Cordless telephone system and communication method thereof

The cordless telephone system according to the present invention comprises a synchronization inhibiting circuitry for inhibiting, when a calling station sends a communication end request code, synchronization with a called station in communication therewith for a prespecified inhibit time after transmission of the communication end request code, and a communication terminating circuitry for terminating communication if a state where synchronism with the called station is lost continues for a prespecified reference time during communication. Thus, communication is terminated without fail when a call ends, and transactions of unnecessary electric waves are reduced.

FIELD OF THE INVENTION 
The present invention relates to a cordless telephone system and a 
communication method thereof which executes communication between a master 
phone and a slave phone based on a time division system, and more 
particularly to a cordless system and communication method thereof which 
can terminate communication without fail. 
BACKGROUND OF THE INVENTION 
In a conventional type of cordless telephone system based on a time 
division system, synchronism of communication frame is established by 
means of transaction of synchronizing request code (SYNC code). When 
terminating a call while synchronism is established, a station hoping to 
terminate a call sends communication end request code (END code) specified 
times (for instance, three times) to a called station and terminates 
communication of the station. On the other hand, the called station 
receiving the END code recognizes end of communication and terminates 
communication of the station. 
In the conventional type of cordless telephone system, however, a station 
hoping to terminate communication sends the END code and then terminates 
communication without checking whether the called station has received the 
END code. For this reason in a case where the END code has not been 
received by the called station due to, for instance, interference among 
radio zones, the called station determines that the radio link had been 
disconnected for some reason or other, and sends a SYNC code to establish 
synchronism again, so that synchronism between the station and the called 
station is again established and communication is enabled. In other words, 
even if a user wants to terminate a call, a communication call is not 
disconnected immediately, and transmission continues despite that the 
station is not used. Such disadvantages to a user as accounting of 
telephone fee or waste of electric power occur. 
As shown in FIG. 8, assume that a calling station A sends the END code 3 
times and then enters an asynchronous state (terminates communication), 
but a called station B does not receive END code, so that the called 
station B determines that the radio link has been disconnected for some 
reason or other and continues to send SYNC code until synchronism is 
established again. The calling station A, receiving this SYNC code, again 
establishes synchronism and enables communication as in a case where a new 
request for event is issued. 
On the other hand, in the conventional type of cordless telephone system, 
it is possible to evade the case where a called station can not detect end 
of communication and synchronism is again established to enable 
communication. This occurs by employing a system in which a calling 
station sends the END code and terminates communication only when the 
calling station confirms that the called station has received the END 
code, but the telephone line is not disconnected in spite that the user 
hopes to terminate the call. A state where transmission continues, even 
though the calling station is not in use, continues for a long time. This 
creates disadvantages to users such as accounting of telephone fee or 
waste of electric power. 
SUMMARY OF THE INVENTION 
It is an object of the invention to terminate communication without fail 
when a call ends and also to reduce transmission of unnecessary electric 
waves after the end of a call. 
In the cordless telephone system and communication method thereof according 
to the present invention, when a calling station sends a communication end 
request code to terminate communication, reestablishment of synchronism 
can be evaded, even if a called station has not received the communication 
end request code, by inhibiting establishment of synchronism with the 
called station for a prespecified period of inhibition after the 
communication end request code is sent. Also, when synchronism with a 
called station is lost for a prespecified reference period of time during 
communication, by terminating communication, a calling station recognizes 
an end of call and terminates communication even if the communication end 
request code sent from the calling station is not received. 
In the cordless telephone system and communication method thereof according 
to the present invention, two types of synchronization request code, 
namely, a first synchronization request code used for notification of a 
new event in a stand-by state where communication is not being executed 
and a second synchronization request code used when synchronism is lost 
due to an error during communication and re-establishment of communication 
is required, are selectively sent. Receiving of the second synchronization 
request code is inhibited for a prespecified inhibition period after the 
communication end request code is sent, or communication is terminated if 
a state where synchronism with a called station is lost continues for a 
prespecified reference period during communication. Hence, a communicating 
state can be suppressed even if the communication end request code has not 
been received by a called station, or when communication end request code 
sent from the called station can not be received. 
In the cordless telephone system and communication method thereof, after 
the communication end request code is sent, if a synchronization request 
code from a called station is received within a prespecified inhibition 
period, a calling station terminates communication by sending the 
communication end request code again even if the called station fails in 
receiving the first communication end request code. 
Other objects and features of this invention will become understood from 
the following description with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Detailed description is made for the cordless telephone system according to 
the present invention in the order of Embodiment 1, Embodiment 2, 
Embodiment 3, Embodiment 4 and Embodiment 5 with reference to the related 
drawings. 
FIG. 1 is a block diagram of a cordless telephone system according to 
Embodiment 1 of the present invention, and in this figure, designated at 
the reference numeral 101 is a transmitter, at 102 a receiver, at 103 an 
antenna, at 104 a switch for switching connection between the transmitter 
101, receiver 102, and antenna 103, at 105 a time-division processing 
circuit for executing communication control according to a time division 
system, at 106 a speaker, at 107 a microphone, and 108 a microcomputer 
control section for providing ON/OFF controls over each of the above 
sections to execute synchronization inhibit control and communication end 
control. 
It should be noted that the microcomputer control section 108 comprises an 
input I/F (interface) 109 for inputting a signal from the time-division 
processing circuit 105, an output I/F 110 for outputting an ON/OFF signal 
to the transmitter 101, receiver 102 and time-division processing circuit 
105, a ROM 111 for storing a control program therein, a RAM 112 which is a 
memory for work, and a CPU 113 executing a control program stored in the 
ROM 111 to execute synchronization inhibit control and communication end 
control, such as a CORDLESS TELEPHONE MODEL: EXP9100 and its Service 
Information Manual, made by Uniden Corporation and Sold by Uniden America 
Corporation, of which disclosure is incorporated herein by the reference. 
With the configuration as described above, next description is made for (1) 
operational principles in Embodiment 1, and (2) control operations by the 
microcomputer control section. (1) Operational principles in Embodiment 1 
The cordless telephone system according to Embodiment 1 automatically stops 
trying to establish synchronism and disconnects a radio line to terminate 
communication when synchronism with a called station is lost for a 
specified period of time during communication (in a state where 
synchronism has been established). To realize the operations as described 
above, the cordless telephone system according to Embodiment 1 executes 
synchronization inhibit control and communication end control as described 
below in the microcomputer control section 108. 
Herein, the synchronization inhibit control is defined as inhibition of 
synchronization with a called station for a prespecified period of 
inhibition time T2 (Refer to FIG. 2) after transmission of an END code 
when a calling station sends the END code to terminate communication, and 
in Embodiment 1, synchronization with a called station is inhibited by 
providing ON/OFF control over the transmitter 101, receiver 102, and 
time-division processing circuit 105 to inhibit input/output of a signal. 
Also herein the communication end control is defined as a control for 
termination of communication when a state where synchronism with a called 
station is lost during communication for a prespecified period of 
reference time T1 (Refer to FIG. 2). 
Next, description is made for a relation between the inhibit time T2 in 
synchronization inhibit control and the reference time T1 in communication 
end control with reference to FIG. 2. It should be noted that FIG. 2 shows 
a case where Station A executes the synchronization inhibit control and 
Station B executes the communication end control. 
At first, Station A executes transmission of END code specified times 
(herein three times), then terminates communication, and also actuates a 
T2 timer (not shown) to start measurement of the inhibit time T2. 
On the other hand, if the END code sent from Station A is not received by 
Station B due to such reasons as interference among radio zones, Station B 
enters the state where a radio link has been disconnected (asynchronous 
state) without being notified of the desire to release the radio link 
(without receiving END code), so that Station B sends the SYNC code to 
establish synchronism again and actuates the T1 timer (not shown) to start 
measurement of the reference time T1. 
However, as shown in FIG. 2, as the relation of inhibit time T2 &gt; reference 
time T1 has been set up, even if Station B tries to establish synchronism 
with Station A during the reference time T1, synchronism between Station A 
and Station B is not established because synchronization to Station B is 
inhibited for the inhibit time T2 due to the synchronization inhibit 
control in Station A. For this reason, Station B automatically terminates 
communication by means of the communication end control at a time when the 
reference time T1 has passed. 
It should be noted that, when the inhibit time T2 has passed, Station A 
cancels inhibition of synchronization with Station B, synchronization 
between Station B and Station A is enabled on the condition that the 
inhibit time T2 has passed. 
It should be noted that the inhibit time T2 is a period when communication 
is disabled if the communication circuit is intentionally turned OFF when 
communication is terminated. The time must be short enough for a user 
using the cordless telephone system not to get embarrassed. It is possible 
to set the inhibit time T2 within a range from 1 to 2 seconds. 
The reference time T1 depends on a width of interference which may occur 
among radio zones. In case of a radio link disconnection due to slight 
interference, it is required that radio communication can be continued by 
re-linking, and the reference time T1 must be a period in which it can be 
determined that the radio line was intentionally disconnected 
(communication was intentionally terminated) by the called station. Also, 
in the cordless telephone system according to Embodiment 1, when a radio 
link is disconnected due to light interference among radio zones, the 
minimum time required for re-linking (synchronizing) to a called station 
is 9 ms. 
Taking the requirements as described above into consideration, in 
Embodiment 1, the reference time T1 is set to 500 ms, while the inhibit 
time T2 after transmission of END code is set, taking into such factors as 
delay between radio zones, to a time longer than the reference time T1 
satisfying the following relation: 
Reference time T1 &lt; inhibit time T2 (= 600 ms) so that the called station 
can recognize disconnection of a radio communication line. 
When set up as described above, even if an event of sending or receiving a 
call occurs after communication is terminated, radio connection can be 
established again without being noticed by a user. (2) Controlling 
operations by microcomputer control section 
During communication with a cordless telephone system, the CPU 113 in the 
microcomputer control section 108 inputs information such as reception of 
END code from the time-division processing circuit 105, asynchronous 
state, transmission of END code or others, and executes synchronization 
inhibit control and communication end control. 
FIG. 3 is a flow chart of controlling operations of the microcomputer 
control section 108 in Embodiment 1. At first, information on reception of 
END code is inputted from the time-division processing circuit 105 (S301), 
and then communication is terminated (S302). 
When information that synchronism has been lost is inputted from the 
time-division processing circuit 105 (S303), communication end control is 
started, the T1 timer is actuated (S304), SYNC code is sent to a called 
station, and retry for synchronization again is executed (S305). This 
retry for synchronization is repeated until the reference time T1 is over 
(S306), and when the reference time T1 is over, communication is 
terminated (S307). 
On the other hand, when information that END code has been transmitted is 
inputted from the time-division processing circuit 105 (S308), 
synchronization inhibit control is started, communication in a calling 
station is terminated, the T2 timer is started (S309, S310), an OFF signal 
is outputted to the transmitter 101, receiver 102, and time-division 
processing circuit 105, the communication circuit is turned OFF, and 
synchronization is inhibited (S311). Then, when the inhibit time T2 is 
over (S312), an ON signal is outputted to the transmitter 101, receiver 
102, and time-division processing circuit 105, the communication circuit 
is turned ON, and synchronization is enabled (S313). 
As described above, in Embodiment 1, synchronization with a called station 
is inhibited for the inhibit time T2 after transmission of the END code, 
and if synchronism is lost and synchronization is not again established 
within the reference time T1, communication is automatically terminated. 
Hence, communication is terminated without fail when a call ends and 
unnecessary transmission of power after the end of transmission can be 
reduced. 
The configuration in Embodiment 2 is similar to that in Embodiment 1, and 
synchronization with a called station is inhibited by disabling use of a 
frequency used in transmission of END code for the inhibit time T2 in 
synchronization inhibit control by the microcomputer control section 108. 
It should be noted that other portions of the configuration and operations 
thereof are the same as those in Embodiment 1 and description is made for 
only different portions herein. 
FIG. 4 is a flow chart of controlling operations by the microcomputer 
control section 108 in Embodiment 2, and the reference numerals common to 
those in the flow chart of controlling operations in Embodiment 1 shown in 
FIG. 3 indicate the same processing respectively. In this figure, when 
information that the END code has been transmitted is inputted from the 
time-division processing circuit 105 (S308), synchronization inhibit 
control is started to terminate communication in a calling station, the T2 
timer is actuated (S309, S310), and an instruction for inhibition of use 
of a frequency used in transmission of END code is issued to the 
transmitter 101, receiver 102, and time-division processing circuit 105; 
in other words, use of only a frequency used in communication with a 
called station is inhibited to suppress synchronization with only a called 
station in communication using the frequency (S401). Then, when the 
inhibit time T2 is over (S312), instruction for releasing inhibition of 
use of the frequency is issued to the transmitter 101, receiver 102 and 
time-division processing circuit 105 to enable synchronization (S402). 
As described above, in Embodiment 2, in addition to the effects achieved in 
Embodiment 1, use of only the frequency used in communication up to the 
current point of time is inhibited, and synchronization of only the called 
station in communication up to the point of time is disabled, and even if 
an event from another station occurs with a different frequency within the 
inhibit time T2, the station can be used without any trouble. 
The configuration in Embodiment 3 is similar to that in Embodiment 1, and 
synchronization with a called station in communication therewith is 
inhibited by not accepting a SYNC code from a called station which sent 
the END code for the inhibit time T2 in synchronization inhibit control by 
the microcomputer control section 108. Other portions of Embodiment 1 are 
the same as those in Embodiment 1, so that description is made for only 
different points. 
FIG. 5 is a flow chart of controlling operations by the microcomputer 
control section 108 in Embodiment 3, and the reference numerals common to 
those in Embodiment 1 shown in FIG.3 indicate the same process 
respectively. In this figure, when information indicating that END code 
has been sent is inputted from the time-division processing circuit 105 
(S308), synchronization inhibit control is started with communication in a 
calling station terminated, the T2 timer is started (S309, S310), and an 
instruction for rejection of SYNC code from a called station which sent 
END code is issued to the time-division processing circuit 105. In other 
words, by inhibiting use of only SYNC code used in communication with a 
called station, synchronization with only a called station using the SYNC 
code is inhibited (S501). Then, when the inhibit time T2 is over (S312), 
an instruction for releasing inhibition of the SYNC code is issued to the 
time-division processing circuit 105, and synchronization is enabled 
(S502). 
As described, in Embodiment 3, in addition to the effects achieved in 
Embodiment 1, as synchronization with only a called station in 
communication is inhibited by rejecting only the SYNC code to the called 
station in communication up to the point of time, a calling station can be 
used without any trouble even if an event from another station occurs 
within the inhibit time T2. 
The configuration in Embodiment 4 is similar to that in the Embodiment 1, 2 
types of synchronization request code, first synchronization request code 
(described as SYNC code hereinafter) used for notification of a new event 
in a stand-by state where communication is not being executed in the 
time-division processing circuit 105 and second synchronization request 
code (described as SYNC* code hereinafter) used when it is necessary to 
establish synchronism again because of an error during communication, are 
selectively sent. As in embodiments 1 and 2, by inhibiting reception of 
SYNC code for the inhibit time T2 in synchronization inhibit control by 
the microcomputer control section 108, communication is terminated if 
synchronization can not be established within the reference time T1 in the 
communication terminating control. It should be noted that other portions 
in this embodiment are the same as those in Embodiment 1 and description 
is made for only different portions thereof. 
FIG. 6 is a flow chart of controlling operations by the microcomputer 
control section 108 in Embodiment 4, and the same reference numerals as 
those in the flow chart for controlling operations in Embodiment 1 shown 
in FIG. 3 indicate the same process respectively. In this figure, when 
information indicating that synchronism has not been established is 
inputted from the time-division processing control 105 (S303), 
communication end control is started with the T1 timer actuated (S304), an 
instruction for retry for synchronization is issued to the time-division 
processing circuit 105, and the time-division processing control 105 sends 
SYNC* code to a called station for retrying synchronization (S601). This 
retry for synchronization is repeated until the reference time T1 is over 
(S306), and communication is terminated when the reference time T1 is over 
(S307). 
When information indicating that an END code was sent is inputted from the 
time-division processing circuit 105 (S308), synchronization inhibit 
control is started with communicating in a calling station terminated and 
the T2 timer actuated (S309, S310), and an instruction for rejection of 
SYNC* code is issued to the time-division processing circuit 105. In other 
words synchronization from a called station is inhibited by inhibiting 
retry for synchronization because of a reception error in the called 
station (S602). Then, when the inhibit time T2 is over (S312), an 
instruction for releasing inhibition of use of SYNC* code is issued to the 
time-division processing circuit 105, and synchronization is enabled 
(S603). 
As described above, in Embodiment 4, only the SYNC code indicating a new 
event is accepted, so that connection to a called station is automatically 
inhibited for a certain period of time even if, for instance, an END code 
is not accepted by a called station, so that a calling station terminates 
communication and enters a stand-by state. For this reason, it is possible 
to terminate communication without fail when a call ends and also to 
reduce unnecessary transmission after end of a call. 
The configuration in Embodiment 5 is similar to that in Embodiment 1, and 
in the microcomputer control section 108. When a SYNC code is received 
from a called station for the inhibit time T2 after transmission of an END 
code, synchronism is established and the END code is sent again to 
terminate communication. It should be noted that other portions of 
Embodiment 5 are the same as those in Embodiment 1, and description is 
made for only different points. 
FIG. 7 is a flow chart of controlling operations by the microcomputer 
control section 108 in Embodiment 5, and the same reference numerals as 
those in the flow chart for controlling operations in Embodiment 1 shown 
in FIG. 3 indicate the same process respectively. In this figure, when 
information indicating that synchronism has not been established is 
inputted from the time-division processing circuit 105 (S303), an 
instruction for retry of synchronization is issued to the time-division 
processing circuit 105, and a SYNC code is sent for retry of 
synchronization (S701). 
On the other hand, when information indicating that an END code was sent is 
inputted from the time-division processing circuit 105 (S308), 
synchronization inhibit control is started with communication in a calling 
station terminated and the T2 timer actuated (S309, S310), determination 
as to whether SYNC code from the called station was received within the 
inhibit time T2 by the time-division processing circuit 105 or not is 
executed (S702, S703), and if a SYNC code is received within the inhibit 
time T2, an END code is sent again (S704). When the inhibit time T2 is 
over, the processing is terminated. 
As described above, in Embodiment 5, if a SYNC code is received within the 
inhibit time T2, an END code is sent again after synchronism is 
established and end of communication is notified, so that even if an END 
code is not received by a called station due to interference or for other 
reason and synchronism is not established, communication can be terminated 
without fail. Also even in this case, transactions of unnecessary electric 
waves after end of a call can be reduced as compared to a method in which 
confirmation of reception of an END code between a calling station and a 
called station is executed and then communication is terminated. 
As described above, the cordless telephone system and communication method 
thereof according to the present invention comprises a synchronization 
inhibiting means for inhibiting synchronization with a called station in 
communication with the calling station for a prespecified inhibit time 
after transmission of communication end request code when the calling 
station sends communication end request code to terminate communication, 
and a communication terminating means for terminating communication when a 
state where synchronism with a called station is lost continues for a 
prespecified reference time during communication, so that communication 
can be terminated without fail when a call ends and transactions of 
unnecessary transmission after end of transmission can be reduced. 
Also the cordless telephone system and communication method thereof, 
according to the present invention, comprises a synchronizing means for 
selectively sending two types of synchronization request code, that is, a 
first synchronization request code used for notification of a new event in 
a stand-by state where communication is not being executed, and a second 
synchronization request code used when it is necessary to establish 
synchronism again because of an error during communication, a 
synchronization inhibiting means for inhibiting reception of a second 
synchronization request code for a prespecified inhibit time after 
transmission of a communication end request code when a calling station 
sends a communication end request code to terminate communication, and a 
communication terminating means for terminating communication if a state 
where synchronism with a called station is lost continues for a 
prespecified reference time during communication. Hence, communication can 
be terminated without fail when a call ends and unnecessary transmission 
of waves after end of a call can be reduced. 
The cordless telephone system and communication method thereof according to 
the present invention comprises a communication terminating means for 
establishing synchronism and then sending communication end request code 
again when a synchronization request code is received from a called 
station for a prespecified inhibit time after transmission of a 
communication end request code, so that communication can be terminated 
without fail when a call ends and unnecessary transmission of electric 
waves after the end of a call can be reduced. 
Although the invention has been described with respect to a specific 
embodiment for a complete and clear disclosure, the appended claims are 
not to be thus limited but are to be construed as embodying all 
modifications and alternative constructions that may occur to one skilled 
in the art which fairly fall within the basic teaching herein set forth.