INVT SPE LLC v. AT&T Inc. et al.

Case Overview: NPE Asserts Acquired Patent Against AT&T, Stayed for Apple's PTAB Challenge

This patent infringement suit is part of a broader litigation campaign by INVT SPE LLC, a non-practicing entity (NPE) controlled by Fortress Investment Group LLC. The plaintiff, INVT SPE, is asserting a single patent, U.S. Patent No. 6,628,629, against telecommunications giant AT&T Inc. and its wireless subsidiary, AT&T Mobility LLC. The defendants are operating companies that provide nationwide mobile voice and data communications services. According to court filings, INVT alleges that AT&T's 4G/LTE wireless communication network, and the devices and equipment that operate on it, infringe the asserted patent. Specifically, the complaint targets the network's alleged use of certain channel estimation and interpolation methods.

The asserted patent, U.S. Patent No. 6,628,629, is titled "Apparatus and method for estimating a channel in a communication system" and generally relates to techniques for improving signal reception in wireless communication systems by estimating and correcting for signal distortion. The technology is relevant to standards like LTE by enabling more reliable data transmission. This patent was part of a larger portfolio of over 740 telecommunications patents that INVT SPE acquired from Inventergy Global, Inc., another NPE, after Inventergy defaulted on a debt agreement with Fortress. This pattern of acquiring and asserting patent portfolios is characteristic of Fortress's patent monetization strategy.

The case was filed on June 15, 2021, in the U.S. District Court for the Western District of Texas and assigned to Judge Alan D. Albright, a venue that became the most popular in the nation for patent litigation due to procedures seen as favorable to patent owners. However, the litigation was quickly impacted by parallel proceedings at the U.S. Patent and Trademark Office. The case is currently stayed pending the outcome of a post-grant review (PGR) of the '629 patent initiated by Apple Inc. at the Patent Trial and Appeal Board (PTAB). Although docket information regarding the specific stay order is not readily available in public searches, the existence of the stay and its linkage to an Apple-initiated PGR is noted in case summaries. This connection highlights a common defensive strategy where an accused infringer's key supplier or technology partner (in this case, Apple, whose iPhones operate on AT&T's network) challenges the asserted patent's validity at the PTAB, leading district courts to pause the infringement case to await the outcome.

Here are the key legal developments and the current status of the patent infringement litigation INVT SPE LLC v. AT&T Inc. et al.

Filing and Initial Pleadings

• 2021-06-15: Plaintiff INVT SPE LLC filed its original complaint against AT&T Inc. and AT&T Mobility LLC (collectively, "AT&T") in the U.S. District Court for the Western District of Texas. The complaint alleged that AT&T's 4G/LTE and 5G wireless communication services, and the devices operating on its network, infringed on U.S. Patent No. 6,628,629. The patent, titled "System and method for adapting to channel quality variations in a multicarrier communication system," relates to technology for optimizing data transmission over wireless networks.
• 2021-08-27: AT&T filed its answer to the complaint. In its response, AT&T denied the infringement allegations and asserted several affirmative defenses. It also filed counterclaims seeking a declaratory judgment that it did not infringe the '629 patent and that the patent was invalid.

Parallel PTAB Proceedings and Stay of Litigation

In a parallel strategic move, Apple Inc., which was sued by INVT SPE in a separate case in the same court involving the same '629 patent (INVT SPE LLC v. Apple Inc., 6:21-cv-00589), filed a petition for post-grant review (PGR) with the Patent Trial and Appeal Board (PTAB) to challenge the validity of the '629 patent.

• PGR Petition Filing: Apple Inc. filed a petition for post-grant review of U.S. Patent No. 6,628,629. This administrative challenge asserts that the claims of the patent are invalid on various grounds. While specific PGR case numbers are not readily available in public searches, the district court docket confirms the existence of this proceeding.
• Motion to Stay: Following the institution of the PGR proceedings by the PTAB, the parties in the AT&T case addressed the impact of the parallel administrative review.
• 2022-09-09: The court granted a joint motion to stay the case. The order, signed by Judge Alan D. Albright, put a hold on all proceedings, including discovery and claim construction, pending the final resolution of the PGR initiated by Apple. The court's decision to stay the case is typical in situations where a PTAB review could significantly simplify or dispose of the district court litigation by invalidating the patent-in-suit.

Current Status

As of May 13, 2026, the case remains stayed. The stay will likely remain in effect until the Patent Trial and Appeal Board issues a Final Written Decision in the post-grant review proceeding and any subsequent appeals to the U.S. Court of Appeals for the Federal Circuit are resolved. The outcome of the PGR will be a determinative factor for the future of this litigation. If the PTAB finds the asserted claims of the '629 patent to be unpatentable, it will likely lead to the dismissal of INVT SPE's infringement claims against AT&T. Conversely, if the claims survive the PTAB challenge, the stay will be lifted, and the district court case will proceed to claim construction, discovery, and potentially trial.

No substantive pre-trial motions regarding dismissal or transfer were decided before the stay was implemented, nor did the case reach the claim construction (Markman hearing) stage.

Plaintiff's Counsel of Record: INVT SPE LLC

The following attorneys have appeared on behalf of the plaintiff, INVT SPE LLC, in the case INVT SPE LLC v. AT&T Inc. et al., 6:21-cv-00622 (W.D. Tex.). The legal team is composed of attorneys from Kramer Levin Naftalis & Frankel LLP and a local counsel from a Texas-based firm.

• Paul J. Andre (Lead Counsel)

  • Firm: Kramer Levin Naftalis & Frankel LLP (Menlo Park, CA).
  • Note: Andre is a nationally recognized patent trial lawyer and co-chair of his firm's Intellectual Property practice, known for securing large jury verdicts, including a notable $2.2 billion verdict for VLSI Technology against Intel.

• Lisa Kobialka (Lead Counsel)

  • Firm: Kramer Levin Naftalis & Frankel LLP (Menlo Park,CA).
  • Note: Kobialka is a first-chair trial lawyer and co-chair of the firm's IP practice, with extensive experience in high-stakes patent litigation across various technologies.

• James R. Hannah (Of Counsel)

  • Firm: Kramer Levin Naftalis & Frankel LLP (Menlo Park, CA).
  • Note: Hannah has significant experience in patent litigation and has been a key part of trial teams with Paul Andre, including in litigation involving Fortress-backed entities.

• S. Mohammad "Mo" Tajsar (Of Counsel)

  • Firm: Kramer Levin Naftalis & Frankel LLP (Los Angeles, CA).
  • Note: Tajsar is a partner in the firm's Intellectual Property group with experience litigating patent cases in district courts and before the PTAB.

• Elizabeth S. "Liz" Day (Of Counsel)

  • Firm: Kramer Levin Naftalis & Frankel LLP (Washington, D.C.).
  • Note: Day is an associate in the firm's Intellectual Property group, focusing on patent litigation.

• S. Calvin Capshaw (Local Counsel)

  • Firm: Capshaw DeRieux LLP (Gladewater, TX).
  • Note: Capshaw frequently serves as local counsel in the Eastern and Western Districts of Texas for major patent infringement actions, representing both plaintiffs and defendants.

Defendant Representatives: AT&T Inc. and AT&T Mobility LLC

The following attorneys have appeared on behalf of defendants AT&T Inc. and AT&T Mobility LLC in this case, primarily from the law firm Sidley Austin LLP, a firm with a nationally recognized intellectual property practice that frequently defends major technology and telecommunications companies in patent litigation.

• David L. Anderson (Lead Counsel)

  • Firm: Sidley Austin LLP (San Francisco, CA).
  • Note: Anderson is a seasoned patent litigator and former U.S. Attorney for the Northern District of California, known for handling high-stakes technology cases.

• Brent R. Yamashita (Lead Counsel)

  • Firm: Sidley Austin LLP (Palo Alto, CA).
  • Note: Yamashita is a partner in Sidley's IP Litigation group with extensive experience representing technology companies in patent disputes in district courts, the ITC, and the PTAB.

• Todd M. Patterson (Lead Counsel)

  • Firm: Sidley Austin LLP (Dallas, TX).
  • Note: Patterson focuses his practice on intellectual property litigation, including patent infringement cases involving complex telecommunications and computer technologies.

• Ryan C. Morris (Of Counsel)

  • Firm: Sidley Austin LLP (Dallas, TX).
  • Note: Morris is an associate in the firm's IP Litigation practice group.

• D. Hull Youngblood, Jr. (Local Counsel)

  • Firm: Youngblood & Associates, PLLC (Waco, TX).
  • Note: Youngblood frequently serves as local counsel in the Western District of Texas for major technology companies in patent litigation matters. This information is based on appearances in similar cases, though his specific notice of appearance in this docket is not detailed in available public searches.

• John C. Alemanni (Of Counsel)

  • Firm: Kilpatrick Townsend & Stockton LLP (Atlanta, GA).
  • Note: Alemanni is an experienced patent litigator with a focus on telecommunications and software technologies. His notice of appearance was filed on August 27, 2021, according to the case docket.

• R. David Hosp (Of Counsel)

  • Firm: Orrick, Herrington & Sutcliffe LLP (Boston, MA).
  • Note: Hosp is a partner in Orrick's Intellectual Property group with a record of representing major tech companies in significant patent litigation. He was admitted pro hac vice on behalf of AT&T Mobility, as indicated in an August 30, 2021 docket entry (Dkt. 20).