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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for measuring approximate figures
of, for example, people or cars for indicating a degree of a traffic jam
state.
2. Description of the Related Art
There is proposed a system for indicating a state of a traffic jam to
control the traffic flow wherein the traffic state is monitored by a TV
camera which is set aside the road or wherein the vehicle number or speed
of the vehicle is measured from the TV camera by processing the video
signal thereof.
Such a system is disclosed, for example, in the Electric Society Report No.
109, 1989, "IV. Municipal Information Service", page 121 to 122, Chapter 1
"2. Traffic Information System".
However, the area which can be covered by one TV camera is limited.
Therefore, a plurality of cameras are required to cover the wide area of a
traffic state, which makes the system complicated and expensive.
Another traffic monitoring system is such that a traffic counter comprising
a supersonic sensor is set on the road to count the numbers of vehicles
passing over the sensor. However, in the event of a traffic jam, the
detection signal from the sensor is discriminated as if the numbers of
vehicles are very small.
The applicant has already filed "System for measuring jam of objects" prior
to this application at the Japanese Patent Office, numbered Japanese
Laying Open Patent Application No. 3-71300. According to the system of the
prior application, the jam degree is measured in such a way that a
transmission device is arranged for measuring the objects so that the jam
degree is determined from the level of white noise which is transmitted
from the transmission device and has a limited band.
However, the sensor of the system is also responsive to the white noise
generated from vehicle engines, which impairs the accuracy of the
measurement.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an
approximate figures measuring system for indicating in round numbers cars
on the road or people gathered in restaurants, shopping houses or
exhibition places, which system is composed of a relatively simple
construction and not influenced from the white noise generated from
engines and which system is able to determine the degree of jam or
crowdedness by comparing the measured round numbers with a predetermined
reference number, if necessary.
Also, it is another object of the present invention to provide an
approximate figures measuring system for indicating the round numbers with
respect to every kind of the objects to be measured.
The above mentioned object of the present invention can be achieved by an
approximate figures measuring system comprising:
a signal transmission device arranged in each of the objects to be measured
for emitting a signal from which a peak can be generated in a
predetermined period; and
a signal receiving device for receiving the signal transmitted from the
signal transmission device and comprising a peak detection circuit and a
calculation circuit for obtaining an output corresponding to number of the
peaks of the signals from the objects.
An advantage of the present invention is that it becomes possible to
reliably discriminate, for example, the traffic conditions from the
approximate figures of people or cars, for example, without being
influenced from the white noise from the vehicle engines.
Also, another advantage of the present invention is that it becomes
possible to obtain the approximate figures for respective kinds of objects
to be measured, such as pedestrians and cars.
Further objects and advantages of the present invention will be apparent
from the following description of the preferred embodiments of the
invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an embodiment of the transmission device
arranged for measuring objects in accordance with the present invention;
FIG. 2 is a block diagram of an embodiment of the receiving device arranged
for obtaining the approximate figures of the objects by integrating the
relative pulses;
FIGS. 3a and 3b are explanatory views for explaining the generation of
pulses used in the present invention;
FIG. 4 is a graphical view of an example of envelope line output of
correlation peaks of pulses;
FIG. 5 is a graphical view of correlation peak outputs in relation to the
threshold level;
FIG. 6 is a block diagram of another embodiment of the receiving device
which detects the number of correlation peaks;
FIG. 7 is a block diagram of still another embodiment of the receiving
device which sorts the objects to be measured and detects the approximate
figures for each of the sorts;
FIG. 8 is a block diagram of a further embodiment of the receiving device
in accordance with the present invention;
FIG. 9 is an explanatory view for explaining the envelope line waveform of
the receiving side when a plurality of PN signals are simultaneously
transmitted from the transmission device;
FIG. 10 is a block diagram of another embodiment of the transmission device
which transmits an FM chirp signal in accordance with the present
invention;
FIG. 11 is a graphical view of the frequency of the generated signal in
relation to the controlling voltage of the variable capacity diode for
controlling the voltage;
FIG. 12 is an explanatory view for explaining the controlling voltage and
the FM chirp signal generated by the voltage;
FIG. 13 is a block diagram of a further embodiment of the receiving device
which receives the FM chirp signal in accordance with the present
invention;
FIG. 14 is a graphical view of a characteristic of the FM chirp filter; and
FIG. 15 is a graphical view of pulses constituted from the envelope lines
of the output from the FM chirp filter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, an arrangement is made in such
away that a PN signal generator is arranged as a transmission device for
each of the objects for which approximate figures are to be measured and
that a receiving device is arranged so as to obtain the number of the
self-correlation (autocorrelation) peaks of the PN signal to obtain the
approximate figures of the object to be measured.
Also, it is possible to obtain the approximate figures of the object from
the sum of the self-correlation levels of the PN signal in the receiving
side. Further, it is possible to shape the waveform of the
self-correlation output of the PN signal as a pulse series and integrate
the pulses for one cycle of the PN signal so as to obtain the approximate
figures of the object.
Further, it is possible to obtain the approximate figures for each sort of
the objects by arranging a specific PN signal generator of a different
group for each sort of the objects so that the approximate figures are
determined from each PN signal from the different groups.
Signals other than the PN signal can be used for determining the
approximate figures of the object. For example, the approximate figures
can be obtained in such a way that FM chirp signal generators having a
specific chirp ratio are arranged for respective objects to be measured
and that in the signal receiving side the pulses are counted in the signal
transmission cycle T which pulses are made by pulse-compression of the FM
chirp signal through a chirp filter.
One method for measuring the approximate figures of the object is such that
a pulse-like signal is transmitted from the object at a predetermined
cycle ratio such as one time per a predetermined cycle period T and that
in the signal receiving side the pulses received in the period T are
counted or the total pulse signal energy in the period T is divided by the
energy of one pulse to obtain the number of the objects. Considering that
at least a part of the pulse-like signal may be overlappingly transmitted
to the signal receiving side at the same time, the above mentioned method
gives the approximate figures of the object.
In accordance with a first measuring system of the present invention, a PN
signal is used as a signal transmitted from the object to be measured. The
PN signal is in itself a signal used for transmitting information and used
as a pseudo noise code in the SSC (Spread Spectrum Communication) as
disclosed in "Asynchronous multichannel SSC transceiver using SAW
convolver" the Electronic Information and Communication Society, the
spectrum diffusion communication and its applied communication document
SSTA89-9, Mar. 22, 1989, chapter 1 to 2.
The PN signal modulated by the PN code has an autocorrelation
characteristic which generates one correlation peak during one period T of
the PN signal as illustrated in FIG. 3a by a matched filter. It is to be
noted that the width 2.DELTA. of the correlation peak is twice as large as
the length of one chip of the PN signal as illustrated in FIG. 3a.
Therefore, it is clear that the approximate figures can be obtained in such
a way that a PN signal generator of a specific signal group is arranged
for each of the objects to be measured and that upon receipt of the PN
signals from the objects, the numbers of the autocorrelation peaks of the
signals are counted to determine the approximate figures.
It is possible to obtain the approximate figures for each of the sorts of
objects by such a way that a PN signal generator of a different signal
group is arranged for each sort of the objects and that the peak numbers
are counted for every sort of object, respectively.
Also, another way for obtaining the approximate figures of the present
invention is such that upon receipt of the PN signals from the objects,
the sum of the autocorrelation levels is calculated. The sum of the
autocorrelation level is equivalent to the total energy of the signals in
one period T of the autocorrelation peak of the PN signal.
Further, it is possible to heighten the reliability of measurement of the
approximate figures by shaping the waveform of the autocorrelation output
of the PN signal to form a pulse series and integrating the pulses for one
period of the PN signal.
In accordance with a second system for measuring the approximate figures of
objects, an FM chirp signal generator of a specific chirp ratio is
arranged for each of the objects to be measured. As illustrated in the
upper graph of FIG. 3b, the FM chirp signal changes its frequency from low
to high in one predetermined period R and this frequency change is
repeated at an interval of one time per one period T wherein T is larger
than R, as illustrated in the graph.
An FM chirp filter is arranged in the signal receiving side. The filter
applies a long delay time to a low frequency signal while it applies a
short delay time to a high frequency signal. The filter may be composed
of, for example, a surface acoustic wave (SAW) delay element as disclosed
in "Acoustic Waves", by G. S. Kino, (Prentice-hall 1987) page 332 to 333.
Therefore, when the FM chirp signal passes through the filter, the width of
the signal in the period R is compressed to form a pulse of a narrow width
as illustrated in the lower graph of FIG. 3b, since the low frequency
signal component in the first part of the period R is delayed longer than
the high frequency signal component in the last part of the period R so
that the signal in the first part comes close to the signal in the last
part of the period R. The envelope line of the compressed FM chirp signal
forms a pulse. Accordingly, the width of the pulse becomes narrow. As a
result, it becomes possible to individually count the pulses even if the
FM chirp signals are transmitted almost at the same time from the
respective objects.
Embodiments in which the present invention is used for detecting traffic
conditions are described hereinafter.
FIG. 1 illustrates a transmission device which is carried by each of
respective people as objects to be measured or arranged in each of the
cars to be measured. The device comprises a PN signal generator 1, a mixer
2, a local oscillator 3, an amplifier 4 and an antenna 5. The generator 1
outputs a PN signal of a specific group. The PN signal is mixed in the
mixer 2 with a high frequency local oscillator signal generated from the
oscillator 3 and converted to a signal having a frequency band of 800 to
900 MHz, for example, which does not disturb the other wireless
communications. The signal output from the mixer 2 is amplified by the
amplifier 4 and emitted from the antenna 5.
It is to be noted that the band of the PN signal is dependent on the clock
frequency of the PN signal. Therefore, it is desirable to choose a clock
frequency of several tens to several hundreds KHz so as to prevent the
signals of adjacent channels from intruding into the band of PN the
signal. Also, as to the PN signal, it is desirable to use an M group
signal which has a small side lobe of self-correlation characteristic as
disclosed "Spectrum Diffusion Communication System", page 397, Kagaku
Gijutsu Publishing Company, 1988.
It is also desirable that the antenna 5 have a band range wide enough to
transmit the PN signal of the above mentioned frequency band and a wide
beam angle so as to certainly transmit the signal toward the receiving
device, the direction of which changes as the transmission device moves.
Further, it is desirable that the output power of the transmission devices
be substantially the same so that signals of the same intensity are
transmitted to the receiving device from the transmission devices.
In the event that the area to be measured is relatively narrow so that the
distance between the receiving device and each transmission device can be
regarded as being almost constant, the power of the signals transmitted
from the transmission devices become substantially the same by arranging
the output power of the transmission devices as being the same.
Therefore, it becomes possible to regard the energy of the received
correlation peaks as being the same also. Therefore, by integrating the
correlation peaks, it becomes possible to obtain an output in proportion
to the number of the above mentioned correlation pulses' which number
corresponds to the approximate figures of the PN signals transmitted from
the area to be measured, whereby the approximate figures of the object to
be measured can be obtained.
FIG. 2 illustrates a structure of the receiving device for obtaining the
approximate figures by integrating the correlation pulses in accordance
with the present invention as mentioned above.
The receiving device comprises an antenna 11, an amplifier 12, a mixer 13,
a local oscillator 14, a bandpass filter 15, a matched filter 16, an
envelope detector 17 and an integration circuit 18. The above mentioned PN
signal is received through the antenna 11 and amplified by the amplifier
12. After that, the signal is mixed with a signal generated from the local
oscillator 14 in the mixer 13 and converted to a signal having an
appropriate frequency band. The signal then passes through the bandpass
filter 15 wherein noise components and undesirable signal components other
than the PN signal component are removed from the signal. After that, the
signal is introduced to the matched filter 16 which is composed of, for
example, a delay element comprising an SAW convolver as mentioned above.
The filter 16 asynchronously detects the PN signal and outputs a signal as
illustrated in FIG. 3a which includes one correlation peak in one period.
The envelope component of the signal output from the filter 16 is taken by
the envelope detector 17 and transmitted to the integrator 18.
FIG. 4 illustrates an example of the output signal from the envelope
detector 17 when a plurality of correlation peaks are transmitted thereto
from the objects.
The integrator 18 integrates the correlation pulses of the PN signal for
one period T in accordance with the integration time control signal to
obtain an output voltage which is in proportion to the number of the
pulses, that is, the number of the objects to be measured.
It is to be noted that if the difference of phase between the signals from
the objects is less than .+-.1 chip of the PN signal, the PN signals
interfere with each other, which results in the fading of the signals so
that the correlation peaks thereof are deleted. Therefore, it is desirable
that if the assumptive number of the objects to be measured is, for
example, 100, the period T be set as T>100 chips.
When the movement of the objects to be measured is slow so that the output
from the filter 16 can be regarded as being constant during the period of
several times as long as the above mentioned period T, it is desirable
that the integration time be elongated to nT from T, multiplying the
period T by a whole number n, so as to heighten the accuracy of the
measurement.
On the other hand, when the movement of the objects is fast and the objects
so into and out of the area to be measured very frequently, it becomes
necessary to shorten the integration time to less than the period T.
It is to be noted that in the event wherein the area to be measured is very
large, the power of the signal transmitted from the transmission device is
attenuated due to the diffusion of the signal and changes according to the
position of the transmission device. Therefore, the output level of the
correlation peak becomes different for each transmission device. FIG. 5
illustrates the output signal of the receiving device which receives such
different level signals from the transmission devices of the objects.
Therefore, the accuracy of measuring the approximate figures is reduced in
accordance with the above mentioned integration method wherein the
correlation peaks are to be integrated.
FIG. 6 illustrates another embodiment of the signal receiving device in
accordance with the present invention. In this embodiment, the correlation
peaks in one period T are counted instead of being integrated by the
integrator 18 of the first embodiment mentioned before. By counting the
peaks, it becomes possible to raise the accuracy of measuring the
approximate figures even when energy levels of the peaks are different,
respectively.
The signal receiving device of FIG. 6 comprises an antenna 21, an amplifier
22, a mixer 23, a local oscillator 24, a bandpass filter 25, a matched
filter 26, an envelope detector 27, a threshold circuit 28 and a pulse
count circuit 29. The circuit structure from the antenna 21 to the
envelope detector 27 is substantially the same as that of the first
embodiment of FIGS. 1 to 3. In accordance with the embodiment of FIG. 6,
the output of the detector 27 is transmitted to the threshold circuit 28.
In the circuit 28, as illustrated in FIG. 5, correlation peaks are
discriminated by the threshold level TH and counted by the circuit 29 for
the period of T mentioned above so as to obtain the approximate figures.
It is to be noted that in order to prevent the shape of the pulses output
from the circuit 28 from influencing the counting function of the circuit
29, a pulse shaping circuit may be disposed between the circuits 28 and
29.
FIG. 7 illustrates a still other embodiment of the signal receiving device
in accordance with the present invention wherein the objects to be
measured are sorted to, for instance, pedestrians and cars and the
approximate figures are measured for each sort of the objects.
In this embodiment, PN signals of different groups such as PN.sub.1,
PN.sub.2 are arranged for different sorts of object, respectively. Also,
the matched filters 26.sub.1 and 26.sub.2 are arranged for respective
groups. Each measuring circuit for counting the approximate figures of
each sort of object comprises the detectors 27.sub.1,27.sub.2 connected
from the filter 26.sub.1, 26.sub.2, the threshold circuit 28.sub.1,
29.sub.2 and the pulse count circuit 29.sub.1, 29.sub.2, so as to perform
the counting operation for each sort of object in the same manner as the
circuit of FIG. 6.
However, in accordance with the measuring system by integrating the
correlation peaks mentioned before, the measurent result is influenced
from the power of the signal which is transmitted to the signal receiving
device from the signal transmission device. Also, in accordance with the
measuring system by counting the correlation peaks mentioned above, count
errors may occur when a plurality of PN signals are simultaneously
transmitted from the objects.
However, it is possible to obviate such problems and raise the reliability
of measurement by shaping the output from the envelope detector to form a
pulse series and integrating the pulses.
FIG. 8 illustrates a further embodiment of the signal receiving device in
accordance with the present invention in which the above mentioned
improvement is made.
The embodiment of FIG. 8 comprises an antenna 31, an amplifier 32, a mixer
33, a local oscillator 34, a bandpass filter 35, a matched filter 36, an
envelope detector 37 and a threshold circuit 38 which are arranged in the
same manner as the embodiment of FIG. 6. The embodiment of FIG. 8 further
comprises a waveform shaping circuit 39 connected to the threshold circuit
38, an integrator 40, a divisional circuit 41 and a circuit 42 for
counting fractions lower than the decimal point as a whole number. The
circuits 41 and 42 constitute a calculator 43 for calculating the
approximate figures of the objects. A reference integration value is input
to the circuit 41 for the calculation.
A graph relating to envelope detector of FIG. 9 represents an output signal
from the detector 37 when a plurality of PN signals are overlappingly
transmitted from the objects so that the width of each pulse is widened in
appearance.
A graph relating to threshold circuit output of FIG. 9 represents an output
signal from the circuit 38 which detects the correlation peaks of the
pulses which are over the threshold level TH when the pulse signal of
graph (a) is input thereto.
A graph relating to waveform shaping circuit output of FIG. 9 represents an
output signal from the circuit 39 which shapes the pulse signal of graph
(b) transmitted from the circuit 38 to form a rectangular pulse series.
Each of the rectangular pulses is widened when a plurality of PN signals
are overlappingly transmitted from the objects. Therefore, by integrating
the rectangular pulses, it becomes possible to obtain an output which is
in proportion to the approximate figures of the objects.
The output from the integrator 40 does not directly indicate the number of
the objects. However, it is possible to calculate the number of the
objects by dividing the output from the integrator 40 by the reference
integration value which corresponds to the output value for one object.
Such a divisional calculation is carried out by the circuit 41.
Further, it becomes possible to raise the accuracy of the measurement of
the approximate figures by counting the fractions lower than the decimal
point as a whole number by the circuit 42 connected to the divisional
circuit 41 so that the reduction of the width of the pulse which is
constituted from a plurality of PN signals is compensated.
A still further embodiment of the present invention is described with
reference to FIGS. 10 to 15 hereinafter.
In this embodiment, the signal transmission device transmits an FM chirp
signal.
As described with reference to FIG. 3b, the FM chirp signal changes its
frequency from low to high in a predetermined period R. The frequency
changing period R is repeated at an interval of once a period of T wherein
T>R.
FIG. 10 illustrates the structure of the signal transmission device that
emits the FM chirp signal.
The device comprises a voltage control oscillator 51, a control signal
generator 52, a switching circuit 53, an amplifier 54 and an antenna 55.
The oscillator 51 comprises a voltage controlling variable capacity diode
as a tuning element for determining the oscillation frequency.
FIG. 11 illustrates the characteristic of the above mentioned diode of the
oscillator 51. As can be seen from the graph of FIG. 11, when the
controlling voltage applied between the terminals of the diode is changed
from V.sub.0 to V.sub.1, the oscillation frequency linearly changes from
f.sub.0 to f.sub.1.
The control signal generator 52 supply the voltage control oscillator 51
with a controlling voltage which linearly changes from 0 to V in a
predetermined period R as illustrated in the graph (a) of FIG. 12.
Receiving the voltage of the graph (a) from the generator 52, the
oscillator 51 outputs an oscillation signal, the frequency of which
continuously changes from f.sub.0 at first to f.sub.1 at the end of the
period R, as illustrated in the graph (b) of FIG. 12. The generator 52
also outputs a control signal to the switch circuit 53 so that the circuit
53 is turned on for the period of R.
The FM chirp signal generated as mentioned above is amplified by the
amplifier 54 and emitted through the antenna 55 which is desirably
nondirectional.
FIG. 13 illustrates a block diagram of the signal receiving device for
receiving the FM chirp signal emitted from the transmission device of FIG.
10 mentioned above. The device comprises an antenna 61, an amplifier 62, a
mixer 63, a local oscillator 64, and a bandpass filter 65 which are
substantially the same as those in FIG. 2.
The device of FIG. 13 further comprises an FM chirp filter 66, an envelope
detector 67 and a pulse counter 68.
FIG. 14 illustrates the characteristics of the FM chirp filter 66. As can
be seen from the graph of FIG. 14, the lower the frequency of the signal
becomes, the longer the filter 66 gives the delay time to the signal that
passes through the filter. The filter 66 may comprises, for example, an
SAW (Surface Acoustic Wave) delay element as disclosed in "Acoustic Waves"
(Prentice-hall 1987) by G. S. Kino, page 332 to 333.
Therefore, when the FM chirp signal output from the bandpass filter 65
passes through the FM chirp filter 66, the low frequency signal component
in the first part of the period R is delayed longer than the high
frequency signal component in the last part of the period R. Accordingly,
the envelope of the FM chirp signal is compressed, as explained with
reference to FIG. 3b before, so that the width of the pulse detected by
the circuit 67 becomes narrow, as illustrated in FIG. 15.
As a result, when a plurality of FM chirp signals are overlappingly
transmitted to the receiving device from the objects, the pulses of the FM
chirp signals are narrowed and separated from each other so that the
pulses can be accurately counted by the pulse count circuit 68, whereby
the approximate figures of the objects are reliably measured.
Many widely different embodiments of the present invention maybe
constructed without departing from the spirit and scope of the present
invention. It should be understood that the present invention is not
limited to the specific embodiments described in the specification, except
as defined in the appended claims.
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