Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-05-23
2001-10-02
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S357490, C701S213000
Reexamination Certificate
active
06297770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Global Positioning System GPS and a Global Positioning method for precisely determining a location by receiving GPS signals from satellites.
2. Description of Related Art
Many satellites orbit the earth, and continuously transmit radio waves at a carrier frequency of 1575.42 GHz. The radio waves are phase modulated by pseudo-random sequences, and a unique pattern is assigned to each satellite so that the different radio waves can be easily identified. As a typical pseudo-random sequence, is known a regularly modulated code pattern called a C/A code (clear and acquisition code) available to the public. Furthermore, the radio waves carry navigation data necessary for users to perform positioning, such as satellite orbit information, satellite correction data, correction coefficients of the ionosphere, etc. The navigation data are transmitted by means of polarity inversions in the C/A code sequence.
FIG. 13
is a diagram showing the C/A code sequence. As shown in
FIG. 13
, the C/A code sequence is a regularly arranged code sequence with its data consisting of 20 PN frames, each which consists of 1023 bits of one millisecond long. Thus, the navigation data is a 50 bit per second signal consisting of 1000 PN frames per second. The polarity of the C/A code sequence is reversed in accordance with the polarity of the bits of the navigation data.
FIG. 14
is a block diagram showing a configuration of a conventional Global Positioning System disclosed in U.S. Pat. No. 5,663,734. In this figure, the reference numeral
101
designates a base station having a GPS receiving antenna
102
and a transmitting and receiving antenna
103
. The reference numeral
104
designates a remote unit.
The remote unit
104
comprises an RF (radio frequency) to IF (intermediate frequency) converter
106
with a GPS receiving antenna
105
; an A/D converter
107
for converting the analog signal from the converter
106
to a digital signal; a memory (digital snapshot memory)
108
for recording the output of the A/D converter
107
; and a general purpose programmable digital signal processor
109
(called DSP from now on) for processing the signal fed from the memory
108
.
The remote unit
104
further comprises a program EPROM
110
connected to the DSP
109
, a frequency synthesizer
111
, a power regulator
112
, a write address circuit
113
, a microprocessor
114
, a RAM (memory)
115
, an EEPROM
116
, and a modem
118
which has a transmitting and receiving antenna
117
, and is connected to the microprocessor
114
.
Next, the operation of the conventional GPS will be described.
The base station
101
commands the remote unit
104
to perform a measurement via a message transmitted over a data communication link
119
. The base station
101
also sends within this message Doppler information for the satellites in view, which is a form of satellite data information. This Doppler information typically is in the format of frequency information, and the message will specify an identification of the particular satellites in view. This message is received by the modem
118
in the remote unit
104
, and is stored in the memory
108
connected to the microprocessor
114
.
The microprocessor
114
handles data information transfer between the modem
118
and the DSP
109
and write address circuit
113
, and controls the power management functions in the remote unit
104
.
Once the remote unit
104
receives a command (e.g., from the base station
101
) for GPS processing together with the Doppler information, the microprocessor
114
activates the RF to IF converter
106
, A/D converter
107
and memory
108
via the power regulator
112
and controlled power lines
120
a
-
120
d,
thereby providing full power to these components. This causes the signal from the GPS satellite which is received by the antenna
105
to be down-converted to an IF frequency, followed by conversion to digital data.
A contiguous set of such data, typically corresponding to a duration of 100 milliseconds to one second (or even longer), is stored in the memory
108
.
Pseudo range calculation is executed by the DSP
109
that uses a fast Fourier transform (FFT) algorithm, which permits very rapid computation of the pseudo ranges by performing quickly a large number of correlation operations between a locally generated reference and the received signals. The fast Fourier transform algorithm permits a simultaneous and parallel search of all positions, thus speeding up the required computation process.
Once the DSP
109
completes its computation of the pseudo ranges for each of the in view satellites, it transmits this information to the microprocessor
114
through an interconnect bus
122
.
Then, the microprocessor
114
utilizes the modem
118
to transmit the pseudo range data over the data link
119
to the base station
101
for final position computation.
In addition to the pseudo data, a time lag may simultaneously be transmitted to the base station
101
that indicates the elapsed time from the initial data collection in the memory
108
to the time of transmission over the data link
119
. This time lag improves the capability of the base station
101
to perform position calculation, since it allows the computation of the GPS satellite positions at the time of data collection.
The modem
118
utilizes a separate transmitting and receiving antenna
117
to transmit and receive messages over the data link
119
. The modem
118
includes a communication receiver and a communication transmitter, which are alternately connected to the transmitting and receiving antenna
117
. Similarly, the base station
101
may use a separate antenna
103
to transmit and receive data link messages, thus allowing continuous reception of GPS signals via the GPS receiving antenna
102
at the base station
101
.
It is expected that the position calculations in the DSP
109
will require less than a few seconds of time, depending upon the amount of the data stored the memory
108
and the speed of the DSP
109
or several DSPs.
As described above, the memory
108
captures a record corresponding to a relatively long period of time. The efficient processing of this large block of data using fast convolution methods contributes to the ability to process signals at low received levels such as when reception is poor due to partial blockage from buildings, trees etc.
All pseudo ranges for visible GPS satellites are computed using the same buffered data. This provides improved performance relative to continuous tracking GPS receivers in situations such as urban blockage conditions in which the signal amplitude is rapidly changing.
The signal processing carried out by the DSP
109
will now be described with reference to FIG.
13
. The objective of the processing is to determine the timing of the received waveform with respect to a locally generated waveform. Furthermore, in order to achieve high sensitivity, a very long portion of such a waveform, typically 100 milliseconds to one second, is processed.
The received GPS signal (C/A mode) is constructed from a high rate (1 MHz) repetitive pseudo random (PN) pattern (PN frame) of 1023 symbols, and successive PN frames are added to one another. For example, there are 1000 PN frames over a period of one second. The first such frame is coherently added to the next frame, the result added to the third frame, followed by the additions as shown in FIGS.
15
(A)-
15
(E). The result is a signal having a duration of one PN frame (=1023 chips). The phase of this sequence is compared to a local reference sequence to determine the relative timing between the two, thus establishing the pseudo range.
With the foregoing configuration, the conventional Global Positioning System carries out preprocessing operation which precedes the correlation calculations, and which is called “preliminary integration of the received GPS signal” to implement high sensitivity. In this process, the preliminary integration is carried out for 5
Hirata Seiichiro
Ueda Fumio
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Phan Dao
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