Obviousness

Obviousness Analysis under 35 U.S.C. § 103

A patent claim is obvious if "the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains" (35 U.S.C. § 103). This analysis requires identifying: (1) the scope and content of the prior art; (2) the differences between the prior art and the claims at issue; (3) the level of ordinary skill in the pertinent art; and (4) secondary considerations of obviousness.

Given the priority date of September 30, 2005, for US8514815, prior art references existing before this date are relevant. Since the patent was filed under pre-AIA rules, the pre-AIA 35 U.S.C. § 102 and § 103 apply to determine prior art status and obviousness.

Identification of Prior Art References

The patent US8514815 itself explicitly cites a number of prior art references in its description:

1. IEEE 802.11n standard (WiFi): This standard, incorporated by reference, specifies a Link Adaptation Control (LAC) frame defined at the MAC layer for MIMO training requests and exchange of link adaptation information. It also details the MAC header and the LAC mask field, including RTS, CTS, TRQ, MRQ, and MFB.
2. IEEE 802.11-04/0889r7, "TGn Sync Proposal Technical Specification": This document provides further details on the control frame structure, particularly the LAC frame.
3. U.S. patent application Ser. No. 11/127,006, "Training Frames for MIMO Stations," filed by Andreas Molisch, Jianxuan Du and Daqing Gu on May 11, 2005: This application describes a training method where a long sequence of training frames is transmitted from a receive station to a transmit station, followed by a short sequence from the transmit station, enabling both to perform channel estimation and antenna selection. (Note: Andreas Molisch and Daqing Gu are also inventors of US8514815).
4. Sudarshan, P., Mehta, N. B., Molisch, A. F., Zhang, J., "Spatial Multiplexing and Channel Statistics-Based RF Pre-Processing for Antenna Selection," Globecom, November 2004: This publication discusses implementing antenna selection in the RF domain using phase-shifters, switches, and linear combiners. (Note: Andreas F. Molisch and Jinyun Zhang are also inventors of US8514815).

Combinations of Prior Art and Motivation for Combination

Claim 1 of US8514815 describes:
"A computer implemented method for selecting antennas in a multiple-input, multiple-output wireless local area network including a plurality of stations, each station includes a set of antennas, comprising the steps of:

• sending a number of sounding packets that are to be sent for antenna selection training, from a station to perform the antenna selection training by receiving the sounding packets, to a station to transmit the sounding packets;
• transmitting multiple consecutively transmitted sounding packets, according to the number, by the station transmitting the sounding packets;
• receiving the multiple consecutively transmitted sounding packets in the station to perform the antenna section training, wherein each sounding packet corresponding to a different subset of the set of antennas, and where the number of consecutive packets is predetermined;
• estimating a channel matrix from the multiple consecutively transmitted sounding packets; and
• selecting a subset of antennas according to the channel matrix."

A person of ordinary skill in the art (POSA) in MIMO WLAN design, as of the 2005 priority date, would be familiar with the IEEE 802.11n standard and the challenges of overhead in MIMO systems. The background section of US8514815 explicitly states that "the additional overheads [of conventional explicit signaling] are undesirable due to practical limitations." The POSA would also be motivated to improve the efficiency of antenna/beam selection training while minimizing changes to existing MAC and PHY layers.

Obviousness Combination 1: IEEE 802.11n Standard (including 802.11-04/0889r7) in view of U.S. patent application Ser. No. 11/127,006

• IEEE 802.11n Standard and 802.11-04/0889r7: These references teach the use of LAC frames at the MAC layer for MIMO training requests and exchange of link adaptation information, including MCS feedback and TXBF training. They establish the framework for control signaling in WLANs.
• U.S. patent application Ser. No. 11/127,006 ("Training Frames for MIMO Stations"): This reference, filed prior to US8514815, describes a MIMO training method involving sequences of training frames exchanged between transmit and receive stations for channel estimation and antenna selection. It specifically teaches transmitting a "long sequence of training frames from a receive station to a transmit station, and in response the transmit station transmits a short sequence of training frames so that both the transmit and receive station can perform channel estimation and antenna selection."

Motivation for Combination:
A POSA would be motivated to combine the MAC layer signaling capabilities of the IEEE 802.11n standard with the antenna selection training concept described in U.S. patent application Ser. No. 11/127,006. The IEEE 802.11n standard already provides a MAC layer control frame (LAC) for MIMO training requests (TRQ) and link adaptation. The 11/127,006 application teaches the concept of using sequences of training frames for antenna selection. However, it does not explicitly detail how these training frames would be embedded or initiated within a standard WLAN MAC layer.

The motivation to combine them would be to integrate the efficiency benefits of sequenced training for antenna selection (from 11/127,006) directly into the established MAC layer signaling of 802.11n. Specifically, a POSA would recognize that the "training frames" of 11/127,006 could be implemented as "sounding packets" within the 802.11n framework. The 802.11n standard already accommodates requests for MIMO training (TRQ) and feedback mechanisms (MFB). Implementing the sequential training packets for different antenna subsets, as taught by US8514815, within a MAC-layer initiated process would reduce overhead compared to purely PHY-layer solutions. The 11/127,006 application's general teaching of "training frames for MIMO stations" combined with the 802.11n MAC layer's existing support for "MIMO training requests" (TRQ) would lead a POSA to use MAC layer signaling to coordinate the transmission of such training frames (sounding packets) for antenna selection.

The specific "sending a number of sounding packets that are to be sent" step in claim 1 could be achieved by adapting the existing MAC layer control frames (like the LAC frame with a TRQ or a new indicator as proposed in 8514815) to specify the number of subsequent sounding packets. The concept of "multiple consecutively transmitted sounding packets, each sounding packet corresponding to a different subset of the set of antennas" is also present in the spirit of 11/127,006, where "training frames" are used for channel estimation and antenna selection. Making these packets "consecutive" would be an obvious design choice for a POSA seeking to minimize channel changes during the estimation period, as acknowledged in US8514815: "the inter-packet time interval introduces some distortion on the estimated full channel matrix. Therefore, the interval between the consecutive sounding packets should be relatively short, and the present training scheme is designed based on this requirement."

Obviousness Combination 2: IEEE 802.11n Standard (including 802.11-04/0889r7) in view of Sudarshan et al. (Globecom, 2004)

• IEEE 802.11n Standard and 802.11-04/0889r7: As above, these references establish the MAC layer signaling for MIMO training and link adaptation.
• Sudarshan et al. (Globecom, 2004): This reference teaches the implementation of antenna selection in the RF domain using phase-shifters, switches, and linear combiners. This demonstrates the technical feasibility and known methods for performing antenna selection once the decision is made.

Motivation for Combination:
A POSA would be motivated to combine the antenna selection implementation described by Sudarshan et al. with the MAC layer signaling provided by the 802.11n standard. While Sudarshan et al. describes how to physically implement antenna selection, it doesn't describe the signaling or training protocol within a WLAN. The 802.11n standard, on the other hand, provides the signaling framework. A POSA seeking to build a complete MIMO WLAN system with antenna selection would naturally look to existing hardware implementation techniques (like those in Sudarshan etal.) and integrate them with the standard's defined control mechanisms (802.11n). The step of "selecting a subset of antennas according to the channel matrix" in claim 1 could then be realized using the techniques taught by Sudarshan et al. after the channel matrix is estimated via MAC-layer initiated sounding packets.

This combination would lead a POSA to use the 802.11n MAC layer to initiate and manage the process of gathering channel information (via sounding packets, potentially for different antenna subsets) and then apply the antenna selection techniques (e.g., using switches in the RF domain as taught by Sudarshan et al.) to optimize performance.

Further Considerations for Obviousness:

• The "MAC layer operation" aspect (Claim 4): The US8514815 description explicitly notes that "The entire training method operates at the MAC layer" and that this "has less overhead than conventional methods that operate at both the MAC and PHY layers." Given that the 802.11n standard already specifies MAC layer control frames for MIMO training, and the general understanding that MAC layer control can reduce overhead compared to PHY layer modifications, a POSA would be motivated to keep the antenna selection training within the MAC layer. This would be an obvious design choice for improving efficiency without significant changes to the PHY layer.
• "Sounding packets include data" (Claim 5): The patent states, "The sounding packets, in addition to training the MIMO channel for selecting antennas/beams, can also include data which makes the method extremely efficient because training and data transfer is performed concurrently." Transmitting data during training periods for efficiency is a common engineering goal. If the PHY layer packet structure allows for data, a POSA would recognize the benefit of concurrently transferring data during the sounding packet sequence to maximize throughput, rather than sending pure training packets.
• "Selecting beams according to the channel matrix" (Claim 6): The patent itself mentions "antenna/beam selection" throughout. The concept of beam selection (or beamforming) in MIMO systems was well-known in 2005. Given that the underlying goal is to optimize signal transmission/reception, a POSA would find it obvious to apply the channel matrix estimation to beam selection techniques, which are analogous to antenna selection in their goal of improving channel quality.

In summary, the core inventive step of US8514815 lies in the specific MAC-layer driven, consecutive sounding packet approach for antenna/beam selection without modifying the PHY layer. However, elements such as MAC layer control for MIMO, the use of training frames for channel estimation and antenna selection, and the physical implementation of antenna selection were known. A POSA, motivated by efficiency and reduced overhead in WLANs, would have found it obvious to combine these known elements to arrive at the claimed invention.