Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF CONNE:CTING A CORDLESS TELEPHONE BY RADIO
BACKGROUND OF THE: INVENTION
The present invention relates to a method of connecting a
cordless telephone bY radio, Particularly a cordless telephone of
the type not using a control channel.
A cordless telephone is constituted by a fixed unit and a
portable unit which serve as a base station and a mobile station,
respectively. The portable unit is connectable to the fixed unit
over a radio link. Each of the two units includes a transmitter
and a receiver which permit full duplex communications. To
promote effective use of electromagnetic waves, a number of
such cordless telephones share a plurality of radio channels.
Each telephone searchs for an idle radio channel and connects its
fixed and portable units to each other over the idle radio
channel. For this reason, the fixed and portable un*s are
l 5 individuallY constructed to tune the transmit and receive
frequency to any of the radio channels by a frequency
synthesizer system. Each telephone is provided with a particular
identification number (ID No. ) so that the fixed ~nd portable
units maY identify electromagnetic waves which are sent from
each other.
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The radio connection systems for cordless telephones maY
generally be classified into two types, i. e., a system using a
control channel and a system not using a control channel.
In the control channel type connection s-,~stem, a fixed and a
5 portable unit each waits on a control channel. The fixed unit
received an incoming call and the portable unit on which a call is
originated send respectively a calling signal including the ID No.
and channel information to be used and a call origination signal.
Then, the fixed and portable units tune their transmit and
10 receive frequencies to the same radio channel. The control
channel is shared by the cordless telephones on a time-sharing
basis.
On the other hand, the prior art connection system which
does llot use a control channel causes each of the fixed and
15 portable units in a waiting condition to sequentially tune the
transmit and receive frequency to radio channels to thereby
cyclically monitor the radio channels available. The fixed unit
received a call or the portable unit on which a call ori~ination
request has been entered fixes its transmit and receive frequencY
20 to one of idle radio channels and then sends a calling signal
including the ID No. or a call o}igination signal over that
channel. Since the other unit is cyclicallY monitoring the radio
channels, that unit received the callin~ signal including the own
station's ID l~o. or the call origination signal fixes the transmit
25 and receive frequency to that radio channel. Thereafter, either
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a call reception flow or a call origination flow is executed over
the particular radio channel. With the radio connection system
without a control channel, it is possible to assiE~n the entire
radio frequency band available to the radio channels for
communication and, hence, efficient use of electromagnetic
waves is achievable.
However, the prior art radio connection system without a
control channel has a problem left unsolved, as follows.
Assume that when the fixed unit transmits a calling signal to the
Portable unit over a certain radio channel, the portable unit is
brought into an off-hook condition before it receives the calling
signal. Then, the portable unit decides that a call is to be
originated and sends a call origination signal to the fixed unit
over another radio chan~el. When the fixed and portable units
are tuned to different radio channels as stated, not onlY the
radio connection for the origination of a call but also the radio
connection for the reception of a call are a~t to fail.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
radio connection method for a cordless telephone of the type not
using a control channel which ensures a radio connection for an
inco~ning call even when a call origination request occurs before
the radio connection for an incoming call is completed.
It is another object of the present invention to provide a
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generally improved method of connecting a cordless telephone by
radio~
A method of connecting by radio a cordless telephone having
a base unit and a mobile unit, having a particular identification
5 number, and sharing a pluralitY of radio channels with other
cordless telephones without using control channels of the present
invention comprises the steps of (a~ selecting priority radio
channels from the radio channels and assigning each of the
priority radio channels to a respective one of the cordless
10 telephones, tb) causing the base unit to monitor the priority
radio channel assigned to the cordless telephone associated with
the base unit when a calling signal is received, ~c) if the priority
radio channel is idle, causing the base unit to send the calling
si~nal to the mobile unit over the priority radio channel, (d)
15 causing the mobile unit to monitor the priority radio channel
assigned to the cordless telephone when a call origination signal
is to be sent, ~e~ causing the mobile unit to send an answer
signal to the base unit when a calling signal meant for the
cordless telephone is received over the priority radio channel,
20 and (f) causing the mobile unit to send a call origination signal
to the base unit over the priority radio channel only if a calling
signal meant for the cordless telephone is not received over the
prioriy radio channel and the prioritY radio channel is idle.
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BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description taken with the accompanying drawings in
5 w hich:
Fig. 1 is a schematic block diagram showing a fixed unit of
a cordless telephone in accordance with the present invention;
Fig. 2 is a schematic block diagram showing a portable unit
which is associated with the fixed unit of Fig. l;
Fig. 3 is a flowchart demonstrating a specific procedure
which occurs in response to an incomin~ call;
Fig. 4 is a flowchart demonstrating a specific procedure
which occurs in response to a call origination reQUeSt;
Fig. 5 is a chart representative of how the fixed unit searchs
15 for a speech channel;
Fig. 6 is a chart showing how the portable unit searchs for a
speech channel; and
Fig. 7 is a block diagram schematically showin~ a specific
construction of a circuit for sensing an idle channel.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the method in accordance with the
present invention will be described in detail with reference to the
accompanying drawings.
S A cordless telephone in accordance with the present invention
is constituted by a fixed unit and a portable unit which serve as
a base station and a mobile station, respectively. The portable
unit is connectable to the fixed unit ~y a radio link. The fixed
unit is generally made up of a power suPply section for supplying
power of predetermined voltage and frequencY, a transmitting
and receiving section for permitting full duplex communications,
and a logic circuit for controlling the entire unit. On the other
hand, the portable unit is generally comprised of a power silpply
section Powered by, for examPle~ a nickel-cadmium (Ni-Cd)
battery of predetermined voltage, an operating section including
a dial keY pad and function keys, ~ transmitting and receiving
section, and a logic circuit adapted to control the entire unit.
Specific constructions of the fixed unit and portable unit except
for their power supply sections will be described with reference
to Figs. 1 and 2, respective]Y.
Referring to ~ig. 1, a fixed unit FU includes a switch 10
which is connected to a telephone line and a 2-4 converter 12.
The 2-4 converter 12 is connected to a transmitter 16 via an
amplifier 14 while the transmitter 16 is connected to an antenna
20 via a duplexer 18. A ringer detector 22 is also connected to
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the telephone line and to a controller or central processing unit
(CPU) 24. Also connected to the controller 24 are an
identification read-only memory (ID-ROM) 26 and a synthesizer
28. The synthesizer 28 is connected to the transmitter 16 ant a
5 receiver 30. A data modulator 32 is interposed between the
controller 24 and the transmitter 16. The receiver 30 is
connected to the antenna 20 by way of the duplexer 18. The
receiver 30 is connected to the controller 24 directly and via a
data demodulator 34. An amplifier 36 is installed between the
receiver 30 and the 2-4 converter 12.
As shown in Fig. 2, a portable unit PU includes a
microphone 40 which is connected to a transmitter 44 via an
amplifier 42. The transmitter 44 is connected to an antenna 48
via a duplexer 46. Key switches 50 are connected to a controller
52. A data modulator 54 is interposed between the controller 52
and the transmitter 44. Also connected to the controller 52 are
an ID-ROM 56 and a synthesizer 58 which is connected to the
transmitter 44 and a receiver 60. The receiver 60 is connected
to the antenna 4~ via the duplexer 46 and to the controller 52
20 directly and via a data demodulator 62. A loudspeaker 64 is
connected to the receiver 60 via an amplifier 66.
Fig. 3 is a flowchart demonstrating a specific operation of
the fixed unit FU which occurs upon reception of a call. Fig. 4
is a flowchart representative of a specific operation of the
25 portable unit PU which is performed for requesting the
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origination of a call.
Priority radio channels are selected from radio channels
which are shared by independent cordless telephones and
individually assigned to the cordless telephones. Assume that ID
5 Nos. are serial and that serial numbers beginning with 0 ~zero)
are assigned to the indi?idual radio channels. Then, the prioritY
radio channels will be evenly assigned if each cordless telephone
with a particular ID No. is provided with a priority radio channel
having a number which corresponds to a residual produced bY
10 dividing the ID No. by the number of radio channels. In the
case where serial numbers beginning with 1 (one) are assigned
to the i~dividual radio channels, the priority radio channel will
be the radio channel having a number which corresponts to the
sum of a residual produced by dividing the ID No. by the number
15 of radio channels and 1. Assuming that forty radio channels are
available and that the ID No. is represented by N, N is given by
40 x A + B (B = 1, 2, 3, . . ., 39). In this case, the prioritY
radio channel for that ID No. or N is expressed as (B + 1 )
channel. For example, when ID No. or N is 10 0 012, the
20 priority radio channel to be assigned thereto is the channel 13
because B is 12 as produced from 100012 = 40 x 2500 + 12 and
therefore (B + 1~ = 13.
Referring to Fig. 3, upon reception of a call, the fixed unit
FU tunes the transmit and receive frequency to the priority radio
25 channel which is assigned to the own station (step Sl) and then
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determines whether that channel is idle, i. e., whether a received
inpllt electric field is present on that channel (step S2). If the
priority radio channel is not idle, the program advances to a
step S3 to search for an idle radio channel and, if any radio
5 channel is idle, tunes the transmit and receive frequency to that
channel (step S4 ) . This is followed by a call reception flow
which is well known in the art and therefore will not be described
to avoid redundancy.
Referring to Fig. 4, the portable unit PU detects a request
10 for the origination of a call when it becomes off-hook. The
program begins with tuning the transmit and receive frequency
to the priority radio channel which is assigned to the own station
(step Sll) and then sees if a calling signal with the own station's
ID No. has arrivet. If such a signal has arrived, the portable
15 unit PU sends an answer signal including the ID No. to enter into
a call reception flow. If the calling si~nal has not arrived, the
program advances to a step Sl 3 to see if the priority radio
channel is idle. If it is idle, the portable unit PU sends a call
origination signal including the ID No. to enter into a call
20 origination flow. If the priority radio channel is not idle, a step
S14 is executed to search for an idle channel and, if any channel
is idle, the transmit and receive frequency is tuned to the idle
channel ~step S15). This is followed by a call origination flow.
A call origination flow will not be described herein because it is
25 also well known in the art.
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How an idle channel is searched for and detected at the step
S3 of the fixed unit FU and the step S14 of the portable unit PU
will be described more specifically. To search for an idle
channel, the units FU and PU each sees if the electric field level
5 on the individual channels is lower than 20 dB for 1 micro ~/m,
the determination being continued for 10 0 ms for each channel.
If the field level on any of the channels remains higher than the
above threshold for a Predetermined period of time, the unit FU
or PU determines that that channel is busy and then checks the
10 field level on the next channel upon the lapse of 30 ms. If the
field level on the channel remains lower than the threshold for
the predetermined period of time, the unit FU or Pl~ decides that
that channel is idle.
Speech channel search performed by the fixed unit FU is as
15 follows. Assuming that forty radio channels are available, as
shown in Fig. ~, the fixed unit FU sequentially scans channels 40
to 1 in this order and then returns to channel 40. If the field
level on any of the channels is lower than 20 dB for 1 micro
~J/m, the unit FU checks the next channel. If it is higher than
20 the above threshold, the unit FU searchs for a bit sync pattern
over a predetermined period of time. If a bit sync pattern is not
detected during that period of time, the unit FIJ switches to the
search on the next channel for a colnmunication channel. When
a bit sync pattern has been detected, the unit FU continuously
2 5 checks the data to the end. Then, at the instant when a
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matching ID code has been detected, the unit FU switches to the
search on the next channel for a speech channel.
While the fixed unit FU performs a search in the waiting
condition as described above, in the event of reception of a call
the fixed unit FU enters into the call reception flow of Fig. 3 after
returnin~ to the priority channel such as channel 30.
As regards the speech channel search performed by the
portable unit PU, assume that forty radio channels are available
as with the search at the fixed unit ~U. As shown in Fig. 6, the
unit PU sequentiallY scans channels 1 to 40 in this order and then
returns to channel 1. The second scanning cycle begins with
channel 2 and ends with channel 2, and the third scanning cycle
begins with channel 3 and ends with channel 3. Such a scanning
cycle is repeated thereafter. At the end of each scanning cycle,
the unit PU deactivates the synthesizer 58 for battery saving
purpose. The duration of such battery saving operation is also
stored in the ID-ROM 56. A procedure which follows the channel
switching is the same as the procedure which has been described
in relation to the fi~ed unit FU.
While the portable unit PU performs a search in the waiting
condition as described above, in the event of reception of a call
the portable unit PU enters into the call reception flow of ~ig. 4
after returning to the priority channel such as channel 30.
Referring to Fig. 7, there is shown a specific construction of
a ciruit for sensing an idle channel which is applicable to any of
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the fixed unit FU and portable unit PU of the present invention.
The circuit, generally 70, is interposed between the receiver 30
of the fixed unit FU or the receiver 6 0 of the portable unit PU
and the controller 2 4 or 5 2 . The circuit 7 0 is made up of an
amplifier 72 for amplifying an output of the receiver 30 or 60, a
band-pass filter 74 for excluding noise outside the speed banch
from an output of the amplifier 72, a detector 7~ for detecting
an outPut of the band-pass filter 74, and a comparator 78 for
comparing an output voltage of the detector 7 6 with a
predetermined threshold value Vre~ and feeding its output to the
controller 24 or 52. Since this kind of idle channel sensing
circuit is well known in the art, a detailed description thereof
will not be made herein.
In summary, it will be seen that a method of the present
invention hardly allows a fixed unit and a portable unit of a
cordless telephone to tune to different radio channels even when
a request for the origination of a call occurs before a radio
connection for an incoming call is completed. Hence, the method
of the present invention eliminates the need for control channels
2 0 otherwise used to minimize the occurrence that a radio
connection for an incoming call is disabled due to the difference
in radio channel. This unprecedented advantage is derived from
selecting priority radio channels from those channels which are
shared by independent cordless telephones and assigning them to
2 5 the latter, causing each cordless telephone to use its priority
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radio channel so long as it is not occupied bY another cordless
telephone, and allowing the portable unit to enter into a call
origination flow in response to a request only after confirming
that an incoming calling signal is absent on the priority radio
5 channel.
~ arious modifications will become possible for those skilled
in the art after recei~ing the teachings of the present disclosure
without departing from the scope thereof.
