Mitsubishi Electric Corporation v Oneplus Technology (Shenzhen) Co, Ltd & Ors

For a term such as length indicator in a telecommunications patent, the relevant field must be capable of performing the ordinary function of indicating where an SDU ends. A field which merely conveys structural information about the payload, but cannot perform that function, falls outside the term, even if it provides similar information in practice. The same distinction applies when assessing infringement by equivalents. The inventive concept must be considered at the level of the particular problem addressed by the patent, rather than at an excessive level of generality such as perfect packing or control information about the payload. Amendments intended to exclude one embodiment fail where the amended claims still cover an indicator capable of indicating only that embodiment.

The claimants alleged that EP 1,925,142 was essential to later versions of the LTE standard and sought licences from the remaining defendants. The patent concerned signalling the structure of data packets in radio link control unacknowledged mode, particularly by using a special length indicator where complete service data units filled a protocol data unit in a specified manner.

The alleged infringement was the use in LTE of the FI=00 value. The claimants contended that FI=00 was a length indicator within claim 1, or alternatively an equivalent. They also applied unconditionally to amend the patent to exclude the so-called single-SDU embodiment. The central issues were the construction of length indicator, infringement by equivalents, and whether the proposed amendments achieved their stated purpose.

1. Construction. The court held that a length indicator in claim 1 had to be capable of specifying the position in the RLC PDU where an SDU ends. Particular values could be repurposed as special length indicators conveying more elaborate structural information, but the field still had to be realistically capable of performing the ordinary length-indicator function. The claim imposed no fixed bit-length or header-position requirement: paras [124], [131]-[140].
2. The LTE FI=00 field conveyed information that the first data octet of the PDU was the first octet of an SDU and the last octet was the last octet of an SDU. It nevertheless could not indicate the position where an SDU ended in the ordinary sense. It was therefore not a length indicator and did not infringe on normal construction: paras [140]-[141].
3. Equivalents. Applying the two-stage approach and the three questions in [2017] UKSC 48, FI=00 achieved substantially the same result, but in a different way. Characterising the invention as perfect packing or as control information about the payload used too high a level of generality and was derived to embrace the alleged infringement. The skilled person would recognise FI=00 as a different, non-length-indicator mechanism. Strict compliance with the ordinary meaning of length indicator was also an essential requirement, because otherwise the claim would be invalid: paras [141]-[152].
4. Amendments. The proposed amendments did not exclude the single-SDU embodiment while retaining the multiple-SDU embodiment. In a working system, a particular length-indicator value could indicate one condition or the other, so the amended wording still covered an indicator capable of indicating only the single-SDU condition: paras [154]-[163].
5. The infringement claim failed under both the granted and proposed amended claims. EP142 was not essential to LTE. It was unnecessary to consider the Qualcomm and WiMAX prior art: paras [163]-[166].