Obviousness

Obviousness Analysis of U.S. Patent 7,742,388 under 35 U.S.C. § 103

This analysis evaluates whether the inventions claimed in U.S. Patent 7,742,388 would have been obvious to a Person Having Ordinary Skill in the Art (PHOSITA) at the time of the invention, given the prior art. The legal standard for obviousness is based on the framework established in Graham v. John Deere Co., 383 U.S. 1 (1966), which requires considering the scope and content of the prior art, the differences between the prior art and the claims at issue, and the level of ordinary skill in the pertinent art. The priority date of the '388 patent is July 20, 2004.

A PHOSITA in this context would be an electrical engineer or computer scientist with knowledge of digital communication systems and practical experience with wireless networking protocols, specifically Orthogonal Frequency-Division Multiplexing (OFDM) and the IEEE 802.11 family of standards.

Analysis of Independent Claim 12

Claim 12: A method comprising generating and transmitting a packet with a preamble containing a first training symbol and a second training symbol, where the quantity of modulated subcarriers in the second training symbol is greater than in the first.

Obviousness Argument: Claim 12 is rendered obvious by the state of the art as embodied in the IEEE 802.11a standard (released in 1999) and described in numerous prior art references that predate the '388 patent's priority date.

• Prior Art Content: As established in the "Prior Art Analysis" section, publications such as Ho (US 2003/0063675 A1), Kwon (US 7,324,483), and Hansen (US 2004/0081098 A1) all explicitly describe the standard IEEE 802.11a packet structure. This structure consists of a preamble with a Short Training Symbol (STS or STF) followed by a Long Training Symbol (LTS or LTF).
• Comparison to Claim: These references explicitly state that the 802.11a STS uses 12 modulated subcarriers, while the LTS uses 52. This is a direct teaching of a packet where the second training symbol (LTS) has a greater quantity of subcarriers than the first training symbol (STS). The claim describes no more than the fundamental, well-known structure of a standard 802.11a packet.
• Motivation: A PHOSITA in 2004 tasked with designing a packet for a wireless LAN would have been motivated to use the existing, widely adopted IEEE 802.11a standard for interoperability and to leverage established technology. Implementing the 802.11a standard would have directly led to the generation and transmission of a packet as described in claim 12. There was no need to combine references; knowledge of the single, dominant standard in the field was sufficient. Therefore, claim 12 is not only obvious, but as noted in the prior art analysis, it is anticipated.

Analysis of Independent Claim 1

Claim 1: A method of generating a packet, "increasing the size of the packet by adding subcarriers to the second training symbol" such that it has more subcarriers than the first, and transmitting it.

Obviousness Argument: Claim 1 attempts to reframe the known structure from claim 12 as a novel process of "increasing" and "adding." This process, however, represents an obvious design choice for any PHOSITA developing an OFDM preamble.

• Known Problem & Motivation to Combine: A PHOSITA would have understood that different parts of a preamble serve distinct functions. The first symbol (STS) is primarily for signal detection, automatic gain control (AGC) setting, and coarse frequency offset estimation. The second symbol (LTS) is for fine frequency offset estimation and, crucially, for channel estimation.
  • Reference 1 (e.g., Ho): Ho teaches the basic 802.11a preamble structure with an STS and an LTS.
  • Reference 2 (General Engineering Knowledge): A fundamental principle of OFDM communication is that accurate channel estimation requires probing the channel at multiple frequency points. The more subcarriers used, the more detailed the picture of the channel's frequency response.
  • Motivation: A PHOSITA would be motivated to design a preamble that performs its functions efficiently and effectively. For initial detection (the STS's role), a simpler signal with fewer subcarriers is sufficient and computationally less intensive. For detailed channel estimation (the LTS's role), it is a known and obvious engineering necessity to use a larger set of subcarriers that span the channel bandwidth. Therefore, the decision to design the LTS with more subcarriers than the STS is not an inventive step but a direct and logical consequence of their different functions. The language "increasing the size... by adding subcarriers" is merely a description of this obvious design trade-off.
• Reasonable Expectation of Success: There would have been a high degree of certainty that using more subcarriers for the LTS, as compared to the STS, would result in more accurate channel estimation, leading to better overall demodulation performance. This was the established and proven method in the field.

Conclusion on Obviousness

The inventions claimed in U.S. Patent 7,742,388 would have been obvious to a person of ordinary skill in the art as of the July 20, 2004 priority date.

1. Claim 12 merely recites the fundamental structure of an IEEE 802.11a packet, which was public knowledge for nearly five years before the patent's priority date and was extensively documented in prior art like Ho (US 2003/0063675 A1).

2. Claim 1 describes the process of arriving at this known structure. This process is nothing more than a series of obvious engineering design choices based on the well-understood functions of the short and long training symbols in an OFDM preamble. A PHOSITA would have been motivated to give the LTS more subcarriers than the STS to achieve the required accuracy for channel estimation, a foundational concept in the field.

The fact that a notice of intent to issue a reexamination certificate to cancel these claims was entered by the USPTO further corroborates the conclusion that the claims lack the novelty and non-obviousness required for patentability.