Sprint Spectrum L.P. v. TC Technology LLC

1. Case Identification

• Case #: IPR2017-00771
• Patent #: 5,815,488
• Filed: January 25, 2017
• Petitioner(s): Sprint Spectrum, L.P.
• Patent Owner(s): TC Technology LLC
• Challenged Claims: 1-2

2. Patent Overview

• Title: Multiple User Access Method Using OFDM
• Brief Description: The ’488 patent discloses a multiple user access method using Orthogonal Frequency Division Multiplexing (OFDM). The system allocates mutually exclusive subsets of orthogonal baseband frequencies to a plurality of remote transmitters, which encode data, perform an inverse orthogonal transform to create a time-domain signal, and modulate it onto a common carrier frequency for transmission to a central location.

3. Grounds for Unpatentability

Ground 1: Obviousness over Fattouche - Claims 1-2 are obvious over Fattouche under 35 U.S.C. §103.

• Prior Art Relied Upon: Fattouche (European Application # 93302325.1).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Fattouche, which discloses a cellular multi-user OFDM system, teaches all limitations of the challenged claims. Fattouche describes allocating distinct subsets of 4096 orthogonal baseband frequencies (termed "vc slots") to different portable transceivers. At each portable, data is coded into symbols (transform coefficients), which are fed to an inverse fast Fourier transform (IFFT) to produce a time-domain baseband signal. At the base station (central location), the received signal is demodulated using in-phase and quadrature (I/Q) signals, and a fast Fourier transform (FFT) reconstructs the original symbols.
  • Motivation to Combine: Although a single-reference ground, the argument relied on an obviousness rationale for the limitation requiring each remote to use the "same carrier frequency." Petitioner contended a POSA would understand that to maintain the critical subcarrier orthogonality in Fattouche’s multi-user OFDM system, all portables must modulate their signals using the same carrier frequency. This was presented as a known requirement and an obvious design choice to prevent intercarrier interference, which would otherwise destroy the signal.
  • Expectation of Success: A POSA would have a high expectation of success, as using a common carrier frequency is a fundamental and well-understood principle for ensuring the proper functioning of multi-user OFDM networks.

Ground 2: Obviousness over Reiners and COST 207 - Claims 1-2 are obvious over Reiners in view of COST 207.

• Prior Art Relied Upon: Reiners (a 1994 IEEE publication) and COST 207 (a 1989 report from the Commission of the European Communities).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that Reiners teaches a broadband cellular mobile communications system using OFDM, where a bandwidth is divided into orthogonal subcarriers and subsets are allocated to different mobile stations. Reiners discloses encoding data into complex symbols, using an IFFT to transform the symbols into a complex time-domain baseband signal (comprising I/Q signals), and using the same "fixed frequency" for modulation. COST 207 was used to supply specific implementation details, showing block diagrams of cellular transmitters with modulators and receivers with I/Q demodulators, analog-to-digital converters, and FFTs.
  • Motivation to Combine: The motivation was explicit, as Reiners states its system was studied "following the COST-207 report." Petitioner argued that a POSA, upon reading Reiners' high-level description, would have been directly motivated to look to the COST 207 report for specific and well-known circuit designs for the required cellular transmitters and receivers.
  • Expectation of Success: Success would be expected because Reiners directly incorporates COST 207 by reference, making the combination a straightforward implementation of Reiners' conceptual framework with the detailed examples provided in COST 207.

Ground 3: Obviousness over Cioffi and Pommier - Claims 1-2 are obvious over Cioffi in view of Pommier.

• Prior Art Relied Upon: Cioffi (Patent 5,625,651) and Pommier (European Patent # 0616445 A1).
• Core Argument for this Ground:
  • Prior Art Mapping: Cioffi was cited for disclosing a bi-directional data transmission system using discrete multitone modulation (DMT), a form of OFDM. Cioffi teaches allocating mutually exclusive subsets of 256 orthogonal tones to a plurality of remote units, encoding bit streams into complex symbols, and using an IFFT to create a time-domain signal for transmission. Pommier was introduced to explicitly teach a "mono-frequency" OFDM system where "each transmitter (each unit) uses the same transmission frequency." Pommier further details a base station receiver with an I/Q demodulator for processing the received signal.
  • Motivation to Combine: Petitioner argued that both references are in the same field of multi-user OFDM systems. A POSA seeking to implement Cioffi's system for cellular or coaxial applications would have been motivated to incorporate Pommier's teaching of using a single carrier frequency. This would address the known problem of intercarrier interference and loss of orthogonality that would occur if different remotes used different carrier frequencies, thereby improving Cioffi's system in a predictable manner.
  • Expectation of Success: A POSA would have a high expectation of success in combining the teachings, as ensuring a common carrier frequency was a well-understood solution to a known problem in multi-user OFDM system design.

4. Key Claim Construction Positions

• "transform coefficient": Petitioner proposed this term should be construed as "transform coefficient or symbol." This was based on the specification's interchangeable use of the terms, such as describing the creation of a "transform coefficient G(n)" via a "symbol encoder" and decoding it with a "symbol decoder."
• "an orthogonal transform": Proposed construction was "an orthogonal transform, a fast Fourier transform, or an FFT." Petitioner argued the ’488 patent uses the terms synonymously, for example, by stating, "The orthogonal transform (e.g., FFT) is applied..."
• "an inverse orthogonal transform": Proposed construction was "an inverse orthogonal transform, an inverse fast Fourier transform, or an IFFT." This was based on the specification's similar interchangeable use of these terms, defining the Fourier transform and its inverse as techniques for data conversion.
• "in-phase and quadrature carrier signals" / "in-phase and quadrature baseband signals": Petitioner proposed these terms should be construed to mean signals that differ in phase by 90 degrees. This construction was grounded in the specification's explicit statement that "the quadrature carrier is shifted 90° with respect to the in-phase carrier."

5. Relief Requested

• Petitioner requested institution of an inter partes review and cancellation of claims 1-2 of Patent 5,815,488 as unpatentable.