Background
Sisvel International S.A. owns patents in the field of wireless telecommunications, including patents related to methods of channel coding and error detection in radio data transmission systems. The patents at issue contain means-plus-function claim limitations — a drafting convention under 35 U.S.C. § 112(f) that claims a function performed by generic “means” rather than a specific structure. In exchange for this flexibility, the law requires that the patent specification disclose the corresponding structure that performs the claimed function.
Sierra Wireless, Inc. challenged Sisvel’s patents in inter partes review (IPR) proceedings before the PTAB, arguing that certain means-plus-function limitations were indefinite because the specification failed to disclose adequate corresponding algorithmic structure for the computer-implemented functions. The PTAB agreed with Sierra Wireless, finding that merely naming software protocols in the specification did not provide sufficient structural disclosure, and categorically refused to consider expert testimony about whether a person of ordinary skill in the art (POSITA) would understand those named protocols as disclosing the required structure. Sisvel appealed.
The Court’s Holding
The Federal Circuit vacated and remanded. The court clarified a two-track framework that governs when expert testimony is permissible for computer-implemented means-plus-function claims. Where the specification contains no structural disclosure whatsoever for a claimed function — essentially a total absence of any corresponding structure — expert testimony cannot substitute for what is simply missing from the specification. However, where the specification does disclose some structure (such as by naming specific software protocols, standards, or algorithms), expert testimony may be considered to explain whether a POSITA would understand that disclosure as providing the algorithmic structure required by § 112(f).
The PTAB had erroneously placed Sisvel’s patents in the first category — treating the named protocols as no structure at all — when in fact they fell in the second category where named protocols constitute at least some structural disclosure. By categorically excluding expert testimony in this second-track scenario, the Board committed legal error. The Federal Circuit remanded for the Board to properly consider whether, in light of expert testimony about what the named protocols mean to a skilled artisan, the specification provides sufficient corresponding structure for the means-plus-function limitations.
Key Takeaways
- Naming specific software protocols or standards in a specification is not the same as having no structural disclosure — it places a means-plus-function claim in the category where expert testimony about a POSITA’s understanding can and must be considered.
- The PTAB cannot categorically reject expert testimony on structural sufficiency where the specification contains some, albeit potentially incomplete, structural disclosure for means-plus-function limitations.
- Patent drafters using means-plus-function claiming for computer-implemented inventions should identify specific protocols, algorithms, or data structures — not just generic “software” — to strengthen the structural disclosure and support expert testimony on adequacy.
- Defendants challenging means-plus-function claims in IPR should carefully assess whether the specification contains any named protocols or algorithms, which will determine whether the Board must consider expert testimony before ruling on structural sufficiency.
Why It Matters
Means-plus-function claims are common in telecommunications and software patents, and their validity frequently turns on whether the specification provides adequate algorithmic structure for a POSITA to understand what structure performs the claimed function. This decision is significant because it prevents the PTAB — and district courts applying analogous principles — from short-circuiting the analysis by refusing to consider expert testimony whenever a computer-implemented function is at issue.
For wireless technology patent holders asserting standard-essential patents (SEPs) or other telecommunications patents, the ruling is particularly relevant. These patents often claim functions described in terms of industry protocols and standards (like HARQ, RLC, or PDCP in cellular systems). The Federal Circuit’s clarification that naming such protocols constitutes some structural disclosure — entitling the patent holder to have expert testimony considered — provides a meaningful procedural protection against summary invalidity rulings at the Board.