PTAB

IPR2021-00739

Zyxel Communications Corp v. UNM Rainforest Innovations

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Key Events
Petition

1. Case Identification

2. Patent Overview

  • Title: Apparatus and method for channel state information feedback
  • Brief Description: The ’204 patent discloses a method for a mobile station in a wireless communication system to provide channel state information (CSI) to a base station. The method involves calculating channel responses for multiple communication channels, selecting a plurality of "channel taps" (samples) from each response, compressing the information from the selected taps, and transmitting the compressed CSI back to the base station.

3. Grounds for Unpatentability

Ground 1: Obviousness over Hui - Claims 1-2 and 11-13 are obvious over Hui.

  • Prior Art Relied Upon: Hui (Patent 8,213,368).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Hui, which was not considered during prosecution, disclosed every limitation of the challenged claims. Hui described a Multiple-Input, Multiple-Output (MIMO) system where a mobile station estimates CSI by calculating an "estimated channel response" for multiple channels. Crucially, Petitioner asserted this response is comprised of a set of Q "non-zero tap coefficients." The mobile station then compresses these coefficients using adaptive quantization and transmits them to the base station. Petitioner contended that these "tap coefficients" are the claimed "channel taps" and that using a set of Q coefficients inherently teaches the key limitation of "selecting a plurality of channel taps." Dependent claims were also allegedly taught, as Hui’s quantized coefficients are parameters representing tap magnitudes (claim 2), and the system is explicitly a MIMO system (claim 12).
    • Motivation to Combine (for §103 grounds): While primarily an anticipation argument, Petitioner argued in the alternative for obviousness. Hui explicitly recognized that its set of Q channel tap coefficients could be a subset of the total number of available taps (K). A person of ordinary skill in the art (POSITA) would have been motivated to select a subset of the most significant taps to reduce the amount of feedback information, thereby conserving bandwidth, a well-known goal in the art.
    • Expectation of Success: A POSITA would have had a high expectation of success because selecting more significant taps was a known technique for data reduction that would predictably result in CSI of reasonable accuracy while reducing bandwidth consumption.

Ground 2: Obviousness over Hui in view of Maltsev - Claims 1-2 and 11-13 are obvious over Hui and Maltsev.

  • Prior Art Relied Upon: Hui (Patent 8,213,368) and Maltsev (Application # 2006/0114816).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground was presented as an alternative in case Hui was found not to explicitly teach selecting a subset of channel taps from a larger calculated response. Hui provided the foundational MIMO system that calculates channel responses composed of taps and feeds back compressed CSI. Maltsev was argued to supply the explicit teaching of selecting only the "most significant predetermined number of rays" (i.e., channel taps) from an estimated channel response before quantization and transmission.
    • Motivation to Combine: A POSITA would combine Hui with Maltsev to improve Hui's system. Maltsev explicitly taught that selecting the most significant taps reduces both the processing required by the mobile station and the bandwidth consumption for feedback. A POSITA would have been motivated to incorporate this known efficiency-improving technique into Hui’s similar CSI feedback system to achieve these predictable benefits.
    • Expectation of Success: Success was expected because combining the teachings was straightforward. It involved applying Maltsev's known data reduction technique (selecting significant taps) to Hui's system, which already operated on the same principles of using channel taps for CSI feedback.

Ground 3: Obviousness over Döttling - Claims 1-2 and 11-13 are obvious over Döttling.

  • Prior Art Relied Upon: Döttling (EP Application # EP 1 760 925 A2).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued Döttling disclosed a method for efficient compression of CSI where a user terminal calculates a "channel impulse response" and explicitly "identifie[s] the most significant channel taps" from that response. Information for these selected taps (complex coefficients and delay information) is then compressed with adaptive resolution (more bits for more relevant taps) and transmitted to the base station. Petitioner contended this directly taught estimating CSI by calculating a response and "selecting a plurality of channel taps." Döttling further taught its method was applicable to MIMO and Orthogonal Frequency-Division Multiplexing (OFDM) systems, meeting the limitations of dependent claim 12.
    • Motivation to Combine (for §103 grounds): As an alternative to anticipation, Petitioner argued that applying Döttling's single-channel teaching to a multi-channel MIMO system would have been obvious. Döttling itself identified MIMO scenarios as a key application for its CSI compression method.
    • Expectation of Success: A POSITA would have reasonably expected success in applying Döttling's method to each channel in a MIMO system, as it would predictably provide efficient CSI compression for all channels, a known objective for such systems.
  • Additional Grounds: Petitioner asserted additional challenges based on Koorapaty (Application # 2006/0018389) alone and in combination with the knowledge of a POSA, as well as Döttling in combination with Maltsev, relying on similar arguments that these references teach selecting a subset of channel taps to create compressed CSI feedback.

4. Key Claim Construction Positions

  • "channel responses": Petitioner adopted a prior construction from related litigation: "communication channels' responses in the time domain to transmitted signals."
  • "a plurality of channel taps": Petitioner adopted a prior construction: "at least two samples of a channel response at different time delays."
  • "channel state information (CSI)": Petitioner argued this term should be construed as "information regarding the communication channels between the base station and the mobile station," based on an express definition in the ’204 patent.

5. Arguments Regarding Discretionary Denial

  • Petitioner argued extensively that discretionary denial under Fintiv would be inappropriate. The co-pending district court litigation was in an early stage with minimal investment by the court and parties. Key factors cited included: the court had not yet conducted a Markman hearing or substantive analysis, trial dates were uncertain and likely to slip past the Final Written Decision (FWD) date, and the invalidity grounds in the petition relied on prior art and arguments not present in the litigation. Petitioner also offered to stipulate that it would not pursue the same invalidity grounds in district court if the IPR was instituted, mitigating concerns of duplicative efforts.

6. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1, 2, 11, 12, and 13 of the ’204 patent as unpatentable.