First published in EPLAW Patent Blog, March 2023.

The Court of Appeal has overturned the finding of Mr Justice Mellor that InterDigital’s patent, EP 3 355 537 (the “Patent”), was invalid. Mellor J had found that the Patent was essential to Release 6 of the 3G UMTS mobile telecommunications standard, but had found the Patent anticipated by the prior art “FDD Enhanced Uplink; Overall Description; Stage 2 (Release 6)” (“Filiatrault”). Filiatrault is a marked-up version of a standards document: 3GPP TS 25.309 which was made available to members of the group working on this standard two days before the priority date. The appeal turned on an issue of construction which the Court of Appeal noted had received relatively little attention in the lower court.

Technical background

The technical background is complex and summarised briefly in the Court of Appeal judgment, making use of cross references to the judgment of Mellor J. The background set out below is aimed at providing the minimum information necessary to understand the Patent claim.

The title of the Patent is “MAC Multiplexing and TFC Selection Procedure for Enhanced Uplink” where “MAC” stands for Medium Access Control, and “TFC” stands for Transport Format Combination. The Enhanced Uplink, also referred to as the High Speed Uplink Packet Access (HSUPA), was being developed for Release 6 of the standard in order to improve the rate at which data packets could be sent on uplink channels (i.e. data from the mobile phone to the Network).

By the priority date it had been determined that a new MAC entity, called the MAC-e, would be used to assemble packets of data, called MAC-e PDUs, for transmission on the Enhanced Uplink. The MAC-e PDUs are not formed out of a continuous stream of data but instead are assembled from other packets of data, called MAC-d PDUs, which are received from the MAC-d. The process of assembling the MAC-e PDUs is called “multiplexing”.

The MAC-e PDUs are transmitted in a time window called a Transmission Time Interval (TTI) and there are limits on the amount of data that can be multiplexed into the MAC-e PDU in each TTI. The limits on the amount of data is controlled through “grants” and different grants will apply depending on the category of the data being transmitted. For scheduled data, a single “scheduled grant” applies and for non-scheduled data one or more “non-scheduled grants” may apply.

A second size limit also applied since the MAC-e PDUs are sent in “envelopes” known as E-TFCs which are only available in particular sizes. As the amount of data in a MAC-e PDU may not match that pre-determined size “padding” bits are used to fill the E-TFC prior to transmission. Padding bits are necessary for this purpose but are otherwise undesirable since they do not comprise useful data and they contribute to interference between different mobile phones. At the priority date, once the multiplexing of the MAC-e PDU had taken place and its overall size was known, an E-TFC would be chosen which was the next largest available in the set of E-TFCs. Therefore, depending on the difference in size between the available E-TFC and the MAC-e PDU it might be necessary to include a large number of padding bits.

The patent

The aim of the Patent is, against the background explained above, to reduce the amount of padding required in the E-TFCs. The Court of Appeal summarised the inventive concept of the Patent as being to more closely match the size of the MAC-e PDUs to the size of the available E-TFCs. The Patent achieves this by linking the E-TFC selected to the amount of data that is allowed under the grant system.

The Court of Appeal noted that the claims of the Patent are “rather wordy” and so a more concise version was agreed between the parties at trial and adopted by Mellor J in his judgment. Claim 1 is as follows (a WTRU is a Wireless Transmit/Receive Unit i.e. a mobile phone):

[1A] A WTRU comprising:

[1B] means for receiving at least one serving grant and at least one non-scheduled grant,

[1C] wherein the at least one serving grant is a grant for scheduled data transmission

[1D] and the at least one non-scheduled grant is a grant for non-scheduled data transmission,

characterised by:

[1E] means for determining supported E-TFCs, within a E-TFC set, based on a remaining transmit power for enhanced uplink transmission; and

[1F] means for limiting MAC-d flow data multiplexed into a MAC-e PDU, to a largest E-TFC size that is smaller than a size of MAC-d flow data allowed by the received serving and non-scheduled grants and available for transmission.

No issues of instruction arose on integers 1[A] to 1[E]. Furthermore, it was common ground that these integers were disclosed in the Filiatrault prior art document. Accordingly, the questions for the court only related to integer 1[F].

Construction issue

The Court of Appeal noted that there was no dispute between the parties as to the principles of claim interpretation. These principles were then summarised as follows: “the words of the claim must be interpreted from the perspective of the skilled person in light of the common general knowledge and having regard to the inventor’s purpose”.

The construction issue arising on integer 1[F] related to the meaning of the words “means for”. The Court of Appeal quotes paragraphs 181 to 184 of the judgment of Mellor J in which the judge explains Lenovo’s contention that “means for” must be construed as means that are operating all the time. This construction had significance for the position on infringement since, in the Release 6 Standard to which the Patent was found essential, the integer 1[F] means are not always employed. Lenovo had based a non-infringement argument on this.

Mellor J considered that Lenovo’s construction was wrong and that a broader interpretation, allowing for the means in integer 1[F] to be used only some of the time, was correct. Mellor J concluded that “integer 1[F] is expressed in very broad terms: it is satisfied by any means which bring about the stated result” (emphasis added). The appeal turned on what the judge meant by the underlined part of the quote.

First instance decision on Filiatrault

The Court of Appeal quoted from Mellor J’s judgment on the nature of the Filiatrault. It is apparent that, as Filiatrault was a “work in progress” document, it had parts which were not internally consistent and which were open to interpretation as to how they would be implemented. Fortunately, however, the parties were agreed that the court could focus on the difference between Filiatrault and the Patent that InterDigital’s expert had identified and consider whether this difference meant that integer 1[F] was or was not disclosed (or made obvious) by Filiatrault.

InterDigital’s expert, Mr Townend, set out in his first expert what he saw as the difference between the Patent and Filiatrault:

305. The invention claimed in the Patent is therefore different from the disclosure in Filiatrault because:

1.  Filiatrault uses the grants as a multiplexing limit in a MAC-e PDU and then selects the smallest E-TFC which is larger than the multiplexed data, and adds any necessary padding. This allows the selected E-TFC to be larger than the sum of the grants, and/or the padding to be larger than a MAC-d PDU which could otherwise be sent.
2. The claimed invention in the Patent uses the grants as a limit on the largest E-TFC which can be used and then uses the size of that largest E-TFC as a multiplexing limit. This guarantees that the selected E-TFC (i.e.the multiplexed data, the headers, and any padding that comprise the MAC-e PDU) will not be larger than the sum of the grants, nor will the size of padding be greater than the size of a MAC-d PDU which could otherwise be sent.

306. It is therefore my understanding that Filiatrault discloses a fundamentally different scheme for MAC-e PDU creation and E-TFC selection compared to the invention claimed in claims 1 and 5 of the Patent.

However, in a document referred to as DXX/14, Mr Townend considered what happens in Filiatrault when “the number of bits allowed by the grants is just slightly larger than the smallest E-TFC which is larger than the multiplexed data …In these circumstances the result is that the multiplexed data is within the limit of the size of the E-TFC although it has not been limited by reference to that size.” In such a scenario, as was confirmed by Mr Townend under cross examination, the method in Filiatrault would produce the same result as the method set out in the Patent. Therefore, given that Mellor J had construed integer 1[F] as being “satisfied by any means which bring about the stated result” it followed, in the first instance judgment, that Filiatrault disclosed integer 1[F].

Rival contentions at the appeal

At the appeal InterDigital contended that integer 1[F] required the multiplexed data be limited “to the size of the E-TFC that is next smaller to the size of the data allowed by the total of the scheduled and non-scheduled grants”. InterDigital said that Mellor J had used this construction in rejecting part of Lenovo’s case on Filiatrault and had erred in relation to DXX/14 since he used a different interpretation.

Lenovo contended that all that is required is that “the amount of MAC-d flow data which is multiplexed into a MAC-e PDU is limited to a largest E-TFC size that is smaller than a size of MAC-d flow data allowed by the scheduled and non-scheduled grants” and that this is why Mellor J found for them in relation to DXX/14. Lenovo also said that InterDigital were, impermissibly, advancing a new construction on appeal and that if the new construction were to be accepted then the essentiality/infringement case would fail. However, Lenovo accepted that it would be difficult for the Court of Appeal to decide the question on essentiality/infringement in the circumstances.

Findings of the Court of Appeal

The Court of Appeal first considered whether InterDigital were, impermissibly, running a new construction on appeal. Arnold LJ, giving the leading judgment, first noted that “the correct interpretation of the claims of a patent is an issue of law for the court to determine. It follows that the court is not bound to accept either party’s construction, either at first instance or upon appeal”. It was still the case, however that InterDigital could not advance a new construction if this would prejudice Lenovo, for example because Lenovo had not been able to adduce evidence relating to this construction.

In support of its contention that the construction it advanced was not new, InterDigital pointed to the evidence and cross examination of Lenovo’s expert, Dr Irvine. The Court of Appeal concluded that this evidence was consistent with InterDigital’s present construction of the claims and, as such, Lenovo could not be prejudiced by InterDigital running the construction at appeal.

Arnold LJ then considered the rival constructions. Lenovo argued
(i) that InterDigital’s construction involved writing words into the claim which were not present in the Patent;

(ii) that InterDigital was interpreting the claims as drafted towards a procedure and not a result (something which is inconsistent with the way the Standard usually works);

(iii) that a claim drafted in the way that InterDigital was suggesting by its construction would not have been essential to the Standard; (iv) that the Skilled Reader would not understand the claim in the way InterDigital construed it; and

(v) that, as the Patent specification disclosed a variety of methods, it did not make sense to limit the claims to any specific method.

InterDigital’s answers to these points were

1.  instead of writing words into the claim it was providing the meaning of the words used;
2.  it is beside the point that the Standard usually specified a result;
3.  essentiality/infringement were not affected by the construction dispute;
4.  the Skilled Person should not construe the claim in a manner which does not achieve the inventor’s purpose; and
5.  although different methods are set out in the specification, their construction was at a level of generality that was consistent with the generality of the claim.

The Court of Appeal found InterDigital’s arguments persuasive and emphasised that, in construing a claim there are three considerations “first, the wording of the relevant integer of the claim, secondly, the context provided by the specification, and thirdly, the inventor’s purpose”. The claim wording requires “limiting MAC-d data … to a largest E-TFC size that is smaller than a size of MAC-d data allowed by … the grants [emphases added]”. Arnold LJ thought that this required identification of the next smaller E-TFC and “it is not sufficient that, at the end of a process, the MAC-d data happens to fit within the next smaller E-TFC” emphasis added. Further, and in relation to the inventor’s purpose, it was “vital to ensure that an E-TFC larger than the sum of grants is not used in order to avoid excess padding overall”. Lenovo’s construction would not do this.

Arnold LJ also agreed that the construction issue did not affect the position on essentiality/infringement.

Novelty over Filiatrault

Having concluded that InterDigital’s construction was the correct one, Arnold LJ then considered whether the claim was novel over Filiatrault. In Arnold LJ’s view, the judge had been mistaken to hold that the claims lacked novelty over Filiatrault on the basis that DXX/14 showed that, with certain MAC-d PDU sizes and grants, Filiatrault produced the result required by integer 1F. Arnold LJ thought that Mellor J “was beguiled by a sleight of hand” during the cross-examination of Mr Townend and, additionally, had failed to cross-check his conclusion by reference to the method claim (claim 5). Arnold LJ thought that if the judge had “asked himself whether DXX/14 showed that Filiatrault disclosed a method for limiting etc. rather than focussing on the end result of the process, I think he would have reached a different conclusion.”

Arnold LJ considered his conclusion was supported by a number of other factors. First, the fact that Lenovo’s case on Filiatrault had evolved over time (and DXX/14 emerged very late) was a pointer against anticipation. Second, Mellor J’s instinct was that Lenovo’s argument had an element of ex post facto synthesis of the kind cautioned against in Hickman v Andrews [1983] RPC 147. Third, it is a general principle that the Skilled Person would not expect the claim to cover prior art acknowledged in the specification of the patent so the Court should avoid a construction which has that effect. Arnold LJ though that this would include Filiatrault even though it was not expressly referred to in the Patent. This was since it was common ground that the earlier part of the Patent specification was based on Filiatrault (or an earlier version of the same specification).

A copy of the judgment can be found here.