Radio communication system

A radio communication system includes a radio port, a fixed radio terminal, a memory unit, a notification unit, and a mobile radio terminal. The radio port communicates in a service area by using a predetermined radio frequency which is multiplexed by time division into a plurality of radio channels. The fixed radio terminal is stationarily set in the service area of the radio port and has a first transmission/reception unit for communicating with the radio port by using a radio channel which is permanently assigned in advance. The memory unit stores the radio channel assigned in advance to the fixed radio terminal. The notification unit provides information, including channel information stored in the memory unit, in the service area of the radio port through the radio port. The mobile radio terminal communicates with the radio port by using a radio channel not assigned to the fixed radio terminal on the basis of the channel information provided in the service area of the radio port.

BACKGROUND OF THE INVENTION 
The present invention relates to a radio communication system for 
performing communication between a radio port of a switching station and a 
fixed or mobile radio terminal and, more particularly, to a radio 
communication system capable of performing communication with both the 
fixed and mobile radio terminals through one radio port. 
Terminals used in a radio communication system are classified into fixed 
radio terminals which are stationarily set and mobile terminals whose 
setting locations change. For subscribers, fixed radio terminals must 
ensure speech lines at any time like a terminal connected to a switching 
station through a cable. Mobile radio terminals including portable 
telephones can be used to make a call while the user is walking or moving. 
However, communication is not always enabled depending on the reception 
field strength at a destination. 
FIG. 8 schematically shows the configuration of a conventional radio 
communication system. This radio communication system performs 
communication with radio terminals in first and second service areas 
101.sub.1 and 101.sub.2. A first radio port 102.sub.1 is a communication 
port communicating with fixed radio terminals 103.sub.1 to 103.sub.3 and 
covers the first service area 101.sub.1. A second radio port 102.sub.2 is 
a communication port communicating with mobile radio terminals 104.sub.1 
to 104.sub.3 and covers the second service area 101.sub.2. A radio port 
controller 105 manages frequencies used by the radio ports 102.sub.1 and 
102.sub.2 and channels assigned for communication with the radio terminals 
103.sub.1 to 103.sub.3 and 104.sub.1 to 104.sub.3. The radio port 
controller 105 is connected to a network (not shown) and allows 
communication with another terminal through the network. 
The radio port controller 105 assigns a frequency f1 to uplinks and a 
frequency f1' to downlinks between the first radio port 102.sub.1 and the 
fixed radio terminals 103.sub.1 to 103.sub.3. In addition, the radio port 
controller 105 assigns a frequency f2 to uplinks and a frequency f2' to 
downlinks between the second radio port 102.sub.2 and the mobile radio 
terminals 104.sub.1 to 104.sub.3. Each frequency has eight time slots set 
by time division. Of these time slots, the eighth slot is used as a 
control channel while the remaining first to seventh slots are assigned 
for communication with the radio terminals 103.sub.1 to 103.sub.3 and 
104.sub.1 to 104.sub.3. These speech channels are assigned to the radio 
terminals 103.sub.1 to 103.sub.3 and 104.sub.1 to 104.sub.3 every time the 
terminals output service requests. 
The radio port controller 105 notifies the radio terminals 103.sub.1 to 
103.sub.3 and 104.sub.1 to 104.sub.3 of idle radio channels in each 
frequency as accessible slots capable of responding to a service request. 
This information is periodically broadcasted in the service areas by using 
the control channels in the corresponding frequencies. When a line must be 
ensured, each of the fixed radio terminals 103.sub.1 to 103.sub.3 and the 
mobile radio terminals 104.sub.1 to 104.sub.3 outputs a service request 
through any one of the notified accessible slots. The fixed radio 
terminals 103.sub.1 to 103.sub.3 and the mobile radio terminals 104.sub.1 
to 104.sub.3 perform communication with the corresponding radio ports 
102.sub.1 and 102.sub.2 in the first and second service areas 101.sub.1 
and 102.sub.2, respectively. A radio communication system in which 
accessible channels in each frequency are informed, and channel assignment 
is performed in accordance with service requests from radio terminals 
103.sub.1 to 103.sub.3 and 104.sub.1 to 104.sub.3 is disclosed in detail 
in the following reference ("Generic Criteria for Version 0.1 Wireless 
Access Communications System", TR-INS-001313 Issue 1 Bellcore (1993)). 
The mobile radio terminals 104.sub.1 to 104.sub.3 select a frequency with a 
high communication quality at a destination to perform communication. For 
this reason, the mobile radio terminals 104.sub.1 to 104.sub.3 and the 
fixed radio terminals 103.sub.1 to 103.sub.3 rush to take accessible 
slots. In some cases, all the accessible slots are occupied by the mobile 
radio terminals 104.sub.1 to 104.sub.3. Without idle slots, service 
requests from the fixed radio terminals 103.sub.1 to 103.sub.3 cannot be 
received, so a communication enable state cannot always be provided to the 
fixed radio terminals 103.sub.1 to 103.sub.3, like a wire terminal. 
In addition, assume that a given one of the fixed radio terminals 103.sub.1 
to 103.sub.3 and a given one of the mobile radio terminals 104.sub.1 to 
104.sub.3 have the same subscriber, i.e., the same subscriber number. When 
the given terminals are present in one area, discrimination between these 
terminals cannot be made. For this reason, in the service area of the 
given one of the fixed radio terminals 103.sub.1 to 103.sub.3, the given 
one of the mobile radio terminals 104.sub.1 to 104.sub.3 which has the 
same subscriber number as that of the given fixed radio terminal cannot 
output a service request. 
SUMMARY OF THE INVENTION 
It is the first object of the present invention to provide a radio 
communication system for allowing a fixed radio terminal to ensure a 
channel at any time. 
It is the second object of the present invention to make it possible to use 
a fixed radio terminal and a mobile radio terminal having the same 
subscriber number as that of the fixed radio terminal in the service area 
of the same radio port. 
In order to achieve the above objects, according to the present invention, 
there is provided a radio communication system comprising a radio port for 
performing communication in a service area by using a predetermined radio 
frequency which is multiplexed by time division into a plurality of radio 
channels, a fixed radio terminal stationarily set in the service area of 
the radio port, the fixed radio terminal having first 
transmission/reception means for performing communication with the radio 
port by using a radio channel which is permanently assigned in advance, 
memory means for storing the radio channel assigned in advance to the 
fixed radio terminal, notification means for notifying information 
including channel information stored in the memory means in the service 
area of the radio port through the radio port, and a mobile radio terminal 
for performing communication with the radio port by using a radio channel 
not assigned to the fixed radio terminal on the basis of the channel 
information notified in the service area of the radio port.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will be described below in detail. 
FIG. 1 shows the system configuration of a radio communication system 
according to an embodiment of the present invention. This radio 
communication system has first and second service areas 11.sub.1 and 
11.sub.2. A first radio port 12.sub.1 is a communication port 
communicating with fixed radio terminals 13.sub.1 and 13.sub.2 and a 
mobile radio terminal 14.sub.1 in the first service area 11.sub.1. In FIG. 
1, the mobile radio terminal 14.sub.1 is present in the first service 
area. However, if another mobile radio terminal enters this area, this 
mobile radio terminal communicates with the first radio port 12.sub.1. A 
second radio port 12.sub.2 is a communication port communicating with 
mobile radio terminals 14.sub.2 and 14.sub.3 and a fixed radio terminal 
13.sub.3. A radio port controller 15 manages frequencies used by the radio 
ports 12.sub.1 and 12.sub.2 and channels assigned for communication with 
the radio terminals. The radio port controller 15 is connected to an ISDN 
(Integrated Service Digital Network) which is not illustrated. 
The radio port controller 15 assigns a frequency f1 to uplinks and a 
frequency f1' to downlinks between the first radio port 12.sub.1 and the 
radio terminals 13.sub.1, 13.sub.2, and 14.sub.1 in the first service area 
11.sub.1. The radio port controller 15 assigns a frequency f2 to uplinks 
and a frequency f2' to downlinks between the second radio port 12.sub.2 
and the radio terminals 13.sub.3, 14.sub.2, and 14.sub.3 in the second 
service area 11.sub.2. The radio terminals in the service areas perform 
communication using the frequencies assigned to the radio ports in the 
corresponding areas. 
FIGS. 2A and 2B show an example of radio channel assignment of each 
frequency. Radio channel assignment of each frequency shown here is 
applied to a case wherein the fixed radio terminals are arranged as shown 
in FIG. 1. Each of the frequencies f1, f1', f2, and f2' has eight time 
slots set by time division. The frequencies f1 and f1', and the 
frequencies f2 and f2' have the same time slot assignments, respectively. 
As shown in FIG. 2A, of time slots 21 corresponding to the repetitive 
period of the frequency f1 or f1', a first time slot 23.sub.1 is 
permanently assigned for communication with the fixed radio terminal 
13.sub.1 shown in FIG. 1. A second time slot 23.sub.2 of the frequency f1 
or f1' is similarly permanently assigned to the fixed radio terminal 
13.sub.2. 
The third to seventh time slots 23.sub.3 to 23.sub.7 of the frequency f1 or 
f1' are assigned to the mobile radio terminal 14.sub.1 in the first 
service area 11.sub.1. An eighth time slot 23.sub.8 is permanently 
assigned as a control channel for transmitting various types of 
information including idle channel information. The fixed radio terminals 
13.sub.1 and 13.sub.2 arranged in the first service area 11.sub.1 
communicate with the first radio port 12.sub.1 through the corresponding 
radio channels which are permanently assigned. The mobile radio terminal 
14.sub.1 in the first service area 11.sub.1 outputs a service request 
through any one of the third to seventh time slots 23.sub.3 to 23.sub.7. 
As shown in FIG. 2B, a first time slot 24.sub.1 of the frequency f2 or f2' 
of the second radio port is permanently assigned for communication with 
the fixed radio terminal 13.sub.3 which is stationarily set in the second 
service area 11.sub.2. Second to seventh time slots 24.sub.2 to 24.sub.7 
are used as channels for mobile radio terminals. An eighth time slot 
24.sub.8 of the frequency f2 or f2' is assigned as a control channel. The 
fixed radio terminal 13.sub.3 arranged in the second service area 11.sub.2 
performs communication through the first channel 24.sub.1 of the frequency 
f2 or f2'. The mobile radio terminal 14.sub.2 or 14.sub.3 in the second 
service area 11.sub.2 performs communication by ensuring any one of the 
second to seventh time slots 24.sub.2 to 24.sub.7. 
FIG. 3 schematically shows the arrangement of the radio port controller 
shown in FIG. 1. The radio port controller 15 can be connected to N (N is 
an arbitrary positive integer) radio ports. Radio port interface units 
32.sub.1 to 32.sub.N are circuits for inputting/outputting signals to/from 
the corresponding radio ports. The radio port interface units 32.sub.1 to 
32.sub.N are connected to a first multiplexing/demultiplexing unit 33. The 
first multiplexing/demultiplexing unit 33 is a circuit for performing 
time-division multiplexing of signals in units of time slots and 
demultiplexing of the multiplexed signals in units of time slots. Signal 
processing units 34.sub.1 to 34.sub.N are connected to the first 
multiplexing/demultiplexing unit 33 in correspondence with the radio 
ports. 
The signal processing units 34.sub.1 to 34.sub.N have uplink channel 
processing units 35.sub.1 to 35.sub.N for performing signal processing for 
uplink radio channels, and downlink channel processing units 36.sub.1 to 
36.sub.N for performing signal processing for downlink radio channels. A 
second multiplexing/demultiplexing unit 37 is a circuit for 
multiplexing/demultiplexing signals in accordance with an interface to the 
ISDN switching system. Network interface units 38.sub.1 to 38.sub.N are 
connected to the second multiplexing/demultiplexing unit 37 to 
input/output signals to/from the ISDN switching system. All the signal 
processing units 34.sub.1 to 34.sub.N are connected to a channel 
assignment information processing unit 39. The channel assignment 
information processing unit 39 stores radio channel assignment 
information. In the radio communication system shown in FIG. 1, the 
frequencies used by the first and second radio port 12.sub.1 and 12.sub.2 
and time slot assignment in each frequency shown in FIG. 2 are stored in 
the channel assignment information processing unit 39 serving as a memory 
means. 
A sequence in assigning the radio channels to the radio terminals in the 
radio communication system with the above arrangement will be described 
below. 
FIG. 4 shows a communication sequence performed in ensuring a radio channel 
in the first service area 11.sub.1 of the radio communication system shown 
in FIG. 1. A vertical line on the left side indicates the fixed radio 
terminal 13.sub.1 or 13.sub.2. A vertical line at the center indicates the 
first radio port 12.sub.1. A vertical line on the right side indicates the 
mobile radio terminal 14.sub.1. Time elapses downward in FIG. 4. The radio 
port controller 15 provides notification information 41 representing the 
usable/unusable state of channels to the area through the radio port 
12.sub.1 on the basis of the information stored in the channel assignment 
information processing unit 39. The information related to the fixed radio 
terminal that is provided, includes the identifier of the radio port where 
the fixed radio terminal is accommodated, the frequencies in use, and the 
time slot numbers permanently assigned in the frequencies. 
Therefore, the fixed radio terminal 13.sub.1 is informed that the radio 
port is the first radio port 12.sub.1, the frequencies in use are the 
frequency f1 for the uplink and the frequency f1' for the downlink, and 
the stationarily assigned channel is the first channel 23.sub.1. The fixed 
radio terminal 13.sub.1 or 13.sub.2 stores these pieces of information as 
notification information and thereafter outputs a service request through 
the assigned channel. 
Idle slot information 42 indicating whether each slot is accessible or not 
from the first radio port 12.sub.1 is notified every predetermined period. 
The channel permanently assigned to the fixed radio terminal 13.sub.1 or 
13.sub.2 is handled as an inaccessible slot in the idle slot information 
42. Even when an inaccessible slot is notified in the idle slot 
information 42, the fixed radio terminal 13.sub.1 or 13.sub.2 uses the 
assigned radio channel which has been provided with the notification 
information 41 to output a service request 43. 
Upon reception of the service request, the radio port controller 15 
determines the normality of the service request on the basis of the radio 
frequency of the service request, the time slot number, and the subscriber 
number of the fixed radio terminal 13.sub.1 or 13.sub.2 which has output 
the service request. In the radio port controller 15, the subscriber 
number assigned to the fixed radio terminal 13.sub.1 or 13.sub.2 is stored 
in advance in the channel assignment information processing unit 39. On 
the basis of this information, matching between the subscriber number for 
the service request and the radio channel is determined. For example, a 
service request received from the mobile radio terminal 14.sub.1 through 
the radio channel assigned to the fixed radio terminal 13.sub.1 or 
13.sub.2 is rejected. If the service request is normal, the radio port 
controller 15 informs the radio terminal 13.sub.1 or 13.sub.2 of a service 
acceptance 44 representing that the service request has been accepted. 
On the other hand, the mobile radio terminal 14.sub.1 outputs a service 
request 46 through an accessible time slot on the basis of received idle 
information 45. The radio port controller 15 determines whether the 
service request is normal, as described above. If the service request is 
normal, a service acceptance 47 is sent back. The radio port controller 15 
stores the time slot through which the service request has been accepted. 
Thereafter, in a busy state, this channel is notified as an inaccessible 
slot. In addition, when an idle slot degrades in its transmission quality, 
the radio port controller 15 informs the terminal of the slot as an 
inaccessible slot. 
As described above, time slots in one frequency are distributed to fixed 
radio terminals and mobile radio terminals, so that both the fixed and 
mobile radio terminals can be handled through the same radio port. For the 
fixed radio terminals, channels are permanently assigned to the respective 
terminals in advance. With this arrangement, even when the number of 
mobile radio terminals in one service area increases, and a lot of service 
requests are output, channels for the fixed radio terminals can always be 
ensured. 
First Modification 
In the first modification, a fixed radio terminal has a repeater function. 
The repeater area is relatively small, e.g., only in the house of a 
person, the garden, and the frontage. In the house or frontage, a radio 
wave from the radio port becomes weaker. For this reason, when the mobile 
terminal is present in this area, the fixed radio terminal relays the 
radio wave to the radio port. 
FIG. 5 schematically shows the configuration of the radio communication 
system of the first modification. For a first radio port 51.sub.1, the 
radio frequencies f1 and f1' are assigned for communication between a 
fixed radio terminal 53.sub.1 and a mobile radio terminal 54.sub.2 in a 
service area 52.sub.1. For a second radio port 51.sub.2, the radio 
frequencies f2 and f2' are assigned for communication between a fixed 
radio terminal 55 and a mobile radio terminal 54.sub.3 in a second service 
area 52.sub.2. The fixed radio terminal 53.sub.1 arranged in the first 
service area 52.sub.1 has a function as a repeater station. The fixed 
radio terminal 53.sub.1 performs transmission/reception with respect to a 
mobile radio terminal 54.sub.1 present in a third service area 52.sub.3 in 
the service area 52.sub.1 by using frequencies f3 and f3', and this 
communication is relayed to the first radio port 51.sub.1 by using an 
accessible slot in the frequency f1 or f1'. A radio port controller 56 has 
the same function as of the radio port controller 15 in FIG. 1. The radio 
frequency used for communication with the mobile radio terminal 54.sub.1 
will be referred to as a fixed-mobile repeater frequency hereinafter. To 
relay the mobile radio terminal 54.sub.1, the fixed radio terminal 
53.sub.1 communicates with the radio port through a channel which is 
permanently assigned to the fixed radio terminal 53.sub.1. 
FIG. 6 schematically shows the arrangement of the fixed radio terminal 
53.sub.1 and the mobile radio terminal 54.sub.1 shown in FIG. 5. A radio 
frequency transmission/reception unit 61 is a transmission/reception 
circuit communicating with the mobile radio terminal 54.sub.1 in the third 
service area 52.sub.3 shown in FIG. 5. A radio frequency 
transmission/reception unit 62 is a transmission/reception circuit 
communicating with the first radio port 51.sub.1 by using the radio 
frequencies f1 and f1'. A reception field strength measurement unit 63 for 
measuring the reception field strength in a plurality of frequencies is 
connected to the radio frequency transmission/reception unit 61 to select 
the fixed-mobile repeater frequency. Modulation/demodulation units 
64.sub.1 and 64.sub.2 are circuits for modulating/demodulating a signal 
into a digital signal. 
A subscriber line interface unit 65 is an interface circuit for 
inputting/outputting a signal to/from a fixed terminal 66. A data analysis 
unit 67 is a circuit for performing various analyses of received data. A 
channel synthesizing/separating unit 68 is a circuit for synthesizing a 
signal at the fixed terminal 66 with a signal at the mobile radio terminal 
54.sub.1 through the radio frequency transmission/reception unit 61 or 
separates the signals. A control unit 69 has a CPU (Central Processing 
Unit) which is not illustrated and performs various control operations 
while integrating the various circuit sections of the fixed radio 
terminal. The control unit 69 is connected to the various circuit sections 
through a control signal line indicated by a dotted line in FIG. 6. 
In the fixed radio terminal 53.sub.1, a radio port identifier, the assigned 
frequencies f1 and f1', and the time slot assigned to the fixed radio 
terminal 53.sub.1 are stored in a memory unit 70 on the basis of the 
notification information 41 described in FIG. 4. First, the reception 
field strength measurement unit 63 measures the reception field strengths 
of the plurality of radio frequencies prepared for communication in 
advance, which are different from the frequencies f1 and f1' and do not 
interfere with the frequencies f1 and f1'. Of these radio frequencies, one 
with the highest reception field strength is selected as the fixed-mobile 
repeater frequency used for communication with the mobile radio terminal 
54.sub.1 present in the third service area 52.sub.3 and stored in the 
memory unit 70. In this case, the radio frequencies f3 and f3' are 
selected for the uplink and downlink, respectively, as the fixed-repeater 
mobile frequencies. 
The channel synthesizing/separating unit 68 in the fixed radio terminal 
53.sub.1 synthesizes a signal at the fixed terminal 66 with a signal to be 
relayed to the mobile radio terminal 54.sub.1 or separates the signals on 
the basis of an instruction from the control unit 69. The signal on the 
fixed terminal 66 side is transmitted to the first radio port 51.sub.1 
through a permanently assigned slot in the frequency f1 or f1', which has 
been informed by notification information. Upon reception of a signal from 
the first radio port 51.sub.1 to the mobile radio terminal 54.sub.1, the 
signal of that time slot is separated by the channel 
synthesizing/separating unit 68 and input to the radio frequency 
transmission/reception unit 61 through the modulation/demodulation unit 
64.sub.1. 
The radio frequency transmission/reception unit 61 transmits a signal to be 
relayed to the mobile radio terminal 54.sub.1 in the third service area 
52.sub.3 by using the frequency f3 stored in advance. On the other hand, 
information received from the mobile radio terminal 54.sub.1 using the 
frequency f3' is transmitted from the radio frequency 
transmission/reception unit 62 to the first radio port 51.sub.1 through 
the radio frequency transmission/reception unit 61 and the channel 
synthesizing/separating unit 68 by using the radio frequency f1'. At this 
time, a radio channel assigned between the fixed radio terminal 53.sub.1 
and the radio port 51.sub.1 in advance is used to relay the mobile radio 
terminal 54.sub.1. 
The mobile radio terminal 54.sub.1 checks the reception field strength at 
the destination using a reception field strength measurement unit 71 to 
select a radio frequency with the highest quality for communication. 
Therefore, When the mobile radio terminal 54.sub.1 comes close to the 
fixed radio terminal 53.sub.1, i.e., when the mobile radio terminal 
54.sub.1 enters the third service area 52.sub.3, the mobile radio terminal 
54.sub.1 also selects the same radio frequencies as the fixed-mobile 
repeater frequencies f3 and f3' selected on the fixed radio terminal 
53.sub.1 side. For this reason, the mobile radio terminal 54.sub.1 can 
perform communication through a radio frequency measurement unit 72 and a 
modulation/demodulation unit 73 without particularly identifying whether 
the mobile radio terminal 54.sub.1 is communicating with the first radio 
port 51.sub.1 or relaying the fixed radio terminal 53.sub.1 for 
communication. 
Second Modification 
In the second modification shown in FIG. 7, it is determined whether the 
mobile radio terminal 54.sub.1 is present in the repeater area 52.sub.3 of 
the fixed radio terminal 53.sub.1 having the same subscriber number as 
that of the mobile radio terminal 54.sub.1. The radio communication system 
and the fixed radio terminal 53.sub.1 of the second modification have the 
same configuration as that shown in FIGS. 5 and 6. However, the fixed 
radio terminal 53.sub.1 and the mobile radio terminal 54.sub.1 in the 
third service area 52.sub.3 have the same subscriber number. As in the 
first modification, in the fixed radio terminal 53.sub.1, a radio port 
identifier, the assigned frequencies f1 and f1', and the assigned time 
slot, which have been informed by notification information, are stored in 
the memory unit 70 in advance. Assume that the fixed-mobile repeater 
frequencies f3 and f3' are determined in advance. As shown in FIG. 7, in 
the mobile radio terminal 54.sub.1, the fixed-mobile repeater frequencies 
f3 and f3' used by the fixed radio terminal 53.sub.1 having the same 
subscriber number as that of the terminal 54.sub.1 and the identifier of a 
radio port for controlling the service area are stored in a memory unit 75 
in advance. 
A control unit 74 of the mobile radio terminal 54.sub.1 recognizes the 
radio port identifier informed in the destination area. A reception field 
strength measurement unit 76 grasps the fixed-mobile repeater frequency 
selected on the basis of the reception field strength. A comparison unit 
74a of the control unit 74 compares the fixed-mobile repeater frequency 
and the radio port identifier used by the fixed radio terminal 53.sub.1 
having the same subscriber number as that of the terminal 54.sub.1, which 
are stored in the memory unit 75 in advance, with those of the mobile 
radio terminal 54.sub.1. If both the radio port identifiers and the radio 
frequencies coincide with each other, it is recognized that the mobile 
radio terminal 54.sub.1 enters the third service area 52.sub.3 as the 
repeater area of the fixed radio terminal 53.sub.1 having the same 
subscriber number as that of the terminal 54.sub.1. If the radio port 
identifiers coincide with each other, and the fixed-mobile repeater 
frequencies do not coincide, it is identified that the mobile radio 
terminal 54.sub.1 is present in the service area 52.sub.1 of the radio 
port 51.sub.1 for controlling the fixed radio terminal 53.sub.1 having the 
same subscriber number as that of the terminal 54.sub.1 and outside the 
repeater area 52.sub.3 of the fixed radio terminal 53.sub.1. If neither 
the fixed-mobile repeater frequencies nor the radio port identifiers 
coincide with each other, it is determined that the mobile radio terminal 
54.sub.1 is located outside the service area 52.sub.1 of the radio port 
51.sub.1 for controlling the fixed radio terminal 53.sub.1 having the same 
subscriber number as that of the terminal 54.sub.1. 
For example, when it is determined, on the basis of the two pieces of 
information, i.e., the radio port identifier and the fixed-mobile repeater 
frequency, that the mobile radio terminal 54.sub.1 is present in the third 
service area 52.sub.3 in FIG. 5, communication is performed using the 
fixed-mobile repeater frequencies f3 and f3'. In addition, communication 
between the fixed radio terminal 53.sub.1 and the first radio port 
51.sub.1, which is performed to relay the mobile radio terminal 54.sub.1, 
is performed using a channel permanently assigned to the fixed radio 
terminal 53.sub.1. When it is determined that the mobile radio terminal 
54.sub.1 is present in the first service area 52.sub.1 in FIG. 5 and 
outside the third service area 52.sub.3, a service request is output to 
the first radio port 51.sub.1 to obtain an accessible slot for mobile 
radio terminals in the radio frequency f1 or f1'. When the mobile radio 
terminal 54.sub.1 is present outside the first service area 52.sub.1 and 
the third service area 52.sub.3, e.g., when it is determined that the 
mobile radio terminal 54.sub.1 is present in the second service area 
52.sub.2, a service request is output such that communication is performed 
through an accessible slot in the frequency f2 or f2' of the second radio 
port 51.sub.2. 
In many cases, residents in a house where the fixed radio terminal is set 
often possess mobile radio terminals having the same subscriber number as 
that of this fixed radio terminal. In the second modification, it is 
determined on the mobile radio terminal 54.sub.1 side whether the mobile 
radio terminal is in the repeater area 52.sub.3 of the fixed radio 
terminal 53.sub.1 having the same subscriber number as that of the mobile 
radio terminal. Only when the subscriber number is the same, a service 
request is output to use the fixed-mobile repeater frequency. For this 
reason, in use in the house where the fixed radio terminal 53.sub.1 having 
the same subscriber number as that of the mobile radio terminal is set, a 
radio channel can be unconditionally ensured, like the fixed radio 
terminal 53.sub.1. More specifically, only the mobile radio terminal 
54.sub.1 having the same subscriber number as that of the fixed radio 
terminal uses the fixed-mobile repeater frequency. Therefore, even when 
another mobile radio terminal enters the repeater area, the mobile 
terminal cannot use the channel assigned to the fixed radio terminal 
53.sub.1. 
In addition, in an area located outside the repeater area 52.sub.3 of the 
fixed radio terminal 53.sub.1 having the same subscriber number as that of 
the mobile radio terminal 54.sub.1, the mobile radio terminal 54.sub.1 and 
the fixed radio terminal 53.sub.1 use different radio channels. For this 
reason, the radio port controller 56 can discriminate the mobile radio 
terminal 54.sub.1 from the fixed radio terminal 53.sub.1 although they 
have the same subscriber number. When the mobile radio terminal 54.sub.1 
enters the repeater area 52.sub.3 of the fixed radio terminal 53.sub.1 
having the same subscriber number as that of the terminal 54.sub.1, the 
radio port controller 56 cannot discriminate the two terminals from each 
other. However, since determination can be made on the fixed radio 
terminal 53.sub.1 side, no problem is posed. In addition, position 
registration for receiving a terminating call need be performed only on 
the mobile radio terminal 54.sub.1 side because the fixed radio terminal 
53.sub.1 does not change its position. In the first radio area 52.sub.1, a 
terminating call must be received on the mobile radio terminal 54.sub.1 
side. That is, the fixed radio terminal 53.sub.1 must be used stand-alone 
only for call origination. 
The positions and numbers of fixed radio terminals and mobile radio 
terminals in the service areas are not limited to those in the 
above-described embodiment and first and second modifications. This is 
also applied to the radio frequencies and time slot assignment. 
As has been described above, according to the present invention, a radio 
channel can be ensured at any time because a channel is permanently 
assigned to the fixed radio terminal, so that a similar service as that of 
a wire terminal can be provided. In addition, the mobile radio terminal 
can be notified of a channel assigned to the fixed radio terminal at the 
destination and output a service request through another channel. 
Furthermore, even when the mobile radio terminal and the fixed radio 
terminal have the same subscriber number, it can be identified on the 
radio port side whether the source of the service request is the fixed 
radio terminal or mobile radio terminal because the channels are 
different. 
The fixed radio terminal has a repeater area where the fixed radio terminal 
is included. When the mobile terminal enters the area, the fixed radio 
terminal relays communication between the radio port and the mobile radio 
terminal. For example, a radio wave from the radio port becomes weaker in 
a house or frontage. However, when the fixed radio terminal set in the 
house is used to relay communication, satisfactory communication can be 
performed by the mobile radio terminal even in the house. 
Communication is relayed only when the mobile radio terminal enters the 
repeater area of the fixed radio terminal having the same subscriber 
number as that of the mobile radio terminal, so another subscriber cannot 
use the ensured radio channel. Therefore, every time the mobile radio 
terminal enters the repeater area of the fixed radio terminal having the 
same subscriber number as that of the mobile radio terminal, a channel can 
be ensured, and the same service as that of a wire terminal can be 
received. 
As a repeater radio frequency, a frequency which does not interfere with a 
radio frequency used by the radio port is selected. Therefore, 
satisfactory communication can be ensured in the repeater area. 
The repeater radio frequency used by the fixed radio terminal having the 
same subscriber as that of the mobile radio terminal and the identifier of 
the radio port for controlling this terminal are stored in advance on the 
mobile terminal side. When the radio frequency detected at the destination 
and the notified radio port identifier are compared with the repeater 
radio frequency and the radio port identifier, which are stored, it is 
determined whether the mobile radio terminal is present in the repeater 
area of the fixed radio terminal having the same subscriber number as that 
of the mobile radio terminal. With this arrangement, it can be relatively 
easily identified whether the mobile radio terminal is present in the 
repeater area of the fixed radio terminal having the same subscriber 
number as that of the mobile radio terminal.