Note: Descriptions are shown in the official language in which they were submitted.
~JVO 96/10871 ~- ~ ;~ ~ ~ ~ ~ ; ~ ' ' PCT/US95/12388
MULTIPLE BAND RADIO
BACKGROUND OF THE INVENTION
I. FIELD OF THE INVENTION
The present invention relates to radio communications. More
particularly, the present invention relates to radios having the capability
of communicating over more than one frequency simultaneously.
II. DESCRIPTION OF THE RELATED ART
There are presently numerous different radiotelephone systems.
The cellular analog advanced mobile phone system (AMPS), the two
digital cellular systems: code division multiple access (CDMA) and time
division multiple access (TDMA), or the new personal communication
systems (PCS) that can use both TDMA and CDMA technologies. The
CDMA cellular system is described in greater detail in
Telecommunications Industry Association/Electronic Industries
Association (TMIA) Interim Star~dard IS-95.
The CDMA cellular system and the CDMA PCS share some
common attributes. They are typically composed of numerous fixed base
stations, each base station transmitting over a forward channel in a
cellular area to one or more mobile radios.
The cell's base station is connected to the public switched telephone
network (PSTN). This enables a mobile radio transmitting within the cell,
over a reverse channel, to communicate with a land line telephone
through the base station. Additionally, a mobile radio can communicate
through the base stations and the PSTN to another mobile radio in the
same cell or another cell.
In a CDMA cellular telephone system or a CDMA PCS, a common
frequency band is used for communication with all base stations in a
system. The common frequency band allows simultaneous
communication between a mobile radio and more than one base station.
The transmitters operate at a low power allowing the frequencies to be
reused in nearby systems without substantial interference.
Signals occupying the common frequency band are discriminated at
the receiving terminal (either within the mobile radio or base station)
through the spread spectrum CDMA waveform properties based on the
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use of high speed pseudo noise (PN) codes and orthogonal Walsh codes.
The high speed PN codes and orthogonal Walsh codes are used to
modulate signals transmitted from the base stations and the mobile
radios. Transmitting terminals (either within a mobile radio or within a
base station), using different PN codes or PN codes that are offset in time,
produce signals that can be separately received at the receiving terminal.
In a typical CDMA system, each base station transmits a pilot
signal having a common PN spreading code that is offset in code phase
from the pilot signal of other base stations. During system operation, the
mobile radio is provided with a list of code phase offsets corresponding to
neighboring base stations surrounding the base station through which
communication is established. The mobile radio is equipped with a
searching element that allows the mobile radio to acquire and track the
signal strength of the pilot signal from a group of base stations including
the neighboring base stations.
CDMA technology provides for soft hand-off between cells across
one frequency by the changing of code phase offsets. When there is a need
to use more than one frequency so that a hand-off between two frequencies
is required, a hard hand-off is performed. Hand-off between sectors of one
cell across one frequency is referred to in the art as a softer hand-off.
A method and system for providing a communication with the
mobile radio through more than one base station during the hand-off
process are disclosed in U.S. Patent No.-5,267,261 issued November 30,
1993, titled Mobile Assisted Soft Hand-Off In a CDMA Cellular Telephone
System and assigned to the assignee of the present invention. Using this
system, communication between the mobile radio and the end user is
uninterrupted by the eventual hand-off from an original base station to a
subsequent base station. This type of hand-off may be considered as a "soft"
hand-off in that communication with the subsequent base station is
established before communication with the original base station is
terminated. When the mobile radio is in communication with two base
stations, a single signal for the end user is created from the signals from
each base station by a cellular or personal communication system
controller.
Mobile radio assisted soft hand-off operates based on the pilot signal
strength of several sets of base stations as measured by the mobile radio.
The Active Set is the set of base stations through which active
communication is established. The Neighbor Set is a set of base stations
surrounding an active base station comprising base stations that have a
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high probability of having a pilot signal strength of sufficient level to
establish communication. The Candidate Set is a set of base stations
having a pilot signal strength of sufficient level to establish
communication.
When communications are initially established, a mobile radio
communicates through a first base station and the Active Set contains
only the first base station. The mobile radio monitors the pilot signal
strength of the base stations of the Active Set, the Candidate Set, and the
Neighbor Set. When a pilot signal of a base station in the Neighbor Set
exceeds a predetermined threshold level, the base station is added to the
Candidate Set and removed from the Neighbor Set at the mobile radio.
The mobile radio communicates a message to the first base station
identifying the new base station. A cellular or PCS controller decides
whether to establish communication between the new base station and the
mobile radio. Should the cellular or PCS controller decide to do so, the
controller sends a message to the new base station with identifying
information about the mobile radio and a command to establish
communications with the mobile radio.
A message is also transmitted to the mobile radio through the first
base station. The message identifies a new Active Set that includes the
first and the new base stations. The mobile radio searches for the new
base station's transmitted information signal and communication is
established with the new base station without termination of
communication through the first base station. This process can continue
with additional base stations.
When the mobile radio is communicating through multiple base
stations, it continues to monitor the signal strength of the base stations of
the Active Set, the Candidate Set, and the Neighbor Set. Should the signal
strength corresponding to a base station of the Active Set drop below a
predetermined threshold for a predetermined period of time, the mobile
radio generates and transmits a message to report the event. The cellular
or PCS controller receives this message through at least one of the base
stations with which the mobile radio is communicating. The controller
may decide to terminate communications through the base station having
a weak pilot signal strength.
The controller, upon deciding to terminate communications
through a base station, generates a message identifying a new Active Set
of base stations. The new Active Set does not contain the base station
through which communication is to be terminated. The base stations
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through which communication is established send a message to the
mobile radio. The controller also communicates information to the base
station to terminate communications with the mobile radio. The mobile
radio communications are thus routed only through base stations
identified in the new Active Set.
Because the mobile radio is communicating with the end user
through at least one base station at all times throughout the soft hand-off
process, no interruption in communications occurs between the mobile
radio and the end user. A soft hand-off provides significant benefits in its
inherent "make before break" communication over conventional hard
hand-off or "break before make" techniques employed in other cellular
communication systems.
When a mobile radio moves from one cell to another, the radio may
need to change frequencies, i.e., execute a hard hand-off. This frequency
change in PCS may be due to the use of Operational Fixed Services (OFS)
that share the PCS spectrum. Near these OFS's, the PCS mobile cannot
use the OFS frequency in order to avoid interference. The PCS mobile,
therefore, has to change frequencies in these areas.
In handing-off from one frequency to another, the mobile radio
searches the Neighbor Set for another pilot channel, synchronizing
channel, paging channel, and traffic channel. If only the pilot and/or
synchronizing channels are present, the mobile radio moves on to the next
frequency.
The problem with a soft hand-ofI' from one frequency to another is
that as the mobile radio searches the Neighbor Set for other pilot
channels, the synthesizer must change frequencies rapidly while
allowing a settling time of 2 milliseconds on the frequency to enable the
frequency to stabilize. This is difficult to accomplish and requires a more
complex design to do so. Additionally, the mobile must leave the frequency
being used, causing an interruption in communications. There is a
resulting need for an economical radio that can rapidly communicate over
multiple frequencies, thus allowing the mobile radio to efficiently perform
a soft hand-off between frequencies.
SUMMARY OF THE INVENTION
The present invention encompasses a multiple band radio that can
transmit and receive multiple frequency signals simultaneously. The
radio has a transmit path and a receive path. The transmit path is
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comprised of a plurality of mixing paths. Each mixing path
has an amplifier whose input is coupled to the signal to be
transmitted. The output of each amplifier is coupled to an
input of a mixer. Another input of the mixers is coupled to
5 an output of a frequency synthesizer. The resulting signals
from the mixers are summed by a summer. The sum signal is
input to a power amplifier which inputs the signal to an
antenna to be radiated.
The receive path is comprised of an amplifier
coupled to the antenna for amplifying received signals. The
output of the amplifier is input to a plurality of down
converting paths. Each down converting path has a mixer
coupled to the amplified signal. Another input of each
mixer is coupled to the frequency synthesizers. The
resulting down converted signals are input to filters. The
output of each filters is input to a variable gain
amplifier. The amplified signals from the down converting
paths are input to a summer. The sum signal is then input
to a common filter that generates a signal for use by the
rest of the radio.
The multiple frequency synthesizers in combination
with the multiple transmit receive paths enables the
apparatus of the present invention to transmit and receive
on multiple frequencies simultaneously, communicate on one
frequency while searching others, and to perform a soft
hand-off between frequencies. This alleviates the problem
of the prior art of settling time of a frequency synthesizer
since the frequency synthesizers do not have to change
frequencies as rapidly and as frequently as previously
required. It also avoids an interruption in communications,
as normally results from monitoring one frequency at a time.
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According to one aspect of the present invention,
there is provided a method for transmitting the same
information simultaneously on a plurality of transmit
frequencies with a dual mode radio communication device, a
first mode being single frequency operation and a second
mode being dual frequency operation, the radio communication
device operating in a cellular radio environment having a
plurality of base stations, each base station communicating
within a cell, the method comprising the steps of:
generating a signal to be transmitted; altering the signal
by a first gain to produce a first gain adjusted signal;
altering the signal by a second gain to produce a second
gain adjusted signal, said second gain being substantially
zero in said first mode and non-zero in said second mode;
multiplying the first gain adjusted signal by a first
oscillator signal having a first frequency to produce a
first transmit frequency signal; multiplying the second gain
adjusted signal by a second oscillator signal having a
second frequency to produce a second transmit frequency
signal, said first and second transmit frequency signals
carrying said same information; summing the first and second
transmit frequency signals to produce a summed signal; power
amplifying the summed signal to produce a power amplified
signal; and radiating the power amplified signal from an
antenna.
According to another aspect of the present
invention, there is provided a method for receiving a same
information signal simultaneously on a plurality of receive
frequencies with a dual-mode radio, a first mode being
single frequency operation and a second mode being dual
frequency operation, the dual-mode radio operating in a
cellular radio environment having a plurality of base
stations, each base station communicating within a cell, the
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5b
method comprising the steps of: receiving a first signal
from a first base station and a second signal from a second
base station when in said second mode, the first and second
base stations being of the plurality of base stations, said
first and second signals carrying said same information;
amplifying the first and second signals to produce an
amplified received signal; multiplying the amplified
received signal by a first signal having a first frequency
to produce a first down converted signal; multiplying the
amplified received signal by a second signal having a second
frequency to produce a second down converted signal;
filtering the first and second down converted signals to
produce first and second filtered signals; altering the
first filtered signal by a first gain to produce a first
amplified, filtered signal; altering the second filtered
signal by a second gain to produce a second amplified,
filtered signal, said second gain being substantially equal
to zero when in said first mode and non-zero when in said
second mode; summing the first and second amplified,
filtered signals to produce a summed signal; and filtering
the summed signal.
According to still another aspect of the present
invention, there is provided a method for transmitting
multiple signals, each signal having a different frequency,
with a dual mode radio, a first mode being single frequency
operation and a second mode being dual frequency operation,
the radio having a transmit path comprising a plurality of
mixing paths, the radio operating in a cellular radio
environment having a plurality of base stations, each base
station communicating within a cell, the method comprising
the steps of: generating a signal to be transmitted;
altering the signal by'a gain to produce a gain adjusted
signal; if the radio is in the first mode, preventing the
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gain adjusted signal from being conducted through more than
one mixing path; if the radio is in the second mode,
conducting the gain adjusted signal through at least two
mixing paths of the plurality of mixing paths; multiplying
each gain adjusted signal that is conducted through a mixing
path of the plurality of mixing paths by a different
oscillator signal, each oscillator signal having a different
frequency to produce at least one transmit frequency signal;
if the radio is in the second mode, summing transmit
frequency signals from the at least two mixing paths to
produce a summed signal; power amplifying the summed signal
to produce a power amplified signal; and radiating the power
amplified signal from an antenna.
According to yet another aspect of the present
invention, there is provided a method for receiving multiple
signals, each signal having a different frequency, with a
dual mode radio, a first mode being single frequency
operation and a second mode being dual frequency operation,
the radio having a receive path comprising a plurality of
down converting paths, the radio operating in a cellular
radio environment having a plurality of base stations, the
method comprising the steps of: in the first mode,
receiving a first signal from a first base station of the
plurality of base stations; in the second mode, receiving a
plurality of signals from the plurality of base stations,
the plurality of received signals each having a power level;
in response to the mode, amplifying either the first signal
or the plurality of signals to produce a first amplified
signal or a plurality of amplified signals; in response to
the mode, multiplying either the first amplified signal or
each of the plurality of amplified signals, by a synthesizer
signal, each synthesizer signal having a different
frequency, thus producing either a first down converted
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signal or a plurality of down converted signals; in response
to the mode, filtering either the first down converted
signal or the plurality of down converted signals, to
produce either a first filtered signal or a plurality of
filtered signals; in the first mode, altering the first
filtered signal by a first gain to produce a first amplified
signal; in the second mode, altering a respective gain of
each of the plurality of filtered signals in response to a
respective power level of each of the plurality of received
signals, thus producing a plurality of amplified signals; in
the second mode, summing the plurality of amplified signals
to produce a summed signal; in the first mode, filtering the
first amplified signal to produce an output signal; and in
the second mode, filtering the summed signal to produce said
output signal.
According to a further aspect of the present
invention, there is provided a multiple band diversity
apparatus that transmits, in a first mode, a same
information signal simultaneously on a plurality of transmit
frequencies through a transmit path and receives, in the
first mode, a same communication signal simultaneously on a
plurality of receive frequencies through a receive path, the
apparatus having a second mode for transmitting and
receiving a single frequency signal, the apparatus
comprising: a plurality of mixing paths in the transmit
path, each of said plurality of mixing paths for
upconverting said same information signal to one of said
plurality of transmit frequencies, each mixing path having a
switch of a first plurality of switches and a mixer coupled
to each switch, the plurality of mixing paths each adapted
to receive a signal to be transmitted, each mixing path
providing said upconverted same information signal at an
output; a plurality of down converting paths in the receive
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path, each of said plurality of down converting paths for
downconverting said same communication signal from one of
said plurality of receive frequencies, each down converting
path having a mixer that is coupled to a filter that is
coupled to a switch of a second plurality of switches, each
down converting path providing a downconverted same
communication signal at an output; a plurality of frequency
synthesizers, each.frequency synthesizer of the plurality of
frequency synthesizers coupled to a different mixing path of
the plurality of mixing paths and a different down
converting path of the plurality of down converting paths; a
first summer coupled to the outputs of the plurality of
mixing paths, the first summer outputting a summed transmit
signal in response to the sum of each of the said
upconverted same information signals; and a second summer
coupled to the outputs of the plurality of down converting
paths, the second summer outputting a summed receive signal
in response to the sum of each of the said downconverted
same communication signals.
According to yet a further aspect of the present
invention, there is provided a multiple frequency radio that
receives a same communication signal on a plurality of
frequencies simultaneously, the radio operating in a
cellular radio environment comprising a plurality of base
stations, each base station transmitting said same
communication signal on said plurality of frequencies, the
radio having a transmit path and a receive path, the radio
comprising: a multiplier, in the transmit path, said
multiplier having a plurality of inputs and an output, a
first input of the plurality of inputs adapted to receive a
signal to be transmitted; a plurality of signal
synthesizers, each generating a signal having a different
frequency; a multiplexing switch having a plurality of
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inputs and a switch output, each input coupled to a
different one of the plurality of signal synthesizers, the
switch output coupled to a second input of the plurality of
inputs of the multiplier; a transmit amplifier in the
transmit path, said transmit amplifier having an input
coupled to the multiplier output, said transmit amplifier
providing an output signal of said transmit path; a receive
amplifier, in the receive path, said receive amplifier
having an input adapted to receive a received signal; a
plurality of down converting paths in the receive path, each
of said plurality of down converting paths for
downconverting said same communication signal from one of
said plurality of frequencies, each down converting path
comprising a mixer having an input coupled to an output of
the receive amplifier and an input coupled to a different
one of the plurality of signal synthesizers, a filter
coupled to an output of the mixer, and a differential
amplifier having a variable gain, an input coupled to an
output of the filter, and an output for providing said
downconverted same communication signal at an output of said
down converting path, said variable gain being determined by
a distance between the radio and the plurality of base
stations such that signals output from the plurality of
differential amplifiers are substantially equal in amplitude
to each other; and a summer in the receive path, said summer
having an input coupled to the outputs of the plurality of
differential amplifiers.
According to still a further aspect of the present
invention, there is provided a method for transmitting the
same information simultaneously on a plurality of transmit
frequencies with a dual mode radio communication device, a
first mode being single frequency operation and a second
mode being dual frequency operation, the radio communication
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5g
device operating in a cellular radio environment having a
plurality of base stations, each base station communicating
within a cell, the method comprising the steps of:
generating a signal to be transmitted; altering the signal
by a first gain to produce a first gain adjusted signal;
altering the signal by a second gain to produce a second
gain adjusted signal; increasing the second gain until it is
substantially equal to the first gain when the radio
communication device is in a hand-off region between a first
base station and a second base station; multiplying the
first gain adjusted signal by a first oscillator signal
having a first frequency to produce a first transmit
frequency signal; multiplying the second gain adjusted
signal by a second oscillator signal having a second
frequency to produce a second transmit frequency signal,
said first and second transmit frequency signals carrying
said same information; summing the first and second transmit
frequency signals to produce a summed signal; power
amplifying the summed signal to produce a power amplified
signal; and radiating the power amplified signal from an
antenna.
According to another aspect of the present
invention, there is provided a multiple frequency dual-mode
receiver for receiving a same information signal
simultaneously on a plurality of receive frequencies, a
first mode being single frequency operation and a second
mode being dual frequency operation, said multiple frequency
dual-mode receiver operating in a cellular radio environment
having a plurality of base stations, said multiple frequency
receiver comprising: an antenna for receiving a first
signal from a first of said plurality of base stations and a
second signal from a second of said plurality of base
stations when in said second mode, said first and second
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signals carrying said same information; a receive amplifier,
coupled to said antenna, for amplifying the first and second
signals to produce an amplified received signal; a first
downconverter, coupled to said receive amplifier, said first
downconverter for multiplying the amplified received signal
by a first signal having a first frequency to produce a
first downconverted signal; a second downconverter, coupled
to said receive amplifier, said second downconverter for
multiplying the amplified received signal by a second signal
having a second frequency to produce a second downconverted
signal; a first filter, coupled to said first downconverter,
said first filter for filtering the first downconverted
signal to produce a first filtered signal; a second filter,
coupled to said second downconverter, said second filter for
filtering the second downconverted signal to produce a
second filtered signal; a first variable gain amplifier,
coupled to said first filter, said first variable gain
amplifier for altering the first filtered signal by a first
gain to produce a first amplified, filtered signal; a second
variable gain amplifier, coupled to said first filter, said
second variable gain amplifier for altering the second
filtered signal by a second gain to produce a second
amplified, filtered signal, said second gain being
substantially equal to zero when in said first mode and non-
zero when in said second mode; a summer, coupled to said
first and second variable gain amplifiers, said summer for
summing the first and second amplified, filtered signals to
produce a summed signal; and a third filter, coupled to said
summer, said third filter for filtering the summed signal.
According to yet another aspect of the present
invention, there is provided a multiple frequency receiver
for receiving multiple signals, each signal having a
different frequency, said multiple frequency receiver having
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a first mode being single frequency operation and a second
mode being dual frequency operation, said multiple frequency
receiver operating in a cellular radio environment having a
plurality of base stations, said multiple frequency receiver
comprising: an antenna for receiving a first signal from a
first base station of the plurality of base stations when in
said first mode, and for receiving a plurality of signals
from the plurality of base stations when in said second
mode, the plurality of received signal each having a power
level; a receive amplifier, coupled to said antenna, said
receive amplifier for amplifying the first signal to produce
a first amplified signal when in said first mode, and for
amplifying the plurality of signals to produce a plurality
of amplified signals when in said second mode; a plurality
of downconverters, each downconverter coupled to said
receive amplifier, a first of said plurality~of
downconverters for multiplying said first amplified signal
by a first of a plurality of synthesizer signals thereby
producing a first downconverted signal when in said first
mode, and said plurality of downconverters further for
respectively multiplying each of said plurality of amplified
signals by a respective synthesizer signal of said plurality
of synthesizer signals thereby producing a plurality of
downconverted signals when in said second mode, each of said
respective synthesizer signals having a different frequency;
a plurality of filters, each of said plurality of filters
respectively coupled to a different one of said plurality of
downconverters, a first of said plurality of filters for
filtering said first downconverted signal thereby producing
a first filtered signal when in said first mode, and said
plurality of filters further for respectively filtering each
of said plurality of downconverters signals thereby
producing a plurality of filtered signals when in said
second mode; a plurality of variable gain amplifiers, each
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of said plurality of variable gain amplifiers respectively
coupled to a different one of said plurality of filters, a
first of said plurality of variable gain amplifiers for
altering said first filtered signal in said first mode, and
said plurality of variable gain amplifiers further for
altering a respective gain of each of said plurality of
filtered signals in response to a respective power level of
each of said plurality of received signals thereby producing
a plurality of amplified signals when in said second mode; a
summer, coupled to each o said plurality of variable gain
amplifiers, said summer for summing the plurality of
amplified signals to produce a summed signal when in said
second mode; and a filter, coupled o sad summer, for
filtering said first amplified signal when in said first
mode and for filtering said summed signal when in said
second mode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of the multiple band
radio of the present invention.
FIG. 2 shows an alternate embodiment of the
multiple band radio of the present invention.
FIG. 3 shows another alternate embodiment of the
multiple band radio of the present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODD~NT
The apparatus and method of the present invention enables a
mobile radio to operate on multiple frequencies. By increasing the number
of intermediate frequency paths in the radio and separately mixing each
signal to be transmitted to different frequencies, the number of
frequencies that the radio can communicate over is increased. The use of
CDMA technology then allows these signals to be separated later.
The apparatus of the present invention is illustrated in FIG. 1. The
apparatus is comprised of a transmit path (103) and a receive path (104).
Both the transmit (103) and receive paths (104) have a common automatic
gain control (AGC) amplifier (101 and 102) for amplifying a signal at the
intermediate frequency. In the preferred embodiment, the receive
intermediate frequency is 85 MHz and transmit intermediate frequency is
130 MHz. Alternate embodiments use other intermediate frequencies.
The common AGC amplifiers (101 and 102) are used for both open
loop power control and closed loop power control of the radio. Open loop
power control is explained in greater detail in U.S. Patent No. 5,056,109 to
Gilhousen et al. and assigned to Qualcomm, Incorporated. Open loop
power control is accomplished by the radio estimating the path loss of the
forward link based on the total power received by the radio. The total
power is the sum of the power from all base stations operating on the
same frequency assignment as perceived by the radio. From the estimate
of the average forward channel loss, the radio sets the transmit level of the
reverse channel signal to compensate for the channel loss. Closed loop
power control is accomplished through commands from the base station.
The apparatus of the present invention performs this power control
using the common AGC amplifiers (101 and 102). When a signal is
received by the radio, the gain of the receive common AGC amplifier (102)
is adjusted so that the gain of the receiver is substantially equal to the
gain
of the transmitter minus 73 dB. The difference is the estimated path loss.
The transmit path (103) of the apparatus of the present invention is
further comprised of multiple mixing paths (110 and 115). In the preferred
embodiment, there are two mixing paths (110 and 115) enabling the radio
to communicate on two different frequencies simultaneously. Alternate
embodiments could use more than two mixing paths to enable the radio to
communicate with a larger number of base stations.
Each mixing path (110 and 115) contains a differential AGC
amplifier (120 and 125) each feeding the input of a mixer (130 and 135).
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These amplifiers (120 and 125) have a variable gain that is adjustable over -
a 20 dB range, in the preferred embodiment. Alternate embodiments have
different ranges for the amplifier gain.
The inputs to the differential AGC amplifiers (120 and 125) are
coupled to the output of the transmit common AGC amplifier (101). The
differential AGC amplifiers (120 and 125) amplify the signal to be
transmitted. During normal operation of the radio, the gain of one of the
amplifiers is set to zero. When the radio is handing-off or searching
another frequency, the gains are approximately equal. If it is desired to
change the hand-off region of the system, one gain can be increased over
the other. This increases the transmit power of one signal over the other
and therefore the distance the radio can operate from the base station
using the frequency of the higher power signal.
Frequency synthesizers (140 and 145) are coupled to the other inputs
of the mixers (130 and 135). These synthesizers (140 and 145), in the
preferred embodiment, are variable frequency synthesizers that cover the
frequency spectrum set aside for either the cellular radiotelephone
systems or the personal communication systems. The frequency output by
the synthesizers (140 and 145) is controlled by the radio's microcontroller.
The radio receives instructions from the base stations on what frequency
to operate and the microcontroller varies the frequency of the synthesizers
(140 and 145) so that the radio transmits and receives at these frequencies.
Each mixer (130 and 135) in the mixing paths (110 and 115)
multiplies the signal from its respective differential AGC amplifier (120 or
125) with the signal from the respective frequency synthesizer (140 or 145).
The outputs of both mixers (130 and 135) are combined by a summer (160).
The sum signal is amplified by a power amplifier (165). In the preferred
embodiment, the amplifier (165) is set at a gain of approximately 30 dB.
Alternate embodiments use other gains depending on the noise levels of
the components.
The amplified signal is input to a duplexer (170) that is connected to
' an antenna (175). The duplexer (170) enables the antenna (175) to be
connected to both the transmit (103) and receive paths (104) by separating
the transmitted signals from the received signals.
The receive path (104) is comprised of a low noise amplifier (180)
feeding multiple down converting paths (116 and 117), each path down
converting a received signal to the same IF frequency. The low noise
amplifier amplifies the received signal by a gain of 20 dB in the preferred
embodiment.
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In the preferred embodiment, the amplified signal is input to the
two down converting paths (116 and 117). Alternate embodiments use
more down converting paths if it is desired to communicate with more
than two base stations simultaneously.
Each down converting path (116 and 117) is comprised of a mixer
(185 and 190) that combines the frequency from one of the frequency
synthesizers (140 or 145) with the received, amplified signal. Therefore, if
a mixing path (110 or 115) operates at a frequency of 850 MHz, there is a
corresponding down converting path (116 or 117) that also operates at that
frequency offset by the duplexor offset. Band pass filters (122 and 132) are
-used to filter the signals from the mixers (185 and 190).
The outputs of the bandpass filters (122 and 132) are each amplified
by a differential amplifier (142 and 152). The amplifiers (142 and 152)
operate in a similar fashion to the differential amplifiers (120 and 125) in
the transmit path. The receive differential amplifiers (142 and 152)
normally have a gain that is approximately equal. The gain of one can be
offset from the other, however, to emphasize one signal frequency over the
other. This enables the mobile to monitor either frequency channel or both
at once.
The outputs of the receive differential amplifiers ( 142 and 152) are
input to a summer (162) that adds them together. The sum signal from the
summer (162) is input to a bandpass filter (172) for filtering. In the
preferred embodiment, this bandpass filter (172) is a surface acoustic
wave (SAW) filter. The filtered signal is input to the common AGC
amplifier (102) that was explained in greater detail above. The amplified
signal from this amplifier (102) is then input to the radio's circuitry for
further processing as is already known in the art. TIA/EIA IS-95
describes this processing in greater detail.
If the differential AGC amplifiers (120, 125, 142, and 152) are always
set equal, in other words the hand-off region is always at the equal power
point, the amplifiers (120, 125, 142, and 152) can be-replaced by switches
(220, 225, 242, and 252). Such an embodiment is illustrated in FIG. 2. The
switches can take the form of diodes, transistors, relays, or other switch
devices to allow the circuit to be simplified.
This alternate embodiment operates in a similar fashion to the
preferred embodiment, the difference being the switches. The switch
position is controlled by the radio's microcontroller, depending on the
number of frequencies required by the radio. If the radio is not operating
near the hand-off region of the cellular system, only one frequency is
~~J~J'~~U
~WO 96/10871 PCT/LTS95/12388
9
required and, therefore, only one switch in each path is closed. As the
radio approaches the hand-off region, the second switch in each path is
closed to enable the radio to communicate over multiple frequencies.
Yet another alternate embodiment is illustrated in FIG. 3. The
structure and operation of the receive path of this embodiment is the same
as the preferred embodiment. The transmit path (301) of this embodiment,
however, is comprised of the common AGC amplifier (302), performing
the same closed loop power control function as in the preferred
embodiment, a mixer (310), a bandpass filter (330), and a power amplifier
(315).
Two frequency synthesizers (320 and 325) each generate a signal
having a different frequency. A switch or multiplexer (330) connects both
of the frequency synthesizers to the mixer (310). The switch is controlled by
the radio's microcontroller as are the frequency synthesizers (320 and
325). The radio can now rapidly switch between the first frequency
synthesizer (320) and the second frequency synthesizer (325) as required by
the frequency of each base station with which the radio is communicating.
These frequencies are determined by the received signals since this
alternate embodiment can still receive on multiple frequencies.
The output of the amplifier (302) is input to the mixer (310). The
other input of the mixer (310) is connected to the switch (330). When
synthesizer 1 (320) is needed, the switch connects it to the mixer (310).
When synthesizer 2 (325) is needed, the switch (330) disconnects
synthesizer 1 (320) and connects synthesizer 2 (325) to the mixer (310). If in
other alternate embodiments additional synthesizers are used, the
operation of the switch would be the same.
The bandpass filter (330) filters the output of the mixer (310). As in
the preferred embodiment, the pass band of the filter (330) is adjusted
depending on the signal desired from the mixer (310).
The output of the bandpass filter (330) is input to a power amplifier
(315). As in the preferred embodiment, this amplifier is adjusted to the
desired transmit power required for the cellular radio system in which
the apparatus of the present invention operates.
The alternate embodiment of FIG. 3 cannot transmit on multiple
frequencies simultaneously. However, it can receive and down convert
multiple frequencies simultaneously. This embodiment requires fewer
components and therefore is less expensive and needs less real estate on a
printed circuit board than the preferred embodiment since it does not
require additional amplifiers, mixers, and bandpass filters. Yet another
WO 96!10871 J PCT/US95/12388
i0
advantage is that the power amplifier only has to transmit one frequency
at a time. This is critical to maintain linearity and efficiency of the power
amplifier.
WE CLAIM:
