Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-03-29
2002-05-14
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C701S213000, C482S008000
Reexamination Certificate
active
06388613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a portable GPS type distance/speed measuring apparatus. More specifically, the present invention is directed to a portable distance/speed meter capable of calculating/displaying both a travel distance and a travel speed based upon positioning data acquired by receiving GPS electromagnetic waves. Furthermore, the present invention is related to such a portable type distance/speed meter suitable for measuring a travel distance and a travel speed when a person having this portable meter who walks, or runs, while selectively using the Doppler speed measuring method.
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 “L
1
(=1.57542 GHz)” and “L
2
(=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 “L
1
”) one GPS transmission frequency “L
1
” is utilized in general-purpose positioning operation. It should be understood that the GPS signal having this frequency “L
1
” 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 “L
1
(=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.
As the method for calculating the travel distance of the main body of this GPS receiver
200
and the travel speed thereof by using the positioning data calculated by this positioning calculating circuit
206
, there are known two typical calculating methods, namely the positional change calculating method and the Doppler speed calculating method. First, in this positional change calculating method, altitude/longitude information is acquired at two separate positions used to define a travel distance, and then the above-explained travel distance is calculated based upon a difference (subtraction) between two sets of the acquired altitude/longitude information. Thereafter, this calculated travel distance is divided by travel time measured by traveling the GPS receiver
200
over these two positions to thereby calculate a travel speed. However, this positional change calculating method has the following problem. That is, a so-called “positional jump” happens to occur due to the below-mentioned reasons, so that large errors are involved in the calculated travel distance as well as travel speed. Namely, the measuring precision of the positional information calculated from the normally-utilized GPS electromagnetic waves is not so high, and this positional information is likely to be adversely influenced by SA (Selective Availability) corresponding to one of the GPS positioning error factors.
On the other hand, in the Doppler speed calculating method, since the Doppler shift frequency is acquired from the positioning data, a relative speed is firstly calculated between each of the GPS satellites and the main body of the GPS receiver
200
. Subsequently, a travel speed of the main body
Nagatsuma Hideaki
Odagiri Hiroshi
Sakumoto Kazumi
Adams & Wilks
Blum Theodore M.
Seiko Instruments Inc.
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