Sprint Spectrum LP 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 multi-user access method using Orthogonal Frequency Division Multiplexing (OFDM). The method allocates mutually exclusive subsets of orthogonal baseband frequencies to a plurality of remote locations, allowing them to simultaneously transmit data to a central location over the same carrier frequency.

3. Grounds for Unpatentability

Ground 1: Obviousness over Fattouche - Claims 1-2 are obvious over Fattouche.

• Prior Art Relied Upon: Fattouche (European Patent Application No. 93302325.1).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Fattouche, a single reference, discloses a cellular multi-user OFDM system that teaches every limitation of the challenged claims. Fattouche describes allocating distinct subsets of orthogonal baseband frequencies ("vc slots") to different portable units. Each portable unit codes data into frequency-domain symbols (transform coefficients), uses an inverse fast Fourier transform (IFFT) to create a time-domain signal, and modulates this signal onto a carrier for transmission to a base station. The base station then receives, demodulates using in-phase (I) and quadrature (Q) signals, performs an FFT to reconstruct the symbols, and decodes them back into data. Petitioner contended that a person of ordinary skill in the art (POSITA) would have understood that all portables must use the same carrier frequency to maintain the critical subcarrier orthogonality required for an OFDM system to function, making this feature implicit or obvious.
  • Motivation to Combine (for §103 grounds): Not applicable as this is a single-reference ground.

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 conference paper) and COST 207 (a 1989 report on mobile radio communications).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that Reiners discloses a broadband cellular OFDM system where subsets of orthogonal subcarriers are allocated to different mobile stations. Reiners teaches encoding data into complex symbols, using an IFFT to generate a complex time-domain signal (comprising I and Q components), and transmitting the signal using a "fixed frequency." Petitioner argued that while Reiners teaches the core system, COST 207 provides the explicit implementation details for the modulator and demodulator. Specifically, COST 207 depicts cellular receivers using I/Q demodulators to multiply a received signal by I and Q carrier signals to produce baseband signals, which are then converted to digital form for processing.
  • Motivation to Combine (for §103 grounds): A POSITA would combine these references because Reiners explicitly states that its system was studied in accordance with the radio channels described in the COST 207 report. Therefore, a POSITA implementing the system in Reiners would have been directly motivated to look to COST 207 for specific, compatible designs for the modulators and demodulators needed to transmit and fully recover the complex signals that Reiners describes.
  • Expectation of Success: The combination involved implementing known modulator and demodulator configurations from COST 207 into the OFDM system of Reiners. This represented a straightforward application of established techniques to achieve the predictable result of a functional cellular communication system.

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 No. 0616445 A1).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Cioffi teaches a multi-user discrete multitone (DMT) system, a form of OFDM, that can be used for wireless subscriber systems. Cioffi discloses allocating mutually exclusive subsets of orthogonal tones to remote units, encoding data, performing an IFFT, and transmitting to a central modem. Petitioner contended that Pommier supplies the explicit teaching that all mobile stations in an OFDM system should use the same carrier frequency to create a "mono-frequency" network, a necessary condition to avoid intercarrier interference. Pommier also explicitly details a base station receiver that uses an I/Q demodulator and an analog-to-digital converter to process received signals, which are then fed to an FFT.
  • Motivation to Combine (for §103 grounds): A POSITA seeking to implement Cioffi's system in a wireless or cellular context would have been motivated to incorporate Pommier's mono-frequency transmission technique. This would solve the known problem of maintaining subcarrier orthogonality, which would be destroyed if different remotes used different carrier frequencies. Using Pommier's established technique would improve the reliability and functionality of Cioffi's system.
  • Expectation of Success: A POSITA would have had a reasonable expectation of success in combining the references because it involved applying a known technique (mono-frequency transmission from Pommier) to a known system architecture (multi-user OFDM from Cioffi) to achieve the predictable benefit of preventing interference.

4. Key Claim Construction Positions

• "transform coefficient": Petitioner proposed this term be construed as "transform coefficient or symbol." The rationale was that the ’488 patent specification uses the terms interchangeably, for example, by describing a "symbol encoder" as creating the transform coefficients and a "symbol decoder" as processing them.
• "an orthogonal transform": Proposed construction was "an orthogonal transform, a fast Fourier transform, or an FFT." The specification was cited as using these phrases interchangeably, such as stating, "The orthogonal transform (e.g., FFT) is applied..."
• "an inverse orthogonal transform": Similarly, this was proposed as "an inverse orthogonal transform, an inverse fast Fourier transform, or an IFFT," based on interchangeable use in the specification.
• "in-phase and quadrature... signals": Petitioner proposed these terms mean signals that differ in phase by 90 degrees, based on the specification's explicit description that "the quadrature carrier is shifted 90° with respect to the in-phase carrier."

5. Relief Requested

• Petitioner requests institution of an inter partes review and cancellation of claims 1-2 of the ’488 patent as unpatentable.