute derivation of the pseudo distance and the like in the GPS module at any time.

[0012]

In order to achieve such an object, the present invention (1) wirelessly receives a signal from a GPS satellite and determines a received signal carrier frequency according to a reference clock supplied from a communication module. (2) A GPS module that searches within the search frequency range and (2) wirelessly receives a signal from the wireless communication system while operating to keep frequency synchronization with the connected wireless communication system as much as possible, and responds to the received signal. A communication module for generating the reference clock according to claim 3, wherein the communication module estimates the accuracy of the reference clock, and the accuracy obtained by the estimation is narrow or low. Is wide, and the above-mentioned search frequency range is set. For example, the communication module
If the received signal strength from the wireless communication system is high, it is estimated that the accuracy of the reference clock is high, and if it is weak, the accuracy is low.

As described above, in the present invention, the search frequency range is narrowed when the accuracy of the reference clock is estimated to be high, and conversely widened when the accuracy of the reference clock is estimated to be low. Therefore, it is possible to prevent a situation where the frequency search fails and the pseudo-range derivation fails because the accuracy of the reference clock is worse (larger) than the ratio of the search frequency range to the carrier frequency. It should be noted that when the accuracy of the reference clock is low, the processing time required by the GPS module will be somewhat longer, but it will be within the acceptable range as compared with the search failure. Further, in the communication module, while performing the frequency synchronization establishment holding operation, the reference clock is generated according to the received signal (whether or not it is in communication) from the wireless communication system of the connection destination, If the received signal strength from the wireless communication system is high, frequency synchronization is preferably established, and it can be considered that the reference clock has high accuracy. On the contrary, if the received signal strength from the wireless communication system is low, frequency synchronization is not so well established, and therefore the reference clock can be regarded as having low accuracy. Therefore, the estimation of the reference clock accuracy and the search frequency range determination based on the result can be realized by a simple method of determining the search frequency range according to the received signal strength. No complicated processing is required.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Since the present invention can be implemented under the apparatus configuration shown in FIG.
However, this is merely for the purpose of simplifying the description, and does not mean that the embodiment of the present invention, particularly the hardware configuration, is limited to the configuration shown in FIG.

The preferred embodiment of the present invention is REFCLK.
Is narrowed when the accuracy obtained by the estimation is high and wide when the accuracy obtained by the estimation is low, and is characterized by setting or controlling the search frequency range. REF
The accuracy of CLK depends on the frequency synchronization state of the transmission / reception unit 22 with respect to the PDC-P network.
REFCLK is highly accurate when frequency synchronization is preferably established by the circuit. In addition, the higher the received signal strength in the transmission / reception unit 22, generally, frequency synchronization with the PDC-P network (automatic frequency control by the AFC circuit).
Is easy to implement and establish. Therefore, in the present embodiment, R
It is used as an estimation index of EFCLK accuracy. PDC
-By setting or controlling the search frequency range according to the received signal strength from the P network, according to the present embodiment,
Even if the REFCLK accuracy is poor, the probability of failing to capture the satellite signal and eventually derive the pseudorange is significantly reduced.

The strength of the received signal in the transmitter / receiver 22 is the RSSI (Receiving) output from the transmitter / receiver 22.
Signal Strength Indicator) signal. The RSSI signal is a signal representing the signal input level from the PDC antenna 21 to the transmission / reception unit 22, and thus the received electric field strength at the PDC antenna 21, and the higher the received electric field strength, the larger the RSSI signal value. Since the RSSI signal is a signal that has been conventionally used for grasping and managing the communication state in the wireless section, this embodiment does not require any special change in the configuration of the transmission / reception unit 22, that is, simply. It also has the advantage that it can be implemented. Also,
For setting the search frequency range based on the RSSI signal value, for example, a table or mathematical expression defining the characteristics shown in FIG.
R stored in the M26 or the like and obtained through the control unit 23 or the like
The CPU 24 determines a search frequency range from this table or a mathematical expression based on the SSI signal value, and sets the search frequency range in the DSP 14 via the control unit 23 or the like. In this respect, the present embodiment is
It can be said that there is an advantage that it can be implemented by only slightly changing the program executed by the CPU 24. Alternatively, as the function of the control unit 23, a search frequency setting function according to the RSSI signal value may be provided.

RSS is used to set and control the search frequency range.
It can be performed at any time, as long as a method for the received signal strength in the form of the I signal is available. An example of the execution timing is immediately after the positioning instruction. For example, when the positioning instruction is received from the server, the CPU 24 or the control unit 23 is provided before and after the positioning instruction is passed to the DSP 14.
Determines the search frequency range based on the RSSI signal value and sets the determined search frequency range in the DSP 14. The operation for setting the search frequency range in the DSP 14 is, for example, a local command for the DSP 14,
It can be executed by a notification from the control unit 23. The former is to add a function for generating a local command in response to a positioning instruction (more generally a server command) to the CPU 24, and to prepare a command for setting a search frequency range as such a local command, and This can be realized by appropriately setting the conditions for issuing the command. The latter can be realized by providing a signal for setting the search frequency range.

The example shown in FIG. 2 is an example of the L1 carrier wave of GPS. In addition to the smooth curve characteristic as in this example, R, linear, stepwise, polygonal, etc.
Among the characteristics that tend to narrow the search frequency range according to the increase in the SSI value, the characteristics can be appropriately determined as necessary.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a GPS receiver (terminal) for a snap track system.

FIG. 2 is a table content diagram showing search frequency range control characteristics in the preferred embodiment of the present invention.

[Explanation of symbols]

10 GPS module, 11 GPS antenna, 12
Downcon section, 13 snapshot RAM, 14
DSP, 15 TCXO, 20 PDC-P module, 21 PDC antenna, 22 transmission / reception part, 23 control part, 24 CPU, 25 RAM, 26 ROM.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5J062 AA08 AA13 CC07 DD01 DD14                       DD22 EE03 FF01                 5K067 AA21 BB04 BB21 BB36 DD20                       DD43 DD44 EE02 FF03 JJ52

Claims (2)

[Claims] 1. A signal for wirelessly receiving a signal from a GPS satellite and searching a received signal carrier frequency within a search frequency range according to a reference clock supplied from a communication module.
A PS module, and a communication module that wirelessly receives a signal from the wireless communication system while operating so as to keep frequency synchronization with the wireless communication system of the connection destination as much as possible, and generates the reference clock according to the received signal. In the GPS receiver including, the communication module estimates the accuracy of the reference clock and sets the search frequency range to be narrow when the accuracy obtained by the estimation is high and wide when the accuracy obtained by the estimation is low. GPS receiver to do. 2. The GPS receiver according to claim 1, wherein the communication module estimates that the accuracy of the reference clock is high when the received signal strength from the wireless communication system is high, and weakly when the reference clock is weak. A GPS receiver characterized by being estimated to be low.