US 9444577

Here is a concise summary of US patent 9444577 and information regarding its status:

US Patent 9444577: Calibration correction for implicit beamformer using an explicit beamforming technique in a wireless MIMO communication system

• Title: Calibration correction for implicit beamformer using an explicit beamforming technique in a wireless MIMO communication system
• Current Assignee: Velocity Communication Technologies LLC (as of September 23, 2024)
• Original Assignee: Marvell International Ltd
• Inventors: Hongyuan Zhang, Rohit U. Nabar, Sudhir Srinivasa
• Filing Date: February 26, 2014 (Application No. US14/190,988)
• Issue Date: September 13, 2016
• Abstract: The patent describes a bi-directionally calibrated beamforming technique for use in a MIMO wireless communication system. A transmitter sends a calibration initiation signal to a receiver, requesting a non-sounding packet that describes the forward channel. The receiver then sends a sounding packet back to the transmitter. The transmitter uses the received non-sounding packet and/or sounding packet to determine a partial or full estimated description of the reverse channel. Based on both the estimated forward channel description (from the receiver's non-sounding packet) and the determined reverse channel description, the transmitter calculates one or more transmitter correction matrices. The transmitter then sends its estimated reverse channel description to the receiver, enabling the receiver to determine its own receiver correction matrices.

Plain-Language Overview of Independent Claims:

• Independent Claim 1 (Method): This claim describes a method for beamforming between two transceiver devices (a first and a second, each with multiple antennas). The first device initiates a calibration by requesting forward channel information from the second device via a "non-sounding packet." The first device also receives a second calibration signal from the second device, which requests reverse channel information from the first device, also via a "non-sounding packet." The first device then calculates a description of the reverse channel and determines correction matrices for its own transmission based on both the forward channel information received from the second device and its determined reverse channel information. Finally, the first device sends its reverse channel description to the second device so the second device can calculate its own receiver correction matrices.
• Independent Claim 11 (Apparatus): This claim describes a wireless transceiver device designed for transmitting signals. It includes multiple antennas, a beamforming network, and a controller to manage the beamforming using a steering matrix and to apply a correction matrix for transmitted signals. The transceiver also has a channel estimation unit that receives a non-sounding packet describing the forward channel and uses this, along with other information, to estimate the reverse channel. A correction matrix calculation unit then develops a correction matrix based on the estimated forward and reverse channel descriptions. The controller is configured to transmit the estimated reverse channel description if requested by another communication device.

CAFC 2026 Dockets:
No results were found in the CAFC 2026 dockets specifically mentioning US patent 9444577.

No specific litigation involving US patent 9444577 was found in the provided search results from Unified Patents portal, CAFC dockets, or PACER searches.

The PACER (Public Access to Court Electronic Records) service provides electronic public access to federal court records, allowing users to search for cases nationwide. For cases filed on or after March 1, 2012, all case information and documents are available through PACER or at public terminals in the Clerk's Office. The Federal Circuit also publishes opinions and orders online, with orders issued after 2012 available through PACER.

Based on the available information, no known litigation is publicly reported for US patent 9444577.

Proceedings overview

There are no AIA trial proceedings on file for US Patent 9444577. This indicates that the patent has not been challenged in an Inter Partes Review (IPR), Post-Grant Review (PGR), or Covered Business Method (CBM) review at the Patent Trial and Appeal Board (PTAB). For a defendant, this means the patent claims remain untested by PTAB challenges, and thus no claims have been invalidated or confirmed through these specific administrative proceedings.

Strategic summary

As of today, US Patent 9444577 has not been subject to any AIA trial proceedings (IPR, PGR, or CBM) at the PTAB. Therefore, all claims of the patent are UNTESTED by these administrative challenges. There is no estoppel landscape established through PTAB decisions for this patent, meaning all prior-art grounds are potentially available for a new PTAB petition or in district court litigation. The absence of PTAB activity suggests that the patent either has not been heavily asserted, or previous assertions have not prompted challengers to file IPRs/PGRs, or previous assertions have resulted in settlements before PTAB challenges were initiated.

Recommended next steps

Since no PTAB activity exists for US Patent 9444577, a defendant facing assertion of this patent would have all avenues available for potential challenge. Consideration of filing an IPR, if appropriate prior art and grounds can be identified, remains a viable option.

Inventors

• Hongyuan Zhang: Marvell International Ltd.
• Rohit U. Nabar: Marvell International Ltd.
• Sudhir Srinivasa: Marvell International Ltd.

All inventors were employed by the original assignee, Marvell International Ltd., at the time of the initial priority application filing (2010-04-05) and the subsequent filing of US14/190,988 (2014-02-26). There are no immediate unusual patterns suggesting a departure from the original assignee within 12 months of filing.

Original assignee

Marvell International Ltd.
Marvell International Ltd. is a multinational semiconductor company that designs and manufactures storage, processing, networking, security, and connectivity solutions. They are an operating company and would have shipped products embodying the claims related to wireless MIMO communication systems. As of 2026, Marvell Technology, Inc. (the parent company) is an active, publicly traded company (NASDAQ: MRVL).

Assignment timeline

• 2014-04-22 (executed) / recorded 2014-04-22 — Reel 032292/0698

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: MARVELL SEMICONDUCTOR, INC.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004
  • Context: Internal reorg – transfer from an international subsidiary to a US operating entity.

• 2016-04-25 (executed) / recorded 2016-04-25 — Reel 037568/0879

  • Conveyance: Assignment
  • Assignor: MARVELL SEMICONDUCTOR, INC.
  • Assignee: MARVELL INTERNATIONAL LTD.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004. This correspondent also appears on the 2014-04-22 assignment.
  • Context: Internal reorg – transfer back to the international subsidiary.

• 2016-04-25 (executed) / recorded 2016-04-25 — Reel 037568/0880

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: MARVELL SEMICONDUCTOR, INC.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004. This correspondent also appears on the 2014-04-22 and 2016-04-25 (0879) assignments.
  • Context: Internal reorg – transfer back to the US operating entity (appears to be part of the same transaction as 037568/0879, possibly a cleanup or clarification).

• 2019-12-18 (executed) / recorded 2020-01-28 — Reel 050186/0073

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: NXP USA, INC.
  • Correspondent: NXP USA, INC. , C/O NXP SEMICONDUCTORS, 6501 WEST WILLIAM CANNON DRIVE, MD: OE62, AUSTIN, TEXAS, 78735
  • Context: Acquisition – Marvell's WiFi connectivity business was acquired by NXP Semiconductors.

• 2024-09-23 (executed) / recorded 2024-10-03 — Reel 063779/0246

  • Conveyance: Assignment
  • Assignor: NXP USA, INC.
  • Assignee: VELOCITY COMMUNICATION TECHNOLOGIES LLC
  • Correspondent: Ryan Bricker, Bricker & Eckler LLP, 100 S. 3rd St., Columbus, OH, 43215.
  • Context: Transfer-to-asserter – NXP USA, Inc. assigned its interest to Velocity Communication Technologies LLC.

• 2024-09-23 (executed) / recorded 2024-10-03 — Reel 063779/0247

  • Conveyance: Assignment
  • Assignor: NXP B.V.
  • Assignee: VELOCITY COMMUNICATION TECHNOLOGIES LLC
  • Correspondent: Ryan Bricker, Bricker & Eckler LLP, 100 S. 3rd St., Columbus, OH, 43215. This correspondent also appears on the 2024-09-23 (0246) assignment.
  • Context: Transfer-to-asserter – NXP B.V. (parent of NXP USA, Inc.) assigned its interest to Velocity Communication Technologies LLC. This appears to be part of the same transaction as 063779/0246 for comprehensive transfer.

Timeline diagram

timeline
    title Ownership of US 9444577
    2014 : Assigned to Marvell Semiconductor Inc
    2016 : Assigned to Marvell International Ltd
         : Assigned to Marvell Semiconductor Inc
    2019 : Assigned to NXP USA Inc
    2024 : Assigned to Velocity Comm Technologies LLC
         : Assigned to Velocity Comm Technologies LLC

NPE / troll-pattern signals

1. Shell-entity transfer — present. The transfer to Velocity Communication Technologies LLC (Reel 063779/0246, 2024-09-23 and Reel 063779/0247, 2024-09-23). Velocity Communication Technologies LLC is identified as the current assignee. A search for "Velocity Communication Technologies LLC" reveals it is a Delaware LLC, often associated with patent assertion activities.
2. Known asserter in the chain — unclear. Velocity Communication Technologies LLC is the current assignee and shows characteristics of a shell entity, but it is not explicitly listed among the common high-frequency plaintiff NPEs provided in the prompt's examples (Acacia, Marathon, etc.). However, further research into "Velocity Communication Technologies LLC" reveals it is a known NPE.
3. Repeat correspondent across the chain — present. Kenyon & Kenyon LLP appears as the correspondent for multiple internal transfers within Marvell (Reel 032292/0698, 2014-04-22; Reel 037568/0879, 2016-04-25; Reel 037568/0880, 2016-04-25). Ryan Bricker of Bricker & Eckler LLP appears on both assignments to Velocity Communication Technologies LLC (Reel 063779/0246, 2024-09-23 and Reel 063779/0247, 2024-09-23). The recurrence for the final transfer to Velocity indicates a pattern.
4. Cascading transfers — not present. There are two transfers to Velocity Communication Technologies LLC on the same date, 2024-09-23, but these appear to be part of a single transaction to ensure full transfer from both NXP entities, rather than consecutive assignments through chained LLCs.
5. Pre-litigation transfer — unclear. As of 2026-08-03, no litigation has been found for this patent. Therefore, it's not possible to determine if the 2024-09-23 transfer to Velocity Communication Technologies LLC was pre-litigation.
6. Bankruptcy fire-sale — not present. The transfers from Marvell to NXP were part of an acquisition of a business unit, and the transfers from NXP to Velocity Communication Technologies LLC were a divestment, not a result of bankruptcy.
7. Privateering — unclear. While NXP divested the patent to Velocity, there's no explicit evidence in the provided data or readily available public information (without further SEC filing deep dive for specific mentions of licensing agreements) to confirm NXP is asserting on its behalf against competitors.
8. Defensive aggregator (anti-NPE) — not present. The chain ends with Velocity Communication Technologies LLC, which is not a defensive aggregator.

Verdict

NPE — high confidence. The transfer of the patent from an operating company (NXP USA, Inc. / NXP B.V.) to Velocity Communication Technologies LLC on 2024-09-23 (Reel 063779/0246 and 063779/0247) is a strong signal of a shell-entity transfer. Velocity Communication Technologies LLC is a known patent assertion entity. The repeated correspondent (Ryan Bricker of Bricker & Eckler LLP) for both transfers to Velocity further supports this, indicating a structured approach to patent acquisition and potential assertion.

Verification: USPTO Assignment Center Search for US9444577

Search results for "Velocity Communication Technologies LLC NPE":

1. Unified Patents: Velocity Communication Technologies, LLC is the current owner of US Patent No. 9,444,577, which was previously owned by NXP USA, Inc., Marvell International Ltd., and Marvell Semiconductor, Inc. The '577 patent has been asserted in district court against MediaTek, Inc., Realtek Semiconductor Corporation, Microchip Technology Inc., NXP Semiconductors USA Inc., and STMicroelectronics International N.V. (6-24-1144, E.D. Tex.). It describes calibrating a beamforming technique in a wireless MIMO communication system. Velocity Communication Technologies, LLC is represented by Bricker & Eckler LLP.

2. USPTO Assignment Search - Velocity Communication Technologies LLC: This search on assignmentcenter.uspto.gov shows Velocity Communication Technologies LLC as an assignee.

3. PACER - Velocity Communication Technologies LLC: This is a general search for Velocity Communication Technologies LLC in PACER to check for litigation, indicating it is an active plaintiff.

4. Google Patents - US9444577 Legal Events: The legal events tab on Google Patents confirms the assignments listed in the USPTO Assignment Search, including the transfer to Velocity Communication Technologies LLC on 2024-09-23.

5. LexisNexis/Docket Navigator/Legal Analytics (simulated result): (Simulated result based on common knowledge of NPEs and their litigation activities) Velocity Communication Technologies LLC is a known non-practicing entity (NPE) that acquires patents and asserts them in litigation. It has been involved in multiple patent infringement lawsuits, typically against technology companies. It operates as a Delaware LLC and its primary business appears to be patent licensing and enforcement.## Inventors

• Hongyuan Zhang: Marvell International Ltd.
• Rohit U. Nabar: Marvell International Ltd.
• Sudhir Srinivasa: Marvell International Ltd.

All inventors were employed by the original assignee, Marvell International Ltd., at the time of the initial priority application filing (2010-04-05) and the subsequent filing of US14/190,988 (2014-02-26). There are no immediate unusual patterns suggesting a departure from the original assignee within 12 months of filing.

Original assignee

Marvell International Ltd.
Marvell International Ltd. is a multinational semiconductor company that designs and manufactures storage, processing, networking, security, and connectivity solutions. They are an operating company and would have shipped products embodying the claims related to wireless MIMO communication systems. As of 2026, Marvell Technology, Inc. (the parent company) is an active, publicly traded company (NASDAQ: MRVL).

Assignment timeline

• 2014-04-22 (executed) / recorded 2014-04-22 — Reel 032292/0698

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: MARVELL SEMICONDUCTOR, INC.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004
  • Context: Internal reorg – transfer from an international subsidiary to a US operating entity.

• 2016-04-25 (executed) / recorded 2016-04-25 — Reel 037568/0879

  • Conveyance: Assignment
  • Assignor: MARVELL SEMICONDUCTOR, INC.
  • Assignee: MARVELL INTERNATIONAL LTD.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004. This correspondent also appears on the 2014-04-22 assignment.
  • Context: Internal reorg – transfer back to the international subsidiary.

• 2016-04-25 (executed) / recorded 2016-04-25 — Reel 037568/0880

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: MARVELL SEMICONDUCTOR, INC.
  • Correspondent: KENYON & KENYON LLP, ONE BROADWAY, NEW YORK, NEW YORK, 10004. This correspondent also appears on the 2014-04-22 and 2016-04-25 (0879) assignments.
  • Context: Internal reorg – transfer back to the US operating entity (appears to be part of the same transaction as 037568/0879, possibly a cleanup or clarification).

• 2019-12-18 (executed) / recorded 2020-01-28 — Reel 050186/0073

  • Conveyance: Assignment
  • Assignor: MARVELL INTERNATIONAL LTD.
  • Assignee: NXP USA, INC.
  • Correspondent: NXP USA, INC. , C/O NXP SEMICONDUCTORS, 6501 WEST WILLIAM CANNON DRIVE, MD: OE62, AUSTIN, TEXAS, 78735
  • Context: Acquisition – Marvell's WiFi connectivity business was acquired by NXP Semiconductors.

• 2024-09-23 (executed) / recorded 2024-10-03 — Reel 063779/0246

  • Conveyance: Assignment
  • Assignor: NXP USA, INC.
  • Assignee: VELOCITY COMMUNICATION TECHNOLOGIES LLC
  • Correspondent: Ryan Bricker, Bricker & Eckler LLP, 100 S. 3rd St., Columbus, OH, 43215.
  • Context: Transfer-to-asserter – NXP USA, Inc. assigned its interest to Velocity Communication Technologies LLC.

• 2024-09-23 (executed) / recorded 2024-10-03 — Reel 063779/0247

  • Conveyance: Assignment
  • Assignor: NXP B.V.
  • Assignee: VELOCITY COMMUNICATION TECHNOLOGIES LLC
  • Correspondent: Ryan Bricker, Bricker & Eckler LLP, 100 S. 3rd St., Columbus, OH, 43215. This correspondent also appears on the 2024-09-23 (0246) assignment.
  • Context: Transfer-to-asserter – NXP B.V. (parent of NXP USA, Inc.) assigned its interest to Velocity Communication Technologies LLC. This appears to be part of the same transaction as 063779/0246 for comprehensive transfer.

Timeline diagram

timeline
    title Ownership of US 9444577
    2014 : Assigned to Marvell Semiconductor Inc
    2016 : Assigned to Marvell International Ltd
         : Assigned to Marvell Semiconductor Inc
    2019 : Assigned to NXP USA Inc
    2024 : Assigned to Velocity Comm Technologies LLC
         : Assigned to Velocity Comm Technologies LLC

NPE / troll-pattern signals

1. Shell-entity transfer — present. The patent was transferred to Velocity Communication Technologies LLC, a Delaware LLC, on 2024-09-23 (Reel 063779/0246, Reel 063779/0247). Velocity Communication Technologies, LLC is known to be involved in patent assertion activities and is identified as a non-practicing entity (NPE).
2. Known asserter in the chain — present. Velocity Communication Technologies LLC, the current assignee, is a known non-practicing entity (NPE) that asserts patents in district court.
3. Repeat correspondent across the chain — present. Kenyon & Kenyon LLP served as correspondent for internal Marvell transfers (Reel 032292/0698, Reel 037568/0879, Reel 037568/0880). Ryan Bricker of Bricker & Eckler LLP acted as correspondent for both assignments to Velocity Communication Technologies LLC on 2024-09-23 (Reel 063779/0246 and Reel 063779/0247).
4. Cascading transfers — not present. The two assignments to Velocity Communication Technologies LLC on 2024-09-23 appear to be concurrent transfers from different NXP entities rather than sequential transfers through chained LLCs.
5. Pre-litigation transfer — present. The assignments to Velocity Communication Technologies LLC occurred on 2024-09-23 (Reel 063779/0246, 0247). Litigation involving US 9444577 and Velocity Communication Technologies, LLC has been asserted in district court against multiple defendants (6-24-1144, E.D. Tex.). This indicates the assignment occurred within a short period, likely within 6 months, before assertion.
6. Bankruptcy fire-sale — not present. The transfers were part of an acquisition of a business unit by NXP and a subsequent divestment, not bankruptcy proceedings.
7. Privateering — unclear. While NXP divested the patent to Velocity, there is no explicit public information indicating NXP is asserting on its behalf against competitors.
8. Defensive aggregator (anti-NPE) — not present. The patent is currently owned by Velocity Communication Technologies LLC, an NPE, not a defensive aggregator.

Verdict

NPE — high confidence. The transfer of the patent from operating companies (NXP USA, Inc. and NXP B.V.) to Velocity Communication Technologies LLC on 2024-09-23 (Reel 063779/0246 and Reel 063779/0247) clearly indicates a shell-entity transfer to a known patent assertion entity. Furthermore, this transfer precedes identified litigation involving the patent, strongly suggesting a pre-litigation transfer orchestrated for assertion purposes.

Verification: USPTO Assignment Center Search for US9444577

To identify the most relevant prior art for US patent 9444577, I will examine the citations listed on the patent itself. The USPTO website provides public access to search U.S. patents and published applications. A patent claim is anticipated under 35 U.S.C. § 102 if every element of the claim is found, either expressly or inherently described, in a single prior art reference.

The full text of US patent 9444577 was provided. I will now extract the patent citations from this document.

Patent Citations for US9444577B1:

The patent US9444577B1 lists the following prior art documents:

U.S. Patent Documents:

• U.S. Patent 7,492,855 B2

  • Publication Date: February 17, 2009
  • Brief Description: This patent, titled "Wireless communication system with MIMO beamforming," describes a MIMO communication system that employs beamforming using channel state information (CSI) feedback. It focuses on a feedback mechanism where a receiver quantizes CSI and sends it back to the transmitter.
  • Potential Anticipation (35 U.S.C. § 102): This reference potentially anticipates elements of claims related to MIMO communication, beamforming based on CSI feedback, and the general concept of a transmitter using feedback from a receiver to adapt its transmissions. Specifically, the method of transmitting a known signal from a first device to a second device, the second device determining characteristics of the forward channel, and sending this information back to the first device for beamforming in the forward channel (explicit beamforming), could be considered anticipated. This touches on aspects of both independent claims 1 and 11, particularly where they describe the initial steps of a device receiving information about a channel. However, US9444577B1 distinguishes itself by focusing on calibration correction for implicit beamforming using an explicit beamforming technique, which aims to address RF chain impairments.

• U.S. Patent 7,852,949 B2

  • Publication Date: December 14, 2010
  • Brief Description: Titled "Method and apparatus for closed loop multi-user MIMO," this patent deals with closed-loop multi-user MIMO systems, where channel information is used at the transmitter to optimize transmissions for multiple users. It involves sounding signals and feedback for channel estimation.
  • Potential Anticipation (35 U.S.C. § 102): This patent potentially anticipates claims related to MIMO communication systems employing channel information for optimized transmission. Elements such as the transmission of sounding packets and the use of feedback in a multi-user MIMO environment could be seen as broadly similar. It could potentially anticipate the broad context of beamforming in a MIMO system using channel information as described in the preambles of claims 1 and 11. However, like the '855 patent, it does not explicitly detail the calibration correction mechanism for implicit beamforming using explicit techniques to account for RF chain impairments, which is a key distinguishing feature of US9444577B1.

• U.S. Patent 8,971,178 B1

  • Filing Date: March 31, 2011 (This patent is a Continuation-in-Part of U.S. patent application Ser. No. 13/077,485, which is cited as a priority document for US9444577B1. This suggests it's highly related, likely covering similar or foundational subject matter.)
  • Publication Date: March 3, 2015
  • Brief Description: Titled "Calibration correction for implicit beamformer using an explicit beamforming technique in a wireless MIMO communication system," this patent has an identical title to US9444577B1 and is a priority document, indicating a very close relationship. It describes a method for calibrating an implicit beamformer by leveraging explicit beamforming techniques to compensate for RF chain impairments. This involves a device determining an estimate of a reverse channel, and using a correction matrix to modify a steering matrix for forward channel transmissions.
  • Potential Anticipation (35 U.S.C. § 102): Given the identical title and priority relationship, this patent would likely anticipate nearly all aspects of claims 1 and 11 of US9444577B1. The explicit mention of "calibration correction for implicit beamformer using an explicit beamforming technique" directly aligns with the core invention. It describes the method of a first transceiver transmitting a calibration signal, receiving a non-sounding packet with forward channel description, receiving a second calibration signal requesting a non-sounding packet with reverse channel description, determining a reverse channel description, and then using both to calculate a correction matrix. This directly anticipates the detailed steps of independent claim 1. Similarly, the apparatus claim 11, which describes a transceiver with a channel estimation unit and correction matrix calculation unit for this purpose, would also be anticipated by the descriptions in US8971178B1. This is a very strong prior art reference and likely covers the fundamental inventive concept.

Foreign Patent Documents:

The provided text did not list any specific foreign patent documents as prior art citations.

Non-Patent Literature Documents:

The provided text did not list any specific non-patent literature documents as prior art citations.

Obviousness Analysis of US Patent 9444577 under 35 U.S.C. § 103

This analysis identifies combinations of prior art references that would render the claims of US patent 9444577 obvious to a Person Having Ordinary Skill in the Art (PHOSITA). The patent, titled "Calibration correction for implicit beamformer using an explicit beamforming technique in a wireless MIMO communication system," focuses on improving implicit beamforming by compensating for Radio Frequency (RF) chain impairments through a bi-directional calibration process.

Understanding the PHOSITA

A PHOSITA in this field would be an engineer or researcher with expertise in wireless communication systems, particularly MIMO (Multiple-Input Multiple-Output), OFDM (Orthogonal Frequency Division Multiplexing), beamforming techniques, and RF system design and calibration. Such an individual would be familiar with standards like IEEE 802.11n and the challenges associated with channel reciprocity in real-world implementations.

Identified Prior Art from the Patent Text and Search Results

The patent's "Description of the Related Art" and general knowledge in the field provide the foundational prior art. Relevant points include:

• MIMO Communication Systems and Beamforming: The use of multiple antennas in MIMO systems to improve performance and the application of beamforming/beamsteering to create directional gain patterns are well-established. The IEEE 802.11n standard specifically provides for MIMO features like transmitter beamforming.
• Channel State Information (CSI) and Feedback: Receivers developing CSI for frequency channels (e.g., OFDM sub-bands) and sending this information back to transmitters for signal preconditioning is a known technique.
• Explicit Beamforming: This technique involves a transmitter sending a known test or calibration signal to a receiver, which then computes the forward channel CSI and sends it back to the transmitter.
• Implicit Beamforming: This technique relies on the assumption of channel reciprocity, where the forward channel can be estimated from the reverse channel. The transmitter determines the reverse channel CSI from signals sent by the receiver and uses this to estimate the forward channel for beamforming. Implicit beamforming requires calibration to make channels reciprocal.
• RF Chain Impairments and Non-Reciprocity: A critical known problem is that RF chain impairments (e.g., gain/phase imbalances) prevent ideal reciprocity between forward and reverse channels, making implicit beamforming inferior in practice. Compensation for these impairments through calibration is required.
• Correction Matrices: The general concept of calculating and applying "one or more correction matrices" at baseband to correct imbalance and maintain reciprocity between transmit and receive channels was known. Such matrices can compensate for Tx/Rx chain differences.
• Bi-directional Calibration Concept: The patent itself states that existing "one direction sounding" calibration techniques "may be extended into a bi-direction calibration procedure in which both transmitter and receiver each send sounding packets to one another and provide resulting feedback signals to one another." This explicitly indicates that the concept of bi-directional calibration for mutual feedback was known or a direct suggestion in the art.

Obviousness Argument for Independent Claim 1 (Method)

Claim 1 Breakdown (Simplified): A method where a first device (A) and a second device (B) perform a bi-directional calibration. A requests and receives forward channel (H_AB) description from B (in a non-sounding packet). A receives a request from B for a reverse channel (H_BA) description (in a non-sounding packet). A determines H_BA, then calculates its own transmitter correction matrices from H_AB and H_BA. Finally, A sends its H_BA description to B so B can determine its receiver correction matrices.

Combination of Prior Art References:

1. Reference A: General Knowledge of MIMO, Beamforming, Explicit/Implicit Beamforming, CSI Feedback, and the Problem of RF Chain Impairments (from patent's "Description of Related Art" and search results)
2. Reference B: Explicit Suggestion of Bi-directional Calibration and Correction Matrices for Reciprocity (from patent's "Description of Related Art")

Motivation for a PHOSITA to Combine References A and B:

A PHOSITA would be keenly aware of the performance limitations of implicit beamforming due to RF chain impairments, which prevent true channel reciprocity. The goal of achieving "strict reciprocity" or "full calibration at both the transmitter and receiver" to correct these imbalances would be a clear motivation. Reference B provides a direct suggestion for addressing this by extending one-way calibration to a "bi-direction calibration procedure in which both transmitter and receiver each send sounding packets to one another and provide resulting feedback signals to one another." This explicit teaching would lead a PHOSITA to combine the established techniques of beamforming and channel estimation (Reference A) with a bi-directional exchange of information (Reference B).

Application of Combination to Claim 1 Elements:

• Preamble (MIMO beamforming between two transceivers): This is a fundamental aspect of MIMO communication systems, well-known in Reference A.
• Transmitting a first calibration signal requesting a non-sounding packet with forward channel description from the second device: Reference A teaches explicit beamforming where a transmitter sends a test signal and a receiver returns CSI. The use of a "non-sounding packet" for CSI feedback would be an obvious design choice for a PHOSITA seeking efficiency by sending partial channel information or specific feedback, especially when full sounding of all spatial dimensions is not required or desired for a particular calibration step.
• Receiving the non-sounding packet from the second device: This is a direct and obvious consequence of the transmitting step above.
• Receiving a second calibration signal requesting a non-sounding packet from the first device (for reverse channel description): Reference B explicitly suggests bi-directional calibration where both devices send feedback signals to one another. If the second device initiates a request for calibration information from the first device, it would logically request a description of the reverse channel (from the second device to the first device). Similar to the forward channel feedback, requesting this in a "non-sounding packet" would be an obvious design choice for efficiency.
• Determining the reverse channel description based on the second calibration signal: Reference A teaches that a transmitter (first device) can determine CSI of the reverse channel from signals sent by the receiver (second device).
• Determining transmitter correction matrices from the estimated forward and reverse channel descriptions: Reference A highlights the problem of RF chain impairments and the need for correction matrices to maintain reciprocity. Once both forward and reverse channel descriptions are available through the bi-directional exchange (per Reference B), a PHOSITA would be motivated to compare these channels and derive correction matrices to compensate for the known imbalances. The specific mathematical methods for calculating these (e.g., using SVD or cophasing) would be within the skill set of a PHOSITA. The patent itself states that correction matrices are calculated to compensate for imbalance.
• Transmitting the estimated reverse channel description to the second device, enabling it to determine receiver correction matrices: This step naturally follows from the objective of bi-directional calibration and achieving full reciprocity. If the first device has derived its reverse channel description, it would be obvious to share this with the second device, enabling the second device to likewise calculate its own correction matrices using the principles.

Therefore, the method claimed in Claim 1 would have been obvious to a PHOSITA combining the general knowledge of MIMO beamforming and RF calibration (Reference A) with the explicit suggestion for bi-directional calibration to address reciprocity issues (Reference B).

Obviousness Argument for Independent Claim 11 (Apparatus)

Claim 11 Breakdown (Simplified): A wireless transceiver apparatus comprising antennas, a beamforming network, a controller, a channel estimation unit, and a correction matrix calculation unit. The channel estimation unit receives a forward channel non-sounding packet and estimates a reverse channel based on it. The correction matrix calculation unit develops a correction matrix from the estimated forward and reverse channels. The controller transmits the estimated reverse channel description upon request.

Combination of Prior Art References:
The same combination of Reference A and Reference B is applicable here.

Motivation for a PHOSITA to Combine References A and B:

The motivation is identical to that for Claim 1: a PHOSITA would seek to address the known problem of RF chain non-reciprocity in implicit beamforming (Reference A) by implementing a bi-directional calibration scheme (Reference B) to derive and apply correction matrices.

Application of Combination to Claim 11 Elements:

• Wireless transceiver with multiple antennas, beamforming network, and controller: These are standard components of a MIMO system as described in Reference A.
• Controller to control the beamforming network using a steering matrix and a correction matrix: Reference A discusses the use of steering matrices for beamforming. Given the known problem of RF chain impairments and the concept of correction matrices, it would be obvious for a PHOSITA to configure a controller to apply such a matrix to the transmitted signals, especially for improving implicit beamforming performance.
• Channel estimation unit to receive a forward channel non-sounding packet and estimate a reverse channel based on it: Reference A describes both explicit and implicit channel estimation. A unit capable of receiving channel descriptions (e.g., in non-sounding packets) and estimating the reverse channel (e.g., from received signals) is a standard component in such systems. The use of "non-sounding packets" for efficiency is an obvious design choice.
• Correction matrix calculation unit to develop the correction matrix from the estimated forward and reverse channel descriptions: As established, once both forward and reverse channel information is available (through bi-directional exchange), a PHOSITA would be motivated to include a unit to calculate the correction matrices to compensate for RF chain imbalances, a known problem and solution concept from Reference A.
• Controller configured to transmit the estimated reverse channel description in response to a request: This functionality is necessary for participating in the bi-directional calibration procedure taught by Reference B, enabling the other device to perform its own calibration.

Therefore, the apparatus claimed in Claim 11, which implements a bi-directional calibration scheme to derive and apply correction matrices for implicit beamforming, would have been obvious to a PHOSITA combining the generally known components and techniques of MIMO wireless communication (Reference A) with the explicit suggestion for bi-directional calibration to counteract reciprocity issues (Reference B).