DCT

2:18-cv-00344

EVS Codec Tech LLC v. ZTE Corp

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 2:18-cv-00344, E.D. Tex., 08/06/2018
  • Venue Allegations: Plaintiff alleges venue is proper in the Eastern District of Texas based on Defendant ZTE (TX) Inc.'s registered office in the district, and Defendant ZTE USA, Inc.'s alleged commission of infringing acts and maintenance of a "regular and established place of business" (a call center) within the district.
  • Core Dispute: Plaintiff alleges that Defendant’s mobile devices implementing the 3GPP Enhanced Voice Services (EVS) Codec infringe five patents related to speech and audio compression technology.
  • Technical Context: The technology concerns digital audio codecs, which are essential for compressing and decompressing speech signals for efficient transmission over modern mobile networks, such as 4G/LTE.
  • Key Procedural History: The complaint alleges that the patents-in-suit were previously asserted by a different entity against Defendant ZTE in the same court in a case concerning the AMR-WB codec. The complaint further notes that the court has issued two claim construction (Markman) opinions and presided over a jury trial related to the patents-in-suit in other litigation, and that the patent owner made ZTE aware of the alleged infringement by the EVS Codec prior to the lawsuit's filing.

Case Timeline

Date Event
1998-10-27 Earliest Priority Date ('805, '524, '802, '521 Patents)
1999-11-18 Earliest Priority Date ('123 Patent)
2004-09-21 U.S. Patent No. 6,795,805 Issues
2004-10-19 U.S. Patent No. 6,807,524 Issues
2006-12-19 U.S. Patent No. 7,151,802 Issues
2007-03-13 U.S. Patent No. 7,191,123 Issues
2007-08-21 U.S. Patent No. 7,260,521 Issues
2016-01-01 T-Mobile launches EVS Codec on its network (at least in 2016)
2018-08-06 Complaint Filed

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

U.S. Patent No. 6,795,805 - "Periodicity Enhancement in Decoding Wideband Signals"

The Invention Explained

  • Problem Addressed: The patent describes that prior art methods for enhancing the periodicity of an excitation signal in speech codecs, while effective for narrowband telephone signals, are "less efficient in case of wideband signals since it introduces the periodicity over the entire spectrum" ('805 Patent, col. 2:22-26).
  • The Patented Solution: The invention proposes a method and device that filters the "innovative codevector" (a component of the excitation signal) with a special "innovation filter." This filtering is designed to "reduce energy of a low frequency portion of the innovative codevector and enhance periodicity of a low frequency portion of the excitation signal," thereby targeting the enhancement where it is most perceptually important in wideband audio ('805 Patent, col. 2:39-44). The decoder block diagram in Figure 2 illustrates this process, showing the innovation filter (205) processing the output of the innovative codebook (218) before it is combined with the pitch contribution ('805 Patent, Fig. 2).
  • Technical Importance: This approach allows for more precise and efficient enhancement of voiced speech sounds in wideband codecs, improving perceived quality without introducing artifacts across the entire frequency spectrum (Compl. ¶29).

Key Claims at a Glance

  • The complaint asserts independent claim 3 (Compl. ¶51).
  • Essential elements of claim 3 include:
    • A device for enhancing periodicity of an excitation signal produced in relation to a pitch codevector and an innovative codevector for supplying a signal synthesis filter in view of synthesizing a wideband speech signal.
    • The device comprises a factor generator for calculating a periodicity factor related to the wideband speech signal.
    • The device also comprises an innovation filter for filtering the innovative codevector in relation to the periodicity factor to thereby reduce energy of a low frequency portion of the innovative codevector and enhance periodicity of a low frequency portion of the excitation signal.
    • The innovation filter has a transfer function of the form F(z) = -az + 1 − az⁻¹, where a is a periodicity factor derived from a level of periodicity of the excitation signal.
  • The complaint does not explicitly reserve the right to assert dependent claims for this patent.

U.S. Patent No. 6,807,524 - "Perceptual Weighting Device and Method for Efficient Coding of Wideband Signals"

The Invention Explained

  • Problem Addressed: The patent explains that conventional perceptual weighting filters in CELP-type encoders have "inherent limitations in modelling the formant structure and the required spectral tilt concurrently," a problem that is particularly "more pronounced in wideband signals" ('524 Patent, col. 10:25-31).
  • The Patented Solution: The invention proposes a novel perceptual weighting structure that combines a signal pre-emphasis filter at the input with a modified perceptual weighting filter that has a "fixed denominator." This configuration "substantially decouples the formant weighting from the tilt," allowing for more effective control over the shaping of quantization noise in wideband signals ('524 Patent, col. 9:8-16, 32-34). The encoder diagram in Figure 1 shows the pre-emphasis filter (103) processing the signal before it reaches the perceptual weighting filter (105) ('524 Patent, Fig. 1).
  • Technical Importance: By separating the control of formant weighting and spectral tilt, the invention enables more efficient and higher-quality encoding for wideband audio, which is crucial for modern high-definition voice communications (Compl. ¶¶28-29, 31).

Key Claims at a Glance

  • The complaint asserts independent claim 4 (Compl. ¶67).
  • Essential elements of claim 4 include:
    • A perceptual weighting device for producing a perceptually weighted signal in response to a wideband speech signal.
    • The device comprises: (a) a signal preemphasis filter for enhancing a high frequency content of the wideband speech signal; (b) a synthesis filter calculator for producing synthesis filter coefficients; and (c) a perceptual weighting filter for filtering the preemphasised signal.
    • The perceptual weighting filter has a transfer function with a fixed denominator, whereby weighting of the wideband speech signal in a formant region is substantially decoupled from a spectral tilt of the wideband speech signal.
    • The signal preemphasis filter has a transfer function of the form P(z) = 1 − μz⁻¹.
    • The perceptual weighting filter has a transfer function of the form W(z) = A(z/γ₁)/(1 – γ₂z⁻¹).
  • The complaint does not explicitly reserve the right to assert dependent claims for this patent.

U.S. Patent No. 7,151,802 - "High Frequency Content Recovering Method and Device for Over-Sampled Synthesized Wideband Signal"

  • Patent Identification: U.S. Patent No. 7,151,802, issued December 19, 2006 (Compl. ¶79).
  • Technology Synopsis: The patent addresses the problem of restoring high-frequency content that is lost when a wideband signal is down-sampled during the encoding process to improve efficiency (Compl. ¶85; '802 Patent, col. 1:9-15). The patented solution is a decoder that generates random noise, shapes its spectrum using parameters from the original signal, and injects this shaped noise into the synthesized signal to reconstruct the high-frequency portion of the audio ('802 Patent, Abstract).
  • Asserted Claims: Representative independent claim 1 is asserted (Compl. ¶84).
  • Accused Features: The complaint alleges that the EVS Codec included in the ZTE EVS Products comprises the decoder disclosed in the patent (Compl. ¶86).

U.S. Patent No. 7,260,521 - "Method and Device for Adaptive Bandwidth Pitch Search in Coding Wideband Signals"

  • Patent Identification: U.S. Patent No. 7,260,521, issued August 21, 2007 (Compl. ¶95).
  • Technology Synopsis: The patent addresses the need for an efficient pitch search method for wideband signals, where the harmonic structure of speech does not cover the entire spectrum ('521 Patent, col. 11:36-44). The solution is a pitch analysis device that uses at least two parallel signal paths to calculate pitch prediction error, with at least one path including a filter to shape the pitch codevector; a selector then chooses the path with the lowest error, allowing for an adaptive bandwidth search (Compl. ¶101).
  • Asserted Claims: Representative independent claim 2 is asserted (Compl. ¶100).
  • Accused Features: The complaint alleges that the EVS Codec included in the ZTE EVS Products comprises the pitch analysis device disclosed in the patent (Compl. ¶102).

U.S. Patent No. 7,191,123 - "Gain-Smoothing in Wideband Speech and Audio Signal Decoder"

  • Patent Identification: U.S. Patent No. 7,191,123, issued March 13, 2007 (Compl. ¶114).
  • Technology Synopsis: The patent addresses a noted problem where decoder performance degrades when background noise is present in the original sampled signal ('123 Patent, col. 2:26-29). The solution is a device that produces a "gain-smoothed codevector" by calculating a "smoothing gain" using a non-linear operation based on factors like voicing and signal stability, and then applies this gain to an innovative codevector to reduce fluctuations in energy during stationary noise periods (Compl. ¶120).
  • Asserted Claims: Representative independent claim 102 is asserted (Compl. ¶119).
  • Accused Features: The complaint alleges that the EVS Codec included in the ZTE EVS Products comprises the gain-smoothing device disclosed in the patent (Compl. ¶121).

III. The Accused Instrumentality

Product Identification

The accused instrumentalities are ZTE mobile devices, including smartphones and tablets, that are capable of "Ultra HD Voice (or HD Voice+)" and contain the Enhanced Voice Services (EVS) Codec (Compl. ¶¶48-49). Specific examples cited include the ZTE Axon M, ZTE Axon 7, and ZTE Nubia Z17, as well as products incorporating certain Qualcomm Snapdragon LTE Modems (Compl. ¶49).

Functionality and Market Context

The relevant functionality is the implementation of the 3GPP EVS Standard, a codec designed for high-quality voice services over LTE networks (Compl. ¶29). The complaint alleges that any device compliant with the EVS Standard necessarily practices the patented technologies (Compl. ¶54, ¶70). The EVS Codec processes wideband speech signals sampled at approximately 16,000 samples/second and is deployed by major U.S. carriers to provide improved voice quality and network capacity (Compl. ¶36, ¶55).
No probative visual evidence provided in complaint.

IV. Analysis of Infringement Allegations

U.S. Patent No. 6,795,805 Infringement Allegations

| Claim Element (from Independent Claim 3) | Alleged Infringing Functionality | Complaint Citation | Patent Citation |
|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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|:--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |:----------------------|:-------------------|
| a device for enhancing periodicity of an excitation signal produced in relation to a pitch codevector and an innovative codevector for supplying a signal synthesis filter in view of synthesizing a wideband speech signal | The EVS Standard includes devices for enhancing the periodicity of an excitation signal for synthesizing a wideband speech signal. | ¶56 | col. 2:45-48 |
| said periodicity enhancing device comprising a factor generator for calculating a periodicity factor related to the wideband speech signal | The periodicity enhancing device of the EVS Standard comprises a factor generator for calculating a periodicity factor. | ¶57 | col. 2:49-51 |
| and an innovation filter for filtering the innovative codevector in relation to said periodicity factor to thereby reduce energy of a low frequency portion of the innovative codevector and enhance periodicity of a low frequency portion of the excitation signal | The EVS Standard's device includes an innovation filter that filters the innovative codevector to reduce low frequency energy and enhance periodicity. | ¶57 | col. 2:52-56 |
| Claim 3 further discloses that the innovation filter has a transfer function of the form F(z) = -az + 1 − az⁻¹ where a is a periodicity factor derived from a level of periodicity of the excitation signal | The innovation filter in the EVS Standard has a transfer function of the form F(z) = -az + 1 – az⁻¹, where a is a periodicity factor derived from the periodicity of the excitation signal. | ¶58 | col. 2:57-63 |

U.S. Patent No. 6,807,524 Infringement Allegations

Claim Element (from Independent Claim 4) Alleged Infringing Functionality Complaint Citation Patent Citation
a signal preemphasis filter responsive to the wideband speech signal for enhancing a high frequency content of the wideband speech signal to thereby produce a preemphasised signal The EVS Standard comprises a signal preemphasis filter responsive to the wideband signal to enhance its high frequency content. ¶73 col. 3:6-10
a synthesis filter calculator responsive to said preemphasised signal for producing synthesis filter coefficients The EVS Standard comprises a synthesis filter calculator responsive to the preemphasised signal to produce synthesis filter coefficients. ¶73 col. 3:11-13
and (c) a perceptual weighting filter... said perceptual weighting filter having a transfer function with fixed denominator whereby weighting of said wideband speech signal in a formant region is substantially decoupled from a spectral tilt of said wideband speech signal The EVS Standard comprises a perceptual weighting filter with a fixed denominator that substantially decouples formant region weighting from spectral tilt. ¶73 col. 3:14-24
Claim 4 further discloses that said signal preemphasis filter has a transfer function of the form P(z) = 1 − μz⁻¹... The signal preemphasis filter in the EVS Standard has a transfer function of the form P(z) = 1 − μz⁻¹. ¶74 col. 4:41-43
and said perceptual weighting filter has a transfer function of the form W(z) = A(z/γ₁)/(1 – γ₂z⁻¹)... The perceptual weighting filter in the EVS Standard has a transfer function of the form W(z) = A(z/γ₁)/(1 – γ₂z⁻¹). ¶75 col. 4:48-50

Identified Points of Contention

Scope Questions

The core of the infringement theory is that compliance with the EVS Standard constitutes infringement. A potential point of contention is whether the EVS Standard allows for non-infringing implementations. The defense may argue that while the accused products are EVS-compliant, their specific implementation of certain functions falls outside the scope of the claims.

Technical Questions

A key technical question will be whether the algorithms and transfer functions specified in the EVS Standard documentation map directly onto the functional and mathematical limitations of the asserted claims. For the ’524 Patent, for example, a central question will be what evidence demonstrates that the EVS Standard's weighting filter achieves a result that is "substantially decoupled from a spectral tilt" as required by the claim.

V. Key Claim Terms for Construction

"periodicity factor" ('805 Patent, claim 3)

Context and Importance

This term is the central input to the claimed "innovation filter." The definition of what constitutes a "periodicity factor" is critical, as it will determine whether the specific value calculated and used within the accused EVS Codec meets this limitation. Practitioners may focus on this term because the patent provides specific exemplary formulas for its calculation, raising the question of whether the claim scope is implicitly limited to those examples.

Intrinsic Evidence for Interpretation

  • Evidence for a Broader Interpretation: The specification describes the factor generally as being "derived from a level of periodicity of the excitation signal" ('805 Patent, col. 2:61-63), which may support a construction not limited to any single formula.
  • Evidence for a Narrower Interpretation: The detailed description provides specific equations for calculating the factor, such as a=qRp or α=0.125(1+rv) ('805 Patent, col. 6:60-61, col. 7:4-5). A party could argue these specific embodiments define and limit the scope of the more general term.

"substantially decoupled from a spectral tilt" ('524 Patent, claim 4)

Context and Importance

This functional language describes the key advantage of the claimed invention. The outcome of the infringement analysis for the ’524 patent may turn on the degree of decoupling required to satisfy "substantially." Practitioners may focus on this term because it is a term of degree, inviting dispute over whether the accused EVS Codec's performance meets the claimed threshold.

Intrinsic Evidence for Interpretation

  • Evidence for a Broader Interpretation: The specification states that the inventive structure "substantially decouples the formant weighting from the tilt" and that this is achieved by using a filter with a "fixed denominator" ('524 Patent, col. 9:17-21, 32-34). This suggests the structural configuration itself may be sufficient evidence of decoupling.
  • Evidence for a Narrower Interpretation: The patent's background criticizes prior art filters for their inability to model formant structure and spectral tilt concurrently ('524 Patent, col. 10:25-31). A party might argue that "substantially decoupled" must be construed in light of this problem, requiring a degree of decoupling that represents a clear and significant improvement over that prior art.

VI. Other Allegations

Indirect Infringement

For each of the five asserted patents, the complaint alleges inducement of infringement. The stated basis is that ZTE "provides, makes, uses, licenses, sells, and offers its ZTE EVS Products for sale with the specific intent that its customers use those phones in an infringing manner" (Compl. ¶59). The complaint also alleges contributory infringement by stating that the EVS Codec has "no substantial non-infringing uses and is known by ZTE to be especially made or especially adapted for use in an infringement" of the patents (Compl. ¶59).

Willful Infringement

Willfulness is alleged for all five patents. The complaint bases this allegation on ZTE's alleged pre-suit knowledge, arising from (1) prior litigation where the same patents were asserted against ZTE products using a different codec, and (2) alleged direct notice from the patent owner to ZTE that the EVS Codec infringes the patents-in-suit (Compl. ¶¶42-43, 61, 78, 94, 113, 131).

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

  • A core issue will be one of technical mapping: does the 3GPP EVS Standard, which the accused products are alleged to practice, require implementation of every limitation of the asserted patent claims? The case will likely hinge on evidence comparing the specific functional and mathematical requirements of the standard to the language of the claims.
  • A key question of legal interpretation and history will be: how will the court’s prior claim construction rulings and the jury trial involving these same patents—albeit against a different accused technology (the AMR-WB codec)—influence the current proceedings? This extensive history may significantly narrow the scope of potential disputes over claim meaning.
  • A central question for damages will be one of intent: given the allegations of direct notice and prior litigation involving the same patents, can Plaintiff establish that ZTE's alleged infringement was willful, potentially justifying an award of enhanced damages?