System and method for mitigating broadband interference

Systems and methods for operating a communication device so as to mitigate intermodulation interference to a signal. The methods comprise: continuously monitoring several communication channels by the communication device; using a noise floor level estimate of the communication device to detect when the communication device is under an influence of hig interference; determining an optimal level of attenuation to be applied by a variable attenuator of the communication device's receiver so as to mitigate the influence of intermodulation interference to the signal; and selectively adjusting an amount of attenuation being applied by the variable attenuator to achieve the optimal level of attenuation for mitigating intermodulation interference.

BACKGROUND

Statement of the Technical Field

The present document concerns communication systems. More particularly, the present document concerns systems and methods for mitigating interference (e.g., broadband and/or narrowband) in receivers.

Description of the Related Art

Conventional radios include Land Mobile Radios (“LMRs”). When LMRs get close to broadband sites operating in neighboring frequency allocations, they experience relatively high levels of the broadband signal as interference. This interference can produce significant intermodulation (“IM”) products which may degrade radio performance or sensitivity by raising the noise floor of the receiver. These effects are further aggravated by the high peak to average power ratio characteristics of broadband signals.

SUMMARY

This document concerns systems and methods for operating a communication device so as to mitigate intermodulation interference (e.g., broadband and/or narrowband) to a signal. The methods comprise: continuously monitoring several communication channels by the communication device; using a noise floor level estimate of the communication device to detect when the communication device is under an influence of high interference; determining an optimal level of attenuation to be applied by a variable attenuator of the communication device's receiver so as to mitigate the influence of intermodulation interference due to the interference signal; and selectively adjusting an amount of attenuation being applied by the variable attenuator to achieve the optimal level of attenuation for best receiver performance.

In some scenarios, the methods also comprise: estimating the noise floor level with an original attenuation level being applied by the variable attenuator of the communication device's receiver. The noise floor level is estimated by acquiring a power measurement value for an on channel, a power measurement value for at least one high side channel, and a power measurement value for at least one low side channel. A same or different number of high channel power measurements and low channel power measurements may be acquired. The noise floor level is set equal to a minimum value of the power measurement values acquired for the measured channels over the receiver's analysis bandwidth (e.g., in some scenarios the following channels will be measured as a minimum: the on channel, at least one high side channel, and at least one low side channel will be measured).

In those or other scenarios, a detection is made as to when the communication device is under the influence of a high level of interference based on results from comparing the estimated noise floor level to a threshold value. The threshold value is equal to a known thermal noise floor level plus a certain amount X. The certain amount X variable represents the amount of noise floor increase allowed before a test is performed to determine if the interference is due to intermodulation and the receiver sensitivity can be improved by adding some attenuation before a low noise amplifier to put the receiver in a more linear operating region.

The optimal level of attenuation is determined by: iteratively adding an incremental level of attenuation (Δ attenuation) and measuring the noise level difference (Δ noise power) from the previous iteration; calculating a slope that is defined by a change in noise power over a change in attenuation; comparing the slope to a threshold value Y; and considering the optimal level of attenuation to be the previous level of attenuation applied by the variable attenuator when the current slope estimate is less than the threshold value Y.

DETAILED DESCRIPTION

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.

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: continuously monitoring a plurality of communication channels by the communication device; using a noise floor level estimate of the communication device to detect when the communication device is under an influence of high interference; determining an optimal level of attenuation to be applied by a variable attenuator of the communication device's receiver so as to mitigate the influence of intermodulation interference due to the interference signal; and selectively adjusting an amount of attenuation being applied by the variable attenuator to achieve the optimal level of attenuation for best receiver performance in the presence of the interfering signal.

In some scenarios, the methods also comprise: estimating the noise floor level with an original attenuation level being applied by the variable attenuator of the communication device's receiver. The noise floor level is estimated by acquiring a power measurement value for an on channel, a power measurement value for at least one high side channel, and a power measurement value for at least one low side channel. A same or different number of high channel power measurements and low channel power measurements may be acquired. The noise floor level is set equal to a minimum value of the power measurement values acquired for the measured channels (e.g., an on channel, at least one high side channel, and at least one low side channel) over the receiver's analysis bandwidth.

In those or other scenarios, a detection is made as to when the communication device is under the influence of a high level of interference based on results from comparing the noise floor level estimate to a threshold value. The threshold value is equal to a known thermal noise floor level plus a certain amount X. The certain amount X variable represents the amount of noise floor increase that is allowed before an attenuation test is performed to determine if the interference is due to intermodulation and the receiver sensitivity can be improved by adding some attenuation before a low noise amplifier to put the receiver in a more linear operating region.

The optimal level of attenuation is determined by: iteratively adding an incremental level of attenuation (Δ attenuation) and measuring the noise level difference (Δ noise power) from a previous iteration; calculating a slope that is defined by a change in noise power over a change in attenuation; comparing the slope to a threshold value Y; and considering the optimal level of attenuation to be the previous level of attenuation (e.g., α(n−1)) applied by the variable attenuator when the current slope estimate is less than the threshold value Y.

Referring now toFIG. 1, there is provided an illustration of an illustrative system100. System100comprises a plurality of communication devices102,104,106, a Central Dispatch Center (“CDC”)108, and a broadband site110. The communication devices102-106include, 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. The broadband site110includes, but is not limited to, an LMR site, a 2G cellular site, a 3G cellular site, a 4G cellular site, and/or a 5G cellular site. CDC108and broadband site110are well known in the art, and therefore will not be described herein.

During operation of system100, signals are communicated between the communication devices102-106and/or between one or more communication devices and the CDC108. For example, communication device102communicates a signal to communication device104, and CDC108communicates a signal to communication device106. Communication devices104and106perform operations to mitigate interference caused by the broadband site110. The interference results because the raised noise floor of received broadband signals (e.g., broadband signal400ofFIG. 4) causes the noise floor of the communication device to be increased when the signal power is above a certain level. The manner in which communication devices104and106mitigate the broadband interference to signals will become evident as the discussion progresses.

Referring now toFIG. 2, there is provided an illustration of an illustrative architecture for a communication device200which is configured for carrying out the various methods described herein for mitigating the broadband interference. Communication devices102-106are the same as or similar to communication device200. As such, the discussion provided below in relation to communication device200is sufficient for understanding communication devices102-106. Communication device200can include more or less components than that shown inFIG. 2in accordance with a given application. For example, communication device200can include one or both components208and210. The present solution is not limited in this regard.

As shown inFIG. 2, the communication device200comprises an LMR communication transceiver202coupled to an antenna216. 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 transceiver202can 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 data from the communication device200over an LMR network.

Although the communication device200has 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 device200could include a cellular network communication transceiver in place of an LMR communication transceiver. In another scenario, the communication device200could 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 broadband interference by another communication system exists that generates interference energy that may be detected in neighboring channels.

The LMR communication transceiver202is connected to a processor204comprising an electronic circuit. During operation, the processor204is configured to control the LMR communication transceiver202for providing LMR services. The processor204also facilitates mitigation of interference to signals. The manner in which the processor facilitates interference mitigation will become evident as the discussion progresses.

A memory206, display208, user interface212and Input/Output (“I/O”) device(s)210are also connected to the processor204. The processor204may be configured to collect and store data generated by the I/O device(s)210and/or external devices (not shown). Data stored in memory206can include, but is not limited to, one or more look-up tables or databases which facilitate selection of communication groups or specific communication device. The user interface212includes, 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 device200. 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 interface212. A battery214or other power source may be provided for powering the components of the communication device200. The battery200may 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 show inFIG. 2should 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 toFIG. 3, there is provided a more detailed illustration of an illustrative receiver portion300of the LMR communication transceiver202. Receiver300comprises a variable attenuator302, a band selection filter303, a Low-Noise Amplifier (“LNA”)304, front end hardware306, and back end hardware308. Each of the listed devices is known in the art, and therefore will not be described herein. Still, it should be noted that the variable attenuator receives signals from the antenna216and applies attenuation to the place the receiver300in a more linear operating region. The amount of attenuation is controlled by the processor204ofFIG. 2. The manner in which the attenuation by the variable attenuator302is controlled will become evident as the discussion progresses.

Referring now toFIG. 4, there is provided a graph that is useful for understanding how the noise interference is caused by an LTE signal400in the LMR band402. Spectrum404represents the relative power of the noise interference that is caused by a spreading of the LTE signal400into the LMR band402. This additional noise that shows up at the receiver's front end degrades the performance of the receiver. Spectrum406represents the noise interference when both LMR carriers and the LTE signal400are present in the LMR band402. In this case, there is an even higher interference to signals in the receiver band. This apparent noise exists because of a limitation in a performance of the receiver. If a signal which is higher than the linear operating region of the receiver and causing intermodulation interference is attenuated prior to the receiver's front end, the noise floor drops rapidly. For example, if 1 dB of attenuation is added in the receiver, then the noise floor decreases by 3 dB if the interference is domination by 3rdorder intermodulation products. Thus, an advantage is obtained by attenuating the signal because the interference generated by intermodulation is more attenuated.

Referring now toFIG. 5, there is provided a graph showing a current performance of an LMR receiver when no attenuation is applied prior to its front end hardware. The current performance is represented by line500. Line500has a slope of 3:1. The slope is defined as the change in noise power over the change in attenuation (i.e., Δ noise power/Δ attenuation). The 3:1 slope is due to the 3rdorder IM products caused by an LTE site's signal level placing the communication device receiver in a non-linear operating region. Line502represents the desired performance of the LMR receiver with an optimal amount of attenuation added to its front end. Line502has a slope of 1:1, which indicates that the LMR receiver is operating in a more linear operating region. Line504represents the LMR receiver performance when a 6 dB attenuation is applied to its front end. As can be seen, there is a 12 dB improvement in LMR receiver performance when the 6 dB attenuation is applied to its front end. Line506represent the LMR receiver performance when a 12 dB attenuation is applied. As can be seen, there is an 18 dB improvement in LMR receiver performance when the 12 dB attenuation is applied to its front end.

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 measured slope p is less than the threshold parameter Y.

Referring now toFIG. 6, there is provided a method600for mitigating LTE interference. Method600begins with602and continues with604where a communication device (e.g., communication device104or106ofFIG. 1) performs operations to continuously monitor a communications channel. Methods for monitoring communications channels are well known in the art, and therefore will not be described herein. The communication device also receives noise signals and/or communications signals in604. Methods for receiving noise signals and communications signals are well known in the art, and therefore will not be described herein.

In606, the noise floor level of the communication device is used to detect when the communication device is under the influence of IM interference or in an IM limited condition. The manner in which the noise floor level is used here will become more evident as the discussion progresses. If the communication device is under the influence of IM interference, then an optimal level of attenuation that is to be applied by a variable attenuator (e.g., variable attenuator302ofFIG. 3) is determined as shown by608. In610, the amount of attenuation being applied by the variable attenuator is selectively adjusted based on the optimal level of attenuation. For example, the level of attenuation being applied by the variable attenuator is set equal to the optimal level of attenuation. Subsequently,612is performed where method600ends or other processing is performed (e.g., return to602).

Referring now toFIG. 7, there is provided an illustrative method700for mitigating LTE interference. Method700includes operations702-724to determine when a communication device is in an environment where the performance is limited by IM products and not thermal noise regardless of what the measured on-channel and adjacent channel powers are. This determination is made based on an estimate noise floor of the communication device's receiver. Notably, operations in box750are performed to detect when there is a high level of interference. Operations in box752are performed to determine if the inference is due to IM and to change the attenuation to the optimal level to mitigate the IM. All or some of the operations702-724can be performed by a communication transceiver (e.g., LMR communication transceiver202ofFIG. 2) and/or a processor (e.g., processor204ofFIG. 2) of a communication device (e.g., communication device102-106ofFIG. 1, or communication device200ofFIG. 2).

As shown inFIG. 7, method700begins with702and continues with704where a communication device (e.g., communication device104or106ofFIG. 1) performs operations to continuously monitor a communications channel. Methods for monitoring communications channels are well known in the art, and therefore will not be described herein. The communication device also receives noise signals and/or communications signals in704. Methods for receiving noise signals and communications signals are well known in the art, and therefore will not be described herein.

Next in706, the communication device estimates a noise floor k with an original attenuation level (e.g., zero) being applied by a variable attenuator (e.g., variable attenuator302ofFIG. 3) of the communication device's receiver (e.g., receiver300ofFIG. 3). The noise floor estimation is achieved in accordance with a process shown inFIG. 8. As shown inFIG. 8, the process begins by acquiring a measurement of an on channel power P0in802, at least one measurement of a high side channel power P+1, . . . , P+Qas shown by804-806, and at least one measurement of a low side channel power P−1, . . . , P−Was shown by808-810. Q and W are any integer values. Q and W can have the same or different value. Techniques for acquiring channel power measurements are well known in the art, and therefore will not be described here. The power measurements are then used in808to determine a noise floor estimate k. The noise floor estimate k may by example be set equal to the minimum acquired power measurement value Pmin. Next, the noise floor estimate k is compared to a threshold value thr in812. The threshold value thr is equal to a thermal noise floor level (which depends on the channel bandwidth the noise measurement is performed over) plus X dB.

X dB is selected based on a given application. The level X is the amount of degradation that is allowed before the attenuation test for the existence of IM is performed and will vary with specific applications and equipment properties

Referring now toFIG. 9, a chart is provided that shows that a high side channel in box900is an interfering adjacent channel, the on channel in box902has a low signal (e.g., due to being far away), and the low channel in box904has the smallest power level. In this scenarios, the noise floor estimate k is set equal to the power level of the low channel since it is the minimal power level of the three channels. The present solution is not limited to the particulars of this scenario.

If the noise floor estimate k is greater than the threshold value thr, then an assumption is made that the signal is in a non-linear region of the receiver and is generating IM (e.g., has at least a 3:1 slope). At this time, a test is performed in method700to determine if an increased amount of attenuation (e.g., 1 dB) improves the communication device's receiver sensitivity, i.e., whether the noise floor level estimate is decreased more than Y times the amount of the added attenuation.

Referring again toFIG. 7, the result R is used in708to determine whether the estimate noise floor k has increased a certain amount above the threshold thr. If not [708: NO], then method700returns to706. If so [708: YES], then method700continues with710.

In710, an amount of attenuation applied by the variable attenuator (e.g., variable attenuator302ofFIG. 3) of the communication device's receiver (e.g., receiver300ofFIG. 3) is changed by a given amount (e.g., >1 dB) to improve the communication device's sensitivity. Typical 3rdorder IM products have a 3× increase in the noise level for a 1× increase in the signal level. Typical 5thorder IM products have a 5× increase in the noise level for a 1× increase in the signal level.

Next in712, a new noise floor level k′ of the communication device is estimated with added attenuation.712can also involve measuring the difference between the new noise floor level k′ and the previous noise floor level k. Upon completing712, method700continues with716. In716, a slope p of the signal is calculated. Methods for computing the slope p of the signal are well known in the art, and therefore will not be described herein. Still, it should be understood that the slope p is the change in noise power over the change in attenuation. If the slope p is less than Y [718: YES], then method700returns to706as shown by720. If the slope p is greater than Y [718: NO], then an assumption is made that signal degradation is occurring due to the IM effects. Y is an integer (e.g., 1, 2, etc.). Accordingly,722is performed where the attenuation is set for the signal to the previous level of attenuation (e.g., α(k−1), i.e., the original attenuation level plus a total amount of added attenuation) to benefit the sensitivity of the receiver. Subsequently,724is performed where method700ends or other processing is performed (e.g., return to702).

Referring now toFIG. 10, there is a graph showing results from operating an LMR receiver in accordance with the above described method for mitigating LTE interference. As can be seen inFIG. 10, an 18 dB noise floor reduction is provided when 6 dB of attenuation to the LMR receiver's front end. This 18 dB noise floor reduction results in an improvement in the LMR receiver's sensitivity.

The described features, advantages and characteristics disclosed herein may be combined in any suitable manner. One skilled in the relevant art will recognize, in light of the description herein, that the disclosed systems and/or methods can be practiced without one or more of the specific features. In other instances, additional features and advantages may be recognized in certain scenarios that may not be present in all instances.