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Mobile Phone Patent Abstract
A dual mode transmitter/receiver adds two-way radio functionality
to a frequency division duplex mobile phone. The dual mode transmitter/receiver
allows short-range and low-power communication between similarly
equipped phones. In the two-way radio mode, the dual mode mobile
phone transmits and receives at a frequency between the normal mobile
transmit and receive frequency bands so that a number of transmitter/receiver
components are utilized for both normal and two-way radio communication.
Mobile Phone Patent Claims
What is claimed is:
1. A dual-function mobile phone that operates as a mobile phone
during a normal operating mode and as a two-way radio during a supplemental
operating mode, comprising:
a receiver receiving at a frequency in a first frequency band during
said normal operating mode to receive communication from another
device via a base station that transmits at the frequency in said
first frequency band and receiving at a frequency in a second frequency
band during said supplemental operating mode to receive direct communication
from another dual-function mobile phone transmitting in said second
frequency band; and
a transmitter transmitting at a frequency in a third frequency
band during said normal operating mode to transmit communication
to a base station and transmitting at a frequency in said second
frequency band during said supplemental operating mode to directly
communicate with another dual-function mobile phone that receives
at a frequency in said second frequency band, said second frequency
band being in-between said first frequency band and said third frequency
band.
2. The dual-function mobile phone according to claim 1, wherein
said dual-function mobile phone is a digital mobile phone.
3. The dual-function mobile phone according to claim 1, wherein
said second frequency band is unlicensed.
4. The dual-function mobile phone according to claim 1, wherein
said device is a personal communication service mobile phone;
said first frequency band is 1930-1990 Mhz; and
said third frequency band is 1850-1910 Mhz.
5. The dual-function mobile phone according to claim 1, further
comprising:
a controller for controlling said receiver and said transmitter
to receive/transmit at a frequency in said second frequency band
during said supplemental operating mode.
6. The dual-function mobile phone according to claim 5, further
comprising:
a supplemental operating mode module for generating a communication
signal at a frequency in said second frequency band during said
supplemental operating mode, and retrieving information from a signal
received from a remote communication device during said supplemental
operating mode.
7. The dual-function mobile phone according to claim 5, further
comprising:
a plurality of switches each receiving a control signal from said
controller to initiate said supplemental operating mode.
8. The dual-function mobile phone according to claim 1, further
comprising:
a duplexer for filtering out frequencies outside said second frequency
band during said supplemental operating mode.
9. The dual-function mobile phone according to claim 8, wherein
said duplexer comprises:
a first band pass filter for filtering out frequencies in a received
signal which are outside said first frequency band during said normal
operating mode;
a second band pass filter for filtering out frequencies in a signal
to be transmitted during said normal operating which are outside
said third frequency band; and
a third band pass filter for filtering out frequencies outside
said second frequency band during said supplemental operating mode.
10. The dual-function mobile phone according to claim 1, wherein
said receiver includes receiver circuitry that is utilized during
both said normal operating mode and said supplemental operating
mode and said transmitter includes transmitter circuitry that is
utilized during both said normal operating mode and said supplemental
operating mode.
11. The dual-function mobile phone according to claim 10, wherein
said receiver circuitry that is utilized during both said normal
operating mode and said supplemental operating mode includes a reference
oscillator and an RF receive amplifier.
12. The dual-function mobile phone according to claim 10, wherein
said transmitter circuitry that is utilized during both said normal
operating mode and said supplemental operating mode includes a reference
oscillator and an RF transmit amplifier.
13. The dual-function mobile phone according to claim 1, further
comprising:
an antenna that receives and transmits RF signals during both said
normal operating mode and said supplemental operating mode.
14. The dual-function mobile phone according to claim 1, further
comprising:
a duplexer that is functional during both said normal operating
mode and said supplemental operating mode.
15. The dual-function mobile phone according to claim 14, wherein
said duplexer filters frequencies outside said first frequency band
and said third frequency band during both said normal operating
mode and said supplemental operating mode.
16. The dual-function mobile phone according to claim 1, wherein
said dual-function mobile phone is an analog mobile phone.
17. A method for transmitting/receiving that enables a dual-function
mobile phone to operate as a mobile phone during a normal operating
mode and as a two-way radio during a supplemental operating mode,
said method comprising:
controlling the dual-function mobile phone to receive at a frequency
in a first frequency band during said normal operating mode to receive
communication from another device via a base station that transmits
at the frequency in said first frequency band and to receive at
a frequency in a second frequency band during said supplemental
operating mode to receive direct communication from another dual-function
mobile phone transmitting in said second frequency band; and
controlling the dual-function mobile phone to transmit at a frequency
in a third frequency band during said normal operating to transmit
communication to a base station and to transmit at a frequency in
said second frequency band during said supplemental operating mode
to directly communicate with another dual-function mobile phone
that receives at the frequency in said second frequency band, said
second frequency band being between said first frequency band and
said third frequency band.
18. The method according to claim 17, wherein the dual-function
mobile phone is a digital mobile phone.
19. The method according to claim 17, wherein said second frequency
band is an unlicensed frequency band.
20. The method according to claim 17, wherein said first frequency
band is 1930-1990 Mhz and said third frequency band is 1850-1910
Mhz.
21. The method according to claim 17, further comprising:
filtering out frequencies which are outside said second frequency
band during said supplemental operating mode.
22. The method according to claim 17, wherein the dual-function
mobile phone is an analog mobile phone.
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual mode mobile phone ("mobile")
which transmits and receives radio frequency (RF) signals during
normal operation using frequency division duplexing, and operates
as a two-way radio during a supplemental operating mode.
2. Description of Prior Art
Consumer demand and competition in the wireless communications
industry has driven a rapid evolution in cellular phone technology.
Analog mobiles introduced in the early 1980s are being replaced
by digital technology which offers enhanced quality, security, and
efficient spectrum use.
Using PCS (personal communication services) devices as an example,
service providers are now able to attract cellular customers by
offering an expanded variety of services, such as voicemail, short
message service, and personal call management (i.e., providing a
single telephone number for a user's home, mobile, and office).
Although it is desirable to offer these and other services to cellular
customers, it is also desirable to minimize the effect of such services
on the cost, size, and convenience of the mobile.
SUMMARY OF THE INVENTION
The present invention adds two-way radio functionality to a frequency
division duplex mobile in an efficient manner. The user of the dual
mode mobile according to the present invention switches between
a normal operating mode, for cellular service, and a two-way radio
mode (also referred to herein as "walkie-talkie," or "W-T"
mode) which enables short-range, low-power communication with similarly
equipped phones without using the service provider's cellular infrastructure
(i.e., without transmitting or receiving to/from a cellular network
base station). In W-T mode, the dual mode mobile transmits and receives
at frequencies between the mobile's normal transmit and receive
frequency bands. By utilizing these in-between frequencies, numerous
transmitter/receiver components are used for both normal cellular
communication and during W-T mode, thereby allowing design efficiencies
to minimize the cost and size of the dual mode mobile.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a dual mode mobile according to a
disclosed embodiment of the present invention;
FIG. 2 illustrates a duplexer configuration for filtering out frequencies
outside the mobile transmit and mobile receive frequency bands;
FIG. 3 illustrates typical mobile transmit and mobile receive frequency
bands, as well as the in-between frequencies used for two-way radio
communication according to the present invention;
FIG. 4 illustrates certain external features of the dual mode mobile
according to an embodiment of the present invention;
FIG. 5 is a block diagram illustrating a configuration of the walkie-talkie
module shown in FIG. 1;
FIG. 6 illustrates an alternative duplexer configuration according
to an embodiment of the present invention; and
FIG. 7 illustrates the filtering results for the mobile transmit,
mobile receive, and the in-between frequency bands using the alternative
duplexer configuration of FIG. 6.
DETAILED DESCRIPTION
The following detailed description relates to a dual mode mobile
which transmits and receives RF communication signals using frequency
division duplexing during a normal operating mode, and which functions
as a two-way radio in a supplemental operating mode by transmitting
and receiving at a frequency in-between the normal mobile transmit
and receive frequency bands.
FIG. 1 is a block diagram of a dual mode mobile in accordance with
an embodiment of the present invention. As shown in FIG. 1, the
dual mode mobile includes an antenna 23, a speech output (e.g.,
a speaker) 24, a speech input (e.g., a microphone) 22, and a dual
mode transmitter/receiver 200. It will be clear to one skilled in
the art that the mobile of FIG. 1 includes additional components,
such as a battery, logic circuitry, a display processor, etc. Since
an explanation of such elements is not necessary for an understanding
of the present invention, these components are not illustrated in
the Figures or discussed herein.
As seen in FIG. 1, the dual mode transmitter/receiver 200 includes
a duplexer 220 connected to the antenna 23 to receive and transmit
RF communication signals via the antenna 23. Frequency division
duplexing allows cellular customers to simultaneously listen and
speak by transmitting and receiving at frequencies in separate frequency
bands.
FIG. 2 illustrates a typical duplexer configuration which is suitable
for implementing the duplexer 220 of the present invention. As illustrated
in FIG. 2, the duplexer 220 includes a mobile transmit band pass
filter (BPF MT) 222 which receives an RF transmit (Tx) signal from
the mobile's transmitter circuitry, filters out frequencies in Tx
which are above and below the mobile transmit band boundaries, and
outputs the result to the antenna 23. The duplexer 220 further includes
a mobile receive band pass filter (BPF MR) 224 which receives RF
reception signals from the antenna 23, filters out frequencies above
and below the normal mobile receive band boundaries, and outputs
the resulting (Rx) signal to the mobile's receiver circuitry.
FIG. 3 illustrates the band pass filtering results of the duplexer
220. In FIG. 3, the lower boundary of the mobile transmit band is
designated as MTL (mobile transmit low), the upper mobile transmit
band boundary is designated as MTH (mobile transmit high), the lower
boundary of the mobile receive band is designated as MRL, and the
upper boundary of the mobile receive band is designated as MRH.
Although the example shown in FIG. 3 specifies that the frequencies
in the mobile transmit band are lower than the frequencies in the
mobile receive band, the mobile transmit frequency band could be
higher than the mobile receive frequency band. As shown in FIG.
3, the filtering characteristics of the BPF MT 222 and the BPF MR
224 create a roll-off effect, such that the duplexer 220 only partially
attenuates frequencies between MTH and MRL. In accordance with the
present invention, such in-between frequencies are used for low-power,
short-range communication during the W-T mode.
Referring again to FIG. 1, the dual mode transmitter/receiver 200
includes a configuration for performing typical mobile RF transmission.
Specifically, the dual mode transmitter/receiver 200 includes an
input audio amplifier 204 which receives an analog audio signal
from the speech input 22 and amplifies the analog audio signal.
A speech encoder 206 receives the amplified analog audio signal
from the input audio amplifier 204, digitizes the amplified analog
audio signal, and encodes, using for example linear predictive encoding,
the digitized audio signal to generate an encoded audio bit stream.
A first digital processor 208 receives the encoded audio bit stream
from the speech encoder 206 and digitally processes the encoded
audio bit stream, using such techniques as encryption and error
correction coding.
A modulator 214 receives the digitally processed audio bit stream
from the first digital processor 208, and receives an RF carrier
signal from a frequency synthesizer 212. To generate the RF carrier
signal, the frequency synthesizer 212 receives a reference oscillating
frequency signal from a reference oscillator 210 and converts the
reference oscillation frequency signal to the RF carrier signal.
The modulator 214 modulates the RF carrier signal with the digitally
processed audio bit steam, using for example known modulation techniques,
to output an RF transmit signal. A transmit amplifier 216 receives
the RF transmit signal from the modulator 214 via a first mobile
phone to walkie-talkie (MP-WT) switch 272 and amplifies the RF transmit
signal. The duplexer 220 receives the amplified RF transmit signal
from the transmit amplifier 216 via a second MP-WT switch 274 and
filters out frequencies from the amplified RF transmit signal which
are below MTL and above MTH, as discussed above. The antenna 23
receives the filtered Tx signal from the duplexer 220 and transmits
the filtered Tx signal to a cellular network base station.
The dual mode transmitter/receiver 200 further includes a configuration
for performing typical mobile RF reception. Specifically, the dual
mode transmitter/receiver 200 includes an RF amplifier 232 which
receives the Rx signal from the duplexer 220 via a third MP-WT switch
277 and amplifies the Rx signal.
A mixer 234 receives the amplified Rx signal from the RF amplifier,
and receives a mixing frequency signal from the frequency synthesizer
212. For reception, the frequency synthesizer 212 converts the reference
oscillating frequency signal from the reference oscillator 210 to
a frequency which, when mixed with the amplified Rx signal by the
mixer 234, results in an intermediate frequency (IF) which is suitable
for subsequent demodulation. The mixer 234 mixes the amplified Rx
signal with the mixing frequency signal to generate an IF Rx signal.
An IF amplifier 235 receives the IF Rx signal from the mixer 234
and amplifies the IF Rx signal.
A demodulator 236 receives the amplified IF Rx signal from the
IF amplifier 235 and demodulates the amplified IF Rx signal to recover
an Rx bit stream. A second digital processor 238 receives the Rx
bit stream from the demodulator 236 and digitally processes the
Rx bit steam, for example to achieve decryption and error correction.
A speech decoder 240 receives the digitally processed Rx bit stream
from the second digital processor 238 and decodes the digitally
processed Rx bit steam to recover an original audio signal. Finally,
an output audio amplifier 242 receives the original audio signal
from the speech decoder 240 via a fourth MP-WT switch 279 and amplifies
the original audio signal. The speech output 24 receives the amplified
original audio signal from the output audio amplifier 242 and outputs
the amplified original audio signal to the user.
To provide two-way radio functionality, the dual mode transmitter/receiver
200 includes a walkie-talkie (WT) module 280 which generates W-T
mode transmission signals in the in-between frequency band, and
retrieves audio signals from RF signals received during the W-T
mode. The dual mode transmitter/receiver 200 further includes a
controller 260 for controlling the positioning of the first MP-WT
switch 272, the second MP-WT switch 274, the third MP-WT switch
277, and the fourth MP-WT switch 279 to enable switching between
normal operation and the W-T mode. The dual mode transmitter/receiver
200 further includes a first listen-talk (L-T) switch 276, positioned
between the second MP-WT switch 274 and the duplexer 220, and a
second L-T switch 278, positioned between the third MP-WT switch
277 and the RF amplifier 232. The controller 260 sets the positioning
of the first and second L-T switches 276 and 278 in a manner discussed
below to achieve time-division duplexing.
As illustrated in FIG. 1, the WT module 280 receives the amplified
audio signal ("Voice in") from the input audio amplifier
204, the reference oscillating signal ("Ref Osc in") from
the reference oscillator 210, and the amplified Rx signal ("RF
Rx in") from the RF amplifier 232. The WT module 280 also receives
a control signal, WT SW ACT, from the controller 260 which indicates
when the W-T mode has been initiated, and a channel selection signal
("Channel Select in") from the controller 260 which indicates
a frequency channel selected during W-T mode.
The WT module 280 outputs an RF transmission signal ("RF tx
out") to the transmit amplifier 216 via the first MP-WT switch
272, an audio output signal ("Audio out") to the output
audio amplifier 242 via the fourth MP-WT switch 279, and a display
output signal ("Display out") to the mobile's display
processor (not shown) to control certain user displays which are
specific to the W-T mode.
FIG. 4 illustrates the external features of the dual mode mobile
which enables the user to initiate and operate in W-T mode. Specifically,
the mobile includes a MP-WT button 27 which the user sets to the
MP position for cellular service, and sets to the WT position for
two-way radio communication. As illustrated in FIG. 4, the mobile
further includes a push-to-talk (PTT) button 28 which the user presses
to transmit during the W-T mode. In contrast to frequency division
duplexing which allows a user to speak and listen simultaneously,
two-way radio communication typically transmits and receives at
the same frequency, thus restricting the user to either speaking
or listening at a give time (i.e., time-division duplexing). Therefore,
in a manner discussed below, the dual mode mobile either transmits
or receives during W-T mode depending on whether the user is pressing
the PTT button 28.
As illustrated in FIG. 4, the mobile further includes a channel
select button 29 which allows the user to change the frequency used
for two-way radio communication during the W-T mode, for example
when the user experiences interference on the original channel.
A display 25 displays to the user certain W-T mode specific information,
such as an indication that the mobile is operating in W-T mode and
what channel is being used.
Referring again to FIG. 1, the controller 260 receives: a WT select
signal from the MP-WT button 27 indicating whether the MP-WT button
27 is set to the MP or WT position; a Push-to-Talk signal from the
PTT button 28 indicating whether the user is pressing the PTT button
28; and a Channel Select signal from the channel select button 29
indicating when the user wishes to change frequency channels during
the W-T mode.
The controller 260 outputs the WT SW ACT signal to the first, second,
third, and fourth MP-WT switches 272, 274, 277, and 279, and the
WT module 280 when the MP-WT button 27 is set in the WT position.
The controller 260 further outputs a second control signal, PTT
SW ACT, to the first and second L-T switches 276 and 278 and the
WT module 280 when the user presses the PTT button 28. As discussed
below, the controller 260 selectively sets the first L-T switch
276 and the second L-T switch 278 to control time-division duplexing
during the W-T mode. The controller 260 further outputs a third
control signal, "Channel Select in," to the WT module
280 to control the frequency, in the in-between band, used for the
W-T mode.
As illustrated in FIG. 5, the WT module 280 includes an FM modulator
282 which receives the "Voice in" signal from the input
audio amplifier 204, and frequency modulates a reference signal
in accordance with "Voice in," using for example direct
frequency modulation, to generate an FM signal. An RF mixer 286
receives the FM signal from the frequency modulator 282 and receives
a mixing frequency signal from a WT frequency synthesizer 284. To
generate the mixing frequency signal, the WT frequency synthesizer
284 receives the "Ref OSC in" signal from the reference
oscillator 210, and converts "Ref OSC in" to a frequency
which, when mixed with the FM signal by the RF mixer 286, produces
an RF signal used for two-way radio communication. The RF frequency
synthesizer 284 further receives the "Channel Select input"
signal from the controller 260 to selectively change the RF within
the in-between frequency band used for two-way radio communication.
The RF mixer 286 converts the FM signal to an RF transmit signal
used for two-way radio communication (i.e., at a frequency in the
in-between frequency band). The transmit amplifier 272 receives
the RF transmit signal, "RF Tx out," from the RF mixer
286 via the first MP-WT switch 272 during the W-T mode.
For extracting audio signals from RF signals received during the
W-T mode, the WT module 280 further includes an IF mixer 287 which
receives the "RF Rx in" signal from the RF amplifier 232.
The IF mixer 287 also receives a mixing frequency signal from the
WT frequency synthesizer 284 to down-convert the "RF Rx in"
signal to an IF signal. An FM demodulator 288 receives the IF signal
from the IF mixer 287 and demodulates the IF signal to recover an
original audio signal. The output audio amplifier 242 receives the
original audio signal, "Audio out," from the FM demodulator
288 during the W-T mode via the fourth MP-WT switch 279.
A WT display controller 285 receives WT SW ACT and "Channel
Select in" from the controller, and outputs display control
signals to the mobile's display processor (not shown) so that the
mobile displays certain W-T display features to the user as discussed
above.
Next, the operation of initiating and operating in the W-T mode
will next be described. In the description of the transmitter and
receiver configurations above, it was assumed that the mobile was
in the normal operating mode, and thus the first, second, third,
and fourth MP-WT switches 272, 274, 277, and 279 were in the MP
position. When the first, second, third, and fourth MP-WT switches
272, 274, 277, and 279 are set in the MP position, the dual mode
transmitter/receiver 200 enables normal cellular communication using
frequency division duplexing to transmit and receive to/from a cellular
network base station.
When a user wishes to communicate directly with a similarly equipped
mobile, the user initiates the W-T mode by moving the MP-WT button
27 from MP to WT. The controller 260 then outputs the WT SW ACT
signal to the first, second, third, and fourth MP-WT switches 272,
274, 277, and 279 to set these switches to the WT position. In the
WT position, the first MP-WT switch 272 connects the input of the
transmit amplifier 216 to the "RF Tx out" signal of the
WT module 280, the second MP-WT switch 274 connects the output of
the transmit amplifier 216 to the first Listen-Talk ("L-T")
switch 276, the third MP-WT switch 277 connects the output of the
duplexer 220 to the second L-T switch 278, and the fourth MP-WT
switch 279 connects the input of the output audio amplifier 242
to the "Audio out" signal of the WT module 280.
After the user has initiated the W-T mode using the MP-WT button
27, when the user presses the PTT button 28 the controller 260 outputs
the PTT SW ACT signal to the first and second L-T switches 276 and
278 to set the first and second L-T switches 276 and 278 to the
T position. In the T position, the first L-T switch 276 connects
the second MP-WT switch 274 to the duplexer 220 so that the "RF
Tx out" signal from the WT module 280 is transmitted by the
antenna 23 after passing through the transmit amplifier 216 and
the duplexer 220. Also, in the T position, the second L-T switch
278 disconnects the Rx output of the duplexer 220 from the RF amplifier
232. Therefore, when the user presses the PTT button 28 during the
W-T mode, two-way radio transmission of input audio signals from
the speech input 22 is realized using the WT module 280, but the
reception signals from the duplexer 220 are not received by the
WT module 280.
On the other hand, when the user does not press the PTT button
28 during the W-T mode, the first and second L-T switches 276 and
278 remain in the L position. In the L position, the first L-T switch
276 disconnects the output of the transmit amplifier 216 from the
input of the duplexer 220 and the second L-T switch 278 connects
the Rx output of the duplexer 220 to the RF amplifier 232. Therefore,
the WT module 280 receives Rx from duplexer 220, after amplification
by the RF amplifier 232, as the "RF Rx in" signal and
retrieves an original audio signal using the FM demodulator 288
described above. Accordingly, the first and second L-T switches
276 and 278 enable time-division duplexing during the W-T mode.
As discussed above, the duplexer configuration illustrated in FIG.
2 partially attenuates frequencies used for two-way radio communication.
Since the W-T mode is generally intended for communication over
relatively short distances and at low power, this attenuation does
not preclude acceptable signal levels at selected frequencies between
MTH and MRL. An alternative duplexer 220 configuration, however,
may be utilized to minimize attenuation in the two-way radio frequency
band.
FIG. 6 illustrates such an alternative duplexer configuration in
accordance with an embodiment of the present invention. The duplexer
220 shown in FIG. 6 includes an additional band pass filter, BPF
WT 226, in addition to the BPF MT 222 and the BPF MR 224 discussed
above. The alternative duplexer 220 shown in FIG. 6 further includes
a fifth MP-WT switch 225 which connects the BPF MT 222 and the BPF
MR 224 to the antenna 23 when set to the MP position (and thus results
in a duplexer operation the same as that in FIG. 2). The fifth MP-WT
switch 225 receives the WT SW ACT signal from the controller 260
when the user positions the MP-WT button 27 to the WT position to
temporarily disconnect both the BPF MT 222 and the BPF MR 224 from
the antenna 23, and instead connects the BPF WT 226 to the antenna
23.
FIG. 7 illustrates the filtering results for this alternative duplexer
configuration. As illustrated in FIG. 7, the BPF WT 226 filters
out frequencies below MTH and above MRL for two-way radio communication.
Furthermore, since the BPF MT 222 and the BPF MR 224 are disconnected
from the antenna 23, frequencies between MTH and MRL are not attenuated.
Therefore, the alternative duplexer configuration illustrated in
FIG. 6 eliminates the attenuation of signals in the in-between frequency
band caused by the BPF MT 222 and the BPF MR 224.
As the above discussion illustrates, the dual mode receiver/transmitter
200 utilizes the duplexer 220, the antenna 23, the reference oscillator
210, the input audio amplifier 204, the transmit amplifier 216,
the RF amplifier 232, and the output audio amplifier 242 in both
normal and W-T operating modes. Thus two-way radio functionality
is implemented efficiently, by reducing the number of additional
components required. Therefore, the dual mode mobile according to
the present invention, in which frequencies between the normal mobile
transmit and receive bands are used for the W-T mode, allows substantial
design efficiencies.
Furthermore, the dual mode mobile according to the present invention
has particular applicability to PCS devices, which are cellular
devices licensed to transmit at frequencies in the range of 1850-1910
Mhz and receive at frequencies in the range of 1930-1990 Mhz. Under
current FCC regulations, frequencies in the range of 1910-1930 Mhz
are reserved for unlicensed communication. Therefore, as incorporated
in a PCS mobile, the dual mode transmitter/receiver 200 according
to the present invention operates at frequencies between 1910-1930
Mhz during the W-T mode, and thus can operate in accordance with
current FCC licensing regulations.
The dual mode mobile described herein is suitable for use in Time
Division Multiple Access (TDMA), Code Division Multiple Access (CDMA),
and Global System for Mobile (GSM) cellular service systems, as
well as other types of cellular networks. Furthermore, although
the dual mode transmitter/receiver 200 illustrated in FIG. 1 incorporates
digital mobile telephone technology, the technique of two-way radio
communication between normal mobile transmit and receive bands is
applicable to analog mobiles, such as those used in Advanced Mobile
Phone Service (AMPS) systems, as well as other communication devices
which normally transmit and receive at separated frequency bands.
Furthermore, although the WT module 280 has been described as using
frequency modulation/demodulation, it should be realized that the
WT module 280 could utilize other modulation techniques. Still further,
although the input/output signals of the dual mode transmitter/receiver
200 described above were audio signals, the dual mode transmitter/receiver
200 is also applicable to other types of communication signals,
such as data signals.
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