Patent Description:
Conventional radios include Land Mobile Radios ("LMRs"). When LMRs get close to base station sites that may be broadband or narrow band operating in the same or neighboring frequency allocations, they experience relatively high levels of the nearby base station signal interference. This interference can produce significant intermodulation ("IM") products which may degrade radio performance or sensitivity by raising the noise floor of the receiver. Receiver sensitivity is most commonly lost as a cube of the interference power (e.g., <NUM> times the rate in dB). More generally, rates from <NUM>-<NUM> dBDesense. /dBInterference are common. These effects are further aggravated by the high peak to average power ratio characteristics of broadband signals. An example for a gain control of a stage of a tuner in a radio frequency receiver based on a quality of the demodulated signal is disclosed by the document <CIT>. In particular, the document discloses a radio frequency receiver for receiving digital signals, which comprises a tuner for selecting a desired channel for reception. A demodulator demodulates the signal in the desired channel and determines at least one quality of the demodulated signal, such as the bit error rate or the mean square error. An automatic gain controller controls the gain of a front-end stage, preferably an attenuator, in accordance with the measured quality, for example so as to minimise the error or error rate or so as to reduce the front-end gain and hence tuner power consumption while maintaining an acceptable demodulator performance. Further examples for frequency receivers and methods for controlling frequency receivers are disclosed by the documents <CIT>, <CIT>, <CIT> and <CIT>.

This document concerns systems and methods for mitigating IM interference. The methods comprise: monitoring performance of at least one demodulator of a communication device; detecting when the communication device is under or will be under an influence of IM interference based on a performance of the demodulator; determining an improved level of gain to be applied by a variable attenuator of the communication device or by a variable gain low noise amplifier of the communication device; and selectively adjusting an amount of gain being applied by the variable attenuator or variable gain low noise amplifier based on the improved level of radio performance. The performance of the demodulator may be defined by a Bit Error Rate ("BER"), a Block Drop Rate ("BDR"), an Average Symbol Error ("ASE"), a synchronization error, a modulation fidelity, and/or other measures of received signal quality well known by those versed in the art.

In some scenarios, the detecting comprises: obtaining at least one first demodulation performance metric for the demodulator that is associated with a first gain setting of a first receiver; configuring the first receiver in accordance with a second gain setting; obtaining at least one second demodulation performance metric for the demodulator that is associated with the second gain setting; and comparing the first demodulation performance metric with the second demodulation performance metric. The operating gain of the receiver is adjusted as required to match the gain setting with the better demodulation performance metric. The measurement process is then repeated ensuring that the receiver gain converges to its optimum value.

In those or other scenarios, the methods further comprise: operating a first receiver in accordance with a first gain setting; and operating a second receiver in accordance with a second gain setting different from the first gain setting. The detecting comprises: obtaining at least one first demodulation performance metric associated with the first gain setting of the first receiver, and at least one second demodulation performance metric associated with the second gain setting of the second receiver; and comparing the first demodulation performance metric of the first receiver to the second demodulation performance metric of the second receiver. The operating gain of the receivers are adjusted as required to match the gain setting with the better demodulation performance metric. The measurement process is then repeated ensuring that the receiver gains converge to an optimum value. The output of a demodulator of the first receiver may be combined with an output of a demodulator of the second receiver to obtain improved performance.

In those or other scenarios, the methods further comprise: operating a primary receiver in accordance with a given gain setting; and operating a secondary receiver with a lower linearity as compared to a linearity of the primary receiver. The detecting comprises: obtaining at least one demodulation performance metric for the secondary receiver; optionally obtaining at least one demodulation performance metric for the primary receiver, and analyzing the demodulation performance metrics to determine whether the communication device is under or will be under an influence of IM interference. A determination of the improved level of gain for the primary receiver is triggered when an analysis the demodulation performance metric indicates that the communication device is under or will be under an influence of IM interference and a gain adjustment is predicted to improve performance.

This disclosure is facilitated by reference to the following drawing figures, in which like numerals represent like items throughout the figures.

It will be readily understood that the solution described herein and illustrated in the appended figures could involve a wide variety of different configurations. Thus, the following more detailed description, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of certain implementations in various different scenarios. While the various aspects are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized should be or are in any single embodiment of the invention.

The terms "memory," "memory device," "data store," "data storage facility" and the like each refer to a non-transitory device on which computer-readable data, programming instructions (e.g., instructions <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) or both are stored. Except where specifically stated otherwise, the terms "memory," "memory device," "data store," "data storage facility" and the like are intended to include single device embodiments, embodiments in which multiple memory devices together or collectively store a set of data or instructions, as well as individual sectors within such devices.

This document generally concerns systems and methods for operating a communication device so as to mitigate intermodulation interference (e.g., broadband and/or narrowband) to a receiver. The methods comprise: monitoring performance of at least one demodulator of a communication device; detecting when the communication device is under or will be under an influence of IM interference based on a performance metric of the demodulator; determining an improved level of gain to be applied to a variable attenuator of the communication device or a variable gain low noise amplifier of the communication device; and selectively adjusting an amount of gain being applied by the variable attenuator or variable gain low noise amplifier based on the improved demodulation metrics. The performance of the demodulator may be defined by a BER, a BDR, an ASE, a synchronization error, a modulation fidelity, and/or other measures of received signal quality well known by those versed in the art.

In some scenarios, the detecting comprises: obtaining at least one first demodulation performance metric for the demodulator that is associated with a first gain setting of a first receiver; configuring the first receiver in accordance with a second gain setting; obtaining at least one second demodulation performance metric for the demodulator that is associate with the second gain setting; and comparing the first demodulation performance metric with the second demodulation performance metric. The improved level of gain is determined by setting the receiver to the value of gain that provided a higher performance value.

In those or other scenarios, the methods further comprise: operating a first receiver in accordance with a first gain setting; and operating a second receiver in accordance with a second gain setting different from the first gain setting. The detecting comprises: obtaining at least one first demodulation performance metric associated with the first gain setting of the first receiver, and at least one second demodulation performance metric associated with the second gain setting of the second receiver; and comparing the first demodulation performance metric of the first receiver to the second demodulation performance metric of the second receiver. The improved level of gain is determined by setting the receiver to the value of the gain that provided a higher performance value. The output of a demodulator of the first receiver may be combined with an output of a demodulator of the second receiver to provide improved performance. Techniques for combining multiple receiver outputs are well known and may include: selecting the better performing receiver, adding receiver outputs, maximum ratio combining, and other techniques.

In those or other scenarios, the methods further comprise: operating a primary receiver in accordance with a given gain setting; and operating a secondary receiver with a lower linearity as compared to a linearity of the primary receiver. The detecting comprises: obtaining at least one demodulation performance metric for the secondary receiver; and analyzing the at least one demodulation performance metric to determine whether the communication device is under or will be under an influence of IM interference. A determination of the improved level of gain for the primary receiver is triggered when an analysis of the demodulation performance metric indicates that the communication device is under or will be under an influence of IM interference.

Notably, the present solution is distinguishable from conventional solutions for mitigating broadband interference. In this regard, it should be understood that, unlike conventional solutions, the present solution does not address broadband interference by: varying a signal's bandwidth for best BER performance; using training sequences for evaluating a plurality of filters and selecting one of the plurality of filters based on the evaluation results; and/or clipping a baseband signal in a receiver when a digitized bandwidth is greater than a channel selection. These are important distinctions between the present solution and that of conventional solutions. For example, the present solution is less computationally and resource intensive as compared to that of the conventional solutions.

The present solution allows an Automatic Gain Controller ("AGC") to deploy different gain profiles either sequentially with one receiver or simultaneously with more than one receiver to evaluate demodulated performance using some combination of selected post demodulation performance metrics. This allows the communication device to perform with better sensitivity as it converges to the best gain profile for the signal and interference it is encountering. A front-end attenuator and/or a variable gain Radio Frequency ("RF") amplifier are used to adjust receiver gain. The basis for AGC action is the quality of the recovered (demodulated) signal. The present solution seeks to optimize receiver gain control based on post-demodulation performance changes with receiver gain profile adjustments. This approach allows the communication device's gain profile to be adjusted for best performance even under severe interference. The present solution estimates IM interference based on post detector performance of the receiver. For example, the BER may be monitored and analyzed with two different gain settings. If decreasing gain improves the demodulator's performance, then the AGC knows that IM interference is present and takes appropriate action (e.g., adjusts the amount of gain to be applied by a variable attenuator or amplifier).

Notably, the present solution uses demodulation metrics as an indirect measurement of IM interference. This feature of the present solution is distinguishable from how IM interference is detected by conventional solution. In conventional solutions, the IM interference is directly observed from the received signal. In effect, the present solution provides improved LMR receivers since conventional LMR receivers are only able to observe a desired channel and not the energy that produces the interference.

Referring now to <FIG>, there is provided an illustration of an illustrative system <NUM>. System <NUM> comprises a plurality of communication devices <NUM>, <NUM>, <NUM>, a Central Dispatch Center ("CDC") <NUM>, and a narrowband or broadband site <NUM>. The communication devices <NUM>-<NUM> include, but are not limited to, a portable radio (e.g., an LMR), a fixed radio with a static location, a smart phone, and/or a base station. In the LMR scenarios, the communication devices <NUM>-<NUM> can be configured to communicate in the VHF band, UHF band, <NUM> band, the <NUM> band, and/or the <NUM> band. As a broadband site <NUM> includes, but is not limited to, an LTE site, a <NUM> cellular site, a <NUM> cellular site, a <NUM> cellular site, and/or a <NUM> cellular site. As a narrowband site <NUM> includes, but is not limited to, LMR sites, commercial communications, Federal communications, and paging signals. CDC <NUM> and site <NUM> are well known in the art, and therefore will not be described herein.

During operation of system <NUM>, signals are communicated between the communication devices <NUM>-<NUM> and/or between one or more communication devices and the CDC <NUM>. For example, communication device <NUM> communicates a signal to communication device <NUM>, and CDC <NUM> communicates a signal to communication device <NUM>. Communication devices <NUM> and <NUM> perform operations to mitigate interference caused by the site <NUM>. The interference results because the nearby site <NUM> signal is captured by communication devices <NUM> and <NUM> at a very high power level. This power level is high enough to cause a non-linear response in the receiver. This response creates an elevated noise floor within the receiver that spreads the interfering site <NUM> signal across a much wider bandwidth than its transmission. This spreading manifests as an elevated noise floor superimposed on the desired signal of communication devices <NUM> and <NUM>. The interference is caused in at least the downlink communications that is the direction of communications associated with reception of signals by the communication devices. For example, an LMR <NUM> down link signal may experience interference from an adjacent <NUM>-<NUM> FirstNet broadband down link signal. Similarly, an LMR <NUM> down link signal may experience interference from an adjacent <NUM>-<NUM> mobile broadband signal. Likewise, an LMR <NUM> down link signal may experience interference from an LTE down link signal contained in the same <NUM>-<NUM> band. The manner in which communication devices <NUM> and <NUM> mitigate the broadband interference to signals will become evident as the discussion progresses.

Referring now to <FIG>, there is provided an illustration of an illustrative architecture for a communication device <NUM> which is configured for carrying out the various methods described herein for mitigating the broadband interference. Communication devices <NUM>-<NUM> are the same as or similar to communication device <NUM>. As such, the discussion provided below in relation to communication device <NUM> is sufficient for understanding communication devices <NUM>-<NUM> of <FIG> Communication device <NUM> can include more or less components than that shown in <FIG> in accordance with a given application. For example, a communication device <NUM> can include one or both components <NUM> and <NUM>. The present solution is not limited in this regard.

As shown in <FIG>, the communication device <NUM> comprises an LMR communication transceiver <NUM> coupled to an antenna <NUM>. The LMR communication transceiver can comprise one or more components such as a processor, an application specific circuit, a programmable logic device, a digital signal processor, or other circuit programmed to perform the functions described herein. The communication transceiver <NUM> can enable end-to-end LMR communication services in a manner known in the art. In this regard, the communication transceiver can facilitate communication of voice and data from the communication device <NUM> over an LMR network.

Although the communication device <NUM> has been described herein as comprising an LMR communication transceiver, it should be understood that the solution is not limited in this regard. In some scenarios, the communication network can comprise a cellular communication network instead of an LMR type network. In that case, the communication device <NUM> could include a cellular network communication transceiver in place of an LMR communication transceiver. In another scenario, the communication device <NUM> could include both an LMR communication transceiver and a cellular network communication transceiver. In this regard, it should be understood that the solutions described herein can be implemented in an LMR communication network, a cellular communication network, and/or any other communication network where interference by another communication system exists that generates energy that may result in interference on neighboring channels.

The LMR communication transceiver <NUM> is connected to a processor <NUM> comprising an electronic circuit. During operation, the processor <NUM> is configured to control the LMR communication transceiver <NUM> for providing LMR services. The processor <NUM> also facilitates mitigation of interference from undesired signals. The manner in which the processor facilitates interference mitigation will become evident as the discussion progresses.

A memory <NUM>, display <NUM>, user interface <NUM> and Input/Output ("I/O") device(s) <NUM> are also connected to the processor <NUM>. The processor <NUM> may be configured to collect and store data generated by the I/O device(s) <NUM> and/or external devices (not shown). Data stored in memory <NUM> can include, but is not limited to, one or more look-up tables or databases which facilitate selection of communication groups or specific communication devices. The user interface <NUM> includes, but is not limited to, a plurality of user depressible buttons that may be used, for example, for entering numerical inputs and selecting various functions of the communication device <NUM>. This portion of the user interface may be configured as a keypad. Additional control buttons and/or rotatable knobs may also be provided with the user interface <NUM>. A battery <NUM> or other power source may be provided for powering the components of the communication device <NUM>. The battery <NUM> may comprise a rechargeable and/or replaceable battery. Batteries are well known in the art, and therefore will not be discussed here.

The communication device architecture shown in <FIG> should be understood to be one possible example of a communication device system which can be used in connection with the various implementations disclosed herein. However, the systems and methods disclosed herein are not limited in this regard and any other suitable communication device system architecture can also be used without limitation. Applications that can include the apparatus and systems broadly include a variety of electronic and computer systems. In some scenarios, certain functions can be implemented in two or more specific interconnected hardware modules or devices with related control and data signals communicated between and through the modules, or as portions of an application-specific integrated circuit. Thus, the illustrative system is applicable to software, firmware, and hardware implementations.

Referring now to <FIG>, there is provided a more detailed illustration of an illustrative receiver portion <NUM> of the LMR communication transceiver <NUM>. Receiver <NUM> comprises a band selection filter <NUM>, a variable attenuator <NUM>, front end hardware <NUM>-<NUM>, back end hardware <NUM>, a demodulator <NUM> (e.g., a baseband filter), and a gain controller <NUM>. Each of the listed devices <NUM>-<NUM> is known in the art, and therefore will not be described herein. Still, it should be noted that the band selection filter <NUM> receives signals from the antenna <NUM> of <FIG>, filters the received signals, and forwards the filtered signals to the variable attenuator <NUM>. The variable attenuator <NUM> applies attenuation to optimize the ability of receiver <NUM> to demodulate signals with the best quality. The receiver gain profile amount of attenuation is controlled by the gain controller <NUM> based on demodulation performance metrics <NUM> generated by the demodulator <NUM>. The demodulation performance metrics <NUM> can be continuously or periodically provided by the demodulator <NUM>. In the periodic scenario, the demodulation performance metrics <NUM> may be provided when the front end gain is in a particular state and when the front end gain state has been changed to another particular state. The manner in which the gain profile by the variable attenuator <NUM> is controlled will become evident as the discussion progresses.

The gain controller <NUM> can include, but is not limited to, a circuit, or a processor executing instructions <NUM> implementing the methods described herein for mitigating broadband and/or IM interference. The gain controller <NUM> may be provided as part of a central processor (e.g., processor <NUM> of <FIG>) for the communication device or is provided as a processor in addition to the central processor. The gain controller <NUM> can constitute machine-readable media. The term "machine-readable media", as used here, refers to a single medium or multiple media (e.g., computer devices) that store the one or more sets of instructions <NUM>. The term "machine-readable media", as used here, also refers to any medium that is capable of storing, encoding or carrying a set of instructions <NUM> for execution by the gain controller <NUM> and that cause the gain controller <NUM> to perform any one or more of the methodologies of the present disclosure.

The present solution is not limited to the architecture shown in <FIG>. For example, in other scenarios, the band selection filter <NUM> may reside after the variable attenuator <NUM>, rather than before the variable attenuator <NUM> as shown in <FIG>.

Another illustrative architecture for a receiver portion of an LMR communications transceiver that can implement the present solution is shown in <FIG>. Referring now to <FIG>, the receiver <NUM> comprises a band selection filter <NUM>, front end hardware <NUM>-<NUM>, back end hardware <NUM>, a demodulator <NUM> (e.g., a baseband filter), and a gain controller <NUM>. The front end hardware comprises a high linearity LNA <NUM>, an image rejection filter <NUM>, and a variable gain LNA <NUM>. Each of the listed devices <NUM>-<NUM> is known in the art, and therefore will not be described herein. Still, it should be noted that the band selection filter <NUM> receives signals from the antenna, filters the received signals, and forwards the filtered signals to the front end hardware <NUM>-<NUM>. At the front end hardware <NUM>-<NUM>, the signal is further processed by LNA <NUM> and filter <NUM>. Next, the signal is passed to the variable gain LNA <NUM>. The variable gain LNA <NUM> applies attenuation to optimize the ability of the receiver <NUM> to demodulate signals with best quality. The amount of attenuation is controlled by the gain controller <NUM> based on demodulation performance metrics <NUM> generated by the demodulator <NUM>. The demodulation performance metrics <NUM> can be continuously or periodically provided by the demodulator <NUM>. In the periodic scenario, the demodulation performance metrics <NUM> may be provided when the front end gain is in a particular state and when the front end gain state has been changed to another particular state. The manner in which the attenuation by the variable gain LNA <NUM> is controlled will become evident as the discussion progresses.

The demodulation performance metrics <NUM> can include, but are not limited to, a BER, a BDR, an ASE, a synchronization error, and/or a modulation fidelity. The BER is the rate at which error occur in the transmission of digital data. The BDR is the percent of data blocks which are not decoded during given time window(s). The ASE is the degree of error between the actual waveform at the time of a bit decision and a reference waveform. The synchronization error is determined using the received waveform prior to demodulation or bit decisions. The synchronization error comprises the difference between an actual correlation of known content (for example synchronization bits) in the received waveform and a reference signal containing the known content and an optimal correlation of the reference signal with itself. The modulation fidelity refers to the quality of a received signal (i.e., how closely does a received waveform match a reference waveform which can be determined by comparing reference symbol values to received symbol values).

Another illustrative architecture for a receiver portion of an LMR communications transceiver that can implement the present solution is shown in <FIG>. Referring now to <FIG>, the receiver <NUM> comprises a band selection filter <NUM>, front end hardware <NUM>-<NUM>, back end hardware <NUM>, a demodulator <NUM> (e.g., a baseband filter), and a gain controller <NUM>. The front end hardware comprises a high linearity variable LNA <NUM>, an image rejection filter <NUM>, and an LNA <NUM>. Each of the listed devices <NUM>-<NUM> is known in the art, and therefore will not be described herein. Still, it should be noted that the band selection filter <NUM> receives signals from the antenna, filters the received signals, and forwards the filtered signals to the front end hardware <NUM>-<NUM>. At the front end hardware <NUM>-<NUM>, the signal is further processed by variable gain LNA <NUM>. More specifically, the high linearity variable gain LNA <NUM> applies an optimal gain to place the receiver <NUM> in the best gain profile to optimize receiver demodulation performance by trading off linearity against sensitivity. The amount of gain is controlled by the gain controller <NUM> based on demodulation performance metrics <NUM> generated by the demodulator <NUM>. The demodulation performance metrics <NUM> can be continuously or periodically provided by the demodulator <NUM>. In the periodic scenario, the demodulation performance metrics <NUM> may be provided when the front end gain is in a particular state and when the front end gain state has been changed to another particular state. The manner in which the attenuation by the high linearity variable gain LNA <NUM> is controlled will become evident as the discussion progresses.

Another illustrative architecture for a receiver portion of an LMR communications transceiver that can implement the present solution is shown in <FIG>. Referring now to <FIG>, the LMR communications transceiver comprises two receivers <NUM>, <NUM>. Receiver <NUM> can be the same as or similar to receiver <NUM> of <FIG>. However, receiver <NUM> is of the same or different type and/or quality as receiver <NUM>. In some scenarios, receiver <NUM> is selected to be of a lower quality as compared to receiver <NUM> so that receiver <NUM> can be used to detect the occurrence of broadband and/or IM interference relatively early, as discussed in more detail below. In other scenarios, the LMR communications transceiver has any number of receivers selected in accordance with a given application, i.e., has N receivers where N is an integer equal to or greater than <NUM>.

The gain controllers <NUM>, <NUM> of receivers <NUM>, <NUM> can include, but are not limited to, a circuit, or a processor executing instructions implementing the methods described herein for mitigating IM interference. The gain controllers <NUM>, <NUM> may be provided as part of a central processor (e.g., processor <NUM> of <FIG>) for the communication device or is provided as a processor in addition to the central processor. The output of the demodulator of the first receiver may be combined with an output of a demodulator of the second receiver to provide improved performance. Techniques for combining multiple receiver outputs are well known and may include selecting the better performance receiver, adding receiver outputs, maximum ratio combining, and other techniques. The present solution is not limited to the architecture shown in <FIG>. For example, other scenarios, only one gain controller is provided instead of two gain controller as shown.

Referring now to <FIG>, there is provided a simulation graph that is useful for understanding how the noise interference is caused by an LTE signal <NUM> in the LMR band <NUM>. The LTE signal <NUM> is a standard <NUM> configuration operating in a test mode designed by 3GPP (TM-<NUM>) for evaluating out of band energy. As shown, the power bandwidth if the signal is about <NUM> wide with the spectrum energy that falls off outside of this power bandwidth. Spectrum <NUM> represents the relative power of the noise interference that is caused by a spreading of the LTE signal <NUM> into the LMR band <NUM> due to <NUM>rd order intermodulation. Higher order products would have even greater frequency spreading effects. This additional noise that shows up at the receiver's front end degrades the performance of the receiver. Spectrum <NUM> represents the noise interference when both LMR carriers and the LTE signal <NUM> are present at higher power to create intermodulation effects between LTE and LMR carriers in the LMR band <NUM>. In this case, there is an even higher interference to signals in the receiver band. This intermodulation induced on channel noise exists because of linearity limitations of the receiver. If an interfering signal captured by the radio is higher power than the linear operating region of the receiver, lowering the gain of the receiver appropriately results in a much larger drop in interference from intermodulation. For example, if <NUM> dB of gain is removed in the receiver, before the linearity limiting components then the noise floor decreases by <NUM> dB if the interference is dominated by <NUM>rd order intermodulation products. Thus, an advantage is obtained by attenuating the desired signal because the interference generated by intermodulation is attenuated <NUM>-<NUM> times as much in decibels.

Referring now to <FIG>, there is provided a graph showing a typical performance of an LMR receiver when no gain reduction is applied prior to its front end hardware. The current performance is represented by line <NUM>. Line <NUM> has a slope of <NUM>:<NUM>, in this example meaning that for every <NUM> dB increase in LTE interference power the receiver sensitivity is diminished by <NUM> dB. The slope is defined as the change in interference noise power over the change in gain (i.e., Δ noise power/Δ gain). The <NUM>:<NUM> slope is due to the <NUM>rd order IM products caused by an LTE site's signal level placing the communication device receiver in a non-linear operating region. Line <NUM> represents an example improved performance of the LMR receiver when an optimal amount of gain adjustment is provided to its front end. Line <NUM> has a slope of <NUM>:<NUM>, which indicates that the LMR receiver is operating in a linear operating region. Line <NUM> represents the LMR receiver performance when <NUM> dB of attenuation is applied to its front end. As can be seen, there is an improvement in LMR receiver performance when <NUM> dB of attenuation is applied to its front end that transitions from no improvement with an LTE power of -<NUM> dBm to <NUM> dB improvement with an LTE power greater than -<NUM> dBm. However, <NUM> dB of sensitivity is lost in the receiver when no interference is present. Line <NUM> represent the LMR receiver performance when <NUM> dB of attenuation is applied. As can be seen, there is an improvement in LMR receiver performance when <NUM> dB of attenuation is applied to its front end that transitions from no improvement with an LTE power of -<NUM> dBm to <NUM> dB improvement with an LTE power greater than -<NUM> dBm. However, <NUM> dB of sensitivity is lost in the receiver when no interference is present.

Notably, the attenuation should not be continuously applied at the receiver front end to mitigate the LTE interference because some sensitivity of the receiver would be lost during times when the IM condition does not exit. So, the present solution waits until the gain controller can estimate based on demodulation performance metrics that the communication device is under the influence of IM interference or is predicted to soon be under the influence of IM interference. The process can be implemented by a continuous adaptive loop or discrete hypothesis testing of demodulation performance metrics.

Notably, the Telecommunications Industry Association ("TIA") has defined test and performance requirements for LMR radios in the presence of LTE signals in the <NUM>, <NUM> and <NUM> bands. These performance requirements include a minimum standard for IM rejection and LTE interference from -<NUM> dBm to -<NUM> dBm. These performance requirements are currently in the approval process. The present solution provides ways of meeting these TIA's test and performance requirements for LMR radios.

Referring now to <FIG>, there is provided a method <NUM> for mitigating broadband and/or IM interference not covered by the scope of protection of the invention but useful for understanding the invention. Method <NUM> begins with <NUM> and continues with <NUM> where a communication device (e.g., communication device <NUM> or <NUM> of <FIG>) performs operations to continuously or periodically monitor the performance of a demodulator (e.g., demodulator <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) of the communication device. This monitoring can involve: generating demodulation performance metrics (e.g., demodulation performance metrics <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) by the demodulator; and providing the demodulation performance metrics to a gain controller (e.g., gain controller <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) of the communication device. The demodulation performance metrics can include, but are not limited to, a BER, a BDR, an ASE, a synchronization error, and/or a modulation fidelity. The demodulation performance metrics can be stored in the communication device's memory (e.g., memory <NUM> of <FIG>), which is accessible to the gain controller.

In <NUM>, the demodulation performance metrics of the communication device's demodulator(s) are used to detect when the communication device is under the influence of broadband and/or IM interference, is predicted to soon be under the influence of IM, or is in an IM limited condition. The manner in which the demodulation performance metrics are used here will become more evident as the discussion progresses. If the communication device is under the influence of broadband and/or IM interference, is predicted to soon be under the influence of IM interference or is in an IM limited condition, then an improved level of gain that is to be applied by a variable attenuator (e.g., variable attenuator <NUM> of <FIG>, <NUM> of <FIG> and/or <NUM> of <FIG>) prior to the front end hardware and/or a variable LNA (e.g., LNA <NUM> of <FIG> or <NUM> of <FIG>) of the front end hardware is determined as shown by <NUM>. In <NUM>, the amount of gain being applied by the variable attenuator and/or LNA is selectively adjusted based on improved demodulator performance metrics. For example, the level of gain being applied by the variable attenuator and/or LNA is set equal to the improved level of gain (which may be a predefined value, a dynamically computed value based on current operating conditions, or a previous gain setting value for the receiver). Subsequently, <NUM> is performed where method <NUM> ends or other processing is performed (e.g., return to <NUM>).

Referring now to <FIG>, there is provided an illustrative method <NUM> for mitigating broadband and/or IM interference not covered by the scope of protection of the invention but useful for understanding the invention. Method <NUM> begins with <NUM> and continues with <NUM> where a communication device (e.g., communication device <NUM> or <NUM> of <FIG>) performs operations to continuously or periodically monitor the performance of a demodulator (e.g., demodulator <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) of the communication device. This monitoring can involve: generating demodulation performance metrics (e.g., demodulation performance metrics <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) by the demodulator; and providing the demodulation performance metrics to a gain controller (e.g., gain controller <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and/or <NUM> of <FIG>) of the communication device. The demodulation performance metrics can include, but are not limited to, a BER, a BDR, an ASE, a synchronization error, and/or a modulation fidelity. The demodulation performance metrics can be stored in the communication device's memory (e.g., memory <NUM> of <FIG>), which is accessible to the gain controller.

Next in <NUM>, the communication device obtains at least one demodulation performance metric (e.g., the BER) that is associated with the current gain settings of the communication device's receiver (e.g., receiver <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG> or <NUM> of <FIG>). Operations are then performed in <NUM> by the communication device to change the gain setting(s) of the receiver. Gain settings are well known in the art, and therefore will not be described herein. Similarly, techniques for changing gain settings for receivers are well known in the art, and therefore will not be described herein. Once the gain settings have been changed, at least one new demodulation performance metric (e.g., BER) is obtained, as shown by <NUM>.

In <NUM>, the new demodulation performance metric is compared to the previous demodulation performance metric (e.g., the demodulation performance metric obtained in <NUM>). If the value of the new demodulation performance metric is better than (e.g., lower than) a value of the previous demodulation performance metric [<NUM>:YES], then method <NUM> returns to <NUM>. In contrast, if the value of the new demodulation performance metric is worse than (e.g., greater than) a value of the previous demodulation performance metric [<NUM>:NO], then method <NUM> continues with <NUM>. In <NUM>, an improved level of gain to be applied by a variable attenuator (e.g., variable attenuator <NUM> of <FIG>, <NUM> of <FIG> and/or <NUM> of <FIG>) prior to the front end hardware and/or a variable LNA (e.g., LNA <NUM> of <FIG> or <NUM> of <FIG>) of the front end hardware is determined. For example, the improved level of gain is determined to be the level of gain that is associated with the previous demodulation performance metric or another previous demodulation performance metric which is associated with the best value of a plurality of previous demodulation performance metrics stored in the communication device's memory (e.g., memory <NUM> of <FIG>). Next in <NUM>, the amount of gain being applied to the variable attenuator and/or variable LNA is selectively adjusted based on changing the gain in a direction toward improved performance metric results determined in <NUM>. Subsequently, <NUM> is performed where method <NUM> ends or other processing is performed.

Referring now to <FIG>, there is provided an illustrative method <NUM> for mitigating broadband and/or IM interference not covered by the scope of protection of the invention but useful for understanding the invention. Method <NUM> begins with <NUM> and continues with <NUM> where a first receiver (e.g., receiver <NUM> of <FIG>) of a communication device (e.g., communication device <NUM> or <NUM> of <FIG>) is configured in accordance with first gain settings and a second receiver (e.g., receiver <NUM> of <FIG>) of the communication device is configured in accordance with second gain settings. Gain settings are well known in the art, and therefore will not be described herein. Also, techniques for configuring attenuators and/or LNAs in accordance with gain settings are well known in the art, and therefore will not be described herein.

Next in <NUM>, gain controllers (e.g., gain controllers <NUM> and <NUM> of <FIG>) perform operations to continuously or periodically monitor the performance of the demodulators of the first and second receivers. This monitoring can involve: generating demodulation performance metrics (e.g., demodulation performance metrics <NUM> and <NUM> of <FIG>) by the demodulators (e.g., demodulators <NUM> and <NUM> of <FIG>) of the first and second receivers; and providing the demodulation performance metrics to gain controllers (e.g., gain controller <NUM> and <NUM> of <FIG>) of the communication device. The demodulation performance metrics can include, but are not limited to, a BER, a BDR, an ASE, a synchronization error, and/or a modulation fidelity. The demodulation performance metrics can be stored in the communication device's memory (e.g., memory <NUM> of <FIG>), which is accessible to the gain controllers.

In <NUM>, the gain controllers obtain at least one first demodulation performance metric associated with the current gain settings of the first receiver and at least one second demodulation performance metric associated with the current gain settings of the second receiver. The first demodulation performance metric is compared to the second demodulation performance metric in <NUM>. If a value of the first demodulation performance metric is better than (e.g., lower than) a value of the second demodulation performance metric [<NUM>:YES], then method <NUM> continues with <NUM>. In <NUM>, an improved level of attenuation for the second receiver is determined. In contrast, if the value of the first demodulation performance metric is worse than (e.g., greater than) the value of the second demodulation performance metric [<NUM>:NO], then method <NUM> continues with <NUM>. In <NUM>, an improved level of gain for the first receiver is determined. Thereafter, <NUM> is performed where an amount of gain by a variable attenuator (e.g., variable attenuator <NUM> or <NUM> of <FIG>) and/or a variable LNA of the first or second receiver is selectively adjusted based on adjusting the gain for predicted improved performance. The outputs of the first and second receiver demodulators may then combined as shown by <NUM> according to several techniques well known in the art. Subsequently, <NUM> is performed where method <NUM> ends or other processing is performed.

Referring now to <FIG>, there is provided a method <NUM> for mitigating broadband and/or IM interference according to the invention as claimed. Method <NUM> begins with <NUM> and continues with <NUM> where a primary receiver (e.g., receiver <NUM> of <FIG>) of a communication device (e.g., communication device <NUM> or <NUM> of <FIG>) is operated in accordance with a given gain setting. A secondary receiver (e.g., receiver <NUM> of <FIG>) of the communication device is also operated in <NUM>. The secondary receiver has a lower linearity as compared with the linearity of the primary receiver. In <NUM>, gain controllers (e.g., gain controllers <NUM>, <NUM> of <FIG>) of the receivers continuously or periodically monitor the performance of their demodulators (e.g., demodulators <NUM>, <NUM> of <FIG>), respectively. This monitoring can involve: generating demodulation performance metrics (e.g., demodulation performance metrics <NUM> and <NUM> of <FIG>) by the demodulators (e.g., demodulators <NUM> and <NUM> of <FIG>) of the primary and secondary receivers; and providing the demodulation performance metrics to gain controllers (e.g., gain controller <NUM> and <NUM> of <FIG>) of the communication device. The demodulation performance metrics can include, but are not limited to, a BER, a BDR, an ASE, a synchronization error, and/or a modulation fidelity. The demodulation performance metrics can be stored in the communication device's memory (e.g., memory <NUM> of <FIG>), which is accessible to the gain controllers.

In <NUM>, a processor (e.g., processor <NUM> of <FIG>) of the communication device obtains at least one demodulation performance metric associated with the secondary receiver. The demodulation performance metric is analyzed in <NUM> to determine if the communication device is under the influence of IM interference. Notably, IM interference is more easily detected by analyzing the performance of the secondary receiver as opposed to the performance of the primary receiver. Accordingly, the secondary receiver's performance is used here to trigger gain adjustments in relation to the primary receiver.

If the communication device is not under the influence of IM interference [<NUM>:NO], then method <NUM> returns to <NUM>, as shown by <NUM>. In contrast, if the communication device is under the influence of IM interference [<NUM>:YES], then method <NUM> continues with <NUM>. In <NUM>, an improved level of gain to be applied by a variable attenuator (e.g., variable attenuator <NUM> or <NUM> of <FIG>) and/or a variable LNA of the primary receiver is determined. The improved level of gain can be determined based on (<NUM>) results from comparing at least one current demodulation performance metric of the primary receiver to at least one previous demodulation performance metric of the primary receiver, or (<NUM>) pre-specified gain settings for respective levels of IM interference experienced by or likely to be experienced by the communication device. Techniques for determining actual or likely levels of IM interference are well known in the art, and therefore will not be described herein. Any known or to be known technique for determining actual or likely levels of IM interference can be used herein without limitation.

In <NUM>, an amount of gain being applied by the variable attenuator and/or LNA of the primary receiver is selectively adjusted in accordance with the improved level of gain. The outputs of the primary and secondary receivers' demodulators can be optionally combined as shown by <NUM>. Methods for combining demodulator outputs are well known in the art, and therefore will not be described herein. Any known or to be known method for combining demodulator outputs can be used herein without limitation. Subsequently, <NUM> is performed where method <NUM> ends or other processing is performed.

In some scenarios, the present solution employs one receiver that changes its linearity dynamically, measures a demodulation metric at different linearity conditions, and then determines how to optimize its gain settings. This is very similar to the methods of <FIG>, but with one physical receiver.

Claim 1:
A method (<NUM>) for mitigating Intermodulation, IM, interference, comprising:
operating (<NUM>) a first receiver (<NUM>) of a communication device in accordance with a given gain setting;
operating (<NUM>) a second receiver (<NUM>) of a communication device with a lower linearity as compared to that of the first receiver (<NUM>);
continuously or periodically monitoring (<NUM>) the performance of demodulators of the first receiver (<NUM>) and the second receiver (<NUM>);
obtaining (<NUM>) at least one demodulation performance metric associated with the second receiver (<NUM>);
analyzing (<NUM>) the at least one demodulation performance metric associated with the second receiver (<NUM>) for determining if the communication device is under an influence of IM interference;
when the communication device is under an influence of IM interference, determining (<NUM>) an improved level of gain to be applied to
(i) a variable attenuator, VA, of the first receiver (<NUM>), and/or
(ii) a variable low noise amplifier, LNA, of the first receiver (<NUM>);
selectively adjusting (<NUM>) an amount of gain being applied by the variable attenuator or variable gain low noise amplifier of the first receiver (<NUM>) based on the improved level attenuation.