Prior art — US Patent 7742388

Prior Art Analysis for U.S. Patent 7,742,388

The following analysis details the prior art references cited during the prosecution of U.S. Patent 7,742,388. The analysis focuses on the potential for these references to anticipate the independent claims (1 and 12) under 35 U.S.C. § 102. The priority date for US 7,742,388 is July 20, 2004.

A crucial point of context is that the IEEE 802.11a standard, which predates the '388 patent, defines a preamble structure for OFDM packets that includes a Short Training Symbol (STS) followed by a Long Training Symbol (LTS). In this standard structure, the STS is formed using 12 modulated subcarriers, and the LTS is formed using 52 modulated subcarriers. This existing standard inherently describes a packet where the second training symbol (LTS) has a greater quantity of modulated subcarriers than the first training symbol (STS).

Key Cited Prior Art References:

1. U.S. Patent Application Publication No. US 2003/0063675 A1 (Ho)

Full Citation: US 2003/0063675 A1, "Preamble for high-throughput OFDM," Inventor: Manyoo Ho, Assignee: Texas Instruments Inc.
Publication Date: April 3, 2003
Filing Date: September 28, 2001
Brief Description: Ho describes a modified preamble for OFDM transmissions intended for high-throughput wireless LANs, building upon the IEEE 802.11a standard. It explicitly discusses the conventional 802.11a preamble, including the Short Training Symbols (STF) and Long Training Symbols (LTF). The invention proposes adding extra training symbols to the preamble to support Multiple-Input Multiple-Output (MIMO) systems, allowing for better channel estimation in more complex environments.
Anticipation Analysis:
- Claim 12: Ho directly anticipates claim 12. In describing the baseline 802.11a system upon which the invention improves, Ho necessarily describes the standard packet structure. Paragraph states, "the short training sequence may consist of 12 sub-carriers" and paragraph states, "the long training sequence may consist of 53 sub-carriers" (52 data and 1 DC). This is a clear disclosure of a packet with a preamble containing a first training symbol (STS) and a second training symbol (LTS), where the quantity of modulated subcarriers in the second is greater than in the first. This structure is generated and transmitted as a matter of standard operation.
- Claim 1: The analysis for claim 1 is more nuanced. Ho does not explicitly describe a process of "increasing the size of the packet by adding subcarriers to the second training symbol." However, the underlying 802.11a standard that Ho describes is the result of a design process where the LTS was defined to have more subcarriers than the STS to achieve its function (e.g., fine frequency offset estimation, channel estimation). An examiner could argue that generating a standard 802.11a packet inherently involves this step. Given the reexamination proceedings, it is highly probable that this or a similar reference was found to be enabling and anticipatory for all independent claims.

2. U.S. Patent No. 7,324,483 (Kwon et al.)

Full Citation: US 7,324,483 B2, "Preamble for an orthogonal frequency division multiplexing system," Inventors: Hyoung-Jin Kwon et al., Assignee: LG Electronics Inc.
Publication Date: January 29, 2008
Filing Date: August 13, 2003
Brief Description: Kwon describes a preamble structure for an OFDM system designed for backward compatibility with legacy systems like 802.11a. The patent discusses generating new preamble formats for enhanced systems (like a potential 802.11n) while allowing legacy devices to correctly interpret at least the initial part of the packet. It explicitly details the structure of the 802.11a short and long training symbols.
Anticipation Analysis:
- Claim 12: Similar to Ho, Kwon anticipates claim 12. The background section of Kwon (Col. 1, lines 30-50) details the conventional 802.11a preamble, describing the short training field (STF) and the long training field (LTF) and their functions. It inherently describes that the LTF uses more subcarriers than the STF. Therefore, it discloses a generated and transmitted packet where the second training symbol has a greater quantity of subcarriers than the first.
- Claim 1: Kwon's disclosure presents the same situation as Ho regarding claim 1. It describes the state of the art, which is a packet that already has the claimed structure. It does not frame this as an active step of "adding" subcarriers to an existing symbol but rather as a description of the final, defined symbol.

3. U.S. Patent Application Publication No. US 2004/0081098 A1 (Hansen et al.)

Full Citation: US 2004/0081098 A1, "Method and system for a configurable radio," Inventors: Christopher J. Hansen et al., Assignee: Broadcom Corp.
Publication Date: April 29, 2004
Filing Date: October 25, 2002
Brief Description: Hansen describes a configurable radio transceiver that can operate in multiple modes, including standard 802.11a/b/g modes and higher-speed proprietary modes. The application discusses generating different packet formats and preambles corresponding to the mode of operation. It details methods for detecting different packet types, including legacy 802.11a packets.
Anticipation Analysis:
- Claim 12: Hansen anticipates claim 12. To achieve its goal of multimode operation and backward compatibility, Hansen must process and generate standard 802.11a packets. In describing this functionality (e.g., paragraph), the application discloses the generation of packets with the standard preamble where the LTS has more subcarriers than the STS.
- Claim 1: Hansen is in the same position as the other references regarding claim 1. It describes the generation of a packet with the claimed features as part of supporting a known standard, not as a novel modification process of "adding" subcarriers.

Conclusion on Prior Art

The most relevant prior art references are those that describe the operation and packet structure of the IEEE 802.11a standard. Publications like Ho (US 2003/0063675 A1), Kwon (US 7,324,483), and Hansen (US 2004/0081098 A1) all predate the '388 patent's priority date and explicitly describe generating and transmitting OFDM packets where the preamble's second training symbol (LTS) contains a greater number of modulated subcarriers (52) than the first training symbol (STS) (12).

This prior art strongly anticipates Claim 12, which broadly claims the generation and transmission of a packet with this structure.

While Claim 1 uses the language "increasing the size of the packet by adding subcarriers to the second training symbol," this can be interpreted as describing the design process that resulted in the standard 802.11a packet. It is highly likely that during reexamination, the USPTO considered this language to be an obvious design choice or inherent in the generation of a standard 802.11a packet, leading to the decision to cancel the claims. The invention of the '388 patent appears to be a description of an already-existing and well-documented feature of the 802.11a standard.