Algorithms, patent records and source rights

Brian Greenforest · Research inventory, September 9, 2026

The engineering question is specific: what algorithms appear in this source, which publications describe them, and what can the retrieved patent records establish? The scope here is the released 1 Mb/s DSSS endpoint, with US patent records as the primary jurisdiction. This is a documented research starting point, not a worldwide freedom-to-operate opinion. No claim chart clearing every implementation step was obtained.

Start with the implemented operations

Operation actually used	Source location / publication	Conclusion supported by the research
11-chip Barker spreading, DBPSK and seven-bit scrambling	Host waveform encoder; receiver and the historical descriptions in the records below	Established PHY techniques. A patent describing a later detector also describing Barker spreading in its background does not make the entire background its invention.
20-position receive correlation, timing-score selection, adjacent-symbol differential dot product	DSSS receiver	Specific implementation must be compared to detector claims; sharing a multiplication or correlation operation is not a complete claim mapping.
Serial signed multiplication/addition and registered dataflow	Greenforest serial arithmetic; construction article	The supplied Greenforest source is MIT-licensed. This search did not establish an exhaustive patent clearance for every possible serial-arithmetic implementation.
CRC-16 PLCP and CRC-32 frame check	Host encoder, receiver, classifier and control transmitter	The code specifies polynomials, bit order and residues. Source availability and longstanding CRC use are not a claim-by-claim patent search.
Local ACK/CTS after SIFS	Scheduler; 1995 IEEE timing minutes	Historical timing documents establish the receive/processing/turnaround budget, not a security rationale or evidence of an ASIC-selling conspiracy.
PBKDF2-HMAC-SHA1, PTK derivation and EAPOL MIC	Crypto/frame helpers; RFC 8018, RFC 2104	The RFCs specify the primitives. They do not by themselves clear all claims on an entire WPA2 exchange or a hardware implementation.
AES-128, CCM data protection, AES key wrap	FIPS 197, RFC 3610 §9, RFC 3394	CCM's authors explicitly relinquished their IP rights and stated no known CCM patent. That is not a claim that a particular patent expired, nor a guarantee about other parties.
ARP, IPv4, UDP, DHCP, DNS, TCP and HTTP	ApProtocol; RFC 826, RFC 791, RFC 2131, RFC 9293	Published protocol definitions explain the on-wire formats. The source implements the narrow endpoint described in the article, not every service or later enhancement.
COBS framing and CRC-protected host transport	GFAP transport; Cheshire/Baker COBS paper	Publicly described framing algorithm; not part of the RF waveform and not a reason to call Wi-Fi patent-free.

Specific records, with their actual relevance

US 7,460,621 B2 — Detection

Publication and event record. Priority June 24, 2003; US filing June 24, 2004; grant December 2, 2008. The retrieved record reports fee-related expiry and a July 21, 2026 adjusted expiration date. Its particular detector combines code correlation, symbol-delayed correlation and preamble correlation. It explicitly presents the ordinary Barker correlator as prior art. Our receiver has related operations, but this inventory does not establish that its complete claimed combination is practiced. The record is an expired, relevant detector reference—not an “all DSSS is now cleared” certificate.

US 7,224,714 B1 — DSSS channel characterization

Publication and event record. Filed April 25, 2003; granted May 29, 2007. The record reports lifetime expiry June 5, 2025. Its subject is multipath channel characterization using correlations and path information. The released receiver does not implement that channel-characterization method. This is an excluded neighboring method, not a patent we claim was necessary to make the AP.

US 2007/0104255 A1 — Barker code detector

Application publication and status. The retrieved US record is abandoned, not an expired granted patent. Its detector forms a normalized maximum/minimum correlation contrast over accumulated data. The released receiver does not implement that specified normalized contrast. An application title matching “Barker” is not sufficient to attribute its claims to this implementation.

Google Patents supplies readable patent publication text and aggregated status/event information; its status labels expressly are not legal conclusions. These labels were not independently reconciled against every official prosecution, fee, adjustment, reinstatement or family record. For commercial reliance, inspect the corresponding official files through USPTO patent search and Patent Center. These findings are deliberately narrower than a legal clearance.

What an expiration guarantee would require

A complete review starts with independent claims mapped element by element to the actual receiver, transmitter, cryptographic protocol and chosen chip implementation. Search continuations and foreign family members; verify grant status, term adjustments, terminal disclaimers and relevant legal events in each intended market. Do not simply subtract twenty from today's year: USPTO MPEP §2701 explains the differing term rules and adjustments.

There is no defensible inference from “2.4 GHz” to “all patents expired.” Frequency does not identify an algorithm, and an old standard can acquire later implementation improvements. Nor does omission from this inventory establish that no relevant patent exists. The specific unresolved work is a comprehensive claim/family search for the exact released implementation and intended jurisdictions; that was not completed here.

The practical contribution is inspectable implementation detail: the full operation graph, source, state machine and timing interface needed to perform that review or replace an operation. No proprietary black box is being passed off as clearance.

Source licenses are a separate question

Original Greenforest C++, RTL, scripts and explanatory assets are supplied under MIT terms. Three retained Ettus FPGA helper files carry their own LGPL notices; the reference RFIC calibration driver carries GPL notices. Read THIRD_PARTY.md, the individual headers and included license texts. Keeping those boundaries explicit permits reuse without pretending that another project's code became MIT simply because it is in this archive.

OFDM, CCK, Viterbi decoding and Reed–Solomon are not used in the final 1 Mb/s radio path. Patent records about those algorithms cannot serve as evidence about this narrower implementation. Similarly, an alternate ADC, radio frontend or custom semiconductor process brings its own implementation questions; the packet protocol does not erase them.

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