The US Court of Appeals for the Federal Circuit reiterated that in the context of construing computer-implemented means-plus-function limitations, if the specification discloses some arguable algorithm, even if a party contends that the algorithm is inadequate, the sufficiency of the purportedly-adequate structure disclosed in the specification must be evaluated in light of the knowledge possessed by a skilled artisan. Sisvel International S. A. v. Sierra Wireless, Inc., Case No. 22-1493 (Fed. Cir. Oct. 6, 2023) (Moore, Clevenger, Chen, JJ.)

Sisvel owns a patent directed to methods of channel coding when transmitting data in radio systems. The patent uses techniques called “link adaptation” and “incremental redundancy,” which are alleged to provide improvement over prior channel coding techniques. Sierra filed a petition for inter partes review (IPR) challenging certain claims as obvious over the Chen reference by itself and challenging those and other claims as obvious over the combination of the Chen and Eriksson references or the combination of the Chen and GSM references. The Patent Trial & Appeal Board found that some challenged claims were obvious based on Chen alone and that other claims were patentable over the proposed combination of references. Both parties appealed.

Sisvel appealed the Board’s unpatentability finding, arguing that Chen failed to disclose a second puncturing pattern. Sisvel also argued that the Board did not provide a sufficiently detailed explanation to support its finding that Chen disclosed the claimed “combining” limitation and ignored Sisvel’s rebuttal arguments. The Federal Circuit disagreed with Sisvel on both counts and affirmed the Board’s determination. Regarding the second puncturing pattern, the Court found that the independent claim required a “first puncturing pattern” and a “second puncturing pattern,” and that Chen expressly described that its coded transmissions are “generated by using punctured codes” and that “[p]uncturing reduces the number of code symbols to be retransmitted.” Therefore, the Court found that substantial evidence supported the Board’s finding that Chen taught a second puncturing pattern. Regarding the “combining” limitation, the Court affirmed the Board’s decision and concluded that Chen’s disclosure of “accumulating the code symbols from the transmitted and retransmitted coded data blocks,” also referred to in Chen as “interleaving,” taught the “combining” limitation. Overall, the Court determined that the Board’s analysis was sufficiently detailed, adequately addressed Sisvel’s related arguments and was supported by substantial evidence.

Sierra appealed the patentability finding, arguing that the Board’s finding that a skilled artisan would not have been motivated to combine Chen and the GSM references was not supported by substantial evidence. Sierra also argued that the Board erroneously found insufficient corresponding structure in the specification for the term “means for detecting.” The Federal Circuit concluded that substantial evidence supported the Board’s finding of a lack of motivation to combine Chen and the GSM references, but that the Board erred in analyzing the “means for detecting” limitation. Regarding motivation to combine, the Court explained that although an IPR petitioner has a low burden of explaining why a skilled artisan would have been motivated to combine various references to form the claimed invention, it nevertheless could not “fault the Board for being at a loss in trying to decipher [Sierra’s] kitchen-sink of unclear and confusing motivation-to-combine arguments.”

Regarding the “means for detecting” limitation, the Federal Circuit found that it required a “means for detecting a need for retransmission” and that the specification disclosed protocols such as “ARG” and “Hybrid ARQ” to accomplish this goal. Citing to its 2012 decision in Noah Systems, Inc. v. Intuit Inc., in which the Federal Circuit created a two-step process for determining whether expert testimony can be used to fill gaps in the structural explanation of algorithmic means-plus-function claims, the Court found that the Board erred by not considering “ARG” and “Hybrid ARQ” as algorithms. The protocols should have been evaluated under Noah step two (“where the specification discloses some arguable algorithm, even if a party contends that the algorithm is inadequate, the sufficiency of the purportedly-adequate structure disclosed in the specification must be evaluated in light of the knowledge possessed by a skilled artisan.”) The Court thus found that the Board should have considered expert testimony and remanded this issue for further proceedings.