Note: Descriptions are shown in the official language in which they were submitted.
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CELLIJLAR TELEPHONE RESPONSIVE TO
SERVICE AVAILABILITY FOR OPERATING
ON DIFFERENT CELLUL~R TELEPHONE SYSTEMS
Backoround of the InventiQn
The present invention is generally related to
1~ radiotelephones, and more particularly to an improved
cellular teiephone for operating on two different cellular
telephone systems.
Cellular telephones currently are designed to operate
on only one type of cellular telephone system. Most
20 countries of the world have adopted only one type of
cellu~ar telophone system. Thus, ce~lular telephones which
operate on only one type of cellular telephone system have
been adequate for the cellular systems in most countries of
the world. In some countries, cellular systems have
25 replacsd and/or supplemented older non-cellular radio
telephone systems. For instance, in the United States,
cellular systems have replaced and/or supplemanted the
non-cellular, improved mobile telephone systems (IMTS)
which provided radio telephone services since the late
30 1960s. In order to allow use of both the IMTS systems and
the cellular systems, a prior art radio telephone included
both an IMTS transceiver and a cellular transceiver which
were coupled to a common handset control unit. In this
prior art radio telephane, audio signals were switched by
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user selection from either the IMTS transceiver or the
cellular transceiver to the common handset control unit
Use of two transceivers to provide services on two
different radio telephone systems is both bulky and
5 relatively expensive. Another type of signal switching
found in prior art test equipment is mechanical bandwidth
switching of the intermediate frequency (IF) section of the
radio receiver in a modulation analyzer. The IF section of
such test equipment was switched between two different
10 bandwidths by diode switching circuitry in response to user
activation of a mechanical switch. However, mechanical I F
bandwidth switching of such test equipment is not suitable
for use in cellular telephones and also requires user
intervention and additional circuitry, increasing the cost
15 and complexity thereof. For the foregoing reasons, there is
a need for a cellular telephone which accommodates
different receiver bandwidths for operating on different
cellular telephone systems.
20 Object of the Invention
Accordingly, it is an object of th0 present invention
to provide a unique dual-system cellular telephone which
includes bandwidth switching in the intermediate frequency
25 section of the receiver thereof and software switching in
the control unit for automatically operating on different
cellular telephone systems using service availability and
radio signal availability as switching criteria..
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~ri~f Description of the Dra~inqs
Figure 1 is a block diagram of the transceiver of a
cellular telephone embodying ~he present invention.
Figure 2 is a block diagram of the audio/logic unit of
a cellular telephone embodying the present invention.
Figure 3 is a block diagram of the handset unit of a
cellular telephone embodying the present invention.
Figure 4 is a circuit diagram af the switched- IF
circuitry of the cellular transceiver in Figure 1.
Figure 5 is a flow diagram for the process used by
microcomputer 202 in Figure 2 for signalling and
communications in cellular system A.
Figure 6 is a flow diagram for the process used by
microcomputer 202 in Figure 2 for signalling and
communications in cellular system B.
Figure 7 is a flow diagram for the process used by
microcomputer 202 in Figure 2 for processing interrupts
and switching between cellular systems A and B.
Detailed Description of the Preferred Embodiment
Referring to Figures 1, 2 and 3, there is illustrated a
block diagram of the transceiver 100, audio/logic control
unit 200, and handset unit 300, respectively, of a dual-
system cellular telephone ernbodying the present invention.
Cellular telephone of the present invention may be
advantageously utilized in any country or cellular service
area where two different cellular telephone systems exist.
For example, a TACS-type cellular telephone system and a
US-type cellular telephone system may provide at least
partial overlapping cellular telephone service to the same
geographical area. Currently, both Japan and Hong Kong
have approved two different cellular telephone systems. In
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cities or highways where only one of the two cellular
telephone systems provides cellular service, the cellular
telephone of the present invention automatically switches
to the serving cellular system insuring that the user will
5 always have access to available cellular service. For
convenience, two different exemplary cellular telephone
systems will be referred to as cellular syst~m A and
csllular system B hereinbelow.
Referring next to ths block diagram in Figure 1,
10 transceiver 100 is preferably a cellular ~ransceiver
operable in the transmitter frequency range from 915 to
940 MHz and the receiver frequency range from 860 to 885
MHz. Except for block 150, the blocks of transceiver 100
may be implemented by conventional cellular transceiver
15 circuitry, such as, for example, the circuitry of the US-type
cellular telephone transceiver shown and described in
Motorola Instruction Manual No. 68P81 070E40, entitled
"DYNATAC Cellular Mobile Telephone," published by and
available from Motorola C & E Parts, 1313 East Algonquin
20 Road, Schaumburg, Illinais 60196.
RF signals on cellular radiQ channels are transmitted
and received by transceiver 100 via antenna 120 and
harmonic filter 122. RF signals for transmission by
antenna 120 are applied to harmonic filter 122 by
25 transmitter duplex filter 126 via duplex transmission line
124. The transmitting circuitry of transceiver 100
includes offset voltage-controlled oscillator (VCO) 108,
offset mixer 110, power amplifier 112, and directional
coupler 114, which generate the transmitter signal of the
30 RF channel to which transceiver 100 is tuned. Synthesizer
104 is coupled to reference oscillator 102 for generating
the receiver injection signal which is split by splitter 106
and coupled to offset mixer 110 and injection filter 116.
Synthesizer 104 is tuned to a particular radia channel by
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audio logic control unit 200 using data signal 907, clock
signal 906, and RX enable signal 905. Offset VCO 108 is
coupled to reference oscillator 102 for generating an offset
signal whlch is mixed with the receiver injection signal in
5 offset mixer 1 10 to generate the transmitter signal. The
circuitry of offset VCO 108 is powered up and down in
response to the TX prekey signal in order to save standby
current drain. Amplifier 112 is responsive to PA control
signal 902 from audio/logic control unit 200 for generating
10 up to eight different power levels at its output. Directional
coupler 114 produces RF detect signal 901 which has a
magnitude that is proportional to the magnitude of the
output of amplifier 112. RF detect signal 901 from
directional coupler 114 is coupled to audio logic control
15 unit 200, where it is converted to digital form and used to
generate PA control signai 902 for maintaining the output
of amplifier 112 at the desired power level.
In the receive path of transceiver 100, receive
signals are coupled from harmonic filter 122 by duplex
20 transrnission line 128 to receiver duplex filter 130, RF
amplifier 132, receiver filter 134 and transmission line
136 to first mixer 138, where the filtered RF signals are
mixed with the receiver injection signal from injection
filter 116 and transmission line 118 to produce the first IF
25 signal. The first IF signal from first mixer 138 is coupled
to crystal filter 140, IF amplifier 142 and crystal filter
144 for selectin~ the desired component thereof. The
output of crystal filter 144 is coupled to second mixer 148,
where it is mix0d with second local oscillator 146 to
30 produce the second IF signal. The second IF signal from
second mixer 148 is coupled to switched IF filter 150,
which includes first and second filters having different
bandwidths for selecting the desired components thereof
for cellular system A and cellular system B, raspectively.
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In the preferred embodiment, the first filter in switched IF
filter 150 has a wide bandwidth, that is a 3 dB bandwidth
of +/- 12 KHz, and the second filter in switched IF filter
1~0 has a narrow bandwidth, that is a 3dB bandwidth of +/-
5 6 kHz. In practicing the present invention, switched IFfilter 150 may include additional filters for selecting the
desired components thereof for additional cellular systems
over and above cellular systems A and B. Bandwidth control
signal 908 from audio/logic control unit 200 is coupled to
10 switched IF filter 150 for switching between the first and
second filters thereof. When bandwidth control signal 908
has a binary one state, the first filter of switched IF filter
150 is selected for providing a wide bandwidth for cellular
system A. When bandwidth control signal 908 has a binary
15 zero state, the second filter of switched IF filter 150 is
selected for providing a narrow bandwidth for cellular
system B. The output of switched IF filter 150 is coupled
to detector 152 which produces discriminator audio signal
909 and received signal strength indicator signal (RSSI)
20 910, which signals are coupled to audio/logic control unit
200.
Referring next to the block diagram of Figure 2,
audio/logic control unit 200 includes microcomputer 202
which controls the operation of transceiver 100 in
25 accordance with a control program stored in EPROM memory
204 and including a first portion for signalling and call
processing in cellular system A, a second portion for
signalling and call processing in cellular system B, and a
third portion for the user interface in cellular systems A
30 and B. In the preferred embodiment, microcomputer 202 is
a Motorola type 68HC11 microprocessor integrated circuit.
Microcomputer 202 is also coupled to EEPROM memory 206
for accessing telephone numbers, serial numbers, and other
call processing information stored therein. In the preferred
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ernbodiment, the dual-system cellular telephone of the
present invention has two telephone numbers, one for
cellular system A and another for cellular system B.
Microcomputer 202 is coupled to audio circuitry 210 for
5 controlling transmit and receive audio paths, the
microphone signal 911 and the RX Hl signal, respectively,
for operation in both cellular systems A and B. Audio
circuitry 210 is described in further detail in U.S. Patent
No. 4,741,018. For operation in cellular system A,
10 microcomputer 202 is coupled to signalling circuitry 208
for generating and processing high-speed signalling data
(FWD DATA and REV DATA), supervisory audio tones (FWD
SAT and REV SAT), and dual tone multifrequency dialing
signals (LOW DTMF and HIGtl DTMF) utilized in call
15 processing. Signalling circuitry 20~ is described in further
detail in U.S. Patent Nos. 4,302,845 and 4,312,074. When
operating in cellular system B, low-speed signalling data in
discriminator audio signal 909 from transceiver 100 is
coupled to microcomputer 202 by way of receiver filter
20 212 and limiter 214. Low-speed signalling data from
microcomputer 202 for transmissi~n in cellular system B
is coupled by transmitter filter 216 to modulation signal
904 for application to offset VCO 108 of transceiver 100.
DC control circuitry 218 is responsive to ON/OFF signal 916
25 from handset unit 300 and ignition sense signal 917 from
the vehicle ignition switch for generating the reset signal
for initializing microcomputer 202, signalling circuitry
208 and audio circuitry 210, and generating the 5V and
switched 9.5V power supplies for powering the circuitry of
30 transceiver 100, audio/logic control unit 200 and handset
unit 300. DC control circuitry 218 includes conventional
voltage regulators and is described in further detail in U.S.
Patent No. 4,798,975.
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Referring next to the block diagram of Figure 3,
handset unit 300 includes microcomputer 302 for scanning
keypad 306 to detect activated keys and for loading
information into display 304 indicating telephone numbers
5 and predetermined status of the dual-mode cellular
telephone of the present invention. Handset unit 300 also
includes microphone 310 and speaker 314 which are coupled
by amplifiers 308 and 312 to microphone signal 911 and ~X
Hl signal 912, respectively, and which may be switched on
10 and off by microcomputer 302. Handset unit 300 also
includes several indicators, one of which is a no-service
indicator providing a visual indication of the availability of
cellular service. Microcomputer 302 generates the ON/OFF
signal 916 in response to activation of the ON/OFF key of
15 keypad 306. Microcomputer 302 communicates with
microcomputer 202 of audio/logic control unit 200 via a
three-wire data bus 913, 914 and 915 which is illustrated
and described in the U.S. Patent No. 4,369,516. The TRU,
CMP and RTN signals 913, 914 and 915 of the three-wire
20 data bus are buffered by amplifiers 316, 317 and 318,
respectively. Handset unit 300 may be located in a
separate housin~ in the case of a mobile cellular telephone
and may bo located together with transceiver 100 and
audio/logic control unit 200 in a common housing in a case
25 of portable cellular telephone.
Referring next to the circuit diagram of Figure 4,
there is illustrated the detailed circuitry comprising the
preferred embodiment of switched IF filter 150 in Figure 1.
Switched IF filter 150 includes first filter 408 and second
30 filter 410 which are selected by bandwidth control signal
908. The output of second mixer 148 is coupled to buffer
amplifier 402, the output of which is applied to the input of
analog switch 404. In the preferred embodiment, analog
switch 404 is a Motorola type MC14551 CMOS analog switch
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integrated circuit. Analog switch 404 includes first and
second switches 405 and 40~ for coupling either first
filtsr 408 or second filter 410 to detector 152. When the
bandwidth control signal 908 has a binary one state, first
filter 40~ is coupled by analog switch 404 to detector 152.
When bandwidth control signal 908 has a binary zero state,
second filter 410 is coupled by analog switch 404 to
detector 152. Irl the preferred embodiment, first filter 408
is a 455 kHz ceramic filter having a wide bandwidth, that
10 is a 3dB bandwidth of +i- 12 kHz, and second filter 410 is a
455 kHz ceramic filter having a narrow bandwidth, that is a
3dB bandwidth of +/- 6 kHz.
Referring next to the flow diagram of Figure 5, there
is illustrated the signalling and communications processes
15 ex0cuted by microcomputer 202 in audio logic control unit
200 in Figure 2 under control of the first portion of the
control program for cellular system A. Initially, display
304 in handset unit 300 is loaded with a pre-selected
message indicating system A operation and is subsequently
20 cleared in response to the first key activation. The flow
diagram of Figure 5 is entere.d at block 502 in response to
either an interrupt, the reset signal or when returning from
systern B. After initialization, the dedicated control
channels are scanned at block 504 and the two strongest
2~ control channels are selected. If no service is available in
system A for a predetermined period of time, program
control may transfer in response to an interrupt from the
first portion of the control program to the second portion
of the control program for operation in cellular system B,
30 as illustrated in Figura 7. For example, a no service
condition would arise when the cellular telephone moves
from a city covered by cellular system A to a highway or
another city covered only by cellular system B. In this
situation, miarocomputor 202 branches to the second
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portion of the control program for resuming operation in
celluiar system B so that cellular service is not
intarrupted, according to a feature of the present invention.
If a control channel is select~d, the paging channels are
5 then scanned at biock 506 and the two strongest paging
channels are selected. If service is available, the overhead
message train transmitted on the paging channel is verified
at block 508 and ther~after program control proceeds to
idle block 510. From idle block 510 a call origination may
10 occur at block 512, location registration may take place at
block 516 and an incoming call termination may be
processed at block 514. From block 512 or block 514,
program control proceeds to blocks 518, 520 and 522 for
processing the call origination or call termination,
15 respectively. At block 518, system access and speech
monitoring is performed and if necessary, a handoff is
executed at block 522 or if service is lost a hang-up and
disconnection clearing function is performed at 520. When
the telephone call is terminated, program control is
20 transferred back to block 504 to repeat the foregoing
process.
Referring next to the flow diagram of Figure 6, there
is illustrated the process performed ~y microcomputer 202
of audio/logic control unit 200 in Figure 2 under control of
25 the second portion of the control program for signalling and
communications in cellular system B. Entering in response
to an interrupt, initialization is performed at block 602.
Durin~ system B operation, a "ROAM" indicator in handset
unit 300 is continuously flashed, and display 304 in handset
30 unit 300 is initially loaded with a pre-selected message
indicatin~ system B operation and is subsequently cleared
in response to the first key activation. Next, at block 604,
the P-channel is scanned, RSSI signal 910 is detected, and
the location code is verified. If no service is available in
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system B for a predetermined period of time, program
control may transfer in response to an interrupt from the
second portion of the control program back to the first
portion of the control program to resume operation in
5 cellular system A, as illustrated in Figure 7. At the time of
such transfer, the current system parameters are stored in
the EEPROM memory of microcomputer 202 of audio/logic
control unit 200 to indicate that operation in cellular
system B was attempted. If the location code indicates a
10 new location was entered, location registration is
performed at block 60~. Otherwise, pro~ram control
proceeds to idle block 608 to wait for an outgoing call
origination or an incoming call termination. Also, at block
608, RSSI signal 910 is continuously checked to determine
15 if an acceptable RF signal is being received. If RSSI signal
910 is less than level L2, program control transfer back to
block 604. As long as the RSSI signal has a magnitude
greater than level L3, program control remains at block
608. In the preferred embodiment, levels L2 and L3
20 correspond to RF signal levels of -96 dBm and -91 dBm,
respecti~lely. From idle black 608, an outgoing call
origination may occur at block 612 or an incoming call
termination may be processed at block 614. From block 612
or block 614, program control proceeds to blocks 618, 620
25 and 622 for processing the call origination or call
termination, r~spectively. At block 618, RSSI and speech
monitoring is performed and if necessary, a handoff is
executed at block 622 or, if seNice is lost, a hang-up and
disconnection clearing function is performed at block 620.
30 When the telephone call is terminated, program control is
transferred back to block 608 to repeat the foregoing
process.
Referring next to the flow diagram of Figure 7,
there is illustrated the process performed by
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microcomputer 202 of audio/logic control unit 200 in
Figure 2 for processing interrupts and au~omatically
switching behNeen cellular systems A and B. Three
programmable timers, the Z timer~ X timer, and Y timer, are
5 used to determina when to switch between systems A and
B. The Z timer is usad for timing the loss of service in
system A. A suitable value for the Z timer is twenty
seconds. The X timer is used for timing the loss of service
in system ~. A suitable value for the X timer is ten
10 seconds. The Y timer is used for timing the duration of
service in system B. A suitable value for the Y timer is
five minutes. During initialization for system A or B, the Z
timar or the X and Y timers are set to their nominal values
and thereafter decremented in response to the one
15 millisecond interrupt as explained hereinbelow. In the
preferred embodiment of the dual-system cellular
telephone, automatic switching may also be disabled and
switching between systems A and B may be done manually
in response to pre-selected key sequences entered by the
20 user on keypad 306.
Entering the flow diagram of Figure 7 in response to
the one millisecond interrupt from the control program for
cellular system A, the interrupt timer is checked at block
702 to determine if five milliseconds has elapsed. If five
25 milliseconds has elapsed and service is not available in
system A, the Z timer is decremented at block 704. If
service is available in system A, the Z timer is set to its
nominal value a~ain. If a call has been initiated or is in
pro~ress, switchin~ between systems A and B will not take
30 place until termination of the call in process.
Next, at block 706, a status check is made to
determine if the Z timer has been decremented to zero. At
this point, block 706 has been reached either when no
service is available in system A or when service has been
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detected for the first time in system B and system A is
checked again before switching to system B. According to
the present invention, switching to sys;em B occurs only if
service was not detected in system A after service was
5 first detected in system B. This unique operation prevents
selection of system B when emerging from a tunnel or
enclosed garage into an area where service is available
from both the preferred system h and the alternate system
B.
If the Z timer has been decremented to zero, then at
block 708, the X and Y timers are set to their nominal
values and the system A call parameters are saved.
Thereafter, operation is switched to system B by branching
to the second portion of the control program when returning
15 from the one millisecond interrupt.
Entering the flow diagram of Figure 7 in response to
the one millisecond interrupt from the control program for
cellular system B, the interrupt timer is checked at block
702 to determine if five milliseconds has elapsed. If five
20 milliseconds has elapsed, the Y timer is decremented at
block 704. If five milliseeonds has elapsed and service is
not available in system B, the X timer is decremented at
block 704. If service is available in system B, the X timer
is set to its nominal value a~ain. If a call has been
25 initiated or is in progress, switching between systems A
and B will not take place until termination of the call in
process..
Next, at block 706, a status check is made to
determine if the X or Y timer has been decremented to zero
30 or if service is availabl0 in system B for the first time
after service was not detected in system A. If the X or Y
timer has been decremented to zero or if service is
available in system B for the first time after service was
not detected in system A, then at block 710, the Z timer is
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sot to its nominal value and the system B call parameters
are saved. Thereafter, operation is switched to system A
by branching to the first portion of the control program
when returning from the one millisecond interrupt. Even if
5 service is available in System B, the Y timer will
decremsnt to zero and resuit in switching back to system
A, since operation in system A is preferred. If there is no
preferred system, only the Z and X timers are needed in
other embodiments.
In summary, a unique dual-system cellular telephone
includes bandwidth switching in the receiver thereof and
software switching in the control unit for automatically
operating on different cellular telephone systems.
Bandwidth switching may be accomplished by switching
1~ between different filters in the intermediate frequency
section of the receiver of the dual-system cellular
telephone depending on which cellular telephone system is
available. Software switching may be accomplished by
switching between different portions of the control
20 program in the control unit of the dual-system cellular
telephon~ depending on which cellular telephone system is
available. When service is not available in one of the
cellular telephone systems, the unique dual-system cellular
telephone automatically switches to the other cellular
25 telephone system.
