US 6370135

I'll verify the patent's bibliographic data and check for any 2026 litigation, then summarize.

The CAFC search returned nothing. Let me run a couple of targeted follow-ups on litigation/docket history.

US Patent 6,370,135 — Analyst Summary

1. Bibliographic data

Assignment chain (as recorded): application filed by Cirrus Logic Inc. (1995-06-07); assignment recorded to Pacific Communication Sciences, Inc. on 1995-09-01 (assignor: Gardner); later reassignment to Cirrus Logic Inc. recorded 2018-03-19 as a merger (assignor: Pacific Communication Sciences Inc.). Note an internal inconsistency in the public records: the printed patent front page lists Cirrus Logic, Inc. as assignee, while the assignment database shows the 1995 assignment running to Pacific Communication Sciences, Inc. I am reporting both records as-is rather than resolving them.

Term note: A June 7, 1995 filing date falls just before the June 8, 1995 URAA change, consistent with the recorded 2019-04-09 expiration (17 years from the 2002-04-09 grant). The patent states a 35 U.S.C. 154(b) adjustment of 0 days. This is my inference from the data, not an official PTO determination.

2. Abstract (verbatim)

"A multi-mode communication system, including controller, base stations and subscriber stations, where the communication system has the capability of operating either in a packet-switched mode or a circuit-switched mode. The packet-switched mode of operation complies with the existing Cellular Digital Packet Data (CDPD) standard with respect to modulation and higher level protocol, and is designated continuous CDPD mode. This mode of operation is highly cost effective for transfers of relatively small amounts of data. For larger data transfers, the more cost-effective continuous CDPD mode is used. Thus, using this mode, the system is capable of providing superior data rate performance over a vastly greater coverage area than existing circuit-switched modems. Requests for access to continuous CDPD channels are initiated at subscriber stations. This initiation can result from manual intervention by the user of the subscriber station, or can be automatic in response to the amount of data to be transferred, as well as comprising structure for each mode of data transfer used by the service provider."

(Note: the abstract's phrase "the packet-switched mode … is designated continuous CDPD mode" appears garbled in the granted text; the specification makes clear it is the circuit-switched mode using CDPD modulation that is designated "continuous CDPD.")

3. Plain-language overview of the independent claims

There are four independent claims — 1, 23, 35 and 39 — each from a different statutory/party perspective (system, method, base station, subscriber station).

Claim 1 — System. A communication system built on a CDPD packet-switched portion that serves many wireless subscriber stations through plural Mobile Data Base Stations (MDBS) under at least one Mobile Data Intermediate System (MD-IS). The system adds three things: (a) a continuous CDPD data portion spread across multiple CDPD MDBSs; (b) means for requesting conversion of a given data transmission from the packet-switched portion to the continuous CDPD portion; and (c) means for allocating a continuous CDPD channel for that transmission. In plain terms: give the existing CDPD network a second, dedicated "circuit-like" mode, and let a request trigger a move of a specific transfer onto an allocated channel. Claims 2–22 depend on it.

Claim 23 — Method. A method of efficient data transmission in a CDPD system, comprising: (a) temporarily designating at least one CDPD packet-switched channel as a continuous CDPD channel that packet-switched transmissions may not use; (b) requesting conversion of a particular transmission from packet-switched mode to continuous CDPD mode; and (c) transferring that transmission to the designated channel and carrying it out in continuous CDPD mode. In plain terms: temporarily repurpose a channel, move one session onto it, run it in the continuous mode. Claims 24–34 depend on it (e.g., claim 28/29 cover marking the continuous-mode data — different cover sequence/sync word — so packet-mode SNODEMs cannot decode it; claim 33 covers MD-IS↔MTSO negotiation of a dedicated channel).

Claim 35 — Base station (MDBS). A CDPD MDBS comprising: (a) multiple transceiver cards dedicated to CDPD packet-switched communication; (b) at least one transceiver card allocated to continuous CDPD communication; and (c) means for assigning a CDPD data communication to that continuous-CDPD card — where the assigning means include means for scanning among available CDPD packet-switched channels to find a channel to use as the continuous CDPD channel. In plain terms: the hardware-side counterpart — add a dedicated card/channel and let it sniff for a free channel. Claims 36–38 depend on it.

Claim 39 — Portable wireless subscriber station. A subscriber station with (i) first circuit(s) enabling CDPD packet-switched mode, (ii) second circuit(s) enabling continuous CDPD mode, and (iii) a selection mechanism between them, where that mechanism includes a subscriber-actuated mechanism for switching modes. In plain terms: the mobile unit itself supports both modes and lets the user switch. Claims 40–42 depend on it.

Notable dependent-claim features: dedicated SNODEM (sniffer/modem/transceiver) modules within each MDBS operating on a single assigned channel not subject to packet-switched pre-emption (claims 7–10); MD-IS + MTSO + data link as the allocating means, with no AMPS pre-emption of the allocated channel (claims 17–18); means for distinguishing packet vs. continuous CDPD communication (claim 19); automatic request generation responsive to cost data (claims 20–21); manual user request (claim 22). The preferred embodiment uses GMSK, 19.2 kbps, a (63,55) Reed Solomon code, and a 15-bit sync word, yielding ~15.84 kbps usable, versus a (63,47) code and distributed sync/busy-idle flags for packet CDPD.

4. Litigation / docket check

• I searched for USPTO and CAFC 2026 docket activity tied to 6,370,135 specifically and found none. A search for "6370135" plus Federal Circuit/litigation produced only different patents with similar numbers (e.g., VirnetX 6,502,135; Andrea 6,363,345; AT&T 6,370,137) — per your instruction, these are not results for the patent you asked about and I have not treated them as such.
• No IPR/PGR, reissue, or reexamination record for 6,370,135 appeared in the sources consulted; the recorded legal status is simply Expired – Lifetime.
• Uncertainty flag: I cannot confirm the absence of any district-court or CAFC matter with high confidence, because I did not get a direct hit on a 2026 docket database. Treat "no 2026 CAFC docket found" as no evidence located, not as proof of none.
• Forward citations of note (showing downstream relevance) include US 6,832,080, US 7,151,943, US 7,233,802, US 7,245,928, US 7,324,070 and US 7,733,901.

5. Sources

• Full patent text and figures: https://patents.google.com/patent/US6370135/en
• Patent PDF (bibliographic front page, references, 42 claims): http://patentimages.storage.googleapis.com/53/16/2a/52ea9ba8775ddb/US6370135.pdf
• Claim text (claims 1, 23, 35, 39 and dependents): https://insight.rpxcorp.com/patent/[US6370135B1](/patent/US6370135B1)
• PubChem patent record (dates, inventor, assignee, CPC): https://pubchem.ncbi.nlm.nih.gov/patent/US-6370135-B1
• Justia patent page: https://patents.justia.com/patent/6370135

Caveats: Claim language for claims 2–5, 24–27 and 36–42 was only partially visible in the sources retrieved; I have summarized those only where text was present. The parent specification refers to related applications Ser. No. 08/152,005 (now U.S. Pat. No. 5,544,222) and Ser. No. 08/117,913; I have not independently verified the current status of those.

I'll research litigation involving US patent 6370135 across patent litigation databases.

Litigation Search Results: US Patent 6,370,135

Summary Finding

No litigation involving US Patent 6,370,135 was identified in the searches I was able to run.

I must be transparent about the scope of this search and its limitations, so you can weigh the confidence level appropriately.

What I Searched

I ran web searches aimed at patent-litigation aggregators and general coverage, including queries for:

• US patent 6370135 litigation
• "6370135" patent infringement lawsuit
• "6,370,135" patent case
• Cirrus Logic patent 6370135 litigation PACER
• unifiedpatents.com litigation "6370135"
• Pacific Communication Sciences patent lawsuit CDPD

I was not able to complete live, direct queries against the specific sources you named (the Unified Patents litigation case list at portal.unifiedpatents.com/litigation/caselist, CAFC, and PACER) before hitting my search-step limit. My searches were also largely unproductive because generic search queries for a seven-digit patent number tend to return noise unrelated to this specific patent (e.g., hits mentioning the unrelated Spangenberg/Orion IP patents such as 5,367,627 and 5,493,490).

Important Caveats

1. I cannot confirm a negative. Because I could not query PACER, the CAFC docket, or the Unified Patents case list directly and exhaustively, I cannot affirmatively state that no litigation exists. All I can honestly report is that no case surfaced in the searches I ran.

2. I have no independent recollection of litigation on this patent. I do not have high-confidence training knowledge of any suit asserting US 6,370,135, and I will not fabricate case names, docket numbers, or outcomes.

3. Prosecution/ownership timeline may bear on litigation likelihood. Per the patent record:

   • Filed: 1995-06-07; Priority: 1995-06-07; Granted: 2002-04-09.
   • Inventor: Steven H. Gardner.
   • Original assignee: Cirrus Logic Inc. (filed by Cirrus Logic), assigned to Pacific Communication Sciences, Inc. (1995-09-01), then assigned to Cirrus Logic Inc. via merger (2018-03-19).
   • Legal status: Expired – Lifetime; anticipated expiration 2019-04-09.

   Because the patent expired in April 2019, any infringement action would have needed to be filed on or before that date (subject to the six-year damages lookback, 35 U.S.C. § 286). This narrows the relevant window but does not eliminate it.

Recommendations to Confirm

To get a definitive answer, the following should be checked directly (I could not complete these):

• Unified Patents Portal – https://portal.unifiedpatents.com/litigation/caselist — search the patent number; look for both district court and PTAB (IPR/PGR/CBM) records.
• PACER — search "6,370,135" across district courts (note: this patent number would not appear in pre-2002 filings; look for litigation between 2002 and 2019).
• CourtListener / RECAP (courtlistener.com) — free docket search by patent number.
• USPTO Patent Trial and Appeal Board — for any IPR/CBM proceedings involving the patent.
• CAFC — for any appeal only if a district court or PTAB case is first identified.
• MaxVal Litigation Datasource / Lex Machina / Docket Navigator — commercial litigation databases with patent-number search.

Bottom Line

As of the searches I could run, I found no known litigation involving US Patent 6,370,135. This should not be read as confirmation that none exists — it reflects the limits of my search this session. I recommend running the patent number directly through Unified Patents, CourtListener/RECAP, and PACER to obtain an authoritative answer. If you can supply results from any of those, I can help compile the per-case details (plaintiff, defendant, jurisdiction, case number, filing date, and status) you requested.

I'll verify the structured "no proceedings" finding with targeted searches before writing up.

Initial searches returned noise. Let me run a second, more targeted round to try to confirm or refute the ODP "no proceedings" result.

Proceedings overview

Total AIA trial proceedings on US 6,370,135: zero (0). Breakdown: 0 active, 0 with claims invalidated, 0 with claims sustained, 0 settled, 0 with institution denied, 0 pending appeal. The structured "PTAB proceedings on file" block — the USPTO Open Data Portal canonical list — returns no AIA trial proceedings for this patent, and independent web searches run this session surfaced nothing that contradicts it.

Bottom-line defensive posture: this is not the "patent has survived two IPRs and is hardened" scenario, and it is also not the "claims 1–5 have been canceled" scenario. It is a third, distinct posture: no claim of 6,370,135 has ever been adjudicated by the PTAB, because no one ever filed. Combined with the patent's expiry (anticipated 2019-04-09) and the § 286 six-year damages lookback (which ran out 2025-04-09), a defendant today is not facing a hardened patent — it is facing an unadjudicated, expired patent whose damages window appears to have closed. That is a materially better position than either of the two the prompt anticipates, but it must be grounded on expiry, not on PTAB estoppel (there is no estoppel to be had).

Proceeding-level detail

There are no proceedings to report at the required per-proceeding granularity. I am deliberately not generating placeholder ### IPR20XX-XXXXX headers, because doing so would require inventing proceeding numbers, petitioner identities, and panel compositions — exactly what the operating rules forbid. The per-proceeding template (petition grounds, institution decision, FWD claim-level verdict, settlement, appeal) is therefore inapplicable, not merely unfilled.

Verification attempts and their limits

Confidence and caveats. The ODP block is the authoritative source and it reports zero; my searches are consistent with it. I could not complete direct queries against PTAB E2E/Patent Public Search's PTAB tab, the Unified Patents litigation-and-trial portal, or CourtListener/RECAP because I exhausted my tool-step budget. Generic seven-digit-number web queries are notoriously low-yield for this purpose (the search results above returned a different patent, '537, purely on digit-pattern matching). I therefore cannot state as an absolute certainty "no AIA trial has ever been filed," but the canonical ODP record plus the absence of any contradicting hit is a strong, mutually corroborating basis for reporting zero.

Data limitation flag. The authoritative patent text supplied in this prompt is truncated inside the "BEST MODE" description (it ends mid-sentence at "…the subscriber unit control processor programming to request the CDPD") and does not include the claims. I therefore cannot independently enumerate the claim set of 6,370,135, and I will not state claim numbers I cannot verify against the record.

Strategic summary

Claim status: entirely UNTESTED. No claim of 6,370,135 has been canceled, confirmed, or otherwise adjudicated — in an AIA trial or, per the earlier litigation section of this analysis, in any district court proceeding that surfaced. There is consequently no "surviving claim" list to give you, because it would be identical to the full claim set, and no "dead claim" list either. Any representation that specific claims are invalidated, or that specific claims have survived scrutiny, would be unsupported by the record. The '222 patent cross-referenced in the specification (U.S. Pat. No. 5,544,222, from application Ser. No. 08/152,005) is a separate asset and its history, whatever it is, says nothing about 6,370,135.

Estoppel landscape: empty, and largely moot. Because no IPR/PGR/CBM was ever instituted, no petitioner is subject to 35 U.S.C. § 315(e)(2) estoppel on this patent. Every prior-art ground — including § 102 and § 103 combinations built on the Analog Devices/AMPS art, the CDPD Specification Version 1.1 itself, and the Anderson/Aulin/Sundberg Digital Phase Modulation text cited in the specification — remains theoretically available. The practical constraint is not estoppel but Article III/§ 286 math: the record shows an anticipated expiration of 2019-04-09 and "Expired – Lifetime" status. A complaint filed today (2026-09-10) could reach back only to 2020-09-10 under § 286 — a date after expiry — which means the recoverable-damages window appears to have closed on 2025-04-09. An IPR is also a poor use of resources in 2026 against a patent with no live exclusionary right left to challenge. (For accuracy: the 2019-04-09 date is consistent with a term of 17 years from issuance — 2002-04-09 grant + 17 years — under the pre-URAA transitional rule for applications filed before 1995-06-08. The application was filed 1995-06-07, one day inside that window. I flag this as my reasoned reading of the dates, not as a quoted authority.)

Pattern signals: there is no pattern, and that is the finding. No serial petitioner, no defensive aggregator (Unified Patents does not appear in any chain here), and no PTAB appeals by the patent owner — because there were no trials to appeal. The ownership chain recorded on the face of the patent is a straightforward corporate lineage: filed by Cirrus Logic Inc. (1995-06-07) → assigned to Pacific Communication Sciences, Inc. (recorded 1995-09-01) → reassigned to Cirrus Logic Inc. by merger (recorded 2018-03-19). Note the merger recordation post-dates the substantive assignment by 23 years and lands one year before expiry; that timing is a housekeeping/chain-of-title event, not evidence of assertion activity. Critically: the absence of IPRs here should not be read as evidence that the patent is strong. The prompt's heuristic — "well-asserted patents eventually attract IPRs" — cuts the other way: this patent appears never to have been meaningfully asserted, so it never attracted a petition. Its 2019 expiry, its 1995 filing date, and the obsolescence of the CDPD air interface make it a poor candidate for either assertion or challenge.

Recommended next steps

If you are a defendant receiving a demand or complaint today:

1. Lead with the expiry/§ 286 argument, not invalidity. The record's "Anticipated expiration 2019-04-09" plus "Expired – Lifetime" status, evaluated under 35 U.S.C. § 286's six-year lookback, means a complaint served on 2026-09-10 cannot reach any act of infringement within the recoverable period. Confirm the expiry date independently via the USPTO Patent Center fee/term record for 08/487,044 (https://patentcenter.uspto.gov) before relying on it in a filing.
2. Do not expect PTAB estoppel to help you, and do not assume you can file an IPR to create it. With no institution on record, § 315(e)(2) bars no one. And an IPR against an expired patent with no live right to enforce is unlikely to be an efficient spend. Validate the Board's treatment of expired-patent petitions before committing.
3. Verify the zero myself if the stakes justify it — the following are the direct queries I could not complete:
   • PTAB E2E / USPTO Patent Public Search PTAB tab: https://ppubs.uspto.gov and https://e2e.uspto.gov
   • Unified Patents litigation and PTAB portals: https://portal.unifiedpatents.com/litigation/caselist
   • CourtListener / RECAP free docket search: https://www.courtlistener.com/
   • Search on both the patent number (6,370,135 / 6370135) and the application number (08/487,044) and the assignee strings "Pacific Communication Sciences" and "Cirrus Logic", since PTAB dockets frequently index by application number rather than issued-patent number.
4. If any proceeding does surface from those checks, send me the proceeding number(s) and I will complete the full per-proceeding template — grounds, institution reasoning, claim-level FWD disposition, settlement, and any CAFC docket — with verbatim claim numbering and links to the PTAB decision PDFs and CourtListener opinions.

If you are conducting diligence rather than defending a suit: treat "no PTAB activity" here as an asset-quality datapoint, not a strength signal. The patent discloses a genuinely interesting technical concept (reusing CDPD GMSK modulation for a continuous/circuit-switched channel to cut per-packet overhead), and its specification cites the CDPD Specification Version 1.1 and U.S. Pat. No. 5,544,222 as foundations — but it was never tested, never asserted, and is now expired. Its value today is as prior art and as a licensing/portfolio artifact, not as an enforcement instrument.

I'll research the assignment record for US 6370135, cross-referencing USPTO Assignment Center data and corporate history of the named entities.

Let me dig further into the assignment record specifics and the corporate history of the chain.

Ownership Analysis — US Patent 6,370,135

Title: Continuous CDPD base station and method of facilitating efficient data transfer
Appl. No.: 08/487,044 | Filed/Priority: 1995-06-07 | Granted: 2002-04-09 | Expired: 2019-04-09

Source-availability caveat (read first). The reel/frame numbers, execution dates, and — critically — the correspondent of record are not exposed in the sources I was able to reach this session. The USPTO Assignment Center (assignmentcenter.uspto.gov) blocks automated retrieval, and Google Patents' legal-events panel reproduces only the assignor/assignee/conveyance-type fields, stripped of reel/frame and attorney metadata. I have therefore not fabricated reel/frame values or correspondent names. Every reel/frame field below is marked as unavailable rather than guessed. What follows is built from the Google Patents legal-events record plus corporate-history corroboration.

Inventors

• Sole inventor. Unlike the sibling PCSI application that matured as US 5,544,222 (Appl. 08/152,005), which named eight inventors (Robinson, Gardner, Wong, Kasmir, Balachandran, Graham, Schjelderup, Quick), this patent names only Gardner. The application is expressly related to PCSI's US 08/117,913 (filed 1993-09-08) and US 08/152,005, and cites Gardner's own earlier US 5,533,029.
• Employer determination: Gardner appears as inventor on a long run of contemporaneous applications assigned to PCSI (e.g., US 5,511,098; US 5,544,222), and PCSI was publicly advertising itself as "the wireless communications division of Cirrus Logic" as of January 1995 — five months before this filing. Employment with PCSI/Cirrus is therefore well supported.
• Departure pattern: Not present. Gardner has continued PCSI/Cirrus-assigned filings well past this filing (multiple mid-1990s applications listed under Cirrus Logic). There is no evidence of the all-inventors-depart-within-12-months pattern that often precedes a portfolio liquidation. His later employment end-date is unclear from available sources.

Original assignee

Cirrus Logic, Inc. (Fremont, CA) is the assignee named on the face of the issued patent and the currently listed assignee. Note the standing anomaly below.

• Primary line of business: fabless semiconductor (analog/mixed-signal and DSP components); NASDAQ: CRUS; still a going concern with 1,000+ patents. Status: operating.
• Did it ship a product embodying the claims? Yes — through its subsidiary. PCSI built and sold CDPD Mobile Data Base Station (MDBS) equipment and subscriber units (the "Ubiquity" wireless CDPD modem line), and in August 1995 reported completing CDPD Specification 1.1 field trials with AT&T Network Systems and Bell Atlantic NYNEX Mobile using PCSI hardware. This patent's claims (multi-mode MDBS, dedicated continuous/circuit-switched CDPD channel) map directly onto that product line.
• ⚠️ Record anomaly to flag: the application as published names Cirrus Logic, Inc. as applicant/assignee, yet the first recorded assignment (1995-09-01) runs from Gardner → Pacific Communication Sciences, Inc. — not to Cirrus Logic. So the patent record and the assignment record point at two different members of the same corporate family. Which entity held equitable title at filing is unclear from the data available; both were inside the Cirrus Logic corporate family.
• ⚠️ Corporate-history conflict: sources disagree on the PCSI/Cirrus merger date — CB Insights records an acquisition dated 1992-12-22; PatSnap records Cirrus acquiring PCSI on 1993-03-02 for ~$66M; a Cirrus FY1995 Form 10-K describes completed mergers with PCSI (among others) "accounted for as poolings of interests," while another Cirrus 10-K snippet refers to PCSI merging with Cirrus Logic "in February" of an unspecified year. The month and year of the merger are unresolved; the direction (PCSI into Cirrus Logic) is not.
• Divestiture: Cirrus sold the PCSI wireless infrastructure equipment group (the CDPD/Personal Handyphone base-station business — i.e., the business practising these claims) to ADC Telecommunications for ~$23M cash, announced November 1996 and closed December 1996. Cirrus also sold PCSI's Wireless Semiconductor Products arm to Rockwell International for ~$18.1M. Cirrus retained the patent while divesting the product line — an "orphaned asset" pattern described under Signal notes below.

Assignment timeline

Two recorded transfers exist in the Google Patents legal-events record. Neither reel/frame number nor correspondent was retrievable.

• 1995-09-01 (executed date not separately surfaced) / recorded 1995-09-01 — Reel not retrieved

  • Conveyance: Assignment of assignors' interest
  • Assignor: Gardner, Steven H.
  • Assignee: Pacific Communication Sciences, Inc. (San Diego, CA)
  • Correspondent: not available — the Assignment Center record could not be retrieved, so I cannot report the recording attorney/firm of record. No recurrence finding can be made.
  • Context: original inventor assignment to the operating subsidiary that built CDPD base stations; routine and pre-issuance.

• 2018-03-19 / recorded 2018-03-19 — Reel not retrieved

  • Conveyance: Merger (see document for details)
  • Assignor: Pacific Communication Sciences, Inc.
  • Assignee: Cirrus Logic, Inc.
  • Correspondent: not available (same limitation as above).
  • Context: internal corporate reorganization — nunc pro tunc cleanup of title at the parent. The recording postdates the underlying merger by decades and lands ~13 months before the patent's expiry, which is characteristic of a title-audit / portfolio-cleanup recording rather than a contemporaneous transfer. The underlying merger document and its execution date were not retrievable.

• 2019-04-09 — anticipated expiration (not an assignment).

Term note: filed 1995-06-07 — one day before the URAA's 1995-06-08 cutoff — this patent's term is 17 years from grant (2002-04-09 → 2019-04-09), not 20 years from filing. That explains the expiry date and compresses the window in which any assertion could have been brought.

Timeline diagram

timeline
    title Ownership of US 6370135
    1995 : Application filed naming Cirrus Logic
         : Gardner assignment to PCSI recorded
    1996 : PCSI CDPD base station unit sold to ADC
    2002 : Patent issued to Cirrus Logic
    2018 : PCSI merger into Cirrus Logic recorded
    2019 : Patent expires

NPE / troll-pattern signals

Analyst note — the "orphaned asset" observation (not scored as a signal). In 1996–97 Cirrus Logic sold the PCSI business that practised these claims (CDPD base stations → ADC Telecommunications) while retaining the patent. That severance of patent from practising product is the standard precondition for a later monetization transfer, and is worth flagging as a risk factor for the family. It is not evidence of an NPE transfer here, because no such transfer is recorded — the patent simply aged out with the original corporate family.

Verdict

Insufficient data.

Substantively, everything I can verify points away from an NPE: the chain contains only the original inventor assignment (1995-09-01, Gardner → Pacific Communication Sciences, Inc.) plus a non-arm's-length corporate merger into Cirrus Logic, Inc. recorded 2018-03-19 — title never left the original corporate family, no licensing-only LLC ever appears, and no known asserter, cascading transfer, bankruptcy, or privateering signal is present. I nevertheless stop at Insufficient data rather than declaring an operating-company or non-asserting posture because (a) I could not retrieve the reel/frame numbers or the correspondent of record from the USPTO Assignment Center, so assignments outside the Google Patents legal-events summary — e.g., security interests, corrective assignments, or a change-of-name — cannot be excluded; and (b) a corporate-history conflict leaves the precise PCSI→Cirrus merger date unresolved. No litigation on this patent was identified in the prior search either, and the patent expired 2019-04-09.

Verification links:

• USPTO Assignment Center (search by patent number): https://assignmentcenter.uspto.gov/
• USPTO Patent Assignment Search (legacy index): https://assignment.uspto.gov/patent/index.html
• Google Patents legal events for this patent: https://patents.google.com/patent/US6370135/en#legal-events

Recommended next pull to close the gaps: run 6370135 through Assignment Center and record, for each of the two entries above, the reel/frame, execution date, and correspondent (attorney + firm + address). Both entries are pre-issuance or intra-family, so one would expect a single recurring correspondent (likely PCSI/Cirrus in-house or the prosecution firm behind US 5,544,222, identified on that patent as Lowe, Price, Leblanc & Becker). A correspondent on the 2018-03-19 merger filing that differs materially from the 1995 filing — particularly a licensing-side firm — would be the one fact capable of moving this verdict.

I'll research the prior art citations for US Patent 6,370,135. Let me start with several targeted searches.

Let me get the actual citation list from the patent's front page.

Let me search directly for the citation table on the patent's page.

Prior Art Analysis — US Patent 6,370,135 B1

Scope and honesty note (read first)

I was unable to complete the requested retrieval before hitting my search-step limit. Specifically:

• I could not retrieve the front-page "References Cited" list (the USPTO/Google Patents citation table) for US 6,370,135. The PubChem mirror of the Google Patents record confirms the field exists and states "9 Citations" (cited patent literature) plus a long "Cited By" list, but the nine cited references themselves were not exposed in the snippets I obtained: https://pubchem.ncbi.nlm.nih.gov/patent/US-6370135-B1
• I did not query the USPTO PatentCenter/Patent Full-Text database directly. My results came from Google Patents mirror pages and Justia, not from an authoritative USPTO citation feed.

Because the rules require me to interpret identifiers literally and not fabricate, I will not invent nine citation entries. Below I give (a) what is confirmed, (b) the references the patent itself cites internally (which are the strongest candidates for the "References Cited" set and are certainly relevant prior art), and (c) a §102 framework — clearly flagging confidence levels.

Part 1 — Confirmed bibliographic anchor

The critical date for §102 prior art is 1995-06-07 (the filing/priority date). Any reference must predate that date to qualify as §102(a)/(b)/(e) art.

Part 2 — References cited within the specification (highest-confidence prior art)

These are expressly named in the 6,370,135 specification itself. Because the patent text is the authoritative source provided, these are the most defensible prior-art citations I can assert:

(1) U.S. Patent No. 5,544,222 — "Cellular digital packet data mobile data base station"

• Full citation: U.S. Patent No. 5,544,222, issued 1996-08-06 (from application Ser. No. 08/152,005). Assignee: Pacific Communication Sciences, Inc.
• Priority/filing: Priority US 1993-11-12 (application 08/152,005, filed 1993-11-12). Pre-dates the 6,370,135 priority date by ~19 months.
• Description (as described by 6,370,135 and its PCT counterpart WO 95/13685): Discloses a CDPD Mobile Data Base Station configured to interface with an AMPS network, with modular transceiver/modem boards, an RF sniffer, and a channel-hopping scheme based on avoidance of AMPS channel use, plus a control/query/response encapsulation protocol. The 6,370,135 specification repeatedly points to this application for the SNODEM/sniffer architecture and the channel-hopping routine.
• Claims potentially affected (§102): The MDBS-architecture claims (directed to a CDPD base station having plural transceiver cards with at least one card allocated to a non-packet mode, and channel assignment means — the "third aspect" claim set in the BRIEF SUMMARY). The RF-sniffer/channel-selection elements are disclosed there, so those claim elements are not novel per se; only the continuous/dedicated channel allocation distinction survives.
• URL: WO 95/13685 abstract (PCT counterpart): https://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=[9513685A3](/patent/9513685A3)

(2) U.S. application Ser. No. 08/117,913 — "Portable communications and data terminal operating to optimize receipt of both incoming CDPD and AMPS messages"

• Full citation: U.S. application Ser. No. 08/117,913 (family resulting in U.S. Patent No. 5,819,184, "Portable communications and data terminal operating to optimize receipt of both incoming CDPD and AMPS messages," Pacific Communication Sciences, Inc., granted 1998-10-06; continued as US 6,334,062 B1).
• Filing/priority: Priority 1993-09-08 region; 5,819,184 filed 1995-06-07 (same day as 6,370,135). To qualify as §102(e) art it must predate the 6,370,135 priority date via its own earlier priority.
• Description: Discloses a dual-mode portable subscriber terminal that receives both CDPD and AMPS messages and optimizes operation between them — i.e., the subscriber-station side.
• Claims potentially affected (§102): The "fourth aspect" claim set (portable wireless subscriber station with means for requesting packet-switched mode and means for selecting between operation modes). This reference is directly on point for the subscriber-station claims.
• Note: 6,370,135 shares its 1995-06-07 filing date with US 5,819,184/6,334,062, and both descend from the same Pacific Communication Sciences program. Common-ownership / §103(c) and double-patenting considerations apply.

(3) The CDPD Specification, Version 1.1 (Parts 402, 403, 408)

• Full citation: Cellular Digital Packet Data System Specification, Release 1.1 (CDPD Forum / industry specification, 1995), Parts 402 (AIRLINK), 403, and 408-32 (modulation).
• Date: Published prior to 1995-06-07 — constitutes a printed publication under pre-AIA §102(b).
• Description: Defines GMSK modulation (BT = 0.5, modulation index 0.50, 19,200 bps), the (63,47) Reed-Solomon-coded 282-bit MDLP block with the 35-bit sync word, busy/idle flags, channel hopping, RF sniffing, and the packet-switched MDBS/MD-IS architecture.
• Claims potentially affected (§102): Strongest art against every "compliant with the existing CDPD standard" limitation — the modulation, coding, sync-word, and channel-hopping limitations are all disclosed by the specification, so any claim reciting only those features (without the continuous-mode/dedicated-channel distinction) is anticipated.

(4) Non-patent literature cited in the specification

• "Digital Phase Modulation," J. B. Anderson, T. Aulin & C. Sundberg, Plenum Press, 1986. Cited as background for CPM/GMSK. Relevant to modulation claims only.
• U.S. application Ser. No. 08/152,005 (the parent of 5,544,222) is cited within the text as the source for the sniffer-based open-channel selection routine.

Part 3 — What I could NOT confirm (do not treat as absent)

The nine front-page "References Cited" entries may include additional U.S. patent references not named in the specification body (e.g., circuit-switched cellular data patents, CDPD-adjacent patents from Motorola, AT&T, IBM, or others). I could not retrieve these and will not guess their numbers. Any of the 9 could alter the §102 analysis, particularly if one discloses "circuit-switched operation over a cellular packet channel."

Part 4 — §102 anticipation framework (given the claim structure)

From the BRIEF SUMMARY, the patent has at least four claim families. Mapping likely anticipation:

Key takeaway: The novelty of 6,370,135 appears to reside in the combination of (i) subscriber-initiated request, (ii) allocation of a CDPD-format channel as a dedicated continuous/circuit-switched channel that packet users cannot access, and (iii) the block-format differentiation ((63,55) RS + 15-bit sync word, no busy/idle flags). Generic CDPD art (the spec + 5,544,222) teaches away from dedicating a CDPD channel to a single continuous stream; the §102 risk is therefore concentrated in whatever the un-retrieved 9 references contain.

Part 5 — Recommended next steps to complete the citation set

To produce the definitive per-reference table (citations, dates, anticipated claims), retrieve:

1. USPTO Patent Full-Text (PatFT) / PatentCenter for 6,370,135 → "References Cited" tab.
2. Google Patents https://patents.google.com/patent/US6370135B1/en → the "Patent Citations" table (the PubChem mirror confirms 9 entries but truncates them).
3. Justia https://patents.justia.com/patent/6370135 → "References Cited" section.
4. USPTO Patent Assignment / Global Dossier for prosecution-history §102 rejections, which name the examiner's actually-applied art (often more probative than the face citation list).

Cross-reference / contradiction check

No contradiction with the previously generated Litigation Summary. Both sections rely on the same bibliographic facts (filed 1995-06-07, granted 2002-04-09, Cirrus Logic / Pacific Communication Sciences, expired 2019-04-09). One date discrepancy to flag: the litigation section's runtime referenced dates in the 2026 timeframe, while this task states "April 26, 2026" — both consistent with an expired patent whose §102 window closed 1995-06-07.

Bottom line: I confirmed US 6,370,135's identity and the prior-art references it names internally (US 5,544,222; Ser. No. 08/117,913 → US 5,819,184/6,334,062; the CDPD Specification v1.1; Anderson et al. 1986), and gave a §102 framework. I could not obtain the nine front-page cited references that the request specifically asks me to enumerate, and I have deliberately not fabricated them. Providing the Google Patents / USPTO citation table (or just the nine reference numbers) would let me complete the exact per-reference citation → claim mapping you requested.

I'll gather prior-art specifics before building the § 103 combinations. Note up front: the Google Patents text supplied above does not contain a "References Cited" / Prior Art list (the fetch captured classifications, description, claims and abstract, but no patent-citation table). I'll search for the cited art directly.

The PDF snippet reveals the examiner-cited reference list. Let me pin down those references precisely.

Obviousness Analysis — US 6,370,135 B1 under 35 U.S.C. § 103

Scope note / contradiction flag. The task directs me to use "the results from the Prior Art section of this page." The page text supplied in the record (Google Patents fetch of https://patents.google.com/patent/US6370135/en) does not contain a "References Cited" / Prior Art section — the fetch captured classifications, description, abstract and claims, but no patent-citation table. Rather than substitute my memory, I searched the granted-PDF front page and retrieved the examiner-cited reference list, which I reproduce below with an explicit confidence marker. Anything I could not verify is flagged rather than filled in.

1. Legal framework and critical date

• The application was filed 1995-06-07 and issued 2002-04-09. Because the application was filed before 2013-03-16, pre-AIA 35 U.S.C. § 103(a) governs. The § 102(b) one-year bar date is therefore 1994-06-07; art published before that date is § 102(b) art regardless of the inventor's date of invention.
• Level of ordinary skill (POSITA): a person with a bachelor's degree in electrical engineering (or equivalent) and roughly two to four years' experience in cellular/wireless data communications, familiar with the AMPS air interface, the CDPD specification, GMSK modulation, Reed-Solomon FEC, and RF channel-hopping base-station design. I state this because several claim elements are "means for" limitations under 35 U.S.C. § 112 ¶ 6, and the ordinary artisan's knowledge matters to what counts as the corresponding structure.
• Key antecedent: the patent's own specification and background are admissions about the state of the art and are usable as prior art against the claims. This is the single most important fact for the analysis below.

2. The prior-art references available (as retrieved)

2.1 Front-page, examiner-cited references

From the granted PDF front page (http://patentimages.storage.googleapis.com/53/16/2a/52ea9ba8775ddb/US6370135.pdf), the following U.S. references appear (asterisked entries are marked "cited by examiner"):

Caveat I must state plainly: I verified numbers, dates and cited names as they appear on the front page. I did not verify the titles/teaching of most of these references (my follow-up searches for US 5,533,029, US 5,533,019, US 5,483,524 and US 5,384,777 returned no usable results before I hit my search limit). I will therefore not attribute specific disclosures to them beyond what the patent's own front page and background supply. The dates matter: the 1996–1997 issue dates are consistent with these being pre-1995-filing § 102(e) art — which is exactly why the examiner cited them against a 1995 application.

2.2 References I can cite with confidence

A. U.S. Patent 5,544,222 — "Cellular digital packet data mobile data base station," Pacific Communication Sciences, Inc.; filed 1993-11-12, issued 1996-08-06. Verified at https://patents.google.com/patent/EP0776549A4/en and https://uspto.report/patent/grant/5544222. This is the patent the '135 specification expressly calls out as application Ser. No. 08/152,005, and the '135 spec states that the same sniffing/channel-selection methodology is reused. Its claim set (as retrieved) recites an MDBS with a controller board and transceiver boards, a backplane (HDLC serial bus), and means for detecting AMPS communications on RF channels plus means for periodically adjusting [a channel] list and means for sending data regarding said list to mobile end systems.

B. The CDPD Specification itself. The patent repeatedly incorporates "CDPD specification, Version 1.1" and cites Parts 402, 403 and 408-32. Separately, CDPD Specification Version 1.0 (July 1993) is documented as prior art in the patent literature — e.g., Ericsson's DE 19681608 B3 / DE 19681600 C2 describe "Die Cellular Digital Packet Data (CDPD) Systemspezifikation, Version 1,0 (Juli 1993)" (https://FreePatentsOnline.com/DE19681608B3.html, https://patents.google.com/patent/DE19681600C2). A July 1993 publication date squarely clears the 1994-06-07 § 102(b) bar.

C. CDPD handoff/channel-hop art: US 5,594,943 ("...handoff... in a CDPD system"), which describes Undirected/forced channel hop mode, a "Best Hop List", and channel scanning ordered by performance criteria (https://patentimages.storage.googleapis.com/49/4e/ab/5a9c35692c7723/US5594943.pdf). Also the survey text Cellular Digital Packet Data confirming the state of the art on dedicated vs. shared RF channels and sniffing/40 ms carrier switch-off.

D. Multi-mode subscriber-terminal art: US 5,127,042 (Gillig et al., cellular/cordless, user- and automatically-switchable — see https://uspto.report/patent/grant/5127042 and the IPR record at https://ptacts.uspto.gov/ptacts/public-informations/petitions/1527841/...), US 5,179,360 (Suzuki, analog/digital mode switching, discussed in https://patents.google.com/patent/EP0709002B1), and the omni-modal radio family (WO 95/17077 A1, https://patents.google.com/patent/WO1995017077A1/en; US 6,934,558, https://www.freepatentsonline.com/6934558.html), which expressly lists CDPD among supported modes and recites user-selectable and automatic service selection based on (1) the cost of sending a data message, with library functions including "request transmission channel in system," "obtain cost information for all systems," and "select data/voice mode."
Date caveat: WO 95/17077 published 1995-06-22, i.e. after the 1995-06-07 filing date, so it is not § 102(a)/(b) art on its face. Its usability depends on the filing date (≈Dec. 1994) of its U.S. priority application, which I did not verify. Treat this reference as conditionally available (§ 102(e)) pending that check.

3. Element-by-element gap analysis of the independent claims

4. Proposed § 103 grounds

Ground 1 — Claims 1, 23 and dependents: CDPD Specification (v1.0, July 1993 / v1.1) in view of conventional circuit-switched cellular data modems

• What the CDPD spec supplies: the whole packet-switched CDPD portion of claim 1 (MDBS, MD-IS, M-ES, multiple base stations under one MD-IS, channel streams, DS0/T1 backhaul); the GMSK/19.2 kbps air interface; dedicated channels "reserved for CDPD use" where "AMPS calls will never attempt to pre-empt"; RF sniffing; and planned/forced channel hopping with a "switch channels" message.
• What the AMPS circuit-switched cellular data art (described in the '135 background itself) supplies: a single channel "set aside for specific communication, and … dedicated thereto until that communication is complete" — i.e., the circuit-switched concept, admittedly old and well known.
• The only real gap is the insight to run a circuit-switched-style dedicated/continuous stream using the CDPD modulation and higher-level protocol. The specification concedes this is a matter of "replicating existing hardware in the base station and … modifying the base station and subscriber station software," and that "[a] SNODEM module identical to that used for packet-switched CDPD can also be used to support the continuous CDPD mode."
• Motivation (explicit and admitted): the '135 background sets out the cost calculus itself — "circuit-switched rate is 40 cents per minute … the CDPD rate is 5 cents per packet … the CDPD rate is less expensive until more than eight packets worth of data must be sent," i.e. a demarcation at "2 and 4 kbits." This is a known, quantified economic incentive to provide a second, connection-oriented mode on the same CDPD infrastructure — the classic KSR "design incentive … market pressure" motivation.
• Predictability: GMSK was selected for CDPD precisely for high bit rate and good error performance; the patent admits that "it is generally easier to achieve good performance in a continuous mode of reception than in a burst mode," so the result of running continuously is not merely predictable but expected to be at least as good.

Ground 2 — Claims 1, 23, 35, 36–38: CDPD Specification in view of US 5,544,222 (Robinson et al., PCSI)

This is the strongest ground, because the '135 specification itself incorporates this reference and directs the reader to it:

"the selection of the open channel for a continuous CDPD communication by the sniffer on SNODEM module 45′ can be conducted in the same way as is done to select a channel during a normal channel hopping routine as described in U.S. patent application Ser. No. 08/152,005 now U.S. Pat. No. 5,544,222."

• 5,544,222 supplies the card-based MDBS (controller board + transceiver boards + backplane + HDLC serial bus), the AMPS-detection means, the periodically adjusted channel list, and the means for sending the list to mobile end systems — mapping onto claim 35's "plurality of transceiver cards," "means for assigning," and "means for scanning among available CDPD packet-switched channels."
• Motivation: same field, same assignee (Pacific Communication Sciences), same cell-site chassis, express incorporation by reference; the '135 spec states the only hardware change is "the additional SNODEM module 45′" inserted "in a spare SNODEM module slot in the existing chassis." Adding a functionally identical card and downloading different software is the paradigmatic predictable use of a known technique to improve a similar device in the same way (KSR). There is also a stated design driver: because "unplanned hops … may require that the subscriber return to the packet-switched mode," the patent itself says it is "desirable to maximize the use of planned hops" — a known problem with a known fix (more/better sniffing, dedicated cards).

Ground 3 — Claims 17–18 and 33: CDPD Specification in view of US 5,594,943 and the spec's own AMPS-coordination teaching

• The Ericsson characterizations of CDPD Spec v1.0 state the commonality between the CDPD and AMPS systems is confined to "the use of the same kind of radio frequency channels and the same base-station installations … and the use of a signalling interface for the coordination of channel assignments between the two systems" (https://FreePatentsOnline.com/DE19681608B3.html; https://patents.google.com/patent/DE19681600C2, my translation).
• That is precisely claim 33's (and, in system form, claims 17–18's) MD-IS ↔ MTSO data link by which the CDPD system negotiates an AMPS channel for continuous CDPD use, plus the corollary that a channel so assigned cannot be pre-empted — which the spec already states for dedicated channels.
• Motivation: channel-assignment coordination between an overlay data system and the host voice system is a known interoperability problem; US 5,594,943 supplies the complementary CDPD-side hop/handoff protocol. Using the existing inter-system signalling path to obtain a guaranteed-clean channel is a finite number of identified, predictable solutions, which KSR deems obvious to try.

Ground 4 — Claim 39 (and 40–42): Subscriber-station claims over dual/multi-mode terminal art

• Gillig (US 5,127,042) discloses a terminal operating with two different radio systems, with automatic transfer and simultaneous operation, including user- and condition-triggered switching.
• Suzuki (US 5,179,360) discloses analog/digital mode switching in a single cellular telephone (https://patents.google.com/patent/EP0709002B1).
• The omni-modal art (WO 95/17077 / US 6,934,558, subject to the date caveat above) discloses precisely claim 39's architecture — circuitry for multiple modes plus a stored-program selection mechanism, with selection under "the control of the end user," criteria including cost of sending a data message, and library functions for "request transmission channel in system" and "obtain cost information."
• Motivation: the subscriber station is the natural party to detect a large file transfer; the '135 spec concedes that "[t]he only change in a typical subscriber station … resides in the software that recognizes that a data file to be transmitted (or received) is more economically handled in the circuit-switched mode," and that cost data for the two modes is "pre-programmed into a PDA or host PC." Combining a known dual-mode terminal with a known cost-per-packet/cost-per-minute comparison is an automation of a known, admitted manual choice — obvious under KSR and under the Federal Circuit's "obvious to program" line.

Ground 5 — Mode-differentiation dependents (illustrated by claims 19, 28–29): CDPD Specification in view of the ordinary skill in data-block/sync design

• The spec furnishes the packet-mode block in full detail: 282 MDLP bits → (63,47) Reed-Solomon → 378-bit block → XOR with a PN cover generated from a specified polynomial → seven 54-bit segments → per-segment decode-status flag and 5-bit busy/idle flag XORed with a 35-bit sync word 11101 00001 11000 00100 11001 01010 01111 (CDPD spec pp. 402-12 to 402-21).
• The '135 differentiation options (different code rate; different cover initializing values; a 15-bit leading sync word instead of a distributed 35-bit one; dropping busy/idle entirely) are alternative parameter selections within a format the artisan already designs, motivated by the admitted fact that "[t]he extensive overhead necessary to maintain packet-switched transmissions is not required for the circuit-switched mode." Selecting a stronger code rate (63,55) to obtain more FEC, or moving the sync word to block-start, are textbook design choices with predictable results.

5. Why a POSITA would have combined these references — the consolidated motivation story

1. Same field, same hardware, same assignee. The '135 spec is a continuation-in-spirit of PCSI's own MDBS work (5,544,222). Combining references that share a chassis, a bus, a sniffer and a channel-hopping protocol is the least speculative kind of combination.
2. The specification's own admissions supply the "known problem." Cost per packet vs. cost per minute (5¢ vs. 40¢; crossover at 8 packets ≈ 2.2 kbit), the overhead penalty of packet mode, and the poor performance of conventional circuit-switched cellular modems (−80 dBm degradation, ≤14.4 kbps ceiling) are all recited as pre-existing knowledge.
3. The specification's own admissions supply the "known solution." Dedicated CDPD channels immune from AMPS pre-emption, sniffing, planned hops with a "switch channels" message, and a signalling interface between CDPD and AMPS for coordinating channel assignments are all recited as existing CDPD capabilities.
4. Predictable result. Reusing GMSK + CDPD higher-level protocol in a continuous (non-burst) mode yields, by the patent's own admission, "receiver sensitivity performance … comparable to that of standard analog cellular voice receivers" and a data rate "approximately twice that available to a packet-switched transmission." No unexpected result is claimed; the asserted benefits are the arithmetic consequence of removing multi-access overhead.
5. Obvious to try where a finite set of options exists. Claims 17–18/33 (dedicated channel vs. sniffed channel vs. MTSO-negotiated channel) are three enumerated alternatives for the same goal, each with a known trade-off — KSR's "finite number of identified, predictable solutions."

6. Where the § 103 case is weakest (and where a patent owner would push back)

• The "continuous CDPD" framing as a whole. A challenger must find art that suggests running CDPD continuously on a full symbol stream rather than art merely showing dedicated channels still carrying packet-mode framing. The specification's GMSK-continuous-phase discussion (Part 408-32) is a modulation fact, not a mode suggestion, and I did not locate art that expressly says "run CDPD in a circuit-switched/continuous framing." That gap is what likely carried the claims to allowance — note that the examiner cited 5,544,222, 5,533,029 (Gardner), 5,483,524 (Lev), 5,533,019 (Jayapalan) and H1641 (Sharma) and the claims still issued, which suggests these references alone did not teach the complete requested/allocated continuous-mode combination.
• Means-plus-function limitations. For claims 1, 35 and 39 the analysis must be run against the disclosed corresponding structures (control computer module 44 + SNODEM 45′; RF module 102 + radio control module 108 + control processor/modem 109). A reference that discloses the function without the structure is weaker.
• Teaching away / AMPS primacy. The CDPD spec gives AMPS absolute priority; an artisan might have viewed increasing CDPD's channel footprint (as a continuous mode does) as contrary to the overlay philosophy. The counter is that the spec expressly permits dedicated CDPD channels and that the patent's own best mode relies on exactly that.
• The abstract is garbled ("the packet-switched mode … is designated continuous CDPD mode"), which is a § 112 / claim-construction problem, not obviously a § 103 problem — but it complicates any claim chart.

7. Secondary considerations

I found no evidence of commercial success, copying, long-felt need, industry praise, or unexpected results attributable to the '135 claims. The patent expired 2019-04-09; the prior sections of this analysis found no litigation and no IPR/PGR/reissue/reexam record, which means there is no adjudicated validity determination to rely on either way. Absent such evidence, nexus to any secondary consideration would be difficult to establish.

8. Confidence statement and recommended verification

• High confidence: the legal framework (pre-AIA § 103, 1994-06-07 § 102(b) bar), the content of the '135 specification and its admissions, the role and content of US 5,544,222, and the prior-art status of the July 1993 CDPD specification.
• Moderate confidence: the specific use of US 5,594,943 and the omni-modal family as secondary references; the WO 95/17077 date caveat may remove Ground 4's strongest reference.
• Low confidence / not established: the disclosures of US 5,228,074, 5,241,537, 5,247,700, 5,282,204, 5,345,597, 5,365,512, 5,365,524, 5,384,777, 5,483,524, 5,533,019, 5,533,029 and H1641. Before this analysis is used in any filing or opinion, each of these must be pulled and read, because the examiner's use of them suggests at least one discloses subject matter materially closer to the claims than anything I could verify here (particularly US 5,533,029, listed as "Gardner," which may be a same-inventor co-pending application — a fact that would also affect its availability under § 102(e)/(f)).

Sources used: https://patents.google.com/patent/US6370135/en; http://patentimages.storage.googleapis.com/53/16/2a/52ea9ba8775ddb/US6370135.pdf; https://uspto.report/patent/grant/5544222; https://patents.google.com/patent/EP0776549A4/en; https://patentimages.storage.googleapis.com/49/4e/ab/5a9c35692c7723/US5594943.pdf; https://FreePatentsOnline.com/DE19681608B3.html; https://patents.google.com/patent/DE19681600C2; https://patents.google.com/patent/WO1995017077A1/en; https://www.freepatentsonline.com/6934558.html; https://uspto.report/patent/grant/5127042; https://patents.google.com/patent/EP0709002B1; https://pubchem.ncbi.nlm.nih.gov/patent/US-6370135-B1.