Court Opinion

ID: 9885815
Source: CourtListenerOpinion
Date Created: 2023-10-06 15:00:52.690568+00
Date Added: 2024-06-11T14:23:32.817476
License: Public Domain

Case: 22-1493   Document: 68     Page: 1    Filed: 10/06/2023

   United States Court of Appeals
       for the Federal Circuit
                 ______________________

            SISVEL INTERNATIONAL S.A.,
                     Appellant

                            v.

   SIERRA WIRELESS, INC., TELIT CINTERION
  DEUTSCHLAND GMBH, F/D/B/A THALES DIS AIS
            DEUTSCHLAND GMBH
                Cross-Appellants
             ______________________

                  2022-1493, 2022-1547
                 ______________________

     Appeals from the United States Patent and Trademark
 Office, Patent Trial and Appeal Board in No. IPR2020-
 01099.
                  ______________________

                 Decided: October 6, 2023
                 ______________________

     ROBERT J. GAJARSA, Devlin Law Firm LLC, Wilming-
 ton, DE, argued for appellant. Also represented by
 TIMOTHY DEVLIN, NEIL A. BENCHELL.

     KOURTNEY MUELLER MERRILL, Perkins Coie LLP, Den-
 ver, CO, argued for all cross-appellants. Cross-appellant
 Sierra Wireless, Inc. also represented by AMANDA TESSAR.

    GUY YONAY, Pearl Cohen Zedek Latzer Baratz LLP,
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 2         SISVEL INTERNATIONAL S.A. v. SIERRA WIRELESS, INC.

 New York, NY, for cross-appellant Telit Cinterion Deutsch-
 land GmbH. Also represented by KYLE AUTERI, I.
                 ______________________

     Before MOORE, Chief Judge, CLEVENGER and CHEN,
                     Circuit Judges.
 CHEN, Circuit Judge.
      The Patent Trial and Appeal Board (Board) determined
 claims 1–3 and 9 of U.S. Patent No. 6,529,561 (’561 patent)
 were unpatentable, but upheld claims 4–8 and 10. Cradle-
 point, Inc. v. Sisvel Int’l S.A., No. IPR2020-01099, 2021 WL
 6655659, at *27 (P.T.A.B. Jan. 18, 2021) (Decision). Sisvel
 International S.A. (Sisvel) appeals the Board’s unpatenta-
 bility determination of claims 1–3 and 9; Sierra Wireless,
 Inc. and Telit Cinterion Deutschland GmbH (collectively,
 Cross-Appellants) appeal the Board’s upholding of claims
 4–8 and 10. As to the appeal, we affirm. As to the cross-
 appeal, we affirm-in-part, vacate-in-part, and remand.
                        BACKGROUND
                              I
      The ’561 patent relates to methods of channel coding
 when transmitting data in radio systems. ’561 patent col. 1
 ll. 10–15, col. 4 ll. 19–30. Channel coding is a technique
 that adds redundant information to a data block, thereby
 creating a coded data block. To account for problems from
 noise and interference during data transmission, the re-
 dundant data allows a receiver to more accurately detect
 and correct errors in the transmitted data, but at the cost
 of requiring more bandwidth and network resource usage.
      The ’561 patent uses techniques called “link adapta-
 tion” and “incremental redundancy,” which it asserts im-
 proves prior channel coding techniques. Id. col. 3 ll. 2–5,
 col. 4 ll. 19–30.    Link adaptation occurs on the
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 SISVEL INTERNATIONAL S.A. v. SIERRA WIRELESS, INC.           3

 transmission side and refers to changing the code rate 1 of
 the transmitted data blocks. Id. col. 1 ll. 39–41. A data
 block is first coded to add redundant data bits, 2 and then
 “punctured” to remove a certain number of coded data bits.
 Id. col. 7 ll. 21–46. In link adaptation, the code rate can be
 adjusted between successive data blocks to optimize radio
 resources based on channel conditions. Id. col. 1 ll. 39–50.
      Incremental redundancy occurs on the receiver side.
 Id. col. 2 ll. 25–27. When a receiver receives a coded data
 block with too many errors to accurately decode, it will
 store that coded data block in memory and request retrans-
 mission of the data block. See id. col. 2 ll. 25–29. After re-
 ceiving the retransmitted data block, the receiver combines
 the stored and the retransmitted coded data blocks. Id.
 col. 2 ll. 27–29. Because the combined coded data block has
 more overall data bits and increased redundancy, it can
 more feasibly be decoded by the receiver. Id. col. 2 ll. 29–
 33.
     The claims recite coding a data block and then punc-
 turing it with a first puncturing pattern to remove some
 data bits from the coded data block. The punctured, coded
 data block is then transmitted to a receiver. The receiver,
 however, may not be able to decode the data and requests
 retransmission. When the transmitter resends the coded
 data block, it performs link adaptation by changing the

     1   The code rate refers to “the ratio of the number of
 user data bits to the coded data bits of a channel.” Id. col. 1
 ll. 50–51. As an example, if 100 data bits are converted into
 200 coded data bits to be transmitted over the channel, the
 code rate is 100/200 = 1/2. Id. col. 1 ll. 51–55.
      2  The ’561 patent appears to refer to the terms “bits”
 and “symbols” interchangeably. ’561 patent col. 8 ll. 10–13
 (“[T]he second puncturing pattern 406 comprises bits
 100100100, i.e. only the first and the third symbol thereaf-
 ter are retained, while other symbols are removed.”).
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 number of bits removed when puncturing the coded data
 block using a second puncturing pattern. Id. col. 1 ll. 39–
 41, col. 9 ll. 60–67. The second puncturing pattern removes
 more bits than the first puncturing pattern, such that the
 retransmitted coded data block transmits fewer bits. When
 the receiver receives the retransmitted coded data block, it
 performs incremental redundancy by combining the origi-
 nal and retransmitted coded data blocks and decoding the
 combined data block. Id. col. 9 ll. 65–67.
     Independent claim 1 of the ’561 patent recites:
     1. A method of transmitting data in a radio system
     from a transmitter to a receiver, the method com-
     prising:
     channel coding a data block into a coded data block
     by using a selected channel coding;
     puncturing the coded data block by using a first
     puncturing pattern;
     transmitting the coded data block punctured by the
     first puncturing pattern to the receiver;
     detecting a need for retransmission of the received
     coded data block;
     transmitting a retransmission request of the coded
     data block to the transmitter;
     increasing the code rate of the coded data block to
     be retransmitted by puncturing the coded data
     block coded by the channel coding of the original
     transmission using a second puncturing pattern in-
     cluding fewer symbols to be transmitted than the
     first puncturing pattern;
     transmitting the coded data block punctured by the
     second puncturing pattern to the receiver;
     combining the received coded data block punctured
     by the first puncturing pattern and the received
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     coded data block punctured by the second punctur-
     ing pattern; and
     decoding the channel coding of the combined coded
     data block.
 Id. at claim 1 (emphasis added).
     Claim 5 is similar to claim 1, but is directed to a radio
 system and further recites a “means for detecting” limita-
 tion 3:
     5. A radio system comprising:
     a transmitter and a receiver having a radio connec-
     tion to the transmitter;
     the transmitter comprising a channel coder for
     channel coding a data block into a coded data block
     by using a selected channel coding and for punctur-
     ing the coded data block by using a first puncturing
     pattern, and transmission means for transmitting
     the coded data block punctured by the first punc-
     turing pattern to the receiver; and
     the receiver comprising a channel decoder for de-
     coding the received coded data block, means for de-
     tecting a need for retransmission of the received
     coded data block, and means for transmitting a re-
     transmission request of the coded data block to the
     transmitter; wherein:
     the channel coder increases the code rate of the
     coded data block to be retransmitted by puncturing
     the coded data block coded by the channel coding of
     the original transmission by using a second

     3   Claim 10 recites the identical limitation “means for
 detecting a need for retransmission of the received coded
 data block.” We treat claim 5 as representative.
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     puncturing pattern comprising fewer symbols to be
     transmitted than the first puncturing pattern;
     the transmission means transmit the coded data
     block punctured by the second puncturing pattern
     to the receiver;
     the receiver comprises means for combining a re-
     ceived coded data block punctured by the first
     puncturing pattern and a received coded data block
     punctured by the second puncturing pattern; and
     the channel decoder decodes the channel coding of
     the combined coded data block.
 Id. at claim 5 (emphasis added).
                              II
     Cross-Appellants filed a petition for inter partes review
 of claims 1–10 of the ’561 patent. Decision, 2021 WL
 6655659, at *1; J.A. 180. Relevant here, Cross-Appellants
 challenged claims 1–3, 5–7, 9, and 10 as unpatentable un-
 der 35 U.S.C. § 103 over Chen, 4 as well as claims 1–10 as
 unpatentable under § 103 over Chen and Eriksson 5 or

     4  World     Intellectual    Property Organization
 (“WIPO”) Patent Application No. PCT/US98/24155, filed
 Nov. 12, 1998, Publication No. WO 99/26371, published
 May 27, 1999, to Tao Chen et al.
    5   S. Eriksson et al., “Comparison of Link Quality
 Control Strategies for Packet Data Services in EDGE,”
 1999 IEEE 49th Vehicular Technology Conference,
 May 16–20, 1999.
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 Chen and GSM 03.64 6. 7 J.A. 186. The Board determined
 that Chen rendered claims 1–3 and 9 obvious, but upheld
 claims 4–8 and 10. Decision, 2021 WL 6655659, at *27.
     First addressing claim 5’s “means for detecting” limita-
 tion, the Board construed it as a means-plus-function limi-
 tation but determined there was “insufficient algorithmic
 structure identified” by Cross-Appellants in its petition.
 Id. at *5–6. The Board acknowledged Cross-Appellants’ as-
 sertion that the “means for detecting” corresponded to var-
 ious protocols mentioned by name in the ’561 patent, such
 as forward error correction (FEC), Automatic Repeat Re-
 quest (ARQ), and hybrid ARQ, and also acknowledged the
 related testimony from Cross-Appellants’ expert, Dr. Ka-
 kaes. Id. at *3, *5–7. Dr. Kakaes testified that a skilled
 artisan would be familiar with “well-known and commonly
 used error detection codes, such as the” cyclic redundancy
 check (CRC) and “[ARQ] protocol and hybrid ARQ,” and
 “would have known from the ’561 specification how to pro-
 gram a processor or hardware to achieve the claimed func-
 tion of ‘detecting a need for retransmission of the received
 coded data block.’” Id. at *7. The Board, however, found
 that this testimony could not remedy the insufficient struc-
 ture disclosed in the specification itself. Id. According to
 the Board, Cross-Appellants “ha[d] not shown that the ’561
 patent presents an algorithm for how the error detection
 code detects an error, nor explained the circumstances

     6    Special Mobile Group (“SMG”) of the European Tel-
 ecommunications Standards Institute (“ETSI”), Global
 System for Mobile Communications (GSM) Technical Spec-
 ification (TS) 101 350 V8.0.0 (1999-07), “Digital cellular tel-
 ecommunications system (Phase 2+); General Packet Radio
 Service (GPRS); Overall description of the GPRS radio in-
 terface; Stage 2,” GSM 03.64, Version 8.0.0, Release 1999.
      7   We collectively refer to Eriksson and GSM 03.64 as
 the “GSM references.”
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 under which the error correcting code cannot correct errors
 and what constitutes ‘sufficient certainty.’” Id. at *8.
     Turning to Cross-Appellants’ prior art challenges, the
 Board found that claims 1–3 and 9 would have been obvi-
 ous in view of Chen. Relevant here, the Board found that
 Chen discloses both the “second puncturing pattern” and
 “combining” limitations of claim 1. Id. at *10–12, *15–18.
 The Board did not evaluate unpatentability of claims 5–7
 and 10 because it was “unable to conclude what structure
 is encompassed” by the “means for detecting” limitation.
 Id. at *19.
     As for the grounds based on Chen with GSM refer-
 ences, the Board found that Cross-Appellants’ many of-
 fered reasons to combine the references “[did] not suffice as
 an articulated reason with a rational underpinning to com-
 bine the respective teachings of the references.” Id. at *24–
 27. The Board also found that many of Cross-Appellants’
 reasons to combine Chen and the GSM references lacked
 clarity. Id. at *25–27. And as with its analysis based on
 Chen alone, the Board again did not reach claims 5–8 and
 10 because it was unable to conclude what structure is en-
 compassed by the “means for detecting” limitation. Id. at
 *27.
     Thus, the Board ultimately determined claims 1–3 and
 9 were unpatentable under § 103 based on Chen, but up-
 held claims 4–8 and 10. Id.
    Sisvel and Cross-Appellants each timely appealed the
 Board’s final written decision. We have jurisdiction under
 28 U.S.C. § 1295(a)(4)(A) and 35 U.S.C. § 141(c).
                    STANDARD OF REVIEW
     We review decisions by the Board under the standards
 set forth in the Administrative Procedure Act (APA).
 5 U.S.C. § 706; Pride Mobility Prods. Corp. v. Permobil,
 Inc., 818 F.3d 1307, 1313 (Fed. Cir. 2016). We set aside the
 Board’s actions if they are “arbitrary, capricious, an abuse
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 of discretion, or otherwise not in accordance with law” or
 “unsupported by substantial evidence.”            5 U.S.C.
 § 706(2)(A), (E). The Board’s “[d]eterminations about gov-
 erning legal standards and about intrinsic evidence are re-
 viewed de novo, and any factual findings about extrinsic
 evidence relevant to the question, such as evidence about
 knowledge of those skilled in the art, are reviewed for” sub-
 stantial evidence. BASF Corp. v. Johnson Matthey Inc.,
 875 F.3d 1360, 1365 (Fed. Cir. 2017); ACCO Brands Corp.
 v. Fellowes, Inc., 813 F.3d 1361, 1365 (Fed. Cir. 2016).
     Obviousness is a question of law based on underlying
 findings of fact. In re Gartside, 203 F.3d 1305, 1316 (Fed.
 Cir. 2000). Relevant underlying factual questions here in-
 clude the scope and content of the prior art, the differences
 between the prior art and the claimed invention, whether
 the prior art reference teaches away, and the presence or
 absence of a motivation to combine. Ariosa Diagnostics v.
 Verinata Health, Inc., 805 F.3d 1359, 1364 (Fed. Cir. 2015);
 Gen. Elec. Co. v. Raytheon Techs. Corp., 983 F.3d 1334,
 1345 (Fed. Cir. 2020). 8
                         DISCUSSION
                          I. Appeal
     On appeal, Sisvel argues that (1) Chen fails to disclose
 a second puncturing pattern, Appellant’s Opening
 Br. 12–15; and (2) the Board did not provide a sufficiently
 detailed explanation to support its finding that Chen dis-
 closes the “combining” limitation, and ignored its rebuttal
 arguments, Appellant’s Opening Br. 16–19. We disagree
 with Sisvel on both counts.

     8   The Board applied pre-AIA law, which the parties
 do not dispute. Decision, 2021 WL 6655659, at *3 n.1. We
 therefore discuss the pre-AIA versions of all relevant pa-
 tentability statutes.
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                A. Second Puncturing Pattern
     Substantial evidence supports the Board’s finding that
 Chen discloses the claimed “second puncturing pattern.”
 Decision, 2021 WL 6655659, at *10–12, *15. Claim 1 re-
 quires a “first puncturing pattern” and a “second punctur-
 ing pattern.” ’561 patent at claim 1. To teach the first and
 second puncturing pattern, the Board relied on Chen’s em-
 bodiment that has an “original transmission” and a “re-
 transmission.” J.A. 1214 ll. 38–39, 1215 ll. 4–37. To create
 the original transmission and the retransmission, Chen
 discloses a convolutional encoder with, for example, four
 generators (g0, g1, g2, and g3) that each output code sym-
 bols. J.A. 1214 l. 38–1215 l. 37. For the original transmis-
 sion, only the code symbols from generators g0 and g1 are
 sent. J.A. 1215 ll. 4–33. When an error occurs in receiving
 the originally transmitted packet, a “retransmitted packet”
 can be sent that includes “code symbols from other genera-
 tors which have not been transmitted previously,” such as
 code symbols from generators g2 and/or g3. J.A. 1215 ll. 6–
 8. Chen expressly describes that its coded transmissions
 are “generated by using punctured codes” and that “[p]unc-
 turing reduces the number of code symbols to be retrans-
 mitted.” J.A. 1215 ll. 25–37. Cross-Appellants’ expert, Dr.
 Kakaes, explained that a skilled artisan would have under-
 stood Chen’s selective transmission of selected code sym-
 bols from certain generators to refer to puncturing, such
 that the original transmission with only code symbols from
 generators g0 and g1 correspond to a “first puncturing pat-
 tern” and the retransmitted packet with additional code
 symbols (e.g., g2) corresponds to a “second puncturing pat-
 tern.” J.A. 2481–88 ¶¶ 31–41. Despite Sisvel’s arguments
 to the contrary, Appellant’s Opening Br. 13–15, Chen’s dis-
 closure and Dr. Kakaes’s testimony are substantial
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 evidence supporting the Board’s finding that Chen teaches
 the “second puncturing pattern” limitation. 9
      Sisvel also contends that Chen teaches away from us-
 ing a second puncturing pattern. Appellant’s Opening
 Br. 15; Appellant’s Reply Br. 4–7. Substantial evidence
 supports the Board’s finding that Chen teaches a second
 puncturing pattern. Although Chen states that puncturing
 “reduces the error correcting capability of the convolutional
 code,” J.A. 1215 ll. 35–37, Chen expressly states that “other
 code rates can also be generated using punctured codes and
 are within the scope of the present invention.” J.A. 1215
 ll. 25–26. The latter statement refutes any suggestion of
 teaching away, as it expressly contemplates “using punc-
 tured codes.” See DePuy Spine, Inc. v. Medtronic Sofamor
 Danek, Inc., 567 F.3d 1314, 1327 (Fed. Cir. 2009) (“A refer-
 ence may be said to teach away when a person of ordinary
 skill, upon reading the reference, would be discouraged
 from following the path set out in the reference, or would
 be led in a direction divergent from the path that was taken
 by the applicant.” (citations omitted)).
                        B. Combining
     Turning to the “combining” limitation, the Board’s
 analysis is sufficiently detailed and did not ignore Sisvel’s
 arguments. The Board found that Chen’s disclosure of “ac-
 cumulating the code symbols from the transmitted and re-
 transmitted coded data blocks,” also referred to in Chen as
 “interleaving,” teaches the “combining” limitation. Deci-
 sion, 2021 WL 6655659, at *12. The Board rejected Sisvel’s

     9   The Board reasonably found that Chen discloses
 the limitation “a second puncturing pattern including
 fewer symbols to be transmitted than the first puncturing
 pattern” through Chen’s retransmission of only the code
 symbols from generator g2. Decision, 2021 WL 6655659,
 at *11–12; J.A. 1215 ll. 16–22.
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 argument that Chen’s “interleaving” is different than the
 ’561 patent’s “combining” limitation, finding them to be the
 same. Decision, 2021 WL 6655659, at *17 (“Petitioner fur-
 ther contends, and we agree, that ‘“combining” in the ’561
 patent and “interleaving” in the second embodiment of
 Chen are the exact same thing . . . .’”). In fact, the Board
 expressly stated that it considered Sisvel’s arguments in
 the Patent Owner Response and Sur-Reply and testimony
 from Sisvel’s expert Mr. Bates, but it found Sisvel’s argu-
 ments “unavailing” because “the record does not support
 the finding that ‘combining’ as recited in claim 1 excludes
 interleaving as taught by Chen.” Id. at *17. Moreover, the
 Board acknowledged Sisvel’s argument that Chen includes
 a statement that “retransmitted packets are interleaved
 (not combined).” J.A. 483, 571–72 (both quoting J.A. 1215
 ll. 9–10). But the Board found this argument unpersuasive
 in light of Chen’s other teachings of accumulating and com-
 bining packets. Decision, 2021 WL 6655659, at *16–17
 (“[A]lthough Chen distinguishes interleaving from combin-
 ing in one instance, it also discloses accumulating packets
 and combining packets.”).
     Sisvel also asserts that it rebutted the Board’s reliance
 on Chen’s disclosure of the “accumulation of packet energy”
 for the “combining” limitation.        Appellant’s Opening
 Br. 17–18 (citing J.A. 484). The Board, however, relied on
 Chen’s alternative embodiment describing a method of ac-
 cumulating code symbols, which is different than accumu-
 lating packet energy. Decision, 2021 WL 6655659, at *12,
 *17–18 (citing J.A. 1215 ll. 9–13, 17–24, 33–35). The Board
 agreed with Cross-Appellants that Chen’s accumulation of
 code symbols through “interleaving” is the same as the ’561
 patent’s “combining” because “[b]oth involve the same con-
 cept: collecting together different coded symbols from the
 transmission and retransmission to be decoded together at
 a lower code rate.” Id. at *17.
     Accordingly, the Board’s analysis of the “combining”
 limitation is sufficiently detailed, adequately addresses
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 Sisvel’s related arguments, and is supported by substantial
 evidence.
                      II. Cross-Appeal
     Cross-Appellants argue that (1) the Board’s finding
 that a skilled artisan would not have been motivated to
 combine Chen and the GSM references is not supported by
 substantial    evidence,      Cross-Appellants’     Opening
 Br. 33–52; and (2) the Board erroneously found insufficient
 corresponding structure in the specification for the term
 “means for detecting,” Cross-Appellants’ Opening
 Br. 52–61. We hold substantial evidence supports 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.
                 A. Motivation to Combine
     The Board found that each of Cross-Appellants’ ten
 reasons for combining Chen and GSM “[did] not suffice as
 an articulated reason with a rational underpinning to com-
 bine the respective teachings of the references.” Decision,
 2021 WL 6655659, at *24–27. That finding was more than
 reasonable in this case, where Cross-Appellants’ proposed
 combinations and rationales were expressed at such a non-
 specific, high level of generality, they never made clear to
 the Board what portions of the references were being com-
 bined and why a skilled artisan would identify those par-
 ticular elements for a combination.
     We agree with the Board that Cross-Appellants’ first,
 second, and third reasons to combine were merely asser-
 tions that the references were analogous art, which, with-
 out more, is an insufficient articulation for motivation to
 combine. Id. at *24; J.A. 250–251. We further agree with
 the Board that Cross-Appellants’ remaining rationales
 were too conclusory, lacked clarity, or suffered from both
 problems. Decision, 2021 WL 6655659, at *24–27; see, e.g.,
 id. at *26 (“[T]he record . . . lacks clarity as to how
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 Petitioner contends Chen is modified and/or improved by
 [the GSM references] or how Chen itself modifies and/or
 improves [the GSM references], respectively, despite Peti-
 tioner having had the opportunity, post-institution, to ad-
 dress this deficiency.”); id. at *27 (“[I]t is not clear that the
 second [modulation coding scheme (MCS)] is that of Chen
 or [the GSM references].”). For example, the Petition does
 not explain what reference is the primary versus secondary
 reference, what elements are missing from the primary ref-
 erence, what elements should be added from the secondary
 reference to reach the claimed invention, or why those par-
 ticular elements would be obvious to add. J.A. 252–262.
 Moreover, Cross-Appellants are inconsistent as to how
 Chen and the GSM references should be combined. In
 some instances, Cross-Appellants allege that a skilled arti-
 san would improve Chen with the GSM references. See,
 e.g., J.A. 252 (“Applying [the GSM references’ teachings] to
 Chen would have been applying known techniques to im-
 prove the similar incremental redundancy techniques al-
 ready taught by Chen in the same manner.”); J.A. 259
 (asserting that a skilled artisan would be “applying [the
 GSM references] to Chen . . .”). In other instances, Cross-
 Appellants allege the converse—that a skilled artisan
 would improve the GSM references with Chen. See, e.g.,
 J.A. 542–44 (discussing applying Chen to the GSM stand-
 ards described in the GSM references); see also Cross-Ap-
 pellants’ Opening Br. 50 (“Cross-Appellants’ argument has
 always been that a [skilled artisan] would take Chen’s dis-
 closed incremental redundancy retransmission method
 and apply it to the mandatory GSM protocols and MCSs to
 arrive at the claimed invention.”). Under the circum-
 stances, we cannot fault the Board for being at a loss in
 trying to decipher Cross-Appellants kitchen-sink of unclear
 and confusing motivation-to-combine arguments.
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                   B. Means for Detecting
     1. Proceedings Before the Board
      The Board found that Cross-Appellants “fail[ed] to
 identify sufficient algorithmic structure” in the specifica-
 tion corresponding to claim 5’s “means for detecting a need
 for retransmission of the received coded data block.” Deci-
 sion, 2021 WL 6655659, at *8. Under the familiar analysis
 from this Court’s decision in Noah Systems, Inc. v. Intuit
 Inc., “our case law regarding special purpose computer-im-
 plemented means-plus-functions claims is divided into two
 distinct groups: First, cases in which the specification dis-
 closes no algorithm; and second, cases in which the specifi-
 cation does disclose an algorithm but a [party] contends
 that disclosure is inadequate.” 675 F.3d 1302, 1313 (Fed.
 Cir. 2012). Where the specification discloses no algorithm,
 the knowledge of a skilled artisan is irrelevant. Id. (citing
 Aristocrat Techs. Austl. Pty Ltd. v. Int’l Game Tech., 521
 F.3d 1328, 1337 (Fed. Cir. 2008)). But where the specifica-
 tion discloses some arguable algorithm, even if a party con-
 tends that the algorithm is inadequate, the sufficiency of
 the purportedly-adequate structure disclosed in the speci-
 fication must be evaluated in light of the knowledge pos-
 sessed by a skilled artisan. Id. (citing Aristocrat, 521 F.3d
 at 1337; and then AllVoice Computing PLC v. Nuance
 Commc’ns, Inc., 504 F.3d 1236, 1245 (Fed. Cir. 2007)).
     Before the Board, Cross-Appellants relied on certain
 software protocols mentioned by name in the specification
 as examples of the corresponding structure, such as “ARQ”
 (Automatic Repeat Request) and “hybrid FEC/ARQ (For-
 ward Error Correction/Automatic Repeat Request” (hybrid
 ARQ). ’561 patent FIG. 2, col. 2 ll. 33–37, col. 10 ll. 41–42;
 J.A. 84. Cross-Appellants further relied on the agreement
 between both parties’ experts that these software protocols
 were well-understood and well-known to a person of ordi-
 nary skill. See, e.g., Cross-Appellants’ Br. 54 (“These pro-
 tocols were not only known in the art, but were included in
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 GSM’s mandatory technical specifications.”); J.A. 523 (pa-
 tentee’s expert testifying that “a [skilled artisan] would
 well understand what Forward Error Correction is and
 where it’s conducted and would also understand what ARQ
 is.”). Before the Board and before us, Cross-Appellants ar-
 gue that these references to the names of software proto-
 cols are sufficient to bring the case out of Noah group one
 (absolutely no disclosure) and into Noah group two (some
 disclosure). Cross-Appellants assert that it is not always
 necessary to set forth in the specification the protocol steps
 themselves, as long as the protocol name is sufficient to
 connote specific structure to a skilled artisan. We agree
 with Cross-Appellants that the Board should have evalu-
 ated the protocols disclosed in the specification in light of
 the knowledge of a skilled artisan and conducted an analy-
 sis appropriate to Noah group two.
      The Board disregarded the expert testimony offered by
 Cross-Appellants because it appeared to classify this case
 as falling within the “no algorithm” group of the Noah
 framework, where evidence of a skilled artisan’s knowledge
 is irrelevant. For example, the Board rejected Dr. Kakaes’s
 apparently undisputed testimony that a skilled artisan
 would be familiar with “well-known and commonly used er-
 ror detection codes” such as CRC, as well as ARQ and hy-
 brid ARQ, and “would have known from the ’561
 specification how to program a processor or hardware to
 achieve the claimed function of ‘detecting a need for re-
 transmission of the received coded data block.’” Decision,
 2021 WL 6655659, at *7. The Board relied on our cases
 stating that “the testimony of one of ordinary skill in the
 art cannot supplant the total absence of structure from the
 specification” because § 112 requires that “the specification
 itself adequately disclose the corresponding structure.” Id.
 (quoting Default Proof Credit Card Sys., Inc. v. Home Depot
 U.S.A., Inc., 412 F.3d 1291, 1302 (Fed. Cir. 2005); and then
 Noah, 675 F.3d at 1312). Thus, the Board asserted that
 even if a skilled artisan “would have known of FEC, CRC,
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 ARQ, and hybrid ARQ,” the Board refused to consider that
 knowledge because the specification itself contained no “al-
 gorithm for performing any one or more of these protocols.”
 Id. at 7 (citing the portion of Noah discussing the “total ab-
 sence of structure from the specification”).
     2. Our Precedents on Noah Group One
     Patents falling into the first Noah group involve “the
 total absence of structure from the specification.” William-
 son v. Citrix Online, LLC, 792 F.3d 1339, 1354 (Fed. Cir.
 2015) (emphasis added). Where there is no arguable dis-
 closure of structure, “the testimony of one of ordinary skill
 in the art” “cannot create structure where none otherwise
 exists.” Id. (emphasis added); accord Noah, 675 F.3d at
 1313 (explaining that group one cases involve “a total omis-
 sion of structure” from the specification).
      Some Noah group one cases arise when the patentee
 concedes that the patent discloses no structure, but at-
 tempts to defend its claims by arguing that structure is not
 needed. Robert Bosch, LLC v. Snap-On Inc., 769 F.3d 1094,
 1101 (Fed. Cir. 2014) (noting that the patentee conceded
 there was no structure in the specification but attempted
 to defend the claims by arguing the claims were not subject
 to § 112, ¶ 6 at all); EON Corp. IP Holdings LLC v. AT & T
 Mobility LLC, 785 F.3d 616, 621, 624 (Fed. Cir. 2015) (ex-
 plaining that “[t]he parties agree that the [asserted] pa-
 tent’s specification discloses no algorithms, so this case
 falls in the first category” of Noah, but noting that the pa-
 tentee attempted to rely on the “Katz exception” 10 to defend
 the lack of structure).

     10   The Katz exception arises from this Court’s deci-
 sion in In re Katz Interactive Call Processing Patent Litiga-
 tion, which held that a microprocessor alone, without an
 algorithm, was sufficient disclosure for claims whose
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     Other cases finding a “total absence” of structure arise
 when we determine that a claim has two (or more) func-
 tions, but we find that the disclosed structure applies only
 to one of the functions. See, e.g., Tomita Techs. USA, LLC
 v. Nintendo Co., 594 F. App’x 657, 662 (Fed. Cir. 2014)
 (non-precedential) (holding that a claim involved the func-
 tions of “offsetting and displaying,” but omitted any struc-
 ture for displaying, and thus fell into Noah group one).
 Noah itself was such a case. There, we explained that
 when there is disclosed structure for “less than all” of the
 functions in a claim, “we must analyze the disclosures as
 we do when no algorithm is disclosed.” Noah, 675 F.3d at
 1318.
      A related line of cases arises when a patentee attempts
 to “rewrite the patent’s specification” by using an expert to
 retroactively import structure that is totally absent from
 the patent. Default Proof, 412 F.3d at 1302; accord Noah,
 675 F.3d at 1313 (citing Default Proof, 412 F.3d at 1301).
 For example, the patentee in Function Media L.L.C. v.
 Google, Inc. sought to excuse its lack of “any disclosure of
 the structure” by trying to “rely on the knowledge of one
 skilled in the art to fill the gaps” in the specification. 708
 F.3d 1310, 1319 (Fed. Cir. 2013). The Function Media pa-
 tentee asserted that it would be “unnecessary and extrane-
 ous” to require a specification to disclose structure that was
 within the background knowledge of a skilled artisan,

 functions are so fundamentally basic that they can be
 “achieved by any general purpose computer without special
 programming.” 639 F.3d 1303, 1316 (Fed. Cir. 2011) (find-
 ing a general-purpose microprocessor sufficient structure
 for otherwise-unspecified functions of “processing,” “receiv-
 ing,” and “storing”). But we immediately characterized In
 re Katz as a “narrow exception” to the “default rule” that
 an algorithm is required. Ergo Licensing, LLC v. Care-
 Fusion 303, Inc., 673 F.3d 1361, 1364–65 (Fed. Cir. 2012).
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 citing our decision in Typhoon Touch Technologies, Inc. v.
 Dell, Inc. for support. Id. at 1318–19 (citing 659 F.3d 1376,
 1385 (Fed. Cir. 2011)). We disagreed with the patentee.
 We distinguished Typhoon because that case involved ex-
 plicit, though brief, disclosures in the specification. Id. at
 1319. Unlike Typhoon’s brief-but-adequately-disclosed al-
 gorithm, Function Media involved no disclosure whatso-
 ever, and thus appropriately fell into Noah’s first group.
 Id. at 1318.
     Function Media’s holding fits squarely within a long
 line of cases recognizing that expert testimony can “shed
 light on” the meaning of a specification’s disclosure without
 being tantamount to a “rewrite” of the specification, but
 only when some actual disclosure exists in the specifica-
 tion. Default Proof, 412 F.3d at 1302 (quoting Omega
 Eng’g, Inc. v. Raytek Corp., 334 F.3d 1314, 1332 (Fed. Cir.
 2003)); Function Media, 708 F.3d at 1318 (quoting Default
 Proof, 412 F.3d at 1302).
      Finally, we have considered cases that involve specifi-
 cation disclosures that are so generic and vague that they
 do not qualify as structure as a matter of law. For example,
 we rejected a disclosure of a “standard microprocessor”
 with “appropriate programming” because such a disclosure
 effectively “imposes no limitation whatever, as any general
 purpose computer must be programmed.” Aristocrat, 521
 F.3d at 1334; accord Function Media, 708 F.3d at 1318
 (holding that a specification’s mere disclosure of “a com-
 puter program that transmits” is not structure as a matter
 of law because it is merely a non-limiting “abstraction that
 simply describes the function”). For similar reasons, we
 have also rejected the “bare statement” that any “known
 techniques or methods can be used” as structure. Biome-
 dino, LLC v. Waters Techs. Corp., 490 F.3d 946, 953 (Fed.
 Cir. 2007). Noah itself rejected a general reference to “off
 the shelf software” as a basis for the patentee to retroac-
 tively “fill the gaps in its specification.” Noah, 675 F.3d at
 1317. Analogizing to our cases that rejected disclosures of
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 “any computer-related device” as insufficient, Noah con-
 cluded that an otherwise-unspecified reference to all “off
 the shelf software” was too generic, and therefore “does not
 disclose an algorithm” as a matter of law. Id. (citing Black-
 board, Inc. v. Desire2Learn, Inc., 574 F.3d 1371, 1383 (Fed.
 Cir. 2009)).
      3. Our Precedents on Noah Group Two
      If there is some disclosure of structure in the specifica-
 tion for performing the claimed function, the question of
 whether the specification discloses sufficient structure
 must be viewed in light of the knowledge of a skilled arti-
 san. For example, in Atmel Corp. v. Information Storage
 Devices, Inc, we considered whether a specification’s refer-
 ence to the title of a scientific article could serve as suffi-
 cient structure for a means-plus function limitation. 198
 F.3d 1374, 1377 (Fed. Cir. 1999) (claiming a “high voltage
 generating means disposed on said semiconductor circuit
 for generating a high voltage from a lower voltage power
 supply” (emphasis added)). We determined that while the
 content of referenced scientific article may not be incorpo-
 rated by reference—because the article was not itself part
 of the specification—we could consider the title of the arti-
 cle, which did appear in the specification. Id. at 1382–83.
      Our inquiry, then, turned on what a skilled artisan
 would understand from the title of the article itself, which
 referenced a particular type of integrated circuit (i.e., on-
 chip NMOS integrated circuits) and a particular approach
 to generating voltage (i.e., voltage multiplication). Id. at
 1377. We noted that the patentee’s expert offered undis-
 puted testimony that the title of the article alone was suf-
 ficient to indicate the precise structure to a skilled artisan.
 Id. at 1382 (“Atmel’s expert, Callahan, testified that this
 title alone was sufficient to indicate to one skilled in the art
 the precise structure of the means recited in the specifica-
 tion. The record indicates that that testimony was essen-
 tially unrebutted.”). Thus, while we did not reach outside
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 of the specification to evaluate portions of the article “that
 do[] not appear in the specification,” we also took account
 of what “the specification plainly states”—i.e., the title of
 the article—and all that it disclosed to a person of ordinary
 skill. Id.; accord S3 Inc. v. NVIDIA Corp., 259 F.3d 1364,
 1370–71 (Fed. Cir. 2001) (approving structure where the
 details of the structure were not described in the specifica-
 tion, but it was a “well known electronic structure and per-
 forms a common electronic function, and is readily
 implemented from the description in the specification”).
     We have applied this skilled artisan perspective for
 means-plus-function limitations in the context of software.
 In AllVoice Computing PLC v. Nuance Communications,
 Inc., we held that “[i]n software cases . . . algorithms in the
 specification need only disclose adequate defining struc-
 ture to render the bounds of the claim understandable to
 one of ordinary skill in the art.” 504 F.3d at 1245 (citing
 Med. Instrumentation & Diagnostics Corp. v. Elekta AB,
 344 F.3d 1205, 1214 (Fed. Cir. 2003)). There, we relied on
 a specification’s reference to “the dynamic data exchange
 (DDE) protocol in the Windows operating system” as an al-
 gorithm. Id. at 1241–42. Though the specification did not
 detail what steps corresponded to the Windows version of
 the DDE protocol, we determined that “the reference to
 DDE in the specification” was sufficient to require consid-
 eration of expert testimony. Id. at 1242. Relying on the
 patentee’s expert testimony that implementation of the
 DDE protocol “would be a trivial matter” for a skilled arti-
 san, we found the claims sufficiently definite. Id.
     Thus, for a means-plus-function limitation where the
 corresponding structure is an algorithm, the specification
 need not disclose all the details of the algorithm to satisfy
 the definiteness requirement of § 112 ¶ 2 so long as what
 is disclosed would be sufficiently definite to a skilled arti-
 san. See Finisar Corp. v. DirecTV Group, Inc., 523 F.3d
 1323, 1340 (Fed. Cir. 2008) (explaining that a patentee may
 disclose algorithmic structure “in any understandable
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 22         SISVEL INTERNATIONAL S.A. v. SIERRA WIRELESS, INC.

 terms including as a mathematical formula, in prose . . . or
 as a flow chart, or in any other manner that provides suffi-
 cient structure” (emphasis added)).
      The line demarking Noah group one from group two is
 thus clear: while an expert’s testimony may “not create or
 infer the structure” that is totally absent from the specifi-
 cation, our cases allow “[e]xpert testimony . . . to show
 what” the disclosures that actually appear in the specifica-
 tion “would convey to one skilled in the art.” Biomedino,
 490 F.3d at 952. Cases where structure is “totally absent”
 fall in Noah group one, while cases with even “arguably”
 adequate disclosure fall into Noah group two. Noah, 675
 F.3d at 1318–19; EON Corp., 785 F.3d at 624 (“Where the
 specification discloses an algorithm that the accused in-
 fringer contends is inadequate, we judge the disclosure’s
 sufficiency based on the skilled artisan’s perspective.” (cit-
 ing Noah, 675 F.3d at 1313)).
    4. Our Precedents Dictate That This is a Noah Group
 Two Case, Requiring Consideration of Expert Testimony
      With these principles in mind, the question presented
 by this case is whether the specification’s explicit reference
 to protocol names—which no party disputes refer to proto-
 cols known in the art—is sufficient to bring this case into
 Noah group two. We hold that it is. As such, the Board
 should have considered the knowledge of a skilled artisan
 to assess whether the protocol name sufficiently discloses
 an understood algorithm corresponding to the means-plus-
 function limitation. Contrary to the Board’s view, that re-
 mains true even though the steps corresponding to the pro-
 tocols are not expressly set out in the specification. Like in
 Noah, the Board thus erred when it “classified this case as
 a case involving no disclosed algorithm, and, because of
 this error, also improperly refused to allow [Cross-Appel-
 lants] to present expert testimony regarding the sufficiency
 of the purportedly disclosed algorithm.” Noah, 675 F.3d at
 1313.
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      This case does not resemble our precedents on Noah
 group one. This is not a case, akin to Default Proof, where
 there is a “total absence” of disclosure in the specification,
 with a party relying on an expert to “rewrite” the specifica-
 tion to retroactively insert certain protocols into the pa-
 tent—the ’561 patent itself identifies by name the relevant
 software protocols in the specification. Nor is this a case,
 like Biomedino, involving a vague catch-all phrase, like re-
 citing all “known techniques” and leaving the reader to
 guess which allegedly known techniques are claimed. The
 ’561 patent gives a concrete answer by disclosing to a
 skilled artisan a discrete, limited, and specific set of soft-
 ware protocols: FEC, ARQ, and hybrid ARQ.
      The ’561 patent’s disclosures resemble our prior prece-
 dents which have permitted reliance on expert testimony,
 most particularly Atmel and AllVoice. Because the protocol
 names are stated within the ’561 patent’s specification, this
 case is indistinguishable from Atmel, where the specifica-
 tion’s reference to an article title “alone” was sufficient to
 permit consideration of expert testimony on its meaning.
 Atmel, 198 F.3d at 1382. Here, Cross-Appellants levy an
 identical contention: that the reference to the names of spe-
 cific protocols would connote a particular set of steps—an
 algorithm—to a skilled artisan. Like the name of the arti-
 cle in Atmel, the names of the protocols in the ’561 patent
 must be considered for all they disclose to a skilled artisan.
 Id. And like the reference to the DDE protocol in AllVoice,
 504 F.3d at 1242, the ’561 patent’s reference to protocol
 names is enough to require the Board to consider the im-
 port of those names in light of the knowledge of a skilled
 artisan.
     Given the protocols identified in the specification, the
 Board should have considered expert testimony to “shed
 light on” these disclosures. Default Proof, 412 F.3d at 1302.
 That does not allow an expert to create new structure or
 imply structure from background knowledge—instead, it
 only reads the existing disclosures in the specification for
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 all they “would convey to one skilled in the art.” Biome-
 dino, 490 F.3d at 952. 11
     As should be clear, we do not reach the merits of the
 factual question of whether the protocols identified in the
 ’561 patent’s specification disclose sufficient structure to
 satisfy § 112 ¶ 2. We instead leave that question for the
 Board. On remand, the Board must conduct the analysis
 appropriate for Noah group two, including whether any of
 the protocols are clearly linked or associated with “the

      11 We are quick to emphasize that we do not hold ref-
 erence to a protocol name will always be sufficient struc-
 ture. For example, it would not be enough to merely
 reference the name of a protocol that is unknown in the art,
 because the name of an unknown protocol, alone, would not
 inform a skilled artisan of the relevant steps that allegedly
 constitute an algorithm. Moreover, even references to the
 name of a known protocol may not always be enough in all
 cases. It may be the case that, as a factual matter, a name
 is merely a generic umbrella term that encompasses a vast
 and inchoate set of methods; or a name may connote a
 meaning that is so vague, varied, or ill-understood that a
 skilled artisan would not understand any algorithmic
 structure from the name of the protocol alone.
      At the same time, the mere fact that a protocol (or other
 disclosure) is amenable to more than one implementation
 does not, by itself, make it insufficient structure. AllVoice,
 504 F.3d at 1245 (approving algorithm as sufficient where
 there were “several straightforward ways that [it] could be
 implemented by one skilled in the art using well-known
 features of the Windows operating system”). Some varia-
 bility in implementation of the corresponding structure or
 algorithm is permissible, so long as a skilled artisan can
 identify “adequate defining structure to render the bounds
 of the claim understandable.” Id.
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 function recited in the claim,” 12 and whether they are “ad-
 equate structure for performing this function.” 13 We ex-
 press no view on those foregoing questions.

     12   It is not clear from the Board’s decision whether it
 ever settled on which of the protocols named in the specifi-
 cation (e.g., ARQ, hybrid ARQ, etc.) are “clearly linked” to
 the “means for detecting” limitation. While the determina-
 tion of “what structure, if any . . . corresponds to the
 claimed function” is a “question[] of law, reviewed de novo,”
 we think it prudent to allow the Board to address the ques-
 tion in the first instance. Egenera, Inc. v. Cisco Sys., Inc.,
 972 F.3d 1367, 1373 (Fed. Cir. 2020).
     13   At one point in the Board’s analysis, it appeared to
 implicitly require the “means for detecting” to include an
 additional function: “detecting the need for retransmission
 by an error detection code or by the fact that an error cor-
 recting code cannot correct errors occurring on the channel
 with sufficient certainty.” Decision, 2021 WL 6655659, at
 *8 (cleaned up) (emphasis added). This articulation dif-
 fered from the Board’s express construction, id. at *5–6,
 which included none of the additional language italicized
 in the preceding sentence. See Applied Med. Res. Corp. v.
 U.S. Surgical Corp., 448 F.3d 1324, 1334 (Fed. Cir. 2006)
 (“A court errs when it improperly imports unclaimed func-
 tions into a means-plus-function claim limitation.”). If the
 Board intended to modify its construction of the function to
 include the additional language, the Board must offer a
 reasoned analysis that “fully and particularly set[s] out the
 bases upon which it” relied, with sufficient specificity to al-
 low “effective judicial review.” Provisur Techs., Inc. v. We-
 ber, Inc., 50 F.4th 117, 123 (Fed. Cir. 2022). The Board
 must also consider whether the specification associates
 that additional function with any of the protocols (such as
 ARQ). Cf. ’561 patent FIG. 2, col. 10 l. 41 – col. 11 l. 4.
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                       C. Impossibility
     If the Board finds that the specification lacks a suffi-
 ciently disclosed algorithm, the Board should state as
 much in its decision. It must then proceed to follow the
 guidance in our opinion in Intel Corp. v. Qualcomm Inc., 21
 F.4th 801 (Fed. Cir. 2021).
      Intel held that when faced with a means-plus-function
 limitation with possibly insufficient corresponding struc-
 ture in the specification, the Board must either (1) deter-
 mine whether the claim is indefinite and then whether
 such indefiniteness renders it impossible to adjudicate a
 prior-art challenge on the merits, or (2) resolve the prior-
 art challenge to the patentability of the claims despite the
 potential indefiniteness of the means-plus-function term.
 Id. at 804, 814. The Board must also “clearly state that the
 final written decision does not include a determination of
 patentability of any claim that falls within the impossibil-
 ity category.” Id. at 813.
     Accordingly, we vacate and remand the Board’s deci-
 sion as to the “means for detecting” limitation.
                         CONCLUSION
     We have considered the parties’ remaining arguments
 and do not find them persuasive. For the foregoing rea-
 sons, the Board’s decision is affirmed-in-part, vacated-in-
 part, and remanded for further proceedings consistent with
 this opinion.
   AFFIRMED-IN-PART, VACATED-IN-PART, AND
                 REMANDED
                             COSTS
 No costs.