Note: Descriptions are shown in the official language in which they were submitted.
~ W095/20249 215 7 10 8 PCT1~95l00047
-- 1 --
DESCRIPTION
SATELLITE-BROADCAST RECEIVING MOBILE ANTENNA APPARATUS
TECHNICAL FIELD
This invention relates to mobile antenna
apparatus for use in receiving satellite broadcasts, and
particularly to a satellite-broadcast receiving mobile
antenna apparatus with an imp.over..ent in the automatic
tracking system rendered small in size and reduced in
cost.
BACKGROUND ART
As satellite broadcasting receivers have been
widely used in recent years, mobile antennas have been
developed which are installed in various mobile means
such as cars and vessels in order to receive satellite
broadcasts. In the future, it will be supposed to
receive radio waves not only from stationary satellites
like broadcasting satellites but also from moving
satellites or to take services including communications
(transmission and reception) with satellites in addition
to receiving broadcasts. In this kind of mobile antenna
apparatus, particularly in the satellite-broadcast
receiving antenna apparatus mounted on a vehicle, it is
absolutely necessary to provide an automatic tracking
mechanism for always directing the antenna body toward
the associated satellite even if the satellite is
stationary as well as moving because the orientation of
_
wossl20249 ~15 7 1~ 8 2 - PCT/~95/OQ0~7 ~
the moving car may change every mom~ t.
This automatic tracking mechanism is
materialized by a combination of an azimuth control
apparatus for controlling the horizontal component
(hereinafter, referred to as "tracking azimuth") of the
direction of the antenna body and an elevation control
apparatus for controlling the elevation ang~e of the
antenna body. This automatic tracking mechanism takes a
considerable part of cost of the whole satellite-
broadcast receiving system including electric circuitcomponents such as a converter and a tuner, and in-
creases the installation height and area of the antenna
apparatus. Therefore, how much this mechanism can be
simplified is one of the important technical subjects.
Since the tracking azimuth of the antenna body
is necessary to be controlled over 360 degrees as the
antenna-installed vehicle moves, it can be considered
practical that the tracking azimuth is controlled by a
mechanically rotating mechanism. The elevation angle of
the antenna body, as contrasted with the above, may be
sufficiently controlled by changing in rather limited
range in accordance with the latitude of the area in
which the vehicle is moving and with the road slope
variations of about + S degrees along which the vehicle
is moving particularly when the antenna is directed
toward a stationary satellite like a broadcasting
satellite. Thus, the control range for the elevation
angle is limited to a relatively small value.
~ W095/20249 2 15 71 0 ~ PCT/~95/000~7
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Accordingly, the satellite-broadcast receiving
mobile antenna apparatuses have been deviced to employ a
single-axis tracking system in which only the tracking
azimuth is controlled with the directivity of the
antenna in the elevation being previously set to be wide
and to employ a system in which the elevation is
discretely ànd coarsely controlled, thereby achieving
the miniaturization and cost-reduction of the whole
receiving system. The tracking azimuth control
apparatus is maintained substantially independent of the
elevation control apparatus whatever elevation control
is made. A relatively important tracking azimuth
control will be described below.
One of the tracking control apparatus fo~r the
mobile-type satellite-broadcast receiving antenna
apparatus, or a phase-difference detecting system, is
known as disclosed in the Japanese Patent Application
No. 3-350103 which the same assignee of this invention
previously filed. In this phase-difference detecting
system, some divided parts of a satellite-broadcast
receiving antenna are arranged in a certain direction
having a spacing from each other so that an error
between the direction of an incoming radio wave and the
antenna parts arranging direction, namely a tracking
error of the whole antenna can be detected from the
phase difference between the radio waves received by the
respective divided parts of the antenna. This tracking
control apparatus has many advantages, but has a problem
wo95l2o24s pcTl~s5lonn47
2~ 10~ _ 4 _
of high cost.
Another tracking control appsratus rotates the
antenna until the received signal level becomes the
~imllm. This type of tracking control apparatus is
known as an auto-threshold system as disclosed in
Japanese Patent Application No. 4-176992 for as a
vibration system as disclosed in Japanese~Patent
Application No. 4-60479. However, the tracking
mechanism of the auto-threshold system or vibration
system is too low in tracking ability to respond to
rapid turning of car at left or right turns.
A direction-sensor system can be considered
which, in principle, uses a direction sensor to detect
the orientation of mobile means in which the associated
satellite-broadcast receiving antenna is installed,
calculates a tracking azimuth at which the antenna is
directed on the basis of the detected orientation of the
mobile means, and controls the antenna direction
according to the calculated result. In this direction-
sensor system, however, the tracking azimuth to becalculated depends on the longitude and latitude of the
spot at which the mobile means exists. Therefore, there
are problems that a positioning system such as a GPS
receiver is also necessary for detecting the longitude
and latitude and that the longitude and latitude must be
roughly set and changed by human hands, this operation
is troublesome.
One of the reasons for the difficulty in the
~ W095/20249 21~ 71-O ~ pcTl~95lono~7
-- 5 --
tracking control of such mobile antenna is that a high
tracking ability is required in order to respond to a
rapid change of direction which, as mentioned above,
occurs when the mobile means turns left or right, such a
large angle change of about 90 degrees, in a relatively
short period of time.
Another reason for the difficulty in the
tracking control of the mobile antenna is that as the
mobile means moves the radio waves from the satellite to
the mobile means is frequently blocked off in short
periods of time by electric light poles or telephone
poles, buildings, bridges, trees and mountains along the
road. Under this situation, the received signal level
is suddenly reduced though the reduction lasts only a
short time, thus disabling the tracking function. If
this sudden reduction of received signal level occurs
just instantaneously due to an obstacle, it is useless
to continue the tracking operation and the received
signal level will be immediately restored to the
original value. Therefore, when the sudden reduction of
received signal level derived from an obstacle, it is
rational to wait for the received signal level to be
restored to the original value without changing the
direction of the antenna.
25 However, it is uncertain whether this sudden
reduction of received signal level has derived from an
obstacle or from the rapid turning of the vehicle which
leads to a rapid increase of tracking error. When a
W095/20249 ~i5~ 10~ pcTm~5looo47 ~
- 6 -
sudden reduction due to the rapid turnlng of the vehicle
is mistaken as it had occurred due to an obstacle, the
received signal level is waited to be restored to the
original value under that condition. Thus, the start of
necessary tracking operation is delayed b~ this waiting
time. On the contrary, when a sudden reduction due to
an obstacle is mistaken as it had occu~red due to the
rapid turning of the vehicle, unnecessary tracking
control is started and the direction of the antenna may
be changed away from the correct direction by this
unnecessary tracking operation. The time in which the
received signal level is reduced by an obstacle greatly
depends on the size of the obstacle and the speed of the
vehicle. This also makes difficult to obtain proper
tracking control, resulting in reduction of reception
efficiency.
DISCLOSURE OF lNV ~:Nl ION
It is an object of the invention to provide a
tracking control apparatus having a high tracking
ability which is responsive to a rapid change of azimuth
angle.
It is another object of the invention to
provide a tracking control apparatus which is capable of
immediately discriminating whether the sudden reduction
of received signal level is caused by an obstacle or by
the rapid turning of the mobile means and starting to
control in accordance with the situation, thereby
~ W095/20249 21~ 7 10 8 PCT/~9S/OQ047
-- 7
improving the tracking ability at the time of rapid
turning and the stability of control at the time of
sudden reduction.
The tracking control apparatus for mobile-type
satellite-broadcast receiving antenna which is installed
on mobile means, according to this invention, has
tracking control executing means for detecting the level
of a radio wave received by the antenna, the angular
velocity of the mobile means and the integrated value of
the angular velocity and controlling the rotation angle
of the antenna on the basis of the detected received
signal level, the angular velocity and the integrated
value.
This tracking control executing means has
lS differentiation control executing means for repeatedly
rotating the antenna over a certain angle at a higher
rotation velocity, when the increment of the received
signal level per unit angle associated with the
preceding rotation is larger.
This tracking control executing means may
further have hold control executing means for comparing
the detected signal level with a predetermined threshold
Lt and, if this received signal level exceeds the
threshold Lt, repeating the detection of a most-recent
25 value of the received signal level and the comparison
with the threshold Lt while holding the rotation angle
of the antenna at the current value. If the angular
velocity or its integrated value is larger than a
W095/20249 21~ ~ 10 8 PCT/~95/~Q0~7
-- 8 --
predetermined threshold when the detected most-recent
received signal level is reduced to be less than the
threshold Lt, the hold control executing means
immediately causes the differentiation control execution
S means to start. If either one of the detected angular
velocity and its integrated value ~ ~less than the
threshold, the hold control execut~ing means causes the
wait control executing means to start waiting over a
certain period for the received signal level to be
restored to a proper value.
Another tracking control apparatus of the
invention for a mobile-type satellite-broadcast
receiving antenna which is installed on mobile means is
constructed so that each inherent effect can be achieved
by a part of the above various control executing means.
This tracking control apparatus has turning-
angle detecting means for detecting the turning angle of
the mobile means by integrating the horizontal component
of the detected angular velocity and satellite searching
means for detecting an amount of change of the turning
angle detected by the turning angle detecting means from
a value detected just before a tracking-off when any
tracking-off occurs in which the received signal level
is reduced to be less than a certain threshold,
correcting the current tracking azimuth on the basis of
this change amount of turning angle, and changing the
tracking azimuth around this corrected value within a
range which is increased with lapse of time, thereby
~ Woss/20249 2 1 5 7 1 0 8 PcT/JP95lono47
g
making a search for the satellite.
The relation between the received signal level
of the antenna and the angular error is approximately
according to the Gaussian distribution curve, namely the
amount of change (or differentiation) of the received
signal level p~er unit angle gets greater when the
angular error gets larger. Therefore, the differen-
tiation control executing means decides that the angular
error becomes larger when the amount of differentiation
goes larger, then rotates the antenna by steps having a
certain angle at a high rotation velocity. Thus, since
the amount of differentiation and the rotation velocity
are reduced stepwise with the decrease of the angular
error as the antenna is rotated, the rotation angle can
be prevented from being excessively passed over the
target, or from overshooting. As a result, the tracking
ability is enhanced enough to easily immediately deal
with the sudden reduction of the received signal level
due to the rapid turning of the vehicle. The amount of
differentiation is rather decreased in the region where
the angular error is extremely large. In this region,
however, the received signal level is so reduced that
the differentiation control itself may be eliminated,
and thus such region is not necessary to be considered.
In addition, according to the hold control
which is executed in addition to the differentiation
control, if the angular velocity or its integrated value
detected when a newly detected value of the received
wogs/2o24s 2 i S 7 ~ 0 8 PCT/~ ~5,000~7
-- 10 --
signal level is less than the threshold is larger than a
certain threshold, the reduction of the received signal
level may be regarded as caused by the reduction of the
tracking precision derived from l..ovell~ent of the vehicle.
In this case, the differentiation control is i~?~iately
started without waiting for the received ~signal level to
be restored to a proper value. On the other hand, if
the angular velocity and its integrated value are both
less than their threshold, the reduction of the received
signal level is considered as having suddenly caused by
an obstacle. In this case, the wait control is started
by which the received signal level is waited over a
certain period to be restored to a proper value. Thus,
by using not only the received signal level but also the
angular velocity or its integrated value which indicate
the movement of the vehicle, it is possible to
~ iately decide whether the reduc~ion of the received
signal level is suddenly caused by an obstacle or by the
increase of the tracking error due to the turn of the
mobile means and to select proper control means, thus
greatly improving the tracking ability.
Moreover, according to the tracking control
apparatus of the invention, which has the turning-angle
detecting means and the satellite searching means, both
the tracking azimuth of the antenna body and the
orientation of the mobile means may be used with their
relative values. In other words, the tracking azimuth
of the antenna may always be expressed by an angle
~ wossl20249 ~ pcTlJp95loon47
215~108
-- 11
measured in the clockwise direction or counter-clockwise
direction relative to the current value as a reference
value (zero). Also, the orientation of the mobile means
is expressed by the integrated value of the detected
angular velocity as a relative value. When a tracking-
off state occurs, the amount of change, just before the
tracking-off, of the turning angle detected by the
turning-angle detecting means is detected.
In other words, if the tracking-off is caused
by the fact that the mobile means has turned by an angle
~ in the clockwise direction, the amount ~ of change
of the integrated value of the angular velocity
developed just before this tracking-off is detected.
The current tracking azimuth of the antenna body is
corrected in the counter-clockwise direction according
to the detected amount of change of the integrated
value, and thereby the center value of the range of the
tracking azimuth can be estimated. Then, the antenna is
rotated around this center value over a range which is
increased with lapse of time, thereby searching for the
satellite. If the search for the satellite becomes
successful at the initial time when the range stays
small, the consumption power can be reduced or saved.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a block diagram of one embodiment of
the tracking control apparatus of the invention, showing
together with the associated satellite-broadcast
W095/20249 2 1 5 71 0 8 PCT/~95/000~7
- 12 -
receiving antenna being controlled.
Fig. 2 is a diagram for explaining the
relation of the angular error of the antenna to the
received signal level and the differentiated value of
the received signal level and the relation between the
received signal level and various thresholds.
Fig. 3 is a flowchart for on~ example of the
differentiation control which is executed by the
tracking control apparatus of the embodiment.
Fig. 4 a flowchart for one example of the hold
control which is executed by the tracking control
apparatus of the embodiment.
Fig. 5 is a flowchart for one example of the
wait control which is executed by the tracking control
apparatus of the embodiment.
Fig. 6 is a flowchart for one example of the
sweeping procedure which is executed by the tracking
control apparatus of the embodiment.
Fig. 7 is a diagram for explaining the
relation between the angle of turn of the mobile means
and the tracking azimuth of the antenna.
Fig. 8 is a waveform diagram of the angular
velocity developed as the mobile means turns, integrated
value of the angular velocity, center value of tracking
azimuth, sweep angle range and sweep velocity with
respect to time.
Fig. 9 is a flowchart for search processing
which is executed by the mobile-type satellite-broadcast
~ wo gs/20249 2 1 5 7 1 0 8
receiving antenna apparatus of another embodiment of the
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Fig. 1 is a block diagram of the tracking
control apparatus for mobile-type satellite-broadcast
receiving antënna of one embodiment of the invention,
showing together with a satellite-broadcast receiving
antenna AT being controlled. Referring to Fig. 1, there
are shown a microprocessor 1, a down converter 2, a
rotation coupler 3, a tuner 4, a received signal level
detector S, an input/output interface circuit 6 having
an A/D converter and a D/A converter, an angular
velocity meter 7, an integrator 8 for integrating the
angular velocity detected by the angular velocity meter
7, a motor driver 9, a pulse motor 10 and a rotation
support mechanism 11.
A television signal of 12 GHz band trans-
mitted from a broadcasting satellite and received by the
satellite-broadcast receiving antenna AT is converted
into a television signal of one-GHz band intermediate
frequency by the down converter 2. The converted
intermediate-frequency signal is fed through the
rotation coupler 3 to the tuner 4, where it is
demodulated into a video signal and an audio signal,
which are then supplied to the associated television
receiver. The received signal level detector 5 detects
the level of the signal received by the antenna AT (, or
wo95/202492~ 0 8 PCT/J~9~/00017
- 14 -
the received signal level) on the basis of the noise
level produced from the automatic gain control amplifier
within the tuner 4. In other words, when the received
signal level is reduced, the gain of the automatic gain
control amplifier is increased and acco ~dingly the noise
level is increased. The received sig ~ l level is
detected on the basis of the increase~or decrease of the
noise level, converted into a digital signal by the
input/output interface circuit 6 and fed to the
microprocessor 1.
The angular velocity meter 7 is mounted at a
proper position in the vehicle which has installed
therein the antenna AT and the tracking control
apparatus of this embodiment. This angular velocity
meter detects the angular velocity of the vehicle
occurring when the vehicle changes the course (turns).
The angular velocity meter 7 may be any one sold in a
market, for example, "GYROSTAR" manufac~ured by Murata
Seisakusho Inc. The detected angular velocity contains
the polarity indicating the turning direction of the
vehicle and it is fed to and held in the input/output
interface circuit 6. The detected angular velocity is
also fed to the integrator 8 where it is integrated.
The integrated angular velocity is supplied to the
input/output interface circuit 6 and held therein. The
held values are updated each time the output from the
angular velocity meter 7 changes at a certain sampling
period, and transferred from the input/output interface
wossl2o249 21$ 710 8 PCT/~95/00047
- 15 -
circuit 6 to the microprocessor 1 in accordance with the
demand from the microprocessor 1. The received signal
level detected by the received signal level detector 5
is also processed in the same way. In place of the
integrator 8, the microprocessor 1 may of course
integrate the angular velocity.
Hereinafter, in place of saying that the
angular velocity or received signal level from the
input/output interface circuit 6 is received by the
microprocessor 1, it will be cited that the angular
velocity or received signal level is detected by the
microprocessor 1. The microprocessor 1 determines the
rotation direction and rotation angle for the tracking
control on the basis of the detected received signal
level, the angular velocity and the integrated value of
the angular velocity. A train of pulses the number of
which corresponds to the rotation angle is supplied from
the microprocessor 1 through the input/output interface
circuit 6 and motor driver 8 to the pulse motor 9. The
rotation direction and rotation velocity will be
described in detail later. The rotating shaft of the
pulse motor 10 is coupled to the antenna AT through the
support mechanism 11 for rotatably supporting the
antenna AT, thus controlling the d~rection angle of the
antenna AT.
Some thresholds for the received signal level
are defined in order for various kinds of control to be
executed in accordance with the received signal level
W095/20249 2 1 5 71 ~ 8 pcTl~s5loow7 ~
_ 16 -
changing every moment. These thresholds are defined as
ratios (or relative values) to a peak value Lp as shown
in Fig. 2. The peak value Lp is the mA~imllm value of
the most recently received signal levels detected by the
microprocessor. Each time a most-recently received
signal level is detected as exceedi`ng a threshold Lo
which is a certain magnifying power larger than the peak
value (for example, 110% of the peak value), the peak
value is updated to be replaced by this larger received
signal level. The reason for providing a hysteresis of
10% for update of the peak value is to prevent from
wasteful processing steps for frequently updating the
peak value when the received signal level changes in a
short time.
A threshold Lt is slightly lower than the peak
value Lp (for example, 93%). As long as the received
signal level exceeds this threshold Lt, antenna rotation
is not rendered in tracking operation. A threshold Lb
is considerably lower than the peak value (for example,
20%). When the received signal level is reduced to be
lower than this threshold Lb, it is regarded as a large
angular error occurs. In this case, the microprocessor
1 starts to execute a sweeping procedure for searching
the direction of the satellite by changing the azimuth
of the antenna up to 360 degrees. A threshold Lm is an
intermediate value between the peak value Lp and the
threshold Lb (for example! 50%). The meAn i ng of this
threshold Lm will be mentioned later.
wo9sl2o24s 2 1 S 7 1 0 8 PCT/~S/00047
- 17 -
The differentiation control which is executed
by the microprocessor will be described with reference
to the flowchart of Fig. 3. This differentiation
control is started chiefly in the following cases:
(1) When a received signal level larger than the
threshold Lb is detected as a result of executing the
sweeping procedure.
(2) When the received signal level is reduced to be
lower than the threshold Lt of about 93% of the peak
value, and when an angular velocity or the integrated
value of the angular velocity of significant value
larger than a threshold is detected, thus it being
decided that a considerable angular error has occurred
as the vehicle turns.
The microprocessor l, when starting the
execution of the differentiation control, first decides
whether the direction in which the antenna rotates is
definite or not (step 11). When the sweeping procedure
had been executed as the tracking control immediately
before this differentiation control, the rotation
direction is already decided in the sweeping procedure
as that is the same direction in which the received
signal level was increased to be higher than the value
Lb in the sweeping procedure. If the differentiation
control is started when the angular velocity or the
integrated value of the angular velocity has exceeded a
significant value, the antenna may be rotated in the
opposite direction to the turning direction of the
W095/20249 2~51 ~ PCT/~9~/00017
- 18 -
vehicle indicated by the sign of the value, thus the
direction in which the antenna is to be rotated is
decided. However, since the sign of the integrated
value of the angular velocity may be indefinite compared
with that of the angular velocity, the;direction in
which the antenna is to be rotated ~s~confirmed only in
that case (step 12). In other words, the microprocessor
first rotates the antenna by a certain angle in the
direction predicted from the sign of the integrated
value of the angular velocity. If the received signal
level increases as the antenna is rotated, this
direction is decided as a correct direction in which the
antenna is to be rotated. If the received signal level
decreases, the opposite direction is decided as a
correct direction in which the antenna is to be rotated.
When the rotation direction is completely
fixed, the microprocessor 1 sets an initial value Vo for
the rotation velocity V of the antenna (step 13), and
causes the antenna to rotate by a predet~rmined angle
in the fixed direction at this rotation velocity Vo
(step 14). Then, the microprocessor detects an
increment ~L, or the difference between a most-recently
received signal level L and the preceding received
signal level before the rotation for this received
signal level L (step 15). Thereafter, the microproces-
sor decides whether the detected most-recently received
signal level exceeds the threshold Lb or not (step 16).
If the answer is yes, the program advances to the next
~ wos~/2024s 215 7 1~ 8 PCTt~95/00~7
-- 19 --
step 17. If the answer is no, the program advances to
the sweeping procedure. At step 17, the microprocessor
1 changes the rotation velocity V of the antenna to a
value which is proportional to ~L.
The microprocessor 1 newly detects the
received signal level L and decides whether the received
signal level L exceeds the threshold Lt or not (step
18). If the decision is no, it is decided that the
antenna is not directed toward the satellite, and thus
the program goes back to step 14, where the antenna is
further rotated by a predetermined angle Q~ at the fixed
velocity V. In this embodiment, the predetermined ~ is
set according to the number of pulses fed to the pulse
motor, and the rotation velocity is changed by altering
lS the time interval between the pulses fed to the pulse
motor. Thus, the microprocessor changes the rotation
velocity to a value proportional to the increment of the
received signal level detected upon the preceding
rotation and causes the antenna to rotate by the angel
~ each time the rotation velocity is changed until the
most-recently received signal level exceeds the
threshold Lt (step 14 to step 18).
After detecting that the most-recently
received signal level has exceeded the threshold Lt at
step 18, the microprocessor 1 executes the next step 19,
where it is decided whether the set rotation velocity V
is smaller than a certain threshold Vth. If the
decision is no, it is decided that the antenna is not
WO 95/20249 215 ~ 10 8 pcTlJpsslono~7
- 20 -
precisely directed toward the satellite yet and thus the
program goes back to step 14. The microprocessor
repeats the control from step 14 to step 19 until the
received signal level L exce3èds the threshold Lt and
until the rotation velocity V decreases below the
threshold Vth. When the most-recently received signal
level is close enough to the peak value Lp, the decision
result of step 19 becomes yes. In this case, the micro-
processor stops the execution of the differentiation
control and starts the execution of the hold control.
The hold control which the microprocessor 1
executes will be described with reference to the
flowchart of Fig. 4. The microprocessor first sets a
new value of the peak value Lp to the received signal
level detected just before the start of this hold
control, and calculates to renew the thresholds Lt, Lb,
Lm and Lo relative to the peak value (step 21). Then,
the microprocessor detects a most-recent value of the
received signal level L (step 22) and compares it with
the threshold Lt (step 23). If the received signal
level L is larger than the threshold Lt, the micro-
processor executes step 24 to compare the received
signal level L with the threshold Lo. If the received
signal level L is smaller than the threshold Lo, the
microprocessor goes back to step 22 and again executes
the steps 22 to 24.
In other words, as long as the receiving
condition is kept stable in which the current received
21~7108
WO9S/20249 ~ PCT/~S/00047
- 21 -
signal level is maintained larger than the threshold Lt,
the steps 22 to 24 are repeatedly executed. This
repeating process may be executed in an asynchronous
state in which a successive processing step is
continuously executed after a preceding step or in a
synchronous state in which certain waiting times are
provided at appropriate locations so that the processing
steps are repeated with a constant period. During the
execution of the hold control, the rotation angle of the
antenna is kept at the value that is set just before the
execution.
If the most-recently received signal level L
is decided to have exceeded the threshold Lo at step 24,
the program goes back to step 21, where the micro-
processor 1 uses this received signal level as the newpeak value Lp and again calculates the thresholds Lt,
Lb, Lm and Lo with relation to this new peak value. If
the new received signal level L is decided to be smaller
than the threshold Lt at step 23, the microprocessor
detects the angular velocity and decides whether it
exceeds the threshold or not (step 25). If the detected
angular velocity is decided not to have exceeded the
threshold yet, the microprocessor detects its integrated
value and decides whether it exceeds the threshold or
not (step 26). The integrated value of the angular
velocity is introduced because, when the vehicle is
running along an expressway with a moderate large curve,
the integrated value over a long time becomes consider-
wos5l2o24s PCT/~5/000~7
2i57 ~ 22 -
ably large though the deviation of the angular velocity
due to the tracking error is small. In that case, the
angular velocity itself is not so large as to exceed the
threshold but its integrated value exceeds a significant
5 value. ~` -
If the received signal level L is lower than
the threshold Lt, the microprocessor 1 executes steps 25
and 26 where it is decided whether the angular velocity
or its integrated value exceeds the corresponding
threshold or not. At this time, if either one of the
angular velocity or its integrated value is decided to
have exceeded the corresponding threshold, the tracking
error is regarded as having been increased as the
vehicle turns. Thus, the differentiation control is
started to execute as already described with reference
to Fig. 3. If the received signal level L is lower than
the threshold Lt, and if, at steps 25 and 26, either one
of the angular velocity or its integrated value is
decided not to have exceeded the corresponding threshold
yet, the microprocessor regards the reduction of the
received signal level as having been suddenly caused by
an obstacle, and starts the execution of the wait
control.
The wait control to be executed by the
microprocessor 1 will be described with reference to the
flowchart of Fig. 5. The wait control is carried out
fundamentally for monitoring that the received signal
level is restored to a larger value than the threshold
~ woss/20249 215 710 8 PCT/~5/000~7
- 23 -
Lt or that the angular velocity is increased to a larger
value than the threshold, and causing the antenna to be
placed under the control corresponding to the result of
the monitoring. In other words, if the received signal
level is restored to a larger value than the threshold
Lt, the reduction of the received signal level is
regarded as having been temporarily (suddenly) caused by
an obstacle and the hold control is ;~e~iately started.
If the angular velocity is detected to have been
increased to a larger value than the threshold within
this waiting period, the reduction of the received
signal level is regarded as having been caused not only
by an obstacle but also an angular error occurring as
the vehicle turns, and the differentiation control is
brought about. Such cases may occur, for example, when
a composite change has occurred in which an angular
error occurring as the vehicle turns is caused
imme~iately after the instantaneous reduction of the
received signal level due to an obstacle.
This wait control is fundamentally divided
into the first portion (first wait control) in which the
above monitoring of the change of state is repeated with
a short period and the second portion (second wait
control) in which the monitoring of the change of state
is repeated with a long period. For example, the whole
period for the execution of the wait control is set to
about two seconds. The period for the first portion is
set to about 0.3 second and that for the second portion
-
wo95l2o24s PCT/~9~/000~7
2157 108 - 24 -
to about 1.7 second. The period for repeating the
monitoring of the presence or absence of the change of
state is set to about 10 milliseconds in the first
portion and to about 100 milliseconds~in the second
portion.
When the wait control is started to execute,
the microprocessor 1 first makes initialization for a
time T which is progressively changed at a constant
speed by a counter in order to control the time lapse
and for a status flag F into zero (step 31). Then, the
microprocessor 1 decides whether the acceleration
becomes so significant as to exceed a certain threshold
or not (step 32). If the acceleration is detected not
to exceed the threshold, a new received signal level L
is detected (step 33) and it is decided whether this
received signal level is larger than the threshold Lt or
not (step 34).
If the received signal level L is not larger
than the threshold Lt, the microprocessor 1 decides
whether or not the lapse time T from the start of the
execution of the wait control is larger than a
predetermined time Tm for determining the first portion
(first wait control) of the wait control tstep 35). If
the decision result is no, the program goes back to step
32, and the microprocessor repeats the steps 32 to step
35. The repeating of those steps may be executed in the
asynchronous way in which the successive processes are
continuously performed after the preceding processes
W095120249 215 710 ~ PCTl~95/00047
- 25 -
without delay or in the synchronous way in which waiting
times are provided at appropriate locations so that the
processes are carried out with a constant period (for
example, 10 millisecond) as shown in Fig. 5.
5 If the acceleration is detected to become
significant during the above repeating process (step
32), the microprocessor regards the reduction of the
received signal level as having been caused not only by
an obstacle but also by the turn of the vehicle, and
10 ;mm~Ai ~tely starts the execution of the differentiation
control. On the contrary, if the received signal level
is detected to have exceeded the threshold Lt during the
above repeating process (step 34), the reduction of the
received signal level is regarded as having been
suddenly caused by an obstacle, and the hold control is
imme~iately started by the microprocessor 1.
If it is detected that the lapse time T has
exceeded the certain time Tm during the repeating
process (step 35), the microprocessor 1 starts the
20 execution of the second wait control which starts with
step 36. After the execution of the second wait
control, the microprocessor 1 decides whether the
acceleration is detected to be larger than the threshold
(step 36). If the acceleration is not so significant as
to exceed the threshold, a new received signal level L
is detected (step 37), and it is decided whether the new
received signal level is larger than the threshold Lt
(step 38). If the received signal level L is not larger
wossl2o24s PCT/Jl95/00~17 ~
2~5~ 26 -
than the threshold Lt, the microprocessor l decides
whether or not the received signal level L exceeds the
threshold Lm (step 39). If the received signal level L
is not larger than the threshold Lm, the microprocessor
sets the status flag F to "0" (step 40) and decides
whether the lapse time T from the e~ëcution of this wait
control exceeds a certain value Tw which defines the
period in which the wait control is executed (step 4l).
If the lapse time T from the beginning of the
execution of the wait control is smaller than the value
Tw, the microprocessor l executes the step 44 where a
waiting time is determined relative to the repeating
period To. After the step 44, the program goes back to
the step 36 and the steps 36 to 44 are repeated. If the
acceleration is decided to become so significant as to
exceed the threshold during the repeating process in the
same way as in the first wait control (step 36), the
microprocessor regards the reduction of the received
signal level as having been caused not only by an
obstacle but also by the turn of the vehicle, and
~ iately starts the execution of the differentiation
control. If the received signal level is decided to
have exceeded the threshold Lt during the repeating
process (step 38), the microprocessor considers the
reduction of the received signal level as having been
suddenly caused by an obstacle, and immediately starts
the execution of the hold control.
If at step 4l it is decided that the lapse
~ woss/2o249 21 5 71 0 8 PCT/~95/00047
- 27 -
time T from the start of execution of the wait control
has exceeded the value Tw, the microprocessor l
considers the sudden reduction of the received signal
level as having not been caused by an obstacle, ends the
execution of the wait control, and starts to execute the
sweeping procedure in order to search for the satellite
up to an angle range of 360 degrees.
If it is decided that the new received signal
level L is smaller than the threshold Lt but larger than
the threshold Lm (step 39), the microprocessor 1
e~mines if the status flag F is 1 (step 42). If the
status flag F is zero, the microprocessor 1 changes it
to 1 (step 43), and goes through the step 44 for the
waiting state and goes back to step 36. After then,
when detecting that the status flag F is 1 at step 42,
the microprocessor 1 ends this wait control and starts
the differentiation control. The reason why the status
flag F is employed is to enhance the tracking ability by
immediately executing the differentiation control
without executing the sweeping procedure because the
tracking error may be regarded not so large when the
received signal level L does not exceed the threshold Lt
but exceeds the threshold Lm twice successively.
The sweeping procedure which the micro-
processor 1 executes will be described with reference tothe flowchart of Fig. 6. This sweeping procedure is
used to search for the direction of the satellite when
the received signal level L does not exceed even the
W095/20249 215 7 1~ 8 pcTl~s~lc~o17
- 28 -
threshold Lm which is a considerably low value relative
to the peak value (for example, 50%), or when a large
tracking error continuously occurs over a certain
period, or in an extreme case when it is decided that
5 the satellite has been tracked-off or when the initial
tracking operation starts immediately after the power
supply. ~
When starting to execute the sweeping
procedure, the microprocessor l causes the antenna to
rotate left and right repeatedly about the present
rotation angle up to a ~o~im-1m range of + 5 degrees,
detects the received signal level during the antenna
rotation and decides whether the received signal level
exceeds the threshold Lb or not (step 51). If the
lS received signal level is smaller than the threshold Lb,
the microprocessor l executes the next step 52, where
the received signal level is detected while the antenna
is being caused to rotate left and right repeatedly
about the current rotation angle up to a ~ l~ range
of + 20 degrees and it is decided whether the received
signal level exceeds the threshold Lb. Thereafter,
similarly the microprocessor stepwise changes the
rotation range of the antenna to + 90 degrees, 360
degrees and performs the sweeping procedure for each
range of rotation until the received signal level L
exceeds the threshold level Lb. If the received signal
level L is decided as exceeding the threshold Lb at each
of the steps 5l to 54, the microprocessor l stores the
~ W095/20249 ~ 15 7 1 0 8 PCT/~/00047
- 29 -
information of the rotational direction of the antenna
(step 55) and starts to execute the differentiation
control.
Each of the steps 51 to 54 is expressed by a
single step for convenience of explanation. However,
each of those steps specifically has an array of units
of three different steps each, arranged in each rotation
direction. The number of units is equal to the ratio of
(maximum rotation angle/unit rotation angle), and those
three different steps are steps for rotating the antenna
by a unit angle, steps for detecting the new received
signal level and steps for comparing the received signal
level L and the threshold Lb.
- According to this embodiment, when the
detected received signal level L is larger than the
threshold Lb, the tracking azimuth is changed to
increase the received signal level L. If the detected
received signal level exceeds another threshold ~t which
is larger than the threshold Lb and when the rate of
change of the preceding tracking azimuth is smaller than
a certain threshold, it is decided that the antenna body
is substantially precisely directed toward the
satellite, or in a good tracking state, and the tracking
azimuth is maintained constant by the hold control.
Thus, the wasteful tracking operation can be omitted by
the addition of this hold control.
However, according to this tracking system for
the radio wave from the satellite, when the received
WosS20249 1 a 8 - PCT/~9~/00047
signal level is suddenly decreased close to about noise
level by the rapid increase of the tracking error due to
a rapid turn of the mobile means, there is the fear that
the tracking operation for the radio wave cannot be
continued. Hereinafter, this sitFation is called
"tracking-off". In this embodiment, when the received
signal level L is reduced to be smaller than the
threshold Lb, it is decided that this tracking-off is
brought about. According to this embodiment, when this
tracking-off occurs, a sweeping mode is added in which
the satellite is searched for, while the antenna body is
being turned with a vibrating movement, with its
vibration amplitude gradually increased, about the
tracking azimuth at which the antenna is directed when
the tracking-off occurs.
The tracking-off is caused not only by the
rapid turn of the mobile means but also when the mobile
means enters in the shadow of an obstacle such 8S a
mountain, tree or building even on a straight road. If
this tracking-off is caused by an obstacle, the tracking
azimuth of the antenna may be deviated far away from a
proper value by the start of the sweeping mode. Thus,
in this embodiment, an angular velocity sensor is
provided, and the detected value therefrom and its
integrated value are used to decide whether the
tracking-off is caused by the rapid turn of the mobile
means or by an obstacle.
According to the tracking system of this
~ W095/20249 215 71~ 8 - PCTt~95/00047
- 31 -
embodiment, when the tracking-off is caused by the rapid
turn of the vehicle, the sweeping mode is im~e~i~tely
started. However, in this sweeping mode, the tracking
azimuth about which the antenna is turned with a
vibrating movement may be largely deviated from a proper
value as the mobile means rapidly turns. Therefore, if
the time in which the antenna is again directed toward
the satellite is tried to be reduced under the presence
of such a large deviation, the antenna is required to
turn faster over a large range of amplitude. As a
result, it is necessary to provide a turning mechanism
of which the structure is solid enough to endure a large
load, but it becomes large-sized, weighty and expensive.
According to the differentiation control, the
antenna is repeatedly turned over a certain range of
angle. The antenna is got to be rotated at higher speed
over this certain range of angle as the increment of the
received signal level per unit angle relative to the
preceding rotation becomes larger. In addition, as
described above, if the received signal level is higher
than the threshold Lt which is larger than the threshold
Lb and if the preceding rotation velocity V of the
antenna is smaller than a certain threshold Vth, the
antenna is regarded as having been substantially
precisely directed toward the satellite, or as being in
a good tracking state, and the tracking azimuth is fixed
by the hold control. In this hold control, the
threshold Lt is defined as a ratio to the m~jmllm
w09s/20249 ~51 ~ PCT/~95/OQo47
- 32 -
received signal level which is changed to a detected
larger received signal level.
In the second embodiment of the invention, the
sweeping mode in the first embodiment is replaced by a
searching mode in which the sate,~lite direction is
presumed. In the second embodiment, the microprocessor
l has a vehicle turning angle detection routine which is
executed in a time-division way in parallel with the
above radio-wave tracking control and a radio-wave
tracking routine which is executed in parallel with the
former routine. In the vehicle turning angle detection
routine, the sampled values of angular velocity are
successively read from the buffer memory of the
input/output interface circuit 6 and integrated to
produce the integrated value of the angular velocity, or
the rotation angle of the vehicle. This value is
written in an incorporated memory. In this vehicle
turning angle detection routine, if the hold control is
being executed in the radio-wave tracking routine which
is performed in parallel with the vehicle turning angle
detection routine, the detected turning angle of the
vehicle is reset to zero.
In the vehicle turning angle detection
routine, the search routine is started when a turning
angle above a certain threshold is detected under the
condition that the hold control is not made in the
radio-wave tracking routine.
Fig. 7 shows the relation between the turning
2157108
OsS/20249 PCT1~95tOo047
- 33 -
angle of the mobile means and the tracking azimuth of
the antenna. When the vehicle is turned by ~, the
tracking azimuth of the antenna is also deviated by ~.
Fig. 8 is a waveform diagram o the angular
S velocity (A) which occurs when the vehicle is turned by
~ and which is detected by the angular velocity meter 7,
its integrated value (turning angle) (B), the center
value (C) of the range of the tracking azimuth ~ of the
antenna body AT which is set by the search routine that
is started under the tracking-off, the sweep angle
amplitude (D) of the tracking azimuth range around the
center of tracking angle, and the sweeping velocity (E)
with respect to time. If a good tracking state is kept
until the vehicle is started to turn, the microprocessor
1 is executing the hold control. In this hold control,
the integrated value of the angular velocity detected by
the angular velocity meter 7 is reset to zero with a
certain period, and thus an accumulation error can be
prevented from being caused by the error of the angular
velocity meter 7.
When the vehicle starts to turn, the antenna
is deviated out of the good tracking state at the
direction indicated by a chain line with one dot. At
this time, the radio-wave tracking operation according
to the differentiation control is started in place of
the hold control. After the start of the radio-wave
tracking operation, the integrated value of the angular
velocity (or the turning angle) is stopped from being
woss/20249 2~S7 ~08 PCTI~5/OOW7 ~
- 34 -
reset to zero and starts to increase. If the vehicle
turns suddenly, the antenna cannot follow the radio wave
from the satellite. At this time, if the received
signal level is reduced below the threshold Lb, giving
rise to the tracking-off, the search routine is started
to execute in place of the radio-wave tracking routine.
If this tracking-off is caused at the time indicated by
the broken line in Fig. 8, the detected turning angle is
~0 when the search routine starts.
When the search routine is started, the
detected turning angle ~0 is subtracted from the current
tracking azimuth (0 degree), and the remainder (-~0) is
used as the center value of the sweeping range of the
tracking azimuth. In addition, before or after this
subtraction, a sweeping angular range ~3i which stepwise
increases, a sweeping velocity Vi and a sweeping time Ti
are fixed. While the azimuth angle of the antenna is
being stepwise changed around the set center value at
the fixed sweeping velocity, over the fixed range and
for the fixed time, repetitive decision is made of
whether the received signal level L has exceeded the
threshold Lb. During this sweeping operation, the
center value of the range of the tracking azimuth is
also repeatedly updated on the basis of the integrated
value of the angular velocity produced after the start
of the search routine. If it is decided that the
received signal level L has exceeded the threshold Lb,
the radio-wave tracking routine is resumed in place of
2157108
~9~/20249 ^ PCT/~95/000~7
- 35 -
the search routine. If the received signal level is
still smaller than the threshold Lb even after a
predetermined time Tmax has elapsed from the start of
the search routine, the final-stage search is started in
which the antenna AT is rotated within an angular range
up to 360 degrees.
Fig. 9 is a flowchart for one example of the
search routine which the microprocessor 1 executes.
When the search routine is started to execute, the
microprocessor 1 resets the incorporated timer (step
61), and subtracts the detected turning angle ~0 of the
mobile means from the tracking azimuth at which the
tracking-off occurs so that the remainder -~0 is used as
the center value of the sweeping range (step 62). Then,
the microprocessor 1 decides whether the lapse time T
from the start of the search operation has arrived at
the time Tmax at which the final-stage search should be
performed (step 63). If it is decided that the lapse
time has not yet arrived, the microprocessor 1 sets, in
addition to the lapse time T from the start of the
search operation, the stepwise increasing sweep angular
range ~i, the sweeping velocity Vi and the sweeping
time Ti (step 64).
Thereafter, the microprocessor 1 decides
whether or not the received signal level L has exceeded
the threshold Lb, while the angular range of -~0 + ~i is
swept at the velocity Vi (step 65, step 66). If the
received signal level is smaller than the threshold Lb,
W095/20249 2 ~ $ ~ i ~ 8 PCTl~95/OQ0~7 ~
- 36 -
the microprocessor 1 subtracts the turning angle
variation which the mobile means has caused after the
setting of the center value from the center value -~0 of
the sweeping range which is being set, and sets the
S remainder as a new center value (step 67). Then, the
microprocessor 1 decides whether or not the sweeping
time has exceeded the time Ti (step 68). If the
decision result is no, the routine goes back to step 65,
and the microprocessor 1 repeats the step 65 to step 68.
If the sweeping time has exceeded the set time Ti, the
microprocessor 1 executes step 63 and step 64 where the
sweeping angular range ~i, sweeping velocity Vi and
sweeping time Ti are once increased by a unit amount,
and then it repeats the step 65 to step 68.
If deciding that the received signal level L
has exceeded the threshold Lb at step 66, the micro-
processor 1 stores the current tracking azimuth (step
70) and starts the radio-wave tracking mode of the
differentiation control. If detecting that the lapse
time T from the start of the search control has exceeded
the certain time Tmax at step 63, the microprocessor 1
changes the tracking azimuth over an angular range of
360 degrees until the received signal level L exceeds
the threshold Lb (step 69). If detecting that the
received signal level L has exceeded the threshold Lb,
the microprocessor 1 stores the tracking azimuth at
which the received signal level has exceeded the
threshold Lb (step 70), and again executes the
~ W095/20249 21~ 710 8 PCT/JP9S/00017
- 37 -
radio-wave tracking mode of the differentiation control.
The step 69 is also executed immediately after the power
supply for the satellite-broadcast receiving antenna
apparatus is turned on.
S This invention is not limited to the above
embodiments. The above embodiments can be modified in
various ways.
In the differentiation control, the rotation
velocity is made proportional to the increment of the
received signal level which occurs in the preceding
rotation over a certain angle. However, the rotation
velocity can be made proportional to the square of the
increment or other proper functional relations can be
established for the rotation velocity. Also, the
increment of the received signal level over the above
certain angle may be replaced by the increment per any
arbitrary unit angle which is different from the above
certain angle, for example, per 1 or per 10.
The integrated value of the angular velocity
is detected together with the angular velocity as
described above, but it can be omitted depending on the
kind of the mobile means and the detection precision of
the angular velocity.
Only when it is decided that the tracking
- 25 state by the radio-wave tracking means has been deviated
out of the good tracking state, the integration of the
stored angular velocity may be started a certain time
early, so that it is possible to detect the turning
wogs/202492~$ ~ 10 8 l PCT/~95100W7 ~
- 38 -
angle that the mobile means has turned i~e~i~tely
before the tracking-off.
In addition, the good tracking state may be
detected only from the magnitude of the received signal
level. '~
The turning angle of the"~obile means before
or after the tracking-off occurs may be detected by
starting the integration from the point at which the
angular velocity has exceeded a certain threshold.
When the tracking-off occurs under the
condition that several most recent values are stored
after periodically integrating the angular velocity
irrespective of the received state, the amount of change
of the integrated value stored immediately before that
may be detected so that it is possible to detect the
turning angle of the mobile means at which the tracking-
off is caused.
After the start of satellite searching
operation, the correction of the center value of the
tracking azimuth range can be omitted in order that the
time necessary for the integration can be reduced.
The sweeping amplitude angle and the sweeping
velocity are not increased stepwise, but may be
increased smoothly.
The pulse motor may be replaced by a
combination of a DC motor and an encoder.
The single-axis tracking system for only the
azimuth has been described above. However, if
~ W095/20249 2 1~ 7 1 0 8 PCT/~95/00047
- 39 -
necessary, the tracking operation for the elevation can
also be made in the tracking control apparatus of the
invention.
The tracking control apparatus of the
invention is not limited to the satellite-broadcast
receiving antenna, but can be applied to other antenna
apparatus for receiving or transmitting a radio wave
from or to another proper stationary satellite or moving
satellite such as a co~lln; cation satellite.
Moreover, the tracking control apparatus of
the invention is not limited to the satellite-broadcast
receiving antenna apparatus installed on a car, but can
be applied to that installed on a vessel, a train or
other mobile means.
INDUSTRIAL APPLICABILITY
As described in detail above, the tracking
control apparatus of the invention has the differen-
tiation control executing means which causes the
satellite-broadcast receiving antenna to turn by a
certain angle at a time at a higher rotation velocity as
the increment of the received signal level per unit
angle which is associated with the preceding rotation
becomes larger. Therefore, a high tracking ability can
be realized.
In addition, the tracking control apparatus of
the invention detects the angular velocity and its
integrated value at which the received signal level is
W095/20249 7 108 - PcT/~g~/o~n~7 ~
- 40 -
suddenly reduced, and immediately starts proper control
according to whether this sudden reduction of the
received signal level is caused by an obstacle or by
rapid turning of the vehicle. Therefore, a further high
tracking ability can be achieved.
Moreover, when the tracking-off occurs, the
tracking control apparatus of the invention corrects the
current tracking azimuth by use of the turning angle of
the mobile means at which the tracking-off is caused,
and causes the range of the tracking azimuth to be swept
around this corrected value over an amplitude which is
increased with lapse of time, so that the satellite is
searched for. Therefore, the possibility that the
center value of the sweeping range coincides with the
direction of the satellite is higher than in the prior
art in which such correction by the turning angle is not
made. Thus, the time necessary for the direction of the
satellite to be again caught under the low-speed and
simple turning mechanism can be reduced as compared with
the prior art.
Also, since the sweeping amplitude, prefer-
ably, the sweeping velocity can be gradually increased,
the consumption power can be reduced together with the
reduction of the time necessary for again catching the
satellite.
Moreover, if the tracking-off is caused only
by an obstacle while the mobile means is running on a
straight road, the sweeping for searching is started to
_ wossl2o24s PCT/JPg5~0017
-- 2157108
- 41 -
be made around the current tracking azimuth since the
turning angle of the mobile means is zero. Thus, it is
possible to increase the possibility that the direction
of the satellite can be again caught at the instant when
the effect of the obstacle disappears.
Furthermore, even when the tracking-off is
caused by simultaneous occurrence of an obstacle and
turn of the mobile means, proper control can be made
without discriminating the causes.