Patent Description:
The present disclosure generally relates to electronics, and, more specifically, to reducing nonlinear effects due to passive intermodulation.

Radio systems are systems that transmit and receive signals in the form of electromagnetic waves in the radio frequency (RF) range of approximately <NUM> kilohertz (kHz) to <NUM> gigaHertz (GHz). Radio systems are commonly used for wireless communications, with cellular/wireless mobile technology (e.g., Long Term Evolution (LTE) and <NUM>th generation (<NUM>) systems) being a prominent example. Linearity of various components of such systems plays a crucial role.

Linearity of an RF component or system is easy to understand in theory. Namely, linearity generally refers to the ability of a component or a system to provide an output signal that is directly proportional to an input signal. In other words, if a component or a system is perfectly linear, the relationship of a ratio of the output signal to the input signal is a straight line. Achieving this behavior in real-life components and systems is far more complicated and many challenges to linearity must be resolved, often at the expense of some other performance parameter, such as efficiency.

Made from semiconductor materials, which are inherently nonlinear, and having to operate at relatively high-power levels, active components such as power amplifiers are usually the first to be analyzed when considering a design of an RF system in terms of linearity. Power amplifier outputs with nonlinear distortions can result in reduced modulation accuracy and/or out-of-band emissions. Therefore, wireless communication systems have stringent specifications on power amplifier linearity and various techniques (e.g., digital predistortion) have been developed to improve the performance of power amplifiers and other active devices during both the design and operational phases.

It is easy to forget that passive devices used in RF systems, e.g., loose cable connections, aged antennas, suboptimal duplexers, or dirty connectors, can also introduce nonlinear effects. Although sometimes relatively small, if not corrected, these nonlinearities can have serious effects on system performance. Passive intermodulation (PIM) is one example of a nonlinear effect caused by nonlinearity of passive devices. A variety of factors can affect the cost, quality and robustness of a PIM reduction solution included in an RF system. Physical limitations such as space/surface area, as well as limitations that may be imposed by regulations, can pose further constraints to the requirements or specifications of PIM reduction circuits. Thus, trade-off and ingenuity must be exercised in designing a PIM reduction solution for RF applications. <CIT> discloses a PIM suppression technique where a PIM signal is estimated by summing multiple input signals with different polarizations. Similarly, <CIT>, <CIT>, <CIT> disclose transceivers with PIM reduction circuits.

The invention is defined by system claim <NUM> and method claim <NUM>.

The systems, methods and devices of this disclosure each have several innovative aspects, no single one of which is solely responsible for all desirable attributes disclosed herein. Details of one or more implementations of the subject matter described in this specification are set forth in the description below and the accompanying drawings.

For purposes of illustrating PIM reduction with frequency shifting proposed herein, it might be useful to first understand phenomena that may come into play in communication systems. The following foundational information may be viewed as a basis from which the present disclosure may be properly explained. Such information is offered for purposes of explanation only and, accordingly, should not be construed in any way to limit the broad scope of the present disclosure and its potential applications.

PIM is a result of having nonlinear passive devices in a signal chain. PIM arises when two or more RF signals are inadvertently mixed as they transit through a passive device with nonlinear properties. In context of the cellular industry, two or more transmitted (TX) carrier signals can mix together and the intermodulation product of this mixing, which may be referred to as a "PIM signal component," could happen to fall into the frequency band of the receiver, thereby reducing receiver's sensitivity, causing performance degradation of the received (RX) signal, or even inhibiting communication altogether. This resultant interference can affect the cell that caused the PIM, as well as other nearby receivers. For example, in LTE Frequency Band <NUM>, the downlink frequency range is specified to be from <NUM> megahertz (MHz) to <NUM>, while the uplink ranges from <NUM> to <NUM>. If two TX carrier signals having frequencies of <NUM> and <NUM> are transmitting from a base station system with PIM, their intermodulation may lead to a PIM signal component at <NUM>, which will fall into the receiver band and will affect the receiver. Furthermore, their intermodulation may also produce a PIM signal component at <NUM>, which may affect other systems.

As the frequency spectrum becomes more crowded with allocated frequency ranges and antenna sharing schemes become more common, there is a corresponding increase in the possibility of PIM generation from the intermodulation of different carrier signals. The traditional way of using frequency planning to avoid PIM becomes almost impossible. Coupled with these challenges, the adoption of new digital modulation schemes means that the peak power of the communication systems also increases, adding to the severity of the PIM issue to the point where it may no longer be ignored. The problem is particularly acute for base stations, where typically several network systems share the same infrastructure and tightly spaced carrier signals could be sharing a single antenna so that different transmitted signals can transit through the same nonlinear passive device(s).

Since the nonlinearity of passive devices varies with temperature, humidity, mechanical stability, and device aging, PIM is intrinsically a time-dependent phenomenon. Therefore, PIM reduction typically involves using an adaptive model of how PIM may affect an RX signal. The model defines coefficients of a filter to be applied to the RX signal, in the digital domain, in an attempt to reduce and/or cancel distortions of the RX signal caused by PIM. In this manner, a PIM reduction circuit will try to compensate for various passive devices contributing to the undesirable nonlinear modification to the TX signal by applying a corresponding modification to the RX signal. The model is adaptive, which means that it is formed in an iterative process by repeatedly running an algorithm that gradually adjusts the filter coefficients based on the comparison between the signal to be transmitted and the signal that has been received. Running the algorithm for estimating the PIM filter coefficients increases power consumption and introduces additional design complexity to the final product.

Inventors of the present disclosure realized that conventional PIM reduction algorithms leave room for improvement in terms of power consumption and design complexity due to running the algorithm for estimating the PIM filter coefficients. In particular, when spacing between carrier signal components of a TX signal is ΔFc (which spacing may, e.g., be defined as center-to-center frequencies of two adjacent carrier signals), the algorithm for estimating the PIM filter coefficients has to be run at a sampling rate higher than <NUM>*ΔFc in order to avoid aliasing. Inventors of the present disclosure realized that the rate at which the algorithm for estimating the PIM filter coefficients is run may be reduced by performing frequency shifting of some signal components before running the algorithm. To that end, one aspect of the present disclosure provides an example system (or an apparatus) for reducing PIM interference in the RX signal. The RX signal includes an RX carrier signal component and may include a PIM signal component. The TX signal includes at least a first and a second TX carrier signal components with a certain frequency spacing between them. The system is configured to use the RX signal and the TX signal to generate a frequency-shifted output that includes the RX carrier signal component, the first TX carrier signal component, and the second TX carrier signal component positioned/aligned in a frequency spectrum so that a frequency spacing between the first and the second TX carrier signal components and a frequency spacing between the RX carrier signal component and a closest one of the first and the TX second carrier signal components is smaller than a frequency spacing between the first and the second TX carrier signal components in the TX signal. This means that at least one of the first and second TX carrier signal components is frequency-shifted, compared to the TX signal, which is the reason why this PIM reduction approach is referred to herein as "PIM reduction with frequency shifting. " For example, if the frequency spacing between the first and the second TX carrier signal components in the TX signal was ΔFc, then the frequency spacing between these components in the frequency-shifted output, as well as the frequency spacing between the RX carrier signal component and the closest one of the first and second TX carrier signal components, is ΔF'c, which is smaller than ΔFc. The system may then use the frequency-shifted output to generate an estimate of a PIM signal component to be applied to the RX signal to generate an RX signal with reduced PIM components. The algorithm for estimating the PIM filter coefficients has to be run at a rate that is only higher than <NUM>*ΔF'c, in order to avoid aliasing, which rate may, be lower than <NUM>*ΔFc. Thus, performing frequency shifting as described herein allows reducing the minimum requirement for the rate at which the algorithm for estimating the PIM filter coefficients has to be run, from <NUM>*ΔFc to <NUM>*ΔF'c. Reducing the rate of the algorithm may advantageously allow reducing power consumption and/or design complexity.

As will be appreciated by one skilled in the art, aspects of the present disclosure, in particular aspects of PIM reduction with frequency shifting as described herein, may be embodied in various manners - e.g. as a method, a system, a computer program product, or a computer-readable storage medium. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," "module" or "system. " Functions described in this disclosure may be implemented as an algorithm executed by one or more hardware processing units, e.g., one or more microprocessors, of one or more computers. In various embodiments, different steps and portions of the steps of any methods described herein may be performed by different processing units. Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer-readable medium(s), preferably non-transitory, having computer-readable program code embodied, e.g., stored, thereon. In various embodiments, such a computer program may, for example, be downloaded (updated) to the existing devices and systems (e.g. to the existing RF transmitters, receivers, and/or their controllers, etc.) or be stored upon manufacturing of these devices and systems.

The following detailed description presents various descriptions of specific certain embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims or select examples. In the following description, reference is made to the drawings, where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the drawings are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings.

The description may use the phrases "in an embodiment" or "in embodiments," which may each refer to one or more of the same or different embodiments. Unless otherwise specified, the use of the ordinal adjectives "first," "second," and "third," etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking or in any other manner. Furthermore, for the purposes of the present disclosure, the phrase "A and/or B" or notation "A/B" means (A), (B), or (A and B), while the phrase "A, B, and/or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). As used herein, the notation "A/B/C" means (A, B, and/or C). The term "between," when used with reference to measurement ranges, is inclusive of the ends of the measurement ranges.

Various aspects of the illustrative embodiments are described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. For example, the term "connected" means a direct electrical connection between the things that are connected, without any intermediary devices/components, while the term "coupled" means either a direct electrical connection between the things that are connected, or an indirect connection (e.g., an indirect electrical connection) through one or more passive or active intermediary devices/components. In another example, the term "circuit" means one or more passive and/or active components that are arranged to cooperate with one another to provide a desired function. Sometimes, in the present descriptions, the term "circuit" may be omitted (e.g., a PIM reduction circuit may be referred to simply as a "PIM reduction," etc.). If used, the terms "substantially," "approximately," "about," etc., may be used to generally refer to being within +/- <NUM>% of a target value, e.g., within +/- <NUM>% of a target value, based on the context of a particular value as described herein or as known in the art.

<FIG> illustrates a wireless communication system <NUM> in which PIM reduction using frequency shifting may be implemented, according to some embodiments of the present disclosure. The wireless communication system <NUM> may include a base station <NUM> and a plurality of mobile stations, examples of which are shown in <FIG> as a first mobile station <NUM>, a second mobile station <NUM>, and a third mobile station <NUM>. The base station <NUM> may be coupled to a backend network (not shown) of the wireless communication system and may provide communication between the mobile stations <NUM>, <NUM>, and <NUM> and the backend network. In various embodiments, the wireless communication system <NUM> may include a plurality of base stations similar to the base station <NUM>, which base stations may, e.g., be arranged in cells, where only one base station <NUM> is shown in <FIG> for simplicity and illustration purposes.

In some embodiments, the wireless communication system <NUM> may support multiple standards and multiple band communication. For example, the wireless communication system <NUM> may support LTE, Wideband Code Division Multiple Access (WCDMA), and Global System for Mobile Communication (GSM) standard communication. Each of the mobile stations <NUM>-<NUM> may support any one or more of these standards. However, the use of these listed standards is merely exemplary and other standards also may be supported by different parts of the wireless communication system <NUM>. In addition to multiple standard capabilities, the wireless communication system <NUM> may also support multiple communication bands. For example, the wireless communication system <NUM> may support DCS/PCS bands and GSM850/GSM900 bands of GSM, N2/N3 bands of <NUM> New Radio (NR), or any other frequency bands of these or other radio access technologies and standards.

The base station <NUM> may support wireless communication with mobile stations <NUM>-<NUM> of various standard technologies as well as in multiple bands. The base station <NUM> may transmit signals to the mobile stations <NUM>, <NUM>, and <NUM> in downlink signals and receive signals from the mobile stations <NUM>-<NUM> in uplink signals. For example, the base station <NUM> may receive LTE compliant signals from the first mobile station <NUM>, WCDMA signals from the second mobile station <NUM>, and GSM signals from the third mobile station <NUM>.

Cellular systems are deployed in many frequency bands that are defined by a combination of standardization organizations such as the 3d Generation Partnership Project (3GPP) and government-sponsored agencies such as the Federal Communications Commission (FCC). There are both frequency division duplex (FDD) and time division duplex (TDD) variants of frequency allocations that are used in commercial cellular networks. In FDD systems, the uplink and downlink use separate frequency bands at the same time while, in TDD systems, the uplink and downlink use the same frequencies at different times. The challenges related to PIM are particularly pronounced for FDD systems. In some embodiments, the wireless communication system <NUM> may be an FDD system, where any of the systems configured to implement PIM reduction using frequency shifting, described herein, may be deployed in the base station <NUM>. In some embodiments, any of the systems configured to implement PIM reduction using frequency shifting, described herein, may be deployed in any of the mobile stations <NUM>, <NUM>, and <NUM>.

As summarized above, embodiments of the present disclosure relate to PIM reduction. To that end, conventionally, a system as shown in <FIG> has been used.

<FIG> illustrates a schematic block diagram of a communication system (e.g., a transceiver) <NUM> that employs a conventional PIM reduction circuit <NUM>. <FIG> illustrates that the communication system <NUM> may include a transmitter circuit (or, simply, a "transmitter") <NUM> and a receiver circuit (or, simply, a "receiver") <NUM> in communication with the PIM reduction circuit <NUM>. The system may further include a duplexer <NUM> and an antenna <NUM>.

As shown in <FIG>, the transmitter <NUM> may be configured to receive a TX signal <NUM> as an input, and provide a TX signal <NUM> as an output, while the receiver <NUM> may be configured to receive a RX signal <NUM> as an input, and provide a RX signal <NUM> as an output. The input TX signal <NUM> may be a sequence of digital samples (e.g., a vector). In some embodiments, the input TX signal <NUM> may include one or more active channels in the frequency domain, but, for simplicity, an input TX signal with only one channel (i.e., a single frequency range of in-band frequencies) is described. In some embodiments, the input TX signal <NUM> may be a baseband digital signal. The output TX signal <NUM> may be an analog signal. In some embodiments, the output TX signal <NUM> may be a TX signal upconverted to RF and amplified by a power amplifier (PA) of the transmitter <NUM>. The input RX signal <NUM> may also be an analog signal, e.g., a RX signal in RF, to be received by a low-noise amplifier (LNA) of the receiver <NUM>. The output RX signal <NUM> may be a sequence of digital samples (e.g., a vector). In some embodiments, the output RX signal <NUM> may be a baseband digital signal.

The communication system <NUM> may be an FDD transceiver, in which case the antenna <NUM> may be configured for concurrent reception and transmission of wireless RF signals in separate, i.e., non-overlapping and non-continuous, bands of frequencies, e.g. in bands having a separation of, for example, several MHz from one another. In various embodiments, the antenna <NUM> may be a single wideband antenna (i.e., a single antenna that may be configured to receive/transmit wideband signals that may include a plurality of RX/TX signal components in different bands) or a plurality of band-specific antennas (i.e., a plurality of antennas each configured to receive and transmit signals in a specific band of frequencies). In some embodiments, an output of the antenna <NUM> may be coupled to one of the inputs of a multi-band duplexer <NUM>. The duplexer <NUM> is an electromagnetic component configured for filtering multiple signals to allow for bidirectional communication over a single path between the duplexer <NUM> and the antenna <NUM>. To that end, the duplexer <NUM> may be configured for providing RX signals to the receiver <NUM> and for receiving TX signals from the transmitter <NUM> (e.g., the output of the transmitter <NUM> may be coupled to another one of the inputs of the duplexer <NUM>).

The duplexer <NUM> may be one of the passive devices that contribute to PIM interference in the RX signals received by the receiver <NUM>. The PIM reduction circuit <NUM> may be used to reduce PIM interference. As shown in <FIG>, the PIM reduction circuit <NUM> may include a PIM estimation circuit <NUM> and a combiner <NUM>. The PIM estimation circuit <NUM> may use an adaptive model to implement a filter that, when applied to the RX signal (e.g., a RX signal <NUM> output by the receiver <NUM>), may reduce or eliminate at least some of the PIM interference in the RX signal <NUM>. To that end, the PIM estimation circuit <NUM> may be configured to receive an RX signal <NUM> (e.g., the RX signal <NUM> may be the same as the RX signal <NUM>, or may be a signal indicative of the RX signal <NUM>), and a TX signal <NUM> (e.g., the TX signal <NUM> may be the same as the TX signal <NUM>, or may be a signal indicative of the TX signal <NUM>). The TX signal <NUM> may be indicative of at least two TX carrier signal components, shown in a frequency spectrum illustration (i.e., the x-axis of all frequency spectrum illustrations described herein refers to frequencies,/) <NUM> of <FIG> as a first TX carrier signal component TX1 and a second TX carrier signal component TX2. As shown in the illustration <NUM>, the first and second carrier signal components TX1 and TX2 may have a frequency spacing of ΔFc in the TX signal. The frequency spacing ΔFc may be a frequency range between TX1 and TX2 when these signals are upconverted to the RF and are wirelessly transmitted by the antenna <NUM>, but the TX signal <NUM> would be indicative of this spacing as it would be indicative of the first and second carrier signal components TX1 and TX2. The PIM estimation circuit <NUM> may then be configured to align the TX carrier signal components obtained from the TX signal <NUM> with signal components obtained from the RX signal <NUM>, namely, with an RX carrier signal component RX1 and with a PIM signal component PIM1, as shown in a frequency spectrum illustration <NUM> of <FIG>. As can be seen from the illustrations <NUM> and <NUM>, shown in <FIG>, if the first and second TX carrier signal components have a frequency spacing of ΔFc in the TX signal (i.e., the illustration <NUM>), then they may be aligned with the RX carrier signal component RX1 so that the frequency spacing between RX1 and the closest one (in frequency) of TX1 and TX2 (which is TX1 for the example shown in <FIG>) is also ΔFc. The PIM signal component PIM1 would typically be substantially centered with the RX1, so the frequency spacing between PIM1 and the closest one of TX1 and TX2 is also ΔFc. Thus, for the conventional PIM estimation circuit <NUM>, TX1-PIM1=TX2-TX1= ΔFc. The PIM estimation circuit <NUM> (e.g., a coefficient generator part of the PIM estimation circuit <NUM>) may then use the signal components RX1, TX1, and TX2 aligned as shown in the frequency spectrum illustration <NUM> to generate/update PIM model coefficients for the filter that, when applied to the RX signal (e.g., a RX signal <NUM> output by the receiver <NUM>), may reduce or eliminate at least some of the PIM interference in the RX signal <NUM>. Because the frequency spacing between the signal components RX1, TX1, and TX2 of the frequency spectrum illustration <NUM> is ΔFc, the algorithm for estimating the PIM model coefficients (i.e., the coefficient generator part of the PIM estimation circuit <NUM>) has to run at a sampling rate that is at least <NUM>*ΔFc. The PIM estimation circuit <NUM> (e.g., an actuator part of the PIM estimation circuit <NUM>) may then use the PIM model coefficients to generate an estimate of the PIM signal component PIM1, the estimate shown in a frequency spectrum illustration <NUM> of <FIG> as an estimate PIMe. The actuator part of the PIM estimation circuit <NUM> also has to run at a sampling rate that is at least <NUM>*ΔFc. The combiner <NUM> may then apply the estimate PIMe to the RX signal <NUM> to generate an RX signal <NUM> with reduced PIM, an example of which is shown in a frequency spectrum illustration <NUM> of <FIG>. For example, the combiner <NUM> may subtract the estimate PIMe from the RX signal <NUM>.

As explained above, in conventional PIM reduction systems and methods, both the PIM model coefficient generator and PIM actuator have to run at a clock rate that is at least <NUM>*ΔFc. Inventors of the present disclosure realized that this rate may be reduced by implementing PIM reduction with frequency shifting, which may advantageously result in reduced power consumption and more efficient/simpler design. A schematic block diagram of an example communication system <NUM> (e.g., a transceiver) that employs a PIM reduction circuit <NUM> with frequency shifting, according to some embodiments of the present disclosure, is shown in <FIG>.

<FIG> illustrates that the communication system <NUM> may include some components shown in <FIG> - namely, the transmitter <NUM>, the receiver <NUM>, the duplexer <NUM>, and the antenna <NUM>. Descriptions of these components provided with respect to <FIG> is applicable to the communication system <NUM> of <FIG>, and, therefore, in the interests of brevity, these descriptions are not repeated here. It should be noted that, in some embodiments, the communication system <NUM> may not include the duplexer <NUM> but may have one connection between the transmitter <NUM> and the antenna <NUM> and another connection between the antenna <NUM> and the receiver <NUM>. When the duplexer <NUM> is included in the communication system <NUM>, the duplexer <NUM> may be one of the passive devices that causes PIM interference. However, in general, various embodiments of PIM reduction with frequency shifting, presented herein, are applicable to reducing PIM interference caused by any nonlinear passive electronic components or devices (i.e., passive devices/components that may exhibit nonlinear behavior) other than duplexers.

As shown in <FIG>, the communication system <NUM> may include a PIM reduction circuit <NUM>. The circuit <NUM> may include a PIM estimation circuit <NUM>, which may be similar to the PIM estimation circuit <NUM>, and the combiner <NUM>. The PIM estimation circuit <NUM> can be implemented by any suitable circuits. For instance, in some embodiments, the PIM estimation circuit <NUM> can be implemented by combinational logic circuits.

In contrast to the conventional communication system shown in <FIG>, the PIM reduction circuit <NUM> may further include one or more frequency-shift circuits <NUM>, <NUM>, and <NUM>, thus implementing PIM reduction with frequency shifting. The frequency-shift circuits <NUM>, <NUM>, and <NUM> are shown in <FIG> as separate circuits only for the purposes of describing the different frequency shifting actions applied to different signals. In various embodiments of the PIM reduction circuit <NUM>, the frequency-shift circuits <NUM>, <NUM>, and <NUM> may be implemented as one or more frequency-shift circuits <NUM> (shown in <FIG> to be enclosed within a dash-dotted contour). The operation of the PIM reduction circuit <NUM> may be described with reference to the illustrations of <FIG> and <FIG>.

<FIG> provides a flow chart of a method <NUM> for implementing PIM reduction using frequency shifting, according to some embodiments of the present disclosure, while <FIG> illustrates a schematic frequency domain representation of steps for performing PIM reduction using the PIM reduction circuit <NUM>. At least portions of the method <NUM> may be implemented by elements of a communication system according to any embodiments of the present disclosure, e.g., by the communication system described with reference to <FIG> and/or <NUM>, and/or by one or more data processing systems, such as the data processing system <NUM> shown in <FIG>. Although described with reference to system components of the systems shown in the present figures, any system, configured to perform operations of the method <NUM>, in any order, is within the scope of the present disclosure.

As shown in <FIG>, the method <NUM> may begin with step <NUM>, in which the PIM reduction circuit <NUM> receives an RX signal that includes (e.g., is indicative of) the RX carrier signal component RX1 and receiving a TX signal that includes (e.g., is indicative of) the first and second TX carrier signal components TX1 and TX2. For example, the RX signal received by the PIM reduction circuit <NUM> may be the RX signal <NUM>, described above, while the TX signal received by the PIM reduction circuit <NUM> may be the TX signal <NUM>, described above. A frequency spacing between the first and second TX carrier signal components TX1 and TX2 in the TX signal may be ΔFc, as shown with a frequency spectrum illustration <NUM>, shown in <FIG>, and both the TX signal <NUM> and the RX signal <NUM> provided to the PIM reduction circuit may be signals having a relatively high sampling rate, at least <NUM>*ΔFc.

The method <NUM> may then proceed with step <NUM>, in which the one or more frequency-shift circuits <NUM> may perform frequency shifting of signal components of one or more of the RX signal <NUM> and the TX signal <NUM> to generate what may be referred to as a "frequency-shifted output" that includes the PIM signal component of the RX signal and the first and the second TX carrier signal components of the TX signal aligned so that a frequency spacing between the first and the second TX carrier signal components of the TX signal, and a frequency spacing between the PIM signal component of the RX signal and a closest one of the first and the TX second carrier signal components of the TX signal (i.e., TX1 for the example described herein) is ΔF'c, where ΔF'c is smaller than ΔFc. A frequency spectrum illustration <NUM>, shown in <FIG>, illustrates how the components RX1, TX1, and TX2 may be aligned with a frequency spacing ΔFc, similar to how it was done in conventional PIM reduction systems described above. In contrast to such systems, the PIM reduction circuit <NUM> is configured to generate the frequency-shifted output that includes components RX1, TX1, and TX2 aligned with a frequency spacing ΔF'c, where ΔF'c is smaller than ΔFc, as can be seen in a frequency spectrum illustration <NUM>, shown in <FIG>. To that end, at least one TX1 and TX2 is frequency-shifted with respect to the other one in order to decrease the frequency spacing between TX1 and TX2 from ΔFc to ΔF'c. In addition, both TX1 and TX2 are aligned with respect to RX1 so that the frequency spacing between RX1 and the one of TX1 and TX2 that is closer, in frequency, to RX1 is also ΔF'c. The frequency shift circuit <NUM>, shown in <FIG>, may be seen as a circuit configured to implement such frequency shifting of at least one of TX1 and TX2. The frequency shift circuit <NUM>, shown in <FIG>, may be seen as a circuit configured to implement frequency shifting of RX1 (and, consequently, the PIM signal component PIM1 of the RX signal <NUM>) if RX1 is frequency shifted to be aligned with TX1 and TX2 so that TX1-PIM1=TX2-TX1=ΔF'c. If, on the other hand, TX1 and TX2 are frequency shifted to align TX1 and TX2 with RX1, then the frequency shift circuit <NUM> may be the circuit configured to implement such frequency shifting. The frequency spectrum illustration <NUM>, shown in <FIG>, illustrates an example of the frequency-shifted output generated in step <NUM>. It should be noted that while the frequency spectrum illustrations shown in <FIG> illustrate the frequency spacings ΔFc and ΔF'c as center-to-center ranges (i.e., a given frequency spacing between two signals of certain bandwidths is measured as a frequency range between center frequencies of the two bandwidths), in other embodiments the frequency spacings ΔFc and ΔF'c may be defined in any other manner, e.g., center-to-edge, edge-to-edge, etc..

With the frequency shifting of step <NUM>, exactly how much smaller can ΔF'c be compared to ΔFc may be dependent on the deployment scenario. For example, consider that TX1 and TX2 are originally at <NUM> spacing (i.e., ΔFc=<NUM>), the spacing measured as center-to-center frequency range, and each has a bandwidth of <NUM>. In such an example, it is possible to reduce the frequency spacing between TX1 and TX2 to as small as <NUM> (i.e., ΔF'c=<NUM>), again, measured as center-to-center range, which would be <NUM> times smaller than the original spacing of <NUM>.

In general, the minimum spacing, ΔF'cmin, may be computed based on the signal bandwidth (BWS) and the PIM bandwidth (BWPIM) as follows: <MAT> Furthermore, if PIM is assumed to be a 3rd order distortion (and higher order PIM contributions may be substantially neglected), then BWPIM is <NUM> times larger than BWS and equation (<NUM>) may be re-written as follows: <MAT> Therefore, for the example above where BWS=<NUM>, ΔF'cmin=<NUM>.

The method <NUM> may then proceed with step <NUM> that includes the PIM estimation circuit <NUM> generating an estimate of the PIM signal component based on the frequency-shifted output <NUM> generated in step <NUM>. In some embodiments, step <NUM> may include, first, the PIM estimation circuit <NUM> (e.g., a coefficient generator part of the PIM estimation circuit <NUM>) using the signal components RX1, TX1, and TX2 aligned as shown in the frequency spectrum illustration <NUM> to generate/update PIM model coefficients for the filter that, when applied to the RX signal (e.g., a RX signal <NUM> output by the receiver <NUM>), may reduce or eliminate at least some of the PIM interference in the RX signal <NUM>. Step <NUM> may further include the PIM estimation circuit <NUM> (e.g., an actuator part of the PIM estimation circuit <NUM>) using the PIM model coefficients to generate an estimate of the PIM signal component PIM1, the estimate shown in a frequency spectrum illustration <NUM> of <FIG> as an estimate PIMe.

In general, step <NUM> may include any known techniques for generating an estimate of the PIM signal component based on the signal components RX1, TX1, and TX2, with the difference being that now these components are aligned in the frequency-shifted output <NUM> generated in step <NUM> at a smaller spacing, ΔF'c. The smaller spacing may allow the algorithm used to generate/update the PIM model coefficients and/or the actuator used to generate the PIM estimate PIMe to be run at a lower rate, because now the rate may only be equal or greater than <NUM>*ΔF'c, which may be smaller than <NUM>*ΔFc that had to be used in conventional PIM reduction systems described above. Furthermore, because the frequency spacing in the frequency-shifted output <NUM> generated in step <NUM> is now smaller, compared to ΔFc, the sampling rate of the RX and TX signals may, correspondingly, be reduced. Therefore, in some embodiments, the PIM reduction circuit <NUM> may also include one or more decimation circuits configured to decimate (i.e., reduce the sampling rate of, or downsample) at least one of the RX signal <NUM> and the TX signal <NUM> prior to the PIM estimation circuit <NUM> generating the estimate of the PIM signal component in step <NUM>. Operating on decimated signals and/or using circuits that may run at lower clock rates, as described above, may advantageously allow reducing power consumption and simplifying circuit design.

For example, in some embodiments, the frequency shift circuit <NUM> may be configured to perform decimation and frequency shifting of the TX signal <NUM> to generate a decimated and frequency-shifted TX signal <NUM>. Similarly, the frequency shift circuit <NUM> may be configured to perform decimation and frequency shifting of the RX signal <NUM> to generate a decimated and frequency-shifted RX signal <NUM>. The PIM estimation circuit <NUM> may then used the decimated version of the TX signal (i.e., the decimated and frequency-shifted signal <NUM>) and/or the decimated version of the RX signal (i.e., the decimated and frequency-shifted signal <NUM>) to generate the estimate PIMe in step <NUM>. In some embodiments, the PIM reduction circuit <NUM> may be configured to first perform the decimation operation and then perform the frequency shifting described herein. In other embodiments, the PIM reduction circuit <NUM> may be configured to first perform the frequency shifting described herein and then perform the decimation operation. Furthermore, in various embodiments, the PIM reduction circuit <NUM> may be configured to implement any of the following: <NUM>) the TX signal <NUM> is decimated but the RX signal <NUM> is not decimated, <NUM>) the RX signal <NUM> is decimated but the TX signal <NUM> is not decimated , and <NUM>) both the TX signal <NUM> and the RX signal <NUM> are decimated. Any of these embodiments may, in turn, be combined with any embodiments described above with respect to which ones of the components RX1, TX1, and TX2 are frequency-shifted by the one or more frequency-shift circuits <NUM>.

The method <NUM> may further include step <NUM>, in which the PIM reduction circuit <NUM> may apply the estimate PIMe generated in step <NUM> to the RX signal <NUM> to reduce or eliminate at least some of the PIM interference in the RX signal <NUM>. In some embodiments, step <NUM> may include the combiner <NUM> applying the estimate PIMe to the RX signal <NUM> to generate an RX signal <NUM> (shown in <FIG>) with reduced PIM, an example of which is shown in a frequency spectrum illustration <NUM> of <FIG>. For example, step <NUM> may include the combiner <NUM> subtracting the estimate PIMe from the RX signal <NUM>.

In general, step <NUM> may include using any known techniques for applying the estimate PIMe, generated in step <NUM>, to reduce PIM interference in the RX signal <NUM>. In the embodiments where the signal component RX1 was frequency-shifted in step <NUM>, then, prior to performing step <NUM>, the PIM reduction circuit <NUM> may be configured to perform frequency shifting of the component PIMe to reverse that frequency shifting. In the embodiments where the RX signal <NUM> was decimated, then, prior to performing step <NUM>, the PIM reduction circuit <NUM> may be configured to perform interpolation (i.e., increase the sampling rate of, or upsample) of a signal that contains the estimate PIMe to reverse that decimation. In this manner, the modeled (i.e., estimate) PIM signal component PIMe may be time and frequency aligned with the PIM interference in the actual RX signal <NUM> so that the estimate PIM signal component PIMe can be used in step <NUM> to reduce the PIM interference in the RX signal <NUM>.

After step <NUM>, the method <NUM> may then proceed with the next iteration, now with the updated model coefficients, as shown in <FIG> with an arrow from <NUM> to <NUM>, i.e., steps <NUM>-<NUM> may be iterated again for new RX and TX signals. This may be the case when the PIM model is an adaptive model, meaning that it is formed in an iterative process by gradually adjusting the filter coefficients based on the comparison between the signal to be transmitted and the signal that has been received.

<FIG> illustrates a schematic block diagram of a communication system (e.g., an RF transceiver) <NUM> that employs the PIM reduction circuit <NUM> as described above, and further illustrates example details of the transmitter <NUM> and the receiver <NUM>, according to some embodiments of the present disclosure. The communication system <NUM> shown in <FIG> is one example implementation of the communication system <NUM> shown in <FIG>, where the same reference numerals as described above refer to the same or analogous elements/components so that descriptions provided with respect to one of these figures are assumed to be applicable and do not have to be repeated for the other, and only the differences are described.

As shown in <FIG>, in some embodiments, the transmitter <NUM> may include a digital filter <NUM>, a digital-to-analog converter (DAC) <NUM>, an analog filter <NUM>, a mixer <NUM>, a PA <NUM>, and a local oscillator (LO) <NUM>. In such a transmitter, the TX signal <NUM> may be filtered in the digital domain by the digital filter <NUM> to generate a filtered input, a digital signal. The output of the digital filter <NUM> may then be converted to an analog signal by the DAC <NUM>. The analog signal generated by the DAC <NUM> may then be filtered by the analog filter <NUM>. The output of the analog filter <NUM> may then be upconverted to RF by the mixer <NUM>, which may receive a signal from the LO <NUM> to translate the filtered analog signal from the analog filter <NUM> from baseband to RF. The PA <NUM>, which may be a PA array in some embodiments, may be configured to amplify the RF signal generated by the transmitter <NUM> (e.g., the RF signal generated by the mixer <NUM>) and provide an amplified RF signal as the TX output signal <NUM> (which may be a vector). The amplified RF signal <NUM> can be provided to the antenna <NUM> to be wirelessly transmitted.

The example of <FIG> illustrates the TX signal <NUM> being based on the TX signal <NUM> provided to the digital filter <NUM>. However, in other embodiments of the present disclosure, the TX signal <NUM> that is provided to the PIM reduction circuit <NUM> may be any other signal in the TX path that includes the transmitter <NUM>, as long as such a signal is indicative of the bandwidths of, and the frequency spacing ΔFc between, various TX carrier signal components (e.g., the first and second TX carrier signal components TX1 and TX2) when these signal components are upconverted to the RF and are wirelessly transmitted by the antenna <NUM>. For example, in other embodiments, the TX signal <NUM> may be a signal based on the output of the digital filter <NUM>, or a signal based on the output of the mixer <NUM> (converted back to digital domain since the PIM reduction circuit <NUM> operates on digital signals), etc..

Besides what is shown in <FIG>, other embodiments of implementing the transmitter <NUM> are also possible and within the scope of the present disclosure. For instance, in another implementation (not illustrated in the present drawings) the output of the digital filter <NUM> can be directly converted to an RF signal by the DAC <NUM>. In such an implementation, the RF signal provided by the DAC <NUM> can then be filtered by the analog filter <NUM>. Since the DAC <NUM> would directly synthesize the RF signal in this implementation, the mixer <NUM> and the local oscillator <NUM> illustrated in <FIG> can be omitted from the transmitter circuit <NUM> in such embodiments.

As further shown in <FIG>, in some embodiments, the receiver <NUM> may include a digital filter <NUM>, an analog-to-digital converter (ADC) <NUM>, an analog filter <NUM>, a mixer <NUM>, an LNA <NUM>, and a LO <NUM>. The LNA <NUM> may receive the RX signal <NUM> as an input. To that end, an input of the LNA <NUM> may be coupled to an output port of the antenna <NUM> (possibly via the duplexer <NUM>). The antenna <NUM> may receive RF signals in different bands, and the LNA <NUM> may amplify the received RF signals. Although not specifically shown in <FIG>, the LNA <NUM> may be coupled to the harmonic or band-pass filter that may filter received RF signals <NUM> that have been amplified by the LNA <NUM> and output by the LNA <NUM> as RX signals <NUM>. The RX signal <NUM> may be downconverted to the baseband by the mixer <NUM>, which may receive a signal from the LO <NUM> (which may be the same or different from the LO <NUM>) to translate the RX signal <NUM> from the RF to the baseband. The output of the mixer <NUM> may then be filtered by the analog filter <NUM>. The output of the analog filter <NUM> may then be converted to a digital signal by the ADC <NUM>. The digital signal generated by the ADC <NUM> may then be filtered in the digital domain by the digital filter <NUM> to generate a filtered downconverted signal <NUM>, which may be a sequence of digital values indicative of the RF signal received by the antenna <NUM>, and which may also be modeled as a vector.

The example of <FIG> illustrates the RX signal <NUM> being based on the RX signal <NUM> provided from the digital filter <NUM>. However, in other embodiments of the present disclosure, the RX signal <NUM> that is provided to the PIM reduction circuit <NUM> may be any other signal in the RX path that includes the receiver <NUM>, as long as such a signal is indicative of the bandwidths and the center frequencies of various RX carrier signal components (e.g., the RX carrier signal component RX1) when these signal components are in the RF and are wirelessly received by the antenna <NUM>. For example, in other embodiments, the TX signal <NUM> may be a signal based on the input to the digital filter <NUM>, or the signal <NUM> provided to the mixer <NUM> (converted back to digital domain since the PIM reduction circuit <NUM> operates on digital signals), etc..

Besides what is shown in <FIG>, other embodiments of implementing the receiver <NUM> are also possible and within the scope of the present disclosure. For instance, in another implementation (not illustrated in the present drawings) the RX signal <NUM> can be directly converted to a baseband signal by the ADC <NUM>. In such an implementation, the downconverted signal provided by the ADC <NUM> can then be filtered by the digital filter <NUM>. Since the ADC <NUM> would directly synthesize the baseband signal in this implementation, the mixer <NUM> and the LO <NUM> illustrated in <FIG> can be omitted from the receiver circuit <NUM> in such embodiments.

Further variations are possible to the communication system <NUM> described above. For example, while upconversion and downconversion is described with respect to the baseband frequency, in other embodiments of the communication system <NUM>, an intermediate frequency (IF) may be used instead. IF may be used in superheterodyne radio receivers, in which a received RF signal is shifted to an IF, before the final detection of the information in the received signal is done. Conversion to an IF may be useful for several reasons. For example, when several stages of filters are used, they can all be set to a fixed frequency, which makes them easier to build and to tune. In some embodiments, the mixers of RF transmitter <NUM> or the receiver <NUM> may include several such stages of IF conversion. In another example, although a single path mixer is shown in each of the TX path (i.e., the signal path for the signal to be processed by the transmitter <NUM>) and the RX path (i.e., the signal path for the signal to be processed by the receiver <NUM>) of the communication system <NUM>, in some embodiments, the TX path mixer <NUM> and the RX path mixer <NUM> may be implemented as a quadrature upconverter and downconverter, respectively, in which case each of them would include a first mixer and a second mixer. For example, for the RX path mixer <NUM>, the first RX path mixer may be configured for performing downconversion to generate an in-phase (I) downconverted RX signal by mixing the RX signal <NUM> and an in-phase component of the local oscillator signal provided by the local oscillator <NUM>. The second RX path mixer may be configured for performing downconversion to generate a quadrature (Q) downconverted RX signal by mixing the RX signal <NUM> and a quadrature component of the local oscillator signal provided by the local oscillator <NUM> (the quadrature component is a component that is offset, in phase, from the in-phase component of the local oscillator signal by <NUM> degrees). The output of the first RX path mixer may be provided to a I-signal path, and the output of the second RX path mixer may be provided to a Q-signal path, which may be substantially <NUM> degrees out of phase with the I-signal path.

Furthermore, it should be noted that, while a differentiation is made, both in the illustration of the communication system shown in <FIG> and the illustration of the communication system shown in <FIG>, between the one or more frequency-shifting circuits <NUM> and the PIM estimation circuit <NUM>, this differentiation may be only functional/logical, to merely differentiate functions that may be performed by a PIM estimation circuit similar to the conventional PIM estimation circuit <NUM> and functions specifically related to frequency shifting for the PIM reduction techniques described herein. In various embodiments, functionality of any of the one or more frequency-shifting circuits <NUM>, or any decimation or interpolation circuits, may be included, or be considered as a part of the PIM estimation circuit <NUM>, or functionalities of any of these circuits may be spread over a larger number of individual circuits.

<FIG> provides a schematic block diagram of an example data processing system <NUM> that may be configured to implement at least portions of PIM reduction with frequency shifting according to the method <NUM>, according to some embodiments of the present disclosure. For example, the data processing system <NUM> may be used to implement at least portions of the communication system as described with reference to <FIG> and <FIG>, in particular, to implement at least portions of the PIM reduction circuit <NUM> as described herein.

As shown in <FIG>, the data processing system <NUM> may include at least one processor <NUM>, e.g. a hardware processor <NUM>, coupled to memory elements <NUM> through a system bus <NUM>. It should be appreciated, however, that the data processing system <NUM> may be implemented in the form of any system including a processor and a memory that is capable of performing the functions described within this disclosure.

In some embodiments, the processor <NUM> can execute software or an algorithm to perform the activities as discussed in this specification, in particular activities related to PIM reduction with frequency shifting, e.g., according to the method <NUM>, such as various techniques implemented by the PIM reduction circuit <NUM> described herein. The processor <NUM> may include any combination of hardware, software, or firmware providing programmable logic, including by way of non-limiting example a microprocessor, a digital signal processor (DSP), a field-programmable gate array (FPGA), a programmable logic array (PLA), an integrated circuit (IC), an application specific IC (ASIC), or a virtual machine processor. The processor <NUM> may be communicatively coupled to the memory element <NUM>, for example in a direct-memory access (DMA) configuration, so that the processor <NUM> may read from or write to the memory elements <NUM>.

In general, the memory elements <NUM> may include any suitable volatile or non-volatile memory technology, including double data rate (DDR) random access memory (RAM), synchronous RAM (SRAM), dynamic RAM (DRAM), flash, read-only memory (ROM), optical media, virtual memory regions, magnetic or tape memory, or any other suitable technology. Unless specified otherwise, any of the memory elements discussed herein should be construed as being encompassed within the broad term "memory. " The information being measured, processed, tracked or sent to or from any of the components of the data processing system <NUM> could be provided in any database, register, control list, cache, or storage structure, all of which can be referenced at any suitable timeframe. Any such storage options may be included within the broad term "memory" as used herein. Similarly, any of the potential processing elements, modules, and machines described herein should be construed as being encompassed within the broad term "processor. " Each of the elements shown in the present figures, e.g., any of the circuits/components shown in <FIG> and <FIG>, can also include suitable interfaces for receiving, transmitting, and/or otherwise communicating data or information in a network environment so that they can communicate with, e.g., the data processing system <NUM> of another one of these elements.

In certain example implementations, mechanisms for implementing PIM reduction with frequency shifting in communication systems as outlined herein may be implemented by logic encoded in one or more tangible media, which may be inclusive of non-transitory media, e.g., embedded logic provided in an ASIC, in DSP instructions, software (potentially inclusive of object code and source code) to be executed by a processor, or other similar machine, etc. In some of these instances, memory elements, such as e.g. the memory elements <NUM> shown in <FIG>, can store data or information used for the operations described herein. This includes the memory elements being able to store software, logic, code, or processor instructions that are executed to carry out the activities described herein. A processor can execute any type of instructions associated with the data or information to achieve the operations detailed herein. In one example, the processors, such as e.g. the processor <NUM> shown in <FIG>, could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., an FPGA, a DSP, an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM)) or an ASIC that includes digital logic, software, code, electronic instructions, or any suitable combination thereof.

The local memory may refer to RAM or other non-persistent memory device(s) generally used during actual execution of the program code.

As shown in <FIG>, the memory elements <NUM> may store an application <NUM>. In various embodiments, the application <NUM> may be stored in the local memory <NUM>, the one or more bulk storage devices <NUM>, or apart from the local memory and the bulk storage devices.

Input/output (I/O) devices depicted as an input device <NUM> and an output device <NUM>, optionally, can be coupled to the data processing system. Examples of input devices may include, but are not limited to, a keyboard, a pointing device such as a mouse, or the like. In some embodiments, the output device <NUM> may be any type of screen display, such as plasma display, liquid crystal display (LCD), organic light emitting diode (OLED) display, electroluminescent (EL) display, or any other indicator, such as a dial, barometer, or light emitting diode (LED). In some implementations, the system may include a driver (not shown) for the output device <NUM>. Input and/or output devices <NUM>, <NUM> may be coupled to the data processing system either directly or through intervening I/O controllers.

A network adapter <NUM> may also, optionally, be coupled to the data processing system to enable it to become coupled to other systems, computer systems, remote network devices, and/or remote storage devices through intervening private or public networks.

While embodiments of the present disclosure were described above with references to exemplary implementations as shown in <FIG>, a person skilled in the art will realize that the various teachings described above are applicable to a large variety of other implementations.

In certain contexts, the features discussed herein can be applicable to automotive systems, safety-critical industrial applications, medical systems, scientific instrumentation, wireless and wired communications, radio, radar, industrial process control, audio and video equipment, current sensing, instrumentation (which can be highly precise), and other digital-processing-based systems.

In the discussions of the embodiments above, components of a system, such as filters, converters, mixers, and/or other components can readily be replaced, substituted, or otherwise modified in order to accommodate particular circuitry needs. Moreover, it should be noted that the use of complementary electronic devices, hardware, software, etc., offer an equally viable option for implementing the teachings of the present disclosure related to PIM reduction with frequency shifting in various communication systems.

Parts of various systems for implementing PIM reduction with frequency shifting as proposed herein can include electronic circuitry to perform the functions described herein. In some cases, one or more parts of the system can be provided by a processor specially configured for carrying out the functions described herein. For instance, the processor may include one or more application specific components, or may include programmable logic gates which are configured to carry out the functions describe herein. The circuitry can operate in analog domain, digital domain, or in a mixed-signal domain. In some instances, the processor may be configured to carrying out the functions described herein by executing one or more instructions stored on a non-transitory computer-readable storage medium.

In one example embodiment, any number of electrical circuits of the present figures may be implemented on a board of an associated electronic device. The board can be a general circuit board that can hold various components of the internal electronic system of the electronic device and, further, provide connectors for other peripherals. More specifically, the board can provide the electrical connections by which the other components of the system can communicate electrically. Any suitable processors (inclusive of DSPs, microprocessors, supporting chipsets, etc.), computer-readable non-transitory memory elements, etc. can be suitably coupled to the board based on particular configuration needs, processing demands, computer designs, etc. Other components such as external storage, additional sensors, controllers for audio/video display, and peripheral devices may be attached to the board as plug-in cards, via cables, or integrated into the board itself. In various embodiments, the functionalities described herein may be implemented in emulation form as software or firmware running within one or more configurable (e.g., programmable) elements arranged in a structure that supports these functions. The software or firmware providing the emulation may be provided on non-transitory computer-readable storage medium comprising instructions to allow a processor to carry out those functionalities.

In another example embodiment, the electrical circuits of the present figures may be implemented as stand-alone modules (e.g., a device with associated components and circuitry configured to perform a specific application or function) or implemented as plug-in modules into application specific hardware of electronic devices. Note that particular embodiments of the present disclosure may be readily included in a system on chip (SOC) package, either in part, or in whole. An SOC represents an IC that integrates components of a computer or other electronic system into a single chip. It may contain digital, analog, mixed-signal, and often RF functions: all of which may be provided on a single chip substrate. Other embodiments may include a multi-chip-module (MCM), with a plurality of separate ICs located within a single electronic package and configured to interact closely with each other through the electronic package.

It is also imperative to note that all of the specifications, dimensions, and relationships outlined herein (e.g., the number of components of the communication system shown in <FIG> and <FIG>) have only been offered for purposes of example and teaching only. Such information may be varied considerably without departing from the spirit of the present disclosure, or the scope of the appended claims. It should be appreciated that the system can be consolidated in any suitable manner. Along similar design alternatives, any of the illustrated circuits, components, modules, and elements of the present figures may be combined in various possible configurations, all of which are clearly within the broad scope of this specification. In the foregoing description, example embodiments have been described with reference to particular processor and/or component arrangements. Various modifications and changes may be made to such embodiments without departing from the scope of the appended claims. The description and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

Claim 1:
A system (<NUM>) for processing a signal to be transmitted, TX signal, (<NUM>) and a received signal, RX signal (<NUM>), the TX signal having a first TX carrier signal component and a second TX carrier signal component, and the RX signal having a RX carrier signal component, the system comprising:
one or more frequency-shift circuits (<NUM>, <NUM>, <NUM>), configured to, when a difference between a center frequency of the first TX carrier signal component and a center frequency of the second TX carrier signal component is a first value, perform frequency shifting of signals components of one or more of the RX signal and the TX signal to generate a frequency-shifted output where the RX carrier signal component and the first and the second TX carrier signal components are aligned in a frequency spectrum, wherein the frequency shifted output includes:
an aligned RX carrier signal component, based on the RX carrier signal component,
an aligned first TX carrier signal component, based on the first TX carrier signal component, and
an aligned second TX carrier signal component, based on the second TX carrier signal component,
wherein each of a difference between a center frequency of the aligned first TX carrier signal component and a center frequency of the aligned second TX carrier signal component and a difference between a center frequency of the aligned RX carrier signal component and the center frequency of the aligned first TX carrier signal component is smaller than the first value; and
a passive inter-modulation (PIM) estimation circuit (<NUM>), configured to generate, based on the frequency-shifted output, an estimate of a PIM signal component to be applied to the RX signal to generate an RX signal with reduced PIM.