[Title of Invention] SPOT TRANSMISSION COMMUNICATION DEVICE AND TIME
CORRECTION METHOD THEREOF
[Technical field]
[0001]
The present invention relates to a spot transmission communication device
and a time correction method thereof.
[Background Art]
[0002]
As background art in this technical field, Japanese Patent Lairi-Open
Publication No. 2011-29756 (Patent Literature 1) can be cited.
This Publication describes that, with respect to current time information
transmitted regularly at a predetermined interval which is to be a basis, a receiving
terminal side makes correction for hardware interruption in accordance with progress
of time of the current time information and thus, time progress can be made close to
equal to progress of time indicated by the current time information transmitted
regularly at the predetermined interval.
[Citation List]
[Patent Literature]
[0003]
[Patent Literature 1] Japanese Patent Laid-Open Publication No. 2011-029756
[Summary of Invention]
[Problem to be Solved by the Invention]
[0004]
A mobile body communication device calculates detection time of a trackside
communication device on the basis of time information obtained from a mobile body
control portion which is its superior device. In order to calculate the detection time
of the trackside communication device with high accuracy, it is important that time of
the mobile body communication device and time of the mobile body control portion
are synchronized with each other.
[0005]
In prior-art time synchronization between each apparatus, clock correction or
the like is performed on the basis of a signal from a synchronization source
apparatus as the technology described in Patent Literature 1, and the time
information of the signal of the synchronization source is trusted and considered to
be without an error. However, re-transmission of a message signal or the like
occurs when a communication failure or the like occurs, and in such a case, an error
can occur in the time information of the synchronization signal.
Thus, the present invention provides a spot transmission communication
device which corrects an error which is likely to be included in the time information of
the synchronization signal.
i l s p s g E ^ w W T — F i r ^
- 2 -
[Means for Solving the Problem]
[0006]
In order to solve the above-described problem, the present invention has, in
the mobile body communication device:
a current time storage portion for storing both system time added to a latest
message received from the mobile body control portion which is a superior device
and a self timer value when the message is received;
a past time storage portion for storing, when a message has been received
prior to the latest message, both the system time of the previous message and the
self timer value when the previous message was received; and
a time synchronization portion which detects occurrence of a communication
failure from the two types of time information, that is, the system time and the self
timer value, and corrects an error of a synchronization signal.
[Advantageous Effect of Invention]
[0007]
According to the present invention, when a communication failure or the like
occurs between the mobile body control portion and the mobile body communication
device, such failure is detected, and the synchronization time can be corrected and
kept accurate.
Problems, configurations and advantageous effects other than the above will
be made apparent from description of the following embodiment.
[Brief Description of Drawings]
[0008]
[FIG. 1] FIG. 1 is an entire configuration diagram of an embodiment of the
present invention.
[FIG. 2] FIG. 2 is an explanatory view when the present invention is applied to
speed control of a mobile body.
[FIG. 3] FIG. 3 is a flowchart of timer value setting for synchronization.
[FIG. 4] FIG. 4 is an explanatory view of accuracy in synchronization between
a mobile body control portion and a mobile body communication device (no retransmission).
[FIG. 5] FIG. 5 is an explanatory view of accuracy in synchronization between
the mobile body control portion and the mobile body communication device (retransmission
other than initial communication).
[FIG. 6] FIG. 6 is an explanatory view of accuracy in synchronization between
the mobile body control portion and the mobile body communication device (retransmission
in initial communication).
[FIG. 7] FIG. 7 is a flowchart of the timer value setting for synchronization with
error detection applied.
[FIG. 8] FIG. 8 is an explanatory view of trackside communication device
detection.
- 3 -
[Mode for Carrying out the Invention]
[0009]
(Embodiment 1)
First, an entire configuration of an embodiment will be described below by
using FIG. 1.
FIG. 1 illustrates entire configurations of a spot transmission communication
device installed on a mobile body and a trackside communication device.
In a communication device transmitting/receiving control information used for
control of a mobile body (1-1) between a trackside and the mobile body, a trackside
communication device (1-16) installed on the ground performs wireless power feed
by an electric power wave from a mobile body communication device (1-7) installed
on the mobile body and conducts information transmission from the trackside
communication device to the mobile body communication device by using this power
through electromagnetic coupling using a frequency different from the electric power
wave.
[0010]
Specifically, in order to transmit road surface information such as inclination
gradient or the like to the mobile device, the road surface information is set in the
trackside communication device (1-16).
The mobile body communication device (1-7) uses signal intensity received
from the trackside communication device in order to determine entry and advance
into a communication range of the trackside communication device (1-16)
(hereinafter referred to as trackside communication device detection). That is, when
a mobile antenna (1-13) passes the trackside communication device (1-13), the
trackside communication device (1-16) transmits a message of the information by the
electromagnetic coupling to the mobile body communication device (1-7).
[0011]
At this time, the signal intensity received by the mobile body communication
device is maximized when electric center positions of the mobile body
communication device and the trackside communication device match each other
and decreases when they go apart from each other.
Thus, by setting an appropriate detection threshold value of 1 value or more, it
can be determined that the trackside communication device has been detected when
the received signal intensity exceeds the detection threshold value (see FIG. 8).
On the other hand, a spot transmission communication device installed on the
mobile body is constituted by the mobile body communication device (1-7) and a
mobile body control portion (1-2) which is its superior device. The mobile body
communication device calculates detection time of the trackside communication
device which made detection on the basis of mobile body speed information and time
information from the mobile body control portion and reports it with the message
received from the trackside communication device to the mobile body control portoT.
_4-
[0012]
Subsequently, an outline of the problem to be solved by the present invention
will be described.
The mobile body communication device (1-7) has a self timer (1-10) in its
inside but basically calculates the detection time of the trackside communication
device on the basis of the time information also from the mobile body control portion
(1-2) which is a superior device. Thus, in order to calculate the time of the trackside
communication device with high accuracy, it is important that time of the mobile body
communication device (1-7) and time of the mobile body control portion (1-2) are
synchronized with each other.
In spot transmission whose communication cover area is local, the mobile
body communication device needs to calculate time within an error of a position of
the trackside communication device at approximately 1 [m], in general. Since,
during high-speed movement, time required for advance of 1 [m] at 500 [km/h], for
example, is only 7.2 [ms], a difference in time recognized by the mobile body control
portion and by the mobile body communication device, respectively, needs to be the
above-described value or less.
[0013]
As described above, prior-art time synchronization between apparatuses is
made on the basis of a signal from a synchronization source apparatus, and though
clock correction or the like is made, occurrence of an error in the synchronization
signal itself is not considered.
However, whether it is wired or wireless, a communication error can occur in
communication due to an external or internal factor, and it is impossible to completely
suppress the communication error. For example, a communication error can occur
due to occurrence of a communication failure or the like in a communication path (1-
6) between the mobile body control portion and the mobile body communication
device.
[0014]
With regard to such phenomena, communication redundancy, that is, detection
or correction of an error can be made by correcting an error by a reed solomon code
in a communication message or by detecting an error of a message by error
detecting means such as a CRC code and then, by re-transmitting the message by
using re-transmission control or the like.
However, if an error correction code is used, a large quantity of calculation
time is required for encoding/decoding, and if communication redundancy is ensured
by the error correction by the reed solomon code or the error detecting means such
as the CRC code, an error occurs between the mobile body control portion and the
mobile body communication device and as a result, there is a concern that accuracy
of the detection time of the trackside communication device is deteriorated to the
- 5 -
contrary. That is, these methods cannot handle processing requiring real time
properties such as spot transmission in many cases.
Moreover, it" the re-transmission control is executed, the time information in the
re-transmitted message is still what it was and there is a problem that the time in the
message is delayed from actual time by time required for re-transmission.
[0015]
The present invention was made in view of the above-described points and
includes a system time management portion (1-5), a communication portion (1-3)
with the mobile body communication device, and a re-transmission control portion (1-
4) of the communication in the mobile body control portion (1-2), and in the mobile
body communication device, includes a trackside communication device detection
portion (1-12) for determining detection of the trackside communication device by
measuring signal intensity received from the trackside communication device, a
communication portion (1-8) which receives system time when management is
performed in the mobile body control portion and transmits reception information of
the trackside communication device, a re-transmission control portion (1-9) in which,
when a failure occurs in communication with the mobile body control portion, it is
reported to the mobile body control portion and re-transmission is prompted, and a
self timer (1-10) for counting time in the mobile body communication device.
Then, from the two kinds of time information, that is, the self timer value and
the system time received from the mobile body control portion, a timer value for
synchronization to be a basis of the trackside communication device detection time is
calculated, and on the basis of the three kinds of time information, that is, the self
timer value, the system time, and the timer value for synchronization, communication
redundancy with the mobile body communication portion is ensured and the
detection time of the trackside communication device is calculated with high accuracy
by performing the following operations (a), (b), and (c):
[0016]
(a) The mobile body communication device stores the system time received
from the mobile body control portion, the self timer value at communication reception,
and the timer value for synchronization each time communication is conducted and
manages them.
(b) An increase of the system time included in communication messages at
previous communication and current communication (when the latest message is
received) and an increase of the self timer value at the previous communication and
the current communication (when the latest message is received) are compared, and
the timer value for synchronization is set as follows:
If no error occurs in the increases of the both, it is determined that a
communication failure such as re-transmission or the like has not occurred in
communication, and the self timer value at message reception is set to a timer value
for synchronization.
jt-jt^ra—:JEfeE"^-iME-.E--- £ -&••" *•=£ ss^—^ft^-fr *SF -—h- f——t-m,—
- 6 -
If an error occurs in the increase of the both, it is determined that a
communication failure such as re-transmission or the like has occurred in
communication, and the self timer value at message reception is not employed as the
timer value for synchronization, and a value obtained by adding the increase in the
system time included in the communication message from the mobile body control
portion to the timer value for the previous synchronization is set to the timer value for
synchronization.
(c) If the mobile body communication device detects the trackside
communication device, it measures elapsed time to detection from the timer value for
synchronization set in the above-described (a) and (b) by the self timer. Then, this
elapsed time measured by the self timer is added to the system time stored at the
same time as the timer for synchronization used as a reference and set to the
trackside communication device detection time.
[0017]
The above-described points will be described by referring to FIG. 1 for each of
the operations.
When the mobile body communication device (1-7) conducts communication
with the trackside communication device (1-16), it transmits the received time of the
message to the mobile body control portion (1-2) with the message.
Subsequently, the mobile body control portion (1-2) uses the communication
portion (1-3) and transmits the system time to the mobile body communication device
(1-7) through a transmission path (1-6). Moreover, the communication is subjected
to re-transmission control by the re-transmission control portions (1-4) and (1-9) in
order to ensure redundancy.
The re-transmission control uses a Stop-and-wait ARQ method or the like, for
example. In the Stop-and-wait ARQ method, means capable of examining errors
such as a CRC is incorporated in a message, and when the message is received on
a receiving side, if the message does not have an error, positive acknowledgement
(ACK) is replied, while if it has an error, negative acknowledgement (NACK) is replied.
A transmitting side considers the communication to be successful if it receives the
positive acknowledgement (ACK) after transmission of the message and if it receives
the negative acknowledgement (NACK), it considers the communication to be failed
and transmits the message again (re-transmission).
[0018]
Moreover, the transmitting side counts time from the transmission and if it
cannot receive either of the positive acknowledgement (ACK) and the negative
acknowledgement (NACK) by certain time, it considers the message transmission to
be failed and re-transmits the message. An upper limit in the number of retransmission
times to one message is determined in view of an environment of a
communication path so that, if a transmission apparatus or a receiving apparatus
fails, re-transmission is not to be conducted permanently.^ 7.^...r
- 7 -
In a case of wired communication as in this embodiment, the upper limit of the
number of re-transmission times is once in general, and if the transmitting side
receives a second timeout or NACK, it determines to be a failure and stops the
system.
Moreover, the communication portion (1-3) of the mobile body control portion
(1-2) also performs a reception work of a message from the mobile body
communication device (1-7), and the re-transmission control similar to the above is
executed also for this communication by the re-transmission control portions (1-4)
and (1-9).
[0019]
Subsequently, the mobile body communication device (1-7) will be described.
In Fig. 1, the mobile body communication device (1-7) includes the trackside
communication device detection portion (1-12), the communication portion (1-8) with
the mobile body control portion, the re-transmission control portion (1-9), a time
synchronization portion (1-15), and the self timer (1-10) for counting time on the basis
also of a hardware clock.
When the mobile body communication device (1-7) detects the trackside
communication device (1-16) by the trackside communication device detection
portion (1-12), it calculates the detection time and transmits it to the mobile body
control portion (1-2) through the communication path (1-6) by using the
communication portion (1-8) together with the message from the trackside
communication device (1 -16). A method of the trackside communication device
detection is to measure reception intensity from the trackside communication device
and to make determination on the basis of the intensity.
At this time, since the detection time of the trackside communication device is
used for control in the mobile body control portion (1-2), it needs to be synchronized
with the system time of the mobile body control portion (1-2). Thus, the mobile body
communication device (1-7) needs to cause the system time received from the
mobile body control portion (1-2) to correspond to the self timer (1-10) in the time
synchronization portion (1-11) at reception of the system time from the mobile body
control portion (1-2).
[0020]
Regarding this, a determination method of the timer value for synchronization
will be described by a flowchart using FIG. 3.
First, in FIG. 3, at Step (3-1), the mobile body communication device (1-7)
receives a message including the system time (Tc, N) from the mobile body control
portion (1-2).
A first suffix C in Tc, N represents the system time, while a second suffix N
represents the N-th system time reception from the mobile body control portion (1-2),
and transmission timing of the message from the mobile body control portion (1-2)
- 8 -
If the mobile body communication measure (1-7) receives the system time
from the mobile body control portion, the received system time Tc, N and the self timer
value (TR, N) at the message reception are stored in a set in a current time storage
portion (1-14).
A first suffix R in TR, N represents the self timer value managed by the mobile
body communication device (1-7), while a second suffix N represents the N-th
system time reception.
If the mobile body communication device has received the system time prior to
that, the information received previously and stored in the current time storage
portion (1-14) is moved to a past time recording portion (1-15).
[0021]
At Step (3-2), whether or not it is a first system time reception from the mobile
body control portion (1-2) is determined, and if it is the first reception (that is, in a
case of Tc, o reception), the received Tc, N is set to the timer value for synchronization
(TG, N) (that is, TG,O = TR,0) at Step (3-3) and recorded in the current time storage
portion (1-14) in a set with the system time and the self timer value.
The timer value for synchronization is an expected self timer value when the
received system time (Tc, N) is created, and a first suffix G in TG, N represents the
timer value for synchronization managed by the mobile body communication device
(1-7), while a second suffix N represents the N-th system time reception.
In a case other than the first reception at Step (3-2), a difference (ATc, N)
between the system time (Tc, N) received this time and the system time (Tc, N-I)
received previous time stored in the current time storage portion (1-14) and the past
time storage portion (1-15) is calculated at Step (3-4).
At Step (3-5), a difference (ATR, N) between the self timer value (TR, N) received
this time and the self timer value (TR, N-I) received previous time stored in the current
time storage portion (1-14) and the past time storage portion (1-15) is calculated.
[0022]
At Step (3-6), a difference value between ATC, N calculated at Step (3-4) and
ATR, N calculated at Step (3-5) is compared with a specified value 1 as a threshold
value and determined whether or not out-of-synchronization has been caused by retransmission.
Specifically, the timer value for synchronization (TG, N) is determined as follows
and recorded in the current time storage portion (1-14) in a set with the system time
and the self timer value.
In a case of ATc, N -ATR, N < specified value 1, it is considered that no delay has
been caused by re-transmission and it is set to TG, N = TR, N and stored at Step (3-7).
In a case of ATc, N -ATR, N > specified value 1, it is considered that a retransmitted
message has been received and it is set to TG, N = TG, N-I + ATC, N and
stored at Step (3-8).
- 9 -
At this time, a method of determining the specified value 1 depends on
calculated position accuracy of the trackside communication device. Assuming that
a position allowable error is L [m] and a use maximum speed is V [m/s], it is
approximately the specified value 1 as a threshold value > LA/ [s].
If a difference between Tc, N and TR, N is compared with a difference between
Tc, N-I and TR, N-I instead of comparison of the differences ATc, N and ATR, N, it is:
ATc, N - ATR, N = (Tc, N - Tc, N-I) - (TR, N - TR, N-I)
= (Tc, N - TR, N) - (Tc, N-1 - TR, N-i)
and thus, it is mathematically equivalent, and equivalent calculation can be made.
[0023]
Subsequently, by using time charts in FIGs. 4 to 6, how the mobile body
control portion is synchronized with the mobile body communication device by
presence of re-transmission when the present invention is applied will be described
in terms of a relation among Tc, N, TR, N, and TG, N.
FIG. 4 is a time chart when re-transmission has not occurred, and in the
determination at Step (3-6) in FIG. 3, all the communication branches to Step (3-7)
side, the system time is synchronized with the internal timer, and the trackside
communication device detection time can be calculated without problem.
In FIG. 5, re-transmission occurred in the second communication in which Tc, 1
was transmitted. In this case, in the second communication, the difference ATR, N of
the internal timer becomes larger than the difference ATC, N of the system time only
by re-transmission delay To. Thus, in the determination at Step (3-6) in Fig. 3, it
branches to the Step (3-8) side and is subjected to correction.
Moreover, in the third communication, on the contrary, the difference ATR, N of
the internal timer becomes smaller than the difference ATc, N of the system time only
by re-transmission delay TD, in the determination at Step 3-6 in FIG. 3, it branches to
the Step (3-8) side similarly to the previous time and is subjected to correction, and
the system time is synchronized with the internal timer substantially accurately.
In the fourth communication and after, correction is not made, and the system
time is accurately synchronized with the internal timer.
[0024]
In FIG. 6, re-transmission occurs in the initial communication in which Tc, o is
transmitted. In this case, since there is no comparison target in the first reception,
an error occurs and the error continues to the second reception but synchronization
can be realized at the third reception. Such an event occurs only in the first
communication and thus, the risk can be avoided in the first communication by
transmitting the system time from the mobile body control portion in a span shorter
than usual and the like.
By executing such processing, even if re-transmission occurs due to
occurrence of a communication failure or the like, the system time can be
- 1 0 -
synchronized with the internal timer with high accuracy, and the detection time of the
trackside communication device can be calculated.
In order to perform the trackside communication device detection more
accurately, a transmission loss of the communication may be pulled in from TR, N
when TG, N = TR, N is set at Steps (3-3), (3-7), and (3-8).
[0025]
The information relating to the trackside communication device received from
the mobile body communication device is used for executing speed control or the like
by adding a speed control portion (2-17) to the mobile body control portion (2-2) as
illustrated in FIG. 2 and by combining it with speed information obtained from a car
speed detection portion (2-20) such as a speed generator and a GPS in the speed
control portion (2-17) so as to control a driving device (2-18) and a brake device (2-
19).
FIG. 8 illustrates a relational view between reception intensity received by the
mobile body communication device and passage time in passage of the trackside
communication device. A method in which a point where the reception intensity
from the trackside communication device (1-16) exceeds a detection threshold value
(8-1) is set to an entry point (8-2), a point where it falls below the detection threshold
value (8-1) to an entry point (8-3), and an intermediate point between the both to a
detection point (8-4), or a method in which a maximum point of the reception intensity
expected to be immediately above the center of the trackside communication device
is set to a detection point (8-5) is considered.
[0026]
If TG, N set as above is used, by measuring time from this TG, N to detection of
the on-trackside communication device (1-16) at all times based on an arbitrary TG, N
by the self timer and by adding the elapsed time by the self timer which has been
measured to Tc which is the system time stored at the same time as TG, N set to the
basis at the detection, even if re-transmission occurs, the trackside communication
detection time synchronized with the mobile body control portion can be calculated
with high accuracy.
According to the present invention, while redundancy by the re-transmission
control is ensured for the communication between the mobile body control portion
and the mobile body communication device, even if re-transmission occurs in the
communication, an error in time recognized by each of the mobile body control
portion and the mobile body communication device can be suppressed, and the
mobile body communication device capable of calculating the detection time of the
trackside communication device can be realized with high accuracy.
[0027]
(Embodiment 2)
In this embodiment, a variation of the embodiment 1 illustrated in FIG. 3 will be
described. _ _ _ _ ,_ , _r.. ^.r.,.—^^
-11 -
Specifically, in case of occurrence of abnormality in the system time itself
caused by clock abnormality in the mobile body control portion (1-2) in FIG. 1, a new
step is provided after Step (3-4) in FIG. 3.
Specifically, as illustrated at Step 7-9 in FIG. 7, ATc, N is compared with a
specified value 2 as a new threshold value so as to conduct an inspection of the
clock or more.
[0028]
Here, regarding how to determine the specified value 2, since there is a
concern that ATc, N might be delayed from a forecast value depending on a load state
of the mobile body control portion (1-2), it can be set to the specified value 2 =
forecast value ± d assuming that fluctuation time of processing time by a
maximum/minimum load state is d.
At this time, d needs to be set smaller than the fluctuation time by an assumed
failure mode. For example, when time is calculated on the basis of a clock
generated by a crystal oscillator, if the failure mode of the crystal oscillator forecasts
that a frequency of the clock is reduced to a half or less, the forecast value d may be
set to approximately a twice or less of a communication time interval.
[0029]
When ATc, N is to be compared with the specified value 2, since it is necessary
to know a transmission interval of the system time to some degree, the transmission
timing of the system time is preferably a regular constant interval.
[0030]
Moreover, in order to conduct an inspection so as to check abnormality in the
self timer such as clock abnormality of the mobile body communication device (1-7),
monitoring may be conducted such that a new branch may be further added to the
branch in Step (3-6) in FIG. 3 so that increases in the respective system time and the
respective self timer values at message reception are compared between the latest
message and the previous message, and if the compared value is larger than the
maximum delay time by re-transmission, it is determined that abnormality occurs in
the self timer (Step 7-6 in FIG. 7).
[0031]
The present invention is not limited to the above-described embodiments but
includes various variations. Moreover, it is possible to replace a part of the
configuration of one embodiment with the configuration of another embodiment.
Furthermore, the above-described embodiments are described in order to explain the
present invention to be easily understood, and the present invention is not
necessarily limited to those provided with all the described configurations.
For example, the method and allowable margin of setting the default value can
be appropriately changed in accordance with the use environment of the
communication device, the characteristics of the mobile body and the like, and it is
natural that the configurations of the mobile body communication device and the
-^,rj^^^^:rjr~jn>ir^£^ *m^v? * ^-^*~*
- 1 2 -
trackside communication device can include various variations according to the type,
size and the like of the mobile body.
Moreover, the present invention has been described on the premise of a
communication failure by re-transmission but it is needless to say that an apparent
delay occurrence phenomenon other than re-transmission of a message can be also
handled.
Furthermore, the present invention can be applied not only to the
communication device for mobile body control but widely to communication devices
and systems that cannot employ error correction codes and the like regardless of
necessity of time synchronization between apparatuses.
[Reference Signs List]
[0032]
1-1 mobile body
1-2 mobile body control portion
1-3 mobile body control portion communication portion
1-4 mobile body control portion re-transmission control portion
1-5 system time management portion
1-6 communication path between mobile body control portion - mobile
body communication device
1-7 mobile body communication device
1-8 mobile body communication device communication portion
1-9 mobile body communication device re-transmission control portion
1-10 self timer
1-11 time synchronization portion
1-12 trackside communication device detection portion
1-13 mobile antenna
1-14 current time storage portion
1-15 past time storage portion
1-16 trackside communication device
2-1 mobile body
2-2 mobile body control portion
2-3 mobile body control portion communication portion
2-4 mobile body control portion re-transmission control portion
2-5 system time management portion
2-6 communication path between mobile body control portion - mobile
body communication device
2-7 mobile body communication device
2-8 mobile body communication device communication portion
2-9 mobile body communication device re-transmission control portion
2-10 self timer
- 1 3 -
2-12
2-13
2-14
2-15
2-16
2-17
2-18
2-19
2-20
8-1
8-2
8-3
8-4
8-5
trackside communication device detection portion
mobile antenna
current time storage portion
past time storage portion
trackside communication device
speed control portion
driving device
brake device
car speed detection portion
detection threshold value
entry point
advance point
intermediate point between entry point and advance point
reception intensity maximum point

[Claim 1]
A spot transmission communication device for conducting spot transmission
communication between a trackside communication device installed on the ground
and a mobile body communication device installed on a mobile body through an onboard
antenna installed on the mobile body and detecting the trackside
communication device by measuring intensity of a signal received from the trackside
communication device, wherein
a mobile body control portion connected to the mobile body communication
device through a transmission path is provided on the mobile body;
the mobile body control portion has a communication portion for transmitting a
message to the mobile body communication device and a system time management
portion for creating system time to be added to the message;
the mobile body communication device has:
a self timer for creating a self timer value;
a current time storage portion for storing both the system time added to a
latest message received from the mobile body control portion and the self timer value
when the message is received;
a past time storage portion for storing, when a message has been received
prior to the latest message, both the system time of the previous message and the
self timer value when the previous message was received; and
a time synchronization portion for creating a timer value for synchronization
which is time for position calculation of the trackside communication device;
in the time synchronization portion, occurrence of a communication failure
between the mobile body communication device and the mobile body control portion
is detected from the respective system time added to the latest message and the
previous message from the mobile body control portion and the self timer values
when the respective messages were received, and the synchronization timer is
corrected in accordance with presence of occurrence of a failure; and
detection time of the trackside communication device is estimated by using the
corrected synchronization timer.
[Claim 2]
The spot transmission communication device according to claim 1, wherein
detection of occurrence of a communication failure between the mobile body
communication device and the mobile body control portion is made by comparing
increases of the respective system time in the latest message and the previous
message and the time of self timer values when the respective messages were
received and if a comparison value is not less than a specified value 1, it is detected
that the communication failure has occurred;
- 1 5 -
the specified value 1 is assumed to be a value larger than a value obtained by
dividing a position allowable error of the mobile body by a maximum speed of the
mobile body; and
the synchronization timer is to correct a value obtained by adding an increase
of the system time to the timer value for synchronization of the previous message as
a timer value for synchronization.
[Claim 3]
The spot transmission communication device according to claim 1 or 2,
wherein
detection of occurrence of a communication failure between the mobile body
communication device and the mobile body control portion is made by comparing
increases of the respective system time in the latest message and the previous
message and the time of self timer values and if a comparison value is less than the
specified value 1, it is detected that the communication failure has not occurred; and
as the timer value for synchronization, the self timer value when the latest
message was received is employed.
[Claim 4]
The spot transmission communication device according to any one of claims 1
to 3, wherein
time obtained by adding a difference between the self timer value at detection
of the trackside communication device and the synchronization timer value to the
system time stored in the current time storage means is calculated as detection time
of the trackside communication device.
[Claim 5]
The spot transmission communication device according to any one of claims 1
to 4, wherein
if the message is sent from the mobile body control portion at a regular
constant interval, a value twice a processing time difference generated between a
case in which a load of the mobile body control portion is maximum and a case in
which the load is minimum is set to a specified value 2, and if an increase of the
system time added to the received message is not less than the specified value 2, it
is determined that abnormality has occurred.
[Claim 6]
The spot transmission communication device according to any one of claims 1
to 5, wherein
increases of the respective system time in the latest message and the previous
message and the self timer values when the respective messages were received are
compared, and if the comparison value is larger than a maximum delay time by retransmission,
it is determined that abnormality has occurred in the self timer.
[Claim 7]
-16-
A time correcting method of a spot transmission communication device
comprising:
a first step in which a mobile body communication device receives a message
including system time (Tc, N) from a mobile body control portion and stores the
received system time (Tc, N) and a self timer value (TR, N) when the message was
received in a set in a current time storage portion;
a second step in which whether or not a reception is a first system time
reception from the mobile body control portion is determined, and in a case of first
reception, the received system time (Tc, N) is set to a timer value for synchronization
(TG, N), and the system time and the self timer value are recorded in a set in the
current time storage portion, while if the reception is not the first reception, a
difference (ATc, N) between the system time (Tc, N) received this time and the system
time (Tc, N-I) received the previous time stored in the current time storage portion and
a past time storage portion is calculated;
a third step of calculating a difference (ATR, N) between the self timer value (TR,
N) received this time and the self timer value (TR, N-I Received the previous time stored
in the current time storage portion and the past time storage portion;
a fourth step of comparing a difference value between the (ATc, N) and the (ATR,
N) calculated at the second step and the third step with a specified value 1 as a
threshold value and determining whether or not out-of-synchronization has been
caused by re-transmission; and
a fifth step in which, in case of ATC, N -ATR, N < the specified value 1, the timer
value for synchronization is set and stored as TG, N = TR, N, while in a case of ATc, N -
ATR, N ^ the specified value 1, the timer value for synchronization is set and stored as
TG, N = TG, N-1 + ATc, N