Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-28
2003-07-08
Urban, Edward F. (Department: 2685)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S332000, C455S010000, C455S517000
Reexamination Certificate
active
06590875
ABSTRACT:
REFERENCE TO RELATED APPLICATIONS
The present invention claims priority from Japanese Patent Application No. 10-374508 filed Dec. 28, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio data communication system in which in data communication utilizing a radio transmission channel, data communication processing on the center side can be continued even if a radio channel is disconnected and data communication is interrupted, by obtaining information on a period where data communication is interrupted, and more particularly, to a radio data communication system in a transportation system such as subway, i.e., a radio data communication system in which a radio communication terminal moves to a radio data communicable section (station or the like) and a radio data incommunicable section (tunnel or the like) alternately, and a period to pass through the radio data incommunicable section can be predicted with a certain level of precision.
2. Description of Related Art
A conventional radio data communication method will be described with reference to FIG.
2
. In
FIG. 2
, a mobile gateway
202
stores the content of data communication with an application server
201
without changing the communication speed. A network
203
uses an existing radio communication network (e.g. PIAFS: PHS Internet Access Forum Standard). Data communication is performed by using a predetermined communication procedure between the application server
201
and a radio communication terminal
204
.
The conventional mobile gateway
202
stores data communication content without consideration of communication speed with the application server
201
. The mobile gateway
202
has a function to store the content of data communication when communication with the radio communication terminal
204
is interrupted, and when the communication with the radio communication terminal
204
is restarted, simply transmit the stored content of data communication to the radio communication terminal
204
. This prevents duplexing of communication procedure (repeating communication from the start between application server and terminal) due to disconnection of communication with the radio communication terminal
204
.
However, the conventional radio data communication system has following problems.
A first problem is that in a case where the radio communication terminal
204
becomes incommunicable in some period, the mobile gateway
202
, which is not informed of the incommunicable period, cannot change the speed of communication with the application server
201
.
A second problem is that in a case where the radio communication terminal
204
becomes incommunicable in some period, as the mobile gateway
202
stores the content of communication from the application server
201
without changing the communication speed, if a predetermined period for each application program has elapsed, the application server
201
cannot continue the sequence of communication.
In a radio data communication system having the conventional mobile gateway
202
with the first and second problems, the transmission efficiency is degraded and the application server
201
is overloaded in the following case. As shown in
FIG. 12
, radio data communication may include an incommunicable section when a radio communication terminal
1207
passes through a tunnel. The time for the terminal to pass through the incommunicable section is an incommunicable period. Conventionally, this incommunicable period is not known on the center side, and the application server suspends communication by using a timer unique to the application program, and enters communication non-restorable status. Accordingly, when the radio communication terminal
1207
has passed through the tunnel and become a communicable status, the communication before the suspension cannot be continued, and communication and application program must be started again from the initial status. Such problem frequently occurs when the terminal moves by subway where communicable and incommunicable sections repeatedly come alternately in a short period. However, in movement by subway, the period of movement is stable in comparison with movement by private car and on foot, and a period between entrance and exit of a tunnel can be easily predicted. By utilizing these factors, a period notification device
1205
which transmits period information on a period for a train to pass the tunnel (the period from a point where the train enters the tunnel and a point where the train goes out of the tunnel and enters a communicable status) by a weak radio wave is placed around the entrance of the tunnel. A radio communication terminal
1207
receives the period information and sends the period information to a mobile gateway in a center
1201
in radio data communication. The mobile gateway controls (delays) the communication time with the application server based on the period information, to prevent the application server from entering a communication nonrestorable status as in the case of conventional system.
SUMMARY OF THE INVENTION
The present invention has its object to provide a radio data communication system in which a mobile gateway continues communication with an application server in expectation that a radio communication terminal restores connection after elapse of incommunicable period.
According to one aspect of the present invention, in data communication utilizing a radio transmission channel, data communication processing can be continued on the center side even if data communication is interrupted due to disconnection of radio channel, by obtaining a period where data is interrupted in advance. More specifically, in a situation where a radio communication terminal moves through a radio data communicable section (station or the like) and a radio data incommunicable section (tunnel or the like) alternately as in subway transportation and a period to pass the radio data incommunicable section can be predicted with a certain level of precision, a device to transmit information on a period necessary for passing the tunnel or the like is placed in front of the tunnel, then the mobile gateway of the present invention reduces the communication speed, and performs communication with an application server on the center side taking the place of the radio communication terminal (client) in correspondence with the period. Thus the communication between the application server and the client application program can be continuously performed without time-out in the application server on the center side.
That is, provided is a radio data communication system comprising: an application server provided in a center; a plurality of radio communication terminals each performs data communication with the application server by utilizing a radio communication channel while moving; means for providing predicted disconnection period information, on radio channel disconnection caused when the radio communication terminal moves to a specific position; delayed communication means for, when it is predicted that the radio communication terminal moves to the specific position, performing communication processing taking the place of the radio communication terminal for a period indicated by the disconnection period information, responding to the application server, storing processed communication content, and when the period indicated by the disconnection period information has elapsed, transmitting the stored communication content to the radio communication terminal.
It is preferable that the delayed communication means has means for reducing the speed of communication with the application server when the delayed communication means performs the communication processing taking the place of the radio communication terminal and when it transmits the stored communication content to the radio communication terminal. In this case, it is preferable that the delayed communication means has means for determining a period where the
Foley & Lardner
NEC Corporation
Smith S.
Urban Edward F.
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