Note: Descriptions are shown in the official language in which they were submitted.
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ALERT METHOD FOR CORDLESS TELEPHONES
Eq~dofl~ vention
The present invention relates generally to the field of
commlmic~t;ons and particularly to cordless telephones.
B~ound of 1 he I~.~lion
l 0 An obvious requirement of any telephone is that it must
ring or generate some form of alert tone. ~;n~inE in a
l~n~lline telephone is initiated by a ring voltage that is turned
on and offby the telephone company. A typical ring is a cycle
of two seconds on and four seconds off. Some telephone
1 5 systems support- distinctive ringing. A distinctive ring is
defined as one short-long-short ring cycle every six seconds as
specified in the Bellcore document CL~ASSsM Feature
Distinctive Ringing/Call Waiting, TR-TSY-000219 Issue 2,
Revision 1. The two short rings are 200 to 500 ms in length
2 0 and the one long ring is 800 to 1000 ms. The off periods
between the long and short Iings are 200 to 500 ms in
duration. An off period after the last short ring is for the
rem~in~ler of the six second cycle.
It is typically desirable that the ringing of all phones at
2 5 a particular number be synchronized. Unsynchronized
ringing sounds strange to the end user. In a cordless
telephone, ringing must be initiated by an RF signal from the
cordless telephone's base unit.
In order to synchronize ringing in a cordless telephone,
3 0 a mes,s~e could be sent to start or stop the ring. This solution
would not work in a system that transmits data sub-audibly at
a low speed since a meSsAEe could take appro~im~tely 700 ms
to transmit. The ring duration is much shorter than the time
to transmit a meSs~e.
~- - 3 5 Another solution would be to dedicate several bits in the
message for a ring indication. These ring indication bits
would be evenly distributed throughout the message. After
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seeing a predetermined number of these bits in the ringer ON
state, the h~ntlset would begin ringing. A predetermined
nllmher of these bits in the ringer OFF state would indicate to
the handset that it should termin~te ringing.
In this case, the h~n~cet needs to sample several bits
prior to rh~nging the ring state to avoid f~lRing Lf the
h~n~l~et neerle~l to receive two bits in the ringer ON state prior
to turning on the ringer, and if the ringer must be turned on
within 100 ms of the land line indication, then the base would
1 0 need to transmit at least two ring indication bits every 100 ms.
Ring infiic~tion bits, the~efo~e, would consume 20 percent of
the message stream in a cordless system that transmits 100
I\/r~nrhester bits per second. Dedicating 20 percent of the
message stream to the ring indication severely tiiminishes the
throughput of the communications channel for other
operations. There is a resulting need for an alert control
method that does not require dedication of a signific~nt
portion of the message stream.
2 0 ~ of l he I~. ~Lion
The process of the present invention encomr~sses a
method for controlling an alert tone in a cordless telephone.
The cordless telephone is comprised of a base unit, a h~n~et
2 5 unit, and an alert generator. The method begins by the base
unit detecting a ring signal. If the ring signal is detected, the
base unit transmits an alert start message and a tone signal
to the handset unit. If the handset unit receives the tone
signal and the alert start message, the alert generator is
3 0 activated.
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B~iefDescriptionof the Dra~vi~gs
FIG. 1 shows a flowchart of the process of the present
invention.
FIG. 2 shows the Ri~n~l~ generated in accordance with
the process of the present invention.
FIG. 3 shows a simple block diagra_ of a cordless
telephone in accordance with the present invention.
1 0 DetailedDescriptionofthe P~ed Emho~ment
A cordless telephone base unit, using the process of the
present invention, transmits a sub-audible alert or ring start
and stop mess~ge to the h~n~l~et unit. After the ring start is
l 5 transmitted, a tone is transmitted to signal the ring to start.
As a result, after a slight delay to receive the initial message,
the handset rings in cadence with other extension telephones
at the particular number being called.
The process of the present invention, illustrated in FIG.
2 0 1, begins when the h~ntlset locks to the base unit (201). This
locking operation occurs when the base unit transmits a
nallowband pattern to the handset so that the handset locks to
the channels assigned to cordless telephones. The handset's
alert generator is also turned off in case it was previously
2 5 turned on (203). A RING_TOTAL value is initialized to zero at
this point. RING_TOTAL contains a rlmning total of the
energy detected on the çh~nnel. The energy level is high
when the tone is turned on and is low when the tone is turned
off.
3 0 The process then continuously checks the sub-audible
data mess~Ee stream for a ring start message (205) sent by the
base unit. This message is one of many mess~Ees that the
base can transmit to the handset unit. After receiving this
m~ss~ge, the h~nflset monitors the audible portion of the
_ ~ - 3 5 rhs~nnel (206). The handset next determines if the ring stop
message was received (207). If the ring stop mess~ge was
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received, the h~n-l~et turns off the ringer and resets
RING_TOTAL (203).
If the ring stop mess~Ee was not ~eceived, the most
recent low speed data bit feceived from the base unit is
eY~minell to dete~ine if it is in error (209). This error check
avoids f~l.einE under poor ~ign~llinE conditions. Ideally, it
also avoids f~lRinE on voice in the event of co-rh~nnel
intelrele~ce. The process of the present invention provides
Ly~lelesis to ~lev~llt f~l~inE and bit error determin~tion to
detect erroneous samples. In an alternate embo-liment, a
severe shift in the received signal strength indicator (RSSI)
could also be utilized to detect erroneous samples.
If the BER indicates that the most recent bit is in error
(211), the process br~nçhes to (207). The audible portion of the
l 5 ch~nn~l is not sampled if the bit is in error. This is done since
an error in sub-audible data indicates that the sample of the
audible band is probably in error.
If the sub-~ lihle data bit is not in error (211), the
audible portion of the rh~nnel is measured to detect for the
2 0 presence of a tone (213). This measurement is done via an
expander A/D conversion. This sample is combined into
RING_TOTAL (215) by the equation:
RING-ToT = RING_TOT * 2 TO
This method of updating RING_TOT provides the hysteresis
to prevent fiqlsinE.
RING_TOT is now compared to a RING_T~Rh'
(217). RING_THRESH is picked so that it is as high as
3 0 possible to avoid f~l~in~ on noise but also low enough so that a
small number of samples will cause the threshold to be
exceeded. In the ~iefelled embo(liment RING_THRESH is
104. In this embodiment, the e~p~n~ler A/D samples are
al,~lo~hllately 40 when the base is transmitting the tone.
3 5 If RING_TOT meets or exceeds RING_THR~,~qH, then
the ringer is turned on (221). In an alternate embo~iment, the
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ringer is cherke~l before it is turned on to avoid a strange
solm~1inE alert. If RING_TOT is less than RING_THRESH,
then the ringer is turned off (219).
Whether the ringer is turned on or off, the process
S continues by checking for a ring stop mess~sEe (207). A
meSsa~e that indicates that ringing should be terminated is
sent sub-audibly by the base once the call is answered or the
land-line ringing stops for ten continuous seconds. Once this
meSss~e is ,eceived, the ringer is turned off and RING_TOT
l 0 reset (203).
FIG. 2 illustrates the audible (401) and sub-audible (402)
portions of the communication channel. The ring start signal
(403) is present on the sub-audible (402) band and the tone (404)
is present on the audible (401). In the preferred embodiment,
l 5 the ring stop signal (405) occurs ten seconds after the last tone.
In an alternate embodiment, the ring start signal (403) can
occur mulitple times before the ring stop signal (405). Also in
this embodiment, the ring stop signal (405) may be
transmitted multiple times after the last tone (404).
2 0 FIG. 3 illustrates a simple block diagr~m of a typical
cordless telephone using the process of the present invention.
The base unit (301) is connected to the land-line telephone
system from which it receives the ring siEn~l The handset
(302) is comprised of a transceiver (303) to transmit and
2 5 receive si~n~l~. The transceiver (303) is connected to audio
circuits (305) that contain the A/D converter and the ring
generation circuits. An interface circuit (311) performs the
.~iEn~llin~ for the h~ntl~et. A microprocessor (307), in
conjunction with the memory (309), controls the operation of
3 0 the handset and uses the process of the present invention.
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