DCT

2:24-cv-00195

Smart RF Inc v. AT&T Mobility LLC

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 2:24-cv-00195, E.D. Tex., 03/19/2024
  • Venue Allegations: Plaintiff alleges venue is proper because Defendant is subject to personal jurisdiction, has committed acts of infringement in the district, and maintains regular and established places of business in the district, including retail stores and its "AT&T Foundry" in Plano, Texas.
  • Core Dispute: Plaintiff alleges that Defendant’s cellular network base stations, which utilize digital pre-distortion technology, infringe five patents related to methods and systems for linearizing radio frequency (RF) power amplifiers.
  • Technical Context: Digital pre-distortion (DPD) is a critical technology in modern wireless communications (4G/5G) that allows power amplifiers in cellular base stations to operate more efficiently while maintaining the signal linearity required by complex transmission standards.
  • Key Procedural History: The complaint does not mention any prior litigation, Inter Partes Review (IPR) proceedings, or licensing history related to the Asserted Patents.

Case Timeline

Date Event
2001-06-08 Priority Date for U.S. Patent No. 7,035,345
2006-04-25 Issue Date for U.S. Patent No. 7,035,345
2006-12-01 Priority Date for U.S. Patent No. 8,078,561
2010-05-14 Priority Date for U.S. Patent No. 8,767,857
2011-10-14 Priority Date for U.S. Patent Nos. 9,641,204 and 10,958,296
2011-12-13 Issue Date for U.S. Patent No. 8,078,561
2014-07-01 Issue Date for U.S. Patent No. 8,767,857
2017-05-02 Issue Date for U.S. Patent No. 9,641,204
2021-03-23 Issue Date for U.S. Patent No. 10,958,296
2024-03-19 Complaint Filing Date

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 7,035,345 - "Adaptive predistortion device and method using digital receiver"

  • Issued: April 25, 2006

The Invention Explained

  • Problem Addressed: The patent describes the fundamental trade-off in RF power amplifiers (PAs) between power efficiency and signal linearity. Operating a PA near its saturation point increases efficiency but introduces nonlinear distortions that degrade signal quality, which is particularly problematic for high-crest-factor signals used in standards like CDMA (’345 Patent, col. 1:10-30).
  • The Patented Solution: The invention proposes an adaptive predistortion system that uses two digital receivers for "instantaneous characterization" of the PA ('345 Patent, Abstract). As depicted in Figure 1 of the patent, a first digital receiver samples the pre-distorted signal before it enters the PA, and a second digital receiver samples the amplified signal at the PA's output. A control module compares the complex envelopes of these two signals to model the PA's nonlinear behavior and memory effects in real time, then dynamically updates amplitude and phase look-up tables in a "distorting generator" to continuously correct the signal ('345 Patent, col. 5:5-30; Fig. 1).
  • Technical Importance: The use of digital receivers to create a real-time, adaptive feedback loop for PA linearization was a key enabling technique for transmitters that needed to handle the complex, wide-bandwidth signals of 3G and later wireless standards while maximizing power efficiency (Compl. ¶10).

Key Claims at a Glance

  • The complaint asserts at least independent method claim 13 and illustratively analyzes infringement of independent method claim 1 (Compl. ¶¶26-27). The elements of claim 1 are:
    • predistorting the RF modulated signal to be transmitted using an I/Q modulator... controlled by means of amplitude and phase look-up tables stored in a distorting generator;
    • producing, via a first digital receiver, a first feedback signal in response to the RF predistorted signal;
    • producing, via a second digital receiver, a second feedback signal in response to the RF amplified output signal from the power amplifier;
    • modeling the power amplifier in response to the first and second feedback signals; and
    • updating the predistortion amplitude and phase look-up tables in response to said modeling of the power amplifier.
  • The complaint expressly reserves the right to assert additional claims (Compl. ¶26, fn. 3).

U.S. Patent No. 8,767,857 - "Multi-cell processing architectures for modeling and impairment compensation in multi-input multi-output systems"

  • Issued: July 1, 2014

The Invention Explained

  • Problem Addressed: In Multiple-Input Multiple-Output (MIMO) systems, which use multiple transmitters and antennas, signal quality is degraded not only by nonlinearities within each signal path but also by "crosstalk," or interference, between the different paths (’857 Patent, col. 3:9-19). Conventional single-path linearization techniques do not account for these complex inter-path interactions (Compl. ¶14).
  • The Patented Solution: The invention describes a pre-compensator architecture based on a "matrix of pre-processing cells" ('857 Patent, Abstract). Each cell in the matrix is designed to model and correct the specific distortions—including both self-distortion and crosstalk from other paths—for a given input-to-output signal path combination ('857 Patent, col. 3:56-66; Fig. 5). This matrix structure allows the system to simultaneously compensate for the impairments of individual transmitters and the coupled interference between them.
  • Technical Importance: This matrix-based architecture provided a conceptual framework for linearizing complex MIMO and multi-band transmitters, which are fundamental to achieving the higher data rates and spectral efficiency of modern 4G and 5G networks (Compl. ¶14).

Key Claims at a Glance

  • The complaint asserts at least independent method claim 1 (Compl. ¶39). The essential elements are:
    • receiving a plurality of input signals forming a multiple-input signal in a multiple-input multiple-output system;
    • generating a pre-distorted multiple-input signal from the received multiple-input signal;
    • generating a multiple-output signal by feeding the pre-distorted multiple-input signal into a multiple-input and multiple-output transmitter;
    • estimating impairments generated by the... transmitter, the impairments comprising nonlinear crosstalk between distinct ones of the plurality of input signals; and
    • adjusting the pre-distorted multiple-input signal to compensate for the estimated impairments, wherein generating the pre-distorted... signal comprises feeding the received... signal to a matrix of pre-processing cells...
  • The complaint expressly reserves the right to assert additional claims (Compl. ¶39, fn. 3).

U.S. Patent No. 9,641,204 - "Digital multi-band predistortion linearizer with non-linear subsampling algorithm in the feedback loop"

  • Issued: May 2, 2017 (Compl. ¶18)
  • Technology Synopsis: This patent addresses the problem of efficiently monitoring the output of a multi-band power amplifier for predistortion (’204 Patent, col. 2:1-13). The invention proposes using a feedback loop with a single subsampling receiver that can concurrently sample multiple amplified RF signals at a frequency lower than the Nyquist rate, simplifying the hardware required for the feedback path ('204 Patent, col. 2:45-54).
  • Asserted Claims: At least independent claim 1 (Compl. ¶52).
  • Accused Features: The accused base stations allegedly include a signal observation feedback loop configured for concurrent sampling of amplified multi-band signals at a subsampling frequency (Compl. ¶¶55-56).

U.S. Patent No. 10,958,296 - "Digital multi-band predistortion linearizer with non-linear subsampling algorithm in the feedback loop"

  • Issued: March 23, 2021 (Compl. ¶19)
  • Technology Synopsis: A continuation of the '204 patent family, this invention describes a method for linearizing a transmitter by using an "analyzing and modelling stage" that receives two sets of feedback signals: a first set from the power amplifier output and a second set taken concurrently from the predistorted signals before amplification (’296 Patent, Abstract, claim 10). This dual-feedback approach allows the system to model the PA's nonlinearity and update the digital predistorter in real time.
  • Asserted Claims: At least independent method claim 10 (Compl. ¶62).
  • Accused Features: The accused products allegedly use an "analyzing and modeling stage," including a "real time Estimator block," that receives feedback from both the PA output and the predistorted signals to model PA nonlinearity and update predistorter coefficients (Compl. ¶¶65-66).

U.S. Patent No. 8,078,561 - "Nonlinear behavior models and methods for use thereof in wireless radio systems"

  • Issued: December 13, 2011 (Compl. ¶20)
  • Technology Synopsis: This patent describes a behavioral model for nonlinear systems that separates distortions into two categories. The model uses a "dynamic weak nonlinear" (DWNL) module, such as a set of FIR filters, to capture memory effects, cascaded with a "static strong nonlinear" (SSNL) module, such as a look-up table, to capture the primary amplitude and phase distortions (’561 Patent, Abstract). This two-module approach aims to more accurately model the complex behavior of wideband power amplifiers.
  • Asserted Claims: At least independent claim 7 (Compl. ¶72).
  • Accused Features: The accused products allegedly comprise a "dynamic nonlinear predistorter module" that is coupled to a "second module characterizing static nonlinear characteristics," which the complaint maps to the actuator and multiband actuator blocks in the accused technology's diagrams (Compl. ¶¶74-76).

III. The Accused Instrumentality

Product Identification

The accused instrumentalities are AT&T's cellular network services and the underlying cellular base stations (e.g., eNodeBs and gNodeBs) that provide these services (Compl. ¶¶26, 39, 52).

Functionality and Market Context

  • The complaint alleges that AT&T's base stations employ DPD technology to linearize their power amplifiers, which is necessary to provide reliable 4G and 5G cellular service while managing power consumption (Compl. ¶¶10-13). The specific technologies identified are hardware and/or software such as the Xilinx LogiCORE IP Digital Pre-Distortion, or alternatively, the MaxLin DPD technology which incorporates the NanoSemi Linearizer Core, or equivalent custom ASICs (Compl. ¶¶26, 39).
  • The complaint provides block diagrams to illustrate the functionality of the accused systems. For example, Figure 2 on page 9 of the complaint depicts the "Xilinx DPD HW Block View," showing a DPD datapath that receives digital baseband data and feeds a predistorted signal to a power amplifier, with a feedback observation path for adaptation (Compl. ¶28; Fig. 2 p. 9). Similarly, Figure 2 on page 15 depicts the "NanoSemi Linearizer," which includes an "Actuator" block to apply predistortion and an "Estimator" block to model system impairments in a 2x2 MIMO configuration (Compl. ¶41; Fig. 2 p. 15).
  • The complaint alleges that these DPD solutions are integral to the operation of AT&T's cellular network, which derives substantial revenue from providing services in the district (Compl. ¶6).

IV. Analysis of Infringement Allegations

U.S. Patent No. 7,035,345 Infringement Allegations

Claim Element (from Independent Claim 1) Alleged Infringing Functionality Complaint Citation Patent Citation
predistorting the RF modulated signal... using an I/Q modulator... controlled by means of amplitude and phase look-up tables stored in a distorting generator. The accused system's DPD block performs predistortion using an I/Q modulator and utilizes predistortion parameters stored in look-up tables. Figure 2 in the complaint shows the DPD datapath interposed between the signal source and the PA. ¶28 col. 2:1-12
producing, via a first digital receiver, a first feedback signal in response to the RF predistorted signal. The accused system produces a first feedback signal, labeled z(n) in the complaint's Figure 1, which is taken from the predistorted signal before the PA. ¶29 col. 2:13-16
producing, via a second digital receiver, a second feedback signal in response to the RF amplified output signal from the power amplifier. The accused system produces a second feedback signal, labeled y(n) in the complaint's Figure 1, which is taken from the amplified output of the PA. ¶30 col. 2:17-20
modeling the power amplifier in response to the first and second feedback signals. An "estimation block" in the accused system takes the first feedback signal z(n) and second feedback signal y(n) as inputs to estimate distortion and model the PA. ¶31 col. 2:21-23
updating the predistortion amplitude and phase look-up tables in response to said modeling of the power amplifier. The accused system updates the parameters of the predistortion function based on the modeling performed in the estimation block, and these parameters are stored in memory or look-up tables. ¶32 col. 2:24-27
  • Identified Points of Contention:
    • Scope Questions: The claim requires a "first digital receiver" and a "second digital receiver." The complaint's evidence shows signal paths z(n) and y(n) feeding a single "Estimation" block (Compl. ¶31; Fig. 1 p. 11). A primary question will be whether this architecture, which uses one estimation function on two signal inputs, meets the claim limitation of two distinct "digital receivers" as described in the patent.
    • Technical Questions: What evidence does the complaint provide that the accused "estimation block" performs the specific step of "modeling the power amplifier"? The provided diagrams are high-level. The actual function of the estimation block—whether it models only the PA or the entire transmit chain, and the specifics of that model—will be a key factual issue.

U.S. Patent No. 8,767,857 Infringement Allegations

Claim Element (from Independent Claim 1) Alleged Infringing Functionality Complaint Citation Patent Citation
receiving a plurality of input signals forming a multiple-input signal in a multiple-input multiple-output system. The accused hardware receives a plurality of input signals in a system identified as a "2x2 MIMO" system. Figure 2 in the complaint identifies the "Input I/Q" signals. ¶41 col. 8:19-22
generating a pre-distorted multiple-input signal from the received multiple-input signal. The accused system uses an "Actuator" block to distort the received multiple-input signal, thereby generating a pre-distorted signal. ¶42 col. 8:23-25
generating a multiple-output signal by feeding the pre-distorted multiple-input signal into a multiple-input and multiple-output transmitter. The pre-distorted signal is amplified by a Power Amplifier (PA) block, which functions as the transmitter, to generate a multiple-output signal. ¶43 col. 8:26-29
estimating impairments generated by the... transmitter, the impairments comprising nonlinear crosstalk between distinct ones of the plurality of input signals. An "Estimator" block estimates signal impairments based on feedback signals. Figure 7 in the complaint, a graph titled "Suppression of inter-band noise and interference," is offered as evidence of compensating for crosstalk. ¶44 col. 8:30-34
adjusting the pre-distorted multiple-input signal... wherein generating the pre-distorted... signal comprises feeding the received... signal to a matrix of pre-processing cells... The "actuators" within the accused system are alleged to comprise a "matrix of pre-processing cells" that adjust the signal to correct for nonlinear distortion and crosstalk. ¶45 col. 8:35-41
  • Identified Points of Contention:
    • Scope Questions: Does the accused "Actuator" block (Compl. ¶42) meet the definition of a "matrix of pre-processing cells"? The patent describes a specific matrix structure where each cell Dij models a path from input i to output j ('857 Patent, col. 5:21-26). The complaint's mapping of a single "Actuator" block to this structured matrix will likely be a central point of dispute.
    • Technical Questions: Does the provided evidence of suppressing "inter-band noise and interference" (Compl. ¶44; Fig. 7 p. 18) prove that the accused system performs the claimed function of estimating "nonlinear crosstalk"? The defense may argue that "inter-band interference" is a different technical phenomenon than "nonlinear crosstalk between distinct ones of the plurality of input signals" and that the graph does not prove the specific estimation mechanism required by the claim.

V. Key Claim Terms for Construction

From U.S. Patent No. 7,035,345

  • The Term: "digital receiver"
  • Context and Importance: Claim 1 of the '345 patent requires two such receivers, one for the pre-distorted signal and one for the amplified output. The infringement theory relies on mapping different signal paths within the accused product's single feedback architecture to these two claimed receivers. Practitioners may focus on this term because its construction could determine whether the accused product's architecture falls within the claim's scope.
  • Intrinsic Evidence for Interpretation:
    • Evidence for a Broader Interpretation: The specification describes the function of the digital receivers as performing complex down-converting, filtering, and decimating on a digitized RF signal to extract its complex envelope ('345 Patent, col. 5:55-62). Plaintiff may argue this functional description does not require a specific, physically separate hardware structure for each "receiver."
    • Evidence for a Narrower Interpretation: The embodiment shown in Figure 1 of the patent depicts two distinct receiver chains (54, 60), each with its own preceding RF translator (50, 56) and A/D converter (52, 58). Defendant may argue that a "digital receiver" must comprise such a complete, independent chain, which may not be present in the accused product's architecture as depicted in the complaint.

From U.S. Patent No. 8,767,857

  • The Term: "matrix of pre-processing cells"
  • Context and Importance: This term describes the core architectural innovation of the '857 patent for handling MIMO impairments. The complaint's infringement theory equates the accused "Actuator" and "Estimator" blocks with this claimed matrix structure. Practitioners may focus on this term because the case hinges on whether the accused product's functional blocks are equivalent to the specific structure claimed.
  • Intrinsic Evidence for Interpretation:
    • Evidence for a Broader Interpretation: The abstract states the invention relates to a pre-compensator comprising "a matrix of pre-processing cells for generating a pre-distorted multiple-input signal." The detailed description explains that these cells compensate for distortions and crosstalk without rigidly defining their physical implementation ('857 Patent, col. 3:56-66). This may support an interpretation where the "matrix" can be a logical construct within a single integrated circuit.
    • Evidence for a Narrower Interpretation: Figure 5 of the patent depicts a clear matrix of four distinct cells (D1,1, D2,1, D1,2, D2,2) for a 2x2 system. Defendant may argue that the term requires this explicit, multi-cell structure and that the singular "Actuator" block shown in the complaint's diagrams (e.g., Compl. Fig. 2 p. 15) does not meet this structural requirement.

VI. Other Allegations

  • Indirect Infringement: The complaint does not contain allegations of indirect infringement.
  • Willful Infringement: The complaint does not allege facts sufficient to support a claim for willful infringement, such as pre-suit knowledge of the patents. The prayer for relief includes a request for a finding of an exceptional case and enhanced damages, but the body of the complaint lacks a corresponding factual basis (Compl. ¶81(v)).

VII. Analyst’s Conclusion: Key Questions for the Case

  • A core issue will be one of architectural equivalence: can the functional blocks shown in the accused products’ high-level diagrams (e.g., a single "Estimation" block or "Actuator" block) be mapped onto the more specific and structured claim limitations, such as the "first and second digital receivers" of the '345 patent or the "matrix of pre-processing cells" of the '857 patent? The outcome will depend heavily on claim construction and detailed evidence of the accused systems' implementation.
  • A key evidentiary question will be one of functional distinction: does the evidence provided in the complaint—such as a graph showing suppression of "inter-band noise"—suffice to prove that the accused system performs the specific functions required by the claims, such as estimating "nonlinear crosstalk between distinct... input signals"? The case may turn on the technical distinctions between the phenomena described in the complaint's exhibits and the precise functions recited in the patent claims.
  • A third central question will be one of technical specificity: for patents with highly specific technical requirements, such as the '204 patent's claim of using a "subsampling frequency lower than twice a highest signal frequency," the dispute will likely focus on whether the accused products actually operate in the manner claimed. The high-level evidence in the complaint raises this question but does not resolve it.