Case: 22-2220   Document: 62     Page: 1   Filed: 07/22/2024




   United States Court of Appeals
       for the Federal Circuit
                 ______________________

         ZYXEL COMMUNICATIONS CORP.,
                   Appellant

                            v.

         UNM RAINFOREST INNOVATIONS,
                  Cross-Appellant
              ______________________

                  2022-2220, 2022-2250
                 ______________________

     Appeals from the United States Patent and Trademark
 Office, Patent Trial and Appeal Board in Nos. IPR2021-
 00375, IPR2021-00734.
                  ______________________

                  Decided: July 22, 2024
                 ______________________

    JONATHAN IAIN MAX DETRIXHE, Reed Smith LLP, San
 Francisco, CA, argued for appellant. Also represented by
 PETER J. CHASSMAN, MICHAEL JOHN FORBES, Houston, TX.

    JAY P. KESAN, DiMuroGinsberg, P.C., Tysons Corner,
 VA, argued for cross-appellant. Also represented by CECIL
 E. KEY; HENNING SCHMIDT, Stradling Yocca Carlson &
 Rauth LLP, Austin, TX; MICHAEL W. SHORE, The Shore
 Firm, Dallas, TX.
                  ______________________

      Before DYK, PROST, and STARK, Circuit Judges.
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 2                            ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 DYK, Circuit Judge.
     In this inter partes review proceeding, the Patent Trial
 and Appeal Board (the “Board”) found claims 1–4, 6, and 7
 of 

 (the “’096 patent”) unpatenta-
 ble as obvious but declined to find claim 8 of the ’096 patent
 unpatentable as obvious. The Board also granted patentee
 UNM Rainforest Innovations’s (“UNMRI”) motion to
 amend, canceling claims 1–4, 6, and 7 and substituting in
 claims 44–47, 49, and 50.
     Petitioner ZyXEL Communications Corp. (“ZyXEL”)
 appeals the Board’s determination that claim 8 was not ob-
 vious and the Board’s decision granting UNMRI’s motion
 to amend. UNMRI cross-appeals the Board’s determina-
 tion that claims 1–4, 6, and 7 are unpatentable as obvious.
     We affirm the Board’s determination that claims 1–4,
 6, and 7 are unpatentable as obvious, but reverse the
 Board’s determination that claim 8 is not obvious. We af-
 firm the Board’s decision to grant UNMRI’s motion to
 amend. However, we remand to the Board to determine if
 the substitute claims are unpatentable as obvious under
 collateral estoppel based on our holding that claims 1–4
 and 6–8 are unpatentable as obvious. We also remand to
 the Board for it to consider whether to exercise its discre-
 tion to evaluate if the substitute claims are unpatentable
 as obvious on a new ground. Thus, as to the main appeal,
 we affirm-in-part, reverse-in-part, and remand-in-part,
 and we affirm as to the cross-appeal.
                        BACKGROUND
                               I
     UNMRI owns the ’096 patent, entitled “Method for
 Constructing Frame Structures.” J.A. 1733. The patent
 relates to methods for constructing frame structures (i.e.,
 the organization of information transmitted across time
 and frequency) in orthogonal frequency-division multiple
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 access (OFDMA) systems. OFDMA “is a multiple access
 scheme for transmitting data in different subcarriers in a
 channel, wherein the data may come from different users
 and may be transmitted in disjoint subsets of sub-channels
 in a transmission bandwidth.” J.A. 1740, col. 1, ll. 21–24.
 “The orthogonality property among the subcarriers may al-
 low simultaneous transmission of data from different users
 without interference from one [an]other.” 

 col. 1, ll. 24–
 27.
      The patent describes a method for constructing a frame
 structure with two sections, each of which is configured for
 a different communication system, where the second com-
 munication system is used to support high mobility users
 (i.e., faster moving users). The advantage of using this type
 of frame structure is that it can support both an older
 OFDMA system for slower moving users and a newer
 OFDMA system for faster moving users, (i.e., it uses newer
 OFDMA systems while also being compatible with older
 systems).
     The ’096 patent provides an example where the frame
 structure employs the older IEEE standard 802.16(e) sys-
 tem 1 as the first communication system and the newer
 IEEE standard 802.16(m) system as the second communi-
 cation system. See, e.g., J.A. 1740, col. 1, ll. 27–35; J.A.
 1741, col. 4, ll. 25–27. The IEEE standard 802.16(m)


     1   The IEEE standard 802.16 protocols are a set of
 wireless broadband standards developed by the Institute of
 Electrical and Electronics Engineers. The 802.16(e) proto-
 col “aims to enhance the specifications to the 802.16 stand-
 ard to support both fixed and mobile subscriber stations to
 accommodate, for example, subscriber stations moving at
 vehicular speeds.” J.A. 2383, ¶ 1. The 802.16(m) protocol
 is newer and provides enhanced spectrum efficiency and
 higher speed tolerance, among other things.
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 4                            ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 system better supports higher mobility users. The ’096 pa-
 tent also discloses that the placement of pilot symbols (i.e.,
 non-data symbols sent at known intervals to help correct
 for changing channel conditions) can be transmitted more
 frequently and/or placed at higher density in the second
 communication system than the first system in order to in-
 crease the accuracy of channel estimation (a method to use
 known transmitted signals to calculate the effect of the
 wireless channel conditions on the signal). Symbol period
 refers to the amount of time between the transmission of
 successive pilot symbols. Symbol density refers to the
 number of pilot symbols transmitted during a particular
 time period across all sub-carriers.
     Independent claims 1 and 8 of the ’096 patent are at
 issue in this appeal:
     1. A method of constructing a frame structure for
        data transmission, the method comprising:
         generating a first section comprising data
         configured in a first format compatible with
         a first communication system using sym-
         bols;
         generating a second section following the
         first section, the second section comprising
         data configured in a second format compat-
         ible with a second communication system
         using symbols, wherein the first communi-
         cation system’s symbols and the second
         communication system’s symbols co-exist
         in one transmission scheme and wherein:
             the second format is compatible
             with the second communication
             system configured to support
             higher mobility than the first com-
             munication system, wherein each
             symbol     in      the       second
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            communication system has a
            shorter symbol period than that in
            the first communication system;
        generating at least one non-data section
        containing information describing an as-
        pect of data in at least one of the first sec-
        tion and the second section; and
        combining the first section, the second sec-
        tion and the at least one non-data section
        to form the frame structure.
    8. A method of constructing a frame structure for
    data transmission, the method comprising:
        generating a first section comprising data
        configured in a first format compatible with
        a first communication system using sym-
        bols;
        generating a second section following the
        first section, the second section comprising
        data configured in a second format compat-
        ible with a second communication system
        using symbols, wherein the first communi-
        cation system’s symbols and the second
        communication system’s symbols co-exist
        in one transmission scheme and wherein
        the second communication system has pilot
        symbols that are denser than those in the
        first communication system;
        generating at least one non-data section
        containing information describing an as-
        pect of data in at least one of the first sec-
        tion and the second section; and
        combining the first section, the second sec-
        tion and the at least one non-data section
        to form the frame structure.
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 6                            ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 J.A. 1743, col. 8, ll. 32–54 (emphasis added); J.A. 1744, col.
 9, ll. 6–25 (emphasis added).
                               II
     Qualcomm Inc. (“Qualcomm”) filed a petition for inter
 partes review as to claims 1–4 and 6–8 of the ’096 patent
 contending that they are unpatentable as obvious. The
 Board instituted review for all the challenged claims
 (IPR2021-00375). ZyXEL also filed a petition for inter
 partes review (IPR2021-00734) raising the same argu-
 ments as to the same claims. The Board granted ZyXEL’s
 motion for joinder, joining it as a petitioner in the IPR2021-
 00375.
     Qualcomm appears to have settled with UNMRI.
 ZyXel is the only petitioner who has appealed the Board’s
 final written decision or defended the Board’s decisions
 that are adverse to UNMRI. Because Qualcomm and
 ZyXEL raised the same arguments in their petitions, we
 will refer to ZyXEL as “petitioner.”
     Before the Board, ZyXEL argued that claims 1–4, 6,
 and 7 were unpatentable as obvious over a combination of
 U.S. Publication No. 2009/0067377 (“Talukdar”) and U.S.
 Publication No. 2007/0155387 (“Li”). The Board found
 claims 1–4, 6, and 7 to be unpatentable as obvious over Ta-
 lukdar and Li. The Board determined that a person of or-
 dinary skill in the art (“POSA”) would apply the teachings
 of Li to Talukdar in order to achieve the same benefits de-
 scribed in Li.
     ZyXEL also argued that claim 8 was unpatentable as
 obvious over a combination of Talukdar and U.S. Publica-
 tion No. 2007/0104174 (“Nystrom”). The Board declined to
 find claim 8 unpatentable as obvious over Talukdar and
 Nystrom, finding that ZyXEL had not shown that a POSA
 would have been motivated to combine the two prior art
 references.
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      On cross-appeal, UNMRI contends that during the pro-
 ceedings the Board improperly admitted and relied upon
 the testimony of ZyXEL’s expert, Dr. Roy, to support its
 findings of unpatentability of claims 1–4, 6, and 7. On De-
 cember 6, 2021, UNMRI took the deposition of Dr. Roy. On
 December 16, 2021, UNMRI filed a motion to exclude Dr.
 Roy’s expert report arguing that Dr. Roy adopted the ex-
 pert report of another, Dr. Akl, as his own and gave false
 testimony as to his role as expert. UNMRI argued that this
 violated Federal Rules of Evidence 702(d), which requires
 an “expert’s opinion reflect[] a reliable application of the
 principles and methods to the facts of the case,” and Fed-
 eral Rules of Evidence 703, which states an “expert may
 base an opinion on facts or data in the case that the expert
 has been made aware of or personally observed,” because
 Dr. Roy’s report was the work of another, and he failed to
 perform the analysis himself. FED. R. EVID. 702, 703. The
 Board denied the motion as untimely, but also found that
 it would have denied the motion had it considered the mer-
 its. J.A. 12–13.
                             III
     During the course of the proceedings, UNMRI filed a
 contingent motion to amend. See 

(d)(1). In
 that motion, UNMRI requested that, if claims 1–4, 6, and
 7 were found to be unpatentable, those claims be canceled
 and that claims 44–47, 49, and 50 be substituted in their
 stead. As part of its motion, UNMRI requested prelimi-
 nary guidance from the Board regarding UNMRI’s motion
 to amend, pursuant to the Board’s “MTA Pilot Program.”
 See generally Notice Regarding a New Pilot Program Con-
 cerning Motion to Amend Practice and Procedures in Trial
 Proceedings under the America Invents Act Before the Pa-
 tent Trial and Appeal Board (“MTA Pilot Program Notice”),
 

 (Mar. 15, 2019).
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 8                           ZYXEL COMMUNICATIONS CORP. v.
                               UNM RAINFOREST INNOVATIONS


     The MTA Pilot Program “provide[s] an improved
 amendment practice in AIA trials in a manner that is fair
 and balanced for all parties and stakeholders.” 

 (internal quotations and citation omitted). Under the pro-
 gram, patent owners may request preliminary guidance
 from the Board as to whether the motion meets statutory
 and regulatory requirements. 

. This mecha-
 nism provides useful information to the parties and allows
 issues with the motion to be addressed.
     Independent claim 44 is representative of the proposed
 substitute claims (with underscoring to distinguish differ-
 ences from claim 1):
     44. A method of constructing a frame structure for
     data transmission, the method comprising:
        generating a first section comprising data
        configured in a first format compatible with
        a first communication system using sym-
        bols;
        generating a second section following the
        first section, the second section comprising
        data configured in a second format compat-
        ible with a second communication system
        using symbols, wherein the first communi-
        cation system’s symbols and the second
        communication system’s symbols co-exist
        in one transmission scheme and wherein:
            the second format is compatible
            with the second communication
            system configured to support
            higher mobility than the first com-
            munication system,
            wherein each symbol in the second
            communication system has a
            shorter symbol period than that in
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                the first communication system;
                and
                wherein the second communication
                system has pilot symbols that are
                denser than those in the first com-
                munication system;
            generating at least one non-data section
            containing information describing an as-
            pect of data in at least one of the first sec-
            tion and the second section; and combining
            the first section, the second section and the
            at least one [non-data] section to form the
            frame structure.
 J.A. 67.
     In its opposition to UNMRI’s motion to amend, ZyXEL
 argued, inter alia, that UNMRI’s motion was deficient be-
 cause it failed to show written description support for all of
 the claim limitations in the proposed substitute claims as
 required by the regulations. See 

(a)–(b).
 ZyXEL contended that UNMRI’s motion only showed sup-
 port for the newly added limitations, instead of showing
 support for the proposed substitute claim as a whole.
     In its preliminary guidance, which is not binding on the
 Board, MTA Pilot Program Notice, 84 Fed. Reg. at 9500,
 the Board “agree[d] with [ZyXEL]’s contentions that ‘Pa-
 tent Owner only purport[ed] to show support for the addi-
 tional features added by the amendments,’ and that ‘Patent
 Owner has not even attempted to show support in the orig-
 inal disclosure for any other limitations of the proposed
 substitute claims.’” J.A. 940 (citations omitted). The Board
 also noted that “it appear[ed] more likely than not that
 there is adequate written description support for the pro-
 posed substitute claims . . . in the Specification, as filed, of
 U.S. Patent Application 12/168,855” (the “’855 Applica-
 tion”), which issued as the ’096 patent. J.A. 940–41.
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 10                           ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


     In response to the Board’s preliminary guidance,
 UNMRI filed a revised motion to amend. In its revised mo-
 tion, UNMRI proposed the same substitute claims, but sup-
 plemented the written description support for the pre-
 existing claim limitations by citing to the ’855 Application.
 ZyXEL opposed.
     The Board rejected UNMRI’s revised motion (and
 ZyXEL’s opposition to it) because it did not include any new
 substitute claims that were not already present in the orig-
 inal motion to amend as required by the regulations. See
 MTA Pilot Program Notice, 84 Fed. Reg. at 9499 (“A revised
 [motion to amend] includes one or more new proposed sub-
 stitute claims in place of previously presented substitute
 claims to address issues identified in the preliminary guid-
 ance and/or the petitioner’s opposition.”).
      However, the Board permitted UNMRI to file a reply
 in support of its original motion to amend, which the Board
 required to be “substantively identical” to UNMRI’s re-
 jected revised motion to amend. Qualcomm Inc. v. UNM
 Rainforest Innov., Case IPR2021-00375, Paper No. 63 at 5
 (PTAB May 19, 2022). The Board waived the usual page
 limit requirement for replies and permitted UNMRI’s reply
 to be 25 pages. Likewise, the Board waived the page limit
 requirement for ZyXEL’s sur-reply and authorized it to file
 a 25-page sur-reply. In its reply, UNMRI included written
 description support for the remaining claim limitations by
 citing to the ’855 Application. 2 ZyXEL filed a sur-reply


      2  ZyXEL argues that the Board erred in granting the
 motion to amend because UNMRI did not show written de-
 scription support to U.S. Provisional App. No. 60/929,798
 (the “’798 Application”). UNMRI had originally sought a
 priority date for its application going back to the ’798 Ap-
 plication. By the time of the motion to amend, it had
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 arguing the procedural point but not disputing that there
 was sufficient written description support in the ’855 Ap-
 plication for all the limitations in the substitute claims.
 ZyXEL also reiterated its argument that the proposed sub-
 stitute claims were unpatentable as obvious over the com-
 bination of Talukdar and Li.
     The Board granted UNMRI’s motion to amend, substi-
 tuting claims 44–47, 49, and 50, and determined those
 claims to be nonobvious over Talukdar and Li (rejecting
 ZyXEL’s argument as to obviousness). Specifically, the
 Board found the limitation “wherein the second communi-
 cation system has pilot symbols that are denser than those
 in the first communication system” (similar to claim 8),
 which was not present in the original claims, was neither
 disclosed nor taught by the combination of Talukdar and
 Li.
     ZyXEL appeals the Board’s decision to grant UNMRI’s
 motion to amend and the Board’s decision finding claim 8
 nonobvious over Talukdar and Li. UNMRI cross-appeals
 the Board’s finding that claims 1–4, 6, and 7 are unpatent-
 able as obvious over Talukdar and Li.
     We have jurisdiction under 

(a)(4)(A).




 abandoned that contention. There was no need under
 these circumstances to provide written description support
 to the ’798 Application. See 

(b) (“A mo-
 tion to amend claims must . . . set forth: . . . (2) The sup-
 port in an earlier-filed disclosure for each claim for which
 benefit of the filing date of the earlier filed disclosure is
 sought.”).
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 12                             ZYXEL COMMUNICATIONS CORP. v.
                                  UNM RAINFOREST INNOVATIONS


                           DISCUSSION
            I.     Obviousness of Claims 1–4, 6, and 7
                      A. Dr. Roy’s Testimony
     UNMRI contends that the Board’s finding that claims
 1–4, 6, and 7 are unpatentable as obvious should be set
 aside because the Board erroneously refused to exclude,
 and relied on, Dr. Roy’s expert testimony (his expert report)
 on obviousness. In moving to exclude Dr. Roy’s expert re-
 port, UNMRI argued that Dr. Roy’s report was actually an
 expert report prepared by another expert, Dr. Akl, in an
 earlier proceeding and that Dr. Roy “simply signed his
 name to” it. Cross-Appellant Opening Br. 59. UNMRI ar-
 gued that Dr. Roy did not disclose that Dr. Akl’s report was
 the basis for his report until he was asked about it during
 his deposition. UNMRI also contended that Dr. Roy mis-
 represented under oath the contributions he made to the
 report. Specifically, UNMRI cited to Dr. Roy’s deposition
 testimony where he stated that he contributed (i.e., pro-
 vided corrections and edits) to various sections of the ex-
 pert report. UNMRI argued that the differences between
 Dr. Akl’s report and Dr. Roy’s report were de minimis, and
 thus Dr. Roy misrepresented his contributions to the re-
 port.
     The Board first denied UNMRI’s motion as untimely.
 Under 

(b)(1), the Board’s regulations pro-
 vide:
      Any objection to evidence submitted during a pre-
      liminary proceeding must be filed within ten busi-
      ness days of the institution of the trial. Once a trial
      has been instituted, any objection must be filed
      within five business days of service of evidence to
      which the objection is directed.
     Dr. Roy’s expert report was submitted with the peti-
 tion, and trial was instituted (began) on July 19, 2021. The
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 Board concluded that the objection to Dr. Roy’s expert re-
 port, filed on December 16, 2021, was untimely because it
 was not filed within 10 business days of the institution of
 trial.
      UNMRI contended that it only became aware of Dr.
 Roy’s alleged misrepresentation on December 6, 2021, the
 date of his deposition, and therefore could not object ear-
 lier. The Board, however, found that even if the first sen-
 tence of the rule was inapplicable, under the second
 sentence of the regulation, the filing was still untimely be-
 cause UNMRI was objecting to evidence presented during
 trial and UNMRI filed its objection eight business days af-
 ter the deposition date, while the regulation requires any
 objection to be filed within five business days of service of
 the evidence.
     “Decisions related to compliance with the Board’s pro-
 cedures are reviewed for an abuse of discretion.” Intelli-
 gent Bio-Sys., Inc. v. Illumina Cambridge Ltd., 

 (Fed. Cir. 2016) (citing Bilstad v. Wakalopulos,
 

 (Fed. Cir. 2004)). We see no abuse in
 discretion by the Board’s interpretation of its own rules to
 require a filing within five business days of service of evi-
 dence to which the objection is directed.
      The Board also concluded that it would have denied the
 motion on the merits even if it had been timely because it
 viewed UNMRI’s challenges to Dr. Roy’s testimony as go-
 ing to the weight that should be given to his testimony, not
 its admissibility. We conclude that the Board did not err
 in concluding that the objection did not merit exclusion of
 the report even if the objection had been timely. We see no
 abuse of discretion by the Board in determining that the
 issues with Dr. Roy’s report go to the credibility and weight
 attributed to the report and not to its admissibility. Unlike
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 14                             ZYXEL COMMUNICATIONS CORP. v.
                                  UNM RAINFOREST INNOVATIONS


 the cases UNMRI relies on, 3 there was evidence here that
 Dr. Roy analyzed the prior art references, the patent, and
 Dr. Akl’s expert report, and reached the same conclusions
 as Dr. Akl. While Dr. Roy may have overstated his contri-
 butions in revising Dr. Akl’s report, he admitted that Dr.
 Akl’s report served as the basis for his report and stated
 that his own report reflected his own opinion, and the
 Board was free to accept the report and to consider any er-
 roneous testimony by Dr. Roy in deciding to attribute
 weight to his testimony.
          B. Substantial Evidence for the Board’s Findings
    “In reviewing the Board’s determination on the ques-
 tion of obviousness, we review the Board’s legal conclusions
 de novo and its factual findings for substantial evidence.”
 Becton, Dickinson & Co. v. Baxter Corp. Englewood, 998



      3   In all of the cases on which UNMRI relies, an ex-
 pert’s testimony was excluded because the expert did not
 actually perform the analysis or falsified the content of the
 analysis. See, e.g., Rembrandt Vision Techs., L.P. v. John-
 son & Johnson Vision Care, Inc., 

 (Fed.
 Cir. 2016) (ordering a new trial when expert falsely testi-
 fied about his involvement and experience, withheld docu-
 ments, and withheld contradictory test results); Puppolo v.
 Welch, 

, 65 (2d Cir. 2019) (finding no abuse
 of discretion by the district court excluding expert’s testi-
 mony when the expert acknowledged “he performed none
 of the legal research”); United States v. Tomasian, 

 (7th Cir. 1986) (excluding expert opinion where
 the expert “had no opinion of his own” and “could only relay
 another’s opinion”); Crowley v. Chait, 

 (D.N.J. 2004) (precluding expert from testifying when
 it constituted “simply summariz[ing] the facts and the dep-
 ositions of others,” but declining to exclude expert testi-
 mony in its entirety).
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 F.3d 1337, 1339 (Fed. Cir. 2021) (internal quotation marks,
 citation, and alterations omitted). “What a reference
 teaches and the differences between the claimed invention
 and the prior art are questions of fact which we review for
 substantial evidence.” In re Cuozzo Speed Techs., LLC, 

 (Fed. Cir. 2015).
      UNMRI contends that a POSA would not know how to
 combine Talukdar and Li in order to render obvious the
 limitation “wherein each symbol in the second communica-
 tion system has a shorter symbol period than that in the
 first communication system.” J.A. 1743, col. 8, ll. 47–49.
 We conclude that the Board’s decision is supported by sub-
 stantial evidence.
     Talukdar discloses a frame structure that includes first
 and second sections, each corresponding to a first and sec-
 ond communication system. See, e.g., J.A. 38–40; 2131–32,
 ¶¶ 27–30. Talukdar discloses using the IEEE standard
 802.16(e) system as an older legacy system and the IEEE
 standard 802.16(m) as a newer system, which are the same
 systems used in the ’096 patent. Li in the context of a leg-
 acy system teaches “using shorter symbol periods for faster
 moving remote units.” Cross-Appellant Opening Br. 53; see
 also J.A. 2386, ¶ 37. UNMRI does not dispute any of these
 facts.
     The Board determined that it would have been obvious
 to apply Li’s teachings to the second communication system
 in Talukdar (i.e., the newer system) because “it would im-
 prove Talukdar’s method in the same way as Li by reducing
 inter-subcarrier interference experienced by the faster
 moving mobile remote users.” J.A. 48. The Board’s conclu-
 sion is supported by substantial evidence. Li teaches that
 using shorter pilot symbol periods for faster mobile users
 has the benefit of reducing inter-subcarrier interference
 that faster mobile users may experience. Faster mobile us-
 ers would be using the second communication system in
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 16                           ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 Talukdar (the 802.16(m) system), the same system in the
 ’096 patent. Dr. Roy’s expert report supports the argument
 that it would be obvious to a POSA to apply Li’s teachings
 to the second system in Talukdar. 4 This is substantial ev-
 idence that supports the Board’s obviousness determina-
 tion.
     Therefore, we affirm the Board’s decision finding
 claims 1–4, 6 and 7 unpatentable as obvious over Talukdar
 and Li.
                 II.    Obviousness of Claim 8
      ZyXEL argues that the Board erred in finding that
 claim 8 was not obvious because there was no motivation
 to combine Talukdar and Nystrom. As the Board noted,
 claim 8 is nearly identical to claim 1, except that claim 8
 recites “wherein the second communication system has pi-
 lot symbols that are denser than those in the first commu-
 nication system,” in place of claim 1’s recitation of “wherein
 each symbol in the second communication system has a
 shorter symbol period than that in the first communication
 system.” J.A. 55. The difference between these two limi-
 tations is subtle, as noted earlier. Symbol period refers to
 the amount of time between the transmission of pilot sym-
 bols, whereas symbol density refers to the number of pilot
 symbols transmitted during a particular time period.
     Before the Board, ZyXEL argued a POSA would have
 been motivated to combine Talukdar and Nystrom to
 achieve the pilot density limitation. ZyXEL contended a


      4  On appeal, UNMRI argues that there is no eviden-
 tiary support for a motivation to combine. We disagree as
 the Board pointed to Li, Talukdar, and Dr. Roy’s testimony
 for support that Li would improve Talukdar’s method in
 the same way as in Li. Thus, there is substantial evidence
 for the Board’s finding of a motivation to combine.
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 UNM RAINFOREST INNOVATIONS


 POSA would be motivated to apply the teachings in Nys-
 trom about using denser pilot symbols to improve Talukdar
 because Nystrom teaches that denser pilot symbols (1)
 counteract the effects of Doppler shift and fading experi-
 enced by faster-moving remote units and (2) enhance a
 faster-moving unit’s ability to perform channel estimation.
     It is undisputed that the limitation pertaining to sym-
 bol density is present in Nystrom. The Board found that
 “Nystrom discloses that it is beneficial to assign resources
 for mobile stations with certain fast varying channel or
 Doppler conditions in the dense parts of the pilot pattern
 and users with more slowly varying conditions in the less
 dense parts.” J.A. 54–55. The Board, however, found that
 Nystrom did not teach that higher density pilot symbols
 are used to counteract high doppler conditions or improve
 channel estimation. We disagree. The Board’s determina-
 tion is not supported by substantial evidence, and the rec-
 ord supports only a conclusion of obviousness. 5




     5   UNMRI argues that the Board found ZyXEL’s ar-
 guments about claim 8 to be forfeited and ZyXEL has not
 challenged the Board’s finding of waiver. Cross-Appellant
 Opening Br. 17, 21. It is true that the Board found ZyXEL
 had forfeited certain arguments by only raising them in its
 reply brief. J.A. 60, 63–64. However, the Board did not
 find ZyXEL to have waived all arguments regarding claim
 8. J.A. 55–58 (citing petition and discussing non-forfeited
 arguments). It is these original arguments that ZyXEL
 raises on appeal. UNMRI indeed concedes that these ar-
 guments were not forfeited as the heading for its discussion
 of these issues is titled “ZyXEL’s Original Motivation To
 Combine Arguments Are Unsupported.” Cross-Appellant
 Opening Br. 22. These issues were not forfeited and are
 properly before us here on appeal.
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 18                            ZYXEL COMMUNICATIONS CORP. v.
                                 UNM RAINFOREST INNOVATIONS


     Nystrom extensively teaches that denser pilot symbols
 should be used in situations when users encounter large
 Doppler shifts, such as moving at high velocity. Nystrom
 recognizes that “different users travel at different speeds
 and thus experience different Doppler shifts.” J.A. 2401,
 ¶ 4. Recognizing users may face different conditions, Nys-
 trom discloses that different pilot symbol patterns (i.e., dif-
 ferent densities) can be used to accommodate these
 different conditions. For example, in Figure 5A, repro-
 duced below, Nystrom discloses four different combinations
 of pilot symbol densities varied in frequency and time:




 J.A. 2394. In describing Fig. 5A, Nystrom explains how
 these different pilot symbol densities should be used for dif-
 ferent conditions, including higher density pilot symbols
 for higher Doppler conditions and lower pilot symbol den-
 sities for lower Doppler conditions. See, e.g., J.A. 2404,
 ¶ 42. Nystrom further teaches “[i]t is beneficial, e.g. to as-
 sign resources for mobiles with certain fast varying chan-
 nel or Doppler conditions in the dense parts of the pilot
 pattern and uses with more slowly varying conditions in
 the less dense parts.” J.A. 2404, ¶ 43. Thus, Nystrom
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 ZYXEL COMMUNICATIONS CORP. v.                                19
 UNM RAINFOREST INNOVATIONS


 plainly teaches that it is beneficial to use higher pilot sym-
 bol densities for higher Doppler conditions.
    While Nystrom may not explicitly state that denser pilot
 symbols counteract the effect of high Doppler shifts or im-
 prove channel estimation, this is not necessary to show ob-
 viousness. A prior art reference does not need to explicitly
 articulate or express why its teachings are beneficial so
 long as its teachings are beneficial and a POSA would rec-
 ognize that their application was beneficial. Intel Corp. v.
 PACT XPP Schweiz AG, 

, 1380–81 (Fed. Cir.
 2023) (“There is a motivation to combine when a known
 technique ‘has been used to improve one device, and a per-
 son of ordinary skill in the art would recognize that it
 would improve similar devices in the same way,’ using the
 ‘prior art elements according to their established func-
 tions.’” (first quoting KSR Int’l Co. v. Teleflex Inc., 

 (2007); and then quoting Intel Corp. v. Qualcomm
 Inc., 

 (Fed. Cir. 2021)). Here, Nystrom
 discloses that it is beneficial to use denser pilot symbol pat-
 terns for higher Doppler conditions, conditions common to
 high mobility users. Indeed, UNMRI seems to concede this
 point as, on appeal, it characterized Nystrom as “dis-
 clos[ing] the use of denser pilots for high mobility users:
 Users with ‘radio conditions demanding a high density of
 pilots’—such as fast-moving users—could be allocated re-
 source space with increased pilot density in the time di-
 mension, frequency dimension, or both.” Cross-Appellant
 Opening Br. 16 (quoting J.A. 2404, ¶ 43). Furthermore, Dr.
 Roy testified that a POSA would have been motivated to
 combine Nystrom and Talukdar and cited to these portions
 of Nystrom for support. See J.A. 1854–56.
     There is no contrary evidence. While UNMRI’s expert,
 Dr. Vojcic, opined that a POSA would not be motivated to
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 20                          ZYXEL COMMUNICATIONS CORP. v.
                               UNM RAINFOREST INNOVATIONS


 combine Talukdar and Nystrom, 6 his opinion offers no sup-
 port for the Board’s reasoning and is not relevant to
 whether Nystrom discloses that high pilot symbol densities
 are beneficial for high Doppler shifts. Indeed, Dr. Vojcic
 acknowledged that Nystrom discloses using a higher den-
 sity of pilot symbols in the time dimension for users moving
 at higher speeds, and that such users may encounter
 higher Doppler shifts. Dr. Vojcic stated “[a] POS[A] would
 also understand that small/larger Doppler spread (or
 equivalently velocity) corresponds to low/high time selec-
 tivity, requiring low/high pilot density over time.” J.A.
 3028. Dr. Vojcic does not state or opine that a POSA would
 not recognize the benefits of using higher pilot symbol den-
 sities for faster mobile users who experience high Doppler
 conditions.
    The Board’s conclusion as to claim 8 lacks substantial
 evidence. We determine that claim 8 is unpatentable as
 obvious and reverse the Board’s contrary decision.
                   III.   Substitute Claims
                      A. Motion to Amend
    ZyXEL argues that the Board erred in granting
 UNMRI’s motion to amend because UNMRI did not satisfy
 the requirement that the motion itself contain written de-
 scription support for all of the claim limitations of the



      6   On appeal, UNMRI suggests that the Board
 adopted Dr. Vojcic’s testimony that “a significant non-obvi-
 ous redesign of the Talukdar system would be required to
 incorporate Nystrom’s disclosure” and that the two would
 otherwise be incompatible with each other. Cross-Appel-
 lant Opening Br. 29. The Board did not find that applying
 Nystrom’s teachings to Talukdar would require such a re-
 design and made no reference to these portions of Dr.
 Vojcic’s report.
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 UNM RAINFOREST INNOVATIONS


 substitute claims. See 

(b) (“A motion to
 amend claims must include a claim listing . . . and set
 forth: (1) The support in the original disclosure of the pa-
 tent for each claim that is added or amended; and (2) The
 support in an earlier-filed disclosure for each claim for
 which benefit of the filing date of the earlier filed disclosure
 is sought.”); Lectrosonics, Inc. v. Zaxcom, Inc., IPR2018-
 01129, Paper 15 at 8 (PTAB Feb. 25, 2019) (“In addition,
 the motion must set forth written description support for
 each proposed substitute claim as a whole, and not just the
 features added by the amendment.”). Even though it is un-
 disputed on appeal that UNMRI provided the missing writ-
 ten description in its reply brief, ZyXEL argues that this
 could not cure the procedural defect. ZyXEL points out
 that the regulations require “[a]ll arguments and evidence
 in support of the motion to amend shall be in the motion
 itself” and cites to a number of Board decisions that held
 supplementing a motion to amend through a reply brief
 was improper. 7 Lectrosonics, IPR2018-01129, Paper 15 at
 8; 

(b). There is nothing in the MTA Pilot
 Program Notice eliminating this requirement. To the con-
 trary, the MTA Pilot Program Notice references Lectroson-
 ics as governing law. MTA Pilot Program Notice, 84 Fed.
 Reg. at 9500.
     But these arguments as to the requirements of the reply
 fail to take into account the MTA Pilot Program’s purpose.
 The MTA Pilot Program introduced the option for patent
 owners to receive preliminary guidance from the Board
 with respect to motions to amend. MTA Pilot Program No-
 tice, 84 Fed. Reg. at 9497 (noting the option to receive pre-
 liminary guidance was “not previously available”). To be
 sure, the MTA Pilot Program did not eliminate



     7 See also Lippert Components, Inc. v. Days Corp.,
 IPR2018-00777, Paper 28 (PTAB Sept. 24, 2019).
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 22                           ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 requirements as to the contents of the original motion or
 the limitations on reply briefs. See MTA Pilot Program No-
 tice, 84 Fed. Reg. at 9500 (citing Lectrosonics, IPR2018-
 01129, Paper 15). But the core purpose of the MTA Pilot
 Program is to allow for the correction of errors in the origi-
 nal motion. The MTA Pilot Program Notice describes the
 purpose of preliminary guidance as “provid[ing] an initial
 discussion about whether there is a reasonable likelihood
 that the [motion to amend] meets statutory and regulatory
 requirements for a [motion to amend.]” Id. at 9497. The
 MTA Pilot Program Notice further explains “the guidance
 may be helpful to patent owner as it determines whether
 and/or how to revise its [motion to amend] or . . . how to
 respond to information discussed in the preliminary guid-
 ance.” Id. at 9500. Thus, a key purpose of issuing prelim-
 inary guidance, and the MTA Pilot Program in general, is
 to provide feedback as to whether the motion to amend sat-
 isfies the statutory and regulatory requirements so the par-
 ties may respond and address any such errors. The MTA
 Pilot Program also permits a patent owner to “respond to
 the Board’s preliminary guidance (if requested) and to the
 petitioner’s opposition,” as well as “file new evidence, in-
 cluding declarations, with its reply.” Id. at 9501. It thus
 appears that the MTA Pilot Program is designed to allow
 reply briefs to address and correct errors. We do not think
 the Board erred in permitting UNMRI to use its reply brief
 to supplement the written description support that should
 have been, but was not, included in its original motion to
 amend.
    Even if allowing the reply brief to supply the missing
 information had been inconsistent with the regulations, we
 conclude that any error was harmless error. “We review
 Board decisions pursuant to the standards of the Adminis-
 trative Procedure Act (‘APA’), 

 et seq.” Core-
 photonics, Ltd. v. Apple Inc., 

 (Fed. Cir.
 2023). “The judicial review provision of the APA includes
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 ZYXEL COMMUNICATIONS CORP. v.                                23
 UNM RAINFOREST INNOVATIONS


 a harmless error rule.” In re Chapman, 

 (Fed. Cir. 2010) (citing 

); see 

 (“[D]ue account shall be taken of the rule of prejudi-
 cial error.”); see also Shinseki v. Sanders, 

 (2009) (“[W]e have previously described § 706 as an ‘admin-
 istrative law . . . harmless error rule.’” (citations omitted));
 In re Watts, 

 (Fed. Cir. 2004) (“We have
 previously made clear that the harmless error rule applies
 to appeals from the Board just as it does in cases originat-
 ing from district courts.”).
     Any error that was committed by the Board was harm-
 less error because ZyXEL was not prejudiced by the
 Board’s decision to allow the reply brief to supplement the
 initial motion. ZyXEL was on notice of the written descrip-
 tion arguments and had ample opportunity to respond in
 its sur-reply. 8 The Board waived the page limits on the
 sur-reply and allowed ZyXEL to respond with a 25-page
 brief in order to ensure it had a proper opportunity to re-
 spond. Qualcomm Inc. v. UNM Rainforest Innov., Case
 IPR2021-00375, Paper No. 63 at 5–6 (PTAB May 19, 2022).
    ZyXEL asserts, however, that it had no opportunity to
 present any expert declarations to refute UNMRI’s new ar-
 guments about written description that were raised in the
 reply brief because under the Board’s rules such evidence
 cannot be raised in a sur-reply. Oral Arg. 13:24–13:32; see
 MTA Pilot Program Notice, 84 Fed. Reg. at 9500 (“[N]ew
 evidence (including declarations) may be submitted with
 every paper in the [motion to amend] process, except a sur-
 reply.”). There are two answers to this. First, ZyXEL never
 made any request to the Board to waive its rules and


     8   In addition to UNMRI’s reply brief, the Board also
 identified where written description support could be lo-
 cated in its preliminary guidance, which ZyXEL received.
 J.A. 940–41.
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 24                           ZYXEL COMMUNICATIONS CORP. v.
                                UNM RAINFOREST INNOVATIONS


 permit it to file an expert declaration. Oral Arg. 12:46–
 13:20; see, e.g., Axonics, Inc. v. Medtronic, Inc., 

, 1384 (Fed. Cir. 2023) (noting that the Board may al-
 low new evidence and expert declarations to be submitted
 with sur-replies if requested by the parties to avoid preju-
 dice); Belden Inc. v. Berk-Tek LLC, 

 (Fed. Cir. 2015) (“Thus, if the petitioner submits a new ex-
 pert declaration with its Reply, the patent owner can re-
 spond in multiple ways. . . . [I]t can request the Board
 waive or suspend a regulation that the patent owner be-
 lieves impairs its opportunity to respond to the declara-
 tion.”); Parkervision, Inc. v. Vidal, 

 (Fed.
 Cir. 2023) (concluding that because patent owner “failed to
 partake in available procedural mechanisms” such as “re-
 quest[ing] that its [s]ur-reply be permitted to include argu-
 ments and evidence that would otherwise be impermissible
 in a sur-reply,” it could not “fault the Board” for excluding
 new arguments in the sur-reply). Second, ZyXEL does not
 to point to any relevant evidence that it would have pre-
 sented if the opportunity had been available. ZyXEL did
 not raise any substantive argument regarding the ’855 Ap-
 plication in its opposition to UNMRI’s revised motion to
 amend or in its sur-reply. Under these circumstances,
 ZyXEL has failed to establish prejudice. We affirm the
 Board’s decision to grant the motion to amend.
                    B. Further Proceedings
     In its opening brief on appeal, ZyXEL only raised two
 arguments regarding the Board’s decision to grant
 UNMRI’s motion to amend. ZyXEL first identified the al-
 leged procedural deficiencies discussed in the previous sec-
 tion and second argued the amended claims were obvious
 over the Talukdar and Li combination. We think the
 Board’s decision finding the amended claims not to be ob-
 vious over the Talukdar and Li combination was supported
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 ZYXEL COMMUNICATIONS CORP. v.                               25
 UNM RAINFOREST INNOVATIONS


 by substantial evidence. 9 However, at oral argument,
 ZyXEL argued that if claim 8 were held to be unpatentable
 (as we now hold), we should remand to the Board to con-
 sider whether the substitute claims are unpatentable. The
 substitute claims are entirely a combination of the limita-
 tions of claims 1–4 and 6–8, all of which we have now held
 unpatentable as obvious. It follows from the invalidation
 of claim 8 and the other claims, says ZyXEL, that the sub-
 stitute claims are unpatentable as a matter of collateral es-
 toppel. 10
      “[A]n IPR decision does not have collateral estoppel ef-
 fect until that decision is affirmed . . . .” United Therapeu-
 tics Corp. v. Liquidia Techs., Inc., 

 (Fed.
 Cir. 2023), cert. denied, 

 (2024) (citing XY,


     9     ZyXEL contended that Li discloses the limitation
 “wherein the second communication system has pilot sym-
 bols that are denser than those in the first communication
 system.” J.A. 67 (emphasis omitted). The Board deter-
 mined that while Li discloses using shorter symbol periods,
 it does not disclose denser pilot symbols as required by the
 amended claims. The testimony of ZyXEL’s own expert
 (Dr. Roy) supports the Board’s conclusion.
      10   See, e.g., Finjan LLC v. SonicWall, Inc., 

, 969 (Fed. Cir. 2023) (“For patent claims, collateral es-
 toppel applies where the ‘issues of patentability’ are iden-
 tical, i.e., where ‘the differences between the unadjudicated
 patent claims and adjudicated patent claims do not mate-
 rially alter the question of invalidity.’” (citation omitted));
 Nestle USA, Inc. v. Steuben Foods, Inc., 

 (Fed. Cir. 2018) (“Importantly, our precedent makes
 clear that collateral estoppel is not limited ‘to patent claims
 that are identical. Rather, it is the identity of the issues
 that were litigated that determines whether collateral es-
 toppel should apply.’” (citation omitted) (emphasis in orig-
 inal)).
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 26                            ZYXEL COMMUNICATIONS CORP. v.
                                 UNM RAINFOREST INNOVATIONS


 LLC v. Trans Ova Genetics, L.C., 

 (Fed.
 Cir. 2018)). We have held that even where the initial deci-
 sion would be the basis for collateral estoppel, “failure to
 raise collateral estoppel before the appeal process in the
 preclusive case has concluded should not necessarily be a
 work of forfeiture,” and that “courts of appeals have discre-
 tion to entertain a party’s res judicata (including issue pre-
 clusion) argument when it is raised for the first time on
 appeal.” Uniloc USA, Inc. v. Motorola Mobility LLC, 

, 1348–49 (Fed. Cir. 2022); see also Stanton v.
 D.C. Ct. of Appeals, 

 (D.C. Cir. 1997) (“As
 res judicata belongs to courts as well as to litigants, even a
 party’s forfeiture of the right to assert it . . . does not de-
 stroy a court’s ability to consider the issue sua sponte.” (em-
 phasis in original)).
      Because the potential for collateral estoppel did not be-
 come available until our reversal of the Board’s finding as
 to claim 8, we conclude that ZyXEL did not forfeit the ar-
 gument by failing to raise it earlier. We remand to the
 Board to determine if, in light of our conclusion that claim
 8 is unpatentable as obvious (together with the unpatenta-
 bility of claims 1–4 and 6–7), collateral estoppel should ap-
 ply, and the substitute claims should be deemed
 unpatentable.
     On the remand, the Board may also wish to consider if
 the substitute claims are unpatentable as obvious on a new
 ground: the combination of Talukdar, Li, and Nystrom. We
 note that before the Board ZyXEL did not argue that the
 substitute claims were obvious in light of Talukdar, Li, and
 Nystrom. However, “the Board may sua sponte identify a
 patentability issue for a proposed substitute claim based on
 the prior art of record.” Nike, Inc. v. Adidas AG, 

 (Fed. Cir. 2020); see also Hunting Titan, Inc. v.
 DynaEnergetics Eur. GmbH, 

 (Fed. Cir.
 2022) (acknowledging the Board may sua sponte advance a
 ground of unpatentability of a substitute claim “where the
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 ZYXEL COMMUNICATIONS CORP. v.                              27
 UNM RAINFOREST INNOVATIONS


 record readily and persuasively establishes that substitute
 claims are unpatentable for the same reasons that corre-
 sponding original claims are unpatentable”); see Q.I. Press
 Controls, B.V. v. Lee, 

 (Fed. Cir. 2014)
 (noting that in the context of a reexamination “the Board
 [of Patent Appeals and Interferences] has the discretion to
 issue a new ground of rejection if it has knowledge of one”).
 We therefore remand to the Board to consider whether it
 should entertain an argument that the substitute claims
 are unpatentable as obvious over the combination of Ta-
 lukdar, Li, and Nystrom.
     We also note that “[i]f the Board sua sponte identifies
 a patentability issue for a proposed substitute claim . . . it
 must provide notice of the issue and an opportunity for the
 parties to respond before issuing a final decision under 

(a).” Nike, 

.
                         CONCLUSION
     We affirm the Board’s determination that claims 1–4,
 6, and 7 are unpatentable as obvious, and the Board’s deci-
 sion to grant UNMRI’s motion to amend. We reverse the
 Board’s determination as to claim 8 and conclude that
 claim 8 is unpatentable as obvious. We remand to the
 Board to determine, based on our determination that
 claims 1–4 and 6–8 are unpatentable as obvious, if collat-
 eral estoppel applies to substitute claims 44–47, 49, and 50,
 and to allow the Board to consider whether to exercise its
 discretion to evaluate if these claims are invalid based on
 a combination of Talukdar, Li, and Nystrom.
    AFFIRMED-IN-PART, REVERSED-IN-PART,
  REMANDED-IN-PART AS TO THE MAIN APPEAL.
     AFFIRMED AS TO THE CROSS-APPEAL.
                            COSTS
 No costs.