PTAB

IPR2016-00824

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 discloses methods and apparatus for adaptively allocating subcarriers in an Orthogonal Frequency Division Multiple Access (OFDMA) wireless system. The system involves a subscriber unit measuring channel quality based on pilot symbols, providing feedback to a base station, and receiving a dynamic allocation of subcarriers and corresponding modulation/coding rates from the base station.

3. Grounds for Unpatentability

Ground 1: Obviousness over Ritter, Gesbert, and Thoumy - Claims 2, 8, 14, 18, 24, and 30 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 foundation of the invention: an OFDMA system where a mobile station measures the quality of subcarrier "segments" and sends feedback to a base station, which then allocates segments based on this feedback. To the extent Ritter did not explicitly teach using "pilot symbols" for measurement or including a modulation and coding rate index in the feedback, Petitioner asserted Gesbert supplied these elements. Gesbert taught using known "training tones" (pilot symbols) for channel quality measurement and using an index to identify specific modulation and coding rates in feedback to improve efficiency. Finally, Petitioner argued that Thoumy taught the base station informing the subscriber unit of the allocated modulation and coding rate to ensure proper decoding of the allocated subcarriers. Dependent claims requiring "coherence clusters" were met by Ritter's allocation of adjacent subcarriers into segments.
    • Motivation to Combine: A POSITA would combine Gesbert's known techniques for channel measurement (using pilot symbols) and efficient feedback (using an index) with Ritter's base OFDMA allocation system to achieve the predictable result of an improved, more efficient channel allocation process. A POSITA would have been further motivated to incorporate Thoumy's teaching of informing the subscriber unit of the selected modulation and coding rate to ensure the system functioned correctly, as decoding requires this information.
    • Expectation of Success: A POSITA would have had a high expectation of success as the combination involved applying well-understood techniques to a compatible system to solve a known problem of adapting to varying channel conditions in wireless OFDMA systems.

Ground 2: Obviousness over Ritter, Gesbert, Thoumy, and Gitlin - Claims 4-7, 11, 13, 20-23, 27, and 29 are obvious over Ritter in view of Gesbert, Thoumy, and Gitlin.

  • Prior Art Relied Upon: Ritter (German Patent DE 19800953 C1), Gesbert (Patent 6,760,882), Thoumy (Patent 7,039,120), and Gitlin (Patent 6,018,528).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground built upon the combination of Ritter, Gesbert, and Thoumy from Ground 1 and added Gitlin to teach limitations related to non-contiguous or disjoint subcarrier allocations. Petitioner argued Gitlin explicitly disclosed a multi-tone (OFDMA) system where non-contiguous frequency arrangements could be employed to benefit users, such as allocating disjoint frequency bands to a single user to achieve frequency diversity. This directly mapped to claim limitations requiring "diversity clusters," disjoint subcarriers, and clusters spread farther apart than the coherence bandwidth.
    • Motivation to Combine: A POSITA would combine Gitlin's teachings into the Ritter/Gesbert/Thoumy system because all references were in the same field of wireless OFDMA systems and addressed the common problem of providing quality service under changing channel conditions. Incorporating Gitlin's known technique for using non-contiguous frequency assignments was a predictable way to improve the system’s robustness against frequency-selective fading.
    • Expectation of Success: A POSITA would have expected success in combining Gitlin's teachings, as it represented a known method for improving spectral use and mitigating multipath fading, which would predictably enhance the performance of the base system.

Ground 3: Obviousness over Thoumy, Gesbert, and Gitlin - Claims 6-8, 11, 13, 22-24, 27, and 29 are obvious over Thoumy in view of Gesbert and Gitlin.

  • Prior Art Relied Upon: Thoumy (Patent 7,039,120), Gesbert (Patent 6,760,882), and Gitlin (Patent 6,018,528).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground used Thoumy as the primary reference, arguing it taught an OFDMA system where a remote device measures channel quality for each subcarrier and provides feedback, allowing the base station to dynamically adapt allocations. Petitioner asserted that Gesbert was added for the same reasons as in prior grounds: to explicitly teach using pilot symbols for measurement and an indexed feedback mechanism for modulation and coding rates. Gitlin was added to teach the allocation of non-contiguous subcarriers to form diversity clusters and achieve frequency diversity, mapping to the same dependent claims as in Ground 2.
    • Motivation to Combine: A POSITA would combine Gesbert’s efficient, indexed feedback mechanism with Thoumy’s system to maximize network resources and optimize feedback. A POSITA would have also been motivated to incorporate Gitlin’s teachings on non-contiguous frequency allocation to improve the performance of Thoumy’s system in the presence of frequency-selective fading.
    • Expectation of Success: Combining these known elements from the same technical field would predictably result in a more robust and efficient OFDMA system without undue experimentation.

  • Additional Grounds: Petitioner asserted additional obviousness challenges based on combinations of Thoumy, Gesbert, and Ritter (Ground 4) and Thoumy, Gesbert, Gitlin, and Ritter (Ground 5), which relied on similar prior art teachings and combination rationales.

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 broad construction was based on the specification and prior constructions in related litigation and was critical for mapping prior art references like Gesbert, which taught "training tones," to this limitation.
  • "cluster": Petitioner argued for the construction "a logical unit that contains at least one physical subcarrier," based on its explicit definition in the specification. This allowed Petitioner to argue that groups of subcarriers in the prior art, referred to as "segments" in Ritter, constituted the claimed "clusters."
  • "diversity cluster": Petitioner proposed construing this term as "a cluster containing multiple subcarriers with at least some of the subcarriers spread far apart over the spectrum." This construction, derived from the specification, was key to mapping Gitlin’s teachings of non-contiguous frequency allocation to the claims.

5. Relief Requested

  • Petitioner requested institution of an inter partes review and cancellation of claims 2, 4-8, 11, 13-14, 18, 20-24, 27, and 29-30 of the ’375 patent as unpatentable.