September 30, 2023
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Case Studies

Even examiner may overlook a winning prior-art during prosecution

As our team continues to work on challenging prior-art search cases, we often encounter interesting scenarios that pushes our limits of logical thinking and analytical abilities. The beauty of prior-art searches lies in the fact that there is no one golden rule or template to locate strong prior-art. The search approach and source of prior-art varies from project to project. At Expertlancing, we always believe in analyzing each search avenue to identify prior-art. Our researchers always intend to scrutinize every aspect in detail. So what if a result is already cited by the examiner as Category-A (not so useful) – should we adjudicate this result to be non-essential or should we analyze it again considering that the examiner might have overlooked some technical aspects of this result? We found the answer to this question while performing a prior-art search related to 5G technology. Let us find out the answer.

The case and our analysis:

We were assigned to work on an invalidation case related to 5G technology wherein the client’s objective was to fetch the closest prior art against a granted European patent. The technology of the target patent was related to a method for resource mapping of a Demodulation Reference Signal (DMRS). Before moving to the searching part for an invalidation case, it is very crucial to understand the true essence behind the patent concepts, key inventors and assignees, crucial classifications, keywords and citations related to the patent’s features. Our team understands this well, and we proceeded accordingly.

Now, our first step was to dig deep into the technology to understand the concepts behind the target patent’s important features. We observed that the concept of pilot demodulation for a Physical Broadcast channel (PBCH), based on full bandwidth CRS 9common reference signal), was already discussed in 4G / LTE systems. However, a full-bandwidth CRS was not introduced in a New Radio synchronization signal block (NR SS block) design. As a result, pilot demodulation cannot be performed for a PBCH in NR. Therefore, it is necessary to design a new mapping scheme for NR-PBCH demodulation pilot.

While developing the understanding of the target patent, we analyzed the prosecution history of the target patent as well its counterparts from other jurisdictions, and observed the following novel elements of the independent claim (can be considered as the core focus area of the search):

  1. To determine an OFDM symbol occupied by a primary synchronization signal (PSS) in the NR SS block and an OFDM symbol occupied by a secondary synchronization signal (SSS) in the NR SS block as the target OFDM symbol for mapping the PBCH-DMRS.
  1. To select one set of subcarriers to which a synchronization signal is not mapped in each of the target OFDM symbol occupied by the synchronization signal to map the PBCH-DMRS, wherein the synchronization signal comprises a PSS and/or an SSS, each set of subcarriers comprises a preset number of subcarriers, and a frequency interval between two adjacent subcarriers of the preset number of subcarriers is a preset frequency threshold.

We initiated our search by first performing a detailed citation analysis (i.e., forward and backward citation search) of the target patent. In such a process, we came across a prior art – US20150341908A1 which seemed very close to the claimed invention.

However, the reference had been already cited by examiner as CATEGORY- A prior art.

We continued our search and executed different search strategies targeting both patent and standard-related non-patent literature. Our team is well acquainted with the importance of conducting a thorough search for 3GPP/ETSI documents in prior-art search projects related to telecom. Accordingly, we examined relevant 3GPP/ETIS literature by exploring meetings/ drafts related to PBCH-DMRS mapping. However, the search did not result in anything substantial.

Then, we moved on to our next step of exploring patents by using search strategies such as keywords, CPC, IPC, US & F-term (Native Japanese Classes) classification search, inventor and assignee-based search. During such an exhaustive search, we again came across the cited Category-A reference US20150341908A1.

At first, we were somewhat hesitant about sharing the reference – US20150341908A1 to the client as it had already been cited as CATEGORY-A result by the examiner. However, our search efforts indicated that this was a significant prior-art in the context of the target patent’s features. Hence, we decided to have detailed discussions and brainstorming sessions with our team-members to verify the credibility of the result. We concluded that that this result can have a greater impact on the case rather than being a simple Category-A result. We prepared a detailed claim-chart with logical overlap of the target patent’s features with the identified result, duly supported by our analyst comments. We shared this detailed overlap with the client, as we were confident of our analysis here.

Few days after sharing the above reference, we got good feedback from the client in this case. This vindicated our approach for the search and thought-process behind sharing the reference. Below is the snapshot from the client’s feedback –

As a team, we took away an important lesson here – for any prior-art search against a target patent, existing references (citations and examiner citations) should not be simply overlooked. In particular, the examiner citations and analysis of these citations by the examiner may not be entirely accurate. An examiner usually processes a large number of applications within a definite period of time, and this can lead to some inaccuracy in the analysis.


While cracking this case, we observed that strong intuition, confidence in one’s own analysis, and having an unbiased approach towards known references are some of the key metrics for a successful prior-art search strategy. We should never skip any prior art that is mentioned in file wrapper just because it has been cited already. As evidenced by this case, we should always analyze all such citations carefully; there may be a chance to identify useful prior-art.

At Expertlancing, we take pride in our expertise in prior-art searches. Our team is constantly innovating and experimenting with new strategies for uncovering strong results in prior-art searches – this is simply the manifestation of our core motto of achieving CLIENT DELIGHT in everything we do.

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