United States Patent (19)
`Clark
`
`5,001,776
`Patent Number:
`11
`(45) Date of Patent: Mar. 19, 1991
`
`54: COMMUNICATION SYSTEM WITH
`ADAPTIVE TRANSCEIVERS TO CONTROL
`INTERMODULATION DISTORTION
`Inventor: Edward T. Clark, Plantation, Fla.
`Assignee: Motorola Inc., Schaumburg, Ill.
`Appl. No.: 263,146
`Filed:
`Oct. 27, 1988
`Int. Cl’............................................... H04B 1/26
`U.S.C. .................................... 455/226; 455/236;
`455/234; 455/343; 455/308
`Field of Search ............... 455/295, 296, 308, 309,
`455/310, 311, 255, 256, 264, 235,236,343,226,
`67, 68, 88
`
`(75)
`(73)
`21
`22)
`(51)
`(52)
`(58)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,352,208 9/1982 Schroeder ........................... 455/266
`4,485,403 11/984 Illetschko .....
`... 455/296
`4,691,382 9/1987 Nakajima .............
`... 455/343
`4,761,646 8/1988 Choquet et al. ...................... 370/13
`4,907,293 3/1990 Veno ................................... 455/295
`
`Primary Examiner-Reinhard J. Eisenzopf
`Assistant Examiner-Edward Urban
`Attorney, Agent, or Firm-Pablo Meles
`57
`ABSTRACT
`A transceiver determines the signal quality of a desired
`signal and the strength of all received signals. When the
`signal quality of the desired signal is low, and the signal
`strength of all received signals is high, the receiver is
`adapted to operate in a higher current mode, thereby
`minimizing intermodulation distortion. Conversely,
`when the quality of the desired signal is low and the
`strength of all received signals is also low, or when the
`quality of the desired signal is above a threshold, the
`receiver operates in a lower current mode to conserve
`power and maximize battery lifetime. Also, when the
`transceiver adapts to operate in the higher current
`mode, a command is sent instructing a transmitting
`party to increase the quality of their message which
`may enable the listening transceiver to adapt (return) to
`a lower current mode.
`17 Claims, 2 Drawing Sheets
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`IPR2023-00697
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`U.S. Patent
`
`Mar. 19, 1991
`
`Sheet 1 of 2
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`5,001,776
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`U.S. Patent
`
`Mar. 19, 1991
`
`Sheet 2 of 2
`
`5,001,776
`
`TRANSCEIVER
`ADAPT
`
`
`
`
`
`2OO
`HIGH
`QUALITY DESIRED
`SIGNAL
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`CURRENT MODE
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`ADAPT TO LOW
`CURRENT MODE
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`CURRENT MODE
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`TRANSMIT COMMAND
`TO INCREASE POWER
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`1.
`
`COMMUNICATION SYSTEM WITH ADAPTIVE
`TRANSCEIVERS TO CONTROL
`NTERMODULATION DISTORTION
`
`TECHNICAL FIELD
`This invention relates generally to radio frequency
`(RF) transceivers, and more specifically to RF tranceiv
`ers designed to conserve a battery power source, and is
`10
`particularly directed toward adapting the power con
`sumption of battery powered RF transceivers to control
`intermodulation distortion while maximizing the opera
`tional lifetime of the tranceiver's battery.
`BACKGROUND ART
`In an RF receiver, intermodulation distortion is
`caused by an interfering signal of sufficient signal
`strength mixing with a local oscillator (or injection)
`signal that results in an undesired signal appearing in the
`passboard of a receiver's intermediate frequency (IF)
`section. Generally, a desired signal is also mixed into the
`IF passboard, and the contemporaneous presence of
`the undesired signal distorts the desired signal thereby
`reducing the intelligibility of the desired signal.
`It is known that the third order IM distortion of a 25
`balanced commutation mixer may be represent by:
`
`20
`
`15
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`30
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`5,001,776
`2
`signals is high (indicating a strong interfering signal),
`the receiver is adapted to operate in a higher current
`mode, which minimizes intermodulation distortion.
`Conversely, when the quality of the desired signal is
`low and the combined strength of all received signals is
`also low, or when the quality of the desired signal is
`above a threshold, the receiver operates in a lower
`current mode to conserve power and maximize battery
`lifetime.
`In another embodiment of the present invention, a
`transceiver operates as described above to determines
`the quality of a desired signal and the combined
`strength of all received signals. When the transceiver
`adapts to operator in the higher current mode, a com
`mand is sent instructing the transmitting party to in
`crease the quality of the transmitted message, such as,
`by increasing transmitter power, adding error correc
`tion information to the transmitted message, or decreas
`ing the transmission rate. By increasing the quality fo the
`transmitted message, the signal quality of the desired
`signal may increase to the point where the transceiver
`may adapt (return) to the lower current mode.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of a transceiver in accor
`dance with the present invention;
`FIG. 2 is a flow diagram illustrating the steps exe
`cuted by the transceiver of FIG. 1 in accordance with
`the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Referring to FIG. 1, a block diagram of a transceiver
`100 in accordance with the present invention is shown.
`Operationally, signals received by an antenna 102 are
`directed via an antenna switch 103 to a pre-selector 104,
`which appropriately band-limits the frequency spec
`trum of the transceiver 100. The signals residing in the
`band-limited spectrum provided by the pre-selector 104
`may be amplified in a radio frequency (RF) amplifier
`108, the output of which is routed to a mixer 110. As a
`second input, the mixer 110 accepts an injection signal
`112 provided by a local oscillator 114. The local oscilla
`tor 114 comprises and oscillattor 116, which may be a
`VXCO or other source of suitable stability. The oscilla
`tor 116 is coupled to an amplifier/limiter 118, which
`controls the peak-to-peak voltage of the injection signal
`112. By controlling the amplifier/limiter 118, the injec
`tion signal may be provided in the form of a square
`wave so that the rise (and fall) time of the injection
`signal 112 is minimized.
`The output of the mixer 110 comprises an intermedi
`ate frequency (IF) signal, which is further filtered in an
`IF filter 120 the band-width of which determines the
`received signals that will be processed to recover a
`desired information signal (either data or voice). Typi
`cally, the filtered IF signal is amplified in an intermedi
`ate frequency amplfier 122, prior to being routed to a
`signal recovery section 124. The signal recovery section
`124 may comprise a demodulator of conventional de
`sign for recovering voice messages, and may further
`comprise any suitable data detector for recovering data
`messages, which are routed (via data line 125) to a con
`troller 130.
`According to the invention, a "front end' signal de
`tector 126, is coupled to the output of the RF amplifier
`108, and operates to provide a DC output voltage signal
`
`2.
`
`Ma (s?. V. )
`
`V.
`
`(1)
`
`35
`
`Where,
`IM is the third order intermodulation distortion;
`Vc is the peak-to-peak local oscillator voltage;
`Vs is the peak received signal voltage;
`t is the rise (and fall) time of Vc, and
`fio is the frequency of the local oscillator.
`As is known, the peak received signal voltage (V)
`may be viewed as a random parameter, and the fre
`quency of the local oscillator (flo) is typically deter
`mined by the frequency of the desired signal Accord
`ingly, for a given received signal level and frequency,
`analysis of equation (1) reveals that the IM of the mixer
`(and thus the receiver) may be minimized (theoretically
`to zero) by increasing the peak-to-peak local oscillator 45
`voltage (V), or by reducing the rise (and fall) time of
`the local oscillator waveform (t), such as by using a
`square wave. However, signal amplification and square
`wave generation require high current to enable active
`devices to operate at high speed. Thus, this practice
`may be detrimental to battery powered RF receivers
`since the radio's operational lifetime may be reduced to
`an impractically short interval. Conversely, merely
`adding more batteries (or cells) to an RF receiver may
`so increase the weight and physical size of the receiver
`55
`as to make it undesirable to the consuming public.
`SUMMARY OF THE INVENTION
`Accordingly, it is an object of the present invention
`to provide an Rf communication system transceiving
`devices capable of adapting their operation to minimize
`intermodulation distortion.
`Briefly, according to the invention, a receiver (or the
`receiving section of a transceiver) determines the signal
`quality of a desired signal, and the combined strength of 65
`all received signals (i.e., both desired and interfering
`signals). When the signal quality of the desired signal is
`low, and the combined signal strength of all received
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`5,001,776
`4.
`3
`127 that varies in proportion to the signal strength of all
`sistors and other circuits to operate at an increased
`speed or enhanced performance, which also reduces IM
`received signals (i.e., both desired signals and interfer
`ing signals). The signal detector 126 is referred to herein
`distortion.
`as a "front end' detector since it operates before the IF
`According to the invention, the Rf transceiver 100 is
`section (i.e., the IF filter 120 and the IF amplifier 122) of 5
`preferably a battery powered device. Thus, it will be
`the transceiver 100. Additionally, a "back end" signal
`appreciated that the gain achieved by the present inven
`detector 126' is coupled to the output of the IF amplifier
`tion in reducing IM distortion is not without cost. As
`122, and operates to provide a DC output voltage signal
`previously mentioned, the injection signal modifica
`127 that varies in proportion to the signal quality of a
`tions, the mixer switching speed adaptions, and other
`desired signal. According to the invention, the quality
`performance enhancements made to minimize IM dis
`parameter of the desired signal monitored by the detec
`tortion require high current. Accordingly, prolonged
`tor 126 preferably comprises received signal strength
`operation in a high current mode may cause the battery
`for voice signals, and bit error rate (BER) for data sig
`of the transceiver 100 to be prematurely exhausted.
`nals, but may also comprise signal-to-noise ratios, inter
`Thus, the present invention operates to balance current
`symbol interference measurements, or other such pa
`15
`drain and battery life against signal distortion and mes
`rameters used to relate or connote signal quality. The
`sage intelligibility. This balance is achieved and main
`signal detector 126' is referred to herein as a “back end'
`tained by the controller 130 as it compares the “back
`detector since it operates after the IF section (i.e., the
`end' signal quality and the "front end" signal strength
`filter 120 and the IF amplifier 122) of the transceiver
`against thresholds selected to correspond to varying
`100. Such signal detectors are well known in the art and
`20
`degrees of desired signal intelligibility. So long as the
`any suitable implementation of a signal detector capable
`desired signal quality remains sufficiently high, the
`of providing a signal strength indicator (127 or 127)
`transceiver 100 may operate in a lower power mode to
`may be used in conjunction with the present invention.
`conserve power. However, as the quality of the desired
`The signal strength indicators 127 and 127" are digi
`signal falls, the injection signal 112 may be adjusted to
`tized vaian analog-to-digit (A/D) convertors (128 and
`25
`counteract any distorting effects that a strong interfer
`128' respectively) prior to being routed to a controller
`ing signal may cause. Conversely, for interfering signals
`130. The controller 130 compares the digital representa
`with lower signal strength, certain degradations in the
`tion of the received signal strength (127) and the desired
`desired signal's intelligibly may be permitted in favor of
`signal quality (127) to at least one threshold to deter
`increased battery life.
`mine whether the received signal contains an interfering
`30
`Optionally, the controller 130 may adapt additional
`signal capable of promoting intermodulation distortion
`of the desired signal. So long as the quality of the de
`parameters when adapting between a lower current and
`sired signal is high, the transceiver 100 operates in a
`a higher current mode. For example, the oscillator 116
`may be shut down or its operation appreciably slowed
`lower current mode so as to conserve power. Con
`versely, when the quality of the desired signal is low,
`(via the control line 136). Also, the amplification factors
`35
`the signal strength of the "front end' received signals is
`(and thus the current drain) of the RF amplifier 108 and
`examined. A weak "front end" signal indicates the ab
`the IF amplifier 122 may be varied (via control lines 138
`sence of any significant interfering signal, while a strong
`and 140 respectively) by the controller 130. Finally, the
`"frone end" signal strength indicates the presence of a
`controller 130 may shut down (or slow down) certain
`strong interfering signal capable of promoting inter
`stages of the signal recovery section 124 (via a control
`modulation distortion of the known low quality desired
`line 142), such as, digital signalling processors (DSP) or
`signal. According to the invention, the transceiver 100
`other circuits known to consume large amounts of cur
`operates to adapt to a higher current operating mode in
`ret.
`the presence of a poor (or low) quality desired signal
`In another embodiment of the present invention, the
`and a strong "front end' signal strength as indicated
`transceiver 100 operates to coupler (101) a transmitter
`below in Table 1. Optionally, when both the "front
`144 to the antenna 102 and send a command to other
`end' signal strength and the "back end" signal quality
`tranceiver's when adapting to operate in the higher
`are high, the high current mode may be more desirable
`current mode. That is, the signal quality of the desired
`than the low current mode for some applications.
`signal is typically associated with another transceiver
`that is also a party to a conversation in progress. When
`TABLE 1.
`the received signal strength (both desired and interfer
`Received Signal
`ing signals) is high, and desired signal quality is low, the
`Strength
`listening transceiver adapts to a higher current mode as
`Low
`discussed above to minimize IM distortion. Addition
`High
`ally however, the listening transceiver may send a com
`Low
`High
`mand code to the transmitting transceiver that instructs
`the transmitting transceiver to increase the quality of its
`signal. This may be accomplished by increasing the
`transmitter power (via control line 146), adding error
`correction codes to the signal (via data line 148), or
`slowing the transmission rate (via control line 146). The
`purpose of this exchange is to cause the quality of the
`desired signal at the listening transceiver to increase to
`a point where the listening transceiver may adapt (re
`turn) to the lower current mode and conserve battery
`power.
`Referring to FIG. 2, a flow diagram illustrating the
`steps executed by the transceiver 100 is shown. The
`
`To minimize intermodulation distortion, the control
`ler 130 of the transceiver 100 operates to adapt at least
`the peak-to-peak voltage of the injection 112 by control
`ling (via a control line 134) the amplifier/limiter 118.
`Depending upon the command of the controller 130,
`the amplifier/limiter 118 increases the peak-to-peak
`voltage of the injection signal 112 to a suitable level, and
`may generate a large amplitude square wave so as to
`65
`further minimize IM distortion. Additionally, the con
`troller 130 may vary (via a control line 132) the current
`consumption of the mixer 110 to enable switching tran
`
`Desired Signal
`Quality
`Low
`Low
`High
`High
`
`Operating
`Mode
`Low Current
`High Current
`Low Current
`Low Current
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`5,001,776
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`routine begins in decision 200, which determines
`(e) transmitting a command code when said signal
`whether the quality of the desired signal is sufficiently
`quality of said desired signal is below said first
`high. If the determination of decision 200 is that a low
`threshold and said strength of said received signal
`quality desired signal has been received, the routine
`is above said second threshold:
`proceeds to decision 202, which determines whether the
`(f) determining whether said desired signal has a sig
`strength of all received signal (both desired and interfer
`nal quality above a first threshold:
`ing) at least equal to (or exceeds) a threshold. A nega
`(g) adjusting at least said injection signal when said
`tive determination of either decision 200 or decision 202
`signal quality of said desired signal is above said
`routes control to decision 204, which determines
`first threshold.
`whether the transceiver 100 is currently operating in a
`2. The method of claim 1, wherein step (d) comprises
`10
`higher current mode (i.e., adapting to minimize IM
`increasing peak voltage of said injection signal when
`distortion). If not, the routine proceeds to reference
`said signal quality of said desired signal is below said
`letter A (decision 200). However, if the determination
`first threshold and said signal strength of said received
`of decision 204 is that the transceiver is currently oper
`signal is above said second threshold.
`ating in the high current mode, the routine proceeds to
`15
`3. The method of claim 2, wherein step (d) further
`step 206, which adapts the receiver from the higher
`comprises reducing rise time of said injection signal
`current mode to a lower current mode thereby conserv
`when said signal quality of said desired signal is below
`ing battery power.
`said first threshold and said signal strength of said re
`Assuming, however, that the determination of deci
`ceived signal is above said second threshold.
`sion 202 is that the strength of the "front end' signal is
`20
`4. The method of claim 1, wherein step (d) comprises
`above the threshold, and thus likely to increase inter
`reducing rise time of said injection signal when said
`modulation distortion (due to the low quality of the
`signal quality of said desired signal is below said first
`desired signal), the routine proceeds to decision 208,
`threshold and said signal strength of said received signal
`which determines whether the transceiver 100 is cur
`is above said second threshold.
`rently oerating in the lower current mode. If so, the
`25
`5. The method of claim 1, wherein step (d) comprise
`routine proceeds to step 210, which adapts the receiver
`adjusting at least a portion of said receiver to operate in
`to a higher current mode, including, at least adapting
`a higher current mode when said signal quality of said
`the injection signal 112. Optionally, amplification fac
`desired signal is below said first threshold and said sig
`tors of the RF amplifier 108 and the IF amplifier 122
`nal strength of said received signal is above said second
`may be varied when adapting from the higher current
`threshold.
`mode to the lower current mode, and also within either
`6. The method of claim 5, wherein step (d) further
`the higher or lower current modes to provide a fine
`comprises adjusting said receiver to operate in a lower
`adjustment. Finally, one or more stages of the signal
`current mode when said signal quality of said desired
`recover section 124 may be provided with more or less
`signal is above said first threshold.
`current drive to vary their performance thereby facili
`7. In a two-way frequency communication system
`tating recovery of the desired information signal, while
`having at least two transceiving devices, a method for
`conserving battery power.
`receiving an information signal in the presence of an
`Optionally, the transceiver may transmit a command
`interfering signal, comprising the step of in a first one
`to another transceiver to increase the quality of its sig
`transceiving device:
`nal (step 212). Following this, the routine returns to 40
`(a) a receiving a signal to provide a received signal
`decision 200, which again determines the quality of the
`comprising at least a desired signal;
`desired signal. If the quality of the desired signal has
`(b) determining whether said received signal has a
`sufficiently improved, the routine proceeds through
`signal strength above a second threshold before
`decision 204 to step 206, which adapts (returns) the
`mixing an injection signal with said received signal;
`transceiver to the lower power mode. In this way, each
`(c) determing whether said desired signal has a signal
`tranceiver operating within the communication system
`quality above a first threshold after mixing said
`cooperates to minimize intermodulation distortion.
`injection signal with said signal; and,
`What is claimed is:
`(d) controlling intermodulation distortion by adjust
`1. In a two-way radio frequency communication sys
`ing at least said injection signal when said signal
`tem having at least two transceiving devices, a method
`50
`quality of said desired signal is below said first
`for receiving an information signal that may be cor
`rupted by an interfering signal, comprising the steps of:
`threshold and said signal strength of said received
`in at least one transceiving device:
`signal is above said second threshold:
`(e) transmitting a command code when said signal
`(a) receiving a signal to provide a received signal
`comprising at least a desired signal;
`quality of said desired signal is below said first
`(ai) mixing the received signal with an injection
`threshold and said signal strength of said received
`signal to provide a mixed signal;
`signal is above said second threshold:
`(f) determining whether said desired signal has a sig
`(b) determining whether said desired signal has a
`signal quality above a first threshold after the re
`nal above a first threshold:
`(g) adjusting at least said injection signal when said
`ceived signal has been mixed;
`(c) determining whether said received signal has a
`signal quailty of said desired signal is above said
`signal strength above a second threshold before the
`first threshold: at a second transceiving device:
`(a) transmitting said desired signal: p1 (b) receiving
`received signal is mixed; and
`(d) controlling intermodulation distortion by adjust
`said command code:
`ing at least said injection signal when said signal
`(c) adjusting said second transceiving device and/or
`quality of said desired signal is below said first
`said desired signal in response to receiving said
`threshold and said signal strength of said received
`command code: and
`signal is above said second threshold:
`(d) transmitting said desired signal.
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`first threshold and said signal strength of said re
`8. The method of claim 7, wherein step d further
`ceived signal is above said second threshold; and,
`comprises adjusting at least a portion of said receiver to
`means for transmitting a command code when said
`operate in a higher current mode when said signal qual
`signal quality of said desired signal is below said
`ity of said desired signal is below said first threshold and
`first threshold and said signal strength of said re
`said signal strength of said received signal is above said
`ceived signal is above said second threshold.
`second threshold.
`12. The radio frequency receiver of claim 11, wherein
`9. The method of claim 7, wherein step (e) further
`said means for controlling comprises means for increas
`comprises adjusting said receiver to operate in a lower
`ing peak voltage of said injection signal quality of said
`current mode when said said signal quality of said de
`desired signal is below said first threshold and said sig
`sired signal is below said first threshold and said signal
`10
`nal strength of said received signal is above said second
`strength of said received signal is above said second
`threshold.
`threshold.
`13. The radio frequency receiver of claim 12, wherein
`10. In a two-way radio frequency communication
`said means for controlling further comprises means for
`system having at least two battery powered transceiv
`reducing rise time of said injection signal when said
`ing devices having at least one converter capable of
`15
`signal quality of said desired signal is below said first
`mixing a received signal with an injection signal to
`threshold and said signal strength of said received siga
`facilitate recovery of an information signal, a method
`nal is above said second threshold.
`for controlling intermodulation distortion in the battery
`14. The radio frequency receiver of claim 11, wherein
`powered transceiving devices comprising the steps of:
`said means for controlling further comprises means for
`in a first transceiving device:
`reducing rise time of said injection signal when said
`(a) receiving a signal to provide a received signal
`signal of said desired signal is below said first threshold
`comprising at least a desired signal;
`and said signal strength of said received siganal is above
`(b) determining whether said desired signal has a
`said second threshold
`signal quality above a first threshold after mixing
`15. The radio frequency receiver of claim 11, which
`25
`said received signal with an injection signal;
`includes means for adjusting at least a portion of said
`(c) determining whether said received signal has a
`receiver to operate in a higher current mode when said
`signal quality of said desired signal is below said first
`signal strength above a second threshold before
`threshold and said signal strength of said received signal
`mixing said received signal with said injection sig
`is above said second threshold.
`nal; and
`16. The radio frequency receiver of claim 15, which
`(d) controlling intermodulation distortion by adjust
`includes means for adjusting said receiver to operate in
`ing at least said injection signal when said signal
`a lower current mode when said signal quality of said
`quality of said desired signal is below said first
`desired signal is above said first threshold,
`threshold and said signal strength of said received
`17. A battery powered radio frequency transceiver
`signal is above said second threshold;
`for use in a two-way radio frequency communication
`(e) transmitting a command code when said signal
`system having at least two of said battery powered
`quality of said desired signal is below said first
`radio frequency transceivers each having at least one
`threshold and said signal strength of said received
`convertor for receiving an injection signal and a re
`signal is above said second threshold;
`ceived signal to facilitate recovery of an information
`(f) determining whether said desired signal has a sig
`signal that may be corrupted by an interfering signal,
`nal quality above a first threshold;
`and each of said at least two battery powered radio
`(g) adjusting at least said injection signal when said
`frequency transceivers being capable of controlling
`signal quality of said desired signal is above said
`intermodulation distortion by adjusting between a low
`first threshold; at a second transceiving device:
`current mode and a high current mode which includes
`(a) transmitting said desired signal;
`adjusting at least the peak voltage and rise time of said
`45
`(b) receiving said command code;
`injection signal, said battery powered radio frequency
`(c) adjusting said second transceiving device and/or
`transceiver comprising:
`said desired signal in reponse to recieving said
`a battery source;
`command code; and,
`means for receiving a signal to provide a received
`(d) transmitting said desired signal.
`signal comprising at least a desired signal;
`50
`11. A radio frequency transceiving device capable of
`means for mixing said received signal to substantially
`receiving an information signal that may be corrupted
`provide said desired signal;
`by an interfering signal, comprising:
`means for determining whether said desired signal
`means for receiving a signal to provide a received
`has a signal quality above a first threshold after
`signal comprising at least a desired signal;
`mixing said received signal;
`means for filtering said received signal to substan
`means for determining whether said received signal
`tially provide said desired signal;
`has a signal strength above a second threshold
`means for determining whether said desired signal
`before mixing said received signal; and,
`has a signal quality above a first threshold after the
`means for controlling intermodulation distortion by
`received signal is filtered to provide said desired
`adjusting at least an injection signal when said
`signal;
`signal quality of said desired signal is below said
`means for determining whether said received signal
`first threshold and said signal strength of said re
`has a signal strength above a second threshold
`ceived signal is above said second threshold; and,
`before the received signal is filtered to provide said
`means for transmitting a command code when said
`desired signal; and,
`signal quality of said desired signal is below said
`65
`means for controlling intermodulation distortion by
`first threshold and said signal strength of said re
`adjusting at least an injection signal when said
`ceived signal is above said second threshold.
`signal quality of said desired signal is below said
`
`30
`
`35
`
`55
`
`s
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`IPR2023-00697
`Theta EX2007
`
`