Mobile communication terminal

A mobile communication apparatus includes a wide area receiver and a cell transceiver. The wide area receiver which is operable at relatively low power receives a selective calling signal from a wide area base station that forms a wide one-way communication area. The cell transceiver operable at higher power than the wide area receiver performs two-way communication with a nearest cell base station that forms a two-way communication area. The wide area receiver is caused to operate at all times. However, when the mobile communication apparatus exists outside the wide one-way communication area, the transceiver is caused to start operating.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mobile communication system and, 
particularly, to a mobile communication terminal and a communication 
method therefor which enable two-way communication with a base station. 
2. Description of the Prior Art 
In general, mobile terminals carried by users are battery-powered. 
Therefore, it is desirable that their power consumption be minimized. 
There has been proposed a radio telephone terminal that is intended for 
such reduction in power consumption in Japanese Patent Application 
Laid-Open No. 7-303077. This radio telephone terminal is equipped with a 
detector for detecting the remaining amount of battery power. If the 
battery remaining power is greater than or equal to a predetermined 
amount, location registration is performed every time the telephone 
terminal moves to an adjacent communicable area (cell). If the battery 
remaining power is smaller than the predetermined amount, the user is 
merely informed of non-effectiveness of location registration. Further, 
the time interval of reception of control signals from a base station and 
that of location registration are varied in accordance with the battery 
remaining power, to reduce the battery consumption and in turn elongate 
the usable time. 
However, a transmission operation for location registration requires a 
large amount of power because of driving of a high-frequency amplifier. In 
the conventional radio communication terminal as described above, because 
it is necessary to perform, on a regular basis, transmission and reception 
operations for location registration with the base station, the battery is 
consumed at a high rate and the usable time cannot be made sufficiently 
long. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a mobile communication 
apparatus which can perform two-way communication with reduced power 
consumption. 
Another object of the invention is to provide a communication method and a 
mobile communication apparatus which can reduce the frequency of execution 
of a location registration process. 
According to the present invention, a mobile communication apparatus 
includes a wide area receiver and a cell transceiver. The wide area 
receiver which is operable at relatively low power receives a selective 
calling signal from a wide area base station that forms a wide one-way 
communication area. The cell transceiver operable at higher power than the 
wide area receiver performs two-way communication with a nearest cell base 
station that forms a two-way communication area. The mobile communication 
apparatus further includes a determiner for determining whether the mobile 
communication apparatus exists within or outside the wide one-way 
communication area based on a received signal of the wide area receiver. 
The wide area receiver is caused to operate at all times. However, when the 
determiner determines that the mobile communication apparatus exists 
outside the wide one-way communication area, the transceiver is caused to 
start operating. 
According to another aspect of the present invention, a mobile 
communication system includes a plurality of mobile terminals each the 
same as the above mobile communication apparatus, a one-way communication 
system where a wide area base station forms a wide one-way communication 
area, a two-way communication system having a cellular service area which 
is formed by a plurality of cell base stations each forming a cellular 
two-way communication area, and a system controller connected to the 
one-way communication system and the two-way communication system, for 
controlling mobile communications in the wide one-way communication area 
and/or the cellular service area. 
In such a system, the communication controller of the mobile terminal 
changes a communication channel from the one-way communication system to 
the two-way communication system by transmitting a channel change request 
to the nearest cell base station while operating the wide area receiver, 
and the system controller changes a communication channel from the one-way 
communication system to the two-way communication system when receiving 
the channel change request from the mobile terminal through the nearest 
cell base station. 
Further, the communication controller of the mobile terminal changes a 
communication channel from the two-way communication system to the one-way 
communication system after disconnecting the communication with the 
nearest cell base station when the determiner determines that the mobile 
communication apparatus exists within the wide one-way communication area, 
and the system controller changes a communication channel from the two-way 
communication system to the one-way communication system when the 
communication between the nearest cell base station and the mobile 
terminal is disconnected. 
During reception waiting, a control signal that is transmitted from the 
wide area base station is received by causing the wide area receiver with 
low power consumption to operate. When necessary, two-way data 
communication is performed with a cell base station by causing the 
transceiver with high power consumption to operate. Therefore, the 
receiving process is usually executed by using the wide area receiver with 
low power consumption, whereby the frequency of high power consumption 
processes such as the location registration process that uses the 
transceiver can be reduced. As a result, useless battery consumption can 
be reduced and hence the usable time can be elongated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Communication System 
Referring to FIG. 1, a communication system is composed of a wide area base 
station 102 for forming a wide radio area 101, a plurality of cell base 
stations (CS) 104 for forming narrow radio areas (cells) 103 that are 
arranged in cellular form, and a plurality of mobile terminals (MT) 
carried by users. There are two kinds of communicable areas: a first radio 
area that belongs to both of the wide radio area 101 and the service area 
of the plurality of cells 103, and a second radio area that belongs to 
only one of those. For example, location 105A as shown in FIG. 1 belongs 
to both areas and location 105B exists outside the wide radio area 101 but 
inside the cell of the nearest cell base station 104. 
The above communication system is controlled by a system management center 
106. That is, the system-management center 106 unifies and controls the 
wide area base station 102 and the plurality of cell base stations 103. 
The system management center 106 is comprised of a two-way communication 
controller 107 that is connected to the plurality of cell base stations 
103, a wide area selective calling controller 108 that is connected to the 
wide area base station 102, a system controller 109 for controlling the 
two-way communication controller 107 and the wide area selective calling 
controller 108, and a storage device 110 for storing data received from 
the respective terminals. Further, the system management center 106 can be 
connected, via a public network 111, to the terminal of a party to 
communicate with. 
As described later in detail, when a certain mobile terminal MT exists in 
the wide radio area 101, data transfer is performed by the wide area base 
station 102 and an intermittent receiving operation is performed in the 
mobile terminal MT. Therefore, when one cell base station 103 receives a 
data transmission request that is directed to a particular mobile 
terminal, the system controller 109 transfers data to the wide area base 
station 102 which then transmits the data to the particular mobile 
terminal. 
On the other hand, when a mobile terminal MT has moved to a location that 
is inside the cell service area of the two-way communication system but 
outside the wide radio area 101 or when a transmission request has 
occurred, the mobile terminal MT performs a location registration 
operation with respect to the nearest cell base station. Then, the system 
controller 109 effects channel switching from the wide area base station 
102 to the location-registered cell base station 103 and the mobile 
terminal MT performs an intermittent receiving operation with the 
location-registered cell base station 103 and, when necessary, transmits 
data thereto. In doing so, the mobile terminal MT always detects control 
signals that are sent from the wide area base station 102. When the mobile 
terminal MT has re-entered the wide radio area 101, it finishes the 
communication with the cell base station 103. At the same time, the system 
controller 109 again effect channel switching from the location-registered 
cell base station 103 to the wide area base station 102, and the mobile 
terminal MT receives data from the wide area base station 102. 
Mobile Terminal 
Referring to FIG. 2, an antenna 201 for receiving a radio signal from the 
wide area base station 102 is connected to a wide area receiver 202. An 
antenna 203 for communication with cell base stations 104 is connected to 
a receiver 205 and a transmitter 206 via an antenna switch 204. The wide 
area receiver 202 demodulates a radio signal that is transmitted from the 
wide area base station 102 and outputs a reception signal R.sub.PG to a 
processor 207. The receiver 205 demodulates a radio signal that is 
received from the cell base stations 104 and outputs a reception signal 
R.sub.CL to the processor 207. The transmitter 206 modulates and 
power-amplifies a transmission signal T.sub.CL received from the processor 
207 and outputs a resulting radio-frequency signal to the antenna 203 via 
the antenna switch 204. 
The processor 207 serves as a decoder for decoding the wide area reception 
signal R.sub.PG and executing a synchronization process, a detector for 
calculating the error rate of decoded reception data, and a channel 
encoder/decoder (codec) for performing channel controls on the reception 
signal R.sub.CL and the transmission signal T.sub.CL, as well as realizes 
other functions and communication controls as will be described later. 
These functions and terminal controls as will be described later are 
performed by the processor 207 executing programs stored in a read-only 
memory (not shown). A memory 208 connected to the processor 207 stores a 
received message addressed thereto that is transmitted from the wide area 
base station 102, messages or data that is input by the user, fixed-form 
data to be used for making an acknowledgement of a received message, and 
other messages and data. 
Further, a display 209 such as a liquid crystal display (LCD), a keypad 
210, an informer 211 such as a speaker or beeper, and an external data 
input/output section 212 are connected to the processor 207. A reception 
message and other necessary messages are displayed on the display 209 in 
accordance with a user's instruction input through the keypad 210. The 
informer 211 makes a sound, light or vibration to the effect that a call 
has occurred. To perform two-way communication via a cell base station 
104, reception data and transmission data are exchanged via the 
input/output section 212. For example, in the case of a wireless 
telephone, a speech reception and transmission are effected by a speaker 
and a microphone through the input/output section 212, respectively. 
A power supply section 213 includes a battery and is turned on/off by a 
control of the processor 207 or by means of a power switch 214. The power 
supply section 213 generates different power supply voltages V.sub.CC1 and 
V.sub.CC2 (here, V.sub.CC1 &lt;V.sub.CC2) While the power supply voltage 
V.sub.CC1 is supplied to the wide area receiver 202 via a power controller 
215, the power supply voltage V.sub.CC2 is supplied to the receiver 205 
and the transmitter 206 for two-way communication via a power controller 
216. The power controller 215 always on/off-controls the intermittent 
receiving operation of the wide area receiver 202 under the control of the 
processor 207. Further, the power controller 216 on/off-controls the 
intermittent receiving operation of the receiver 205 and controls the 
transmission power of the transmitter 206 under the control of the 
processor 207. 
The wide area receiver 202 can operate on lower power than the receiver 205 
and the transmitter 206 for two-way communication, because neither the 
location registration nor the channel switching is necessary unlike the 
case of two-way communication and the intermittent receiving operation is 
performed at a relatively low voltage. Therefore, the wide area receiver 
202 can operate for a long time. 
Communication Control 
A communication operation of the above mobile communication terminal will 
be hereinafter described with reference to FIGS. 3-5. 
Assuming a wide area selective calling signal as shown in FIG. 3, which is 
transmitted by the wide area base station 102. The wide area selective 
calling signal includes a plurality of batches each including a sync 
signal followed by a plurality of groups. Each group is composed of a 
plurality of pairs of address section (ID) and message section (M). Each 
message section (M) includes desired message data such as a reply request 
code 301 and a message 302. 
Referring to FIG. 4, when the switch 214 is closed (S401), the power supply 
voltage V.sub.CC1 is supplied from the power supply section 213 to the 
power controller 215 which supplies power to the wide area receiver 202, 
whereby an intermittent receiving operation is started (S402). More 
specifically, the processor 207 executes a synchronization process in 
accordance with a reception signal that is received from the wide area 
base station 102. When detecting a signal including a message addressed to 
the terminal itself, that is, when detecting the receiving timing of its 
own group (see FIG. 3), the processor 207 outputs an intermittent control 
signal to the power controller 215 to render the wide area receiver 202 in 
an intermittent receiving state. The wide area receiver 202 is always in 
the intermittent receiving state and hence can always receive a signal 
from the wide area base station 102. 
The processor 207 checks whether the terminal is within the wide service 
area 101 by monitoring the error rate of a reception signal of its own 
group (S403). If it is judged that the terminal is within the wide service 
area 101 (yes at step S403), the processor 207 checks whether the self 
address is included in that group (S404). If the self address is detected 
(yes at step S404), the processor 207 stores received data of a message 
section (for instance, a message section M.sub.1 shown in FIG. 3) onto the 
memory 208 (step S405). Further it is checked whether a reply request code 
301 exists in the reception message section M.sub.1 (S406). In the case 
where the reply request is for confirmation of call acceptance, the reply 
request code 301 includes a reply destination address, i.e., a source 
address. 
If there is no reply request code (no at step S406), the processor 207 
drives the informer 211 to informs the user of the occurrence of an 
incoming call and, if the user thinks it necessary, he/she operates the 
keypad 210 so that the reception message 302 are displayed on the display 
209 (S407). The wide area intermittent receiving operation S402-S405 is 
thereafter repeated whereby the wide area receiver 202 can receive data 
that is transmitted from the wide area base station 102 at all times. 
On the other hand, if it is judged that the terminal is out of the wide 
service area 101 (no at step S403), the processor 207 starts a 
communication with a cell base station 104 by outputting a control signal 
to the power controller 216 so that the power controller 216 supplies 
power supply voltages to the receiver 205 and the transmitter 206 of 
two-way communication to activate those sections (S408). First, since the 
wide area receiver 202 is incapable of reception, the processor 207 
generates a channel change request for requesting a communication channel 
change and causes the transmitter 206 to transmit location registration 
information including the communication change request to the nearest cell 
base station 104 (S409). The cell base station 104 that has received the 
location registration information performs location registration of the 
mobile communication terminal concerned. 
Once the location registration is effected, the mobile communication 
terminal performs two-way communication with the location-registered cell 
base station 104 through the receiver 205 and the transmitter 206 unless 
it re-enters the wide service area 101 (S410-S415). More specifically, if 
the terminal is outside the wide service area 101 (no at step S411) and 
within the same cell (yes at step S412), the receiver 205 intermittently 
receives a signal that is transmitted from the location-registered cell 
base station 104 in accordance with the intermittent reception power 
control by the power controller 216 (S410) unless there comes a 
transmission request (no at step S413). In the case of transmitting data 
(yes at step S413), the user operates the keypad 210, whereupon a 
fixed-form sentence or other data stored in the memory 208 is read out and 
sent to the transmitter 206 as a transmission signal T.sub.CL, and finally 
transmitted to the location-registered cell base station 104 (S414). If 
the mobile communication terminal moves to an adjacent cell (no at step 
S412), an operation for location registration is performed with respect to 
the cell base station 104 of the adjacent cell (S415) in the same manner 
as described above and the above-described steps (S410-S415) are repeated. 
In this manner, the mobile communication terminal can receive data from 
the cell base station 104 rather than the wide area base station 102 as 
well as can transmit data when necessary. 
As described above, while the cell receiver 205 is in an intermittent 
receiving state, the wide area receiver 202 intermittently receives a 
signal from the wide area base station 102 at all times (S411). If the 
terminal is still outside the wide service area 101 (no at step S411), the 
two-way communication state is maintained, that is, communication is 
performed with the location-registered cell base station 104 (S410-S415). 
On the other hand, if it is detected that the terminal has entered the 
wide service area 101 (yes at step S411), the processor 207 generates a 
communication termination notice and the transmitter 206 transmits it to 
the cell base station 104 concerned, whereby the communication with the 
cell base station 104 is finished (S416). The processor 207 then effects a 
transition to the intermittent receiving mode with the wide area receiver 
202 (S402). A signal that is transmitted from the wide area base station 
102 is intermittently received (S402-S407) until a transmitting operation 
becomes necessary (yes at step S406). 
Two-way communication with a cell base station 104 is started in the same 
manner as described above (S408-S415) also when the reception message 
section M.sub.1 includes a reply request code 301 (yes at step S406). 
As described above, the mobile communication terminal has the function of 
always judging whether it exists within the wide service area 101. If the 
terminal is within the wide service area 101, an in intermittent receiving 
operation is performed by the wide area receiver 202. If it is detected 
that the terminal has moved outside the wide service area 101, a two-way 
communication with the nearest cell base station 104 is started and an 
operation for location registration is performed with respect to the cell 
base station 104. If it is detected that the terminal has moved into the 
wide service area 101 while a signal that is transmitted from the 
location-registered cell base station 104 is received intermittently, the 
communication with the cell base station 104 is finished and switching is 
made to the intermittent receiving channel with the wide area base station 
102. 
A channel switching control is also performed in the system management 
center 106 in link with the above-described communication operation of the 
mobile communication terminal. 
FIG. 5 is a flowchart showing a communication control operation of the 
system management center 106 of the communication system according to the 
invention. As described above, when the mobile communication terminal 
moves out of the wide service area 101, location registration information 
including a communication change request is transmitted to the nearest 
cell base station 104. Upon reception of the location registration 
information, the cell base station 104 performs location registration of 
the mobile communication terminal concerned. At the same time, the cell 
base station 104 that has performed location registration in response to 
the communication change request from the mobile communication terminal is 
transmitted to the system controller 109 via the two-way communication 
controller 107 of the system management center 106. 
When the system controller 109 has received a communication change request 
or a communication channel is disconnected (yes at step S501), the system 
controller 109 switches from the channel connecting the mobile 
communication terminal concerned to the wide area base station 102 to a 
channel connecting the mobile communication terminal to the 
location-registered cell base station 104 (S502). If the storage device 
110 has data addressed to the mobile communication terminal concerned (yes 
at step S503), the system controller 109 causes the data to be transmitted 
to the mobile communication terminal via the location-registered cell base 
station 104 (S504). During the data transmission, the system controller 
109 continues to monitor a two-way communication termination notice from 
the mobile communication terminal (S505). When the mobile communication 
terminal has moved into the wide service area 101 and a two-way 
communication termination notice has been received (yes at step S505), the 
system controller 109 switches from the channel connecting the mobile 
communication terminal to the cell base station 104 to a channel 
connecting the mobile communication terminal to the wide area base station 
102. (S506). 
Then, if the storage device 110 has data directed to the mobile 
communication terminal concerned (yes at step S507), the system controller 
109 causes the data to be transmitted to the mobile communication terminal 
via the wide area base station 102 (S508). Step S507 is also executed when 
no communication change request has been received (no at step S501). 
In the above embodiments, the processor 207 checks whether the mobile 
communication terminal concerned is within the wide service area 101 by 
using the error rate of a reception signal of its own group when receiving 
it. The wide service area check can be also performed in a similar manner 
by monitoring the electric field strength of a reception signal. 
As described above in detail, according to the invention, during signal 
reception waiting, a signal that is transmitted from the wide area base 
station is received intermittently by using the wide area receiver that is 
low in power consumption. When the mobile communication terminal concerned 
has moved out of the wide service area or when data transmission has 
become necessary, two-way communication is performed with a cell base 
station having a cellular service area. 
Therefore, the receiving process with relatively low power consumption is 
usually executed whereby the frequency of high power consumption processes 
such as the process of location registration with respect to a cell base 
station can be reduced. As a result, useless battery consumption can be 
reduced and hence the usable time can be elongated.