Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-06-03
2002-10-29
Bost, Dwayne (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S560000, C455S552100
Reexamination Certificate
active
06473627
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a mobile communication system and a mobile communication method which is capable of reducing “service disable period” occurring when the communication terminal side switches systems in a communication terminal side which is capable of utilizing a plurality of radio communication system.
BACKGROUND ART
In a communication terminal which is capable of utilizing a plurality of radio communication system, when one system is switched to another system at the communication terminal side, even if these systems have similar electromagnetic wave (electric wave) environments, the operation starts from the normal initial sequences of the respective systems.
For that reason, for example, in the case where a user intends to switch from a system
1
to a system
2
, a long period of time is required until a line on the system
2
side is acquired and the service of the system
2
can be actually supplied to the user.
In more detail, as shown in
FIG. 12
, the initial sequence is roughly classified into (1) tracking in Steps
20
to
22
(in the case where an antenna having directivity is used), (2) frequency correction in Steps
23
to
24
, and (3) evaluation of a radio line in Steps
25
to
27
. Hereinafter, the respective processes will be described with reference to specific examples.
FIG. 11
shows an arrangement of a conventional mobile communication terminal. In the figure, reference numeral
1
denotes an antenna for transmitting and receiving electromagnetic waves;
2
, a tracking unit for directing the orientation of the antenna
1
to an arrival direction of the electromagnetic waves;
3
, a receiver for demodulating the received electromagnetic waves;
4
, a transmitter for modulating the contents to be transmitted to electromagnetic waves;
5
, a handset for conducting indication for the user or receiving an instruction from the user;
6
, a controller for controlling the above-mentioned tracking unit
2
to the handset
5
; and
100
is a communication terminal.
Also, in the figure, reference numeral
61
denotes a system switching function section;
62
is a control function section for the system
1
; and
63
is a control function section for the system
2
.
The conventional communication terminal operates as follows: Upon turning on a power supply of the communication terminal
100
, the controller
6
first instructs an initial acquirement frequency inputted from the handset
5
by the user (or stored in the controller
6
) to the receiver
3
to conduct “an instruction of wide-band acquiring operation” of an electromagnetic wave which is relatively wide in received band (in the figure, those instructions are mentioned as “receiver control signal”).
Also, the controller
6
instructs the tracking unit
2
to “search” the arrival direction of the electromagnetic waves simultaneously. upon receiving this instruction, the tracking unit
2
successively monitors a receive state signal (a signal indicative of a receive state such as a receiving signal strength or a bit error rate) obtained from the receiver
3
while changing the orientation of the antenna
1
, thus controlling the direction of the antenna
1
so as to direct the antenna
1
to a direction excellent in the electromagnetic wave state. Further, the tracking unit
2
notifies the controller
6
of “completion of search” after the antenna
1
has been directed in the direction excellent in the electromagnetic wave state. After that, the tracking unit
2
controls the antenna so as to maintain the direction excellent in the electromagnetic wave state.
Subsequently, upon being notified of “completion of search” by the tracking unit
2
, the controller
6
transmits the receiver
3
the receiver control signal which is called “frequency correction” to switch from the receive of wide-band electromagnetic waves to the receive of narrow-band electromagnetic waves with respect to the same initial acquirement frequency and to start a frequency shift correction of the subject communication terminal
100
. The controller
6
confirms that the correction can be sufficiently made from the receive state signal obtained by the receiver
3
at a timing when the correction is completed.
Finally, the controller
6
transmits to the receiver
3
a frequency to be received for actually conducting communication which is inputted from the handset
5
by the user (or stored in the controller
6
), as well as the receiver control signal which is called “normal receiving operation”, thereby starting to receive the frequency for conducting communication (in this situation, the receiver
3
conducts the narrow-band receive and corrects the frequency by use of a correction value of the frequency shift which has been obtained in advance). The controller
6
evaluates a state of the line on the basis of the receive-state signal obtained at this time and then permits the user to conduct communication upon confirmation that sufficient receive can be made.
The communication terminal in the above-described conventional mobile communication system suffers from such a problem that when the user is switching from one system to another system, the acquiring operation of an artificial satellite is caused to be made as described above although the same direction must be maintained as it is because the same artificial satellite is used.
Also, there arises such a problem that the above-described frequency correction is caused to made, though the same frequency correction is applied because the same artificial satellite is used, the base station also uses the same reference frequency, and a deviation of frequency is the same.
Further, there arises such a problem that the above-described evaluation of a radio line is conducted although the possibility of having substantially the same quality of the radio line is high because the same artificial satellite is used, and the base station is also the same.
For those reasons, there arises such a problem that a period of time during which communication service is disenabled occurs for about 20 seconds in the above-described conventional communication terminal at the time of switching from one system to another system.
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a mobile communication system and a mobile communication method which enable a communication terminal to remarkably reduce an initial sequence by the application of a fact that systems to be switched therebetween have very similar electromagnetic wave environments.
In other words, in recent years, a large number of radio communication systems have been proposed, and commercial services have been started. Up to now, a communication terminal has been provided for each of those communication systems, however, a demand that a plurality of systems are utilized by one communication terminal is being increased. The present invention relates to a communication terminal which is capable of utilizing a plurality of systems, and an object of the present invention is to obtain a communication terminal by which the user can quickly receive a service with a reduction in a period of time required for switching from one system to another system.
DISCLOSURE OF THE INVENTION
A mobile communication system according to the present invention comprises: a radio base station for transmitting and receiving the electromagnetic waves of a first radio communication system and the electromagnetic waves of a second radio communication system; and a communication terminal having an antenna for transmitting and receiving the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system, a tracking unit for directing the orientation of the antenna to an arrival direction of the electromagnetic waves, a receiver for demodulating the electromagnetic waves of the first radio communication system and the electromagnetic waves of the second radio communication system which are recei
Bost Dwayne
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
Trinh Sonny
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