EVS Codec Tech LLC v. ZTE Corp

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: EVS Codec Technologies, LLC (Texas)
  • Defendant: ZTE Corporation (China), ZTE USA, Inc. (New Jersey), and ZTE (TX) Inc. (Texas)
  • Plaintiff’s Counsel: Ahmad, Zavitsanos, Anaipakos, Alavi & Mensing P.C.
• 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 because Defendant ZTE USA, Inc. maintains a regular and established place of business (a call center) within the district, and because the Defendants have committed acts of infringement and sell accused products within the district.
• Core Dispute: Plaintiff alleges that Defendant’s mobile devices, such as smartphones and tablets, that implement the Enhanced Voice Services ("EVS") Codec standard infringe five patents related to speech and audio compression technologies.
• Technical Context: The technology at issue involves speech and audio codecs, which are fundamental for compressing and decompressing voice data for efficient transmission over modern digital communication networks like 4G/LTE.
• Key Procedural History: The complaint states that the patents-in-suit have been the subject of prior litigation against other major mobile device manufacturers, as well as against Defendant ZTE in a case involving a different codec (AMR-WB). The complaint also notes that the Court has previously issued two claim construction opinions and presided over a jury trial involving the same patents, suggesting a significant history of judicial interpretation and a basis for the Plaintiff's allegations of pre-suit knowledge.

Case Timeline

Date	Event
1998-10-27	Earliest Priority Date for ’805, ’524, ’802, and ’521 Patents
1999-11-18	Earliest Priority Date for ’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 reported to have launched EVS Codec on its networks
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," Issued September 21, 2004

The Invention Explained

• Problem Addressed: The patent addresses the challenge of improving the quality of synthesized speech in wideband codecs. Prior methods for enhancing the periodicity of an excitation signal—a key step for creating natural-sounding voiced speech—were inefficient for wideband signals because they introduced periodicity across the entire frequency spectrum. (’805 Patent, col. 2:22-29).
• The Patented Solution: The invention proposes a method and device that filter the "innovative" part of the excitation signal to specifically reduce its energy in the low-frequency portion. This selectively enhances the periodicity of the overall excitation signal at lower frequencies, which is more effective and efficient for wideband speech and improves perceived quality. (’805 Patent, Abstract; col. 2:31-41).
• Technical Importance: This technique allows for more accurate modeling of voiced speech in wideband applications (e.g., Voice over LTE), leading to higher-quality and more natural-sounding synthesized voice. (Compl. ¶¶29, 31).

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,
  • said periodicity enhancing device comprising a factor generator for calculating a periodicity factor related to the wideband speech signal;
  • 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.
  • Claim 3 further specifies that the innovation filter has a transfer function of the form F(z) = -az + 1 − az⁻¹, where α is a periodicity factor. (Compl. ¶52).
• The complaint does not explicitly reserve the right to assert dependent claims but makes general allegations of infringement of one or more claims. (Compl. ¶59).

U.S. Patent No. 6,807,524 - "Perceptual Weighting Device and Method for Efficient Coding of Wideband Signals," Issued October 19, 2004

The Invention Explained

• Problem Addressed: The patent identifies a limitation in prior art speech coders where perceptual weighting filters struggled to concurrently model both the formant structure (spectral peaks) and the overall spectral tilt (slope) of wideband signals, which have a wide dynamic range between low and high frequencies. (’524 Patent, col. 1:50-57).
• The Patented Solution: The invention introduces a pre-emphasis filter at the input of the encoder, which enhances the high-frequency content of the signal before analysis. It then uses a modified perceptual weighting filter with a fixed denominator. This architecture "substantially decouples" the formant weighting from the spectral tilt, enabling more efficient perceptual weighting and thus better encoding quality for wideband signals. (’524 Patent, Abstract; col. 2:56-66).
• Technical Importance: This approach improves the ability of a speech codec to shape quantization noise to be less perceptible to the human ear, resulting in higher perceived audio quality at a given data compression rate. (Compl. ¶¶28-29).

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...
  • comprising: (a) 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;
  • (b) a synthesis filter calculator responsive to said preemphasised signal for producing synthesis filter coefficients; and
  • (c) a perceptual weighting filter... for filtering said preemphasised signal... 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.
  • Claim 4 further specifies the mathematical forms of the transfer functions for the preemphasis and perceptual weighting filters. (Compl. ¶68).
• The complaint makes general allegations of infringement of one or more claims of the ’524 Patent. (Compl. ¶76).

U.S. Patent No. 7,151,802 - "High Frequency Content Recovering Method and Device for Over-Sampled Synthesized Wideband Signal," Issued December 19, 2006

Technology Synopsis

The patent describes a decoder that restores high-frequency content lost when a wideband signal is down-sampled for efficient encoding. The solution involves generating random noise, shaping its spectrum using linear prediction filter coefficients, and injecting this shaped noise into the over-sampled, synthesized signal to create a full-spectrum output. (Compl. ¶85).

Asserted Claims

Independent claim 1 is asserted as representative. (Compl. ¶84).

Accused Features

The EVS Codec implemented in ZTE's products is accused of infringing by including a decoder that performs high-frequency content recovery as claimed. (Compl. ¶¶86, 89-91).

U.S. Patent No. 7,260,521 - "Method and Device for Adaptive Bandwidth Pitch Search in Coding Wideband Signals," Issued August 21, 2007

Technology Synopsis

The patent discloses a pitch analysis device for speech coding that uses at least two different signal paths to assess a pitch codevector. At least one of these paths includes a filter. A selector then chooses the path that results in the lowest pitch prediction error, allowing for more accurate and adaptive pitch analysis suitable for wideband signals. (Compl. ¶101).

Asserted Claims

Independent claim 2 is asserted as representative. (Compl. ¶100).

Accused Features

The EVS Codec in ZTE's products is accused of infringing by employing a pitch analysis device that uses at least two signal paths, one filtered and one unfiltered, to select pitch codebook parameters. (Compl. ¶¶102, 107-110).

U.S. Patent No. 7,191,123 - "Gain-Smoothing in Wideband Speech and Audio Signal Decoder," Issued March 13, 2007

Technology Synopsis

This patent describes a device within a decoder that improves performance in the presence of background noise. It does so by "smoothing" the gain applied to an innovative codevector. A "smoothing gain" is calculated using a non-linear operation based on a factor representing the amount of voicing in the signal, and this gain is used to amplify the codevector to produce a "gain-smoothed" output. (Compl. ¶120).

Asserted Claims

Independent claim 102 (a means-plus-function claim) is asserted as representative. (Compl. ¶119).

Accused Features

The EVS Codec in ZTE's products is accused of infringing by including a device that produces a gain-smoothed codevector using the claimed means. (Compl. ¶¶121, 124-128).

III. The Accused Instrumentality

• Product Identification: The accused instrumentalities are ZTE's mobile devices, including smartphones and tablets, that are capable of practicing the EVS Standard (also marketed as "Ultra HD Voice" or "HD Voice+"). (Compl. ¶¶48-49). Specific examples cited include the ZTE Axon M, ZTE Axon 7, and ZTE Nubia Z17, as well as any ZTE products containing certain Qualcomm Snapdragon LTE Modems (X12, X16, X20, X24). (Compl. ¶49).
• Functionality and Market Context: The core accused functionality is the implementation of the 3GPP EVS Codec. (Compl. ¶53). This codec was standardized to provide vastly improved voice quality and network capacity for voice services over LTE/4G networks. (Compl. ¶29). The complaint alleges that any mobile device marketed as "HD Voice+" capable must support the EVS Codec, and that compliance with the EVS Standard constitutes infringement of the patents-in-suit. (Compl. ¶¶37, 54).
• Visual Evidence: 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
a device for enhancing periodicity of an excitation signal...comprising a factor generator for calculating a periodicity factor related to the wideband speech signal;	The EVS Standard includes a periodicity enhancing device that comprises a factor generator for calculating a periodicity factor related to the wideband speech signal.	¶57	col. 12:40-44
and an innovation filter for filtering the innovative codevector...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 periodicity enhancing device of the EVS Standard also comprises an innovation filter for filtering the innovative codevector to reduce low-frequency energy and enhance periodicity of the excitation signal's low-frequency portion.	¶57	col. 12:25-34
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 is alleged to have a transfer function of the form F(z) = -az + 1 – az⁻¹, where α is a periodicity factor derived from the excitation signal's periodicity level.	¶58	col. 12:35-39

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

Claim Element (from Independent Claim 4)	Alleged Infringing Functionality	Complaint Citation	Patent Citation
(a) a signal preemphasis filter responsive to the wideband speech signal for enhancing a high frequency content...to thereby produce a preemphasised signal;	The EVS Standard's perceptual weighting device comprises a signal preemphasis filter that enhances the high-frequency content of the wideband speech signal to produce a preemphasised signal.	¶73	col. 7:42-46
(b) a synthesis filter calculator responsive to said preemphasised signal for producing synthesis filter coefficients;	The EVS Standard's device includes a synthesis filter calculator that produces synthesis filter coefficients from the preemphasised signal.	¶73	col. 7:12-15
(c) a 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's device includes a perceptual weighting filter with a fixed denominator, which is alleged to substantially decouple the weighting in the formant region from the signal's spectral tilt.	¶73	col. 9:11-16
Claim 4 further discloses that said signal preemphasis filter has a transfer function of the form P(z) = 1 − μz⁻¹...and said perceptual weighting filter has a transfer function of the form W(z) = A(z/γ₁)/(1 – γ₂z⁻¹)	The EVS Standard allegedly specifies a signal preemphasis filter and a perceptual weighting filter having these exact transfer functions.	¶¶74-75	col. 7:47; col. 9:1-4

Identified Points of Contention

• Standards vs. Implementation: The complaint's infringement theory rests on the assertion that compliance with the 3GPP EVS Standard necessarily infringes the patents (e.g., Compl. ¶54, ¶70). A primary point of contention will be whether the EVS standard can be practiced in a non-infringing manner, and whether ZTE's specific implementation of the EVS Codec in its products meets every limitation of the asserted claims.
• Scope Questions: The case may raise questions about the scope of functional language in the claims. For the ’524 Patent, the court will need to determine what degree of separation between formant weighting and spectral tilt is required to meet the "substantially decoupled" limitation.

V. Key Claim Terms for Construction

For the ’805 Patent

• The Term: "periodicity factor"
• Context and Importance: This term is central to claim 3, as it governs the operation of the claimed "innovation filter." The infringement analysis depends on whether the method used in the EVS Standard to quantify periodicity falls within the patent's definition of this term. Practitioners may focus on this term because its construction will determine whether the accused standard-compliant function is equivalent to the claimed function.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The specification discloses multiple methods for calculating a value representing periodicity, including one based on "The ratio of pitch contribution to the total excitation signal" and another based on the relative energies of the pitch and innovative codevectors. (’805 Patent, col. 12:49-55; col. 13:1-12). This could support a construction that encompasses any quantitative measure of a signal's periodic nature used for the claimed purpose.
  • Evidence for a Narrower Interpretation: The specification provides specific equations, such as "a=qRp", for calculating the factor. (’805 Patent, col. 13:1). A defendant might argue that the term should be limited to these specific mathematical relationships or their equivalents.

For the ’524 Patent

• The Term: "substantially decoupled"
• Context and Importance: This term describes the functional result of the claimed invention and is a term of degree. The dispute will likely center on whether the perceptual weighting filter in the accused EVS Codec achieves a sufficient degree of separation between formant weighting and spectral tilt to meet this limitation.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The patent describes the objective of the invention as providing a "structure [that] substantially decouples the formant weighting from the tilt." (’524 Patent, col. 9:30-32). This could suggest that any filter structure achieving this functional outcome is covered.
  • Evidence for a Narrower Interpretation: A defendant may argue the term must be interpreted in light of the specific embodiment that achieves the decoupling: a perceptual weighting filter with a "fixed denominator" and a specific transfer function form, "W(z)=A(z/γ₁)/(1-γ₂z⁻¹)". (’524 Patent, col. 9:1-4). This suggests the structure itself, not just the result, is key to the meaning of the term.

VI. Other Allegations

• Indirect Infringement: The complaint alleges inducement of infringement, stating that ZTE provides products with the EVS Codec and promotes their use with the specific intent that customers will use them in an infringing manner (e.g., making HD Voice+ calls). (Compl. ¶59). The complaint also alleges contributory infringement, asserting that the EVS Codec has no substantial non-infringing uses and is especially made or adapted for use in an infringing manner by complying with the EVS Standard. (Compl. ¶59).
• Willful Infringement: The complaint alleges willful infringement based on ZTE's purported pre-suit knowledge of the patents-in-suit. (Compl. ¶61). This knowledge is allegedly derived from ZTE's status as a defendant in prior litigation involving the same patents (asserted against the AMR-WB codec), as well as from public information regarding the patents and their relation to the EVS standard. (Compl. ¶42).

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

• A core issue will be one of standards-essentiality: does compliance with the 3GPP EVS Standard, as the complaint alleges, necessarily require practicing the asserted claims? The case will likely require a technical deep-dive into the mandatory versus optional portions of the standard to determine if a non-infringing implementation is possible.
• A key evidentiary question will be one of technical implementation: beyond the standard itself, what is the precise structure and operation of the EVS Codec as implemented in ZTE's accused devices? Discovery will likely focus on whether ZTE's source code and hardware design meet each limitation of the asserted claims.
• The case may also turn on claim construction: specifically, can the functional term "substantially decoupled" (’524 Patent) be defined with sufficient objective boundaries to support a finding of infringement, or will it be found indefinite? Similarly, the scope of "periodicity factor" (’805 Patent) will be critical in determining if the accused devices perform the claimed function.