Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2000-04-14
2001-05-29
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C342S357490, C342S357490
Reexamination Certificate
active
06240366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a GPS reception ratio detecting apparatus, and also to a portable type distance/speed meter capable of measuring both a travel distance and a travel speed, equipped with this GPS reception ratio detecting apparatus. The GPS reception ratio detecting apparatus detects a GPS reception ratio indicative of a ratio at which effective GPS electromagnetic waves are received by a GPS receiver.
2. Description of the Related Art
In the GPS (Global Positioning System), 24 sets of the GPS satellites orbit on 6 sets of orbit courses located at an inclined angle of 55 degrees at a distance of approximately 20,200 km on the earth, and travels for approximately 12 hours per one turn. While navigation data required for positioning, transmitted from more than 3 GPS satellites under the most receivable condition are received by a GPS receiver, positioning calculations are carried out by measuring propagation delay time of these navigation data so as to determine travel direction/present position of a user.
In this GPS, two different frequencies “L1 (=1.57542 GHz)” and “L2 (=1.22760 GHz)” are prepared for the transmission frequencies of the GPS satellites. Since the C/A code (namely commercial-purpose code being free-opened) is transmitted at the frequency of 1.57542 GHz (equal to GPS transmission frequency “L1”), one GPS transmission frequency “L1” is utilized in general-purpose positioning operation. It should be understood that the GPS signal having this frequency “L1” is modulated in the PSK (Phase Shift Keying) modulating method by using the pseudonoise code, and then the PSK-modulated GPS signal is transmitted by way of the spread spectrum communication system. This pseudonoise code corresponds to the synthesized wave made from the C/A code used to discriminate the desirable GPS satellite from all of the GPS satellites, and also the navigation data such as the GPS satellite orbit, the GPS satellite orbit information, and the time information.
FIG. 6
is a schematic block diagram representing an arrangement of a GPS receiver
200
capable of receiving a GPS electromagnetic wave (namely, GPS signal having frequency of “L1 (=1.57542 GHz)”) transmitted from a GPS satellite. As shown in
FIG. 6
, the GPS receiver
200
is arranged by a reception antenna
201
, an L-band amplifying circuit
202
, a down-converter circuit
203
, a voltage comparing circuit
204
, a message decrypting circuit
205
, and a positioning calculating circuit
206
. The reception antenna
201
receives GPS electromagnetic waves transmitted from the GPS satellites. The L-band amplifying circuit
202
amplifies a GPS signal having an L-band frequency among the received GPS signals. The down-converter circuit
203
performs a down-converting operation of the amplified GPS signal by multiplying this received GPS signal by a signal produced from a local oscillating circuit
107
. The voltage comparing circuit
204
digitally converts the GPS signal down-converted by the down-converter circuit
203
into a digital GPS signal. In the message decrypting circuit
205
, the digital GPS signal inputted from the voltage comparing circuit
204
is multiplied by a C/A code generated from a C/A code generating circuit
208
so as to acquire both navigation data and carrier wave phase information corresponding to a pseudodistance. The positioning calculating circuit
206
calculates positioning data by using both the navigation data and the carrier wave phase information, which are entered from the message decrypting circuit
205
. It should also be noted that the local oscillating circuit
107
corresponds to such a circuit capable of producing a signal used to convert a received GPS signal into another signal having a desirable frequency.
Next, reception operation of this GPS receiver
200
will now be described. In
FIG. 6
, the L-band amplifying circuit
202
selectively first amplifies the GPS signal having the frequency of 1.57542 GHz received by the reception antenna
201
. The GPS signal amplified in the L-band amplifying circuit
202
is entered into the down-converter circuit
203
. This down-converter circuit
203
converts this entered GPS signal into a first IF (intermediate frequency) signal having a frequency of from several tens of MHz to 200 MHz by using the local oscillation signal produced from the local oscillating circuit
107
, and furthermore, converts this first IF signal into a second IF signal having a frequency on the order of from 2 MHz to 5 MHz. Then, the voltage comparing circuit
204
enters thereinto this second IF signal so as to digitally convert the second IF signal into the digital GPS signal by employing a clock signal having a frequency several times higher than the frequency of this entered second IF signal. In this circuit, this digitally-converted GPS signal will constitute spectrum-spread data (digital signal).
This spectrum-spread data outputted from the voltage comparing circuit
204
is entered into the message decrypting circuit
205
. Then, this message decrypting circuit
205
reverse-spreads the C/A code produced from the C/A code generating circuit
208
to the entered digital signal so as to acquire both the navigation data and the carrier wave phase information corresponding to the pseudodistance. The C/A code implies the pseudonoise code identical to that of the GPS satellite.
The above-explained reception operation is carried out with respect to the respective GPS satellites in this GPS receiver
200
. Normally, the message decrypting circuit
205
of the GPS receiver
200
may acquire the navigation data and also the carrier wave phase information of 4 sets of the GPS satellites, and then the positioning calculating circuit
206
acquires the positioning data (speed, present position, time information etc.) based upon the acquired navigation data/carrier wave phase information. The positioning data acquired by the positioning calculating circuit
206
is outputted to a CPU (not shown) for controlling the overall reception operation of this GPS receiver
200
, or externally outputted as a digital signal. Such a GPS receiver is utilized as a car navigation system by combining positional information of GPS with map information produced from a CD-ROM.
On the other hand, the above-explained GPS receiver
200
is realized in the form of such a portable type GPS receiving apparatus capable of measuring travel speeds/travel distances of persons, since the GPS receiver
200
may be supplied as a digital ASIC (Application Specific IC) due to current technical progresses in semiconductor fields. This portable type GPS receiving apparatus calculates the travel distance and the travel speed of the user based upon the positioning data acquired by employing the GPS receiver
200
, and then displays both the travel distance and the travel speed.
However, there are many possibilities that the above-explained GPS receiver
200
cannot receive the GPS electromagnetic waves, because the reception of these GPS electromagnetic waves is disturbed by various disturbing objects, for example, bottom places among buildings and places inside tunnels, and/or when one GPS satellite captured by this GPS receiver
200
is switched to another GPS satellite. As a result, the GPS receiver
200
can hardly acquire the positioning data. Such an unreceivable condition of the GPS electromagnetic waves may be avoided by restricting the utilization environment of this GPS receiver
200
. However, this environmental restriction cannot sufficiently achieve the advantages specific to the GPS capable of acquiring global geographical information.
On the other hand, in the above-explained portable type GPS receiving apparatus, both the travel speed and the travel distance when the user walks or runs are calculated by employing the GPS receiver
200
. As a consequence, in such a case that the reception of these GPS electromagnetic waves cannot be carried out, the correct GPS calculation results cannot be obtained. More spe
Nagatsuma Hideki
Odagiri Hiroshi
Sakumoto Kazumi
Adams & Wilks
Cuchlinski Jr. William A.
Hernandez Olga
Seiko Instruments Inc.
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