Note: Descriptions are shown in the official language in which they were submitted.
20~333
- 1 - CE001 55R
CEllULAR TELEPHONE
OPERABLE ON DIFFERENT CELLULAR TEL~PHONE SYSTEMS
Bac~c~ the InventiQn
The present invention is generally related to
radiotelephones, and more particularly to an improved
15 cellular telephone for operating on two different cellular
telephone systems.
Cellular telephones currently are designed to operate
on only one type of cellular telephone system. Most
countries of the world have adopted oniy one type of
20 cellular telephone system. Thus, cellular 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
replaced and/or supplemented older non-cellular radio
25 telephone systems. For instance, in the United States,
cellular systems have replaced and/or supplemented the
non-cellular, improved mobile telephone systems (IMTS)
which provided radio telephone servlces since the late
1960s. In order to allow use of both the IMTS systems and
30 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 telephone, audio signals were switched by
user selection from either the IMTS transceiver or the
"
-`` 2~6~3
- 2 - CE001 55R
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
relatively expensive. Another type of signal switching
5 found in prior art tast 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
bandwidths by diode switching c,rcuitry in response to user
10 activation of a mechanical switch. However, mechanical IF
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
and complexity thereof. For the foregoing reasons, there is
15 a need for a cellular telephone which accommodates
different receiver bandwidths for operating on different
cellular telephone systems.
Objects of the Invention
Accordingly, it is an object of the present invention
to provide a unique dual-system cellular telephone which
includes bandwidth switching in the receiver thereof for
automatically operating on different Gellular telephone
25 systems.
It is another object of the present invention to
provide a unique dual-system eellular telephone which
includes bandwidth switehin~ in the intermediate frequency
section of the reeeiver thereof and software switching in
30 the eontrol unit for automatieally operating on different
cellular telephone systems.
... , .~ . .
.' , ~ .. : ,
-
2~333
- 3 - CE001 55R
~rief ~escrietion of the Drawillgs
Figure 1 is a block diagram of the transceiver of a
cellular telephone embodying the present invention.
Figure 2 is a block diagram of the audio/logic unit of
a cellular telephone embodying the present invention.
Figur~ 3 is a block diagram of the handset unit of a
cellular telephone embodying the present invention.
Figure 4 is a circuit diagram of 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.
Detail~d 12~i~Qf th~ Prefer~ed Embgdim~n~
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 embodying 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
~ . .. . . . ~ . ..
2Q~333
- 4 - CEoo1ssR
cities or highways where only one of the two cellular
telephone systems provides cellular service, the celOular
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 system A and
cellular system B hereinbelow.
Referring next to the block diagram in Figure 1,
10 transceiver 100 is preferably a cellular transceiver
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, Illinois 60196.
RF signals on cellular radio 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 1 12, 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 radio channel by
,
2 ~ ?~
- ~ - CE001 ssR
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 which is mixed with the receiver injection signal in
5 offset mixer 110 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 signal 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 transmission 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 selecting the desired component thereof. The
output of crystal filter 144 is coupled to second mixer 148,
where it is mixed 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, respectively.
,........ . . ,. , . :.,
- -
.
. . . .
2016333
- 6 - CE001 ssR
In the preferred embodiment, the first filter in switched IF
filter 150 has a wide bandwidth, that is a 3 dB bandwidth
of +t- 12 KHz, and the second filter in switched IF filter
150 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 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
* trade-mark
~,
: . . ; ~ . :
2~6333
- 7 - CE001 55R
embodiment, 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 HIGH DTMF) utilized in call
15 processing. Signalling circuitry 208 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 transmission 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.
- .- ........ , ............ ~ . . .
. .
.,
20~ ~333
- 8 - CE00155R
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 30~ 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 RX
Hl signal 912, respectively, and which may be switched on
10 and off by microcomputer 302. Handset unit 300 alsc
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 housing in the case of a mobile cellular telephone
and may be 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 C~IAOS analog switch
, . :
,
2~3 ~3
- 9 - CE001 55R
integrated circuit. Analog switch 404 includes first and
second switches 405 and 406 for coupling either first
filter 408 or second filter 410 to detector 152. When the
bandwidth control signal 908 has a binary one state, first
5 filter 408 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. In the preferred embodiment, first filter 408
is a 455 kHz ceramic filter having a wide bandwidth, that
10 is a 3dB bandwidth of +/- 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 executed 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 subsequsntly
20 cleared in response to the first key activation. The flow
diagram of Figure 5 is entered at block 502 in response to
either an interrupt, the reset signal or when returning from
system B. After initialization, the dedicated control
channels are scanned at block 504 and the two strongest
25 control channels are selected. If no service is available in
system A for a predstermined 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 Figure 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, microcomputer 202 branches to the second
- ~ -. ,. . . :
.. .
- . - . .. - . . .. . .
2~333
- 10 - CE001 ssR
portion of the control program for resuming operation in
cellular system B so that cellular service is not
interrupted, according to a feature of the present invention.
If a control channel is selected, the paging channels are
5 then scanned at block 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 thereafter 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
processéd 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
diseonneetion clearing function is performed at 520. When
the telephons eall is terminated, program control is
20 transferred baek to block 504 to repeat the foregoing
proeess.
Referring next to the flow diagram of Figure 6, there
is illustrated the proeess performed by mieroeomputer 202
of audio/logie eontrol unit 200 in Figure 2 under eontrol of
25 the seeond portion of the eontrol program for signalling and
eommunieations in eellular system B. Entering in response
to an interrupt, initialization is performed at bloek 602.
During system B operation, a "ROAM" indieator in handset
unit 300 is eontinuously flashed, and display 304 in handset
30 unit 300 is initially loaded with a pre-seleeted message
indieating system B operation and is subsequently eleared
in response to the first key aetivation. Next, at bloek 604,
the P-ehannel is seanned, RSSI signal 910 is deteeted, and
the loeation eode is verified. If no serviee is available in
- . . .
.
- .
20~ 6333
CE001 55R
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 controi program to resume operation in
5 cellular system A, as illustrated in Figure 7. At the time of
sueh transf~r, the eurrent system parameters are stored in
the EEPROM memory of microcomputer 202 of audio/logic
eontrol unit 200 to indicate that operation in cellular
system B was attempted. If the location code indicates a
10 new loeation was entered, loeation registration is
performed at bloek 606. Otherwise, program control
proeeeds to idle bloek 608 to wait for an outgoing call
origination or an ineoming eall termination. Also, at block
608, RSSI signal 910 is eontinuously checked to determine
15 if an aeeeptable RF signal is being reeeived. If RSSI signal
910 is less than level L2, program eontrol transfer baek to
bloek 604. As long as the RSSI signal has a magnitude
greater than level L3, program eontrol remains at block
608. In the preferred embodiment, levels L2 and L3
20 eorrespond to RF signal levels of -96 dBm and -91 dBm,
respeetively. From idle bloek 608, an outgoing eall
origination may oeeur at bloek 612 or an ineoming eall
termination may be proeessed at bloek 614. From bloek 612
or block 614, program eontrol proeeeds to blocks 618, 620
25 and 622 for proeessing the eall origination or eall
termination, respeetively. At block 618, RSSI and speeeh
monitoring is performed and if neeessary, a handoff is
exeeuted at block 622 or, if serviee is lost, a hang-up and
diseonneetion elearing funetion is performed at bloek 620.
30 When the telephone eall is terminated, program eontrol is
transferred baek to block 608 to repeat the foregoing
proeess.
Referring next to the flow diagram of Figure 7,
there is illustrated the proeess performed by
, ............. . . . . . .
, , . - . , : .
.. . . . ..
2~ ~333
-1 2 - CE0~1 55R
microcomputer 202 of audio/logic control unit 200 in
Figure 2 for processing interrupts and automatically
switching between cellular systems A and B. Three
programmable timers, the Z timer, X timer, and Y timer, are
used to determine when to switch between systems A and
B. The Z timer is used for timing the loss of service in
system A. A suitable value for the Z timer is one minute.
The X timer is used for timing the loss of service in system
B. A suitable value for the X timer is one-half minute. The
Y timer is used for timing the duration of service in system
B. A suitable value for the Y timer is one minute. During
initialization for system A or B, the Z timer or the X and Y
timers are set to their nominal values and thereafter
decremented in response to the one 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 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
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 again. Next, at block 706, a status check is
made to determine if the Z timer has been decremented to
zero. 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
from the one millisecond interrupt. Entering the flow
.. . . ,.. . - . ~ .. . . . - ....
3 3 ~
- 13 - CE00155R
diagram of Figure 7 in response to the one millisecond
interrupt from the control program for csllular system B,
the interrupt timer is checked at block 702 to determine if
five milliseconds has elapsed. If five milliseconds has
5 elapsed and ser~ice 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 again.
If five milliseconds has elapsed, the Y timer is
decremented at block 704. Next, at block 706, a status
10 check is made to determine if the X or Y timer has been
decremented to zero. If the X or Y timer has been
decremented to zero, then at block 710, the Z timer is set
to its nominal value and the system B call parameters are
saved. Thereafter, operation is switched to system A by
15 branching to the first portion of the control program when
returning from the one millisecond interrupt. Even if
service is available in System B, the Y timer will
decrement to zero and result in switching back to system
A, since operation in system A is preferred. If there is no
20 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
25 operating on different cellular telephone systems.
Bandwidth switching may be accomplished by switching
between different filters in the intermediate frequency
section of the receiver of the dual-system cellular
telephone depending on which cellular telephone system is
30 available. Software switching may be accomplished by
qswitching between different portions of the control
program in the control unit of the dual-system cellular
telephone depending on which cellular telephone system is
available. When service is not available in one of the
2~333
- 1 4 - CEOOl 55R
cellular telephone systems, the unique dual-system cellular
telephone automatically switches to the other cellular
telephone system.
.
