PTAB

IPR2015-01170

Solid Inc v. Corning Optical Communications Wireless Ltd

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: MIMO-ADAPTED DISTRIBUTED ANTENNA SYSTEM
  • Brief Description: The ’504 patent describes a method for propagating multiple-input multiple-output (MIMO) signals over a distributed antenna system (DAS) network. The method uses frequency shifting to combine multiple signals having the same spectrum for transmission over a single coaxial cable, thereby avoiding interference, and then reconstructs the original signals at a second endpoint.

3. Grounds for Unpatentability

Ground 1: Claims 1-6 are obvious over Larkin in view of Fifield and Skarby.

  • Prior Art Relied Upon: Larkin (Patent 6,268,946), Fifield (Application # US 2003/0002604), and Skarby (Application # 2007/0173288).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Larkin disclosed all elements of the challenged claims for a spatial diversity system, which is a broader category that includes MIMO. Larkin taught a DAS that frequency shifts one of two same-frequency input signals, combines it with the un-shifted signal, propagates the combined signal over a single transmission medium (explicitly suggesting a coaxial cable), and reconstructs the original signals. Fifield was cited to provide the express teaching of applying such a frequency-shifting technique specifically to MIMO signals. Skarby was cited to explicitly teach the use of a single coaxial cable for bidirectional signal propagation in a DAS, addressing a claim construction requiring bidirectional capability.
    • Motivation to Combine: A POSITA would combine Larkin with Fifield because both addressed the same problem of propagating multiple same-spectrum signals over a single medium and shared design incentives like reducing hardware complexity. Applying Larkin's established frequency-shifting solution to the specific context of MIMO signals taught by Fifield was presented as an obvious step. A POSITA would incorporate Skarby’s teaching of a bidirectional coaxial cable to Larkin's system to reduce cable count and complexity, a goal shared by both references.
    • Expectation of Success: The combination was argued to be a predictable application of known techniques (frequency division multiplexing) to a known signal type (MIMO) using standard components (coaxial cables), leading to a high expectation of success.

Ground 2: Claims 1, 2, 5, and 6 are obvious over Oren in view of Fifield.

  • Prior Art Relied Upon: Oren (Application # US 2008/02323054) and Fifield (Application # US 2003/0002604).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted that Oren, titled "Distributed Antenna System for MIMO Technologies," disclosed nearly all limitations of the claims, including propagating MIMO signals over a single coaxial cable in a DAS. However, Oren taught frequency shifting all input signals. Fifield was introduced for its teaching of frequency shifting all but one of the input signals to achieve the same result of interference-free propagation. Petitioner argued that replacing Oren’s method with Fifield’s slightly different, well-known method was an obvious design choice. For dependent claims, Oren was alleged to teach multiple services (claim 2), the use of mixers for frequency shifting (claim 5), and a bidirectional system with corresponding master/remote units (claim 6).
    • Motivation to Combine: A POSITA would combine Oren and Fifield as they were in analogous technical arts, both addressing MIMO signal propagation in a DAS while aiming to reduce system complexity. Modifying Oren’s system to leave one signal un-shifted, as taught by Fifield, was presented as a trivial design modification that would provide the same result with one less frequency-shifting operation at each end of the network.
    • Expectation of Success: A POSITA would expect success in implementing Fifield's well-understood frequency-shifting scheme within Oren's MIMO DAS framework, as it involved predictable signal processing techniques.

Ground 3: Claims 3 and 4 are obvious over Oren in view of Fifield and Tang.

  • Prior Art Relied Upon: Oren (Application # US 2008/02323054), Fifield (Application # US 2003/0002604), and Tang (Patent 5,339,184).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground built upon the combination of Oren and Fifield from Ground 2. Petitioner argued that while Oren/Fifield taught the core method, they did not expressly disclose propagating a "reference frequency signal" to assist in reconstruction, as required by claims 3 and 4. Tang was introduced to supply this missing element, as it explicitly taught transmitting a pilot frequency (reference signal) along with data signals in a communications link to lock the remote site's reference oscillator. This ensured error-free frequency conversion and accurate reconstruction of the original signals.
    • Motivation to Combine: A POSITA, implementing the frequency-shifting system of Oren/Fifield, would recognize the need to synchronize local oscillators at both endpoints to ensure accurate frequency conversion. Petitioner argued that a POSITA would have looked to analogous art like Tang, which addressed this exact problem by propagating a reference signal. Combining Tang's solution was motivated by the predictable improvement in system performance and reconstruction accuracy.
    • Expectation of Success: Adding a pilot tone for frequency synchronization, as taught by Tang, was a well-known and reliable technique in communication systems, giving a POSITA a high expectation of success when applying it to the Oren/Fifield system.
  • Additional Grounds: Petitioner asserted additional obviousness challenges, including grounds based on Larkin or Skarby combined with POSITA knowledge, and Skarby combined with Larkin, which relied on similar technical principles and motivations.

4. Key Claim Construction Positions

  • "MIMO signals": Petitioner proposed this term be construed as “multiple signals having the same or overlapping spectrum, each signal carrying a different data stream.” This construction was central to applying prior art that taught handling "spatial diversity" signals more broadly to the specific MIMO context.
  • "endpoint [of a DAS network]": Petitioner argued this meant either an "antenna endpoint" (remote unit) or a "distribution endpoint" (master unit where signals are processed). This construction allowed mapping the "microbase station" and "diversity antenna system" of references like Larkin to the claimed master and remote units.
  • "a single coaxial cable extending for at least part of a path...": Petitioner contended this term required the cable to carry both uplink and downlink signals (i.e., be bidirectional). This construction was key to grounds that used secondary references like Skarby to explicitly teach bidirectional coaxial cable use.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-6 of the ’504 patent as unpatentable.