Obviousness

Obviousness Analysis of US Patent 9628310 under 35 U.S.C. § 103

This analysis of US Patent 9628310 under 35 U.S.C. § 103 identifies combinations of prior art references that would render the independent claims obvious, along with the motivation for a person having ordinary skill in the art (PHOSITA) to combine them. For this analysis, "Prior Art" is interpreted as the technologies and standards explicitly described within the US9628310B2 patent itself, particularly those identified as existing or preceding the claimed invention, as instructed by the prompt to "Use the results from the Prior Art section of this page," which includes "Prior art keywords" and the patent's own descriptions of previous IEEE 802.11 standards.

Identifiable Prior Art from Patent US9628310B2

The patent US9628310B2 provides extensive background on existing wireless communication standards and techniques, which serve as direct evidence of prior art for the purpose of this obviousness analysis. Key prior art disclosures within the patent include:

1. IEEE 802.11ac (Very High Throughput - VHT) Standard: The patent explicitly describes the Very High Throughput (VHT) frame format, including VHT Long Training Field (VHT-LTF) sequences, and the specific phase rotation mechanisms applied to these sequences for various channel bandwidths (20 MHz, 40 MHz, 80 MHz, and 160 MHz) [cite: Col 10, lines 45-48, Col 11, lines 34-42, FIGS. 6, 7A-7D]. Specifically, the patent details:

   • VHT-LTF sequences (e.g., VHTLTF_20,28, VHTLTF_58,58, VHTLTF_122,122, VHTLTF_250,250) are defined over sets of tone indices [cite: Col 10, lines 45-56].
   • Phase rotation is applied to these VHT-LTF sequences, with specific examples provided for 20 MHz (Equation 11), 40 MHz (Equation 12), 80 MHz (Equation 13 and 14), and 160 MHz (Equation 15) channel bandwidths [cite: Col 11, lines 34-42, FIGS. 7A-7D].
   • These phase rotations use predefined phase rotation values (1, -1, j, -j) corresponding to specific tone index ranges. For example, for an 80 MHz VHT-LTF, Equation (14) explicitly uses rotations of 1, -1, 1, and -1 for tone index ranges less than -64, between -64 and -1, between 0 and 63, and greater than 63, respectively [cite: Col 11, lines 38-42, FIG. 7C].
   • The VHT-LTF fields are utilized for channel estimation, fine frequency-offset correction, and symbol timing, and phase rotation is employed for purposes such as Peak-to-Average Power Ratio (PAPR) reduction [cite: Col 9, lines 16-17, Col 10, lines 55-58].

2. IEEE 802.11ax (High Efficiency - HE) Standard (as an emerging concept prior to the invention): The patent introduces the concept of High Efficiency (HE) WLAN systems and HE preambles (FIG. 8), which support the IEEE 802.11ax standard [cite: Col 6, lines 5-13, Col 13, lines 10-12]. It describes the need for HE LTF sequences within these HE preambles for channel estimation [cite: Col 4, lines 49-51, Col 14, lines 17-23]. The patent states that one goal for HE LTF sequences is to achieve lower PAPR [cite: Col 4, lines 55-58].

Obviousness Argument

Independent Claims 1, 11, and 19 of US9628310B2 fundamentally claim a method, apparatus, and computer-readable medium, respectively, for constructing and transmitting an HE LTF sequence. The core of these claims involves:

• Defining an HE LTF sequence for a channel bandwidth, including multiple tones with indices.
• Applying phase rotation to a subset of these tones, where the phase rotation is based on tone indices and predefined phase rotation values (1, -1, j, -j) corresponding to specific tone index ranges (e.g., less than -64, between -64 and -1, between 0 and 63, and greater than 63).
• Transmitting the resulting HE LTF sequence.

Combination of Prior Art:

A PHOSITA would have found the claimed subject matter obvious by combining the teachings of IEEE 802.11ac VHT-LTF phase rotation (Prior Art 1) with the known need for HE LTF sequences in an IEEE 802.11ax (HE) preamble (Prior Art 2).

Reasoning and Motivation to Combine:

1. Known Technique for LTF Construction and Phase Rotation: The IEEE 802.11ac standard, as described within US9628310B2, clearly teaches the construction of VHT-LTF sequences and the application of phase rotation to subsets of tones based on their indices [cite: Col 10, lines 45-56]. This prior art explicitly discloses the use of specific phase rotation values (1, -1, j, -j) and tone index ranges (e.g., those detailed in Equation (14) for 80 MHz VHT-LTF, which perfectly align with the ranges recited in Claim 1) [cite: Col 11, lines 38-42, FIGS. 7A-7D]. This technique was employed in 802.11ac for critical functions like channel estimation and PAPR reduction [cite: Col 9, lines 16-17, Col 10, lines 55-58].

2. Motivation for HE Preamble and LTF: A PHOSITA working on the development of the next-generation WLAN standard (IEEE 802.11ax, or "High Efficiency" WLAN) would understand the requirement for new preamble structures, including HE LTF fields, to facilitate operations such as OFDMA and MU-MIMO [cite: Col 6, lines 5-13, Col 13, lines 10-12]. The patent itself states that HE LTF sequences are utilized for channel estimation and that lower PAPR values are desirable for these sequences [cite: Col 4, lines 49-51, Col 4, lines 55-58, Col 14, lines 17-23].

3. Obviousness of Applying Known VHT Techniques to HE: Given the established success and functionality of phase rotation in VHT-LTF for channel estimation and PAPR management, it would have been obvious for a PHOSITA to adapt or re-use these proven techniques for the new HE LTF sequences. The motivation for this combination is strong and includes:

   • Maintaining backward compatibility and facilitating coexistence: The patent explicitly mentions that HE WLAN systems are designed to coexist with VHT STAs [cite: Col 6, lines 5-13]. Reusing similar LTF construction and phase rotation methods would naturally promote interoperability and ease the transition to the new standard.
   • Achieving similar performance benefits: Since PAPR reduction is a stated goal for HE LTF sequences, and phase rotation was successfully used for this purpose in VHT, a PHOSITA would be motivated to apply the known VHT phase rotation scheme to HE LTF sequences to achieve similar desirable PAPR characteristics [cite: Col 4, lines 55-58].
   • Design efficiency and standardization: When developing a new standard (like 802.11ax), engineers typically build upon and refine existing, effective solutions rather than inventing entirely new and unrelated methods, unless a compelling reason for a complete departure exists. Adapting the known phase rotation scheme is a logical and efficient design choice.

Therefore, a PHOSITA would have been motivated to combine the known VHT-LTF phase rotation techniques, as described within the IEEE 802.11ac standard, with the known need for HE LTF sequences in the developing IEEE 802.11ax standard, to achieve similar benefits in channel estimation and PAPR performance, while also promoting compatibility. The specific phase rotation values (1, -1, j, -j) and tone index ranges claimed in US9628310B2 are directly taught by the patent's own description of prior art VHT-LTF phase rotations, particularly for 80 MHz bandwidths. Consequently, the claims are rendered obvious under 35 U.S.C. § 103.