US 8514815

US Patent 8514815, titled "Training signals for selecting antennas and beams in MIMO wireless LANs," was filed on September 30, 2005, and issued on August 20, 2013. The inventors are Daqing Gu, Hongyuan Zhang, Jinyun Zhang, and Andreas F. Molisch. The current assignee is Freedom Patents LLC, though the patent document notes that listed assignees may be inaccurate and Google has not performed a legal analysis for accuracy. The original assignee was Mitsubishi Electric Research Laboratories Inc.

Abstract:
A computer-implemented method for selecting antennas in a multiple-input, multiple-output (MIMO) wireless local area network (WLAN) involves several steps. It begins with a station sending a predetermined number of sounding packets to another station for antenna selection training. The transmitting station then sends these multiple, consecutive sounding packets, each corresponding to a different subset of its available antennas. The receiving station receives these packets, estimates a channel matrix from them, and subsequently selects a subset of antennas based on this estimated channel matrix.

Independent Claims Overview:

• Claim 1: This claim describes a computer-implemented method for antenna selection in a MIMO wireless local area network. The method involves one station (the "performing" station) initiating antenna selection training by communicating to another station (the "transmitting" station) the number of sounding packets to be sent. The transmitting station then sends these specified multiple sounding packets consecutively, where each packet uses a different subset of its antennas. The performing station receives these packets, uses them to estimate the characteristics of the wireless channel (a "channel matrix"), and then selects an optimal subset of antennas based on this matrix. The total number of sounding packets used for this training is decided beforehand.

Litigation Status:
US Patent 8514815 is actively involved in litigation, primarily in the Texas Eastern District Court. The patent, along with US8374096B2 and US8284686B2, is part of a campaign by Freedom Patents LLC. For example, a case against Charter Communications (and Spectrum Gulf Coast, LLC) was dismissed with prejudice on March 8, 2024, meaning Freedom Patents LLC is permanently barred from re-filing those specific infringement claims against Charter. However, the patents remain valid and enforceable against other parties. Freedom Patents LLC has continued to file new suits as recently as April 26, 2025, against multiple defendants including Broadcom, MediaTek, Realtek Semiconductor, and Renesas Electronics, targeting devices that comply with the IEEE 802.11ax-2021 standard and implement MIMO Wi-Fi functionality. Other cases were filed in 2023 and 2024 against companies such as ASUSTek, Cisco, Deutsche Telekom (T-Mobile), HP Enterprise, Hon Hai Precision Industry (Sharp), LG Electronics, Micro-Star, Razer, Samsung, Sony, and Vantiva. These cases generally relate to the provision of devices that implement MIMO Wi-Fi capabilities. No specific CAFC dockets for 2026 directly concerning US8514815 were explicitly identified in the search results, but the ongoing district court litigation indicates active enforcement of the patent.

As of April 26, 2026, US Patent 8514815 has been involved in litigation.

Known Litigation for US Patent 8514815:

• Plaintiff(s): Freedom Patents, LLC
• Defendant(s): [[Samsung Electronics Co.](/litigations/by-defendant/Samsung%20Electronics%20Co.), Ltd.](/litigations/by-plaintiff/Samsung%20Electronics%20Co.%2C%20Ltd.), Samsung Electronics America, Inc., and Harman International Industries, Inc.
• Jurisdiction: Eastern District of Texas
• Case Number: Not explicitly provided in the snippets, but multiple case numbers are listed under "Family has litigation" on the Google Patents page, all in the Eastern District of Texas, e.g., 4:23-cv-00422, 4:24-cv-00534, etc.
• Filing Date: June 14, 2024
• Outcome/Current Status: Dismissed with prejudice on August 23, 2024, by Chief Judge Amos L. Mazzant. The dismissal with prejudice means Freedom Patents cannot refile the same claims against Samsung on these patents. Each party was ordered to bear its own attorney fees, costs, and expenses.

Proceedings overview

There is no PTAB activity on file for US patent 8514815. This suggests that the patent has not yet faced validity challenges at the USPTO's Patent Trial and Appeal Board.

Strategic summary

As of today, May 29, 2026, all claims of US8514815 (claims 1-21) are untested by AIA trial proceedings. This means there is no estoppel landscape established by prior PTAB decisions, and all prior art grounds are theoretically available for a potential challenger. The absence of PTAB activity could indicate that the patent has not been extensively asserted, or that prior challenges have been handled through other legal avenues. However, for a well-asserted patent, the lack of IPRs can sometimes signal that the claims are considered robust or that previous attempts at invalidation were unsuccessful outside of PTAB.

Recommended next steps

If you are a defendant facing assertion of US patent 8514815, the absence of PTAB activity means that the full spectrum of prior art arguments remains available for an AIA trial challenge. This could be an opportune time to explore an Inter Partes Review (IPR) if strong prior art invalidating the asserted claims can be identified.

Inventors

• Daqing Gu (Mitsubishi Electric Research Laboratories, Inc.)
• Hongyuan Zhang (Mitsubishi Electric Research Laboratories, Inc.)
• Jinyun Zhang (Mitsubishi Electric Research Laboratories, Inc.)
• Andreas F. Molisch (Mitsubishi Electric Research Laboratories, Inc.)

Original assignee

The original assignee, Mitsubishi Electric Research Laboratories Inc., is a subsidiary of Mitsubishi Electric US Holdings, Inc., which is the principal subsidiary of Mitsubishi Electric in the United States. MERL acts as the North American arm of Mitsubishi Electric's Corporate R&D organization. Mitsubishi Electric Corporation is a Japanese multinational electronics and electrical equipment manufacturing company. They produce a wide array of products, including factory automation systems, power and energy systems, infrastructure solutions, automotive equipment, electronic devices, and home appliances, and are actively involved in wireless communication systems research. The company is publicly traded and is currently operating.

Assignment timeline

• 2008-09-22 (executed) / recorded 2008-09-22 — Reel 021570/0411
  • Conveyance: Assignment of Assignors Interest
  • Assignor: GU, DAQING; MOLISCH, ANDREAS F.; ZHANG, JINYUN; ZHANG, HONGYUAN
  • Assignee: MITSUBISHI ELECTRIC RESEARCH LABORATORIES, INC.
  • Correspondent: NOT LISTED
  • Context: Transfer from inventors to the initial corporate assignee.
• 2019-06-14 (executed) / recorded 2019-06-14 — Reel 045339/0819
  • Conveyance: Assignment of Assignors Interest
  • Assignor: MITSUBISHI ELECTRIC RESEARCH LABORATORIES, INC.
  • Assignee: MITSUBISHI ELECTRIC CORPORATION
  • Correspondent: DANIEL E. WEINGARTEN, KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004
  • Context: Internal corporate reorganization/transfer to parent company.
• 2022-10-10 (executed) / recorded 2022-10-10 — Reel 060596/0916
  • Conveyance: Assignment of Assignors Interest
  • Assignor: MITSUBISHI ELECTRIC CORPORATION
  • Assignee: FREEDOM PATENTS LLC
  • Correspondent: JOSEPH A. ANTONELLI, ANTONELLI, HARRINGTON & THOMPSON LLP, 1600 WEST LAKE DRIVE, SUITE 200, TAYLOR, TX, 76574. This correspondent appears multiple times in other litigation for Freedom Patents LLC.
  • Context: Sale of patent portfolio from operating company to a patent assertion entity.

Timeline diagram

timeline
    title Ownership of US 8514815
    2005 : Filed by Mitsubishi Electric Research Laboratories Inc
    2008 : Assigned to Mitsubishi Electric Research Laboratories Inc
    2013 : Patent granted
    2019 : Assigned to Mitsubishi Electric Corporation
    2022 : Assigned to Freedom Patents LLC
    2023 : First infringement suit filed

NPE / troll-pattern signals

1. Shell-entity transfer — present. The transfer to "Freedom Patents LLC" (Reel 060596/0916) is a strong indicator. Freedom Patents LLC is described as a non-practicing entity (NPE) or patent assertion entity (PAE) whose primary business model is monetizing patented innovations through licensing and litigation rather than manufacturing.
2. Known asserter in the chain — present. Freedom Patents LLC is explicitly identified as a patent assertion entity (NPE) in multiple sources, including the litigation summary for cases involving this patent. RPX also identifies Freedom Patents LLC as a litigating NPE.
3. Repeat correspondent across the chain — present. Joseph A. Antonelli of Antonelli, Harrington & Thompson LLP is listed as the correspondent for the transfer to Freedom Patents LLC (Reel 060596/0916). Antonelli, Harrington & Thompson LLP is also consistently listed as legal representation for Freedom Patents LLC in its infringement lawsuits in the Eastern District of Texas.
4. Cascading transfers — not present. There is only one transfer from Mitsubishi Electric Corporation to Freedom Patents LLC recorded.
5. Pre-litigation transfer — present. The patent was assigned to Freedom Patents LLC on October 10, 2022 (recorded October 10, 2022, Reel 060596/0916). The first infringement suit involving this patent (e.g., Freedom Patents LLC v. Charter Communications, Inc.) was filed in April 2023, which is within 6 months of the assignment. Another case, Freedom Patents LLC v. [[Samsung Electronics Co.](/litigations/by-defendant/Samsung%20Electronics%20Co.), Ltd.](/litigations/by-plaintiff/Samsung%20Electronics%20Co.%2C%20Ltd.), was filed on June 14, 2024.
6. Bankruptcy fire-sale — not present. The assignors, Mitsubishi Electric Research Laboratories, Inc. and Mitsubishi Electric Corporation, are operating companies and no bankruptcy proceedings were indicated in the assignment records or available search results.
7. Privateering — unclear. While the patent was transferred from an operating company (Mitsubishi Electric Corporation) to an NPE (Freedom Patents LLC), there is no explicit information to suggest that Freedom Patents LLC is asserting the patent on behalf of Mitsubishi Electric Corporation against its competitors.
8. Defensive aggregator (anti-NPE) — not present. The chain terminates with Freedom Patents LLC, a known patent asserter, not a defensive aggregator.

Verdict

NPE — high confidence
This verdict is based on multiple strong signals. The patent was transferred to Freedom Patents LLC (Reel 060596/0916), which is a known patent assertion entity. This transfer occurred within 6 months of the first recorded infringement lawsuit naming this patent, and the same correspondent attorney (Joseph A. Antonelli) appears on the assignment to Freedom Patents LLC and in their subsequent litigation activities.

To verify, search for US Patent 8514815 on the USPTO Assignment Center: https://assignmentcenter.uspto.gov/

The following is an analysis of the most relevant prior art for US patent 8514815, based on the provided patent text and search results. The patent's priority date is September 30, 2005.

Most Relevant Prior Art for US Patent 8514815

US patent 8514815 claims a computer-implemented method for selecting antennas in a MIMO WLAN, involving sending a number of sounding packets for training, transmitting multiple consecutively transmitted sounding packets, receiving these packets (each corresponding to a different antenna subset), estimating a channel matrix, and selecting an antenna subset. The method primarily operates at the MAC layer without requiring PHY layer modification, and the sounding packets can include data.

The most directly relevant prior art cited in US8514815 itself is:

• 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.
  • Full Citation: US 7,486,720 B2 (granted Feb. 3, 2009) or US 2006/0067277 A1 (published Mar. 30, 2006). The snippet specifically references the application number and filing date.
  • Publication/Filing Date: Filed May 11, 2005.
  • Brief Description: This patent application describes a training method where a long sequence of training frames is transmitted from a receive station to a transmit station, and in response, the transmit station transmits a short sequence of training frames. This enables both stations to perform channel estimation and antenna selection.
  • Potential Anticipated Claim(s) under 35 U.S.C. § 102: This reference explicitly discloses "channel estimation and antenna selection" using "training frames for MIMO stations." It potentially anticipates the core concept of estimating a channel matrix and selecting antennas (claim 1, and by extension claims 2, 3, 6, 7, 8, 17, 18, 19, 20, 21), particularly the general idea of using training frames for this purpose. The distinction might lie in the specific "consecutively transmitted sounding packets, each corresponding to a different subset of the set of antennas" operating at the MAC layer without PHY layer modification, which is emphasized in 8514815 as an improvement.

Other prior art documents cited in US8514815 that provide relevant background include:

• IEEE 802.11n standard (also known as WiFi)

  • Brief Description: This standard specifies a Link Adaptation Control (LAC) frame defined at the MAC layer for supporting MIMO training requests and exchange of link adaptation information. It also defines components like the MAC header, LAC mask, MCS feedback field, and FCS.
  • Potential Anticipated Claim(s) under 35 U.S.C. § 102: This reference provides the foundational MAC layer structure and protocols for MIMO WLANs. It anticipates the general use of LAC frames, MAC headers, and MCS feedback in WLANs (claims 9, 10, 11). However, it does not explicitly describe the novel use of consecutive sounding packets for antenna selection as claimed in US8514815.

• IEEE 802.11-04/0889r7, "TGn Sync Proposal Technical Specification"

  • Brief Description: This document describes the control frame in detail, which includes the MAC header, LAC mask, MCS feedback field, and FCS.
  • Potential Anticipated Claim(s) under 35 U.S.C. § 102: Similar to the IEEE 802.11n standard, this document establishes the prior art for the structure of control frames in WLANs, thus potentially anticipating elements related to the LAC frame structure (claims 9, 10, 11).

• 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.

  • Brief Description: This publication describes that antenna selection for beamforming, where magnitudes of elements in the selection matrix are zero or one, can be implemented in the RF domain using phase-shifters, switches, and linear combiners.
  • Potential Anticipated Claim(s) under 35 U.S.C. § 102: This reference provides background on the physical implementation of antenna selection and beamforming. It does not appear to directly anticipate the method of using consecutive sounding packets at the MAC layer for channel estimation and antenna selection but rather the hardware aspects of selection.

It is crucial to note that while these references provide a foundation for the technology, the novelty of US8514815 lies in the specific method of "rapidly send[ing] consecutively multiple training frames, designated as sounding packets... Each sounding packet conforms to a conventional PHY layer design and is for a different subset of all of the available antennas so that characteristics of the entire channel can be estimated by the receiver of the sounding packets" and that "the entire training method operates at the MAC layer." The prior art would need to demonstrate this specific combination and its MAC layer operation to anticipate the claims of US8514815.

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.