Tuesday, 21 March 2017

T 0396/14 - Meaningful interpretation of claim by skilled person

What is the upper end of this range?

Granted claim 1 in this case contains the step 'positioning an upper end of the retransmission window'. Unfortunately, the description does not contain a clear definition of what the upper end is, and in fact the term only occurs a few times in the summary of the invention. Furthermore, with a (according to the opposition division) conventional understanding of the upper end, the claims would not work. The granted claims were then revoked for being insufficiently disclosed. 
The board gives more credit to the skilled person to come to a working embodiment that falls under the terms of the claims, then the opposition division did. 

Reasons for the Decision
2. Main request - Article 83 EPC
2.1 The breakdown of granted claim 1 into features A - F and the breakdown of granted claim 2 into features G - M, used throughout the opposition and appeal proceedings (see in particular the opponent's letter of 3 September 2014), will be used in the following.
2.2 The opposition division has found that claim 1 of the main request and consequently the main request as a whole did not meet the requirements of Article 83 EPC. The reasons given in the decision under appeal were in substance that the skilled person would not be able to carry out the invention defined in claim 1, because the teaching of the description in respect of the wording "upper end of the retransmission window" was in contradiction with what was stated in that claim. According to the opposition division, the general understanding was that the "upper end" of a sliding window in HARQ protocols corresponded to a sequence number transmitted later in time, and that a retransmission or receiving window was moved in the ascending direction, i.e. to positions corresponding to higher sequence numbers. The skilled person would read the description and the claims having only this interpretation in mind (Reasons 11.2). Further, according to the opposition division, there was no hint in the patent to think that a different understanding of lower end corresponding to lower sequence numbers, i.e. numbers having a smaller value than higher numbers, and of upper end corresponding to higher sequence numbers, was applicable (Reasons 11.3). Still further, according to the opposition division, the embodiment described with respect to the transmitter window was inconsistent with claim 1 (Reasons 11.4), whereas the embodiment described with respect to the receiver window supported the opposition division's understanding of "upper end" (Reasons 11.5). Lastly, according to the opposition division, the terms used in the patent document should be given their normal meaning in the relevant art unless the description gave them a special meaning, which was not the case here. Thus, according to the opposition division, the skilled person had to apply the same general and common interpretation to both windows, namely that the "upper end" of both the retransmission and the receiving window was associated with the data unit last transmitted or received (Reasons 11.7 and 11.8).
2.3 The board however agrees with the proprietor that the description and drawings disclose the invention defined in claim 1, in particular feature E, in a manner sufficiently clear and complete for it to be carried out by a skilled person.
Firstly, there is no explicit definition of the term "upper end" for a retransmission window since this term appears only once in the description in a passage summarising claim 1 ([0018]). It is also clear that a simple definition based on the sequence numbers of the data units present in the window is not possible, due to the repetitive nature of the modulo-N numbering. Similarly, a definition based on the position of a data unit at the top of a vertical representation of the retransmission window, as shown in Figures 5A and 8A, would be unsatisfactory since the figures could be turned to represent the retransmission window horizontally or in the other vertical direction without changing the technical teaching of the description. Therefore neither the general understanding of the skilled person nor the description and drawings limit the meaning of an "upper end" of a retransmission window to the highest sequence number in the window or the top of the window when represented in the vertical direction along the time line.
Even more to the point, the meaning of the term "upper end" in respect of a retransmission window is to be determined on the basis of the whole technical teaching of the patent, including the claims, description and drawings. The skilled person trying to carry out the invention in respect of the claimed retransmission window has to determine which end of the window is to be regarded technically as the "upper end" in the disclosure of the patent. Figure 6 and the corresponding paragraphs [0031] to [0033] show that, when the most recently transmitted sequence number is SN, the retransmission window permits only retransmission of data units having a sequence number between SN minus the window size and SN (see for instance step 64 in Figure 6 where SN = 4 and the window of size 4 comprises the numbers 1 to 4). Similarly, Figure 8A and the corresponding paragraph [0037] show that at time t1 the most recently transmitted data unit has the sequence number SN = 7 and the retransmission window of size 4 permits the retransmission of data units having a sequence number between 2 and 5, i.e. an end of the window of size 4 is positioned at a sequence number which is less than SN minus the window size. It is thus clear from the description passages and figures related to the retransmission window that the "upper end" in claim 1 corresponds to the sequence number which should have been transmitted earliest in time and which is usually, but not necessarily, due to the modulo-N numbering, the lowest sequence number of the window, as in the illustrated embodiments of Figures 6 and 8A.
The board is convinced that the above understanding of the term "upper end" in the context of the retransmission window in independent claim 1 is the only one which makes technical sense for the skilled person, taking into account the whole disclosure of the patent with respect to the retransmission. The fact that the term "upper end" has a different meaning with respect to a receiving window in independent claim 2 does not affect the above reasoning, since the two claimed methods operate independently of each other, even if they may be implemented in the same transmission system. Contrary to the opponent's arguments based on the observation that claims 1 and 2 had not been challenged for non-unity, the board judges that claims 1 and 2 indeed do not define interrelated products in the sense of Rule 43(2)(a) EPC, since the positioning of the retransmission window is performed independently of the positioning of the receiving window.
The board further notes that the opposition division itself, by acknowledging in the decision that the description "leads to think that SN-window corresponds in fact to the lower end of the window, and SN to the upper end of the window" (Reasons 11.4), correctly understood claim 1 based on the description. The opposition division went on to assess novelty and inventive step with respect to the retransmission window, based on the amended claims according to the first auxiliary request. All this emphasises that a meaningful interpretation of the invention in respect of the retransmission window defined in claim 1, based on the whole disclosure, is readily possible for a person skilled in the art.
The opponent further argued that, due to the use of the expression "less than or equal to" when defining the positioning of the upper end of the retransmission window in claim 1, different positions of the retransmission window were possible, such that the technical teaching could not be achieved across the full scope of claim 1. The opposition division held that, in view of the wording "less than", it was impossible to avoid ambiguity (Reasons 11.9).
However, the board is persuaded that ambiguity is avoided due to the limited size of the retransmission window which is moved in time, and that different positions of the retransmission window are possible, as supported by paragraphs [0031] and [0032] of the patent specification and as argued by the patent proprietor.
For these reasons the board judges that claim 1 of the main request complies with Article 83 EPC.
This decision T396/13 (pdf) has European Case Law Identifier:  ECLI:EP:BA:2016:T039614.20161220. The file wrapper can be found here. Photo by Pexels via Pixabay under a CC0 license (no changes made). 

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