Note: Descriptions are shown in the official language in which they were submitted.
CA 02151516 2001-10-04
METHOD FOR CONTINUALLY MONITORING THE
STATUS OF A RADIO FREQUENCY LINK
FIELD OF THE INVENTION
The present invention relates to a Method for Continually Monitoring Status of
a
Radio Frequency Link.
The present application is a divisional Application of Application Serial
Number
2,059,734 filed January 21, 1992.
BACKGROUND OF THE INVENTION
The present invention relates generally to the transmission and reception of a
telephone signal between a remote battery powered cordless handset unit and
fixed hard
wired base unit, and in particular, to a microprocessor based digital cordless
telephone
apparatus capable of transmitting both digitized voice data and digitized
command data
between a hand unit and a base unit. In the present cordless digital telephone
apparatus
the handset and base unit communicate with one another using FSK modulated
digital
signals transmitted on an RF carrier in the 902-928 MHz band.
The function of the conventional prior art cordless telephone is to provide
the user
with the ability to freely move about while speaking on the telephone without
the hindrance
of being "tied" down by the coiled cord connecting the handset to the
conventional
telephone set. The typical prior art cordless telephone comprises a base unit
which is
physically connected to the user's telephone company lines and a hand-held
handset unit.
The physical hard wire connection between the conventional hand- set and
telephone set
is replaced by an radio frequency (RF) link, usually in the 46 and 49 MHz
bands. The
spoken voice is usually communicated between the base and handset by first
converting
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2
the user's voice into an analog electrical signal and modulating the signal
using an RF
carrier for radio transmission to the receiver, typically through the use of a
Narrow-Band
Frequency Modulation (NBFM) technique. At the receiver the modulated analog
voice
signal is demodulated and directed' to a speaker through which the voice is
heard. The
various command functions which must be communicated between the handset and
the
base are instead communicated in the digital format. To accommodate both
formats of data
the digital command signal is usually modulated as either a 600 Hz or 1 kHz
square wave
and transmitted as an "in-band" signal on top of the analog voice signal.
One shortcoming of the in-band transmission of digital command data is that
the
command data is part of the voice data signal and thus is inherently audible
to the user
when the analog voice signal is demodulated and listened to. Moreover, the
command data
in addition to being audible to the user is also transmitted very slowly
precluding
implementation of channel monitoring. Another limitation inherent in
transmitting an analog
voice signal using the NBFM technique is the often occur- ring static,
interference and
1 ~ otherwise poor reception which accompanies the transmission and reception
of the analog
voice signal. While some recent cordless telephone designs have sought to
include
"enhanced" circuitry to improve the transmission and reception of the analog
voice, hoping
to obtain a "corded" sound quality, many are still subject to troublesome
static and
interference.
One way in which the prior art has attempted to overcome static and
interference
has been by providing the user with the ability to select among several
different RF channel
frequencies in hopes of finding a "clearer" RF link. While the ability to
change channels is
CA 02151516 2001-10-04
3
useful, prior art devices require that channel changing be done manually by
the user who
must elect to change channel based upon how much interference he or she
perceives.
Should the interference be in the transmission from the handset only, it will
usually not be
heard by the handset user, but may be very annoying to the party at the other
end of the
line.
When a handset is transmitting command data to a base, such as when the user
accesses an outgoing line and dials a telephone number, it is essential that
the base
receive the complete command if the cordless telephone is to operate as
intended. Static
and interference in the RF link may obscure the flow of command data and cause
the
complete command data not to be received. The user will learn of the missing
or lost
command data only as a result of the device's failure to respond to the user's
command
request or the execution of an unintended command.
Moreover, while virtually every RF communication device has a physical range
limitation beyond which a transmitter and receiver cannot communicate with one
another,
the implication of this limitation represents a significant shortcoming in the
operation of a
cordless telephone. For example, when the handset is physically located at the
outer edge
of the communication range the received signal is often weak and interference
from other
signals may result in intermittent loss of the RF link when a conversation is
in progress. In
addition, when the handset unit is in a "standby mode" awaiting receipt of an
incoming
telephone call and the user moves out of range from the base unit, the user is
unable to
receive an incoming telephone call from the base unit and more importantly is
totally
unaware of being out of range unless an attempt is made to use the handset at
which time
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the out of range condition would be discovered due to the inability to
establish
communication with the base unit.
When the prior art handset unit is in a standby mode it must nevertheless be
able
to receive an incoming call from the base unit and accordingly at least the
receiver circuits
of the hand- set must remain energized. The need to maintain power to the
receiver as well
as other portions of the handset, even when in a standby mode, places a
continuing power
drain on the handset batteries and will ultimately serve to deplete the
handset battery
charge necessitating that the handset be returned to the base unit for
recharging even if no
telephone conversations have been made or received.
Accordingly, the present invention seeks to address the foregoing limitations
of the
prior art cordless telephone by providing a cordless telephone apparatus which
comprises
a base unit and handset unit which each transmit and receive digitized voice
signals toward
providing true noise free conversations with significantly greater immunity to
static and
interference, and with increased range.
Another object of the present invention is to provide for the combined
communication of digitized voice signals and digital command signals toward
the wireless
transmission and reception of such signals on an RF band of 902-928 MHz taking
advantage of revised FCC regulations which have allocated portions of this
band for just
such an application.
Moreover, the present invention seeks to provide for the seamless intermixing
of
digital command data into the stream of digital voice data flowing between the
base unit and
the handset.
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It is an associated object of the present invention to provide a means by
which
transmitted digital command data is received and captured by the receiving
unit from the
stream of incoming digital data and replaced with a quiet sequence so as to
prevent the
command data from causing an otherwise undesirable audible sound to be heard
by the
5 user.
It is a still further object of the present invention to implement a command
data
protocol incorporating positive acknowledgment with retransmission technology
in order to
insure that each transmitted command is acknowledged when received and if lost
or
damaged is repeated until acknowledged all before further commands are
transmitted.
It is yet another object of the present invention to provide a command data
protocol
which incorporates a randomly generated security code which prevents ah
unintended
person from gaining access to the user's telephone line and placing
unauthorized telephone
calls.
It is additionally an object of the present invention to provide for the
selection and
changing of RF channel frequencies without intervention by the user in
response to the
automatic detection of interference in the RF link or a total loss of the RF
link.
Another object of the present invention is to provide twenty frequency
channels for
operation of the handset at operating frequencies of 925.5 to 927.4 MHZ and
twenty paired
frequency channels for operation of the base unit where such channels are
paired in a
manner which permits rapid channel scanning.
It is yet a further object of the present digital cordless telephone apparatus
to
provide for the transmission of a link check command signal by the base unit
and the
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E1
acknowledgment of receipt by the handset unit in order to continually monitor
the viability
and existence of the RF link while a call in progress as well as to detect an
out of range
condition toward signaling the user at the handset of the inability to make or
receive a
telephone call.
Yet another object of the present invention is to provide a means by which the
handset and base unit can communicate data between one another through a
physical
connection when the hand- set unit is in its storage cradle within the baseset
unit, there- by
precluding the need to modulate the recharge power source as a way of
establishing
communication between the handset and the base unit when in storage.
It is yet a further object of the present invention to provide a power saving
mode
wherein the handset unit automatically powers down when a call is not in
progress and
periodically automatically awakens to check for the presence of an incoming
call, incoming
link check command signals or the actuation by the user of the keypad, thereby
serving to
extend handset battery life.
An additional object of the present invention is to provide for the scrambling
of the
digital voice signal prior to transmission and for the unscrambling of the
digital voice signal
upon reception in order to minimize the possibility that the telephone
conversation may be
monitored by unintended persons listening to the RF channel frequency.
These and other objects of the invention will become apparent in light of the
present
specification and drawings.
SUMMARY OF THE INVENTION
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7
The present invention includes a microprocessor based transportable battery
powered handset unit and a microprocessor based stationary base unit which
cooperate
with one another and together comprise a digital cordless telephone apparatus.
The
handset unit provided is a cordless battery powered hand-held instrument which
incorporates a numeric telephone dial pad as well as other function keys and
light emitting
diode status indicators.
The base unit provided is intended to be located in a fixed position,
connected to an
external source of electrical power and hard wire connected to the user's
telephone
company lines via the conventional telephone jack present in most households
and
businesses. The base unit includes a handset storage cradle for storing the
handset unit.
While in its storage cradle, two pairs. of metallic contacts located
respectively on the
handset face and within the storage cradle contact one another provide power
to the
handset for recharging its internal batteries and a third contact provides a
physical data fink
between the handset unit and base unit. A speakerphone and telephone dial pad
are
provided in the base unit to enable one to make and receive telephone calls
from the base
unit, as well as to permit an intercom communication between the base unit and
handset
unit to take place.
The handset unit and the base unit are each microprocessor based devices which
incorporate computer software routines which govern the operation of various
operations
of the apparatus and execute the various command functions which the user may
initiate
during operation of the apparatus.
The base unit and handset unit communicate with one another via a radio
frequency
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(RF) link which is established between the two units thereby permitting the
handset unit to
make and receive telephone calls to and from the telephone company's "outside
lines".
Both the handset unit and base unit each include an antenna for transmitting
and receiving
RF signals.
S In order to provide for full duplex operation of the digital cordless
telephone
apparatus, two radio frequency links are established between the base unit and
handset
unit. One RF link, a handset channel, is the frequency at which the handset
transmits, and
thus at which the base unit receives, digital voice and command data signals.
The second
RF link, a base unit channel, is the frequency at which the base unit
transmits, and thus at
which the handset unit receives, digital voice and command data signals.
Accordingly, both
RF links may be active simultaneously such that the human voice may be both
spoken and
heard at the handset and base unit at the same time.
A total of 20 channels in the base unit operating frequency band of 905.6 -
907.5
MHZ, and 20 channels in the handset operating frequency band of 925.5 - 927.4
MHZ, are
provided. For fast channel scanning handset channels are paired with base unit
channels
and are divided into four groups of five channels as shown in Table 1. Each
adjacent
channel within a group is separated by 400 kHz.
FREQUENCY CHANNELGROUP
NUMBER
0 1 2 3
BU 905.6 MHZ 905.7 MHZ 905.8 MHZ 905.9 MHZ
0
HS 925.5 MHZ 925.6 MHZ 925.7 MHZ 925.8 MHZ
BU 906.0 MHZ 906.1 MHZ 906.2 MHZ 906.3 MHZ
1
p HS 925.9 MHZ 926.0 MHZ 926.1 MHZ 926.2 MHZ
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BU 906.4 MHZ 906.5 MHZ 906.6 MHZ 906.7 MHZ
HS 926.3 MHZ 926.4 MHZ 926.5 MHZ 926.6 MHZ
BU 906.8 MHZ 906.9 MHZ 907.0 MHZ 907.1 MHZ
3
HS 926.7 MHZ 926.8 MHZ 926.9 MHZ 927.0 MHZ
BU 907.2 MHZ 907.3 MHZ 907.4 MHZ 907.5 MHZ
~4
HS 927.1 MHZ 927.2 MHZ 927.3 MHZ 927.4 MHZ
Each channel frequency can be referenced by a coordinate (channel group,
frequency number) where channel groups are either 0, 1, 2 or 3 and frequency
numbers
are 0, 1, 2, 3 or 4.
When the handset unit is placed into the handset storage cradle of the base
unit
a cradle initialization software routine is activated. The base unit software
and
microprocessor randomly select a channel group and startup frequency. This
information is transferred to the handset unit microprocessor via the physical
data
contact adjacent to the battery recharge contacts on the handset face and in
the
handset storage cradle. The handset, in turn, acknowledges receipt of channel
group
and startup frequency information through the RF link.
The principal type of data which is exchanged between the base and handset is
voice data corresponding to the spoken conversation taking place between the
user
operating the handset and the other party to the conversation connected to the
handset
via the baseset. Unlike prior art cordless telephone devices which typically
utilize a
narrow band frequency modulation technique and transmit an analog voice
signal; the
present invention transmits purely digital voice signals. Accordingly, the
handset and
base unit each digitize the spoken word to be transmitted to the other, the
handset
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digitizing the user spoken word and the base digitizing the analog voice
signal coming
from the telephone company line. A second type of data is exchanged between
the
handset and the base unit and is referred to herein as digital command data.
While the
present apparatus principally exchanges digital voice data between the handset
and
base, commands must also be exchanged for the apparatus to function and for
the user
to access the various options contained within the apparatus.
The transmission and reception of the spoken voice takes place as follows. The
handset microphone picks up the user's voice and converts it into an analog
baseband
electrical signal which is then amplified and filtered. The baseband analog
signal is next
digitized using the Adaptive Delta Modulation technique thereby generating a
baseband
digital voice data signal. The baseband digital voice data passes through a
command
data -voice data interface where it is recognized as being voice data. The
signal is then
scrambled and modulated onto a carrier frequency in the 925.5- 927.4 MHZ band
for
transmission to the base unit via the handset antenna.
The modulated digital voice data signal is received by the base unit antenna
and
amplified and filtered before it is down converted from 926 MHZ to 10.7 MHZ.
The down
converted digital voice signal is a modulated signal which is filtered and
then
demodulated into a baseband digital voice signal which is there- after
descrambled and
then passed through a command data -voice data interface, where it is
recognized as
digital voice data. The signal is thereafter decoded into a baseband analog
voice signal.
The decoded analog voice signal is further filtered and amplified before being
connected
to the telephone company line via a standard telephone interface circuit.
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Voice signals are transmitted from the base unit to the handset unit in a like
manner except that they are transmitted in the frequency band of 905.6- 907.5
MHZ.
The digital modulated voice signals are also received by the handset unit in a
like
manner except for the receiving frequency being in the frequency band of 905.6-
907.5
MHZ
The command data signals exchanged between the handset unit and the base
unit differ from voice data signals in that they are not part of the voice
communication
between the user and the other party to the conversation, but rather, take the
form of
instructions and/or status checks which are exchanged between the handset and
base
unit. The dialing of a telephone number from the handset is a representative
task and
can be used to illustrate the use and operation of command data in the present
digital
cordless telephone apparatus.
In order to place an outgoing telephone call one must access the local
telephone
company's lines. In a conventional hard wired telephone set one merely picks
up the
handset thereby releasing a switch hook which makes connection to the
telephone
company lines. Dialing a telephone number is done by pressing a sequence of
push
buttons, each of which generates a DTMF tone which are, in turn, read by the
telephone
company switch to complete the desired telephone call. In rotary dial
telephones a fixed
number of pulses are generated in response to the particular digit dialed by
the user.
With a cordless telephone the user perceives the operation of the device to be
essentially identical to the operation of a conventional corded telephone set.
In actuality
certain critical differences exist. When the user wishes to make a telephone
call from the
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handset unit an RF link must first be established between the handset and base
unit in
order for the handset unit to obtain a dial tone. Once the dial tone is heard,
the user
dials the desired phone number depressing the numerically labeled buttons on
the
handset dial pad. The selection of a dial tone and the dialing of a telephone
number are
each command functions which must be transmitted from the handset to the base
unit.
In the present apparatus the "switch hook" is located in the base unit and is
remotely
activated by the handset when the user selects an outgoing line. This
selection is
performed by pressing the "phone" key located on the handset keypad. The user
will
then hear the dial tone and may dial the desired phone number using the dial
pad in the
conventional manner. A DTMF tone generator is located in the base unit and is
thus
remotely activated by the handset. Should the user press the "intercom" key, a
conversation may take place between the handset unit and the base unit
speakerphone.
In an intercom call no telephone line is accessed.
The remote selection of an outgoing line and generation of DTMF tones, as well
as other command functions described herein are accomplished by transmitting
command data signals between the handset and the base unit. In the typical
prior art
cordless phone command data is transmitted in the digital format over an RF
link. In
order to permit both data and command data to be transmitted over the same
link the
digital data is modulated on top of the analog voice data signal prior to
transmission and
is recovered at the receiving device but nevertheless is audible to the
listener and
consumes significant time in transmission and recovery.
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13
In the present invention where voice data and the command data are both in the
digital format a unique design has been created to facilitate the intermixing
of digital
voice data and digital command data being based upon the interruption of the
flow of
digital voice data to permit command data to be inserted into the data path
and thus
transmitted over the RF link. In addition, in the present apparatus, the
transmission of
command data is accomplished using a data protocol incorporating a verified
transmission scheme to insure that transmitted command data has been received
by the
intended unit and that no new command is transmitted until the prior command
is
acknowledged as received.
The transmission of digital command data is performed by inserting a command
data packet into the digital voice data stream for transmission to the base
unit.
Commands may be initiated either by the user depressing the handset keypad or
by the
handset microprocessor generating link check commands. When it is necessary to
transmit a command between the handset and base unit the handset
microprocessor
transmits the command code to a command data -voice data interface. This
interface
then interrupts the flow of digital voice data and inserts a command data
packet. When
the digital data is received by the target unit another identical command data
-voice data
interface checks for the presence of a command data packet in the stream of
incoming
digital data, and if one is found, captures the command data packet and
replaces the
data packet with a quiet data sequence which then is then treated as digital
voice data
by the receiving unit. The quiet data sequence is treated as silence and thus
causes a
short undetectable dropout of about one millisecond in the otherwise
continuous stream
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14
of spoken words heard by the user through the speaker. The command data -voice
data
interface then transfers the captured data packet to the receiving unit's
microprocessor
which interprets and executes the command code contained within the command
data
packet.
Commands are transmitted from the handset to the base unit, and from the base
unit to the handset in the form of a command data packet which conforms to the
following protocol. The command data packet is composed of a 48 bit code. The
first 8
bits are a preamble and are all "ones". The next 16 bits comprise the security
code. The
security code is selected randomly from one of approximately 65,000 possible
codes by
the base unit micro- processor and is downloaded into the command data-voice
data
interfaces in the handset and the base unit. The remaining 24 bits of the
command data
packet comprise an 8 bit data word repeated three times. The first S bit data
word is
composed of an initial "0" bit followed by a 5 bit data code, a 1 bit transmit
sequence
counter number and a 1 bit receiver sequence counter number. The initial bits
of the
second and third data words are either both "01s" or "lis" depending on
whether the
base or handset, respectively, is sending so as to prevent a feedback
situation where a
device may inadvertently receive a command it just transmitted to the other
device.
When the user presses a button on the handset keyboard which necessitates that
a
command be transmitted, the microprocessor transmits the command to the
handset
command data-voice data interface which assembles the 48 bit command data
packet.
The interface then interrupts the otherwise continuous flow of digital voice
data and
inserts the 48 bit command data packet in place of 48 bits of digital voice
data. The
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command data packet then travels to the base unit,' effectively as part of the
digital
voice data.
At the base unit, all incoming digital data passes through a command data-
voice
data interface identical to that in the hand- set unit which continuously
scans the flow of
5 incoming digital data. When the interface finds that any consecutive 24 bits
match the
predetermined preamble and security code, a command data packet has been
located
since the trailing 24 bits are, by definition, digital command data which is
then captured
and transferred to the base unit microprocessor whose software exe-cutes the
command corresponding to the received command code. The command data -voice
10 data interface having captured a 48 bit command data packet replaces the 48
bits with a
48 bit quiet data sequence which comprises 48 bits of alternating ones and
zeros. The
quiet data sequence then flows as part of the surrounding digital voice data
to the digital
to analog converter. The quiet data sequence becomes a momentary period of
silence
when converted by the digital-to-analog converter and results in a mere one
millisecond
15 dropout of voice when played into the speaker.
The foregoing method of combined digital and command data transmission and
reception permits the implementation of several new and useful features.
For each command which is sent between the base and handset, a
corresponding acknowledgment is returned to the transmitting device signaling
that the
target device received the command. The PAR (Positive Acknowledgment with
Retransmission) protocol is implemented such that the transmitting unit sends
a single
command and then waits for an acknowledgment before proceeding to send the
next
CA 02151516 2001-10-04
l6
command. The transmitter sequence counter number bit and the receiver sequence
counter number bit of the command data packet facilitate implementation of
this feature.
When the cordless phone is first powered up, or otherwise initialized by being
placed
into the handset storage cradle of the base unit, the software in the handset
and base
unit initialize the transmit and receive sequence counter numbers to zero.
When, for
example, the handset transmits a data packet to the base unit, the first
sequence
number is zero. A software timer is initiated upon transmission of a command
data
packet. When the base unit receives the data packet, the base unit transmits
an
acknowledgment with a sequence counter number of zero. An acknowledgment is
another "command" and thus is transmitted as part of a command data packet.
The
receiver, the base unit, increments its sequence number by Modulo 2, such that
zero
becomes one and one becomes zero. The handset unit receives the acknowledgment
with a sequence zero and stops and resets the software timer and then
increments its
sequence counter number by Modulo 2.
Two possible types of error can occur. One is that the command data packet
was received incorrectly or otherwise lost. The second is that the
acknowledgment
packet transmitted by the receiving device was received incorrectly or lost by
the
transmitter device. If the command data packet was incorrectly received or
lost the base
unit will not send back an acknowledgment. The handset software timer will
time out
after a certain amount of time and automatically cause the command data packet
to ,-- ,
be resent with the same sequence number. If the second type of error occurs,
the base
unit will have received a correct data packet and will have sent out a
corresponding
CA 02151516 2001-10-04
17
acknowledgment. The base unit will have incremented its received sequence
counter
number. If the acknowledgment packet is subsequently lost or damaged, the
handset
unit will time out and send the command data packet again. The base unit will
then
receive the command data packet with the old sequence number and will assume
that
the previous acknowledgment transmitted by the base unit did not arrive at the
handset.
Accordingly, the incoming command data packet will be ignored and the
acknowledgment with the old sequence number will be resent. This will continue
until
both handset and base unit have received their correct data packets.
An additional feature of the present invention is the transmission by the base
unit
l0 of a link check signal and the subsequent transmission by the handset of an
link check
acknowledgement signifying reception of the link check signal toward deter-
mining if
there is an acceptable RF channel and if unacceptable to initiate an automatic
change of
the RF frequency channel. If several consecutive link check signals are not
received by
the handset, or if several link check acknowledgement signals are not returned
to and
received by the base unit it is assumed that the RF channel selected is no
longer
usable, either due to poor reception caused by interference or due to the
handset unit
being out of range of the base unit. If link check command signals are not
received by
the handset unit or link check acknowledgement signals are not received by the
handset
unit within a predetermined time the handset and base units will each commence
to
perform their channel scanning routines in an attempt to find a clear RF
channel and
reestablish the RF link.
During standby operation, a link check command is sent once every ten seconds
CA 02151516 2001-10-04
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from the base to the handset. This timing is selected to minimize the handset
power
consumption during the standby mode. If the base does not receive a link check
acknowledgement from the handset within five milliseconds, it will start
sending link
check commands continuously to the handset for a period of 200 milliseconds.
If there is
no reply, the base unit will start its scanning sequence. If an outgoing call
is in progress
or an intercom conversation is under way, a link check command is sent four
times per
second from the base unit to the handset. If the base does not receive any
reply for the
last eight link checks, it will start its scanning sequence. Eight missed link
check
acknowledgements is the threshold beyond which it is assumed that the RF line
quality
is unacceptable and another channel must be sought out and is selected such
that short
fades in the RF link are ignored so that unnecessary channel changes are
avoided. The
handset utilizes a time out approach. If the handset does not receive any link
check for
two seconds {8 link checks), it will start its scanning sequence. If the hand-
set does not
receive any link checks for more than one second, it will beep to indicate an
out-of-
range condition. The beeping continues until any key is pressed or a link
check
command is received.
The handset scanning sequence is as follows. The handset scans all five
frequencies within the channel group at a rate of 200 milliseconds per
channel. The
entire scanning cycle is one second. The handset will only monitor the base
unit for valid
link check command signals. The handset will not transmit a link check
acknowledgement until a valid link check command is received. Once received,
the
scanning sequence will stop and the RF link is set up for communication.
CA 02151516 2001-10-04
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The base scans all five frequencies within the channel group at a rate of one
second per channel. This will enable the two scanning sequence to overlap with
each
other. After the base unit has switched to the next channel, it will "listen"
for 30
milliseconds to check if the channel is noise-free and unused. During this
time the base
unit will not send any link check commands to the handset in order to insure
that the
handset is not transmitting. If there is interference, the base unit will
switch to the next
channel and repeat scanning on the noise-free or unoccupied channel. Once a
free
channel is identified the base will transmit link checks at a rate of 100
times per second
continuously. Once it receives a link check acknowledgment from the handset it
will stop
the scanning sequence and resume its normal operation, since link checks must
be sent
and acknowledged, both RF links are evaluated and the possibility that the
handset user
may be unaware that his transmission is noisy does not exist.
The present apparatus implements a power saver or "sleep" mode in order to
conserve handset battery power thus minimizing the frequency of battery
recharge.
l~ When the handset unit is not in use, such as when no call is in progress,
the unit is
placed into a sleep mode during which the oscillator of the handset
microprocessor is
disabled, thereby prolonging battery life. Power is however maintained to a
timer circuit
in the command data-voice data interface which periodically reactivates the
microprocessor. For example, a duty cycle may be selected such that the
microprocessor may "awaken" for a tenth of a second once every second. When
the
microprocessor is awakened, the handset is able to receive an incoming call
and is able
to accept and acknowledge an incoming link check signal generated by the base
unit.
CA 02151516 2001-10-04
Additionally, when awakened, the microprocessor scans the handset keypad
checking
to see if the user has depressed any keys. Should the user attempt to initiate
a phone
call from the handset by depressing the phone key or the intercom key, the
microprocessor is automatically awakened if asleep.
The present digital cordless telephone apparatus is a microprocessor based
system which provides software control of the hardware and maintains
communications
between the handset and base unit. The handset software resident in the
microprocessor within the handset performs the following functions. Each time
the
handset is returned to the handset storage cradle within the base unit the
handset
software performs an initialization which copies a new security code,
generated by the
base unit microprocessor, into the command data-voice data interface.
Information
relative to the channel group and frequency number for setting the phase
locked loops
of the modulator and demodulators in the transmitter and receiver paths is
also copied
to the handset unit. The software further maintains operation of handset
status such as
idle, on-line, intercom and hold. The software causes the microprocessor to
scan the
keypad looking for a keypad command to be pressed as well as executes the
keypad
functions and transmits key commands to the base unit. The software addition-
ally
receives command data from the voice data-command data interface transmitted
from
the base unit and processes the received data including maintaining the
transmission
sequence and receiver sequence counter numbers for providing positive
acknowledgment with retransmission in the event of error. The software further
implements channel scanning if communication with the base unit is lost as
well as
CA 02151516 2001-10-04
21
maintains the timers for the power saving mode and other "time out" functions.
Inputs to the handset are achieved through one of three methods. The first is
through the handset keypad which is in a matrix configuration. Keypad scanning
is
performed by rapidly polling the keypad rows. The second input to the handset
microprocessor is via the command data-voice data interface. When the
interface
identifies a match between the security code and any consecutive 24 bits, the
interface
will trigger the microprocessor through a timer capture interrupt to signal
the
microprocessor to read in the trailing 24 bits which by design are the command
data
words. Lastly, when the handset is placed in the handset storage cradle, the
base unit
will initialize the handset with a new security code, channel group and
frequency number
via the cradle data contact.
The handset software uses a central processing routine to maintain the handset
status and a priority flow control depending upon the particular input to the
handset. The
handset operates in nine different modes: standby, on, cradle, phone, page,
paged,
intercom, program, hold and test. In the standby mode, the handset is idle and
is waiting
for a valid keypad input or a valid command from the base unit. In order to
receive this
information, the power to the microprocessor and receiver section must be on
and in
operation. This will consume power constantly and accordingly reduce the
battery life
while the handset is not in the cradle. Therefore, the periodic power shutdown
is
implemented in the standby mode in order to extend the battery life while
maintaining
the capability to receive data inputs.
After switching to the standby mode, the microprocessor will wait for inputs
for
CA 02151516 2001-10-04
2?
50 milliseconds. If no inputs are received, the microprocessor will turn off
the receiver
and transmitter power and then hold its own operation. The control data-voice
data
interface remains powered and the watchdog timer contained therein will time
out after
one second if not receiving any further inputs from a microprocessor. If the
watch dog
timer times out, it will reset the microprocessor thereby waking it up. Upon
restarting, the
microprocessor will turn on the receiver power to allow the command data-voice
data
interface to read in data from the base unit as well as scan the keypad. If no
input is
detected the power saving sequence is executed again. During the sleep mode,
the
"phone" and "intercom" keys remain enabled such that actuation of either of
them by the
user will cause an immediate interrupt and reset of the microprocessor and an
immediate carrying out of the particular function.
Each time the handset is returned to the handset storage cradle within the
base
unit, the microprocessor detects that the handset is on the cradle and will
terminate all
operation and commence a cradle initialization. During initialization data is
received from
I S the base unit through the cradle data contact automatically. When the
security code,
channel group and frequency numbers are transferred from the baseset
microprocessor
to the handset, the handset will acknowledge the base unit after the data is
received and
remain in that state until the handset is removed from the cradle.
When the user wishes to initiate a call from the handset or answer an incoming
call from the base unit, the software will cause the handset to 9° into
the "phone" mode.
The transmitter power will be turned on to enable communications with the base
unit.
The microprocessor will accept inputs from all keys except the "intercom" key
which is
CA 02151516 2001-10-04
23
disabled while a call is in progress and activated only if the call is placed
on hold.
The "page" mode can be entered by pressing the intercom button when the
handset is in a standby or hold mode. This will enable the microprocessor to
page the
base unit. If the page is answered by the baseset the handset will enter an
intercom
mode permitting communication between the handset and speaker phone in the
baseset.
The paged mode can be entered by receiving a page command from the base
set while the handset is in the standby or hold mode. The hold mode can be
entered by
pressing the hold key if the handset is already in the phone mode or by
receiving a hold
command by the base all towards placing an in-progress call on hold.
The program mode can be entered only by pressing the program key on the
handset while in the standby mode. This mode allows the user to program phone
numbers into memory as well as programming ring types. A test mode is provided
and is
accessed only during production testing of the device.
1 ~ The base unit microprocessor contains a comparable software routine to
control
the functions of the base unit corresponding and/or complementary to those
carried out
by the handset unit. In addition, the base unit software will perform the
functions relative
to memory storage and redial, security code generation and channel group and
frequency selection, during the initialization routine, sensing on-hold phone
lines and
selecting different types of ringing tones.
BRIEF DESCRIPTION OF THE DRAWINGS
CA 02151516 2001-10-04
24
Fig. 1 of the drawings is a top plan view of the handset unit and the base
unit which
together comprise the present digital cordless telephone apparatus;
Fig. 2 of the drawings is a simplified functional block diagram of the various
stages
in the transmit path and reception path of the circuitry found in both the
handset unit and
the base unit;
Fig. 3 of the drawings is diagram of the 48 bit command data packet;
Fig. 4 of the drawings is a diagram of the 8 bit base unit data word;
Fig. 5 of the drawings is a representation of the 8 bit handset unit data
word;
Fig. 6 of the drawings is a functional layout of the handset unit keypad and
light
emitting diodes;
Fig. 7 of the drawings is a functional layout of the base unit keypad and
light emitting
diodes;
Fig. 8 of the drawings is a detailed functional block diagram common to the
handset
unit and base unit of the present apparatus;
Fig. 9 of the drawings is a schematic circuit diagram of the microphone,
transmitter
baseband audio stage and analog-to-digital converter of the handset unit;
Fig. 10 of the drawings is a schematic circuit diagram of the microprocessor,
command data-voice data interface, power regulator and low battery indicator
circuitry of
the handset unit;
Fig. 11 of the drawings is a schematic circuit diagram of the PLL based
modulator
stage of the handset unit shown comprising the modulator, transmit oscillator,
divider,
frequency synthesizer and low pass filter;
CA 02151516 2001-10-04
Fig. 12 of the drawings is a schematic circuit diagram illustrating the
bandpass filter,
duplexer and transmit antenna of the handset unit transmitter path as well as
the bandpass
filter and RF amplifiers of the receiver path of the handset unit;
Fig. 13 of the drawings is a schematic circuit diagram illustrating PLL based
down
5 converter comprising the mixer and associated oscillator, divider, frequency
synthesizer and
lowpass filter, as well as IF amplifier, bandpass filter and second IF
amplifier in the receiver
path of the handset unit;
Fig. 14 of the drawings is a schematic circuit diagram of the second down
converter
stage comprising the second mixer and local oscillator, as well as bandpass
filter, limiter,
10 and demodulator circuitry of the handset unit;
Fig. 15 of the drawings is a schematic circuit diagram of the digital-to-
analog
converter, receiver baseband audio section output amplifier/filter and speaker
of the
handset unit;
Fig. 16 of the drawings is a schematic circuit diagram of the keypad and
status
15 LEDs of the handset unit;
Fig. 17 of the drawings is a schematic circuit diagram of the telephone
interface of
the base unit;
Fig. 18 of the drawings is a schematic circuit diagram of the speakerphone and
hybrid of the base unit;
20 Fig. 19 of the drawings is a schematic circuit diagram of the analog-to-
digital
converter and digital-to-analog converter circuitry of the base unit;
Fig. 20 of the drawings is a schematic circuit diagram of the microprocessor,
CA 02151516 2001-10-04
26
command data-voice data interface, DTMF tone generator and on-cradle indicator
circuit
of the base unit;
Fig. 21 of the drawings is a schematic circuit diagram of the volume control
and
power regulator circuits of the base unit;
Fig. 22 of the drawings is a schematic block diagram of the command data-voice
data interface implemented as an application specific integrated circuit, and
watchdog timer;
Fig. 23 of the drawings is a schematic block diagram of the command data-voice
data interface;
Fig. 24 of the drawings is a schematic circuit diagram of
the watchdog timer;
Fig. 25 of the drawings is a schematic circuit diagram of the microprocessor
interface of the command data-voice data interface;
Fig. 26 of the drawings is a schematic circuit diagram of the clock generator
of the
command data -voice data interface;
Fig. 27 of the drawings is a schematic circuit diagram of the clock data
recovery
circuitry of the command data - voice data interface;
Fig. 28 of the drawings is a schematic circuit diagram of the security code
register
of the command data -voice data interface;
Fig. 29 of the drawings is a schematic circuit diagram of the transmitter
register
controller of the command data -voice data interface;
Fig. 30 of the drawings is a schematic circuit diagram of the transmitter
register of
the command data - voice data inter- face;
CA 02151516 2001-10-04
27
Fig. 31 of the drawings is a schematic circuit diagram of the descrambler
circuitry
of the command data - voice data interface;
Fig. 32 of the drawings is a schematic circuit diagram of the scrambler
circuitry of
the command data - voice data interface;
Fig. 33 of the drawings is a schematic circuit diagram of the receiver
register
controller of the command data - voice data interface;
Fig. 34 of the drawings is a schematic circuit diagram of the receiver
register of the
command data -voice data interface;
Fig- 35 of the drawings is a schematic circuit diagram of the security code
comparator circuitry of the command data - voice data interface;
Fig. 36 of the drawings is a flow diagram of the software routine for the
power saving
mode of the handset of the invention;
Fig. 37 of the drawings is a flow diagram of the software routine for writing
command
code data to the command data - voice data interface of the invention;
l 5 Fig. 38 of the drawings is a flow diagram of the software routine for
sending data to
the serial peripheral interface of the handset unit and base unit
microprocessors of the
invention;
Fig. 39 of the drawings is a flow diagram of the software routine for reading
command code data from the command data - voice data interface of the
invention;
Figs. 40, 41 and 42 of the drawings are diagrams of the software routine
resident
in the base unit for performing the link check function while a call is in
progress;
Figs. 43 and 44 of the drawings are flow diagrams of the software routine
resident
CA 02151516 2001-10-04
28
in the base unit for performing the link check function when there is no call
in progress;
Figs. 45 and 46 of the drawings are flow diagrams of the software routine
resident
in the handset unit for performing the link check function while a call is in
progress; and
Fig. 47 of the drawings is a flow diagram of the software routine resident in
the
handset unit for performing the link check function when there is not call in
progress;
CA 02151516 2001-10-04
DETAILED DESCRIPTION OF THE DRAWINGS
While this invention is susceptible of embodiment in many different forms,
there are
shown in the drawings and will herein be described in detail a specific
embodiment, with the
under- standing that the present disclosure is to be considered as an
exemplification of the
principals of the invention and is not intended to limit the invention to the
embodiment
illustrated.
Fig. 1 of the drawings illustrates handset unit 101 and base unit 110 which
together
form the present digital cordless telephone apparatus 100. Handset unit 101 is
shown
comprising a hand held telephone instrument which communicates with base unit
110 via
radio frequency (RF) links "A" and "B" established between antenna 102 of
handset unit
101 and antenna 115 of base unit 110. Handset unit 101 is shown including
microphone
105 into which the user speaks and speaker 103 through which the user listens.
Keypad
104 is shown incorporating both the push button keys and light emitting diodes
through
which the user operates the digital cordless telephone apparatus 100 and
monitors its
status. Contacts 106, 107 and 108 are shown positioned on the face of hand-
set unit 101.
Contacts 106, 107 and 108 are metallic terminals which provide connection to
the internal
batteries and microprocessor.
Base unit 110 is shown comprising a housing which is intended to remain fixed
in
place and hard-wire connected to the user's, local telephone network via
connector cord
118 which is designed to plug into the RJ 11 type wall jack found in most
homes and
businesses. Base unit 110 includes handset storage cradle 111 which is
designed to
receive and retain handset unit 101 for storage and recharging of the handset
batteries.
CA 02151516 2001-10-04
When in its storage position, in a face-down position, contacts 106, 107 and
108 of handset
unit 101 align with and juxtapose contacts 114, 113 and 112, respectively,
such that
recharge power may be sup- plied to handset unit 101 via contacts 112 and 114
and such
that a physical data link may be established between the microprocessor
resident in each
S of handset 101 and base unit 110. Base unit 110 further includes key pad 117
which
permits the user to actuate and access the local telephone service using
speakerphone 116
which includes speaker 116A and microphone 1168. Base unit 110 is shown
connected to
an external source of power via power connector 119.
Fig. 2 of the drawings is a simplified block diagram of the of the functional
stages
I 0 which make up the present digital cordless telephone apparatus 100. As
shown in Fig. 1,
the present digital cordless phone apparatus 100 comprises handset unit 101
and base unit
110 which is hard-wired connected to the user's local telephone company
exchange in the
same manner as is a conventional telephone set.
Two types of digital data are exchanged between base unit 110 and handset 101.
I S The first type of data is referred to herein as digital voice data and
represents the spoken
conversation which takes place between the user operating handset 101 and the
other
party to the conversation represented by base unit 110. The second type of
data which is
exchanged between base unit 110 and handset 101 is referred to herein as
digital
command data. Digital command data represents the instructions and/or status
requests
20 which are transmitted between handset unit 101 and base unit 110 to
facilitate operation
of digital cordless telephone apparatus 100.
Each of handset 101 and base unit 110 include two data paths indicated by
arrows
CA 02151516 2001-10-04
31
133 and 134. Data path 133 corresponds to the transmission of voice and
command data
while data path 134 corresponds to the reception of voice and command data. To
avoid
unnecessary duplication, the transmission of a spoken voice from handset unit
101 to base
unit 110 and reception by base unit 110 from handset unit 101 will each be
described with
the understanding that the corresponding transmission by and reception from
base unit 110
occurs in the same manner with the exception that handset 101 transmits on the
RF link
frequency received by base unit 110 and base unit 110 transmits on the RF link
frequency
received by handset 101.
The transmission of a human voice from handset unit 101 to base unit 110
occurs
as follows. The user speaks into microphone 105 of handset unit 101 which
picks up the
user's voice and generates an analog electrical signal onto line 129 in
response to the
user's voice. The analog electrical signal is amplified and put through a
lowpass filter both
contained in transmitter baseband audio stage 130. The output of stage 130 is
a baseband
analog voice signal. The analog voice signal is then digitized by digital
transmitter stage 131
which includes an analog-to- digital converter the output of which is a
baseband digital
voice data signal. In the present digital cordless telephone apparatus 100 the
Adaptive
Delta Modulation digitization technique is utilized. It is contemplated that
anyone of a variety
of other available digitization techniques could be utilized. The base- band
digital voice data
signal is passed through command data - voice data interface 125 which
recognizes the
signal intended to be transmitted as being a digital voice signal (as opposed
to a command
signal) and scrambles the baseband digital voice data for transmission to base
unit 110.
The scrambled baseband digital voice data is then modulated by RF transmitter
stage 132
CA 02151516 2001-10-04
32
onto a 926 MHz carrier using Frequency Shift Keying (FSK) modulation.
Duplexer 121 serves to isolate transmission path 133 from reception path 134
of
handset unit 101 through the use of a high impedance network which induces the
digitally
modulated RF signal to antenna 120 and prevents the transmitted digitally
modulated RF
voice data from being fed into reception path 134. The modulated digital voice
data is then
transmitted to base unit 110 via antenna 120.
Base unit 110 functions to transmit and likewise receive digital voice data
and
accordingly reference will be made to Fig. 2 to describe this function. Base
unit 110
receives the modulated digital voice signal via antenna 120 and directs the
received digital
voice signal to RF receiver stage 124 by way of duplexer 121. RF receiver
stage 124
amplifies and filters the incoming modulated digital voice signal and down
converts the
signal from 926 MHz to 10.7 MHz where it is filtered and demodulated into a
baseband
digital voice signal. The baseband digital voice signal is passed through
command data -
voice data interface 125 which first unscrambles the digital voice data and
then recognizes
the received signal as a digital voice signal. The baseband digital voice
signal is then
converted into a baseband analog voice signal by digital receiver stage 126
which
incorporates a digital-to-analog converter. The output, a baseband analog
voice signal, is
then filtered and amplified by receiver baseband audio stage 127 before being
sent out on
line 128 to the local telephone company telephone lines, via a telephone
interface, not
shown.
Analog voice signals presented to base unit 110 via either the telephone
interface
or speakerphone 116 are transmitted to handset unit 101 using the same process
used by
CA 02151516 2001-10-04
33
handset unit 101 to transmit to base unit 110 except that base unit 110 will
transmit at a
frequency of 906 MHz. In addition to transmitting digital voice data signals
to base unit 110,
handset unit 101 transmits digital command signals to base unit 110. The
command data
signals differ from voice data signals in that they are not part of the voice
communication
between the user and the other party to the conversation, but rather, take the
form of
instructions and/or status checks which are exchanged between handset 101 and
base unit
110.
The remote selection of an outgoing line and generation of DTMF tones, as well
as
other command functions described herein are accomplished by transmitting
command
data signals between handset 101 to base unit 110.
In the present invention where the voice data and the command data are both in
the
digital format a unique solution has 1 been created to facilitate the
intermixing of digital
voice data and digital command data through the interruption of the flow of
digital voice data
to permit command data to be inserted into the data path and thus transmitted
over the RF
link. In addition, in the present apparatus, the transmission of command data
is
accomplished using a unique data protocol incorporating a verified
transmission scheme
to insure that transmitted command data has been received by the intended
unit.
The transmission of digital command data is performed by inserting a command
data packet into the digital voice data stream for transmission to base unit
110. Commands
are initiated by either the user pressing keypad 122 or by microprocessor 123
under
software control. When it is necessary to transmit a command between handset
101 and
base unit 110 the microprocessor 123 transmits the command code to command
data -
CA 02151516 2001-10-04
34
voice data interface 125. Interface 125 then interrupts the flow of digital
voice data
generated by digital transmitter stage 131 and inserts a command data packet.
As the
digital data is received by the target unit command data -voice data interface
125 checks
for the presence of a command data packet in the stream of incoming digital
data, and if
one is found, captures the command data packet and replaces the data packet
with a quiet
data sequence which is then treated as digital voice data by apparatus 100.
The quiet data
sequence is treated by digital receiver stage 126 as silence and thus causes a
short
dropout in the otherwise continuous stream of spoken words heard by the user
through the
speaker. Command data-voice data interface 125 transfers the captured data
packet to
microprocessor 123 which interprets and executes the command contained within
the data
packet.
The format of the command data packet is illustrated in Fig. 3. The data
packet is
48 bits in length and comprises an 8 bit preamble followed by a 16 bit
security code and
then an 8 bit command word repeated three times. The preamble comprises 8 bits
all set
to "1 ". The security code consists of 16 bits of random data.
The command data is repeated three times. If all three data packets are not
the
same an error is assumed to have occurred and the data is ignored. A "majority
rules" type
of arrangement could also be implemented.
The base unit 110 command data packet is illustrated in Fig. 4 and is shown
comprising an initial bit, which is set to "0" in the first data word 135 and
is set to "0" in the
second and third data words 136 and 137, a 5 bit command code, a 1 bit
transmission
sequence counter number 138 and a 1 bit reception sequence counter number 139.
The
CA 02151516 2001-10-04
handset 101 data format is illustrated in Fig. 5 and comprises an initial bit,
which is set to
"0" in the first data word 135 and set to'1' in the second and third data
words 136 and 137,
a 5 bit command code, a 1 bit reception sequence counter number and a 1 bit
transmission
sequence counter number.
5 In apparatus 100, base unit 101 loads one of approximately 65,000 possible
security
codes into handset 101 each time handset 101 is returned to handset storage
cradle 111
in base unit 110. The security code is generated by software resident in base
unit 110 and
is used by handset 101 and base unit 110 to insure the stability and integrity
of the RF link.
The data formats illustrated in Figs. 4 and 5 indicate that since the data
format
10 include both transmit and receive sequence counter numbers the information
may be piggy-
backed onto each data sequence sent .
Fig. 6 of the drawings is a functional layout of keypad 104 of handset 101, a
review
which is useful towards understanding and interaction of handset 101 and base
unit 110.
Keys 201 through 212 correspond to keys numbered 1 through 9 plus the "'*",
zero and "#"
15 keys found on typical "touch tone" telephone sets. Additionally illustrated
in Fig. 6, are keys
219, 221 and 223 labeled "phone", "intercom" and "off", respectively. Phone
key 219 is
used by the user to initiate the call from handset 101 whereby the user would
depress
phone key 219 in order to establish an RF link between handset 101 and base
unit 110 and
access a telephone line. LED 220 positioned above phone key 219 is illuminated
when an
20 outside line is being used.
Intercom key 221 is provided towards permitting the user to establish an RF
link
between handset 101 and base unit 110 for the purpose of conducting an
intercom call
CA 02151516 2001-10-04
36
between handset 101 and base unit 110 such that an outgoing line is not
accessed. As
illustrated in Fig. 1, the user with the handset 101 would be conversing
through the speaker
and microphone present in handset 101 while the other party to the intercom
call would be
conveys- ing through microphone 116A and speaker 1168 of speakerphone 116
present
in base unit 110. Once the user depresses intercom key 221, a voice
conversation can be
carried on between handset 101 and base unit 110.
Off key 223 is provided and is utilized to disconnect access to a telephone
line as
well as to disconnect and discontinue an intercom conversation. If a three-way
conversation
is being carried on (the use of an outside line, speakerphone and handset)
depressing off
key 223 will disconnect the handset from the conversation and leave the party
at the
speakerphone connected to the outside line.
When keys 201 through 210, 1 through 9 plus 0 are depressed and an outside
line
has been previously selected by depressing phone key 219, a DTMF tone is
transmitted
over the line and is echoed back to handset speaker 103. If keys 201 through
210 are
continually depressed, the tone is continuously sent. For pulse lines,
depression of any key
201 through 210 causes the appropriate pulse pattern to be sent out over the
line as well
as being echoed back through handset speaker 103.
Star/tone key 211 is provided and permits the user to cause handset 101 to
operate
in the tone mode if base unit 110 has been placed into the pulse mode.
Pressing the tone
key 211 will cause DTMF tones to be generated upon the depression of keys 201
through
210 and 211 and 212 for the duration of a call. "Pound" key 212 is provided
and when
depressed generates the appropriate DTMF tone. If handset 101 is in the pulse
mode, this
CA 02151516 2001-10-04
37
key is inactive. Pound key 212 is also used to program the ringer type.
Additionally, six function keys are provided. Memory key 213 is provided and
is used
by the user to program phone numbers into the memory storage resident in base
unit 110.
Ten memory locations, 0-9, are provided, each of which may store up to sixteen
digits. To
store a phone number in memory, the user first presses program button 214 then
selects
a memory location by pressing one of keys 201 through 210, and using the
keypad 104
enters the number that the user desires to store in memory. When complete, the
user
presses memory key 213 which assigns the phone number to the key location
selected. To
dial a phone number from its memory location, the user merely selects an
outgoing line by
pressing "phone", thereby getting a dial tone, and then pressing memory key
213 followed
by the storage location number, 0-9.
Redial key 215 is provided and automatically dials the number which the user
has
dialed most recently. To use the redial, the user simply selects a dial tone
by pressing
phone key 219 and then presses redial key 215.
Hold key 216 is provided for placing an outgoing call on hold. To take a call
off hold,
the user merely presses phone key 219. As a safety feature, if the user has
placed a call
on hold by first pressing hold key 216, pressing off key 223 will not
disconnect a call. If a
call is on hold and handset 101 is put into the storage position in base unit
110, the call is
still held. If the user then goes to another phone and picks up the phone, the
call is
automatically taken off hold and the cordless phone 100 is released. Once the
user hangs
up the other phone, the call is disconnected and nothing further need be done
to disconnect
cordless phone 100. If a three-way conversation is taking place between
handset 101, base
CA 02151516 2001-10-04
38
unit 110 and an outgoing call, depressing hold key 216 will cause both handset
101 and
base unit 110 to be put on hold such that pressing phone key 219 or
speakerphone key 323
will disable the hold function. In order to signal to the party placed on hold
that a connection
is still is place, cordless phone apparatus 100 generates a tone pulse which
is sent out
every five seconds. In addition, handset 101 will beep once every ten seconds
to alert the
user a call has been placed on hold. Depressing the hold key when attempting
to store a
phone number into a memory location, as previously de- scribed, will cause a
pause to be
inserted into the dialing sequence as may be necessary when accessing certain
telecommunication devices and/or systems.
Program/privacy key 214 serves two functions. When an outside line has been
selected by handset 101, depressing programlprivacy key 214 results in speaker
116A
resident in base unit 101 to be toggled from an enabled to a disabled status
for the duration
of the call. This allows the user to have a conversation from handset 101 to
an outgoing call
without anyone listening into the conversation through speakerphone 116 in
base unit 110.
I 5 Depressing programlprivacy key 214 again will toggle the speakerphone 116
from disabled
to enabled. Once the call is completed by depressing off key 223, speakerphone
116 is
automatically reset to enabled. When handset 101 is off line and has not
accessed an
outgoing line, pressing program/privacy key 214 causes handset 101 to be
placed in the
program mode. In the program mode, the user can store phone numbers as
previously
described or may select the ringer type. To set the ringer type, the handset
101 and base
unit 110 must be off. The user first depresses the programlprivacy 214, then
depresses
pound key 212 and then depresses a key 1 through 4, 201 through 204, in order
to select
CA 02151516 2001-10-04
39
a ringer type. Once a ringer type has been selected, handset 101 will ring
once to indicate
to the user the type of ring that has been selected. In addition, the user may
select between
a high and a low volume ring by depressing the privacy key, the pound key 212
and then
the zero key to toggle between a high and low volume ringer. Once selected,
the ringer
stays in its mode until reprogrammed. Flash key 217 is provided and has the
same affect
as momentarily pressing the switch hook on a conventional telephone set. This
function is
used with such services as call waiting and/or call forwarding as supplied by
local telephone
companies.
Mute key 218 is provided and serves to disable handset microphone 105. When
disabled, low battery/mute LED 224 will flash. Depressing mute button 218 will
again
disable the mute feature.
Low battery/mute LED 224 serves to indicate to the user that the battery
charge of
handset 101 is low. When the battery is detected as being low, a warning tone
is emitted
from handset 101 when a call is first activated. During a call the low battery
LED 224 will
remain lit indicating to the user that the unit 101 needs to be recharged. In
addition, volume
up and down buttons are provided on the side of handset 101 (not shown) which
controls
the volume of speaker 103 and may be increased/decreased between low, medium
and
high settings.
Fig. 7 of the drawings is a function layout of keypad 117 of base unit 110.
Keys 301
through 315 function identical to hand- set 101 keys 201 through 215. Intercom
key 321,
hold key 316, flash key 318 and mute key 319 also function is accordance with
their
counterpart keys resident in keypad 104 of handset 101. Present in base unit
and not
CA 02151516 2001-10-04
present in handset 101 is speaker phone key 323, which operates in several
different
modes. When an outgoing line is not selected, pressing speakerphone key 323
will cause
base unit 110 to retrieve an outside line. Once selected, LED 324 will
illuminate. A
telephone number may then be called manually by depressing keys 301 through
312 or by
5 depressing redial key 315. When a phone line is engaged by handset 101,
depressing
speakerphone key 323 will cause a three- way conversation to take place
between handset
101, base unit 110 and the outgoing line. If this feature is selected, handset
101 will be
alerted to its selection by the emission of an audible tone and the flashing
illumination of the
intercom LED 222 on handset 101. Should the user of handset 101 elect not to
permit a
10 three-way conversation to occur, the user may simply press privacy key 214
to disconnect
the speakerphone 116 of base unit 110. If a phone line has been engaged only
by base unit
110, pressing speakerphone 323 will disengage the line. If an outgoing line is
engaged by
both handset 101 and base unit 110, pressing speakerphone button 323 during a
three-way
conversation will disconnect speakerphone 116 from the conversation. Handset
101 and
15 the outside line will continue to be connected. If a call has been placed
on hold by having
pressed hold key 316, pressing speakerphone key 323 will take the call off
hold. In addition,
if the speakerphone is being used and handset 101 is in handset storage cradle
111,
retrieving handset 101 from cradle 111 will automatically disconnect
speakerphone 116.
Base unit 110 may be activated by merely pressing speakerphone key 323. Charge
LED
20 329 is provided and when lit indicates to the user that the handset 101 is
resident in cradle
111 and is charging. Speakerphone volume control 325 is composed of a down
button 326
and an up button 327 which serves to provide variable control of speakerphone
116.
CA 02151516 2001-10-04
41
Fig. 8 of the drawings is a functional detailed block diagram of the handset
unit 101
and base unit 110 of the present digital cordless telephone apparatus 100.
Portions of the
block diagram which are common to both handset unit 101 and base unit 110 are
shown
by solid lines whereas the remaining portions, shown in dash lines, are
applicable only to
base unit 110. As can be seen from the drawing, two data paths designated by
arrows 133
and 134 exist respectively between microphone 140 and antenna 152, and antenna
152
and speaker 182. Data path 133 corresponds to the transmitter portion of
handset 101
whereby the spoken word is received and transmitted via antenna 152 while data
path 134
corresponds to the receiver portion of handset 101 wherein the radio frequency
signal is
received antenna 152 and made audible at speaker 182. In operation, microphone
140 of
handset 101 picks up the user's spoken voice and converts it into an analog
electrical
signal. This signal is then amplified and filtered by transmitter baseband
audio stage 141
the output of which is a baseband analog audio signal. This baseband analog
signal then
passes to analog-to-digital converter 142 which serves to digitize the
incoming analog
I S signal such that the output of analog-to-digital converter 142 is a
baseband digital audio
signal. The digital audio signal passes through transmitter register 143 and
is then
scrambled by scrambler 144. The digitization technique utilized in the present
invention is
the Adaptive Delta Modulation (ADM) technique. If the output of analog-to-
digital converter
142 were to be modulated onto a carrier frequency and transmitted by antenna
152 without
scrambling, it is possible that due to the modulation technique utilized the
radio signal if
intercepted might to some degree be audible such that the voice transmission
would be
discernible and understandable by the intercepting party. Accordingly,
scrambler 144
CA 02151516 2001-10-04
42
serves to scramble the digital voice data such that the transmitted radio
signal if intercepted
would not be able to be directly understood.
The output of scrambler 144 is sent to voltage controlled oscillator (VCO) 145
which
modulates a carrier using Frequency Shift Keying (FSK) modulation. The actual
carrier
frequency 'is dependent upon the DC voltage from lowpass filter 148. Lowpass
filter 148
comprises part of a PLL frequency synthesizer circuit consisting of voltage
controlled
oscillator 145, lowpass filter 148, frequency synthesizer 147 and divider 146.
Frequency
synthesizer 147 basically determines what frequency the VCO 145 is operating
at by
dividing its frequency down with a divider 146. This signal is then compared
against a
reference frequency by frequency synthesizer 147 and an error voltage is
applied through
lowpass filter 148 which corrects any drift in the VCO 145. The net result is
that at the
output of VCO 145 there is a modulated carrier at a frequency determined by
microprocessor 183.
The output of VCO 145 is thus a modulated carrier at one of 20 frequencies
from
925.5 MHz to 927.4 MHz. The modulated digital voice signal is then amplified
by RF
amplifier 149 and filtered by bandpass filter 150 which serves to pass only
those
frequencies between 925.5 and 927.5 MHz. The filtered output of bandpass
filter 150 is
then applied to antenna 152 via duplexer 151 where it is broadcast to base
unit 110.
Incoming modulated digital data having been transmitted from base unit 110 at
one
of 20 different frequencies is received by antenna 152. The frequency channels
are from
905.6 MHz to 907.5 MHz. .The modulated digital voice signal is induced into
antenna 152
and filtered by bandpass filter 160. The filter is centered on 906 MHz and is
about 2 MHz
CA 02151516 2001-10-04
43
wide such that it only passes those frequencies between 905.5 MHz and 907.5
MHz.
Accordingly, de- sired frequencies are passed while undesired frequencies are
attenuated.
The output of bandpass filter 160 is a modulated digital voice signal which is
then
amplified by RF amplifier 161 and passed to mixer 162. Mixer 162 serves to
down convert
the incoming 900 MHz signal bringing it to a 60 MHz signal through the use of
a PLL circuit
comprising voltage controlled oscillator 163, lowpass filter 166, frequency
synthesizer 165
and divider 164. The frequency synthesizer 165 basically determines what
frequency VCO
163 is operating at by dividing its frequency down with divider 164 comparing
it against a
reference frequency by frequency synthesizer 165 such that an error voltage is
applied
through lowpass filter 166 which corrects drift in VCO 163. Microprocessor 183
thus serves
to select the precise frequency at which the signal will be down converted
corresponding
to one of the 20 possible frequency channels. The circuit takes in the
appropriate "channel
number" from microprocessor 183 making it possible for microprocessor 183 to
specify the
particular channel that is to be received toward permitting auto channel
changing under
microprocessor control. The output of mixer 162 is amplified by IF amplifier
167, filtered by
bandpass filter 168, and again amplified by IF amplifier 169 before it is
further down
converted by mixer 170 driven by fixed oscillator 171 operating at 49.3 MHz.
Mixer 170 and
oscillator 171 serve to provide a fixed amount of down conversion bringing the
received
modulated digital voice signal down to 10.7 MHz where it is amplified and
further filtered by
amplifier 172 and bandpass filter 173. The output of bandpass filter 173
passes through
limiter 174 which serves to remove any amplitude modulated noise. Limiter 174
further
generates a mute signal on line 198 should a poor voice signal be detected.
CA 02151516 2001-10-04
44
Demodulator/comparator stage 175 serves to demodulate the baseband digital
voice signal
by the FSK method. The output of demodulator 175 is thus a baseband digital
signal.
Data/clock recovery stage 176 serves to recover the data and clock signal from
the
incoming digital baseband wave form signal. The data signal is then sent to
descrambler
177 which descrambles the baseband digital data performing the inverse
operation of that
performed by scrambler 144 and the clock signal is connected to digital-to-
analog converter
179 by line 197. The descrambled digital data and the recovered clock signal
generated by
clockldata recovery stage 176 are fed to receiver register 178 and then to
digital-to-analog
converter 179 which serves to convert the incoming digital voice signal into a
baseband
analog, ': signal. The analog signal is then filtered by a baseband receiver
audio filter 180
and is amplified by amplifier 181 before being directed to speaker 182. Mute
line 198 from
limiter 174 serves to mute amplifier 181 if a poor signal is detected to
thereby prevent static
from being heard through speaker 182.
Base set unit 110 operates in the same fashion as thatjust described except
for the
following differences. The receiver section of base unit 110 operates in the
925.5 to 927.5
MHz range corresponding to the frequency channels at which handset 101 is
transmitting.
Conversely, the transmitter portion of base unit 110 operates in the 905 to
907 MHz range
corresponding to the frequency channels which are being received handset 101.
In addition, in order to provide an interface to the telephone company lines,
telephone interface 193 is provided for connection to telephone jack 194.
Interposed
between telephone interface 193, input 191 to speaker 182 and output 192 of
micro- phone
140 is a standard speakerphone hybrid circuit.
CA 02151516 2001-10-04
Digital command data is transmitted and received in the following manner. When
the user pushes a button on keypad 184, microprocessor 183 transmits a
corresponding
command code to microprocessor interface 187. Microprocessor interface 187 in
turn
transfers the command code to transmitter register 143 which together with
associated
5 circuitry assembles a command data packet from the security code 'and
command code
and inserts the command data packet into the stream of digital voice data. The
command
data packet thus replaces a small portion of the digital voice data. The
digital voice data
with intermixed command data packets is connected to scrambler 144 toward
being
transmitted on the RF link.
10 Digital command data is recovered from the digital voice data stream as
follows. The
output of descrambler 177 is a data stream consisting of demodulated digital
voice signal
with intermittently spaced command data packets which is connected to receiver
register
178. Receiver register :L 78 arid associated, circuitry continually scans the
incoming stream
of digital data looking for a match between the 24 bit preamble and security
code and any
1 ~ corresponding number of bits in the data stream. When a match is found the
trailing 24 bits
by design comprise the command data packet which is transferred by receiver
register to
microprocessor interface 187. Microprocessor interface in turn transfers the
command data
packet to microprocessor 183 which executes the command associated with the
command
code contained in the command data packet. Receiver register 178 further re-
places the
20 command data packet with a quiet data sequence packet which interposed into
the data
stream is passed to digital-to- analog converter 179. Digital-to-analog
converter 179 treats
the quiet data sequence packet as silence which is not noticeable to the user
due to the
CA 02151516 2001-10-04
46
small number of voice data bits which are replaced.
Fig. 9 - Fig. 12 of the drawings comprise the schematic circuit diagrams of
the
transmitter path 133 of handset 101.
Fig. 9 of the drawings illustrates connection of microphone 140 to transmitter
baseband audio stage 141. The output of microphone 140 is an analog electrical
signal
corresponding to the user's voice. This analog electrical signal is fed to
transmitter
baseband audio stage 141 wherein amplifier 400, an LM324 type device,
amplifies the
analog baseband voice signal which is then filtered by filter 101 also based
around a type
LM324 device. The output, an analog voice signal is shown connecting to analog-
to-digital
converter 402, based upon an MC3418 integrated circuit. As configured, this
device
converts the incoming base- band audio signal into a baseband digital signal
using the
adaptive delta modulation technique. The output of analog-to-digital converter
402 is a
baseband digital signal on line 404 as well as the corresponding clock signal
on line 403,
which signals carry onto Fig. 10 of the drawings.
Fig. 10 of the drawings illustrates microprocessor 183 together with command
data-
voice data interface 125 and watchdog, timer shown implemented on an
application specific
integrated circuit 195. Microprocessor 183 is shown comprising a type
MC68HC05C4
integrated circuit, "a microcomputer on a chip" type device incorporating
internal RAM and
ROM storage. Crystal 405 serves to supply the clock signals to microprocessor
183 and
command data-voice data interface 125 and the reference frequency for
frequency
synthesizers 147 and 165. Baseband digital voice signal 404 and clock signal
403 are
shown connected to command data-voice data interface 195, the output of which
appears
CA 02151516 2001-10-04
47
on line 413 and is labeled TXData corresponding to the digital voice data
signal and which
carries onto Figure 11.
Further shown in Fig. 10 are connections 406 and 407 which provide the row and
column connections for matrix keypad 104 of handset unit 101. Additionally
shown are
volume input lines 412 which connect to the volume buttons on handset unit
101. The
power supply for handset unit 101 is supplied by battery 411 which drives
voltage regulators
410 configured around l_M2931 devices which provide a regulated five volt
output. In
addition, low battery circuit 409 serves to monitor the charge status of
battery 411 in order
that a low battery condition may be signaled to the user. Additionally shown
are contacts
106 and 108 through which base unit 110 may recharge battery 411 and 107
through which
a "physical" data link may be established with base unit 110.
Fig. 11 of the drawings continues the transmission data path 133 of handset
101
wherein the digital voice data signal appears on line 413 having come from
command data-
voice data interface 195 of Fig. 10. Fig. 11 of the drawings illustrates
voltage controlled
oscillator 145 shown comprising modulator 414, course frequency adjustment 415
and
transmit oscillator 416. Further illustrated is lowpass filter 148 and
frequency divider 146
and frequency synthesizer 147 implemented on a single MB1501 integrated
circuit. Inputs
416 are shown and provide connection to microprocessor 183 towards the
selection of the
particular channel/frequency at which handset unit 101 is to transmit. pin 5
of frequency
synthesizer 147 generates an error voltage which passes through lowpass filter
148 toward
performing channel selection by affecting the frequency of the transmit
oscillator 146. The
output of mixer 145, on line 417, passes the modulated digital voice data to
RF amplifier
CA 02151516 2001-10-04
48
149 based upon a type NE85639 transistor. The output of RF amplifier 149 on
line 418
continues on Fig. 12 of the drawings.
Fig. 12 of the drawings illustrates the balance of transmitter data path 133
beginning
with input line 419. The modulated 42 digital voice signal passes through the
four dB pad
420 and bandpass filter 150, a ceramic type bandpass filter. The output of
bandpass filter
150 is connected to duplexer 151 which is a high impedance network. The output
of
bandpass filter 150 sees the receiver data path 134 commencing with circuits
422 and 423
as a high impedance network such that the signal is induced through antenna
matching
circuit 421 onto antenna 152. As shown, duplexer 151 is constructed of
microstrip devices.
Incoming modulated digital voice data is received by antenna 152 and is
connected
to bandpass filter 160 via duplexer circuit 151. Just as the transmitted
signal sees a high
impedance and low impedance path the incoming signal likewise is induced into
the
receiver path 134 as opposed to transmitter path 133. Circuit 422 converts a
50 ohm
impedance to a 90 ohm impedance where as circuit 423 converts back to a 5 O
ohm
impedance prior to bandpass filter 160 shown comprising a ceramic bandpass
filter.
Microstrip device 424 is illustrated and serves to provide matching of
bandpass filter 160
to RF amplifier 161. RF amplifier 161 is illustrated as a two-stage RF
amplifier circuit
wherein the first stage 161 a is based upon a type NE85639 transistor which
provides 13.5
dB of gain with a noise figure (NF) of approximately 2.0 dB. A four dB pad 425
provides
isolation between RF amplifiers 161 a and 161 b to prevent oscillation between
the two,
reducing gain and providing better stability. The second stage, RF amplifier
161 b is also
CA 02151516 2001-10-04
49
based on a NE85639 transistor and provides 13.5 dB of gain. The output of
which appears
on line 426 and continues on Fig. 13 of the drawings.
Input line 426 is shown connected to mixer 162 which imparts a 10 dB
conversion
loss with a noise figure (NF) equal to 10 dB. Voltage controlled oscillator
163 is illustrated
and comprises course frequency adjustment 427 together with oscillator 428.
Variable
capacitance diode 429 comprises the tank circuit. Fine tuning of the frequency
is provided
by the microprocessor using input lines 430 to frequency synthesizer and
divider 164 and
165 which together are present on the MB1501 integrated circuit device. The
inputs 430
from microprocessor 183 serve to designate the particular channel frequency to
be received
by handset 101. Lowpass filter 166 is illustrated as two-pole loop filter
based upon the
TL072 device. The output of mixer 162 on line 431 passes through lowpass
filter 432 having
a 60 MHZ lowpass set- ting, the output of which is connected to IF amplifier
167 based on
the NE85633 transistor. IF amplifier 167 provides a plus 23 dB gain at 60 MHZ.
Bandpass
filter 168 is illustrated with a 60 MHZ center frequency and 50 ohm impedance.
IF amplifier
169 is shown comprising an NE85633 transistor which provides 23 dB of gain and
generates a 50 ohm output which consists of an amplified filtered digital
signal. This signal
is an FSK modulated digital signal which passes on line 433 to Fig. 14 for
demodulation.
The incoming 60 MHZ input on line 433 is shown connected to the RF-IN terminal
pin of the
NE615 integrated circuit which comprises a mixer with local oscillator
designated 170 and
171. within this integrated circuit is an IF amplifier designated 172. The 60
MHZ input is
thus down converted by the internal oscillator and mixer to a 10.7 MHZ signal.
The internal
oscillator 171 is operating at 49.3 MHZ per crystal 171. Also shown connected
is bandpass
CA 02151516 2001-10-04
filter 173. The mute pin of the integrated circuit of line 435 provides a
recovered signal
strength indicator which is connected to dB mute line output 436. Coupled
thereto is a mute
adjust circuit 437. Output 438 is illustrated and comprises a demodulated
digital signal
which is connected to the command data-voice data interface 125. Fig. 10 shows
the output
5 of the command data-voice data interface appearing on 439 and 440 which
continue to Fig.
15 of the drawings.
Fig. 15 of the drawings illustrates the digital-to-analog converter 179
comprising an
MC3418 type integrated circuit, the output of which on line 441 is a analog
baseband audio
voice signal corresponding to the voice signal transmitted by handset 101. The
output of
10 digital-to-analog converter 179 is connected to receiver lowpass audio
stage 180. The
output of receiver baseband audio stage 180 is connected to speaker 182.
Further shown
is incoming mute signal 436 from Fig. 14 which serves to disable baseband
stage 180
thereby muting speaker 182 if the signal strength drops below the level set by
mute
adjustment 437.
I S Further shown in Fig. 15 is ringer circuitry 443 which receives an input
from
microprocessor 183 on Fig. 10 for triggering ringer 444 signaling an incoming
call.
Fig. 16 of the drawings illustrates key pad 184 and its connections 406 and
407 to
microprocessor 183. Additionally shown are LEDs 445 and connection point 408
for
connection to microprocessor 183.
20 The foregoing description of Figs. 9- 16 while described in the context of
handset
unit 101 are equally applicable to base unit 110 with the additions and/or
modifications
illustrated in Figs. 17- 21.
CA 02151516 2001-10-04
51
Fig. 17 of the drawings illustrates telephone interface 193 which provides
connection
to RJ 11 jack 450 through lines 194. Telephone interface illustrated in this
Fig. 17 is a
standard telephone interface readily understandable to those skilled in the
art.
Fig. 18 of the drawings is a schematic circuit diagram of the speakerphone and
hybrid which drives microphone 451 and speaker 452 which together form
speakerphone
116. As with Fig. 17, Fig. 18 discloses a conventional speakerphone and hybrid
readily
understandable by those skilled in the art. Fig. 19 of the drawings are the
schematic circuit
diagrams of the delta modulator (analog-to-digital converter) and demodulator
(digital-to-
analog converter) of base unit 110 and illustrate the minor changes made
thereto when
resident in base unit 110.
Fig. 20 of the drawings illustrates microprocessor 183 and command data-voice
data interface 195 as installed in base unit 110. Further illustrated is DTMF
tone generator
453, power contacts 112, 114 and data contact 113.
Fig. 21 of the drawings illustrates the schematic circuit diagrams for digital
volume
control 454 as well as voltage regulator circuit 456 for providing power to
the component
of base unit 110.
The foregoing discussion and description of drawings while relevant to the
flow of
digital voice data also applies to the flow of digital command data through
handset unit 101.
The following description of Figs. 22 - 35 further illustrate and describe the
flow of digital
command data through handset unit 101.
Fig. 22 of the drawings is a schematic circuit diagram of the command data -
voice
data interface circuit 125 which in the present invention is fabricated as an
application
CA 02151516 2001-10-04
52
specific integrated circuit 195. In the present apparatus 100, the functions
of scrambling,
descrambling, and data and clock recovery and digital command data
communication are
performed by this single integrated circuit. rig. 22 illustrates a watchdog
timer 501 whose
function is in part to provide an escape in the event that microprocessor 183
"hangs up".
In such event, watchdog timer 501 will time out and cause a reset of
microprocessor 183
thereby re- initializing the software. While this will result in any call in
progress being
disconnected it does serve to obviate the need for the user to return to base
unit 110 to
perform a manual reset.
In addition, watchdog timer 501 performs an essential function relative the
power
saving mode. The software of handset 101 is designed to place the unit into a
power saving
mode whenever a call is not in progress or handset 101 is placed in the phone
off mode by
the user pressing off key 223. By shutting down microprocessor 183 there
results a saving
of power thus extending the battery life. Watchdog timer 501 causes
microprocessor 183
to periodically "wake up" to look to see if the user has depressed keypad 104,
if there is an
incoming call from base unit 110 or if a link check command has been received.
Watchdog
timer 501 may function on a ten percent duty cycle, thus waking the
microprocessor once
a second for a tenth of a second.
The circuit for watchdog timer 501 is illustrated in Fig. 24. In operation
watchdog
timer 501 utilizes an oscillator clock signal on line 504 to drive counter 502
which counts
from zero to five hundred twelve. Counter 502 is a ten bit ripple counter
designated RCnt10.
If counter 502 gets to five hundred twelve the microprocessor is reset by line
505. If counter
502 is cleared by line 503 before counter 502 gets to five hundred twelve the
reset will not
CA 02151516 2001-10-04
53
occur and the counter resets to zero. A clear is signaled when a call is in
progress with the
software in microprocessor 183 serving to reset counter 502 periodically and
prevent a
microprocessor reset from occurring. Accordingly if the microprocessor gets
hung up
counter 502 will time out and a reset will occur but if a call is in progress
or some other
active function is taking place the counter 502 will be reset to zero before a
time out can
occur and no master reset will take place.
The remainder of command data - voice data interface 125 resides in block 502
the
diagram of which is illustrated in Fig. 23. Functionally the circuitry of Fig.
23 serves to detect
the presence of a command data packet, capture the digital command data and
replace the
command data packet with a silence data sequence as well as to interrupt the
flow of digital
voice data, and insert a command data packet for transmission to the target
unit.
When handset unit 101 is placed in handset storage cradle 111, contact 107
abuts
contact 113 and an initialization cycle is activated. The software resident in
microprocessor
183 generates a twenty four bit security code (including a 8-bit preamble)
which is loaded
into security code register 511 by microprocessor interface 510. The circuit
diagram of
microprocessor interface 510 is illustrated in Fig. 25. The security code is
passed serially
by microprocessor 183 into microprocessor interface 510 on SDI IN line 520
into twenty four
bit shift register 521. All security codes begin with a "1" and all first data
words begin with
a "0". Microprocessor 183 toggles the write enable line SDIWEN 512 which
combined with
the preceding "1" toggles line SCLOAD 543 shown in Fig. 25 which loads the
contents of
twenty four bit shift register 521 into security code register 511 via Data
bus 513. Thus,
security code register 511 serves as the security code memory of handset 101.
A diagram
CA 02151516 2001-10-04
54
0~ security code register 511 is shown in Fig. 28.
During the transmission of digital voice data the command data -voice data
interface
125 is essentially passive except for the scrambling function performed by
scrambler 514.
The output of analog-to-digital converter 142 enters interface 125 on ENCDA-
TA line 515.
The digitized voice data passes serially through transmitter register 516 to
scrambler 514.
A schematic diagram of the transmitter register 516 is shown in Fig. 30. The
output of
scrambler 514 is passed to VCO 145 on TXOUT line 517. Schematic diagram of
scrambler
514 is shown in Fig. 32. Scrambler 514, and descrambler 533 are implemented to
induce
a "quasi- randomness" to the digital data stream toward making it difficult to
understand the
data should it be intercepted. Scrambler 514 and descrambler 533 as
implemented are self-
synchronizing circuits.
When the user has actuated a command which requires a command data packet
to be transmitted to the target unit microprocessor 183 serially shifts the
twenty four bit
command data (eight bits repeated three times) into shift register 521 upon
toggling of
SDIWEN serial data write enable line 512. The incoming twenty four bit word is
recognized
as command data since the initial bit is a "0" whereas security codes begins
with a "1".
Transmitter register controller 518 is activated to control transmitter
register 516. .The
circuit diagrams of transmitter controller 518 and transmitter register 516
are illustrated in
Figs. 29 and 30 respectively. The security code stored in security code
register 511 is
retrieved by transmitter register 516 via bus 525 towards forming the first
twenty four bits
of the forty eight bit command data packet. The last twenty four bits of the
command data
packet are formed from the command data stored in shift register 521 in
microprocessor
CA 02151516 2001-10-04
interface 510. The command data is transferred into twenty four bit latch 522
of transmitter
register 516 and in turn transferred into register 523 a parallel loading
twenty four bit shift
register. with the security code stored in shift register 524 and the command
data stored
in shift register 523 transmitter controller 518 generates forty eight clock
cycles and serially
5 shifts the security code and command data out on DOUT line 519 to scrambler
514 thus
inserting into the steam of digital voice data the forty eight bit command
data packet.
Transmitter controller 518 effectively turns off the incoming stream of
digital voice
data. Since the voice data is clocked at a high rate the "loss" of forty eight
bits of digital
voice data results in only a one millisecond dropout of the voice. Such a
small dropout goes
10 unnoticed by the user.
When handset 101 is receiving digital data, the command data -voice data
interface
operates as follows. The demodulated digital data output of demodulator 175 is
connected
to clock data recovery stage 530 which recovers the clock signal and data
signal from the
incoming digital signal. Clock generator 531 and clock-data recovery stage 530
are
15 illustrated in schematic diagrams in Figs. 26 and 27 of the drawings,
respectively. The
recovered data signal is descrambled by descrambler 533 the output of which is
descrambled digital voice data with intermittently placed forty eight bit
command data
packets. circuit diagram of descrambler is illustrated in Fig. 31. The
incoming digital data
flows into receiver register 534 and specifically into the forty eight bit
shift register contained
20 therein. The circuit diagram of receiver register 534 is illustrated in
Fig. 34 wherein it can
be seen that the forty eight bit shift register is composed of six eight bit
serial and parallel
loading clearable shift registers. At each clock cycle the first twenty four
bits contained in
CA 02151516 2001-10-04
56
the "last" three eight bit shift registers are compared to the security code.
When a match
is found by design the trailing twenty four bits represent the command data
portion of the
command data packet.
The contents of the first twenty four bits of the forty eight bits contained
in receiver
register 534 are accessed by security code comparator 536 via bus 542. The
security code.
stored in security code register 511 is likewise accessed by security code
comparator 536
via bus 537. Security code comparator 536 compares the two twenty four bit
words by
exclusive OR'ing the two words. A circuit diagram of security code comparator
536 is shown
in Fig. 35 of the drawings. The comparison is made for each clock cycle thus
effectively
scanning for a security code which would signal the presence and position of a
command
data packet. When security code comparator 536 finds a match the EQUAL line
538 goes
high to signal receiver register controller 535. Receiver register controller
535 latches the
twenty four bits residing in the "last" three eight bit shift registers of
receiver register 534
into microprocessor interface 510, and specifically into twenty four bit shift
register 540 via
1 ~ bus 539. The receive data ready line RDRDY 541 of receiver register
controller 535 goes
low to signal microprocessor 183 that data is there such that the
microprocessor interface
510 may serially shift the command data out to microprocessor 183. A circuit
diagram of
receiver register controller 535 is shown in Fig. 33.
As the twenty four bits of command data are shifted out of receiver register
534 the
six eight bit shift registers are each parallel loaded with a quiet sequence
consisting of an
eight bit word of alternating "1's" and "0's". The end result is that the
forty eight bits of digital
voice data which were "lost" are replaced with a forty eight bit pattern of
alternating "1's and
CA 02151516 2001-10-04
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0's" which are interpreted by the digital-to-analog converter as silence. The
user thus
"hears" a one millisecond dropout or moment of silence which is not actually
perceived by
the user. Through this mechanism there is no loss of command data and no
perceivable
loss of voice due to the high voice data rate.
Figs. 36- 47 are flow diagrams of various software routines contained within
either
the handset microprocessor, the base unit microprocessor, or both. The various
flow
diagrams are provided and are explained with such detail that one skilled in
the relevant art
having these software flow diagrams and descriptions would be able to
implement the
software routines with relative ease.
Fig. 36 of the drawings is a flow diagram of the software routine for the
power saving
mode of the present invention. The power saving software routine begins at
entry point 600
having branched from the main software program and initially resets the watch
dog timer,
operation 601. The routine then checks to see if a RF link is currently
established, i.e. is the
phone "on- line", operation 602. The main program will set a flag to true if
an on-line
condition exists. If an RF link exists and the phone is on-line the watch dog
timer is reset.
If no RF link is established and the handset unit is off-line the routine
checks to see of the
power saving timer has timed out, operation 603. If the timer has not timed
out the watch
dog timer is reset. If the power saving timer has timed out the routine turns
off the power
supply to the transmitter and the receiver of the handset unit, and then the
microprocessor
is halted, operations 604 and 605, respectively.
Fig. 37 of the drawings is a flow diagram of the software routine for writing
command
data to the command data - voice date interface. When the user has pressed the
keypad
CA 02151516 2001-10-04
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actuating a function which necessitates that a command code be transmitted,
the
microprocessor generates a five bit command code which is provided to the
software
routine, operation 610. The routine then commences to assemble the command
data
portion of the command data packet which will be transmitted. The command word
is
converted into an eight bit sequence 611, "OOOCCCCC", with "C" equaling a bit
of
command code data. The eight bit code is then shifted to the left two bits and
the sequence
and acknowledgement bits are added, operation 612 as represented by the eight
bit
sequence, 613, "OCCCCCSA", where "S" is the sequence bit and "A" is the
acknowledgment bit. The eight bit command word sequence is then duplicated
three times,
operation 614, to generate sequence 615. In base unit 110, the first bits of
the second and
third bytes are set to "1" in place of "0" in order to identify base unit 110
as the source of
the transmission and sequence 617 is generated. In handset 101, the first bits
of the
second and third bytes are left as "0" to identify handset 101 as the source
of that
command data packet. The software then disables all of the microprocessor
interrupts, 618,
I S and then calls the serial peripheral interface (SPI) send routine to
transmit the twenty four
bit command code to the command data -voice data interface, operation 619. The
routine
then returns to the main program. As previously described the twenty four bit
command
data sequence is transferred from the microprocessor via the serial peripheral
interface to
the microprocessor interface of the command data - voice data interface.
Thereafter a
command data packet is assembled within the command data - voice data
interface by
mating the security code to the twenty four bit command code sequence within
the
transmitter receiver toward insertion into the stream of, digital voice data
flowing through
CA 02151516 2001-10-04
59
the command data - voice data interface for transmission.
Fig. 38 illustrates the flow diagram of the SPI Send routine. When the routine
is
called the three byte command sequence 617 of Fig. 37 is passed to the SPI
Send routine,
operation 621. The routine sends the first byte of the command through the
serial peripheral
interface one bit at a time, operation 622, continually checking to see if the
transmission of
the first byte is complete, operation 623. If not, the transmission of the
first byte continues.
If complete, the second byte is sent one bit at a time, operation 624, until
transmission
through the serial peripheral interface of the microprocessor is complete,
operation 625.
Processes 626 and 627 are repeated for the third byte. Once the complete third
byte of the
command code sequence has been sent the software routine activates and then
deactivates the write enable line of the command data -voice data interface to
initiate
operation of the interface as previously described, operation 628 and the
routine ends, 629.
Fig. 39 of the drawings is a flow diagram for reading data from the command
data
-voice data interface. When data is present in the interface and ready for
transmission to
the micro- processor the interface signal an interrupt, TCAP Interrupt 630.
This activates
the routine which sets the command data -voice data interface read enable pin
to high,
operation 631, and the read counter to 0, operation 632. Dummy data is stored
into the SPI
data register. If the SPI read is ready, 634, the data is saved to the SPI
data register and
the read counter is incremented, operation 635. If the read counter is less
than three the
process is repeated. Once the read counter is greater or equal to 3 the
command data -
voice data interface read enable pin is cleared, set low, operation 637.
within base unit 110,
the seventh bit of the second and third bytes are examined to see if they
equal "0". If so an
CA 02151516 2001-10-04
error has occurred since base 110 unit has received its own transmission. If
the bits are
equal to' "1" they are cleared, operation 640, and the first byte is checked
against the
second and third to see that all three are the same, operation 641. If not, an
error is
assumed to have occurred in transmission and the routine is exited, 644. In
handset 101
5 the bits are checked to they are equal to "0", if so the routine proceeds.
If not, handset 101
has received its own transmission and the routine is exited. If the three
bytes are the same
the data is received into the receiver data register, operation 642, and the
data ready flag
is set, operation 643, to indicate to the microprocessor that data is ready to
be processed.
The routine is then exited 644.
10 Figs. 40, 41 and 42 of the drawings illustrate the flow diagram of the
software
routine resident in the base unit for performing the link check function while
a call is in
progress, i.e. the phone is "on-line". Upon entry at 630 the routine
initializes the link check
timer, operation 631. The link check timer measures the interval between link
check
transmissions to the handset unit. When link check timer times out a link
check is sent,
l 5 operation 632, to the handset and the link check timer is decremented,
operation 633. The
routine then looks to see if a link check acknowledgment has been received
from the
handset unit, operation 634. If not the link check timer is examined to see if
it has timed
out be reaching zero. If not, the routine continues to decrement the link
check timer and
looks to see if a link check acknowledgment has been received. If a link check
20 acknowledgment has been received the link check count is set to zero and
the scan flag
is set to false, operation 641. The link check count counts the number of
consecutive
missed link check acknowledgments up to a maximum of eight (8). Thereafter the
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61
microprocessor is freed to perform some other function of the remainder of 250
ms left of
the link check timer, operation 642. The scan flag is set to true if the
microprocessor is in
the scan mode and is looking for the handset unit. In the false mode no
scanning is done.
If the link check timer has timed out to zero the link check count is
incremented,
operation 636, and the counter is checked to see if it is equal to eight,
operation 637. If the
count is not equal to eight the process of sending link checks and listening
for link check
acknowledgments is repeated by returning to operation 631. If the link check
count is equal
to eight then eight consecutive link check signals have been sent to the
handset and none
have been acknowledged. In this case the scan flag is set to true, operation
638, and
scanning begins after the transmitter is turned off, operation 639. The
process continues
on Fig. 41.
Since eight link checks have gone unacknowledged the channel is assumed to be
unusable and automatic channel chance takes place by entering the scanning
mode. The
scanning mode, shown on fig. 41 starts with operation 643 which causes the
microprocessor to switch the channel in the channel group loaded into the base
unit and
handset unit upon initialization. The scan timer is initialized and counts
down from one
second, operation 644. The scan timer governs the amount of time that the
transmitter will
stay on one channel waiting for a link check acknowledgement during the scan
mode. The
routine then looks to see if a carrier is present the, operation 645, and if
not the transmitter
is turned on, operation 646. If a carrier is present then the channel is in
use by another
device and is unavailable and the routine switches to the next channel. Once
the
transmitter is turned on link send timer is initialized to 10 me such that
link check signals
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62
are transmitted, operation 648. The link send timer governs the time between
consecutive
link check commands in the scan mode.
The link send timer is decremented and the scan timer is decremented,
operation
649 and 650. If a link check acknowledgment has been received the scan flag is
set to
false, the link check count and link check timer are reinitialized and the
routine returns to
transmitting link check signals once every 250 ms, operation 652. Continuing
on fig. 42,
if no link check acknowledgement has been received the link scan timer is
checked to see
if it has expired, operation 655. If not, the link send timer is checked to
see if it has expired,
operation 656. If it has expired the routine branches on "E", 653, and
commences to send
link check signals beginning with operation 647. If the link check timer has
not expired the
routine branches to "D" 654 and repeats as before from operation 649.
If the link scan timer has expired, the routine checks to see if all of the
channels in
the channel group have been scanned twice, operation 657. If not, the routine
branches
on "F", to operation 641, and repeats as before until a link check
acknowledgment is
received or all channels are scanned twice, which ever occurs first. If all
the channels have
been scanned twice the transmitter is turned off, operation 658, and the call
is
disconnected, operation 659. The on-line flag is set to false indicating that
no conversation
is taking place and the off-line link check mode is entered, operations 660
and 661. The
routine then ends, operation 662.
Figs. 43 and 44 of the drawings illustrate the flow diagram of the software
routine
resident in the base unit for performing the link check function when there is
no call in
progress, i.e. when the phone is "off-line". Upon entry at 670 the routine
initializes the scan
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63
count to 10, operation 671. The scan count is a maximum number of times
channel
switching will take place before giving up. The routine looks to see if a
carrier is present,
operation 672 and if not the transmitter is turned on, operation 673. The scan
timer is set
to 1 second, operation 674, the link send timer is set to 10 ms and a link
check signal is
transmitted by operation 676.
If a carrier is present the scan timer is initialized to 50 ms and the routine
looks to
see if a valid command has been received, operations 685 and 686. If a valid
command
has been received the scan flag is set to false, operation 687, and the
command is
examined to see if it is a link check acknowledgment, operation 688. If so the
transmitter
is turned off, operation 695, and the microprocessor is freed to do other
things for 10
seconds, and the process at operation 671 is begun again. If the command is
not a link
check acknowledgment the command is processed, operation 689, and the on link
flag is
set to true, operation 690, indicating that an on-line condition exists. The
on-line link check
mode is then begun, operation 691 and the routine ends, 692.
After operation 676 which sends a link check to the handset, the routine
checks to
see if a valid command was received, operation 677, and if so the routine
branches to
operation 687 and proceeds as indicated. If the command is not valid the link
send timer
is decremented, operation 678, and the scan timer is decremented, operation
679. The
scan timer is examined to see if it has expired, operation 680, and if not the
link send timer
is examined, operation 682. If it has not expired the routing branches and
operation 677
is begun again. If the link send timer has expired the link send timer is
restarted and link
checks are sent again, operations 675 and 676.
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64
Continuing on Fig. 44, if the scan timer has expired the transmitter is turned
off,
operation 697, and the next channel in the channel group is selected,
operation 698. The
scan count is decremented, operation 699, and examined, operation 700. If the
scan count
is "0" the microprocessor is freed up to do other operations for 10 seconds,
operation 701,
and the routine begins again at the start, 670. If the scan count is not equal
to "0" the
routine begins again at operation 672.
Figs. 45 and 46 of the drawings illustrate the flow diagram of the software
routine
resident in the handset unit for performing the link check function while a
call is in progress,
"on-line". The handset unit performs link checks in the on-line and off-line
modes. In the
on-line mode the link check routine starts at point 710 and initializes the
link check timer to
2 seconds, operation 711. The routine then examines to see if a link check
command has
been received by the handset unit, operation 712, and if so a link check
acknowledge is
sent to the base unit, operation 724. If no link check command was received
the link check
timer is decremented, operation 713. If the link check timer has not reached
zero the
routine continues to check if a link check command has been received,
operation 714.
If a link check timer reaches zero, the scan flag is set to true signifying
that a "on-
line" mode exists and the scan duration is initialized, operation 715.
Operation 716 then
mutes the audio and turns off the transmitter after which the channel is
charged, operation
717. The scan timer is set to 50 ms and the routine again looks to see if a
link check
command has been received, operations 718 and 719. If so, the audio mute is
disabled
and the transmitter is turned on, operation 726. The scan flag is then set to
false and a link
check acknowledgment is sent to the base unit, operations 725 and 724. If no
link check
CA 02151516 2001-10-04
command has been received the scan timer is decremented, operation 720. If the
scan
timer then still does not equal zero the unit continues to "listen" for an
incoming link check
command, operation 721.
Continuing on Fig. 46, once the scan timer reaches zero the scan duration is
5 incremented, operation 727. If the scan duration is not greater than or
equal to 10 seconds
the routine causes the channel to change, operation 717 and the routine begins
again from
that point. If the scan duration is greater than or equal to 10 ms the scan
flag is sent to
false, operation 729, the out of range indicator is turned on, operation 730
and the off-line
link check mode is entered, operation 731. The routine then ends, operation
732.
10 Fig. 47 of the drawings illustrates the flow diagram of the software
routine resident
in the handset unit for performing the link check function when there is not a
call in
progress. The routine received link check command and transmits link check
acknowledgments in the off-line mode. The link check timer is the maximum
interval
allowed between receiving link check commands from the base unit. The routine
then
15 sleeps for 1.5 seconds, operation 737, after which the scan duration is
initialized to zero,
operation 738. The scan duration is the total time spend in the scanning mode
and equals
the number of channels scanned times the time spend on each channel.
The scan timer is then initialized to 50 ms, operation 739. The scan timer
corresponds to the maximum time interval allowed on one channel during
scanning while
20 waiting for a command from the base unit. The routine checks to see if a
valid command
has been received, operation 740. If so, the out of range indicator is turned
off, operation
741. If the received command is a link check the transmitter is turned on and
a link check
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66
acknowledgment is sent to the base unit, operations 743 and 744. The
transmitter is then
turned off, operation 745. The off-line link check mode then begins again. If
the received
command received is not a link check command the on-line mode is entered in
order that
the command may be processed by the handset microprocessor, operation 746, and
the
routine ends, 747.
If at operation 740 no valid command is received the scan timer is decremented
and
then is examined to see if it has reached zero, operations 748 and 749. If
not, the handset
continues to listen for a valid command by starting again with operation 740.
If the scan
timer has reached zero the scan duration is incremented and if it is not
greater than of
equal to 500 ms the next channel will be selected and the scan timer reset by
restarting at
operation 739, operations 750, 751 and 752. If the scan duration timer has
been exceeded
the link check timer is decremented, operation 753, and is examined to see if
it is equal to
zero, operation 754. If not operation 737 is re-executed. If the link check
timer is zero, the
out of range indicator is turned on, operation 755.
