Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2003-02-21
2004-08-03
Marc-Coleman, Marthe Y. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C342S357490
Reexamination Certificate
active
06772065
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
The present document is based on Japanese Priority Document JP 2002-053845, filed in the Japanese Patent Office on Feb. 28, 2002, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a GPS (Global Positioning System) receiver and a method receiving of a GPS signal to be used for, for example, a portable navigation system and a navigation system of a movable body such as an automobile, an aircraft and a vessel or the like.
2. Description of Related Art
In a GPS system for measuring a position of a movable body or the like by using a satellite (a GPS satellite), according to its basic function, a GPS receiver receives a signal from four or more GPS satellites, calculates a location of the receiver from this received signal and notifies a user of the location thereof.
The GPS receiver demodulates a signal from the GPS satellite and acquires orbit data of the GPS satellite. Then, from an orbit of the GPS satellite and time information, and a delay time of a received signal, the GPS receiver derives a three-dimensional location of itself by using a simultaneous equation. There is an error between the time within the GPS receiver and the time of the satellite. Accordingly, in order to delete an influence due to this error, at least four GPS satellites, from which the received signals are acquired, are required.
A consumer GPS receiver receives an L1 band from the GPS satellite, namely, a spectrum diffusion signal electric wave referred to as a C/A (Coarse/Acquisition) code and carries out a positioning calculation.
The C/A code comprises a code of PN (Pseudorandom Noise) sequence with a transmitted signal rate (chip rate) of 1.023 MHz and a code length of 1023, for example, a Gold code, and also comprises a signal, in which a carrier wave with a frequency of 1575.42 MHz is BPSK (Binary Phase Shift Keying) modulated by a signal in which the data of 50 bps is diffused. In this case, since the code length is 1023, as shown in FIG.
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(A), in the C/A code, the PN sequence code is repeated with 1023 chips as one frequency (namely, one frequency=1 millisecond).
This PN sequence code in this C/A code is varied for each GPS satellite. However, in the GPS receiver, it is possible to detect which GPS satellite uses which PN sequence code in advance. In addition, according to a navigation method to be described later, it is possible for the GPS receiver to know a signal from which GPS satellite can be received at that position and at that time. Accordingly, for example, in a case of performing the three-dimensional positioning, the GPS receiver receives electric waves from four and more GPS satellites available at that position and at that time, performs an inverted spectrum diffusion, and performs a positioning calculation to obtain a location of itself.
As shown in FIG.
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(B), one bit of the satellite signal data is transmitted as 20 periods of the PN sequence code, namely, in a unit of 20 milliseconds. In other words, the data transmission rate is 50 bps. The 1023 chips corresponding to one period of the PN sequence code are inverted when the bit is “1” and when the bit is
As shown in FIG.
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(C), in a GPS, 30 bits (i.e., 600 milliseconds) forms one word, and as shown in FIG.
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(D), 10 words forms one sub frame (6 seconds). As shown in FIG.
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(E), in a head word of one sub frame, a preamble is inserted, which always serves as a regular bit pattern even when the data is updated, and after this preamble, the data is transmitted.
Further, one main frame (30 sec) is formed by 5 sub frames. Then, the navigation message is transmitted in a data unit comprising this one main frame. The first three sub frames in the data of this one main frame are the orbit information referred to as ephemeris information, which are peculiar to each satellite. This ephemeris information is repeatedly transferred in one main frame unit (30 sec), and it contains a parameter for obtaining the orbit of the satellite transmitting the foregoing information, and a transmission time of a signal from the satellite.
In other words, the second word of the three sub frames in the ephemeris information contains the time data referred to as Week Number and TOW (Time Of Week). The Week Number is the information for counting up the week for each week starting with Jan. 6, 1980 (Sunday) defined as the 0th week. In addition, the TOW is the time information for counting up the time (counting up in a period of the sub frame) every six seconds providing that the hour of zero a.m. on Sunday is defined as 0.
All GPS satellites are provided with atomic clocks and use the common time data, and the transmission time of a signal from each GPS satellite is synchronized with the atomic clock. By receiving the above-described two time data, the absolute time is obtained. A value not more than 6 seconds comes to be synchronized with the time of a satellite in an accuracy of a reference oscillator provided to the present GPS receiver in the process of synchronous-locking with the electric wave of the satellite.
In addition, the PN sequence code of each GPS satellite is also generated as being synchronized with the atomic clock. Further, from this ephemeris information, a location of the satellite and a rate of the satellite which are to be used for the positioning calculation in the GPS receiver are acquired.
The ephemeris information is an almanac having a high accuracy to be updated with a relative frequency under a control of a control station on the earth. In the GPS receiver, by storing this ephemeris information in a memory, it is possible to use the ephemeris information for the positioning calculation. However, in view of its accuracy, a usable duration of the ephemeris information may be ordinarily about two hours. Accordingly, an elapsed time from a point of time when the ephemeris information is stored in the memory is monitored, and if the monitored elapsed time exceeds this time duration, the GPS receiver may update the ephemeris information in the memory and may rewrite it.
By the way, in order to acquire the new ephemeris information from the GPS receiver and update a content of the memory into this acquired ephemeris information, a minimum of 18 seconds (corresponding to three sub frames) is needed. When the data is acquired from a midstream of the sub frame, consecutive 30 seconds are needed for the updating.
The navigation message in the remaining two sub frames of the data in one frame comprises information referred to as the almanac information, which is to be transmitted in common from all satellites. This almanac information is needed for 25 frames in order to acquire the all information thereof. The almanac information comprises the information for showing a rough location of each GPS satellite and the information for indicating the available GPS satellite.
This almanac information is also updated for every several days as a result of control from the control station on the earth. It is also possible to store the almanac information in the memory of the GPS receiver and to use it. However, its duration of life is about several months, and this almanac information in the memory is normally updated into new information acquired from the GPS satellite for every several months. If this almanac information is accumulated in the memory of the GPS receivers, it is possible to know a suitable channel for a certain satellite, when a power is turned on, by the calculation.
In order to acquire the above described data by receiving the signal from the GPS satellite, at first, after removing the carrier wave, by using a PN sequence code (hereinafter, a PN sequence code is simply referred to as a PN code) prepared in the GPS receiver similar to the C/A code used in the GPS satellite to be received, the phase synchronization of the C/A code is acquired with respect to a signal from this GPS satellite to acquire a signal from the GPS satellite, so that the inverted spectrum diffusio
Awata Hideki
Nitta Manabu
Sanmiya Jason
Takada Masayuki
Tanaka Katsuyuki
Maioli Jay H.
Marc-Coleman Marthe Y.
Sony Corporation
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