PTAB

IPR2016-00823

Sprint Spectrum LP v. Adaptix Inc

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1. Case Identification

2. Patent Overview

  • Title: Adaptive Allocation of Subcarriers in an OFDMA System
  • Brief Description: The ’375 patent describes a method and system for adaptively allocating wireless frequency channels, called subcarriers, in an Orthogonal Frequency Division Multiple Access (OFDMA) system. The system dynamically adjusts subcarrier allocations to remote subscriber units based on changing channel conditions reported by those units.

3. Grounds for Unpatentability

Ground 1: Obviousness over Ritter, Gesbert, and Thoumy - Claims 1, 9, 12, 15-17, 25, 28, and 31-32 are obvious over Ritter in view of Gesbert and Thoumy.

  • Prior Art Relied Upon: Ritter (German Patent DE 19800953 C1), Gesbert (Patent 6,760,882), and Thoumy (Patent 7,039,120).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Ritter taught the core OFDMA system where a mobile station measures channel quality for sets of subcarriers ("segments"), reports suitable segments to a base station, and receives an allocation based on that feedback. However, to the extent Ritter did not explicitly teach using pilot symbols or including modulation and coding rate (MCR) information, Gesbert and Thoumy supplied these missing elements. Gesbert taught using known "training tones" (pilot symbols) for channel measurement and using an index in the feedback to efficiently communicate a desired MCR. Thoumy taught the final necessary step: the base station transmitting an indication of the selected MCR back to the subscriber unit along with the subcarrier allocation. The challenged claims require a two-step allocation process, which Petitioner contended was taught by Ritter’s disclosure that allocations can be changed as needed and Gesbert’s disclosure that the feedback process repeats to account for changing conditions.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine these references to improve the functionality of a known system. A POSITA would modify Ritter's base system with Gesbert’s well-known technique of using pilot symbols for more accurate channel estimation and indexed MCR feedback for greater efficiency. The resulting system would then logically be modified per Thoumy to inform the subscriber unit of the selected MCR, a necessary step for the subscriber to decode the transmission. This combination involved applying known techniques to yield predictable results.
    • Expectation of Success: A POSITA would have a high expectation of success as all three references operated in the same technical field (OFDMA systems), addressed the common problem of adapting to changing channel conditions, and their combination represented a predictable integration of complementary functionalities.

Ground 2: Obviousness over Thoumy and Gesbert - Claims 1, 9, 15-17, 25, and 31-32 are obvious over Thoumy in view of Gesbert.

  • Prior Art Relied Upon: Thoumy (Patent 7,039,120) and Gesbert (Patent 6,760,882).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner asserted this ground with Thoumy as the primary reference. Thoumy taught an OFDMA system that dynamically allocates carrier frequencies and adapts modulation based on continuously monitoring channel conditions and receiving feedback. The system included repeatedly measuring channel quality, providing feedback, and receiving an allocation of carriers with an associated modulation type. To the extent Thoumy did not explicitly detail using base-station-transmitted pilot symbols for measurement or an indexed MCR in feedback, Gesbert supplied these features. Gesbert disclosed an OFDMA system where subscribers measure channel quality based on "training tones" received from a base station and report back a mode "index" corresponding to a desired MCR.
    • Motivation to Combine: A POSITA would be motivated to incorporate Gesbert’s techniques into Thoumy’s system to enhance efficiency and performance. Using Gesbert's pilot symbol-based measurement and indexed feedback mechanism was a well-known, simple design choice for improving the channel estimation and feedback loops in a system like Thoumy's. The combination was a mere substitution of one known element for another to yield predictable results without requiring undue experimentation.
    • Expectation of Success: Success was expected because both references described analogous OFDMA systems. Combining Gesbert's efficient feedback and measurement techniques with Thoumy's adaptive allocation framework was a straightforward integration of known methods in the same field of endeavor.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, primarily adding Gitlin (Patent 6,018,528) to the combinations above (i.e., Ritter/Gesbert/Thoumy/Gitlin and Thoumy/Gesbert/Gitlin). Gitlin was relied upon for its teaching of allocating "non-contiguous" subcarriers and "disjoint" clusters to obtain frequency diversity and mitigate the effects of frequency-selective fading.

4. Key Claim Construction Positions

  • "pilot symbols": Petitioner argued for the construction "symbols, sequences, or signals known to both the base station and subscriber." This construction was based on the patent’s specification and prior constructions in related litigation and PTAB proceedings, ensuring that the "training tones" taught by prior art like Gesbert would meet the claim limitation.
  • "cluster": Petitioner argued for the construction "a logical unit that contains at least one physical subcarrier," based on the explicit definition provided in the ’375 patent’s specification. This broad definition allowed a single subcarrier to be considered a cluster.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1, 3, 9-10, 12, 15-17, 19, 25-26, 28, and 31-32 of Patent 8,934,375 as unpatentable.