Patent Description:
A significant cause of wireless network problems is interference. The most common sources of such interference are narrowband continuous wave (CW) signals, narrowband sweeping signals, and passive intermodulation distortion (PIM). Of these three interference sources, PIM is particularly problematic for frequency division duplex (FDD) wireless networks in which network base stations receive uplink signals (i.e., mobile device to base station signals) while concurrently transmitting downlink signals (i.e., base station to mobile device signals) at significantly greater power.

PIM is typically the result of non-linearities that cause the more powerful downlink signals to create interference in the base station receiver at the frequency for the weaker uplink signals. The effect of PIM is to reduce the signal-to-noise-plus- interference ratio (SINR) at the base station receiver. When PIM is sufficiently severe, reception at the base station receiver may not be possible during transmission by the base station transmitter. Consequently, there is a need in the art for an automated solution for identifying and mitigating sources of interference, including PIM, in FDD wireless networks. <CIT> discloses a method of handling interference caused by inter- modulation in a network node site comprising a set of network nodes for wireless communication capable of communication with a set of stations for wireless communication.

There are provided devices and methods for automating interference mitigation in frequency division duplex (FDD) wireless networks, substantially as shown in and/or described in connection with at least one of the figures, and as set forth more completely in the claims.

The following description contains specific information pertaining to implementations in the present disclosure. One skilled in the art will recognize that the present disclosure may be implemented in a manner different from that specifically discussed herein. The drawings in the present application and their accompanying detailed description are directed to merely exemplary implementations. Unless noted otherwise, like or corresponding elements among the figures may be indicated by like or corresponding reference numerals. Moreover, the drawings and illustrations in the present application are generally not to scale, and are not intended to correspond to actual relative dimensions.

It is noted that, as used in the present application, the terms"automation," "automated", and"automating" refer to systems and processes that do not require human intervention. Although, in some implementations, a human wireless network controller may review or even modify the interference mitigation strategies generated by the automated devices and according to the automated methods disclosed herein, that human involvement is optional. Thus, the interference mitigation strategies described in the present application may be determined and implemented under the control of hardware processing components executing them.

<FIG> shows a diagram illustrating communication among constituents of exemplary frequency division duplex (FDD) wireless network <NUM>, according to one implementation. In various implementations, FDD wireless network <NUM> may be implemented as a fourth generation wireless systems (<NUM>) technology network utilizing a Long-Term Evolution (LTE) standard, or a fifth generation wireless systems (<NUM>) technology network, for example.

As shown in <FIG>, FDD wireless network <NUM> includes radio access network (RAN) <NUM> having base station (BS) <NUM> communicatively coupled with mobile communication devices 102a and 102b, shown as exemplary smartphones in <FIG> and typically referred to as"user equipment" or"UE" (hereinafter"UE 102a/ 102b"). As further shown in <FIG>, communications between base station <NUM> and UE 102a/102b occurs via uplink transmission signals 104a and 104b, downlink transmission signals 106a and 106b, and via antenna <NUM> of base station <NUM> configured to transmit downlink transmission signals 106a and 106b as well as to receive uplink transmission signals 104a and 104b. Also shown in <FIG> is conceptual block <NUM> representing elements of FDD wireless network <NUM> other than RAN <NUM>.

It is noted that although <FIG> shows a single instance of RAN <NUM> for conceptual clarity, FDD wireless network <NUM> would typically include many instances of RAN <NUM>, each communicatively coupled to other elements <NUM> of FDD wireless network <NUM>, as well as to other communication networks, such as the Internet and the Public Switched Telephone Network for example. Moreover, the base stations included in each RAN may be communicatively coupled to one another via a fiber optic communication network included in other elements <NUM> of FDD wireless network <NUM>. In such an implementation, each separate link in a chain of communication between UE 102a/102b in RAN <NUM> and another UE in another RAN may take the form of one of uplink transmission signals 104a and 104b or downlink transmission signals 106a and 106b, fiber optic signals between base station <NUM> and other elements <NUM> of FDD wireless network <NUM>, and fiber optic signals between nodes of the fiber optic network linking RAN <NUM> with another RAN and other networks. Nevertheless, <FIG> emphasizes RAN <NUM> because it is the RAN environment that is typically the limiting factor in the reliability of FDD wireless network <NUM>.

In addition to reliability problems, there are also capacity constraints in the RAN environment. The capacity for data transfer (measured in bits per second) over a fiber optic line coupling base station <NUM> to other elements <NUM> of FDD wireless network <NUM>, for example, is much greater than the data transmission capacity of RAN <NUM>. In addition, frequency spectrum is a shared public resource that is regulated and controlled by government agencies. Due to the limited supply of frequency spectrum, and because of the growth in demand for wireless services by consumers, licensing costs are high, making frequency spectrum a costly investment for mobile service providers.

The performance of RAN <NUM> depends on the signal-to-noise ratio-plus- interference (SINR) at base station <NUM>. SINR is defined as: <MAT>.

As seen above, SINR decreases when signal power goes down, or when noise or interference goes up, and as a result, reliability, capacity, and data throughput all go down. With respect to SINR, the most challenged receiver in FDD wireless network <NUM> is the receiver of base station <NUM> that must recover uplink transmission signals 104a and 104b transmitted by UE 102a/102b. However, the transmit power of UE 102a/102b is typically low, and typically cannot be increased due to safety concerns and practical limitations on size and battery power.

Moreover, the uplink transmission signals 104a and 104b transmitted by UE 102a/ 102b are subject to conditions such as reflection, absorption, and scattering within the environment of RAN <NUM> that can only be predicted using statistical models. The interaction of such effects is termed "fading" and can result in temporary reductions of the uplink transmission signal level by factors of approximately ten to approximately one hundred. Consequently, FDD wireless network <NUM> may often operate near its reliable limits of transmission based on the SINR. If a connection between a transmitter of UE 102a/ 102b and a receiver of base station <NUM> is operating near that limit and interference or noise level rises, the radio link can become unusable, resulting in speech becoming garbled or in the communication being dropped entirely.

<FIG> shows a more detailed exemplary diagram of base station <NUM> for use in FDD wireless network <NUM> in <FIG>, according to one implementation. As shown in <FIG>, base station <NUM> is communicatively coupled to other elements <NUM> of FDD wireless network <NUM>, in <FIG>. As further shown in <FIG>, base station <NUM> includes transmit and receive antenna <NUM>, radio equipment (RE) <NUM>, and radio equipment controller (REC) <NUM> including scheduler <NUM>. Also shown in <FIG> are uplink communication channel <NUM> supporting uplink data communications from RE <NUM> to REC <NUM>, and downlink communication channel <NUM> supporting downlink data communications from REC <NUM> to RE <NUM>.

Base station <NUM> having antenna <NUM> corresponds in general to base station <NUM> having antenna <NUM>, in <FIG>, and those corresponding features may share any of the characteristics attributed to either corresponding feature by the present disclosure. Thus, although not shown in <FIG>, base station <NUM> may include features corresponding to RE <NUM>, REC <NUM> including scheduler <NUM>, uplink communication channel <NUM>, and downlink communication channel <NUM>. Moreover, uplink communication channel <NUM> is configured to communicate data received from UE <NUM>/102b via uplink transmission signals 104a and 104b, in <FIG>, while downlink communication channel <NUM> is configured to communicate data for transmission to UE 102a/102b via downlink transmission signals 106a and 106b.

It is noted that although in some implementations RE <NUM> and REC <NUM> may be integrated into a combined unit, RE <NUM> and REC <NUM> need not be co-located, and can in fact be separated by a considerable distance. For example, in some implementations, base station <NUM>/<NUM> may be situated in a single tower location. In those implementations, the RE <NUM> is typically mounted near the top of the tower while REC <NUM> may be ten or more meters away at the bottom of the tower. However, in other implementations, REC <NUM> may be situated together with other RECs in a central location remote from RE <NUM>, and RE <NUM> may be connected to REC <NUM> over a distance of up to many kilometers. RE <NUM> transmits downlink transmission signals 106a and 106b to UE 102a/ 102b and receives uplink transmission signals 104a and 104b from UE 102a/102b. RE <NUM> may include multiple transmitters and receivers at the same frequency, for diversity or for what is termed MIMO (Multiple Input Multiple Output) functionality. REC <NUM> processes the baseband modulation data in the mathematical format of I/Q vectors, where"I" represents the in-phase signal component and"Q" represents the quadrature phase signal component, as known in the art.

In the base station architecture shown in <FIG>, REC <NUM> and RE <NUM> have digital data connections provided by uplink communication channel <NUM> and downlink communication channel <NUM> that can be extended up to many kilometers via highly reliable fiber optic connections. Uplink communication channel <NUM> and downlink communication channel <NUM> carry I/Q data providing a digital representation of the analog modulation included in uplink transmission signals 104a and 104b, and downlink transmission signals 106a and 106b, respectively. That is to say, the I and Q components of the uplink data carried by uplink communication channel <NUM> corresponds to communications from UE 102a/102b to base station <NUM>/<NUM>.

In downlink communication channel <NUM>, the I/Q data has no distortion because it has not been subjected to the effects of the environment of RAN <NUM>, or to any other sources of distortion. However, in uplink communication channel <NUM>, the I/Q data contains uplink transmission signals 104a and 104b created by UE 102a/102b as well as the environmental effects of RAN <NUM>, e.g., path loss and fading effects, as well as distortion from interference sources.

As stated above, a significant cause of wireless network problems is interference in the form of narrowband continuous wave (CW) signals, narrowband sweeping signals, and passive intermodulation distortion (PIM). Of these three interference sources, PIM may be particularly problematic for FDD wireless network <NUM> in which RE <NUM> of base station <NUM>/<NUM> receives uplink radio signals 104a and 104b while concurrently transmitting downlink transmission signals 106a and 106b at significantly greater power. For example, in a <NUM> LTE wireless network, downlink transmission signals 106a and 106b may be up to approximately one hundred and thirty decibels (<NUM> dB) stronger than uplink transmission signals 104a and 104b.

As further stated above, PIM is typically the result of non-linearities that enable more powerful downlink transmission signals 106a and 106b to create interference in the receiver of RE <NUM> at the frequency for weaker uplink transmission signals 104a and 104b. The effect of PIM is to reduce the SINR at the receiver of RE <NUM>. <FIG> shows exemplary graph <NUM> of the effects of PIM on the SINR and capacity in FDD wireless network <NUM>. As shown by traces <NUM> and <NUM> in <FIG>, reduction in SINR can severely limit the ability to receive signals.

The overall effect of PIM is to reduce the transmission capacity of RAN <NUM>, as uplink transmission signals 104a and 104b from some of UEs 102a/ 102b can still be received by RE <NUM> of base station <NUM>/<NUM>, but only UEs 102a/102b that are relatively close. UEs 102a/102b that are farther away from RE <NUM> may suffer a communication drop, slower data throughput, or even no data throughput at all. When PIM is sufficiently severe, reception at the receiver of RE <NUM> may not be possible during transmission by the transmitter of RE <NUM>.

<FIG> shows exemplary diagram <NUM> A of PIM caused by two signals at different frequencies. As shown in <FIG>, intermodulation (IM) causes input frequencies 420a and 420b to create other signals, i.e., IM products, at new frequencies. The frequency of these IM products depends on the frequencies of input signals 420a and 420b. The frequencies of the IM products can be predicted based on combinations of input frequencies 420a and 420b from transmitters of RE <NUM>. For example, the frequency of IM product 425b may be three times the frequency of input signal 420b minus two times the frequency of input signal 420a (i.e., <NUM>*420b - <NUM>*420a), while the frequency IM product 423a may be twice the frequency of input signal 420a minus the frequency of input signal 420b (i.e., <NUM>*420a - 420b).

It is noted that the sum of the numbers used to multiply the input frequencies 420a and 420b to produce an IM product is called the intermodulation order. Thus, IM product 425a is a fifth order (<NUM> + <NUM>) intermodulation signal, as is IM product 425b. By contrast IM product 423a is a third order intermodulation signal (<NUM> + <NUM>), as is IM product 423b. Although an infinite number of IM products can be defined, their amplitudes drop rapidly as their order increases, so that higher order IM products become insignificant.

Modulated signals can also cause PIM, and can generate IM products that typically have a larger frequency range than IM products resulting from non- modulated input signals. Also the frequency ranges of the IM products resulting from modulated signals get progressively wider as their order increases. Diagram 400B in <FIG>, depicts PIM caused by a single modulated signal. It is noted that PIM may be caused by a single modulated signal, or by multiple modulated signals.

PIM produced by single modulated signal <NUM> may be multiple signals that are close in frequency, or may be modeled as multiple signals that are close in frequency. In <NUM> LTE, for example, there are multiple subcarriers included as part of the transmitted <NUM> LTE signal. As shown in <FIG>, third order IM products <NUM>, fifth order IM products <NUM>, and seventh order IM products <NUM> from single modulated signal <NUM> are close in frequency to signal <NUM>. Moreover, as their order increases, the frequency band of the IM products get wider and their power level reduces.

It is noted that the narrower the modulation of modulated input signal <NUM>, the narrower the frequency ranges of the IM products are as well. In addition, reduction in the power of modulated input signal <NUM> results in the amplitudes of higher order IM products being reduced faster than the amplitude of modulated input signal <NUM>. For example, if modulated input signal <NUM> is reduced by ten percent (<NUM>%) third order IM products <NUM> are reduced by approximately <NUM>%, fifth order IM products <NUM> are reduced by approximately <NUM>%, and seventh order IM products <NUM> are reduced by approximately <NUM>%. It is further noted that the shapes of the IM products of modulated input signal <NUM> are not accurately depicted in <FIG>, but rather will gradually slope away in frequency from the frequency of modulated input signal <NUM>. One conventional approach to reducing the interference produced by PIM is through downlink power reduction. Because, as discussed above, the IM products reduce in power faster than the transmitted power, a small power reduction can help with PIM problems. Although effective in reducing PIM interference, reducing transmitted power also reduces the coverage of RAN <NUM>. In some use cases the reduction in coverage can be compensated for by changing the tilt of antenna <NUM>/<NUM> and increasing power to adjacent wireless network cells. However, sometimes that conventional interference mitigation solution cannot be implemented, or does not provide adequate interference mitigation.

<FIG> shows diagram 500A of base station 510A communicatively coupled to device <NUM> configured to perform automated interference mitigation in FDD wireless network <NUM>, according to one exemplary implementation. As shown in <FIG>, base station 510A is communicatively coupled to other elements <NUM> of FDD wireless network <NUM>, in <FIG>, as well as to interference analyzer <NUM> and device <NUM> configured to provide automated interference mitigation for FDD wireless network <NUM>. As further shown in <FIG>, base station 510A includes transmit and receive antenna <NUM>, RE <NUM>, and REC <NUM> including scheduler <NUM>. Also shown in <FIG> are uplink communication channel <NUM> supporting uplink data communications from RE <NUM> to REC <NUM>, and downlink communication channel <NUM> supporting downlink data communications from REC <NUM> to RE <NUM>.

Base station 510A having antenna <NUM> corresponds in general to base station <NUM>/<NUM> having antenna <NUM>/<NUM>, in <FIG> and <FIG>. That is to say, base station <NUM>/<NUM> may share any of the characteristics attributed to base station 510A by the present disclosure, and vice versa. Thus, RE <NUM>, REC <NUM> including scheduler <NUM>, uplink communication channel <NUM> and downlink communication channel <NUM>, in <FIG>, correspond respectively in general to RE <NUM>, REC <NUM> including scheduler <NUM>, uplink communication channel <NUM> and downlink communication channel <NUM>, in <FIG>. In addition, and although not shown in <FIG>, base station <NUM> may include features corresponding to RE <NUM>/<NUM>, REC <NUM>/<NUM> including scheduler <NUM>/<NUM>, uplink communication channel <NUM>/<NUM>, and downlink communication channel <NUM>/<NUM>.

Like RE <NUM>, RE <NUM> transmits downlink transmission signal 106a and 106b to UE 102a/ 102b and receives uplink transmission signals 104a and 104b from UE 102a/ 102b. Also like RE <NUM>, RE <NUM> may have multiple transmitters and receivers at the same frequency, for diversity or for MIMO functionality. Like REC <NUM>, REC <NUM> processes the baseband modulation data in the mathematical format of I/Q vectors. As discussed above, in downlink communication channel <NUM>/<NUM>, the I/Q data has no distortion because it has not yet been subjected to the effects of the environment of RAN <NUM> or to any other sources of distortion. However, in uplink communication channel <NUM>/<NUM>, the I/Q data contains uplink transmission signals 104a and 104b created by UE 102a/ 102b plus the environmental effects of RAN <NUM>, e.g., path loss and fading effects, as well as distortion from interference sources.

According to the exemplary implementation shown in <FIG>, device <NUM> may be co-located with or may be integrated with interference analyzer <NUM> and may be configured to use interference analyzer <NUM> to provide automated interference mitigation for base station <NUM>/<NUM>/<NUM> A of FDD wireless network <NUM>. Interference analyzer <NUM> monitors the communication between RE <NUM>/<NUM> and REC <NUM>/<NUM> by sampling data transferred via uplink communication channel <NUM>/<NUM> and downlink communication channel <NUM>/<NUM>. That data is typically transferred over fiber optic connections, but other connections are possible, such as wireless connections, for example. Thus, the network medium having uplink communication channel <NUM>/<NUM> supporting uplink data communications from RE <NUM>/<NUM> to REC <NUM>/<NUM> and also having downlink communication channel <NUM>/<NUM> supporting downlink data communications from REC <NUM>/<NUM> to RE <NUM>/<NUM> may take the form of a fiber optic or other wired connection, or a wireless connection.

It is noted that the described monitoring of communication between RE <NUM>/<NUM> and REC <NUM>/<NUM> may be triggered by alarms from FDD wireless network <NUM>, may be performed in response to an input by a network operator, or may be performed during automated scanning among the connections between REC <NUM>/<NUM> and RE <NUM>/<NUM>.

In implementations in which the network medium having uplink communication channel <NUM>/<NUM> and downlink communication channel <NUM>/<NUM> is a fiber optic connection, the I/Q data sampled from uplink communication channel <NUM>/<NUM> and downlink communication channel <NUM>/<NUM> may be converted from optical format to electrical format. For example such a conversion may be performed using optical to electrical converter <NUM> of interference analyzer <NUM>. The I/Q data in the electrical format may then be fed into high speed digital signal processor (DSP) <NUM>.

DSP <NUM> of interference analyzer <NUM> may take the form of a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), for example, configured to perform various operations to extract information about the performance of RAN <NUM>. The data generated by DSP <NUM> may be passed to analysis unit <NUM> for additional processing, such as the automated analysis and identification of interference sources, as well as storage of I/Q data and traces for further analysis.

<FIG> shows diagram 500B in which device <NUM> configured to perform automated interference mitigation in FDD wireless network <NUM> is co-located with or integrated with REC <NUM>/<NUM> of base station 510B, according to another exemplary implementation. It is noted that any feature in <FIG> identified by a reference number identical to one shown in <FIG> A corresponds respectively to that previously described feature and may share any of the characteristics attributed to it by the present disclosure. Moreover, base station 510B corresponds in general to base station 510A, in <FIG>, as well as to base station <NUM>/<NUM> in <FIG> and <FIG>. That is to say, base station 510B may share any of the characteristics attributed to base station <NUM>/<NUM>/510A by the present disclosure, and vice versa.

The implementation shown in <FIG> differs from the implementation shown in <FIG> A with respect to the location and communicative coupling of device <NUM>. In the implementation shown in <FIG>, device <NUM> is co-located with or integrated with interference analyzer <NUM> while being in remote communication with REC <NUM>/<NUM> of base station <NUM>/<NUM>/510A. By contrast, in the implementation shown in <FIG>, device <NUM> is co-located with or integrated with REC <NUM>/<NUM> of base station <NUM>/<NUM>/510B while being in remote communication with interference analyzer <NUM>.

In either of the implementations shown in <FIG> and <FIG>, and as discussed in greater detail below, device <NUM> may utilize interference analyzer <NUM> to determine and implement an interference mitigation strategy in an automated process. For example, device <NUM> may communicate with scheduler <NUM>/<NUM> of REC <NUM>/<NUM> to adjust the power, and/or bandwidth, and/or timing of downlink signals transmitted in downlink communication channel <NUM>/<NUM>, i.e., signals for producing downlink transmission signals 106a and 106b by RE <NUM>/<NUM>, in order to reduce or otherwise mitigate interference resulting from PIM, narrowband CW signals, or narrowband sweeping signals.

<FIG> shows an exemplary diagram of the device configured to perform automated interference mitigation shown in <FIG> and <FIG>, according to one implementation. As shown in <FIG>, device <NUM> includes hardware processor <NUM> and memory <NUM> implemented as a non-transitory storage medium. As further shown in <FIG>, memory <NUM> stores interference mitigation software code <NUM>, which, when executed by hardware processor <NUM> of device <NUM>, instantiates a method for performing automated interference mitigation in FDD wireless network <NUM>. Device <NUM> corresponds in general to device <NUM>, in <FIG> and <FIG>. That is to say, device <NUM> may share any of the characteristics attributed to device <NUM> by the present disclosure, and vice versa. Thus, although not shown in <FIG> and <FIG>, device <NUM> may include features corresponding respectively to hardware processor <NUM>, memory <NUM>, and interference mitigation software code <NUM>.

It is noted that, although the present application refers to interference mitigation software code <NUM> as being stored in memory <NUM> of device <NUM>/<NUM> for conceptual clarity, more generally, memory <NUM> may take the form of any computer- readable non-transitory storage medium. The expression"computer-readable non- transitory storage medium," as used in the present application, refers to any medium, excluding a carrier wave or other transitory signal that provides instructions to a hardware processor, such as hardware processor <NUM> of device <NUM>/<NUM>. Thus, a computer-readable non-transitory medium may correspond to various types of media, such as volatile media and non-volatile media, for example. Volatile media may include dynamic memory, such as dynamic random access memory (dynamic RAM), while non-volatile memory may include optical, magnetic, or electrostatic storage devices. Common forms of computer-readable non-transitory media include, for example, optical discs, RAM, programmable read-only memory (PROM), erasable PROM (EPROM), and FLASH memory.

The functionality of device <NUM>/<NUM> will be further described by reference to <FIG> in combination with <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>. <FIG> shows flowchart <NUM> presenting an exemplary method for use in FDD wireless network <NUM> for automating interference mitigation, according to one implementation. With respect to the method outlined in <FIG>, it is noted that certain details and features have been left out of flowchart <NUM> in order not to obscure the discussion of the inventive features in the present application.

Referring now to <FIG> in combination with <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, flowchart <NUM> begins with identifying an uplink frequency spectrum in uplink communication channel <NUM>/<NUM> having transmission signal 104a and/or 104b that is being affected by an interfering signal (action <NUM>). Identification of the uplink frequency spectrum in uplink communication channel <NUM>/<NUM> having transmission signal 104a and/or 104b that is being affected by the interfering signal may be performed by interference mitigation software code <NUM>, for example, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM>.

As discussed above, uplink communication channel <NUM>/<NUM> and downlink communication channel <NUM>/<NUM> carry I/Q data providing a digital representation of the analog modulation included in uplink transmission signals 104a and 104b, and downlink transmission signals 106a and 106b, respectively. The I/Q data sampled from uplink communication channel <NUM>/<NUM> and downlink communication channel <NUM>/<NUM> may be fed into DSP <NUM>, which can perform various operations to extract information about the performance of RAN <NUM>, including identifying the uplink frequency spectrum being affected by the interfering signal. Thus, identifying the uplink frequency spectrum in uplink communication channel <NUM>/<NUM> having transmission signal 104a and/or 104b that is being affected by the interfering signal can be based on I and Q components of the uplink data communications from RE <NUM>/<NUM> to the REC <NUM>/<NUM>, i.e., the I and Q components within a receiver of base station <NUM>/<NUM>/<NUM> A/<NUM> OB.

Flowchart <NUM> continues with determining an uplink power level of the interfering signal in uplink communication channel <NUM>/<NUM> having transmission signal 104a and/or 104b (action <NUM>). Determination of the uplink power level of the interfering signal in uplink communication channel <NUM>/<NUM> having transmission signal 104a and/or 104b may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM>. For example, the data generated by DSP <NUM> as part of action <NUM> may be passed to analysis unit <NUM> of interference analyzer <NUM> for additional processing, which may include determination of the uplink power level of the interfering signal.

Flowchart <NUM> continues with determining whether the interfering signal is caused by PIM (action <NUM>). As discussed above, PIM can be especially problematic as an interference source in FDD wireless network <NUM>. Moreover, in some cases, the effects of PIM in FDD wireless network <NUM> can be dynamic. That is to say, PIM levels can change with time, and in some cases change rapidly due to environmental changes such as wind or changes in sunlight due to clouds. Consequently, the real- time measurement of the PIM level can facilitate using the available transmission capability optimally to mitigate PIM at each moment in time.

A solution enabling real-time identification and measurement of PIM is disclosed in <CIT>. Action <NUM> may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM> and the solution disclosed by <CIT>.

Real-time measurement of PIM can be important because if PIM is small, little or no mitigation may be necessary. By contrast, if PIM is severe, more aggressive mitigation techniques are typically required. In the process of measuring PIM, access to downlink transmission signals 106a and 106b transmitted by RE <NUM>/<NUM> and uplink transmission signals 104a and 104b received by RE <NUM>/<NUM> can be very helpful, and in some cases may be necessary. It is noted that PIM may be measured or estimated in a variety of ways.

For example, if there are no transmissions by UE 102a/ 102b, it may be relatively easy to correlate the uplink signal level seen in uplink communication channel <NUM>/<NUM> with the power transmitted in downlink communication channel <NUM>/<NUM>. The absence of transmissions by UE 102a/102b could be the result of REC <NUM>/<NUM> causing scheduler <NUM>/<NUM> to not schedule such transmissions during a particular time interval. In a <NUM> LTE wireless network, for example, such scheduling would result in only relatively rare physical random access channel (PRACH) transmissions as well as transmission of small signals intended to be received by neighboring cells during that scheduling interval.

If it is necessary to have transmissions by UE 102a/ 102b and PIM is very high, it may also be relatively easy to determine the level of PIM. However, that set of circumstances is undesirable because RE <NUM>/<NUM> may be rendered substantially unable to detect transmissions by UE 102a/102b.

Measurement of PIM is more challenging and complex if PIM is low and many transmissions by UE 102a/102b are occurring. Those circumstances might by present, for example, after a PIM mitigation strategy has been applied, or as a way to monitor the level of PIM before it becomes too large. In those cases, the PIM level may be measured by correlating uplink transmission signal 104a and 104b signal with a mathematical model of PIM applied to downlink transmission signals 106a and 106b.

In that case, the processing gain of the correlation can be used to extract an estimate of the level of PIM. That is to say, the correlation will vary with the level of uplink transmission signals 104a and 104b as well as the PIM level, and the total signal level (mostly transmissions by UE 102a/102b + PIM) is easy to measure. As a result, an estimate of the PIM level can be achieved by measuring those two quantities. If the correlation is high, almost all of the uplink power is coming from PIM. However, if the correlation is low, nearly none of the uplink power is coming from PIM.

Flowchart <NUM> continues with, in response to determining that that the interfering signal is caused by PIM, adjusting, based on the uplink frequency spectrum of the interfering signal identified in action <NUM> and the uplink power level of the interfering signal determined in action <NUM>, one or more of a downlink power level of a downlink signal being transmitted in downlink communication channel <NUM>/<NUM> and a downlink frequency range in downlink communication channel <NUM>/<NUM> (action <NUM>).

In situations in which PIM is severe, scheduler <NUM>/<NUM> of REC <NUM>/<NUM>, which decides when downlink transmission signals 106a and 106b and uplink transmission signals 104a and 104b are to be transmitted, could reduce transmissions in the downlink to allow better reception for uplink transmission signals 104a and 104b. Such a reduction of downlink transmissions could occur in several ways in addition to simply reducing downlink transmission power.

For example, a reduction in downlink transmissions can be the result of scheduling no transmissions at all during intermittent time intervals. In a <NUM> LTE wireless network, for instance, such intermittent time intervals may correspond to LTE downlink subframes, while in a <NUM> wireless network such intermittent time intervals may be measured as slots. This interference mitigation strategy would cause FDD wireless network <NUM> to operate more like a time division duplex (TDD) wireless network. It is noted that there would typically be some power transmitted even during the time intervals when no transmissions are scheduled due to needed control channels, but those transmissions would be at substantially lower power levels. This interference mitigation solution allows RE <NUM>/<NUM> to receive more transmissions by UE 102a/102b, due to much lower PIM levels during the intermittent time intervals when no transmissions are scheduled.

Thus, in some implementations, in response to determining that that the interfering signal is caused by PIM, the downlink signal being transmitted in downlink communication channel <NUM>/<NUM> may be substantially minimized during multiple intermittent time intervals by scheduling no downlink signal transmission during those intermittent time intervals. Moreover, where FDD wireless network <NUM> is a <NUM> LTE network, substantially minimizing the downlink signal being transmitted in downlink communication channel <NUM>/<NUM> during the multiple intermittent time intervals may be the result of scheduling no downlink signal transmission during some LTE downlink subframes.

As another example, a reduction in downlink transmissions can result from reducing the downlink frequency range of the downlink signal being transmitted in downlink communication channel <NUM>/<NUM>, which makes the intermodulation order needed for an IM product to appear in uplink communication channel <NUM>/<NUM> higher, thereby tending to reduce the level of PIM as can be seen from <FIG> and <FIG>. In the case of <NUM> LTE, for example, the modulation bandwidth can be made narrower by scheduling no transmissions for some of the <NUM> LTE resource blocks (RBs), e.g., the outermost resource blocks, which are units of time and frequency used for scheduling downlink transmissions.

<FIG> shows exemplary RBs 800A of a downlink signal, according to one implementation. As shown by <FIG>, the spectrum of downlink transmission RBs 800A includes RB(<NUM>,<NUM>), RB(<NUM>,<NUM>), RB (<NUM>,<NUM>), RB (<NUM>,<NUM>) RB(<NUM>,<NUM>), RB (<NUM>,<NUM>). , RB(M-<NUM>,N-l), RB(M-<NUM>,N-<NUM>), RB(M-<NUM>,N), RB(M-<NUM>,N), RB(M,N-<NUM>), and RB(M,N) (hereinafter"downlink transmission RB(<NUM>,<NUM>)-RB(M,N)"), where"M" is an integer identifying the <NUM> LTE subframe or <NUM> slot, and"N" is an integer identifying a <NUM> LTE or <NUM> subband. As a specific example, in <NUM> LTE, each of downlink transmission RB(x,<NUM>)-RB(x,N) may include twelve <NUM> LTE subcarriers having a frequency range of fifteen kilohertz (<NUM>) each, where"x" may assume any integer value from zero to M, inclusive. Thus, each of downlink transmission RB(x,<NUM>)- RB(x,N) may correspond to a frequency range of <NUM>.

Under normal operating conditions, that is to say low or negligible PIM or other network interference, the power allocated to each of downlink transmission RB(<NUM>,<NUM>)-RB(M,N) may be substantially equal, as shown by the uniform shading of downlink transmission RB(<NUM>,<NUM>)-RB(M,N) in <FIG>. However, and as noted above, the modulation bandwidth of downlink transmissions can be made narrower by scheduling no transmissions for some of the outermost frequencies of downlink transmission RB(<NUM>,<NUM>)-RB(M,N). For example, referring to RBs 800B, in <FIG>, the number of downlink transmission RBs used by RE <NUM>/<NUM> to transmit downlink transmission signals 106a and 106b may be reduced by scheduling no transmissions for downlink transmission RB(x,<NUM>) and RB(x,N), where again"x" may assume any integer value from zero to M, inclusive thereby restricting downlink transmission to RB(<NUM>,<NUM>)-RB(M,N-<NUM>), and thereby also reducing downlink power level.

This reduces the bandwidth of the IM products as well as reducing the bandwidth of desired downlink transmission signals 106a and 106b. Because the lowest order IM product at the frequency of uplink transmission signals 104a and 104b (i.e., the strongest IM product at that frequency) comes from the highest and lowest frequencies in downlink transmission signals 106a and 106b, not scheduling a few of the highest frequency and/or lowest frequency downlink transmission RBs (i.e., turning them off, or nearly so) results in only higher order IM products being present in the uplink frequency range. Since higher order IM products are lower in power than lower order IM products, the level of PIM should be reduced.

Thus, in some implementations, in response to determining that the interfering signal is caused by PIM, adjusting the power level of the downlink signal being transmitted in downlink communication channel <NUM>/<NUM> may include reducing the number of downlink transmission RBs used by RE <NUM>/<NUM> to transmit downlink transmission signals 106a and 106b. In addition, or alternatively, in response to determining that the interfering signal is caused by PIM, adjusting the downlink frequency range of the downlink signal being transmitted in downlink communication channel <NUM>/<NUM> may include turning off one or more downlink transmission RBs at an extreme frequency of the downlink frequency range.

In choosing what downlink transmission RBs to not schedule, it may be more effective to choose downlink transmission RBs that are closest to the frequency of uplink transmission signals 104a and 104b. This is due to the mathematical relationship amongst the respective frequencies of the IM products. For example, referring to <FIG>, if the IM product comes from <NUM>*420b - 420a, a reduction in signal 420b (from not scheduling those downlink frequency RBs for transmission) reduces the highest frequency of IM twice as fast as increasing signal 420a. Not scheduling those downlink frequency RBs may also reduce the overall transmission power somewhat, additionally reducing the PIM problem, while still enabling the transmission of significant information.

Alternatively, the power to the scheduled downlink transmission RB(<NUM>,<NUM>)- RB(M,N-l) can be increased somewhat, allowing a higher modulation and coding scheme (MCS) for downlink transmissions. Those transmissions can be of either data or control signals. Both data transmissions and most of the control signals in <NUM> LTE, for example, (everything except the Reference Signal or RS) can be scheduled away from the outermost downlink transmission RBs when necessary. It may even be possible to reduce the power of the RS in those downlink transmission RBs as well.

A simple but inefficient way to reduce downlink frequency range is to change the nominal channel bandwidth of downlink operation, such as from <NUM> to <NUM> for example. Although reducing downlink frequency range in this way has the added benefit of not transmitting any RS, it is typically less efficient than turning off a few downlink transmission RBs. Nevertheless, this simple but generally inefficient technique may be advantageous or desirable in some extreme situations.

In some cases, it may be advantageous or desirable to vary the power of different downlink transmission RBs. REC <NUM>/<NUM> could lower the power to some downlink transmission RBs, i.e., downlink transmission RB(<NUM>,<NUM>), RB(l,<NUM>), RB(<NUM>,l), RB(M-<NUM>,<NUM>), RB(M,<NUM>), RB(M,l), RB(<NUM>,N-l), RB(<NUM>,N), RB(<NUM>,N), RB(M,N-l), RB(M- <NUM>,N), and RB(M,N), as shown by RBs 800C, in <FIG>, and only use those downlink transmission RBs to transmit to UEs 102a/102b that are close to RE <NUM>/<NUM>. Meanwhile the innermost downlink transmission RBs, i.e., downlink transmission RB(<NUM>,l)-RB(M-<NUM>,N-l) could be transmitted at higher power, potentially allowing transmissions to UE 102a/ 102b that are farther away, or using higher MCS for faster throughput. Thus, in some implementations, in response to determining that the interfering signal is caused by PIM, adjusting the power level of the downlink signal being transmitted in downlink communication channel <NUM>/<NUM> may include decreasing the power level of some downlink transmission RBs relative to other downlink transmission RBs.

The scheduling of downlink transmissions can also be dynamically adjusted, both in power and bandwidth, depending on the need for uplink transmissions and the level of PIM. For example, if no uplink transmissions are needed, the downlink can be scheduled for full bandwidth at full power, while if many uplink transmissions are needed, the downlink can be reduced in power, bandwidth, or both.

The scheduling for PIM reduction can also be refined by knowledge of the transmission channel for different UEs 102a/ 102b. There are several possible sources for this information. For example, UE 102a/ 102b can transmit reference signals for measuring the transmission channel. Some UEs need to transmit at higher power or with a lower MCS, as controlled by REC <NUM>/<NUM>. REC <NUM>/<NUM> may also control the timing advance of UE 102a/102b, which gives a coarse measure of the distance from UE 102a/ 102b to RE <NUM>/<NUM> since transmitted signals reduce in amplitude approximately as a function of the distance squared. This estimated distance of UE 102a/ 102b from RE <NUM>/<NUM> provides a rough prediction of the transmission difficulty of UE 102a/102b to RE <NUM>/<NUM>. As a result, and because as discussed above PIM does not affect the entire uplink frequency range equally, UE 102a/ 102b with a more difficult transmission channel could be scheduled to transmit using portions of the uplink frequency range that are less affected by PIM, i.e., typically frequencies that are farther away from the frequency of downlink transmission signal 106a and 106b.

A further refinement may be necessary in use cases in which RE <NUM>/<NUM> is required to transmit acknowledgements of reception. In severe cases of PIM even this small transmission could cause problems in uplink reception. One interference mitigation strategy for addressing the problems introduced by the requirement of reception acknowledgements is to schedule downlink transmission at the same times (e.g., in the same <NUM> LTE subframe) as transmission of reception acknowledgements.

An additional challenge arises because some transmissions from UE 102a/ 102b are unscheduled and therefore not entirely controlled by REC <NUM>/<NUM>. Nevertheless, REC <NUM>/<NUM> may be able to exercise some control over such unscheduled transmission from UE 102a/ 102b. In <NUM> LTE, for example, there is a configuration index (Cl) for the PRACH mentioned above, which can limit when unscheduled transmissions by UE 102a/ 102b are sent. By using a Cl that invokes some limits on these unscheduled transmissions, and taking account of those limits when scheduling for reduced PIM, the problems that can potentially arise due to unscheduled transmissions from UE 102a/ 102b can be avoided.

In addition, the frequency of the transmission for the PRACH can be controlled by the CL Since PIM often has a significant slope across the uplink frequency range, having the PRACH be transmitted on the frequency with lower PIM can help. Moreover, various combinations of the interference mitigation strategies described above are also possible, such as reducing the downlink frequency range slightly while also reducing the downlink power level slightly.

Adjustment of one or more of the downlink power level of the transmission signal 106a and/or 106b and the downlink frequency range of downlink transmission signal 106a and/or 106b based on the uplink frequency spectrum of the interfering signal identified in action <NUM> and the uplink power level of the interfering signal determined in action <NUM>, in response to determining that that the interfering signal is caused by PIM, may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using REC <NUM>/<NUM>.

In some implementations, flowchart <NUM> may conclude with action <NUM> described above. However, in other implementations, flowchart <NUM> may continue with determining whether the interfering signal is external to FDD wireless network <NUM> (action <NUM>). For example, and as discussed above, in addition to PIM, another source of wireless network interference may be narrowband CW signals. Such narrowband CW signals may originate from transmitters external to FDD wireless network <NUM>, i.e., from foreign transmitters. Determination that the interfering signal is a narrowband CW signal external to wireless network <NUM> may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM>.

Flowchart <NUM> may then further continue with, in response to determining that the interfering signal is external to FDD wireless network <NUM>, selectively scheduling uplink transmissions to avoid the interfering signal (action <NUM>). One solution for mitigating narrowband CW interference is disclosed in <CIT>. Action <NUM> may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM> and the solution disclosed by <CIT>.

In some cases, a source of wireless network interference may be a narrowband sweeping signal external to FDD wireless network <NUM>, such as a narrowband signal having a time varying bandwidth. In those cases, the method outlined by flowchart <NUM> may further include determining, in response to determining that the interfering signal is external to FDD network <NUM>, whether the frequency spectrum of the interfering signal changes as a function of time. Such a determination may be made by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using interference analyzer <NUM>.

Moreover, and in response to determining that the frequency spectrum of the interfering signal does change as a function of time, hardware processor <NUM> of device <NUM>/<NUM> may further execute interference mitigation software code <NUM> to utilize interference analyzer <NUM> to identify the rate of change with respect to time of the frequency spectrum of the interfering signal. The narrowband sweeping signal interference external to FDD wireless network <NUM> may then be mitigated by selectively scheduling uplink transmissions to avoid the interfering signal based on the rate of change with respect to time of the frequency spectrum of the interfering signal. Such selective scheduling of uplink transmissions may be performed by interference mitigation software code <NUM>, executed by hardware processor <NUM> of device <NUM>/<NUM>, and using REC <NUM>/<NUM> including scheduler <NUM>/<NUM>.

It is noted that in some use cases, it may be advantageous or desirable to utilize other mitigation techniques, either in addition to or as one or more alternatives to the mitigation solution outlined by flowchart <NUM>. For example, and as discussed above, the Cl may be utilized to avoid interference between PIM and PRACFI communications. As another interference mitigation technique, uplink transmissions may be scheduled at edges of the uplink frequency range to avoid PIM, or at other specific frequencies to avoid narrow-bank CW or sweeping interference signals. As yet another interference mitigation technique, difficult transmissions, i.e., those from UE that are far away, may be scheduled to occur during low-PIM <NUM> LTE subframes or <NUM> slots with reduced bandwidth or no downlink transmissions.

Claim 1:
A method for use in a frequency division duplex wireless network (<NUM>) including a base station (<NUM>) and a user equipment (102a) being in communication through a medium having an uplink communication channel (104a) supporting uplink data communications from the user equipment (102a) to the base station (<NUM>), and a downlink communication channel (106a) supporting downlink data communications from the base station (<NUM>) to the user equipment (102a), the method comprising:
identifying, by an interference analyzer (<NUM>), an uplink frequency spectrum in the uplink communication channel (104a) being affected by an interfering signal;
determining, by the interference analyzer (<NUM>), whether the interfering signal is external to the frequency division duplex wireless network; and
in response to determining that that the interfering signal is external to the frequency division duplex wireless network, determining whether a frequency spectrum of the interfering signal changes as a function of time;
in response to determining that the frequency spectrum of the interfering signal changes as a function of time, identifying a rate of change with respect to time of the frequency spectrum of the interfering signal; and
selectively scheduling uplink transmissions to avoid the interfering signal based on the rate of change with respect to time of the frequency spectrum of the interfering signal.