TAKEAWAY: The recent Sierra Wireless decision highlights the importance of precise language in claims with limitations potentially construed as conditional.
In the recent Federal Circuit decision Sierra Wireless, ULC v. Sisvel S.P.A. (March 10, 2025), the Federal Circuit addressed the interpretation of claim limitations with different preconditions.
U.S. Patent No. 7,869,396 issued January 11, 2011, to Sisvel S.P.A. and relates to a data transmission and retransmission method to reduce data loss in wireless communication systems. The claims recite a first step of “detecting whether at least one data block to be received from a transmitter is missed,” and employing a timer “when the at least one data block is detected as missed.” If the missing data block is received before the timer expires, the timer is stopped, preventing a status report from being sent to a transmitter. If the data block is still missing when the timer expires, a status report is transmitted. Sierra petitioned the USPTO Patent Trial and Appeal Board (“the Board”) for inter partes review of the ’396 patent, arguing that the claims were anticipated and/or obvious.
The Board found that limitations requiring stopping a timer upon receipt of a missing data block and sending a status report after the timer expired were conditional and mutually exclusive. As a result, the Board concluded that the prior art reference needed to disclose only one of those conditions to anticipate the claim. Accordingly, the Board found the prior art reference disclosed stopping a timer to prevent a status report being sent to a transmitter and held the independent claims to be unpatentable.
On appeal, the Federal Circuit rejected this interpretation, emphasizing that the plain and unambiguous language of the claim was not conditional and required both limitations to be satisfied when their respective preconditions occurred. The Court clarified that limitations must be interpreted to require performance when the relevant requirement is met unless the language explicitly states otherwise. The Court vacated and remanded the Board’s decision.
This ruling underscores the significance of precise claim drafting and clear language in conditional limitations. When drafting claims, practitioners should consider and potentially try to avoid language that may be interpreted as creating alternative or mutually exclusive steps unless that is the intended result. It may be helpful to avoid ambiguity by explicitly stating whether conditions must occur concurrently, independently, or sequentially. Ambiguities in conditional language risk broader interpretations that may expose claims to invalidity challenges.