In many cases, “free” isn't really free.
As an electrical engineer with an automotive background, when I think of Linux, I think of servers, PCs, supercomputers, and so forth. Embedded applications don't really come to mind when I consider Linux. However, Linux is used as an operating system for many phones, games, and other devices with embedded software.
Computer programs, often protected by copyright or trade secrets, can't be directly patented unless they're used for something tangible, such as signal processing or hardware control. For example, an operating system could be patented as a business method or a method to control computer hardware. Even though Linux is open source (free), certain companies could have patents that could be infringed by people using Linux in embedded applications.
Linux is generally considered free software, but is its use in embedded devices protected by U.S. patents? A patent consists of several parts, including the abstract, specification, and claims. The abstract is a concise summary of the specification while the specification is a complete description of the invention. The claims are where the majority of the legalese is found and are generally difficult for a nonlawyer to understand. Reviewing patent specifications and claims can give insight into the popularity and application of certain technologies throughout the years.
The claims are the most important part of a patent from a legal point of view because they define exactly what part or aspect of the invention is patented and, therefore, legally protected. From a technical point of view, the specification is often the most useful as it's a complete technical description of the invention and usually has less of the legalese that's found in the claims. If a feature is found in the claims, it'll definitely be in the specification. However, a feature may be discussed in the specification but not in the claims.
Patent office databases
The United States Patent and Trademark Office (USPTO) makes a lot of patent information available online at www.uspto.gov/patft/index.html. You can actually look at patents dating back to 1790 (Abe Lincoln's patent #6,469 for “A Device for Buoying Vessels Over Shoals,” on May 22, 1849, is in the online database!). Published patent applications can also be searched and viewed using the site. Patent applications are usually published on the site 18 months after they're filed. Batches of applications are published every Tuesday.
Patents are assigned to certain technical classes based on the nature of the invention. Each class has multiple subclasses that can be used to further specify the type of invention. You can see the patent classes at www.uspto. gov/go/classification/selectnumwithtitle.htm. As an example, patents related to operating systems might be contained in class 713, Electrical computers and digital processing systems: support; or class 719, Electrical computers and digital processing systems: interprogram communication or interprocess communication.
You can search for patents by looking in the appropriate classes and subclasses if you can determine them. However, embedded Linux applications could be located in many different classes because they can be classified by the end system's application.
Another way the databases can be searched is by keywords in the abstract, specification, or claims. The databases can also be searched by inventor, assignee, filing date, or several other parameters. You can combine the different search parameters logically using AND, OR, and the appropriate parentheses.
Finding embedded Linux
I searched the issued patent database, on 10/26/07, for titles, specifications, claims, or abstracts containing “linux” and “embedded” using the search logic ttl/(LINUX and embed$) OR abst/(LINUX and embed$) OR ACLM/(LINUX and embed$) OR spec/(LINUX and embed$) where $ represents a wildcard. This resulted in 1,445 hits. However, this included many patents discussing such things as embedded URLs and embedded images, which aren't really of interest for our topic.
By eliminating the specification from the search and limiting it to the title, abstract, or claims, I reduced the chaff, leaving only patents strongly related to Linux and embedded systems. Again, I searched the issued patent database for titles, claims, or abstracts containing “linux” and “embedded” using the search logic ttl/(LINUX and embed$) OR abst/(LINUX and embed$) OR ACLM/(LINUX and embed$). This resulted in just five hits.
I searched the pending patent publication database for titles, specifications, claims, or abstracts containing “linux” and “embedded” using the search logic ttl/(LINUX and embed$) OR abst/(LINUX and embed$) OR ACLM/(LINUX and embed$) OR spec/(LINUX and embed$). This resulted in 6,289 hits. However, like the issued patents, most of these weren't of interest. So, again I eliminated the specification from the search parameters to reduce the chaff.
I searched the pending patent publication database for titles, claims, or abstracts containing “linux” and “embedded” using the search logic ttl/(LINUX and embed$) OR abst/(LINUX and embed$) OR ACLM/(LINUX and embed$). This resulted in 56 hits.
Because patent application publications are left in the database even after the patent issues, you'll find some repetition of inventions between the issued patent and patent application databases (although the application and the patent often differ substantially after the examiner gets through with them). After eliminating the replication and remaining nonrelevant patents, only around 29 patents/publications were left. Table 1 shows some examples of relevant U.S. patents and publications related to embedded Linux as of 10/26/07.
The patent documents located reveal that a variety of companies/investors are involved with embedded Linux. There isn't one company that really dominates the list and several of them are foreign companies. So, if you work with embedded Linux, searching patents can provide you with a nice target list of companies.
Most of these patent applications were filed in the 2002 to 2005 timeframe, although two were filed in 2000. Figure 1 shows a graph of the number of documents per filing year. Applications from 2006 aren't fully represented in the data due to the 18 month delay between filing and publication of the application. So the 2006 applications related to embedded Linux are likely much higher than represented by the data.
In summary, most of the patent documents related to embedded Linux located in this search were filed between 2002 and 2005. No one company dominates the list of assignees but, rather, several companies from across the world. The number of U.S. patent applications filed related to the subject has seen as generally upward trend over the last few years, indicating increased popularity. Finally, even though Linux is a free-software operating system, it would be wise to search the U.S. patent database before commercially using Linux in an embedded application. Of course, refer to a licensed patent attorney if there is any doubt.
Danny Graves is a freelance patent analyst, patent agent, engineer, college instructor, author, and inventor with two U.S patents. He was a finalist for the 2001 Charles C. Gates Award for Excellence. He has researched numerous inventions across a wide range of technologies. Graves can be reached at .