Obviousness

Obviousness Analysis of U.S. Patent No. 7,154,961 under 35 U.S.C. § 103

This analysis evaluates whether the invention claimed in U.S. Patent No. 7,154,961 ("the '961 patent") would have been obvious to a Person Having Ordinary Skill in the Art (PHOSITA) at the time of the invention, based on the prior art references cited during the patent's prosecution.

A PHOSITA in this technical field as of the priority date (October 18, 2002) would be an electrical engineer or computer scientist with a graduate degree in a relevant field and/or several years of experience in digital wireless communication systems, particularly in the areas of modulation techniques, error control coding (including ARQ and FEC schemes), and multiple-antenna (diversity) systems.

The independent claims of the '961 patent are likely obvious under 35 U.S.C. § 103 in view of a combination of prior art references, most notably the combination of EP0735701A2 ('701 patent) and WO2002067491A1 ('491 application) or, alternatively, '701 patent in combination with US 6,769,085 B2 ('085 patent).

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Primary Obviousness Combination: '701 patent and '491 application

1. Summary of the References:

• EP0735701A2 ('701 patent): This reference teaches a system that explicitly combines switched antenna diversity with an ARQ protocol. It discloses transmitting a data packet from a first antenna (a first diversity branch) and, upon receiving a retransmission request from the receiver, re-transmitting the packet from a second, different antenna (a second diversity branch). The '701 patent thus establishes the foundational framework of using transmit diversity within an ARQ scheme to improve reliability. The primary element it lacks is the use of different modulation schemes for the separate transmissions.

• WO2002067491A1 ('491 application): This reference teaches a method for improving HARQ performance by changing the signal constellation mapping for retransmissions. It explains that for higher-order modulations like 16-QAM, bits mapped to different positions in a symbol have different reliability levels. The '491 application discloses that by using a second, different constellation mapping for a retransmission, the bit reliabilities can be averaged, leading to a better overall chance of successful decoding. It teaches the "why" and "how" of constellation rearrangement for ARQ but does not explicitly require the retransmission to be sent over a different diversity branch.

2. Motivation to Combine:

A PHOSITA starting with the transmit diversity ARQ system taught by the '701 patent would be motivated to find ways to further enhance its performance. The goal of any diversity or retransmission scheme is to maximize the probability of correct decoding. The '491 application provides a known, documented solution for improving the performance of ARQ systems by rearranging the signal constellation.

A skilled artisan would have recognized that the two techniques address different, yet complementary, aspects of transmission reliability:

• The '701 patent's antenna switching combats large-scale fading and interference specific to a physical path.
• The '491 application's constellation rearrangement combats errors related to the inherent properties of the modulation scheme itself.

Therefore, a PHOSITA would have been motivated to apply the known performance-enhancing technique from the '491 application to the known diversity ARQ system of the '701 patent. This combination would be a predictable and logical step to create a more robust system that leverages both spatial diversity (different paths) and modulation diversity (different bit-to-symbol mappings). The expected result would be a system with a lower error rate than a system using either technique alone.

3. Mapping the Combination to the Claims:

• Independent Claim 1: This method claim is rendered obvious by the combination.

  • "modulating data packets ... using a first modulation scheme...": Disclosed by both '701 and '491 as part of a standard initial transmission.
  • "transmitting the first data symbols over a first diversity branch...": Explicitly taught by the '701 patent's use of a first antenna.
  • "modulating said data packets ... using a second modulation scheme...": This is the key contribution of the '491 application, which teaches using a different constellation for the ARQ retransmission.
  • "transmitting the second data symbols over a second diversity branch...": This is taught by the '701 patent's instruction to re-transmit from a second antenna upon receiving an ARQ request.
  • "diversity combining the demodulated data...": This is an inherent and necessary step at the receiver in any system using transmit diversity and retransmissions, as described in both references.
  • The dependent claims are likewise obvious. Claim 2 (reducing differences in bit reliabilities) is the explicit purpose stated in the '491 application. Claim 5 (using interleaving or inverting) is a known method for achieving constellation rearrangement, as further detailed in the '085 patent.

• Independent Claim 11: This claim for a transmitter is also obvious. The '701 patent teaches a transmitter with a "transmission unit" capable of sending signals over a first and a second diversity branch. The '491 application teaches the use of a "mapping unit" that can apply different modulation schemes. The '085 patent goes further, explicitly disclosing a transmitter with an "interleaver or inverter to obtain different modulation schemes." Combining these teachings would lead a PHOSITA to a straightforward design of a transmitter that incorporates both the antenna-switching capability of the '701 patent's transmitter and the re-mapping/interleaving capability of the '491/'085 transmitter to implement the combined method.

Conclusion

The core inventive concept of the '961 patent lies in the specific combination of transmit diversity for ARQ retransmissions with the use of constellation rearrangement for those same retransmissions. The prior art shows that both of these techniques were individually known in the art as methods to improve wireless communication reliability. The '701 patent taught using diversity for ARQ, and the '491 application and '085 patent taught using constellation rearrangement for ARQ. Combining these known techniques to achieve their expected benefits would have been an obvious design choice for a person of ordinary skill in the art seeking to create a more robust communication system. Therefore, the independent claims of U.S. Patent No. 7,154,961 are rendered obvious by the combination of the cited prior art.