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Leaving No Stone Unturned – Utilizing Direct & Indirect Patent Citations

Leaving No Stone Unturned – Utilizing Direct & Indirect Patent Citations

Are examiners overlooking known citations?

A recent PIUG presentation by Matt Beers of Ocean Tomo found that many (24 out of 65) of the prior art patents that were successfully used as the basis of Inter Partes Reviews were already listed as patent citations, but their importance had been missed by examiners. For example, these patents might have been listed as applicant citations, but it is thought that examiners routinely overlook applicant citations. A further 25, and 12 of the critical prior art patents were two, or three citation steps out respectively from the patent being challenged.

This suggests that parties looking to invalidate patents might want to start with the known, and closely related citations, but be certain that they pay attention to applicant citations as well.

Practically this can be an issue because in some cases there are a high number of total citations, and it can be impractical to carefully review them all.

There is a potential short cut though. Ambercite has recently released Cluster Searching, which can rank a series of known (direct), and indirect citations based on their predicted similarity to the starting patent (or patents) via an algorithm that ranks similarity based on citation profiles. It may be surprising to hear that Cluster Searching does not directly rely on keywords, but instead relies on the judgment of patent examiners, and applicants about which patents are similar, even if these similar patents use different technical terms to describe the same concepts.

A billion dollar case study

As an example of this, consider US patent 6778085 filed by Discovery Patents in January 2003 for a Security system and method with realtime imagery. This is part of a trio of patents being asserted against the US Government by its exclusive licensee 3rd Eye Surveillance LLC. 3rd Eye claim that the government infringes their patents through the use of their ubiquitous video monitoring systems, and is claiming damages of more than $1 billion.


This patent covers in its first claim:

A security system comprising:
an imaging device positioned at a secured location;
means, associated with a security system central station, for receiving and processing realtime imagery generated by said imaging device and received over a communications link; and
means, associated with an emergency response agency, for receiving, processing and displaying realtime imagery generated by said imaging device and received over a communications link from the central station.

Examination reports showed that the examiner cited nine patents. The ‘085 patent includes a WO patent family member WO2004006201, which has a search report that lists a single ‘X’ (‘of particularly relevance’) citation. This patent is US20020005894 filed in April 2001 for an Internet based emergency communication system. That patent discloses:

..a system for detecting an event within a premises and providing data such as live or recorded video, audio and data regarding that event to a website. … The website may be accessed by a variety of authorized users including the owner or manager of the premises, a central monitor, local police, fire, or emergency medical personnel, or other entities specified by the owner or manager of the premises.

There were other examiner citations, of mixed relevance to the Discovery patent:

  • US5694867 – Fail-safe access control chamber security system, which does not refer to video imaging
  • US5926210 – Mobile, ground-based platform security system which transmits images that were taken prior to the generation of an input signal – which stores the image before review rather than providing real time access
  • US6559769 – Early warning real-time security system– this is quite relevant to the Discovery patent
  • US20020106998 – Wireless rich media conferencing
  • US20030041330 – Security camera in dispenser – which only cover video cameras in fuel pumps
  • US20030086000 – Remote surveillance system – this is also quite relevant
  • US20030094541 – Security & anti suicide-hijacking system for airplanes – this does not refer to remote video monitoring
  • US20030117494 – Airplane cbb/security camera system interface – refers to remote monitoring of aircraft cabins

Overall, there were a total of 14 patent citations, i.e. another five citations were submitted by the applicant. Fourteen is not a large number of patents to review, but a guide to the most similar patents would likely be appreciated especially when a user is faced with a much longer list.  Often times there will likely be many more than 14 patent citations.

How to rank citations using Cluster Searching

Cluster Searching is a web application that only requires patent numbers to run a search, along with an optional date filter. In this case US6778085 was inputted into the search box, and a search was run for the most similar patents filed before the priority date of July 2002. In this case the most ‘similar’ 1000 patents have been displayed. ‘Similarity’ here is assessed by algorithms that compare the citation profiles of the patents involved.

Ambercite Cluster searching feature.

The top five listed patents are shown below. These are ranked in the order of predicted similarity to the Discovery patent. The last column indicates whether the patents are ‘directly’ (known citations) or ‘indirectly’ (no known citation references, but still thought to be similar) linked to the Discovery patent:


Direct and indirect citations are combined in this ranking because it is often convenient to look at both at the same time. However for the purpose of this exercise, we will treat the too types of citation separately in the next couple of sections

Direct Citations

The top ranked direct  citation is US6400265, filed in April 2001 for a System and method for monitoring security systems by using video images. This discloses:

a monitoring system for providing image… In addition, the image and other relevant data may be conveyed to a central security network where identified individuals may be alerted via identified methods.

Of interest, this was ranked in second position overall, with a indirectly ranked patent having a higher overall position (see the next section)

The second ranked direct citation is US8520068 for a Video security system, filed in September 2001 for:

a monitoring system for providing images (e.g., photos, pictures, video, diagram, illustration, etc.) where an alarm situation may be defected by comparing images. In addition, the image and other relevant data may be conveyed to a central security network where identified individuals may be alerted via identified methods.

This patent was only ranked in 77th position overall.

Third on the list of directly cited patents was US6476858, filed in 1999 for a Video monitoring and security system, which is focused on transmitting images after changes are detected in these images.  This is ranked in 109th position overall.

What about indirect citations?

Besides the known direct prior art citations, there is another source of potential prior art listed in Cluster Searching. These are indirect citations which are patents not listed as direct citations to the start patent, but which are instead linked to the starting patents via their relationships to other patents in the area.

At the top of the list is US6975220 for Internet based security, fire and emergency identification and communication system. The known ‘X’ citation US20020005894, is a Continuation-in-Part of this initially filed application.

In third position overall is US6661340 for a System and method for connecting security systems to a wireless device, which is closely related to the top ranked direct patent US6661340 (sharing the same inventors and filing date)

The fourth ranked overall patent is US6060994, filed in 1999 for a Method for controlling united home security system. This discloses:

A control method for united home security system includes steps of defining a set of signal codes which are transmitted between a client-side monitor/control server and a remote administrant …. The remote administrant performs a predetermined handling process which is corresponding to the incident code sent by the server. The remote administrant start performing a rescue process when receiving an emergency/rescue handling signal from the server.  The formats of transmitted signals comprise: …., video communication,

The fifth ranked patent is US7015806 for a Distributed monitoring for a video security system, filed in October 2001 for:

The security gateway transmits an alarm notification and the video across a network to a security system server in substantially real time… The security system server relays information to one or more distributed monitoring clients using rules-based routines for verification of the alarm condition.

In seventh position overall US6970183 Multimedia surveillance and monitoring system including network configuration, filed in June  2000 for:

A comprehensive, wireless multimedia surveillance and monitoring system .. A server provides a centralized location for data collection, alarm detection and processing, access control, dispatch processing, logging functions and other specialized functions

These patents are clearly relevant to the Discovery patent, perhaps more than some of the examiner citations, for example US20020106998 – Wireless rich media conferencing, which as a matter of interest only ranks 354 in the ranking of similar patents.

While a list of 705 patents can seem daunting to review, this can be simplified by reviewing the top ranked patents carefully. A user can filter out the less relevant or the bottom ranked patents using title, keyword and/or date filters,  and then further investigate any relevant patents with promising titles using the hyperlinks to further information provided in the table. Alternatively patent numbers can be copied, or exported to other applications for review there.

Is the Discovery patent valid in the light of this unlisted prior art? This is for others to decide, but it would be surprising if an opponent, such as the Federal Government, trying to invalidate this patent would not at least seriously consider these references as the basis for an obviousness, or novelty objection.


There are many different ways of searching for prior art, and keyword and class code searching remain popular. Nonetheless it is very likely that many of the most relevant patents are already known, as direct (whether examiner or applicant) citations. Similarly indirect citations can also be highly relevant, even if these patents used during the examination process. Cluster Searching allows users to quickly identify, rank and review these direct and indirect citations, potentially saving many hours of time, and in some cases finding patents completely missed by conventional searching.

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